Miscellany

Jai Ganesh · 2018-12-07 02:00:58

255) Inverter

One of the most significant battles of the 19th century was fought not over land or resources but to establish the type of electricity that powers our buildings.
At the very end of the 1800s, American electrical pioneer Thomas Edison (1847–1931) went out of his way to demonstrate that direct current (DC) was a better way to supply electrical power than alternating current (AC), a system backed by his Serbian-born arch-rival Nikola Tesla (1856–1943). Tesla's system won the day and the world has pretty much run on AC power ever since.

The only trouble is, though many of our appliances are designed to work with AC, small-scale power generators often produce DC. That means if you want to run something like an AC-powered gadget from a DC car battery in a mobile home, you need a device that will convert DC to AC—an inverter, as it's called. Let's take a closer look at these gadgets and find out how they work!

What's the difference between DC and AC electricity?

When science teachers explain the basic idea of electricity to us as a flow of electrons, they're usually talking about direct current (DC). We learn that the electrons work a bit like a line of ants, marching along with packets of electrical energy in the same way that ants carry leaves. That's a good enough analogy for something like a basic flashlight, where we have a circuit (an unbroken electrical loop) linking a battery, a lamp, and a switch and electrical energy is systematically transported from the battery to the lamp until all the battery's energy is depleted.

In bigger household appliances, electricity works a different way. The power supply that comes from the outlet in your wall is based on alternating current (AC), where the electricity switches direction around 50–60 times each second (in other words, at a frequency of 50–60 Hz). It can be hard to understand how AC delivers energy when it's constantly changing its mind about where it's going! If the electrons coming out of your wall outlet get, let's say, a few millimeters down the cable then have to reverse direction and go back again, how do they ever get to the lamp on your table to make it light up?

The answer is actually quite simple. Imagine the cables running between the lamp and the wall packed full of electrons. When you flick on the switch, all the electrons filling the cable vibrate back and forth in the lamp's filament—and that rapid shuffling about converts electrical energy into heat and makes the lamp bulb glow. The electrons don't necessarily have to run in circle to transport energy: in AC, they simply "run on the spot."

What is an inverter?

One of Tesla's legacies (and that of his business partner George Westinghouse, boss of the Westinghouse Electrical Company) is that most of the appliances we have in our homes are specifically designed to run from AC power. Appliances that need DC but have to take power from AC outlets need an extra piece of equipment called a rectifier, typically built from electronic components called diodes, to convert from AC to DC.

An inverter does the opposite job and it's quite easy to understand the essence of how it works. Suppose you have a battery in a flashlight and the switch is closed so DC flows around the circuit, always in the same direction, like a race car around a track. Now what if you take the battery out and turn it around. Assuming it fits the other way, it'll almost certainly still power the flashlight and you won't notice any difference in the light you get—but the electric current will actually be flowing the opposite way. Suppose you had lightning-fast hands and were deft enough to keep reversing the battery 50–60 times a second. You'd then be a kind of mechanical inverter, turning the battery's DC power into AC at a frequency of 50–60 hertz.

Of course the kind of inverters you buy in electrical stores don't work quite this way, though some are indeed mechanical: they use electromagnetic switches that flick on and off at high speed to reverse the current direction. Inverters like this often produce what's known as a square-wave output: the current is either flowing one way or the opposite way or it's instantly swapping over between the two states.

These kind of sudden power reversals are quite brutal for some forms of electrical equipment. In normal AC power, the current gradually swaps from one direction to the other in a sine-wave pattern.

Electronic inverters can be used to produce this kind of smoothly varying AC output from a DC input. They use electronic components called inductors and capacitors to make the output current rise and fall more gradually than the abrupt, on/off-switching square wave output you get with a basic inverter.

Inverters can also be used with transformers to change a certain DC input voltage into a completely different AC output voltage (either higher or lower) but the output power must always be less than the input power: it follows from the conservation of energy that an inverter and transformer can't give out more power than they take in and some energy is bound to be lost as heat as electricity flows through the various electrical and electronic components. In practice, the efficiency of an inverter is often over 90 percent, though basic physics tells us some energy—however little—is always being wasted somewhere!

How does an inverter work?

We've just had a very basic overview of inverters—and now let's go over it again in a little bit more detail.

Imagine you're a DC battery and someone taps you on the shoulder and asks you to produce AC instead. How would you do it? If all the current you produce flows out in one direction, what about adding a simple switch to your output lead? Switching your current on and off, very rapidly, would give pulses of direct current—which would do at least half the job. To make proper AC, you'd need a switch that allowed you to reverse the current completely and do it about 50‐60 times every second. Visualize yourself as a human battery swapping your contacts back and forth over 3000 times a minute. That's some neat fingerwork you'd need!

In essence, an old-fashioned mechanical inverter boils down to a switching unit connected to an electricity transformer. If you've studied our article on transformers, you'll know that they're electromagnetic devices that change low-voltage AC to high-voltage AC, or vice-versa, using two coils of wire (called the primary and secondary) wound around a common iron core. In a mechanical inverter, either an electric motor or some other kind of automated switching mechanism flips the incoming direct current back and forth in the primary, simply by reversing the contacts, and that produces alternating current in the secondary—so it's not so very different from the imaginary inverter I sketched out above. The switching device works a bit like the one in an electric doorbell. When the power is connected, it magnetizes the switch, pulling it open and switching it off very briefly. A spring pulls the switch back into position, turning it on again and repeating the process—over and over again.

Types of inverters

If you simply switch a DC current on and off, or flip it back and forth so its direction keeps reversing, what you end up with is very abrupt changes of current: all in one direction, all in the other direction, and back again. Draw a chart of the current (or voltage) against time and you'll get a square wave. Although electricity varying in that fashion is, technically, an alternating current, it's not at all like the alternating current supplied to our homes, which varies in a much more smoothly undulating sine wave). Generally speaking, hefty appliances in our homes that use raw power (things like electric heaters, incandescent lamps, kettles, or fridges) don't much care what shape wave they receive: all they want is energy and lots of it—so square waves really don't bother them. Electronic devices, on the other hand, are much more fussy and prefer the smoother input they get from a sine wave.

This explains why inverters come in two distinct flavors: true/pure sine wave inverters (often shortened to PSW) and modified/quasi sine wave inverters (shortened to MSW). As their name suggests, true inverters use what are called toroidal (donut-shaped) transformers and electronic circuits to transform direct current into a smoothly varying alternating current very similar to the kind of genuine sine wave normally supplied to our homes. They can be used to power any kind of AC appliance from a DC source, including TVs, computers, video games, radios, and stereos. Modified sine wave inverters, on the other hand, use relatively inexpensive electronics (thyristors,diodes, and other simple components) to produce a kind of "rounded-off" square wave (a much rougher approximation to a sine wave) and while they're fine for delivering power to hefty electric appliances, they can and do cause problems with delicate electronics (or anything with an electronic or microprocessor controller). Also, if you think about it, their rounded-off square waves are delivering more power to the appliance overall than a pure sine wave (there's more area under a square than a curve), so there's some risk of overheating with MSW inverters. On the positive side, they tend to be quite a bit cheaper than true inverters and often work more efficiently (which is important if you want to run something off a battery with a limited charge—because it will run for longer).

Although many inverters work as standalone units, with battery storage, that are totally independent from the grid, others (known as utility-interactive inverters or grid-tied inverters) are specifically designed to be connected to the grid all the time; typically they're used to send electricity from something like a solar panel back to the grid at exactly the right voltage and frequency. That's fine if your main objective is to generate your own power. It's not so helpful if you want to be independent of the grid sometimes or you want a backup power source in case of an outage, because if your connection to the grid goes down, and you're not making any electricity of your own (for example, it's night-time and your solar panels are inactive), the inverter goes down too, and you're completely without power—as helpless as you would be whether you were generating your own power or not. For this reason, some people use bimodal or birectional inverters, which can either work in standalone or grid-tied mode (though not both at the same time). Since they have extra bits and pieces, they tend to be more bulky and more expensive.

What are inverters like?

Inverters can be very big and hefty—especially if they have built-in battery packs so they can work in a standalone way. They also generate lots of heat, which is why they have large heat sinks (metal fins) and often cooling fans as well. As you can see from our top photo, typical ones are about as big as a car battery or car battery charger; larger units look like a bit like a bank of car batteries in a vertical stack. The smallest inverters are more portable boxes the size of a car radio that you can plug into your cigarette lighter socket to produce AC for charging laptop computers or cellphones.

Just as appliances vary in the power they consume, so inverters vary in the power they produce. Typically, to be on the safe side, you'll need an inverter rated about a quarter higher than the maximum power of the appliance you want to drive. That allows for the fact that some appliances (such as fridges and freezers or fluorescent lamps) consume peak power when they're first switched on. While inverters can deliver peak power for short periods of time, it's important to note that they're not really designed to operate at peak power for long periods.

What is an uninterruptible power supply?

One very common use for inverters is in emergency power supplies, also called uninterruptible power supplies or uninterruptible power sources (both going by the acronym UPS). If your household power fails in an outage (blackout), you might have a UPS as a backup—but how does it work?

A typical UPS stores energy in electrical form using rechargeable batteries (some UPS systems store energy in mechanical form using a high-speed flywheel, spun to high speed by an electric motor). When the power is flowing normally, the batteries are being trickle charged by DC, which is produced from the AC power supply using a transformer and rectifier circuit. If the power fails, what you have at your disposal is charged-up batteries that will produce direct current, but which need to produce alternating current to power your home. So when the UPS is supplying energy, the batteries pump DC through an inverter to produce AC.

A UPS is often combined with a surge protector and voltage optimization equipment to produce a resilient power supply capable of surviving spikes, surges, over-voltage, under-voltage, or a complete loss of power.

Jai Ganesh · 2018-12-09 00:18:41

256) Banana

Bananas are one of the world's most appealing fruits. Global banana exports reached about 18 million tons in 2015, according to the United Nations. About half of them went to the United States and the European market. In the United States, each person eats 11.4 lbs. of bananas per year, according to the U.S. Department of Agriculture, making it Americans' favorite fresh fruit.

A wide variety of health benefits are associated with the curvy yellow fruit. Bananas are high in potassium and pectin, a form of fiber, said Laura Flores, a San Diego-based nutritionist. They can also be a good way to get magnesium and vitamins C and B6.

"Bananas are known to reduce swelling, protect against developing type-2 diabetes, aid in weight loss, strengthen the nervous system and help with production of white blood cells, all due to the high level of vitamin B6 that bananas contain," Flores told Live Science.

"Bananas are high in antioxidants, which can provide protection from free radicals, which we come into contact with every day, from the sunlight to the lotion you put on your skin," Flores added.

From green to black

A 2017 meta-analysis published by Prilozi Section of Medical Sciences suggested that unripe green bananas offer some health benefits. They may help with controlling gastrointestinal problems such as diarrhea and ulcers, and may lower cholesterol and blood pressure. Some studies have suggested that the lectins in green bananas could provide treatment for HIV patients.

At the other end of a banana's life, research has shown that the levels of nutrients rise in bananas as they ripen. Bananas with dark spots were eight times more effective in enhancing the power of white blood cells than green-skin bananas, according to a 2009 study published in Food Science and Technology Research. White blood cells fight infections from bacteria, fungi, viruses and other pathogens.

Health benefits

Heart health

Bananas are good for your heart. They are packed with potassium, a mineral electrolyte that keeps electricity flowing throughout your body, which is required to keep your heart beating. Bananas' high potassium and low sodium content may also help protect your cardiovascular system against high blood pressure, according to the FDA.

A 2017 animal study conducted by researchers at the University of Alabama found that the potassium in bananas is also linked to arterial effectiveness; the more potassium you have, the less likely your arteries are to harden. In the study, mice with lower-potassium diet had harder arteries than mice consuming a normal amount of potassium. Arterial stiffness in humans is linked to heart disease.

Depression and mood

Bananas can be helpful in overcoming depression "due to high levels of tryptophan, which the body converts to serotonin, the mood-elevating brain neurotransmitter," Flores said. Plus, vitamin B6 can help you sleep well, and magnesium helps to relax muscles. Additionally, the tryptophan in bananas is well known for its sleep-inducing properties.

Digestion and weight loss

Bananas are high in fiber, which can help keep you regular. One banana can provide nearly 10 percent of your daily fiber requirement. Vitamin B6 can also help protect against type 2 diabetes and aid in weight loss, according to Flores. In general, bananas are a great weight loss food because they taste sweet and are filling, which helps curb cravings.

Bananas are particularly high in resistant starch, a form of dietary fiber in which researchers have recently become interested. A 2017 review published in Nutrition Bulletin found that the resistant starch in bananas may support gut health and control blood sugar. Resistant starch increases the production of short chain fatty acids in the gut, which are necessary to gut health.

Exercise

For replenishing energy and electrolytes, bananas can be more effective than sports drinks. A 2012 study published in PLOS One looked at male athletes competing in long-distance cycling races. They compared athletes refueling with Gatorade every 15 minutes to athletes refueling with a banana and water. Researchers saw that the athletes' performance times and body physiology were the same in both cases. But the banana's serotonin and dopamine improved the athletes' antioxidant capacity and helped with oxidative stress, improving performance overall.

Vision

Carrots may get all the glory for helping your eyes, but bananas do their share as well. The fruits contain a small but significant amount of vitamin A, which is essential for protecting your eyes, maintaining normal vision and improving vision at night, according to the National Institutes of Health. Vitamin A contains compounds that preserve the membranes around your eyes and are an element in the proteins that bring light to your corneas. Like other fruits, bananas can help prevent macular degeneration, an incurable condition, which blurs central vision.

Bones

Bananas may not be overflowing with calcium, but they are still helpful in keeping bones strong. According to a 2009 article in the Journal of Physiology and Biochemistry, bananas contain an abundance of fructooligosaccharides. These are nondigestive carbohydrates that encourage digestive-friendly priobotics and enhance the body's ability to absorb calcium.

Cancer

Some evidence suggests that moderate consumption of bananas may be protective against kidney cancer. A 2005 Swedish study found that women who ate more than 75 servings of fruits and vegetables cut their risk of kidney cancer by 40 percent, and that bananas were especially effective. Women eating four to six bananas a week halved their risk of developing kidney cancer.

Bananas may be helpful in preventing kidney cancer because of their high levels of antioxidant phenolic compounds.

Pregnancy

Bananas may also help prevent gestational diabetes. Lack of sleep during pregnancy can contribute to gestational diabetes, according to a meta-analysis published in Sleep Medicine Reviews. But the magnesium and tryptophan in bananas can help ensure a good night's rest.

Health risks

Eaten in moderation, there are no significant side effects associated with eating bananas. However, eating the fruits in excess may trigger headaches and sleepiness, Flores said. She said that such headaches are caused by "the amino acids in bananas that dilate blood vessels." Overripe bananas contain more of these amino acids than other bananas. "Bananas can also contribute to sleepiness when eaten in excess due to the high amount of tryptophan found in them," she said. Magnesium also relaxes the muscles — another sometimes-benefit, sometimes-risk.

Bananas are a sugary fruit, so eating too many and not maintaining proper dental hygiene practices can lead to tooth decay. They also do not contain enough fat or protein to be a healthy meal on their own, or an effective post-workout snack.

Eating bananas becomes significantly risky only if you eat too many. The USDA recommends that adults eat about two cups of fruit a day, or about two bananas. If you eat dozens of bananas every day, there may be a risk of excessively high vitamin and mineral levels.

The University of Maryland Medical Center reported that potassium overconsumption can lead to hyperkalemia, which is characterized by muscle weakness, temporary paralysis and an irregular heartbeat. It can have serious consequences, but you would have to eat about 43 bananas in a short time for any symptoms of hyperkalemia to occur.

According to the NIH, consuming more than 500 milligrams of vitamin B6 daily can possibly lead to nerve damage in the arms and legs. You would have to eat thousands of bananas to reach that level of vitamin B6.

Banana peels: edible or poisonous?

It turns out that the biggest risk from a banana peel might really be slipping on it. Banana peels are not poisonous. In fact, they're edible, and packed with nutrients. "Banana peel is eaten in many parts of the world, though [it's] not very common in the West," Flores said. "It contains high amounts of vitamin B6 and B12, as well as magnesium and potassium. It also contains some fiber and protein." According to a 2011 article in the journal of Applied Biochemistry and Biotechnology, banana peels also have "various bioactive compounds like polyphenols, carotenoids and others."

It is important to carefully wash a banana peel before eating it due to the pesticides that may be sprayed in banana groves.

Banana peels are usually served cooked, boiled or fried, though they can be eaten raw or put in a blender with other fruits. They are not as sweet as banana flesh. Riper peels will be sweeter than unripe ones.

Other banana facts

Bananas may have been the world's first cultivated fruit. Archaeologists have found evidence of banana cultivation in New Guinea as far back as 8000 B.C.
The banana plant is classified as an arborescent (tree-like) perennial herb, and the banana itself is considered a berry. A bunch of bananas is called a hand; a single banana is a finger.

There are almost 1,000 varieties of bananas, according to the Food and Agriculture Organization of the United Nations (FAO). Nearly all the bananas sold in stores are cloned from just one variety, the Cavendish banana plant, originally native to Southeast Asia. The Cavendish replaced the Gros Michel after that variety was wiped out by fungus in the 1950s. The Gros Michel reportedly was bigger, had a longer shelf life and tasted better. The Cavendish are resistant to the fungus that killed off the Gros Michel, but they are susceptible to another fungus and may face the same fate within the next 20 years, botanists say.

Botanically, there is no difference between plantains and bananas. But in general use, "banana" refers to the sweeter form of the fruit, which is often eaten uncooked, while "plantain" refers to a starchier fruit that is often cooked before eating.

Ecuador is the leading producer of bananas worldwide, followed by the Philippines. Bananas are produced in other tropical and subtropical areas of Asia, Africa, and the Americas, as well as the Canary Islands and Australia.

Wild bananas grow throughout Southeast Asia, but most are inedible for humans, as they are studded with hard seeds.

Jai Ganesh · 2018-12-11 01:02:39

257) Academy Award

Academy Award, in full Academy Award of Merit, byname Oscar, any of a number of awards presented annually by the Academy of Motion Picture Arts and Sciences, located in Beverly Hills, California, U.S., to recognize achievement in the film industry. The awards were first presented in 1929, and winners receive a gold-plated statuette commonly called Oscar.

Categories And Rules

Winners are chosen from the following 24 categories: best picture, actor, actress, supporting actor, supporting actress, directing, original screenplay, adapted screenplay, cinematography, production design, editing, original score, original song, costume design, makeup and hairstyling, sound mixing, sound editing, visual effects, foreign-language film, animated feature film, animated short, live-action short, documentary feature, and documentary short. The academy also presents scientific and technical awards, special achievement awards, honorary awards, the Jean Hersholt Humanitarian Award, the Irving G. Thalberg Memorial Award (for excellence in producing), and the Gordon E. Sawyer Award (for technological contributions), although these are not necessarily awarded annually.

In August 2018 the academy announced that it was adding an annual category for “outstanding achievement in popular film,” to debut at the 2019 ceremony. However, following criticism and confusion, the academy decided to postpone the introduction of the new category.

To be eligible for an award in a given year, a film must be publicly exhibited for paid admission for at least one week at a commercial theatre in Los Angeles county between January 1 and midnight of December 31 of that year. Exceptions to this rule include foreign-language films, which are submitted by their country of origin and need not have been shown in the United States. Documentaries and short films have different eligibility requirements and are officially submitted by their producers, whereas music awards require the musical artist to file a submission form.

Only members of the Academy of Motion Picture Arts and Sciences may nominate and vote for candidates for the Oscars. The academy is divided into various branches of film production, and the nominees in each award category are chosen by the members of the corresponding branch; thus, writers nominate writers, directors nominate directors, and so forth. The entire academy membership nominates the candidates for best picture and votes to determine the winners in most of the categories.
Aside from bestowing international recognition and prestige, an Academy Award can play a crucial role in the success of the major winners. The best picture award, for example, can significantly increase the box office earnings of the winning film. For actors and directors, the award often results in higher salaries, increased media attention, and better film offers.

History

When the academy was founded in 1927, the awards committee was only one of several that had been formed by the new organization. The idea of presenting awards was considered but not immediately pursued, because the academy was preoccupied with its role in labour problems, its efforts to improve the tarnished image of the film industry, and its function as a clearinghouse for the exchange of ideas about production procedures and new technologies. It was not until May 1928 that the academy approved the committee’s suggestions to present Academy Awards of Merit in 12 categories—most outstanding production, most artistic or unique production, and achievement by an actor, by an actress, in dramatic directing, in comedy directing, in cinematography, in art directing, in engineering effects, in original story writing, in adaptation writing, and in title writing.

The first awards covered films that had been released between August 1, 1927, and July 31, 1928. The awards were presented on May 16, 1929, in a ceremony at the Hollywood Roosevelt Hotel. The entire membership of the academy had nominated candidates in all categories. Five boards of judges (one from each of the academy’s original branches—actors, writers, directors, producers, and technicians) then determined the 10 candidates with the most votes in each category and narrowed those 10 down to 3 recommendations. A central board of judges, which consisted of one member from each branch, selected the final winners.

By the time of the second annual awards ceremony, on April 3, 1930 (honouring films from the second half of 1928 and from 1929), the number of categories was reduced to seven, and the two major film awards were collapsed into one, called best picture. The academy has since continued to make frequent alterations in rules, procedures, and categories. Indeed, so many changes have been made through the years that the only constant seems to be the academy’s desire to remain flexible and to keep abreast of the industry’s evolution. Among the most significant changes have been the decision in 1933 to alter the eligibility period for award consideration to the calendar year and the addition of the supporting actor and actress categories in 1936.

Originally the names of the award winners had been given to the press in advance with the stipulation that the information not be revealed until after the awards presentation. However, the Los Angeles Times printed the names of the 1939 winners in an early evening edition before the ceremony, draining the event of all its suspense during one of the industry’s biggest years. Thus, since then, the winners’ names have been a closely guarded secret until the official announcement at the awards ceremony.

The Academy Awards were first televised in the United States in 1953, and since 1969 they have been broadcast internationally. By the late 20th century, the ceremony had become a major happening, viewed by millions. Notable hosts over the years included Bob Hope, Johnny Carson, and Billy Crystal. Red-carpet interviews also became an integral part of the event, with much attention focused on the attendees’ ensembles. Steeply declining viewership in the late 2010s, however, led the academy to announce several changes to the ceremony’s broadcast, which included a limit of three hours, beginning in 2019, and an earlier air date, beginning in 2020.

Oscar Statuette

The design for the award statuette—a knight standing on a reel of film and holding a sword—is credited to Metro-Goldwyn-Mayer (MGM) art director Cedric Gibbons. Sculptor George Stanley was commissioned to create the original statuette based on Gibbons’s design. For many years the statuettes were cast in bronze, with 24-karat gold plating. During World War II the statuettes were made of plaster because of metal shortages. They are now made of gold-plated britannium. The design, however, has remained unchanged, with the exception of the pedestal base, the height of which was increased in 1945. The statuette stands 13.5 inches (34.3 cm) tall and weighs 8.5 pounds (3.8 kg).

The origins of the statuette’s nickname, Oscar, have been traced to three sources. Actress Bette Davisclaimed that the name derived from her observation that the backside of the statuette looked like that of her husband Harmon Oscar Nelson. Columnist Sidney Skolsky maintained that he gave the award its nickname to negate pretension. The name has also been attributed to academy librarian Margaret Herrick, who declared that the statuette looked like her Uncle Oscar. The true origin of the nickname has never been determined.

Jai Ganesh · 2018-12-13 00:28:58

258) Potato

Potato, (Solanum tuberosum), annual plant in the nightshade family (Solanaceae), grown for its starchy edible tubers. The potato is native to the Peruvian-Bolivian Andes and is one of the world’s main food crops. Potatoes are frequently served whole or mashed as a cooked vegetable and are also ground into potato flour, used in baking and as a thickener for sauces. The tubers are highly digestible and supply vitamin C, protein, thiamin, and niacin.

Potatoes are thought to have been independently domesticated several times and were largely cultivated in South America by the Incas as early as 1,800 years ago. Encountered by the invading Spaniards, potatoes were introduced into Europe during the second half of the 16th century. By the end of the 17th century the plant was a major crop in Ireland, and by the end of the 18th century it was a major crop in continental Europe, particularly Germany, and in the west of England. It continued to spread, in both Western and Eastern hemispheres, during the first four decades of the 19th century, and the Irish economy itself became dependent upon the potato. However, the disastrous failures of the Irish crops in the mid-19th century (especially in 1846 and 1848), because of late blight (Phytophthora infestans), and the resulting Irish Potato Famine generated a more-cautious attitude toward dependence on the plant.

The potato is one of some 150 tuber-bearing species of the genus Solanum (a tuber is the swollen end of an underground stem). The compound leaves are spirally arranged; each leaf is 20–30 cm (about 8–12 inches) long and consists of a terminal leaflet and two to four pairs of leaflets. The white, lavender, or purple flowers have five fused petals and yellow stamens. The fruit is a small poisonous berry with numerous seeds.

The stems extend underground into structures called stolons. The ends of the stolons may enlarge greatly to form a few to more than 20 tubers, of variable shape and size, usually ranging in weight up to 300 grams (10 ounces) but occasionally to more than 1.5 kg (3.3 pounds). The skin varies in colour from brownish white to deep purple; the starchy flesh normally ranges in colour from white to yellow, but it too may be purple. The tubers bear spirally arranged buds (eyes) in the axils of aborted leaves, of which scars remain. The buds sprout to form clones of the parent plant, allowing growers to vegetatively propagate desired characteristics. Indeed, vegetative reproduction is always used commercially, though the resulting decrease in genetic diversity has made the popular varieties more vulnerable to pests and diseases.

Jai Ganesh · 2018-12-15 00:19:50

259) Jackfruit

The jackfruit (Artocarpus heterophyllus), also known as jack tree, is a species of tree in the fig, mulberry, and breadfruit family (Moraceae) native to southwest India.

The jackfruit tree is well-suited to tropical lowlands, and its fruit is the largest tree-borne fruit, reaching as much as 55 kg (120 lb) in weight, 90 cm (35 in) in length, and 50 cm (20 in) in diameter. A mature jackfruit tree can produce about 100 to 200 fruits in a year. The jackfruit is a multiple fruit, composed of hundreds to thousands of individual flowers, and the fleshy petals are eaten.

Jackfruit is commonly used in South and Southeast Asian cuisines. The ripe and unripe fruit and seeds are consumed. The jackfruit tree is a widely cultivated throughout tropical regions of the world. It is the national fruit of Bangladesh and Sri Lanka, and the state fruit of the Indian states of Kerala and Tamil Nadu.

Etymology

The word "jackfruit" comes from Portuguese jaca, which in turn is derived from the Malayalam language term chakka (Malayalam chakka pazham). When the Portuguese arrived in India at Kozhikode (Calicut) on the Malabar Coast (Kerala) in 1498, the Malayalam name chakka was recorded by Hendrik van Rheede (1678–1703) in the Hortus Malabaricus, vol. iii in Latin. Henry Yule translated the book in Jordanus Catalani's (f. 1321–1330) Mirabilia descripta: the wonders of the East.

The common English name "jackfruit" was used by physician and naturalist Garcia de Orta in his 1563 book Colóquios dos simples e drogas da India. Centuries later, botanist Ralph Randles Stewart suggested it was named after William Jack (1795–1822), a Scottish botanist who worked for the East India Company in Bengal, Sumatra, and Malaya.

Botanical description

Shape, trunk and leaves

Artocarpus heterophyllus grows as an evergreen tree that has a relatively short trunk with a dense treetop. It easily reaches heights of 10 to 20 meters and trunk diameters of 30 to 80 centimeters. It sometimes forms buttress roots. The bark of the jackfruit tree is reddish-brown and smooth. In the event of injury to the bark, a milky juice is released.

The leaves are alternate and spirally arranged. They are gummy and thick and are divided into a petiole and a leaf blade. The petiole is 1 to 3 inches long. The leathery leaf blade is 7 to 15 inches long, and 3 to 7 inches wide and is oblong to ovate in shape.

In young trees, the leaf edges are irregularly lobed or split. On older trees, the leaves are rounded and dark green, with a smooth leaf margin. The leaf blade has a prominent main nerve and starting on each side six to eight lateral nerves. The stipules are egg-shaped at a length of 1.5 to 8 centimeters.

Flowers and fruit

The inflorescences are formed on the trunk, branches or twigs (caulifloria). Jackfruit trees are monoecious, that is there are both female and male flowers on a tree. The inflorescences are pedunculated, cylindrical to ellipsoidal or pear-shaped, to about 10-12 centimeters long and 5-7 centimeters wide.

Inflorescences are initially completely enveloped in egg-shaped cover sheets which rapidly slope off.

The flowers are very small, there are several thousand flowers in an inflorescence, which sit on a fleshy rachis . The male flowers are greenish, some flowers are sterile. The male flowers are hairy and the perianth ends with two 1 to 1.5 millimeters membrane. The individual and prominent stamens are straight with yellow, roundish anthers. After the pollen distribution, the stamens become ash-gray and fall off after a few days. Later all the male inflorescences also fall off. The greenish female flowers, with hairy and tubular perianth, have a fleshy flower-like base. The female flowers contain an ovary with a broad, capitate or rarely bilobed scar. The blooming time ranges from December until February or March.

The ellipsoidal to roundish fruit is a multiple fruit formed from the fusion of the ovaries of multiple flowers. The fruits grow on a long and thick stem on the trunk. They vary in size and ripen from an initially yellowish-greenish to yellow, and then at maturity to yellowish-brown. They possess a hard, gummy shell with small pimples surrounded with hard, hexagonal tubercles. The very large and variously shaped fruit have a length of 30 to 100 centimeters and a diameter of 15 to 50 centimeters and can weigh 10-25 kilograms or more.

The fruits consist of a fibrous, whitish core (rachis) about 5-10 centimeters thick. Radiating from this are many 10 centimeter long individual fruits. They are elliptical to egg-shaped, light brownish achenes with a length of about 3 centimeters and a diameter of 1.5 to 2 centimeters.
There may be about 100-500 seeds per fruit. The seed coat consists of a thin, waxy, parchment-like and easily removable testa (husk) and a brownish, membranous tegmen. The cotyledons are usually unequal in size.

The fruit matures during the rainy season from July to August. The bean-shaped achenes of the jackfruit are coated with a firm yellowish aril(seed coat, flesh), which has an intense sweet taste at maturity of the fruit. The pulp is enveloped by many narrow strands of fiber (undeveloped perianth), which run between the hard shell and the core of the fruit and are firmly attached to it. When pruned, the inner part (core) secretes a very sticky, milky liquid, which can hardly be removed from the skin, even with soap and water. To clean the hands after "unwinding" the pulp an oil or other solvent is used. For example, street vendors in Tanzania, who sell the fruit in small segments, provide small bowls of kerosene for their customers to cleanse their sticky fingers.

An average fruit consists of 27% edible seed coat, 15% edible seeds, 20% white pulp (undeveloped perianth, rags) and bark and 10% core.

The number of chromosomes is 2n = 56.

As food

Ripe jackfruit is naturally sweet, with subtle flavoring. It can be used to make a variety of dishes, including custards, cakes, or mixed with shaved ice as es teler in Indonesia or halo-halo in the Philippines. For the traditional breakfast dish in southern India, idlis, the fruit is used with rice as an ingredient and jackfruit leaves are used as a wrapping for steaming. Jackfruit dosas can be prepared by grinding jackfruit flesh along with the batter. Ripe jackfruit arils are sometimes seeded, fried, or freeze-dried and sold as jackfruit chips.

The seeds from ripe fruits are edible, and are said to have a milky, sweet taste often compared to Brazil nuts. They may be boiled, baked, or roasted. When roasted, the flavor of the seeds is comparable to chestnuts. Seeds are used as snacks (either by boiling or fire-roasting) or to make desserts. In Java, the seeds are commonly cooked and seasoned with salt as a snack. They are quite commonly used in curry in India in the form of a traditional lentil and vegetable mix curry.

Aroma

Jackfruit has a distinctive sweet and fruity aroma. In a study of flavour volatiles in five jackfruit cultivars, the main volatile compoundsdetected were ethyl isovalerate, propyl isovalerate, butyl isovalerate, isobutyl isovalerate, 3-methylbutyl acetate, 1-butanol, and 2-methylbutan-1-ol.

A fully ripe and unopened jackfruit is known to "emit a strong aroma", with the inside of the fruit described as smelling of pineapple and banana. After roasting, the seeds may be used as a commercial alternative to chocolate aroma.

Nutritional value

The flesh of the jackfruit is starchy and fibrous and is a source of dietary fiber. The pulp is composed of 74% water, 23% carbohydrates, 2% protein, and 1% fat. In a 100-g portion, raw jackfruit provides 400 kJ (95 kcal) and is a rich source (20% or more of the Daily Value, DV) of vitamin B6 (25% DV). It contains moderate levels (10-19% DV) of vitamin C and potassium, with no other nutrients in significant content.

The jackfruit also provides a potential part of the solution for tropical countries facing problems with food security, such as several countries of Africa.

Culinary uses

The flavor of the ripe fruit is comparable to a combination of apple, pineapple, mango, and banana. Varieties are distinguished according to characteristics of the fruit flesh. In Indochina, the two varieties are the "hard" version (crunchier, drier, and less sweet, but fleshier), and the "soft" version (softer, moister, and much sweeter, with a darker gold-color flesh than the hard variety). Unripe jackfruit has a mild flavor and meat-like texture and is used in curry dishes with spices in many cuisines. The skin of unripe jackfruit must be peeled first, then the remaining jackfruit flesh is chopped in a labor-intensive process into edible portions and cooked before serving.

The cuisines of many Asian countries use cooked young jackfruit. In many cultures, jackfruit is boiled and used in curries as a staple food. The boiled young jackfruit is used in salads or as a vegetable in spicy curries and side dishes, and as fillings for cutlets and chops. It may be used by vegetarians as a substitute for meat. It may be cooked with coconut milk and eaten alone or with meat, shrimp or smoked pork. In southern India, unripe jackfruit slices are deep-fried to make chips.

South Asia

In Bangladesh, the fruit is consumed on its own. The unripe fruit is used in curry, and the seed is often dried and preserved to be later used in curry. In India, two varieties of jackfruit predominate: muttomvarikka and sindoor. Muttomvarikka has a slightly hard inner flesh when ripe, while the inner flesh of the ripe sindoor fruit is soft.

A sweet preparation called chakkavaratti (jackfruit jam) is made by seasoning pieces of muttomvarikka fruit flesh in jaggery, which can be preserved and used for many months. The fruits are either eaten alone or as a side to rice. The juice is extracted and either drunk straight or as a side. The juice is sometimes condensed and eaten as candies. The seeds are either boiled or roasted and eaten with salt and hot chilies. They are also used to make spicy side dishes with rice. Jackfruit may be ground and made into a paste, then spread over a mat and allowed to dry in the sun to create a natural chewy candy.

Southeast Asia

In Indonesia and Malaysia, jackfruit is called nangka. The ripe fruit is usually sold separately and consumed on its own, or sliced and mixed with shaved ice as a sweet concoction dessert such as es campur and es teler. The ripe fruit might be dried and fried as kripiknangka, or jackfruit cracker. The seeds are boiled and consumed with salt, as it contains edible starchy content; this is called beton. Young (unripe) jackfruit is made into curry called gulai nangka or stewed called gudeg.

In the Philippines, jackfruit is called langka in Filipino and nangka in Cebuano. The unripe fruit is usually cooked in coconut milk and is eaten with rice. The ripe fruit is often an ingredient in local desserts such as halo-halo and the Filipino turon. The ripe fruit, besides also being eaten raw as it is, is also preserved by storing in syrup or by drying. The seeds are also boiled before being eaten.

Thailand is a major producer of jackfruit, which are often cut, prepared, and canned in a sugary syrup (or frozen in bags or boxes without syrup) and exported overseas, frequently to North America and Europe.

In Vietnam, jackfruit is used to make jackfruit chè, a sweet dessert soup, similar to the Chinese derivative bubur cha cha. The Vietnamese also use jackfruit purée as part of pastry fillings or as a topping on xôi ngọt (a sweet version of sticky rice portions).

Jackfruits are found primarily in the eastern part of Taiwan. The fresh fruit can be eaten directly or preserved as dried fruit, candied fruit, or jam. It is also stir-fried or stewed with other vegetables and meat.

Americas

In Brazil, three varieties are recognized: jaca-dura, or the "hard" variety, which has a firm flesh, and the largest fruits that can weigh between 15 and 40 kg each; jaca-mole, or the "soft" variety, which bears smaller fruits with a softer and sweeter flesh; and jaca-manteiga, or the "butter" variety, which bears sweet fruits whose flesh has a consistency intermediate between the "hard" and "soft" varieties.

Africa

From a tree planted for its shade in gardens, it became an ingredient for local recipes using different fruit segments. The seeds are boiled in water or roasted to remove toxic substances, and then roasted for a variety of desserts. The flesh of the unripe jackfruit is used to make a savory salty dish with smoked pork. The jackfruit arils are used to make jams or fruits in syrup, and can also be eaten raw.

Wood and manufacturing

The golden yellow timber with good grain is used for building furniture and house construction in India. It is termite-proof and is superior to teak for building furniture. The wood of the jackfruit tree is important in Sri Lanka and is exported to Europe. Jackfruit wood is widely used in the manufacture of furniture, doors and windows, in roof construction, and fish sauce barrels.

The wood of the tree is used for the production of musical instruments. In Indonesia, hardwood from the trunk is carved out to form the barrels of drums used in the gamelan, and in the Philippines, its soft wood is made into the body of the kutiyapi, a type of boat lute. It is also used to make the body of the Indian string instrument veena and the drums mridangam, thimila, and kanjira.

Cultural significance

The jackfruit has played a significant role in Indian agriculture for centuries. Archeological findings in India have revealed that jackfruit was cultivated in India 3000 to 6000 years ago. It has also been widely cultivated in Southeast Asia.

The ornate wooden plank called avani palaka, made of the wood of the jackfruit tree, is used as the priest's seat during Hindu ceremonies in Kerala. In Vietnam, jackfruit wood is prized for the making of Buddhist statues in temples. The heartwood is used by Buddhist forest monastics in Southeast Asia as a dye, giving the robes of the monks in those traditions their distinctive light-brown color.

Jackfruit is the national fruit of Bangladesh, and the state fruit of the Indian states of Kerala and Tamil Nadu.

Cultivation

In terms of taking care of the plant, minimal pruning is required; cutting off dead branches from the interior of the tree is only sometimes needed. In addition, twigs bearing fruit must be twisted or cut down to the trunk to induce growth for the next season. Branches should be pruned every three to four years to maintain productivity.

Some trees carry too many mediocre fruits and these are usually removed to allow the others to develop better to maturity.
Stingless bees such as Tetragonula iridipennis are jackfruit pollinators, so play an important role in jackfruit cultivation.
Production and marketing.

In 2017, India produced 1.4 million tonnes of jackfruit, followed by Bangladesh, Thailand, and Indonesia.

The marketing of jackfruit involves three groups: producers, traders, and middlemen, including wholesalers and retailers. The marketing channels are rather complex. Large farms sell immature fruit to wholesalers, which helps cash flow and reduces risk, whereas medium-sized farms sell the fruit directly to local markets or retailers.

Commercial availability

Outside of its countries of origin, fresh jackfruit can be found at food markets throughout Southeast Asia. It is also extensively cultivated in the Brazilian coastal region, where it is sold in local markets. It is available canned in sugary syrup, or frozen, already prepared and cut. Jackfruit industries are established in Sri Lanka and Vietnam, where the fruit is processed into products such as flour, noodles, papad, and ice cream. It is also canned and sold as a vegetable for export.

Outside of countries where it is grown, jackfruit can be obtained year-round, both canned or dried. Dried jackfruit chips are produced by various manufacturers.

Invasive species

In Brazil, the jackfruit can become an invasive species as in Brazil's Tijuca Forest National Park in Rio de Janeiro. The Tijuca is mostly an artificial secondary forest, whose planting began during the mid-19th century; jackfruit trees have been a part of the park's flora since it was founded.

Recently, the species has expanded excessively, and its fruits, which naturally fall to the ground and open, are eagerly eaten by small mammals, such as the common marmoset and coati. The seeds are dispersed by these animals; this allows the jackfruit to compete for space with native tree species. Additionally the supply of jackfruit as a ready source of food has allowed the marmoset and coati populations to expand. Since both prey opportunistically on birds' eggs and nestlings, increases in marmoset or coati population are detrimental for local bird populations.

Monox D. I-Fly · 2018-12-16 15:29:52

ganesh wrote:

The fruit matures during the rainy season from July to August. The bean-shaped achenes of the jackfruit are coated with a firm yellowish aril(seed coat, flesh), which has an intense sweet taste at maturity of the fruit. The pulp is enveloped by many narrow strands of fiber (undeveloped perianth), which run between the hard shell and the core of the fruit and are firmly attached to it. When pruned, the inner part (core) secretes a very sticky, milky liquid, which can hardly be removed from the skin, even with soap and water. To clean the hands after "unwinding" the pulp an oil or other solvent is used. For example, street vendors in Tanzania, who sell the fruit in small segments, provide small bowls of kerosene for their customers to cleanse their sticky fingers.

Jackfruit is my third most favorite fruit, but I hate that it's one of the stickiest fruits I have ever eaten.

Jai Ganesh · 2018-12-16 16:27:35

Monox D. I-Fly wrote:

ganesh wrote:
The fruit matures during the rainy season from July to August. The bean-shaped achenes of the jackfruit are coated with a firm yellowish aril(seed coat, flesh), which has an intense sweet taste at maturity of the fruit. The pulp is enveloped by many narrow strands of fiber (undeveloped perianth), which run between the hard shell and the core of the fruit and are firmly attached to it. When pruned, the inner part (core) secretes a very sticky, milky liquid, which can hardly be removed from the skin, even with soap and water. To clean the hands after "unwinding" the pulp an oil or other solvent is used. For example, street vendors in Tanzania, who sell the fruit in small segments, provide small bowls of kerosene for their customers to cleanse their sticky fingers.
Jackfruit is my third most favorite fruit, but I hate that it's one of the stickiest fruits I have ever eaten.

Some advantages, some disadvantages....Something to like, something to dislike....

Jai Ganesh · 2018-12-17 00:51:37

260) Oscillators

Oscillators are important in many different types of electronic equipment. For example, a quartz watch uses a quartz oscillator to keep track of what time it is. An AM radio transmitter uses an oscillator to create the carrier wave for the station, and an AM radio receiver uses a special form of oscillator called a resonator to tune in a station. There are oscillators in computers, metal detectors etc.

To understand how electronic oscillators work, it is helpful to look at examples from the physical world. In this article, you'll learn the basic idea behind oscillators and how they're used in electronics.

Oscillation Basics

One of the most commonly used oscillators is the pendulum of a clock. If you push on a pendulum to start it swinging, it will oscillate at some frequency -- it will swing back and forth a certain number of times per second. The length of the pendulum is the main thing that controls the frequency.

For something to oscillate, energy needs to move back and forth between two forms. For example, in a pendulum, energy moves between potential energy and kinetic energy. When the pendulum is at one end of its travel, its energy is all potential energy and it is ready to fall. When the pendulum is in the middle of its cycle, all of its potential energy turns into kinetic energy and the pendulum is moving as fast as it can. As the pendulum moves toward the other end of its swing, all the kinetic energy turns back into potential energy. This movement of energy between the two forms is what causes the oscillation.

Eventually, any physical oscillator stops moving because of friction. To keep it going, you have to add a little bit of energy on each cycle. In a pendulum clock, the energy that keeps the pendulum moving comes from the spring. The pendulum gets a little push on each stroke to make up for the energy it loses to friction.

An electronic oscillator works on the same principle.

Oscillator Circuits

Energy needs to move back and forth from one form to another for an oscillator to work. You can make a very simple oscillator by connecting a capacitor and an inductor together. If you've read How Capacitors Work and How Inductors Work, you know that both capacitors and inductors store energy. A capacitor stores energy in the form of an electrostatic field, while an inductor uses a magnetic field.

If you charge up the capacitor with a battery and then insert the inductor into the circuit, here's what will happen:
i) The capacitor will start to discharge through the inductor. As it does, the inductor will create a magnetic field.
ii) Once the capacitor discharges, the inductor will try to keep the current in the circuit moving, so it will charge up the other plate of the capacitor.
iii) Once the inductor's field collapses, the capacitor has been recharged (but with the opposite polarity), so it discharges again through the inductor.

This oscillation will continue until the circuit runs out of energy due to resistance in the wire. It will oscillate at a frequency that depends on the size of the inductor and the capacitor.

Resonators

In a simple crystal radio capacitor/inductor, oscillator acts as the tuner for the radio.

Thousands of sine waves from different radio stations hit the antenna. The capacitor and inductor want to resonate at one particular frequency. The sine wave that matches that particular frequency will get amplified by the resonator, and all of the other frequencies will be ignored.

In a radio, either the capacitor or the inductor in the resonator is adjustable. When you turn the tuner knob on the radio, you are adjusting, for example, a variable capacitor. Varying the capacitor changes the resonant frequency of the resonator and therefore changes the frequency of the sine wave that the resonator amplifies. This is how you "tune in" different stations on the radio!

In electronic oscillators, a similar activity is happening, only it is based in an electronic source. Generally, a battery will be connected to a capacitor, which is a device that stores a very small amount of energy. The capacitor is connected to a working device, a light bulb for example. The battery transfers a charge to the capacitor untilthe capacitor is full. When the capacitor is full, it releases all of its charge at once to the light bulb, causing it to burn very bright for a moment, and then die gradually. The battery is meanwhile recharging the capacitor so the process can repeat. As a result, a blinking light is produced.

The oscillator works because of the difference between the battery and the capacitor. A battery can store a significantly higher amount of energy than a capacitor, but it takes longer to release. The capacitor can only contain a small charge, but it can dispense all of its charge at once. This sudden release powers the light bulb or other device very quickly, and leads to a slowly diminishing charge.

Relaxation Oscillators

There are two main types of oscillators: relaxation and harmonizing. The difference between the two types is based on the shape of the released signal. A relaxation oscillator will discharge in a square wave or a sawtooth wave. When graphed, this type of wave rises gradually and then drops suddenly, creating a shark-fin type shape. An inverse sawtooth drops gradually and then rises suddenly. This type of signal is differentiated from a sine wave in that it is less direct but contains a number of odd and even integer signals, covering the spectrum of its apex and zenith. As such, it has a distinct audio signal that makes it clear for producing musical sounds. Additionally, despite its harshness compared to other waves, it is still a very clear sound.

Variable Parts in Relaxation Oscillators

When choosing a relaxation oscillator, there are two very important aspects common in any electronic power source: the amp and voltage capabilities. Amperes, or amps, represent electric charge in motion. Technically, one amp is equivalent to 6.242 x {10}^{18} electrons passing by a given point in one second. Voltage represents the amount of driving force between two given electrons in a charge. The higher the voltage, the “higher” the electric current and therefore the more driving power.

To determine if a relaxation oscillator is appropriate for a given application, it is necessary to find the appropriate amp and voltage capabilities of both a power source (battery) as well as the capacitor. If the electric charge is too great for the capacitor or device, a short out can occur when the device is overcharged. Alternatively, an electric charge that is too low, or “flat” will fail to “turn over,” or activate, a device.

Additionally, relaxation oscillators are composed of resistors which can control the charge flow. This is represented by the battery in the example above. Some oscillator functions require a linear, or constant input of charge. This is called a “constant current source,” and reflects the way current will be constantly added to the capacitor in order to affect a constant charge. To differentiate from a constant current source, see a camera’s flash capability. The capacitor is charged only once, until the threshold is met and the flash is discharged.

Finally, relaxation oscillators can be affixed with different kind of “desynchronous” controls. These controls allow the charge to be controlled by a third control connection. In other words, the charge is produced by a separate signal and then converted into use by the capacitor. Oscilloscopes are examples of oscillators that employ synchronous control pulses.

Jai Ganesh · 2018-12-19 01:02:40

261) Squirrel

Alternative Title: Sciuridae

Squirrel, (family Sciuridae), generally, any of the 50 genera and 268 species of rodents whose common name is derived from the Greek skiouros, meaning “shade tail,” which describes one of the most conspicuous and recognizable features of these small mammals. These distinctive animals occupy a range of ecological niches worldwide virtually anywhere there is vegetation. The squirrel family includes ground squirrels, chipmunks, marmots, prairie dogs, and flying squirrels, but to most people squirrel refers to the 122 species of tree squirrels, which belong to 22 genera of the subfamily Sciurinae. The North American gray squirrel (Sciurus carolinensis) has adapted to urban and suburban areas where it is regarded as aesthetic or as a minor annoyance. In northern Europe the red squirrel (S. vulgaris) is valued for its soft, thick fur. Villagers in tropical forests keep squirrels as pets. Most species are hunted for food.

General Features

Tree squirrels have slender, lanky bodies, long, muscular limbs, and furred feet. The forefeet have four long digits plus a short, stubby thumb, and the five-toed hind feet are narrow or moderately wide. The bald soles of the feet take the form of prominent, fleshy pads. Because the ankle joints are flexible and can be rotated, squirrels can rapidly descend trees headfirst with the hind feet splayed flat against the trunk. Their large, bright eyes convey an alert demeanour, and the broad, short head tapers to a blunt muzzle adorned with long whiskers. The rounded ears, small in relation to body size, are densely covered with short, fine hairs, which form a long tuft at the tips of the ears in some species. The tail is about as long as head and body or appreciably longer. Furred from base to tip, the tail appears bushy and cylindrical when the hairs grow evenly around the tail; the tail appears flatter if the fur originates only from opposite sides. Claws are large, strong, curved, and very sharp, which enables tree squirrels to navigate vertical surfaces and slim branches.

Variation in body size is considerable. Largest are the four species of Oriental giant squirrels (genus Ratufa) native to the tropical forests of Southeast Asia. Weighing 1.5 to 3 kg (3 to almost 7 pounds), it has a body length of 25 to 46 cm (about 10 to 18 inches) and a tail about as long. Two species of pygmy squirrels are the smallest: the neotropical pygmy squirrel (Sciurillus pusillus) of the Amazon Basin weighs 33 to 45 grams (1 to 1.5 ounces), with a body 9 to 12 cm long and an equally long tail; but the African pygmy squirrel (Myosciurus pumilio) of the West African tropical forests is even smaller, at 13 to 20 grams, with a body length of 6 to 8 cm and a somewhat shorter tail.

Squirrels’ soft, dense fur is moderately long in most species but can be very long and almost shaggy in some. Colour is extraordinarily variable. Some species are plain, covered in one or two solid shades of brown or gray. A few species are striped along the sides and back; sometimes the head is also striped. Tropical species exhibit combinations of white, gray, yellow, orange, red, maroon, brown, and black, yielding a variety of complex coat patterns.

Natural History

All tree squirrels are diurnal and arboreal, but the range of vertical activity in species differs widely, especially among those living in tropical rainforests. Some, such as the Oriental giant squirrels (genus Ratufa) and the African giant squirrels (genus Protoxerus), rarely descend from the high canopy. Others, like the pygmy squirrel of Sulawesi (Prosciurillus murinus), travel and forage at intermediate levels between ground and canopy. Some large tropical squirrels, such as the Sulawesi giant squirrel (Rubrisciurus rubriventer) and the northern Amazon red squirrel (Sciurus igniventris), nest at middle levels but travel and forage low in the understory or on the ground. The African palm squirrels (genus Epixerus) are long-legged runners that forage only on the ground. Certain species, such as the red-tailed squirrel (S. granatensis) of the American tropics and the African pygmy squirrel, are active from ground to canopy. In the United States, the Eastern fox squirrel (S. niger) runs along the ground from tree to tree, but others, including the Eastern gray squirrel (S. carolinensis), prefer to travel through the treetops and regularly cross rivers by swimming with the head up and tail flat on the water’s surface. Thomas’s rope squirrel (Funisciurus anerythrus) of Africa even submerges itself and swims underwater.

Most tree squirrels have strong chisel-like incisors and powerful jaws, which are required for gnawing open the hard nuts that, along with fruits, are a primary component of their diet. They also eat seeds, fungi, insects and other arthropods, the cambium layer of tree bark, nectar, leaves, buds, flowers, and sometimes bird eggs, nestlings, and carrion. Some red squirrels (genus Tamiasciurus) and Sciurus species of temperate climates will stalk, kill, and eat other squirrels, mice, and adult birds and rabbits for food, but such predation in tropical tree squirrels seems rare.

Nests are constructed among branches in the forest canopy or at lower levels in tree crowns, vine tangles, tree hollows, or undergrowth near the ground. Some species of tropical tree squirrels produce several litters per year; breeding season in the Northern Hemisphere may extend from December to September and may result in one or two litters that average three to seven young, depending upon the species.

In the New World, tree squirrels range from the boreal forests of Canada and Alaska southward through coniferous and deciduous woodlands in the United States to the tropical rainforests of South America. In Africa, tree squirrels are native to rainforests and some woodland savannas. Their distribution in the remainder of the Old World extends from the northern boreal forests of Europe and Asia to the Indonesian tropical rainforests. East of the Asian continental margin, tree squirrels inhabit the forests of Taiwan, some islands in the Philippines, and Sulawesi, but they do not occur naturally anywhere east of those islands. Most of the species in 20 of the 22 genera are found in tropical rainforests.

Classification And Evolutionary History

Tree squirrels belong to the subfamily Sciurinae; it and the subfamily Pteromyinae (flying squirrels) constitute the family Sciuridae of the order Rodentia. Fossils record the evolutionary history of tree squirrels back to the Late Eocene Epoch (41.3 million to 33.7 million years ago) in North America and the Miocene Epoch (23.8 million to 5.3 million years ago) in Africa and Eurasia.

Jai Ganesh · 2018-12-21 00:49:33

262) Coconut palm

Coconut palm, (Cocos nucifera), tree of the palm family (Arecaceae). It is one of the most important crops of the tropics. The slender, leaning, ringed trunk of the tree rises to a height of up to 25 metres (80 feet) from a swollen base and is surmounted by a graceful crown of giant featherlike leaves. Mature fruits, ovoid or ellipsoid in shape, 300–450 mm (12–18 inches) in length, and 150–200 mm in diameter, have a thick fibrous husk surrounding the familiar single-seeded nut of commerce. A hard shell encloses the insignificant embryo with its abundant endosperm, composed of both meat and liquid.

Coconut fruits float readily and have been dispersed widely by ocean currents and by humans throughout the tropics; they probably originated somewhere in Indo-Malaya. Marco Polo was among the first Europeans to describe coconuts.

Coconut palms flourish best close to the sea on low-lying areas a few feet above high water where there is circulating groundwater and an ample rainfall. Most of the world’s coconuts are produced on small native plantations. Propagation is by unhusked ripe nuts. These are laid on their sides close together in nursery beds and almost covered with soil. After 4 to 10 months the seedlings are transplanted to the field, where they are spaced at distances of 8–10 metres. Palms usually start bearing after 5 to 6 years. Full bearing is obtained in 15 years. Fruits require a year to ripen; the annual yield per tree may reach 100, but 50 is considered good. Yields continue profitably until trees are about 50 years old.

The harvested coconut yields copra, the dried extracted kernel, or meat, from which coconut oil, the world’s ranking vegetable oil, is expressed. The Philippines and Indonesia lead in copra production, and throughout the South Pacific copra is one of the most important export products. The meat may also be grated and mixed with water to make coconut milk, used in cooking and as a substitute for cow’s milk.

Although the coconut finds its greatest commercial utilization in the industrial countries of the Western world, its usefulness in its native areas of culture is even greater. Indonesians claim that coconuts have as many uses as there are days in a year. Besides the edible kernels and the drink obtained from green nuts, the husk yields coir, a fibre highly resistant to salt water and used in the manufacture of ropes, mats, baskets, brushes, and brooms.

Other useful products derived from the coconut palm include toddy, palm cabbage, and construction materials. Toddy, a beverage drunk fresh, fermented, or distilled, is produced from the sweetish sap yielded by the young flower stalks when wounded or cut; toddy is also a source of sugar and alcohol. Palm cabbage, the delicate young bud cut from the top of the tree, is, like the buds from other palms, eaten as a salad vegetable. Mature palm leaves are used in thatching and weaving baskets. The fibrous, decay-resistant tree trunk is incorporated into the construction of huts; it is also exported as a cabinet wood called porcupine wood.

Jai Ganesh · 2018-12-23 00:59:07

263) Flagellum

Flagellum, plural flagella, hairlike structure that acts primarily as an organelle (See below) of locomotion in the cells of many living organisms. Flagella, characteristic of the protozoan group Mastigophora, also occur on the gametes of algae, fungi, mosses, slime molds, and animals. Flagellar motion causes water currents necessary for respiration and circulation in sponges and coelenterates. Most motile bacteria move by means of flagella.

The structures and pattern of movement of prokaryotic and eukaryotic flagella are different. Eukaryotes have one to many flagella, which move in a characteristic whiplike manner. The flagella closely resemble the cilium in structure. The core is a bundle of nine pairs of microtubules surrounding two central pairs of microtubules (the so-called nine-plus-two arrangement); each microtubule is composed of the protein tubulin. The coordinated sliding of these microtubules confers movement. The base of the flagellum is anchored to the cell by a basal body.

Bacterial flagella are helically shaped structures containing the protein flagellin. The base of the flagellum (the hook) near the cell surface is attached to the basal body enclosed in the cell envelope. The flagellum rotates in a clockwise or counterclockwise direction, in a motion similar to that of a propeller.
The movement of eukaryotic flagella depends on adenosine triphosphate (ATP) for energy, while that of the prokaryotes derives its energy from the proton-motive force, or ion gradient, across the cell membrane.

(Organelle: any of the specialized structures within a cell that perform a specific function (e.g., mitochondria, ribosomes, endoplasmic reticulum). Organelles in unicellular organisms are the equivalent of organs in multicellular organisms. The contractile vacuole of protozoans, for example, extracts fluid wastes from the cell and eliminates them from the organism, as does the kidney in larger organisms.)

Flagellum Definition

A flagellum is a microscopic hair-like organelle used by cells and microorganisms for movement. The word flagellum in Latin means whip, just like the whipping motion flagella (plural) often use for locomotion. Specialized flagella in some organisms are also used as sensory organelles that can detect changes in temperature and pH.

Function of Flagellum

Flagella are filamentous protein structures found in bacteria, archaea, and eukaryotes, though they are most commonly found in bacteria. They are typically used to propel a cell through liquid (i.e. bacteria and male gamete). However, flagella have many other specialized functions. Some eukaryotic cells use flagellum to increase reproduction rates. Other eukaryotic and bacterial flagella are used to sense changes in the environment, such as temperature or pH disturbances. Recent work with the green alga Chlamydomonas reinhardtii has shown that flagellum may also be used as a secretory organelle, but this discovery needs more time to be fully understood.

Examples of Flagellum

A flagellum can be comprised of different structures depending on the organism, especially when flagellum from eukaryotes and bacteria are compared. Since eukaryotes are usually complex organisms, the attached flagellum is more complex as well. The flagellum is made up of microtubules composed from a protein called tubulin. Nine microtubule pairs surround another two pairs of microtubules in the center to form the core of the flagellum; this is known as the nine-plus-two arrangement. The whole nine-plus-two structure is anchored in a basal body within the organism. These bundled microtubules use ATP to bend back and forth in a whip-like motion together.

Although few multicellular eukaryotes have true flagellum, almost half the human population produces cells with them in the form of male gamete. This is the only cell in the human body with flagellum, and for good reason. In order to move through the tract to meet the egg, male gamete must be able to swim, or move, very long distances (in comparison of cell to body size). Without the flagellum, there would be very little chance of fertilization or population stability.
On the other hand, bacterial flagella are structured and function completely differently than the eukaryotic counterparts. These flagella are made of a protein called flagellin. ATP isn’t needed because bacterial flagellum can use the energy of the proton-motive force. This means the energy is derived from ion gradients – usually hydrogen or sodium – which lie across cell membranes. These flagella are helix shaped and rotate quickly like a windmill to move the organism instead of whipping back and forth. The bacteria Escherichia coli uses this windmill-like locomotion to propel up the urethra to cause urinary tract infections. Salmonella enterica, a harmful pathogen, uses several windmill-like flagella to infect human hosts.

Types of Flagellum

The flagellar structure consists of three different parts: rings embedded in the basal body, a hook near the surface of the organism to keep it in place, and the flagellar protein filaments. Every flagellum has these three things in common, regardless of organism. However, there are four distinct types of bacterial flagellum based on location:
A. Monotrichous: A single flagellum at one end of the organism or the other.
B. Lophotrichous: Several flagellum on one end of the organism or the other.
C. Amphitrichous: A single flagellum on both ends of the organism.
D. Peritrichous: Several flagellum attached all over the organism.

Monotrichous, amphitrichous, and lophotrichous flagellum are considered polar flagellum because the flagellum is strictly located on the ends of the organism. These flagella can rotate both clockwise and counterclockwise. A clockwise movement propels the organism (or cell) forward, while a counterclockwise movement pulls the organism backwards.

Peritrichous flagella are not considered polar because they are located all over the organism. When these flagella rotate in a counterclockwise movement, they form a bundle that propels the organism in one direction. If a few of the flagellum break away and begin rotating clockwise, the organism then begins a tumbling motion. During this time, the organism cannot move in any real direction.

If any flagellum stops rotating—regardless of polarity—the organism will change direction. This is caused by Brownian motion (constant movement of liquid particles) and fluid currents catching up with the organism and spinning it around. Some organisms that cannot change direction on their own rely on Brownian motion and fluid currents to do it for them.

Related Biology Terms

(i) ATP – Adenosine triphosphate, a small molecule used in cells as a coenzyme that transfers energy.
(ii) Microtubules – A microscopic tubular structure present in the cytoplasm of cells that helps form the cytoskeleton.
(iii) Basal body – An organelle that forms the very base of a flagellum; it is similar to a centriole in structure.
(iv) Brownian motion – The random movement of particles in a fluid (liquid or gas), caused by bumping into other molecules within the same fluid.

Jai Ganesh · 2018-12-25 00:46:14

264) Lemon

Lemon, (Citrus ×limon), small tree or spreading bush of the rue family (Rutaceae) and its edible fruit. Lemon juice is a characteristic ingredient in many pastries and desserts, such as tarts and the traditional American lemon meringue pie. The distinctive astringent flavour of the fruit, either fresh or preserved, is also used to enhance many poultry, fish, and vegetable dishes worldwide. Lemonade, made with lemon, sugar, and water, is a popular warm-weather beverage, and the juice itself is commonly added to tea. Citric acid may amount to 5 percent or more by weight of the lemon’s juice, which is also rich in vitamin C and contains smaller amounts of the B vitamins, particularly thiamin, riboflavin, and niacin.

The lemon was introduced into Spain and North Africa sometime between the years 1000 and 1200 CE. It was further distributed through Europe by the Crusaders, who found it growing in Palestine. In 1494 the fruit was being cultivated in the Azores and shipped largely to England. The lemon was thought by 18th-century Swedish botanist Carolus Linnaeus to be a variety of citron (Citrus medica), though it is now known to be a separate hybrid species.

The lemon plant forms an evergreen spreading bush or small tree, 3–6 metres (10–20 feet) high if not pruned. Its young oval leaves have a decidedly reddish tint; later they turn green. In some varieties the young branches of the lemon are angular; some have sharp thorns at the axils of the leaves. The flowers have a sweet odour and are solitary or borne in small clusters in the axils of the leaves. Reddish-tinted in the bud, the petals are usually white above and reddish purple below. The fruit is oval with a broad, low, apical nipple and forms 8 to 10 segments. The outer rind, or peel, yellow when ripe and rather thick in some varieties, is prominently dotted with oil glands. The white spongy inner part of the peel, called the mesocarp or albedo, is nearly tasteless and is the chief source of commercial grades of pectin. The seeds are small, ovoid, and pointed; occasionally fruits are seedless. The pulp is decidedly acidic.

As a cultivated tree, the lemon is now grown to a limited extent in most tropical and subtropical countries. Lemon trees for commercial planting are usually propagated by grafting or budding the desired variety on seedlings of other Citrus species, such as the sweet orange, grapefruit, mandarin orange, sour orange, or tangelo. Seedlings of these species are superior to lemon seedlings as rootstocks because they are more uniform and less susceptible to the various crown- and foot-rot diseases.

The relatively cool, equable climatic zones of coastal Italy and California are especially favourable for lemon cultivation. The trees are commonly grown in orchards, where they are spaced 5–8 metres (16–26 feet) apart. Lemon trees usually bloom throughout the year, and the fruit is picked 6 to 10 times a year. Full-sized fruit for commercial purposes is about 50 mm (2 inches) in diameter. The fruit is usually picked while still green and, after curing, may be kept three months or more in storage.
Young lemon trees reach bearing age as early as the third year after planting, and commercial crops may be expected during the fifth year. The average orchard yield per tree is 1,500 lemons a year. Careful handling is essential to prevent the loss of fruit in storage and transit because of fungal diseases. Picked lemons are graded in the packing house according to their maturity, which is indicated by their colour; yellow fruits are already fully ripe and must be sold immediately, while fruits that are still green are held in storage until they become a uniform yellow in colour.

Among the important by-products of lemons are citric acid, citrate of lime, lemon oil, and pectin. Preparation of the oil, used in perfumes, soap, and flavouring extract, is an important industry in Sicily. Citric acid is used in beverage manufacturing. Pectin has long been an important material for making fruit jellies; it has also been used in medicine in the treatment of intestinal disorders, as an antihemorrhagic, as a plasma extender, and for other purposes.

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Jai Ganesh · 2018-12-27 01:10:22

265) Espresso

Espresso, (Italian: “fast, express”) a strong brew of coffee produced by forcing boiled water under pressure through finely ground coffee. The finely ground coffee beans means an increased amount of surface contact with the water, resulting in a highly flavoured and aromatic brew. The nuances of brewing and enjoying the drink have spurred international barista championships and detailed discussions of the drink by aficionados worldwide. Espresso is especially associated with Italy, where it is woven into the fabric of daily life.

A culture of refinement has long surrounded this dark, rich, and exotic beverage, an aura doubtless tied to the beginning of coffeehouses in the Middle East in the 15th and 16th centuries, when such establishments attracted the leading thinkers and writers of the day. But the surprising truth is that espresso is an innovation of the late 19th and early 20th centuries. In fact, espresso is arguably the first example of “fast food,” its very name meaning speed.

Drinking coffee was very popular in Europe in the 19th century, but the boiled-water process of brewing it was laborious and time-consuming, especially for workers on a “coffee break.” To accelerate its production, Italian inventor Angelo Moriondo patented in 1884 a “new steam machinery for the economic and instantaneous confection of coffee beverage.” In short, he invented the prototype of the espresso machine, albeit one that produced the beverage only in bulk. To orient the process toward quick individualized servings, Italian inventor and businessman Luigi Bezzera created the first known machine to force, by pressure, steam and hot water through ground coffee into an individual cup so that each customer could have the freshest possible brew in the fastest possible way, reducing the brewing time from a few minutes to 30 seconds. Bezzera’s 1902 patents were then purchased the following year by Desiderio Pavoni, who made improvements to Bezzara’s brewing machine by devising the pressure-release valve and the steam wand for frothing beverages by tapping into the system’s built-up steam. Working together, Pavoni and Bezzera introduced their new coffee machine, called the Ideale (because they had mastered the “ideal” temperature and pressure for brewing coffee), and their fast new product, caffè espresso, at the 1906 World’s Fair in Milan. By mid-century there were espresso systems in use that resemble many of the machines still in use today.

Many subtle factors are at work in the production of each shot of espresso: the gauge pressure, the water temperature, the amount and fineness of the ground coffee, the duration (in seconds) of extraction, and the volume of liquid produced; even tiny variations in the size of the coffee particles in the grind can make an enormous difference in the quality of the espresso. The quality of the espresso machine is also key. The goal is to keep the pressure and temperature absolutely consistent from shot to shot. That uniformity is not easy to maintain, and the high price of top-ranked espresso machines is typically because of their ability to deliver that much-desired consistency.

On a well-pulled shot, the much-celebrated golden to reddish-brown foam known as crema lingers on the surface for a minute or two rather than dissipating immediately. Because it blankets the surface, the crema helps trap the aromatics in the liquid below. Although the crema is traditionally considered an important characteristic of a well-prepared espresso shot, many leading baristas have been experimenting with skimming the crema off the shot before serving. The result is a sweeter-tasting shot.
But in all cases a shot of espresso should be drunk immediately, before the highly volatile aromas dissipate.

Because the espresso procedure tends to amplify the distinct character of the beans both for good and for bad, roasters generally use a blend of beans from different sources. Further, the beans might also be roasted to different degrees, bringing out various levels of fruity, floral, spicy, earthy, or other flavours. In the manner that vintners blend wine grapes, baristas blend coffees to balance the best qualities of individual beans—aroma, taste, richness, and body.

There is, however, a growing following for single-origin coffees. Although roasters certainly define their style and personality with signature blends that become standards for their regular customers, they will also offer special selections of coffees from one specific farm or region. That venture comes with some risk. As with a single varietal wine, it can be trickier to create an outstanding beverage out of a single product instead of from a blend. That is especially true in brewing espresso, which is less forgiving than other brewing methods.

Espresso vs Cappuccino: What’s on Top?

Even for a coffee aficionado, it can sometimes be hard to understand what really separates different espresso drinks. Especially when those drinks both have a very strong, present taste and mouthfeel.

That’s the case when you compare espresso and cappuccino.

But don’t worry, we aren’t going to let you embarrass yourself in front of your hipster friends. Read on for the breakdown on what’s what and how to know if the drink you have is worth appreciating.

What’s the base?

Both of these drinks start with espresso, usually brewed with an espresso machine. (You can also make it yourself with a bit of extra effort.)
Espresso is made using high amounts of pressure to force hot water through a “puck” of densely packed, very fine grounds. This process produces takes between 25 and 30 seconds and produces about a shot’s worth of very strong java.

There are some variations on this basic process involving tampering with the pull time and drink volume that you can read about here. But we’re here to talk about the difference between a basic espresso shot and a cappuccino.

And the main difference is that the espresso shot stops here (save for maybe a little sugar), and is held to certain standards that we’l discuss later. Whereas, with a cappuccino you still have a few more steps involving steamed and frothed milk.

Espresso Yourself

Espresso, along with many espresso-based drinks, originated in Italy in the early 1900s. An entire social phenomenon developed around them, to the point where espresso bars still exist in Italy today. 50 years later, the beverage and its variants spread to other parts of the world.

Today, making the perfect espresso is half art, half science. It’s the drink at the center of a lot of seemingly pretentious coffee discussions, with good reason. If done right, a good espresso will give you a wonderfully distinct, strong flavor that’s hard to beat.

Espresso is typically thicker and much stronger than regular American coffee. It has more caffeine per unit but due to the small serving size you are going to get a comparable kick from a shot of espresso as you would from one cup of black coffee.

It’s All About the Crema

Often fondly referred to as the holy grail of coffee foam, this potentially overhyped bubbly little layer is commonly considered the biggest indicator of top-notch espresso.
The crema is a thin, delicate layer of brown foam that is the natural result of the extraction process. It may have a slightly acidic flavor because the coffee grounds degas under the pressure releasing carbon dioxide, which the ions in the hot water react with. These processes result in an increased pH and ultimately bubbles.

Additionally, certain oils from the grounds mix with the hot water, which contributes to the crema formation. Once the shot has been pulled, the crema can last for up to 40 minutes before dissolving into your cup. But we recommend drinking it before then.

The appreciation of crema is a relatively new coffee practice. The thin layer of foam wasn’t possible until higher pressure, lever operated machines were produced in the late 1940’s. Crema was then marketed as an indicator of richer, higher-quality espresso.

Overall the crema itself will not impact the taste of espresso very much, if at all. But it does show you how much fresh the beans that were used in your coffee were, which can be a good indicator of the quality of establishment you’re in.

Cappucci-yes

Cappuccinos also originated in Italy and were some of the first espresso based drinks to become popular in English-speaking regions. It really got its start during the second World War where it evolved into the drink we recognize today.

Cappuccinos are typically served in 6 oz glass or ceramic cups, as opposed to the 1-1.5 oz shot glasses that espresso comes in. They include the base 1-2 shots of espresso along with steamed milk and frothed milk (milk foam).

So a cappuccino INCLUDES an espresso. However, because milk is added and the top layer disrupted, crema does not matter when making these drinks.

It’s All About the Balance

What does matter is the ratio of espresso to steamed milk to foam. It should be 1:1:1.

When making a cappuccino, a talented barista will give you 1/3 espresso, topped with (not mixed with) 1/3 steamed milk and 1/3 airy milk foam (not super creamy).
Because this is such a structured drink, you can often tell by the weight and feel of the cup in your hand whether or not you have received a quality cappuccino.
Often times, cappuccinos in high-volume, lower-quality shops will have a more latte-esque. To circumvent this problem, you can ask for a dry cappuccino or one one the dry side. This will get the barista to prepare the drink without or with less steamed milk respectively, resulting in a more balanced, classic cappuccino feel.

What’s on top?

So as you may have guessed, the main difference in these drinks is what sits on top of the espresso itself.

In a plain espresso shot, you’ll have a nice tanish brown layer of bubbly crema. Whereas with a cappuccino you’ll have steamed milk and foam.

Got Milk?

Speaking of milk, can you add it to espresso?

NO. Well, you could try, but it would no longer be an espresso- just another espresso based drink. However, it is socially acceptable to add sugar to an espresso if the regular taste is a little too much for you. Don’t add too much though because the point of an espresso shot (unlike some other shots) is to taste the espresso.
On the other hand, you can’t make a cappuccino without steamed milk. Just be careful not to add too much because it will weaken the espresso underneath and give you latte vibes.

Capp or Spresso?

Whichever beverage you choose, you are going to get a cup of java where the classic “coffee” flavor is very present and strong. With an espresso, that will be accompanied by a crema and maybe a bit of sugar. With a cappuccino, that flavor will be balanced by steamed milk and airy foam.

Either way… Happy Caffeinating!

Jai Ganesh · 2018-12-29 00:15:08

266) Number Theory - 1

Perfect number

Perfect number, a positive integer that is equal to the sum of its proper divisors. The smallest perfect number is 6, which is the sum of 1, 2, and 3. Other perfect numbers are 28, 496, and 8,128. The discovery of such numbers is lost in prehistory. It is known, however, that the Pythagoreans (founded c. 525 BCE) studied perfect numbers for their “mystical” properties.

The mystical tradition was continued by the Neo-Pythagorean philosopher Nicomachus of Gerasa (fl. c. 100 CE), who classified numbers as deficient, perfect, and superabundant according to whether the sum of their divisors was less than, equal to, or greater than the number, respectively. Nicomachus gave moral qualities to his definitions, and such ideas found credence among early Christian theologians. Often the 28-day cycle of the Moon around the Earth was given as an example of a “Heavenly,” hence perfect, event that naturally was a perfect number. The most famous example of such thinking is given by St. Augustine, who wrote in The City of God (413–426):

Six is a number perfect in itself, and not because God created all things in six days; rather, the converse is true. God created all things in six days because the number is perfect.

The earliest extant mathematical result concerning perfect numbers occurs in Euclid’s Elements (c.300 BCE), where he proves the proposition:

If as many numbers as we please beginning from a unit [1] be set out continuously in double proportion, until the sum of all becomes a prime, and if the sum multiplied into the last make some number, the product will be perfect.

Here “double proportion” means that each number is twice the preceding number, as in 1, 2, 4, 8, …. For example, 1 + 2 + 4 = 7 is prime; therefore, 7 × 4 = 28 (“the sum multiplied into the last”) is a perfect number. Euclid’s formula forces any perfect number obtained from it to be even, and in the 18th century the Swiss mathematician Leonhard Euler showed that any even perfect number must be obtainable from Euclid’s formula. It is not known whether there are any odd perfect numbers.

Abundant Number

A number n is said to be Abundant Number if sum of all the proper divisors of the number denoted by sum(n) is greater than the value of the number n. And the difference between these two values is called the abundance.

Mathematically, if below condition holds the number is said to be Abundant number:
sum(n)> n

abundance = sum(n) - n

sum(n): aliquot sum - The sum of all proper divisors of n

Given a number n, our task is to find if this number is Abundant number or not.

The first few Abundant Numbers are: 12, 18, 20, 24, 30, 36, 40, 42, 48, 54, 56, 60, 66 …..

Deficient Number

A number n is said to be Deficient Number if sum of all the divisors of the number denoted by divisorsSum(n) is less than twice the value of the number n. And the difference between these two values is called the deficiency.

Mathematically, if below condition holds the number is said to be Deficient:
divisorsSum(n) < 2 * n

deficiency = (2 * n) - divisorsSum(n)

The first few Deficient Numbers are:
1, 2, 3, 4, 5, 7, 8, 9, 10, 11, 13, 14, 15, 16, 17, 19 …..

Given a number n, our task is to find if this number is Deficient number or not.

Examples :

Input: 21
Output: YES
Divisors are 1, 3, 7 and 21. Sum of divisors is 32.
This sum is less than 2*21 or 42.

Input: 12
Output: NO

Input: 17
Output: YES

Pairs of Amicable Numbers

Given an array of integers, print the number of pairs in the array that form an amicable pair. Two numbers are amicable if the first is equal to the sum of divisors of the second, and if the second number is equal to the sum of divisors of the first.

Examples :

Input : arr[] = {220, 284, 1184, 1210, 2, 5}
Output : 2

Explanation : (220, 284) and (1184, 1210) form amicable pair

Input : arr[] = {2620, 2924, 5020, 5564, 6232, 6368}
Output : 3
Explanation : (2620, 2924), (5020, 5564) and (6232, 6368) forms amicable pair

Friendly Numbers

In number theory, friendly numbers are two or more natural numbers with a common abundancy index, the ratio between the sum of divisors of a number and the number itself. Two numbers with the same abundancy form a friendly pair; n numbers with the same abundancy form a friendly n-tuple.

Being mutually friendly is an equivalence relation, and thus induces a partition of the positive naturals into clubs (equivalence classes) of mutually friendly numbers.

A number that is not part of any friendly pair is called solitary.

The abundancy index of n is the rational number σ(n) / n, in which σ denotes the sum of divisors function. A number n is a friendly number if there exists m ≠ n such that σ(m) / m = σ(n) / n. Note that abundancy is not the same as abundance, which is defined as σ(n) − 2n.

The numbers 1 through 5 are all solitary. The smallest friendly number is 6, forming for example the friendly pair 6 and 28 with abundancy σ(6) / 6 = (1+2+3+6) / 6 = 2, the same as σ(28) / 28 = (1+2+4+7+14+28) / 28 = 2. The shared value 2 is an integer in this case but not in many other cases. Numbers with abundancy 2 are also known as perfect numbers. There are several unsolved problems related to the friendly numbers.

In spite of the similarity in name, there is no specific relationship between the friendly numbers and the amicable numbers or the sociable numbers, although the definitions of the latter two also involve the divisor function.

Sociable Numbers

Sociable numbers are numbers whose aliquot sums form a cyclic sequence that begins and ends with the same number. They are generalizations of the concepts of amicable numbers and perfect numbers. The first two sociable sequences, or sociable chains, were discovered and named by the Belgian mathematician Paul Poulet in 1918. In a set of sociable numbers, each number is the sum of the proper factors of the preceding number, i.e., the sum excludes the preceding number itself. For the sequence to be sociable, the sequence must be cyclic and return to its starting point.

The period of the sequence, or order of the set of sociable numbers, is the number of numbers in this cycle.

If the period of the sequence is 1, the number is a sociable number of order 1, or a perfect number—for example, the proper divisors of 6 are 1, 2, and 3, whose sum is again 6. A pair of amicable numbers is a set of sociable numbers of order 2. There are no known sociable numbers of order 3, and searches for them have been made up to 5 x {10}^7 as of 1970.

It is an open question whether all numbers end up at either a sociable number or at a prime (and hence 1), or, equivalently, whether there exist numbers whose aliquot sequence never terminates, and hence grows without bound.

Jai Ganesh · 2018-12-30 20:40:14

267) Number Theory - 2

Number theory, branch of mathematics concerned with properties of the positive integers (1, 2, 3, …). Sometimes called “higher arithmetic,” it is among the oldest and most natural of mathematical pursuits.

Number theory has always fascinated amateurs as well as professional mathematicians. In contrast to other branches of mathematics, many of the problems and theorems of number theory can be understood by laypersons, although solutions to the problems and proofs of the theorems often require a sophisticated mathematical background.

Until the mid-20th century, number theory was considered the purest branch of mathematics, with no direct applications to the real world. The advent of digital computers and digital communications revealed that number theory could provide unexpected answers to real-world problems. At the same time, improvements in computer technology enabled number theorists to make remarkable advances in factoring large numbers, determining primes, testing conjectures, and solving numerical problems once considered out of reach.

Modern number theory is a broad subject that is classified into subheadings such as elementary number theory, algebraic number theory, analytic number theory, geometric number theory, and probabilistic number theory. These categories reflect the methods used to address problems concerning the integers.

From Prehistory Through Classical Greece

The ability to count dates back to prehistoric times. This is evident from archaeological artifacts, such as a 10,000-year-old bone from the Congo region of Africa with tally marks scratched upon it—signs of an unknown ancestor counting something. Very near the dawn of civilization, people had grasped the idea of “multiplicity” and thereby had taken the first steps toward a study of numbers.

It is certain that an understanding of numbers existed in ancient Mesopotamia, Egypt, China, and India, for tablets, papyri, and temple carvings from these early cultures have survived. A Babylonian tablet known as Plimpton 322 (c. 1700 BC) is a case in point.

Despite such isolated results, a general theory of numbers was nonexistent. For this—as with so much of theoretical mathematics—one must look to the Classical Greeks, whose groundbreaking achievements displayed an odd fusion of the mystical tendencies of the Pythagoreansand the severe logic of Euclid’s Elements (c. 300 BC).

Pythagoras

According to tradition, Pythagoras (c. 580–500 BC) worked in southern Italy amid devoted followers. His philosophy enshrined number as the unifying concept necessary for understanding everything from planetary motion to musical harmony. Given this viewpoint, it is not surprising that the Pythagoreans attributed quasi-rational properties to certain numbers.

For instance, they attached significance to perfect numbers—i.e., those that equal the sum of their proper divisors. Examples are 6 (whose proper divisors 1, 2, and 3 sum to 6) and 28 (1 + 2 + 4 + 7 + 14). The Greek philosopher Nicomachus of Gerasa (flourished c. AD 100), writing centuries after Pythagoras but clearly in his philosophical debt, stated that perfect numbers represented “virtues, wealth, moderation, propriety, and beauty.” (Some modern writers label such nonsense numerical theology.)

In a similar vein, the Greeks called a pair of integers amicable (“friendly”) if each was the sum of the proper divisors of the other. They knew only a single amicable pair: 220 and 284. One can easily check that the sum of the proper divisors of 284 is 1 + 2 + 4 + 71 + 142 = 220 and the sum of the proper divisors of 220 is 1 + 2 + 4 + 5 + 10 + 11 + 20 + 22 + 44 + 55 + 110 = 284. For those prone to number mysticism, such a phenomenon must have seemed like magic.

Modern Number Theory

The period from 1400 to 1650 saw important advances in geometry, algebra, and probability, not to mention the discovery of both logarithms and analytic geometry. But number theory was regarded as a minor subject, largely of recreational interest.

Pierre de Fermat

Credit for changing this perception goes to Pierre de Fermat (1601–65), a French magistrate with time on his hands and a passion for numbers. Although he published little, Fermat posed the questions and identified the issues that have shaped number theory ever since.

Despite Fermat’s genius, number theory still was relatively neglected. His reluctance to supply proofs was partly to blame, but perhaps more detrimental was the appearance of the calculus in the last decades of the 17th century. Calculus is the most useful mathematical tool of all, and scholars eagerly applied its ideas to a range of real-world problems. By contrast, number theory seemed too “pure,” too divorced from the concerns of physicists, astronomers, and engineers.

Number theory in the 18th century

Credit for bringing number theory into the mainstream, for finally realizing Fermat’s dream, is due to the 18th century’s dominant mathematical figure, the Swiss Leonhard Euler (1707–83). Euler was the most prolific mathematician ever—and one of the most influential—and when he turned his attention to number theory, the subject could no longer be ignored.

Initially, Euler shared the widespread indifference of his colleagues, but he was in correspondence with Christian Goldbach (1690–1764), a number theory enthusiast acquainted with Fermat’s work. Like an insistent salesman, Goldbach tried to interest Euler in the theory of numbers, and eventually his insistence paid off.

Number theory in the 19th century

Disquisitiones Arithmeticae

Of immense significance was the 1801 publication of Disquisitiones Arithmeticae by Carl Friedrich Gauss (1777–1855). This became, in a sense, the holy writ of number theory. In it Gauss organized and summarized much of the work of his predecessors before moving boldly to the frontier of research. Observing that the problem of resolving composite numbers into prime factors is “one of the most important and useful in arithmetic,” Gauss provided the first modern proof of the unique factorization theorem. He also gave the first proof of the law of quadratic reciprocity, a deep result previously glimpsed by Euler. To expedite his work, Gauss introduced the idea of congruence among numbers—i.e., he defined a and b to be congruent modulo m if m divides evenly into the difference a − b. This innovation, when combined with results like Fermat’s little theorem, has become an indispensable fixture of number theory.

From classical to analytic number theory

Inspired by Gauss, other 19th-century mathematicians took up the challenge. Sophie Germain (1776–1831), who once stated, “I have never ceased thinking about the theory of numbers,” made important contributions to Fermat’s last theorem, and Adrien-Marie Legendre(1752–1833) and Peter Gustav Lejeune Dirichlet (1805–59) confirmed the theorem for n = 5—i.e., they showed that the sum of two fifth powers cannot be a fifth power. In 1847 Ernst Kummer (1810–93) went further, demonstrating that Fermat’s last theorem was true for a large class of exponents; unfortunately, he could not rule out the possibility that it was false for a large class of exponents, so the problem remained unresolved.

The same Dirichlet (who reportedly kept a copy of Gauss’s Disquisitiones Arithmeticae by his bedside for evening reading) made a profound contribution by proving that, if a and b have no common factor, then the arithmetic progression a, a + b, a + 2b, a + 3b, … must contain infinitely many primes. Among other things, this established that there are infinitely many 4k + 1 primes and infinitely many 4k − 1 primes as well. But what made this theorem so exceptional was Dirichlet’s method of proof: he employed the techniques of calculus to establish a result in number theory. This surprising but ingenious strategy marked the beginning of a new branch of the subject: analytic number theory.

Prime number theorem

One of the supreme achievements of 19th-century mathematics was the prime number theorem, and it is worth a brief digression. To begin, designate the number of primes less than or equal to n by π(n). Thus π(10) = 4 because 2, 3, 5, and 7 are the four primes not exceeding 10. Similarly π(25) = 9 and π(100) = 25. Next, consider the proportion of numbers less than or equal to n that are prime—i.e., π(n)/n. Clearly π(10)/10 = 0.40, meaning that 40 percent of the numbers not exceeding 10 are prime.

A pattern is anything but clear, but the prime number theorem identifies one, at least approximately, and thereby provides a rule for the distribution of primes among the whole numbers. The theorem says that, for large n, the proportion π(n)/n is roughly 1/log n, where log n is the natural logarithm of n. This link between primes and logs is nothing short of extraordinary.

One of the first to perceive this was the young Gauss, whose examination of log tables and prime numbers suggested it to his fertile mind. Following Dirichlet’s exploitation of analytic techniques in number theory, Bernhard Riemann (1826–66) and Pafnuty Chebyshev (1821–94) made substantial progress before the prime number theorem was proved in 1896 by Jacques Hadamard (1865–1963) and Charles Jean de la Vallée-Poussin (1866–1962). This brought the 19th century to a triumphant close.

Number Theory In The 20th Century

The next century saw an explosion in number theoretic research. Along with classical and analytic number theory, scholars now explored specialized subfields such as algebraic number theory, geometric number theory, and combinatorial number theory. The concepts became more abstract and the techniques more sophisticated. Unquestionably, the subject had grown beyond Fermat’s wildest dreams.

One of the great contributors from early in the 20th century was the incandescent genius Srinivasa Ramanujan (1887–1920). Ramanujan, whose formal training was as limited as his life was short, burst upon the mathematical scene with a series of brilliant discoveries. Analytic number theory was among his specialties, and his publications carried titles such as “Highly composite numbers” and “Proof that almost all numbers n are composed of about log(log n) prime factors.”

A legendary figure in 20th-century number theory was Paul Erdős (1913–96), a Hungarian genius known for his deep insights, his vast circle of collaborators, and his personal eccentricities. At age 18, Erdős published a much-simplified proof of a theorem of Chebyshev stating that, if n ≥ 2, then there must be a prime between n and 2n. This was the first in a string of number theoretic results that would span most of the century. In the process, Erdős—who also worked in combinatorics, graph theory, and dimension theory—published over 1,500 papers with more than 500 collaborators from around the world. He achieved this astonishing output while living more or less out of a suitcase, traveling constantly from one university to another in pursuit of new mathematics. It was not uncommon for him to arrive, unannounced, with the declaration that “My brain is open” and then to plunge into the latest problem with gusto.

Twentieth-century number theory reached a much-publicized climax in 1995, when Fermat’s last theorem was proved by the Englishman Andrew Wiles, with timely assistance from his British colleague Richard Taylor. Wiles succeeded where so many had failed with a 130-page proof of incredible complexity, one that certainly would not fit into any margin.

Unsolved Problems

This triumph notwithstanding, number theory remains the source of many unsolved problems, some of the most perplexing of which sound innocent enough. For example:

1. Do any odd perfect numbers exist?
2. Are there infinitely many primes of the form n^2 + 1 (i.e., one more than a perfect square)?
3. Are there infinitely many pairs of twin primes (i.e., primes that differ by 2, like 5 and 7 or 41 and 43)?
4. Is Goldbach’s conjecture true? (Euler failed to prove it; so has everyone since.)

(Goldbach's conjecture is one of the oldest and best-known unsolved problems in number theory and all of mathematics. It states:

Every even integer greater than 2 can be expressed as the sum of two primes.

The conjecture has been shown to hold for all integers less than 4 × {10}^{18}, but remains unproven despite considerable effort.)

Although there has been no lack of effort, these questions remain open. Perhaps, like Fermat’s last theorem, they will eventually be resolved. Or perhaps they will remain as challenges into the indefinite future. In order to spur research efforts across a wide range of mathematical disciplines, the privately funded Clay Mathematics Institute of Cambridge, Massachusetts, named seven “Millennium Prize Problems” in 2000, each with a million-dollar award for a correct solution. In any case, these mysteries justify Eric Temple Bell’s characterization of number theory as “the last great uncivilized continent of mathematics.”

The theory of numbers, then, is a vast and challenging subject as old as mathematics and as fresh as today’s news. Its problems retain their fascination because of an apparent (often deceptive) simplicity and an irresistible beauty. With such a rich and colorful history, number theory surely deserves to be called, in the famous words of Gauss, “the queen of mathematics.”

Jai Ganesh · 2018-12-31 12:54:10

268) Periodic Table : 2019 is proclaimed the International Year of the Periodic Table of Chemical Elements

The Periodic Table of Chemical Elements is more than just a guide or catalogue of the entire known atoms in the universe; it is essentially a window on the universe, helping to expand our understanding of the world around us. Next year will mark the 150th anniversary of its creation by Russian scientist Dmitry Ivanovich Mendeleev.

"The periodic table of chemical elements is one of the most important and influential achievements in modern science reflecting the essence not only of chemistry, but also of physics, biology and other disciplines. It is a unique tool, giving scientists the opportunity to predict the appearance and properties of elements on Earth and in the universe as a whole,” said Jean-Paul Ngome-Abiaga, coordinator for the celebration of the Year at UNESCO. “This observance, including activities around the world, will underscore its importance for science, technology and sustainable human development."

Further proof of the periodic table’s continuing relevance to science will be a tribute during the Year of the recently completed advanced discoveries of four super heavy elements of the Periodic Table of Mendeleev with atomic numbers 113 (Nihonium), 115 (Moskovi), 117 (Tennesin) and 118 (Oganesson), which were only possible through international scientific cooperation.

The International Year of the Periodic Table of Chemical Elements is an extension of the International Year of Chemistry in 2011 and the International Year of Crystallography in 2014. This year also provides an opportunity for UNESCO to promote the basic sciences for sustainable development, including through UNESCO’s International Basic Sciences Programme (IBSP).

"I believe these events planned for 2019 will demonstrate the important role of the basic sciences in solving problems around the world, demonstrating the progress generated by scientific discoveries, and encouraging the next generation to expand the boundaries of human knowledge, just as Dmitry Mendeleyev demonstrated in the 19th century, "said Jean-Paul Ngome-Abiaga.

On 20 December 2017, during its 72nd session, the UN General Assembly proclaimed 2019 the International Year of the Periodic Table of Chemical Elements. Previously, this initiative was sponsored by the Russian Federation within the framework of UNESCO and was approved at the 39th session of the General Conference of the Organization.

More than 150 leading scientific centers around the world supported the idea of proclaiming the Year, including the International Union of Pure and Applied Chemistry (IUPAC), the International Union of Theoretical and Applied Physics, the European Association for Chemical and Molecular Sciences, the International Council for Science (ICSU), the International Astronomical Union, Joint Institute for Nuclear Research (JINR), and the International Union of History and Philosophy of Science and Technology. UNESCO-IBSP and IUPAC will coordinate the International Year in cooperation with national, regional and international chemical societies and unions.

Preparations for the celebration of the Year have already begun with some planned to take place in the Russian Federation.

The International Year of the Periodic Table

A Common Language for Science

The Periodic Table of Chemical Elements is one of the most significant achievements in science, capturing the essence not only of chemistry, but also of physics and biology.

1869 is considered as the year of discovery of the Periodic System by Dmitri Mendeleev. 2019 will be the 150th anniversary of the Periodic Table of Chemical Elements and has therefore been proclaimed the "International Year of the Periodic Table of Chemical Elements (IYPT2019)" by the United Nations General Assembly and UNESCO.

Periodic Table

The periodic table, or periodic table of elements, is a tabular arrangement of the chemical elements, arranged by atomic number, electron configuration, and recurring chemical properties, whose structure shows periodic trends. The seven rows of the table, called periods, generally have metals on the left and non-metals on the right. The columns, called groups, contain elements with similar chemical behaviours. Six groups have accepted names as well as assigned numbers: for example, group 17 elements are the halogens; and group 18 are the noble gases. Also displayed are four simple rectangular areas or blocks associated with the filling of different atomic orbitals.

The organization of the periodic table can be used to derive relationships between the various element properties, and also to predict chemical properties and behaviours of undiscovered or newly synthesized elements. Russian chemist Dmitri Mendeleev published the first recognizable periodic table in 1869, developed mainly to illustrate periodic trends of the then-known elements. He also predicted some properties of unidentified elements that were expected to fill gaps within the table. Most of his forecasts proved to be correct. Mendeleev's idea has been slowly expanded and refined with the discovery or synthesis of further new elements and the development of new theoretical models to explain chemical behaviour. The modern periodic table now provides a useful framework for analyzing chemical reactions, and continues to be widely used in chemistry, nuclear physics and other sciences.

The elements from atomic numbers 1 (hydrogen) through 118 (oganesson) have been discovered or synthesized, completing seven full rows of the periodic table. The first 98 elements all occur naturally, though some are found only in trace amounts and a few were discovered in nature only after having first been synthesized. Elements 99 to 118 have only been synthesized in laboratories or nuclear reactors. The synthesis of elements having higher atomic numbers is currently being pursued: these elements would begin an eighth row, and theoretical work has been done to suggest possible candidates for this extension. Numerous synthetic radionuclides of naturally occurring elements have also been produced in laboratories.

Jai Ganesh · 2019-01-02 01:05:33

269) Glaucoma and Visual Field Test

What is Glaucoma?

Glaucoma is a complex disease in which damage to the optic nerve leads to progressive, irreversible vision loss. Glaucoma is the second leading cause of blindness.

Glaucoma and Reading Ability

Glaucoma is usually described as a disease affecting peripheral vision. So, it wouldn’t have any effect on reading, the ultimate task of central vision, right?

In fact, glaucoma does affect reading. Why? First, while glaucoma does affect peripheral vision, it also affects central vision. Glaucoma patients with moderate or severe disease often describe looking through a fog which extends into their central vision. Because of this fogging, people with glaucoma recognize fewer letters in one glance. They must therefore look at text more times to make their way through a passage. The result is slower reading and particular difficulty with longer words.

Second, reading also brings in one’s mid-peripheral vision. For example, we use our field of view when moving from the end of one line to the start of a new line of text, or when searching a page of information for the specific details we wish to learn about. Glaucoma patients have particular difficulty with these aspects of reading.

Even when glaucoma patients can read, it is more difficult. Over long periods of time, individuals with more severe glaucoma tire, and their reading speed slows. They also understand less of what they read. Because of all these difficulties, persons with glaucoma read less often. As a result, they may become less independent and more disconnected from the world.

So, while we continue to fight for treatments that restore vision, what can be done to make reading easier for those with glaucoma? You can start by trying some things on your own.
* Increase the text size when working on the computer or other electronic devices.
* Use spot lighting when reading a book.
* Consider reading on a tablet or other device that enables reverse polarity (white letters on a black background instead of black letters on a white background).

These tips are not so easy to perfect on your own. So, if you’re having trouble reading and haven’t seen a vision rehabilitation specialist, ask your doctor for a referral.

These professionals specialize in helping you live as functionally and independently as possible with the vision that you have.

What is a Visual Field Test?

If you have been diagnosed with glaucoma, chances are, you will have taken several visual field tests.

This test helps your doctor detect and monitor glaucoma. Usually, the visual field test is taken once a year but depending on the severity of your glaucoma, your doctor may decide to check your visual field more frequently.

A visual field test maps out what your world looks like to you. It measures the area of vision, or how wide of an area your eye can see. Glaucoma is often called “The Sneak Thief of Sight” because it usually is a painless process that mostly affects the peripheral, or side vision, first.

The visual field shows changes that are not noticed by the patient until the damage is severe. Other diseases, such as cataract, stroke, macular degeneration and diabetes, can also influence the visual field. Your doctor will take these possible effects on your exam when interpreting the results.

Types of Visual Field Tests

There are different types of visual field tests. The one most commonly used in the United States is the Humphrey visual field, which consists of a center fixation light and blinking test lights in your side vision.

It is important when taking this test that you concentrate on the fixation light in the center and press the button when the blinking test light is seen with your side vision.
If you move your eyes to follow or look for the blinking lights, it decreases the reliability of the test and the ability of your doctor to monitor your disease.

Areas that appear gray or black on the test results reflect areas in your vision that are blurred or missing. If your glaucoma remains uncontrolled, these areas will get darker and larger.

Another type of visual field test is the Goldmann visual field. This test is done with a moving target controlled by a trained technician.

Monitoring Progress

Your doctor can tailor the type of test to best monitor your disease and adjust treatment appropriately. If your visual field is worsening, it could mean that your pressures are too high and further treatment is necessary to lower your eye pressure.

It is important to get a visual field test as often as is recommended by your eye doctor, in order to monitor progress and preserve vision.

Why Do I Need a Visual Field Test?

Another year has passed and it is time for your visual field test, a.k.a. “the clicky test” that frazzles many glaucoma patients and can feel like a waste of time.

The staff at your eye doctor’s office reassures you that it is a necessary part of your exam and you cooperate to the best of your ability. But why do you need to take this test?

The visual field test is a subjective measure of central and peripheral vision, or “side vision,” and is used by your doctor to diagnose, determine the severity of, and monitor your glaucoma. The most common visual field test uses a light spot that is repeatedly presented in different areas of your peripheral vision. Less common testing may be performed by a technician manually moving a target to map areas of damage.

Diagnosis and Staging

A visual field test is performed at the initial visit or as soon as glaucoma is suspected. It evaluates vision loss due to glaucoma, damage to the visual pathways of the brain, and other optic nerve diseases. When glaucoma is diagnosed the visual field data is used to determine the severity of disease. This staging information is useful in choosing a target intraocular pressure and determining follow-up.

Following for Progression

After the initial diagnosis the doctor will repeat the visual field test to check for worsening disease. This may be done in three to twelve months depending on the severity. If there are worsening defects or new areas of damage, a lower intraocular pressure and change in therapy may be needed. Many studies have shown that visual fields are variable over time and there is a learning curve when taking the test, so your doctor may ask you to repeat the test to confirm your results.

Isn’t There Something Easier?

Imaging of the optic nerve and surrounding tissues is an objective test that can also detect glaucoma damage and progression. This information can help your doctor make treatment decisions, and as the technology improves it will be even more useful. However, at this time it has not replaced the visual field test. We still need both types of testing because there are times that the optic nerve changes before the visual field, but also times when changes to the visual field are observed before damage to the optic nerve is detected.

So for now, get comfortable, relax, and only press that button when you are sure you see the light spot. Don’t try to “ace” the test by looking around or pressing the button indiscriminately. Your results will be most consistent and most useful for the doctor if you follow the directions carefully. We promise to keep looking for a test that is easier on our patients, but for now you are stuck with “the clicky test.”

How to make the best of your tests

Visual field testing is a crucial part in the diagnosis and treatment of all glaucomas and many neurological diseases. It is used to measure how well you can see throughout visual space and a large number of locations need to be tested to obtain an accurate map of your vision; hence the test takes several minutes. Some people find this tiring and you can have days when you perform well on the test and not so well on other days. As a result you may need multiple tests to obtain an accurate measurement of any vision loss.

All field testing is a partnership between your eye care professional, the technician and you. Here are some tips to smooth your way through the process; helping to improve reliability and enhance the quality of the information obtained, which is vital for your proper care.

There are many things done to assist you to perform at your best. The eye care professional will choose the most appropriate test and strategy for you but the technician is responsible for setting up the equipment so you are comfortable and to explain what you need to do. Your back, arms, feet and legs should be supported; your chin should be firmly on the chin-rest and your forehead gently against the brow-band to produce an accurate test reading. Do not hesitate to ask for anything that makes you more comfortable (e.g. a cushion for your back, a tissue to dab your eyes if needed, or to raise or lower the chair or equipment) as this will assist you to concentrate and to do your best. Make sure you completely understand what you need to do, and ask repeatedly for a clearer explanation, if required.

If you have special concerns, tell the technician. These might include a feeling of claustrophobia or being too hot or cold. You must play your part to eliminate all distractions so that you can focus entirely on the test. This may include being well rested and having eaten. Let the technician know if you are feeling unwell at any stage.

What is required of you during this test?

a) Firstly, keep your eye fixed on the central point target straight ahead of you.

b) Let the little flashes come to you, don’t go looking for them. You won’t see the lights a good deal of the time, so don’t worry if time seems to be passing without a light appearing. The machine makes the light very dim so that it can tell when you can just see it at each position tested. It is expected that some of the time the lights will be too dim for you to see, regardless if your eyes are normal or not.

c) Press the button when you think you see the light. Respond to all lights – they can be fuzzy, dim, or bright – it doesn’t matter as long as you know they are there.

d) Blinking is essential from time to time, to stop your eyes drying out and hurting. Try to time it so that you blink as you press the button. That way you can’t miss another light.

e) Remember you are in charge of the machine – not the other way around! You can pause the test whenever you wish by holding down the button on the buzzer- when you are ready to resume, focus back onto the central target first, and then release the buzzer. The test will automatically continue from where it left off.

f) If you are doing the test for the first time, ask the technician to take you through a practice session before you begin the test itself.

The technician should monitor your progress intermittently throughout the test, and give you feedback on how well you’re doing.

As the technology improves; machines become faster, quieter, friendlier, more accurate and therefore more reliable.

Jai Ganesh · 2019-01-04 00:06:40

270) Wax gourd

Wax gourd, (Benincasa hispida), also called winter melon, ash gourd, Chinese watermelon, or white gourd, fleshy vine of the gourd family (Cucurbitaceae), grown for its edible fruits. The waxgourd is native to tropical Asia, where it is commonly used in soups, curries, and stir-fries and is sometimes made into a beverage. Like other gourds, the fruit has a long shelf life and can be stored for many months.

The wax gourd is an annual plant that grows as a trailing vine. Its solitary yellow flowers are 8 to 10 cm (3 to 4 inches) wide and are unisexual. The hairy leaves are heart-shaped at the base and are typically palmately lobed. The round or oblong fruits can reach up to 40 cm (16 inches) in length and are hairy when young. Mature fruits are green with a whitish waxy covering and contain flat white seeds about 1 cm (0.4 inch) long.

The nutrients value of Wax Gourd also high. It contains Calcium, Phosphorus, Magnesium, Iron, CHD, Protein, Fat, Vitamin B and Vitamin C.

Introduction of Wax Gourd

Scientific name - Benincasa hispida

Wax gourd also known as white gourd is commonly identified with the name winter melon. It is a plant grown mainly for its large fruit, as it gets mature they are consumed as a vegetable. Nebulous when young, the fruit has a chunky white flesh which is sweet to taste. The best part about wax gourd is that it provides a long shelf life and by ripeness, the fruit loses its hair and develops a waxy coat, thereby giving rise to the name wax gourd. Even though the fruit is referred to as a melon, the fully grown crop is not that sweet to taste and as a matter of fact the melon may grow as large as 80 cm in length.

Health Benefits of Wax Gourd

Alkaline in nature, it is used as a brain food to treat nervous disorders like epilepsy, paranoia, and insanity. In addition, it also treats mental illness. Seeing that, they have alkaline temperament and so has a cooling and neutralizing effect on stomach acids, with that said they are used to treat digestive sicknesses like hyperacidity, dyspepsia, and ulcers. Effective in the treatment of diabetes, the juice of ash gourd is a great home remedy for peptic ulcers. Spaced out from treating the above said ailments, they also help in treating respiratory disorders like asthma, blood-related diseases, and urinary diseases like kidney stones. Every single part of the fruit is considered useful and is used in treating several disorders. Leaves of the gourd are simply rubbed on bruises which are proved effective, seeds are used to eject out intestinal worms. The ash made by burning the rind and seeds are mixed with coconut oil and applied on hair to promote hair growth and to treat dandruff.

Cultivation details

It takes up rich and well-drained soil together with ample amount of moisture in the growing season to thrive. Grows well in a warm and sunny position, established plants of wax gourd are quite drought tolerant. It can bear a pH in the range 5.8 to 6.8 and are best grown in a greenhouse, however it can grow well outdoors in good summers if started off in a greenhouse and planted out subsequent to the last expected frosts, given that they are very frost hardy. In order to do well, the plants require stable temperature, probably in excess of 25 degrees c. The female flower development happens with short day lengths and lower temperatures; on the other hand, it takes up higher temperatures to stimulate male flower production. Though the fruits can be consumed they are immature, it takes up duration of 5 months from seed to produce a mature crop. With many named varieties, they are cultivated frequently for their edible fruit.

Propagation

In a greenhouse, the seeds are sown in march/April; germination takes place within 3 weeks. When they grow up and become large enough to handle, prick the seedlings out into individual pots and grow them fast in rich droppings in the greenhouse. For the seedlings first few weeks, it is suggested to maintain a minimum night temperature of at least 10 degrees c. After the last expected frosts, they are planted out during the May/June.

nurserylive-ash-gourd-methai-petha-agri-petha-seeds.jpg

Jai Ganesh · 2019-01-06 00:14:37

271) Albatross

Albatross, Classification, and Evolution

The Albatross is a large species of sea-bird found throughout the southern Pacific and even into the colder Antarctic regions. There are 21 different species of Albatross found across the southern seas, but sadly 19 of the different Albatross species are said to be threatened with extinction today. The Albatross is closely related to other sea-birds including Petrels, which are all unique among Birdsdue to the tubular nostrils on either side of the top of their bill, meaning these Birds are often referred to as Tubenoses. The Albatross was first brought into the public spotlight with Coleridge's 1798 poem, the ‘Rime of the Ancient Mariner’.

Albatross, Anatomy, and Appearance

The Albatross is one of the largest Birds in the skies as the wingspan of the male Wandering Albatross can easily reach 3.5 meters or more in length, meaning that it has the largest wingspan of any Bird. The Wandering Albatross also has a body that is more than 1 meter long (including the tail), with the size of other species generally being slightly smaller. The Albatross is an easily identifiable Bird with long, narrow wings, a large head, and a long, strong bill which is hooked at the end and has sharp blades on either side to handle slippery prey. There are three toes on each of the Albatross's feet with webbed skin between each one. Unlike many other species of Bird, the Albatross has no hind toes as these sea-birds simply have no need for them.

Albatross, Distribution, and Habitat

All 21 different species of Albatross are mainly distributed throughout the southern Pacific, with some species found far into the Southern Ocean. Although the Albatross is not found in the northern parts of the Atlantic, a number of species of found in the north Pacific, with the Wading Albatross being the highest up, with its nesting sites found on the Galapagos Islands. The Albatross is unique among many Birds as it is air-bound for the majority of its life. Albatrosses spend their entire lives gliding above the waves and are known to fly thousands of miles in a very short space of time. During the breeding season, the Albatross finally returns to dry land, where they nest in large colonies on the cliffs of remote, rocky islands that are generally inside the Antarctic Tundra.

Albatross, Behaviour and Lifestyle

The tapered wings of the Albatross means that it tends to glide through the air rather than flying which uses much more energy. The Albatross is known to practice a flying technique known as dynamic soaring, meaning that the Albatross makes use of the up-drafts of wind above the waves to give it extra lift, for longer periods of time, and without really doing anything. The Albatross has excellent eyesight as it sees its prey from the sky, swooping down to snap a Fish from the surface or sometimes even diving into the water. They are known to also have an exceptional sense of smell which allows them to detect both prey and their breeding grounds, even in the dark.

Albatross, Reproduction and Life Cycles

The Albatross nests in large colonies on islands, where there can be thousands of other Albatross individuals, some of which have been flying solidly for up to 7 seven years until they reach the age of mating maturity. After a unique courtship display which involves grunting and scraping their beaks, males and females pair off to mate. The female Albatross lays just one egg that can weigh up to half a kilo, in a basic nest on the ground. The Albatross parents take it in turns to incubate the egg for 2-3 months depending on the size of the Albatross species. The Albatross parents protect and clean their chick until it is able to fly. Albatross chicks can take anywhere from 5 to 10 months to fledge, depending on the size of the Albatross species. They are very long living Birds with an average age of between 40 and 50 years old.

Albatross, Diet and Prey

The Albatross is a carnivorous Bird as the diet of the Albatross solely consists of Fish and other aquatic animals. The Albatross feeds on Fish, Squid, Krill, Crabs and other Crustaceans by either diving, swooping down onto the water's surface, or from scavenging the kill from another animal. They are also known to eat both carrion and refuge that is floating on or close to the surface of the water. The excellent sight and smell of the Albatross, along with its well-designed and razor-sharp beak, means that this animal is perfectly adapted for a life at sea. Chicks are fed by the highly nutritious yet foul smelling stomach oil of their parents until they are able to handle solid, and more slippery meals.

Albatross, Predators and Threats

Due to the fact that the Albatross is so big and the fact that the Albatross spends nearly its whole life in the safety of the sky, the Albatross has no real predators besides Humans who have hunted them in the past. The Albatross also nests in such remote places that they are safe from nearly all other animals with the exception of some Tiger Sharks who are known to lay in wait when the young Albatross chicks are learning how to fly, greedily hoping to snap up any stragglers. The interesting thing about this is that the Tiger Sharks appear to return to the same spot every year, knowing that the Albatross chicks will be practising their launching and gliding techniques, and they are therefore guaranteed an easy snack.

Albatross, Interesting Facts and Features

Albatrosses are known to be able to cover thousands of miles in a short space of time with the Grey-Headed Albatross being able to fly so far, with such little effort that they can complete a full circle around the Earth in just over a month. The Albatross was made famous by Samuel Taylor Coleridge's poem at the end of the 1700s, which indicated that these enormous sea-birds embodied the souls of drowned sailors. This led to a great deal of superstition surrounding the hunting of the Albatross, as it was thought to be very bad luck amongst seafarers.

Albatross, Relationship with Humans

An estimated 100,000 Albatrosses, of various different species, are thought to be killed every year by illegal fishing in the Southern Ocean, predominantly for Tuna. These fishermen use long fishing lines, with baited hooks which Albatross can be easily caught up in when they are simply trying to catch their supper. It is thought that the females are actually at a greater risk from these lines than the males, due to the fact that the two tend to feed in differing regions. Despite some superstition towards killing the Albatross by sailors, they were hunted quite vigorously by Humans during the 19th century for their feathers which were used to stuff pillows.

Albatross, Conservation Status and Life Today

Today, 19 out of the 21 different Albatross species are listed as animals that are Endangered in their natural environments. Although the populations of the remaining two species are not quite as low, numbers are falling and both are considered to be Threatened species. The main reason for the drastic decline in Albatross numbers across the southern seas, is lone-line Tuna fishing, which these enormous sea-birds can become easily caught on.

Jai Ganesh · 2019-01-08 00:06:52

272) Aurora

Aurora, luminous phenomenon of Earth’s upper atmosphere that occurs primarily in high latitudes of both hemispheres; auroras in the Northern Hemisphere are called aurora borealis, aurora polaris, or northern lights, and in the Southern Hemisphere aurora australis, or southern lights. A brief treatment of auroras follows.

Auroras are caused by the interaction of energetic particles (electrons and protons) of the solar windwith atoms of the upper atmosphere. Such interaction is confined for the most part to high latitudes in oval-shaped zones that surround Earth’s magnetic poles and maintain a more or less fixed orientation with respect to the Sun. During periods of low solar activity, the auroral zones shift poleward. During periods of intense solar activity, auroras occasionally extend to the middle latitudes; for example, the aurora borealis has been seen as far south as 40° latitude in the United States. Auroral emissions typically occur at altitudes of about 100 km (60 miles); however, they may occur anywhere between 80 and 250 km (about 50 to 155 miles) above Earth’s surface.

Auroras take many forms, including luminous curtains, arcs, bands, and patches. The uniform arc is the most stable form of aurora, sometimes persisting for hours without noticeable variation. However, in a great display, other forms appear, commonly undergoing dramatic variation. The lower edges of the arcs and folds are usually much more sharply defined than the upper parts. Greenish rays may cover most of the sky poleward of the magnetic zenith, ending in an arc that is usually folded and sometimes edged with a lower red border that may ripple like drapery. The display ends with a poleward retreat of the auroral forms, the rays gradually degenerating into diffuse areas of white light.

Auroras receive their energy from charged particles traveling between the Sun and Earth along bundled, ropelike magnetic fields. The particles are driven by the solar wind, captured by Earth’s magnetic field, and conducted downward toward the magnetic poles. They collide with oxygen and nitrogen atoms, knocking away electrons to leave ions in excited states. These ions emit radiation at various wavelengths, creating the characteristic colours (red or greenish blue) of the aurora.

In addition to Earth, other planets in the solar system that have atmospheres and substantial magnetic fields—i.e., Jupiter, Saturn, Uranus, and Neptune—display auroral activity on a large scale. Auroras also have been observed on Jupiter’s moon Io, where they are produced by the interaction of Io’s atmosphere with Jupiter’s powerful magnetic field.

Northern lights, also called Aurora Borealis, luminous atmospheric display visible in the Northern Hemisphere.

Southern lights, also called Aurora Australis, luminous atmospheric display visible in the Southern Hemisphere.

Ionosphere and magnetosphere

Ionosphere and magnetosphere, regions of Earth’s atmosphere in which the number of electrically charged particles—ions and electrons—are large enough to affect the propagation of radio waves. The charged particles are created by the action of extraterrestrial radiation (mainly from the Sun) on neutral atoms and molecules of air. The ionosphere begins at a height of about 50 km (30 miles) above the surface, but it is most distinct and important above 80 km (50 miles). In the upper regions of the ionosphere, beginning several hundred kilometres above Earth’s surface and extending tens of thousands of kilometres into space, is the magnetosphere, a region where the behaviour of charged particles is strongly affected by the magnetic fields of Earth and the Sun. It is in the lower part of the magnetosphere that overlaps with the ionosphere that the spectacular displays of the aurora borealis and aurora australis take place. The magnetosphere also contains the Van Allen radiation belts, where highly energized protons and electrons travel back and forth between the poles of Earth’s magnetic field.

This article describes the layers of the ionosphere and the mechanisms by which these ionized layers are created and altered. The features of the magnetosphere are also described, particularly as they are manifested in the auroras and the Van Allen belts.

Ionosphere

Discovery of the ionosphere

Discovery of the ionosphere extended over nearly a century. As early as 1839, the German mathematician Carl Friedrich Gauss speculated that an electrically conducting region of the atmosphere could account for observed variations of Earth’s magnetic field. The notion of a conducting region was reinvoked by others, notably in 1902 by the American engineer Arthur E. Kennelly and the English physicist Oliver Heaviside, to explain the transmission of radio signals around the curve of Earth’s surface before definitive evidence was obtained in 1925. For some years the ion-rich region was referred to as the Kennelly-Heaviside layer.

Magnetosphere

The overall structure of the outer ionosphere—the magnetosphere—is strongly influenced by the configuration of Earth’s magnetic field. Close to the planet’s surface, the magnetic field has a structure similar to that of an ideal dipole. Field lines are oriented more or less vertically at high latitudes, sweep back over the Equator, where they are essentially horizontal, and connect to Earth in a symmetrical pattern at high latitudes. The field departs from this ideal dipolar configuration, however, at high altitudes. There the terrestrial field, Earth’s magnetic field, is distorted to a significant extent by the solar wind, with its embedded solar magnetic field. Ultimately the terrestrial field is dominated by the interplanetary field, which is generated by the Sun.

The solar wind compresses the magnetic field on Earth’s dayside at a distance of about 10 Earth radii, or almost 65,000 km (40,000 miles) from the planet. At this distance the magnetic field is so weak that the pressure associated with particles escaping from Earth’s gravity is comparable to the opposing pressure associated with the solar wind. This equilibrium region, with a characteristic thickness of 100 km (60 miles), is called the magnetopause and marks the outer boundary of the magnetosphere. The lower boundary of the magnetosphere is several hundred kilometres above Earth’s surface.

On the nightside, the terrestrial field is stretched out in a giant tail that reaches past the orbit of the Moon, extending perhaps to distances in excess of 1,000 Earth radii. The magnetotail can extend to such great distances because on the nightside the forces associated with the magnetic field and the solar wind are parallel.
The outermost regions of the magnetosphere are exceedingly complex, especially at high latitudes, where terrestrial field lines are open to space. Ionization from the solar wind can leak into the magnetosphere in a number of ways. It can enter by turbulent exchange at the dayside magnetopause or more directly at cusps in the magnetopause at high latitudes where closed loops of the magnetic field on the dayside meet fields connecting to the magnetotail. In addition, it can enter at large distances on the nightside, where the magnetic pressure is relatively low and where field lines can reconnect readily, providing easy access to the giant plasma sheet in the interior of Earth’s magnetotail.

The magnetosheath, a region of magnetic turbulence in which both the magnitude and the direction of Earth’s magnetic field vary erratically, occurs between 10 and 13 Earth radii toward the Sun. This disturbed region is thought to be caused by the production of magnetohydrodynamic shock waves, which in turn are caused by high-velocity solar wind particles. Ahead of this bow shock boundary, toward the Sun, is the undisturbed solar wind.

Auroras are perhaps the most spectacular manifestations of the complex interaction of the solar wind with the outer atmosphere. The energetic electrons and protons responsible for an aurora are directed by the solar wind along magnetic fields into Earth’s magnetosphere.

Auroras occur in both hemispheres, confined for the most part to high latitudes in oval-shaped regions that maintain a more or less fixed orientation with respect to the Sun. The centre of the auroral oval is displaced a few degrees to the nightside with respect to the geomagnetic pole. The midnight portion of the oval is, on average, at a geomagnetic latitude of 67°; the midday portion is at about 76°. An observer between 67° and 74° magnetic latitudes generally encounters auroras twice a day—once in evening and once in morning.

Auroral zones

The portion of Earth that traverses the midnight portion of the auroral oval is known as the auroral zone. In the Northern Hemisphere this zone lies along a curve extending from the northern regions of Scandinavia through Iceland, the southern tip of Greenland, the southern region of Hudson Bay, central Alaska, and on to the coast of Siberia. This is the prime region from which to view an aurora in the Northern Hemisphere. The phenomenon is by no means static, however. The auroral zone shifts poleward at times of low solar activity, while during periods of high solar activity it has been known to move as far south as 40° (geographic latitude). At low latitudes, an aurora assumes a characteristic red colour. In ancient times this colour was often interpreted as evidence of impending disaster. More recently it has been taken as a sign of approaching fires. Auroras assume a variety of forms, depending on the vantage point from which they are observed. The luminosity of an aurora is generally aligned with the magnetic field. Field lines are close to vertical in polar regions, and so an aurora occurring there appears to stand on end, hanging from the sky in great luminous drapes. It is a spectacular sight indeed, especially if viewed from a distance either from the north or south. At lower latitudes, the magnetic field lines are inclined with respect to the vertical. There an aurora appears as streamers radiating from the zenith. Such is the majesty of the aurora that no two displays are totally alike. Light can move rapidly across the sky on some occasions, and at other times it can appear to stand in place, flickering on and off.

Causes of auroral displays

The most common type of aurora is associated with bombardment of the atmosphere by electrons with energies of up to 10,000 electron volts. The energy source for these electrons originates ultimately from the Sun. It is propagated through space by the solar wind along bundled, ropelike magnetic fields that form temporarily between the Sun and Earth’s magnetosphere, most probably to the plasma sheet. Energetic electrons enter the atmosphere along magnetic field lines. They produce a shower of secondary and tertiary electrons, approximately one for every 35 electron volts of energy in the primary stream. Primaries can propagate to altitudes as low as 100 km (60 miles). Most of the luminosity is produced, however, by low-energy secondary and tertiary electrons. Prominent emissions in the spectrum of this luminosity are associated with the red line of atomic oxygen at 633 nm, the green line of atomic oxygen at 558 nm, the first negative bands of ionized molecular nitrogen at 391 nm and 428 nm, and a host of emissions from atomic oxygen, molecular oxygen, ionized molecular oxygen, and molecular nitrogen. Many of these features are present also in the day and night airglow. They are most notable in auroras because of their intensity and the rapidity with which they switch on and off in response to changes in the flux and energy of incoming primaries. An aurora has a characteristic red colour if the energy of primaries is relatively low. Emission in this case is dominated by atomic oxygen and is confined for the most part to altitudes above 250 km (150 miles). If the energy of the primaries is high, an aurora has a greenish blue colour and extends downward to altitudes as low as 90 km (55 miles).

Auroral displays are also produced by bombardment of the atmosphere by energetic protons. Protons with energies of up to 200,000 electron volts are responsible for auroral activity in a diffuse belt that is equatorward of the main auroral zone. These protons can be detected from the ground by observation of Doppler-shifted radiation emitted by fast hydrogen atoms formed by charge transfer from atmospheric atomsand molecules. Protons also play a role at higher latitudes, especially at times following major solar flares. It is thought that the protons responsible for auroras at the polar caps are solar in origin. Associated energies may reach as high as one million electron volts, and particles may penetrate as deep as 80 km (50 miles). Polar cap auroras can provide a significant transient source of mesospheric and stratospheric nitric oxide (NO). They can be responsible for small but detectable short-term fluctuations in the abundance of stratospheric ozone.

Van Allen radiation belts

The magnetosphere includes two doughnut-shaped radiation belts, or zones, centred on the Equator that are occupied by appreciable numbers of energetic protons and electrons trapped in the outermost reaches of the atmosphere. No real gap exists between the two zones; they actually merge gradually, with the flux of charged particles showing two regions of maximum density. The inner belt extends from roughly 1,000 to 5,000 km (600 to 3,000 miles) above the terrestrial surface and the outer belt from some 15,000 to 25,000 km (9,300 to 15,500 miles). The belts were named in honour of James A. Van Allen, the American physicist who discovered them in 1958. His was a triumph of serendipity—he detected the presence of the trapped particles with a Geiger counter designed to measure the flux of cosmic rays in space. It was the first great discovery of the space age and was achieved by combining data obtained with instruments carried by three of the earliest United States scientific satellites—Explorer 1, Explorer 4, and Pioneer 3.

The flux of protons crossing a square centimetre of surface in the inner Van Allen belt can be as large as 20,000 per second, higher than the flux of cosmic radiation in space by a factor of 10,000. Protons in the inner belt have energies in excess of 7 × {10}^8 electron volts, enough to enable them to penetrate about 10 cm (4 inches) of lead. Spacecraft flying through the belts must be protected; otherwise, their electronic components would be subjected to irreparable damages.

The high-energy protons in the inner Van Allen belt are thought to originate from the decay of neutrons that are produced by the interaction of the atmosphere with energetic cosmic rays of galactic origin. Some of these short-lived neutrons—they have a lifetime of 12 minutes—are ejected upward. A fraction of them decay into energetic protons and electrons as they pass through the region occupied by the Van Allen belts. These protons and electrons become trapped and travel in spiral paths along the flux lines of Earth’s magnetic field. The particles reverse their direction at intermediate altitudes (about 500 km [300 miles]) and low latitudes because, as the particles approach either of the magnetic poles, the increase in the strength of the field causes them to be reflected back toward the other pole. Collisions with atoms in the thin atmosphere eventually remove the particles from the belts, but they generally survive for about 10 years. This relatively long lifetime allows particles to accumulate in the radiation belts, providing high fluxes despite the small magnitude of the intrinsic source.

The inner belt merges gradually with the outer belt, which extends from about two to eight Earth radii. A portion of the ionization in the outer belt is derived from the solar wind, as demonstrated by the presence of helium ions in addition to protons. Unlike the outer zone, the inner belt contains no helium ions, while it has been established that helium ions account for about 10 percent of solar wind. The flux of electrons in the outer belt can vary by orders of magnitude over intervals as short as a few days. These changes appear to correlate with times of strong magnetic disturbances. They are not, however, as yet well understood.

Jai Ganesh · 2019-01-09 02:57:18

273) How Old is Earth?

Since the planet Earth doesn't have a birth certificate to record its formation, scientists have spent hundreds of years struggling to determine the age of the planet. By dating the rocks in the ever-changing crust, as well as neighbors such as the moon and visiting meteorites, scientists have calculated that Earth is 4.54 billion years old, with an error range of 50 million years.

How old are your rocks?

Several attempts to scientifically date the planet have occurred over the past 400 years. Scientists attempted to predict the age based on changing sea levels, the time it took for Earth or the sun to cool to present temperatures, and the salinity of the ocean. As science progressed, these methods were proven to be unreliable; for instance, the rise and fall of the ocean was shown to be an ever-changing process rather than a gradually declining one.
In an effort to calculate the age of the planet, scientists turned to the rocks that cover its surface. However, because plate tectonics constantly changes and revamps the crust, the first rocks have long since been recycled, melted down and reformed into new outcrops.

In the early 20th century, scientists refined the process of radiometric dating. Earlier research had shown that isotopes of some radioactive elements decay into other elements at rates that can be easily predicted. By examining the existing elements, scientists can calculate the initial quantity, and thus how long it took for the elements to decay, allowing them to determine the age of the rock.

The oldest rocks on Earth found to date are the Acasta Gneisses in northwestern Canada near the Great Slave Lake, which are 4.03 billion years old. Rocks older than 3.5 billion years can be found on all continents. Greenland boasts the Isua Supracrustal rocks (3.7 to 3.8 billion years old), while rocks in Swaziland are 3.4 to 3.5 billion years. Samples in Western Australia run 3.4 to 3.6 billion years old.

Research groups in Australia found the oldest mineral grains on Earth. These tiny zirconium silicate crystals have ages that reach 4.3 billion years, making them the oldest materials found on Earth so far. Their source rocks have not yet been found.

The rocks and zircons set a lower limit on the age of Earth of 4.3 billion years, because the planet itself must be older than anything that lies on its surface.

Meet the neighbors

In an effort to further refine the age of Earth, scientists began to look outward. The material that formed the solar system was a cloud of dust and gas that surrounded the young sun. Gravitational interactions coalesced this material into the planets and moons at roughly the same time. By studying other bodies in the solar system, scientists are able to find out more about the early history of the planet.

The nearest body to Earth, the moon, does not suffer from the resurfacing problems that cover Earth's landscape. As such, rocks from early lunar history should be present on the moon. Samples returned from the Apollo and Luna missions revealed ages between 4.4 and 4.5 billion years, helping to constrain the age of Earth.

In addition to the large bodies of the solar system, scientists have also studied smaller rocky visitors to that fell to Earth. Meteorites spring from a variety of sources. Some are cast off from other planets after violent collisions, while others are leftover chunks from the early solar system that never grew large enough to form a cohesive body.

Although no rocks have been deliberately returned from Mars, samples exist in the form of meteorites that fell to Earth long ago, allowing scientists to make approximations about the age of rocks on the red planet. Some of these samples have been dated to 4.5 billion years old, supporting other calculations of the date of early planetary formation.

More than 70 meteorites have fallen to Earth to have their ages calculated by radiometric dating. The oldest of these have ages between 4.4 and 4.5 billion years.
Fifty thousand years ago, a rock hurled down from space to form Meteor Crater in Arizona. Shards of that asteroid have been collected from the crater rim and named for the nearby Canyon Diablo. In 1953, Clair Cameron Patterson measured ratios of lead isotopes in samples that put tight constraints on Earth's age.

The Canyon Diablo meteorite is important because it represents a class of meteorites with components that allow for more precise dating. Samples of the meteorite show a spread from 4.53 to 4.58 billion years. Scientists interpret this range as the time it took for the solar system to evolve, a gradual event that took place over approximately 50 million years.

By using not only the rocks on Earth but also information gathered about the system that surrounds it, scientists have been able to place the age of the Earth at approximately 4.54 billion years. For comparison, the Milky Way galaxy that contains the solar system is approximately 13.2 billion years old, while the universe itself has been dated to 13.8 billion years.

Jai Ganesh · 2019-01-10 00:28:08

274) Oasis

An oasis is an area made fertile by a source of freshwater in an otherwise dry and arid region. Oases (more than one oasis) are irrigated by natural springs or other underground water sources.

An oasis is an area made fertile by a source of freshwater in an otherwise dry and arid region. Oases (more than one oasis) are irrigated by natural springs or other underground water sources. They vary in size from a cluster of date palms around a well or a spring to a city and its irrigated cropland. Dates, cotton, olives, figs, citrus fruits, wheat and corn (maize) are common oasis crops.

Underground water sources called aquifers supply most oases. In some cases, a natural spring brings the underground water to the surface. At other oases, manmade wells tap the aquifer. In some oasis settlements, these wells might be centuries old and might have been diligently maintained for generations to preserve access to their life-giving water.

Sands blown by desert winds threaten wells as well as agricultural areas in oases. Sand can destroy crops and pollute water. Communities have traditionally planted strong trees, such as palms, around the perimeter of oases to keep the desert sands from their delicate crops and water.

Some of the world's largest supplies of underground water exist beneath the Sahara Desert, supporting about 90 major oases there. The Sahara is the largest desert on Earth—about the size of the continental United States. Though there are many oases there, traveling between them can take days because the desert is so vast.

For this reason, oases in the Sahara and throughout the world have become important stops along trade routes. Merchants and traders who travel along these routes must stop at oases to replenish food and water supplies. This means that whoever controls an oasis also controls the trade along the route—making oases desirable to political, economic, and military leaders.

Al-Hasa, Saudi Arabia, has been an important farming area for the Arabian Peninsula for thousands of years. Today, it continues to be a leading agricultural region, producing dates, rice, corn, sheep, cattle, and eggs. The al-Hasa region also lies above one of the richest oil fields in the world, making the oasis an important center of international trade.

Rivers that flow through some deserts provide permanent sources of water for large, elongated oases. The fertile Nile River valley and delta in Egypt, supplied with water from the Nile River, is an example of this type of large oasis. At 22,000 square kilometers, it might be the largest oasis in the world.

Jai Ganesh · 2019-01-11 00:25:18

275) Gooseberries

Small and firm but sometimes ribbed and translucent, gooseberries are a unique little plant-based food growing on relatively small, thorny bushes. Although their history is rooted in Europe, gooseberries were cultivated in Asia and Africa before the British began developing new varieties in at least the sixteenth century. There are now around 2,000 cultivars and two main gooseberry types: American and European (Ribes uva-crispa), which are larger and said to be tastier. They're from the same botanical family as currants, and grow wild and prolific in places like North America and Siberia.

Interestingly, this one berry comes in varying shades of yellow, green, red, or black, and can be round, oval, pear-shaped, or elongated. There can be tart and sweet berries on one bush, each containing a plethora of miniscule, edible seeds. Gooseberries thrive in changing seasons involving frigid winters and humid summers, and they're more shade-tolerant than other fruits.

The Indian gooseberry (Emblica officinalis, or amla) is light green and extremely bitter. The Cape gooseberry - sometimes called a Peruvian cherry - is yellow-orange and surrounded by a paper-thin husk that falls off as it dries. In the U.S., fresh gooseberries are usually ripe for the picking around July; red berries are generally sweeter.

Because ripe but not quite ready berries offer the most tartness, our great-grandmothers often made their gooseberry pies less sour by mixing in other fruits. Gooseberries are also excellent in meat dishes as a sauce.

Unfortunately, gooseberries can host a serious fungal disease that can kill white pines. They're actually banned from cultivation in some states. Gardeners are advised not to plant gooseberries within 1,000 feet of white pine trees or within 1,500 feet of areas where white pine seedlings are growing because of this problem.

Health Benefits of Gooseberries

Flavones and anthocyanins are compounds in gooseberries found to have numerous health beneficial effects against cancer, aging, inflammation, and neurological diseases. Rich in antioxidant polyphenolics and vitamins, the fiber content constitutes 26 percent of the daily recommended value, which has the ability to prevent colon cancer.

Gooseberries also contain a healthy dose of scurvy-preventing vitamin C – 69 percent of the daily value, and nearly 20 times the C in oranges. And get this: gooseberries lose none of the vitamin C nutrition in the cooking process.

A wide array of other vitamins and minerals, plus protein, superoxide dismutase, and omega-3 fatty acids make this little berry exceptionally nutritious. A comprehensive list would include vitamin A, folates, pantothenic acid (vitamin B5 - for healthy adrenal glands), pyridoxine (vitamin B-6), and thiamin (vitamin B1), as well as the minerals calcium (to prevent osteoporosis), magnesium, potassium (to help balance blood pressure and balance acids), copper, phosphorus, and manganese. The iron content maintains good blood circulation and red blood regeneration.

All these compounds are meaningful to the human body, but in more understandable terms, benefits include diabetes prevention and control by stimulating the body's ability to produce insulin; strengthened heart muscles; antioxidant power for slowing the aging process; and cataract-correction due to the retinol in the vitamin A. Gooseberry juice is also said to improve skin tone, prevent and restore hair loss, and rejuvenate for a general feeling of well being.

However, consume gooseberries in moderation because they contain fructose, which may be harmful to your health in excessive amounts.

The Indian gooseberry - amla - has been used in traditional Indian medicine, called Ayurveda, for millennia. Clinical studies suggest it has a positive effect on Alzheimer's disease, but on prevention, rather than cure.

Another study showed gooseberries to block breast cancer cell growth and metastasis potential in vitro. They also may have anti-cancer properties, as well as cough-, fever-, pain-, stress-, and diarrhea-suppressing effects. To gain these health benefits of gooseberries, however, ways to make the sour berry more palatable is an ongoing conversation.

Studies Done on Gooseberries

Gooseberries were one of four plant-based foods evaluated for their total phenolics and antioxidant capacity in relation to the potential management of hyperglycemia and hypertension. The major phenolic compounds were found to be quercetin derivatives in the black currants and green gooseberries, and chlorogenic acid in the red currants and red gooseberries.

Scientists reported in another study that Indian gooseberries (amla) are used either alone or with other plants to treat such maladies as cold and fever; as a diuretic, laxative, a tonic for the liver and stomach, to fight inflammation, prevent peptic ulcer and dyspepsia, and aid digestion.

Preclinical studies indicated that amla has properties that can be cardio- and neuro-protective, prevent high levels of cholesterol in the blood, relieve pain, prevent anemia, diarrhea, and hardening of the arteries, balance blood glucose levels, suppress coughs, and improve wound healing. Not least, amla contains properties that can treat and prevent cancer, and warrants further studies for these purposes.

How to Grow Gooseberries

Gooseberries grow as small trees and shrubs being 1.5m in height and width and they fruit green, red, purpe, yellow, or even white gooseberries.

Wild gooseberries have smaller berries than cultivated ones, but their taste is often excellent.

Jostaberry is the hybrid of the black currant (Ribes Nigrum), the North American coastal black gooseberry (Ribes Divaricatum) and the European gooseberry (Ribes Uva-Crispa). Gooseberries were also used to produce the Jochelbeere, which is hybrid of the black currant (Ribes Nigrum) and the European gooseberry (Ribes Uva-Crispa).

Gooseberries are native to colder areas of Europe and parts of Asia. It can be grown even in warmer area, but in partial or full shade of other trees.

Gooseberries are easy to grow in small gardens - if you happen to find great tasting gooseberry in nature, be sure to cut a small branch. At home, put cutting in a suitable pot with good wet soil and soon it will grow new roots and new fruits can be expected in year or two. Gooseberries can be grown from seeds, too.

Gooseberries are self-fertilized plants, so growing single tree can yield with plenty of fruits. However, gooseberries are great for hedges, due to their height (1.5m), large number of thorns, and generally being a resilient plant.

When grown as hedge, plant them around 1m apart (3 feet) and prune regularly in order to remove weak or dead canes, especially from center of the bush and to open up the canopy and let the sun in and increase air circulation, decreasing disease problems. Also, pruning makes fruits easier to harvest - did we mention the thorns? Also, canes older than 4 years should be removed, too - they are still producing the fruit, but not nearly as much as younger canes.

Without regular pruning, gooseberry bush will soon become dense, thorny thicket. Often, gooseberries are grown on the trellis, similar to those used for grapes, as a single species, or mixed with other similar plants.

Soil Preparation

Gooseberries tolerate different types of soil, however, they will grow best on rich, moist, well-drained positions with pH around 6.5.

If you have sandy or heavy soil, add aged manure, compost, humus and other organic material to improve the soil. Also, add balanced NPK fertilizers with gradual release of nutrients in late winter, just be sure to avoid adding plenty of nitrogen. Nitrogen will make plants grow big, but weak and prone to various diseases.

Plants start to grow early in the spring, so be sure to plant gooseberries in early fall or in very early spring.

Mulching prevents weeds, but also protects the soil from heat and direct sunlight. Good mulches include organic materials like straw, composted manure, compost, wood chips and similar. Mulch such as wood chips or sawdust are considered as being low-nitrogen and high-carbon mulch, so one may need to apply extra nitrogen fertilizer. Nitrogen deficiency is easy to spot - plants grow slowly and older leaves start to change color - turn yellow. If younger leaves start to change color into yellow, it is sign of serious nitrogen deficiency, or there might be some other serious problem.

Pest and Diseases

The biggest problem for gooseberries is powdery mildew - if one grows cultivated varieties, choose those varieties that are resistant to powdery mildew. Also, keeping good air circulation and having plenty of sunlight prevents powdery mildew.

Birds and especially pigeons in some locations, can make a plenty of damage - they must be prevented from eating the fruits, but also breaking young canes. Protective nets are the only option for protecting gooseberries and other berries from birds.

Gooseberries are easy plants to grow in the small garden or on the balcony. They require some work in order to grow properly and bear great tasting fruits, but that work is negligible when compared with great tasting fruits and their fragrance and aroma.

Gooseberry Fun Facts

Gooseberry fool has remained a favorite dessert in Britain since the Tudors controlled the throne. This reflects a national hysteria over the fruit, especially since competitive gooseberry growing was a popular pastime up to World War I, when there were 170 shows in Northern England.
The Egton Bridge Old Gooseberry Society, established in 1800, is the oldest surviving gooseberry show in the country.

Summary

They're tart. They're wild. Despite these facts, the little gooseberry is quite underutilized in the culinary world. Gooseberries offer a piquant flavor that's still a favorite in England for jams, jellies, juice and the old "fool" recipe.

Rich in antioxidant polyphenols, vitamins, and other beneficial nutrients, gooseberries can vary in color, flavor, and shape, but all come with many tiny, edible seeds. They also come with 26 percent of the daily recommended value in vitamin C - 20 times that of oranges. A wide array of other vitamins and minerals, plus protein and omega-3 fatty acids, makes this little berry exceptionally nutritious.

Able to defend the body against infection, gooseberries are said to produce insulin, strengthen heart muscles, slow aging, protect the eyes, improve the skin, and prevent hair loss. Ayurveda, traditional Indian medicine, uses it for many cures, but clinical studies reveal gooseberries to have true nutritional benefits. The one gram of fat? That's unsaturated.

Jai Ganesh · 2019-01-13 00:15:06

276) Jellyfish

Jellyfish, common name for the free-swimming stage, of certain invertebrate animals of the phylum Cnidaria (the coelenterates). The body of a jellyfish is shaped like a bell or umbrella, with a clear, jellylike material filling most of the space between the upper and lower surfaces. A mouth is located in the center of the under surface and tentacles dangle from the bell margin. Many jellyfish are colored, with pink or orange internal structures visible through the colorless or delicately tinted bell, and all are exquisitely designed; they are among the most beautiful of animal types.

Typically, jellyfish catch their prey with the aid of stinging cells located in the tentacles; many jellyfish can cause irritating or even dangerous stings to humans. Food is carried by the tentacles to the mouth, then is moved into the stomach and is distributed to the body through radial canals. Jellyfish move up and down by contracting and relaxing the bell, using muscles that circle the bell margin; they are carried horizontally by waves and currents.

Jellyfish of the class Hydrozoa are small, ranging from 1/8 in. (0.32 cm) to several inches in diameter, and usually have four tentacles. They have several (often four) unbranched radial canals and simple sense organs. In this group the polyp, or attached stage, is often larger and more conspicuous than the medusa.

Jellyfish of the class Scyphozoa, sometimes called true jellyfish, are larger and often have numerous tentacles; they have branched radial canals and complex sense organs. In this group the medusa is the prominent form and the polyp is reduced to a small larval stage. Scyphozoan jellyfish are commonly 3/4 in. to 16 in. (2–40 cm) in diameter, though one species of Cyanea found in cold northern seas may reach 6 ft (1.8 m) across and have tentacles over 100 ft (30 m) long. Aurelia, the flattened jellyfish common along North American coasts, is usually 1 ft (30 cm) or less across.

Tiny Craspedacusta, a hydrozoan jellyfish less than 1 in. (2.5 cm) long, occurs in freshwater lakes and ponds, but all other jellyfish are marine, living in ocean depths as well as along the coasts. The hydrozoan Physalia, or Portuguese man-of-war, is actually a large colony of modified individuals, some medusalike and some polyplike; a large gas-filled sac acts as a float for the colony. The tentacles of such a colony may extend 60 ft (18 m) into the water and can cause severe injuries to swimmers. Physalia is usually bright blue, sometimes with tints of pink and orange. The purple sail, Velella, a floating hydrozoan colony 1 to 3 in. (2.5–7.5 cm) across, may be blue or purple.

Jellyfish are classified in the phylum Cnidaria.

Polyp And Medusa

Polyp and medusa, names for the two body forms, one nonmotile and one typically free swimming, found in the aquatic invertebrate phylum Cnidaria (the coelenterates). Some animals of this group are always polyps, some are always medusae, and some exhibit both a polyp and a medusa stage in their life cycle. The polyp is a sessile, or nonmotile, organism; well-known solitary polyps are the sea anemone and the freshwater hydra. The medusa, when free swimming, is popularly known as a jellyfish.

Anatomy

The two forms are similar in construction; both consist of a cylindrical body surrounding a digestive cavity, with a single opening, the mouth, at one end. The mouth is surrounded by tentacles, which are used to capture food and convey it to the mouth; these tentacles are armed with stinging cells which paralyze the prey. The body wall is composed of three layers of tissue. Thin layers called endoderm and ectoderm line the outside and inside, respectively; between these is a layer of jellylike material, called mesoglea, of varying thickness.

The polyp, also called the hydroid, tends to be elongated, with a thin body wall; it is attached to the ocean bottom or other surface by the end opposite the mouth, its tentacles pointing upward. The medusa tends to be rounded, with a thick body wall containing much mesoglea; it swims or is carried in the current with the mouth side down and the tentacles dangling.

Jellyfish Characteristics

Jellyfish are marine invertebrates belonging to the Scyphozoan class, and in turn the phylum Cnidaria. The body of an adult jellyfish is composed of a bell-shaped, jellylike substance enclosing its internal structure, from which the creatures tentacles suspend.

Jellyfish come in all different shapes and colors and range in size from 3 millimeters to 3 meters in diameter.

One species of jellyfish in the cold arctic sea is huge, its body can be more than 7 feet wide and its tentacles can be up to 120 feet long.

Although Jellyfish often appear clear or pale bluish in color, they can also be yellow, deep blue, bright purple, pale lilac, bright orange, deep red. Some Jellyfish, when they are disturbed at night, give off a cold bright light called luminescence.

Jellyfish are made up of a layer of epidermis, gastrodermis and a thick jellylike layer called mesoglea that separates the epidermis from the gastrodermis.

If you have never been stung by a Jellyfish, then you are very lucky as they have a painful sting and some can even kill you. The tentacles on a Jellyfish are covered with stinging cells (cnidocytes) that sting or kill other animals: most jellyfish use them to secure prey or as a defense mechanism. Others, such as Rhizostomae, do not have tentacles at all.

Jellyfish Behavior

Jellyfish have survived a long time in their watery habitats. Jellyfish have lived on earth for millions of years and can be found in all the oceans of the would. There are even some Jellyfish that live in fresh water lakes and rivers.

Jellyfish usually drift, however, occasionally you will see them swimming. Jellyfish swim by rhythmic pulsations of the umbrella or bell. The movement is very like an umbrella being open and shut slowly. It is coordinated by a very simple nervous system and by sense organs around the edge that are sensitive to light and gravity and chemicals in the water. Jellyfish are slow swimmers but speed and low water resistance are not important because they are drifters that feed on plankton. It is more important for them that their movements create a current where the water (which contains their food) is being forced within reach of their tentacles.

Jellyfish Diet

Most jellyfish are passive drifters that feed on small fish and zooplankton that become caught in their tentacles. Jellyfish also eat small animals such as shrimps. Some of the animals Jellyfish eat are microscopic, too small to be seen by the human eye. Jellyfish also eat other Jellyfish of other species. They catch their prey by using nematocysts, small stinging organs present in the tentacles and oral arms.

Jellyfish Stings

The complete lack of a brain means that the jellyfish cannot help but sting you – unless it is a Box Jellyfish (Chironex fleckeri) which can control itself efficiently, even without a brain. This Jellyfish has 3 million stinging cells every centimeter of its tentacles. The Box jelly is responsible for at least one death a year around Australia and has killed 67 people since records began in 1883, though the total is misleading since many deaths attributed to heart attacks or drowning could have been caused by toxic jellies.

If the stinging cells [nematocysts] of a jellyfish make contact with your skin they will release their poison into it.

Symptoms include:

i) severe pain
ii) headache, nausea, vomiting, diarrhoea
iii) skin swelling/wounds/redness
iv) difficulty breathing, swallowing and speech
v) shivering, sweating
vi) irregular pulse/heart failure

Sting treatments:

a) pour vinegar over tentacles. Urine does not work on the Box Jelly or Irukandji.
b) lift off any tentacles with a stick or similar.
c) use pressure-immobilisation on limbs if possible. i.e. quickly wrap a light bandage above and below the sting (if you cannot get two fingers under the bandage, it is too tight).
d) Immobilize/splint the stung area and keep it at heart level [gravity-neutral] if possible. Too high causes venom to travel to the heart, too low causes more swelling.
e) Do not drink alcohol, or take any medicine or food.
f) get medical treatment urgently or apply antivenom if available.

Some kinds of Jellyfish stings are like miniature harpoons with barbs on the end that inject poison to paralyze their prey. Some Jellyfish have sticky harpoons and others wrap their harpoons around their prey to trap it.

Jai Ganesh · 2019-01-14 00:05:07

277) VY Canis Majoris

Put the Sun next to a supergiant star and you’ll have a hard time finding it. Supergiant stars are the largest stars in the universe. They can be thousands of times bigger than our Sun and have a mass up to 100 times greater. The largest known supergiant star, VY Canis Majoris, is up to 2,100 times the size of the Sun (based on upper estimates). If it were put in the position of the Sun, it would extend out to the orbit of Saturn.

Supergiants come in a variety of sizes and temperatures, but they are generally classed as being either red or blue. Red supergiants have a mass at least eight times that of our Sun, and are generally old stars that were once similar in size to the Sun. They form when a star more than 10 times the mass of our Sun runs out of its hydrogen fuel in its core, preventing fusion from occurring there. It subsequently begins collapsing but, as it does so, the hydrogen in its outer shells begins fusion of its own. At this point the entire star experiences fusion and begins to burn through the rest of its hydrogen at an astounding rate. In fact, they can burn all of their remaining hydrogen in just a few million years, compared to the several billion year lifetime of stars like our Sun. During this time they will shine at least 100,000 times brighter than the Sun. At the end of their life, red supergiant stars often explode as a supernova, producing either a neutron star or a black hole in the process. The nearby red supergiant Betelgeuse, which is 1,000 times the mass of the Sun, is only 8.5 million years old but it is expected to go supernova within the next 1,000 years.
Blue supergiants are considerably hotter than red supergiants, but generally much smaller, only about 25 times the size of the Sun. Like red supergiants they have very short lifetimes of only a few million years. They usually form when a star more than 10 times the mass of the Sun heading towards its own demise enters a slow burning phase. However, red supergiants can also turn blue if their own rate of nuclear fusion begins to slow down. In fact, a star can actually continually switch between being a red and blue supergiant over its lifetime. Between the two extremes it becomes a yellow supergiant such as the north star, Polaris. However, stars of this nature generally spend the majority of their time as red supergiants rather than blue or yellow.

The star VY Canis Majoris is the largest star in our Galaxy with a known size. It is estimated to have 30-40 times the mass of our Sun, but a gigantic 2000 times the size - that means that if it were suddenly placed in our Solar System, it would extend out to the orbit of Saturn! It is also very bright - producing around 500,000 times as much light as our Sun - but is far enough away that it can't be seen with the unaided eye. Stars this massive are burning so brightly that they live for only a few tens of millions of years - not for ten billion of years like our Sun.

The star is a "red hypergiant" star, and is shedding its outer layers, producing a cloud of gas around it. Each molecule emits light preferentially at a series of particular wavelengths, called emission lines, which are seen as spikes in the spectrum. By comparing the observed emission lines with what has been measured in laboratories on Earth, astronomers can identify the molecules.

In a few million years, when the star explodes in a supernova, these molecules will all be spread through the surrounding environment. When a new generation of stars forms they will contain these molecules, as will any planetary systems that eventually form around them. Stars like VY Canis Majoris are likely existed in our part of the galaxy before the Sun formed, and been the source of many of the complex molecules present in the early Solar System and, later, on the Earth.

• VY Canis Majoris is around 4,000 light years from Earth in the constellation of Canis Major.
• It is one of the largest known stars in the Milky Way galaxy.
• VY Canis Majoris is a red hypergiant with a radius of around 1,500 times larger than the sun.
• Hypergiant stars such as VY Canis Majoris are extremely rare in our galaxy, in fact most stars in the Milky Way are smaller than the sun.
• Large stars burn their fuel extremely quickly, as a result they only exist for a few million years, smaller stars like our sun exist for billions of years.
• It is estimated that VY Canis Majoris has already ejected around half of its mass, which has surrounded the star in a nebula cloud.
• VY Canis Majoris is near the end of its lifespan and is expected to explode as a supernova in the next 100,000 years.
• After the star explodes the collapse of its remaining core could be massive enough to create a black hole.
• The French astronomer Jerome Laland was the first to record and catalogue the star in 1801.

VY Canis Majoris Radius

Estimates of the star's radius have previously ranged up to 2,000 times larger than the sun, but it is now thought its radius is around 1,500 times that of the sun. If VY Canis Majoris was placed in the center of our solar system it would almost reach the orbit of Saturn!

VY Canis Majoris Mass

VY Canis Majoris is estimated to have a mass of around 10 to 25 times that of the sun.

VY Canis Majoris Temperature

VY Canis Majoris is estimated to have surface temperatures of around 3,200C (5,800F).

VY Canis Majoris Luminosity (energy emitted)

Measurements of the star's luminosity vary quite dramatically, from around 250,000 to 500,000 times as luminous as the sun.

VY Canis Majoris Statistics

Also Known As: VY CMa

Distance From Earth: 4,000 to 5,000 light years

Constellation: Canis Major

Star Type: Red Hypergiant - M Class

Mass: 20 to 40 x Sun

Luminosity: 250,000 to 500,000 x Sun

Diameter: Approx 1.5 billion miles (2.4 billion km) - 1,750 x Sun

Temperature: Approx 3,200C (5,800F)

Age: Approx 10 million years old

Rotation Period: Unknown

Information compiled from different sources.

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