Math Is Fun Forum
  Discussion about math, puzzles, games and fun.   Useful symbols: ÷ × ½ √ ∞ ≠ ≤ ≥ ≈ ⇒ ± ∈ Δ θ ∴ ∑ ∫ • π ƒ -¹ ² ³ °

You are not logged in.

#1 Re: Dark Discussions at Cafe Infinity » crème de la crème » Today 00:48:22

437) Ward Christensen

Born    October 23, 1945 (age 73), West Bend, Wisconsin, United States.
Known for    first bulletin board system (BBS), XMODEM Protocol.

Ward Christensen (born 1945 in West Bend, Wisconsin, United States) is the co-founder of the CBBS bulletin board, the first bulletin board system (BBS) ever brought online. Christensen, along with partner Randy Suess, started development during a blizzard in Chicago, Illinois, and officially established CBBS four weeks later, on February 16, 1978.

Christensen was noted for building software tools for his needs. He wrote a cassette-based operating system before floppies and hard disks were common. When he lost track of the source code for some programs he wrote ReSource, an iterative disassembler for the Intel 8080, to help him regenerate the source code. When he needed to send files to Randy Suess he wrote XMODEM.

Jerry Pournelle wrote in 1983 of a collection of CP/M public-domain software that "probably 50 percent of the really good programs were written by Ward Christensen, a public benefactor." Christensen received two 1992 Dvorak Awards for Excellence in Telecommunications, one with Randy Suess for developing the first BBS, and a lifetime achievement award "for outstanding contributions to PC telecommunications." In 1993 he received the Pioneer Award from the Electronic Frontier Foundation.

Christensen worked at IBM from 1968 until his retirement in 2012. His last position with IBM was field technical sales specialist.

ward_christensen.jpg

#3 Re: Ganesh's Puzzles » Oral puzzles » Today 00:21:09

Hi,

#4294. At present, A's age is 1.5 times the age of B. Eight years hence, the ratio of the ages of A and B will be 25:18. What is B's present age?

#4 Re: Ganesh's Puzzles » 10 second questions » Yesterday 16:22:43

Hi,

.

Well tried, Monox D. I-Fly!

#7129. Find the value of m.

.

#5 Re: Ganesh's Puzzles » Oral puzzles » Yesterday 16:07:50

Hi,

.

#4293. On Teachers' Day, were to be equally distributed among 540 children. But, on that particular day, 135 children remained absent, henthe, each child got 2 sweets extra. How many sweets was each child originally supposed to get?

#6 Re: This is Cool » Miscellany » Yesterday 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.

Academy_Award_trophy.jpg

#7 Jokes » Orangutan Jokes - 1 » Yesterday 00:33:44

ganesh
Replies: 0

Q: What do you call a monkey who can't hear the telephone and who has a wife called Tang?
A: Who-rang-o-tang!
* * *
Q: What is a orangutan's favorite cookie?
A: Chocolate chimp!
* * *
Q: What does a Orangutan attorney study?
A: The Law of the jungle!
* * *
Q: What does a Orangutan learn first in school?
A: The Apey-cees!
* * *
Q: What's orange, brown and white, orange, brown and white, brown and white, etc.?
A: An Orangutan riding down a snowbank!
* * *
Q: What is as big as an orangutan but weighs nothing?
A: Its shadow!
* * *
Q: Which drink makes a Orangutan feel tipsy?
A: An ape-ricot sour!
* * *
Q: Why did the female Orangutan, engaged to the invisible man, call off the wedding?
A: Because in the last analysis she just couldn't see it!
* * *
Q: Why did the Orangutan fail English?
A: He had little Ape-titude!
* * *
Q: Why do waiters like Orangutans better than flies?
A: Did you ever hear a customer complain 'Waiter, there's a Orangutan in my soup!'
* * *
Q: Why do orangutans have big nostrils?
A: They have big fingers.
* * *

#8 Re: Ganesh's Puzzles » 10 second questions » Yesterday 00:22:31

Hi,

.

#7128. Find the value of t:
t% of 800 = 293 - 22% of 750.

#9 Re: Ganesh's Puzzles » Oral puzzles » Yesterday 00:12:36

Hi,

.

#4292. Find the average of the following set of scores: 253, 124, 255, 534, 836, 375, 101, 443, and 760.

#10 Re: Dark Discussions at Cafe Infinity » crème de la crème » 2018-12-10 01:04:10

436) Ruth Benerito

Born January 22 1916, died October 5 2013.

Ruth Benerito, who has died aged 97, was an American chemist and inventor; among her 55 patents was a process for treating cotton that would lead to the creation of wash-and-wear fabrics, effectively revitalising America’s cotton industry.

From the early 1950s Ruth Benerito was a physical chemist at the Southern Regional Research Center for the United States Department of Agriculture (USDA), where her early work had focused on creating an intravenous fat emulsion that could be used to provide hospital patients with sufficiently high-calorie nutrition. In 1958, however, she became head of a research team hoping to develop a new cotton-based fabric, as easy to care for as the nylons and polyesters that had enjoyed such popularity in the post-war years.

Cotton’s biggest drawback, against its synthetic rivals, was its tendency to crease. This is down to the molecular structure of cotton fibres, which are comprised of long cellulose chains – polymers – held in place end-to-end by hydrogen bonds. Since these links are weak and easily broken, the heat and agitation of washing causes the molecules to shift position, resulting in the wrinkles that are corrected by ironing.

The secret to cotton that would not crease therefore lay in the chemical manipulation of the hydrogen bonds . The innovation that Ruth Benerito and her fellow researchers devised was a process called cross-linking, in which epoxides – ring-shaped organic compounds comprised of an oxygen atom and two other connected atoms – are inserted between cellulose chains like rungs in a ladder, creating a longer and sturdier polymer.

Though early treatments using formaldehyde as a cross-linking agent were not wholly successful – the formaldehyde proved toxic and caused an unpleasant smell – the implications extended far beyond crease-free fabric. Cross-linking with other compounds would later produce stain-resistant and fireproof clothes, while Ruth Benerito’s study of epoxides led to separate breakthroughs in the film and paper industries, in the creation of epoxy plastics, and in the preservation of wood.

The third of six children, she was born Ruth Mary Rogan in New Orleans, Louisiana, on January 22 1916. Her father, John, was a civil engineer; her mother, Bernadette, an artist and prototypical feminist. Both encouraged their daughter to pursue a scientific career from an early age. When she was 15 Ruth enrolled at Sophie Newcomb Memorial College, the women’s college of Tulane University, as one of the institution’s two female chemists, graduating with a BS in 1935, an MS in 1938 and a PhD from the University of Chicago in 1948. After earning her doctorate she became an assistant professor of chemistry at Newcomb College, a position she held until 1953 .

Following her departure from the USDA’s Southern Regional Research Center in 1989, Ruth Benerito taught Chemistry at the University of New Orleans, before macular degeneration forced her into permanent retirement aged 84. Her home of 56 years was destroyed by Hurricane Katrina, and she spent the last years of her life in Metairie, Louisiana.

Among the honours she received were the Federal Woman Award in 1968; the Garvan Medal from the American Chemical Society in 1970; and the Lemelson-Mit Lifetime Achievement Award in 2002. She was inducted into the National Inventors Hall of Fame in 2008.

Ruth Benerito was quick to play down her scientific contribution, citing the research that had preceded hers, and the properties of cotton itself. “Nature made cotton pretty good to begin with,” she insisted. “I just gave it a little boost.”

Her husband, Frank Benerito, whom she married in 1950, died in 1970.

3-29-Ruth-Benerito-205x300.jpg

#12 Re: Ganesh's Puzzles » Oral puzzles » 2018-12-10 00:12:52

Hi,

#4291. The average marks in English subject of a class of 24 students is 56. If the marks of three students were misread as 44, 45, and 61 of the actual marks 48, 59, and 67 respectively, then what would be the correct average?

#13 Re: Ganesh's Puzzles » 10 second questions » 2018-12-09 01:01:02

Hi,

.

#7126. Find the value of p.

.

#14 Re: Ganesh's Puzzles » Oral puzzles » 2018-12-09 00:43:47

Hi,

#4290. The height of 5 boys is recorded as 146 centimeters, 154 centimeters, 164 centimeters, 148 centimeters, and 158 centimeters. What is the average height of all these boys?

#15 Jokes » Monkey Jokes - 2 » 2018-12-09 00:31:22

ganesh
Replies: 0

Q: What does a logger say before he cuts down a tree?
A: Let the chimps fall where they may.
* * *
Q: Where should a monkey go when he loses his tail?
A: To a retailer!
* * *
Q: What did the banana do when he saw a monkey?
A: The banana split!
* * *
Q: What is a monkey's favorite game?
A: Hangman!
* * *
Q: Why don't monkeys play cards in the jungle?
A: There are too many cheetahs there!
* * *
Q: Why shouldn't you get into a fight with a monkey?
A: They use gorilla warfare.
* * *
Q: What do you call a monkey that succeeds at every sport?
A: A chimpion!
* * *
Q: Where do chimps get their gossip?
A: On the ape vine!
* * *
Q: How do you get an escaped lion back into his habitat?
A: With a bargaining chimp.
* * *
Q: What do you call a restaurant that throws food in your face?
A: A Monkey Business.
* * *
Q: How do you catch a monkey?
A: Climb a tree and act like a banana!
* * *

#16 Re: This is Cool » Miscellany » 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.

Banana-3-bananas-34512812-398-302.jpg

#18 Re: Ganesh's Puzzles » Oral puzzles » 2018-12-08 00:45:51

Hi,

#4289. The average age of 80 girls was 20 years, the average age of 20 of them was 22 years and that of another 20 was 24 years. Find the average age age of the remaining girls.

#19 Re: Dark Discussions at Cafe Infinity » crème de la crème » 2018-12-08 00:23:14

435) Anders Knutsson Ångström

Anders Knutsson Ångström (1888, Stockholm – 1981) was a Swedish physicist and meteorologist who was known primarily for his contributions to the field of atmospheric radiation. However, his scientific interests encompassed many diverse topics.

He was the son of physicist Knut Ångström. He graduated with a BS from the University of Upsala in 1909. Then he completed his MS at the University of Upsala in 1911. He taught at the University of Stockholm Later, he was the department head of the Meteorology department at State Meteorological and Hydrological Institute (SMHI) of Sweden 1945–1949 and SMHI's chancellor 1949–1954.

He is credited with the invention of the pyranometer, the first device to accurately measure direct and indirect solar radiation.

In 1962 he was awarded the International Meteorological Organization Prize by the World Meteorological Organization.

Pyranometer

A pyranometer is a type of actinometer used for measuring solar irradiance on a planar surface and it is designed to measure the solar radiation flux density (W/m²) from the hemisphere above within a wavelength range 0.3 μm to 3 μm.

A typical pyranometer does not require any power to operate. However, recent technical development includes use of electronics in pyranometers, which do require (low) external power.

Explanation

The solar radiation spectrum that reaches earth's surface extends its wavelength approximately from 300 nm to 2800 nm. Depending on the type of pyranometer used, irradiance measurements with different degrees of spectral sensitivity will be obtained.

To make a measurement of irradiance, it is required by definition that the response to “beam” radiation varies with the cosine of the angle of incidence. This ensures a full response when the solar radiation hits the sensor perpendicularly (normal to the surface, sun at zenith, 0° angle of incidence), zero response when the sun is at the horizon (90° angle of incidence, 90° zenith angle), and 0.5 at a 60° angle of incidence. It follows that a pyranometer should have a so-called “directional response” or “cosine response” that is as close as possible to the ideal cosine characteristic.

Actinometer

Actinometers are instruments used to measure the heating power of radiation. They are used in meteorology to measure solar radiation as pyranometers, pyrheliometers and net radiometers.

An actinometer is a chemical system or physical device which determines the number of photons in a beam integrally or per unit time. This name is commonly applied to devices used in the ultraviolet and visible wavelength ranges. For example, solutions of iron(III) oxalate can be used as a chemical actinometer, while bolometers, thermopiles, and photodiodes are physical devices giving a reading that can be correlated to the number of photons detected.

anders_knutsson_angstrom_medium.jpg

#20 Re: Ganesh's Puzzles » 10 second questions » 2018-12-07 15:59:56

Hi,

Good work, Monox D. I-Fly! The solution #7123 is correct!

#7124. Find the value of j.

.

#21 Re: This is Cool » Miscellany » 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.

microtek-jumbo-ups-jm1250-va-250x250.png

#23 Re: Ganesh's Puzzles » Oral puzzles » 2018-12-07 00:40:00

Hi,

The solution #4287 is correct. Neat work,  Monox D. I-Fly!

#4288. Ronit's age is 10 years more that Rohit's age. Also, Ronit was twice old as Rohit 15 years ago. What will be the age of Ronit 6 years after?

#24 Jokes » Monkey Jokes - 1 » 2018-12-07 00:16:48

ganesh
Replies: 0

Q: How do monkeys get down the stairs?
A: They slide down the banana-ster!
* * *
Q: What do you call a monkey that sells potato chips?
A: A chipmunk.
* * *
Q: What kind of a key opens a banana?
A: A monkey!
* * *
Q: Why did the monkey like the banana?
A: Because it had appeal!
* * *
Q: What do monkeys do for laughs?
A: They tell jokes about people!
* * *
Q: What do you call a baby monkey?
A: A Chimp off the old block.
* * *
Q: What do you tell a bad monkey?
A: Stop chimping about.
* * *
Q: What do you call a monkey with a banana in each ear?
A: Anything you want, it can't hear you!
* * *
Q: What did the monkey say when he cut off his tail?
A: It won't be long now.
* * *
Q: Where do monkeys go to drink?
A: The monkey bars!
* * *

#25 Re: Jokes » Lion Jokes - 2 » 2018-12-07 00:13:09

Thought-provoking, Monox D. I-Fly! smile smile

Board footer

Powered by FluxBB