Miscellany

Jai Ganesh · 2020-09-27 00:43:04

779) Tamarind

Tamarind, (Tamarindus indica), evergreen tree of the pea family (Fabaceae), native to tropical Africa. It is widely cultivated in tropical and subtropical regions for its edible fruit, the sweet and sour pulp of which is extensively used in foods, beverages, and traditional medicines. The plant is especially popular in the Indian subcontinent and in Central America and Mexico and is a common ingredient in the cuisine of those regions. The tree is also grown as an ornamental, and the wood is used in carpentry.

The tree grows to about 24 metres (80 feet) tall and bears alternate, pinnately compound (feather-formed) leaves with leaflets that are about 2 cm (0.75 inch) long. The yellow flowers are borne in small clusters. The fruit is a plump legume 7.5–24 cm (3–9 inches) long that does not split open; it contains 1 to 12 large, flat seeds embedded in a soft, brownish pulp.

Tamarind (Tamarindus indica) is a leguminous tree (family Fabaceae) bearing edible fruit that is indigenous to tropical Africa. The genus Tamarindus is monotypic, meaning that it contains only this species.

The tamarind tree produces brown, pod-like fruits that contain a sweet, tangy pulp, which is used in cuisines around the world. The pulp is also used in traditional medicine and as a metal polish. The tree's wood can be used for woodworking and tamarind seed oil can be extracted from the seeds. Tamarind's tender young leaves are used in Indian cuisine. Because tamarind has multiple uses, it is cultivated around the world in tropical and subtropical zones.

Tamarindus indica is probably indigenous to tropical Africa, but has been cultivated for so long on the Indian subcontinent that it is sometimes reported to be indigenous there. It grows wild in Africa in locales as diverse as Sudan, Cameroon, Nigeria, Kenya, Zambia, Somalia, Tanzania and Malawi. In Arabia, it is found growing wild in Oman, especially Dhofar, where it grows on the sea-facing slopes of mountains. It reached South Asia likely through human transportation and cultivation several thousand years ago. It is widely distributed throughout the tropics, from Africa to South Asia, northern Australia, and throughout Oceania, Southeast Asia, Taiwan and China.

In the 16th century, it was introduced to Mexico and Central America, and to a lesser degree to South America, by Spanish and Portuguese colonists, to the degree that it became a staple ingredient in the region's cuisine.

Today, India is the largest producer of tamarind. The consumption of tamarind is widespread due to its central role in the cuisines of the Indian subcontinent, Southeast Asia, and the Americas, especially Mexico.

Description

The tamarind is a long-lived, medium-growth tree, which attains a maximum crown height of 12 to 18 metres (40 to 60 feet). The crown has an irregular, vase-shaped outline of dense foliage. The tree grows well in full sun. It prefers clay, loam, sandy, and acidic soil types, with a high resistance to drought and aerosol salt (wind-borne salt as found in coastal areas).

The evergreen leaves are alternately arranged and pinnately lobed. The leaflets are bright green, elliptic-ovular, pinnately veined, and less than 5 cm (2 in) in length. The branches droop from a single, central trunk as the tree matures, and are often pruned in agriculture to optimize tree density and ease of fruit harvest. At night, the leaflets close up.

As a tropical species, it is frost-sensitive. The pinnate leaves with opposite leaflets give a billowing effect in the wind. Tamarind timber consists of hard, dark red heartwood and softer, yellowish sapwood.

The tamarind flowers (although inconspicuously), with red and yellow elongated flowers. Flowers are 2.5 cm wide (one inch), five-petalled, borne in small racemes, and yellow with orange or red streaks. Buds are pink as the four sepals are pink and are lost when the flower blooms.

Fruit

The fruit is an indehiscent legume, sometimes called a pod, 12 to 15 cm (4 1⁄2 to 6 in) in length, with a hard, brown shell.

The fruit has a fleshy, juicy, acidic pulp. It is mature when the flesh is coloured brown or reddish brown. The tamarinds of Asia have longer pods (containing six to 12 seeds), whereas African and West Indian varieties have shorter pods (containing one to six seeds). The seeds are somewhat flattened, and a glossy brown. The fruit is best described as sweet and sour in taste, and is high in tartaric acid, sugar, B vitamins, and, unusually for a fruit, calcium.

The fruit is harvested by pulling the pod from its stalk. A mature tree may be capable of producing up to 175 kg (386 lb) of fruit per year. Veneer grafting, shield (T or inverted T) budding, and air layering may be used to propagate desirable cultivars. Such trees will usually fruit within three to four years if provided optimum growing conditions.

Culinary use

The fruit pulp is edible. The hard green pulp of a young fruit is considered by many to be too sour, but is often used as a component of savory dishes, as a pickling agent or as a means of making certain poisonous yams in Ghana safe for human consumption. As the fruit matures it becomes sweeter and less sour (acidic) and the ripened fruit is considered more palatable. The sourness varies between cultivars and some sweet tamarind ones have almost no acidity when ripe. In Western cuisine, tamarind pulp is found in Worcestershire Sauce and HP Sauce.

Tamarind paste has many culinary uses including a flavoring for chutnies, curries, and the traditional sharbat syrup drink. Tamarind sweet chutney is popular in India as a dressing for many snacks. Tamarind pulp is a key ingredient in flavoring curries and rice in south Indian cuisine, in the Chigali lollipop, and in certain varieties of Masala Chai tea. Across the Middle East, from the Levant to Iran, tamarind is used in savory dishes, notably meat-based stews, and often combined with dried fruits to achieve a sweet-sour tang. In the Philippines, the whole fruit is used as an ingredient in the traditional dish called sinigang to add a unique sour taste, unlike that of dishes that use vinegar instead. Indonesia also has a similarly sour, tamarind-based soup dish called sayur asem.

In Mexico and the Caribbean, the pulp is diluted with water and sugared to make an agua fresca drink.

Tamarind seed oil

Tamarind seed oil is the oil made from the kernel of tamarind seeds.[26] Isolation of the kernel without the thin but tough shell (or testa) is difficult. Tamarind kernel powder is used as sizing material for textile and jute processing, and in the manufacture of industrial gums and adhesives. It is de-oiled to stabilize its colour and odor on storage.

Cultivation

Seeds can be scarified or briefly boiled to enhance germination. They retain their germination capability for several months if kept dry.

The tamarind has long been naturalized in Indonesia, Malaysia, Sri Lanka, the Philippines, the Caribbean, and Pacific Islands. Thailand has the largest plantations of the ASEAN nations, followed by Indonesia, Myanmar, and the Philippines. In parts of Southeast Asia, tamarind is called asam. It is cultivated all over India, especially in Maharashtra, Chhattisgarh, Karnataka, Telangana, Andhra Pradesh, and Tamil Nadu. Extensive tamarind orchards in India produce 275,500 tons (250,000 MT) annually.

Tamarind flowers

In the United States, it is a large-scale crop introduced for commercial use (second in net production quantity only to India), mainly in southern states, notably south Florida, and as a shade tree, along roadsides, in dooryards and in parks.

A traditional food plant in Africa, tamarind has the potential to improve nutrition, boost food security, foster rural development and support sustainable landcare. In Madagascar, its fruit and leaves are a well-known favorite of the ring-tailed lemur, providing as much as 50 percent of their food resources during the year if available.

Folk medicine

Throughout Southeast Asia, the fruit of the tamarind is used as a poultice applied to foreheads of fever sufferers. The fruit exhibits laxative effects due to its high quantities of malic acid, tartaric acid, and potassium bitartrate. Its use for the relief of constipation has been documented throughout the world.

Woodworking

Tamarind lumber is used to make furniture, carvings, turned objects such as mortars and pestles, chopping blocks, and other small specialty wood items. Tamarind heartwood is reddish brown, sometimes with a purplish hue. The heartwood in tamarind tends to be narrow and is usually only present in older and larger trees. The pale yellow sapwood is sharply demarcated from the heartwood. Heartwood is said to be durable to very durable in decay resistance, and is also resistant to insects. Its sapwood is not durable and is prone to attack by insects and fungi as well as spalting. Due to its density and interlocked grain, tamarind is considered difficult to work. Heartwood has a pronounced blunting effect on cutting edges. Tamarind turns, glues, and finishes well. The heartwood is able to take a high natural polish.

Metal polish

In homes and temples, especially in Buddhist Asian countries, the fruit pulp is used to polish brass shrine statues and lamps, and copper, brass, and bronze utensils. The copper alone or in brass reacts with moist carbon dioxide to gain a green coat of copper carbonate. Tamarind contains tartaric acid, a weak acid that can remove the coat of copper carbonate. Hence, tarnished copper utensils are cleaned with tamarind or lime, another acidic fruit.

Horticulture

Throughout South Asia and the tropical world, tamarind trees are used as ornamental, garden, and cash crop plantings. Commonly used as a bonsai species in many Asian countries, it is also grown as an indoor bonsai in temperate parts of the world.

Research

In hens, tamarind has been found to lower cholesterol in their serum, and in the yolks of the eggs they laid. Due to a lack of available human clinical trials, there is insufficient evidence to recommend tamarind for the treatment of hypercholesterolemia or diabetes. Different parts of tamarind (T. indica) are recognized for their various medicinal properties. A previous study reported that the seed, leaf, leaf veins, fruit pulp and skin extracts of tamarind possessed high phenolic content and antioxidant activities. The presence of lupanone and lupeol, catechin, epicatechin, quercetin and isorhamnetin[38] in the leaf extract could have contributed towards the diverse range of the medicinal activities. On the other hand, ultra-high performance liquid chromatography (UHPLC) analyses revealed that tamarind seeds contained catechin, procyanidin B2, caffeic acid, ferulic acid, chloramphenicol, myricetin, morin, quercetin, apigenin and kaempferol. The treatment of tamarind leaves on liver HepG2 cells significantly regulated the expression of genes and proteins involved with consequential impact on the coagulation system, cholesterol biosynthesis, xenobiotic metabolism signaling and antimicrobial response.

Scientific classification:
Kingdom: Plantae
(unranked): Angiosperms
(unranked): Eudicots
(unranked): Rosids
Order: Fabales
Family: Fabaceae
Subfamily: Detarioideae
Genus: Tamarindus
Species: T. indica
Binomial name : Tamarindus indica.

Jai Ganesh · 2020-09-28 00:33:36

780) Atlas Mountains

The Atlas Mountains are a mountain range in the Maghreb. It separates the Mediterranean and Atlantic coastlines from the Sahara Desert. It stretches around 2,500 km (1,600 mi) through Morocco, Algeria and Tunisia. The range's highest peak is Toubkal, which is in southwestern Morocco, with an elevation of 4,167 metres (13,671 ft). The Atlas mountains are primarily inhabited by Berber populations. The terms for 'mountain' are adrar and adras in some Berber languages. These terms are believed to be cognates of the toponym Atlas. The mountains are also home to a number of animals and plants which are mostly found within Africa but some of which can be found in Europe. Many of these species are endangered and a few are already extinct.

Geology

The basement rock of most of Africa was formed during the Precambrian supereon and is much older than the Atlas Mountains lying on the continent. The Atlas was formed during three subsequent phases of Earth's geology.

The first tectonic deformation phase involves only the Anti-Atlas, which was formed in the Paleozoic Era (~300 million years ago) as the result of continental collisions. North America, Europe and Africa were connected millions of years ago.

The Anti-Atlas Mountains are believed to have originally been formed as part of Alleghenian orogeny. These mountains were formed when Africa and America collided, and were once a chain rivaling today's Himalayas. Today, the remains of this chain can be seen in the Fall Line region in the Eastern United States. Some remnants can also be found in the later formed Appalachians in North America.

A second phase took place during the Mesozoic Era (before ~66 My). It consisted of a widespread extension of the Earth's crust that rifted and separated the continents mentioned above. This extension was responsible for the formation of many thick intracontinental sedimentary basins including the present Atlas. Most of the rocks forming the surface of the present High Atlas were deposited under the ocean at that time.

Finally, in the Paleogene and Neogene Periods (~66 million to ~1.8 million years ago), the mountain chains that today constitute the Atlas were uplifted, as the land masses of Europe and Africa collided at the southern end of the Iberian Peninsula. Such convergent tectonic boundaries occur where two plates slide towards each other forming a subduction zone (if one plate moves underneath the other), and/or a continental collision (when the two plates contain continental crust). In the case of the Africa-Europe collision, it is clear that tectonic convergence is partially responsible for the formation of the High Atlas, as well as for the closure of the Strait of Gibraltar and the formation of the Alps and the Pyrenees. However, there is a lack of evidence for the nature of the subduction in the Atlas region, or for the thickening of the Earth's crust generally associated with continental collisions. In fact, one of the most striking features of the Atlas to geologists is the relative small amount of crustal thickening and tectonic shortening despite the important altitude of the mountain range. Recent studies suggest that deep processes rooted in the Earth's mantle may have contributed to the uplift of the High and Middle Atlas.

Natural resources

The Atlas are rich in natural resources. There are deposits of iron ore, lead ore, copper, silver, mercury, rock salt, phosphate, marble, anthracite coal and natural gas among other resources.

Subranges of the Atlas Mountains

The range can be divided into four general regions:

• Anti-Atlas, High Atlas and Middle Atlas (Morocco).
• Tell Atlas (Morocco, Algeria, Tunisia).
• Aurès Mountains (Algeria, Tunisia).
• Saharan Atlas (Algeria).

Anti-Atlas ranges

The Anti-Atlas extends from the Atlantic Ocean in the southwest of Morocco toward the northeast to the heights of Ouarzazate and further east to the city of Tafilalt (altogether a distance of approximately 500 kilometres or 310 miles). In the south it borders the Sahara. The easternmost point of the anti-Atlas is the Jbel Saghro range and its northern boundary is flanked by sections of the High Atlas range. It includes the Djebel Siroua, a massif of volcanic origin with the highest summit of the range at 3,304 m. The Jebel Bani is a much lower range running along the southern side of the Anti Atlas.

High Atlas

The High Atlas in central Morocco rises in the west at the Atlantic coast and stretches in an eastern direction to the Moroccan-Algerian border. It has several peaks over 4,000 m (2.5 mi), including the highest summit in North Africa, Toubkal (4,167 m (13,671 ft)) and further east Ighil m'Goun (4,071 m (13,356 ft)) the second major summit of the range. At the Atlantic and to the southwest, the range drops abruptly and makes a transition to the coast and the Anti-Atlas range. To the north, in the direction of Marrakesh, the range descends less abruptly.

On the heights of Ouarzazate the massif is cut through by the Draa Valley which opens southward. It is mainly inhabited by Berber people, who live in small villages and cultivate the high plains of the Ourika Valley.

Near Barrage Cavagnac there is a hydroelectric dam that has created the artificial lake Lalla Takerkoust. The lake serves also as a source for fish for the local fishermen.

The largest villages and towns of the area are Ouarzazate, Tahannaout, Amizmiz, Imlil, Tin Mal and Ijoukak.

Middle Atlas range

The Middle Atlas is completely in Morocco and is the northernmost of its main three Atlas ranges. The range lies north of High Atlas, separated by the Moulouya and Oum Er-Rbia rivers, and south of the Rif mountains, separated by the Sebou River. To the west are the main coastal plains of Morocco with many of the major cities and, to the east, the high barren plateau that lies between the Saharan and Tell Atlas. The high point of the range is the jbel Bou Naceur (3340m). The Middle Atlas experiences more rain than the ranges to the south, making it an important water catchment for the coastal plains and important for biodiversity. It is home to the majority of the world's population of Barbary macaque.

Saharan Atlas range

The Saharan Atlas of Algeria is the eastern portion of the Atlas mountain range. Though not as high as the Grand Atlas, they are far more imposing than the Tell Atlas range that runs to the north of them and closer to the coast. The highest peak in the range is the 2,236 m (7,336 ft) high Djebel Aissa. They mark the northern edge of the Sahara Desert. The mountains see some rainfall and are better suited to agriculture than the plateau region to the north. Today most of the population of the region are Berbers (Imazighen).

Tell Atlas range

The Tell Atlas is a mountain chain over 1,500 kilometres (930 mi) in length, belonging to the Atlas mountain ranges and stretching from Morocco, through Algeria to Tunisia. It parallels the Mediterranean coast. Together with the Saharan Atlas to the south it forms the northernmost of two more or less parallel ranges which gradually approach one another towards the east, merging in Eastern Algeria. At the western ends at the Middle Atlas range in Morocco. The area immediately to the south of this range is the high plateau of the Hautes Plaines, with lakes in the wet season and salt flats in the dry.

Aurès mountain range

The Aurès Mountains are the easternmost portion of the Atlas mountain range. It covers parts of Algeria and Tunisia. The Aurès natural region is named after the range.

Flora and fauna

Flora in the mountains include the Atlas cedar, evergreen oak and many semi-evergreen oaks such as the Algerian oak.

Examples of animals in that live in the area include the Barbary macaque,Barbary leopard, Barbary stag, Barbary sheep, Atlas Mountain badger, Cuvier's gazelle, northern bald ibis, Algerian nuthatch, dipper, and Atlas mountain viper.

Many animals used to inhabit the Atlas mountains such as the Atlas bear, North African elephant, North African aurochs and bubal hartebeest but these species are all extinct. Barbary lions are currently extinct in the wild but there are members of the species in captivity.

Jai Ganesh · 2020-09-29 00:12:07

781) Cork

Cork, the outer bark of an evergreen type of oak tree called the cork oak (species Quercus suber) that is native to the Mediterranean region. Cork consists of the irregularly shaped, thin-walled, wax-coated cells that make up the peeling bark of the birch and many other trees, but, in the restricted commercial sense of the word, only the bark of the cork oak merits the designation of cork. The cork oak grows abundantly in Portugal, Spain, parts of southern France and Italy, and North Africa. The tree is usually about 18 m (60 feet) tall, with a broad, round-topped head and glossy green, hollylike leaves.

Cork is obtained from the new outer sheath of bark formed by the inner bark after the original rough outer bark is removed. The outer sheath may then be stripped and will form again. Unlike the inner bark, the outer bark, or cork, is not vital to the tree’s survival and functions merely to protect it from the heat and dry winds of the Mediterranean summer. The repeated stripping of cork is possible because the inner bark of the cork oak develops an especially uniform and continuous regenerative tissue. After the outer bark has been peeled, this tissue proliferates sufficient cork cells to the outside so that, in a healthy tree, 2.5–5 cm (1–2 inches) of a uniform new cork sheathing forms in from 3 to 10 years. Stripping this regenerated layer yields commercial cork slabs.

The uniqueness of cork derives from its structure of air-filled cells, each of which consists of a watertight, flexible compartment. En masse these cells constitute a remarkably effective insulating medium that is also impervious to liquids. Because of its internal matrix of air pockets, cork is also among the lighter natural substances in weight, being only one-fifth as heavy as water. Specialized plastics and other artificial substances have supplanted cork in a number of its former uses, but cork has retained its traditional importance as a stopper for bottles of wine and other alcoholic beverages.

The cork oak lives on average for about 150 years. The tree yields hardly any cork for its first 20 years, and the bark obtained at the first stripping (at about 25 years of age) is rough and uneven and has little commercial value. The bark obtained at the second stripping (several years later) is of better quality, though, and the tree will continue to produce cork thereafter for many decades. The stripping itself is still done by hand and consists of cutting slits in the outer bark, which is then carefully pried loose from the inner bark and peeled away with the help of various levers and wedges. Care is taken not to injure the deeper regenerative layers of the inner bark. The removed peel of cork is boiled or steamed to remove soluble tannic acids from it and increase its flexibility, and its rough woody surface is scraped clean by hand. It is then ready for commercial distribution.

Jai Ganesh · 2020-09-30 00:48:38

782) Brain Cells

The brain and spinal cord are made up of many cells, including neurons and glial cells. Neurons are cells that send and receive electro-chemical signals to and from the brain and nervous system. There are about 100 billion neurons in the brain. There are many more glial cells; they provide support functions for the neurons, and are far more numerous than neurons.

There are many type of neurons. They vary in size from 4 microns (.004 mm) to 100 microns (.1 mm) in diameter. Their length varies from a fraction of an inch to several feet.

Neurons are nerve cells that transmit nerve signals to and from the brain at up to 200 mph. The neuron consists of a cell body (or soma) with branching dendrites (signal receivers) and a projection called an axon, which conduct the nerve signal. At the other end of the axon, the axon terminals transmit the electro-chemical signal across a synapse (the gap between the axon terminal and the receiving cell). The word "neuron" was coined by the German scientist Heinrich Wilhelm Gottfried von Waldeyer-Hartz in 1891 (he also coined the term "chromosome").

The axon, a long extension of a nerve cell, and take information away from the cell body. Bundles of axons are known as nerves or, within the CNS (central nervous system), as nerve tracts or pathways. Dendrites bring information to the cell body.

Myelin coats and insulates the axon (except for periodic breaks called nodes of Ranvier), increasing transmission speed along the axon. Myelin is manufactured by Schwann's cells, and consists of 70-80% lipids (fat) and 20-30% protein.

The cell body (soma) contains the neuron's nucleus (with DNA and typical nuclear organelles). Dendrites branch from the cell body and receive messages.

A typical neuron has about 1,000 to 10,000 synapses (that is, it communicates with 1,000-10,000 other neurons, muscle cells, glands, etc.).

Different Types Of Neurons

There are different types of neurons. They all carry electro-chemical nerve signals, but differ in structure (the number of processes, or axons, emanating from the cell body) and are found in different parts of the body.

• Sensory neurons or Bipolar neurons carry messages from the body's sense receptors (eyes, ears, etc.) to the CNS. These neurons have two processes. Sensory neuron account for 0.9% of all neurons. (Examples are retinal cells, olfactory epithelium cells.)
• Motoneurons or Multipolar neurons carry signals from the CNS to the muscles and glands. These neurons have many processes originating from the cell body. Motoneurons account for 9% of all neurons. (Examples are spinal motor neurons, pyramidal neurons, Purkinje cells.)
• Interneurons or Pseudopolare (Spelling) cells form all the neural wiring within the CNS. These have two axons (instead of an axon and a dendrite). One axon communicates with the spinal cord; one with either the skin or muscle. These neurons have two processes. (Examples are dorsal root ganglia cells.)

Life Span Of Neurons

Unlike most other cells, neurons cannot regrow after damage (except neurons from the hippocampus). Fortunately, there are about 100 billion neurons in the brain.

Glial Cells

Glial cells make up 90 percent of the brain's cells. Glial cells are nerve cells that don't carry nerve impulses. The various glial (meaning "glue") cells perform many important functions, including: digestion of parts of dead neurons, manufacturing myelin for neurons, providing physical and nutritional support for neurons, and more. Types of glial cells include Schwann's Cells, Satellite Cells, Microglia, Oligodendroglia, and Astroglia.

Neuroglia (meaning "nerve glue") are the another type of brain cell. These cells guide neurons during fetal development.

Jai Ganesh · 2020-10-01 00:25:46

783) Placebo

A placebo is a substance or treatment which is designed to have no therapeutic value. Common placebos include inert tablets (like sugar pills), inert injections (like saline), sham surgery, and other procedures.

In general, placebos can affect how patients perceive their condition and encourage the body's chemical processes for relieving pain and a few other symptoms, but have no impact on the disease itself. Improvements that patients experience after being treated with a placebo can also be due to unrelated factors, such as regression to the mean (a natural recovery from the illness). The use of placebos in clinical medicine raises ethical concerns, especially if they are disguised as an active treatment, as this introduces dishonesty into the doctor–patient relationship and bypasses informed consent. While it was once assumed that this deception was necessary for placebos to have any effect, there is now evidence that placebos can have effects even when the patient is aware that the treatment is a placebo.

In drug testing and medical research, a placebo can be made to resemble an active medication or therapy so that it functions as a control; this is to prevent the recipient or others from knowing (with their consent) whether a treatment is active or inactive, as expectations about efficacy can influence results. In a clinical trial any change in the placebo arm is known as the placebo response, and the difference between this and the result of no treatment is the placebo effect. Some researchers now recommend comparing the experimental treatment with an existing treatment when possible, instead of a placebo.

The idea of a placebo effect—a therapeutic outcome derived from an inert treatment—was discussed in 18th century psychology but became more prominent in the 20th century. An influential 1955 study entitled ‘The Powerful Placebo’ firmly established the idea that placebo effects were clinically important, and were a result of the brain's role in physical health. A 1997 reassessment found no evidence of any placebo effect in the source data, as the study had not accounted for regression to the mean.

Etymology

‘Placebo’ is Latin for I shall be pleasing. It was used as a name for the Vespers in the Office of the Dead, taken from a phrase used in it, a quote from the Vulgate's Psalm 114:9 From that, a singer of placebo became associated with someone who falsely claimed a connection to the deceased to get a share of the funeral meal, and hence a flatterer, and so a deceptive act to please.

Definitions

The American Society of Pain Management Nursing define a placebo as "any sham medication or procedure designed to be void of any known therapeutic value".

In a clinical trial, a ‘placebo response’ is the measured response of subjects to a placebo; the ‘placebo effect’ is the difference between that response and no treatment. It is also part of the recorded response to any active medical intervention.

Any measurable placebo effect is termed either objective (e.g. lowered blood pressure) or subjective (e.g. a lowered perception of pain).

Effects

Placebos can improve patient-reported outcomes such as pain and nausea. This effect is unpredictable and hard to measure, even in the best conducted trials. For example, if used to treat insomnia, placebos can cause patients to perceive that they are sleeping better, but do not improve objective measurements of sleep onset latency. A 2001 Cochrane Collaboration meta-analysis of the placebo effect looked at trials in 40 different medical conditions, and concluded the only one where it had been shown to have a significant effect was for pain.

By contrast, placebos do not appear to affect the actual diseases, or outcomes that are not dependent on a patient's perception. One exception to the latter is Parkinson's disease, where recent research has linked placebo interventions to improved motor functions.

Measuring the extent of the placebo effect is difficult due to confounding factors. For example, a patient may feel better after taking a placebo due to regression to the mean (i.e. a natural recovery or change in symptoms). It is harder still to tell the difference between the placebo effect and the effects of response bias, observer bias and other flaws in trial methodology, as a trial comparing placebo treatment and no treatment will not be a blinded experiment. In their 2010 meta-analysis of the placebo effect, Asbjørn Hróbjartsson and Peter C. Gøtzsche argue that "even if there were no true effect of placebo, one would expect to record differences between placebo and no-treatment groups due to bias associated with lack of blinding."

Hróbjartsson and Gøtzsche concluded that their study "did not find that placebo interventions have important clinical effects in general." Jeremy Howick has argued that combining so many varied studies to produce a single average might obscure that "some placebos for some things could be quite effective." To demonstrate this, he participated in a systematic review comparing active treatments and placebos using a similar method, which generated a clearly misleading conclusion that there is "no difference between treatment and placebo effects".

Factors influencing the power of the placebo effect

A review published in JAMA Psychiatry found that, in trials of antipsychotic medications, the change in response to receiving a placebo had increased significantly between 1960 and 2013. The review's authors identified several factors that could be responsible for this change, including inflation of baseline scores and enrollment of fewer severely ill patients. Another analysis published in ‘Pain’ in 2015 found that placebo responses had increased considerably in neuropathic pain clinical trials conducted in the United States from 1990 to 2013. The researchers suggested that this may be because such trials have "increased in study size and length" during this time period.

Children seem to have greater response than adults to placebos.

Some studies have investigated the use of placebos where the patient is fully aware that the treatment is inert, known as an ‘open-label placebo’. A meta-analysis found some evidence that open-label placebos may have positive effects in comparison to no treatment,[8] which may open new avenues for treatments, but noted the trials were done with a small number of participants and hence should be interpreted with "caution" until further better controlled trials are conducted.

Symptoms and conditions

A 2010 Cochrane Collaboration review suggests that placebo effects are apparent only in subjective, continuous measures, and in the treatment of pain and related conditions.

Pain

Placebos are believed to be capable of altering a person's perception of pain. "A person might reinterpret a sharp pain as uncomfortable tingling."

One way in which the magnitude of placebo analgesia can be measured is by conducting "open/hidden" studies, in which some patients receive an analgesic and are informed that they will be receiving it (open), while others are administered the same drug without their knowledge (hidden). Such studies have found that analgesics are considerably more effective when the patient knows they are receiving them.

Depression

In 2008, a controversial meta-analysis led by psychologist Irving Kirsch, analyzing data from the FDA, concluded that 82% of the response to antidepressants was accounted for by placebos. However, there are serious doubts about the used methods and the interpretation of the results, especially the use of 0.5 as cut-off point for the effect-size. A complete reanalysis and recalculation based on the same FDA data discovered that the Kirsch study suffered from "important flaws in the calculations". The authors concluded that although a large percentage of the placebo response was due to expectancy, this was not true for the active drug. Besides confirming drug effectiveness, they found that the drug effect was not related to depression severity.

Another meta-analysis found that 79% of depressed patients receiving placebo remained well (for 12 weeks after an initial 6–8 weeks of successful therapy) compared to 93% of those receiving antidepressants. In the continuation phase however, patients on placebo relapsed significantly more often than patients on antidepressants.

Negative effects

A phenomenon opposite to the placebo effect has also been observed. When an inactive substance or treatment is administered to a recipient who has an expectation of it having a negative impact, this intervention is known as a nocebo (Latin nocebo = "I shall harm"). A nocebo effect occurs when the recipient of an inert substance reports a negative effect or a worsening of symptoms, with the outcome resulting not from the substance itself, but from negative expectations about the treatment.

Another negative consequence is that placebos can cause side-effects associated with real treatment. Failure to minimise nocebo side-effects in clinical trials and clinical practice raises a number of recently explored ethical issues.

Withdrawal symptoms can also occur after placebo treatment. This was found, for example, after the discontinuation of the Women's Health Initiative study of hormone replacement therapy for menopause. Women had been on placebo for an average of 5.7 years. Moderate or severe withdrawal symptoms were reported by 4.8% of those on placebo compared to 21.3% of those on hormone replacement.

Ethics

In research trials

Knowingly giving a person a placebo when there is an effective treatment available is a bioethically complex issue. While placebo-controlled trials might provide information about the effectiveness of a treatment, it denies some patients what could be the best available (if unproven) treatment. Informed consent is usually required for a study to be considered ethical, including the disclosure that some test subjects will receive placebo treatments.

The ethics of placebo-controlled studies have been debated in the revision process of the Declaration of Helsinki. Of particular concern has been the difference between trials comparing inert placebos with experimental treatments, versus comparing the best available treatment with an experimental treatment; and differences between trials in the sponsor's developed countries versus the trial's targeted developing countries.

Some suggest that existing medical treatments should be used instead of placebos, to avoid having some patients not receive medicine during the trial.

In medical practice

The practice of doctors prescribing placebos that are disguised as real medication is controversial. A chief concern is that it is deceptive and could harm the doctor–patient relationship in the long run. While some say that blanket consent, or the general consent to unspecified treatment given by patients beforehand, is ethical, others argue that patients should always obtain specific information about the name of the drug they are receiving, its side effects, and other treatment options. This view is shared by some on the grounds of patient autonomy. There are also concerns that legitimate doctors and pharmacists could open themselves up to charges of fraud or malpractice by using a placebo. Critics also argued that using placebos can delay the proper diagnosis and treatment of serious medical conditions.

About 25% of physicians in both the Danish and Israeli studies used placebos as a diagnostic tool to determine if a patient's symptoms were real, or if the patient was malingering. Both the critics and the defenders of the medical use of placebos agreed that this was unethical. The ‘British Medical Journa’l editorial said, "That a patient gets pain relief from a placebo does not imply that the pain is not real or organic in origin ...the use of the placebo for 'diagnosis' of whether or not pain is real is misguided." A survey in the United States of more than 10,000 physicians came to the result that while 24% of physicians would prescribe a treatment that is a placebo simply because the patient wanted treatment, 58% would not, and for the remaining 18%, it would depend on the circumstances.

Referring specifically to homeopathy, the House of Commons of the United Kingdom Science and Technology Committee has stated:

In the Committee's view, homeopathy is a placebo treatment and the Government should have a policy on prescribing placebos. The Government is reluctant to address the appropriateness and ethics of prescribing placebos to patients, which usually relies on some degree of patient deception. Prescribing of placebos is not consistent with informed patient choice—which the Government claims is very important—as it means patients do not have all the information needed to make choice meaningful. A further issue is that the placebo effect is unreliable and unpredictable.

In his 2008 book ‘Bad Science’, Ben Goldacre argues that instead of deceiving patients with placebos, doctors should use the placebo effect to enhance effective medicines. Edzard Ernst has argued similarly that "As a good doctor you should be able to transmit a placebo effect through the compassion you show your patients." In an opinion piece about homeopathy, Ernst argues that it is wrong to support alternative medicine on the basis that it can make patients feel better through the placebo effect. His concerns are that it is deceitful and that the placebo effect is unreliable. Goldacre also concludes that the placebo effect does not justify alternative medicine, arguing that unscientific medicine could lead to patients not receiving prevention advice.

Mechanisms

Expectation plays a clear role. A placebo presented as a stimulant may trigger an effect on heart rhythm and blood pressure, but when administered as a depressant, the opposite effect.

Psychology

In psychology, the two main hypotheses of placebo effect are expectancy theory and classical conditioning.

In 1985, Irving Kirsch hypothesized that placebo effects are produced by the self-fulfilling effects of response expectancies, in which the belief that one will feel different leads a person to actually feel different. According to this theory, the belief that one has received an active treatment can produce the subjective changes thought to be produced by the real treatment. Similarly, the appearance of effect can result from classical conditioning, wherein a placebo and an actual stimulus are used simultaneously until the placebo is associated with the effect from the actual stimulus. Both conditioning and expectations play a role in placebo effect, and make different kinds of contribution. Conditioning has a longer-lasting effect, and can affect earlier stages of information processing. Those who think a treatment will work display a stronger placebo effect than those who do not, as evidenced by a study of acupuncture.

Additionally, motivation may contribute to the placebo effect. The active goals of an individual changes their somatic experience by altering the detection and interpretation of expectation-congruent symptoms, and by changing the behavioral strategies a person pursues. Motivation may link to the meaning through which people experience illness and treatment. Such meaning is derived from the culture in which they live and which informs them about the nature of illness and how it responds to treatment.

Placebo analgesia

Functional imaging upon placebo analgesia suggests links to the activation, and increased functional correlation between this activation, in the anterior cingulate, prefrontal, orbitofrontal and insular cortices, nucleus accumbens, amygdala, the brainstem periaqueductal gray matter, and the spinal cord.

It has been known that placebo analgesia depends upon the release in the brain of endogenous opioids since 1978. Such analgesic placebos activation changes processing lower down in the brain by enhancing the descending inhibition through the periaqueductal gray on spinal nociceptive reflexes, while the expectations of anti-analgesic nocebos acts in the opposite way to block this.

Functional imaging upon placebo analgesia has been summarized as showing that the placebo response is "mediated by "top-down" processes dependent on frontal cortical areas that generate and maintain cognitive expectancies. Dopaminergic reward pathways may underlie these expectancies". "Diseases lacking major 'top-down' or cortically based regulation may be less prone to placebo-related improvement".

Brain and body

In conditioning, a neutral stimulus saccharin is paired in a drink with an agent that produces an unconditioned response. For example, that agent might be cyclophosphamide, which causes immunosuppression. After learning this pairing, the taste of saccharin by itself is able to cause immunosuppression, as a new conditioned response via neural top-down control. Such conditioning has been found to affect a diverse variety of not just basic physiological processes in the immune system but ones such as serum iron levels, oxidative DNA damage levels, and insulin secretion. Recent reviews have argued that the placebo effect is due to top-down control by the brain for immunity and pain. Pacheco-López and colleagues have raised the possibility of "neocortical-sympathetic-immune axis providing neuroanatomical substrates that might explain the link between placebo/conditioned and placebo/expectation responses." There has also been research aiming to understand underlying neurobiological mechanisms of action in pain relief, immunosuppression, Parkinson's disease and depression.

Dopaminergic pathways have been implicated in the placebo response in pain and depression.

Confounding factors

Placebo-controlled studies, as well as studies of the placebo effect itself, often fail to adequately identify confounding factors. False impressions of placebo effects are caused by many factors including:

• Regression to the mean (natural recovery or fluctuation of symptoms)
• Additional treatments
• Response bias from subjects, including scaling bias, answers of politeness, experimental subordination, conditioned answers;
• Reporting bias from experimenters, including misjudgment and irrelevant response variables.
• Non-inert ingredients of the placebo medication having an unintended physical effect

History

The word placebo was used in a medicinal context in the late 18th century to describe a "commonplace method or medicine" and in 1811 it was defined as "any medicine adapted more to please than to benefit the patient". Although this definition contained a derogatory implication it did not necessarily imply that the remedy had no effect.

It was recognized in the 18th and 19th centuries that drugs or remedies often worked best while they were still new:

We know that, in Paris, fashion imposes its dictates on medicine just as it does with everything else. Well, at one time, pyramidal elm bark had a great reputation; it was taken as a powder, as an extract, as an elixir, even in baths. It was good for the nerves, the chest, the stomach — what can I say? — it was a true panacea. At the peak of the fad, one of Bouvard’s [sic] patients asked him if it might not be a good idea to take some: "Take it, Madame", he replied, "and hurry up while it [still] cures." [dépêchez-vous pendant qu’elle guérit]
— Gaston de Lévis quoting Michel-Philippe Bouvart in the 1780s

Placebos have featured in medical use until well into the twentieth century. In 1955 Henry K. Beecher published an influential paper entitled ‘The Powerful Placebo’ which proposed idea that placebo effects were clinically important. Subsequent re-analysis of his materials, however, found in them no evidence of any "placebo effect".

Placebo-controlled studies

The placebo effect makes it more difficult to evaluate new treatments. Clinical trials control for this effect by including a group of subjects that receives a sham treatment. The subjects in such trials are blinded as to whether they receive the treatment or a placebo. If a person is given a placebo under one name, and they respond, they will respond in the same way on a later occasion to that placebo under that name but not if under another.

Clinical trials are often double-blinded so that the researchers also do not know which test subjects are receiving the active or placebo treatment. The placebo effect in such clinical trials is weaker than in normal therapy since the subjects are not sure whether the treatment they are receiving is active.

Jai Ganesh · 2020-10-02 00:49:01

784) Candle

Candle, light source now mostly used for decorative and ceremonial purposes, consisting of wax, tallow, or similar slow-burning material, commonly in cylindrical form but made in many fanciful designs, enclosing and saturating a fibrous wick.

Candles were among the earliest inventions of the ancient world, as shown by candlesticks from Egypt and Crete dating to at least 3000 BC. By the European Middle Ages tallow candles were in wide use: in a Paris tax list of 1292, 71 chandlers, or candlemakers, are named.

In the 19th century a French chemist, Michel-Eugène Chevreul, separated the fatty acid from the glycerin of fat to produce stearic acid, from which superior candles could be made. New processes for producing candle stock appeared in rapid succession. In addition to stearin, two other important sources were found: spermaceti, from the head cavity of the sperm whale, and paraffin wax, from petroleum. A composite of paraffin and stearic acid became the basic candle stock.

In use, heat from the flame liquefies the wax near the base of the wick. The liquid flows upward by capillary action, then is vaporized by the heat. The flame is the combustion of the wax vapour.

Candle-molding machinery, also developed in the 19th century, consists of rows of molds in a metal tank that is alternately heated and cooled. After the molds are cooled, the candles are ejected by pistons. Spools of wicking from the bottom of the machine are threaded through the pistons to pass through the candle mold. As the cooled candles are ejected, the wicks are cut.

The Standard, or International, Candle is a measurement of light source intensity. It was originally defined as a one-sixth-pound candle of sperm wax, burning at the rate of 120 grains per hour. This intensity of light was standardized in 1921 in terms of incandescent lamps, and candles are no longer used for reference.

Modern candles are produced in a wide variety of colours, shapes, and sizes. Beeswax and bayberry wax are occasionally employed as additives, and some candles are scented. Candlemaking has become a popular hobby.

Jai Ganesh · 2020-10-03 00:11:46

785) Geyser

Geyser, hot spring that intermittently spouts jets of steam and hot water. The term is derived from the Icelandic word geysir, meaning “to gush.”

Geysers result from the heating of groundwater by shallow bodies of magma. They are generally associated with areas that have seen past volcanic activity. The spouting action is caused by the sudden release of pressure that has been confining near-boiling water in deep, narrow conduits beneath a geyser. As steam or gas bubbles begin to form in the conduit, hot water spills from the vent of the geyser, and the pressure is lowered on the water column below. Water at depth then exceeds its boiling point and flashes into steam, forcing more water from the conduit and lowering the pressure further. This chain reaction continues until the geyser exhausts its supply of boiling water.

The boiling temperature of water increases with pressure; for example, at a depth of 30 metres (about 100 feet) below the surface, the boiling point is approximately 140 °C (285 °F). Geothermal power from steam wells depends on the same volcanic heat sources and boiling temperature changes with depth that drive geyser displays.

As water is ejected from geysers and is cooled, dissolved silica is precipitated in mounds on the surface. This material is known as sinter. Often geysers have been given fanciful names (such as Castle Geyser in Yellowstone National Park) inspired by the shapes of the colourful and contorted mounds of siliceous sinter at the vents.

Geysers are rare. There are more than 300 of them in Yellowstone in the western United States—approximately half the world’s total—and about 200 on the Kamchatka Peninsula in the Russian Far East, about 40 in New Zealand, 16 in Iceland, and 50 scattered throughout the world in many other volcanic areas. Perhaps the most famous geyser is Old Faithful in Yellowstone. It spouts a column of boiling water and steam to a height of about 30 to 55 metres (100 to 180 feet) on a roughly 90-minute timetable.

Jai Ganesh · 2020-10-04 00:25:22

786) Sugarcane

Sugarcane, (Saccharum officinarum), perennial grass of the family Poaceae, primarily cultivated for its juice from which sugar is processed. Most of the world’s sugarcane is grown in subtropical and tropical areas. The plant is also grown for biofuel production, especially in Brazil, as the canes can be used directly to produce ethyl alcohol (ethanol). The by-products from cane sugar processing, namely the straw and bagasse (cane fibres), can be used to produce cellulosic ethanol, a second-generation biofuel. Other sugarcane products include molasses, rum, and cachaça (a Brazilian alcohol), and the plant itself can be used as thatch and as livestock fodder. This article treats the cultivation of the sugarcane plant.

The sugarcane plant produces a number of stalks that reach 3 to 7 metres (10 to 24 feet) high and bear long sword-shaped leaves. The stalks are composed of many segments, and at each joint there is a bud. When the cane becomes mature, a growing point at the upper end of the stalk develops into a slender arrow bearing a tassel of tiny flowers.

Culture

Sugarcane is propagated primarily by the planting of cuttings. The sections of the stalk of immature cane used for planting are known as seed cane, or cane sets, and have two or more buds (eyes), usually three. Seed cane is planted in well-worked fields. Mechanical planters that open the furrow, fertilize, drop the seed cane, and cover it with soil are widely used.

Seed cane is spaced 1.4 to 1.8 metres (4.5 to 6 feet) apart at densities 10,000 to 25,000 per hectare (4,000 to 10,000 per acre). Under favourable conditions, each bud germinates and produces a primary shoot. Root bands adjacent to each bud give rise to a large number of roots, and each young shoot develops its own root system. Tillering, or sprouting at the base of the plant, takes place, and each original seed cane develops into a number of growing canes, forming a stool. The plant crop is obtained from these stools.

Another method of cane propagation is by ratooning, in which, when the cane is harvested, a portion of stalk is left underground to give rise to a succeeding growth of cane, the ratoon or stubble crop. The ratooning process is usually repeated three times so that three economical crops are taken from one original planting. The yield of ratoon crops decreases after each cycle, and at the end of the last economical cycle all stumps are plowed out and the field is replanted.

Sugarcane is grown in various kinds of soils, such as red volcanic soils and alluvial soils of rivers. The ideal soil is a mixture of sand, silt, and clay particles, with a measure of organic material. The land is plowed and left to weather for a time before subsoiling (stirring up the subsoil) is carried out. The crop demands a well-drained soil, and drains—on the surface, underground, or both—are provided according to the topographic conditions of the fields.

To attain good yields, sugarcane requires 2,000 to 2,300 mm (80 to 90 inches) of water during the growing period. When precipitation is deficient, irrigation, either by spraying or by applying water in furrows, can make up for the deficiency. The growth period for cane crops varies considerably according to the region: 8–9 months in Louisiana, U.S.; 15 months in Australia and Taiwan; 18–22 months in Hawaii, South Africa, and Peru. The lowest temperature for good cane-plant growth is about 20 °C (68 °F). Continuous cooler temperature promotes the maturation of cane, as does withholding water. Harvesting and milling begin in the dry, relatively cool season of the year and last for five to six months.

Fertilizers are applied to sugarcane from the beginning of planting through the whole growth cycle but not during the ripening period. Optimum amounts of fertilizers (nitrogen, phosphorus, and potassium) vary greatly with soil types, climatic conditions, and the kind and length of the growing cycle.

To secure a good crop, weeds in the cane fields must be attacked until the cane stools develop a good canopy, which checks weed growth. Weeding, still largely manual, is done with a hoe, though mechanical cane weeders with attached rakes have been developed. Chemical herbicides are widely used.

The mature cane is harvested by both manual and mechanical means. Some mechanical harvesters are able to sever and discard the tops of erect crops and cut cane stalks, which are delivered into a bin trailer for transport to the mill by tractor or light railway wagon.

Diseases

The sugarcane plant is subject to many diseases. Sereh, a blackening and degeneration of the fanlike tops, is caused by an East Indian virus. Mosaic, which causes mottling or spotting of foliage and sometimes curling, dwarfing, and narrowing of the leaves, is due to infection by any of several viruses. Red rot (important in Indonesia and South Asia) is characterized by interrupted red and white patches within the cane along with a sour alcoholic odour when the cane is split open. Caused by the fungus Colletotrichum falcatum (Glomerella tucumanensis), red rot first attracts attention by a yellowing and withering of the leaf, and eventually the entire plant dies. Gumming disease (important in New South Wales, Australia) is characterized by gummosis, the pathological production of gummy exudates as a result of cell degeneration; it is caused by the bacterium Xanthomonas vasculorum. Fiji disease, a virus disease first reported from the Fiji islands, is characterized by elongated white to brown swellings on the underside of the leaves, followed by stunting and death. Leaf scald is a vascular disease caused by the bacterium Xanthomonas albilineans, characterized by creamy or grayish streaking and later withering of the leaves. Eyespot, characterized by yellowish oval lesions on leaves and stems, is a disease caused by the fungus Helminthosporium sacchari. Epidemics of these diseases have been checked by replacing the susceptible varieties of cane with varieties resistant to the disease.

Pests

Sugarcane is attacked and damaged by various insect pests that bore into and feed on the different parts of the plant. Control measures include biological control by parasites or predators, chemical control by insecticides, and the introduction of resistant cane varieties.

The moth borer, Diatraea saccharalis, which is widely distributed throughout cane-growing areas, is capable of causing extensive damage when out of control. The sugarcane leafhopper and the anomala grub yielded to biological control in Hawaii when other measures were unsuccessful. Various predator animals live on insects destructive to the sugarcane. For example, in Queensland, Australia, the bandicoot, an insectivorous marsupial, is a diligent destroyer of white grubs.

The insect pest responsible for some of the greatest crop losses is the grayback beetle in its larval stage. Effective grub control is obtained by applying the insecticide benzene hexachloride after the young cane plant has germinated and stooled, though this chemical has been banned in many countries. Sugarcane can be protected against wireworms by applying insecticides when cane sets are planted. Rats, which destroy part of the stalk, are controlled by poisoning and trapping.

Breeding

Sugarecane was originally cultivated by natives of southern Pacific islands. Most present-day commercial canes are the offsprings or hybrids directly descended from the Cheribon cane (Saccharum officinarum), a Javan noble cane which was developed from a wild cane species, S. robustom. Noble canes, which represent the highest development of the species, are characterized by thick barrel-shaped internodes, or segments; large soft-rinded juicy stalks; and high sugar content.

The purpose of sugarcane breeding is to produce new hybrid varieties that will be immune, or resistant, to diseases and insect pests and will increase the production of sugar per unit area, yielding canes of higher sugar content and better fabrication qualities. Many of the original noble canes were susceptible to some serious diseases, but their hybridization with wild canes has improved their hardiness. For example, the wild cane S. spontaneum contains little sugar, and it is immune to most diseases; it has been used extensively by breeders to improve commercial varieties.

The first task of breeding is to obtain new cane seeds by sexually crossing selected parent varieties and then to select seedlings from the new seeds. The crossing is effected by enclosing in a cloth lantern two flower tassels from two different cane varieties selected as a male and a female parent. The commercially superior varieties are not necessarily ideal parents. Many of the best varieties were bred from parents unsuitable for commercial use. The production of such cane seeds and seedlings by crossbreeding has been established in Java and Barbados since the 1880s.

A selected seedling is planted and tested in the fields, and usually takes up to 10 years before being released as a new commercial variety.

Jai Ganesh · 2020-10-05 00:21:46

787) Spacecraft

Spacecraft, vehicle designed to operate, with or without a crew, in a controlled flight pattern above Earth’s lower atmosphere.

Although early conceptions of spaceflight usually depicted streamlined spacecraft, streamlining has no particular advantage in the vacuum of space. Actual vehicles are designed with a variety of shapes depending on the mission. The first spacecraft, the Soviet Union’s Sputnik 1, was launched on October 4, 1957; it weighed 83.6 kg (184 pounds). It was soon followed by other unmanned Soviet and U.S. spacecraft and, within four years (April 12, 1961), by the first manned spacecraft, Vostok 1, which carried the Soviet cosmonaut Yury Gagarin. Since then, numerous other manned and unmanned craft have been launched to increase scientific knowledge, augment national security, or provide important services in areas such as telecommunications and weather forecasting.

Most spacecraft are not self-propelled; they depend on the initial velocity provided by a launch vehicle, which separates from the spacecraft when its task is done. The spacecraft typically either is placed into an orbit around Earth or, if given sufficient velocity to escape Earth’s gravity, continues toward another destination in space. The spacecraft itself often carries small rocket engines for maneuvering and orienting in space. The Lunar Module, the manned Moon-landing vehicle used in the Apollo program, had rocket engines that allowed it to soft-land on the Moon and then return its crew to the lunar-orbiting Command Module. The latter craft, in turn, carried sufficient rocket power in its attached Service Module to leave lunar orbit for the return journey to Earth. The U.S. space shuttle orbiter uses three onboard liquid-fuel engines supplied by a disposable external tank and a pair of solid-fuel boosters to reach space.

Spacecraft require an onboard source of electrical power to operate the equipment that they carry. Those designed to remain in Earth orbit for extended periods generally use panels of solar cells, often in conjunction with storage batteries. The shuttle orbiter, designed for stays in space of one to two weeks, uses hydrogen-oxygen fuel cells. Deep-space probes, such as the Galileo spacecraft that went into orbit around Jupiter in 1995 and the Cassini spacecraft launched to Saturn in 1997, are usually powered by small, long-lived radioisotope thermoelectric generators, which convert heat emitted by a radioactive element such as plutonium directly into electricity.

Jai Ganesh · 2020-10-06 00:19:35

788) Unidentified flying object

Unidentified flying object (UFO), also called flying saucer, any aerial object or optical phenomenon not readily identifiable to the observer. UFOs became a major subject of interest following the development of rocketry after World War II and were thought by some researchers to be intelligent extraterrestrial life visiting Earth.

History

Flying saucers and Project Blue Book

The first well-known UFO sighting occurred in 1947, when businessman Kenneth Arnold claimed to see a group of nine high-speed objects near Mount Rainier in Washington while flying his small plane. Arnold estimated the speed of the crescent-shaped objects as several thousand miles per hour and said they moved “like saucers skipping on water.” In the newspaper report that followed, it was mistakenly stated that the objects were saucer-shaped, hence the term flying saucer.

Sightings of unidentified aerial phenomena increased, and in 1948 the U.S. Air Force began an investigation of these reports called Project Sign. The initial opinion of those involved with the project was that the UFOs were most likely sophisticated Soviet aircraft, although some researchers suggested that they might be spacecraft from other worlds, the so-called extraterrestrial hypothesis (ETH). Within a year, Project Sign was succeeded by Project Grudge, which in 1952 was itself replaced by the longest-lived of the official inquiries into UFOs, Project Blue Book, headquartered at Wright-Patterson Air Force Base in Dayton, Ohio. From 1952 to 1969 Project Blue Book compiled reports of more than 12,000 sightings or events, each of which was ultimately classified as (1) “identified” with a known astronomical, atmospheric, or artificial (human-caused) phenomenon or (2) “unidentified.” The latter category, approximately 6 percent of the total, included cases for which there was insufficient information to make an identification with a known phenomenon.

The Robertson Panel and the Condon Report

An American obsession with the UFO phenomenon was under way. In the hot summer of 1952 a provocative series of radar and visual sightings occurred near National Airport in Washington, D.C. Although these events were attributed to temperature inversions in the air over the city, not everyone was convinced by this explanation. Meanwhile, the number of UFO reports had climbed to a record high. This led the Central Intelligence Agency to prompt the U.S. government to establish an expert panel of scientists to investigate the phenomena. The panel was headed by H.P. Robertson, a physicist at the California Institute of Technology in Pasadena, California, and included other physicists, an astronomer, and a rocket engineer. The Robertson Panel met for three days in 1953 and interviewed military officers and the head of Project Blue Book. They also reviewed films and photographs of UFOs. Their conclusions were that (1) 90 percent of the sightings could be easily attributed to astronomical and meteorologic phenomena (e.g., bright planets and stars, meteors, auroras, ion clouds) or to such earthly objects as aircraft, balloons, birds, and searchlights, (2) there was no obvious security threat, and (3) there was no evidence to support the ETH. Parts of the panel’s report were kept classified until 1979, and this long period of secrecy helped fuel suspicions of a government cover-up.

A second committee was set up in 1966 at the request of the Air Force to review the most interesting material gathered by Project Blue Book. Two years later this committee, which made a detailed study of 59 UFO sightings, released its results as Scientific Study of Unidentified Flying Objects—also known as the Condon Report, named for Edward U. Condon, the physicist who headed the investigation. The Condon Report was reviewed by a special committee of the National Academy of Sciences. A total of 37 scientists wrote chapters or parts of chapters for the report, which covered investigations of the 59 UFO sightings in detail. Like the Robertson Panel, the committee concluded that there was no evidence of anything other than commonplace phenomena in the reports and that UFOs did not warrant further investigation. This, together with a decline in sighting activity, led to the dismantling of Project Blue Book in 1969.

Other investigations of UFOs

Despite the failure of the ETH to make headway with the expert committees, a few scientists and engineers, most notably J. Allen Hynek, an astronomer at Northwestern University in Evanston, Illinois, who had been involved with projects Sign, Grudge, and Blue Book, concluded that a small fraction of the most-reliable UFO reports gave definite indications for the presence of extraterrestrial visitors. Hynek founded the Center for UFO Studies (CUFOS), which continues to investigate the phenomenon. Another major U.S. study of UFO sightings was the Advanced Aviation Threat Identification Program (AATIP), a secret project that ran from 2007 to 2012. When the existence of the AATIP was made public in December 2017, the most newsworthy aspect of it was a report that the U.S. government possessed alloys and compounds purportedly attained from UFOs that were of unidentifiable nature, but many scientists remained skeptical about this claim.

Aside from the American efforts, the only other official and fairly complete records of UFO sightings were kept in Canada, where they were transferred in 1968 from the Canadian Department of National Defense to the Canadian National Research Council. The Canadian records comprised about 750 sightings. Less-complete records have been maintained in the United Kingdom, Sweden, Denmark, Australia, and Greece. In the United States, CUFOS and the Mutual UFO Network in Bellvue, Colorado, continue to log sightings reported by the public.

In the Soviet Union, sightings of UFOs were often prompted by tests of secret military rockets. In order to obscure the true nature of the tests, the government sometimes encouraged the public’s belief that these rockets might be extraterrestrial craft but eventually decided that the descriptions themselves might give away too much information. UFO sightings in China have been similarly provoked by military activity that is unknown to the public.

Possible Explanations For UFO Sightings And Alien Abductions

UFO reports have varied widely in reliability, as judged by the number of witnesses, whether the witnesses were independent of each other, the observing conditions (e.g., fog, haze, type of illumination), and the direction of sighting. Typically, witnesses who take the trouble to report a sighting consider the object to be of extraterrestrial origin or possibly a military craft but certainly under intelligent control. This inference is usually based on what is perceived as formation flying by sets of objects, unnatural—often sudden—motions, the lack of sound, changes in brightness or colour, and strange shapes.

That the unaided eye plays tricks is well known. A bright light, such as the planet Venus, often appears to move. Astronomical objects can also be disconcerting to drivers, as they seem to “follow” the car. Visual impressions of distance and speed of UFOs are also highly unreliable because they are based on an assumed size and are often made against a blank sky with no background object (clouds, mountains, etc.) to set a maximum distance. Reflections from windows and eyeglasses produce superimposed views, and complex optical systems, such as camera lenses, can turn point sources of light into apparently saucer-shaped phenomena. Such optical illusions and the psychological desire to interpret images are known to account for many visual UFO reports, and at least some sightings are known to be hoaxes. Radar sightings, while in certain respects more reliable, fail to discriminate between artificial objects and meteor trails, ionized gas, rain, or thermal discontinuities in the atmosphere.

“Contact events,” such as abductions, are often associated with UFOs because they are ascribed to extraterrestrial visitors. However, the credibility of the ETH as an explanation for abductions is disputed by most psychologists who have investigated this phenomenon. They suggest that a common experience known as “sleep paralysis” may be the culprit, as this causes sleepers to experience a temporary immobility and a belief that they are being watched.

Jai Ganesh · 2020-10-07 00:28:58

789) Center of gravity

What goes up must come down—that's one way of understanding gravity. We think of gravity as a force that pulls things downward (toward Earth's center), but it doesn't always work like that. Sometimes gravity can make things turn and topple over, especially if they are high up and unbalanced. Tightrope walkers understand this better than anyone. Tiptoeing over the high wire, they often teeter and wobble from side to side just to entertain us, yet they hardly ever fall off. Instinctively understanding the physics of forces helps them staying firmly on the wire. If, like them, you understand a simple concept called center of gravity, you'll find balancing is child's play!

What is "center of gravity"?

Throw a ball in the air and gravity pulls it straight back down. Not everything moves like this when gravity acts on it. Most objects are not nice, neat shapes like balls. That means gravity acts on them in more complex ways. Even so, all objects behave as though their mass (the stuff they're made from) is concentrated at a point called their center of gravity. A simple object like a ball has its center of gravity in a very obvious place: right at its center. But in a more complex object, like your body, the center of gravity is slightly higher than your waist because there's more weight in the top half of your body than in the bottom half.

Why do tall things topple over?

Thinking about center of gravity helps us answer questions like this. Stand up straight, then try leaning over to one side. Very quickly you'll reach a point where your whole body feels like it's about to topple over. You're not actually moving but turning about your ankles. Your head moves faster than your knees. In fact, your whole body turns around your ankles like a wheel. You might think gravity is something that pulls things downward, but here it's making you turn in a circle! The taller you are, the more you'll turn because your whole body is acting like a lever, helping the force of gravity to turn you around.

To see how that works, try opening a door by pushing the handle with one finger. Easy, isn't it? When a force pushes something that can freely pivot (like a door on its hinges), that thing will turn instead of moving. Now try opening the same door by pushing with one finger near the hinge. This time it's much harder. The shorter the distance between the force and the pivot point, the harder it is for the force to make something turn. Wider doors are easier to open than narrower ones because the entire door acts like a lever, multiplying the force you use when you push on the handle. In exactly the same way, it's much easier to make something tall topple over than to topple something that's close to the ground.

Why does gravity make your body tip over?

Imagine your body is not a single, solid mass but a huge sack of potatoes standing upright. Gravity pulls on the whole sack, but it also acts on each potato separately, pulling each one downward. When you lean over to one side, the "potatoes" at the top of your body work like a lever, making your top half turn and topple about your ankles. The more you lean, the bigger the lever effect at the top of your body—and the more likely you are to topple.

There's another way of thinking about your weight. Yes, your body is a bit like a sack of potatoes. But it's also a bit like one giant potato, weighing as much as you do and concentrated in an infinitely tiny point, somewhere in your middle—roughly where your stomach is. This is your own, personal center of gravity. As long as your center of gravity is more or less above your feet, your body will always be balanced and you won't tip over. But start leaning to the side, and everything changes. Your head is one of the heaviest parts of your body—like a giant potato perched right on top. If you lean to your left, your center of gravity is no longer directly above the midpoint of your feet. The more you lean, the more torque (turning force) this creates and the more likely you are to topple over. Gravity makes your whole body rotate about your ankles like a finger pushing on a door handle.

What's the best way to balance?

The lower your center of gravity, the easier it is to keep your balance. If you're sitting on a chair, you can lean over more than if you're standing up. With your center of gravity low, you can lean further to one side or the other without creating enough turning force to tip you over. That's why racing cars (and military vehicles like Humvees) are designed with very low centers of gravity: the lower they are to the ground, the less risk there is that they'll tip over, no matter how fast they go.

Tightrope walkers use a slightly different trick to master their center of gravity. If you've ever watched a tightrope walker, you'll have noticed they never simply walk across the rope. Some stretch their arms out or carry a long stick or an umbrella. Others crouch down or bend their knees. Still others ride bicycles with weights dangling some way beneath them. These balancing aids help to give tightrope walkers more control over their center of gravity. If they can keep their center of gravity directly above the rope at all times, they will never fall off. If they start moving to one side, a turning force will start to topple them in that direction. So they have to quickly move part of their body to the other side to make a turning force in the opposite direction and restore their balance.

Inertia (the tendency still objects have to stay still and moving objects to keep moving) helps too. A tightrope walker weighs quite a lot. That means they have a certain amount of inertia and it takes quite a bit of time for their body to move to one side or the other. If they feel themselves tipping, they have enough time to move another part of their body (or a stick or umbrella they're carrying) to the other side. That produces a tipping force in the opposite direction that keeps them balanced. Looking at a tightrope walker who's momentarily stationary, you might think no forces are acting—but you'd be wrong. Gravity acting on a walker's left arm will try to make him tip to the left, while the weight of his right arm will tip him to the right. The walker stays perfectly upright, perfectly motionless when all the different turning forces are exactly balanced and canceling one another out.

How does it help to know about center of gravity?

If you're a skeptic, you might think science is full of useless bits of information you never really need to know, but center of gravity isn't one of them. Last winter, the lane where I live froze over completely and turned to a sheet of ice. What's the best way to walk down a frozen street? Assuming you don't have mountaineering boots, the safest way to do it is to get down on all fours and crawl along, like a polar bear, on your hands and knees. You might get wet or dirty but you won't tumble over and break your neck. If you make your center of gravity very low, it's impossible to fall.

Thinking about center of gravity is also key to playing many sports effectively. Anything that involves balance—pretty much every sport from figure skating to surfing—involves thinking about where your weight is and how to move it quickly without using too much energy or losing control. You've noticed how tennis players plant their feet wide apart? And how high jumpers do weird things curling their bodies up and round the pole? All that kind of thing is based on understanding center of gravity—and putting it to practical use!

Jai Ganesh · 2020-10-08 00:38:29

790) Wood Buffalo National Park

Wood Buffalo National Park, park in northern Alberta and southern Northwest Territories, Canada, between Athabasca and Great Slave lakes. It has an area of 17,300 sq mi (44,807 sq km) and was established in 1922 as a refuge to protect the few remaining bison herds in northern Canada. A vast region of forests and plains crossed by the Peace River, it has many lakes (including Lake Claire). It is the habitat of both plains and wood buffalo (bison), as well as of bears, caribou, moose, deer, and beavers. In the park are the only remaining nesting grounds for the whooping crane, the tallest native North American bird, which is dangerously close to extinction. Because of its rare animal population and abundant natural resources, the park was designated a UNESCO World Heritage site in 1983.

Location: Alberta and Northwest Territories
Date Established: 1922
Size: 11,070,000 acres

Wood Buffalo is Canada’s largest national park. Covering more territory than Switzerland, it sprawls across northeastern Alberta and juts into the southern part of the Northwest Territories. Designated a UNESCO World Heritage site, it is home to one of the last remaining free-roaming wood bison herds in the world, the nesting habitat for endangered whooping cranes, and the world’s largest beaver dam.

Park Facts

• Flyway Central The southern portion of the park features the Peace-Athabasca Delta, one of the largest inland freshwater deltas in the world. All four North American flyways converge over the delta each spring and fall. The last remaining flock of migratory whooping cranes nests in a remote corner of the boreal forest every summer.
• Protected Area In 1982, the International Union for the Conservation of Nature (IUCN) recognized Wood Buffalo for protecting the Peace-Athabasca Delta and the whooping crane nesting area. The two areas were designated as Ramsar sites under the Ramsar Convention, which focuses on identifying and protecting critical habitat for migratory birds.
• Landscape The park’s varied landscape includes boreal forest, salt plains, and gypsum karst landforms. The boreal plains near the Northwest Territories town of Fort Smith are the most accessible and popular area of the park. Day hikes take visitors through boreal forests of spruce, jackpine, aspen, and poplar to see salt flats, underground streams, sinkholes, and saline streams.
• Hard-to-Find Wildlife Wood Buffalo is home to such elusive species as black bears, wolves, moose, foxes, beavers, and sandhill cranes. But seeing these shy creatures is completely left to chance.
• River Country The Slave, Peace, and Athabasca Rivers flow through the park. Opportunities for backcountry hiking and camping include a trip down the Peace River followed by a 7.5- mile hike into Sweetgrass Station, which features a restored warehouse and former bison corrals.

How to Get There

The park has two main gateway communities, Fort Smith and Fort Chipewyan. To reach Fort Smith, home to the park’s headquarters, take Mackenzie Hwy. from northern Alberta. Connect to Hwy. 5, an all-weather road of partly hardpacked gravel that starts near Hay River, Northwest Territories. Watch for black bears and bison that sometimes lumber across the highway.

The park office in Fort Chipewyan is only accessible by air or water, except for a few months every winter when an ice road links it to Fort Smith and Fort McMurray. Northwestern Air Lease offers commercial flights from Edmonton, Alberta. Flight-seeing tours into the park can also be arranged.

When to Go

The best time to visit the park is between the Victoria Day weekend and Labour Day, when the Pine Lake Campground is open. Summer temperatures range from 68°F–86°F. Community events include the Pine Lake Picnic in mid-July and the Paddlefest Flotilla in early August. Contact the visitor center for regularly scheduled programs and activities.

The park is open in winter. January and February are the best months for viewing the aurora borealis, due to the long nights. Temperatures hover between minus 13°F and minus 22°F. The winter road from Fort McMurray, up to Fort Chipewyan and through the park to Fort Smith, is an experience in itself. Driving the winter road requires proper preparation.

How to Visit

A car provides the best means to see the park. A few pull-offs just past Hay River as well as the Salt Plains Lookout give visitors a chance to start experiencing the park before reaching the visitors center in Fort Smith. Be sure to spend some time exploring Fort Smith. It was on the fur-trade route during the 18th and 19th centuries, and the administrative center of the Northwest Territories until 1967. The town is a mix of mostly Chipewyan, Métis, and nonaboriginal people. Spend another day in the Salt River Day Use Area hiking, then head to Pine Lake to camp.

Wood Buffalo National Park is the largest national park of Canada at 44,807 square kilometers (17,300 sq mi). It is located in northeastern Alberta and the southern Northwest Territories. Larger in area than Switzerland, it is the second-largest national park in the world. The park was established in 1922 to protect the world's largest herd of free roaming hybridized wood bison, currently estimated at more than 5,000. It is one of two known nesting sites of whooping cranes.

The park ranges in elevation from 183 m (600 ft) at the Little Buffalo River to 945 m (3,100 ft) in the Caribou Mountains. The park headquarters is located in Fort Smith, with a smaller satellite office in Fort Chipewyan, Alberta. The park contains one of the world's largest fresh water deltas, the Peace-Athabasca Delta, formed by the Peace, Athabasca and Birch Rivers. It is also known for its karst sinkholes in the north-eastern section of the park. Alberta's largest springs (by volume, with an estimated discharge rate of eight cubic meters per second), Neon Lake Springs, are located in the Jackfish River drainage. Wood Buffalo is located directly north of the Athabasca Oil Sands.

This area was designated a UNESCO World Heritage Site in 1983 for the biological diversity of the Peace-Athabasca Delta, one of the world's largest freshwater deltas, as well as the population of wild bison. It is also the most ecologically complete and largest example of the Great Plains-Boreal grassland ecosystem of North America.

On June 28, 2013, the Royal Astronomical Society of Canada designated Wood Buffalo National Park as Canada's newest and the world's largest dark-sky preserve. The designation helps preserve nighttime ecology for the park's large populations of bats, night hawks and owls, as well as providing opportunities for visitors to experience the northern lights.

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Jai Ganesh · 2020-10-09 00:39:59

791) Elasticity

Elasticity, ability of a deformed material body to return to its original shape and size when the forces causing the deformation are removed. A body with this ability is said to behave (or respond) elastically.

To a greater or lesser extent, most solid materials exhibit elastic behaviour, but there is a limit to the magnitude of the force and the accompanying deformation within which elastic recovery is possible for any given material. This limit, called the elastic limit, is the maximum stress or force per unit area within a solid material that can arise before the onset of permanent deformation. Stresses beyond the elastic limit cause a material to yield or flow. For such materials the elastic limit marks the end of elastic behaviour and the beginning of plastic behaviour. For most brittle materials, stresses beyond the elastic limit result in fracture with almost no plastic deformation.

The elastic limit depends markedly on the type of solid considered; for example, a steel bar or wire can be extended elastically only about 1 percent of its original length, while for strips of certain rubberlike materials, elastic extensions of up to 1,000 percent can be achieved. Steel is much stronger than rubber, however, because the tensile force required to effect the maximum elastic extension in rubber is less (by a factor of about 0.01) than that required for steel. The elastic properties of many solids in tension lie between these two extremes.

The different macroscopic elastic properties of steel and rubber result from their very different microscopic structures. The elasticity of steel and other metals arises from short-range interatomic forces that, when the material is unstressed, maintain the atoms in regular patterns. Under stress the atomic bonding can be broken at quite small deformations. By contrast, at the microscopic level, rubberlike materials and other polymers consist of long-chain molecules that uncoil as the material is extended and recoil in elastic recovery. The mathematical theory of elasticity and its application to engineering mechanics is concerned with the macroscopic response of the material and not with the underlying mechanism that causes it.

In a simple tension test, the elastic response of materials such as steel and bone is typified by a linear relationship between the tensile stress (tension or stretching force per unit area of cross section of the material), σ, and the extension ratio (difference between extended and initial lengths divided by the initial length), e. In other words, σ is proportional to e; this is expressed σ = Ee, where E, the constant of proportionality, is called Young’s modulus. The value of E depends on the material; the ratio of its values for steel and rubber is about 100,000. The equation σ = Ee is known as Hooke’s law and is an example of a constitutive law. It expresses, in terms of macroscopic quantities, something about the nature (or constitution) of the material. Hooke’s law applies essentially to one-dimensional deformations, but it can be extended to more general (three-dimensional) deformations by the introduction of linearly related stresses and strains (generalizations of σ and e) that account for shearing, twisting, and volume changes. The resulting generalized Hooke’s law, upon which the linear theory of elasticity is based, provides a good description of the elastic properties of all materials, provided that the deformations correspond to extensions not exceeding about 5 percent. This theory is commonly applied in the analysis of engineering structures and of seismic disturbances.

The elastic limit is in principle different from the proportional limit, which marks the end of the kind of elastic behaviour that can be described by Hooke’s law, namely, that in which the stress is proportional to the strain (relative deformation) or equivalently that in which the load is proportional to the displacement. The elastic limit nearly coincides with the proportional limit for some elastic materials, so that at times the two are not distinguished; whereas for other materials a region of nonproportional elasticity exists between the two.

The linear theory of elasticity is not adequate for the description of the large deformations that can occur in rubber or in soft human tissue such as skin. The elastic response of these materials is nonlinear except for very small deformations and, for simple tension, can be represented by the constitutive law σ = f (e), where f (e) is a mathematical function of e that depends on the material and that approximates to Ee when e is very small. The term nonlinear means that the graph of σ plotted against e is not a straight line, by contrast with the situation in the linear theory. The energy, W(e), stored in the material under the action of the stress σ represents the area under the graph of σ = f (e). It is available for transfer into other forms of energy—for example, into the kinetic energy of a projectile from a catapult.

The stored-energy function W(e) can be determined by comparing the theoretical relation between σ and e with the results of experimental tension tests in which σ and e are measured. In this way, the elastic response of any solid in tension can be characterized by means of a stored-energy function. An important aspect of the theory of elasticity is the construction of specific forms of strain-energy function from the results of experiments involving three-dimensional deformations, generalizing the one-dimensional situation described above.

Strain-energy functions can be used to predict the behaviour of the material in circumstances in which a direct experimental test is impractical. In particular, they can be used in the design of components in engineering structures. For example, rubber is used in bridge bearings and engine mountings, where its elastic properties are important for the absorption of vibrations. Steel beams, plates, and shells are used in many structures; their elastic flexibility contributes to the support of large stresses without material damage or failure. The elasticity of skin is an important factor in the successful practice of skin grafting. Within the mathematical framework of the theory of elasticity, problems related to such applications are solved. The results predicted by the mathematics depend critically on the material properties incorporated in the strain-energy function, and a wide range of interesting phenomena can be modeled.

Gases and liquids also possess elastic properties since their volume changes under the action of pressure.

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Jai Ganesh · 2020-10-10 00:36:33

792) Atomic weight

Atomic weight, also called relative atomic mass, ratio of the average mass of a chemical element’s atoms to some standard. Since 1961 the standard unit of atomic mass has been one-twelfth the mass of an atom of the isotope carbon-12. An isotope is one of two or more species of atoms of the same chemical element that have different atomic mass numbers (protons + neutrons). The atomic weight of helium is 4.002602, the average that reflects the typical ratio of natural abundances of its isotopes.

The concept of atomic weight is fundamental to chemistry, because most chemical reactions take place in accordance with simple numerical relationships among atoms. Since it is almost always impossible to count the atoms involved directly, chemists measure reactants and products by weighing and reach their conclusions through calculations involving atomic weights. The quest to determine the atomic weights of elements occupied the greatest chemists of the 19th and early 20th centuries. Their careful experimental work became the key to chemical science and technology.

Reliable values for atomic weights serve an important purpose in a quite different way when chemical commodities are bought and sold on the basis of the content of one or more specified constituents. The ores of expensive metals such as chromium or tantalum and the industrial chemical soda ash are examples. The content of the specified constituent must be determined by quantitative analysis. The computed worth of the material depends on the atomic weights used in the calculations.

The original standard of atomic weight, established in the 19th century, was hydrogen, with a value of 1. From about 1900 until 1961, oxygen was used as the reference standard, with an assigned value of 16. The unit of atomic mass was thereby defined as 1/16 the mass of an oxygen atom. In 1929 it was discovered that natural oxygen contains small amounts of two isotopes slightly heavier than the most abundant one and that the number 16 represented a weighted average of the three isotopic forms of oxygen as they occur in nature. This situation was considered undesirable for several reasons, and, since it is possible to determine the relative masses of the atoms of individual isotopic species, a second scale was soon established with 16 as the value of the principal isotope of oxygen rather than the value of the natural mixture. This second scale, preferred by physicists, came to be known as the physical scale, and the earlier scale continued in use as the chemical scale, favoured by chemists, who generally worked with the natural isotopic mixtures rather than the pure isotopes.

Although the two scales differed only slightly, the ratio between them could not be fixed exactly, because of the slight variations in the isotopic composition of natural oxygen from different sources. It was also considered undesirable to have two different but closely related scales dealing with the same quantities. For both of these reasons, chemists and physicists established a new scale in 1961. This scale, based on carbon-12, required only minimal changes in the values that had been used for chemical atomic weights.

Since there were mixtures of isotopes of different atomic weights in samples of elements found in nature, the International Union of Pure and Applied Chemistry (IUPAC) began publishing atomic weights with uncertainties. The first element to receive an uncertainty in its atomic weight was sulfur in 1951. By 2007, 18 elements had associated uncertainties, and in 2009, IUPAC began publishing ranges for the atomic weight of some elements. For example, the atomic weight of carbon is given as [12.0096, 12.0116].

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Jai Ganesh · 2020-10-11 00:37:33

793) Meninges

Meninges, singular meninx, three membranous envelopes—pia mater, arachnoid, and dura mater—that surround the brain and spinal cord. Cerebrospinal fluid fills the ventricles of the brain and the space between the pia mater and the arachnoid. The primary function of the meninges and of the cerebrospinal fluid is to protect the central nervous system.

The pia mater is the meningeal envelope that firmly adheres to the surface of the brain and spinal cord. It is a very thin membrane composed of fibrous tissue covered on its outer surface by a sheet of flat cells thought to be impermeable to fluid. The pia mater is pierced by blood vessels that travel to the brain and spinal cord.

Over the pia mater and separated from it by a space called the subarachnoid space is the arachnoid, a thin, transparent membrane. It is composed of fibrous tissue and, like the pia mater, is covered by flat cells also thought to be impermeable to fluid. The arachnoid does not follow the convolutions of the surface of the brain and so looks like a loosely fitting sac. In the region of the brain, particularly, a large number of fine filaments called arachnoid trabeculae pass from the arachnoid through the subarachnoid space to blend with the tissue of the pia mater. The arachnoid trabeculae are embryologic remnants of the common origin of the arachnoid and pia mater, and they have the frail structure characteristic of these two of the meninges. The pia mater and arachnoid together are called the leptomeninges.

The outermost of the three meninges is the dura mater (or pachymeninx), a strong, thick, and dense membrane. It is composed of dense fibrous tissue, and its inner surface is covered by flattened cells like those present on the surfaces of the pia mater and arachnoid. The dura mater is a sac that envelops the arachnoid and has been modified to serve several functions. The dura mater surrounds and supports the large venous channels (dural sinuses) carrying blood from the brain toward the heart.

The dura mater is partitioned into several septa, which support the brain. One of these, the falx cerebri, is a sickle-shaped partition lying between the two hemispheres of the brain. Another, the tentorium cerebelli, provides a strong, membranous roof over the cerebellum. A third, the falx cerebelli, projects downward from the tentorium cerebelli between the two cerebellar hemispheres. The outer portion of the dura mater over the brain serves as a covering, or periosteum, of the inner surfaces of the skull bones.

Within the vertebral canal the dura mater splits into two sheets separated by the epidural space, which is filled with veins. The outer of these two sheets constitutes the periosteum of the vertebral canal. The inner sheet is separated from the arachnoid by the narrow subdural space, which is filled with fluid. In a few places, the subdural space is absent, and the arachnoid is intimately fused with the dura mater. The most important area of fusion between these two meninges is in the walls of the large venous channels of the dura mater where elongations of the arachnoid, like fingers, penetrate the dura mater and project into the veins. These fingerlike processes of the arachnoid, called arachnoid villi or arachnoid granulations, are involved in the passage of cerebrospinal fluid from the subarachnoid space to the dural sinuses. Spinal anesthetics are often introduced into the subarachnoid space.

Jai Ganesh · 2020-10-12 00:45:11

794) Vesuvius

Vesuvius, also called Mount Vesuvius or Italian Vesuvio, active volcano that rises above the Bay of Naples on the plain of Campania in southern Italy. Its western base rests almost upon the bay. The height of the cone in 2013 was 4,203 feet (1,281 metres), but it varies considerably after each major eruption. At about 1,968 feet (about 600 metres), a high semicircular ridge, called Mount Somma, begins, girding the cone on the north and rising to 3,714 feet (1,132 metres). Between Mount Somma and the cone is the Valle del Gigante (Giant’s Valley). At the summit of the cone is a large crater about 1,000 feet (about 305 metres) deep and 2,000 feet (about 610 metres) across; it was formed in the eruption of 1944. More than two million people live in the vicinity of Vesuvius and on its lower slopes. There are industrial towns along the coast of the Bay of Naples and small agricultural centres on the northern slopes.

Vesuvius probably originated somewhat less than 200,000 years ago. Although a relatively young volcano, Vesuvius had been dormant for centuries before the great eruption of 79 CE that buried the cities of Pompeii, Oplontis, and Stabiae under ashes and lapilli and the city of Herculaneum under a mudflow. The writer Pliny the Younger, who was staying at a place west of Naples, gave an excellent account of the catastrophe in two letters to the historian Tacitus. Between the years 79 and 1037, several eruptions were reported, which include those occurring in 203, 472, 512, 685, 787, 968, 991, 999, and 1007. The explosions of 512 were so severe that Theodoric the Goth released the people living on the slopes of Vesuvius from payment of taxes.

After some centuries of quiescence, a series of earthquakes, lasting six months and gradually increasing in violence, preceded a major eruption that took place on December 16, 1631. Many villages on the slopes of the volcano were destroyed, about 3,000 people were killed, the lava flow reached the sea, and the skies were darkened for days. After 1631 there was a change in the eruptive character of the volcano, and activity became continuous. Two stages could be observed: quiescent and eruptive. During the quiescent stage the volcano’s mouth would be obstructed, whereas in the eruptive stage it would be almost continuously open.

Between 1660 and 1944 several of these cycles were observed. Severe paroxysmal (suddenly recurring) eruptions, concluding an eruptive stage, occurred in 1660, 1682, 1694, 1698, 1707, 1737, 1760, 1767, 1779, 1794, 1822, 1834, 1839, 1850, 1855, 1861, 1868, 1872, 1906, 1929, and 1944. The eruptive stages varied in length from 6 months to 30 3/4 years. The quiescent stages varied from 18 months to 7 1/2 years.

Scientific study of the volcano did not begin until late in the 18th century. An observatory was opened in 1845 at 1,995 feet (608 metres), and in the 20th century numerous stations were set up at various heights for making volcanologic measurements. A large laboratory and a deep tunnel for seismo-gravimetric measurements were also built.

The slopes of Vesuvius are covered with vineyards and orchards, and the wine grown there is known as Lacrima Christi (Latin for “tears of Christ”); in ancient Pompeii the wine jars were frequently marked with the name Vesuvinum. Higher up, the mountain is covered with copses of oak and chestnut, and on the northern side along the slopes of Mount Somma the woods proceed to the very summit. On the western side the chestnut groves give way above 2,000 feet to undulating plateaus covered with broom, where the crater left by the great eruption of the year 79 CE has been filled in. Still higher, on the slopes of the great cone and on the inner slope of Mount Somma, the surface is almost barren; during quiescent periods it is covered by tufts of meadow plants.

The soil is very fertile, and in the long period of inactivity before the eruption of 1631 there were forests in the crater and three lakes from which pasturing herds drank. Vegetation on the slope dies off during eruptive periods because of the volcanic gases. After the eruption of 1906, forests were planted on the slopes in order to protect inhabited places from the flows of mud that usually occur after violent eruptions, and in the fertile soil the trees grew rapidly.

In 73 BCE the gladiator Spartacus was besieged by the praetor Gaius Claudius Glaber on the barren summit of Mount Somma, which was then a wide, flat depression walled by rugged rocks festooned with wild vines. He escaped by twisting ropes of vine branches and descending through unguarded fissures in the rim. Some paintings excavated in Pompeii and Herculaneum represent the mountain as it looked before the eruption of 79 CE, when it had only one peak.

Jai Ganesh · 2020-10-13 00:30:53

795) Surgery

Surgery, branch of medicine that is concerned with the treatment of injuries, diseases, and other disorders by manual and instrumental means. Surgery involves the management of acute injuries and illnesses as differentiated from chronic, slowly progressing diseases, except when patients with the latter type of disease must be operated upon.

A general treatment of surgery follows.

History

Surgery is as old as humanity, for anyone who has ever stanched a wound has acted as a surgeon. In some ancient civilizations surgery reached a rather high level of development, as in India, China, Egypt, and Hellenistic Greece. In Europe during the Middle Ages, the practice of surgery was not taught in most universities, and ignorant barbers instead wielded the knife, either on their own responsibility or upon being called into cases by physicians. The organization of the United Company of Barber Surgeons of London in 1540 marked the beginning of some control of the qualifications of those who performed operations. This guild was the precursor of the Royal College of Surgeons of England.

In the 18th century, with increasing knowledge of anatomy, such operative procedures as amputations of the extremities, excision of tumours on the surface of the body, and removal of stones from the urinary bladder had helped to firmly establish surgery in the medical curriculum. Accurate anatomical knowledge enabled surgeons to operate more rapidly; patients were sedated with opium or made drunk with alcohol, tied down, and a leg amputation, for example, could then be done in three to five minutes. The pain involved in such procedures, however, continued to limit expansion of the field until the introduction of ether anesthesia in 1846. The number of operations thereafter increased markedly, but only to accentuate the frequency and severity of “surgical infections.”

In the mid-19th century the French microbiologist Louis Pasteur developed an understanding of the relationship of bacteria to infectious diseases, and the application of this theory to wound sepsis by the British surgeon Joseph Lister from 1867 resulted in the technique of antisepsis, which brought about a remarkable reduction in the mortality rate from wound infections after operations. The twin emergence of anesthesia and antisepsis marked the beginning of modern surgery.

Wilhelm Conrad Röntgen’s discovery of X-rays at the turn of the 20th century added an important diagnostic tool to surgery, and the discovery of blood types in 1901 by Austrian biologist Karl Landsteiner made transfusions safer. New techniques of anesthesia involving not only new agents for inhalation but also regional anesthesia accomplished by nerve blocking (spinal and local anesthesia) were also introduced. The use of positive pressure and controlled respiration techniques (to prevent the lung from collapsing when the pleural cavity was opened) made chest surgery practical and relatively safe for the first time. The intravenous administration (injection into the veins) of anesthetic agents was also adopted. In the period from the 1930s to the 1960s, the replenishment of body fluids by intravenous infusion, the introduction of chemicals and antibiotics to fight infection and to treat the metabolically disturbed body, and the development of heart-lung machines helped bring surgery to a state in which every body cavity, system, organ, and area could safely be operated on.

Present-Day Surgery

Contemporary surgical therapy is greatly helped by monitoring devices that are used during surgery and during the postoperative period. Blood pressure and pulse rate are monitored during an operation because a fall in the former and a rise in the latter give evidence of a critical loss of blood. Other items monitored are the heart contractions as indicated by electrocardiograms; tracings of brain waves recorded by electroencephalograms, which reflect changes in brain function; the oxygen level in arteries and veins; carbon dioxide partial pressure in the circulating blood; and respiratory volume and exchange. Intensive monitoring of the patient usually continues into the critical postoperative stage.

Asepsis, the freedom from contamination by pathogenic organisms, requires that all instruments and dry goods coming in contact with the surgical field be sterilized. This is accomplished by placing the materials in an autoclave, which subjects its contents to a period of steam under pressure. Chemical sterilization of some instruments is also used. The patient’s skin is sterilized by chemicals, and members of the surgical team scrub their hands and forearms with antiseptic or disinfectant soaps. Sterilized gowns, caps, and masks that filter the team’s exhaled air and sterilized gloves of disposable plastic complete the picture. Thereafter, attention to avoiding contact with nonsterilized objects is the basis of maintaining asepsis.

During an operation, hemostasis (the arresting of bleeding) is achieved by use of the hemostat, a clamp with ratchets that grasps blood vessels or tissue; after application of hemostats, suture materials are tied around the bleeding vessels. Absorbent sterile napkins called sponges, made of a variety of natural and synthetic materials, are used for drying the field. Bleeding may also be controlled by electrocautery, the use of an instrument heated with an electric current to cauterize, or burn, vessel tissue. The most commonly used instruments in surgery are still the scalpel (knife), hemostatic forceps, flexible tissue-holding forceps, wound retractors for exposure, crushing and noncrushing clamps for intestinal and vascular surgery, and the curved needle for working in depth.

The most common method of closing wounds is by sutures. There are two basic types of suture materials; absorbable ones such as catgut (which comes from sheep intestine) or synthetic substitutes; and nonabsorbable materials, such as nylon sutures, steel staples, or adhesive tissue tape. Catgut is still used extensively to tie off small blood vessels that are bleeding, and since the body absorbs it over time, no foreign materials are left in the wound to become a focus for disease organisms. Nylon stitches and steel staples are removed when sufficient healing has taken place.

There are three general techniques of wound treatment; primary intention, in which all tissues, including the skin, are closed with suture material after completion of the operation; secondary intention, in which the wound is left open and closes naturally; and third intention, in which the wound is left open for a number of days and then closed if it is found to be clean. The third technique is used in badly contaminated wounds to allow drainage and thus avoid the entrapment of microorganisms. Military surgeons use this technique on wounds contaminated by shell fragments, pieces of clothing, and dirt.

The 20th and 21st centuries witnessed several new surgical technologies to supplement the techniques of manual incision. Lasers became widely used to destroy tumours and other pigmented lesions, some of which are inaccessible by conventional surgery. They are also used to surgically weld detached retinas back in place and to coagulate blood vessels to stop them from bleeding. Stereotaxic surgery uses a three-dimensional system of coordinates obtained by X-ray photography to accurately focus high-intensity radiation, cold, heat, or chemicals on tumours located deep in the brain that could not otherwise be reached. Cryosurgery uses extreme cold to destroy warts and precancerous and cancerous skin lesions and to remove cataracts. Some traditional techniques of open surgery were replaced by the use of a thin flexible fibre-optic tube equipped with a light and a video connection; the tube, or endoscope, is inserted into various bodily passages and provides views of the interior of hollow organs or vessels. Accessories added to the endoscope allow small surgical procedures to be executed inside the body without making a major incision.

Preoperative and postoperative care both have the same object: to restore patients to as near their normal physiologic state as possible. Blood transfusions, intravenous administration of fluids, and the use of measures to prevent common complications such as lung infection and blood clotting in the legs are the principal features of postoperative care.

There are four major categories of surgery: (1) wound treatment, (2) extirpative surgery, (3) reconstructive surgery, and (4) transplantation surgery. The technical aspects of wound surgery, already partly discussed, centre on procuring good healing and the avoidance of infection. Extirpative surgery involves the removal of diseased tissue or organs. Cancer surgery usually falls into this category, with mastectomy (removal of the breast), cholecystectomy (removal of the gallbladder), and hysterectomy (removal of the uterus) among the most frequent procedures. Reconstructive surgery deals with the replacement of lost tissues, whether from fractures, burns, or degenerative-disease processes, and is especially prominent in the practice of plastic surgery and orthopedic surgery. Grafts from the patient or from others are frequently used to replace lost tissues. Reconstructive surgery also uses artificial devices (prostheses) to replace damaged or diseased organs or tissues. Common examples are the use of metal in reconstructing hip joints and the use of plastic valves to replace heart valves. Transplantation surgery involves the use of organs transplanted from other bodies to replace diseased organs in patients. Kidneys are the most commonly transplanted organs.

The major medical specialties involving surgery are general surgery, plastic surgery, orthopedic surgery, obstetrics and gynecology, neurosurgery, thoracic surgery, colon and rectal surgery, otolaryngology, ophthalmology, and urology. General surgery is the parent specialty and now centres on operations involving the stomach, intestines, breast, blood vessels in the extremities, endocrine glands, tumours of soft tissues, and amputations. Plastic surgery is concerned with the bodily surface and with reconstructive work of the face and exposed parts. Orthopedic surgery deals with the bones, tendons, ligaments, and muscles; fractures of the extremities and congenital skeletal defects are common targets of treatment. Obstetricians perform cesarean sections, while gynecologists operate to remove tumours from the uterus and ovaries. Neurosurgeons operate to remove brain tumours, treat injuries to the brain resulting from skull fractures, and treat ruptured intravertebral disks that affect the spinal cord. Thoracic surgeons treat disorders of the lungs; the subspecialty of cardiovascular surgery is concerned with the heart and its major blood vessels and has become a major field of surgical endeavour. Colon and rectal surgery deals with disorders of the large intestine. Otolaryngologic surgery is performed in the area of the ear, nose, and throat (e.g., tonsillectomy), while ophthalmologic surgery deals with disorders of the eyes. Urologic surgery treats diseases of the urinary tract and, in males, of the genital apparatus.

Jai Ganesh · 2020-10-14 00:24:40

796) Endoscopy

Endoscopy, medical examination of the interior of the body, usually through a natural body opening, by the insertion of a flexible, lighted optical shaft or open tube. Instruments used include the endoscope, a flexible tube for examination of the esophagus, stomach, and duodenum, and the bronchoscope, a flexible tube for examination of the bronchial tubes. These are passed through the mouth into the respective organs. The examinations are usually performed in a hospital or a physician’s office with local anesthesia. The colonoscope, a flexible tube used for examination of the colon, and the proctosigmoidoscope, a similar instrument used for examination of the rectum and lower colon, are passed through the anal orifice; mild sedation and pain medication are typically administered during these procedures. The cystoscope, a lighted rod, is passed through the urethra for examination of the bladder with local, spinal, or general anesthesia. Today these procedures are generally accompanied by the use of camera or video technology in order to collect images of the tissues being examined. In addition, endoscopes may be designed with digital modifications that facilitate the visualization of tissues.

Three endoscopic procedures require incisions for the introduction of the lighted shaft. The thoracoscope permits examination of the chest cavity and surface of the lungs through a small incision between the ribs. The peritoneoscope allows examination of the abdominal cavity and lower surfaces of the liver and gallbladder through a small incision in the abdominal wall. The culdoscope permits examination of the female pelvic organs through a small incision.

Fibre-optic endoscopes are pliable, highly maneuverable instruments that allow access to channels in the body that older, semirigid instruments cannot access at all or can access only at great discomfort to the patient. Composed of multiple hairlike glass rods bundled together, these instruments can be more easily bent and twisted, and the intense light enables the endoscopist to see around corners as well as forward and backward. Accessories can be added to the instrument that make it possible to obtain cell and tissue samples, excise polyps and small tumours, and remove foreign objects.

Although fibre-optic endoscopes can be used to visualize the stomach and duodenum, they are unable to reach farther into the small intestine. As a result, examination of the small intestine may require the use of wireless capsule endoscopy (video capsule endoscopy), which consists of a pill-sized camera that is swallowed. The camera transmits data to sensors that are attached to the abdomen with adhesive, and a data recorder that stores image information collected by the camera is attached to a belt worn around the waist. In most cases, the sensors and belt are worn for a period of eight hours, during which time the camera capsule obtains images of nearly the entire length of the small intestine. The images stored in the data recorder are downloaded onto a computer for analysis. The capsule eventually travels the length of the gastrointestinal tract and is excreted in a bowel movement.

Jai Ganesh · 2020-10-15 00:41:11

797) Atomic clock

Atomic clock, type of clock that uses certain resonance frequencies of atoms (usually cesium or rubidium) to keep time with extreme accuracy. The electronic components of atomic clocks are regulated by the frequency of the microwave electromagnetic radiation. Only when this radiation is maintained at a highly specific frequency will it induce the quantum transition (energy change) of the cesium or rubidium atoms. In an atomic clock these quantum transitions are observed and maintained in a feedback loop that trims the frequency of the electromagnetic radiation; like the recurrent events in other types of clocks, these waves are then counted.

In 1967 the 13th General Conference on Weights and Measures redefined the second, the unit of time in the International System of Units, in terms of the cesium standard so as to equal the second of Ephemeris Time. The conference defined the second as “the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium-133 atom.”

Until the 1990s the cesium beam atomic clock was the most accurate standard of atomic time and frequency. The principle underlying the cesium clock is that all atoms of cesium-133 are identical and, when they absorb or release energy, produce radiation of exactly the same frequency, which makes the atoms perfect timepieces. Since that time, laboratories around the world have steadily improved the accuracy of cesium fountain atomic clocks. These clocks get their name from the fountainlike motion of the constituent cesium gas. The timing process begins by introducing cesium gas into a vacuum chamber and directing six infrared lasers (located at right angles to one another) to compact and cool (slow down) the cesium atoms to a temperature near absolute zero. Then two vertical lasers are used to nudge the atoms up about a metre (creating a “fountain”) through a microwave-filled cavity. The microwave frequency is tuned to maximize the observed fluorescence, which occurs at the natural resonance frequency (9,192,631,770 Hz) of the cesium atom. Because the round-trip through the microwave cavity takes about a second, control of the microwave frequency has resulted in greater timekeeping accuracy. The best cesium fountain atomic clocks are now predicted to be off by less than one second in more than 50 million years.

How Does an Atomic Clock Work?

Timekeeping can be as simple as counting "one Mississippi, two Mississippi . . ." prior to blitzing in backyard football, or tracking the back-and-forth swings of a pendulum in a grandfather clock.

In both cases, the trick is counting the intervals of something that occurs repeatedly with as little variation as possible. A pendulum swing, say, or a 'Mississippi' just about equates to a second, the unit of timekeeping that as we know comprises minutes and hours.

But even the best mechanical pendulums and quartz crystal-based clocks develop discrepancies. Far better for timekeeping is the natural and exact "vibration" in an energized atom.

When exposed to certain frequencies of radiation, such as radio waves, the subatomic particles called electrons that orbit an atom's nucleus will "jump" back and forth between energy states. Clocks based on this jumping within atoms can therefore provide an extremely precise way to count seconds.

It is no surprise then that the international standard for the length of one second is based on atoms. Since 1967, the official definition of a second is 9,192,631,770 cycles of the radiation that gets an atom of the element called cesium to vibrate between two energy states.

Inside a cesium atomic clock, cesium atoms are funneled down a tube where they pass through radio waves . If this frequency is just right 9,192,631,770 cycles per second then the cesium atoms "resonate" and change their energy state.

A detector at the end of the tube keeps track of the number of cesium atoms reaching it that have changed their energy states. The more finely tuned the radio wave frequency is to 9,192,631,770 cycles per second, the more cesium atoms reach the detector.

The detector feeds information back into the radio wave generator. It synchronizes the frequency of the radio waves with the peak number of cesium atoms striking it. Other electronics in the atomic clock count this frequency. As with a single swing of the pendulum, a second is ticked off when the frequency count is met.

The first quality atomic clocks made in the 1950s were based on cesium, and such clocks honed to greater precisions over the decades remain the basis used to keep official time throughout the world.

In the United States, the top clocks are maintained by the National Institutes of Standards and Technology (NIST) in Boulder, Colo., and the United States Naval Observatory (USNO) in Washington, D.C.

The NIST-F1 cesium atomic clock can produce a frequency so precise that its time error per day is about 0.03 nanoseconds, which means that the clock would lose one second in 100 million years.

Super-accurate timekeeping is integral to many elements of modern life, such as high-speed electronic communications, electrical grids and the Global Positioning System (GPS) and of course knowing when your favorite television show comes on.

Jai Ganesh · 2020-10-16 00:33:54

798) Sea lion

Sea lion, any of six species of eared seals found primarily in Pacific waters. Sea lions are characterized by a coat of short coarse hair that lacks a distinct undercoat. Except for the California sea lion (Zalophus californianus), males have lion-like manes and constantly roar to defend their harems (hence their name).

Unlike the true, or earless, seals (family Phocidae), sea lions and other eared seals (family Otariidae) are able to rotate their hind flippers forward to use all four limbs when moving about on land. Sea lions also have longer flippers than true seals. Sea lions feed principally on fish, crustaceans, and cephalopods (squid and octopus), but they also will consume penguins. Breeding occurs in large herds, the males establishing harems of 3 to 20 females. Brown pups are born after a gestation period of 12 months. Sea lions are hunted, though not on a large scale, for their meat, hides, and blubber.

The California sea lion, found along the western coast of North America from the Gulf of Alaska to Costa Rica, is the trained seal commonly seen in animal acts and zoos. Large-eyed and playful, it is pale to dark brown but appears black when wet. The male reaches a maximum length of about 2.5 metres (8 feet) and a weight of 400 kg (880 pounds), and the female grows to about 1.8 metres and 90 kg. In captivity it can live more than 30 years (less in the wild). The California sea lion is mostly a coastal animal that frequently leaps from the water when swimming. A fast swimmer and excellent diver, it forages underwater for an average of three minutes at a time, but dives can last up to nine minutes. The maximum recorded dive depth is 274 metres (900 feet). California sea lions commonly gather on man-made structures.

The California sea lion shares the genus Zalophus with the Galapagos sea lion (Z. wollebaeki). Both species are similar in appearance, the Galapagos sea lion being the smaller of the two. Adult males weigh as much as 250 kg (550 pounds), and adult females weigh between 50 and 100 kg (110 and 220 pounds). Although most of the Galapagos sea lion population is concentrated in the waters surrounding the Galapagos archipelago, some individuals have established a semipermanent colony at Isla de la Plata near the coast of Ecuador.

The northern, or Steller, sea lion (Eumetopias jubatus) is a pale- to golden-brown sea lion of the Bering Sea and both sides of the North Pacific Ocean. It is the largest member of the eared seals. Males are about 3.3 metres in length and weigh 1,000 kg, while females measure about 2.5 metres and weigh less than 300 kg. Northern sea lions eat fish, octopus, and squid, as well as bivalves, other mollusks, and crustaceans. Because of their massive size and aggressive nature, they are rarely kept in captivity.

The southern, or South American, sea lion (Otaria byronia) is generally brown with a yellowish orange belly. It swims in coastal waters from northern Peru southward to Tierra del Fuego and even around the Falkland Islands in the South Atlantic. The male is about 2.5 metres in length and weighs 200–350 kg, and the female is about 1.8 metres long and 140 kg. South American sea lions eat mostly fish, squid, and crustaceans but occasionally kill and eat other seals.

The Australian sea lion (Neophoca cinerea) is found along the southern coast of Western Australia into South Australia. Adult males are 2.0–2.5 metres in length and weigh 300 kg, whereas females measure 1.5 metres long and weigh less than 100 kg.

The New Zealand, or Hooker’s, sea lion (Phocarctos hookeri) inhabits only New Zealand. Males are 2.0–2.5 metres in length, females 1.5–2.0 metres. Their weight is slightly less than that of Australian sea lions.

The five genera of sea lions, together with fur seals (genus Arctocephalus) and northern fur seals (Callorhinus), constitute the family Otariidae (eared seals). All seals and sea lions, along with the walrus, are grouped together as pinnipeds.

Jai Ganesh · 2020-10-17 00:46:40

799) Cocoa

Cocoa, highly concentrated powder made from chocolate liquor—a paste prepared from cocoa beans, the fruit of the cacao—and used in beverages and as a flavouring ingredient. Cocoa is the key ingredient in chocolate and chocolate confections.

The cocoa bean is the seed of the cacao tree (Theobroma cacao), a tropical plant indigenous to the equatorial regions of the Americas. From the processed cocoa bean comes the fluid paste, or liquor, from which cocoa powder and chocolate are made. Chocolate is sold directly to the consumer as solid bars of eating chocolate, as packaged cocoa, and as baking chocolate. It is also used by confectioners as coating for candy bars and boxed or bulk chocolates, by bakery product manufacturers and bakers as coating for many types of cookies and cakes, and by ice-cream companies as coating for frozen novelties. Cocoa powders, chocolate liquor, and blends of the two are used in bulk to flavour various food products and to provide the flavours in such “chocolate” products as syrups, toppings, chocolate milk, prepared cake mixes, and pharmaceuticals.

History Of Use

Cacao residues on pottery in Ecuador suggest that the plant was consumed by humans as early as 5,000 years ago. The tree was likely domesticated in the upper Amazon region and then spread northward. It was widely cultivated more than 3,000 years ago by the Maya, Toltec, and Aztec peoples, who prepared a beverage from the bean (sometimes using it as a ceremonial drink) and also used the bean as a currency.

Christopher Columbus took cocoa beans to Spain after his fourth voyage in 1502, and the Spanish conquistadores, arriving in Mexico in 1519, were introduced to a chocolate beverage by the Aztec. The Aztec beverage was made from sun-dried shelled beans, probably fermented in their pods. The broken kernels, or nibs, were roasted in earthen pots and then ground to a paste in a concave stone, called a metate, over a small fire. Vanilla and various spices and herbs were added, and corn (maize) was sometimes used to produce milder flavour. The paste, formed into small cakes, was cooled and hardened on shiny leaves placed under a tree. The cakes were broken up, mixed with hot water, and beaten to foamy consistency with a small wooden beater, a molinet, producing the beverage called xocoatl (from Nahuatl words meaning “bitter water”).

Too bitter for European taste, the mixture was sweetened with sugar when introduced to the Spanish court. Although Spain guarded the secret of its xocoatl beverage for almost 100 years, it reached Italy in 1606 and became popular in France with the marriage of the Spanish princess Maria Theresa to Louis XIV in 1660. In 1657 a Frenchman opened a London shop, selling solid chocolate to be made into the beverage, and chocolate houses, selling the hot beverage, soon appeared throughout Europe. By 1765 chocolate manufacture had begun in the American colonies at Dorchester, in Massachusetts, using cocoa beans from the West Indies.

In 1828 C.J. van Houten of the Netherlands patented a process for obtaining “chocolate powder” by pressing much of the cocoa butter from ground and roasted cocoa beans. In 1847 the English firm of Fry and Sons combined cocoa butter, a by-product of the pressing, with chocolate liquor and sugar to produce eating chocolate, and in 1876 Daniel Peter of Switzerland added dried milk to make milk chocolate. The proliferation of flavoured, solid, and coated chocolate foods rapidly followed.

Starting in the Americas in an area stretching from southern Mexico to the northern countries of South America, commercial cacao cultivation spread around the world to areas within 20° of the Equator where rainfall, temperatures, and soil conditions were suitable for its growth.

Cocoa Bean Processing

Harvesting

Harvesting of cocoa beans can proceed all year, but the bulk of the crop is gathered in two flush periods occurring from October to February and from May to August. The ripe seed pods are cut from the trees and split open with machetes. The beans, removed from the pods with their surrounding pulp, are accumulated in leaf-covered heaps, in leaf-lined holes dug in the ground, or in large shallow boxes having perforated bottoms to provide for drainage.

Fermentation

The pulp of common grades (Forastero) is allowed to ferment for five to seven days, and the pulp of the more distinctively flavoured grades (Criollo) for one to three days. Frequent turnings dissipate excess heat and provide uniformity. During fermentation, the juicy sweatings of the pulp are drained away, the germ in the seed is killed by the increased heat, and flavour development begins. The beans become plump and full of moisture, and the interior develops a reddish brown colour and a heavy, sharp fragrance. The fermented beans are sun-dried or kiln-dried to reduce moisture content to 6–7 percent and bagged for shipment.

Cleaning, roasting, and grinding

Cocoa beans are subjected to various cleaning processes to remove such contaminants as twigs, stones, and dust. Roasting develops flavour, reduces acidity and astringency, lowers moisture content, deepens colour, and facilitates shell removal. After roasting comes a cracking and fanning (winnowing) process, in which machines crack the shells and then separate them from the heavier nibs by means of blowers. The cell walls of the nibs are in turn broken by grinding, releasing the fat, or cocoa butter, and forming a paste called chocolate liquor, or cocoa mass. If alkalized (Dutched) chocolate liquor is to be produced, the cocoa beans may be winnowed raw; the raw nibs will be alkalized and then roasted prior to grinding.

Conching

Conching, a flavour-developing, aerating, and emulsifying procedure performed by conche machines, requires from 4 to 72 hours, depending on the results desired and the machine type. Temperatures used in this process range from 55 to 88 °C (130 to 190 °F) and are closely controlled to obtain the desired flavour and uniformity.

Molding

In molding, the chocolate is cast in small consumer-size bars or in blocks weighing about 4.5 kg (10 pounds) for use by confectioners and is then subjected to cold air to produce hardening.

Cocoa Bean Products

Cocoa powders

Cocoa powders are produced by pulverizing cocoa cakes, made by subjecting the chocolate liquor of about 53 to 56 percent cocoa butter content to hydraulic pressing to remove a predetermined amount of cocoa butter. The cocoa butter content remaining in the powder may range from 8 to 36 percent, with the most common commercial grades in the United States containing 11, 17, or 22 percent cocoa butter. In the United Kingdom, cocoa sold for beverage use must contain a minimum of 20 percent.

Natural process

Natural-process cocoa powders and chocolate liquors receive no alkali treatment. Cocoa beans are normally slightly acidic, with a pH of 5.2–5.8. When the pH remains unchanged, the beans produce pleasantly sharp flavours blending well in many foods and confections.

Dutch process

Dutch-process cocoa powders and chocolate liquors are treated at the nib, liquor, or powder stage. The treatment is frequently referred to as “Dutching” because the process, first applied by C.J. van Houten in the Netherlands, was introduced as “Dutch cocoa.” In this alkalizing process, a food-grade alkali solution may be applied in order partially to neutralize the natural cocoa acids, mostly acetic acid like that in vinegar; or it may be used to produce a strictly alkaline product, with a pH as high as 8.0. Potassium carbonate is most commonly used as an alkalizer, although other alkalies, such as sodium carbonate, may be used. In addition to altering the pH of the cocoa powder, the process darkens colour, mellows flavour, and alters taste characteristics.

Chocolate products

Chocolate products usually require the addition of more cocoa butter to that already existing in the chocolate liquor. The various forms of chocolate are available in consumer-size packages and in large bulk sizes for use by food manufacturers and confectioners. Most European confectioners make their own chocolate; other confectioners buy chocolate from chocolate-manufacturing specialists. For large commercial orders, chocolate is shipped, warm and in liquid form, in heated sanitary tank trucks or tank cars.

Baking chocolate

Baking (bitter) chocolate, popular for household baking, is pure chocolate liquor made from finely ground nibs, the broken pieces of roasted, shelled cocoa beans. This chocolate, bitter because it contains no sugar, can be either the natural or the alkalized type.

Sweet chocolate

Sweet chocolate, usually dark in colour, is made with chocolate liquor, sugar, added cocoa butter, and such flavourings as vanilla beans, vanillin, salt, spices, and essential oils. Sweet chocolate usually contains at least 15 percent chocolate liquor content, and most sweet chocolate contains 25–35 percent. The ingredients are blended, refined (ground to a smooth mass), and conched. Viscosity is then adjusted by the addition of more cocoa butter, lecithin (an emulsifier), or a combination of both.

Milk chocolate

Milk chocolate is formulated by substituting whole milk solids for a portion of the chocolate liquor used in producing sweet chocolate. It usually contains at least 10 percent chocolate liquor and 12 percent whole milk solids. Manufacturers usually exceed these values, frequently going to 12–15 percent chocolate liquor and 15–20 percent whole milk solids. Milk chocolate, usually lighter in colour than sweet chocolate, is sweeter or milder in taste because of its lower content of bitter chocolate liquor. Processing is similar to that of sweet chocolate. “Bitter chocolate” refers to either baking chocolate or bittersweet chocolate. Bittersweet is similar to sweet chocolate but contains less sugar and more chocolate liquor. Minimum percentages of chocolate liquor are fixed by law in some countries, such as the United States.

Chocolate-type coatings

Confectionery coatings are made in the same manner as similar chocolate types, but some or all of the chocolate liquor is replaced with equivalent amounts of cocoa powder, and instead of added cocoa butter, with a melting point of about 32–33 °C (90–92 °F), other vegetable fats of equal or higher melting points are used. In the United States the legal name of this coating is “sweet cocoa and vegetable fat (other than cocoa fat) coatings.” In the “chocolate” coating usually applied to ice cream and other frozen novelties, legally known as “sweet chocolate and vegetable fat (other than cocoa fat) coatings,” the added cocoa butter usual in chocolate is replaced by lower-melting-point vegetable fats, such as coconut oil.

By-products

Shells, the major by-product of cocoa and chocolate manufacturing, represent 8–10 percent of raw cocoa bean weight and are blown off in the cracking and fanning, or winnowing, operation. They are used for fertilizer, mulch, and fuel.

Chocolate and cocoa grades

In chocolate and cocoa products, there is no sharp difference from one grade or quality to the next. Chocolate quality depends on such factors as the blend of beans used, with about 20 commercial grades from which to choose; the kind and amount of milk or other ingredients included; and the kind and degree of roasting, refining, conching, or other type of processing employed. Chocolate and cocoa products are only roughly classified; there are hundreds of variations on the market, alone or in combination with other foods or confections.

Care and storage

Chocolate and cocoa require storage at 18–20 °C (65–68 °F), with relative humidity below 50 percent. High (27–32 °C, or 80–90 °F) or widely fluctuating temperatures will cause fat bloom, a condition in which cocoa butter infiltrates to the surface, turning products gray or white as it recrystallizes.

High humidity causes mustiness in cocoa powder and can lead to mold formation in cocoa powder or on chocolate. Excessive moisture can also dissolve sugar out of chocolate, redepositing it on the surface as sugar bloom, distinguished from fat bloom by its sandy texture.

Nutritive value

Cocoa, a highly concentrated food providing approximately 1,000 calories per kilogram, provides carbohydrates, fat, protein, and minerals. Its theobromine and caffeine content produce a mildly stimulating effect. The carbohydrates and easily digested fats in chocolate make it an excellent high-energy food.

Jai Ganesh · 2020-10-18 00:29:32

800) Measles

Measles, also called rubeola, contagious viral disease marked by fever, cough, conjunctivitis, and a characteristic rash. Measles is most common in children but may appear in older persons who escaped it earlier in life. Infants are immune up to four or five months of age if the mother has had the disease. Immunity to measles following an attack is usually lifelong.

Transmission And Symptoms

Measles is so highly communicable that the slightest contact with an active case may infect a susceptible person. After an incubation period of about 10 days, the patient develops fever, redness and watering of the eyes, profuse nasal discharge, and congestion of the mucous membranes of the nose and throat—symptoms often mistaken for those of a severe cold. This period of invasion lasts for 48 to 96 hours. The fever increases with appearance of a blotchy rash, and the temperature may rise as high as 40 °C (about 105 °F) when the rash reaches its maximum. Twenty-four to 36 hours before the rash develops, there appear in the mucous membranes of the mouth typical maculae, called Koplik spots—bluish white specks surrounded by bright red areas about 1/32 inch (0.75 mm) in diameter. After a day or two the rash becomes a deeper red and gradually fades, the temperature drops rapidly, and the catarrhal symptoms disappear.

Treatment And Complications

No drug is effective against measles. The only treatment required is control of fever, rest in bed, protection of the eyes, care of the bowels, and sometimes steam inhalations to relieve irritation of the bronchial tree. When no complications occur, the illness lasts 10 days. Although uncomplicated measles is seldom fatal, infection with the virus has been shown to induce a form of “immune amnesia,” whereby measles virus eliminates as many as half of the antibodies generated against other infectious agents to which an individual was exposed previously. Thus, persons who survive measles infection may become vulnerable once again to a range of other diseases, such as chickenpox and polio. By contrast, individuals vaccinated against measles do not experience a loss of immunity to other infectious agents.

Deaths attributed to measles usually result from secondary bronchopneumonia caused by bacterial organisms entering the inflamed bronchial tree. Complications of measles are frequent and include a superimposed bacterial ear infection or pneumonia or a primary measles lung infection. Encephalitis is a rare occurrence. Measles virus can invade various organ systems and cause hepatitis, appendicitis, and gangrene of the extremities. A large percentage of cases of severe measles are associated with inadequate intake of vitamin A, and there is evidence that treatment with vitamin A may reduce measles complications.

On very rare occasions, persistent infection with a mutant measles virus can cause a degenerative central nervous system disease called subacute sclerosing panencephalitis (SSPE), in which there is a gradual onset of progressive behavioral and intellectual deterioration. Motor incoordination and impairment of speech and sight subsequently develop. The final stages of stupor, dementia, blindness, and death occur within six to nine months. There is no treatment for SSPE.

Measles Vaccine And Eradication Efforts

Mortality caused by measles declined steadily in the 20th century as the health of children and infants improved and effective treatment of complications became possible through the use of sulfonamide and antibiotic drugs. The widespread use of measles vaccine, beginning in the late 1960s, raised hopes for the eventual eradication of the disease. In the following decades, however, measles remained a leading cause of childhood mortality worldwide, primarily because attack rates remained high in less-developed countries, where factors such as malnutrition and weak public health infrastructure challenged infant health and the establishment of immunization programs. In the early 21st century, campaigns were initiated to increase vaccination, particularly in less-developed countries. International efforts led to a significant reduction in measles cases and deaths, bringing global elimination of the disease within reach. At the same time, supporting this progress, many wealthier countries, including the United States and some countries in the European Union, had successfully eradicated measles.

In the second decade of the 21st century, however, large measles outbreaks continued to occur in countries with low vaccination rates. In late 2019 in Samoa, for instance, a severe outbreak of measles resulted in school closures and government shutdown, followed by a mass vaccination campaign to prevent further spread of the disease. Measles also reemerged in several countries where it previously had been eradicated, a trend attributed to alarming declines in vaccination coverage. Of particular concern was the return of measles in developed countries such as the United States, where the disease had been eliminated by 2000, and the United Kingdom. In these countries, measles reemerged in the form of small outbreaks that were typically concentrated in areas with relatively high proportions of unvaccinated individuals. Coincident with the return of measles in those countries, however, was a massive surge in the disease in countries with traditionally low vaccination coverage, resulting in large increases in measles cases worldwide. Global incidence was notably high in 2019, with more than 364,800 cases reported between June and July alone that year—far exceeding the number of cases reported worldwide over that time frame for any year since 2006, according to officials with the World Health Organization (WHO). The largest increases occurred in countries in Africa, Europe, and the Western Pacific. By early 2020 the Democratic Republic of the Congo was in the midst of a severe measles epidemic, with more than 6,000 deaths according to WHO. WHO and health officials in regions affected by measles outbreaks increased efforts to bolster vaccination rates to stop the disease from spreading further.

Measles vaccines are live vaccines that work against measles alone or in combination against other agents, specifically with rubella (MR), mumps and rubella (MMR), or mumps, rubella, and varicella (MMRV). The vaccines typically are given in two doses. In the United States, for example, the first dose is given at 12 to 15 months of age, and the second dose is recommended at four to six years. In other countries, the vaccine is given first at nine months and the second dose later. The second dose of MMR must be given at least four weeks after the first dose; in adults whose vaccination status is uncertain, the two doses typically are given four weeks apart. The youngest age at which the vaccines can be given is six months, though revaccination (with two doses) is needed later.

Similar Illnesses

Measles must be differentiated from other disorders accompanied by an eruption. In roseola infantum, a disease seen in babies, a measleslike rash appears after the child has had a high temperature for two or three days, but there is no fever at the time of the rash. German measles (rubella) can be superficially differentiated from measles by the shorter course of the disease and mildness of the symptoms. Sometimes the rashes of scarlet fever, serum reactions, and other conditions may, on certain parts of the body, look like measles. Drugs that may produce rashes similar to measles are phenobarbital, diphenylhydantoin, the sulfonamides, phenolphthalein, and penicillin.

Jai Ganesh · 2020-10-19 00:08:03

801) Bitumen

Bitumen, dense, highly viscous, petroleum-based hydrocarbon that is found in deposits such as oil sands and pitch lakes (natural bitumen) or is obtained as a residue of the distillation of crude oil (refined bitumen). In some areas, particularly in the United States, bitumen is often called asphalt, though that name is almost universally used for the road-paving material made from a mixture of gravel, sand, and other fillers in a bituminous binder. Bitumen is also frequently called tar or pitch—though, properly speaking, tar is a byproduct of the carbonization of coal and pitch is actually obtained from the distillation of coal tar.

Bitumen is defined by the U.S. Geological Survey as an extra-heavy oil with an API gravity less than 10° and a viscosity greater than 10,000 centipoise. At the temperatures normally encountered in natural deposits, bitumen will not flow; in order to be moved through a pipe, it must be heated and, in some cases, diluted with a lighter oil. It owes its density and viscosity to its chemical composition—mainly large hydrocarbon molecules known as asphaltenes and resins, which are present in lighter oils but are highly concentrated in bitumen. In addition, bitumen frequently has a high content of metals, such as nickel and vanadium, and nonmetallic inorganic elements, such as nitrogen, oxygen, and sulfur. Depending on the use to which bitumen is put, these elements may be contaminants that have to be removed from the finished product. By far most refined bitumen is used in paving asphalt and roofing tiles, as is a large amount of natural bitumen. However, most of the bitumen extracted from Canada’s oil sands is upgraded into synthetic crude oil and sent to refineries for conversion into a full range of petroleum products, including gasoline.

Jai Ganesh · 2020-10-20 01:24:55

802) Mumps

Mumps , also called epidemic parotitis, acute contagious disease caused by a virus and characterized by inflammatory swelling of the salivary glands. It frequently occurs as an epidemic and most commonly affects young persons who are between 5 and 15 years of age.

The incubation period is about 17 to 21 days after contact; danger of transmission begins one week before symptoms appear and lasts about two weeks. Mumps generally sets in with symptoms of a slightly feverish cold, soon followed by swelling and stiffening in the region of the parotid salivary gland in front of the ear. The swelling rapidly increases and spreads toward the neck and under the jaw, involving the numerous glands there. The condition is often found on both sides of the face. Pain is seldom severe, nor is there much redness or any tendency to discharge pus; there is, however, interference with chewing and swallowing. After four or five days the swelling subsides.

In patients past puberty, there is occasionally swelling and tenderness in other glands, such as the testicles in males (orchitis) and the breasts (mastitis) or ovaries (oophoritis) in females, and, rarely, involvement of the pancreas, but these are of short duration and usually of no serious significance. The testicles may become atrophied, but sterility from this cause is uncommon. Meningoencephalitis (inflammation of the brain and its membranous covering) is a fairly common concomitant of mumps, but the outlook for recovery is favourable.

Mumps itself requires no special treatment; a single attack usually confers lifelong immunity. Infection with mumps virus was once common in childhood, but the frequency of infection was drastically reduced with the introduction in 1967 of routine immunization for prevention of the disease with a vaccine made from attenuated (weakened) live mumps virus. This vaccine is administered after the age of about one year, often in combination with measles and rubella vaccines.

Jai Ganesh · 2020-10-21 00:10:57

803) Analgesic

Analgesic, any drug that relieves pain selectively without blocking the conduction of nerve impulses, markedly altering sensory perception, or affecting consciousness. This selectivity is an important distinction between an analgesic and an anesthetic.

Analgesics may be classified into two types: anti-inflammatory drugs, which alleviate pain by reducing local inflammatory responses; and the opioids, which act on the brain. The opioid analgesics were once called narcotic drugs because they can induce sleep. The opioid analgesics can be used for either short-term or long-term relief of severe pain. In contrast, the anti-inflammatory compounds are used for short-term pain relief and for modest pain, such as that of headache, muscle strain, bruising, or arthritis.

Anti-Inflammatory Analgesics

Most anti-inflammatory analgesics are derived from three compounds discovered in the 19th century—salicylic acid, pyrazolone, and phenacetin (or acetophenetidin). Although chemically unrelated, the drugs in these families have the ability to relieve mild to moderate pain through actions that reduce inflammation at its source. Acetylsalicylic acid, or aspirin, which is derived from salicylic acid, is the most widely used mild analgesic. It is considered the prototype for anti-inflammatory analgesics, the two other major types of which include acetaminophen (a derivative of phenacetin) and the aspirin-like drugs, or nonsteroidal anti-inflammatory drugs (NSAIDs), which include compounds such as ibuprofen, naproxen, and fenoprofen. Pyrazolone derivatives, with some exceptions, are no longer widely used in many countries, because of their tendency to cause an acute infection known as agranulocytosis.

Aspirin and NSAIDs appear to share a similar molecular mechanism of action—namely, inhibition of the synthesis of prostaglandins (natural products of inflamed white blood cells) that induce the responses in local tissue that include pain and inflammation. In fact, aspirin and all aspirin-like analgesics, including indomethacin and sulindac, which are derived from a heterocyclic organic compound known as indole, inhibit prostaglandin synthesis and release. All these agents can be further divided into nonselective COX inhibitors and selective COX inhibitors. COX, or cyclooxygenase, is an enzyme responsible for the synthesis of prostaglandins and related compounds. It has two forms, COX-1, which is found in most normal tissues, and COX-2, which is induced in the presence of inflammation. Because COX-2 is not normally expressed in the stomach, the use of COX-2 inhibitors (e.g., rofecoxib, celecoxib) seems to result in less gastric ulceration than occurs with other anti-inflammatory analgesics, particularly aspirin. However, COX-2 inhibitors do not reduce the ability of platelets to form clots, a benefit associated with aspirin and other nonselective COX inhibitors.

Preferences in COX selectivity and the possibility of additional molecular actions of NSAIDs may explain differences in the therapeutic effects between aspirin, acetaminophen, and NSAIDs. For example, while aspirin is effective in reducing fever, as well as relieving inflammation, acetaminophen and NSAIDs are more potent antipyretic (fever-reducing) analgesics. Acetaminophen, on the other hand, possesses inferior anti-inflammatory activity compared with aspirin and NSAIDs and thus is relatively ineffective in treating inflammatory conditions such as rheumatoid arthritis. Despite this, acetaminophen is a popular mild analgesic and antipyretic and is a suitable alternative to aspirin for patients who develop severe symptoms of stomach irritation, because it is not as harmful to the gastrointestinal tract.

As might be expected from their common mechanisms of action, many of the anti-inflammatory analgesic drugs share similar side effects. Hypersensitivity responses to aspirin-like drugs are thought to be due to an accumulation of prostaglandins after the pathways that break down prostaglandins are blocked. These responses can be fatal when very strong anti-inflammatory compounds are given. Inhibition of prostaglandin synthesis may result in other serious side effects, such as peptic ulcers and a reduced ability of platelets in the blood to aggregate and form clots. The latter effect, however, has given aspirin an added use as a prophylactic antithrombotic drug to reduce chances of cardiac or cerebral vascular thrombosis—the formation of a clot in a blood vessel in the heart or brain. Some aspirin-like analgesics also have specific toxic effects: liver damage occasionally occurs after administration of acetaminophen, and renal toxicity is sometimes seen with use of NSAIDs. Aspirin itself, taken in overdose, can cause deafness, ringing in the ears, diarrhea, nausea, and headache, which disappear when the dose is reduced or stopped. Aspirin is also thought to be a causative agent of Reye syndrome, a rare and serious degenerative disease of the brain and fatty tissue of the liver that accompanies certain viral infections in children and young adults.

Opioid Analgesics

The term opioid has been adopted as a general classification of all those agents that share chemical structures, sites, and mechanisms of action with the endogenous opioid agonists (endogenous substances are those produced inside the human body). Opioid substances encompass all the natural and synthetic chemical compounds closely related to morphine, whether they act as agonists (cellular activators) or antagonists (substances that block the actions of agonists). Although interest in these drugs had always been high because of their value in pain relief and because of problems of abuse and addiction, interest intensified in the 1970s and ’80s by discoveries about the naturally occurring morphinelike substances, the endogenous opioid neuropeptides.

Opium is the powder from the dried juice of the poppy Papaver somniferum. When taken orally, opium produces sleep and induces a state of peaceful well-being. Its use dates back at least to Babylonian civilization. In the early 19th century opium extract was found to contain more than 20 distinct complex organic bases, called alkaloids, of which morphine, codeine, and papaverine are the most important. These pure alkaloids replaced crude opium extracts in therapeutics.

In the 1950s several new morphinelike drugs were developed. Despite the increase in the number of compounds available for pain relief, however, little was understood of their sites and mechanisms of action. The first real breakthrough came from the discovery, by neuroscientists John W. Hughes and Hans W. Kosterlitz at the University of Aberdeen in Scotland, of two potent naturally occurring analgesic pentapeptides (peptides containing five linked amino acids) in extracts of pig brain. They called these compounds enkephalins, and since then at least six more have been found. Larger peptides, called endorphins, have been isolated, and these contain sequences of amino acids that can be split off as enkephalins. There are at least three types of receptors on brain neurons that are activated by the enkephalins. Morphine and its congeners are thought to exert their effects by activating one or more of these receptors.

Opioid drugs are useful in the treatment of general postoperative pain, severe pain, and other specific conditions. The use of opioids to relieve the pain associated with kidney stones or gallstones presumably depends on their ability to affect opioid receptors in these tissues and to inhibit contractility. By a similar mechanism, opioids are also able to relieve the abdominal distress and fluid loss of diarrhea. Central receptors appear to account for the ability of morphine and analogs to suppress coughing, an effect that requires lower doses than those needed for analgesia. Low doses of opioids are also used for relief of the respiratory distress that accompanies acute cardiac insufficiency complicated by the buildup of fluid in the lungs.

Several commonly used natural or synthetic derivatives of morphine are used in drug therapeutics. Codeine, a naturally occurring opium alkaloid that can be made synthetically, is a useful oral analgesic, especially when used in combination with aspirin. Meperidine was an early synthetic analog of morphine, marketed under the trade name Demerol, that was originally thought to be able to provide significant short-lasting analgesia and little or no addiction because of its shortened duration of action; however, this belief proved false. Methadone, a synthetic opioid analgesic, has long-lasting analgesic effects (six to eight hours) when taken orally and is used to moderate the effects of withdrawal from heroin addiction. Among the opioid antagonist drugs, naloxone and its longer-lasting orally active version, naltrexone, are used primarily to reverse morphine overdoses and to reverse the chemical stupor of a wider variety of causes, including alcohol intoxication and anesthesia. In opioid overdoses, these drugs provide recovery within minutes of injection. They can, however, also precipitate severe withdrawal reactions in a person addicted to opiates.

The effectiveness of a given dose of an opioid drug declines with its repeated administration in the presence of intense pain. This loss in effectiveness is called tolerance. Evidence suggests that tolerance is not due to alterations in the brain’s responses to drugs. Animals exhibiting tolerance to morphine after repeated injections in a familiar environment show little or no tolerance when given the same doses and tested for pain sensitivity in new environments. Thus, there is almost certainly a learned aspect of tolerance. The cellular and molecular mechanisms underlying this loss of responsiveness are not clear. Physical dependence and addiction in a person using intravenous administration closely follow the dynamics of drug tolerance; increasing doses are required to produce the psychological effects, while tolerance protects the brain against the respiratory depressant actions of the drug. In the tolerant individual, intense adverse reactions can be precipitated by administration of an opioid antagonist, thus revealing the dynamic internal equilibrium that previously appeared to neutralize the response of the brain to the opioids. The signs of the withdrawal response (e.g., anxiety, tremors, elevation of blood pressure, abdominal cramps, and hyperthemia) can be viewed as signs of an activated sympathetic nervous system and to some extent an extreme, but nonspecific, arousal response.

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