Economics and Commerce

(Note:- This page is updated regularly)

Classical Economy

Economy policies

• Acceptance
•  Three Factor of Economics

Agriculture

Indian population

Indian economy and poverty

Banks

International Trade

Accordian

Accordian

Portable musical instrument that uses a hand-pumped bellows and two keyboards to sound free reeds, small metal tongues that vibrate when air flows past them.

Photograph:Italian accordion, 19th century

Accordian

  

* Italian accordion, 19th century

The keyboards on either side of the bellows effectively resemble individual reed organs. The right-hand keyboard plays the treble line or lines. Most of the keys on the left-hand (bass) keyboard sound three-note chords; “free-bass” accordions permit the playing of single-note lines. A prototype accordion, using buttons rather than keys, was patented in Berlin in 1822 by Friedrich Buschmann (also inventor of the harmonica). The instrument gained wide popularity in dance bands and as a folk instrument. See also concertina.

Source: Brittanica Encyclopedia

Adi grant

Adi grant

(Punjabi: “First Book”) Sacred scripture of Sikhism.

Adi Grant

Composed of nearly 6,000 hymns of the Sikh Gurus and Hindu and Islamic saints, it is the central object of worship in all gurdwaras (temples). It is ritually opened and closed daily and is read continuously on special occasions. First compiled in 1604 by Arjan, it included his own hymns and those of his predecessors and the devotional songs of saints. In 1704 the last Guru, Gobind Singh, added more hymns and decreed that after his death the Granth would take the place of the Guru. Written mostly in Punjabi or Hindi, it contains the Mul Mantra (basic prayer), Japji (the most important scripture, written by Nanak), and hymns arranged according to the ragas in which they are to be sung.

Amazon river

Amazon river

Portuguese Rio Amazonas

River, northern South America.

Amazon River

It is the largest river in the world in volume and area of drainage basin; only the Nile River of eastern and northeastern Africa exceeds it in length. It originates within 100 mi (160 km) of the Pacific Ocean in the Peruvian Andes Mountains and flows some 4,000 mi (6,400 km) across northern Brazil into the Atlantic Ocean. Its Peruvian length is called the Marañón River; the stretch of river from the Brazilian border to the mouth of the Negro River is the Solimões River. Its more than 1,000 known tributaries rise in the Guiana Highlands, the Brazilian Highlands, and (principally) the Andes; 7 of these are longer than 1,000 mi (1,600 km), and the Madeira River exceeds 2,000 mi (3,200 km). The Amazon can accommodate large freighters as far upriver as the city of Manaus, Braz., 1,000 mi (1,600 km) from the Atlantic. The first European descent was made by Francisco de Orellana in 1541–42; he is said to have given the river its name after reporting battles with tribes of women, whom he likened to the Amazons of Greek legend. Pedro Teixeira achieved the first ascent in 1637–38, but the river remained little explored until the mid-19th century. Many indigenous peoples originally lived along the river, but they moved inland as exploring parties and raiders (see bandeira) sought to enslave them. The river was opened to world shipping in the mid-19th century; traffic increased exponentially with the coming of the rubber trade, which reached its height c. 1910 but soon declined. Its basin encompasses the world's most extensive rainforest and is home to an extraordinary diversity of birds, mammals, and other wildlife. Since the 1960s the effects of economic exploitation on the region's ecology and the destruction of the rainforest have generated worldwide concern.source:Britannica encyclopedia

Kofi Annan

Kofi annan( Ex seceratry general of UNO)

 born April 8, 1938, Kumasi, Gold Coast

Seventh secretary-general of the United Nations (1997–2006), who shared, with the UN, the 2001 Nobel Prize for Peace.

Kofi Annan

He was the son of a provincial governor and hereditary paramount chief of the Fante people. He did graduate work at Geneva's Institute for Advanced International Studies and at MIT. He has spent almost his entire career within the UN, beginning at the World Health Organization (1962). As undersecretary-general for peacekeeping (from 1993), he transferred peacekeeping operations in Bosnia from the UN to NATO. Elected in December 1996, he became the first UN secretary-general from sub-Saharan Africa, and he enjoyed a mandate to reform the UN bureaucracy. He criticized the UN's failure to prevent or minimize genocide in Rwanda (1994) and unsettled many by declaring that the UN should address human-rights violations perpetrated by governments against their own people. His priorities included restoring public confidence in the organization and strengthening the UN's activities for peace and development. Annan was appointed to a second term in 2001, and terrorism and global security became major issues following the September 11, 2001, attacks in the U.S. He also oversaw the adoption of a number of reforms, including many institutional and administrative changes, though some measures, such as the expansion of the UN Security Council, were rejected. Annan left office in 2006, succeeded by Ban Ki-moon.

Source: Britannica encyclopedia

Anabaena

Anabaena(single cell bacteria)

Genus of blue-green algae (cyanobacteria).

Anabaena

Found as plankton in shallow water and on moist soil, they occur in both solitary and colonial forms and are capable of nitrogen fixation. In northern latitudes in summer, extensive growth of Anabaena may form water blooms that remain suspended instead of forming a surface scum. A toxic substance produced is fatal to cattle and other animals if present in drinking water in sufficient concentration.

source:britannica encyclopedia

Amoeba

Amoeba (a single cell protozoan)

One-celled protozoan that can form temporary extensions of cytoplasm (pseudopodia) in order to move about.

Amoeba

   Some amoebas are found on the bottom of freshwater streams and ponds. Others live in the human digestive system; one type causes amebic dysentery in humans. Each amoeba contains a small mass of jellylike cytoplasm with vacuoles and a nucleus. Food is taken in and material is excreted at any point on the cell surface. Amoebas are used extensively in cell research for determining the relative functions and interactions of the nucleus and the cytoplasm.

source:Britannica encyclopedia

Adenine

Adenine (a base in the use of DNA)

Organic compound of the purine family, often called a base, consisting of two rings, each containing both nitrogen and carbon atoms, and an amino group.

It occurs free in tea and in combined form in nucleic acids, ATP, vitamin B12, and several coenzymes. In DNA its complementary base is thymine. It or its corresponding nucleoside or nucleotide may be prepared from nucleic acids by selective techniques of hydrolysis.

Source:Britannica encyclopedia

Acceptance

Acceptance

Short-term credit instrument consisting of a written order that requires a buyer to pay a specified sum to the seller at a given date, signed by the buyer as a promise to honor the obligation.

Instruments of Credit

Acceptances are often used in export/import transactions: an exporter may require a buyer to sign and return an acceptance, which the exporter can then sell to the bank at a discount, thereby obtaining payment promptly. The buyer then has until the bill's maturity date to dispose of the goods and pay the promised sum (now owed to the bank). See also bill of exchange; promissory note.

Source; Britannica encyclopedia

Physics

(Note :- This page is updated regularly)

Measurement,

Force, motion,

Operating Rules of Attention

Work capacity.

Dynamics Energy

NEWTON'S law

Heat, temperature

Wave Motion and Acoustics

Optical

universal

Atomic, Nuclear Physics

Energy Resources

Electricity

Anemometer
Amplifer
Ampere's law
Alpha decay (Alpha rays)
Alternative energy
Altimeter
Alternator
Alternative current (A.C.)
Acoustics
Accelerometer
Acceleration
archimedes principle
Vaccum tube
Vander Waals Force
Zodiac Light

Anemometer

Anemometer

Instrument for measuring the speed of airflow.

Anemometer

The most familiar instruments for measuring wind speeds are the revolving cups that drive an electric generator (useful range approximately 5–100 knots). For very low airspeeds, a unit in which revolving vanes operate a counter measures the airspeed. For strong, steady wind speeds (in wind tunnels and aboard aircraft in flight), a pitot-tube anemometer is often used; the pressure difference between the interior of the tube and the surrounding air can be measured and converted to airspeed.

Source: Britannica encyclopedia

Amplifer

Amplifer

Device that responds to a small input signal (voltage, current, or power) and delivers a larger output signal with the same waveform features.

Amplifier

Amplifiers are used in radio and television receivers, high-fidelity audio equipment, and computers. Amplification can be provided by electromechanical devices (e.g., transformers and generators) and vacuum tubes, but most electronic systems now employ solid-state microcircuits. One amplifier is usually insufficient, so its output is fed into a second, whose output is fed to a third, and so on, until the output level is satisfactory.

source:Britannica encyclopedia

Ampere's law

Ampere's law (ampere's swimming law)

Law of electromagnetism that describes mathematically the magnetic force between two electric currents.

It was named after A.-M. Ampère, who discovered that such forces exist. If two currents flow in the same direction, the force between the two wires is attractive; if they flow in opposite directions, the force is repulsive. In each case, the force is directly proportional to the currents.

source:Britannica encyclopedia

Alpha decay (Alpha rays)

Alpha decay (Alpha rays)

Type of radioactive disintegration (see radioactivity) in which some unstable atomic nuclei dissipate excess energy by spontaneously ejecting an alpha particle.

Alpha

Alpha particles have two positive charges and a mass of four atomic mass units; they are identical to helium nuclei. Though they are emitted at speeds about one-tenth that of light, they are not very penetrating and have ranges in air of about 1–4 in. (2.5–10 cm). Alpha decay commonly occurs in elements with atomic numbers greater than 83 (bismuth), but can occur in some rare-earth elements in the atomic-number range of 60 (neodymium) to 71 (lutetium). Alpha decay half-lives range from about a microsecond (10−6 second) to billions of years (1017 seconds).

Source: Britannica encyclopedia

Alternative Energy

Alternative energy (RENEWABLE ENERGY)

Any of various renewable power sources to use in place of fossil fuels and uranium.

Fusion devices (see nuclear fusion) are believed by some to be the best long-term option, because their primary energy source would be deuterium, abundant in ordinary water. Other technologies include solar energy, wind power, tidal power, wave power, hydroelectric power, and geothermal energy. The amount of energy in such renewable and virtually pollution-free sources is large in relation to world energy needs, yet at present only a small portion of it can be converted to electric power at reasonable cost.

.source: Britannica encyclopedia

Altimeter

Altimeter (INSTRUMENT)

Instrument that measures the altitude of the land surface or of any object, such as an airplane.

Altimeter

The mechanical pressure altimeter measures atmospheric pressure relative to sea level through a series of bellows, gears, and springs, which move pointers on a dial. Radio altimeters measure the distance of an aircraft above the ground rather than above sea level by indicating the time a pulse of radio energy takes to travel from the aircraft to the ground and back; they are used in automatic navigation and blind-landing systems

source: Britannica encyclopedia

Alternator

Alternator

Source of direct electric current in modern vehicles for ignition, lights, fans, and other uses.

Art:Exploded view of an automotive alternator. The engine's turning crankshaft, connected to the …

 Exploded view of an automotive alternator. The engine's turning crankshaft, connected to the …

The electric power is generated by an alternator mechanically coupled to the engine, with a rotor field coil supplied with current through slip rings, and a stator with a three-phase winding. A rectifier converts the power from alternating to direct form. A regulator ensures that the output voltage is properly matched to the battery voltage as engine speed varies. An inductor alternator is a special kind of synchronous generator in which both the field and the output winding are on the stator.

source:Britannica encyclopedia

Alternative current (A.C.)

Alternative current (A.C.)

Flow of electric charge that reverses periodically, unlike direct current.

Alternative Current

It starts from zero, grows to a maximum, decreases to zero, reverses, reaches a maximum in the opposite direction, returns again to zero, and repeats the cycle indefinitely. The time taken to complete one cycle is called the period (see periodic motion), and the number of cycles per second is the frequency; the maximum value in either direction is the current's amplitude. Low frequencies (50–60 cycles per second) are used for domestic and commercial power, but frequencies of around 100 million cycles per second (100 megahertz) are used in television and of several thousand megahertz in radar and microwave communication. A major advantage of alternating current is that the voltage can be increased and decreased by a transformer for more efficient transmission over long distances. Direct current cannot use transformers to change voltage. See also electric current.

source:Britannica encyclopedia

Acoustics

Acoustics

Science of production, control, transmission, reception, and effects of sound.

Its principal branches are architectural, environmental, musical, and engineering acoustics, and ultrasonics. Environmental acoustics focuses on controlling noise produced by aircraft engines, factories, construction machinery, and general traffic. Musical acoustics deals with the design and use of musical instruments and how musical sounds affect listeners. Engineering acoustics concerns sound recording and reproduction systems. Ultrasonics deals with ultrasonic waves, which have frequencies above the audible range, and their applications in industry and medicine.

Source:Britannica encyclopedia

Accelerometer

Accelerometer

Instrument that measures acceleration

Because it is difficult to measure acceleration directly, the device measures the force exerted by restraints placed on a reference mass to hold its position fixed in an accelerating body. The output is usually either a varying electrical voltage or displacement of a moving pointer over a fixed scale. Specially designed accelerometers are used in varied applications: control of industrial vibration test equipment, detection of earthquakes (seismographs), and input to navigational and inertial guidance systems

Source: Britannica Encyclopedia

Acceleration

Acceleration

Rate of change of velocity

Acceleration

Acceleration, like velocity, is a vector quantity: it has both magnitude and direction. The velocity of an object moving on a straight path can change in magnitude only, so its acceleration is the rate of change of its speed. On a curved path, the velocity may or may not change in magnitude, but it will always change in direction, which means that the acceleration of an object moving on a curved path can never be zero. If velocity is stated in metres per second (m/s) and the time interval in seconds (s), then the units of acceleration are metres per second per second (m/s/s, or m/s2). See also centripetal acceleration.

Source:Britanica Encyclopedia

Neutron

Neutron

One of the constituent particles of every atomic nucleus except ordinary hydrogen.

Discovered in 1932 by James Chadwick (1891–1974), it has no electric charge and has nearly 1,840 times the mass of the electron. Free neutrons undergo beta decay with a half-life of about 10 minutes. Thus, they are not readily found in nature, except in cosmic rays. They are a penetrating form of radiation. When bombarded with neutrons, various elements undergo nuclear fission and release more free neutrons. If enough free neutrons are produced, a chain reaction can be sustained. This process led to the development of nuclear power as well as the atomic bomb. Neutron beams produced in cyclotrons and nuclear reactors are important probes of matter, revealing details of structure in both organic and inorganic substances.

Source: Britannica encyclopedia

Kaniska

Kaniska
or Kanishka
flourished 1st century AD


Greatest king of the Kushān dynasty that ruled over the northern part of the Indian subcontinent, Afghanistan, and possibly regions north of Kashmir in Central Asia.

He is thought to have taken the throne between AD 78 and 144 and to have ruled for 23 years. Kaniṣka is noted for having convened a Buddhist council that marked the beginnings of Mahayana Buddhism. He was a tolerant king who honoured the Zoroastrian, Greek, and Brahmanic deities as well as Buddha. During his reign, trade with the Roman Empire increased significantly, and contact between him and the Chinese in Central Asia may have inspired the transmission of Buddhism to China.

Anesthsiolgy

Anesthesiology

Medical specialty dealing with anesthesia and related matters, including resuscitation and pain.

Originally concerned only with general anesthesia in the operating room, anesthesiology now includes epidural anesthesia (injection of local anesthetics into the spinal fluid, cutting off feeling below the point of injection); artificial respiratory support during operations requiring paralyzing drugs that render patients unable to breathe; clinical management of all unconscious patients; management of pain relief and cardiac and respiratory resuscitation problems; respiratory therapy; and treatment of fluid, electrolyte, and metabolic disturbances. Progress in anesthesiology has made possible more complex operations and surgery for more critically ill patients. The anesthesiologist's role has become increasingly important and complex.

Source: Britannica encyclopedia

Tamil Nadu Open University Course

Clerical Jobs at 19 Nationalised Banks

Geography

(Note :- This page is updated regularly)
Solar system
solar family
Astronimical unit
Inner Earth
Earth movement
Canyon
Animal project in india

Absal plain
Alluvial Deposit(a sand deposit in delta region)
Andromeda Galaxy

Agronomy
Alps hills (Europe)
Astronomy
Global Eco System
Peninsular Region in World

• Pacific Ocean Region
•     Chinese Huang Hai 
• Atlantic Region
• Indian Ocean

Miscellaneous

(Note :- This page is updated regularly)

Ankor 
Ankor wat
Angel falls
Alligator
Altruism(ethical  thoeru-agasthe gamthe -A Father of Sociology)
AldrinEdwine
Alanbrooke
Adriatic Sea (Arm of the Mediterranean Sea, lying between Italy and the Balkan Peninsul
Important dates for TNPSC exams
Agronamy
Alps Hills
Accordian(musical instruments)
Tamil nadu open university Courses
Adi Grant
Amazon river
Kofi annan
Arches National Park
Aral sea
Arabian peninsula
Arabian desert
Appalachian mountains
APEC
Antartic region
Atlantic ocean
Atacama Desert
Astrology

Angkor

Angkor(Thailand-Combodia)

Archaeological site, northwestern Cambodia.

Angor Wat

Located 4 mi (6 km) north of the modern town of Siem Reap, it was the capital of the Khmer (Cambodian) empire from the 9th to the 15th century. Its most imposing monuments are Angkor Wat, a temple complex built in the 12th century by King Suryavarman II, and Angkor Thom, a temple complex built c. 1200 by King Jayavarman VII. During the period of great construction that lasted more than 300 years, there were many changes in architecture as the religious focus changed from Hindu to Buddhist cults. After the Siamese conquest of the Khmer in the 15th century, the ruined city and its temples were buried in the jungle. When the French colonial regime was established in 1863, the entire site became the focus of scholarly interest. During Cambodia's political upheavals of the late 20th century there was some war damage, but the major problem was one of neglect. Angkor was added to the World Heritage site list in 1992.

Source: Britannica encyclopedia

Ankor wat

Ankor wat(the biggest vishnu temble in combodia)

Temple complex in Angkor (now in northwestern Cambodia), the crowning work of Khmer architecture.

Angor Wat

About 1,700 yards (1,550 m) long by 1,500 yards (1,400 m) wide, it is the world's largest religious structure. Dedicated to Vishnu, it was built in the 12th century by Suryavarman II. The Wat, an artificial mountain originally surrounded by a vast external wall and moat, rises in three enclosures toward a flat summit. The five remaining towers (shrines) at the summit are composed of the repetitive diminishing tiers typical of Asian architecture.

Source: Britannica encyclopedia

Angel falls

Angel falls

Waterfall, southeastern Venezuela.

Angel Falls,Venezuela

Photograph:Angel Falls (Salto Ángel), La Gran Sabana region of Bolívar state, Venezuela

* Angel Falls (Salto Ángel), La Gran Sabana region of Bolívar state, Venezuela.

It lies on the Churún River, a tributary of the Caroní, southeast of Ciudad Bolívar. The highest waterfall in the world, the cataract drops 3,212 ft (979 m) and is 500 ft (150 m) wide at its base. It was named for James Angel, an American who crash-landed his plane nearby in 1937.

Source: Britannica encyclopedia

Altruism

Altruism(ethical  thoeru-agasthe gamthe -A Father of Sociology)

Ethical theory that regards the good of others as the end of moral action; by extension, the disposition to take the good of others as an end in itself.

The term (French, altruisme, derived from Latin alter: “other”) was coined in the 19th century by Auguste Comte and adopted generally as a convenient antithesis to egoism. Most altruists have held that each person has an obligation to further the pleasures and alleviate the pains of other people. The same argument holds if happiness, rather than pleasure, is taken as the end of life.

source:Britannica encyclopedia

Alligator

Alligator(Differ  from crocodile)Either of two species of long-snouted reptiles constituting the genus Alligator (family Alligatoridae, order Crocodilia).

Photograph:Alligator (Alligator mississippiensis)

Alligator

   * Alligator (Alligator mississippiensis)

Alligators differ from crocodiles in snout shape and tooth placement. Living in large bodies of water such as lakes, swamps, and rivers, these lizardlike carnivores use their powerful tail for defense and swimming. The eyes, ears, and nostrils, located on top of the long head, project above the water's surface. Alligators dig burrows in which they shelter from danger and hibernate in cold weather. The once-endangered American alligator of the southeastern U.S. may grow to 19 ft (5.7 m) long but usually ranges from 6 to 12 ft (1.8 to 3.7 m) long. The Chinese alligator of the Chang (Yangtze) River region, which grows to 5 ft (1.5 m), is critically endangered.

source:Britannica encyclopedia

Aldrin Edwine

Aldrin Edwine

known as Buzz Aldrin

born Jan. 20, 1930, Montclair, N.J., U.S.

Buzz Aldrin

U.S. astronaut.

He graduated from West Point and flew 66 combat missions in the Korean War. In 1963 he received a Ph.D. from MIT and was chosen as an astronaut. In 1966 he joined James A. Lovell, Jr. (b. 1928) on the four-day Gemini 12 flight. Aldrin's 51/2-hour walk in space proved that humans can function effectively in the vacuum and weightlessness of space. In July 1969, on the Apollo 11 mission, he became the second human to walk on the Moon.

Alanbrooke

Alanbrooke(of Brookeborough)

Alan Francis Brooke,1st  viscount

born July 23, 1883, Bagnères-de-Bigorre, France

died June 17, 1963, Hartley Wintney, Hampshire, Eng.

British military leader.

He served in World War I and later became director of military training (1936–37) and an expert on gunnery. In World War II he began as commander of a corps in France and covered the Dunkirk evacuation. After serving as commander of the British home forces (1940–41), he was promoted to chief of staff (1941–46). He established good relations with the U.S. forces and exercised a strong influence on Allied strategy. He was promoted to field marshal in 1944 and created a viscount in 1946.

source:Britannica encyclopedia

Agronomy

Agronomy

Branch of agriculture that deals with field crop production and soil management.

Agronomy

Agronomists generally work with crops that are grown on a large scale (e.g., small grains) and that require relatively little management. Agronomic experiments focus on a variety of factors relating to crop plants, including yield, diseases, cultivation, and sensitivity to factors such as climate and soil.

Source;Britannica encyclopedia

Adriatic Sea

Adriatic Sea (Arm of the Mediterranean Sea, lying between Italy and the Balkan Peninsula.)

Arm of the Mediterranean Sea, lying between Italy and the Balkan Peninsula.

It is about 500 mi (800 km) long, with an average width of 110 mi (175 km), a maximum depth of 4,035 ft (1,324 m), and an area of 50,590 sq mi (131,050 sq km). The Italian coast is relatively straight and continuous, having no islands, but the Balkan coast is full of islands, generally running parallel to the shore. The Strait of Otranto at its southeasterly limit links it with the Ionian Sea.

Source:Britannica encyclopedia

Alps hills (Europe)

Alps hills (Europe)

Alps Hills

Mountain system, south-central Europe.

The Alps extend in a crescent about 750 mi (1,200 km) from the Mediterranean coast between France and Italy to Vienna and cover more than 80,000 sq mi (207,000 sq km). Several peaks rise above 10,000 ft (3,000 m); the highest is Mont Blanc. The Alps form a divide between the Atlantic Ocean, the Mediterranean Sea, and the Black Sea and give rise to several major European rivers, including the Rhône, Danube, and Po. Glaciers cover about 1,500 sq mi (3,900 sq km), mostly at elevations above 10,000 ft (3,000 m). The Saint Gotthard Pass is one of the Alps's notable tunnels. Grenoble, Innsbruck, and Bolzano are major Alpine cities.

source:Britannica encyclopedia

Absal palin

Absal palin ( Death of the sea,seafloor plain area ia called absal land )

Flat seafloor area at a depth of 10,000–20,000 ft (3,000–6,000 m), generally adjacent to a continent.

Abyssal Plain

The larger plains are hundreds of miles wide and thousands of miles long. The plains are largest and most common in the Atlantic Ocean, less common in the Indian Ocean, and even rarer in the Pacific Ocean, where they occur mainly as small, flat floors of marginal seas or as long, narrow bottoms of trenches. They are thought to be the upper surfaces of land-derived sediment that accumulates in abyssal depressions.

Source:Britannica encyclopedia

Alluvial Deposit

Alluvial Deposit(a sand deposit in delta region)

Material deposited by rivers.

Alluvial Deposit

It consists of silt, sand, clay, and gravel, as well as much organic matter. Alluvial deposits are usually most extensive in the lower part of a river's course, forming floodplains and deltas, but they may form at any point where the river overflows its banks or where the flow of a river is checked. They yield very fertile soils, such as those of the deltas of the Mississippi, Nile, Ganges and Brahmaputra, and Huang (Yellow) rivers. They contain most of the world's supply of tin ore, as well as, in some regions, gold, platinum, and gemstones.

source:Britannica encyclopedia

Andromeda Galaxy

Andromeda Galaxy

M31

Andromeda Galaxy

Great spiral galaxy in the constellation Andromeda.

It is the nearest spiral galaxy outside the Milky Way Galaxy and one of the few visible to the unaided eye, appearing as a milky blur. About 2 million light-years from Earth, it has a diameter of about 200,000 light-years, which makes it the largest galaxy in the Local Group. For centuries astronomers considered it part of the Milky Way; only in the 1920s did Edwin Hubble determine conclusively that it was a separate galaxy.

Source:Britannica encyclopedia

Annealing

Annealing

Annealed wires

Annealing  Treatment of a metal, alloy, or other material by heating to a predetermined temperature, holding for a certain time, and then cooling to room temperature, done to improve ductility and reduce brittleness.  Process annealing is carried out intermittently during the working of a piece of metal to restore ductility lost through repeated hammering or other working, if several cold-forming operations are required but the metal is so hardened after the first operation that further cold working would cause cracking (see hardening). Full annealing is done to give workability to such parts as forged blanks destined for use in the machine-tool industry. Annealing is also done for relief of internal stresses in metal and glass. Annealing temperatures and times differ for different materials and with properties desired; steel is usually held for several hours at about 1,260°F (680°C) and then cooled for several hours. See also heat treating, solid solution.

source: Britannica encyclopedia

Acid and basic rocks

Acid and basic rocks

Division of igneous rocks on the basis of their silicate mineral content, these minerals usually being the most abundant in such rocks.

Acid and Basic rocks

Rocks are described as acid, intermediate, basic, and ultrabasic, in order of decreasing silica content, because it was earlier thought that silica is present in rock magmas in the form of silicic acid. In modern usage the terms do not refer to acidity in the chemical sense. In general, the gradation from acid to basic corresponds to an increase in colour (i.e., light to dark).

source;Britannica encyclopedia

Acid

Acid

Any substance that in water solution tastes sour, changes the colour of acid-base indicators (e.g., litmus), reacts with some metals (e.g., iron) to yield hydrogen gas, reacts with bases to form salts, and promotes certain chemical reactions (e.g., acid catalysis).

Acids contain one or more hydrogen atoms that, in solution, dissociate as positively charged hydrogen ions. Inorganic, or mineral, acids include sulfuric acid, nitric acid, hydrochloric acid, and phosphoric acid. Organic acids include carboxylic acids, phenols, and sulfonic acids. Broader definitions of acids cover situations in which water is not present. See also acid-base theory.

source; Britannica encyclopedia

Acetylcholine

Acetylcholine

Ester of choline and acetic acid, a neurotransmitter active at many nerve synapses and at the motor end plate of vertebrate voluntary muscles.

It affects several of the body's systems, including the cardiovascular system (decreases heart rate and contraction strength, dilates blood vessels), gastrointestinal system (increases peristalsis in the stomach and amplitude of digestive contractions), and urinary system (decreases bladder capacity, increases voluntary voiding pressure). It also affects the respiratory system and stimulates secretion by all glands that receive parasympathetic nerve impulses (see autonomic nervous system). It is important in memory and learning and is deficient in the brains of those with late-stage Alzheimer disease.

source:Britannica encylopedia

Acetone or Dimethyl Ketone

Acetone  or Dimethyl Ketone

Simplest and most important ketone (CH3COCH3).

It is a colourless, flammable liquid, boiling at 133 °F (56.2 °C). Many fats, resins, and organic materials dissolve easily in it, so it is used to make artificial fibres, explosives, resins, paints, inks, cosmetics (including nail-polish remover), coatings, and adhesives. Acetone is used as a chemical intermediate in pharmaceuticals and many other compounds.

source:Britannica encylopedia

Adipose tissue

Adipose tissue(seen at under the skin and stored the fator fatty tissue )

Connective tissue consisting mainly of fat cells, specialized to synthesize and contain large globules of fat, within a structural network of fibres.

 It is found mainly under the skin but also in deposits between the muscles, in the intestines and in their membrane folds, around the heart, and elsewhere. The fat stored in this tissue comes from dietary fats or is produced in the body. It acts as a fuel reserve for times of starvation or great exertion, helps conserve body heat, and forms pads between organs.

Source:Britannica encyclopedia

Angioplasty

Angioplasty(Therapeutic opening of a blocked blood vessel.)

Usually a balloon is inflated near the end of a catheter (see catheterization) to flatten plaques (see atherosclerosis) against an artery's wall. Performed on a coronary artery, angioplasty is a less invasive alternative to coronary bypass surgery in the treatment of coronary heart disease. Complications, including embolisms and tearing, are rare and results are excellent, but plaques tend to build up again after the procedure. Angioplasty is also used to expand a severely obstructed heart valve.

Source: Britannica encyclopedia

Angiography

Angiography (arteriography)

Angiogram

X-ray examination of arteries and veins with a contrast medium to differentiate them from surrounding organs.

 The contrast medium is introduced through a catheter to show the blood vessels and the structures they supply, including organs. Angiography of diseased leg, brain, or heart arteries is necessary before corrective surgery. See also angiocardiography.

Source: Britannica encyclopedia

Angiocardiography

Angiocardiography

method of diagnostic imaging that shows the flow of blood through the heart and great vessels.

It is used to evaluate patients for surgery on the cardiovascular system. A contrast medium is introduced through a catheter into a heart chamber. A series of X-ray images shows where the flow narrows, signaling blockage of a blood vessel by atherosclerosis.

Source: Britannica encyclopedia