Sleep is a recurring state of mind and body, characterized by altered consciousness inhibited sensory activity, inhibition of nearly all voluntary muscles, reduced interactions with surroundings. It is distinguished from wakefulness by a decreased ability to react to stimuli, but more reactive than coma or disorders of consciousness, sleep displaying different and active brain patterns. Sleep occurs in repeating periods, in which the body alternates between two distinct modes: REM sleep and non-REM sleep. Although REM stands for "rapid eye movement", this mode of sleep has many other aspects, including virtual paralysis of the body. A well-known feature of sleep is the dream, an experience recounted in narrative form, which resembles waking life while in progress, but which can be distinguished as fantasy. During sleep, most of the body's systems are in an anabolic state, helping to restore the immune, nervous and muscular systems; the internal circadian clock promotes sleep daily at night. The diverse purposes and mechanisms of sleep are the subject of substantial ongoing research.
Sleep is a conserved behavior across animal evolution. Humans may suffer from various sleep disorders, including dyssomnias such as insomnia, hypersomnia and sleep apnea; the advent of artificial light has altered sleep timing in industrialized countries. The most pronounced physiological changes in sleep occur in the brain; the brain uses less energy during sleep than it does when awake during non-REM sleep. In areas with reduced activity, the brain restores its supply of adenosine triphosphate, the molecule used for short-term storage and transport of energy. In quiet waking, the brain is responsible for 20% of the body's energy use, thus this reduction has a noticeable effect on overall energy consumption. Sleep increases the sensory threshold. In other words, sleeping persons perceive fewer stimuli, but can still respond to loud noises and other salient sensory events. During slow-wave sleep, humans secrete bursts of growth hormone. All sleep during the day, is associated with secretion of prolactin.
Key physiological methods for monitoring and measuring changes during sleep include electroencephalography of brain waves, electrooculography of eye movements, electromyography of skeletal muscle activity. Simultaneous collection of these measurements is called polysomnography, can be performed in a specialized sleep laboratory. Sleep researchers use simplified electrocardiography for cardiac activity and actigraphy for motor movements. Sleep is divided into two broad types: non-rapid eye movement sleep and rapid eye movement sleep. Non-REM and REM sleep are so different that physiologists identify them as distinct behavioral states. Non-REM sleep after a transitional period is called slow-wave sleep or deep sleep. During this phase, body temperature and heart rate fall, the brain uses less energy. REM sleep known as paradoxical sleep, represents a smaller portion of total sleep time, it is the main occasion for dreams, is associated with desynchronized and fast brain waves, eye movements, loss of muscle tone, suspension of homeostasis.
The sleep cycle of alternate NREM and REM sleep takes an average of 90 minutes, occurring 4–6 times in a good night's sleep. The American Academy of Sleep Medicine divides NREM into three stages: N1, N2, N3, the last of, called delta sleep or slow-wave sleep; the whole period proceeds in the order: N1 → N2 → N3 → N2 → REM. REM sleep occurs as a person returns to stage 1 from a deep sleep. There is a greater amount of deep sleep earlier in the night, while the proportion of REM sleep increases in the two cycles just before natural awakening. Awakening can mean the end of sleep, or a moment to survey the environment and readjust body position before falling back asleep. Sleepers awaken soon after the end of a REM phase or sometimes in the middle of REM. Internal circadian indicators, along with successful reduction of homeostatic sleep need bring about awakening and the end of the sleep cycle. Awakening involves heightened electrical activation in the brain, beginning with the thalamus and spreading throughout the cortex.
During a night's sleep, a small amount of time is spent in a waking state. As measured by electroencephalography, young females are awake for 0–1% of the larger sleeping period. In adults, wakefulness increases in cycles. One study found 3% awake time in the first ninety-minute sleep cycle, 8% in the second, 10% in the third, 12% in the fourth, 13–14% in the fifth. Most of this awake time occurred shortly. Today, many humans wake up with an alarm clock. Many sleep quite differently on workdays versus days off, a pattern which can lead to chronic circadian desynchronization. Many people look at television and other screens before going to bed, a factor which may exacerbate disruption of the circadian cycle. Scientific studies on sleep have shown that sleep stage at awakening is an important factor in amplifying sleep inertia. Sleep timing is controlled by the circadian clock, sleep-wake homeostasis, to some extent by individual will. Sleep timing depends on hormo
Ivan Petrovich Pavlov was a Russian physiologist known for his work in classical conditioning. From his childhood days Pavlov demonstrated intellectual curiosity along with an unusual energy which he referred to as "the instinct for research". Inspired by the progressive ideas which D. I. Pisarev, the most eminent of the Russian literary critics of the 1860s, I. M. Sechenov, the father of Russian physiology, were spreading, Pavlov abandoned his religious career and devoted his life to science. In 1870, he enrolled in the physics and mathematics department at the University of Saint Petersburg in order to study natural science. Pavlov won the Nobel Prize for Physiology or Medicine in 1904, becoming the first Russian Nobel laureate. A survey in the Review of General Psychology, published in 2002, ranked Pavlov as the 24th most cited psychologist of the 20th century. Pavlov's principles of classical conditioning have been found to operate across a variety of behavior therapies and in experimental and clinical settings, such as educational classrooms and reducing phobias with systematic desensitization.
Ivan Pavlov, the eldest of eleven children, was born in Ryazan, Russian Empire. His father, Peter Dmitrievich Pavlov, was a village Russian orthodox priest, his mother, Varvara Ivanovna Uspenskaya, was a devoted homemaker. As a child, Pavlov willingly participated in house duties such as doing the dishes and taking care of his siblings, he loved to garden, ride his bicycle, row and play gorodki. Although able to read by the age of seven, Pavlov was injured when he fell from a high wall onto a stone pavement; as a result of the injuries he sustained he did not begin formal schooling until he was 11 years old. Pavlov attended the Ryazan church school before entering the local theological seminary. In 1870, however, he left the seminary without graduating in order to attend the university at St. Petersburg. There he took natural science courses. In his fourth year, his first research project on the physiology of the nerves of the pancreas won him a prestigious university award. In 1875, Pavlov completed his course with an outstanding record and received the degree of Candidate of Natural Sciences.
Impelled by his overwhelming interest in physiology, Pavlov decided to continue his studies and proceeded to the Imperial Academy of Medical Surgery. While at the Academy, Pavlov became an assistant to Elias von Cyon, he left the department. After some time, Pavlov obtained a position as a laboratory assistant to Konstantin Nikolaevich Ustimovich at the physiological department of the Veterinary Institute. For two years, Pavlov investigated the circulatory system for his medical dissertation. In 1878, Professor S. P. Botkin, a famous Russian clinician, invited the gifted young physiologist to work in the physiological laboratory as the clinic's chief. In 1879, Pavlov graduated from the Medical Military Academy with a gold medal award for his research work. After a competitive examination, Pavlov won a fellowship at the Academy for postgraduate work; the fellowship and his position as director of the Physiological Laboratory at Botkin's clinic enabled Pavlov to continue his research work. In 1883, he presented his doctor's thesis on the subject of The centrifugal nerves of the heart and posited the idea of nervism and the basic principles on the trophic function of the nervous system.
Additionally, his collaboration with the Botkin Clinic produced evidence of a basic pattern in the regulation of reflexes in the activity of circulatory organs. He was inspired to pursue a scientific career by D. I. Pisarev, a literary critique and natural science advocate of the time and I. M. Sechenov, a Russian physiologist, whom Pavlov described as'The father of physiology'. After completing his doctorate, Pavlov went to Germany where he studied in Leipzig with Carl Ludwig and Eimear Kelly in the Heidenhain laboratories in Breslau, he remained there from 1884 to 1886. Heidenhain was studying digestion in dogs. However, Pavlov perfected the technique by overcoming the problem of maintaining the external nerve supply; the exteriorized section became known as the Pavlov pouch. In 1886, Pavlov returned to Russia to look for a new position, his application for the chair of physiology at the University of Saint Petersburg was rejected. Pavlov was offered the chair of pharmacology at Tomsk University in Siberia and at the University of Warsaw in Poland.
He did not take up either post. In 1890, he was appointed the role of professor of Pharmacology at the Military Medical Academy and occupied the position for five years. In 1891, Pavlov was invited to the Imperial Institute of Experimental Medicine in St. Petersburg to organize and direct the Department of Physiology. Over a 45-year period, under his direction, the Institute became one of the most important centers of physiological research in the world. Pavlov continued to direct the Department of Physiology at the Institute, while taking up the chair of physiology at the Medical Military Academy in 1895. Pavlov would head the physiology department at the Academy continuously for three decades. Starting in 1901, Pavlov was nominated over four successive years for the Nobel Prize in Physiology or Medicine, he did not win the prize until 1904 because his previous nominations were not specific to any discovery, but based on a variety of laboratory findings. When Pavlov received the Nobel Prize it was specified that he did so "in recognition of his work
Clifton is both a suburb of Bristol and the name of one of the city's thirty-five council wards. The Clifton ward includes the areas of Cliftonwood and Hotwells. Other parts of the suburb lie within the ward of Clifton East. Notable places in Clifton include Clifton Suspension Bridge, Clifton Cathedral, Clifton College, The Clifton Club, Bristol Zoo, Goldney Hall and Clifton Down. Clifton is an inner suburb of the English port city of Bristol. Clifton was recorded in the Domesday book as Clistone, the name of the village denoting a'hillside settlement' and referring to its position on a steep hill; until 1898 Clifton St Andrew was a separate civil parish within the Municipal Borough of Bristol. Various sub-districts of Clifton exist, including Whiteladies Road, an important shopping district to the east, Clifton Village, a smaller shopping area near the Avon Gorge to the west. Although the suburb has no formal boundaries, the name Clifton is applied to the high ground stretching from Whiteladies Road in the east to the rim of the Avon Gorge in the west, from Clifton Down and Durdham Down in the north to Cornwallis Crescent in the south.
This area corresponds with the city wards of Clifton and Clifton East, although the former includes the riverside suburb of Hotwells. Clifton is one of the oldest and most affluent areas of the city, much of it having been built with profits from tobacco and the slave trade. Situated to the west of Bristol city centre, it was at one time a separate settlement but became attached to Bristol by continuous development during the Georgian era and was formally incorporated into the city in the 1830s. Grand houses. Although some were detached or semi-detached properties, the bulk were built as terraces, many with three or more floors. One famous terrace is the majestic Royal York Crescent, visible from the Avon Gorge below and looking across the Bristol docks. Berkeley Square and Berkeley Crescent, which were built around 1790, are examples of Georgian architecture. Secluded squares include the triangular Canynge Square; the Whiteladies Picture House on Whiteladies Road was converted into offices and a gymnasium in 2001 but it was re-opened as a cinema by Everyman Cinemas in 2016.
Clifton Lido was built in 1850 but closed to the public in 1990, it was redeveloped and opened again to the public in November 2008. On 17 December 1978 a bomb on Queen's Road in Clifton detonated; the Provisional IRA was responsible. Parts of Clifton itself are now in the process of being pedestrianised. Clifton ward, which includes Hotwells, has a population of 10,452 in 5,007 households, according to adjusted figures for the 2001 census. On the same basis, Clifton East ward has a population of 9,538 in 4,741 households. In Clifton ward, 27% of the adult population is in full-time education. North of Clifton is Durdham Down, a flat and open area, used for recreation purposes. On the western edge of Clifton is Clifton Down, a less open/more wooded area, adjacent to the gorge. Clifton is home to many buildings of the University including Goldney Hall, it has road links to the city centre and outer western suburbs, across the Clifton Suspension Bridge to Leigh Woods in North Somerset. Between 1893 and 1934, it was connected to Hotwells by the Clifton Rocks Railway.
Angela Carter - author Eliza Walker Dunbar - early female doctor Eugénie de Montijo - Empress Eugenie of France, wife of Napoleon III, was a student in Royal York Crescent where she was known as "Carrots" Keith Floyd - restaurateur and TV personality Catherine Grace - founder of St Christopher's School for students with special needs in 1945 W. G. Grace - cricketer and surgeon Francis Greenway - renowned Australian architect and designer of The Clifton Club John Grimshaw - founder of Sustrans and a voice for cyclists in the UK. Sarah Guppy - inventor and collaborator with Isambard Kingdom Brunel Charles Hansom - architect of Clifton College Henry Selby Hele-Shaw - engineer and inventor of the Hele-Shaw clutch, Professor at the University of Bristol Victoria Hughes - carer for prostitutes whilst cleaning the public toilets on Clifton Down Annie Kenney - leading suffragette Thomas MacAulay - historian Peter Nichols - actor and playwright at the Bristol Old Vic Frank Norman - novelist and playwright Peter O'Toole - actor starting his career at the Bristol Old Vic Svetlana Alliluyeva - known as Lana Peters, Stalin's daughter Ellen Sharples and Rolinda Sharples - artist family Tom Stoppard - playwright John Addington Symonds - writer Paule Vézelay - artist William West - artist and builder of Clifton Observatory Lewis Brindley - Videogaming Youtuber and Twitch stream, founder of the Yogscast.
J. D. Sedding - English church architect Elizabeth Martin-Silverstone - Canadian Paleontologist In Frances Burney's novel Evelina, young gentlemen are racing their phaetons on the public highways of Clifton, not without incident. Part of the background to Philippa Gregory's historical novel "A Respectable Trade" – dealing with the slave trade in late 18th-century Bristol – is the start of construction at Clifton a far area outside the city limits as they were at the time. In some passages characters debate whether Clifton could be
Westminster School is an independent day and boarding school in London, located within the precincts of Westminster Abbey. With origins before the 12th century, the educational tradition of Westminster dates back as far as 960, in line with the Abbey's history. Boys are admitted to the Under School to the senior school at age thirteen; the school has around 750 pupils. The school motto, Dat Deus Incrementum, is taken from the New Testament 1 Corinthians 3:6, it is one of the original nine public schools of England as defined by the Clarendon Commission of 1861. Charging up to £7,800 per term for day pupils and £11,264 for boarders in 2014/15, Westminster is the 13th most expensive HMC day school and 10th most expensive HMC boarding school in the UK. Westminster School is the most prestigious academic secondary school in the UK, having achieved the highest percentage of students accepted by Oxbridge colleges over the period 2002–2006, has been ranked as the best boy's school in the country in terms of GCSE results in 2017.
The earliest records of a school at Westminster date back to the 1370s and are held in Westminster Abbey's Muniment Room, with parts of the buildings now used by the school dating back to the 10th century Anglo-Saxon Abbey at Westminster. In their annual accounts the school cites their origin as lying in a decree of Pope Alexander III in 1179 though the evidence for this is unclear. In 1540, Henry VIII ordered the dissolution of the monasteries in England, including that of the powerful Abbots of Westminster, but ensured the School's survival by his royal charter; the Royal College of St. Peter carried on with forty "King's Scholars" financed from the royal purse. By this point Westminster School had become a public school. During Mary I's brief reign the Abbey was reinstated as a Roman Catholic monastery, but the school continued. Elizabeth I refounded the school in 1560, with new statutes to select 40 Queen's Scholars from boys who had attended the school for a year. Queen Elizabeth visited her scholars, although she never signed the statutes nor endowed her scholarships, 1560 is now taken as the date that the school was "founded".
Elizabeth I appointed William Camden as headmaster, he is the only layman known to have held the position until 1937. It was Dr Busby, himself an Old Westminster, who established the reputation of the school for several hundred years, as much by his classical learning as for his ruthless discipline by the birch, immortalised in Pope's Dunciad. Busby prayed publicly Up School for the safety of the Crown, on the day of Charles I's execution, locked the boys inside to prevent their going to watch the spectacle a few hundred yards away. Regardless of politics, he thrashed Puritan boys alike without fear or favour. Busby took part in Oliver Cromwell's funeral procession in 1658, when a Westminster schoolboy, Robert Uvedale, succeeded in snatching the "Majesty Scutcheon" draped on the coffin. Busby remained in office throughout the Civil War and the Commonwealth, when the school was governed by Parliamentary Commissioners, well into the Restoration. In 1679, a group of scholars killed a bailiff, ostensibly in defence of the Abbey's traditional right of sanctuary, but because the man was trying to arrest a consort of the boys.
Dr Busby obtained a royal pardon for his scholars from Charles II and added the cost to the school bills. Until the 19th century, the curriculum was predominantly made up of Latin and Greek, all taught Up School; the Westminster boys were uncontrolled outside school hours and notoriously unruly about town, but the proximity of the school to the Palace of Westminster meant that politicians were well aware of the boys' exploits. After the Public Schools Act 1868, in response to the Clarendon Commission on the financial and other malpractices at nine pre-eminent public schools, the school began to approach its modern form, it was separated from the Abbey, although the organisations remain close and the Dean of Westminster Abbey is ex officio the Chairman of the Governors. There followed a scandalous public and parliamentary dispute lasting a further 25 years, to settle the transfer of the properties from the Canons of the Abbey to the school. School statutes have been made by Order in Council of Queen Elizabeth II.
The Dean of Christ Church and the Master of Trinity College, are ex officio members of the school's governing body. Unusually among public schools, Westminster did not adopt most of the broader changes associated with the Victorian ethos of Thomas Arnold, such as the emphasis on team over individual spirit, the school retained much of its distinctive character. Despite many pressures, including evacuation and the destruction of the school roof during the Blitz, the school refused to move out of the city, unlike other schools such as Charterhouse and St. Paul's, remains in its central London location. Westminster Under School was formed in 1943 in the evacuated school buildings in Westminster, as a distinct preparatory school for day pupils between the ages of eight to 13. Only the separation is new: for example, in the 18th century, Edward Gibbon attended Westminster from the age of 11 and Jeremy Bentham from the age of eight; the Under School has since moved to Vincent Square. Its current Master is Mark O'Donnell
Hans Berger was a German psychiatrist. He is best known as the inventor of electroencephalography in 1924, coining the name, as the discoverer of the alpha wave rhythm known as the "Berger wave". Berger was born in Germany. After attending Casimirianum, where he gained his abitur in 1892, Berger enrolled as a mathematics student at the Friedrich Schiller University of Jena with a view to becoming an astronomer. After one semester, he enlisted for a year of service in the cavalry. During a training exercise, his horse reared and he landed in the path of a horse-drawn cannon; the driver of the artillery battery halted the horses in time, leaving the young Berger shaken but with no serious injuries. His sister, at home many kilometres away, had a feeling he was in danger and insisted their father telegram him; the incident made such an impression on Berger that, years in 1940, he wrote: "It was a case of spontaneous telepathy in which at a time of mortal danger, as I contemplated certain death, I transmitted my thoughts, while my sister, close to me, acted as the receiver."On completion of his military service, obsessed by the idea of how his mind could have carried a signal to his sister, Berger returned to Jena to study medicine with the goal of discovering the physiological basis of "psychic energy".
His central theme became "the search for the correlation between objective activity in the brain and subjective psychic phenomena". After obtaining his medical degree from Jena in 1897, Berger joined the staff of Otto Ludwig Binswanger who held the Chair in psychiatry and neurology at the Jena clinic. Habilitated in 1901, he qualified as a senior university lecturer in 1906 and physician-in-chief in 1912 succeeding Binswanger in 1919, he collaborated with two famous scientists and physicians, Oskar Vogt and Korbinian Brodmann, in their research on lateralization of brain function. Berger married his technical assistant, Baroness Ursula von Bülow, in 1911 and served as an army psychiatrist on the Western front during World War I, he was elected Rector of Jena University in 1927. In 1924, Berger succeeded in recording the first human electroencephalogram. Filled with doubt, he took five years to publish his first paper in 1929 which demonstrated the technique for "recording the electrical activity of the human brain from the surface of the head".
His findings were met with incredulity and derision by the German medical and scientific establishments. Having visited the EEG laboratory at Jena in 1935, American roboticist William Grey Walter noted that Berger:was not regarded by his associates as in the front rank of German psychiatrists, having rather the reputation of being a crank, he seemed to me to be a modest and dignified person, full of good humour, as unperturbed by lack of recognition as he was by the fame it brought upon him. But he had one fatal weakness: he was ignorant of the technical and physical basis of his method, he knew nothing about mechanics or electricity. After British electrophysiologists Edgar Douglas Adrian and B. H. C. Matthews confirmed Berger's basic observations in 1934, the importance of his discoveries in electroencephalography were recognized at an international forum in 1937. By 1938, electroencephalography had gained widespread recognition by eminent researchers in the field, leading to its practical use in diagnosis in the United States and France.
In 1938, at the retirement age of 65, Berger was made Professor Emeritus in Psychology. According to biographers Niedermeyer and Lopes da Silva, the appointment occurred in an unceremonious manner as his relationship with the Nazi regime was strained. Numerous sources report that, given their hostile relationship, the Nazis forced Berger into retirement that same year with a complete ban of any further work on EEG; these biographical accounts were contradicted in 2005 by Ernst Klee, a German journalist specializing in the exposure and documentation of Nazi medical crimes. In 2005, Dr Susanne Zimmermann, medical historian at the University of Jena, found evidence that Berger had not been forced into retirement but had "served on the selection committee for his successor" Berthold Kihn, sacked as a Nazi after the war. Moreover, official records at the University of Jena dating from the 1930s proved that Berger had served on the Erbgesundheitsgericht that imposed sterilizations while his diaries contained anti-Semitic comments.
Dr Zimmermann's findings corroborated research published in Germany in 2003 documenting Berger's invitation by the SS racial hygienist Karl Astel to work for the EGOG in 1941. Berger replied: "I am gladly willing to work again as an assessor at the Court for Genetic Health in Jena, for which I thank you." Berger did not join the SS, SA or Nazi party "despite the significant Nazification of the University of Jena, but was a supporting SS member for self-protection."After a long period of clinical depression, suffering from a severe skin infection, Berger committed suicide by hanging on June 1, 1941 in the southern wing of the clinic. Among his many research interests in neurology, Berger studied brain circulation and brain temperature; however his main contribution to medicine and neurology was the systematic study of the electrical activity of human brain and the development of electroencephalography, following the pioneering work done by Richard Caton in England with animals. In 1924, Berger made the first EEG recording of human brain activity and call
World War II
World War II known as the Second World War, was a global war that lasted from 1939 to 1945. The vast majority of the world's countries—including all the great powers—eventually formed two opposing military alliances: the Allies and the Axis. A state of total war emerged, directly involving more than 100 million people from over 30 countries; the major participants threw their entire economic and scientific capabilities behind the war effort, blurring the distinction between civilian and military resources. World War II was the deadliest conflict in human history, marked by 50 to 85 million fatalities, most of whom were civilians in the Soviet Union and China, it included massacres, the genocide of the Holocaust, strategic bombing, premeditated death from starvation and disease, the only use of nuclear weapons in war. Japan, which aimed to dominate Asia and the Pacific, was at war with China by 1937, though neither side had declared war on the other. World War II is said to have begun on 1 September 1939, with the invasion of Poland by Germany and subsequent declarations of war on Germany by France and the United Kingdom.
From late 1939 to early 1941, in a series of campaigns and treaties, Germany conquered or controlled much of continental Europe, formed the Axis alliance with Italy and Japan. Under the Molotov–Ribbentrop Pact of August 1939, Germany and the Soviet Union partitioned and annexed territories of their European neighbours, Finland and the Baltic states. Following the onset of campaigns in North Africa and East Africa, the fall of France in mid 1940, the war continued between the European Axis powers and the British Empire. War in the Balkans, the aerial Battle of Britain, the Blitz, the long Battle of the Atlantic followed. On 22 June 1941, the European Axis powers launched an invasion of the Soviet Union, opening the largest land theatre of war in history; this Eastern Front trapped most crucially the German Wehrmacht, into a war of attrition. In December 1941, Japan launched a surprise attack on the United States as well as European colonies in the Pacific. Following an immediate U. S. declaration of war against Japan, supported by one from Great Britain, the European Axis powers declared war on the U.
S. in solidarity with their Japanese ally. Rapid Japanese conquests over much of the Western Pacific ensued, perceived by many in Asia as liberation from Western dominance and resulting in the support of several armies from defeated territories; the Axis advance in the Pacific halted in 1942. Key setbacks in 1943, which included a series of German defeats on the Eastern Front, the Allied invasions of Sicily and Italy, Allied victories in the Pacific, cost the Axis its initiative and forced it into strategic retreat on all fronts. In 1944, the Western Allies invaded German-occupied France, while the Soviet Union regained its territorial losses and turned toward Germany and its allies. During 1944 and 1945 the Japanese suffered major reverses in mainland Asia in Central China, South China and Burma, while the Allies crippled the Japanese Navy and captured key Western Pacific islands; the war in Europe concluded with an invasion of Germany by the Western Allies and the Soviet Union, culminating in the capture of Berlin by Soviet troops, the suicide of Adolf Hitler and the German unconditional surrender on 8 May 1945.
Following the Potsdam Declaration by the Allies on 26 July 1945 and the refusal of Japan to surrender under its terms, the United States dropped atomic bombs on the Japanese cities of Hiroshima and Nagasaki on 6 and 9 August respectively. With an invasion of the Japanese archipelago imminent, the possibility of additional atomic bombings, the Soviet entry into the war against Japan and its invasion of Manchuria, Japan announced its intention to surrender on 15 August 1945, cementing total victory in Asia for the Allies. Tribunals were set up by fiat by the Allies and war crimes trials were conducted in the wake of the war both against the Germans and the Japanese. World War II changed the political social structure of the globe; the United Nations was established to foster international co-operation and prevent future conflicts. The Soviet Union and United States emerged as rival superpowers, setting the stage for the nearly half-century long Cold War. In the wake of European devastation, the influence of its great powers waned, triggering the decolonisation of Africa and Asia.
Most countries whose industries had been damaged moved towards economic expansion. Political integration in Europe, emerged as an effort to end pre-war enmities and create a common identity; the start of the war in Europe is held to be 1 September 1939, beginning with the German invasion of Poland. The dates for the beginning of war in the Pacific include the start of the Second Sino-Japanese War on 7 July 1937, or the Japanese invasion of Manchuria on 19 September 1931. Others follow the British historian A. J. P. Taylor, who held that the Sino-Japanese War and war in Europe and its colonies occurred and the two wars merged in 1941; this article uses the conventional dating. Other starting dates sometimes used for World War II include the Italian invasion of Abyssinia on 3 October 1935; the British historian Antony Beevor views the beginning of World War II as the Battles of Khalkhin Gol fought between Japan and the fo
An amplifier, electronic amplifier or amp is an electronic device that can increase the power of a signal. It is a two-port electronic circuit that uses electric power from a power supply to increase the amplitude of a signal applied to its input terminals, producing a proportionally greater amplitude signal at its output; the amount of amplification provided by an amplifier is measured by its gain: the ratio of output voltage, current, or power to input. An amplifier is a circuit. An amplifier can either be a separate piece of equipment or an electrical circuit contained within another device. Amplification is fundamental to modern electronics, amplifiers are used in all electronic equipment. Amplifiers can be categorized in different ways. One is by the frequency of the electronic signal being amplified. For example, audio amplifiers amplify signals in the audio range of less than 20 kHz, RF amplifiers amplify frequencies in the radio frequency range between 20 kHz and 300 GHz, servo amplifiers and instrumentation amplifiers may work with low frequencies down to direct current.
Amplifiers can be categorized by their physical placement in the signal chain. The first practical electrical device which could amplify was the triode vacuum tube, invented in 1906 by Lee De Forest, which led to the first amplifiers around 1912. Today most amplifiers use transistors; the first practical device that could amplify was the triode vacuum tube, invented in 1906 by Lee De Forest, which led to the first amplifiers around 1912. Vacuum tubes were used in all amplifiers until the 1960s–1970s when the transistor, invented in 1947, replaced them. Today, most amplifiers use transistors; the development of audio communication technology in form of the telephone, first patented in 1876, created the need to increase the amplitude of electrical signals to extend the transmission of signals over long distances. In telegraphy, this problem had been solved with intermediate devices at stations that replenished the dissipated energy by operating a signal recorder and transmitter back-to-back, forming a relay, so that a local energy source at each intermediate station powered the next leg of transmission.
For duplex transmission, i.e. sending and receiving in both directions, bi-directional relay repeaters were developed starting with the work of C. F. Varley for telegraphic transmission. Duplex transmission was essential for telephony and the problem was not satisfactorily solved until 1904, when H. E. Shreeve of the American Telephone and Telegraph Company improved existing attempts at constructing a telephone repeater consisting of back-to-back carbon-granule transmitter and electrodynamic receiver pairs; the Shreeve repeater was first tested on a line between Boston and Amesbury, MA, more refined devices remained in service for some time. After the turn of the century it was found that negative resistance mercury lamps could amplify, were tried in repeaters, with little success; the development of thermionic valves starting around 1902, provided an electronic method of amplifying signals. The first practical version of such devices was the Audion triode, invented in 1906 by Lee De Forest, which led to the first amplifiers around 1912.
Since the only previous device, used to strengthen a signal was the relay used in telegraph systems, the amplifying vacuum tube was first called an electron relay. The terms amplifier and amplification, derived from the Latin amplificare, were first used for this new capability around 1915 when triodes became widespread; the amplifying vacuum tube revolutionized electrical technology, creating the new field of electronics, the technology of active electrical devices. It made possible long distance telephone lines, public address systems, radio broadcasting, talking motion pictures, practical audio recording, radar and the first computers. For 50 years all consumer electronic devices used vacuum tubes. Early tube amplifiers had positive feedback, which could increase gain but make the amplifier unstable and prone to oscillation. Much of the mathematical theory of amplifiers was developed at Bell Telephone Laboratories during the 1920s to 1940s. Distortion levels in early amplifiers were high around 5%, until 1934, when Harold Black developed negative feedback.
Other advances in the theory of amplification were made by Hendrik Wade Bode. The vacuum tube was the only amplifying device, other than specialized power devices such as the magnetic amplifier and amplidyne, for 40 years. Power control circuitry used magnetic amplifiers until the latter half of the twentieth century when power semiconductor devices became more economical, with higher operating speeds; the old Shreeve electroacoustic carbon repeaters were used in adjustable amplifiers in telephone subscriber sets for the hearing impaired until the transistor provided smaller and higher quality amplifiers in the 1950s. The replacement of bulky electron tubes with transistors during the 1960s and 1970s created another revolution in electronics, making possible a large class of portable electronic devices, such as the transistor radio developed in 1954. Today, use of vacuum tubes is limited for some high power applications, such as radio transmitters. Beginning in the 1970s, more and more transistors were connected on a single chip thereby creating higher scales of integration (small-scale, medium-scale, large-s