- J F Allen building, hosting the School of Physics and Astronomy of the University of St Andrews
- Helium liquifier built by John F. Allen in 1952 at the University of St Andrews
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John F. Allen | |
---|---|
Born | John Frank Allen May 5, 1908 |
Died | April 22, 2001 92) | (aged
Nationality | Canada, England |
Alma mater | University of Manitoba University of Toronto |
Known for | Superfluid phase of matter |
Scientific career | |
Fields | Physics |
Institutions | University of St Andrews |
Doctoral advisor | John McLennan |
John Frank Allen, FRS [1] FRSE (May 5, 1908 – April 22, 2001) was a Canadian physicist. At the same time as Pyotr Leonidovich Kapitsa in Moscow, Don Misener and Allen independently discovered the superfluid phase of matter in 1937 using liquid helium in the Royal Society Mond Laboratory in Cambridge, England. [2]
Allen was born in Winnipeg; he was also known as Jack Allen. His father, Frank Allen, was a professor in physics at the University of Manitoba. [3] John Allen studied physics initially at the University of Manitoba, where he received his bachelor's degree in 1928. Afterwards, he went to the University of Toronto to pursue postgraduate studies. He obtained his master's degree in 1930 [4] and undertook his PhD working with John McLennan about superconductivity. He there developed and built his first cryostat which was taken by John McLennan for a demonstration of superconductivity in a public lecture to the Royal Institution in London. [5] [6] He obtained his PhD degree in 1933. With a two-year US National Research Council Fellowship which he obtained in 1933, [4] he went to work as a postdoctoral researcher at Caltech between 1933 and 1935. [4] In 1935, he joined the Mond Laboratory of the Royal Society in Cambridge to work with Pyotr Kapitsa on low temperature experiments. However, Kapitsa could not return from a visit of his mother in the Soviet Union in 1934 and never returned to Cambridge. So John Allen worked independently of Kapitsa on properties of helium at very low temperatures and published reports on the discovery of superfluidity in helium which were published side by side in Nature in January 1938. [7] [8] Despite the independent discovery at about the same time, the Nobel prize for Superfluidity was awarded only to Kapitsa in 1978. [9]
He stayed in Cambridge until 1947, when he took up an appointment as a professor in natural philosophy at the University of St Andrews, Scotland in 1947. [10]
In 1949, he was elected a Fellow of the Royal Society. [11] During his tenure at the University of St Andrews, he was twice dean of the Faculty of Science, and oversaw the creation of a separate Faculty of Applied Science at Dundee as well as the development of the Science complex on the North Haugh in St Andrews, which opened in 1966.
He was chair of the Very Low Temperature Commission of the International Union of Pure and Applied Physics from 1966 to 1969 and member of the British National Committee for Physics of the Royal Society. [10]
In 1978, he retired, retaining emeritus status until his death. He died in St Andrews in Fife [12] of a stroke. [11]
Allen received an honorary doctorate from Heriot-Watt University in 1984. [13] The building of the School of Physics and Astronomy of the University of St Andrews is named after John Allen, as is the library in the J.F. Allen building.
Allen died of a stroke on 22 April 2001. [14]
Allen married his wife, Elfriede Hiebert, in 1933. The two divorced later. They had one adopted son. [10]
During his work on low temperature physics, Allen developed a number of techniques that are still in use today. In 1937, he introduced the O-ring for use as a seal for vacuum systems. [2] [11] He further invented in 1947 indium gaskets to create leak tight seals for low temperature applications. [4]
In 1937, Allen discovered superfluid helium together with his student Don Misener in the Mond laboratory in Cambridge, independent of Pyotr Kapitsa in Moscow. His student, Ernest Ganz, later observed the second sound in liquid helium, and Allen and his collaborator possibly also measured the third sound that occurs in thin films, however they did not report their results. [2] When World War II broke out and he worked on projects supporting the army. During World War II, this included the development of on-board oxygen generators for bombers, and a variable time fuse for anti-aircraft shells. [10]
Allen also used a movie camera to film his experiments, such as the superfluid helium fountain, which he discovered in 1938 with the help of a pocket flashlight. Over a ten-year period Allen made a movie of the various two-fluid phenomena exhibited by liquid helium-4. The photography of these effects was a real challenge, because liquid helium-4 is essentially transparent. This unique colour movie (the fifth edition was completed in 1982) is one of Allen's great legacies to physics. His was an early user of moving images to document experiments and inform students and the general public.
At some stage (likely in 1984) he modified the long-running St. Andrews pitch drop experiment to bring its setup closer to that of the University of Queensland's similar pitch-drop experiment. [15]
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(help)In condensed matter physics, a Bose–Einstein condensate (BEC) is a state of matter that is typically formed when a gas of bosons at very low densities is cooled to temperatures very close to absolute zero. Under such conditions, a large fraction of bosons occupy the lowest quantum state, at which microscopic quantum-mechanical phenomena, particularly wavefunction interference, become apparent macroscopically. More generally, condensation refers to the appearance of macroscopic occupation of one or several states: for example, in BCS theory, a superconductor is a condensate of Cooper pairs. As such, condensation can be associated with phase transition, and the macroscopic occupation of the state is the order parameter.
Helium is a chemical element; it has symbol He and atomic number 2. It is a colorless, odorless, non-toxic, inert, monatomic gas and the first in the noble gas group in the periodic table. Its boiling point is the lowest among all the elements, and it does not have a melting point at standard pressures. It is the second-lightest and second most abundant element in the observable universe, after hydrogen. It is present at about 24% of the total elemental mass, which is more than 12 times the mass of all the heavier elements combined. Its abundance is similar to this in both the Sun and Jupiter, because of the very high nuclear binding energy of helium-4, with respect to the next three elements after helium. This helium-4 binding energy also accounts for why it is a product of both nuclear fusion and radioactive decay. The most common isotope of helium in the universe is helium-4, the vast majority of which was formed during the Big Bang. Large amounts of new helium are created by nuclear fusion of hydrogen in stars.
Superfluid helium-4 is the superfluid form of helium-4, an isotope of the element helium. A superfluid is a state of matter in which matter behaves like a fluid with zero viscosity. The substance, which resembles other liquids such as helium I, flows without friction past any surface, which allows it to continue to circulate over obstructions and through pores in containers which hold it, subject only to its own inertia.
Heike Kamerlingh Onnes was a Dutch physicist and Nobel laureate. He exploited the Hampson–Linde cycle to investigate how materials behave when cooled to nearly absolute zero and later to liquefy helium for the first time, in 1908. He also discovered superconductivity in 1911.
Lev Davidovich Landau was a Soviet physicist who made fundamental contributions to many areas of theoretical physics. He was considered as one of the last scientists who were universally well-versed and made seminal contributions to all branches of physics.
Pyotr Leonidovich Kapitsa or Peter Kapitza was a leading Soviet physicist and Nobel laureate, whose research focused on low-temperature physics.
Liquid helium is a physical state of helium at very low temperatures at standard atmospheric pressures. Liquid helium may show superfluidity.
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A fermionic condensate is a superfluid phase formed by fermionic particles at low temperatures. It is closely related to the Bose–Einstein condensate, a superfluid phase formed by bosonic atoms under similar conditions. The earliest recognized fermionic condensate described the state of electrons in a superconductor; the physics of other examples including recent work with fermionic atoms is analogous. The first atomic fermionic condensate was created by a team led by Deborah S. Jin using potassium-40 atoms at the University of Colorado Boulder in 2003.
Don Misener (1911–1996) was a physicist. Along with Pyotr Leonidovich Kapitsa and John F. Allen, Misener discovered the superfluid phase of matter in 1937.
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Superfluidity is the characteristic property of a fluid with zero viscosity which therefore flows without any loss of kinetic energy. When stirred, a superfluid forms vortices that continue to rotate indefinitely. Superfluidity occurs in two isotopes of helium when they are liquefied by cooling to cryogenic temperatures. It is also a property of various other exotic states of matter theorized to exist in astrophysics, high-energy physics, and theories of quantum gravity. The theory of superfluidity was developed by Soviet theoretical physicists Lev Landau and Isaak Khalatnikov.
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: CS1 maint: multiple names: authors list (link)Professor Allen says he has altered his apparatus (which was too small to produce separate drips) so that it duplicates more precisely the experiment at Queensland