Month: July 2018
Локна на Шарбојцa
Hartley (unit)
The hartley (symbol Hart), also called a ban, or a dit (short for decimal digit), is a logarithmic unit which measures information or entropy, based on base 10 logarithms and powers of 10, rather than the powers of 2 and base 2 logarithms which define the bit, or shannon. One ban or hartley is the information content of an event if the probability of that event occurring is 1/10.[1] It is therefore equal to the information contained in one decimal digit (or dit), assuming a priori equiprobability of each possible value.
As a bit corresponds to a binary digit, a ban corresponds to a decimal digit. A deciban is one tenth of a ban; the name is formed from ban by the SI prefix deci-.
One hartley corresponds to log2(10) bit = ln(10) nat, or approximately 3.322 Sh,[a] or 2.303 nat. A deciban is about 0.332 Sh.
Though not an SI unit, the hartley is part of the International System of Quantities, defined by International Standard IEC 80000-13 of the International Electrotechnical Commission. It is named after Ralph Hartley.
Ralph Hartley
Ralph Vinton Lyon Hartley (November 30, 1888 – May 1, 1970) was an electronics researcher. He invented the Hartley oscillator and the Hartley transform, and contributed to the foundations of information theory.
Vladimir Kotelnikov
Vladimir Aleksandrovich Kotelnikov (Russian Владимир Александрович Котельников, scientific transliteration Vladimir Alexandrovič Kotelnikov, 6 September 1908 in Kazan – 11 February 2005 in Moscow) was an information theory and radar astronomy pioneer from the Soviet Union. He was elected a member of the Russian Academy of Science, in the Department of Technical Science (radio technology) in 1953. From 30 July 1973 to 25 March 1980 Kotelnikov served as Chairman of the RSFSR Supreme Council.
Harry Nyquist
Harry Nyquist (born Harry Theodor Nyqvist /ˈnaɪkwɪst/, Swedish: [nyːkvɪst]; February 7, 1889 – April 4, 1976) was a Swedish-born American electronic engineer who made important contributions to communication theory.
Hans Bethe
Hans Albrecht Bethe (German: [ˈhans ˈalbʁɛçt ˈbeːtə]; July 2, 1906 – March 6, 2005) was a German-American nuclear physicist who made important contributions to astrophysics, quantum electrodynamics and solid-state physics, and won the 1967 Nobel Prize in Physics for his work on the theory of stellar nucleosynthesis.[1][2]
For most of his career, Bethe was a professor at Cornell University.[3] During World War II, he was head of the Theoretical Division at the secret Los Alamos laboratory which developed the first atomic bombs. There he played a key role in calculating the critical mass of the weapons and developing the theory behind the implosion method used in both the Trinity test and the “Fat Man” weapon dropped on Nagasaki in August 1945.
After the war, Bethe also played an important role in the development of the hydrogen bomb, though he had originally joined the project with the hope of proving it could not be made. Bethe later campaigned with Albert Einstein and the Emergency Committee of Atomic Scientists against nuclear testing and the nuclear arms race. He helped persuade the Kennedy and Nixon administrations to sign, respectively, the 1963 Partial Nuclear Test Ban Treaty and 1972 Anti-Ballistic Missile Treaty (SALT I).
His scientific research never ceased and he was publishing papers well into his nineties, making him one of the few scientists to have published at least one major paper in his field during every decade of his career – which, in Bethe’s case, spanned nearly seventy years. Freeman Dyson, once one of his students, called him the “supreme problem-solver of the 20th century”.[4]
John Archibald Wheeler
John Archibald Wheeler (July 9, 1911 – April 13, 2008) was an American theoretical physicist. He was largely responsible for reviving interest in general relativity in the United States after World War II. Wheeler also worked with Niels Bohr in explaining the basic principles behind nuclear fission. Together with Gregory Breit, Wheeler developed the concept of the Breit–Wheeler process. He is best known for linking the term “black hole” to objects with gravitational collapse already predicted early in the 20th century, for coining the terms “quantum foam“, “neutron moderator“, “wormhole” and “it from bit“, and for hypothesizing the “one-electron universe“.
Wheeler earned his doctorate at Johns Hopkins University under the supervision of Karl Herzfeld, and studied under Breit and Bohr on a National Research Council fellowship. In 1939 he teamed up with Bohr to write a series of papers using the liquid drop model to explain the mechanism of fission. During World War II, he worked with the Manhattan Project‘s Metallurgical Laboratory in Chicago, where he helped design nuclear reactors, and then at the Hanford Site in Richland, Washington, where he helped DuPont build them. He returned to Princeton after the war ended, but returned to government service to help design and build the hydrogen bomb in the early 1950s.
For most of his career, Wheeler was a professor at Princeton University, which he joined in 1938, remaining until his retirement in 1976. At Princeton he supervised 46 PhDs, more than any other professor in the Princeton physics department.
Julian Schwinger
Julian Seymour Schwinger (/ˈʃwɪŋər/; February 12, 1918 – July 16, 1994) was a Nobel Prize winning American theoretical physicist. He is best known for his work on the theory of quantum electrodynamics (QED), in particular for developing a relativistically invariant perturbation theory, and for renormalizing QED to one loop order. Schwinger was a physics professor at several universities.
Schwinger is recognized as one of the greatest physicists of the twentieth century, responsible for much of modern quantum field theory, including a variational approach, and the equations of motion for quantum fields. He developed the first electroweakmodel, and the first example of confinement in 1+1 dimensions. He is responsible for the theory of multiple neutrinos, Schwinger terms, and the theory of the spin 3/2 field.
Fifth force
In physics, the fifth force is a proposed fundamental force, additional to the four known fundamental forces of nature. The conventionally accepted fundamental forces that form the basis of all known interactions are the gravitational, electromagnetic, strong nuclear, and weak nuclear forces. Some speculative theories have proposed a fifth force to explain various anomalous observations that do not fit existing theories; the characteristics of this fifth force depend on the theory being advanced. Many postulate a force roughly the strength of gravity(i.e. it is much weaker than electromagnetism or the nuclear forces) with a range of anywhere from less than a millimeter to cosmological scales. Another proposal is a new weak force, mediated by W’ and Z’ bosons.
The search for a fifth force has increased in recent decades due to the discovery that most of the mass of the universe is accounted for by an unknown form of matter called dark matter. Most physicists believe that dark matter is some new undiscovered subatomic particle, but some believe that it could be related to an unknown fundamental force. It has also recently been discovered that the expansion of the universe is accelerating, which has been attributed to a form of energy called dark energy, and some physicists speculate that a form of dark energy called quintessence could be the fifth force.[1][2][3