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Stefano Fantoni
Stefano Fantoni (born 4 June 1945) is an Italian theoretical physicist, now retired from the International School for Advanced Studies in Trieste (SISSA), still working in the fields of nuclear physics and low temperature physics. The common denominator of his research was to go beyond the mean-field models in solving the so-called many-body theory that occurs in quantum Bose or/and Fermi systems, characterized by the presence of strong correlations among their components. In the seventies he has been the author, together with Sergio Rosati, of the Power Series cluster theory for strongly interacting fermions, known as FR cluster expansion, and later, of the Fermion Hyper Netted Chain (FHNC) integral equations to compute the FR expansion terms at all orders. Such theories have opened up the modern many-body studies on strongly interacting Fermi systems, such as nuclear matter and Quantum fluids. It is due to him and to V. R. Pandharipande and O. Benhar, the extension at al ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Physicist
A physicist is a scientist who specializes in the field of physics, which encompasses the interactions of matter and energy at all length and time scales in the physical universe. Physicists generally are interested in the root or ultimate causes of phenomena, and usually frame their understanding in mathematical terms. Physicists work across a wide range of research fields, spanning all length scales: from sub-atomic and particle physics, through biological physics, to cosmological length scales encompassing the universe as a whole. The field generally includes two types of physicists: experimental physicists who specialize in the observation of natural phenomena and the development and analysis of experiments, and theoretical physicists who specialize in mathematical modeling of physical systems to rationalize, explain and predict natural phenomena. Physicists can apply their knowledge towards solving practical problems or to developing new technologies (also known as applie ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Electron
The electron ( or ) is a subatomic particle with a negative one elementary electric charge. Electrons belong to the first generation of the lepton particle family, and are generally thought to be elementary particles because they have no known components or substructure. The electron's mass is approximately 1/1836 that of the proton. Quantum mechanical properties of the electron include an intrinsic angular momentum ( spin) of a half-integer value, expressed in units of the reduced Planck constant, . Being fermions, no two electrons can occupy the same quantum state, in accordance with the Pauli exclusion principle. Like all elementary particles, electrons exhibit properties of both particles and waves: They can collide with other particles and can be diffracted like light. The wave properties of electrons are easier to observe with experiments than those of other particles like neutrons and protons because electrons have a lower mass and hence a longer de Broglie wavele ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Green's Function (many-body Theory)
In many-body theory, the term Green's function (or Green function) is sometimes used interchangeably with correlation function, but refers specifically to correlators of field operators or creation and annihilation operators. The name comes from the Green's functions used to solve inhomogeneous differential equations, to which they are loosely related. (Specifically, only two-point 'Green's functions' in the case of a non-interacting system are Green's functions in the mathematical sense; the linear operator that they invert is the Hamiltonian operator, which in the non-interacting case is quadratic in the fields.) Spatially uniform case Basic definitions We consider a many-body theory with field operator (annihilation operator written in the position basis) \psi(\mathbf). The Heisenberg operators can be written in terms of Schrödinger operators as \psi(\mathbf,t) = e^ \psi(\mathbf) e^, and the creation operator is \bar\psi(\mathbf,t) = psi(\mathbf,t)\dagger, where K = H - ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Renormalization
Renormalization is a collection of techniques in quantum field theory, the statistical mechanics of fields, and the theory of self-similar geometric structures, that are used to treat infinities arising in calculated quantities by altering values of these quantities to compensate for effects of their self-interactions. But even if no infinities arose in loop diagrams in quantum field theory, it could be shown that it would be necessary to renormalize the mass and fields appearing in the original Lagrangian. For example, an electron theory may begin by postulating an electron with an initial mass and charge. In quantum field theory a cloud of virtual particles, such as photons, positrons, and others surrounds and interacts with the initial electron. Accounting for the interactions of the surrounding particles (e.g. collisions at different energies) shows that the electron-system behaves as if it had a different mass and charge than initially postulated. Renormalization, in th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Eugene Feenberg
Eugene Feenberg (October 6, 1906 in Fort Smith, Arkansas – November 7, 1977) was an American physicist who made contributions to quantum mechanics and nuclear physics. Education In 1929, Feenberg graduated from the University of Texas at Austin in three years, first in his class; he majored in physics and mathematics. Upon the urging of one of his professors, C. P. Boner, Feenberg then went to Harvard University to study with Edwin C. Kemble for a doctorate in physics. While at Harvard, during 1930 and 1931, he also worked part-time at a Raytheon laboratory, as the Great Depression was in full swing. In 1931, Harvard awarded him a Parker Traveling Fellowship; he left for Europe in the fall of that year. During his stay in Europe, he studied with Arnold Sommerfeld at the Ludwig Maximilian University of Munich, Wolfgang Pauli at the Eidgenössische Technische Hochschule Zürich, and Enrico Fermi at the University of Rome. [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Perturbation Theory
In mathematics and applied mathematics, perturbation theory comprises methods for finding an approximate solution to a problem, by starting from the exact solution of a related, simpler problem. A critical feature of the technique is a middle step that breaks the problem into "solvable" and "perturbative" parts. In perturbation theory, the solution is expressed as a power series in a small parameter The first term is the known solution to the solvable problem. Successive terms in the series at higher powers of \varepsilon usually become smaller. An approximate 'perturbation solution' is obtained by truncating the series, usually by keeping only the first two terms, the solution to the known problem and the 'first order' perturbation correction. Perturbation theory is used in a wide range of fields, and reaches its most sophisticated and advanced forms in quantum field theory. Perturbation theory (quantum mechanics) describes the use of this method in quantum mechanics. The ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Vijay Raghunath Pandharipande
Vijay Raghunath Pandharipande (August 7, 1940 – January 3, 2006) was an Indian-American physicist, who played a leading role in the development of the nuclear many-body problem. Biography Pandharipande obtained his bachelor's and master's degree from Nagpur University in 1959 and 1961 respectively. He earned his PhD degree from University of Bombay in 1969. After working at Niels Bohr Institute and Cornell University, Pandharipande joined the University of Illinois at Urbana-Champaign in 1972, becoming a faculty member there in the next year. He became a full professor in 1977 and stayed there the rest of his life. In recognition of his fundamental contributions to determining the structure of light nuclei by solving the Schrödinger problem with more than three nucleons using realistic nucleon-nucleon interactions supplemented by three-body forces, Pandharipande was awarded the prestigious Tom W. Bonner Prize in Nuclear Physics of the American Physical Society in 1999. His ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Quantum Fluid
A quantum fluid refers to any system that exhibits quantum mechanical effects at the macroscopic level such as superfluids, superconductors, ultracold atoms, etc. Typically, quantum fluids arise in situations where both quantum mechanical effects and quantum statistical effects are significant. Most matter is either solid or gaseous (at low densities) near absolute zero. However, for the cases of helium-4 and its isotope helium-3, there is a pressure range where they can remain liquid down to absolute zero because the amplitude of the quantum fluctuations experienced by the helium atoms is larger than the inter-atomic distances. In the case of solid quantum fluids, it is only a fraction of its electrons or protons that behave like a “fluid”. One prominent example is that of superconductivity where quasi-particles made up of pairs of electrons and a phonon act as bosons which are then capable of collapsing into the ground state to establish a supercurrent with a resistivity near ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Nuclear Matter
Nuclear matter is an idealized system of interacting nucleons ( protons and neutrons) that exists in several phases of exotic matter that, as of yet, are not fully established. It is ''not'' matter in an atomic nucleus, but a hypothetical substance consisting of a huge number of protons and neutrons held together by only nuclear forces and ''no'' Coulomb forces. Volume and the number of particles are infinite, but the ratio is finite. Infinite volume implies no surface effects and translational invariance (only differences in position matter, not absolute positions). A common idealization is ''symmetric nuclear matter'', which consists of equal numbers of protons and neutrons, with no electrons. When nuclear matter is compressed to sufficiently high density, it is expected, on the basis of the asymptotic freedom of quantum chromodynamics, that it will become quark matter, which is a degenerate Fermi gas of quarks. Some authors use "nuclear matter" in a broade ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Correlation And Dependence
In statistics, correlation or dependence is any statistical relationship, whether causal or not, between two random variables or bivariate data. Although in the broadest sense, "correlation" may indicate any type of association, in statistics it usually refers to the degree to which a pair of variables are ''linearly'' related. Familiar examples of dependent phenomena include the correlation between the height of parents and their offspring, and the correlation between the price of a good and the quantity the consumers are willing to purchase, as it is depicted in the so-called demand curve. Correlations are useful because they can indicate a predictive relationship that can be exploited in practice. For example, an electrical utility may produce less power on a mild day based on the correlation between electricity demand and weather. In this example, there is a causal relationship, because extreme weather causes people to use more electricity for heating or cooling. However ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Fermion
In particle physics, a fermion is a particle that follows Fermi–Dirac statistics. Generally, it has a half-odd-integer spin: spin , spin , etc. In addition, these particles obey the Pauli exclusion principle. Fermions include all quarks and leptons and all composite particles made of an odd number of these, such as all baryons and many atoms and nuclei. Fermions differ from bosons, which obey Bose–Einstein statistics. Some fermions are elementary particles (such as electrons), and some are composite particles (such as protons). For example, according to the spin-statistics theorem in relativistic quantum field theory, particles with integer spin are bosons. In contrast, particles with half-integer spin are fermions. In addition to the spin characteristic, fermions have another specific property: they possess conserved baryon or lepton quantum numbers. Therefore, what is usually referred to as the spin-statistics relation is, in fact, a spin statistics-quantum numb ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
