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Zeldovich
Yakov Borisovich Zeldovich (, ; 8 March 1914 – 2 December 1987), also known as YaB, was a leading Soviet physicist of Belarusian origin, who is known for his prolific contributions in physical cosmology, physics of thermonuclear reactions, combustion, and hydrodynamical phenomena. From 1943, Zeldovich, a self-taught physicist, started his career by playing a crucial role in the development of the former Soviet program of nuclear weapons. In 1963, he returned to academia to embark on pioneering contributions on the fundamental understanding of the thermodynamics of black holes and expanding the scope of physical cosmology. Biography Early life and education Yakov Zeldovich was born into a Belarusian Jewish family in his grandfather's house in Minsk. However, in mid-1914, the Zeldovich family moved to Saint Petersburg. They resided there until August 1941, when the family was evacuated together with the faculty of the Institute of Chemical Physics to Kazan to avoid the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sunyaev–Zeldovich Effect
The Sunyaev–Zeldovich effect (named after Rashid Sunyaev and Yakov B. Zeldovich and often abbreviated as the SZ effect) is the spectral distortion of the cosmic microwave background (CMB) through inverse Compton scattering by high-energy electrons in galaxy clusters, in which the low-energy CMB photons receive an average energy boost during collision with the high-energy cluster electrons. Observed distortions of the cosmic microwave background spectrum are used to detect the disturbance of density in the universe. Using the Sunyaev–Zeldovich effect, dense clusters of galaxies have been observed. Overview The Sunyaev–Zeldovich effect was predicted by Rashid Sunyaev and Yakov Zeldovich to describe anisotropies in the CMB. The effect is caused by the CMB interacting with high energy electrons. These high energy electrons cause inverse Compton scattering of CMB photons which causes a distortion in the radiation spectrum of the CMB. The Sunyaev–Zeldovich effect is mos ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Zeldovich Pancake
A Zeldovich pancake is a theoretical condensation of gas out of a primordial density fluctuation following the Big Bang. In 1970, Yakov B. Zeldovich showed that for an ellipsoid of gas on a supergalactic scale, an approximation can be used that will model the collapse as occurring most rapidly along the shortest axis, resulting in a pancake form. This approximation assumes that the ellipsoid of gas is sufficiently large that the effect of pressure is negligible and only gravitational attraction needs to be considered. That is, the gas will collapse without being significantly perturbed by outward pressure. This assumption is especially valid if the collapse occurs before the recombination era that resulted in the formation of hydrogen atoms. In 1989, Zeldovich and S. F. Shandarin showed that initial overlapping density fluctuations of random Gaussian fields would result in "dense pancakes, filaments, and compact clumps of matter". This model became known as a top-down model of ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Rashid Sunyaev
Rashid Alievich Sunyaev (, ; born 1 March 1943 in Tashkent, USSR) is a German, Soviet, and Russian astrophysicist of Tatar descent. He got his MS degree from the Moscow Institute of Physics and Technology (MIPT) in 1966. He became a professor at MIPT in 1974. Sunyaev was the head of the High Energy Astrophysics Department of the Russian Academy of Sciences, and has been chief scientist of the Academy's Space Research Institute since 1992. He has also been a director of the Max Planck Institute for Astrophysics in Garching, Germany since 1996, and Maureen and John Hendricks Distinguished Visiting Professor in the School of Natural Sciences at the Institute for Advanced Study in Princeton since 2010. In February 2022, he signed an open letter from Russian scientists and science journalists condemning Russia's invasion of Ukraine. Works Sunyaev and Yakov B. Zeldovich developed the theory for the evolution of density fluctuations in the early universe. They predicted the patte ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Alexei Starobinsky
Alexei Alexandrovich Starobinsky (; 19 April 1948 – 21 December 2023) was a Soviet and Russian-Jewish theoretical physicist and cosmologist. He was a pioneer of the theory of cosmic inflation, for which he received the 2014 Kavli Prize in Astrophysics together with Alan Guth and Andrei Linde. Born in Moscow, Starobinsky obtained a degree in physics from Moscow State University in 1972 and a doctorate in theoretical and mathematical physics from the Landau Institute for Theoretical Physics in 1975, the latter under the supervision of Yakov Zeldovich. Starobinsky remained at the Landau Institute, becoming its principal research scientist in 1997 and holding this position until his death. While still a doctoral student, in 1973 he showed that, according to the uncertainty principle, rotating black holes must emit particles. This work led to Stephen Hawking conjecturing Hawking radiation. In 1979, he became the first to propose a model of cosmic inflation, postulating what ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Zeldovich Regularization
Zeldovich regularization refers to a regularization method to calculate divergent integrals and divergent series, that was first introduced by Yakov Zeldovich Yakov Borisovich Zeldovich (, ; 8 March 1914 – 2 December 1987), also known as YaB, was a leading Soviet people, Soviet Physics, physicist of Belarusians, Belarusian origin, who is known for his prolific contributions in physical Physical c ... in 1961. Zeldovich was originally interested in calculating the norm of the Gamow wave function which is divergent since there is an outgoing spherical wave. Zeldovich regularization uses a Gaussian type-regularization and is defined, for divergent integrals, by : \int_0^\infty f(x) dx \equiv \lim_\int_0^\infty f(x) e^ dx. and, for divergent series, byOrlov, Y. V., & Irgaziev, B. F. (2008). On the normalization of the Gamov resonant wave function in the configuration space. Bulletin of the Russian Academy of Sciences: Physics, 72, 1539-1543. :\sum_n c_n \equiv \lim_\sum_ ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Classical Nucleation Theory
Classical nucleation theory (CNT) is the most common theoretical model used to quantitatively study the kinetics of nucleation.H. R. Pruppacher and J. D. Klett, ''Microphysics of Clouds and Precipitation'', Kluwer (1997)P.G. Debenedetti, ''Metastable Liquids: Concepts and Principles'', Princeton University Press (1997) Nucleation is the first step in the spontaneous formation of a new thermodynamic phase or a new structure, starting from a state of metastability. The kinetics of formation of the new phase is frequently dominated by nucleation, such that the time to nucleate determines how long it will take for the new phase to appear. The time to nucleate can vary by orders of magnitude, from negligible to exceedingly large, far beyond reach of experimental timescales. One of the key achievements of classical nucleation theory is to explain and quantify this immense variation. Description The central result of classical nucleation theory is a prediction for the rate of nucleation ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Superradiance
In physics, superradiance, or superradiation, is the radiation enhancement effects in several contexts including quantum mechanics, astrophysics and relativity. Quantum optics In quantum optics, superradiance is a phenomenon that occurs when a group of ''N'' emitters, such as excited atoms, interact with a common light field. If the wavelength of the light is much greater than the separation of the emitters, then the emitters interact with the light in a collective and coherent fashion. This causes the group to emit light as a high-intensity pulse (with rate proportional to ''N''2). This is a surprising result, drastically different from the expected exponential decay (with rate proportional to ''N'') of a group of independent atoms (see spontaneous emission). Superradiance has since been demonstrated in a wide variety of physical and chemical systems, such as quantum dot arrays and J-aggregates. This effect has been used to produce a superradiant laser. Rotational superra ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Zeldovich Mechanism
Zel'dovich mechanism is a chemical mechanism that describes the oxidation of nitrogen and NO''x'' formation, first proposed by the Russian physicist Yakov Borisovich Zel'dovich in 1946. The reaction mechanisms read as : + O _1 + : + O2 _2 + where k_1 and k_2 are the reaction rate constants in Arrhenius law. The overall global reaction is given by : + 2NO The overall reaction rate is mostly governed by the first reaction (i.e., rate-determining reaction), since the second reaction is much faster than the first reaction and occurs immediately following the first reaction. At fuel-rich conditions, due to lack of oxygen, reaction 2 becomes weak, hence, a third reaction is included in the mechanism, also known as extended Zel'dovich mechanism (with all three reactions), : + _3 + Assuming the initial concentration of NO is low and the reverse reactions can therefore be ignored, the forward rate constants of the reactions are given by :\begin k_ &= 1.47\times 10^ \, T^ \m ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Zeldovich Number
The Zeldovich number is a dimensionless number which provides a quantitative measure for the activation energy of a chemical reaction which appears in the Arrhenius exponent, named after the Russian scientist Yakov Borisovich Zeldovich, who along with David A. Frank-Kamenetskii, first introduced in their paper in 1938. In 1983 ICDERS meeting at Poitiers, it was decided that the non-dimensional number will be named after Zeldovich.Clavin, P. (1985). Dynamic behavior of premixed flame fronts in laminar and turbulent flows. Progress in energy and combustion science, 11(1), 1-59. It is defined as :\beta = \frac \cdot \frac where *E_a is the activation energy of the reaction *R is the universal gas constant *T_b is the burnt gas temperature *T_u is the unburnt mixture temperature. In terms of heat release parameter q, it is given by :\beta = \frac \frac For typical combustion phenomena, the value for Zel'dovich number lies in the range \beta\approx 8-20. Activation energy asy ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Antidynamo Theorem
In physics and in particular in the theory of magnetism, an antidynamo theorem is one of several results that restrict the type of magnetic fields that may be produced by dynamo action. One notable example is Thomas Cowling's antidynamo theorem which states that no axisymmetric magnetic field can be maintained through a self-sustaining dynamo action by an axially symmetric current. Similarly, the Zeldovich's antidynamo theorem states that a two-dimensional, planar flow cannot maintain the dynamo action.Zeldovich, Y. B. (1957). The magnetic field in the two-dimensional motion of a conducting turbulent fluid. Sov. Phys. JETP, 4, 460-462. Consequences Apart from the Earth's magnetic field, some other bodies such as Jupiter and Saturn, and the Sun have significant magnetic fields whose major component is a dipole, an axisymmetric magnetic field. These magnetic fields are self-sustained through fluid motion in the Sun or planets, with the necessary non-symmetry for the planets deri ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Matter Power Spectrum
The matter power spectrum describes the density contrast of the universe (the difference between the local density and the mean density) as a function of scale. It is the Fourier transform of the matter correlation function. On large scales, gravity competes with cosmic expansion, and structures grow according to linear theory. In this regime, the density contrast field is Gaussian, Fourier modes evolve independently, and the power spectrum is sufficient to completely describe the density field. On small scales, gravitational collapse is non-linear, and can only be computed accurately using N-body simulations. Higher-order statistics are necessary to describe the full field at small scales. Definition Let \delta(\mathbf x) represent the matter overdensity, a dimensionless quantity defined as: \delta(\mathbf x) = \frac, where \bar\rho is the average matter density over all space. The power spectrum is most commonly understood as the Fourier transform of the autocorrela ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Novodevichy Cemetery
Novodevichy Cemetery () is a cemetery in Moscow. It lies next to the southern wall of the 16th-century Novodevichy Convent, which is the city's third most popular tourist site. History The cemetery was designed by Ivan Mashkov and inaugurated in 1898. Its importance dates from the 1930s, when the necropolises of the medieval Muscovite monasteries (Simonov Monastery, Simonov, Danilov Monastery, Danilov, Donskoy Monastery, Donskoy) were scheduled for demolition. Only the Donskoy survived the Joseph Stalin era relatively intact. The remains of many famous Russians buried in other abbeys, such as Nikolai Gogol and Sergey Aksakov, were disinterred and reburied at the Novodevichy. A 19th-century necropolis within the walls of the Novodevichy convent, which contained the graves of about 2000 Russian noblemen and university professors, also underwent reconstruction. The vast majority of graves were destroyed. It was at that time that the remains of Anton Chekhov were moved outside the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
