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Yakov Zel'dovich
Yakov Borisovich Zeldovich ( be, Я́каў Бары́савіч Зяльдо́віч, russian: Я́ков Бори́сович Зельдо́вич; 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 19 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Minsk
Minsk ( be, Мінск ; russian: Минск) is the capital and the largest city of Belarus, located on the Svislach and the now subterranean Niamiha rivers. As the capital, Minsk has a special administrative status in Belarus and is the administrative centre of Minsk Region (voblast) and Minsk District (raion). As of January 2021, its population was 2 million, making Minsk the 11th most populous city in Europe. Minsk is one of the administrative capitals of the Commonwealth of Independent States (CIS) and the Eurasian Economic Union (EAEU). First documented in 1067, Minsk became the capital of the Principality of Minsk before being annexed by the Grand Duchy of Lithuania in 1242. It received town privileges in 1499. From 1569, it was the capital of the Minsk Voivodeship, an administrative division of the Polish–Lithuanian Commonwealth. It was part of a region annexed by the Russian Empire in 1793, as a consequence of the Second Partition of Poland. From 1919 to 1991, aft ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Zeldovich–Liñán Model
In combustion, Zel'dovich–Liñán model is a two-step reaction model for the combustion processes, named after Yakov Borisovich Zel'dovich and Amable Liñán. The model includes a chain-branching and a chain-breaking (or radical recombination) reaction. The model was first introduced by Zel'dovich in 1948 and later analysed by Liñán using activation energy asymptotics in 1971. The mechanism reads as : \begin \rm + \rm &\rightarrow 2\rm \\ \rm + \rm + \rm &\rightarrow 2\rm +\rm \end where \rm is the fuel, \rm is an intermediate radical, \rm is the third body and \rm is the product. The first reaction is the chain-branching reaction, which is considered to be auto-catalytic (consumes no heat or releases no heat), with very large activation energy and the second reaction is the chain-breaking (or radical-recombination) reaction, where all of the heat in the combustion is released, with almost negligible activation energy In chemistry and physics, activation energy is the minimu ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Zeldovich Spontaneous Wave
A Zeldovich spontaneous wave, also referred to as Zeldovich gradient mechanism, is a reaction wave that propagates spontaneously in a reacting medium with a nonuniform initial temperature distribution when there is no interaction between different fluid elements. The concept was put forward by Yakov Zeldovich in 1980, based on his earlier work with his coworkers. The spontaneous wave is different from the other two conventional combustion waves, namely the subsonic deflagrations and supersonic detonations. The wave, although strictly speaking unrealistic because gasdynamic effects are neglected, is often cited to explain the yet-unsolved problem of deflagration to detonation transition (DDT). The mechanism behind the spontaneous wave is readily explained by considering a reaction medium at rest with a nonuniform temperature distribution such that the spatial temperature gradients are small or at least it is not sufficiently large (large temperature gradients will evidently lead t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Superradiance
In physics, superradiance 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 superradiance Rotational supe ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Zeldovich Pancake
A Zel'dovich pancake is a theoretical condensation of gas out of a primordial density fluctuation following the Big Bang. In 1970, Yakov B. Zel'dovich 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, Zel'dovich 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 o ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Zeldovich Number
The Zel'dovich 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 Zel'dovich, who along with David A. Frank-Kamenetskii, first introduced in their paper in 1938. In 1983 ICDERS meeting at Poitiers, it was decided to name after Zel'dovich.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 \alpha, it is given by :\beta = \frac \alpha For typical combustion phenomena, the value for Zel'dovich number lies in the range \beta\approx 8-20. Activation energy asymptotics Activation energy asymp ... [...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 + . The forward rate constants of the reactions are given by :\begin k_ &= 1.47\times 10^ \, T^ \mathrm e^,\\ k_ &= 6.40\times 10^9 \, T \mathrm e^, \\ k_ &= 3.80\times 10^, \end where the pre-exp ... [...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 nucleati ... [...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 derivi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Deborah Dultzin
Deborah Dultzin Kessler (also published as Deborah Dultzin-Hacyan) is a Mexican astrophysicist specializing in quasars, blazars, active galactic nuclei, and supermassive black holes. She is a professor and researcher in the National Autonomous University of Mexico (UNAM) Institute of Astronomy. Education and career Dultzin is the daughter of Arieh Dulzin, a Zionist activist from Minsk in the Russian Empire and Soviet Union (now Belarus) who emigrated to Mexico in 1928, and to Israel in 1956. Her mother was Fredzia Kessler, an oil painter from Warsaw, Poland, who had also emigrated to Mexico as a child in 1929. She was born in Monterrey in 1945, and grew up with her mother after her father left Mexico. As a high school student and later at UNAM, she loved mathematics but struggled with physics. Nevertheless, she completed a degree in physics in order to aim for a career in astronomy. Her anti-American political stance, and the influence of Guillermo Haro, persuaded her to contin ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Varun Sahni
Varun Bhisham Sahni (born March 29, 1956) is an Indian theoretical physicist, astrophysicist and a Distinguished Professor at the Inter-University Centre for Astronomy and Astrophysics. Known for his research on cosmology, Sahni is an elected fellow of all the three major Indian science academies viz. Indian Academy of Sciences, Indian National Science Academy and National Academy of Sciences, India. The Council of Scientific and Industrial Research, the apex agency of the Government of India for scientific research, awarded him the Shanti Swarup Bhatnagar Prize for Science and Technology, one of the highest Indian science awards, for his contributions to physical sciences in 2000. Sahni is reported to have studied the universe, more specifically its large-scale structure, the early inflationary phase and cosmological constant. His achievements include the establishment of a cosmic no-hair theorem related to inflation, analysis of the universe structure using self-developed statist ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
