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Search Results: 1 - 10 of 138842 matches for " Sumiyoshi K "
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Numerical modeling of core-collapse supernovae and compact objects
K. Sumiyoshi
Physics , 2012, DOI: 10.1017/S1743921312023186
Abstract: Massive stars (M> 10Msun) end their lives with spectacular explosions due to gravitational collapse. The collapse turns the stars into compact objects such as neutron stars and black holes with the ejection of cosmic rays and heavy elements. Despite the importance of these astrophysical events, the mechanism of supernova explosions has been an unsolved issue in astrophysics. This is because clarification of the supernova dynamics requires the full knowledge of nuclear and neutrino physics at extreme conditions, and large-scale numerical simulations of neutrino radiation hydrodynamics in multi-dimensions. This article is a brief overview of the understanding (with difficulty) of the supernova mechanism through the recent advance of numerical modeling at supercomputing facilities. Numerical studies with the progress of nuclear physics are applied to follow the evolution of compact objects with neutrino emissions in order to reveal the birth of pulsars/black holes from the massive stars.
Thermal history of the string universe
H. Cateau,K. Sumiyoshi
Physics , 1992, DOI: 10.1103/PhysRevD.46.2366
Abstract: Thermal history of the string universe based on the Brandenberger and Vafa's scenario is examined. The analysis thereby provides a theoretical foundation of the string universe scenario. Especially the picture of the initial oscillating phase is shown to be natural from the thermodynamical point of view. A new tool is employed to evaluate the multi state density of the string gas. This analysis points out that the well-known functional form of the multi state density is not applicable for the important region $T \leq T_H$, and derives a correct form of it.
Quantum entanglement inferred by the principle of maximum Tsallis entropy
Sumiyoshi Abe,A. K. Rajagopal
Physics , 1999, DOI: 10.1103/PhysRevA.60.3461
Abstract: The problem of quantum state inference and the concept of quantum entanglement are studied using a non-additive measure in the form of Tsallis entropy indexed by the positive parameter q. The maximum entropy principle associated with this entropy along with its thermodynamic interpretation are discussed in detail for the Einstein-Podolosky-Rosen pair of two spin-1/2 particles. Given the data on the Bell-Clauser-Horne-Shimony-Holt observable, the analytic expression is given for the inferred quantum entangled state. It is shown that for q greater than unity, indicating the sub-additive feature of the Tsalls entropy, the entangled region is small and enlarges as one goes into super-additive regime where q is less than unity. It is also shown that quantum entanglement can be quantified by the generalized Kullback-Leibler entropy.
Implications of Form Invariance to the Structure of Nonextensive Entropies
A. K. Rajagopal,Sumiyoshi Abe
Physics , 1999, DOI: 10.1103/PhysRevLett.83.1711
Abstract: The form invariance of the statement of the maximum entropy principle and the metric structure in quantum density matrix theory, when generalized to nonextensive situations, is shown here to determine the structure of the nonextensive entropies. This limits the range of the nonextensivity parameter to so as to preserve the concavity of the entropies. The Tsallis entropy is thereby found to be appropriately renormalized.
Validity of the second law in nonextensive quantum thermodynamics
Sumiyoshi Abe,A. K. Rajagopal
Physics , 2003, DOI: 10.1103/PhysRevLett.91.120601
Abstract: The second law of thermodynamics in nonextensive statistical mechanics is discussed in the quantum regime. Making use of the convexity property of the generalized relative entropy associated with the Tsallis entropy indexed by q, Clausius' inequality is shown to hold in the range of q between zero and two. This restriction on the range of the entropic index, q, is purely quantum mechanical and there exists no upper bound of q for validity of the second law in classical theory.
Quantum dynamics in view of Einstein's theory of Brownian motion
Sumiyoshi Abe,A. K. Rajagopal
Physics , 2005,
Abstract: A quantum-mechanical version of Einstein's 1905 theory of Brownian motion is presented. Starting from the Hamiltonian dynamics of an isolated composite of objective and environmental systems, subdynamics for the objective system is derived in the spirit of Einstein. The resulting master equation is found to have the Lindblad structure.
Properties of convergence of nonextensive statistical distribution to the Levy distribution
Sumiyoshi Abe,A. K. Rajagopal
Physics , 2000,
Abstract: It is shown that the distribution derived from the principle of maximum Tsallis entropy is a superposable Levy-type distribution. Concomitantly, the leading order correction to the limit distribution is also deduced. This demonstration fills an important gap in the derivation of the Levy-stable distribution from the nonextensive statistical framework.
Levy distribution in half space based on nonextensive statistical mechanics
A. K. Rajagopal,Sumiyoshi Abe
Physics , 2000,
Abstract: Probability distributions defined on the half space are known to be quite different from those in the full space. Here, a nonextensive entropic treatment is presented for the half space in an analytic and self-consistent way. In this development, the ordinary first moment of the random variable X is divergent in contrast to the case of the full space. A general (nu)-th moment of X is considered as a constraint in the principle of maximum Tsallis entropy. The infinite divisibility of the distribution with an arbitrary (nu) larger than zero and convergence of its N-fold convolution to the exact Levy-stable distribution is discussed in detail. A feature of this derivation is that the Levy index is related to both the values of (nu) and the index of nonextensivity.
Towards Nonadditive Quantum Information Theory
Sumiyoshi Abe,A. K. Rajagopal
Physics , 2000,
Abstract: A definition of the nonadditive (nonextensive) conditional entropy indexed by q is presented. Based on the composition law in terms of it, the Shannon-Khinchin axioms are generalized and the uniqueness theorem is established for the Tsallis entropy. The nonadditive conditional entropy, when considered in the quantum context, is always positive for separable states but takes negative values for entangled states, indicating its utility for characterizing entanglement. A criterion deduced from it for separability of the density matrix is examined in detail by using a bipartite spin-half system. It is found that the strongest criterion for separability obtained by Peres using an algebraic method is recovered in the present information-theoretic approach.
Justification of Power-Law Canonical Distributions Based on Generalized Central Limit Theorem
Sumiyoshi Abe,A. K. Rajagopal
Physics , 2000, DOI: 10.1209/epl/i2000-00481-1
Abstract: A self-consistent thermodynamic framework is presented for power-law canonical distributions based on the generalized central limit theorem by extending the discussion given by Khinchin for deriving Gibbsian canonical ensemble theory. The thermodynamic Legendre transform structure is invoked in establishing its connection to nonextensive statistical mechanics.
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