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Search Results: 1 - 10 of 462031 matches for " A. Ohnishi "
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Entropy current for the relativistic Kadanoff-Baym equation and H-theorem in $O(N)$ theory with NLO self-energy of $1/N$ expansion
A. Nishiyama,A. Ohnishi
Physics , 2010, DOI: 10.1143/PTP.126.249
Abstract: We derive an expression of the kinetic entropy current in the nonequilibrium $O(N)$ scalar theory from the Schwinger-Dyson (Kadanoff-Baym) equation with the 1st order gradient expansion. We show that our kinetic entropy satisfies the H-theorem for the leading order of the gradient expansion with the next-to-leading order self-energy of the $1/N$ expansion in the symmetric phase, and that entropy production occurs as the Green's function evolves with an nonzero collision term. Entropy production stops at local thermal equilibrium where the collision term contribution vanishes and the maximal entropy state is realized. Next we also compare our entropy density with that in thermal equilibrium which is given from thermodynamic potential or equivalently 2 particle irreducible effective action. We find that our entropy density corresponds to that in thermal equilibrium with the next-to-leading order skeletons of the $1/N$ expansion if skeletons with energy denominators in momentum integral can be regularized appropriately. We have a possibility that memory correction terms remain in entropy current if not regularized.
Quantum Fluctuations Affect the Critical Properties of Noble Gases
A. Ohnishi,J. Randrup
Physics , 1996, DOI: 10.1103/PhysRevA.55.R3315
Abstract: Interacting argon atoms are simulated with a recently developed quantum Langevin transport treatment that takes approximate account of the quantum fluctuations inherent in microscopic many-body descriptions based on wave packets. The mass distribution of the atomic clusters is affected significantly near the critical temperature and thus it may be important to take account of quantum fluctuations in molecular-dynamics simulations of cluster formation processes.
Quantum Fluctuation Effects on Nuclear Fragment Formation
A. Ohnishi,J. Randrup
Physics , 1996, DOI: 10.1016/S0370-2693(97)00032-4
Abstract: Multifragmentation in Au+Au collisions is investigated at incident energies in the range 100-400 MeV per nucleon by means of a recently developed quantal Langevin model. The inclusion of quantum fluctuations enhances the average multiplicity of intermediate mass fragments, especially in central collisions. This is mainly because the excitation energies of fragments are reduced due to the quantal behavior of intrinsic specific heat.
Inclusion of Quantum Fluctuations in Wave Packet Dynamics
A. Ohnishi,J. Randrup
Physics , 1996, DOI: 10.1006/aphy.1996.5626
Abstract: We discuss a method by which quantum fluctuations can be included in microscopic transport models based on wave packets that are not energy eigenstates. By including the next-to-leading order term in the cumulant expansion of the statistical weight, which corresponds to the wave packets having Poisson energy distributions, we obtain a much improved global description of the quantum statistical properties of the many-body system. In the case of atomic nuclei, exemplified by 12C and 40Ca, the standard liquid-drop results are reproduced at low temperatures and a phase transformation to a fragment gas occurs as the temperature is raised. The treatment can be extended to dynamical scenarios by means of a Langevin force emulating the transitions between the wave packets. The general form of the associated transport coefficients is derived and it is shown that the appropriate microcanonical equilibrium distribution is achieved in the course of the time evolution. Finally, invoking Fermi's golden rule, we derive specific expressions for the transport coefficients and verify that they satisfy the fluctuation-dissipation theorem.
SU(2) Chiral sigma model and the properties of neutron stars
P. K. Sahu,A. Ohnishi
Physics , 2000, DOI: 10.1143/PTP.104.1163
Abstract: We discuss the {\it SU}(2) chiral sigma model in the context of nuclear matter using a mean field approach at high density. In this model we include a dynamically generated isoscalar vector field and higher-order terms in the scalar field. With the inclusion of these, we reproduce the empirical values of the nuclear matter saturation density, binding energy, and nuclear incompressibility. The value of the incompressibility is chosen according to recently obtained heavy-ion collision data. We then apply the same dynamical model to neutron-rich matter in beta equilibrium, related to neutron star structure. The maximum mass and corresponding radius of stable non-rotating neutron stars are found to be in the observational limit.
Inventories and Mixed Duopoly with State-Owned and Labor-Managed Firms  [PDF]
Kazuhiro Ohnishi
iBusiness (IB) , 2010, DOI: 10.4236/ib.2010.22014
Abstract: This paper considers a two-period mixed market model in which a state-owned firm and a labor-managed firm are allowed to hold inventories as a strategic device. The paper then shows that the equilibrium in the second period occurs at the Stackelberg point where the state-owned firm is the leader.
Price-Setting Mixed Duopoly Models with Complementary Goods  [PDF]
Kazuhiro Ohnishi
Modern Economy (ME) , 2010, DOI: 10.4236/me.2010.11003
Abstract: This paper considers domestic (resp. international) Bertrand mixed duopoly competition in which a state-owned welfare-maximizing public firm and a domestic (resp. foreign) profit-maximizing private firm produce complementary goods. The main purpose of the paper is to present and to compare the equilibrium outcomes of the two mixed duopoly models.
Partial Privatization in Price-Setting Mixed Duopolies with Complementary Goods  [PDF]
Kazuhiro Ohnishi
Modern Economy (ME) , 2011, DOI: 10.4236/me.2011.21007
Abstract: We consider a domestic (resp. international) mixed duopoly model in which a domestic public firm and a domestic (resp. foreign) private firm produce complementary goods. First, the domestic government chooses the level of privatization to maximize domestic social welfare. Second, observing the level of privatization, the firms simultaneously and independently choose prices. We present the equilibrium outcomes of the two mixed duopoly models and shows that our result is in marked contrast to that of the price-setting mixed du-opoly model with substitute goods.
Labor Investment in a New International Mixed Market  [PDF]
Kazuhiro Ohnishi
Technology and Investment (TI) , 2010, DOI: 10.4236/ti.2010.12017
Abstract: This paper considers a continuous-time dynamic mixed market model of labor investment decisions of a domestic public firm and a foreign private firm. The paper studies the optimal levels of preemptive investment for the long-run structure of the international mixed market. It is then demonstrated that there are no perfect equilibria in which neither firm invests to its steady-state reaction curve.
Nuclear Matter and Finite Nuclei in the Effective Chiral Model
P. K. Sahu,K. Tsubakihara,A. Ohnishi
Physics , 2009, DOI: 10.1103/PhysRevC.81.014002
Abstract: We systematically investigate the vacuum stability and nuclear properties in the effective chiral model with higher order terms in $\sigma$. We evaluate the model parameters by considering the saturation properties of nuclear matter as well as the normal vacuum to be globally stable at zero and finite baryon densities. We can find parameter sets giving moderate equations of state, and apply these models to finite nuclei.
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