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Search Results: 1 - 10 of 4716 matches for " Kei Sato "
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An integrated IDTIMS, EVTIMS and SHRIMP zircon dating study
SATO KEI
Anais da Academia Brasileira de Ciências , 2002,
Abstract:
Espectrometria de Massas em Geologia Isotópica
Kei Sato,Koji Kawashita
Geologia USP : Série Científica , 2002,
Abstract: The present paper discusses the main types of mass spectrometers available in 2002 (TIMS, ICP-MS, SIMS andelectron impact-MS) with application to isotope geology and especially to geochronology. Brief comments on theprinciples of operation of the main components, ionization sources, mass analyzers and ion detectors are made. Finally,the performance of the different types of spectrometers is compared.
Spin-Down of Neutron Stars and Compositional Transitions in the Cold Crustal Matter
Kei Iida,Katsuhiko Sato
Physics , 1996, DOI: 10.1086/303685
Abstract: Transitions of nuclear compositions in the crust of a neutron star induced by stellar spin-down are evaluated at zero temperature. We construct a compressible liquid-drop model for the energy of nuclei immersed in a neutron gas, including pairing and shell correction terms, in reference to the known properties of the ground state of matter above neutron drip density, $4.3 \times 10^{11} g cm^{-3}$. Recent experimental values and extrapolations of nuclear masses are used for a description of matter at densities below neutron drip. Changes in the pressure of matter in the crust due to the stellar spin-down are calculated by taking into account the structure of the crust of a slowly and uniformly rotating relativistic neutron star. If the initial rotation period is $\sim$ ms, these changes cause nuclei, initially being in the ground-state matter above a mass density of about $3 \times 10^{13} g cm^{-3}$, to absorb neutrons in the equatorial region where the matter undergoes compression, and to emit them in the vicinity of the rotation axis where the matter undergoes decompression. Heat generation by these processes is found to have significant effects on the thermal evolution of old neutron stars with low magnetic fields; the surface emission predicted from this heating is compared with the $ROSAT$ observations of X-ray emission from millisecond pulsars and is shown to be insufficient to explain the observed X-ray luminosities.
Effects of hyperons on the dynamical deconfinement transition in cold neutron star matter
Kei Iida,Katsuhiko Sato
Physics , 1998, DOI: 10.1103/PhysRevC.58.2538
Abstract: The influence of the presence of hyperons in dense hadronic matter on the quantum nucleation of quark matter is examined at low temperatures relevant to neutron star cores. We calculate the equation of state and the composition of matter before and after deconfinement by using a relativistic mean-field theory and an MIT bag model, respectively; the case in which hyperons are present in the hadronic system is considered, together with the case of the system without hyperons. We find that strangeness contained in hyperons acts to reduce a density jump at deconfinement as well as a lepton fraction in the hadronic phase. As a result of these reductions, a quark matter droplet being in a virtual or real state has its effective mass lightened and its electric charge diminished into nearly zero. The Coulomb screening of leptons on the droplet charge, which has significance to the droplet growth after nucleation in the absence of hyperons, is thus shown to be of little consequence. If the effective droplet mass is small enough to become comparable to the height of the potential barrier, the effect of relativity brings about an exponential increase in the rate of droplet formation via quantum tunneling, whereas the role played by energy dissipation in decelerating the droplet formation, dominant for matter without hyperons, becomes of less importance. For matter with and without hyperons, we estimate the overpressure needed to form the first droplet in the star during the compression due to stellar spin-down or mass accretion from a companion star. The temperature at which a crossover from the quantum nucleation to the Arrhenius-type thermal nucleation takes place is shown to be large compared with the temperature of matter in the core.
Quantum Nucleation of Two-Flavor Quark Matter in Neutron Stars
Kei Iida,Katsuhiko Sato
Physics , 1997, DOI: 10.1143/PTP.98.277
Abstract: Rates for nucleation of two-flavor quark matter in a neutron star core, originally composed of nuclear matter in $\beta$ equilibrium, are calculated at zero temperature by a quantum tunneling analysis incorporating the electrostatic energy. We find that a nucleated droplet would develop into bulk matter due to electron screening effects.
Gender Differences in Coffee Consumption and Its Effects in Young People  [PDF]
Shinichi Demura, Hiroki Aoki, Toshihide Mizusawa, Kei Soukura, Masahiro Noda, Toshiro Sato
Food and Nutrition Sciences (FNS) , 2013, DOI: 10.4236/fns.2013.47096
Abstract: This study aimed to examine gender differences in coffee consumption and awareness of its effects in young people. To examine the above problem, a survey was conducted in 1189 young people (567 males aged 19.3 ± 1.5 years; 622 females aged 19.1 ± 1.2 years). The coffee consumption rate was significantly higher in males (50.8%) than in females (32.8%). In the coffee consumption group, no significant differences were found in the reasons for consumption, the components of coffee, and its effects on health. In the coffee nonconsumption group, significant gender differences were noted in the reasons for avoiding coffee; females (64.8%) disliked its taste more than males (39.4%). More young people of both genders in the consumption group were aware that coffee contains caffeine (79.9% - 86.5%) as compared with the nonconsumption group (67.0% - 74.2%). However, few people in both groups were aware about the components other than caffeine. In addition, more people in the nonconsumption group were unaware of the adverse effects of coffee on the body. The results of this study demonstrated that young males drink coffee more than young females. Among those who avoided coffee consumption, females disliked its taste more than males. Many people regardless of coffee consumption were aware about the components of coffee, but few knew about the other ingredients in this beverage. In addition, few people were aware of the negative effects of coffee on the health and body.
Thermodynamic properties of nuclear "pasta" in neutron star crusts
Gentaro Watanabe,Kei Iida,Katsuhiko Sato
Physics , 2000, DOI: 10.1016/S0375-9474(00)00197-4
Abstract: Equilibrium phase diagrams for neutron star matter at subnuclear densities are obtained at zero temperature. Spherical, rod-like and slab-like nuclei as well as spherical and rod-like nuclear bubbles are taken into account by using a compressible liquid-drop model. This model is designed to incorporate uncertainties in the nuclear surface tension and in the proton chemical potential in a gas of dripped neutrons. The resultant phase diagrams show that for typical values of these quantities, the phases with rod-like nuclei and with slab-like nuclei occur in the form of Coulomb lattice at densities below a point where the system becomes uniform. Thermal fluctuations leading to displacements of such nuclei from their equilibrium positions are considered through explicit evaluations of their elastic constants; these fluctuations can be effective at destroying the layered lattice of slab-like nuclei in the temperature region typical of matter in the neutron star crust.
Formation of Nuclear "Pasta" in Cold Neutron Star Matter
Kei Iida,Gentaro Watanabe,Katsuhiko Sato
Physics , 2001, DOI: 10.1143/PTP.106.551
Abstract: Formation and decay of rod-like and slab-like nuclei, as may be encountered in the outer parts of neutron stars, are examined within a zero-temperature stability analysis with respect to perturbations inducing fission and proton clustering. The nonspherical nuclei are found to be stable against these perturbations, implying the possibility that the size of the stellar region containing such nuclei exceeds the equilibrium prediction.
Application of chaos degree to some dynamical systems
Kei Inoue,Masanori Ohya,Keiko Sato
Physics , 1998,
Abstract: Chaos degree defined through two complexities in information dynamics is applied to some deterministic dynamical models. It is shown that this degree well describes the chaostic feature of the models.
Effects of Neutrino Trapping on Thermodynamic Properties of Nuclear ``Pasta''
Gentaro Watanabe,Kei Iida,Katsuhiko Sato
Physics , 2000, DOI: 10.1016/S0375-9474(00)00585-6
Abstract: Geometrical structure of matter at subnuclear densities is investigated in the presence of a degenerate gas of neutrinos as encountered in stellar collapse. The crystalline phases with spherical, cylindrical and planar nuclei as well as with spherical and cylindrical nuclear bubbles are considered by using a compressible liquid-drop model. This model allows for uncertainties in the lepton fraction $Y_{\rm L}$ in addition to those in the nuclear surface tension $E_{\rm surf}$ and in the proton chemical potential in bulk neutron matter $\mu_{\rm p}^{(0)}$. The phase diagrams obtained at zero temperature show that only the phases with rod-like and slab-like nuclei occur at typical values of $Y_{\rm L}$, $E_{\rm surf}$ and $\mu_{\rm p}^{(0)}$, whereas the bubble phases, especially with spherical bubbles, are at best expected at hypothetically low values of $Y_{\rm L}$ and/or $E_{\rm surf}$. For the rod-like and slab-like nuclei, thermally induced displacements are calculated from their respective elastic constants. It is found that at temperatures appropriate to supernova cores, thermal fluctuations would destroy the layered lattice of slab-like nuclei almost independently of the nuclear models and of the degree of the neutrino degeneracy.
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