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Search Results: 1 - 10 of 139777 matches for " K. Maeda "
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Bipolar Supernova Explosions: Nucleosynthesis & Implication on Abundances in Extremely Metal-Poor Stars
K. Maeda,K. Nomoto
Physics , 2003, DOI: 10.1086/378948
Abstract: Hydrodynamics and explosive nucleosynthesis in bipolar supernova explosions are examined to account for some peculiar properties of hypernovae as well as peculiar abundance patterns of metal-poor stars. The explosion is supposed to be driven by bipolar jets which are powered by accretion onto a central remnant. We explore the features of the explosions with varying progenitors' masses and jet properties. The outcomes are different from conventional spherical models. (1) In the bipolar models, Fe-rich materials are ejected at high velocities along the jet axis, while O-rich materials occupy the central region whose density becomes very high as a consequence of continuous accretion from the side. This configuration can explain some peculiar features in the light curves and the nebular spectra of hypernovae. (2) Production of $^{56}$Ni tends to be smaller than in spherical thermal bomb models. To account for a large amount of $^{56}$Ni observed in hypernovae, the jets should be initiated when the compact remnant mass is still smaller than $2-3\msun$, or the jets should be very massive and slow. (3) Ejected isotopes are distributed as follows in order of decreasing velocities: $^{64}$Zn, $^{59}$Co, $^{56}$Fe, $^{44}$Ti, and $^{4}$He at the highest velocities, $^{55}$Mn, $^{52}$Cr, $^{32}$S, and $^{28}$Si at the intermediate velocities, and $^{24}$Mg, $^{16}$O at the lowest velocities. (4) The abundance ratios (Zn, Co)/Fe are enhanced while the ratios (Mn, Cr)/Fe are suppressed. This can account for the abundance pattern of extremely metal-poor stars. These agreements between the models and observations suggest that hypernovae are driven by bipolar jets and have significantly contributed to the early Galactic chemical evolution.
Jets and Black Holes in Hypernova Explosions
K. Maeda,K. Nomoto
Physics , 2003, DOI: 10.1143/PTPS.151.211
Abstract: Bipolar explosion models for hypernovae (very energetic supernovae), associated with the black hole formation, are presented. The model features are as follows: (1) Fe-peak elements are ejected at high velocities to reach the surface region, while dense O-rich materials occupy the central region at low velocities. (2) The abundance ratios (Zn, Co)/Fe are enhanced while the ratios (Mn, Cr)/Fe are suppressed. The overall abundances are consistent with those observed in extremely metal-poor stars formed at the very early phase of the Galaxy, suggesting significant contribution of such explosions to the early Galactic chemical evolution. (3) Certain relations among the optical luminosity, the chemical composition, and the property of the central remnant are predicted. Such relations may serve for identifying possible gravitational wave emitters in the future.
Significance test for seismicity rate changes before the 1987 Chiba-toho-oki earthquake (M 6.7) Japan
K. Maeda,S. Wiemer
Annals of Geophysics , 1999, DOI: 10.4401/ag-3764
Abstract: A precursory seismic quiescence lasting 1.5 ± 0.5 years was observed prior to the 1987 M 6.7 Chiba-toho-oki earthquake, Central Japan. This event was the largest mainshock to occur in the region in 60 years. A quantitative analysis of the seismicity rates, using two independent catalogs provided by the NIED and JMA networks, shows that the precursory seismic quiescence is centered in the shallower part of the rupture zone of the subsequent mainshock, at a depth of 20-40 km. At the hypocenter of the 1987 Chiba-toho-oki mainshock, a 50% increase in the seismicity rate was detected in the NIED data, coinciding in time with the onset of quiescence (1986.4 ± 0.5). The simultaneous appearance of both quiescence in the shallow part of the rupture zone observed in two catalogs, and a rate increase in the immediate hypocenter region, suggest that these phenomena are causally linked to the subsequent mainshock. However, a quantitative analysis of both catalogs reveals that the precursory quiescence and rate increase are not unique, since rate changes of this duration and significance often occur in the data. A rate change of this significance rating could probably not be detected as a precursor in a real time approach. For the aid of real time monitoring of seismicity rate changes, we introduce the method to calculate the 95-percentile of confidence level for the significant rate changes.
Negative Pressure of Anisotropic Compressible Hall States : Implication to Metrology
K. Ishikawa,N. Maeda
Physics , 2000,
Abstract: Pressure, compressibility, and Hall conductance of anisotropic states at higher Landau levels are computed. Pressure and compressibility become negative. Hall conductance is unquantized and varies with filling factor. These facts agree with the recent experimental observations of highly anisotropic compressible states at higher Landau levels. It is shown, as an implication of negative pressure, that the quantum Hall effect has extraordinary stability, that is, Hall resistance is quantized even when the longitudinal resistance does not vanish.
Unusual Properties of Anisotropic Hall Gas: Implication to Metrology of the Integer Quantum Hall Effect
K. Ishikawa,N. Maeda
Physics , 2001,
Abstract: Physical properties of anisotropic compressible quantum Hall states and their implications to integer quantum Hall effect are studied based on a mean field theory on the von Neumann lattice. It is found that the Hall gas has unusual thermodynamic properties such as negative pressure and negative compressibility and unusual transport properties. Transport properties and density profile of Hall gas states at half fillings agree with those of anisotropic states discovered experimentally in higher Landau levels. Hall gas formed in the bulk does not spread but shrinks, owing to negative pressure, and a strip of Hall gas gives abnormal electric transport at finite temperature. Conductances at finite temperature and finite injected current agree with recent experiments on collapse and breakdown phenomena of the integer quantum Hall effect. As a byproduct, existence of new quantum Hall regime, dissipative quantum Hall regime, in which Hall resistance is quantized exactly even in the system of small longitudinal resistance is derived.
Pressure, Resistance, and Current Activation of Anisotropic Compressible Hall States
K. Ishikawa,N. Maeda
Physics , 2000, DOI: 10.1016/S0921-4526(01)00292-7
Abstract: Thermodynamic and electric properties of anisotropic compressible Hall states at higher Landau levels are studied using a mean field theory on the von Neumann lattice basis. It is shown that resistances agree with the recent experiments of anisotropic compressible states and the states have negative pressure. As implications, the collapse phenomena of the integer quantum Hall effect are discussed.
Pre-Service Elementary Generalist Teachers’ Past Experiences in Elementary Physical Education and Influence of These Experiences on Current Beliefs
Lynn Randall,Julienne K. Maeda
Brock Education : a Journal of Educational Research and Practice , 2010,
Abstract: A lack of formal training in physical education leave pre-service generalist teachers little choice but to remember their past experiences for lesson ideas. Past experiences as elementary students may shape what and how pre-service generalists will teach. This study explored the past experiences of pre-service generalists teachers and the extent those experiences shape what they see as the purposes for elementary physical education. Findings indicate past experiences can influence current views. The implications for teacher education are discussed.
Pre-Service Elementary Generalist Teachers’ Past Experiences in Elementary Physical Education and Influence of These Experiences on Current Beliefs
Lynn Randall,Julienne K. Maeda
Brock Education : a Journal of Educational Research and Practice , 2010,
Abstract: A lack of formal training in physical education leave pre-service generalist teachers little choice but to remember their past experiences for lesson ideas. Past experiences as elementary students may shape what and how pre-service generalists will teach. This study explored the past experiences of pre-service generalists teachers and the extent those experiences shape what they see as the purposes for elementary physical education. Findings indicate past experiences can influence current views. The implications for teacher education are discussed. Keywords: elementary generalist teachers, physical education, teacher beliefs, past experiences
Is Hall Conductance in Hall Bar Geometry a Topological Invariant?
K. Ishikawa,N. Maeda,K. Tadaki
Physics , 1994,
Abstract: A deep connection between the Hall conductance in realistic situation and a topological invariant is pointed out based on von-Neumann lattice representation in which Landau level electrons have minimum spatial extensions. We show that the Hall conductance has no finite size correction in quantum Hall regime, but a coefficient of induced Chern-Simons term in QED$_3$ has a small finite size correction, although both of them are similar topological invariant.
Magnetic von-Neumann lattice for two-dimensional electrons in the magnetic field
K. Ishikawa,N. Maeda,K. Tadaki
Physics , 1994, DOI: 10.1103/PhysRevB.51.5048
Abstract: One-particle eigenstates and eigenvalues of two-dimensional electrons in the strong magnetic field with short range impurity and impurities, cosine potential, boundary potential, and periodic array of short range potentials are obtained by magnetic von-Neumann lattice in which Landau level wave functions have minimum spatial extensions. We find that there is a dual correspondence between cosine potential and lattice kinetic term and that the representation based on the von-Neumann lattice is quite useful for solving the system's dynamics.
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