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Search Results: 1 - 10 of 2196 matches for " Yosuke Matsumoto "
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Stability Property of Numerical Cherenkov Radiation and its Application to Relativistic Shock Simulations
Naoki Ikeya,Yosuke Matsumoto
Physics , 2014, DOI: 10.1093/pasj/psv052
Abstract: We studied the stability property of numerical Cherenkov radiation in relativistic plasma flows employing particle-in-cell simulations. Using the implicit finite-difference time-domain method to solve Maxwell equations, we found that nonphysical instability was greatly inhibited with a Courant-Friedrichs-Lewy (CFL) number of 1.0. The present result contrasts with recently reported results (Vay, J. L., et al. 2011, J. Comp. Phys, 230, 5908; Godfrey. B., & Vay, J. L. 2013, J. Comp. Phys, 243, 260; Xu, X., et al. 2013, Comput. Phys. Commun, 184, 2503) in which magical CFL numbers in the range 0.5-0.7 were obtained with explicit field solvers. In addition, we found employing higher-order shape functions and an optimal implicitness factor further suppressed long-wavelength modes of the instability. The findings allowed the examination of the long-term evolution of a relativistic collisionless shock without the generation of nonphysical wave excitations in the upstream. This achievement will allow us to investigate particle accelerations in relativistic shocks associated with, for example, gamma-ray bursts.
The Kelvin-Helmholtz instability in Orion: a source of turbulence and chemical mixing
Olivier Berne,Yosuke Matsumoto
Physics , 2012, DOI: 10.1088/2041-8205/761/1/L4
Abstract: Hydrodynamical instabilities are believed to power some of the small scale (0.1-10 pc) turbulence and chemical mixing in the interstellar medium. Identifying such instabilities has always been difficult but recent observations of a wavelike structure (the Ripples) in the Orion nebula have been interpreted as a signature of the Kelvin-Helmholtz instability (KHI), occurring at the interface between the HII region and the molecular cloud. However, this has not been verified theoretically. In this letter, we investigate theoretically the stability of this interface using observational constraints for the local physical conditions. A linear analysis shows that the HII/molecular cloud interface is indeed KH unstable for a certain range of magnetic field orientation. We find that the maximal growth-rates correspond to typical timescales of a few 1e4 years and instability wavelengths of 0.06 to 0.6 pc. We predict that after 2e5 years the KHI saturates and forms a turbulent layer of thickness ~0.5 pc. The KHI can remain in linear phase over a maximum distance of 0.75 pc. These spatial and time scales are compatible with the Ripples representing the linear phase of the KHI. These results suggest that the KHI may be crucial to generate turbulence and to bring heavy elements injected by the winds of massive stars in HII regions to colder regions where planetary systems around low mass stars are being formed. This could apply to the transport of 26Al injected by a massive star in an HII region to the nascent solar-system.
Electron Accelerations at High Mach Number Shocks: Two-Dimensional Particle-In-Cell Simulations in Various Parameter Regimes
Yosuke Matsumoto,Takanobu Amano,Masahiro Hoshino
Physics , 2012, DOI: 10.1088/0004-637X/755/2/109
Abstract: Electron accelerations at high Mach number collision-less shocks are investigated by means of two-dimensional electromagnetic Particle-in-Cell simulations with various Alfven Mach numbers, ion-to-electron mass ratios, and the upstream electron beta_e (the ratio of the thermal pressure to the magnetic pressure). We found electrons are effectively accelerated at a super-high Mach number shock (MA~30) with a mass ratio of M/m=100 and beta_e=0.5. The electron shock surfing acceleration is an effective mechanism for accelerating the particles toward the relativistic regime even in two dimensions with the large mass ratio. Buneman instability excited at the leading edge of the foot in the super-high Mach number shock results in a coherent electrostatic potential structure. While multi-dimensionality allows the electrons to escape from the trapping region, they can interact with the strong electrostatic field several times. Simulation runs in various parameter regimes indicate that the electron shock surfing acceleration is an effective mechanism for producing relativistic particles in extremely-high Mach number shocks in supernova remnants, provided that the upstream electron temperature is reasonably low.
Anomalous specific heat behaviour in the quadrupolar Kondo system PrV2Al20
Masaki Tsujimoto,Yosuke Matsumoto,Satoru Nakatsuji
Physics , 2014, DOI: 10.1088/1742-6596/592/1/012023
Abstract: We have measured the specific heat of PrV$_2$Al$_{20}$ at very low temperatures, using high quality single crystals with the residual resistivity ratio ~ 20. The high-quality single crystals exhibit clear double transitions at $T_{\rm Q} =$ 0.75 K and $T^* =$ 0.65 K. These transitions are clearer and shift to higher temperature in higher quality single crystals. Besides, there was no hysteresis in those transitions in warming and cooling process of the heat capacity measurements. In the ordered state below $T^*$, the specific heat shows a $T^4$ dependence, indicating the gapless mode associated with the quadrupole and/or octupole ordering.
Multi-moment advection scheme in three dimension for Vlasov simulations of magnetized plasma
Takashi Minoshima,Yosuke Matsumoto,Takanobu Amano
Physics , 2012, DOI: 10.1016/j.jcp.2012.11.024
Abstract: We present an extension of the multi-moment advection scheme (Minoshima et al., 2011, J. Comput. Phys.) to the three-dimensional case, for full electromagnetic Vlasov simulations of magnetized plasma. The scheme treats not only point values of a profile but also its zeroth to second order piecewise moments as dependent variables, and advances them on the basis of their governing equations. Similar to the two-dimensional scheme, the three-dimensional scheme can accurately solve the solid body rotation problem of a gaussian profile with little numerical dispersion or diffusion. This is a very important property for Vlasov simulations of magnetized plasma. We apply the scheme to electromagnetic Vlasov simulations. Propagation of linear waves and nonlinear evolution of the electron temperature anisotropy instability are successfully simulated with a good accuracy of the energy conservation.
Multi-Moment Advection scheme for Vlasov simulations
Takashi Minoshima,Yosuke Matsumoto,Takanobu Amano
Physics , 2011, DOI: 10.1016/j.jcp.2011.05.010
Abstract: We present a new numerical scheme for solving the advection equation and its application to Vlasov simulations. The scheme treats not only point values of a profile but also its zeroth to second order piecewise moments as dependent variables, for better conservation of the information entropy. We have developed one- and two-dimensional schemes and show that they provide quite accurate solutions within reasonable usage of computational resources compared to other existing schemes. The two-dimensional scheme can accurately solve the solid body rotation problem of a gaussian profile for more than hundred rotation periods with little numerical diffusion. This is crucially important for Vlasov simulations of magnetized plasmas. Applications of the one- and two-dimensional schemes to electrostatic and electromagnetic Vlasov simulations are presented with some benchmark tests.
Multi-Moment Advection scheme for Vlasov simulations
Takashi Minoshima,Yosuke Matsumoto,Takanobu Amano
Physics , 2012,
Abstract: We present a new numerical scheme for solving the advection equation and its application to the Vlasov simulation. The scheme treats not only point values of a profile but also its zeroth to second order piecewise moments as dependent variables, and advances them on the basis of their governing equations. We have developed one- and two-dimensional schemes and show that they provide quite accurate solutions compared to other existing schemes with the same memory usage. The two-dimensional scheme can solve the solid body rotation problem of a gaussian profile with little numerical diffusion. This is a very important property for Vlasov simulations of magnetized plasma. The application of the scheme to the electromagnetic Vlasov simulation of collisionless shock waves is presented as a benchmark test.
Realistic two-sublattice spin model for the finite-temperature magnetism of NdFe$_{12}$N: toward the next-generation rare-earth-based permanent magnet
Munehisa Matsumoto,Hisazumi Akai,Yosuke Harashima,Shotaro Doi,Takashi Miyake
Physics , 2015,
Abstract: We build a classical spin model ab initio for NdFe$_{12}$N, a material that goes beyond today's champion magnet compound Nd$_{2}$Fe$_{14}$B in its intrinsic magnetic properties. Within our target temperature-range motivated by practical operation of permanent magnets, we have obtained a quantitative agreement with the latest experimental results on the temperature dependence of the magnetization and the anisotropy field. Having put the realistic observables under our numerical control, we propose a scheme for $5d$-electron control over the operation-temperature magnetism to enhance its possible utility.
Heavy Fermion Superconductivity in the Quadrupole Ordered State of PrV2Al20
Masaki Tsujimoto,Yosuke Matsumoto,Takahiro Tomita,Akito Sakai,Satoru Nakatsuji
Physics , 2014, DOI: 10.1103/PhysRevLett.113.267001
Abstract: PrV$_2$Al$_{20}$ is a rare example of a heavy fermion system based on strong hybridization between conduction electrons and nonmagnetic quadrupolar moments of the cubic $\Gamma_3$ ground doublet. Here, we report that a high-quality single crystal of PrV$_2$Al$_{20}$ exhibits superconductivity at $T_{\rm c}=$ 50 mK in the antiferroquadrupole-ordered state under ambient pressure. The heavy fermion character of the superconductivity is evident from the specific heat jump of $\Delta C/T \sim 0.3$ J/mol K$^2$ and the effective mass $m^*/m_0 \sim 140$ estimated from the temperature dependence of the upper critical field. Furthermore, the high-quality single crystals exhibit double transitions at $T_{\rm Q}$ = 0.75 K and $T^{*}$ = 0.65 K associated with quadrupole and octapole degrees of freedom of the $\Gamma_3$ doublet. In the ordered state, the specific heat $C/T$ shows a $T^3$ dependence, indicating the gapless mode associated with the quadrupole and/or octapole order. The strong sensitivity to impurity of the superconductivity suggests unconventional character due to significant quadrupolar fluctuations.
Anisotropic transverse magnetoresistivity in alpha-YbAlB4
Yosuke Matsumoto,Jinpyo Hong,Kentaro Kuga,Satoru Nakatsuji
Physics , 2014, DOI: 10.1088/1742-6596/592/1/012086
Abstract: We measured the transverse magnetoresistivity of the mixed valence compound $\alpha$-YbAlB$_4$. Two configurations were used where current was applied along [110] direction for both and magnetic field was applied along [-110] and $c$-axis. We found the transverse magnetoresistivity is highly anisotropic. In the weak field below 1 T, it is consistent with stronger $c$-$f$ hybridization in the $ab$ plane which was suggested from the previous zero field resistivity measurements. At the higher field above 3 T, we observed a negative transverse magnetoresistivity for the field applied along the $c$-axis. The temperature dependences of the resistivity measured at several different fields suggest the suppression of the heavy fermion behavior at the characteristic field of $\sim 5.5$ T.
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