Crossover from negative to positive shear rate dependence in granular friction

We conduct an experiment on the frictional properties of granular matter over a wide range of shear rate that covers both the quasistatic and the inertial regimes. We show that the friction coefficient exhibits negative shear-rate dependence in the quasistatic regime, whereas the shear-rate dependence is positive in the inertial regime. This crossover from negative to positive shear-rate dependence occurs at a critical inertial number. This is explained in terms of the competition between two physical processes, namely frictional healing and anelasticity. We also find that the result does not depend on the shape of the grains and that the behavior in the inertial regime is quantitatively the same as that in numerical simulations.Comment: 4 page

Cyclotron radiation and emission in graphene

Peculiarity in the cyclotron radiation and emission in graphene is theoretically examined in terms of the optical conductivity and relaxation rates to propose that graphene in magnetic fields can be a candidate to realize the Landau level laser, proposed decades ago [H. Aoki, Appl. Phys. Lett. {\bf 48}, 559 (1986)].Comment: 4 pages, 3 figure

Radiative Corrections to Low-Energy Neutrino-Deuteron Reactions Revisited

The one-loop QED and electroweak radiative corrections to neutrino-deuteron scattering induced by the neutral current are reexamined, paying a particular attention to the constant term which has never been treated properly in literature. This problem is closely related to the definition of the axial-vector coupling constant $g_{A}$ and requires thorough calculations of the constant terms in the charged current processes, too. We find that the radiative corrections to the neutral current induced reactions amount to 1.7 (1.5) per cent enhancement, if the Higgs boson mass is $m_{H}=1.5 \: m_{Z} (m_{H}=5.0 \: m_{Z})$ This number happens to be close to that given by Kurylov et al., but we argue that this is accidental.Comment: Talk given at "Particles and Nuclei International Conference" (PANIC'05, at Santa Fe in U.S.A., October 2005), 3 pages, Added reference

Eurographics

The Fluid Implicit Particle method (FLIP) reduces numerical dissipation by combining particles with grids. To improve performance, the subsequent narrow band FLIP method (NB‐FLIP) uses a FLIP‐based fluid simulation only near the liquid surface and a traditional grid‐based fluid simulation away from the surface. This spatially‐limited FLIP simulation significantly reduces the number of particles and alleviates a computational bottleneck. In this paper, we extend the NB‐FLIP idea even further, by allowing a simulation to transition between a FLIP‐like fluid simulation and a grid‐based simulation in arbitrary locations, not just near the surface. This approach leads to even more savings in memory and computation, because we can concentrate the particles only in areas where they are needed. More importantly, this new method allows us to seamlessly transition to smooth implicit surface geometry wherever the particle‐based simulation is unnecessary. Consequently, our method leads to a practical algorithm for avoiding the noisy surface artifacts associated with particle‐based liquid simulations, while simultaneously maintaining the benefits of a FLIP simulation in regions of dynamic motion

Critical behavior of two-dimensional random hopping fermions with \pi-flux

A two dimensional random hopping model with N-species and \pi-flux is studied. The field theory at the band center is shown to be in the universality class of GL(4m,R)/O(4m) nonlinear sigma model. Vanishing beta function suggests delocalised states at the band center. Contrary to the similar universality class with broken time reversal symmetry, the present class is expected to have at least two fixed point. Large N-systems are shown to be in the weak-coupling fixed point, which is characterized by divergent density of state, while small N systems may be in the strong-coupling fixed point.Comment: 12 pages, revtex, 1 figur

Pre-DECIGO can get the smoking gun to decide the astrophysical or cosmological origin of GW150914-like binary black holes

Pre-DECIGO consists of three spacecraft arranged in an equilateral triangle with 100km arm lengths orbiting 2000km above the surface of the earth. It is hoped that the launch date will be in the late 2020s. Pre-DECIGO has one clear target: binary black holes (BBHs) like GW150914 and GW151226. Pre-DECIGO can detect $\sim 30M_\odot-30M_\odot$ BBH mergers up to redshift $z\sim 30$. The cumulative event rate is $\sim 1.8\times 10^{5}\,{\rm events~yr^{-1}}$ in the Pop III origin model of BBHs like GW150914, and it saturates at $z\sim 10$, while in the primordial BBH (PBBH) model, the cumulative event rate is $\sim 3\times 10^{4}\,{\rm events~ yr^{-1}}$ at $z=30$ even if only $0.1\%$ of the dark matter consists of PBHs, and it is still increasing at $z=30$. In the Pop I/II model of BBHs, the cumulative event rate is $(3-10)\times10^{5}\,{\rm events~ yr^{-1}}$ and it saturates at $z \sim 6$. We present the requirements on orbit accuracy, drag free techniques, laser power, frequency stability, and interferometer test mass. For BBHs like GW150914 at 1Gpc, SNR$\sim 90$ is achieved with the definition of Pre-DECIGO in the $0.01-100$Hz band. Pre-DECIGO can measure the mass spectrum and the $z$-dependence of the merger rate to distinguish various models of BBHs like GW150914. Pre-DECIGO can also predict the direction of BBHs at $z=0.1$ with an accuracy of $\sim 0.3\,{\rm deg}^2$ and a merging time accuracy of $\sim 1$s at about a day before the merger so that ground-based GW detectors further developed at that time as well as electromagnetic follow-up observations can prepare for the detection of merger in advance. For intermediate mass BBHs at a large redshift $z > 10$, the QNM frequency after the merger can be within the Pre-DECIGO band so that the ringing tail can also be detectable to confirm the Einstein theory of general relativity with SNR$\sim 35$. [abridged]Comment: 17 pages, 10 figures, added some references, modifications to match the published version in PTE

Optical Hall conductivity in 2DEG and graphene QHE systems

We have revealed from a numerical study that the Hall plateaus are retained in the optical Hall conductivity $\sigma_{xy}(\omega)$ in the ac ($\sim$ THz) regime in both of the ordinary two-dimensional electron gas and graphene in the quantum Hall regime, although the plateau height in ac deviates from integer multiples of $e^2/h$. The effect remains unexpectedly robust against a significant strength of disorder, which we attribute to an effect of localization. We predict the ac Hall plateaus are observable through the Faraday rotation with the rotation angle characterized by the fine-structure constant $\alpha$. In this paper we clarify the relationship between plateau structures and the disorder strength by performing numerical calculation.Comment: 4 pages, 2 figures, EP2DS-18 in Kobe (2009

Low-level laser therapy for spinal cord injury in rats: effects of polarization

Abstract. The effects of laser polarization on the efficacy of near-infrared low-level laser therapy for spinal cord injury (SCI) are presented. Rat spinal cords were injured with a weight-drop device, and the lesion sites were directly irradiated with a linearly polarized 808-nm diode laser positioned either perpendicular or parallel to the spine immediately after the injury and daily for five consecutive days. Functional recovery was assessed daily by an open-field test. Regardless of the polarization direction, functional scores of SCI rats that were treated with the 808-nm laser irradiation were significantly higher than those of SCI alone group (Group 1) from day 5 after injury. The locomotive function of SCI rats irradiated parallel to the spinal column (Group 3) was significantly improved from day 10 after injury, compared to SCI rats treated with the linear polarization perpendicular to the spinal column (Group 2). There were no significant differences in ATP contents in the injured tissue among the three groups. We speculate that the higher efficacy with parallel irradiation is attributable to the deeper light penetration into tissue with anisotropic scattering