682 research outputs found
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 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 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 BBH mergers up to
redshift . The cumulative event rate is in the Pop III origin model of BBHs like GW150914, and it
saturates at , while in the primordial BBH (PBBH) model, the
cumulative event rate is at
even if only of the dark matter consists of PBHs, and it is
still increasing at . In the Pop I/II model of BBHs, the cumulative event
rate is and it saturates at . 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 is achieved with the definition of Pre-DECIGO in
the Hz band. Pre-DECIGO can measure the mass spectrum and the
-dependence of the merger rate to distinguish various models of BBHs like
GW150914.
Pre-DECIGO can also predict the direction of BBHs at with an accuracy
of and a merging time accuracy of 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
, 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.
[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 in the ac ( 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 . 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 . 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
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