50,362 research outputs found
Pulsar Velocity with Three-Neutrino Oscillations in Non-adiabatic Processes
We have studied the position dependence of neutrino energy on the
Kusenko-Segr\`{e} mechanism as an explanation of the proper motion of pulsars.
The mechanism is also examined in three-generation mixing of neutrinos and in a
non-adiabatic case. The position dependence of neutrino energy requires the
higher value of magnetic field such as Gauss in order
to explain the observed proper motion of pulsars. It is shown that possible
non-adiabatic processes decrease the neutrino momentum asymmetry, whereas an
excess of electron neutrino flux over other flavor neutrino fluxes increases
the neutrino momentum asymmetry. It is also shown that a general treatment with
all three neutrinos does not modify the result of the two generation treatment
if the standard neutrino mass hierarchy is assumed.Comment: 8 pages, REVTEX, no figure
Scalable Mining of Common Routes in Mobile Communication Network Traffic Data
A probabilistic method for inferring common routes from mobile communication network traffic data is presented. Besides providing mobility information, valuable in a multitude of application areas, the method has the dual purpose of enabling efficient coarse-graining as well as anonymisation by mapping individual sequences onto common routes. The approach is to represent spatial trajectories by Cell ID sequences that are grouped into routes using locality-sensitive hashing and graph clustering. The method is demonstrated to be scalable, and to accurately group sequences using an evaluation set of GPS tagged data
Shockley-Ramo theorem and long-range photocurrent response in gapless materials
Scanning photocurrent maps of gapless materials, such as graphene, often
exhibit complex patterns of hot spots positioned far from current-collecting
contacts. We develop a general framework that helps to explain the unusual
features of the observed patterns, such as the directional effect and the
global character of photoresponse. We show that such a response is captured by
a simple Shockley-Ramo-type approach. We examine specific examples and show
that the photoresponse patterns can serve as a powerful tool to extract
information about symmetry breaking, inhomogeneity, chirality, and other local
characteristics of the system.Comment: 7 pgs, 3 fg
Disorder-Assisted Electron-Phonon Scattering and Cooling Pathways in Graphene
We predict that graphene is a unique system where disorder-assisted
scattering (supercollisions) dominates electron-lattice cooling over a wide
range of temperatures, up to room temperature. This is so because for
momentum-conserving electron-phonon scattering the energy transfer per
collision is severely constrained due to a small Fermi surface size. The
characteristic temperature dependence and power-law cooling dynamics
provide clear experimental signatures of this new cooling mechanism. The
cooling rate can be changed by orders of magnitude by varying the amount of
disorder which offers means for a variety of new applications that rely on
hot-carrier transport.Comment: 4 pgs, 2 fg
Connections of activated hopping processes with the breakdown of the Stokes-Einstein relation and with aspects of dynamical heterogeneities
We develop a new extended version of the mode-coupling theory (MCT) for glass
transition, which incorporates activated hopping processes via the dynamical
theory originally formulated to describe diffusion-jump processes in crystals.
The dynamical-theory approach adapted here to glass-forming liquids treats
hopping as arising from vibrational fluctuations in quasi-arrested state where
particles are trapped inside their cages, and the hopping rate is formulated in
terms of the Debye-Waller factors characterizing the structure of the
quasi-arrested state. The resulting expression for the hopping rate takes an
activated form, and the barrier height for the hopping is ``self-generated'' in
the sense that it is present only in those states where the dynamics exhibits a
well defined plateau. It is discussed how such a hopping rate can be
incorporated into MCT so that the sharp nonergodic transition predicted by the
idealized version of the theory is replaced by a rapid but smooth crossover. We
then show that the developed theory accounts for the breakdown of the
Stokes-Einstein relation observed in a variety of fragile glass formers. It is
also demonstrated that characteristic features of dynamical heterogeneities
revealed by recent computer simulations are reproduced by the theory. More
specifically, a substantial increase of the non-Gaussian parameter, double-peak
structure in the probability distribution of particle displacements, and the
presence of a growing dynamic length scale are predicted by the extended MCT
developed here, which the idealized version of the theory failed to reproduce.
These results of the theory are demonstrated for a model of the Lennard-Jones
system, and are compared with related computer-simulation results and
experimental data.Comment: 13 pages, 5 figure
Tensor coupling effects on spin symmetry in anti-Lambda spectrum of hypernuclei
The effects of -tensor coupling on the spin
symmetry of spectra in -nucleus systems have
been studied with the relativistic mean-field theory. Taking
C+ as an example, it is found that the tensor coupling
enlarges the spin-orbit splittings of by an order of magnitude
although its effects on the wave functions of are negligible.
Similar conclusions has been observed in -nucleus of different
mass regions, including O+, Ca+ and
Pb+. It indicates that the spin symmetry in
anti-lambda-nucleus systems is still good irrespective of the tensor coupling.Comment: 12 pages, 3 figures
Photo-excited Carrier Dynamics and Impact Excitation Cascade in Graphene
Photo-excitation in solids can trigger a cascade in which multiple
particle-hole excitations are generated. We analyze the carrier multiplication
cascade of impact excitation processes in graphene and show that the number of
pair excitations has a strong dependence on doping, which makes carrier
multiplication gate-tunable. We also predict that the number of excited pairs
as well as the characteristic time of the cascade scale linearly with
photo-excitation energy. These dependences, as well as sharply peaked angular
distribution of pair excitations, provide clear experimental signatures of
carrier multiplication
Finite temperature effects on the neutrino decoupling in the early Universe
Leading finite temperature effects on the neutrino decoupling temperature in
the early Universe have been studied. We have incorporated modifications of the
dispersion relation and the phase space distribution due to the presence of
particles in the heat bath at temperature around MeV. Since both the expansion
rate of the Universe and the interaction rate of a neutrino are reduced by
finite temperature effects, it is necessary to calculate thermal corrections as
precisely as possible in order to find the net effect on the neutrino
decoupling temperature. We have performed such a calculation by using the
finite temperature field theory. It has been shown that the finite temperature
effects increase the neutrino decoupling temperature by 4.4%, the largest
contribution coming from the modification of the phase space due to the thermal
bath.Comment: 18 pages, LaTeX (uses RevTeX), 6 figures added as PS files, submitted
to Phys.Rev.
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