34,465 research outputs found
Dynamical AC study of the critical behavior in Heisenberg spin glasses
We present some numerical results for the Heisenberg spin-glass model with
Gaussian interactions, in a three dimensional cubic lattice. We measure the AC
susceptibility as a function of temperature and determine an apparent finite
temperature transition which is compatible with the chiral-glass temperature
transition for this model. The relaxation time diverges like a power law
with and . Although our
data indicates that the spin-glass transition occurs at the same temperature as
the chiral glass transition, we cannot exclude the possibility of a chiral-spin
coupling scenario for the lowest frequencies investigated.Comment: 7 pages, 4 figure
Reconnection of Stable/Unstable Manifolds of the Harper Map
The Harper map is one of the simplest chaotic systems exhibiting reconnection
of invariant manifolds. The method of asymptotics beyond all orders (ABAO) is
used to construct stable/unstable manifolds of the Harper map. When the
parameter changes to the reconnection threshold, the stable/unstable manifolds
are shown to acquire new oscillatory portion corresponding to the heteroclinic
tangle after the reconnection.Comment: 24 pages, 11 figure
Modulation of a Chirp Gravitational Wave from a Compact Binary due to Gravitational Lensing
A possible wave effect in the gravitational lensing phenomenon is discussed.
We consider the interference of two coherent gravitational waves of slightly
different frequencies from a compact binary, due to the gravitational lensing
by a galaxy halo. This system shows the modulation of the wave amplitude. The
lensing probability of such the phenomenon is of order 10^{-5} for a high-z
source, but it may be advantageous to the observation due to the magnification
of the amplitude.Comment: 3 pages, PRD in pres
Decoherence of flux qubits due to 1/f flux noise
We have investigated decoherence in Josephson-junction flux qubits. Based on
the measurements of decoherence at various bias conditions, we discriminate
contributions of different noise sources. In particular, we present a Gaussian
decay function of the echo signal as evidence of dephasing due to flux
noise whose spectral density is evaluated to be about /Hz
at 1 Hz. We also demonstrate that at an optimal bias condition where the noise
sources are well decoupled the coherence observed in the echo measurement is
mainly limited by energy relaxation of the qubit.Comment: 4 pages, error in Fig.4 corrected, to appear in PR
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How Accurately Can We Measure the Reconnection Rate E M for the MMS Diffusion Region Event of 11 July 2017?
We investigate the accuracy with which the reconnection electric field E M can be determined from in situ plasma data. We study the magnetotail electron diffusion region observed by National Aeronautics and Space Administration's Magnetospheric Multiscale (MMS) on 11 July 2017 at 22:34 UT and focus on the very large errors in E M that result from errors in an L M N boundary normal coordinate system. We determine several L M N coordinates for this MMS event using several different methods. We use these M axes to estimate E M. We find some consensus that the reconnection rate was roughly E M = 3.2 ± 0.6 mV/m, which corresponds to a normalized reconnection rate of 0.18 ± 0.035. Minimum variance analysis of the electron velocity (MVA-v e), MVA of E, minimization of Faraday residue, and an adjusted version of the maximum directional derivative of the magnetic field (MDD-B) technique all produce reasonably similar coordinate axes. We use virtual MMS data from a particle-in-cell simulation of this event to estimate the errors in the coordinate axes and reconnection rate associated with MVA-v e and MDD-B. The L and M directions are most reliably determined by MVA-v e when the spacecraft observes a clear electron jet reversal. When the magnetic field data have errors as small as 0.5% of the background field strength, the M direction obtained by MDD-B technique may be off by as much as 35°. The normal direction is most accurately obtained by MDD-B. Overall, we find that these techniques were able to identify E M from the virtual data within error bars ≥20%
Localization length of a soliton from a non-magnetic impurity in a general double-spin-chain model
A localization length of a free-spin soliton from a non-magnetic impurity is
deduced in a general double-spin-chain model ( model). We have
solved a variational problem which employs the nearest-neighbor singlet-dimer
basis. The wave function of a soliton is expressed by the Airy function, and
the localization length is found to obey a power law of the
dimerization with an exponent -1/3; .
This explains why NaV_2O_5 does not show the antiferromagnetic order, while
CuGeO_3 does by impurity doping. When the gap exists by the bond-dimerization,
a soliton is localized and no order is expected. Contrary, there is a
possibility of the order when the gap is mainly due to frustration.Comment: 4 pages, REVTeX, Figures are in eps-file
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