6,566 research outputs found
Relativistic Conformal Magneto-Hydrodynamics from Holography
We use the AdS/CFT correspondence to study first-order relativistic viscous
magneto-hydrodynamics of (2+1) dimensional conformal magnetic fluids. It is
shown that the first order magneto-hydrodynamics constructed following Landau
and Lifshitz from the positivity of the entropy production is inconsistent. We
propose additional contributions to the entropy motivated dissipative current
and, correspondingly, new dissipative transport coefficients. We use the
strongly coupled M2-brane plasma in external magnetic field to show that the
new magneto-hydrodynamics leads to self-consistent results in the shear and
sound wave channels.Comment: 11 page
Randomly Spread CDMA: Asymptotics via Statistical Physics
This paper studies randomly spread code-division multiple access (CDMA) and
multiuser detection in the large-system limit using the replica method
developed in statistical physics. Arbitrary input distributions and flat fading
are considered. A generic multiuser detector in the form of the posterior mean
estimator is applied before single-user decoding. The generic detector can be
particularized to the matched filter, decorrelator, linear MMSE detector, the
jointly or the individually optimal detector, and others. It is found that the
detection output for each user, although in general asymptotically non-Gaussian
conditioned on the transmitted symbol, converges as the number of users go to
infinity to a deterministic function of a "hidden" Gaussian statistic
independent of the interferers. Thus the multiuser channel can be decoupled:
Each user experiences an equivalent single-user Gaussian channel, whose
signal-to-noise ratio suffers a degradation due to the multiple-access
interference. The uncoded error performance (e.g., symbol-error-rate) and the
mutual information can then be fully characterized using the degradation
factor, also known as the multiuser efficiency, which can be obtained by
solving a pair of coupled fixed-point equations identified in this paper. Based
on a general linear vector channel model, the results are also applicable to
MIMO channels such as in multiantenna systems.Comment: To be published in IEEE Transactions on Information Theor
Low temperature electronic properties of Sr_2RuO_4 II: Superconductivity
The body centered tetragonal structure of Sr_2RuO_4 gives rise to umklapp
scattering enhanced inter-plane pair correlations in the d_{yz} and d_{zx}
orbitals. Based on symmetry arguments, Hund's rule coupling, and a bosonized
description of the in-plane electron correlations the superconducting order
parameter is found to be a orbital-singlet spin-triplet with two spatial
components. The spatial anisotropy is 7%. The different components of the order
parameter give rise to two-dimensional gapless fluctuations. The phase
transition is of third order. The temperature dependence of the pair density,
specific heat, NQR, Knight shift, and susceptibility are in agreement with
experimental results.Comment: 20 pages REVTEX, 3 figure
Regular binary thermal lattice-gases
We analyze the power spectrum of a regular binary thermal lattice gas in two
dimensions and derive a Landau-Placzek formula, describing the power spectrum
in the low-wavelength, low frequency domain, for both the full mixture and a
single component in the binary mixture. The theoretical results are compared
with simulations performed on this model and show a perfect agreement. The
power spectrums are found to be similar in structure as the ones obtained for
the continuous theory, in which the central peak is a complicated superposition
of entropy and concentration contributions, due to the coupling of the
fluctuations in these quantities. Spectra based on the relative difference
between both components have in general additional Brillouin peaks as a
consequence of the equipartition failure.Comment: 20 pages including 9 figures in RevTex
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