96,584 research outputs found
Chaos and residual correlations in pinned disordered systems
We study, using functional renormalization (FRG), two copies of an elastic
system pinned by mutually correlated random potentials. Short scale
decorrelation depend on a non trivial boundary layer regime with (possibly
multiple) chaos exponents. Large scale mutual displacement correlation behave
as , the decorrelation exponent proportional to
the difference between Flory (or mean field) and exact roughness exponent
. For short range disorder but small, e.g. for random bond
interfaces , , and for the one component Bragg glass. Random field
(i.e long range) disorder exhibits finite residual correlations (no chaos ) described by new FRG fixed points. Temperature and dynamic chaos
(depinning) are discussed.Comment: 5 page
Weak local rules for planar octagonal tilings
We provide an effective characterization of the planar octagonal tilings
which admit weak local rules. As a corollary, we show that they are all based
on quadratic irrationalities, as conjectured by Thang Le in the 90s.Comment: 23 pages, 6 figure
Thermodynamic dislocation theory of high-temperature deformation in aluminum and steel
The statistical-thermodynamic dislocation theory developed in previous papers
is used here in an analysis of high-temperature deformation of aluminum and
steel. Using physics-based parameters that we expect theoretically to be
independent of strain rate and temperature, we are able to fit experimental
stress-strain curves for three different strain rates and three different
temperatures for each of these two materials. Our theoretical curves include
yielding transitions at zero strain in agreement with experiment. We find that
thermal softening effects are important even at the lowest temperatures and
smallest strain rates.Comment: 7 pages, 8 figure
Distinguishing Among Strong Decay Models
Two competing models for strong hadronic decays, the and
models, are currently in use.
Attempts to rule out one or the other have been hindered by a poor
understanding of final state interactions and by ambiguities in the treatment
of relativistic effects.
In this article we study meson decays in both models, focussing on certain
amplitude ratios for which the relativistic uncertainties largely cancel out
(notably the ratios in and
), and using a Quark Born Formalism to estimate the
final state interactions.
We find that the model is strongly favoured.
In addition, we predict a amplitude ratio of for the decay
.
We also study the parameter-dependence of some individual amplitudes (as
opposed to amplitude ratios), in an attempt to identify a ``best'' version of
the model.Comment: 20 pages, uuencoded postscript file with 7 figures, MIT-CTP-2295;
CMU-HEP94-1
Disordered free fermions and the Cardy Ostlund fixed line at low temperature
Using functional RG, we reexamine the glass phase of the 2D random-field Sine
Gordon model. It is described by a line of fixed points (FP) with a
super-roughening amplitude as
temperature is varied. A speculation is that this line is identical to the
one found in disordered free-fermion models via exact results from ``nearly
conformal'' field theory. This however predicts , contradicting
numerics. We point out that this result may be related to failure of
dimensional reduction, and that a functional RG method incorporating higher
harmonics and non-analytic operators predicts a non-zero which
compares reasonably with numerics.Comment: 8 pages, 3 figures, only material adde
Chance constrained robust downlink beamforming in multicell networks
We introduce a downlink robust optimization approach that minimizes a combination of total transmit power by a multiple antenna base station (BS) within a cell and the resulting aggregate inter-cell interference (ICI) power on the users of the other cells. This optimization is constrained to assure that a set of signal-to-interference-plus-noise ratio (SINR) targets are met at user terminals with certain outage probabilities. The outages are due to the uncertainties that naturally emerge in the estimation of channel covariance matrices between a BS and its intra-cell local users as well as the other users of the other cells. We model these uncertainties using random matrices, analyze their statistical behaviour and formulate a tractable probabilistic approach to the design of optimal robust downlink beamforming vectors. The proposed approach reformulates the original intractable non-convex problem in a semidefinite programming (SDP) form with linear matrix inequality (LMI) constraints. The resulting SDP formulation is convex and numerically tractable under the standard rank relaxation. We compare the proposed chance-constrained approach against two different robust design schemes as well as the worst-case robustness. The simulation results confirm better power efficiency and higher resilience against channel uncertainties of the proposed approach in realistic scenarios
Infrared point source variability between the Spitzer and MSX surveys of the Galactic mid-plane
We present a list of 552 sources with suspected variability, based on a
comparison of mid-infrared photometry from the GLIMPSE I and MSX surveys, which
were carried out nearly a decade apart. We were careful to address issues such
as the difference in resolution and sensitivity between the two surveys, as
well as the differences in the spectral responses of the instruments. We
selected only sources where the IRAC 8.0 and MSX 8.28 micron fluxes differ by
more than a factor of two, in order to minimize contamination from sources
where the difference in fluxes at 8 micron is due to a strong 10 micron
silicate feature. We present a subset of 40 sources for which additional
evidence suggests variability, using 2MASS and MIPSGAL data. Based on a
comparison with the variability flags in the IRAS and MSX Point-Source Catalogs
we estimate that at least a quarter of the 552 sources, and at least half of
the 40 sources are truly variable. In addition, we tentatively confirm the
variability of one source using multi-epoch IRAS LRS spectra. We suggest that
most of the sources in our list are likely to be Asymptotic Giant Branch stars.Comment: 47 pages, 12 Figures, 3 Tables, accepted for publication in A
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