23,089 research outputs found
A microscopic mechanism for rejuvenation and memory effects in spin glasses
Aging in spin glasses (and in some other systems) reveals astonishing effects
of `rejuvenation and memory' upon temperature changes. In this paper, we
propose microscopic mechanisms (at the scale of spin-spin interactions) which
can be at the origin of such phenomena. Firstly, we recall that, in a
frustrated system, the effective average interaction between two spins may take
different values (possibly with opposite signs) at different temperatures. We
give simple examples of such situations, which we compute exactly. Such
mechanisms can explain why new ordering processes (rejuvenation) seem to take
place in spin glasses when the temperature is lowered. Secondly, we emphasize
the fact that inhomogeneous interactions do naturally lead to a wide
distribution of relaxation times for thermally activated flips. `Memory spots'
spontaneously appear, in the sense that the flipping time of some spin clusters
becomes extremely long when the temperature is decreased. Such memory spots are
capable of keeping the memory of previous ordering at a higher temperature
while new ordering processes occur at a lower temperature. After a qualitative
discussion of these mechanisms, we show in the numerical simulation of a
simplified example that this may indeed work. Our conclusion is that certain
chaos-like phenomena may show up spontaneously in any frustrated and
inhomogeneous magnetic system, without impeding the occurrence of memory
effects.Comment: 9 pages (11 figures) - revised version, to appear in Eur. Phys. J. B
(2001
Sound Source Separation
This is the author's accepted pre-print of the article, first published as G. Evangelista, S. Marchand, M. D. Plumbley and E. Vincent. Sound source separation. In U. Zölzer (ed.), DAFX: Digital Audio Effects, 2nd edition, Chapter 14, pp. 551-588. John Wiley & Sons, March 2011. ISBN 9781119991298. DOI: 10.1002/9781119991298.ch14file: Proof:e\EvangelistaMarchandPlumbleyV11-sound.pdf:PDF owner: markp timestamp: 2011.04.26file: Proof:e\EvangelistaMarchandPlumbleyV11-sound.pdf:PDF owner: markp timestamp: 2011.04.2
Enhancing quantum transduction via long-range waveguide mediated interactions between quantum emitters
Efficient transduction of electromagnetic signals between different frequency
scales is an essential ingredient for modern communication technologies as well
as for the emergent field of quantum information processing. Recent advances in
waveguide photonics have enabled a breakthrough in light-matter coupling, where
individual two-level emitters are strongly coupled to individual photons. Here
we propose a scheme which exploits this coupling to boost the performance of
transducers between low-frequency signals and optical fields operating at the
level of individual photons. Specifically, we demonstrate how to engineer the
interaction between quantum dots in waveguides to enable efficient transduction
of electric fields coupled to quantum dots. Owing to the scalability and
integrability of the solid-state platform, our transducer can potentially
become a key building block of a quantum internet node. To demonstrate this, we
show how it can be used as a coherent quantum interface between optical photons
and a two-level system like a superconducting qubit.Comment: The maintext has 6 pages, two column and 4 figure
Elementary constraints on autocorrelation function scalings
Elementary algebraic constraints on the form of an autocorrelation function
C(tw+t,tw)= rule out some two-time scalings found in the
literature as possible long-time asymptotic forms. The same argument leads to
the realization that two usual definitions of {\em many-time scale} relaxation
for aging systems are not equivalent
Method of forming thin window drifted silicon charged particle detector Patent
Method of forming thin window drifted silicon charged particle detecto
Photon Scattering from a System of Multi-Level Quantum Emitters. I. Formalism
We introduce a formalism to solve the problem of photon scattering from a
system of multi-level quantum emitters. Our approach provides a direct solution
of the scattering dynamics. As such the formalism gives the scattered fields
amplitudes in the limit of a weak incident intensity. Our formalism is equipped
to treat both multi-emitter and multi-level emitter systems, and is applicable
to a plethora of photon scattering problems including conditional state
preparation by photo-detection. In this paper, we develop the general formalism
for an arbitrary geometry. In the following paper (part II), we reduce the
general photon scattering formalism to a form that is applicable to
-dimensional waveguides, and show its applicability by considering explicit
examples with various emitter configurations.Comment: This is first part of a two part series of papers. It has 11 pages,
double column, and one figur
A general framework for online audio source separation
We consider the problem of online audio source separation. Existing
algorithms adopt either a sliding block approach or a stochastic gradient
approach, which is faster but less accurate. Also, they rely either on spatial
cues or on spectral cues and cannot separate certain mixtures. In this paper,
we design a general online audio source separation framework that combines both
approaches and both types of cues. The model parameters are estimated in the
Maximum Likelihood (ML) sense using a Generalised Expectation Maximisation
(GEM) algorithm with multiplicative updates. The separation performance is
evaluated as a function of the block size and the step size and compared to
that of an offline algorithm.Comment: International conference on Latente Variable Analysis and Signal
Separation (2012
Detailed gravimetric geoid confirmation of short wavelength features of sea surface topography detected by the Skylab S-193 altimeter in the Atlantic Ocean
A detailed gravimetric geoid was computed for the Northwest Atlantic Ocean and Caribbean Sea area in support of the calibration and evaluation of the GEOS-C altimeter. This geoid, computed on a 15 ft. x 15 ft. grid was based upon a combination of surface gravity data with the GSFC GEM-6 satellite derived gravity data. A comparison of this gravimetric geoid with 10 passes of SKYLAB altimeter data is presented. The agreement of the two data types is quite good with the differences generally less than 2 meters. Sea surface manifestations of numerous short wavelength (approximately 100 km) oceanographic features are now indicated in the gravimetric geoid and are also confirmed by the altimetry data
A comparison and evaluation of satellite derived positions of tracking stations
A comparison is presented of sets of satellite tracking station coordinate values published in the past few years by a number of investigators, i.e. Goddard Space Flight Center, Smithsonian Astrophysical Observatory, Ohio State University, The Naval Weapons Laboratory, Air Force Cambridge Research Laboratories, and Wallops Island. The comparisons have been made in terms of latitude, longitude and height. The results of the various solutions have been compared directly and also with external standards such as local survey data and gravimetrically derived geoid heights. After taking into account systematic rotations, latitude and longitude agreement on a global basis is generally 15 meters or better, on the North American Datum agreement is generally better than 10 meters. Allowing for scale differences (of the order of 2 ppm) radial agreement is generally of the order of 10 meters
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