11,547 research outputs found
Evidence for thermal spin transfer torque
Large heat currents are obtained in Co/Cu/Co spin valves positioned at the
middle of Cu nanowires. The second harmonic voltage response to an applied
current is used to investigate the effect of the heat current on the switching
of the spin valves. Both the switching field and the magnitude of the voltage
response are found to be dependent on the heat current. These effects are
evidence for a thermal spin transfer torque acting on the magnetization and are
accounted for by a thermodynamic model in which heat, charge and spin currents
are linked by Onsager reciprocity relations.Comment: 4 pages, 4 figure
Audio Classification from Time-Frequency Texture
Time-frequency representations of audio signals often resemble texture
images. This paper derives a simple audio classification algorithm based on
treating sound spectrograms as texture images. The algorithm is inspired by an
earlier visual classification scheme particularly efficient at classifying
textures. While solely based on time-frequency texture features, the algorithm
achieves surprisingly good performance in musical instrument classification
experiments
On generalized Gaussian free fields and stochastic homogenization
We study a generalization of the notion of Gaussian free field (GFF).
Although the extension seems minor, we first show that a generalized GFF does
not satisfy the spatial Markov property, unless it is a classical GFF. In
stochastic homogenization, the scaling limit of the corrector is a possibly
generalized GFF described in terms of an "effective fluctuation tensor" that we
denote by . We prove an expansion of in the regime of
small ellipticity ratio. This expansion shows that the scaling limit of the
corrector is not necessarily a classical GFF, and in particular does not
necessarily satisfy the Markov property.Comment: 20 pages, revised versio
Scaling limit of fluctuations in stochastic homogenization
We investigate the global fluctuations of solutions to elliptic equations
with random coefficients in the discrete setting. In dimension and
for i.i.d.\ coefficients, we show that after a suitable scaling, these
fluctuations converge to a Gaussian field that locally resembles a
(generalized) Gaussian free field. The paper begins with a heuristic derivation
of the result, which can be read independently and was obtained jointly with
Scott Armstrong.Comment: 27 pages, revised version with a new section obtained jointly with
Scott Armstron
Pointwise two-scale expansion for parabolic equations with random coefficients
We investigate the first-order correction in the homogenization of linear
parabolic equations with random coefficients. In dimension and higher and
for coefficients having a finite range of dependence, we prove a pointwise
version of the two-scale expansion. A similar expansion is derived for elliptic
equations in divergence form. The result is surprising, since it was not
expected to be true without further symmetry assumptions on the law of the
coefficients.Comment: 25 pages. Minor revisions, to appear in PTR
Smaller population size at the MRCA time for stationary branching processes
We present an elementary model of random size varying population given by a
stationary continuous state branching process. For this model we compute the
joint distribution of: the time to the most recent common ancestor, the size of
the current population and the size of the population just before the most
recent common ancestor (MRCA). In particular we show a natural mild bottleneck
effect as the size of the population just before the MRCA is stochastically
smaller than the size of the current population. We also compute the number of
old families which corresponds to the number of individuals involved in the
last coalescent event of the genealogical tree. By studying more precisely the
genealogical structure of the population, we get asymptotics for the number of
ancestors just before the current time. We give explicit computations in the
case of the quadratic branching mechanism. In this case, the size of the
population at the MRCA is, in mean, less by 1/3 than size of the current
population size. We also provide in this case the fluctuations for the
renormalized number of ancestors
A Differential Approach for Gaze Estimation
Non-invasive gaze estimation methods usually regress gaze directions directly
from a single face or eye image. However, due to important variabilities in eye
shapes and inner eye structures amongst individuals, universal models obtain
limited accuracies and their output usually exhibit high variance as well as
biases which are subject dependent. Therefore, increasing accuracy is usually
done through calibration, allowing gaze predictions for a subject to be mapped
to his/her actual gaze. In this paper, we introduce a novel image differential
method for gaze estimation. We propose to directly train a differential
convolutional neural network to predict the gaze differences between two eye
input images of the same subject. Then, given a set of subject specific
calibration images, we can use the inferred differences to predict the gaze
direction of a novel eye sample. The assumption is that by allowing the
comparison between two eye images, annoyance factors (alignment, eyelid
closing, illumination perturbations) which usually plague single image
prediction methods can be much reduced, allowing better prediction altogether.
Experiments on 3 public datasets validate our approach which constantly
outperforms state-of-the-art methods even when using only one calibration
sample or when the latter methods are followed by subject specific gaze
adaptation.Comment: Extension to our paper A differential approach for gaze estimation
with calibration (BMVC 2018) Submitted to PAMI on Aug. 7th, 2018 Accepted by
PAMI short on Dec. 2019, in IEEE Transactions on Pattern Analysis and Machine
Intelligenc
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