12,239 research outputs found
Study of the long-term evolution of the accretion dynamics of GX 339-4
We study the dynamical behaviour of the galactic black hole source GX 339-4
during 2002-2011 outbursts using RXTE, Swift(XRT), XMM-Newton(PN) archival
data. We present the spectral evolution of the source using four outbursts data
and discuss their similarities/differences between outbursts. We infer that the
second peak in 2002/03 and 2004/05 outbursts can be due to a second instant of
triggered instability in the accretion disc due to irradiation from the central
X-ray source after peak-I. This propagates in viscous time scale and takes
~80-90 days after peak-I to produce peak-II. This unifies all four outbursts
having a long rising time of ~90 days. The dynamical evolution of accretion
parameters have been studied by modeling the individual observed spectrum with
two-component accretion disc model where a Keplerian accretion disc produces
the soft photons and the hard part of the spectrum originates from a hot
sub-Keplerian central corona. A generic mathematical model has been proposed to
understand the evolution of accretion parameters for sources like GX 339-4
which have longer rising time. Also, the possible differences of physical
scenario for outbursts with shorter rising time are also discussed.Comment: Accepted for publication in mnra
Maxwell's Refrigerator: An Exactly Solvable Model
We describe a simple and solvable model of a device that -- like the
"neat-fingered being" in Maxwell's famous thought experiment -- transfers
energy from a cold system to a hot system by rectifying thermal fluctuations.
In order to accomplish this task, our device requires a memory register to
which it can write information: the increase in the Shannon entropy of the
memory compensates the decrease in the thermodynamic entropy arising from the
flow of heat against a thermal gradient. We construct the nonequilibrium phase
diagram for this device, and find that it can alternatively act as an eraser of
information. We discuss our model in the context of the second law of
thermodynamics.Comment: 9 pages (Main Text + Supplemental Material), 3 figures, to appear in
Physical Review Letter
Anti-chiral edge states in an exciton polariton strip
We present a scheme to obtain anti-chiral edge states in an exciton-polariton
honeycomb lattice with strip geometry, where the modes corresponding to both
edges propagate in the same direction. Under resonant pumping the effect of a
polariton condensate with nonzero velocity in one linear polarization is
predicted to tilt the dispersion of polaritons in the other, which results in
an energy shift between two Dirac cones and the otherwise flat edge states
become tilted. Our simulations show that due to the spatial separation from the
bulk modes the edge modes are robust against disorder.Comment: 6 pages, 5 figure
Distinguishing Posed and Spontaneous Smiles by Facial Dynamics
Smile is one of the key elements in identifying emotions and present state of
mind of an individual. In this work, we propose a cluster of approaches to
classify posed and spontaneous smiles using deep convolutional neural network
(CNN) face features, local phase quantization (LPQ), dense optical flow and
histogram of gradient (HOG). Eulerian Video Magnification (EVM) is used for
micro-expression smile amplification along with three normalization procedures
for distinguishing posed and spontaneous smiles. Although the deep CNN face
model is trained with large number of face images, HOG features outperforms
this model for overall face smile classification task. Using EVM to amplify
micro-expressions did not have a significant impact on classification accuracy,
while the normalizing facial features improved classification accuracy. Unlike
many manual or semi-automatic methodologies, our approach aims to automatically
classify all smiles into either `spontaneous' or `posed' categories, by using
support vector machines (SVM). Experimental results on large UvA-NEMO smile
database show promising results as compared to other relevant methods.Comment: 16 pages, 8 figures, ACCV 2016, Second Workshop on Spontaneous Facial
Behavior Analysi
An analysis of the Bayesian track labelling problem
In multi-target tracking (MTT), the problem of assigning labels to tracks (track labelling) is vastly covered in literature, but its exact mathematical formulation, in terms of Bayesian statistics, has not been yet looked at in detail. Doing so, however, may help us to understand how Bayes-optimal track labelling should be performed or numerically approximated. Moreover, it can help us to better understand and tackle some practical difficulties associated with the MTT problem, in particular the so-called ``mixed labelling'' phenomenon that has been observed in MTT algorithms. In this memorandum, we rigorously formulate the optimal track labelling problem using Finite Set Statistics (FISST), and look in detail at the mixed labeling phenomenon. As practical contributions of the memorandum, we derive a new track extraction formulation with some nice properties and a statistic associated with track labelling with clear physical meaning. Additionally, we show how to calculate this statistic for two well-known MTT algorithms
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