3,171 research outputs found
Exact results for spatial decay of the one-body density matrix in low-dimensional insulators
We provide a tight-binding model of insulator, for which we derive an exact
analytic form of the one-body density matrix and its large-distance asymptotics
in dimensions . The system is built out of a band of single-particle
orbitals in a periodic potential. Breaking of the translational symmetry of the
system results in two bands, separated by a direct gap whose width is
proportional to the unique energy parameter of the model. The form of the decay
is a power law times an exponential. We determine the power in the power law
and the correlation length in the exponential, versus the lattice direction,
the direct-gap width, and the lattice dimension. In particular, the obtained
exact formulae imply that in the diagonal direction of the square lattice the
inverse correlation length vanishes linearly with the vanishing gap, while in
non-diagonal directions, the linear scaling is replaced by the square root one.
Independently of direction, for sufficiently large gaps the inverse correlation
length grows logarithmically with the gap width.Comment: 4 pages, 2 figure
BSUV-Net: a fully-convolutional neural network for background subtraction of unseen videos
Background subtraction is a basic task in computer vision and video processing often applied as a pre-processing step for object tracking, people recognition, etc. Recently, a number of successful background-subtraction algorithms have been proposed, however nearly all of the top-performing ones are supervised. Crucially, their success relies upon the availability of some annotated frames of the test video during training. Consequently, their performance on completely “unseen” videos is undocumented in the literature. In this work, we propose a new, supervised, background subtraction algorithm for unseen videos (BSUV-Net) based on a fully-convolutional neural network. The input to our network consists of the current frame and two background frames captured at different time scales along with their semantic segmentation maps. In order to reduce the chance of overfitting, we also introduce a new data-augmentation technique which mitigates the impact of illumination difference between the background frames and the current frame. On the CDNet-2014 dataset, BSUV-Net outperforms stateof-the-art algorithms evaluated on unseen videos in terms of several metrics including F-measure, recall and precision.Accepted manuscrip
Emotional agents at the square lattice
We introduce and investigate by numerical simulations a number of models of
emotional agents at the square lattice. Our models describe the most general
features of emotions such as the spontaneous emotional arousal, emotional
relaxation, and transfers of emotions between different agents. Group emotions
in the considered models are periodically fluctuating between two opposite
valency levels and as result the mean value of such group emotions is zero. The
oscillations amplitude depends strongly on probability ps of the individual
spontaneous arousal. For small values of relaxation times tau we observed a
stochastic resonance, i.e. the signal to noise ratio SNR is maximal for a
non-zero ps parameter. The amplitude increases with the probability p of local
affective interactions while the mean oscillations period increases with the
relaxation time tau and is only weakly dependent on other system parameters.
Presence of emotional antenna can enhance positive or negative emotions and for
the optimal transition probability the antenna can change agents emotions at
longer distances. The stochastic resonance was also observed for the influence
of emotions on task execution efficiency.Comment: 28 pages, 19 figures, 3 table
Semiconductor quantum ring as a solid-state spin qubit
The implementation of a spin qubit in a quantum ring occupied by one or a few
electrons is proposed. Quantum bit involves the Zeeman sublevels of the highest
occupied orbital. Such a qubit can be initialized, addressed, manipulated, read
out and coherently coupled to other quantum rings. An extensive discussion of
relaxation and decoherence is presented. By analogy with quantum dots, the spin
relaxation times due to spin-orbit interaction for experimentally accessible
quantum ring architectures are calculated. The conditions are formulated under
which qubits build on quantum rings can have long relaxation times of the order
of seconds. Rapidly improving nanofabrication technology have made such ring
devices experimentally feasible and thus promising for quantum state
engineering.Comment: 16 pages, 3 figure 3 table
Complete One-Loop MSSM Predictions for B --> lepton lepton' at the Tevatron and LHC
During the last few years the Tevatron has dramatically improved the bounds
on rare B-meson decays into two leptons. In the case of B_s --> mu+ mu-, the
current bound is only ten times greater than the Standard Model expectation.
Sensitivity to this decay is one of the benchmark goals for LHCb performance
and physics. The Higgs penguin dominates this rate in the region of large
tan(beta) of the MSSM. This is not necessarily the case in the region of low
tan(beta), since box and Z-penguin diagrams may contribute at a comparable
rate. In this article, we compute the complete one-loop MSSM contribution to B
--> l+l'- for l,l' = e, mu. We study the predictions for general values of
tan(beta) with arbitrary flavour mixing parameters. We discuss the possibility
of both enhancing and suppressing the branching ratios relative to their
Standard Model expectations. In particular, we find that there are
"cancellation regions" in parameter space where the branching ratio is
suppressed well below the Standard Model expectation, making it effectively
invisible to the LHC.Comment: 30 pages, 4 figures; v.3: corrected factors of (2 pi) in (2.11),
(3.1), (A.11), (A.13-14
Detection of atrial fibrillation episodes in long-term heart rhythm signals using a support vector machine
Atrial fibrillation (AF) is a serious heart arrhythmia leading to a significant increase of the risk for occurrence of ischemic stroke. Clinically, the AF episode is recognized in an electrocardiogram. However, detection of asymptomatic AF, which requires a long-term monitoring, is more efficient when based on irregularity of beat-to-beat intervals estimated by the heart rate (HR) features. Automated classification of heartbeats into AF and non-AF by means of the Lagrangian Support Vector Machine has been proposed. The classifier input vector consisted of sixteen features, including four coefficients very sensitive to beat-to-beat heart changes, taken from the fetal heart rate analysis in perinatal medicine. Effectiveness of the proposed classifier has been verified on the MIT-BIH Atrial Fibrillation Database. Designing of the LSVM classifier using very large number of feature vectors requires extreme computational efforts. Therefore, an original approach has been proposed to determine a training set of the smallest possible size that still would guarantee a high quality of AF detection. It enables to obtain satisfactory results using only 1.39% of all heartbeats as the training data. Post-processing stage based on aggregation of classified heartbeats into AF episodes has been applied to provide more reliable information on patient risk. Results obtained during the testing phase showed the sensitivity of 98.94%, positive predictive value of 98.39%, and classification accuracy of 98.86%.Web of Science203art. no. 76
Morphology and Evolution of Simulated and Optical Clusters: A Comparative Analysis
We have made a comparative study of morphological evolution in simulated DM
halos and X-ray brightness distribution, and in optical clusters. Samples of
simulated clusters include star formation with supernovae feedback, radiative
cooling, and simulation in the adiabatic limit at three different redshifts, z
= 0.0, 0.10, and 0.25. The optical sample contains 208 ACO clusters within
redshift, . Cluster morphology, within 0.5 and 1.0 h Mpc
from cluster center, is quantified by multiplicity and ellipticity.
We find that the distribution of the dark matter halos in the adiabatic
simulation appear to be more elongated than the galaxy clusters. Radiative
cooling brings halo shapes in excellent agreement with observed clusters,
however, cooling along with feedback mechanism make the halos more flattened.
Our results indicate relatively stronger structural evolution and more clumpy
distributions in observed clusters than in the structure of simulated clusters,
and slower increase in simulated cluster shapes compared to those in the
observed one.
Within , we notice an interesting agreement in the shapes of
clusters obtained from the cooling simulations and observation. We also notice
that the different samples of observed clusters differ significantly in
morphological evolution with redshift. We highlight a few possibilities
responsible for the discrepancy in morphological evolution of simulated and
observed clusters.Comment: Accepted for publication in MNRAS, 2006; 15 pages, 13 postscript
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