54,369 research outputs found
Sign Changes of Intrinsic Spin Hall Effect in Semiconductors and Simple Metals: First-Principles Calculations
First-principles calculations are applied to study spin Hall effect in
semiconductors and simple metals. We found that intrinsic spin Hall
conductivity (ISHC) in realistic materials shows rich sign changes, which may
be used to distinguish the effect from the extrinsic one. The calculated ISHC
in n-doped GaAs can be well compared with experiment, and it differs from the
sign obtained from the extrinsic effect. On the other hand, the ISHC in W and
Au, which shows opposite sign respectively, is robust and not sensitive to the
disorder.Comment: 4 pages, 4 figure
A Monitoring System Based on Behavior Analysis
[[abstract]]This paper presents a vision-based infant-monitoring system that adopts an infant behavior analysis approach to reduce infant injuries. In our study, the video camera is set above the crib to capture infant sequences. The system first preprocesses the input sequence to filter out the noise and reduce the effects of lights and shadows. Then, the infant’s head and limbs are detected from the input frames and compared with pre-defined posture maps to select the most similar map. A posture map describes the current infant posture; the selected posture map can be regarded as a node to be linked by the occurrence order to construct a dynamic behavior graph that describes infant behaviour captured over time. If an input posture map does not exist in the dynamic behavior graph, this means that an unexpected situation has occurred and the system would then alert the baby sitter to attend to the infant immediately. A weighted dynamic behavior graph adjustment algorithm is used to accomplish the behavior analysis. Since infants grow very quickly and their growth processes may differ, the dynamic behavior graph should be continuously updated to fit the current behavior of infants. The experimental results show that the proposed method is able to perform robustly in real-time.
Impulsive cylindrical gravitational wave: one possible radiative form emitted from cosmic strings and corresponding electromagnetic response
The cosmic strings(CSs) may be one important source of gravitational
waves(GWs), and it has been intensively studied due to its special properties
such as the cylindrical symmetry. The CSs would generate not only usual
continuous GW, but also impulsive GW that brings more concentrated energy and
consists of different GW components broadly covering low-, intermediate- and
high-frequency bands simultaneously. These features might underlie interesting
electromagnetic(EM) response to these GWs generated by the CSs. In this paper,
with novel results and effects, we firstly calculate the analytical solutions
of perturbed EM fields caused by interaction between impulsive cylindrical GWs
(would be one of possible forms emitted from CSs) and background celestial high
magnetic fields or widespread cosmological background magnetic fields, by using
rigorous Einstein - Rosen metric. Results show: perturbed EM fields are also in
the impulsive form accordant to the GW pulse, and asymptotic behaviors of the
perturbed EM fields are fully consistent with the asymptotic behaviors of the
energy density, energy flux density and Riemann curvature tensor of
corresponding impulsive cylindrical GWs. The analytical solutions naturally
give rise to the accumulation effect which is proportional to the term of
distance^1/2, and based on it, we for the first time predict potentially
observable effects in region of the Earth caused by the EM response to GWs from
the CSs.Comment: 34 pages, 12 figure
Determination of and Extraction of from Semileptonic Decays
By globally analyzing all existing measured branching fractions and partial
rates in different four momentum transfer-squared bins of decays, we obtain the product of the form factor and magnitude of
CKM matrix element to be . With this
product, we determine the semileptonic form factor
in conjunction with the value of
determined from the SM global fit. Alternately, with the product together with
the input of the form factor calculated in lattice QCD recently, we
extract , where the error is
still dominated by the uncertainty of the form factor calculated in lattice
QCD. Combining the
extracted from all existing measurements of decays and
together, we find the most
precisely determined to be , which improves
the accuracy of the PDG'2014 value by
Abundance of moderate-redshift clusters in the Cold + Hot dark matter model
Using a set of \pppm simulation which accurately treats the density
evolution of two components of dark matter, we study the evolution of clusters
in the Cold + Hot dark matter (CHDM) model. The mass function, the velocity
dispersion function and the temperature function of clusters are calculated for
four different epochs of . We also use the simulation data to test
the Press-Schechter expression of the halo abundance as a function of the
velocity dispersion . The model predictions are in good agreement
with the observational data of local cluster abundances (). We also
tentatively compare the model with the Gunn and his collaborators' observation
of rich clusters at and with the x-ray luminous clusters at
of the {\it Einstein} Extended Medium Sensitivity Survey. The
important feature of the model is the rapid formation of clusters in the near
past: the abundances of clusters of \sigma_v\ge 700\kms and of \sigma_v\ge
1200 \kms at are only 1/4 and 1/10 respectively of the present values
(). Ongoing ROSAT and AXAF surveys of distant clusters will provide
sensitive tests to the model. The abundance of clusters at would
also be a good discriminator between the CHDM model and a low-density flat CDM
model both of which show very similar clustering properties at .Comment: 21 pages + 6 figures (uuencoded version of the PS files), Steward
Preprints No. 118
Video Saliency Detection by 3D Convolutional Neural Networks
Different from salient object detection methods for still images, a key
challenging for video saliency detection is how to extract and combine spatial
and temporal features. In this paper, we present a novel and effective approach
for salient object detection for video sequences based on 3D convolutional
neural networks. First, we design a 3D convolutional network (Conv3DNet) with
the input as three video frame to learn the spatiotemporal features for video
sequences. Then, we design a 3D deconvolutional network (Deconv3DNet) to
combine the spatiotemporal features to predict the final saliency map for video
sequences. Experimental results show that the proposed saliency detection model
performs better in video saliency prediction compared with the state-of-the-art
video saliency detection methods
Understanding the white-light flare on 2012 March 9 : Evidence of a two-step magnetic reconnection
We attempt to understand the white-light flare (WLF) that was observed on
2012 March 9 with a newly constructed multi-wavelength solar telescope called
the Optical and Near-infrared Solar Eruption Tracer (ONSET). We analyzed WLF
observations in radio, H-alpha, white-light, ultraviolet, and X-ray bands. We
also studied the magnetic configuration of the flare via the nonlinear
force-free field (NLFFF) extrapolation and the vector magnetic field observed
by the Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamics
Observatory (SDO). Continuum emission enhancement clearly appeared at the 3600
angstrom and 4250 angstrom bands, with peak contrasts of 25% and 12%,
respectively. The continuum emission enhancement closely coincided with the
impulsive increase in the hard X-ray emission and a microwave type III burst at
03:40 UT. We find that the WLF appeared at one end of either the sheared or
twisted field lines or both. There was also a long-lasting phase in the H-alpha
and soft X-ray bands after the white-light emission peak. In particular, a
second, yet stronger, peak appeared at 03:56 UT in the microwave band. This
event shows clear evidence that the white-light emission was caused by
energetic particles bombarding the lower solar atmosphere. A two-step magnetic
reconnection scenario is proposed to explain the entire process of flare
evolution, i.e., the first-step magnetic reconnection between the field lines
that are highly sheared or twisted or both, and the second-step one in the
current sheet, which is stretched by the erupting flux rope. The WLF is
supposed to be triggered in the first-step magnetic reconnection at a
relatively low altitude.Comment: 4 pages, 4 figures, published in A&A Lette
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