54,371 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 infantâ€™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.

### 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 $z\le 0.5$. We also use the simulation data to test
the Press-Schechter expression of the halo abundance as a function of the
velocity dispersion $\sigma_v$. The model predictions are in good agreement
with the observational data of local cluster abundances ($z=0$). We also
tentatively compare the model with the Gunn and his collaborators' observation
of rich clusters at $z\approx 0.8$ and with the x-ray luminous clusters at
$z\approx 0.5$ 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 $z=0.5$ are only 1/4 and 1/10 respectively of the present values
($z=0$). Ongoing ROSAT and AXAF surveys of distant clusters will provide
sensitive tests to the model. The abundance of clusters at $z\approx 0.5$ 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 $z=0$.Comment: 21 pages + 6 figures (uuencoded version of the PS files), Steward
Preprints No. 118

### 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 $f_+^K(0)$ and Extraction of $|V_{cs}|$ from Semileptonic $D$ Decays

By globally analyzing all existing measured branching fractions and partial
rates in different four momentum transfer-squared $q^2$ bins of $D\to
Ke^+\nu_e$ decays, we obtain the product of the form factor and magnitude of
CKM matrix element $V_{cs}$ to be $f_+^K(0)|V_{cs}|=0.717\pm0.004$. With this
product, we determine the $D\to K$ semileptonic form factor
$f_+^K(0)=0.737\pm0.004\pm0.000$ in conjunction with the value of $|V_{cs}|$
determined from the SM global fit. Alternately, with the product together with
the input of the form factor $f_+^K(0)$ calculated in lattice QCD recently, we
extract $|V_{cs}|^{D\to Ke^+\nu_e}=0.962\pm0.005\pm0.014$, where the error is
still dominated by the uncertainty of the form factor calculated in lattice
QCD. Combining the $|V_{cs}|^{D_s^+\to\ell^+\nu_\ell}=1.012\pm0.015\pm0.009$
extracted from all existing measurements of $D^+_s\to\ell^+\nu_\ell$ decays and
$|V_{cs}|^{D\to Ke^+\nu_e}=0.962\pm0.005\pm0.014$ together, we find the most
precisely determined $|V_{cs}|$ to be $|V_{cs}|=0.983\pm0.011$, which improves
the accuracy of the PDG'2014 value $|V_{cs}|^{\rm PDG'2014}=0.986\pm0.016$ by
$45\%$

- â€¦