30,938 research outputs found
Very Old Isolated Compact Objects as Dark Matter Probes
Very old isolated neutron stars and white dwarfs have been suggested to be
probes of dark matter. To play such a role, two requests should be fulfilled,
i.e., the annihilation luminosity of the captured dark matter particles is
above the thermal emission of the cooling compact objects (request-I) and also
dominate over the energy output due to the accretion of normal matter onto the
compact objects (request-II). Request-I calls for very dense dark matter medium
and the critical density sensitively depends on the residual surface
temperature of the very old compact objects. The accretion of
interstellar/intracluster medium onto the compact objects is governed by the
physical properties of the medium and by the magnetization and rotation of the
stars and may outshine the signal of dark matter annihilation. Only in a few
specific scenarios both requests are satisfied and the compact objects are dark
matter burners. The observational challenges are discussed and a possible way
to identify the dark matter burners is outlined.Comment: 9 pages including 1 Figure, to appear in Phys. Rev.
A novel objective no-reference metric for digital video quality assessment
A novel objective no-reference metric is proposed for video quality assessment of digitally coded videos containing natural scenes. Taking account of the temporal dependency between adjacent images of the videos and characteristics of the human visual system, the spatial distortion of an image is predicted using the differences between the corresponding translational regions of high spatial complexity in two adjacent images, which are weighted according to temporal activities of the video. The overall video quality is measured by pooling the spatial distortions of all images in the video. Experiments using reconstructed video sequences indicate that the objective scores obtained by the proposed metric agree well with the subjective assessment scores
ELECTROMYOGRAPHIC FACTORS CORRELATED WITH SOFTBALL BATTING PERFORMANCE
Specific muscle strength and coordination are required to produce a successful hit after a fast downswing in response to a high-velocity ball (Katsumata, 2007). Electromyographic (EMG) recording during the muscle contraction was a measurement to realize the motor strategy of sports. Several EMG researches about baseball or softball pitching have been documented in literature (Saito et al., 2001). However, there was very little research about softball batting surveyed in literature. Therefore, the purposes of this study were to investigate the muscle activities in upper extremities during softball batting and to analyze if any muscle activity is correlated with the ball exit velocity and bat head velocity
Inferring forest fate from demographic data: from vital rates to population dynamic models
As population-level patterns of interest in forests emerge from individual vital rates, modelling forest dynamics requires making the link between the scales at which data are collected (individual stems) and the scales at which questions are asked (e.g. populations and communities). Structured population models (e.g. integral projection models (IPMs)) are useful tools for linking vital rates to population dynamics. However, the application of such models to forest trees remains challenging owing to features of tree life cycles, such as slow growth, long lifespan and lack of data on crucial ontogenic stages. We developed a survival model that accounts for size-dependent mortality and a growth model that characterizes individual heterogeneity. We integrated vital rate models into two types of population model; an analytically tractable form of IPM and an individual-based model (IBM) that is applied with stochastic simulations. We calculated longevities, passage times to, and occupancy time in, different life cycle stages, important metrics for understanding how demographic rates translate into patterns of forest turnover and carbon residence times. Here, we illustrate the methods for three tropical forest species with varying life-forms. Population dynamics from IPMs and IBMs matched a 34 year time series of data (albeit a snapshot of the life cycle for canopy trees) and highlight differences in life-history strategies between species. Specifically, the greater variation in growth rates within the two canopy species suggests an ability to respond to available resources, which in turn manifests as faster passage times and greater occupancy times in larger size classes. The framework presented here offers a novel and accessible approach to modelling the population dynamics of forest trees
Reconstruction of Fractional Quantum Hall Edges
We study the interplay of interaction, confining potential and effects of
finite temperature at the edge of a quantum Hall liquid. Our exact
diagonalization calculation indicates that edge reconstruction occurs in the
fractional quantum Hall regime for a variety of confining potential, including
ones that correspond to a "sharp" edge. Our finite temperature Hartree-Fock
calculation for integer quantum Hall edges indicates that reconstruction is
suppressed above certain temperature. We discuss the implication of our results
on recent edge tunneling and microwave absorption experiments.Comment: Revised version. 5 papges RevTex with 5 eps figures embedded in the
tex
Effect of in-plane magnetic field on magnetic phase transitions in nu=2 bilayer quantum Hall systems
By using the effective bosonic spin theory, which is recently proposed by
Demler and Das Sarma [ Phys. Rev. Lett. 82, 3895 (1999) ], we analyze the
effect of an external in-plane magnetic field on the magnetic phase transitions
of the bilayer quantum Hall system at filling factor nu=2. It is found that the
quantum phase diagram is modified by the in-plane magnetic field. Therefore,
quantum phase transitions can be induced simply by tilting the magnetic field.
The general behavior of the critical tilted angle for different layer
separations and interlayer tunneling amplitudes is shown. We find that the
critical tilted angles being calculated agree very well with the reported
values. Moreover, a universal critical exponent for the transition from the
canted antiferromagnetic phase to the ferromagnetic phase is found to be equal
to 1/2 within the present effective theory.Comment: RevTeX, 4 pages with 3 EPS figures include
The Decays to -wave Charmonium by Improved Bethe-Salpeter Approach
We re-calculate the exclusive semileptonic and nonleptonic decays of
meson to a -wave charmonium in terms of the improved Bethe-Salpeter (B-S)
approach, which is developed recently. Here the widths for the exclusive
semileptonic and nonleptonic decays, the form factors, and the charged lepton
spectrums for the semileptonic decays are precisely calculated. To test the
concerned approach by comparing with experimental measurements when the
experimental data are available, and to have comparisons with the other
approaches the results obtained by the approach and those by some approaches
else as well as the original B-S approach, which appeared in literature, are
comparatively presented and discussed.Comment: 33 pages, 5 figures, 3 table
Persistent spin current in mesoscopic ferrimagnetic spin ring
Using a semiclassical approach, we study the persistent magnetization current
of a mesoscopic ferrimagnetic ring in a nonuniform magnetic field. At zero
temperature, there exists persistent spin current because of the quantum
fluctuation of magnons, similar to the case of an antiferromagnetic spin ring.
At low temperature, the current shows activation behavior because of the
field-induced gap. At higher temperature, the magnitude of the spin current is
proportional to temperature T, similar to the reported result of a
ferromagnetic spin ring.Comment: 6 pages, 3 figures, one more reference adde
- …