arXiv subjects

W. Wang

Publications and source records attributed to W. Wang.

191 records · Page 11Linked to original sources

arXiv2003

Spectral properties, generation order parameters and luminosities for spin-powered X-ray pulsars

We show the spectral properties of 15 spin-powered X-ray pulsars, and the correlation between the average power-law photon index and spin-down rate. Generation order parameters (GOPs) based on polar-cap models are introduced to characterize the X-ray pulsars. We calculate three definitions of generation order parameters due to the different effects of magnetic and electric fields on photon absorption during cascade processes, and study the relations between the GOPs and spectral properties of X-ray pulsars. There exists a possible correlation between the photon index and GOP in our pulsar sample. Furthermore, we present a method due to the concept of GOPs to estimate the non-thermal X-ray luminosity for spin-powered pulsars. Then X-ray luminosity is calculated in the context of our polar-cap accelerator model which is well consistent with the most observed X-ray pulsar data. The ratio between X-ray luminosity estimated by our method and the pulsar's spin-down power is well consistent with the $L_{\rm X}\sim 10^{-3}L_{\rm sd}$ feature.

astro-ph↗

arXiv2003

Spectral properties of anomalous X-ray pulsars

In this paper, the spectra of the persistent emission from anomalous X-ray pulsars (AXPs) and their variation with spin-down rate $\dotΩ$ is considered. Firstly, based on an accretion-powered model, the influences of both magnetic field and mass accretion rate on the spectra properties of AXPs are addressed. Subsequently, the relation between the spectral property of AXPs and mass accretion rate $\dot{M}$ is investigated. The result shows that there exists a linear correlation between the photon index and mass accretion rate, and the spectral hardness increases with increasing $\dot{M}$. A possible emission mechanism for the explanation of spectral properties of AXPs is also discussed.

astro-ph↗

arXiv2003

Dynamics of Distillability

The time evolution of a maximally entangled bipartite systems is presented in this paper. The distillability criterion is given in terms of Kraus operators. Using the criterion, we discuss the distillability of $2\times 2$ and $n\times n (n>2)$ systems in their evolution process. There are two distinguished processes, dissipation and decoherence, which may destroy the distillability. We discuss the effects of those processes on distillability in details.

quant-ph↗

arXiv2002

Cerenkov Line Emission as a Possible Mechanism of X-ray Lines in Gamma-ray Bursts

The recent discoveries of X-ray lines in the afterglows of gamma-ray bursts (GRBs) provide significant clues to the nature of GRB progenitors and central environments. However, the iron line interpretation by fluorescence or recombination mechanism requires a large amount of iron material. We argue that the very strong iron line could be attributed to an alternative mechanism: Cerenkov line emission since relativistic electrons and dense medium exist near GRB sites. Therefore, the broad iron lines are expected, and line intensity will be nearly independent of the iron abundance, the medium with the anomalously high Fe abundance is not required.

astro-ph↗

arXiv2001

Gamma-ray burst: probe of a black hole

There is strong evidence for the existence of black holes(BHs) in some X-ray binaries and most galatic nuclei, based on different measuremental approaches, but black holes aren't finally identified for the lack of very firm observational evidence up to now. Because the direct evidence for BHs should come from determination of strong gravitational redshift, we hope an object can fall into the region near the BH horizon where radiation can be detected. Therefore the object must be compact stars as neutron stars(NSs), then the intense astrophysical processes will release very high energy radiation which is transient, fast-variant. These phenomena may point to gamma-ray bursts(GRBs) observed. And recent observations of iron lines suggest that afterglows of GRBs show the similar property in active galatic nuclei(AGNs), implying GRBs may originate from intense events related to black holes. In this letter, a model for GRBs and afterglows is proposed to obtain the range of gravitational redshifts($z_g$) of GRBs with known cosmological redshifts. Hence, we provide a new method that with a search for high-energy emission lines(X- or $γ$-rays) in GRBs, one can determine the gravitational redshift. We expect $z_g>0.5$ or even larger, so that we can rule out the possibility of other compact objects such as NSs, suggesting that the central progenitors of GRBs should be black holes.

astro-ph↗

arXiv2001

Peak Effect of Jc and Nonlinear E-J Characteristies of High-Tc Superconductors

The critical current density Jc in high-Tc superconductors (HTS) often shows a maximum at field far above the self-field. We study this peak effect(PE) with the nonlinear I-V response of type-II superconductors and find analytical equation of Jc in the dependence of filed and temperature. Theis equation is compared with some experimental data of R-Ba-Cu-O single crystals with fair agreement.

cond-mat.supr-con↗

arXiv2001

Scaling Behavior of Anomalous Hall Effect and Longitudinal Nonlinear Response in High-Tc Superconductors

Based on existing theoretical model and by considering our longitudinal nonlinear response function, we derive a nonliear equation in which the mixed state Hall resistivity can be expressed as an analytical function of magnetic field, temperature and applied current. This equation enables one to compare quantitatively the experimental data with theoretical model. We also find some new scaling relations of the temperature and field dependency of Hall resistivity. The comparison between our theoretical curves and experimental data shows a fair agreement.

cond-mat.supr-con↗

arXiv2001

Gamma-Ray Burst Afterglows with Energy Injection: Homogeneous Versus Wind External Media

Assuming an adiabatic evolution of a gamma-ray burst (GRB) fireball interacting with an external medium, we calculate the hydrodynamics of the fireball with energy injection from a strongly magnetic millisecond pulsar through magnetic dipole radiation, and obtain the light curve of the optical afterglow from the fireball by synchrotron radiation. Results are given both for a homogeneous external medium and for a wind ejected by GRB progenitor. Our calculations are also available in both ultra-relativistic and non-relativistic phases. Furthermore, the observed R-band light curve of GRB{000301C} can be well fitted in our model, which might provide a probe of the properties of GRB progenitors.

astro-ph↗

arXiv2001

Modeling two-state cooperativity in protein folding

A protein model with the pairwise interaction energies varying as local environment changes, i.e., including some kinds of collective effect between the contacts, is proposed. Lattice Monte Carlo simulations on the thermodynamical characteristics and free energy profile show a well-defined two-state behavior and cooperativity of folding for such a model. As a comparison, related simulations for the usual Gō model, where the interaction energies are independent of the local conformations, are also made. Our results indicate that the evolution of interactions during the folding process plays an important role in the two-state cooperativity in protein folding.

cond-mat.soft↗

arXiv1999

The Structure of Weighting Coefficient Matrices of Harmonic Differential Quadrature and Its Applications

The structure of weighting coefficient matrices of Harmonic Differential Quadrature (HDQ) is found to be either centrosymmetric or skew centrosymmetric depending on the order of the corresponding derivatives. The properties of both matrices are briefly discussed in this paper. It is noted that the computational effort of the harmonic quadrature for some problems can be further reduced up to 75 per cent by using the properties of the above-mentioned matrices.

cs.CE↗

arXiv1994

W_{1+\infty} and W(gl_N) with central charge N

We study representations of the central extension of the Lie algebra of differential operators on the circle, the W-infinity algebra. We obtain complete and specialized character formulas for a large class of representations, which we call primitive; these include all quasi-finite irreducible unitary representations. We show that any primitive representation with central charge N has a canonical structure of an irreducible representation of the W-algebra W(gl_N) with the same central charge and that all irreducible representations of W(gl_N) with central charge N arise in this way. We also establish a duality between "integral" modules of W(gl_N) and finite-dimensional irreducible modules of gl_N, and conjecture their fusion rules.

hep-th↗