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Dong Wang

Publications and source records attributed to Dong Wang.

At least 829 records · Page 46Linked to original sources
arXiv2013

FEL Polarization Control Studies on Dalian Coherent Light Source

The polarization switch of a free-electron laser (FEL) is of great importance to the user scientific community. In this paper, we investigate the generation of controllable polarization FEL from two well-known approaches for Dalian coherent light source, i.e., crossed planar undulator and elliptical permanent undulator. In order to perform a fair comparative study, a one-dimensional time-dependent FEL code has been developed, in which the imperfection effects of an elliptical permanent undulator are taken into account. Comprehensive simulation results indicate that the residual beam energy chirp and the intrinsic FEL gain may contribute to the degradation of the polarization performance for the crossed planar undulator. And the elliptical permanent undulator is not very sensitive to the undulator errors and beam imperfections. Meanwhile, with proper configurations of the main planar undulators and additional elliptical permanent undulator section, circular polarized FEL with pulse energy exceeds 100 $μ$J could be achieved at Dalian coherent light source.

physics.acc-ph↗
arXiv2012

Status of polarization control experiment at Shanghai deep ultraviolet free electron laser

A polarization control experiment by utilizing a pair of crossed undulators has been proposed for the Shanghai deep ultraviolet free electron laser test facility. Numerical simulations indicate that, with the electromagnetic phase-shifter located between the two crossed planar undulators, fully coherent radiation with 100 nJ order pulse energy, 5 picoseconds pulse length and circular polarization degree above 90% could be generated. The physical design study and the preparation status of the experiment are presented in the paper.

physics.acc-ph↗
arXiv2012

On a relationship between high rank cases and rank one cases of Hermitian random matrix models with external source

We prove an identity on Hermitian random matrix models with external source relating the high rank cases to the rank 1 cases. This identity was proved and used in a previous paper of ours to study the asymptotics of the top eigenvalues. In this paper, we give an alternative, more conceptual proof of this identity based on a connection between the Hermitian matrix models with external source and the discrete KP hierarchy. This connection is obtained using the vertex operator method of Adler and van Moerbeke. The desired identity then follows from the Fay-like identity of the discrete KP tau vector.

math.PR↗
arXiv2012

Chemical Constraints on the Oxygen Abundances in Jupiter and Saturn

We perform a comparative analysis of the chemical kinetics of CO and $\rm PH_3$ in Jupiter and Saturn to assess the full set of constraints available on the troposphere water abundance in the two giant planets. For carbon monoxide we employ both a widely used CO kinetic scheme from Yung et al, and a newly identified CO chemical scheme from Visscher and Moses. For $\rm PH_3$ chemical scheme, we use the same chemical scheme as in Visscher and Fegley. Yung's chemical scheme for CO yields a water enrichment of 0.95 - 23.0 times solar abundance on Jupiter, and an upper limit of 14.0 for Saturn. Visscher's chemical scheme in contrast produces a water enrichment of 0.24 - 2.6 times solar abundance in Jupiter, and for Saturn an upper limit for water enrichment of 8.0. From this scheme, which takes advantage of the most up-to-date kinetics, we preclude high water enrichments on Jupiter and Saturn, and show that the kinetics approach yields Jovian bulk abundance in which values of C/O elevated relative to solar are admissible. Our result is consistent with recent reinterpretation of Galileo Probe data in which Jupiter formed in a water-depleted portion of the protoplanetary disk (Mousis et al).

astro-ph.EP↗
arXiv2012

On the largest eigenvalue of a Hermitian random matrix model with spiked external source II. Higher rank cases

This is the second part of a study of the limiting distributions of the top eigenvalues of a Hermitian matrix model with spiked external source under a general external potential. The case when the external source is of rank one was analyzed in an earlier paper. In the present paper we extend the analysis to the higher rank case. If all the eigenvalues of the external source are less than a critical value, the largest eigenvalue converges to the right end-point of the support of the equilibrium measure as in the case when there is no external source. On the other hand, if an external source eigenvalue is larger than the critical value, then an eigenvalue is pulled off from the support of the equilibrium measure. This transition is continuous, and is universal, including the fluctuation laws, for convex potentials. For non-convex potentials, two types of discontinuous transitions are possible to occur generically. We evaluate the limiting distributions in each case for general potentials including those whose equilibrium measure have multiple intervals for their support.

math-ph↗
arXiv2012

Polarization control proposal for Shanghai deep ultraviolet free electron laser

In this paper, a fully coherent radiation option with controllable polarization is proposed for Shanghai deep ultraviolet free electron laser (FEL) test facility. Intensive start-to-end simulation suggests that, the two crossed planar undulators which generate the horizontal and vertical linear polarized FEL respectively, should be placed as close as possible for avoiding the polarization performance degradation of the final combined FEL radiation. With the existence of the phase-shifter between the two crossed radiators, Fourier-Transform-Limited output radiation with 100 nJ order pulse energy, 5 ps full pulse length and circular polarization degree above 90% could be achieved.

physics.acc-ph↗
arXiv2012

Species Diversity in Rock-Paper-Scissors Game Coupling with Levy Flight

Rock-paper-scissors (RPS) game is a nice model to study the biodiversity in ecosystem. However, the previous studies only consider the nearest- neighbor- interaction among the species. In this paper, taking the long range migration into account, the effects of the interplay between nearest-neighbor-interaction and long-range-interaction of Levy flight obey the power law distance distribution with the exponent h (-0.3<h<-0.1) in spatial RPS game is investigated. Taking the probability of long range Levy flight and the power exponent as parameters, the coexistence conditions of three species are found. The critical curves for stable coexistence of three species in the parameters space are presented. It is also found that long-range-interaction with Levy flight has interesting effects on the final spatiotemporal pattern of the system. The results reveal that the long-range-interaction of Levy flight exhibit pronounced effects on biodiversity of ecosystem.

physics.bio-ph↗
arXiv2012

The largest eigenvalue of real symmetric, Hermitian and Hermitian self-dual random matrix models with rank one external source, part I

We consider the limiting location and limiting distribution of the largest eigenvalue in real symmetric ($β$ = 1), Hermitian ($β$ = 2), and Hermitian self-dual ($β$ = 4) random matrix models with rank 1 external source. They are analyzed in a uniform way by a contour integral representation of the joint probability density function of eigenvalues. Assuming the one-band condition and certain regularities of the potential function, we obtain the limiting location of the largest eigenvalue when the nonzero eigenvalue of the external source matrix is not the critical value, and further obtain the limiting distribution of the largest eigenvalue when the nonzero eigenvalue of the external source matrix is greater than the critical value. When the nonzero eigenvalue of the external source matrix is less than or equal to the critical value, the limiting distribution of the largest eigenvalue will be analyzed in a subsequent paper. In this paper we also give a definition of the external source model for all $β$ > 0.

math-ph↗
arXiv2011

Recoiling Supermassive Black Holes in Spin-flip Radio Galaxies

Numerical relativity simulations predict that coalescence of supermassive black hole (SMBH) binaries not only leads to a spin flip but also to a recoiling of the merger remnant SMBHs. In the literature, X-shaped radio sources are popularly suggested to be candidates for SMBH mergers with spin flip of jet-ejecting SMBHs. Here we investigate the spectral and spatial observational signatures of the recoiling SMBHs in radio sources undergoing black hole spin flip. Our results show that SMBHs in most spin-flip radio sources have mass ratio $q\ga 0.3$ with a minimum possible value $q_{\rm min} \simeq 0.05$. For major mergers, the remnant SMBHs can get a kick velocity as high as $2100 km s^{-1}$ in the direction within an angle $\la 40^\circ$ relative to the spin axes of remnant SMBHs, implying that recoiling quasars are biased to be with high Doppler-shifted broad emission lines while recoiling radio galaxies are biased to large apparent spatial off-center displacements. We also calculate the distribution functions of line-of-sight velocity and apparent spatial off-center for spin-flip radio sources with different apparent jet reorientation angles. Our results show that the larger the apparent jet reorientation angle is, the larger the Doppler-shifting recoiling velocity and apparent spatial off-center displacement will be. We investigate the effects of recoiling velocity on the dust torus in spin-flip radio sources and suggest that recoiling of SMBHs would lead to "dust poor" AGNs. Finally, we collect a sample of 19 X-shaped radio objects and for each object give the probability of detecting the predicted signatures of recoiling SMBH.

astro-ph.CO↗
arXiv2011

The contribution of spin torque to spin Hall coefficient and spin motive force in spin-orbit coupling system

We derive rigorously the relativistic angular momentum conservation equation by means of quantum electrodynamics. The novel nonrelativistic spin current and torque in the spin-orbit coupling system, up to the order of $1/c^{4}$, are exactly investigated by using Foldy-Wouthuysen transformation. We find a perfect spin Hall coefficient including the contribution of spin torque dipole. A novel spin motive force, analogue to the Lorentz force, is also obtained for understanding of the spin Hall effect.

cond-mat.str-el↗
arXiv2011

Characterizing Temporal Structure of the Relativistic Electron Bunch

Using proper beam energy chirp and the undulator detuning effect, we propose a modified optical replica synthesizer scheme to characterize the temporal structure of a relativistic electron bunch, which predicts a 100-fs temporal resolution in numerical simulation. The proof of principle experiment demonstrates a peak current of 9 A and a slice energy spread of about 0.5 keV for the uncompressed electron beam of the Shanghai Deep UV Free Electron Laser Facility.

physics.acc-ph↗
arXiv2011

A genuine maximally seven-qubit entangled state

Contrary to A.Borras et al.'s [1] conjecture, a genuine maximally seven-qubit entangled state is presented. We find a seven-qubit state whose marginal density matrices for subsystems of 1,2- qubits are all completely mixed and for subsystems of 3-qubits is almost completely mixed.

quant-ph↗
arXiv2011

Continuous variable entanglement measurement without phase locking

A new simple entanglement measurement method is proposed for the bright EPR beams generated from a non-degenerate optical parametric amplifier operating at deamplification. Due to the output signal and idler modes are frequency degenerate and in phase, the needed phase shift of interference for the measurement of the correlated phase quadratures and anti-correlated amplitude quadratures can be accomplished by a quarter-wave plate and a half wave plate without separating the signal and idler beam. Therefore, phase locking and local oscillators are avoided.

quant-ph↗
arXiv2010

On the largest eigenvalue of a Hermitian random matrix model with spiked external source I. Rank one case

Consider a Hermitian matrix model under an external potential with spiked external source. When the external source is of rank one, we compute the limiting distribution of the largest eigenvalue for general, regular, analytic potential for all values of the external source. There is a transitional phenomenon, which is universal for convex potentials. However, for non-convex potentials, new types of transition may occur. The higher rank external source is analyzed in the subsequent paper.

math-ph↗
arXiv2009

The largest sample eigenvalue distribution in the rank 1 quaternionic spiked model of Wishart ensemble

We solve the largest sample eigenvalue distribution problem in the rank 1 spiked model of the quaternionic Wishart ensemble, which is the first case of a statistical generalization of the Laguerre symplectic ensemble (LSE) on the soft edge. We observe a phase change phenomenon similar to that in the complex case, and prove that the new distribution at the phase change point is the GOE Tracy--Widom distribution.

math.PR↗
arXiv2009

Empirical likelihood for estimating equations with missing values

We consider an empirical likelihood inference for parameters defined by general estimating equations when some components of the random observations are subject to missingness. As the nature of the estimating equations is wide-ranging, we propose a nonparametric imputation of the missing values from a kernel estimator of the conditional distribution of the missing variable given the always observable variable. The empirical likelihood is used to construct a profile likelihood for the parameter of interest. We demonstrate that the proposed nonparametric imputation can remove the selection bias in the missingness and the empirical likelihood leads to more efficient parameter estimation. The proposed method is further evaluated by simulation and an empirical study on a genetic dataset on recombinant inbred mice.

math.ST↗
arXiv2008

Quantum interference structures in trapped ion dynamics beyond the Lamb-Dicke and rotating wave approximations

We apply wave packet methods to study an ion-trap system in the strong excitation regime imposing neither the rotating wave nor the Lamb-Dicke approximations. By this approach we show the existence of states with restricted phase space evolution, as a genuine consequence of quantum interference between wave packet fractions. A particular instance of such a state oscillates between maximal entanglement and pure disentanglement between the constitute subsystems. The characteristic crossover time is very rapid making them suitable for state preparations of EPR or Schrodinger cat states. Over longer time periods the dynamics of these states exhibits collapse-revival patterns with well resolved fractional revivals in autocorrelation, inversion and entanglement.

quant-ph↗