Correlation between the cohesive energy and the onset of radiation-enhanced diffusion in ion mixing

A correlation between the cohesive energy of elemental solids and the characteristic temperature Tc for the onset of radiation-enhanced diffusion during ion mixing is established. This correlation enables one to predict the onset of radiation-enhanced diffusion for systems which have not yet been investigated. A theoretical argument based on the current models of cascade mixing and radiation-enhanced diffusion is provided as a basis for understanding this observation

Analytical Solution to Transport in Brownian Ratchets via Gambler's Ruin Model

We present an analogy between the classic Gambler's Ruin problem and the thermally-activated dynamics in periodic Brownian ratchets. By considering each periodic unit of the ratchet as a site chain, we calculated the transition probabilities and mean first passage time for transitions between energy minima of adjacent units. We consider the specific case of Brownian ratchets driven by Markov dichotomous noise. The explicit solution for the current is derived for any arbitrary temperature, and is verified numerically by Langevin simulations. The conditions for vanishing current and current reversal in the ratchet are obtained and discussed.Comment: 4 pages, 3 figure

Modelling the multi-wavelength emissions from PSR B1259-63/LS 2883: the effects of the stellar disc on shock radiations

PSR B1259-63/LS 2883 is an elliptical pulsar/Be star binary and emits broadband emissions from radio to TeV $\gamma$-rays. The massive star possesses an equatorial disc, which is inclined with the orbital plane of the pulsar. The non-thermal emission from the system is believed to be produced by the pulsar wind shock and the double-peak profiles in the X-ray and TeV $\gamma$-ray light curves are related to the phases of the pulsar passing through the disc region of the star. In this paper, we investigate the interactions between the pulsar wind and stellar outflows, especially with the presence of the disc, and present a multi-wavelength modelling of the emission from this system. We show that the double-peak profiles of X-ray and TeV $\gamma$-ray light curves are caused by the enhancements of the magnetic field and the soft photons at the shock during the disc passages. As the pulsar is passing through the equatorial disc, the additional pressure of the disc pushes the shock surface closer to the pulsar, which causes the enhancement of magnetic field in the shock, and thus increases the synchrotron luminosity. The TeV $\gamma$-rays due to the inverse-Compton (IC) scattering of shocked electrons with seed photons from the star is expected to peak around periastron which is inconsistent with observations. However, the shock heating of the stellar disc could provide additional seed photons for IC scattering during the disc passages, and thus produces the double-peak profiles as observed in the TeV $\gamma$-ray light curve. Our model can possibly be examined and applied to other similar gamma-ray binaries, such as PSR J2032+4127/MT91 213, HESS J0632+057, and LS I+61$^{\circ}$303.Comment: 14 pages, 6 figure

Bridgeness: A Local Index on Edge Significance in Maintaining Global Connectivity

Edges in a network can be divided into two kinds according to their different roles: some enhance the locality like the ones inside a cluster while others contribute to the global connectivity like the ones connecting two clusters. A recent study by Onnela et al uncovered the weak ties effects in mobile communication. In this article, we provide complementary results on document networks, that is, the edges connecting less similar nodes in content are more significant in maintaining the global connectivity. We propose an index named bridgeness to quantify the edge significance in maintaining connectivity, which only depends on local information of network topology. We compare the bridgeness with content similarity and some other structural indices according to an edge percolation process. Experimental results on document networks show that the bridgeness outperforms content similarity in characterizing the edge significance. Furthermore, extensive numerical results on disparate networks indicate that the bridgeness is also better than some well-known indices on edge significance, including the Jaccard coefficient, degree product and betweenness centrality.Comment: 10 pages, 4 figures, 1 tabl

The Kinematic Evolution of Erupting Structures in Confined Solar Flares

In this Letter, we study the kinematic properties of ascending hot blobs associated with confined flares. Taking advantage of high-cadence extreme-ultraviolet images provided by the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory, we find that for the 26 events selected here, the hot blobs are first impulsively accelerated outward, but then quickly slow down to motionlessness. Their velocity evolution is basically synchronous with the temporal variation of the Geostationary Operational Environmental Satellite soft X-ray flux of the associated flares, except that the velocity peak precedes the soft X-ray peak by minutes. Moreover, the duration of the acceleration phase of the erupting blobs is moderately correlated with that of the flare rise phase. For nine of the 26 cases, the erupting blobs even appear minutes prior to the onset of the associated flares. Our results show that a fraction of confined flares also involve the eruption of a magnetic flux rope, which sometimes is formed and heated prior to the flare onset. We suggest that the initiation and development of these confined flares are similar to that of eruptive ones, and the main difference may lie in the background field constraint, which is stronger for the former than for the latter.Comment: 13 pages,4 figure

Remedial brushless AC operation of fault-tolerant doubly salient permanent-magnet motor drives

The doubly salient permanent-magnet (DSPM) machine is a new class of stator-PM brushless machines, which inherently offers the fault-tolerant feature. In this paper, a new operation strategy is proposed and implemented for fault-tolerant DSPM motor drives. The key is to operate the DSPM motor drive in a remedial brushless ac (BLAC) mode under the open-circuit fault condition, while operating in the conventional brushless dc mode under normal condition. Both cosimulation and experimental results confirm that the proposed remedial BLAC operation can maintain the average torque, reduce the torque ripple, and retain the self-starting capability under the open-circuit fault. © 2006 IEEE.published_or_final_versio

A transient cosimulation approach to performance analysis of hybrid excited doubly salient machine considering indirect field-circuit coupling

This paper presents a hybrid excited doubly salient (HEDS) machine, which can be used as the integrated starter-generator (ISG) for modern automobile and hybrid electric vehicles (HEVs). The key of the proposed machine is to incorporate both direct current (dc) field windings and permanent magnets (PMs) in the stator, hence, offering a compact arrangement of hybrid field excitations, while the rotor is simply composed of salient poles without windings or FMs. The air-gap flux can be strengthened or weakened with a reasonable dc field current so that the electromagnetic torque and induced electromotive force (EMF) can be effectively regulated. To predict the electromagnetic performances of the machine more accurately, a new transient cosimulation approach considering indirect field-circuit coupling is proposed. Experimental results on a prototype machine have been given to verify the technique. The method is not only more efficient and flexible, but also more accurate and stable, which can also be used in analyzing other electric machine and drive systems. © 2007 IEEE.published_or_final_version10th Joint Magnetism and Magnetic Materials Conference/International Magnetics Conference, Balitmore, MD, 07-11 JAN 2007. In IEEE Transactions On Magnetics, 2007, v. 43 n. 6, p. 2558-256