Orbital-resolved vortex core states in FeSe Superconductors: calculation based on a three-orbital model

We study electronic structure of vortex core states of FeSe superconductors based on a t$_{2g}$ three-orbital model by solving the Bogoliubov-de Gennes(BdG) equation self-consistently. The orbital-resolved vortex core states of different pairing symmetries manifest themselves as distinguishable structures due to different quasi-particle wavefunctions. The obtained vortices are classified in terms of the invariant subgroups of the symmetry group of the mean-field Hamiltonian in the presence of magnetic field. Isotropic $s$ and anisotropic $s$ wave vortices have $G_5$ symmetry for each orbital, whereas $d_{x^2-y^2}$ wave vortices show $G^{*}_{6}$ symmetry for $d_{xz/yz}$ orbitals and $G^{*}_{5}$ symmetry for $d_{xy}$ orbital. In the case of $d_{x^2-y^2}$ wave vortices, hybridized-pairing between $d_{xz}$ and $d_{yz}$ orbitals gives rise to a relative phase difference in terms of gauge transformed pairing order parameters between $d_{xz/yz}$ and $d_{xy}$ orbitals, which is essentially caused by a transformation of co-representation of $G^{*}_{5}$ and $G^{*}_{6}$ subgroup. The calculated local density of states(LDOS) of $d_{x^2-y^2}$ wave vortices show qualitatively similar pattern with experiment results. The phase difference of $\frac{\pi}{4}$ between $d_{xz/yz}$ and $d_{xy}$ orbital-resolved $d_{x^2-y^2}$ wave vortices can be verified by further experiment observation

A spatially resolved plerionic X-ray nebula around PSR B0540-69

We present a high resolution Chandra X-ray observation of PSR B0540-69, the Crab-like 50 msec pulsar in the Large Magellanic Cloud. We use phase-resolved imaging to decompose the extended X-ray emission, as expected of a synchrotron nebula, from the point-like emission of the pulsar. The image of the pulsed X-ray emission shows a well-defined point-spread function of the observation, while the resolved nebula has a morphology and size remarkably similar to the Crab nebula, including evidence for a jet-like feature from PSR B0540-69. The patchy outer shell, which most likely represents the expanding blast-wave of the supernova, is reminiscent of that seen in radio. Based on morphology, size, and energetics there can be little doubt that PSR B0540-69 is an analogous system to the Crab but located in our neighboring galaxy.Comment: 5 pages with 5 figures, LaTex, emulateapj.sty. Revision based on data corrected for instrumental artifacts; main result unchanged. This version to appear in the Astrophysical Journal Letter

Delay-induced multiple stochastic resonances on scale-free neuronal networks

We study the effects of periodic subthreshold pacemaker activity and time-delayed coupling on stochastic resonance over scale-free neuronal networks. As the two extreme options, we introduce the pacemaker respectively to the neuron with the highest degree and to one of the neurons with the lowest degree within the network, but we also consider the case when all neurons are exposed to the periodic forcing. In the absence of delay, we show that an intermediate intensity of noise is able to optimally assist the pacemaker in imposing its rhythm on the whole ensemble, irrespective to its placing, thus providing evidences for stochastic resonance on the scale-free neuronal networks. Interestingly thereby, if the forcing in form of a periodic pulse train is introduced to all neurons forming the network, the stochastic resonance decreases as compared to the case when only a single neuron is paced. Moreover, we show that finite delays in coupling can significantly affect the stochastic resonance on scale-free neuronal networks. In particular, appropriately tuned delays can induce multiple stochastic resonances independently of the placing of the pacemaker, but they can also altogether destroy stochastic resonance. Delay-induced multiple stochastic resonances manifest as well-expressed maxima of the correlation measure, appearing at every multiple of the pacemaker period. We argue that fine-tuned delays and locally active pacemakers are vital for assuring optimal conditions for stochastic resonance on complex neuronal networks.Comment: 7 two-column pages, 5 figures; accepted for publication in Chao

Maximum Path Information and Fokker-Planck Equation

We present in this paper a rigorous method to derive the nonlinear Fokker-Planck (FP) equation of anomalous diffusion directly from a generalization of the principle of least action of Maupertuis proposed by Wang for smooth or quasi-smooth irregular dynamics evolving in Markovian process. The FP equation obtained may take two different but equivalent forms. It was also found that the diffusion constant may depend on both q (the index of Tsallis entropy) and the time t.Comment: 7 page

Supernova Blastwaves in Low-density Hot Media: a Mechanism for Spatially Distributed Heating

Most supernovae are expected to explode in low-density hot media, particularly in galactic bulges and elliptical galaxies. The remnants of such supernovae, though difficult to detect individually, can be profoundly important in heating the media on large scales. We characterize the evolution of this kind of supernova remnants, based on analytical approximations and hydrodynamic simulations. We generalize the standard Sedov solution to account for both temperature and density effects of the ambient media. Although cooling can be neglected, the expansion of such a remnant deviates quickly from the standard Sedov solution and asymptotically approaches the ambient sound speed as the swept-up thermal energy becomes important. The relatively steady and fast expansion of the remnants over large volumes provides an ideal mechanism for spatially distributed heating, which may help to alleviate the over-cooling problem of hot gas in groups and clusters of galaxies as well as in galaxies themselves. The simulations were performed with the FLASH code.Comment: 12 pages, 3 figures, 1 table, accepted for ApJ, uses aaste

ROSAT HRI Detection of the 16 ms Pulsar PSR J0537-6910 Inside SNR N157B

Based on a deep ROSAT HRI observation, we have detected a pulsed signal in the 0.1-2 keV band from PSR J0537-6910 --- the recently discovered pulsar associated with the supernova remnant N157B in the Large Magellanic Cloud. The measured pulse period 0.01611548182 ms (+- 0.02 ns), Epoch MJD 50540.5, gives a revised linear spin-down rate of $5.1271 \times 10^{-14} s s^{-1}$, slightly greater than the previously derived value. The narrow pulse shape (FWHM = 10% duty cycle) in the ROSAT band resembles those seen in both XTE and ASCA data (> 2 keV), but there is also marginal evidence for an interpulse. This ROSAT detection enables us to locate the pulsar at R.A., Dec (J2000) = $5^h37^m47^s.2, -69^\circ 10' 23''$. With its uncertainty $\sim 3''$, this position coincides with the centroid of a compact X-ray source. But the pulsed emission accounts for only about 10% of the source luminosity $\sim 2 \times 10^{36} ergs^{-1}$ in the 0.1-2 keV band. These results support our previous suggestions: (1) The pulsar is moving at a high velocity ($\sim 10^3 km/s$); (2) A bow shock, formed around the pulsar, is responsible for most of the X-ray emission from the source; (3) A collimated outflow from the bow shock region powers a pulsar wind nebula that accounts for an elongated non-thermal radio and X-ray feature to the northwest of the pulsar.Comment: 6 pages including 3 figures. To be published in ApJ

High Speed Dim Air Target Detection Using Airborne Radar under Clutter and Jamming Effects

The challenging potential problems associated with using airborne radar in detection of high Speed Maneuvering Dim Target (HSMDT) are the highly noise, jamming and clutter effects. The problem is not only how to remove clutter and jamming as well as the range migration and Doppler ambiguity estimation problems due to high relative speed between the targets and airborne radar. Some of the recently published works ignored the range migration problems, while the others ignored the Doppler ambiguity estimation. In this paper a new hybrid technique using Optimum Space Time Adaptive Processing (OSTAP), Second Order Keystone Transform (SOKT), and the Improved Fractional Radon Transform (IFrRT) was proposed. The OSTAP was applied as anti-jamming and clutter rejection method, the SOKT corrects the range curvature and part of the range walk, then the IFrRT estimates the target’ radial acceleration and corrects the residual range walk. The simulation demonstrates the validity and effectiveness of the proposed technique, and its advantages over the previous researches by comparing its probability of detection with the traditional methods. The new approach increases the probability of detection, and also overcomes the limitation of Doppler frequency ambiguity

G359.95-0.04: Pulsar Candidate Near Sgr A*

We report the discovery of a prominent nonthermal X-ray feature located near the Galactic center that we identify as an energetic pulsar wind nebula. This feature, G359.95-0.04, lies 1 lyr north of Sgr A* (in projection), is comet-like in shape, and has a power law spectrum that steepens with increasing distance from the putative pulsar. The distinct spectral and spatial X-ray characteristics of the feature are similar to those belonging the rare class of ram-pressure confined pulsar wind nebulae. The luminosity of the nebula at the distance of \sgra, consistent with the inferred X-ray absorptions, is 1 10^{34} ergs s^{-1} in the 2--10 keV energy band. The cometary tail extends back to a region centered at the massive stellar complex IRS 13 and surrounded by enhanced diffuse X-ray emission, which may represent an associated supernova remnant. Furthermore, the inverse Compton scattering of the strong ambient radiation by the nebula consistently explains the observed TeV emission from the Galactic center. We also briefly discuss plausible connections of G359.95-0.04 to other high-energy sources in the region, such as the young stellar complex IRS 13 and SNR Sgr A East.Comment: 11 pages, accepted for publication in MNRAS, higher resolution version at http://www.astro.umass.edu/~wqd/papers/xcomet.pd