Mixed partial-wave scattering with spin-orbit coupling and validity of pseudo-potentials

We present exact solutions of two-body problem for spin-1/2 fermions with isotropic spin-orbit(SO) coupling and interacting with an arbitrary short-range potential. We find that in each partial-wave scattering channel, the parametrization of two-body wavefunction at short inter-particle distance depends on the scattering amplitudes of all channels. This reveals the mixed partial-wave scattering induced by SO couplings. By comparing with results from a square-well potential, we investigate the validity of original pseudo-potential models in the presence of SO coupling. We find the s-wave pseudo-potential provides a good approximation for low-energy solutions near s-wave resonances, given the length scale of SO coupling much longer than the potential range. However, near p-wave resonance the p-wave pseudo-potential gives low-energy solutions that are qualitatively different from exact ones, based on which we conclude that the p-wave model can not be applied to the fermion system if the SO coupling strength is larger or comparable to the Fermi momentum.Comment: 10 pages, 8 figures. Published version with figures improve

Metallic and semi-metallic <100> silicon nanowires

Silicon nanowires grown along the -direction with a bulk Si core are studied with density functional calculations. Two surface reconstructions prevail after exploration of a large fraction of the phase space of nanowire reconstructions. Despite their energetical equivalence, one of the reconstructions is found to be strongly metallic while the other one is semi-metallic. This electronic-structure behavior is dictated by the particular surface states of each reconstruction. These results imply that doping is not required in order to obtain good conducting Si nanowires.Comment: 13 pages, 4 figures; Phys. Rev. Lett., in pres

Opaque Service Virtualisation: A Practical Tool for Emulating Endpoint Systems

Large enterprise software systems make many complex interactions with other services in their environment. Developing and testing for production-like conditions is therefore a very challenging task. Current approaches include emulation of dependent services using either explicit modelling or record-and-replay approaches. Models require deep knowledge of the target services while record-and-replay is limited in accuracy. Both face developmental and scaling issues. We present a new technique that improves the accuracy of record-and-replay approaches, without requiring prior knowledge of the service protocols. The approach uses Multiple Sequence Alignment to derive message prototypes from recorded system interactions and a scheme to match incoming request messages against prototypes to generate response messages. We use a modified Needleman-Wunsch algorithm for distance calculation during message matching. Our approach has shown greater than 99% accuracy for four evaluated enterprise system messaging protocols. The approach has been successfully integrated into the CA Service Virtualization commercial product to complement its existing techniques.Comment: In Proceedings of the 38th International Conference on Software Engineering Companion (pp. 202-211). arXiv admin note: text overlap with arXiv:1510.0142

Spectroscopic signatures of the Larkin-Ovchinnikov state in the conductance characteristics of a normal-metal/superconductor junction

Using a discrete-lattice approach, we calculate the conductance spectra between a normal metal and an s-wave Larkin-Ovchinnikov (LO) superconductor, with the junction interface oriented {\em along} the direction of the order-parameter (OP) modulation. The OP sign reversal across one single nodal line can induce a sizable number of zero-energy Andreev bound states around the nodal line, and a hybridized midgap-states band is formed amid a momentum-dependent gap as a result of the periodic array of nodal lines in the LO state. This band-in-gap structure and its anisotropic properties give rise to distinctive features in both the point-contact and tunneling spectra as compared with the BCS and Fulde-Ferrell cases. These spectroscopic features can serve as distinguishing signatures of the LO state.Comment: 8 pages, 5 figures; version as publishe

Possible discovery of the r-process characteristics in the abundances of metal-rich barium stars

We study the abundance distributions of a sample of metal-rich barium stars provided by Pereira et al. (2011) to investigate the s- and r-process nucleosynthesis in the metal-rich environment. We compared the theoretical results predicted by a parametric model with the observed abundances of the metal-rich barium stars. We found that six barium stars have a significant r-process characteristic, and we divided the barium stars into two groups: the r-rich barium stars ($C_r>5.0$, [La/Nd]\,$<0$) and normal barium stars. The behavior of the r-rich barium stars seems more like that of the metal-poor r-rich and CEMP-r/s stars. We suggest that the most possible formation mechanism for these stars is the s-process pollution, although their abundance patterns can be fitted very well when the pre-enrichment hypothesis is included. The fact that we can not explain them well using the s-process nucleosynthesis alone may be due to our incomplete knowledge on the production of Nd, Eu, and other relevant elements by the s-process in metal-rich and super metal-rich environments (see details in Pereira et al. 2011).Comment: 5 pages, 5 figures, accepted for publication in A&

Evidence for "Propeller" Effects In X-ray Pulsars GX 1+4 And GROJ1744-28

We present observational evidence for "propeller" effects in two X-ray pulsars, GX 1+4 and GROJ1744-28. Both sources were monitored regularly by the Rossi X-ray Timing Explorer (RXTE) throughout a decaying period in the X-ray brightness. Quite remarkably, strong X-ray pulsation became unmeasurable when total X-ray flux had dropped below a certain threshold. Such a phenomenon is a clear indication of the propeller effects which take place when pulsar magnetosphere grows beyond the co-rotation radius as a result of the decrease in mass accretion rate and centrifugal force prevents accreting matter from reaching the magnetic poles. The entire process should simply reverse as the accretion rate increases. Indeed, steady X-ray pulsation was reestablished as the sources emerged from the non-pulsating faint state. These data allow us to directly derive the surface polar magnetic field strength for both pulsars: 3.1E+13 G for GX 1+4 and 2.4E+11 G for GROJ1744-28. The results are likely to be accurate to within a factor of 2, with the total uncertainty dominated by the uncertainty in estimating the distances to the sources. Possible mechanisms for the persistent emission observed in the faint state are discussed in light of the extreme magnetic properties of the sources.Comment: 12 pages including 3 ps figures. To appear in ApJ Letters Vol. 48

Learning a Mixture of Deep Networks for Single Image Super-Resolution

Single image super-resolution (SR) is an ill-posed problem which aims to recover high-resolution (HR) images from their low-resolution (LR) observations. The crux of this problem lies in learning the complex mapping between low-resolution patches and the corresponding high-resolution patches. Prior arts have used either a mixture of simple regression models or a single non-linear neural network for this propose. This paper proposes the method of learning a mixture of SR inference modules in a unified framework to tackle this problem. Specifically, a number of SR inference modules specialized in different image local patterns are first independently applied on the LR image to obtain various HR estimates, and the resultant HR estimates are adaptively aggregated to form the final HR image. By selecting neural networks as the SR inference module, the whole procedure can be incorporated into a unified network and be optimized jointly. Extensive experiments are conducted to investigate the relation between restoration performance and different network architectures. Compared with other current image SR approaches, our proposed method achieves state-of-the-arts restoration results on a wide range of images consistently while allowing more flexible design choices. The source codes are available in http://www.ifp.illinois.edu/~dingliu2/accv2016

Continuous volumetric imaging via an optical phase-locked ultrasound lens

In vivo imaging at high spatiotemporal resolution is key to the understanding of complex biological systems. We integrated an optical phase-locked ultrasound lens into a two-photon fluorescence microscope and achieved microsecond-scale axial scanning, thus enabling volumetric imaging at tens of hertz. We applied this system to multicolor volumetric imaging of processes sensitive to motion artifacts, including calcium dynamics in behaving mouse brain and transient morphology changes and trafficking of immune cells