We report the discovery of 28 candidate high-velocity stars (HVSs) at heliocentric distances of less than 3 kpc, based on the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) Data Release 1. All candidates have velocities, with respect to the Galactic rest frame, in excess of 300 km s−1; 12 objects move faster than 400 km s−1. Our sample of HVS candidates covers a much broader color range than the equivalent ranges discussed in previous studies and comprises the first and largest sample of HVSs in the solar neighborhood. The observed as well as the derived parameters for all candidates are sufficiently accurate to allow us to ascertain their nature as genuine HVSs, of which a subset of 12 objects represents the most promising candidates. Our results also highlight the great potential of discovering statistically large numbers of HVSs of different spectral types in LAMOST survey data. The results reported here also highlight the great potential of discovering statistically large numbers of HVSs of different spectral types in LAMOST survey data. We will continue to perform further systematic HVS searches based on the LAMOST data; the resulting stellar samples will eventually enable us to better understand the nature of the HVSs themselves and ultimately constrain the structure of the Galaxy. As a consequence, it is of great importance for investigating the various HVS ejection mechanisms, which may be more complex than previously thought.

Precipitates of Cr at Σ3 <110> {112} GB in α-Fe have been studied using molecular dynamics with a two-band embedded atomic model potential. The accumulation and segregation of Cr atoms and the evolution of the GB depend on local Cr concentration and temperature. At the early stage, with the existence of vacancies, the strong attraction of Cr with the GB core provides a pathway for Cr atoms to quickly accumulate within the GB core. With the increase of Cr concentration, the size of Cr dilute precipitates increases dramatically. And the strong segregation of Cr at the GB is observed, when Cr concentration reach 20%. Also, the size of Cr precipitates increases with increasing the temperatures from 300 K to 1000 K. The accumulation and segregation of Cr atoms at the GB lead to significant deformation of the GB structure and the formation of GB steps, causing the displacement and broadening of the GB.

Extended abstract of a paper presented at Microscopy and Microanalysis 2013 in Indianapolis, Indiana, USA, August 4 – August 8, 2013.

In this paper, the characteristic impedance matching of the inner line and outer line of the multi-filar tape-helix Blumlein pulse forming line (BPFL) is analyzed in detail by dispersion theory of tape helix. Analysis of the spatial harmonics of multi-filar tape-helix BPFL shows that the integer harmonic numbers of the excited spatial harmonics are not continuous. In addition, the basic harmonic component still dominates the dispersion characteristics of the multi-filar tape-helix BPFL at low frequency band. The impedance mismatching phenomenon caused by the discontinuity of filling dielectrics in the inner line of BPFL is studied as an important issue. Effects of dielectric discontinuity on the coupled electromagnetic fields and the parameters of the outer line are also analyzed. The impedance matching conditions are both obtained under the situations of continuous filling dielectric and discontinuous dielectrics, respectively. Impedance characteristics of these two situations are analyzed by comparison, and effects of the thickness of support dielectric on the impedance are also presented. When the 6 mm-thickness nylon support of the multi-filar tape helix is used in the filling dielectric of de-ionized water, the characteristic impedances of the inner line and outer line of BPFL are 53 Ω and 14.7 Ω, respectively. After the improvement about substituting de-ionized water by castor oil, the relative permittivities of the support dielectric and filling dielectric are almost the same, and the impedances of the inner and outer line of BPFL become 80 Ω and 79 Ω, respectively. That is to say, the impedance mismatching problem caused by dielectric discontinuity is solved. Circuit simulation and experimental results basically correspond to the theoretical results, and the fact demonstrates that impedance analysis of the multi-filar tape-helix BPFL based on dispersion theory is correct.

In this paper, the tape-helix model is firstly introduced in the field of intense electron beam accelerator to analyze the dispersion effects on the electromagnetic parameters of helical Blumlein pulse forming line (PFL). Work band and dispersion relation of the PFL are analyzed, and the normalized coefficients of spatial harmonics are calculated. Dispersion effects on the important electromagnetic parameters of PFL, such as phase velocity, slow-wave coefficient, electric length and pulse duration, are analyzed as the central topic. In the PFL, electromagnetic waves with different frequencies in the work band of PFL have almost the same phase velocity. When de-ionized water, transformer oil and air are used as the PFL filling dielectric, respectively, the pulse duration of the helical Blumlein PFL is calculated as 479.6 ns, 81.1 ns and 53.1 ns in order. Electromagnetic wave simulation and experiments are carried out to demonstrate the theoretical calculations of the electric length and pulse duration which directly describe the phase velocity and dispersion of the PFL. Simulation results prove the theoretical analysis and calculation on pulse duration. Experiment is carried out based on the tape-helix Blumlein PFL and magnetic switch system. Experimental results show that the pulse durations are tested as 460 ns, 79 ns and 49 ns in order when de-ionized water, transformer oil and air are used respectively. Experimental results basically demonstrate the theoretical calculations and the analyses of dispersion.

The effects of laser incidence angle on lateral fast electron transport at front target surface, when a plasma is preformed, irradiated by intense (>1018 W/cm2) laser pulses, are studied by Kα imaging technique and electron spectrometer. A horizontally asymmetric Kα halo, resulting from directional lateral electron transport and energy deposition, is observed for a large incidence angle (70°). Moreover, a group of MeV high energy electrons is emitted along target surface. It is believed that the deformed preplasma and the asymmetrical distribution of self-generated magnetic field, at large incidence angle, play an important role in the directional lateral electron transport.

Enhancement of Kα yield from a metal foil covered with metal rods of submicron sizes, with low aspect ratio, irradiated by a p-polarized femtosecond laser pulses of about 1017 W/cm2 intensity is demonstrated. Obtained relative increase in Kα X-ray line emission is explained with a model of vacuum heating of fast electrons.

The pulse forming line (PFL) is the key part of the intense electron-beam accelerators (IEBA), which determines the quality and characteristic of the output beam current of the IEBA. Compared with the accelerator with traditional Blumlein line, an IEBA based on strip spiral Blumlein line (SSBL) can increase the duration of the output pulse in the same geometrical dimension. But the disadvantage of the SSBL is that the output voltage waveform at the matched load may be distorted, which influences the electron beam quality. In this paper, according to the electromagnetic theory, formulas for calculating the main electric parameters of SSBL (inductance, capacitance, transmission time, and characteristic impedance) are deduced. The effect of the geometric parameters of SSBL on the slowing coefficient is analyzed. The designed condition of SSBL for the output ideal voltage pulse in the matched load is obtained by theoretical analysis. Furthermore, the Karat code is used to simulate the output voltage waveform of SSBL on the matched load for different spiral angels. At last, a couple of contrastive experiments are performed on an electron-beam accelerator based on the SSBL with water dielectric. The experimental results agree with the theoretical and simulated results.

An electron-beam accelerator based on spiral water pulse forming line which consists of a primary storage capacitor system, an air core spiral strip transformer, a spiral pulse forming line of water dielectric, and a field-emission diode, is described. The experimental results showed that the diode voltage is more than 500 kV, the electron beam current of diode is about 24 kA, and the pulse duration is about 200 ns. The main parameters of the accelerator were calculated theoretically. The distributions for electrical field in the pulse forming line were obtained by the simulations. In addition, the process of the accelerator charging a spiral pulse forming line was simulated through the Pspice software to get the waveforms of charging voltage of pulse forming line, the diode voltage and diode current of accelerator. The theoretical and simulated results agree with the experimental results. This accelerator is very compact and works stably and reliably.

We present a theoretical model in order to describe both thermal and electronic in-plane transports in quantum dot superlattice. The model takes into account the modifications of electron and phonon transport due to the space confinement caused by the mismatch in electronic and thermal properties between dot and host materials. The developed model provides the analysis of the in-plane superlattice electronic and thermal properties versus quantum dot size and their arrangement. Numerical calculations were carried out for a structure that consists of multiple layers of Si with regimented germanium quantum dots. The simulation results of the lattice thermal conductivity are in a good agreement with experimental data.

We carried out the Gaussian fitting to the profile of PSR B1237+25 and found that six components rather than five are necessary to make a good fit. In the central part, we found that the core emission is not filled pencil beam but is a small hollow cone. This implies that the impact angle could be β < 0.5°. The “hollow core” is in agreement with Inverse Compton Scattering model of radio pulsars.

We demonstrate a self-organized pattern formation on vicinal Si(111) surfaces that are miscut toward the [211] direction. All the patterns, consisting of a periodic array of alternating (7×7) reconstructed terraces and step-bunched facets, have the same periodicity and facet structure, independent of the miscut angle; while the width of the facets increases linearly with miscut angle. We attribute such unique pattern formation to a surface faceting transition that involves two transition steps: the first step forms a stress-domain structure defining the universal periodicity; the second step forms the low-energy facets controlling the facet width.

We have investigated the preferential positioning of self-organized Ge quantum dots on Si (001) mesas fabricated in a selective epitaxial growth (SEG) mode of gas-source molecular beam epitaxy. The surface morphology was evaluated by atomic force microscopy, and for the Si SEG structures, showed mass accumulation at the periphery. Using micro-Raman spectroscopic imaging, the strain-field distribution of Si structures was studied before Ge deposition, and the results suggest a tensile strain at/near the periphery of the structure while a compressive strain at the center. These structures were subsequently used as a template for Ge dots, which tended to align along the mesa edge. The strain field distribution on Si mesas is speculated to be the driving force for preferential nucleation of Ge dots.