真空中铝单丝电爆炸的实验研究

开展了铝单丝在负极性电流脉冲作用下电爆炸特性的研究.利用皮秒激光探针,搭建了阴影、纹影和干涉的光学诊断平台,得到了不镀膜铝丝典型的能量沉积过程,在电压崩溃时刻其沉积能量为2.4 eV/atom.为了增加金属丝内的沉积能量,开展了相同电参数及金属丝尺寸下的镀膜铝丝电爆炸实验,其沉积能量可达到5 eV/atom,实现了在电压崩溃之前铝丝完全气化(完全气化所需能量为4 eV/atom).阴影图像展示了高密度丝核区域的膨胀过程,不镀膜铝丝平均膨胀速度为2.2 km/s,而镀膜铝丝因为沉积能量大,其膨胀速度约为不镀膜铝丝的2.3倍,高密度区域膨胀速度为5 km/s.由于阴影不能反映低密度等离子体的膨胀,开展了平行双丝实验,通过测量自发光辐射,估算了低密度等离子体的膨胀速度.利用条纹相机拍摄了不镀膜铝丝电爆炸过程中自发光区域的图像.纹影图像清晰地展示了不镀膜铝丝在电爆炸过程中形成的核冕结构,而镀膜铝丝电爆炸过程中核冕结构得到了一定程度的抑制.从干涉图像计算了相移,在轴对称假设下对相移进行阿贝尔逆变换,重构了三维的铝原子数密度分布.     

Experimental simulation of the Unruh effect on an NMR quantum simulator

A triad mode resonance, or three-wave resonance, is typical of dynamical systems with quadratic nonlinearities. Suspended cables are found to be rich in triad mode resonant dynamics. In this paper, modulation equations for cable’s triad resonance are formulated by the multiple scale method. Dynamic conservative quantities, i.e., mode energy and Manley-Rowe relations, are then constructed. Equilibrium/dynamic solutions of the modulation equations are obtained, and full investigations into their stability and bifurcation characteristics are presented. Various bifurcation behaviors are detected in cable’s triad resonant responses, such as saddle-node, Hopf, pitchfork and period-doubling bifurcations. Nonlinear behaviors, like jump and saturation phenomena, are also found in cable’s responses. Based upon the bifurcation analysis, two interesting properties associated with activation of cable’s triad resonance are also proposed, i.e., energy barrier and directional dependence. The first gives the critical amplitude of high-frequency mode to activate cable’s triad resonance, and the second characterizes the degree of difficulty for activating cable’s triad resonance in two opposite directions, i.e., with positive or negative internal detuning parameter.     

Applications of two-way satellite time and frequency transfer in the BeiDou navigation satellite system

A two-way satellite time and frequency transfer(TWSTFT) device equipped in the BeiDou navigation satellite system(BDS)can calculate clock error between satellite and ground master clock. TWSTFT is a real-time method with high accuracy because most system errors such as orbital error, station position error, and tropospheric and ionospheric delay error can be eliminated by calculating the two-way pseudorange difference. Another method, the multi-satellite precision orbit determination(MPOD)method, can be applied to estimate satellite clock errors. By comparison with MPOD clock estimations, this paper discusses the applications of the BDS TWSTFT clock observations in satellite clock measurement, satellite clock prediction, navigation system time monitor, and satellite clock performance assessment in orbit. The results show that with TWSTFT clock observations, the accuracy of satellite clock prediction is higher than MPOD. Five continuous weeks of comparisons with three international GNSS Service(IGS) analysis centers(ACs) show that the reference time difference between BeiDou time(BDT) and golbal positoning system(GPS) time(GPST) realized IGS ACs is in the tens of nanoseconds. Applying the TWSTFT clock error observations may obtain more accurate satellite clock performance evaluation in the 104 s interval because the accuracy of the MPOD clock estimation is not sufficiently high. By comparing the BDS and GPS satellite clock performance, we found that the BDS clock stability at the 103 s interval is approximately 10.12, which is similar to the GPS IIR.     

Hybrid process for texturization of diamond wire sawn multicrystalline silicon solar cell

Acid texture is difficult for diamond wire sawn (DWS) multicrystalline silicon (mc‐Si) wafer owing to the inhomogeneous distribution of damage layer on the surface. In this article, metal‐assisted chemical etching (MACE) has been selected for introducing a porous seeding layer to induce acid texturing etching. SEM results show that the oval pit structures coverage get obvious improvement even on the smooth areas. Owing to the further improved light absorption ability by second MACE and nanostructure rebuilding (NSR) process, nanostructured DWS mc‐Si solar cell has exhibited a conversion efficiency of 17.96%, which is 0.45% higher than that of DWS wafer with simple acid texture process. (© 2016 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Slow-light fourier transform interferometer

We describe a new type of Fourier transform (FT) interferometer in which the tunable optical delay between the two arms is realized by using a continuously variable slow-light medium instead of a moving arm as in a conventional setup. The spectral resolution of such a FT interferometer exceeds that of a conventional setup of comparable size by a factor equal to the maximum group index of the slow-light medium. The scheme is experimentally demonstrated by using a rubidium atomic vapor cell as the tunable slow-light medium, and the spectral resolution is enhanced by a factor of approximately 100.     

Protected nodes and the collapse of Fermi arcs in high-T{c} cuprate superconductors

Angle resolved photoemission on underdoped Bi2Sr2CaCu2O8 reveals that the magnitude and d-wave anisotropy of the superconducting state energy gap are independent of temperature all the way up to T{c}. This lack of T variation of the entire k-dependent gap is in marked contrast to mean field theory. At T{c} the point nodes of the d-wave gap abruptly expand into finite length "Fermi arcs." This change occurs within the width of the resistive transition, and thus the Fermi arcs are not simply thermally broadened nodes but rather a unique signature of the pseudogap phase.     

Surface resonant-states-enhanced acoustic wave tunneling in two-dimensional phononic crystals

We show that by placing a metal plate next to a two-dimensional phononic crystal, acoustic waves can tunnel through the combined structure at a specific frequency that lies inside the band gap of the phononic crystal. The enhanced transmission is attributed to the coupling of the input waves with the acoustically resonant states created between the metal plate and the phononic crystal. Experiments are in excellent agreement with the theoretical predictions.     

Enhanced photovoltaic properties of polymer-fullerene bulk heterojunction solar cells by thermal annealing

The effect of a thermal annealing treatment on the performance of bulk heterojunction photovoltaic cells based on poly[2-methoxy-5-(2′-ethyl-hexyloxy)-p-phenylene vinylene] (MEH-PPV) and fullerene (C₆₀) composites is investigated. Upon thermal annealing at 120 ^°C, short-circuit current and power conversion efficiency (η) are more than tripled, while a sharp rise by eight times in and η is found for the device annealed at 200 ^°C. It is concluded that the improved phase separation between MEH-PPV and C₆₀ leads to the enhancement of and η at 120 ^°C, while thermodynamic molecule arrangement at the higher temperature of ∼200 ^°C induces a significant increase in all photovoltaic parameters of composite devices except the open-circuit voltage .     

Role of NMDA receptor subtypes in different forms of NMDA-dependent synaptic plasticity

Background  

The involvement of different NMDA receptor (NMDAR) subunits has been implicated in several forms of synaptic plasticity. However, it is still controversial to what extent the involvement is specific, and little is known about the role of NMDAR subunits in certain "non-conventional" forms of plasticity. In this study we used subunit-specific blockers to test the roles of NR2A- and NR2B-containing NMDARs in a type of chemical long-term depression (LTD) induced by brief bath application of the NMDAR agonist NMDA to hippocampal slices from 12–18 days old rats. For comparison, we also examined other forms of plasticity, including a "slow LTD" induced by 0.1 Hz stimulation under low Mg²⁺ conditions as well as long-term potentiation (LTP).     

基于机械-化学的方法在硅表面制造功能化结构

"利用机械与化学结合的方法在芳烃重氮盐溶液中用金刚石刀具切削硅片,使得芳香烃分子和硅之间以共价键连接,实现了对硅片的"成形并功能化"的一步完成．研究了在大气环境如何利用金刚石刀具在硅表面加工出表面质量较好的微结构,为下一步在溶液中"成形并功能化"硅提供好的基底．在溶液中对硅表面进行可控自组装实验,初步研究了切削速度和组装时间对切削处生成自组装膜质量的影响,总结出较适合膜生长的参数．用X射线光电子能谱对自组装膜进行了检测,用扫描电子显微镜和原子力显微镜对自组装膜的表面形貌进行了表征,并用原子力显微镜对自