过渡金属化合物OsB2与OsO2低压缩性的第一性原理计算研究

利用基于密度泛函理论平面波赝势法的第一性原理计算,研究了过渡金属化合物OsB2和OsO2的金红石相、黄铁矿相与萤石相三种结构在高压下的状态方程和结构特性以及OsO2可能的高压相变.理论计算结果支持OsB2与OsO2的萤石相是潜在超低可压缩性的硬性材料.同时,也分析了它们的电子结构,力求理解大体变模量和高硬度的微观机制.结果表明,可以利用过渡金属高的价电子浓度,掺入硼、氧、碳、氮等轻的元素形成强的方向键,这可能提供了一种合成超硬材料的新途径.     

Atom-photon entanglement in the system with competing k-photon and l-photon transitions

We have investigated the evolution of the atomic quantum entropy and the entanglement of atom-photon in the system with competing k-photon and l-photon transitions by means of fully quantum theory, and examined the effects of competing photon numbers （k and l）, the relative coupling strength between the atom and the two-mode field （A/g）, and the initial photon number of the field on the atomic quantum entropy and the entanglement of atom-photon. The results show that the multiphoton competing transitions or the large relative coupling strength can lead to the strong entanglement between atoms and photons. The maximal atom-photon entanglement can be prepared via the appropriate selection of system parameters and interaction time.     

Characteristics of an add-drop filter composed of a Mach-Zehnder interferometer and double ring resonators

A planar lightwave circuit (PLC) add-drop filter is proposed and analyzed, which consists of a symmetric Mach-Zehnder interferometer (MZI) combined with double microring resonators. A critical coupling condition is derived for a better box-like drop spectrum. Comparisons of its characteristics with other schemes,such as a MZI with a single ring resonator, are presented, and some of the issues about device design and fabrication are also discussed.     

类金钢石非晶碳薄膜的光吸收和光致发光研究

我们用激光轰击石墨靶成功地制备出类金刚石无氢非晶碳薄膜.测量了光学吸收、光致发光及其随入射光强度的变化关系.结果表明,这种薄膜具有类金刚石的性质,光学带隙在1.67-2.25eV,发光在可见光区呈宽带结构.低激发强度下发光强度超线性变化,而在高激发强度下则为线性发光.我们用非成对载流子复合的模型对结果给出了合理的解释.用带尾态饱和的模型解释了发光峰值随激发光强增加而蓝移的现象.     

Monitoring of the ducting by a ground-based GPS receiver

In this paper, we describe the estimation of low-altitude refractivity structure from simulation and real ground-based GPS delays. The vertical structure of the refractive environment is modeled using three parameters, i.e., duct height, duct thickness, and duct slope. The refractivity model is implemented with a priori constraints on the duct height, thickness, and strength, which might be derived from soundings or numerical weather-prediction models. A ray propagation model maps the refractivity structure into a replica field. Replica fields are compared with the simulation observed data using a squared-error objective function. A global search for the three environmental parameters is performed using genetic algorithm. The inversion is assessed by comparing the refractivity profiles from the radiosondes to those estimated. This technique could provide near-real-time estimation of ducting effect. The results suggest that ground-based GPS provides significant atmospheric refractivity information, despite certain fundamental limitations of ground-based measurements. Radiosondes typically are launched just a few times daily. Consequently, estimates of temporally and spatially varying refractivity that assimilate GPS delays could substantially improve over-estimates using radiosonde data alone.     

Analysis of resistive switching behaviors of vanadium oxide thin film

We demonstrated the polarization of resistive switching for Cu/VO_x/Cu memory cell. Switching behaviors of Cu/VO_x/Cu cell were tested by semiconductor device analyzer (Agilent B1500A), and the relative micro-analysis of I-V characteristics of VO_x/Cu was characterized by conductive atomic force microscope (CAFM). The I-V test results indicated that both forming and the reversible resistive switching between low resistance state (LRS) and high resistance state (HRS) can be observed under either positive or negative sweep. The CAFM images for LRS and HRS directly exhibited evidences of the formation and rupture of filaments based on positive or negative voltage. Cu/VO_x/Cu sandwiched structure exhibits a reversible resistive switching behavior and shows potential applications in the next generation nonvolatile memory field.     

不同纯度硼粉搭配对MgB2多芯线材性能的影响

采用in-situ PIT工艺,以不同纯度硼粉相互搭配做为前驱粉末中的硼源,选用中心铜铌复合棒增强的导体结构制备了MgB2六芯线材,研究了不同纯度硼粉搭配对线材粉末相组成、微观结构以及超导电性的影响,其结果表明当高纯硼粉含量不低于50%时,自场下的临界电流不存在明显的衰减,因此以适当低纯硼粉(95～97%)和高纯硼粉(99.999%)相互搭配不但不会降低线材的临界电流,而且可以很大程度上降低线材的制造成本,为线材的实用化提供了很好的经济基础.     

波纹管对超导电缆出口液氮温度的影响

建立了30米长高温超导电缆的二维模型,利用Fluent软件对该模型进行仿真分析。在该模型中,采用波纹管恒温器,分析了波纹管的波距、波高等因素对出口液氮温度的影响。结果表明:在相同的热负荷及流量下,波纹管的波距越小,波高越大,出口液氮温度越高。超导电缆波纹管内液氮温度模拟,为低温冷却系统的优化设计提供理论依据。     

110kV冷绝缘高温超导电缆在故障电流下的温度计算与分析

研究了110kV冷绝缘高温超导电缆失超时,故障电流的分流情况,并以此为依据,建立了电缆在故障电流下失超时,温升与时间关系的计算模型;通过MATLAB对计算模型进行了求解,并对求解结果进行了分析;计算出了电缆在不同故障电流下,温度上升到不同值所需要的时间,进一步明确了故障电流的大小对电缆温升的影响。