多晶LaB6阴极的脉冲热发射特性

 采用多晶LaB₆材料制成平板二极管阴极，阳极采用钼材料，阴极采用热传导与热辐射加热，加热体为石墨。实验研究了不同阴极温度、不同真空度下的脉冲发射特性，并对热发射稳定性进行了分析。结果表明： 在动态真空系统中， 阴极发射面积为0.012 1 cm²， 工作真空度为2×10^-4 Pa， 阴极温度分别为1 600， 1 650和1 700 ℃，在脉冲宽度为40 ms、重复频率为107 Hz的条件下，最大脉冲发射电流密度分别为34.0，44.0和53.8 A/cm²; 2×10^-4，5×10^-4和2×10^-3 Pa压强下的发射能力没有明显的差异;脉冲宽度的变化不影响发射电流密度的变化。     

Influences of the Current Transverse Profile on the Transverse Mode Competition of VCSELs Diodes

A spatially independent model of vertical-cavity surface-emitting lasers (VCSELs) is derived by integrating the spatially dependent rate equations over the cross section of the cavity of a VCSEL. The angular and radial non-uniformities of the injection current are taken into account. The well-known LP modes of a weakly-guiding cylindrical waveguide are employed to describe the transverse modal structure in the VCSEL cavity. This model is solved in a self-consistent way by using the 4th order Runge-Kutta method. The dependence of transverse mode competition on the current intensity, the angular and radial non-uniformities of the injection current, and the geometrical parameters of the electrical contact are thoroughly investigated and analyzed. The results are useful to the optimum design of the optical transverse modal structure of VCSELs.     

Mean reversion in the current account of forty-eight african countries: Evidence from the Panel SURADF test

Here, the Panel seemingly unrelated regressions augmented Dickey-Fuller test (SURADF) test, first introduced and advanced by Breuer et al. [Misleading inferences from panel unit-root tests with an illustration from purchasing power parity, Rev. Int. Econ. 9(3) (2001) 482-493], is used to investigate the mean-reverting behavior of the current account of 48 African countries during the 1980-2004 periods. The empirical results from numerous panel-based unit root tests, conducted earlier, indicated that the current account of each of these countries is stationary; however, when Breuer et al.'s (2001) Panel SURADF test is conducted, it is found that a unit root exists in the current account of 11 of the countries studied. These results have one extremely important policy implication for the 48 African countries studied: the current account deficit of most is sustainable, and thus signifying that those nations should have no incentive to default on their international debt.     

Improvement of corrosion properties of microarc oxidation coating on magnesium alloy by optimizing current density parameters

The microstructure, composition and corrosion performance of oxide coatings formed on AM60B alloy using microarc oxidation techniques at different waveforms of applied current densities were investigated within this study. It is found that the use of optimizing current density waveforms, i.e. decaying freely current density in the later stage and stepped decreasing current density, significantly improved the microstructure of oxide coatings compared with the constant current density mode, which are connected with changes in behaviors of spark discharges on the surface in oxidation process. The optimal waveform of current density is showed to be decaying freely current density in the later stage, which results in sealing the originally formed large micropores. The optimisation of the microstructure results in a significant improvement of the corrosion resistance of oxide coating.     

Effects of Cs treatment on field emission properties of capped carbon nanotubes

Within the methodology [M. Khazaei, A.A. Farajian, Y. Kawazoe, Phys. Rev. Lett. 95 (2005) 177602] based on first-principles electronic structure calculations, the effects of Cs treatment on current emissions and emission patterns of capped carbon nanotubes are considered at low deposition densities when the nanotubes are under an electric field 0.2 V/Å. The results show that the current emission from the cap with one adsorbed Cs is 3.4 times larger than the cap without any Cs. It is 9.6 times larger in the cap with two adsorbed Cs atoms. After Cs deposition the emission patterns become asymmetric (current emission from the carbon atoms located at the topmost pentagon ring close to Cs atoms is larger than the other atomic sites). There are very few localized states on Cs atoms. Hence, although the tunneling probability of electron emission from Cs atoms is significant, there is no current from Cs atoms. In addition, the effect of Cs on work function reduction of nanotubes is explained in terms of Cs deposition densities and the surface dipole moments.     

流夸克质量对奇异星性质的影响

本文用有效质量口袋模型描述夸克物质研究了流夸克质量的选取对奇异星性质的影响，结果表明，随着流夸克质量的增大，奇异夸克物质的状态方程变软，奇异星的最大质量及对应的半径变小．奇异流夸克质量由90MeV增到200MeV，奇异星最大质量由1．38M⊙减小至1．32M⊙，相应的半径由8．0km变到7.64km.可知，流夸克质量的选取对奇异星的性质有一定的影响．     

江苏省普通高校高水平足球运动员文化学习现状分析研究

采用问卷调查等研究方法,分析江苏省普通高校高水平足球运动员的文化学习现状,剖析影响运动员文化学习的因素,提出改善运动员文化学习的对策,为提高高水平足球运动员培养质量提供借鉴。     

PVDF介电吸收电流的研究

研究了0℃和35℃下PVDF样品的吸收电流,发现吸收电流和释放电流不相等,所遵循的规律也不相同。吸收电流依赖于样品的历史,与样品的老化有关,遵从随机驰豫规律。依照铁电陶瓷受束缚的空间电荷激活模型,及结晶高聚物与铁电陶瓷空间电荷分布的类似性,上述现象可得到解释。     

强流相对论性电子束在低压中性气体中传输的研究

本文给出了强流相对论性电子束(IREB)在低压中性气体中传输特性的理论和实验研究结果。660kV,40kA,脉宽100ns的电子束注入充有H_2,N_2的漂移管,稳定的传输气压范围在(0.7-6.7)×10~2Pa间,传输效率可达80％以上;极低气压时(P≈13.3Pa)由于空间电荷效应,束电子被虚阴极阻滞并径向发散,不能有效传输;而较高气压时,束电子除受自身电磁场作用及库仑碰撞散射外,等离子体不稳定性使束流传输效率明显降低。用蒙特·卡洛法及数值解析法对电荷中和、电流中和过程进行了模拟计算并解释了实验结果。