导电介质中电磁波相移常数与振幅衰减常数的方向关系的讨论

对文献上给出的非均匀电磁波在同一均匀导电介质中传播时,电磁波的相移常数和振幅衰减常数方向之间满足定量关系的结论,重新进行了分析和推导,利用电磁波在导电介质界面的边界条件,给出了两种情况下的相移常数和振幅衰减常数的表达式,以及它们与界面法线的夹角正弦的表达式.结果表明,在同一均匀导电介质中,非均匀电磁波的相移常数的方向和振幅衰减常数的方向之间一般不满足定量关系.     

ZnO纳米棒在Si衬底上外延生长研究

运用热蒸发ZnO粉末法,以金做催化剂,分别在Si(100)和Si(111)两种基片上外延生长了ZnO纳米棒(样品分别标为1#和2#).通过X射线衍射(XRD)和扫描电子显微镜(SEM)分析,结合ZnO与Si的晶格结构特征,从理论上得出了两个样品的晶格匹配关系.1#样品:[0001]ZnO∥[114]Si,[0001]ZnO∥[1-1-4]Si,[0001]ZnO∥[11-4]Si,[0001]ZnO∥[1-14]Si,失配度为1.54;;2#样品:[0001]ZnO∥[111]Si,[21-1-0]ZnO∥[11-0]Si,[1-21-0]ZnO∥[1-01]Si ,[1-1-20]ZnO∥[011-]Si,失配度为18.12;.研究表明Si衬底对ZnO纳米棒生长方向具有调控作用.     

3D Multiphase Piecewise Constant Level Set Method Based on Graph Cut Minimization

Segmentation of three-dimensional (3D) complicated structures is of great importance for many real applications. In this work we combine graph cut minimization method with a variant of the level set idea for 3D segmentation based on the Mumford-Shah model. Compared with the traditional approach for solving the Euler-Lagrange equation we do not need to solve any partial differential equations. Instead, the minimum cut on a special designed graph need to be computed. The method is tested on data with complicated structures. It is rather stable with respect to initial value and the algorithm is nearly parameter free. Experiments show that it can solve large problems much faster than traditional approaches.     

Impedance Response of a Thin Film on an Electrode: Deciphering the Influence of the Double Layer Capacitance

The different contributions of the interfacial capacitance are identified in the case of passive materials or thin protective coatings deposited on the electrode surface. The method is based on a graphical analysis of the EIS results to determine both the passive-film capacitance in the high-frequency domain and the double-layer capacitance in the low-frequency domain. The proposed analysis is shown to be independent of the physicochemical origins of the frequency dispersion of the interfacial capacitances which results, from an analysis point of view of the experimental results, in the use of a constant-phase element However, for a correct evaluation of the thin-film properties such as its thickness, the high-frequency data must be corrected for the double-layer contribution. In particular, it is shown that if the double-layer capacitance gives a frequency-dispersed response, it is necessary to correct the high-frequency part for the double-layer constant-phase elements. This is first demonstrated on synthetic data and then used for the determination of the thickness of thin oxide film formed on Al in neutral pH solution.     

Determining binding constants for 1:1 and 1:2 inclusion complexes of ester betulin derivatives with (2-hydroxypropyl)-β-cyclodextrin by affinity capillary electrophoresis

The complexation of ester betulin derivatives with (2-hydroxypropyl)-β-cyclodextrin (HP-β-CD) was studied by mobility shift affinity CE. Electrophoretic mobility for triangular peaks was calculated using the parameter a₁ of the Haarhoff–Van der Linde function instead of the peak top time. Dependences of the viscosity corrected electrophoretic mobility on HP-β-CD concentration were not described on the basis of only complexes with 1:1 stoichiometry due to the fact that these binding curves did not reach a plateau. However, the dependences were well described taking into account both 1:1 and 1:2 complexes. The presence of higher order equilibria was also revealed by x-reciprocal plots. The values of apparent binding constant logarithm, obtained for the first time, for 1:1 and 1:2 HP-β-CD complexes of betulin 3,28-diphthalate and betulin 3,28-disuccinate with 95% confidence interval limits in brackets are the same within error and are equal to 4.85 (4.73–4.95), 8.56 (7.75–8.82), 4.92 (4.86–4.97), and 8.54 (8.23–8.72) at 25°C, respectively. These values for 1:1 and 1:2 HP-β-CD complexes of betulin 3,28-disulfate at 25°C are 4.61 (4.57–4.64) and 7.11 (6.57–7.34), respectively. The binding constants for betulin 3,28-disulfate agree with the previously obtained results from the separation in the thermostatted capillary segment.     

Novel low-dielectric constant and soluble polyimides from diamines containing fluorene and pyridine unit

Polyimides (PI's) with low-dielectric constant and excellent organic solubility have broad application prospects in the electronic field. Herein, this study designed a series of novel, low dielectric, organic soluble PI films by creatively introducing fluorene and pyridine ring into diamine monomers. Because of the noncoplanar structure of fluorenyl and the polarization of pyridine ring, PI films achieved a low-dielectric constant (2.22–3.09 at 10 MHz) and excellent organic solubility. Even in some organic solvents with low-boiling points, these PI films still exhibited outstanding solubility. In addition, all the films possessed high-tensile strength (≈120 MPa) and excellent optical transparency (>70%, 450 nm). It was worth noting that the glass transition temperature of films was all above 280°C and 5% weight loss temperature (T_5%) was at 486–553°C. In general, the novel high-performance low-dielectric PI films are expected to be used in the field of microelectronics.     

翼片加载螺旋线慢波结构的螺旋带模型

翼片加载螺旋线慢波结构广泛应用于大功率、宽频带行波管中。建立了翼片加载螺旋线慢波结构的螺旋带模型,得到了实用的色散方程、耦合阻抗和衰减常数的表达式。利用导出的方程对实际行波管的螺旋慢波结构进行计算,并与测量结果和导电面模型进行了比较,计算结果与测量结果具有良好的一致性。分析了不同管壳半径对色散特性的影响。     

基于磁场闪络抑制技术的真空沿面闪络实验研究

为解决脉冲功率系统中击穿电压最低的部分,即真空固体绝缘界面,采用磁场闪络抑制技术提高闪络电压,为研究磁场和沿面闪络电压的关系,针对不同介电常数的样品开展了一系列相关实验。实验结果表明：采用电容器对通电螺线管充电产生的脉冲强磁场稳定可靠,并且当施加在绝缘子表面磁场强度为1.1 T时,PMMA材料的闪络电压可以提高至1.8倍。     

MV级Marx发生器恒流充电过程分析

设计了一种输出电压为4 MV的超前触发型Marx发生器,为了进一步优化采用电阻充电的Marx发生器输出特性,提高系统的充电效率并且减小级间充电电压不均匀性,对Marx发生器恒流充电过程进行了解析求解。结果表明：各级间充电电压差为与充电电阻、电容和充电速率成正比,与时间无关的定值,充电时间越长电压效率越高,且与电压变化率无关 。该结论具有普遍适用性。结合我们设计的4 MV超前触发型Marx发生器回路,利用PSpice对Marx发生器的恒流充电过程进行了模拟,得到了自洽的结果,并且与恒压充电进行了对比。当充电电阻为10 k,各级电容为400 nF,充电速率为10 kV/s时,恒流充电能量效率达到90%,约为恒压充电能量效率的2倍,充电时间为恒压充电的1/3。     

基于PIC单片机的种子源设计

对种子源结构进行了优化设计,为了缩短充电时间,在现有的电容和DC变换器基础之上,选用单片机作为控制芯片,利用其脉冲宽度调制(PWM）输出功能产生用于控制DC变换器的线性电压。对单片机PWM输出转化为线性控制电压的性能以及控制DC变换器恒流充电的可行性开展了实验研究。实验结果表明,基于PIC单片机的种子源储能可以达到250 J,充电时间缩短到6 min以内,满足实验要求。