基于Labview的脉冲漏磁检测系统的研究

研究了一种脉冲信号激励的漏磁检测系统;利用USB数据采集卡I/O口输出脉冲方波信号经过功率放大环节生成激励信号,通过数据采集卡触发采样功能实现检测信号的同步采样;基于Labview软件搭建了漏磁检测虚拟仪器平台,实现了漏磁检测信号的采集、调理、储存、回放和分析功能;通过实验对加工有宽度为2 mm深度分别为2 mm、5 mm、10 mm的3个裂纹缺陷的钢样本进行检测,应用霍尔传感器检测漏磁场信号;检测信号经过调理和采集,在电脑中实时显示漏磁信号随时间的变化波形;通过分析回放采样信号的峰值和峰值到达时间评估缺陷的位置和深度;实验结果表明缺陷深度越大采样信号的峰值越大,峰值到达时间越长。     

Comparison of electrical characteristic between AIN/GaN and AIGaN/GaN heterostructure Schottky diodes

Ni/Au Schottky contacts on A1N/GaN and A1GaN/GaN heterostructures are fabricated. Based on the measured current-voltage and capacitance-voltage curves, the electrical characteristics of AlN/GaN Schottky diode, such as Schottky barrier height, turn-on voltage, reverse breakdown voltage, ideal factor, and the current-transport mechanism, are analyzed and then compared with those of an A1GaN/GaN diode by self-consistently solving Schrodinger＇s and Poisson＇s equations. It is found that the dislocation-governed tunneling is dominant for both AlN/GaN and AlGaN/GaN Schottky diodes. However, more dislocation defects and a thinner barrier layer for AlN/GaN heterostrncture results in a larger tunneling probability, and causes a larger leakage current and lower reverse breakdown voltage, even though the Schottky barrier height of AlN/GaN Schottky diode is calculated to be higher that of an A1GaN/GaN diode.     

Simultaneous reduction in leakage current and enhancement in magnetic moment in BiFeO3 nanofibers via optimized Sn doping

Sn⁴⁺‐doped BiFeO₃ (BFO) nanofibers have been fabricated by sol–gel based electrospinning method with nanofiber diameter in the range of 30–100 nm in the annealed state. The leakage current density dropped by two orders of magnitude in 3% Sn‐doped BFO nanofibers compared to undoped BFO samples. Our density functional theory (DFT) simulation results indicate that Sn⁴⁺ prefers to occupy the Fe³⁺ site in BFO with a formation energy of 1.89 eV. The impurity Sn acts as a shallow donor with a low transition energy level of 41 meV. Furthermore, an enhancement in the saturation magnetization was simultaneously observed for 3% Sn‐doped nanofibers, which correlated well with our theoretical calculations. In other words, by carefully tailoring the degree of Sn doping in BFO nanofibers, we can reduce the leakage current and concurrently enhance the magnetic moment. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Information leakage in three-party simultaneous quantum secure direct communication with EPR pairs

In 2007, Wang et al. [M. Y. Wang and F. L. Yan, Chin. Phys. Lett. 24 (2007) 2486] proposed a three-party simultaneous quantum secure direct communication (3P-SQSDC) scheme with EPR pairs. Recently, Chong et al. [S. K. Chong and T. Hwang, Opt. Commun. OPTICS-15438 (2010(online))] proposed an enhancement on Wang et al.'s scheme. The communications in Chong et al.'s 3P-SQSDC can be paralleled and thus their scheme has higher efficiency. However, we find that both of the schemes have the information leakage, because the legitimate parties' secret messages have a strong correlation. This kind of security loophole leads to the consequence that any eavesdropper (Eve) can directly conjecture some information about the secrets without any active attack.     

Role of guard rings in improving the performance of silicon detectors

BARC has developed large-area silicon detectors in collaboration with BEL to be used in the pre-shower detector of the CMS experiment at CERN. The use of floating guard rings (FGR) in improving breakdown voltage and reducing leakage current of silicon detectors is well-known. In the present work, it has been demonstrated that FGRs can also be used to improve the spectroscopic response of silicon detectors. The results have been confirmed by carrying outα-particle (≈5 MeV) andγ-ray (60 keV) spectroscopies with the FGR floating or biased and the underlying physics aspect behind the change in spectra is explained. Although reduction in leakage current after biasing one of the guard rings has been reported earlier, the role of a guard ring in improving the spectroscopic response is reported for the first time. Results of TCAD simulations for silicon detectors with the guard ring under different biasing conditions have been presented. Low yield in producing large-area silicon detectors makes them very costly. However, with one of the FGRs biased even a detector having large surface leakage current can be used to give the same response as a very good detector. This makes the use of large-area silicon detectors very economical as the yield would be very high (>90%).     

Characterization of post-copper CMP surfaces with scanning probe microscopy: Part 1: Surface leakage measurement with conductive atomic force microscopy

We demonstrate in this paper for the first time the use of conductive atomic force microscopy (AFM) to measure surface leakage between copper structures with varying line width and spacing in the micro and sub micrometer ranges. Conducting atomic force microscopy allows subsequent measurement of the topography as well as the electrical properties of surfaces. The feasibility and interest of these measurements will be shown by studying the impact of chemical mechanical polishing (CMP) of an electrical interface bearing different micrometric copper structures. As expected the polishing time has a crucial impact on the current determined between closely spaced copper structures. This paper will also deal with issues observed during the measurement.     

InGaN/GaN超晶格厚度对Si衬底GaN基蓝光发光二极管光电性能的影响

采用有机金属化学气相沉积技术在Si(111)衬底上生长蓝光多量子阱发光二极管(LED) 结构, 通过在量子阱下方分别插入两组不同厚度的InGaN/GaN超晶格, 比较了超晶格厚度对LED光电性能的影响. 结果显示: 随超晶格厚度增加, 样品的反向漏电流加剧; 300 K下电致发光仪测得随着电流增加, LED发光光谱峰值的蓝移量随超晶格厚度增加而减少, 但不同超晶格厚度的两个样品在300 K下的电致发光强度几乎无差异. 结合高分辨X射线衍射仪、扫描电子显微镜、透射电子显微镜对样品的位错密度和V形坑特征分析, 明确了两样品反向漏电流产生巨大差异的原因是由于超晶格厚度大的样品具有更大的V形坑和V形坑密度, 而V形坑可作为载流子的优先通道, 使超晶格更厚的样品反向漏电流加剧. 通过对样品非对称(105)面附近的X射线衍射倒易空间图分析, 算得超晶格厚度大的样品其InGaN量子阱在GaN上的弛豫度也大, 即超晶格厚度增加有利于减小InGaN量子阱所受的应力. 综合以上影响LED发光效率的消长因素, 导致两样品最终的发光强度相近.     

基于虚拟变形法的供水管网漏损定位方法

针对供水管网的漏损探测与定位问题,采用虚拟变形法对管网各参数进行计算,通过漏损影响矩阵和流量影响矩阵来表征管网的状态,并提出了漏损探测定位的优化计算模型.由于管网漏损点数量事先难以预先获取,提出了基于贝叶斯理论的管网漏损探测、定位模型,并结合Matlab和Epanet编制了相应的优化计算程序,数值仿真结果验证了方法的有效性和可行性.     

Finite‐time stability of CNNs with neutral proportional delays and time‐varying leakage delays

In this paper, a class of cellular neural networks with neutral proportional delays and time‐varying leakage delays is considered. Some results on the finite‐time stability for the equations are obtained by using the differential inequality technique. In addition, an example with numerical simulations is given to illustrate our results, and the generalized exponential synchronization is also established. Copyright © 2016 John Wiley & Sons, Ltd.     

浅析升钟水库右总干渠石爬明渠填方段滑坡形成的原因

本文阐述了升钟水库右总干渠石爬明渠填方段滑坡的地质环境、规模及特征，分析了渗漏对填筑土、粉砂质泥岩C、φ值的影响，论述了红层丘陵区填方输水渠道滑坡形成的原因，计算了孔隙水压力、渗透压力对填方渠堤稳定性的影响，介绍了该区的防渗整治措施。