Three dimensional parametrization of electromagnetic shower in Alpha Magnetic Spectrometer Ⅱ ECAL

We develop an empirical formula to parameterize the 3-dimension (3D) distribution of electromagnetic showers in the Alpha Magnetic Spectrometer Ⅱ electromagnetic calorimeter(ECAL). The formula was verified by ECAL test beam data in 2002 and found to perform well. The distribution of electron showers in the ECAL are well described by the formula, which has parameters that allow one to determine the 3D shape of electromagnetic showers in the ECAL. We use this formula to correct for lateral energy leakage and dead channels in the ECAL; good results are obtained.     

Study of ammonium fluoride passivation time on CdZnTe bulk crystal wafers

The chemical etching and the passivation processes of CdZnTe wafers were studied. The treatment effects were tested through an X‐Ray Photoelectron Spectroscopy (XPS) analysis and I–V measurement. The chemical etching in 2%Br–MeOH solution may effectively remove the damaged layer and improve the ohmic contact between CdZnTe wafer and Au electrodes making rich the surface with Te. After different etching times, the CdZnTe wafers were passivated with NH₄F/H₂O₂.CdZnTe wafer passivated immediately after etching showed the best passivation efficiency because the enriched Te on the surface was fully oxidized to TeO₂, which results in the thickest oxide layer, and the most stoichiometric surface. Also the surface leakage current was reduced in comparison with the sample passivated 24 h after etching. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Leakage current reduction by thermal oxidation in Ni/Au Schottky contacts on lattice-matched Ino.18Al0.82N/GaN heterostructures

By using temperature-dependent current-voltage, variable-frequency capacitance-voltage, and Hall measurements, the effects of the thermal oxidation on the electrical properties of Ni/Au Schottky contacts on lattice-matched Ino.18Alo.82N/GaN heterostructures are investigated. Decrease of the reverse leakage current down to six orders of magni- tude is observed after the thermal oxidation of the Ino.18Alo.82N/GaN heterostructures at 700 ℃. It is confirmed that the reverse leakage current is dominated by the Frenkel-Poole emission, and the main origin of the leakage current is the emis- sion of electrons from a trap state near the metal/semiconductor interface into a continuum of electronic states associated with the conductive dislocations in the InxAll-xN barrier. It is believed that the thermal oxidation results in the formation of a thin oxide layer on the InxAll-xN surface, which increases the electron emission barrier height.     

基于腔QED的无信息泄露量子对话(英文)

良好的安全性对量子保密通信协议而言是不可或缺的,但信息泄露已成为量子对话的一个严重安全威胁.为了解决信息泄露问题,利用腔QED中原子的演化规律提出一个基于腔QED的无信息泄露量子对话协议,利用腔QED中两个Bell态纠缠交换后的测量相关性来克服信息泄露问题.研究表明:该协议能够通过安全检测探测到外部窃听者的主动攻击,如截获-重发攻击、测量-重发攻击和纠缠-测量攻击;在每轮通信可以安全交换4比特秘密信息;对信息泄露问题和外部窃听者的主动攻击,都具备良好的安全性.     

Infrared thermography based defect detection in ferromagnetic specimens using a low frequency alternating magnetic field

A new active infrared thermography based technique is proposed for defect detection in ferromagnetic specimens using a low frequency alternating magnetic field induced heating. The test specimens (four mild steel specimens with artificial rectangular slots of 8.0, 5.0, 3.3 and 3.0 mm depths) are magnetized using a low frequency alternating magnetic field and by using an infrared camera, the surface temperature is remotely monitored in real time. An alternating magnetic field induces an eddy current in the specimen which increases the specimen temperature due to the Joule’s heating. The experimental results show a thermal contrast in the defective region that decays exponentially with the defect depth. The observed thermal contrast is attributed to the reduction in induction heating due to the leakage of magnetic flux caused by magnetic permeability gradient in the defective region. The proposed technique is suitable for rapid non-contact wide area inspection of ferromagnetic materials and offers several advantages over the conventional active thermography techniques like fast direct heating, no frequency optimization, no dependence on the surface absorption coefficient and penetration depth.     

数字全息图的非同步采样对再现像的影响

基于香农采样定理和傅里叶频谱分析,通过模拟数字全息光栅的实验,对非同步采样数字全息图的一些基本问题进行了分析。模拟实验结果表明：全息图透射率函数中的低频调制现象随非同步采样光栅空间频率的增大而变得更明显;全息图再现过程中的频谱泄漏使再现波前发生高频起伏,其影响大小取决于非同步采样的偏离程度,与光栅本身的空间频率无关。另由数值模拟实验表明,频谱泄漏对再现波前的影响可通过数字全息图加窗切趾方法来抑制,以提高再现像质量。     

叶顶间隙对冲压叶轮激波结构的影响

本文采用数值模拟方法研究了带有叶顶间隙的冲压叶轮内部流场结构,分析了叶顶间隙泄漏流对冲压叶轮内部激波波系的影响。研究表明,由于叶顶间隙泄漏流的影响,在叶片展向高度85%以上的区域,冲压叶轮通道内的激波波系受到较大的影响,甚至导致叶尖区域的激波波系完全被泄漏流的影响破坏,并在叶片吸力面形成一道斜激波,形成了新的激波波系,并且由于泄漏流的存在使得流动损失增加。     

利用荧光法检测磷酸酯液压油的泄漏

提出了一种检测飞机液压油泄漏的方法--荧光法,以美孚磷酸酯液压油为例,实验验证了荧光法检测磷酸酯液压油泄漏的可行性。采用LS-55型荧光分光光度计以及实验室搭建系统对HyJet Ⅴ磷酸酯液压油以及Jet Oil Ⅱ、2197润滑油的荧光特性进行了分析。研究结果表明,可以用不同荧光发射光谱峰值来区分三种油,荧光法检测磷酸酯液压油泄漏是可行的。该技术可实现对飞机液压油泄漏的实时、在线、现场测量。     

Measurements, characteristics, and origin of new electromagnetic interference on magnetocardiographic measurements

In order to eliminate the influence of the large-amplitude magnetic field noise that has complicated magnetocardio-graphic studies since October 2009, we have performed high-accuracy measurement of the environmental magnetic field noise in the vicinity of Beijing Subway Line 4 using a three-component height T c radio frequency (rf) superconducting quantum interference device (SQUID). By analysing the spatial form and other characteristics of the time and the frequency domains and by calculating the circumferential magnetic field distribution based on a duel-end feeding system model, we reach the following conclusions: (i) the main source of magnetic field noise is the magnetic field generated by the subway trains, and (ii) the magnetic field interference results mainly from the imbalance between traction current and return rail current that is caused by the leakage current.