On the minimum pseudo-codewords of LDPC codes

In this letter, we study the minimum pseudo-codewords of low-density parity-check (LDPC) codes under linear programming (LP) decoding. We show that a lower bound of Chaichanavong and Siegel on the pseudo-weight of a pseudo-codeword is tight if and only if this pseudo-codeword is a real multiple of a codeword. Using this result we further show that for some LDPC codes, e.g., Euclidean plane and projective plane LDPC codes, there are no other minimum pseudo-codewords except the real multiples of minimum codewords.     

On the stopping distance of finite geometry LDPC codes

In this letter, the stopping sets and stopping distance of finite geometry LDPC (FG-LDPC) codes are studied. It is known that FG-LDPC codes are majority-logic decodable and a lower bound on the minimum distance can be thus obtained. It is shown in this letter that this lower bound on the minimum distance of FG-LDPC codes is also a lower bound on the stopping distance of FG-LDPC codes, which implies that FG-LDPC codes have considerably large stopping distance. This may explain in one respect why some FG-LDPC codes perform well with iterative decoding in spite of having many cycles of length 4 in their Tanner graphs.     

Comprehensive Study of Emitter-Ledge Thickness of InGaP/GaAs HBTs

A comprehensive study of emitter-ledge thickness of InGaP/GaAs heterojunction bipolar transistors (HBTs) has been undertaken. It is shown that the recombination rate and electron densities are drastically increased near the exposed base surface between the base contact and the emitter ledge. In contrast, the corresponding hole densities are decreased. If the emitter ledge is too thick, current will flow through the undepleted ledge, which increases the emitter-size effect. In contrast, if the emitter ledge is too thin, it may not effectively passivate the surface. Therefore, the thickness of the emitter ledge is a crucial issue and should be carefully considered. It is shown that, from simulated and experimental results, the optimum emitter-ledge thickness of InGaP/GaAs HBT is 100-200 Aring     

A Novel Pt/In0.52Al0.48As Schottky Diode-Type Hydrogen Sensor

On the basis of a Pt/In_0.52Al_0.48As metal-semiconductor structure, a novel hydrogen sensor is fabricated and demonstrated. The studied Pt/In_0.52Al_0.48As Schottky diode-type hydrogen sensor exhibits significant sensing performance including high relative sensitivity ratio of about 2600% (under the 1% H₂/air gas and V_R=-0.5 V at 30 degC), large current variation of 310 muA (under the 1% H₂/air gas and V_R=-5 V at 200 degC), widespread reverse-voltage regime (0~-5 V), stable hydrogen-sensing current-voltage (I-V) curves, and fast transient response time of 1.5 s. The calculated Schottky barrier-height change and series-resistance variation, from the thermionic-emission model and Norde method, are 87.0 meV and 288 Omega, respectively (under the 1% H₂/air gas at 30 degC). The hydrogen concentrations and operating temperatures tested in this letter are in the range of 15 ppm-1% H₂/air and 30 degC-250 degC, respectively. Based on the excellent integration compatibility with InP-based electronic devices, the studied device provides the potentiality in high-performance sensor-array applications     

反应堆系统数字化实时仿真的高效实现

根据实验反应堆的物理特性，建立堆芯动态模型，探讨多种实时仿真算法的实现途径。研究提出了进行数字化实时仿真的一种高效实现方法。为配合功率调节系统半实物仿真试验而实现了一座实验反应堆在Windows平台下的实时仿真系统。      

用磁控溅射和退火方法制备AlSb多晶薄膜

采用磁控溅射法在玻璃衬底上制备Al/Sb预制多层薄膜,然后将Al/Sb预制多层薄膜在退火炉中退火得到AlSb多晶薄膜.用X射线衍射(XRD)法测薄膜结构;用扫描电镜(SEM)测薄膜Al/Sb成分比,结果表明AlSb多晶薄膜具有单一的晶相、均匀的结构,以及粒径大约20nm的晶粒.根据电导率(lnσ)与温度(T)的关系得到电导激活能为0.21和0.321eV,为制备出适用于太阳电池的AlSb多晶薄膜奠定了一定的技术基础.     

基于心理声学参数的水下目标识别特征提取方法

研究了响度、尖锐度、粗糙度、波动强度等主要的心理声学参数及其计算方法，利用主要的心理声学参数作为目标特征参数用于水下目标分类识别，并以正确识别率为准则对这些特征参数进行了修改。使用K-均值聚类方法对3类舰船噪声实测数据进行了目标分类识别仿真实验。实验结果表明，该方法提取的特征能够较好地反映信号本质，取得了较好的分类识别效果，特别是以修改后的心理声学参数为特征具有更高的识别率。     

Labview在HT-7极向场电源监控系统中的应用

为满足核聚变装置HT-7极向场电源控制系统的要求,利用Labview编程环境设计了状态监控界面。监控界面实现实时、可靠的监控极向场电源状态,并通过ODBC接口与数据库连接,实现实验过程回放。本文简述了状态监控界面的构造与实现。多次实验表明在Labview环境下利用UDP协议、LabSQL工具包实现实时通信和过程回放,是可行、可靠而高效的。     

数据仓库的建立与维护的一个实例

本文描述了在学校学生管理系统的基础上建立和维护数据仓库的过程,包括数据仓库模型设计、异构数据的转换、数据冗余、汇总数据存储等数据仓库设计过程和数据的抽取、转换和加载(ETL)以及元数据管理等维护过程,并简单地介绍了数据仓库在OLAP方面的应用。     

基于随机共振的纳米碳管气体传感器的研究

基于气体电晕放电原理,利用纳米碳管独特的物理结构和尖端发射效应,提出了一种新型的纳米碳管离子型气体传感器.采用阳极氧化铝模板法生长的定向纳米碳管阵列所构成的传感器,纳米碳管和电极是一体的,简化了器件结构和工艺.在外加直流电压激励下,纳米碳管顶部形成很强的非均匀电场,在电压相对低的情况下能很容易地电离气体,根据气体的击穿电压和放电电流来实现对单一气体和确定性混合气体的检测.为了提高检测混合气体的灵敏度,创新地在检测回路中引入随机共振发生装置,有效地提高了混合气体浓度检测的范围.实验中还分析了温度、湿度对传感器的影响,对该传感器的性能也作了评价.实验结果表明该传感器具有选择性好、体积小、响应时间快、灵敏度高、稳定性好,室温操作等优点,而且实现方便,操作简单,有较大的实用价值.