Lead-free piezoelectric ceramics with composition of (0.97−x)Na1/2Bi1/2TiO3-0.03NaNbO3-xBaTiO3

Compositions in (Na_1/2Bi_1/2)TiO₃ based ternary system, (0.97 – x) (Na_1/2Bi_1/2)TiO₃-0.03NaNbO₃-xBaTiO₃ (x = 0, 0.01, 0.02, 0.04, 0.05, 0.06, 0.08) are synthesized using conventional solid state reaction method. Influence of BaTiO₃ on crystal structure, dielectric and piezoelectric properties are investigated. All compositions can form single perovskite phase. Powder x-ray diffraction patterns can be indexed assuming a pseudo-cubic structure. Lattice constant increases with the increase of BaTiO₃ concentration. Rhombohedral distortion is observed in poled samples with BaTiO₃ concentration up to 6 mol%. Temperature dependence of dielectric constant and dissipation factor measurement reveals that all compositions experience two phase transitions: from ferroelectric to antiferroelectric and from antiferroelectric to paraelectric. Both transition temperatures, T _c and T _f, are lowered due to introduction of BaTiO₃. Ferroelectric to antiferroelectric phase transition has relaxor characteristics. Piezoelectric properties have relatively higher value around 1 mol% to 4 mol% BaTiO₃. In ceramics with x = 0.02, thickness electromechanical coupling factor (k _t) of 0.51 and piezoelectric charge constant (d ₃₃) of 110 × 10^–12 C/N are obtained. Addition of small amount of BaTiO₃ (x = 0.01, 0.02) improves piezoelectric properties compared to NBT-NN binary system, while T _f remains above 140°C, higher than that of NBT-BT binary system composition with similar piezoelectric properties. This is in favor of the possible application of them as lead-free piezoelectric ceramics.     

单向实时数字视频传输中帧同步锁定技术研究

提出一种适用于单向实时数字视频传输系统的帧同步锁定方案。其方法在接收端采用本地参考时钟、状态机、锁相环，并结合CIMT编码方式实现系统自动维持帧同步锁定，而无需周期性加入帧同步码。对该帧同步锁定方案与周期性加入帧同步码强制锁定方案进行性能比较．并将其应用到单向实时数字视频光纤传输系统中。实验证明，系统自动实现帧同步锁定的方案是单向实时数字视频传输系统实现帧同步锁定的最佳方案。     

新版《建筑抗震设计规范》的主要改进

作者通过新旧抗震设计规范几个方面的对比，简要介绍了抗震设计新规范的主要改进情况，对结构设计人员学习抗震设计新规范有一定的指导作用。     

Attentional Biases for Negative Interpersonal Stimuli in Clinical Depression.

An information-processing paradigm was used to examine attentional biases in clinically depressed participants, participants with generalized anxiety disorder (GAD), and nonpsychiatric control participants for faces expressing sadness, anger, and happiness. Faces were presented for 1,000 ms, at which point depressed participants had directed their attention selectively to depression-relevant (i.e., sad) faces. This attentional bias was specific to the emotion of sadness; the depressed participants did not exhibit attentional biases to the angry or happy faces. This bias was also specific to depression; at 1,000 ms, participants with GAD were not attending selectively to sad, happy, or anxiety-relevant (i.e., angry) faces. Implications of these findings for both the cognitive and the interpersonal functioning of depressed individuals are discussed and directions for future research are advanced. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

复合固体超强酸SO42-/Fe2O3-γ-Al2O3催化合成丁酸丁酯

采用沉淀硫酸化法制备了复合固体超强酸催化剂SO2-4/Fe2O3-γ-Al2O3,确定了其最佳制备工艺条件:硫酸浸渍浓度为0.6 mol/L,浸渍时间4 h;焙烧温度550℃,焙烧时间3 h.并采用该催化剂合成丁酸丁酯,考察了物料配比、催化剂用量和反应时间对酯化反应的影响,确定了丁酸丁酯的最佳合成条件:丁醇与丁酸摩尔比为1.4:1,催化剂用量0.9%(以反应物质量计),回流条件下反应3.0 h,在此最佳合成条件下,酯化率可达95.6%.     

MPEG-4 AAC解码器在NIOS Ⅱ平台上的实现和优化

给出了MEPG-4AAC实时解码器在NIOSⅡ平台的实现方案，介绍了MPEG-4AAC—LC解码算法及各关键模块优化算法。在完成实时解码要求下，结合NIOSⅡ平台特性，对解码器在软件代码与处理器上进行优化。实验结果表明CPU时钟为80MHz时能达到实时解码要求。     

Profile-Driven Component Placement for Cluster-Based Online Services

The growth of the Internet and of various intranets has spawned a wealth of online services, most of which are implemented on local-area clusters using remote invocation (for example, remote procedure call/remote method invocation) among manually placed application components. Component placement can be a significant challenge for large-scale services, particularly when application resource needs are workload dependent. Automatic component placement has the potential to maximize overall system throughput. The key idea is to construct (offline) a mapping between input workload and individual-component resource consumption. Such mappings, called component profiles, then support high-performance placement. Preliminary results on an online auction benchmark based on J2EE (Java 2 Platform, Enterprise Edition) suggest that profile-driven tools can identify placements that achieve near-optimal overall throughput.     

Monte Carlo simulation of gas phase polymerization of 1,3‐butadiene. Part II: Kinetics optimization and confirmation

Studies on the deactivations and initiations of gas phase polymerizations of 1,3‐butadiene have been achieved by Monte Carlo simulation. Initiation and deactivation control the reaction before and after the peak of the polymerization rate, respectively. The influence of polymerization temperature has been studied. Monte Carlo modeling of polymerization kinetics and mechanism was confirmed by the agreement of experimental data and simulation results of polymerizations run with a temporary evacuation of monomer. The balance of catalysts and active chains is established by both initiation and chain transfer reactions with cocatalyst, which causes a ‘pseudo‐stability’ stage. © 2003 Society of Chemical Industry     

身份诈骗日益猖獗主因: 当散兵游勇碰到黑道联盟

军队能够剿灭土匪,因为通常前者军纪严明,而后者为乌合之众;警察能打击歹徒,因为惩治单位比一般罪犯训练有素,如果上述情况反转过来,黑道人物组成联盟, 互通情报,而正义之师只是散兵游勇,那么必然会“道高一尺、魔高一丈”。现今商业活动高度依赖网络,而随之萌生的身份盗窃及诈骗罪行日益猖獗,上述“角色错配”是其中一个主因。     

高斜效率高功率850nm氧化限制型垂直腔面发射激光器

报道了MOCVD生长的高性能850nm氧化限制型垂直腔面发射激光器.研制出的氧化直径为9μm的激光器25℃时的斜效率和阈值电流分别为0.82mW/mA和2.59mA,激光器在23mA时输出16mW最大光功率.氧化直径为5μm的激光器25℃时的最小阈值电流为570μA,其最大饱和光功率为5.5mW.