Low-field magnetoresistance of Ag-substituted perovskite-type manganites

A series of bulk polycrystalline Nd_1−xAg_xMnO₃ samples were prepared by conventional solid-state reaction processing, for x between 0.1 and 0.5. The structure, magnetism, and magnetoresistance (MR) of the samples are investigated. The X-ray diffraction patterns show that the x=0.1 sample is a single perovskite structure, while x0.167, samples consist of a ferromagnetic perovskite phase and two nonmagnetic phases, Ag and Mn₃O₄. The MR of Nd_1−xAg_xMnO₃ is enhanced by increasing the composition of Ag. Compared with the sample of x=0.1, the x=0.5 sample has a significantly larger value of low-field MR. The enhanced low-field MR is related to the spin-dependent scattering of spin-polarized electrons at the interfaces between the perovskite grains and silver granules.     

Separate spatial soliton pairs in a biased series centrosymmetric photorefractive crystal circuit

It is shown theoretically that three types of separate soliton pairs: bright-bright, bright-dark, and dark-dark, can be established in a biased series circuit consisting of two centrosymmetric photorefractive crystals and the two solitons in a separate soliton pair can affect each other by the light-induced current. The effects of the intensities of soliton beams and background lights on the normalized profiles of solitons are discussed.     

Improving the resolution and the uniformity of AFM tip induced oxide patterns with pulsed voltages

Oxide line patterns were fabricated on the surface of titanium (Ti) film using atomic force microscopy (AFM) tip induced local oxidation technique. The growth behavior of the oxide under static voltages was studied. It was found the lateral growth of the oxide experienced two stages and the growth rate at the initial stage was very high. Pulsed voltages were employed and their effects on the controlling of the oxidation dynamics were examined. The results indicated that the high lateral and vertical growth rates of oxide at the initial stage could be suppressed with pulsed voltages. A minimum line width of 8 nm and highly uniform patterns were obtained with optimized voltage pulses. These results indicated that applying pulsed voltage is an effective method for improving both the resolution and the uniformity of the fabricated structures with scanning probe microscopy (SPM) tip induced local oxidation technique.     

有机/无机复合结构光电导型器件的光激发机制

制备了PVK/ZnS有机无机复合的光电导型器件 ,器件结构分别为Glass/ITO/PVK/Al;Glass/ITO/ZnS/Al;Glass/ITO/ZnS/PVK/Al。通过研究此复合器件在外加电场作用下的稳态光电导激发谱 ,得到了基本光激发过程。把PVK/ZnS的吸收谱和器件的光电导谱进行比较 ,知道虽然两者的吸收对器件光电流都有贡献 ,但有效部分在PVK和ZnS的界面处。最大光电流对外加电场的依赖性与器件的暗电流和光电流谱为此提供了证据     

First measurement of inclusive B→Xsη decays

We report a first measurement of inclusive B→Xsη decays, where Xs is a charmless state with unit strangeness. The measurement is based on a pseudoinclusive reconstruction technique and uses a sample of 657×10(6)BB pairs accumulated with the Belle detector at the KEKB e+e- collider. For MXs < 2.6 GeV/c2, we measure a branching fraction of [26.1±3.0(stat)-2.1+1.9(syst)-7.1+4.0(model)]×10(-5) and a direct CP asymmetry of ACP=-0.13±0.04-0.03+0.02. Over half of the signal occurs in the range MXs > 1.8 GeV/c2.     

Seasonal changes in antifreeze protein gene transcription and water content of beetle Microdera punctipennis (Coleoptera, Tenebrionidae) from Gurbantonggut desert in Central Asia

Desert beetle Microdera punctipennis (Coleoptera: Tenebriondae) is a special species in Gurbantonggut Desert in Central Asia. To investigate the possible strategy it employs for cold survival, seasonal changes in supercooling point (SCP), body water content, haemolymph osmolality and antifreeze protein gene (Mpafp) expression were measured over 13 months. Our results show SCPs in M. punctipennis adults changed from -8.0°C in summer to -18.7°C in winter. During winter, adults endured modest water loss; total water decreased from 65.4 percent in summer to 55.9% in winter. Mpafp mRNAs level increased by 13.1 fold from summer to early winter, and haemolymph osmolality increased accordingly from 550 mOsm to 1486 mOsm. Correlation coefficient of Mpafp mRNAs level and SCP indicates that Mpafp mRNA explained 65.3 percent of the variation in SCPs. The correlation between Mpafp mRNA level and total water reflected an indirect influence of antifreeze protein on water content via reducing SCP.     

高增益双层组合GaAs光电导开关设计与实验研究

设计制备了一种由双层半绝缘GaAs:EL2晶体组成的新型超快光电导功率开关.由于触发状态下双层GaAs晶体之间满足动态分压关系,使该开关在强电场偏置下触发时,双层GaAs晶体既能先后发生高增益过程,又能相互抑制对方进入锁定状态,开关输出为近似方波的双峰脉冲.因此,这种开关的工作方式既具有非线性模式特有的所需触发光能小、上升速度快等优点,又具有线性模式特有的重复工作频率高、使用寿命长等优点.偏压6500V时用脉宽8ns、能量3mJ的1064nm激光触发,输出电脉冲的上升沿为13.2ns,下降沿为54.6ns 关键词： 光电半导体开关 高增益 锁定效应     

基于搜索平均法的气象观测数据的非线性去噪

介绍了一种新型基于相空间重构和返回图法的非线性降噪方法——搜索平均法，首先将该方法应用于被高斯白噪声所污染的Henon映射时间序列，说明根据降噪理论所编写的计算程序的正确性；然后应用于中国气象局公布全国435站1960—2000年的逐日气温观测时间序列，并利用非线性预报方法衡量降噪的效果，验证了该方法的有效性.     

基于典型工况的半导体制冷系统优化方式探讨

半导体制冷的特殊性,使制冷优化探讨对其工程应用具有重要指导意义.文中阐述了作为制冷片工作参数优化依据的最大效率E、等增量I、等功率P、综合最佳S、最大制冷量Q和最大温差T六种典型制冷工况.工况对比分析指出,温差亦是影响制冷性能的重要因素.在讨论各工况应用场合和制冷片损坏机理的基础上.探讨了温差优化和供电与控制方式优化措...     

新课程背景下改进物理实验教学的实践与思考

物理新课程标准要求物理实验贴近学生生活,加强课程与学生生活和现实社会的联系.实验是培养学生动手能力的最佳途径,因此要尽可能地创造条件和不断改进,让学生亲自动手实验.笔者结合自己的实践与思考通过几个实例谈些关于新课程实验改进的做法.