测定不同形状物体空气阻力系数的实验

设计空气流速连续可调的小型风洞,对圆形平板、圆柱体、流线体的空气阻力系数进行测量.利用U型管中水柱的高度差表达孔板法中空气的流速,通过悬臂梁力传感器测量测试物受到的空气阻力,根据空气阻力和U型管中水柱的高度差的关系测定空气阻力系数.     

Power dissipation characteristics of great power and super high speed semiconductor switch

The power dissipation characteristics of pulsed power switch reversely switched dynistors （RSDs） are investigated in this paper. According to the expressions of voltage on RSD, derived from the plasma bipolar drift model and the RLC circuit equations of RSD main loop, the simulation waveforms of current and voltage on RSD are acquired through iterative calculation by using the fourth order Runge-Kutta method, then the curve of transient power on RSD versus time is obtained. The result shows that the total dissipation on RSD is trivial compared with the pulse discharge energy and the commutation dissipation can be nearly ignored compared with the quasi-static dissipation. These characteristics can make the repetitive frequency of RSD increase largely. The experimental results prove the validity of simulation calculations. The influence factors on power dissipation are discussed. The power dissipation increases with the increase of the peak current and the n-base width and with the decrease of n-base doping concentration. In order to keep a low power dissipation, it is suggested that the n-base width should be smaller than 320μm when doping concentration is 1.0×10^14cm^-3 while the doping concentration should be higher than 5.8×10^13cm^-3 when n-base width is 270μm.     

具有空穴传输基团的超支化聚合物发光材料的结构与光谱性质

利用A2 B3反应,合成了带有空穴传输基团——三苯胺为联接单元,以1,3,5-三苯基苯为核的超支化聚合物（TPA-TPP）,并对这类聚合物的合成方法、结构、光物理性质进行了系统的研究。通过溶剂效应观察到了TICT（分子内电荷转移态）,发射谱为宽而无结构的带谱,且发射波长随溶剂极性的增大而明显红移。因而可利用此特性来调节发光波长。研究结果表明,以三苯基苯为核心,引入三苯胺基团作为连接基团,加大了空间位阻,使由溶液到固体膜状态的发射光谱红移减小。     

具有特大磁电阻效应钙钛矿材料的制备及性能分析

通过固相烧结法制备了具有特大磁电阻效应的钙钛矿材料Pr0.64Ag0.044MnAl0.2O3.利用结构和成分分析,发现此材料只有在1 100℃高温烧结下才能生成完整的钙钛矿结构,且属于立方晶系,晶格常量a≈0.386 nm.在0.4 T的外磁场下,磁电阻值在122 K处达到最大,约为19.2%,为巨磁电阻实验提供了较好的样品.     

磁性隧道结Ni80Fe20/Al2O3/Co的制备和物性

用等离子体氧化形成绝缘层的方法，重复性地制备出了Ni     

Procreating tiles of double commutative-step digraphs

Double commutative-step digraph generalizes the double-loop digraph. A double commutative-step digraph can be represented by an L-shaped tile, which periodically tessellates the plane. Given an initial tile L（l, h, x, y）, Aguil5 et al. define a discrete iteration L（p） = L（l ＋ 2p, h ＋ 2p, x ＋ p, y ＋ p）, p = 0, 1, 2,..., over L-shapes （equivalently over double commutative-step digraphs）, and obtain an orbit generated by L（l, h, x,y）, which is said to be a procreating k-tight tile if L（p）（p = 0, 1, 2, ~ ~ ~ ） are all k-tight tiles. They classify the set of L-shaped tiles by its behavior under the above-mentioned discrete dynamics and obtain some procreating tiles of double commutative-step digraphs. In this work, with an approach proposed by Li and Xu et al., we define some new discrete iteration over L-shapes and classify the set of tiles by the procreating condition. We also propose some approaches to find infinite families of realizable k-tight tiles starting from any realizable k-tight L-shaped tile L（l, h, x, y）, 0 ≤ y - x ≤ 2k ＋ 2. As an example, we present an infinite family of 3-tight optimal double-loop networks to illustrate our approaches.     

Negative Resistance in a Two-Dimensional System with Entropic Barrier

A phenomenon of negative resistance is found in two-dimensional bistable and periodic potentials via Langevin simulation, where output quantities for noise and signal driven system, such as the power-spectrum density modulus and the signal power amplification, can become minima at finite temperatures. In such a system, the curvature of the potential along non-transport degree of freedom at the barrier is larger than that at the local minima. The temperature-dependent effective barrier, i.e. entropic barrier, is introduced via integration over the non-transport variables. The system shows the negative resistance because of the competence between the signal and the entropic barrier.     

La2/3Ca1/3MnO3样品的磁和电子输运性质研究

实验研究了La2/3CamMnO3样品零磁场下的电阻率和低磁场下的磁化强度随温度的变化行为．结果表明，除了居里温度(Tc)外还存在另一特征温度Tonset，高于Tonset的样品为典型的顺磁绝缘体，而低于Tc的样品为典型的铁磁金属，但在Lonset和Tc之间，样品的磁化率大大偏离居里一外斯定律，同时其导电特性显示出明显的反常．对观察到的不寻常导电特性，根据铁磁金属集团在顺磁绝缘体背景上随机分布的假设，进行了分析与探讨。     

巨磁电阻效应——2007年诺贝尔物理学奖简介

瑞典皇家科学院宣布，法国科学家阿尔伯特·费尔（Albert Vert）和德国科学家彼得·格鲁伯格（Peter Grunberg），共同获得2007年诺贝尔物理学奖．获奖的原因是这两位科学家先后独立发现了“巨磁电阻”（giant magnetoresistance，GMR）效应．这个发现引发的技术进步极大地提高了计算机硬盘磁头的数据读取能力，使硬盘无论从容量还是体积上都产生了质的飞越．这个发现还导致了新一代磁传感器的出现，而且巨磁电阻被认为是纳米技术最重要的应用之一．     

垂直各向异性Ho3Fe5O12薄膜的外延生长与其异质结构的自旋输运

垂直磁各向异性稀土-铁-石榴石纳米薄膜在自旋电子学中具有重要应用前景.本文使用溅射方法在(111)取向掺杂钇钪的钆镓石榴石(Gd_0.63Y_2.37Sc₂Ga₃O₁₂,GYSGG)单晶衬底上外延生长了2—100 nm厚的钬铁石榴石(Ho₃Fe₅O₁₂,HoIG)薄膜,并进一步在HoIG上沉积了3 nm Pt薄膜.测量了室温下HoIG的磁各向异性和HoIG/Pt异质结构的自旋相关输运性质.结果显示,厚度薄至2 nm的HoIG薄膜(小于2个单胞层)在室温仍具有铁磁性,且由于外延应变,2—60 nm厚HoIG薄膜都具有很强的垂直磁各向异性,有效垂直各向异性场最大达350 mT;异质结构样品表现出非常可观的反常霍尔效应和“自旋霍尔/各向异性”磁电阻效应,前者在HoIG厚度小于4 nm时开始缓慢下降,而后者当HoIG厚度小于7 nm时急剧减小,说明相较于反常霍尔效应,磁电阻效应对HoIG的体磁性相对更加敏感;此外,自旋相关热电压随HoIG厚度减薄在整个厚度范围以指数方式下降,说明遵从热激化磁振子运动规律的自旋塞贝克效应是其主要贡献者.本文结果表明HoIG纳米薄膜具有可调控的垂直磁各向异性,厚度大于4 nm的HoIG/Pt异质结构具有高效的自旋界面交换作用,是自旋电子学应用发展的一个重要候选材料.