低温透平膨胀机的热力参数计算及数值模拟校核北大核心

针对某液化装置用一级透平膨胀机进行一维热力参数设计计算并使用商业软件ANSYS进行三维数值模拟的校核。计算表明,一维设计所得结果具有一定准确性。三维校核过程中,分别使用理想气体、PR方程以及He Pak三种不同的氦气体工质物性库,三者对工质密度计算的数据存在较大差别,且压力越大差别越大;喷嘴叶片表面压力分布差别较小,温度分布差别较大;工作轮叶片表面压力分布在前缘处有一定差别,尾缘处变化曲线基本重合,温度分布同样差别较大。此次模拟校核表明,理想气体物性库与实际气体物性库的结果存在一定偏差,故对于小型低温透平膨胀机而言,即便温区在20K以上,也应使用实际气体物性库对其进行数值模拟。     

基于引导滤波和核相关滤波的红外弱小目标跟踪

为了解决传统跟踪算法不能有效区分背景边缘和红外弱小目标的问题,基于图像引导滤波和核相关滤波,提出了一种改进型的红外弱小目标跟踪算法。将采用6组红外弱小目标图像序列得到的实验结果与采用经典跟踪算法得到的实验结果进行了比较。实验结果表明,所提算法在主观视觉和客观评价指标方面均优于传统算法,具有更高的目标跟踪精度与较好的实时性。     

基于MEMS加速度传感器的步态识别

针对最小采集约束条件和经历长时间跨度下识别率低的问题,提出一种基于MEMS加速度传感器的步态识别算法。该算法以右髋部位置采集加速度信号构造多个高斯差分尺度空间,利用局部关键点生成稀疏表示的步态特征位置模板,并采用模板融合来有效转换稀疏性步态周期特征,最后利用最近邻算法和投票机制对步态特征进行识别。在公开的含175名测试者的步态加速度数据集上进行测试,实验结果显示识别率为98.67%和认证率为99.89%,并进一步研究了测试集和训练集样本数目对识别效果的影响,验证了特征提取的有效性和稳定性。     

The 650-nm variable optical attenuator based on polymer/silica hybrid waveguide

Visible light variable optical attenuators(VOA) are essential devices in the application of channel power regulation and equalization in wavelength-division multiplexing cross-connect nodes in plastic optical fiber(POF) transmission systems.In this paper, a polymer/silica hybrid waveguide thermo–optic attenuator based on multimode interference(MMI) coupler is designed and fabricated to operate at 650 nm. The single-mode transmission condition, MMI coupler, and transition taper dimensions are optimized through the beam propagation method. Thermal analysis based on material properties provides the optimized heater placement angle. The fabricated VOA presents an attenuation of 26.5 dB with a 21-mW electrical input power at 650 nm. The rise time and fall time are 51.99 and 192 μs, respectively. The time–stability measurement results prove its working reliability.     

单分散的二氧化硅微球表面印迹壳层的制备及其对食品包装材料中邻苯二甲酸二苄酯的检测

以邻苯二甲酸二苄酯(DBz P)为模板,以Stber和"种子生长法"相结合获得的二氧化硅微球为载体,采用表面印迹技术成功制备了纳米印迹壳层(MIPs)。采用红外光谱与扫描电镜对其结构和形貌进行表征,同时进行了一系列的吸附性能实验,结果表明,MIPs达到平衡吸附的时间约为30 min,吸附行为符合伪二级动力学。等温吸附实验结果表明,室温条件下MIPs的最大吸附量达47.35 mg/g。对不同温度条件下的等温实验数据进行拟合发现,Langmuir模型与实验数据的吻合度比Freundlich模型更高;Scatchard拟合结果证实该印迹壳层仅含1种结合位点,且印迹位点为均相分布。选择性吸附实验表明MIPs对DBz P的吸附明显高于其他结构类似物。MIPs经10次循环吸附后,吸附效率为83%,表明MIPs具有较长的使用寿命。采用超高效液相色谱(UPLC)技术,以MIPs为吸附剂提取食品包装材料中的DBzP,其加标回收率为88.8%~93.1%,相对标准偏差低于6%。MIPs可作为食品及其包装材料中DBz P提取的备选材料。     

Zero-determinant strategy:An underway revolution in game theory

Repeated games describe situations where players interact with each other in a dynamic pattern and make decisions according to outcomes of previous stage games. Very recently, Press and Dyson have revealed a new class of zero-determinant(ZD) strategies for the repeated games, which can enforce a fixed linear relationship between expected payoffs of two players, indicating that a smart player can control her unwitting co-player’s payoff in a unilateral way [Proc. Acad. Natl. Sci.USA 109, 10409(2012)]. The theory of ZD strategies provides a novel viewpoint to depict interactions among players,and fundamentally changes the research paradigm of game theory. In this brief survey, we first introduce the mathematical framework of ZD strategies, and review the properties and constrains of two specifications of ZD strategies, called pinning strategies and extortion strategies. Then we review some representative research progresses, including robustness analysis,cooperative ZD strategy analysis, and evolutionary stability analysis. Finally, we discuss some significant extensions to ZD strategies, including the multi-player ZD strategies, and ZD strategies under noise. Challenges in related research fields are also listed.     

具有非均匀渐变界面DBR的光学特性分析

应用特征矩阵法研究了非均匀渐变界面Al_0.9Ga_0.1As/Al_yGa_1-yAs/GaAs/Al_xGa_1-xAs DBR的光学特性.建立了非均匀渐变界面Al_yGa_1-yAs的折射率模型，并得到了渐变界面特征矩阵的解析解，通过特征矩阵法分别计算了突变GaAs/Al_0.9Ga_0.1As DBR和渐变DBR的反射谱和反射相移，分析了非均匀渐变层对DBR光学特性的影响，对渐变DBR，需要在DBR前面再增加一定厚度的非均匀渐变相位匹配层才能使整个DBR满足中心波长相位匹配条件，并通过光学厚度近似方法求出相位匹配层厚度. 关键词： DBR 反射谱 反射相移 特征矩阵法     

Transport properties and anomalous fatigue effect of Ag/Bi0.9La0.lFeO3/La0.7Sr0.3MnO3 heterostructures

The transport properties and fatigue effect of Ag/Bi0.9La0.lFeO3/La0.7Sr0.3MnO3 heterostructures are described. By examining the I-V curves, an anomalous fatigue effect was found and its influences on resistive states were studied. I-V curves combined with C-f spectra were used to directly analyze the transport properties and fatigue effect. Compared to the first I-V cycle state, this structure shows more than one order increase of resistance after 100 cycles of ＂I-V curve training＂. The redistribution of oxygen vacancies in the depletion layer of Ag/Bi0.9La0.lFeO3 is believed to be responsible for the different resistance mechanisms and tenfold magnitude drop in resistance. The resistive switching is understood to be caused by electric field-induced carrier trapping and detrapping, which changes the depletion layer thickness at the Ag/Bi0.9La0.lFeO3 interface.     

以四氟苯甲酸根及联吡啶为配体的铜配合物的合成、晶体结构及量子化学研究

水热条件下,合成了一个新的单核铜(Ⅱ)配合物[Cu(TFBA)(2,2′-bipy)(H2O)2](TFBA)(HTFBA=2,3,4,5-四氟苯甲酸,2,2′-bipy=2,2′-联吡啶),并通过元素分析、红外光谱,热重分析和X-射线单晶衍射对其进行了表征。铜(Ⅱ)分别与来自1个2,2′-bipy的2个氮原子、1个2,3,4,5-四氟苯甲酸根的1个氧原子和2个水分子中的2个氧原子配位,形成变形的四方锥的配位构型。配合物通过强的O-H…O氢键作用形成了二聚体结构,该二聚体又通过分子间弱的C-H…O氢键和C-H…π作用形成了一维链状结构。对配合物中[Cu(TFBA)(2,2′-bipy)(H2O)2]+进行了量子化学从头计算,探讨了配合物的稳定性、分子轨道能量以及一些前沿分子轨道的组成特征。     

四杆型射频四极场加速器的极间电压调谐及测定北大核心CSCD

为了提高射频四极场加速器(RFQ)的束流传输效率,需要对纵向分布不均匀的极间电压进行补偿,并且准确测量束流实验中极间电压的绝对数值。考虑到极间电压分布不均匀是由于分布电容和端部效应造成的,而采用调谐块可以调节分布电感,通过电磁场数值模拟研究了调谐块对极间电压分布的影响,最终极间电压的平整度被调整到优于95%。在束流实验中,通过测量轫致辐射谱测定了极间电压的数值,通过束流动力学模拟研究了多能峰产生的原因,并最终标定了70kV极间电压对应的输入功率值284kW。