A first-principles study of B2 NiAl alloyed with rare earth element Pr, Pm, Sm, and Eu

The structural, elastic, and electronic properties of NiAl alloyed with rare earth elements Pr, Pm, Sm, and Eu are investigated by using density functional theory (DFT). The study suggests that Pr, Pm, Sm, and Eu are all tend to be substituted for Al site. Ni₈Al₇Pm possesses the largest ductility. Only the hardness and ductility of Ni₈Al₇Eu are enhanced simultaneously. The covalency strength of Ni-Al bond in Ni₈Al₇Pm is higher than that in Ni₈Al₇Eu. The covalency strength of Al-Al bond and that of Ni-Ni bond in Ni₈Al₇Eu are higher than that in Ni₈Al₇Pm. Ni-Pm bond and Ni-Eu bond are covalent, and the covalency strength of Ni-Pm bond is greater. Al-Pm bond and Al-Eu bond show great covalency strength and ionicity, respectively.     

非稳态弹流润滑状态下滚动体-滚道摩擦副的动力特性研究

针对滚动体-滚道摩擦副,建立了点接触非稳态弹流润滑数学模型,利用FFT技术和半解析算法数值求解了接触体在自由振动过程中油膜压力和膜厚的变化,同时结合有阻尼系统的自由振动模型,给出了预测点接触摩擦副动力特性的方法,在较宽的载荷和速度范围内分析了接触副的等效刚度系数和阻尼系数的变化.结果表明：根据接触副的实际工作载荷和速度所确定的无量纲自然频率来进行非稳态弹流的计算所得到的膜厚结果更接近实验值;在接触体的振动过程中油膜的压力和厚度在平衡位置附近上下波动,且由于润滑油膜的作用接触体的振动幅值逐渐减小;刚度系数随载荷参数的增加而增加,随速度参数的增加而减小,而阻尼系数的变化规律较复杂,在不同的载荷和速度范围内呈现出不同的变化趋势.     

大变倍比光学被动半无热化变焦系统设计

针对传统变焦光学系统在环境温度变化的情况下,变焦全程无法一致清晰成像以及需频繁调焦的问题,提出了一种光学被动半无热化变焦系统设计方法,并设计了一种光学被动半无热化变焦系统.变焦系统的焦距为30～1000mm,工作波段为486～656 nm,光圈为F4.4～F8,短焦采用光学被动无热化设计.变焦系统的成像质量良好,结构非...     

Effect of Mg-Preflow for p-AlGaN Electron Blocking Layer on the Electroluminescence of Green LEDs with V-Shaped Pits

In GaN-based green light-emitting diodes(LEDs) with and without Mg-preflow before the growth of p-Al GaN electron blocking layer(EBL) are investigated experimentally.A higher Mg doping concentration is achieved in the EBL after Mg-preflow treatment,effectively alleviating the commonly observed efficiency collapse and electrons overflowing at cryogenic temperatures.However,unexpected decline in quantum efficiency is observed after Mg-preflow treatment at room temperature.Our conclusions are drawn such that the efficiency decline is probably the result of different emission positions.Higher Mg doping concentration in the EBL after Mg-preflow treatment will make it easier for a hole to be injected into multiple quantum wells with emission closer to pGaN side through the(8-plane rather than the V-shape pits,which is not favorable to luminous efficiency due to the preferred occurrence of accumulated strain relaxation and structural defects in upper QWs closer to p-GaN.Within this framework,apparently disparate experimental observations regarding electroluminescence properties,in this work,are well reconciled.     

量子阱生长气压对InGaN/GaN黄光LED光电性能的影响

采用MOCVD技术在图形化硅衬底上生长了InGaN/GaN多量子阱黄光LED外延材料,研究了不同的量子阱生长气压对黄光LED光电性能的影响。使用高分辨率X射线衍射仪（HRXRD）和荧光显微镜（FL）对晶体质量进行了表征,使用电致发光系统积分球测试对光电性能进行了表征。结果表明：随着气压升高,In的并入量略有降低且均匀性更好,量子阱中的点缺陷数目降低,但是阱垒间界面质量有所下降。在实验选取的4个气压4,6.65,10,13.3 kPa下,外量子效率最大值随着量子阱生长气压的上升而显著升高,分别为16.60%、23.07%、26.40%、27.66%,但是13.3 kPa下生长的样品在大电流下EQE随电流droop效应有所加剧,在20 A·cm^-2的工作电流下,样品A、B、C、D的EQE分别为16.60%、19.77%、20.03%、19.45%,10 kPa下生长的量子阱的整体光电性能最好。     

微波促进酸性离子液体催化水杨酸酯化

用自制的硫酸氢1-甲基-3-(3-磺酸基丙基)咪唑([MIMPS]HSO4)酸性离子液体作为水杨酸与醇的酯化反应催化剂,考察了温度、时间、物料配比和离子液体用量等因素对酯化反应的影响,优化的最佳反应条件为: 微波辐射时间20 min,反应温度95 ℃,醇与酸摩尔比3∶1(水杨酸的量为0.02 mol),[MIMPS]HSO4用量10 mmol,水杨酸甲酯的产率和选择性分别为91.9%和99.0%。 离子液体回收循环使用4次,催化效率不变。 与热催化酯化反应相比,微波辐射可缩短反应时间;水杨酸与不同碳链醇的酯化产率随着碳链的增加而降低,同碳链的伯醇酯化率比仲醇高。     

Community detection in signed networks based on discrete-time model

Community detection in signed networks has been studied widely in recent years. In this paper, a discrete difference equation is proposed to imitate the consistently changing phases of the nodes. During the interaction, each node will update its phase based on the difference equation. Each node has many different nodes connected with it, and these neighbors have different influences on it. The similarity between two nodes is applied to describe the influences between them. Nodes with high positive similarities will get together and nodes with negative similarities will be far away from each other.Communities are detected ultimately when the phases of the nodes are stable. Experiments on real world and synthetic signed networks show the efficiency of detection performance. Moreover, the presented method gains better detection performance than two existing good algorithms.     

GC-MS测定血清胆固醇及其标志物前处理条件正交试验优化研究

采用正交试验优化GC-MS测定血清胆固醇及其标志物的样品前处理条件,并对最优试验方案进行方法学评价。采用L₁₆(211)正交设计对影响GC-MS测定血清胆固醇及其标志物前处理的3个关键步骤共7个因素——皂化(KOH-乙醇浓度、皂化温度和时间)、萃取(正己烷用量)和衍生化(衍生化温度、时间和用量)进行优化。得到最优前处理条件组合如下：KOH-乙醇溶液浓度为1 mol·L-1;皂化温度70 ℃;皂化时间60 min;萃取剂用量2 mL;衍生化温度70 ℃;衍生化时间60 min;衍生化试剂用量100 μL。所建方法准确性和精密性良好,方法学评价指标优于文献报道。     

改进的基于积分时间定标的红外焦平面阵列非均匀性校正算法(英文)

红外焦平面阵列各探测元响应的非均匀性降低了图像的质量和温度分辨率,定标类和场景类校正算法为解决该问题提供了可行的途径.传统的基于黑体定标的校正算法由于其简单有效而被广泛使用,但是其缺点在于依赖黑体及其相关控温装置.本文提出了一种改进的基于积分时间定标的两级校正算法.在保持入射辐射不变的情况下,首先通过改变积分时间得到系列响应数据,然后利用最小二乘法估计出两点校正所需的初始校正系数,并对不同积分时间下的响应数据进行初校正,最后估计出一点校正系数.实验结果证明该方法具有计算量小、校正准确度高的优点,可取得优良的校正效果,并易于在硬件平台中实现.     

AlN插入层对硅衬底GaN薄膜生长的影响

利用金属有机化合物气相外延沉积技术在2inch(5.08cm)Si(111)图形衬底上生长了GaN外延薄膜,在Al组分渐变AlGaN缓冲层与GaN成核层之间引入了AlN插入层,研究了AlN插入层对GaN薄膜生长的影响。结果表明,随着AlN插入层厚度的增加,GaN外延膜(002)面与(102)面X射线衍射摇摆曲线半峰全宽明显变小,晶体质量变好,同时外延膜在放置过程中所产生的裂纹密度逐渐减小直至不产生裂纹。原因在于AlN插入层的厚度对GaN成核层的生长模式有明显影响,较厚的AlN插入层使GaN成核层倾向于岛状生长,造成后续生长的nGaN外延膜具有更多的侧向外延成分,从而降低了GaN外延膜中的位错密度,减少了GaN外延膜中的残余张应力。同时还提出了一种利用荧光显微镜观察黄带发光形貌来表征GaN成核层形貌和生长模式的新方法。