Time evolution of Wikipedia network ranking

X-ray circular magnetic dichroism, polarized neutron diffraction, ac susceptibility, and Seebeck effect have been measured for several members of the RCo₂ series (R = Ho, Tm, Er) as a function of temperature and applied magnetic field. The experimental results show robust parimagnetism (a general behaviour along the RCo₂ series with R being a heavy rare earth ion) and two reversal temperatures in some systems, which is an unexpected result. Polarised neutron diffraction show differences between results obtained on single crystals or polycrystalline ingots. We propose an interpretation of parimagnetic RCo₂ as a Griffiths phase of the high temperature, magnetically ordered, amorphous RCo₂ phase.     

Poly(lactic acid) composites with poly(lactic acid)‐modified carbon nanotubes

This work reports the study of the effect of chemical functionalization of carbon nanotubes on their dispersion in poly(lactic acid). The nanotubes were functionalized by the 1,3‐dipolar cycloaddition reaction, generating pyrrolidine groups at the nanotube surface. Further reaction of the pyrrolidine groups with poly(lactic acid) was studied in solution and in the polymer melt. The former involved refluxing the nanotubes in a dimethylformamide/polymer solution; the latter was carried out by direct melt mixing in a microcompounder. The carbon nanotubes collected after each process were characterized by thermogravimetry and by X‐ray photoelectron spectroscopy, showing evidence of polymer bonded to the nanotube surface only when the reaction was carried out in the polymer melt. The composites with polymer modified nanotubes present smaller average agglomerate area and a narrower agglomerate area distribution. In addition, they show improved tensile properties at low CNT concentration and present lower electrical resistivity. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 3740–3750     

Hiv-1 Specific Reverse Transcriptase Inhibitors: why are Tsao-Nucleosides so Unique?

1. INTRODUCTION

AIDS will still be one of the most important challenges for the Scientific Community in the approaching new century. Since the identification, in 1983-84,^1,2 of human immunodeficiency virus (HIV) as the etiological agent of AIDS, significant progress has been made in the treatment of HIV-infected patients. This has been in part due to the discovery and clinical use of an increasing number of anti-HIV drugs. However, while highly active antiretroviral therapy (HAART)³ approaches have reduced the morbidity and mortality, the intertwined problems of drug induced viral resistance, poor compliance with complex regimens and therapy failure continue. Therefore, there remains a pressing need for the development of new antiviral agents that can be used not only as first line therapeutic candidates, but also in the antiretroviral-experienced patient population.     

Tellurium delta‐doped InGaP layers grown by metalorganic vapour phase epitaxy

Heavily n‐type doped and several nanometres thick In_0.485Ga_0.515P layers are necessary for various devices. We studied the delta‐doping of this ternary with tellurium; the layers were grown by metalorganic vapour phase epitaxy (MOVPE), and diethyltelluride was used as the precursor. A maximum Hall sheet concentration of 2.75 × 10¹³ cm^–2 was achieved in our samples grown at 560 °C. The Te profiles were analyzed with secondary ion mass spectrometry (SIMS), and a very narrow spectrum with a full width at half maximum of 7.5 nm was measured. This value indicates that the memory effect, referred to in the literature, was practically eliminated with appropriate growth conditions. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

用SiCl4-H2低温沉积多晶硅薄膜微结构的Raman分析

关键词：     

支撑介质对平面型电磁带隙结构带隙特性的影响

运用直线法对含有不同参数支撑介质的平面型电磁带隙（EBG）结构进行了分析.概述了算法的实现过程,使用周期边界条件隔离出一个结构单元作为计算区域,并利用直线法得到了位函数在各层介质界面间的传输方程.通过联立场分量与位函数的变换关系和界面处切向场分量的连续性条件,建立了本征方程, 得到了表征该EBG 结构表面波带隙的本征模频带图.同时,使用该方法对含有不同介电常数、不同厚度支撑介质的表面波带隙进行了计算.通过对计算结果的分析,得到了支撑介质对平面型EBG 结构带隙特性影响的六条结论,为平面型EBG 结构的设计 关键词： 超媒质 光子带隙 周期结构 表面波     

基于SESAM被动调Q的激光二极管泵浦Yb∶CaYAlO_4脉冲激光器

采用发射波长约为976 nm的半导体激光器作为泵浦源,Yb~(3+)掺杂浓度为1. 5at.%、通光长度为2 mm的Yb∶CaYAlO_4晶体作为增益介质,本文提出了一种基于半导体可饱和吸收镜(SESAM)被动调Q的激光二极管泵浦Yb∶CaYAlO_4以获取稳定脉冲输出的方案。通过合理设计谐振腔,实现了稳定的被动调Q激光脉冲输出,并分析了泵浦功率的大小对输出脉冲的重复频率、脉冲宽度、单脉冲能量以及脉冲峰值功率的影响。     

参数不确定的分数阶混沌系统广义错位延时投影同步

为进一步增强通信系统中保密通信的安全性,结合广义错位投影同步和延时投影同步,提出了广义错位延时投影同步.以分数阶Chen系统和Lü系统为例,针对两系统参数都不确定,基于分数阶稳定性理论与自适应控制方法,设计了非线性控制器和参数自适应律,实现了广义错位延时同步,并辨识出驱动系统和响应系统中所有不确定参数.理论分析和数值仿真验证了该方法的可行性与有效性.     

基于有限元法分析宝石级金刚石的合成腔体温度场

以有限元法为理论分析手段模拟分析了温度梯度法合成宝石级金刚石大单晶的腔体温度场,实现了对宝石级金刚石的合成腔体内各位置温度同时测量.模拟结果表明:在宝石级金刚石合成过程中,其温度分布呈不均匀分布.腔体内高温区分布在样品(碳源+触媒)边缘,低温区分布在籽晶附近.样品腔内热量的传递方式和样品腔内的碳源输运方式相同,均由碳源的两侧向籽晶附近传输.籽晶附近轴向温度梯度大于径向温度梯度,导致单位时间内其轴向生长尺寸大于径向生长尺寸.宝石级金刚石腔体温度场分析的理论模型的成功构建,为新型宝石级金刚石腔体的研制提供了良好的设计基础,对促进优质宝石级金刚石的生长技术具有指导意义.     

InAs/GaSb量子阱中太赫兹光电导特性

太赫兹技术由于具有重大的科学价值及应用前景而引起了广泛关注,其核心问题是性能优异的室温太赫兹辐射源和探测器研究.本文用半经典的玻尔兹曼方程方法研究了In As/Ga Sb量子阱系统中载流子对电磁场的响应,运用平衡方程方法求解玻尔兹曼方程得到了量子阱系统中的光电导,系统地研究了量子阱结构对光电导的影响,揭示了在该量子阱系统中光电导产生的物理机制.研究发现,量子阱结构主要通过调节载流子的能级、浓度和波函数的耦合影响光电导,对称性较好的量子阱结构(8 nm-8 nm)的光电导信号更强,其峰值落在太赫兹区(0.2 THz),并且在低温下器件的性能较好,温度升高则吸收峰略有降低,且光电导峰值发生红移.研究结果表明该量子阱系统可以用作室温太赫兹光电器件.