Effective way of modeling chemical catalysis: Empirical valence bond picture of role of solvent and catalyst in alkylation reactions

A general methodology for the study of chemical catalysis is presented and demonstrated in a study of Friedel–Crafts‐type alkylation reactions that are constrained to collinear configurations. Ab initio potential energy surfaces in solution and relevant experimental results are used to calibrate general empirical valence bond (EVB) potential surfaces for studies of such reactions. The EVB surfaces allow one to interpolate the ab initio results to studies of the effect of different solvents, substituents, and catalysts on the alkylation reactions. This implicit approach introduces such effects by shifting the diagonal energies of the corresponding resonance structures. Such an EVB/shift approach appears valuable for assessing the effects of different catalysts and solvents on complex chemical reactions. © 2000 John Wiley & Sons, Inc. J Comput Chem 21: 607–625, 2000     

Analysis of questioned documents: A review

During the last years (2000–2014), many publications concerning the forensic analysis of questioned documents have been published, and new techniques and methodologies are nowadays employed to overcome forensic caseworks. This article reviews a comprehensive collection of the works focused on this issue, including dating studies, the analysis of inks from pens and printers, the analysis of paper, the analysis of other samples related to questioned documents and studies on intersecting lines. These sections highlight the most relevant analytical studies by a wide range of analytical techniques. Separation and spectrometric techniques are critically discussed and compared, emphasizing the advantages and disadvantages of each one. Finally, concluding remarks on the research published are included.     

Fluorescence intensity and lifetime-based cyanide sensitive probes for physiological safeguard

We characterize six new fluorescent probes that show both intensity and lifetime changes in the presence of free uncomplexed aqueous cyanide, allowing for fluorescence based cyanide sensing up to physiological safeguard levels, i.e. <30 μM. One of the probes, m-BMQBA, shows a ≈15-fold reduction in intensity and a ≈10% change in mean lifetime at this level.The response of the new probes is based on their ability to bind the cyanide anion through a boronic acid functional group, changing from the neutral form of the boronic acid group R-B(OH)₂ to the anionic R-B⁻(CN)₃ form, a new cyanide binding mechanism which we have recently reported. The presence of an electron deficient quaternary heterocyclic nitrogen nucleus, and the electron rich cyanide bound form, provides for the intensity changes observed. We have determined the disassociation constants of the probes to be in the range ≈15-84 μM³. In addition we have synthesized control compounds which do not contain the boronic acid moiety, allowing for a rationale of the cyanide responses between the probe isomers to be made.The lifetime of the cyanide bound probes are significantly shorter than the free R-B(OH)₂ probe forms, providing for the opportunity of lifetime based cyanide sensing up to physiologically lethal levels.Finally, while fluorescent probes containing the boronic acid moiety have earned a well-deserved reputation for monosaccharide sensing, we show that strong bases such as CN⁻ and OH⁻ preferentially bind as compared to glucose, enabling the potential use of these probes for cyanide safeguard and determination in physiological fluids, especially given that physiologies do not experience any notable changes in pH.     

半导体激光器相对光频偏的干涉测量法

通过检测LD输出激光在干涉场中干涉条纹位移的变化 ,得到LD在一定时间内相对自身输出光频偏情况。实验装置中采用较为简单的迈克耳逊干涉系统 ,用CCD实时采集反映输出光频偏情况的干涉图像信号 ,通过计算机处理得到LD的相对光频偏值     

A new solution to the K-shortest paths problem and its application in wavelength routed optical networks

In communication networks, traffic carried over long paths suffers from a higher call blocking probability (CBP) than those carried over short paths. This is a well-known fairness problem. Such a problem becomes more serious in wavelength-routed optical networks (WRONs) due to the wavelength continuity constraint. This paper aims to enhance the fairness characteristic in WRONs by the novel classified alternate routing (CAR) approach. As a foundation of this approach, the first K-shortest paths (KSP) between a designated source/destination node pair in a given network should be obtained simultaneously. This has been studied as the KSP problem in the literature. In this paper, a new loopless deviation (LD) algorithm for solving such a loopless KSP problem will be proposed. It outperforms existing solutions in terms of running time in real-life implementations. In order to measure the fairness characteristic, we first classify all connection requests into categories such as 1-hop traffic, 2-hop traffic, etc., according to the number of minimal hop count between the corresponding source/destination node pair. We then quantify the fairness characteristic by the ratio of the average CBP of each traffic category to that of 1-hop traffic such that CBP ratios with a value closer to 1 are preferred. We will show that such a measure criterion is more precise and robust than existing ones in the literature. Finally, numerical experiments will reveal that the CAR approach outperforms existing fairness enhancement methods when considering the comprehensive performance in terms of the balance between the fairness characteristic and the overall CBP feature.     

吸收光栅增益耦合DFB—LD电路模型

本文以激光器单模速率方程为基础,针对ＤＦＢ－ＬＤ推导了光子寿命与激光器内部损耗及端面出射损耗的关系,以及端面出射光功率与平均光子密度的关系,给出吸收光栅增益耦合ＤＦＢＬＤ电路模型,用该模型研究了ＡＧ－ＧＣ－ＤＦＢ－ＬＤ的自脉动效应及影响自脉动幅度和频率的主要因素。     

LD双端端面泵浦的高功率连续单频Nd:YVO4激光器

研制了高功率连续单频Nd：YVO4激光器。在考虑激光晶体因吸收泵浦光而产生的热透镜效应的基础上，设计了六镜环行激光谐振腔，采用两个光纤耦合输出的高功率激光二极管双端端面泵浦结构，在总泵浦功率为32．3W的情况下，得到10．4W的单频1．064μm红外输出，斜效率为43．7％，长期功率稳走性优于1％(4h)，激光器自由运转时的频率漂移小于150MHz（1min)。     

LD抽运Nd:YVO_4腔内倍频连续波8.8W绿光激光器

报道了用 LD双向抽运 Nd:YVO4晶体 ,KTP作腔内倍频的大功率绿光激光器。通过对大功率抽运情况下所产生的热透镜效应进行分析和估算 ,优化了热稳腔参数 ,获得了较稳定的功率输出。在抽运功率为 2 8W时 ,获得最大连续波绿光输出 8.8W,光 -光转换效率达 31 .5%。     

LD抽运Nd:YAG激光器声光调Q高效内腔谐波转换

报道了一台半导体激光器(LD)抽运的声光调Q高效内腔谐波转换Nd:YAG激光器,当注入抽运功率为12W时,声光调Q的基频波(1.064 μm)输出平均功率为2.6 W,采用内腔倍频技术,在简单腔情况下,二次谐波(532nm)输出平均功率达到了2.1 W,光-光转换效率分别达到21.7%和17.5%.     

微型化LD泵浦Er3+,Yb3+共掺磷酸盐玻璃被动调Q激光器

报道了一种主要应用于激光测距的微型化激光二极管泵浦Er3+/Yb3+共掺磷酸盐玻璃被动调Q激光器。采用中心波长940 nm的二极管作为泵浦源,Er3+/Yb3+共掺磷酸盐玻璃作为增益介质,Co2+:MgAl2O4作为被动调Q晶体,通过优化增益介质和被动调Q晶体参数,获得了最佳的增益介质长度和被动调Q晶体初始透过率。当泵浦能量14 mJ,重复频率10 Hz,泵浦脉宽5 ms时,获得了单脉冲能量480 J,脉宽5 ns,峰值功率大于20 kW的激光输出,激光光束质量因子为1.2。