Mo_2C/γ-Al_2O_3催化剂上苯加氢反应的原位红外光谱研究

采用程序升温反应法制备了钝化态、还原钝化态和新鲜态Mo2C/γ-Al2O3催化剂,结合原位红外光谱表征技术和反应性能评价,考察、比较了三种催化剂苯加氢反应活性.原位红外光谱结果表明,新鲜态Mo2C/γ-Al2O3催化剂在室温就显示了较好的苯加氢反应活性,表现了类贵金属的催化活性.CO吸附在反应前后新鲜态Mo2C/γ-Al2O3催化剂上的对比结果表明,低价态的Mo位(Moδ+(0δ2))是苯加氢反应活性中心.三种催化剂的反应活性结果表明,新鲜态Mo2C/γ-Al2O3催化剂反应活性最好,催化剂寿命最长,失活之后在500°C下H2处理即可恢复原有活性.     

Lipase-catalyzed Knoevenagel condensation between α,β-unsaturated aldehydes and active methylene compounds

A simple and efficient Knoevenagel condensation between a b-unsaturated aldehydes and active methylene compounds is reported.Notably,this condensation can be catalyzed by PPL(lipase from porcine pancreas) with satisfied yields(49%–92%).Moreover,PPL induces moderate Z/E selectivity in the Knoevenagel condensation.     

Performance of an optical stabilization system at NSLS beamline U12IR

A low-cost optical feedback system using dynamic mirrors has been developed at the NSLS for stabilizing the position and direction of an infrared synchrotron beam against thermal drift and mechanical noise. The system design has some unique features that potentially simplify installation into an existing infrared beamline. We describe the system and its features along with some performance results.     

Recent advances in biodegradable matrices for active ingredient release in crop protection: Towards attaining sustainability in agriculture

Climate changes, emerging species of plant pests, and deficits of clean water and arable land have made availability of food to the ever-increasing global population a challenge. Excessive use of synthetic pesticides to meet ever-increasing production needs has resulted in development of resistance in pest populations, as well as significant ecotoxicity, which has directly and indirectly impacted all life-forms on earth. To meet the goal of providing safe, sufficient, and high-quality food globally with minimal environmental impact, one strategy is to focus on targeted delivery of pesticides using eco-friendly and biodegradable carriers that are derived from naturally available materials. Herein, we discuss some of the recent approaches to use biodegradable matrices in crop protection, while exploring their design and efficiency. We summarize by discussing associated challenges with the existing approaches and future trends that can lead the world to more sustainable agricultural practices.     

Optimization and detailed stability study on Pb doped ceria nanocubes for enhanced photodegradation of several anionic and cationic organic pollutants

A series of Pb doped CeO₂ nanocubes with seven different Pb loadings (2–12 mol%) were synthesized via modified hydrothermal technique. The prepared samples were characterized by XRD, XPS, FT-IR, TGA, SEM, HR-TEM, EDS and UV–Vis DRS analysis. According to XRD analysis, the crystalline structure of synthesized pure CeO₂ and Pb-doped CeO₂ samples are cubic structure. The ceria nanocubes showed an increase in amount of oxygen vacancies with increasing the dopant concentrations. When the doping level of Pb is 6 mol%, the optical band gap of Pb-CeO₂ is smaller than that of pure CeO₂ nanocubes. The HR-TEM results confirms the cubic structure of 6% Pb-CeO₂ with average crystallite size of about 15 nm. The photocatalytic ability of Pb-CeO₂ catalysts were studied by degrading several anionic and cationic organic pollutants like methylene blue (MB), methylene orange (MO), methylene red (MR), rhodamine B (RhB), reactive blue 160 (RB160), salicylic acid (SA), coumarin and phenol. The 6% Pb-CeO₂ nanocubes shows better photocatalytic performance against anionic dyes especially for MB. To find the optimum condition for better photocatalytic performance of 6% Pb-CeO₂ nanocubes, the photocatalytic process was conducted in different initial reaction conditions like reaction temperature, catalytic dosage, dye concentration and pH of the reaction solution. The stability and recyclability of 6% Pb-CeO₂ photocatalyst was studied by XRD, FT-IR and EDS analysis after 5 cycles of MB degradation. The hydroxyl radical estimation and trapping experiments were conducted to observe the photocatalytic mechanism process in 6% Pb-CeO₂ nanocubes. The perfect doping concentration for better organic pollutant degradation by Pb-CeO₂ is found to be 6 mol% of Pb.     

一种新的快速响应的AQM算法

该文应用控制理论,设计了具有快速响应特征的比例积分(Proportional-Integral, PI)控制器,并以此提出了一个新的主动队列管理(Active Queue Management, AQM)算法,称为Active PI算法(简称A-PI)。A-PI用一组参数实现快速响应,用另一组参数保证队长稳定,使用门限值实现两组参数间平滑切换,算法实现简单。理论分析和仿真实验表明,A-PI算法在保证队长稳定的同时实现了对不同网络环境的快速响应。     

A 4th order fully integrated active RC complex filter with novel automatic tuning systems

This letter introduces a 4th order active RC complex filter with 1.5MHz center frequency and 1MHz bandwidth. The total harmonic distortion of the filter is less than –60dB and the image rejection ratio is greater than 60dB. A novel technique is also proposed in this letter to automatically adjust the variation of the time constant. The advantages of the proposed method are its high precision and simplicity. Using 5bits control words, the tuning error is less than ±1.6%.     

一种InGaP/GaAs HBT高速预分频器MMIC

采用Foundry提供的InGaP/GaAs HBT工艺设计了一种数字静态除2高速预分频器MMIC.流片测试结果与仿真结果基本吻合,最高工作频率高于仿真结果.设计过程在速度和功耗之间进行了折中,并且考虑了自谐振频率对电路的影响.测试结果显示:在5V电源电压下,该预分频器静态电流为60mA,最高工作频率达到15GHz,自谐振频率为19.79GHz.该MMIC可以直接应用到S-X波段射频微波系统中.     

活性炭复合滤嘴吸附性能的热脱附研究

采用热脱附与气相色谱-质谱联用技术对活性炭滤嘴中活性炭和乙酸纤维脱附的组分进行了定性分析,并用峰面积归一化法测定了所含挥发性成分的质量分数,活性炭脱附组分共鉴定出芳香族化合物、醛酮类、烟碱、酸类、酯类等62种挥发性化合物.结果表明方法具有较好的重现性;为评价活性炭滤嘴的吸附性能提供了一种参考方法.     

云南重楼中的新甾体皂苷

从云南重楼Paris polyphylla Sm. var. yunnanensis(France. )Hand.-Mazz.的干燥根茎中分离鉴定了4个甾体皂苷(1~4), 其中化合物1是新化合物, 采用波谱技术鉴定其结构为24-O-β-D-吡喃半乳糖基-(23S,24S)-螺甾-5, 25(27)-二烯-1β,3β,23,24-四醇-1-O-β-D-吡喃木糖基(1→6)-β-D-吡喃葡萄糖基(1→3)[α-L-吡喃鼠李糖基(1→2)]-β-D-吡喃葡萄糖苷.