MgO/HMCM-22择形催化乙苯与碳酸二乙酯烷基化合成对二乙苯

以硝酸镁为前驱体,通过等体积浸渍法制备不同负载量的MgO/HMCM-22催化剂.用X射线衍射、NH<,3>程序升温脱附和吡啶吸附红外光谱表征催化剂的结构和酸性.在气相连续流动固定床反应器上考察了MgO负载量、反应温度、乙苯(EB)与碳酸二乙酯(DEC)摩尔比对EB与DEC烷基化反应合成对二乙苯(p-DEB)的影响.实验...     

Lithium ion batteries cathode material: V2O5

Among all the known electrode materials, vanadium pentoxide (V₂O₅) has high reversible capacity. It is a very valuable material for research of the complexity, rich structure and morphology. However, it also has some disadvantages, such as poor cycle stability, low discharge voltage, low conductivity and Li⁺ diffusion coefficient. In this regard, researchers have carried out a lot of research, such as using various methods to improve the nanostructures, introducing heterostructures, introducing point defects or cation doping in the crystal structure, etc. The electrochemical performance of V₂O₅ has been significantly improved in reversible capacity, high-rate capacity and long-term cycle stability. In this paper, V₂O₅ based nanostructure with different chemical composition are briefly introduced, and it covers V₂O₅ nanomaterials with different morphology, including 1D nanorods, nanobelts, nanotubes, 2D leaf like nanosheets and other nanosheets, and 3D hollow structures, porous nanostructures, porous eggshell microsphere structures. The composite nanomaterials of V₂O₅ and different carbonaceous supports are also introduced. Finally, the V₂O₅ composite materials doped with cations are discussed. The electrochemical performance of V₂O₅ based electrode can be improved effectively by obtaining appropriate nanostructure and optimized chemical composition.     

侧链型液晶聚合物对手性向列相液晶螺旋结构的影响研究

通过改变表面的锚定条件,可以在不借助外部条件的情况下获得热力学稳定态的长程有序的螺旋结构.通过调节沉积在硅晶片上的液晶聚合物[6-(4-甲氧基-偶氮苯-4'-氧基)甲基丙烯酸乙酯](PMMAZO)的接枝密度来调节表面锚定,从而实现对螺旋结构的螺距和螺旋方向的准确控制.随着接枝密度的增加,螺旋结构的倾斜变形增加,螺距的大小被抑制;随着液晶盒厚度的增加,形态会从长程有序的条纹状逐渐过渡到指纹状.     

紫外分光光度法检测溶氧对bFGF发酵的影响

探索溶氧对碱性成纤维细胞生长因子(basic Fibroblast growth factor,bFGF)发酵过程的影响及其控制方法.采用补料分批发酵,在不同溶氧控制方式下,紫外分光光度法测定bFGF蛋白质浓度和发酵液中菌体的产量,考察发酵过程中溶氧对bFGF表达的影响.结果表明控制溶氧为50％,30L罐发酵20h,产菌达34.54g/L,bFGF为18mg/L,与其他溶氧组比较产量显著增高,由此建立了最佳溶氧条件.溶氧对bFGF发酵表达有重要影响,优化溶氧条件有利于改进生产工艺从而节约成本和提高产量.     

Design and performance study of the LEPD silicon tracker onboard the CSES satellite

The low energy particle detector (LEPD) is one of the main payloads onboard the China seismic electromagnetic satellite (CSES). The detector is designed to ascertain space electrons (0.1-10 MeV) and protons (2-50 MeV). It has the capability of identifying the electrons and protons, to measure the energy spectrum and the incident angle of the particles. The LEPD is made up of a silicon tracker system, a CsI (Tl) mini-calorimeter, an anti-coincidence system made by plastic scintillator, as well as electronics and a data acquisition system (DAQ). The tracker is also a kind of E-E telescope; it consists of two layers of double-sided silicon strip detectors (DSSD). The signals emerging from the silicon tracker can be read out by two pieces of application specific integrated circuit (ASIC), which also can generate an event trigger for the LEPD. The functions of the DSSD system in the LEPD for charged particles were tested by 241Am @5.486 MeV α particles. The results show that the DSSD system works well, and has high performance to detect charged particles and measure the position of incident particles.     

A geometric factor calculation method based on the isotropic flux assumption

One of the instruments onboard the China Seismic Electromagnetic Satellite （CSES） is the Low Energy Particle Detector （LEPD）. The primary objective of LEPD is to provide measurements of the fluxes, energy spectra and pitch angles of 100 keV to 10 MeV electrons and protons from 2 to 50 MeV in the Earth＇s magnetosphere. The geometric factor is one of the principle parameters of a detector, which converts the physical quantity-count rate to the particle quantity-flux. In this paper, we calculated the geometric factor of LEPD via computer modeling of an isotropic radiation environment. It was first demonstrated that the radiation intensity related should obey a cosine-law, then a general sampling method of generating this distribution via GPS of GEANT4 was explained. Furthermore, combined with flux normalization, a comparison of the geometric factor calculation of a set of 2-layer detectors with different shapes （cylinder, truncated cone and rectangle） was performed. Results show a generally good agreement between simulation and analytical calculations for the cylinder and truncated cone detectors, and the result of the rectangular one, for which there is no accurate analytical formula, is consistent with the previous simulated results by others. As a practical instance of the 2-layer rectangle detector, the geometric factor of LEPD is 10.336±0.036 m cm2·sr for 10 MeV proton and 8.211±0.032 m cm2·sr for 8 MeV electron.     

用电势分析法解一段含源电路和复杂电路

在高中物理电路问题的教学中,经常用部分电路欧姆定律和全电路欧姆定律配合求解简单电路问题,但在求解一段含源电路和复杂电路问题时,采用这种方法往往无能为力。笔者在教学中尝试引入求解这类问题的有效方法——电势分析法,从而解决了上述困难,提高了学生对电路规律的认识.     

重复频率电磁脉冲对氢闸流管栅极的触发干扰

针对重复频率电磁脉冲（EMP）干扰,以氢闸流管的栅极触发电路为研究对象,进行了氢闸流管悬置与共地两种不同的条件下氢闸流管第一栅极与第二栅极的电磁干扰研究。结果表明,两种条件下两个栅极均存在较强烈的电磁干扰,干扰主要来源于空间电磁辐射与共地耦合两个方面;针对重复频率EMP环境下氢闸流管触发的可靠性,分别进行了不同重复频率EMP数量与不同重复频率EMP时间间隔下氢闸流管的输出实验。结果表明,两种情况均对氢闸流管的触发产生影响,重复频率EMP数量增多与间隔减小均使氢闸流管误触发的可能性增大,对比理论分析与实验结果,认为该现象是由于重复频率EMP累积效应与重复频率EMP高频分量增强从而导致交互作用耦合增强所引起。     

新型被动在轨非连接支撑研究现状

支撑结构是低温贮箱及飞行器杜瓦瓶的关键部件,对低温燃料液体的承装及其漏热有重要影响。文中阐述了低温绝热支撑近几年的研究进展,针对新型被动在轨非连接支撑(简称PODS),就其结构、材料及其他相关问题进行了分析。随着新型被动在轨非连接支撑研究的深入,其在空间及工业低温贮箱领域将会获得广泛应用。     

In-Band Pumped High Power Ho：YAG Ceramic Laser by a Tm：YLF Laser

High-power 2 μm lasers are promising candidates for a variety of applications including remote sens- ing, wind lidar, and medicine as well as mid- infrared generation via pumping of optical parametric oscillators. Due to the advantages of low quantum defects and high efficiency, resonantly pumped Ho- doped lasers have attracted great attention. Ho：YAG single crystals have also been widely studied to ob- tain cw and Q-switched laser operation in the 2 μm wavelengths range.