排序方式: 共有49条查询结果,搜索用时 15 毫秒
41.
光折变介质中空间光孤子自弯曲现象研究 总被引:1,自引:0,他引:1
光折变非线性介质在外加直流电压时会引起介质内部电荷移动,而移动后的电荷又会导致空间电荷的扩散效应,从而产生非局域非线性现象。从理论上研究了具有流动和扩散非局域非线性的光折变晶体中所支持的空间光学孤子的传播行为。应用等效粒子近似方法分析了这类介质中(1 1)维空间光学孤子动力学行为,得出孤子运动"加速度"显式解。孤子的有效"加速度"决定于孤子参量和光折变非局域参量。所得的解析结果可在一定参量范围内直接用来计算孤子的传播轨迹。对孤子在光折变非局域非线性作用下的传播动力学行为做了仿真模拟,数值模拟结果与理论分析结论符合得很好。 相似文献
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电子背散衍射(EBSD)花样揭示了材料的物相成分、晶体结构、晶粒取向、晶粒大小和晶界的信息。EBSD花样非常复杂,通常需要借助专门的计算软件才能解析。本文系统地研究了EBSD花样的数学特征,建立了任意晶体取向与EBSD花样之间的数理关系,推导了面心立方、体心立方和六方晶体的基本晶带轴的理论EBSD花样的数学特征,以及面心立方晶体的(001)<110>取向和(001)<100>取向的理论菊池(Kikuchi)花样特征。在实测EBSD花样的分析中与各晶系各点阵的基本晶带轴的理论EBSD花样特征比较,即通过图像特征对比,就可以直接确定实测EBSD花样所属的晶系、点阵和Kikuchi线交点对应的晶带轴[uvw],再由基本晶带轴的坐标计算出晶体取向,还能提供基本晶面信息,如原子密排晶面在样品中的空间分布,这有利于晶体的变形或生长机理研究。EBSD为单晶芯片质量检验提供了新方法。 相似文献
43.
Dong Cao Yangjun Zhang Huihui Zhang Liangwei Zhong Xiaohong Qian 《Rapid communications in mass spectrometry : RCM》2009,23(8):1147-1157
(?)‐Epigallocatechin gallate (EGCG) is a major bioactive component in leaves of green tea, and has been widely investigated for its anti‐tumor activity. The interaction between EGCG and the key peptides or proteins (e.g. glutathione, enzymes) in vivo is thought to be involved in the toxicity and anti‐cancer mechanism of EGCG. However, the true anti‐tumor mechanism of EGCG is not clear, and few studies have focused on the reactivity of EGCG toward peptides or proteins under physiological conditions (pH 7.4, 37°C). In this work, the covalent interactions between EGCG and model peptides containing one or more nucleophilic residues (i.e. Arg, Cys, Met, and α‐NH2 of the N‐terminus of peptides) under physiological condition were fully characterized using mass spectrometry. It was found that EGCG can react with the thiol groups of peptides to form adducts under physiological conditions (pH 7.4, 37°C), even in the absence of the peroxidase/hydrogen peroxide system. Besides the thiol groups of peptides, it is firstly reported that EGCG also reacts with α‐NH2 of the N‐terminus or arginine residues of model peptides to form Schiff base adducts, and the methionine residues of model peptides can be easily oxidized by hydrogen peroxide (H2O2) generated during the process of EGCG auto‐oxidation to form methionine sulfoxide products. The preference for the reaction of nucleophlic residues of peptides with EGCG was determined to have the following order: Cys > α‐NH2 of the N‐terminus > Arg. The neutral loss ions of [M+H–170]+ and [M+H‐138]+ were detected in all tandem mass spectra of the EGCG adducts of peptides, which indicates that these two neutral loss ions can be considered as the characteristic neutral loss ions of peptides modified by EGCG. Results of the present research provide insights into the toxicology and anti‐tumor mechanism of EGCG in vivo. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
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Protein electrochemistry affords a direct method to study the biological electron transfer processes. However, supplying a biocompatible environment to maintain the native state of protein is all‐important and challengeable. Here, we chose vaterite, one of the crystalline polymorphs of calcium carbonate, with highly porous nature and large specific surface area, which was doped with phospholipids, as the matrix to immobilize horseradish peroxidase (HRP). The integrity of HRP was kept during the simple immobilization procedure. By virtue of this organic/inorganic complex matrix, the direct electrochemistry of HRP was realized, and the activity of HRP for catalyzing reduction of O2 and H2O2 was preserved. 相似文献
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Density functional theory investigation of 14N nuclear quadrupole coupling constants (NQCC) for HMX polymorphs was performed. During the calculation of NQCC and asymmetry parameter (η) of β‐HMX, single molecule model is found to be worse than cluster model. The calculated results are more sensitive to the proper model than to the basis set. The calculation for β‐HMX using cluster model at B3LYP/6‐311++G(d,p) level gives better agreement with experiment. This approach was subsequently applied to α, γ, and δ‐HMXs. The difference of simulated 14N NQR frequency was found. The NQR spectrum is useful for the study of explosive or propellant on their detection, phase transition, and aging process. 相似文献
47.
Hongge Chen Liangwei Liu Shuai Lv Xinyu Liu Mingdao Wang Andong Song Xincheng Jia 《Applied biochemistry and biotechnology》2010,162(1):24-32
Dialdehyde starch (DAS) was used as a novel coupling agent to prepare chitosan carrier to immobilize the xylanase from Aspergillus niger A-25. Compared with glutaraldehyde-cross-linked chitosan (CS-GA) and pure chitosan beads, the DAS-cross-linked chitosan (CS-DAS)
beads exhibited the highest xylanase activity recovery. The DAS adding amount and cross-linking time in CS-DAS preparation
process were optimized with respect to activity recovery to the values of 1.0 g (6.7% w/v concentration) and 16 h, respectively. The optimum temperature of both the CS-DAS- and CS-GA-immobilized xylanase was observed
to be 5 °C higher than that of free enzyme (50 °C). The CS-DAS-immobilized xylanase had the highest thermal and storage stability
as compared to the CS-GA-immobilized and free xylanase. The apparent K
m and V
max values of the CS-DAS-immobilized xylanase were estimated to be 1.29 mg/ml and 300.7 μmol/min/mg protein, respectively. The
CS-DAS-immobilized xylanase could produce from birchwood xylan high-quality xylo-oligosaccharides, mainly composed of xylotriose,
as free xylanase did. The proposed CS-DAS carrier was more advantageous over the CS-GA or pure chitosan carrier for xylanase
immobilization application. 相似文献
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The existence and stability of gap solitons in the nonlinear fractional Schrödinger equation are investigated with a quasi‐periodic lattice. In the absence of nonlinearity, the exact band‐gap spectrum of the proposed system is obtained, and it is found that the spectrum gap size can be adjusted by the sublattice depth and the Lévy index. Under self‐defocusing nonlinearity, both in‐phase and out‐of‐phase gap solitons have been searched in the first four gaps. It is revealed that in‐phase gap solitons are generally stable in wide regions of their existence, whereas stable out‐of‐phase gap solitons can only exist in the fourth spectrum gap. Linear stability analysis of gap solitons is in good agreement with their corresponding nonlinear evolutions in fractional dimensions. The presented numerical findings may lead to interesting applications, such as transporting of light beams through the optical medium, and other areas connected with the Kerr effect and fractional effect. 相似文献
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碳纳米管作为锂离子电池正极导电剂已经在中国得到了普遍应用,作为电池导电剂的碳纳米管需要提纯处理。本文研究了利用艾奇逊炉对化学气相沉积的碳纳米管在3 000℃进行提纯处理后的组织结构和电学性能,利用扫描电子显微镜(SEM),电子能谱仪(EDS),等离子体发射光谱仪(ICP),红外光谱仪(FT-IR),热重分析仪(TGA),X射线光电子谱仪(XPS),拉曼光谱分析仪,四探针薄膜电阻仪对艾奇逊炉提纯的碳纳米管进行了检测。结果表明高温提纯的碳纳米管的含铁量可降低到71ppm,氧化物含量低于0.45wt%,晶格缺陷大幅减少,石墨组织结构完整,表面官能团少,具有体积电阻率0.050~0.035Ω·cm,作为电池电极的导电材料,可以用于动力电池正极。 相似文献