排序方式: 共有27条查询结果,搜索用时 281 毫秒
1.
This contribution touches on essential requirements for instrument stability and resolution that allows operating advanced electron microscopes at the edge to technological capabilities. They enable the detection of single atoms and their dynamic behavior on a length scale of picometers in real time. It is understood that the observed atom dynamic is intimately linked to the relaxation and thermalization of electron beam-induced sample excitation. Resulting contrast fluctuations are beam current dependent and largely contribute to a contrast mismatch between experiments and theory if not considered. If explored, they open the possibility to study functional behavior of nanocrystals and single molecules at the atomic level in real time. 相似文献
2.
C.T. Peng 《Journal of chromatography. A》2010,1217(23):3683-3694
The Kováts retention index system with n-alkanes as reference standards has properties not fully explored when single, isolated or stand-alone analytes are analyzed by isothermal gas chromatography. When a homologous series of analytes are analyzed by either linear or non-linear temperature-programmed gas chromatography, the retention data of the entire series can be treated systematically to produce an I vs. Z plot that is linear, thereby giving insight into the relationship between chemical structure and retention index. Dead time tM is both instrument and temperature dependent. With no dead time tM adjustment, the retention indices of analytes calculated from experimental retention times by the method of either linear or logarithmic interpolation give statistically identical values. Linear regression analysis of the data shows the slope as methylene value (A) and intercept as functionality constant or group retention factor (GRF) of the homologous series. The A and (GRF) values vary with chemical structures, intermolecular electronic and steric interactions, and polarity of column liquid phases, and can link gas chromatographic retention index to chemical structure. Examples of the influence of molecular electronic effects and steric effects on retention index are given and discussed. 相似文献
3.
Majid Montazer Esfandiar PakdelAuthor vitae 《Journal of Photochemistry and Photobiology, C: Photochemistry Reviews》2011,12(4):293-303
The consumption of titanium dioxide in today's world is on the increase. As the most popular nano substance, TiO2 is used in various industries notably in the textile industry. More and more recently, through a synergistic combination of photocatalytic features of nanoparticles, fabrics with novel properties are produced. Self-cleaning and stability against UV rays as well as chemical media, to name but a few, are among new prominent properties, obtained on textiles. A common subject reported in most studies has been the diverse approaches to immobilize the nanoparticles on the surface of fabrics. Wool is among common textile materials that have undergone numerous processes to be modified. This review intends to bring to light different aspects of application of nano titanium dioxide in the textile industry especially on wool, and also presents a concise overview on the rigorous pieces of research conducted in this realm. 相似文献
4.
自由基聚合是高分子化学课程中的重要一章,自由基聚合动力学(包括聚合速率、平均相对分子质量及分布)是教学中的重要内容。本文讨论了建立自由基聚合微观动力学模型的基础:三个基本假设和四个简化条件,阐释了传统单官能度引发剂引发的聚合体系速率方程推导中这些假设和条件的运用,并扩展到双官能度引发剂体系,得到基元反应速率和总速率。提出从三个层次讨论影响自由基聚合速率的因素,深化了对自由基聚合速率教和学。 相似文献
5.
利用FTIR分析技术,对3种不同煤阶的我国电站典型动力用煤——神木烟煤、铜川贫煤和宜宾无烟煤的挥发份中氮的赋存形态进行了研究。为克服研究工作中的微氮现象,在研究过程中采用了16 m光程的长程气池。研究结果显示,红外光线在16 m长程气池构造作用下多次穿过挥发份,检测出含量微少的氮元素,成功地克服了微氮现象,取得了较好的研究结果;我国电站用煤的挥发分中氮的赋存形态有4种,分别为吡啶型氮化合物、吡咯型氮化合物、吡啶-N氧化物和腈类化合物。氮在煤与挥发分中赋存形态的差别主要是由于煤分子中的大分子量含氮结构在温度作用下发生分解所致。 相似文献
6.
ZHENG Fu-an 《高等学校化学研究》1993,(4)
By means of the functionality distribution deduced and weight averaged functionality a and molecular size vb2, the sol-gel distribution equations of HTPB(Hydroxyl terminated polybutadiene) + TDI (Toluene-2, 4-diisocyanate) expressed by the model of Aai-B2 type polycondensation were solved and the elastic modulus were calculated. The experimental results of HTPB+TDI curing process indicate that a, vb2 and functionality distribution function are available basically. 相似文献
7.
Andrey A. Krasovskii Alexander M. Tarasyev 《Applied mathematics and computation》2010,217(3):1125-1134
The problem of regulation of logistic growth trends is examined in the framework of control theory for problems with infinite horizon. The problem statement is related to microeconomic models of dynamic optimization of a company’s indicator of functionality development. Various control regimes of functionality development are studied for identification of plausible production trends. Optimal control problem is posed to optimize the utility function of logarithmic consumption index of the system entropy type. Solution of the problem is constructed in analysis of the Hamiltonian system and its algebraic properties. Based on this analysis nonlinear stabilizers are elaborated which lead the system to the steady state with the same growth rates as the optimal control regime. The model is tested on the real time series of dynamic trends of functionality development for two generations of mobile phones in Japan. 相似文献
8.
In this review, the recent applications of power ultrasound technology in improving the functional properties and biological activities of biopolymers are reviewed. The basic principles of ultrasonic technology are briefly introduced, and its main effects on gelling, structural, textural, emulsifying, rheological properties, solubility, thermal stability, foaming ability and foaming stability and biological activity are illustrated with examples reviewing the latest published research papers. Many positive effects of ultrasound treatment on these functional properties of biopolymers have been confirmed. However, the effectiveness of power ultrasound in improving biopolymers properties depends on a variety of factors, including frequency, intensity, duration, system temperature, and intrinsic properties of biopolymers such as macromolecular structure. In order to obtain the desired outcomes, it is best to apply optimized ultrasound processing parameters and use the best conditions in terms of frequency, amplitude, temperature, time, pH, concentration and ionic strength related to the inherent characteristics of each biopolymer. This will help employ the full potential of ultrasound technology for generating innovative biopolymers functionalities for various applications such as food, pharmaceuticals, and other industries. 相似文献
9.
10.
Alterations in molecular structure are responsible for the differential biological response(s) of a chemical inside a biosystem. Structural and functional parameters that govern a chemical's metabolic course and determine its ultimate outcome in terms of mutagenic/carcinogenic potential are extensively reviewed here. A large number of environmentally-significant organic chemicals are addressed under one or more broadly classified groups each representing one or more characteristic structural feature. Numerous examples are cited to illustrate the influence of key structural and functional parameters on the metabolism and DNA adduction properties of different chemicals. It is hoped that, in the event of limited experimental data on a chemical's bioactivity, such knowledge of the likely roles played by key molecular features should provide preliminary information regarding its bioactivation, detoxification and/or mutagenic potential and aid the process of screening and prioritising chemicals for further testing. 相似文献