Fluorine in pharmaceuticals: looking beyond intuition

Fluorine substituents have become a widespread and important drug component, their introduction facilitated by the development of safe and selective fluorinating agents. Organofluorine affects nearly all physical and adsorption, distribution, metabolism, and excretion properties of a lead compound. Its inductive effects are relatively well understood, enhancing bioavailability, for example, by reducing the basicity of neighboring amines. In contrast, exploration of the specific influence of carbon-fluorine single bonds on docking interactions, whether through direct contact with the protein or through stereoelectronic effects on molecular conformation of the drug, has only recently begun. Here, we review experimental progress in this vein and add complementary analysis based on comprehensive searches in the Cambridge Structural Database and the Protein Data Bank.     

The role of inheritance in behavior

Inheritance plays a major role in behavior as shown by selection and strain studies for animal behavior and by twin and adoption studies for human behavior. Unlike simple Mendelian characteristics, genetic variance for behavioral dimensions and disorders rarely accounts for more than half of the phenotypic variance, and multiple genes with small effects appear to be involved rather than one or two major genes. Genetic research on behavior will be transformed by techniques of molecular biology that can be used to identify DNA sequences responsible for behavioral variation. However, the importance of nongenetic factors and the multigenetic control of behavior require new strategies to detect DNA markers that account for small amounts of behavioral variation.     

网络教学中教师作用的探讨

高校的校园网建设近几年从开始起步的,到现在大都已经建立起来。很多院校在建立校园网时,都不惜重金,而且,一般都采用最前沿的技术,因而校园网所建的规模、档次都比较高,在网上进行多媒体传输都很顺畅,因而都具备了利用网络进行辅助教学的条件。大多数高校已开始依托网络进行各种形式的教学,教师们已开始在教学中应用网络来提高教学的效果。网络的随时、随地的方便性,以及交互性的特点,使人们认识到网络辅助教学的显著优势。然而,在利用网络进行教学的过程中,出现了一些新的问题,特别是教师在网络教学中应该起什么作用,怎样发挥作用,就…     

论音乐在素质教育中的作用

为适应我国教育改革以及学生自我完善的需要,素质教育已成为一种全新的教育思想。音乐作为美育的有机组成部分,是素质教育的重要内容之一。在素质教育中,音乐有着不同于其他教育形式的功能,从5个方面进行分析、论述,说明音乐在素质教育中的地位和作用,进而提出音乐教育的重要性。     

The Sun's role in climate variations

Is the Sun the controller of climate changes, only the instigator of changes that are mostly forced by the system feedbacks, or simply a convenient scapegoat for climate variations lacking any other obvious cause? This question is addressed for suggested solar forcing mechanisms operating on time scales from billions of years to decades. Each mechanism fails to generate the expected climate response in important respects, although some relations are found. The magnitude of the system feedbacks or variability appears as large or larger than that of the solar forcing, making the Sun's true role ambiguous. As the Sun provides an explicit external forcing, a better understanding of its cause and effect in climate change could help us evaluate the importance of other climate forcings (such as past and future greenhouse gas changes).     

The role of pair dispersion in turbulent flow

Mixing and transport in turbulent flows-which have strong local concentration fluctuations-are essential in many natural and industrial systems including reactions in chemical mixers, combustion in engines and burners, droplet formation in warm clouds, and biological odor detection and chemotaxis. Local concentration fluctuations, in turn, are intimately tied to the problem of the separation of pairs of fluid elements. We have measured this separation rate in an intensely turbulent laboratory flow and have found, in quantitative agreement with the seminal predictions of Batchelor, that the initial separation of the pair plays an important role in the subsequent spreading of the fluid elements. These results have surprising consequences for the decay of concentration fluctuations and have applications to biological and chemical systems.     

小议英语阅读理解中的非语言文化因素

针对目前英语阅读教学中的存在的问题,阐明了非语言文化因素在英语阅读理解中的作用,并且提出了今后阅读教学中应注重语篇教学法的应用.     

The role of collinear interaction in dislocation-induced hardening

We connected dislocation-based atomic-scale and continuum models of plasticity in crystalline solids through numerical simulations of dislocation intersections in face-centered cubic crystals. The results contradict the traditional assumption that strain hardening is governed by the formation of sessile junctions between dislocations. The interaction between two dislocations with collinear Burgers vectors gliding in intersecting slip planes was found to be by far the strongest of all reactions. Its properties were investigated and discussed using a multiscale approach.     

The role of protein structure in chromatographic behavior

Chromatographic retention is determined by a relatively small number of amino acids located in a chromatographic contact region on the surface of a polypeptide. This region is determined by the mode of separation and the amino acid distribution within the polypeptide. The contact area may be as small as a few hundred square angstroms in bioaffinity chromatography. In contrast, the contact region in ion exchange, reversed phase, hydrophobic interaction and the other nonbioaffinity separation modes is much broader, ranging from one side to the whole external surface of a polypeptide. Furthermore, structural changes that alter the chromatographic contact region will alter chromatographic properties. Thus, although immunosorbents can be very useful in purifying proteins of similar primary structure, they will be ineffective in discriminating between small, random variations within a structure. Nonbioaffinity columns complement affinity columns in probing a much larger portion of solute surface and being able to discriminate between protein variants.