Improved peptide function from random mutagenesis over short 'windows'

We have applied random mutagenesis over short contiguous residuetracts (‘windows’) within an active peptide (the-peptide of ß-galactosidase) such that all windowresidues are replaced simultaneously. A novel technique usingmixed synthetic oligonucleotides and selection against an EcoKrestrictionsite has allowed the construction of libraries of mutants fortwo separate windows, sites A and B. Mutant phenotypes can beeasily assessed in vivoby a complementation test, and panelsof mutants have been quantitatively tested in vivoThis allowedthe rapid probing of structural requirements for each site.The two windows yielded markedly disparate results. Site B wasmuch less stringent in its sequence requirements for significantfunction than Site A, and mutants with improved function wereisolated at Site B alone. In addition, one Site B mutant withwild-type levels of activity showed enhanced stability to heator a protein denaturant. We propose that short tracts with thecharacteristics of Site B constitute ‘secondary’interaction sites which are more tolerant of sequence diversity.Random manipulation of such secondary sites is thus more likelyto yield up-mutations for standard or altered environments.Window mutagenesis can in principle be applied to any protein-proteinor protein-Ugand interaction.     

基于遗传算法并考虑稳定约束的最优潮流开发

功角稳定(暂态或振荡)是电力系统运行的一个重要约束.本文描述了一种基于遗传算法(GA)并考虑功角稳定性约束的最优潮流求解方法.在该GA算法中,染色体的控制参量为发电机组的出力.本文应用实例选择英国电力市场中的平衡机制发电机组(BMU).平衡机制机组的选择和优化由GA算法依据BMU的出价(竞价)高低或其出力变化对系统稳定性影响的程度来确定.本文使用灵敏度因子来代表BMU机组对系统稳定性的影响程度,而这些灵敏度因子则是通过开展系统扰动仿真得出的.为确保发电出力始终与用电负荷相匹配,本文采用一种新的映射方法来保持系统有功平衡.文中使用因停电而导致的罚金成本或费用来处理系统稳定性约束,且这些稳定约束对系统目标函数适切性的贡献也被单独评估,以使算法对最优潮流的搜索集中于切实可行的解.对一个化简的英国电力系统开展的仿真测试表明,本文提出的GA算法能够应付此类高度非线性的最优化问题,并给出了对测试系统的数值仿真结果.     

Structure of directionally solidified two phase ternary alloys

Simple theories developed in a series of recent papers, describing solid/liquid interface stability and solute redistribution in three phase ternary alloys are summarized and extended to apply to ternary alloys that are two phase on equilibrium solidification. Calculated results compare well with experiments on alloys from the Al-rich corner of the Al-Cu-Ni ternary phase diagram. These alloys represent the type currently under development for gas turbine applications. At sufficiently high values ofG/R (thermal gradient divided by growth rate) the alloys grow with a fully plane front. At moderate values ofG/r they exhibit a unique structure of single phase cells and two phase intercellular root material which grows with a “plane front”. Further decreases inG/R produce more typical ternary cellular structures with regions of one, two and three phases.     

The effects of electrolyte concentration in the emulsion polymerization of styrene

Using concentrations below that required to coagulate the latex, the effects of the addition of potassium chloride on the emulsion polymerization of styrene have been investigated. When potassium decanoate (an emulsifier with a high critical micelle concentration (c.m.c.)) is used the increase in the concentration of micellar emulsifier and the decrease in the area occupied by an emulsifier molecule at the polymer/water interface are significant. When this is taken into account Gardon's equation for latex particle size reproduces the trend of the experimental results at the lower electrolyte concentrations. The agreement can be made quantitative by choosing alternative values for the propagation rate constant of styrene and the rate of radical formation from persulphate. With potassium octadecanoate (which has a low c.m.c.) and with potassium decanoate at the higher electrolyte concentrations these factors cannot account for the results observed.     

Wear behavior of Pb–Mo–S solid lubricating coatings

Amorphous Pb–Mo–S coatings 200 to 510 nm thick were deposited by dual ion-beam deposition (IBD) onto steel and Si substrates. Coating wear studies were performed using ball-on-flat reciprocating sliding with steel ball counterfaces in dry air. Tests were run between 1 and 100,000 sliding cycles, and wear depths measured by interference microscopy. Morphology and chemistry of the as-deposited coatings and worn surfaces were investigated with optical microscopy, micro-Raman spectroscopy and cross-section high resolution transmission electron microscopy (HRTEM). Pb–Mo–S coatings were found to be quite wear resistant; no more than 25% of the coating thickness was removed by 10,000 sliding cycles. Two wear mechanisms were identified. At the nanometer scale, wear proceeded in a two-part process: transformation of the coating surface to MoS₂, then layer-by-layer removal of MoS₂. At the micrometer scale, wear occurred by plowing. The long endurance of Pb–Mo–S coatings was attributed to slow wear of the coatings, with lubricant redistribution processes playing a minor role.     

Sulphur Analogues of Deoxyvasicinone

The synthesis of the 2-thioanalogue of deoxyvasicinone ( 1 ) 5 and some higher analogues 6 and 7 are described. Oxidation of these heterocycles with 3-chloroperoxybenzoic acid gave the sulphoxides 12 , 13 and 14 which underwent facile Pummerer rearrangement to yield, after deacetylation, the alkanols 18 , 19 and 20 . Under more vigorous oxidising conditions 5 and 6 were oxidatively ring opened to yield the sulphonic acids 21 and 22 whereas 7 gave the sulphone 23 .     

Three-Dimensional Modeling of Microsphere Contact/Impact with Smooth,Flat Surfaces

A three-dimensional (3D) simulation model of a microsphere in contact with a nominally-smooth, flat surface is established. The model is based on Hertzian contact stresses, an idealized ring force distribution of adhesion, nonlinear damping, and friction. Although originally developed for the study of oblique impact, the model also is shown to describe the motion of a microsphere in sustained contact with a flat surface, including nonlinear normal oscillatory motion in the presence of sliding and rolling. Nonlinear, normal oscillatory motion is illustrated using conventional phaseplane techniques. Methods for the determination of damping coefficients associated with normal motion from impact experiments are discussed. The significance and modeling of rolling resistance and implications of asymmetric contact stress distributions are presented. Simulations show that energy exchange between translation and rotation can play an important role during oblique impact. The effects of complex initial conditions on the rebound and capture of a microsphere are significant as are the effects of contact friction. Results show that the inability to measure and the failure to account for rotational velocities in experimental measurements can limit the intepretation of the results.