An analysis of simultaneous variation in protein structures

The simultaneous substitution of pairs of buried amino acid side chains during divergent evolution has been examined in a set of protein families with known crystal structures. A weak signal is found that shows that amino acid pairs near in space in the folded structure preferentially undergo substitution in a compensatory way. Three different physicochemical types of covariation 'signals' were then examined separately, with consideration given to the evolutionary distance at which different types of compensation occur. Where the compensatory covariation tends towards retaining the combined residue volumes, the signal is significant only at very low evolutionary distances. Where the covariation compensates for changes in the hydrogen bonding, the signal is strongest at intermediate evolutionary distances. Covariations that compensate for charge variations appeared with equal strength at all the evolutionary distances examined. A recipe is suggested for using the weak covariation signal to assemble the predicted secondary structural elements, where the evolutionary distance, covariation type and weighting are considered together with the tertiary structural context (interior or surface) of the residues being examined.      

Predictive capability of Large Eddy Simulation for point-wise and spatial turbulence statistics in a confined rectangular jet

Large Eddy Simulations (LESs) were performed for a confined rectangular liquid jet with a co-flow and compared in detail with particle image velocimetry (PIV) measurements. A finite-volume CFD library, OpenFOAM, was used to discretize and solve the filtered Navier–Stokes equation. The effects of grid resolution, numerical schemes and subgrid models on the LES results were investigated. The second and fourth order schemes gave similar performance, while the fourth order scheme costs much more computationally. Subgrid model comparison showed that the locally dynamic procedure is necessary for complex flow simulation. Model validation was performed by comparing LES data for the point-wise velocity statistics such as the mean and the root-mean-square velocity, shear stress, correlation coefficient, velocity skewness and flatness with the PIV data. In addition, LES data for the two-point spatial correlations of velocity fluctuations that provide structural information were computed and compared with PIV data. Good agreement was observed leading to the conclusion that the LES velocity field accurately captures the important characteristics of all the turbulent length scales present in the flow, from the fully resolved energy-containing eddies to the subgrid-scale dissipative eddies.     

Chemical synthesis of a dual branched malto-decaose: a potential substrate for alpha-amylases

A convergent block strategy for general use in efficient synthesis of complex alpha-(1-->4)- and alpha-(1-->6)-malto-oligosaccharides is demonstrated with the first chemical synthesis of a malto-oligosaccharide, the decasaccharide 6,6'-bis(alpha-maltosyl)-maltohexaose, with two branch points. Using this chemically defined branched oligosaccharide as a substrate, the cleavage pattern of seven different alpha-amylases were investigated. Alpha-amylases from human saliva, porcine pancreas, barley alpha-amylase 2 and recombinant barley alpha-amylase 1 all hydrolysed the decasaccharide selectively. This resulted in a branched hexasaccharide and a branched tetrasaccharide. Alpha-amylases from Asperagillus oryzae, Bacillus licheniformis and Bacillus sp. cleaved the decasaccharide at two distinct sites, either producing two branched pentasaccharides, or a branched hexasaccharide and a branched tetrasaccharide. In addition, the enzymes were tested on the single-branched octasaccharide 6-alpha-maltosyl-maltohexaose, which was prepared from 6,6'-bis(alpha-maltosyl)-maltohexaose by treatment with malt limit dextrinase. A similar cleavage pattern to that found for the corresponding linear malto-oligosaccharide substrate was observed.     

Active Oxidation of Liquid Silicon: Experimental Investigation of Kinetics

Small scale laboratory experiments on the oxidation of liquid silicon have reproduced important features of the industrial refining of liquid silicon: active oxidation led to the formation of amorphous silica spheres as a reaction product. The boundary condition for active oxidation in terms of maximum oxygen partial pressure in the bulk gas was found to lie between 2·10^?3 and 5·10^?3?atm at T?=?1,500?°C. The active oxidation of liquid silicon had linear kinetics, and the rate was proportional to bulk oxygen partial pressure and the square root of the linear gas flow rate, consistent with viscous flow mass transfer theory. Classical theory for unconstrained flow over a flat plate led to mass transfer rates for SiO_(g) which were 2–3 times slower than observed. However, computational fluid dynamic modeling to take into account the effects of reactor tube walls on flow patterns yielded satisfactory agreement with measured volatilization rates.     

CY-61100车床尾座铸造过程仿真优化研究

对CY-61100车床尾座铸件充型及凝固过程进行了数值模拟及优化研究。根据模拟的结果及铸造缺陷预测,改进及优化了尾座浇注系统,在工厂实际浇铸生产应用中取得了良好效果。并由此建立了铸造过程CAE仿真优化技术与传统铸造工艺设计有效结合的先进铸造工艺设计模式。     

Iodine-131: a potential short-lived, wastewater-specific particle tracer in an urbanized estuarine system

The short-lived, fission-produced radioisotope, 131I (t1/2 = 8.04 days), was detected in wastewater, surficial sediment, and suspended particulate matter (SPM) samples collected from New York Harbor (NYH) between 2001 and 2002. lodine-131 is used as a radiopharmaceutical for medical imaging, diagnostics, and treatments for conditions of the thyroid. It is introduced into the municipal waste stream by medical facilities and patients and is subsequently released into the estuary via wastewater effluent. Measured 131I activities in surface sediments were correlated with those of 7Be (t1/2 = 53.2 days), a naturally occurring radioisotope that is widely used to quantify particle dynamics, sediment focusing, and short-term sediment deposition and accumulation in aquatic systems. Surficial sediment 131I activities were also compared with measured trace metal (Cu, Pb) and organic carbon (OC(sed)) concentrations which can be linked to wastewater inputs. These preliminary results from NYH introduce 131I as a potentially valuable source-specific, shortlived biogeochemical tracer (timescales < 1 month) for particles, sediments, and wastewater-sourced contaminants in urbanized aquatic systems.     

Butvar B-98 as a thin support film

Support films prepared from butvar B-98 resin are mechanically stable, electron transparent, and possess minimum intrinsic structure. A simple procedure for routine preparation of support films using this resin is provided.     

Measurements of low angle fading in the Canadian arctic

In July 1974, an experiment was conducted at Eureka, Canada (80° N, 86° W), to measure the tropospheric fading of satellite signals at 4 and 6 GHz. At Eureka, the 4.6 m antenna was located on a hill 250 m above sea level providing a clear path at an elevation angle of 1° to the Anik II satellite. The 4 GHz downlink signal strength was recorded at Eureka. Fading of the 6 GHz uplink signal from Eureka was measured at the Communications Research Centre, Ottawa. The uplink and downlink fading contributions for the entire experimental period are nearly identical, indicating that the fading distributions are essentially frequencyindependent over the 4–6 GHz range. For the 18 days period of the experiment, the link margins are 10.8 dB and 20.3 dB for 99 % and 99.9 % reliability, respectively. For the worst twohour period, the margins are 18 dB and 28 dB, corresponding to those for a Rayleigh distribution. No marked diurnal effect is discernible. Distributions of the fade durations indicate, for example, that 90 % of all fades exceeding 6 dB do not exceed 36 seconds duration. Although fading at 4 GHz is always accompanied by fading at 6 GHz, their correlation is sometimes poor, yielding correlation coefficients as low as 0.34. The amplitude correlation of two 6 GHz signals separated by up to 10 MHz always exceeds 0.90, indicating minimal amplitude distortion across the band. The implications of these results on the design of a satellite link are discussed.