Ablation behavior and mechanism of boron nitride - magnesium aluminum silicate ceramic composites in an oxyacetylene combustion flame

In the present study, ablation behavior and properties of BN-MAS (magnesium aluminum silicate) composites impinged with an oxyacetylene flame at temperatures up to 3100 °C were investigated. As ablation time ranged from 5 to 30 s, the mass and linear ablation rates increased from 0.0027 g/s and 0.001 mm/s to 0.0254 g/s and 0.087 mm/s, respectively. A SiO₂-rich protective oxide layer formed during the ablation process, which contributed to the oxidation resistance of the composites. Ablation products mainly consisted of magnesium-aluminum borosilicate glass, mullite, spinel and indialite. The thermal oxidation of h-BN during flame ablation and scouring of MAS by high-speed gas flow were the main ablation mechanisms.     

Membrane treatment of side-stream cooling tower water for reduction of water usage

A pilot study was conducted to determine whether membrane treatment on a side stream of recirculating cooling-tower water could reduce overall water usage and discharge. The treated permeate was returned to the cooling tower while the concentrate was discharged to the sanitary sewer. Flow rates, pressures and water chemistry were monitored. The pilot demonstrated potential substantial water savings. Maximum make-up water and discharge reduction were 16% and 49%, respectively. As high as possible permeate recovery is needed to maximize water conservation. Silica scaling on the membranes limited water savings in this pilot. Development of membranes with a solute-rejection capacity less than the 92% average of the membranes used in the pilot would assist in optimizing water savings. Decreased water outlays compensated for the additional energy used by membrane treatment. Scaling control is critical for economic operation.     

A software reliability engineering practice

A recently adopted best current practice (BCP) at AT&T involving performing software reliability engineering (SRE) tasks over the software life cycle is discussed. Software reliability is defined as the capability of a software product to operate failure-free for a given period under specified operating conditions. The support mechanisms for the SRE BCP are described     

Mapping of coastal-water turbidity using LANDSAT imagery

Secchi disk depth was recorded in the field all along the Swedish coastline and compared with LANDSAT data. Chromaticity analysis was applied in the evaluation to allow for Sun angle and atmospheric corrections. The data were used to study the relative nutrient and solids loading situations around the Swedish coast and as a basis for the applicability of laser bathymetry for water depth soundings     

卫星通信技术的新进展

本文对国内外卫星通信的最新发展作了详尽论述;并综合概括了未来卫星通信技术的发展趋势;最后,对卫星通信市场进行了预测。     

低轨小型卫星的发展和应用

本文介绍低轨小卫星的发展和应用前景。低轨小卫星,体积和重量小,轨道低,功能单一,智能化,制造和发射都很容易,投资费用低,受到用户的普遍欢迎,有广阔的发展和应用前景。 小卫星在近几年发展迅速,应用广泛,已经受到世界各国的重视。在许多方面,已经应用小卫星和计划中应用小卫星的例子很多,本文只作简要介绍,目的在于引起人们的重视,发展我国的小卫星事业。     

Systematic environmental, direct, and service sire effects on conception rate in artificially inseminated Holstein cows

Result of insemination was verified for 329,314 artificial inseminations by 882 service sires to 97,245 Holstein cows in 1,075 herds between May 1970 and December 1983. Estimates of systematic environmental and genetic components of cow and service sire components of conception rate were obtained preliminary to development of a fertility monitoring system. Conception rate was 2.9% higher in stanchion than loose housed herds and 2.3% higher in grade than registered cows. Fall months were superior to winter months, the greatest difference being 6.1% between October and January. Conception rate increased with herd milk production, decreased with both increased cow age, and increased herd size in mature and old cows. Regions and inseminators within regions were highly variable. Conception may be influenced by semen price; however, week day of insemination and duration of semen storage had no effect. Conception rate decreased for semen by bulls 8 yr and older, was lowest for semen harvested in June, but no season of collection effect was detected. No genetic trends for cow and service sire conception rate were found; heritability and repeatability were .08 and .06, respectively. Genetic correlations between cow and service sire conception rate and these components with first lactation production and semen output measures were all near zero. Therefore, the relationship between sire fertility and daughter fertility is near zero.     

Parallel Dynamic Graph Partitioning for Adaptive Unstructured Meshes

A parallel method for the dynamic partitioning of unstructured meshes is described. The method introduces a new iterative optimization technique known as relative gain optimization which both balances the workload and attempts to minimize the interprocessor communications overhead. Experiments on a series of adaptively refined meshes indicate that the algorithm provides partitions of an equivalent or higher quality to static partitioners (which do not reuse the existing partition) and much more rapidly. Perhaps more importantly, the algorithm results in only a small fraction of the amount of data migration compared to the static partitioners.