分布系统中多米诺效应的分析与消除

分布系统中发生故障后,错误信息在进程间的传播,以及由此引起的系统恢复过程中的多米诺效应是分布系统容错恢复技术所面临的最重要与最困难的问题.目前各种研究工作偏重于具体的系统动态恢复技术.本文的研究重点在于首次揭示多米诺效应本身固有的数量特征及其与分布系统技术参数间的联系,给出多米诺效应动态消除技术,引入系统额外开销的下限,并针对动态技术的缺点,探讨多米诺效应的静态消除技术,为解决困难开辟新途径.     

The effect of different protein diets on longevity and various biochemical parameters of aged rats]

In this work 23 month old rats were fed for 200 days with different protein diets (NT-diet: 19% protein, 72% of animal origin and LP-diet: 8.8% protein exclusively of vegetable origin). Some metabolic parameters and lifespan (on the base of a 50% death-rate) were determined. The relations of the liver free amino acids glycine + alanine and tyrosine + phenylalanine + branched chain amino acids and the ratio of phenylalanine/tyrosine were determined to be higher in the LP-group. Phenylalanine in liver and urea concentrations in liver and serum were lower in the LP-group. Furthermore the dopamine or serotonin levels were significantly lower in lateral and medial or lateral regions of the hypothalamus respectively in LP-diet fed rats. The norepinephrine content was not modified by the diets. The median lifespan of 23 month old rats was higher by 24% following LP-treatment. These results suggest that the protein component (amino acids) of different diets may modify metabolic parameters and lifespan of animals by mechanisms in which the central regulation may be involved.     

Ti-silicalite as catalyst for gas-phase ammoximation of cyclohexanone with molecular oxygen

The catalyst behaviour of titanium silicalite, which was found the most active and selective catalyst for liquid-phase ammoximation of cyclohexanone to the corresponding oxime with hydrogen peroxide, was investigated in the gas-phase ammoximation with molecular oxygen in and compared with those of pure silicalite and samples of vanadium and chromium silicalites. The results showed that Ti-silicalite is a selective catalyst not only in the reaction with hydrogen peroxide but also in the reaction with molecular oxygen. However, a big limitation was found in the poor activity of the silicalites which do not allow to reach high oxime yields.     

Continuous and discontinuous fatigue crack growth of irradiated ultrahigh molecular mass polyethylene in saline solution at 37°C

To provide data for prosthesis design, the fatigue crack growth resistance of irradiated ultrahigh molecular mass polyethylene (UHMMPE) in saline solution at 37°C was determined from tests performed on compact tension specimens, comparable in size to the components in knee prostheses. The specimens were cyclically loaded by using a sinusoidal wave form at 1 Hz with a minimum-to-maximum load ratio of 0.1. Scanning electron microscopic fractography was used to examine the fracture surfaces. At higher stress levels, the Paris's Law was used to analyse the data, and a striation pattern with each striation corresponding to multi-cycles was observed. At lower stress levels, discontinuous fatigue crack growth was found, a phenomenon which dominated the fatigue life of the material and had not been reported previously in this material. A craze zone ahead of the crack tip was observed, which formed the discontinuous crack growth band with a length relevant to the Dugdale plastic zone length.     

Spectral predictions for pulse interval and width modulation

An expression for the frequency spectrum of pulse interval and width modulation (PIWM) is presented. Experimental results obtained have shown close agreement with spectral predictions from the formula. Performance figures are also included from a practical PIWM optical-fibre transmission system intended for use with TV and video signals.<>     

A solenoid-derived wiggler

A novel wiggler design for use in free-electron lasers (FELs) is proposed, consisting of a staggered array of magnetic poles situated inside the bore of a solenoid. The resultant field pattern consists of a periodic transverse magnetic field on axis, as well as a longitudinal guide field. Such a wiggler has several advantages: the longitudinal field acts to confine the electrons near the FEL axis, high fields can be attained at short wiggler periods, the field strength is easily varied, and fabrication and testing of the wiggler are relatively easy. It is planned to use this wiggler design in a far infrared FEL to be built at Stanford University     

Stress intensity factor for a surface semielliptical crack

A method is proposed for calculating the stress intensity factor K_I of a surface semielliptical crack for almost any monotonie stress function in the crack section. The equations are derived for calculating correction and adjustment coefficients M_i and A_i. Computed values of K_I are compared with the published data. The results of comparison show that agreement between these results is satisfactory.Translated from Problemy Prochnosti, No. 1, pp. 33–36, January, 1992.