混凝土虛裂紋模型的数值模拟与计算规律的研究

本文采用虚裂纹模型(FCM)对三点弯曲梁的裂缝开裂过程及规律进行了研究。结果表明:对几何相似的梁,当选取的FCM计算参数保持关系H_1/I_(ch1)=H_2/L_(ch2),时,则由此计算的梁的P～δ曲线也相似。这样,G_c/G_F(或K_c(EG_F)~(1/2))和△α_1/H将仅是变量H/L_(ch)的函数。通过计算表明,随着H/L(ch)值的增加,G_c/G_F的值趋于1和△α_1/H的值趋于σ。分析还表明,时任意两条形状相似的软化曲线,通过它们计算几何相似的三点弯曲梁时所得到的梁的P～δ曲线仍相似。     

在BWR环境中低合金钢和碳素钢的疲劳裂纹扩展特性

为探讨在BWR(Boiling Water Reactor)环境中,影响低合金钢A533B和碳素钢STS42疲劳裂纹扩展速度的因素,进行了大量实验研究,其结果如下:(1)两种钢材的疲劳裂纹扩展速度均受温度改变的影响;(2)纯水中溶氧浓度的改变仅对碳素钢的疲劳裂纹扩展速度产生影响;(3)循环频率的改变,特别是在低循环频率时,两种钢材的疲劳裂纹扩展速度均有明显加速的倾向.     

科学技术进步与纺织工业的经济增长

本文运用R·索洛增长速度方程,结合我国1978～1985年纺织系统的主要行业、各省市的经济发展数据,计算出科学技术进步对经济的具体影响;并对纺织工业发展中依靠科技进步的作用进行了预测。     

二维畴区长大过程的Monte Carlo模拟 Ⅱ、长大指数、畴区线度分布

本文介绍了对二维畴区长大过程的Monte Carlo 模拟结果所进行的处理.并将得到的长大指数、畴区线度分布与理论和实验结果作了比较     

Reduced insulin-like growth factor-I after acute feed restriction in lactating dairy cows is independent of changes in growth hormone receptor 1A mRNA

Growth hormone receptor (GHR) and insulin-like growth factor-I (IGF-I) mRNA decrease in the liver of dairy cows at parturition. Epinephrine is released and feed intake is decreased at the same time. The objective of this study was to determine whether feed restriction and (or) administration of epinephrine could recapitulate the changes in the hepatic GHR 1A and IGF-I mRNA that occur at parturition. Eight lactating cows were randomly assigned to one of two rations (ad libitum or restricted). The cows assigned to the restricted ration were fed 75, 60, 60, and 25% of feed consumed by the ad libitum cows on successive days to mimic the changes in feed intake around parturition. Liver samples were collected by needle biopsy before and after feed restriction. Cows received either 0.02 mg/kg of epinephrine or saline approximately 24 h before the second liver biopsy so that a 2 x 2 factorial arrangement of treatments was created. Feed restriction increased plasma nonesterified fatty acids and liver triglyceride percentages and decreased plasma IGF-I concentrations. The decrease in plasma IGF-I after feed restriction was associated with a decrease in IGF-I mRNA in feed-restricted cows. The amount of GHR 1A mRNA did not change after feed restriction. Epinephrine treatment did not affect the amount of GHR 1A or IGF-I mRNA. We conclude that the decrease in feed intake at parturition may be partially responsible for the decrease in IGF-I but may not cause the decrease in GHR 1A.     

Polymorphism in the bovine growth hormone gene affects endocrine release in dairy calves

The objective was to test whether calves with the Leu/Leu genotype release more growth hormone (GH) than calves with Leu/Val and Val/Val genotypes. Danish Holstein (n = 286), Danish Red (n = 68), and Danish Jersey (n = 61) calves were genotyped for the Leu/Val polymorphism in the GH gene and assessed for GH release following inducement by the growth hormone releasing hormone (GHRH). Three GH traits were assessed for each calf: BASELINE, PEAK, and RATE. BASELINE and PEAK are the mean concentration of GH in blood sampled before and after GHRH inducement. RATE is the disappearance rate of GH in blood sampled after GHRH inducement. Danish Jersey calves with Leu/Leu genotype had a higher PEAK and RATE than calves with the Val/Val genotype, whereas the Leu/Val genotype had an intermediate response. The contribution of the Leu/Val polymorphism to the total genetic variation of the BASELINE, PEAK, and RATE traits was 5, 30, and 27%, respectively. By contrast, the amount of GH released by the Danish Holstein and Danish Red calves was not influenced by their GH genotype. Further studies involving calves with all three genotypes are required to further elucidate whether this polymorphism has a functional role or whether it works through a linked-gene effect specific to certain cattle breeds.     

重金属对大肠杆菌生长繁殖的影响研究

汞、镉、铅、砷、铬等是工业废物中常见的重金属。本论文采用琼脂扩散法,寻求对大肠杆生长繁殖无影响的重金属界点浓度,以此为大肠杆菌的重金属的抗性、浓缩研究及大肠杆菌的驯化及其生物治理应用等方面的深入探讨提供实验依据。     

Theory of Initial Microcavity Growth in a Liquid Metal Around a Gas - Releasing Particle. Part 2. Bubble Initiation Conditions and Growth Kinetics

A theory is presented that includes capillary, hydrodynamic, and diffusion aspects. The main attention is devoted to capillary and hydrodynamic effects. The hydrodynamic process (bubble growth) is governed by a nonlinear integrodifferential equation, whose coefficients are dependent on the surface tension, density, and viscosity of the liquid, and also on the difference between the pressure in the gas within the bubble and that in the surrounding liquid. The gas pressure in the bubble is dependent on the rate of gas release from the inclusion (source). An expression is derived for the bubble radius as a function of time. The theory can be useful for developing the technology of powder materials and foam metals.     

Correlations Between Growth Kinetics and Microstructure for Scales Formed by High-Temperature Oxidation of Pure Nickel. II. Growth Kinetics

The oxidation kinetics of high-purity nickel were studied between 500 and 1200°C, in pure oxygen at atmospheric pressure, for average oxide-scale thicknesses of 1, 5, 10, and 30 m. In the overall temperature range studied, a decrease in the parabolic rate constant k_p with increasing scale thickness was observed. Depending on temperature and oxide-scale thickness, growth kinetics can be interpreted as a mixture of parabolic- and cubic-growth kinetics. Possible correlations between growth kinetics and microstructures of the oxide scales were investigated. From this set of experimental data, oxidation-kinetics models were tested. In particular, the effect of grain-boundary diffusion on NiO-growth kinetics was discussed. The correlations between growth kinetics and oxide microstructures appear to be more complex than usually reported.     

Congestion and Fiscal Policy in a Two-Sector Economy with Public Capital: A Quantitative Assessment

This paper analyzes the role of public capital when the services it yields is subject to two forms of congestion, which we characterize as relative and aggregate. We employ a two-sector growth model in which there are conventional profit-maximizing private firms, together with “public firms”, whose objective is to produce a specified quantity of government investment goods – determined by government policy – at minimum cost. We characterize the equilibrium dynamics, and analyze two forms of fiscal disturbances – an increase in public investment, and a decrease in the tax on capital income – by simulating a calibrated economy. We contrast the effects of these two types of congestion on both the existing steady-state equilibrium, as well as for the effectiveness of fiscal policy.