Improving the thickness accuracy of cold rolled narrow strip by piezoelectric roll gap control at high rolling speed

Particularly in fast rolling mills, conventional actuators reach their dynamic limits, when longitudinal thickness variations of the incoming strip shall be reduced with high accuracy by model-predictive roll gap control. Accordingly, the applicability of highly dynamic piezoelectric actuators in combination with electromechanical spindles and a high frequency precision measurement of the thickness in front of the roll gap was examined. Rolling tests in a cold rolling mill for narrow slit strips show that this novel concept is suitable to provide the required dynamic actuation especially at high rolling speed.     

Oxidative damage and fumonisin B1-induced toxicity in primary rat hepatocytes and rat liver in vivo

The particle size distribution and the metal speciation of the heavy metals were investigated on dredged sediment and on the fractions obtained by mechanical agitated (Denver) flotation. The transition metal ions (cadmium, copper, lead and zinc) were flotated specifically independent of the particle size. Particle size analysis, EDTA extraction and sequential extracts indicated that during flotation a redistribution of metals occurred due to the oxidation of metal sulphides. This oxidation process was more pronounced when the flotation was performed at higher pH values and resulted in a decrease in flotation specificity.     

Spermatid injection into human oocytes. I. Laboratory techniques and special features of zygote development

Spermatid injection into the oocyte cytoplasm has been shown recently to yield viable human embryos developing to term after transfer to the mother. This study provides details of the laboratory techniques related to round spermatid injection (ROSI) and elongated spermatid injection (ELSI) and focuses on some special features of zygote development associated with the use of these types of sperm precursor cells for fertilization. A spermatid-enriched fraction was obtained by centrifugation of cells from azoospermic ejaculates through a discontinuous Percoll gradient column. Individual round or elongated spermatids were identified in this fraction and injected deep into oocytes. Oocyte activation was boosted by a vigorous aspiration of the ooplasm at the time of injection. The fertilization rates after ROSI and ELSI were 45 and 44% respectively. A single large syngamy nucleus was detected in 36% of the zygotes that previously showed two normal-sized pronuclei. This condition did not appear to delay the first cleavage division. These observations underscore the importance of distinguishing the syngamy nucleus of diploid zygotes from the female pronucleus of haploid, parthenogenetically activated eggs.     

Fluid dynamics and flow patterns in stirred tanks with a turbine impeller

Velocity profiles were measured in a stirred tank with a turbine impeller using a three-dimensional, pitot tube probe. A tangential jet model was used to describe the flow in the region of the impeller, and two-dimensional potential flow models and a circular jet were used to describe the flow in the rest of the tank. The tangential jet model accurately predicted the measurements from this work and comparable measurements reported in the literature for water and air, for varying impeller diameter and speeds and for different tank diameters. In the rest of the tank a three-dimensional, low velocity, flow field exists; and the center of circulation is not a true stagnation point. The flow at this point is tangential. The two-dimensional models only qualitatively described the flow in this region, and a three-dimensional model would be required. It was experimentally and theoretically confirmed that standard practice of using 10% baffles effectively controls the flow in the tank.     

Function of tacit knowing in learning to design

This paper criticizes the various attempts to rationalize architectural design. Polanyi's theory of tacit knowing in human science is examined and its relevance to the initiation of students into architecture is discussed. The importance of the tacit (inexplicit) is emphasized.     

Study of the oxidation kinetics of finely-divided magnetites. II - Influence of chromium substitution

The oxidation kinetics of magnetites substituted by chromium (Fe²⁺Fe³⁺_2?xCr³⁺_x)O^2?₄ (0 < x < 2) into γ(Fe³⁺_1?yCr³⁺_y)₂O^2?₃, (x = 3y), which is a metastable phase, was found out to be ruled by the law of diffusion, under variable working conditions, of vacancies generated at the surface. The chemical diffusion coefficient is a function of the substitution ratio, crystallite size and the number of vacancies in the spinel lattice. Contrary to magnetites substituted by aluminum, the activation energy varies irregularly with the substitution ratio.     

问答

Q:在刚刚过去的2006财年,NetApp实现了28亿美元的销售额,同比增长36%,对存储领域的领头羊EMC保持了巨大压力。请问公司快速成长的秘诀是什么? A:关于我们为什么能取得近30亿美元的销售收入并成为这一个市场的领先者,大体上可以归结为三点,第一是因为我们正处于这个市场最黄金的