环氧棉子油增塑剂的合成及其在聚氯乙烯塑料中的特性研究

本文报导了无溶剂一步法合成无毒环氧棉子油增塑剂的新工艺,并讨论了不同工艺条件对产品环氧值的影响.利用Brabender 331流变仪,对不同DOP/环氧棉子油配比的聚氯乙烯样品进行了测试,结果证明环氧棉子油增塑剂不仅可以部分取代DOP,同时又提高了PVC制品的热稳定性,是一种理想的耐热增塑剂.     

二自由度自谐式机器人动力学的研究

本文对引用弹性元件的二自由度谐式机器人的动力学进行了分析,在该模型中引入了负反馈系统。按预期的机构运动规律和系统的稳定性要求,研究了反馈放大系数的合理选择,并对构件单独和同时运动的仿真图线进行了分析。     

可用于累煤层露天矿山的多周期目标规划模型

本文给出了一个可应用于复合煤层露天矿短期生产计划优化的目标规划模型.模型考虑了与煤质、煤产量及开采程序合理性有关的亏损与盈利.该方法利用了带有客观地确定权重系数的目标规划加权法.文后又给出了一个能说明该模型应用于实际采矿问题的例子.     

Manufacturing''s Roel in Innovation Diffusion and Technological Substitution

Successful innovation management depends upon both, the intrinsic attributes of the new product to be marketed and the firm's internal performance like cost management, timely delivery and quality assurance. The impact of these latter aspects is frequently neglected in the design of models for supporting decision making in innovative firms.A model is outlined to study the market response of different manufacturing policies for innovative goods. It allows e.g. the evaluation of an aggressive strategy with large production capacities from the outset, or a more tentative behavior to. avoid the pressures stemming from high fixed cost and the risks of eventually idle capacity.     

Highly cooperative feedback control of retinal rod guanylate cyclase by calcium ions

Visual excitation in retinal rod cells is mediated by a cascade that leads to the amplified hydrolysis of cyclic GMP (cGMP) and the consequent closure of cGMP-activated cation-specific channels in the plasma membrane. Recovery of the dark state requires the resynthesis of cGMP, which is catalysed by guanylate cyclase, an axoneme-associated enzyme. The lowering of the cytosolic calcium concentration (Cai) following illumination is thought to be important in stimulating cyclase activity. This hypothesis is supported by the finding that the cGMP content of rod outer segments increases several-fold when Cai is lowered to less than 10 nM. It is evident that cGMP and Cai levels are reciprocally controlled by negative feedback. Guanylate cyclase from toad ROS is strongly stimulated when the calcium level is lowered from 10 microM to 10 nM, but only if they are excited by light. We show here that the guanylate cyclase activity of unilluminated bovine rod outer segments increases markedly (5 to 20-fold) when the calcium level is lowered from 200 nM to 50 nM. This steep dependence of guanylate cyclase activity on the calcium level in the physiological range has a Hill coefficient of 3.9. Stimulation at low calcium levels is mediated by a protein that can be released from the outer segment membranes by washing with a low salt buffer. Calcium sensitivity is partially restored by adding the soluble extract back to the washed membranes. The highly cooperative activation of guanylate cyclase by the light-induced lowering of Cai is likely to be a key event in restoring the dark current after excitation.     

A new A4 amyloid mRNA contains a domain homologous to serine proteinase inhibitors

The amyloid proteins isolated from neuritic plaques and the cerebrovasculature of Alzheimer's disease are self-aggregating moieties termed A4 protein and beta-protein, respectively. A putative A4 amyloid precursor (herein termed A4(695] has been characterized by analysis of a human brain complementary DNA. We report here the sequence of a closely related amyloid cDNA, A4(751), distinguished from A4(695) by the presence of a 168 base-pair (bp) sequence which adds 57 amino acids to, and removes one residue from, the predicted A4(695) protein. The peptide predicted from this insert is very similar to the Kunitz family of serine proteinase inhibitors. The two A4-specific messenger RNAs are differentially expressed: in a limited survey, A4(751) mRNA appears to be ubiquitous, whereas A4(695) mRNA has a restricted pattern of expression which includes cells from neuronal tissue. These data may have significant implications for understanding amyloid deposition in Alzheimer's disease.     

Type I phosphatidylinositol kinase makes a novel inositol phospholipid, phosphatidylinositol-3-phosphate

The generation of second messengers from the hydrolysis of phosphatidylinositol-4,5-bisphosphate (PtdInsP2) by phosphoinositidase C has been implicated in the mediation of cellular responses to a variety of growth factors and oncogene products. The first step in the production of PtdInsP2 from phosphatidylinositol (PtdIns) is catalysed by PtdIns kinase. A PtdIns kinase activity has been found to associate specifically with several oncogene products, as well as with the platelet-derived growth factor (PDGF) receptor. We have previously identified two biochemically distinct PtdIns kinases in fibroblasts, and have found that only one of these, designated type I, specifically associates with activated tyrosine kinases. We have now characterized the site on the inositol ring phosphorylated by type I PtdIns kinase, and find that this kinase specifically phosphorylates the D-3 ring position to generate a novel phospholipid, phosphatidylinositol-3-phosphate (PtdIns(3)P). In contrast, the main PtdIns kinase in fibroblasts, designated type II, specifically phosphorylates the D-4 position to produce phosphatidylinositol-4-phosphate (PtdIns(4)P), previously considered to be the only form of PtdInsP. We have also tentatively identified PtdIns(3)P as a minor component of total PtdInsP in intact fibroblasts. We propose that type I PtdIns kinase is responsible for the generation of PtdIns(3)P in intact cells, and that this novel phosphoinositide could be important in the transduction of mitogenic and oncogenic signals.     

Multiple liquid crystal phases of DNA at high concentrations

DNA packaging in vivo is very tight, with volume concentrations approaching 70% w/v in sperm heads, virus capsids and bacterial nucleoids. The packaging mechanisms adopted may be related to the natural tendency of semi-rigid polymers to form liquid crystalline phases in concentrated solutions. We find that DNA forms at least three distinct liquid crystalline phases at concentrations comparable to those in vivo, with phase transitions occurring over relatively narrow ranges of DNA concentration. A weakly birefringent, dynamic, 'precholesteric' mesophase with microscopic textures intermediate between those of a nematic and a true cholesteric phase forms at the lowest concentrations required for phase separation. At slightly higher DNA concentrations, a second mesophase forms which is a strongly birefringent, well-ordered cholesteric phase with a concentration-dependent pitch varying from 2 to 10 micron. At the highest DNA concentrations, a phase forms which is two-dimensionally ordered and resembles smectic phases of thermotropic liquid crystals observed with small molecules.