卷取张力控制新方法

介绍了一种新的卷取机张力控制方法,其关键技术在于取消传统动态力矩补偿,同时满足无冲击张力给定和升速过程中恒张力指标要求.采取的一系列措施后,这种新的方法已成功应用于高精度生产轧机.     

三相绕线式异步电动机无级起动控制的一种方法

三相绕线式异步电动机转子回路外接并联阻抗 ,可以改善起动性能 ,简化控制电路 ,适用于重复短时工作制负载的起动控制。讨论了阻抗参数的计算方法。     

磁共振成像中磁体的匀场线圈设计与磁场计算

根据静磁场的基本特征及有源匀场的方法，分析了具有柱面形状的两类匀场线圈的结构设计与优化方法，并导出线圈磁场的高精度数值算法．以此设计的匀场线圈成功应用于超低场ＭＲＩ的０．０４Ｔ常导磁体的匀场中．     

一种新型偏转线圈的大偏转角技术

为了利用现有 CRT颜色逼真、分辨率高、技术成熟等优点 ,克服其体积大、笨重的不足 ,提出将两组平面主线圈和两组圆柱形辅助线圈组成一个全新的偏转线圈 ,利用这种新型偏转线圈制作成的 CRT能较大幅度减薄显像管的厚度 ,并在保证图像质量前提下实现电子束的大角度偏转 .实验结果表明 ,电子束最大偏转角可达 1 2 6°以上 ,光点测试结果良好 ,电子束聚焦特性有所改善     

Protein folding revisited. A polypeptide chain at the folding – misfolding – nonfolding cross-roads: which way to go?

The structure-function paradigm claims that a specific function of a protein is determined by its unique and rigid three-dimensional (3D) structure. Thus, following its biosynthesis on the ribosome, a protein must fold to be functional. This idea represents one of the cornerstones of modern biology. Numerous cases when, due to the effect of environmental factors or because of genetic defects (mutations), a polypeptide chain has lost its capability to gain a proper functional 3D structure (i.e. became misfolded), seem to confirm this concept. Consequences of such misfolding are well known and represent lost of function, aggregation, development of conformational disorders and cell death. However, the recent revelation of countless examples of intrinsically disordered proteins has cast doubt on the general validity of the structure-function paradigm and revealed an intriguing route of functional disorder. Thus, in a living cell, a polypeptide chain chooses between three potential fates – functional folding, potentially deadly misfolding and mysterious nonfolding. This choice is dictated by the peculiarities of amino acid sequence and/or by the pressure of environmental factors. The aim of the present review is to outline some interesting features of these three routes.Received 5 March 2003; received after revision 28 March 2003; accepted 31 March 2003     

Modification of the rib operon derived from Bacillus subtilis and its expression in Escherichia coli

A riboflavin operon （rib operon） derived from Bacillus subtilis 368 was modified on structure and the resulting operons were expressed in various strains of Escherichia coli. The results showed that the optimization of the rib operon and the host strain used for expression are two main factors affecting the riboflavin production. Replacing the promoterl and rfn box of the rib operon with a strong constructive promoter spol drastically increased the expression of the rib genes. When E. coli JM109 was used as the host strain, the highest riboflavin production reached 95.3μg/mL （about eight times higher than that of the unmodified r/b operon）. In addition, when tetracycline （20 μg/mL） was used as the selective pressure, compared with the ampicillin resistant transformants, a higher riboflavin yield was obtained in tetracycline resistant host strain.     

鸭致病性大肠杆菌中耶尔森菌强毒力岛的分子流行病学调查

为了解耶尔森菌强毒力岛(HPI)在鸭致病性大肠杆菌中的流行情况,根据HPI结构基因irp2和fyuA参考序列设计了引物,用PCR方法对从成都等地分离的64株鸭致病性大肠杆菌和28株健康雏鸭泄殖腔拭子分离的大肠杆菌基因进行了扩增和检测,并对5个菌株相关基因进行了克隆和序列分析.结果表明,irp2和fyuA携带率在鸭大肠杆菌病分离株分别为40.6%(26/64)和39.1%(25/64),在健康鸭泄殖腔大肠杆菌分离株分别25.0%(7/28)和21.4%(6/28).鸭大肠杆菌病分离株携带fyuA和irp2的阳性率显著高于健康鸭大肠杆菌分离株(P<0.05),HPI毒力岛的携带率与菌株的致病性呈明显的正相关.分析表明相关基因与GenBank中参考序列的同源性高达98%以上.     

气动成型机的设计

采用气动系统控制进行设计的钢管端口成型机，能在一次装夹中将胀形和卷边两个动作连续完成，提高了工作效率。     

微生物合成黄酮类化合物的研究进展

目前,工业生产黄酮类化合物面临价格昂贵等一系列问题,因此用微生物廉价生产黄酮类化合物具有重要意义。近年来系统代谢工程的出现,提供了一个全新的角度来解决传统受限制的生物工业过程。介绍了利用代谢流调控、强化前体物质积累等代谢工程策略,实现微生物法生产黄酮类化合物的国际研究状况,希望对解决目前大规模生产黄酮类物质存在的限制和挑战提供参考。