基于幂函数控制指令的垂直飞行仿真性能分析

基于模态直接切换的飞行高度控制方法,在输入控制指令后,存在控制量输出震荡,甚至发散的问题。幂函数符合飞行高度指令变化规律,以此为原型函数,推导给定高度,当前高度和垂直速度之间的关系,将这一变换关系作为垂直速度控制回路的输入指令,设计了平稳控制系统,该系统不需要进行控制模态切换,就可以实现飞行高度保持,以及飞行高度的改变。通过A320飞行仿真平台对设计的平稳控制系统进行性能分析,结果表明该系统可以实现高度的平稳控制,且稳态误差得到了很好抑制。     

Effects of medium nutrition on cell growth and isocamptothecin A and B production by suspension cell culture of Camptotheca acuminata

The effects of initial sucrose concentration, nitrate to ammonium ratio, total N concentration and phosphate concentration in medium on cell growth and isocamptothecin A and B synthesis by suspension call culture of Camptotheca acuminata were investigated in 250 mL shake flasks. 30 g L^-1 sucrose concentration was beneficial to secondary metabolites synthesis. The cell growth and metabolites synthesis were also affected by the ratio of NO3^-/NH4^＋ , and nitrate was tavourable for cell growth. The maximum dry weight was achieved when nitrate was used as the sole N souree. The effect of total initial N on the cell cultures was also investigated with NO3^-/NH4^＋ ratio of 1 ： 2. The final dry cell weight was similar throughout culture period and 50 mM initial N was favourable for secondary metabolite synthesis. 50 mM initial phosphate concentration facilitated both cell growth and secondary metabolites synthesis.     

Digoxin and ouabain increase the synthesis of cholesterol in human liver cells

Digoxin and ouabain are steroid drugs that inhibit the Na⁺/K⁺-ATPase, and are widely used in the treatment of heart diseases. They may also have additional effects, such as on metabolism of steroid hormones, although until now no evidence has been provided about the effects of these cardioactive glycosides on the synthesis of cholesterol. Here we report that digoxin and ouabain increased the synthesis of cholesterol in human liver HepG2 cells, enhancing the activity and the expression of the 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGCR), the rate-limiting enzyme of the cholesterol synthesis. This effect was mediated by the binding of the sterol regulatory element binding protein-2 (SREBP-2) to the HMGCR promoter, and was lost in cells silenced for SREBP-2 or loaded with increasing amounts of cholesterol. Digoxin and ouabain competed with cholesterol for binding to the SREBP-cleavage-activating protein, and are critical regulators of cholesterol synthesis in human liver cells. Received 10 January 2009; received after revision 11 February 2009; accepted 6 March 2009     

A356.2铝合金生产过程中的设备管理效益

介绍了在当前铝加工行业较为困难的情况下,A356.2铝合金生产线的设备选型,提出了几种创造效益的新思路,论证了设备管理不再是狭义上的设备技术管理,而是更广义的生产力管理.设备管理需根据市场经济要求,不仅为生产服务,更要为提高企业的经济效益服务,为提高产品质量、降低能耗、控制污染、减少成本和占领市场服务.     

动车组车体底边梁用6005A铝型材检验分析

6005A铝合金大截面复杂制品作为轨道车体的边梁或枕梁,对轨道车体的整体起连接和承重作用,是动车组车体的关键部位。采用电子万能试验机、铝型材压力试验机、光学显微镜等研究了速度达400 km·h^-1动车组车体底边梁用6005A铝型材的强度、显微组织和断口形貌等,旨在为动车组用铝挤压型材产品检验和工艺制度制定提供技术支持与指导。     

退火温度对5A06挤压型材组织及性能的影响

通过对型材微观组织的观察及维氏硬度、晶间腐蚀和剥落腐蚀等的测试,研究了退火温度对5A06挤压型材组织及性能的影响。结果表明,随着退火温度的升高,晶粒发生了回复、再结晶和晶粒长大三个阶段。当退火温度达到175 ℃时,型材发生低温回复,硬度变化不大,耐蚀性较差;在225～325 ℃退火,型材发生完全再结晶,硬度变化较明显,耐蚀性得到改善;当退火温度高于325 ℃时,晶粒长大,硬度略降低,耐蚀性变差。结合5A06挤压型材组织及性能研究可知,确定退火温度为225～325 ℃。     

CCD精密测量系统及其数字信号处理

介绍了ＣＣＤ精密测量系统中的信号采集和处理的工作原理,阐述了测量系统和数字信号处理芯片（ＤＳＰ芯片）在系统中的工作原理,同时还介绍了测量系统的软件工作过程。文中概要介绍了ＣＣＤ器件的工作原理和ＣＣＤ器件用于测量中的特点。通过本文,我们可以了解到ＣＣＤ精密测量系统中ＤＳＰ芯片的作用。     

Regulation of cell adhesion by PP2A and SV40 small tumor antigen: An important link to cell transformation

The serine/threonine protein phosphatase 2A (PP2A) represents a large family of highly conserved heterotrimeric enzymes. Their critical importance in cell homeostasis is underlined by the fact that they are targets of natural toxins like the tumor promoter okadaic acid, and of simian virus 40 small tumor antigen (SV40 small t), a viral protein known to promote cell transformation. Furthermore, mutated or lower expression levels of PP2A subunits have been found in certain cancers. One major known event in PP2A-dependent cell transformation is the alteration of key signaling pathways that control cell growth and survival. In this review, we focus on how PP2A enzymes also affect cell adhesion and cytoskeletal dynamics, the disruption of which is linked to loss of cell polarity, increased cell motility and invasiveness. We also examine how those various pathways participate in the transforming activity of SV40 small t. Received 29 June 2006; received after revision 3 August 2006; accepted 20 September 2006     

混凝土早龄期热膨胀系数试验研究

通过设计开发新的早龄期混凝土热膨胀系数测量装置,测量了不同配合比的混凝土从初凝后开始的热膨胀系数,总结了在早龄期混凝土热膨胀系数随龄期的发展规律,并给出了其拟合公式。     

传承与超越——白盾新时期红学理论的贡献

虽然以往的红学研究不乏真知灼见,但它们大都专注一个或数个具体问题。在继承前人成果的基础上,白盾就小说主题、作者研究、版本比较提出一系列有违传统的新观点,最大程度地接近了曹雪芹和《红楼梦》的本真。这正是他新时期红学理论的最大贡献。