Histone methylation and ubiquitination with their cross-talk and roles in gene expression and stability

Methylation of lysine residues of histones is associated with functionally distinct regions of chromatin, and, therefore, is an important epigenetic mark. Over the past few years, several enzymes that catalyze this covalent modification on different lysine residues of histones have been discovered. Intriguingly, histone lysine methylation has also been shown to be cross-regulated by histone ubiquitination or the enzymes that catalyze this modification. These covalent modifications and their cross-talks play important roles in regulation of gene expression, heterochromatin formation, genome stability, and cancer. Thus, there has been a very rapid progress within past several years towards elucidating the molecular basis of histone lysine methylation and ubiquitination, and their aberrations in human diseases. Here, we discuss these covalent modifications with their cross-regulation and roles in controlling gene expression and stability. Received 24 September 2008; received after revision 21 November 2008; accepted 28 November 2008     

有限元法在电机温度场仿真中的运用

运行的超声电机会产生温升,过高的温升对超声电机的机械特性及使用寿命都有较大影响。本文首先通过实验证明压电陶瓷元件发热和摩擦层摩擦发热是超声电机温升的主要热源;然后,分别以压电陶瓷元件发热和摩擦层摩擦发热为热源,建立其相应的温度场热分布模型。并用有限元软件分别对压电陶瓷元件发热场和接触摩擦发热场进行仿真计算。计算结果表明,压电陶瓷片发热源部分,热量最大处为压电陶瓷片粘贴面的内圈;接触摩擦发热中,摩擦产生的热量集中在接触表面。     

SRM点火瞬间流固耦合研究现状与发展探索

随着美国“大力神4”首发全尺寸静态试验发动机PQM-1的失败,固体发动机点火瞬间的流固耦合现象逐渐得到了人们的重视。本文将流固耦合研究现状分为点火燃气流动、药柱变形和实验研究三个方面,综述了国内外的发展现状与趋势。结合我国发展的实际情况,初步探讨了研究固体发动机点火瞬间流固耦合的新方法。     

基于细分控制原理的步进电机通用驱动器设计

阐述了细分控制原理,介绍了一种基于细分控制原理的步进电机通用驱动器.并以86BYG步进电机为负载,用实际运行试验验证设计的可行性,得到比较满意的结果.     

脉冲直接力控制简易制导弹药命中精度研究

研究了基于弹体捷联激光四象限探测器体制下,利用脉冲力进行质心控制的弹道修正技术.通过外弹道模型的建立和数值仿真,研究了弹丸落角、脉冲发动机作用位置偏离质心距离、脉冲发动机工作宽度和总冲散布等因素对于弹道修正精度的影响,对比得出了影响弹丸修正精度的主要因素,为工程实现提供理论支持.     

Myosin V from head to tail

Myosin V (myoV), a processive cargo transporter, has arguably been the most well-studied unconventional myosin of the past decade. Considerable structural information is available for the motor domain, the IQ motifs with bound calmodulin or light chains, and the cargo-binding globular tail, all of which have been crystallized. The repertoire of adapter proteins that link myoV to a particular cargo is becoming better understood, enabling cellular transport processes to be dissected. MyoV is processive, meaning that it takes many steps on actin filaments without dissociating. Its extended lever arm results in long 36-nm steps, making it ideal for single molecule studies of processive movement. In addition, electron microscopy revealed the structure of the inactive, folded conformation of myoV when it is not transporting cargo. This review provides a background on myoV, and highlights recent discoveries that show why myoV will continue to be an active focus of investigation. Received 31 October 2007; received after revision 4 December 2007; accepted 2 January 2008     

潜艇侧推无位置传感器永磁同步电机控制系统

为满足潜艇侧推系统快速启动性和高可靠性要求,解决机械传感器的海水密封问题,研究了扩展卡尔曼滤波器无位置传感器永磁同步电动机控制系统,建立了标幺制下的EKF位置和转速估算模型,使应用扩展卡尔曼滤波器估算电机位置和转速时,矩阵的参数不依赖于电机参数,具有更广范围的适用性,降低了使用难度.针对电机初始位置误差造成EKF估算失败的问题提出了一种修正方法,仿真和实验证明了该方法的有效性.     

交流永磁同步伺服系统仿真

在分析矢量控制原理的基础上,利用MATLAB/SIMULINK设计了交流永磁同步伺服系统的仿真模型,进行仿真研究。仿真结果验证了该仿真模型的有效性。     

浅析实现单相异步电动机正反转的三种电路

单相异步电动机在家用电器中运用非常广泛,有些电器设备需要其电机可正反转,这就需要我们了解实现单相异步电动机正反转的原理及实现电机正反转的外部接线图,文章就该问题展开论述。