Actin dynamics in the contractile ring during cytokinesis in fission yeast

Cytokinesis in many eukaryotes requires a contractile ring of actin and myosin that cleaves the cell in two. Little is known about how actin filaments and other components assemble into this ring structure and generate force. Here we show that the contractile ring in the fission yeast Schizosaccharomyces pombe is an active site of actin assembly. This actin polymerization activity requires Arp3, the formin Cdc12, profilin and WASP, but not myosin II or IQGAP proteins. Both newly polymerized actin filaments and pre-existing actin cables can contribute to the initial assembly of the ring. Once formed, the ring remains a dynamic structure in which actin and other ring components continuously assemble and disassemble from the ring every minute. The rate of actin polymerization can influence the rate of cleavage. Thus, actin polymerization driven by the Arp2/3 complex and formins is a central process in cytokinesis. Our studies show that cytokinesis is a more dynamic process than previously thought and provide a perspective on the mechanism of cell division.     

Crystallization dynamics of supersaturated NaClO4 aerosols studied by high-speed photography

Single supersaturated NaClO4 aerosol droplets on a quartz substrate were observed by a high-speed video camera for their morphologic changes with decreasing relative humidity （RH）. The supersaturated droplets were found to form anhydrous NaClO4 at -10% RH. Three stages were roughly observed in this process, i.e., the main stem appearance, primary and secondary branches growth, and the deep dehydration. The main stem grew steadily and finished in 120 ms. Affected by both crystal precipitation and water evaporation, primary branches grew for 1200 ms, accompanied by a slower growth of secondary branches. The deep dehydration was more complicated, and lasted for a longer time.     

Crystallization dynamics of supersaturated NaClO_4 aerosols studied by high-speed photography

Single supersaturated NaClO4 aerosol droplets on a quartz substrate were observed by a high-speed video camera for their morphologic changes with decreasing relative humidity (RH). The supersatu- rated droplets were found to form anhydrous NaClO4 at ~10% RH. Three stages were roughly observed in this process, i.e., the main stem appearance, primary and secondary branches growth, and the deep dehydration. The main stem grew steadily and finished in 120 ms. Affected by both crystal precipitation and water evaporation, primary branches grew for 1200 ms, accompanied by a slower growth of sec- ondary branches. The deep dehydration was more complicated, and lasted for a longer time.     

Video imaging of walking myosin V by high-speed atomic force microscopy

The dynamic behaviour of myosin V molecules translocating along actin filaments has been mainly studied by optical microscopy. The processive hand-over-hand movement coupled with hydrolysis of adenosine triphosphate was thereby demonstrated. However, the protein molecules themselves are invisible in the observations and have therefore been visualized by electron microscopy in the stationary states. The concomitant assessment of structure and dynamics has been unfeasible, a situation prevailing throughout biological research. Here we directly visualize myosin V molecules walking along actin tracks, using high-speed atomic force microscopy. The high-resolution movies not only provide corroborative 'visual evidence' for previously speculated or demonstrated molecular behaviours, including lever-arm swing, but also reveal more detailed behaviours of the molecules, leading to a comprehensive understanding of the motor mechanism. Our direct and dynamic high-resolution visualization is a powerful new approach to studying the structure and dynamics of biomolecules in action.     

X-chromosome inactivation may explain the difference in viability of XO humans and mice

Only about 1% of human XO conceptuses survive to birth and these usually have the characteristics of Turner's syndrome, with a complex and variable phenotype including short stature, gonadal dysgenesis and anatomical defects. Both the embryonic lethality and Turner's syndrome are thought to be due to monosomy for a gene or genes common to the X and Y chromosomes. These genes would be expected to be expressed in females from both active and inactive X chromosomes to ensure correct dosage of gene product. Two genes with these properties are ZFX and RPS4X, both of which have been proposed to play a role in Turner's syndrome. In contrast to humans, mice that are XO are viable with no prenatal lethality (P. Burgoyne, personal communication) and are anatomically normal and fertile. We have devised a system to analyse whether specific genes on the mouse X chromosome are inactivated, and demonstrate that both Zfx and Rps4X undergo normal X-inactivation in mice. Thus the relative viability of XO mice compared to XO humans may be explained by differences between the two species in the way that dosage compensation of specific genes is achieved.     

超高速导弹红外凝视成像导引头技术研究

对弹道导弹采用的红外凝视成像导引头的几个关键问题进行了讨论,并结合导弹使用的实际需要以及国内红外成像器件的水平给出了较合适的设计方案。用该方案设计的导引头基本满足弹道导弹的使用要求。研究结果表明：该方案设计正确、可行,是目前易于设计实现的一种方案。     

Population dynamics of Schistosoma mansoni in mice repeatedly exposed to infection

Studies of host resistance to parasite infection are usually based on experimental designs involving a primary infection and subsequent challenge exposure, resistance being recorded as the percentage reduction in parasite establishment in challenged hosts when compared with that in uninfected animals. Few studies have focused on the dynamic nature of helminth establishment and mortality (and their presumed dependency on the rate of current exposure and past experiences of infection) in hosts repeatedly exposed to low levels of infection. Here, we report the results of population studies on the dynamics of resistance to Schistosoma mansoni infection (a helminth parasite) in mice repeatedly exposed to cercarial invasion. Parasite burdens created by different levels and durations of exposure to infection reflect a dynamic interplay between rates of helminth establishment and mortality. Depending on the intensity of exposure, changes in worm load with duration of host infection vary from monotonic growth to a stable average parasite burden to convex curves in which the average load attains a maximum value before decaying in old animals. These trends are similar to observed patterns of S. mansoni infection in human communities.     

The design of the robot assisted magnetic resonance imaging guidance for minimally invasive surgery system

assisted Minimally lnvasive Surgery (MIS) is one of the rapidest developing directiorls in the current surgical reahn. Magnetic Resonance Imaging (MRI) is an optimal imaging modality which was applied in MIS in recent years. By combination of precise positioning to the target by intra-operative MRI guided surgery and dexterous motion by the robot, safe and smooth operation is expected to be peffurmed.An overview of the MR I-guided robotic system for MIS is offered. The design of the intra-operative MR scalmer system is described. The MR-compatible robotic system is carefully desigaled for safety and sterilization issues. This system unifies image information from open MRI, an optical endoscope and conventional vital-sign detectors. It helps and guides the surgeon and other medical staffs so they can make the right decisions. The high-performance manipulator can mimic the movement of the surgeon‘ s hand precisely. And the analysis for active and passive interventional surgical instrument tracking is provided.     

高速比较器的设计机理研究

针对高速比较器,定性分析了影响比较器速度的因素,探讨了在设计预放大锁存比较器时,如何调整前置放大器增益大小及减小比较器延时,定量给出比较器的前置放大器的增益及延时时间。最后基于VIS 0.4μm BCD工艺,使用Hspice进行了电路仿真分析,仿真结果验证了理论分析的正确性。     

当归对吊尾大鼠比目鱼肌收缩功能的影响

探讨当归对吊尾14天大鼠比目鱼肌(SOL)收缩功能的影响及可能的作用机制。以尾部悬吊法建立大鼠废用性肌萎缩模型,将24只雌性SD大鼠分为正常组(CON),吊尾组(TS)和灌胃当归组(TS+Ang)。用PowerLab系统测定比目鱼肌等长收缩与强直收缩最大张力;定磷法测定Ca2+-ATP酶活性。结果显示:1 TS组肌肉湿重(MWW)和肌肉湿重/体重(MWW/BW)比CON组显著降低,TS+Ang组肌肉湿重升高了17%(P0.05),而肌肉湿重/体重不具统计学意义;2 TS组等长收缩最大张力(Pt)和强直收缩最大张力(Po)比CON组均显著降低;与TS组相比,TS+Ang组Pt值和Po值分别增加91%和49%(P0.01);3与CON组相比,TS组等长收缩最大张力达到一半的时间(TP50),达到等长收缩最大张力的时间(TPT)以及从最大张力峰值到舒张50%(RT50)和75%(RT75)的时间均显著缩短;与TS组相比,灌胃当归组分别增加109%,51%,57%和76%(P0.01);4吊尾组肌浆网Ca2+-ATP酶活性显著升高,灌胃当归后,Ca2+-ATP酶活性降低10%(P0.05)。结果说明:当归能有效缓解吊尾造成的肌肉收缩张力的下降和时程的缩短,当归对抗吊尾引起的比目鱼肌Ca2+-ATP酶活性的升高可能是其抗废用性肌萎缩的重要机制之一。     

高速模数转换器中格雷码与二进制编码对比

为了实现高速模数转换器中的编码电路,研究了编码电路常用的格雷码和二进制编码2种编码方式.结合模数转换器的实际工作条件,从误差来源、误差分布、整体功耗、电路规模等方面对2种编码进行了对比.分析结果表明,在不同的应用条件下2种编码方式具有各自的优缺点,在量化位数较低的情况下,二进制编码比格雷码在某些方面更具有优势.最后基于一个量化精度为6位的高速模数转换器,在中芯国际(SMIC)0.18μm互补金属氧化物半导体(CMOS)工艺下,采用二进制编码方式设计了一个高速编码电路.实际测试结果表明,该编码电路在2GHz速度下工作状态良好.     

高速数字PCB板的信号完整性仿真与验证

高密度PCB(printed circuit board)设计中,高速时钟信号的信号完整性设计面临越来越大的挑战。针对该问题,文章研究了传输线的特性阻抗及其对信号传输延时的影响,利用Cadence的信号完整性分析软件Allegro PCB SI,对一款基于ARM的嵌入式运动控制平台的时钟信号存在的信号完整性(signal integrity,SI)问题进行了再现仿真,重点分析了信号反射与串扰现象及其产生原因,提出了减小时钟信号串扰和反射的措施;结合阻抗匹配原则,以嵌入式运动控制平台的SDRAM和USB时钟信号为例,利用Allegro PCB SI对并行端接、串行端接、改变线间距等方法进行了试验,试验结果表明,端接匹配的方法能有效地减小时钟信号的反射和串扰现象。     

传统点火系统应用于高速多缸发动机

对传统点火系统进行了分析 ,以发动机提供电能的点火系统 ,由断电器触点的闭合和打开来控制点火线圈的初级电流 ,使次级产生点火所需的高压。     

我国高速铁路经济可持续及发展路径

在阐释高速铁路公益性和营利性经济属性特征的基础上,剖析了高速铁路经济可持续发展的内涵,从偿债可持续、经营可持续和发展可持续三个方面对高速铁路财务可持续发展进行论述,并从这三个方面构建了高铁财务可持续评价指标体系,提出了高速铁路实现财务可持续发展的对策建议.     

传统点火系统应用于高速多缸发动机

对传统点火系统进行了分析,以发动机提供电能的点火系统,由断电器触点的闭合和打开来控制点火线圈的初级电流,使次级产生点火所需的高压。     

豚鼠离体小肠电活动与机械收缩

以小肠电活动和环肌张力、纵肌张力为指标，用同步记录的方法研究了豚鼠离体小肠电活动与环肌张力、纵肌张力之间的关系，结果表明：（１）豚鼠离体小肠的电活动包括慢波与峰波；（２）豚鼠离体小肠始终存在着节律性张力活动，其环肌收缩与纵肌收缩的关系表现为拮抗收缩、共同收缩、交互抑制等形式；（３）峰波可增加收缩力，峰波的个数、振幅与小肠张力呈正变关系，尤其与环肌收缩的对应关系更为显著．（４）慢波可触发收缩，尤其是纵肌收缩．在没有峰波仅有慢波时，亦可有收缩活动甚至活跃的收缩活动．     

高速汽油机活塞的热分析

文章建立了某轿车用高速汽油机活塞的几何模型,应用有限元分析软件,对活塞温度场和热变形进行了三维有限元分析计算,得到了活塞三维温度场分布和热变形数据.结果表明,活塞温度场分布和热变形呈明显的非轴对称性;变形后的裙部中凸形状发生了较大改变,导致裙部外形轮廓产生变化;由于裙部的形状将对其润滑特性产生重要影响,此结果为进一步准确分析其润滑特性提供了基础.