The myosin motor in muscle generates a smaller and slower working stroke at higher load

Muscle contraction is driven by the motor protein myosin II, which binds transiently to an actin filament, generates a unitary filament displacement or 'working stroke', then detaches and repeats the cycle. The stroke size has been measured previously using isolated myosin II molecules at low load, with rather variable results, but not at the higher loads that the motor works against during muscle contraction. Here we used a novel X-ray-interference technique to measure the working stroke of myosin II at constant load in an intact muscle cell, preserving the native structure and function of the motor. We show that the stroke is smaller and slower at higher load. The stroke size at low load is likely to be set by a structural limit; at higher loads, the motor detaches from actin before reaching this limit. The load dependence of the myosin II stroke is the primary molecular determinant of the mechanical performance and efficiency of skeletal muscle.     

The mechanism of membrane-associated steps in tail-anchored protein insertion

Tail-anchored (TA) membrane proteins destined for the endoplasmic reticulum are chaperoned by cytosolic targeting factors that deliver them to a membrane receptor for insertion. Although a basic framework for TA protein recognition is now emerging, the decisive targeting and membrane insertion steps are not understood. Here we reconstitute the TA protein insertion cycle with purified components, present crystal structures of key complexes between these components and perform mutational analyses based on the structures. We show that a committed targeting complex, formed by a TA protein bound to the chaperone ATPase Get3, is initially recruited to the membrane through an interaction with Get2. Once the targeting complex has been recruited, Get1 interacts with Get3 to drive TA protein release in an ATPase-dependent reaction. After releasing its TA protein cargo, the now-vacant Get3 recycles back to the cytosol concomitant with ATP binding. This work provides a detailed structural and mechanistic framework for the minimal TA protein insertion cycle.     

计算机视觉系统的二步法颜色恒常性

理论研究表明 ,三色视觉系统在单视野条件下 ,三维颜色恒常性的计算问题只有在一些约束下才能解决。约束选择的合理与否和后续的任务密切相关。针对不同环境光照条件下的人体肤色分割的具体任务 ,提出了一个新的关于三色系统颜色恒常性问题的物理模型 :1 )将视觉系统所获得的原始信息分裂为亮度信息和颜色信息。 2 )将传统的颜色恒常性问题分解为基于亮度的亮度恒常性和基于颜色信息的颜色恒常性 ,并用二维描述子描述等亮度彩色图像中物理表面的颜色特征。该描述子具有颜色恒常的特性。基于颜色的图像分割实验结果表明 ,二步法颜色恒常性技术是一种非常有效的方法。     

Regular steps in bending cilia during the effective stroke.

A ciliary beat cycle consists of an effective stroke in which the extended cilium makes an oar-like movement towards one side, and a recovery stroke in which the cilium moves back by propagating a bend from base to tip (Fig. 1A). In the sliding microtubule model of ciliary and flagellar movement, which is now supported by substantial evidence1-3, the sliding displacement of microtubules in any region of the cilium is related linearly to the angular change in the direction of that region (Fig. 1B). Thus, during the effective stroke, microtubule sliding is not confined to the region near the base of the cilium but involves the whole length of the extended organelle, and the relative speed of sliding can be measured as the angular velocity of the ciliary motion. I report here that in molluscan cilia the effective stroke consists of regularly alternating rapid and slow phases of angular movement. This suggests that the microtubules slide in quantal steps.     

Direct observation of steps in rotation of the bacterial flagellar motor

The bacterial flagellar motor is a rotary molecular machine that rotates the helical filaments that propel many species of swimming bacteria. The rotor is a set of rings up to 45 nm in diameter in the cytoplasmic membrane; the stator contains about ten torque-generating units anchored to the cell wall at the perimeter of the rotor. The free-energy source for the motor is an inward-directed electrochemical gradient of ions across the cytoplasmic membrane, the protonmotive force or sodium-motive force for H+-driven and Na+-driven motors, respectively. Here we demonstrate a stepping motion of a Na+-driven chimaeric flagellar motor in Escherichia coli at low sodium-motive force and with controlled expression of a small number of torque-generating units. We observe 26 steps per revolution, which is consistent with the periodicity of the ring of FliG protein, the proposed site of torque generation on the rotor. Backwards steps despite the absence of the flagellar switching protein CheY indicate a small change in free energy per step, similar to that of a single ion transit.     

二冲程内燃机扫气流场的数值模拟

用分块结构化网格对二冲程内燃机的扫气流场进行了三维数值模拟，在缺内代数方法生成贴体网格，用ＡＬＥ法求解控制方程组，提高了离心力源项的计算精度。通过在一个两气口气缸模型上进行的大量数值实验，探讨了数值计算中出现的问题及解决方法，模拟了两种二冲程发动机的扫气过程，其结果与实验对比是令人满意的。     

下水道硫化氢产生的原因及施工中的监测

城市下水道产生大量的有害气体,最常见的是硫化氢气体,本文对下水道中产生硫化氢气体的原因进行了分析并提出了减少硫化氢产生的措施和在下水道施工作业中硫化氢气体监测的方法。     

The Drosophila claret segregation protein is a minus-end directed motor molecule

A product encoded at the claret locus in Drosophila is needed for normal chromosome segregation in meiosis in females and in early mitotic divisions of the embryo. The predicted amino-acid sequence of the segregation protein was shown recently to be strikingly similar to Drosophila kinesin heavy chain. We have expressed the claret segregation protein in bacteria and have found that the bacterially expressed protein has motor activity in vitro with several novel features. The claret motor is slow (4 microns min-1), unlike either kinesin or dyneins. It has the directionality, the ability to generate torque and the sensitivity to inhibitors reported previously for dyneins. The finding of minus-end directed motor activity for a protein with sequence similarity to kinesin suggests that the dynein and kinesin motor domains are ancestrally related. The minus-end directed motor activity of the claret motor is consistent with a role for this protein in producing chromosome movement along spindle microtubules during prometaphase and/or anaphase.     

ZTP62-A/L电机机座方孔加工机床的设计

针对ZTP62－A／L电机机座方孔加工的问题，设计出的集机、液、电于一体的机座方孔切割机床，给出了该机床机械及液压系统的工作原理和结构组成，论述了设计该机床的基本思想。应用该机床加工该机座方孔，效果较好。     

基于双空间交替学习的机器人运动技能获取

针对如何基于示范任务学习让机器人自主获得完成新任务的能力的难题,提出一种高斯混合回归结合路径积分策略提升(GMR-PI2)的表达、模仿和优化框架,同时采用基函数、策略表达权系数两个空间上交替搜索执行方案来解决上述问题.核心思想是当权系数探索到最佳逼近点附近时,根据经验最优轨迹集进行基函数的自重组,然后再重启权系数搜索,从而实现从示范任务到指标集约束任务的渐进运动技能获取.经典的轨迹规划过点实验结果表明该方法是有效和可行的.     

The protein kinase A anchoring protein mAKAP coordinates two integrated cAMP effector pathways

Cyclic adenosine 3', 5'-monophosphate (cAMP) is a ubiquitous mediator of intracellular signalling events. It acts principally through stimulation of cAMP-dependent protein kinases (PKAs) but also activates certain ion channels and guanine nucleotide exchange factors (Epacs). Metabolism of cAMP is catalysed by phosphodiesterases (PDEs). Here we identify a cAMP-responsive signalling complex maintained by the muscle-specific A-kinase anchoring protein (mAKAP) that includes PKA, PDE4D3 and Epac1. These intermolecular interactions facilitate the dissemination of distinct cAMP signals through each effector protein. Anchored PKA stimulates PDE4D3 to reduce local cAMP concentrations, whereas an mAKAP-associated ERK5 kinase module suppresses PDE4D3. PDE4D3 also functions as an adaptor protein that recruits Epac1, an exchange factor for the small GTPase Rap1, to enable cAMP-dependent attenuation of ERK5. Pharmacological and molecular manipulations of the mAKAP complex show that anchored ERK5 can induce cardiomyocyte hypertrophy. Thus, two coupled cAMP-dependent feedback loops are coordinated within the context of the mAKAP complex, suggesting that local control of cAMP signalling by AKAP proteins is more intricate than previously appreciated.     

基于化学共沉淀的两步法合成LiMnPO_4正极材料研究进展

磷酸锰锂(LiMnPO_4)是一种非常有应用前景的锂离子电池正极材料,化学共沉淀法是制备这种材料的理想方法。针对LiMnPO_4正极材料目前研究过程中存在的电子电导率低和锂离子扩散慢等问题,本文从Mn_3(PO_4)_2、MnPO_4、NH_4MnPO_4等不同Mn-P前驱体合成LiMnPO_4出发,综述了近年来基于化学共沉淀工艺的两步法合成LiMnPO_4正极材料并采用碳包覆和离子掺杂两种手段改性的国内外研究进展。对当前研究过程中存在的不同Mn-P前驱体获得LiMnPO_4产品性能差异的问题,认为应该通过进一步地探讨化学共沉淀过程的反应机理并进行相关反应动力学及热力学研究解决。本文为LiMnPO_4正极材料的研究及产业化提供了参考。     

The DExH protein NPH-II is a processive and directional motor for unwinding RNA

All aspects of cellular RNA metabolism and processing involve DExH/D proteins, which are a family of enzymes that unwind or manipulate RNA in an ATP-dependent fashion. DExH/D proteins are also essential for the replication of many viruses, and therefore provide targets for the development of therapeutics. All DExH/D proteins characterized to date hydrolyse nucleoside triphosphates and, in most cases, this activity is stimulated by the addition of RNA or DNA. Several members of the family unwind RNA duplexes in an NTP-dependent fashion in vitro; therefore it has been proposed that DExH/D proteins couple NTP hydrolysis to RNA conformational change in complex macromolecular assemblies. Despite the central role of DExH/D proteins, their mechanism of RNA helicase activity remains unknown. Here we show that the DExH protein NPH-II unwinds RNA duplexes in a processive, unidirectional fashion with a step size of roughly one-half helix turn. We show that there is a quantitative connection between ATP utilization and helicase processivity, thereby providing direct evidence that DExH/D proteins can function as molecular motors on RNA.     

城建档案的利用应做好四个环节

城建档案的利用是城建档案工作的重要环节，是实现城建档案信息资源转化为社会、经济效益的重要途径。新形势下，为做好城建档案的综合利用工作，应着重做好城建档案利用的推介与宣传、创新、保密与保护及反馈四个方面的工作。     

基于两道工序加工顺序安排的解法创新

针对一项工程或者一种产品生产的各工序之间复杂的衔接关系,在加工顺序安排的常规解决办法基础上,认真分析研究其数字规律,揭示其数字下的奥秘,在工序条形图解决办法的基础上进行解法创新,建立了“数字分析法解法”.并通过实例分析说明,能较好地解决原解法的不足,其实用性、快捷性更强,工作效率更高.     

A structural change in the kinesin motor protein that drives motility

Kinesin motors power many motile processes by converting ATP energy into unidirectional motion along microtubules. The force-generating and enzymatic properties of conventional kinesin have been extensively studied; however, the structural basis of movement is unknown. Here we have detected and visualized a large conformational change of an approximately 15-amino-acid region (the neck linker) in kinesin using electron paramagnetic resonance, fluorescence resonance energy transfer, pre-steady state kinetics and cryo-electron microscopy. This region becomes immobilized and extended towards the microtubule 'plus' end when kinesin binds microtubules and ATP, and reverts to a more mobile conformation when gamma-phosphate is released after nucleotide hydrolysis. This conformational change explains both the direction of kinesin motion and processive movement by the kinesin dimer.     

等速肌力训练对脑卒中偏瘫患者上肢运动功能的影响

为了解决等速肌力训练对脑卒中偏瘫患者上肢运动功能影响的研究,选择2017年5月～2018年5月在某医院住院的脑卒中偏瘫患者共50例;随机将其划分成观察组和对照组,每组25例。对照组通过常规康复训练和临床药物治疗,康复训练主要有运动治疗、作业治疗、物理因子治疗等,共治疗8周,每周治疗5 d,每天训练2次。观察组除采用对照组治疗方法外,还进行等速肌力训练。通过、FMA评分表、ARAT上肢运动测量评分表、上肢肩关节外展和腕关节背伸主动关节活动度、肌电积分值对上肢功能进行评价。通过BI指数和DASH量表对生活方面进行评价。通过、峰力矩、峰值力矩体重比、平均功率、总功四个力学指标对肌力进行评价。对观察组和对照组治疗前后的上肢运动功能恢复指标、生活方面评分指标和力学指标进行比较。结果表明,观察组治疗后较对照组和治疗前各指标均有很大的改善。可见等速肌力训练能够提高脑卒中偏瘫患者的关节屈伸肌力,促进脑卒中偏瘫患者上式运动功能改善,帮助患者加强自理生活能力。     

The dead-end elimination theorem and its use in protein side-chain positioning

The prediction of a protein's tertiary structure is still a considerable problem because the huge amount of possible conformational space1 makes it computationally difficult. With regard to side-chain modelling, a solution has been attempted by the grouping of side-chain conformations into representative sets of rotamers2??. Nonetheless, an exhaustive combinatorial search is still limited to carefully indentified packing units?? containing a limited number of residues. For larger systems other strategies had to be developed, such as the Monte Carlo Procedure?? and the genetic algorithm and clustering approach?. Here we present a theorem, referred to as the 'dead-end elimination' theorem, which imposes a suitable condition to identify rotamers that cannot be members of the global minimum energy conformation. Application of this theorem effectively controls the computational explosion of the rotamer combinatorial problem, thereby allowing the determination of the global minimum energy conformation of a large collection of side chains.     

A nut-type ultrasonic motor and its application in the focus system

This article reports a screw-driven polyhedron linear ultrasonic motor （USM） of nut-type. It is comprised of a stator, which is a threaded metal nut bonded with piezoelectric plates on its external surface, and a rotor with external threads, which engage with the internal threads of the stator. A traveling wave in the plane is stimulated on the stator when harmonic electric signals are applied to the piezoelectric plates. The traveling wave drives the rotor to rotate, and the threads transform the rotation into a linear motion. The lens can be fixed in the rotor and realize the integrated design of the auto focus system. This structure can omit retarder and directly drive to obtain a high accuracy of positioning, and it is shockproof. A mini AF cellular phone module （8.5 mm×8.5 mm×5.9 mm） driven by this motor was made and an image resolution of 3-5 MP was obtained in the module prototypes of the cellular phone.     

面向绿色设计的客户驱动型二级材料选择方法

传统的材料选择方法已很难满足现代产品设计需求。文章通过剖析传统选材方法,提出了一种支持绿色设计的材料选择方法。该方法是以环境意识为基础,选材时全面考虑材料的各种性能指标,在满足产品基本性能的基础上,充分考虑其环境性能,并运用层次分析方法,选出最优材料。