Dynamic instability of collective myosin Ⅱ motors

Some kinds of muscles can oscillate spontaneously,which is related to the dynamic instability of the collective motors.Based on the two-state ratchet model and with consideration of the motor stiffness,the dynamics of collective myosin Ⅱmotors are studied.It is shown that when the motor stiffness is small,the velocity of the collective motors decreases monotonically with load increasing.When the motor stiffness becomes large,dynamic instability appears in the forcevelocity relationship of the collective-motor transport.For a large enough motor stiffness,the zero-velocity point lies in the unstable range of the force-velocity curve,and the motor system becomes unstable before the motion is stopped,so spontaneous oscillations can be generated if the system is elastically coupled to its environment via a spring.The oscillation frequency is related to the motor stiffness,motor binding rate,spring stiffness,and the width of the ATP excitation interval.For a medium motor stiffness,the zero-velocity point lies outside the unstable range of the force-velocity curve,and the motion will be stopped before the instability occurs.     

基于EtherCAT总线的串联型分布式数据采集系统设计

针对海洋工程实验室现场数据采集过程中,数据量大、测点分散、实时性要求高、数据种类不一致的问题,设计了一种基于实时工业以太网EtherCAT总线的串联式数据采集系统。从整体结构、工作原理、主站软件和从站软硬件方面详细介绍了系统的方案设计。在实验水池中,通过采集实际波浪信号对数据采集系统进行了测试。结果表明,系统性能稳定,精度高,实时性好,为分布式数据采集监控系统的研究提供了应用和技术上的参考。     

浓悬浮液中纳米SiO_2团聚体的渗透率

本文基于悬浮液中渗透性颗粒的短时扩散动力学理论,采用低相干光纤动态光散射方法,测量了相同粒径的纳米SiO_2团聚体在不同体积分数时的扩散系数,利用扩散系数随渗透率的变化关系得到纳米SiO_2团聚体的渗透率.结果表明:恒温条件下,具有一定渗透率的团聚体颗粒扩散得比硬球颗粒快.实验测量得到的团聚体渗透率与采用photoshop CS6对团聚体SEM图像进行处理计算得到的渗透率符合较好.     

Mechanical and tribological enhancement of polyoxymethylene-based composites with long basalt fiber through melt pultrusion

Abstract

The polyoxymethylene (POM)/basalt fiber composites were prepared by use of long fiber-reinforced thermoplastic technology through melt pultrusion. The mechanical and tribological properties, morphology, and thermal stability of the resulting composites were investigated. The composites exhibit significant improvements in tensile, flexural, and notched impact strength. These mechanical strength and toughness are dependent on the fiber content over the full range of the study. The residual fiber length and distribution in the injection-molded specimens were characterized. The prominent reinforcement effect of basalt fiber on POM is derived from the supercritical fiber length, which is much longer than that of the short fiber-reinforced ones and thus makes the composites take full advantage of the strength of the reinforcing fibers. The Kelly–Tyson model was used to predict the ultimate tensile strength of POM composites using the measured values of residual fiber length in the matrix, but the deviations were observed at the high contents of basalt fiber. The morphologic investigation indicates that the fiber pullout and fiber breakage both contribute energy dissipation to the tensile fracture of the composites. The tribological characterization indicates that the friction coefficients and specific wear rates of POM composites also decrease remarkably. Such an improvement of tribological performance is due to the presence of the high wear-resistant basalt fibers on the top of the worn surface bearing the dynamic loadings under sliding. Moreover, the dynamic mechanical analysis reveals that the storage moduli of the composites increase with increasing the fiber content, whereas the loss factors present an opposite trend.     

一类相对转动时滞非线性动力系统的稳定性分析

建立了具有时变刚度、非线性阻尼和谐波激励的一类相对转动时滞非线性动力系统的动力学方程.采用多尺度法推导出时滞动力系统的分岔响应方程,运用奇异性理论研究系统结构稳定性,得到主共振稳态响应方程的转迁集以及不同参数下分岔曲线的拓扑结构.应用Hopf分岔理论讨论了时滞动力系统动态稳定性,给出了系统产生极限环的条件,最后用数值模拟的方法研究了时滞参数对系统极限环幅值的影响。     

基于图像亮度特性统计的水下距离选通成像自动增益控制方法

对水下激光距离选通成像质量与系统增益的关系进行了分析,提出了一种基于图像亮度特性统计的普适性自动增益控制方案。该方案通过设定不同灰度统计阈值,甄别目标图像的亮度特性,并以此作为控制系统增益的主要依据。在对水下大动态范围照度目标或慢速运动目标等进行成像的特殊场合,该方案也具备较强的适用性,能实时反馈控制系统增益,使成像质量优化。     

湿斜压热动力耦合强迫激发辐合增长和暴雨维持的一种机制

打破将散度演化分析局限于水平动力学框架内的传统认识思维,针对大气的斜压性与层结特征将对大气运动散度场演化产生显著影响的事实,从湿斜压原始方程出发,将大气的斜压热力作用通过热力学方程引入散度方程,在替换平衡近似（alternative balance）下,导出了显式包含湿非地转Q矢量与垂直风切变耦合强迫作用的新型散度方程.阐明了潮湿大气中非地转斜压强迫激发散度场演化的物理机制,为利用常规观测资料诊断散度场演化提供了一种有效的数学工具.通过对流层中低层气柱内总体辐合增长影响因子的分 关键词： 暴雨天气 散度演变 正压非平衡强迫 湿斜压热动力耦合强迫     

Bi，Sb及稀土元素对AZ91镁合金高温性能影响机理研究

利用大角重位点阵概念建立了AZ91镁合金基体(α相)和镁［0001］对称倾斜晶界原子结构模型,应用实空间的连分数方法计算了体系的结构能,环境敏感镶嵌能以及相互作用能.结果发现,在镁合金基体中,Al和稀土形成团簇时比较稳定,Al,Bi或Sb与稀土形成团簇时不稳定.Bi或Sb和稀土元素同时存在于AZ91镁合金中时,一方面Bi或Sb将可与RE结合形成RE₂Bi(RE₂Sb)或RE-Bi(RE-Sb)化合物弥散分布于晶界,另一方面镁合金基体中会形成Al_{11关键词： 电子理论 晶界偏聚 合金元素 高温性能}     

信息技术下大学物理实验“三步骤”教学探讨

信息技术的快速发展使实验教学过程的改变成为可能,针对实验教学中的两个薄弱环节,我们将CAI实验教学课件、计算机网络技术、以及传统的实验教学手段结合在一起,对普通物理实验教学过程进行了改革.实施过程主要分为以下3个步骤:1) 使用CAI课件对实验原理的难点进行动态分析;2) 学生利用计算机进行交互模拟实验操作;3) 进行真实实验--更注重解决问题能力的培养和提高.     

Preparation of CoFe alloy nanoparticles with tunable electromagnetic wave absorption performance

CoFe alloy nanoparticles with different particle sizes were successfully prepared by hydrogen-thermal reduction of CoFe₂O₄ microspheres at different temperatures. It was found that the real part of the permeability of the CoFe alloy nanoparticles increased with the decrease of the particle size, and accordingly the reflection loss (RL) peak moved towards the low-frequency region. The maximum RL of the coating based on CoFe alloy nanoparticles exceeded −23 dB, and a wide effective absorption band width (RL≤−10 dB) of about 6 GHz was simultaneously achieved. The EMA performance was confirmed to be tunable by the control of the absorber's particle size, and thus a new clue for the design of the EMA applications was supplied.