用功的互等定理求解矩形薄板的自然频率

从虚功原理出发，证明了薄板小挠度弯曲问题的功的互等定理，并由此推出了求解矩形薄板自然频率的公式．算例表明，该公式计算简便，精度较高．     

Optimal paths for a light-driven engine with a linear phenomenological heat transfer law

An irreversible light-driven engine is described in this paper, in which the heat transfer between the working fluid and the environment obeys a linear phenomenological heat transfer law [ q ∝Δ(T -1)], with a working fluid composed of the bimolecular reacting system 2SO 3 F■S 2 O 6 F2. Piston trajectories maximizing work output and minimizing entropy generation are determined for such an engine with rate-dependent loss mechanisms of friction and heat leakage. The optimal control theory is applied to determi...     

激光等离子体微推进技术的研究进展

为了加快激光等离子体微推进技术(μLPP)在航天领域的应用,介绍了该项技术近10年的发展状况。讨论了激光等离子体微推进技术发展过程中衍生出的各种工作模式,并简略分析了不同工作模式的优缺点。着重介绍了靶特性对激光微推进性能的影响,包括靶材的选择、靶的结构、靶材掺杂,以及靶物相特性等。针对该项技术的最终发展目标是研制微小卫星姿轨控的激光等离子体微推力器(μLPT),介绍并分析了美国Phipps小组开展的激光微推力器的研制工作。最后,指出了激光等离子体微推进技术目前存在的一些问题,并展望了它的发展前景。     

双稳系统的随机能量共振和作功效率

分析了处于双稳系统中的布朗粒子与外界的周期性外力和热随机力的功、热交互作用,建立了基于Langevin方程的随机能量平衡方程.围绕着受周期力、随机力和阻尼力共同作用的Langevin方程,采用动力学和非平衡热力学相结合的方法,从以"力"为立足点转到以"能量"为研究核心,深入分析了布朗粒子沿单一轨线运动时系统与环境之间的能量交换和作功效率,揭示了双稳系统的随机能量共振现象. 关键词： 双稳系统 随机能量共振 作功效率     

线性唯象传热定律下光驱动发动机的最优路径

以存在热漏、摩擦等不可逆性,以双分子反应系统2SO3FS2O6F2为工质的光驱动发动机为研究对象,考虑工质与环境之间传热服从线性唯象传热定律[q∝Δ(T-1)],分别以输出功最大和熵产生最小为目标对整个循环活塞运动的最优路径进行研究.利用最优控制理论得出了活塞运动路径及工质温度的最优构型,给出了最优构型的数值算例,并与牛顿传热定律[q∝Δ(T)]下的最优构型进行了比较.     

Hydrophilicity of amorphous TiO2 ultra-thin films

The UV-light-induced hydrophilicity of amorphous titanium dioxide thin films obtained by radio frequency magnetron sputtering deposition was studied in relation with film thickness. The effect of UV light irradiation on the film hydrophilicity was fast, strong and did not depend on substrate or thickness for films thicker than a threshold value of about 12 nm, while for thinner films it was weak and dependent on substrate or thickness. The weak effect of UV light irradiation observed for the ultra-thin films (with thickness less than 12 nm) is explained based on results of measurements of surface topography, UV-light absorption and photocurrent decay in vacuum. Comparing to thicker films, the ultra-thin films have a smoother surface, which diminish their real surface area and density of defects, absorb partially the incident UV light radiation, and exhibit a longer decay time of the photocurrent in vacuum, which proves a spatial charge separation. All these effects may contribute to a low UV light irradiation effect on the ultra-thin film hydrophilicity.     

Morphology and fracture behaviour of polyethylene/Mg-Al layered double hydroxide (LDH) nanocomposites

Fracture behaviour of polyethylene (PE)/Mg-Al layered double hydroxide (LDH) based nanocomposites has been studied by essential work of fracture (EWF) approach. Transmission electron microscopy (TEM and X-ray diffraction (XRD) analysis have been used to investigate the morphological features of these nanocomposites. A maximum in the non-essential work of fracture was observed at 5 wt.% LDH demonstrating enhanced resistance to crack propagation compared to pure PE. Morphological analyses of the nanocomposites show that the dispersed LDH platelets are partially exfoliated and also forms clusters with polymer chains remaining entrapped within. Rheological analyses show that the typical low-frequency Newtonian flow behaviour, as observed in unfilled polymer, shifts to shear-thinning behaviour with increasing LDH concentration. At 5 wt.% LDH a ductile-to-brittle transition has been observed. Fracture surface investigation by SEM reveals the arresting of the plastic crack growth by the LDH particle clusters, which is more significant at 5 wt.% LDH content. At higher LDH concentrations, the number of such particle clusters increases causing decrease in the average distance between them. As a result large-scale plastic deformation of the matrix at higher LDH concentration is effectively arrested favouring small strain failure and this in turn reaffirms the possible existence of a ductile-to-brittle transition. The study in general reveals that the resistance against crack initiation (essential work of fracture: EWF) and crack propagation (non-essential work of fracture: βw_p) in these nanocomposites are structurally correlated with the matrix behaviour and the morphology (state of LDH particle dispersion) respectively.     

热机的第二定律效率与不可逆性

利用热机的功－熵关系和可用能概念，给出热机经二定律效率的表达式，同时了热机相对损失功的概念，并用它们比较了几个实际动力源的不可逆程度。     

The principle of virtual work in mechanical and electromechanical systems

Summary The principle of virtual work is applied to electromechanical systems as the foundation of a unifying concept for modelling mechatronical systems. After the presentation of an important result in the field of mechanics, the expansion of the principle on electrical networks and electromechanical systems is shown. The use of the principle of virtual work in the domain of electromechanics yields an analogous form to the central equation of mechanics which is valid for holonomic and nonholonomic systems. The electrotechnical part of the system is confined to networks. The derivation of the mathematical model is demonstrated on the example of a simple electromechanical oscillation circuit. In addition, the physical systems are separately treated, taking into account the explicit constraints on the basis of the Lagrangian multiplier method.     

冲击作用下凝聚态含能材料热点形成热－机械分析

应用动力有限元方法分析含能材料中热点形成机理。在假定凝聚态含能材料为可压缩的情况下，研究圆形和椭圆形微孔洞附近介质在冲击作用下热－机械响应过程，结果显示冲击波强度、空隙率、微孔洞尺寸和形状、熔点对热点温升有强烈影响，并讨论粘塑性功和固相压缩成为主要机制的条件。