运用欧拉动力学方程解决力学竞赛两道理论力学试题1)

针对两道力学竞赛试题,从欧拉动力学方程出发分别给出了更加简化的固连系选取方法,分别命名为"Serret-Andoyer近似固连系"和"虚固连系",在此基础上对第1届全国青年力学竞赛理论力学试题第9题,拓展讨论了大球同步旋转时,小球的稳 定性条件,结果表明后者的稳定临界转速要求更低,这将更有利于提高旋转结构的稳定性;对第12届全国周培源大学生力学 竞赛第3题,剖析了任一纬度的运动规律,发现当体系初始角动量为零时会出现一种简洁又优美的运动模式。     

简议“力”和“力学”的含义变迁1)

在古代中国,“力”字和“力学”一词早就出现了。“力”的含义最初是对“人的力量”的直观描述,后来发展到对一般物体的重力的描述,再到对运动状态原因的描述。本文对“力”字含义的变迁进行了辨析。中国现代“力学”是西学东渐的结果,学科名字的确定过程也有不小的 曲折。通过分析确定“力学”为学科名字的过程,揭示了中国古人对“力学”学科理解的变迁。     

光梯度力与激光捕获

从电偶极子在非均匀电磁场中所受梯度力出发,用光的电磁理论和电解质小球的电偶极子模型,论述了介质小球在光场中所受光梯度力与光强梯度成正比,并以此来定量说明激光对介质小球的捕获原理.     

MOCVD生长的InN薄膜中In分凝现象

利用金属有机物化学气相淀积(MOCVD)方法不同生长条件下在c面蓝宝石衬底上制备了InN薄膜,通过不同的物理表征手段研究了InN薄膜的物理性质,结果表明:合适的生长温度可以抑制InN薄膜表面分凝现象。研究认为较低的生长温度使作为N源的NH3分解率较低,In—N的成键可能性小,导致In在表面聚集出现分凝;而较高生长温度时,InN薄膜中In—N键能较小,易发生断裂,反应活性较强的N和H原子逸离薄膜表面,In滞留在薄膜表面也导致In分凝现象的出现。相对于表面分凝的样品,未出现表面分凝的样品的薄膜晶体质量和表面形貌也得到了提高。同时,通过Raman散射谱研究了晶格振动E2声子模的应力效应。     

不同刺激条件下人外周血淋巴细胞超微结构与粘滞力的AFM分析

应用原子力显微镜（atomic force microscopy,AFM）探测了静息、脂多糖（LPS）或伴刀豆蛋白（ConA）活化的人外周血淋巴细胞的形态结构、超微结构及粘滞力特性。从AFM图像可知,经LPS或ConA刺激活化后的淋巴细胞比静息状态的淋巴细胞有所增大,并且表面分布着大小不一的颗粒状聚合物。利用AFM高空间分辨的力位移曲线测量系统,发现经LPS或ConA刺激活化后淋巴细胞的粘滞力是静息状态淋巴细胞的2~3倍。通过AFM探测淋巴细胞活化状态的可视化数据,可以更好地理解淋巴细胞的行为。     

Interfacial Adhesion between Fatty Acid Collectors and Hydrophilic Surfaces: Implications for Low-Rank Coal Flotation

Fatty acids, which are enriched in vegetable oil, have attracted much attention in low-rank coal flotation because of their unique chemical structure. In this study, density functional theory calculations, molecular dynamics simulations, and atomic force microscopy were employed to investigate the adsorption structure and forces between collectors and hydrophilic surfaces. The results show that fatty acids can be easily adsorbed onto surfaces through hydrogen bonds, and can cover the oxygen sites. The existence of hydration film on hydrophilic surfaces prevented nonpolar molecules from being able to adsorb, while polar fatty acids could adsorb and expel water molecules. The adhesion force between the RCOOH-terminated probe and the surface appeared in the retraction process, which differed significantly from that of the RCH₃-terminated probe, indicating that polar fatty acids are more suitable as flotation collectors for low-rank coal than nonpolar hydrocarbon oil. The simulation and AFM test revealed the mechanisms of polar fatty acids, and can provide guidance for low-rank coal flotation applications.     

DUAL RECIPROCITY HYBRID BOUNDARY NODE METHOD FOR THREE-DIMENSIONAL ELASTICITY WITH BODY FORCE

Combining Dual Reciprocity Method （DRM） with Hybrid Boundary Node Method （HBNM）, the Dual Reciprocity Hybrid Boundary Node Method （DRHBNM） is developed for three-dimensional linear elasticity problems with body force. This method can be used to solve the elasticity problems with body force without domain integral, which is inevitable by HBNM. To demonstrate the versatility and the fast convergence of this method, some numerical examples of 3-D elasticity problems with body forces are examined. The computational results show that the present method is effective and can be widely applied in solving practical engineering problems.     

On the Effect of the Various Assumptions and Approximations used in Molecular Simulations on the Properties of Bio-Molecular Systems: Overview and Perspective on Issues

Computer simulations of molecular systems enable structure-energy-function relationships of molecular processes to be described at the sub-atomic, atomic, supra-atomic or supra-molecular level and plays an increasingly important role in chemistry, biology and physics. To interpret the results of such simulations appropriately, the degree of uncertainty and potential errors affecting the calculated properties must be considered. Uncertainty and errors arise from (1) assumptions underlying the molecular model, force field and simulation algorithms, (2) approximations implicit in the interatomic interaction function (force field), or when integrating the equations of motion, (3) the chosen values of the parameters that determine the accuracy of the approximations used, and (4) the nature of the system and the property of interest. In this overview, advantages and shortcomings of assumptions and approximations commonly used when simulating bio-molecular systems are considered. What the developers of bio-molecular force fields and simulation software can do to facilitate and broaden research involving bio-molecular simulations is also discussed.     

脉冲电流冲击力对电极间距的影响

利用时变场理论和瞬态动力学方程建立了电极及其支撑结构的瞬态耦合模型,分析了瞬态电磁场各参数的分布特点,并求解了电极及其支撑结构的动态响应状态参数。计算结果表明:玻璃钢支撑结构对于脉冲电流形成的冲击力载荷具有很好的缓冲作用;低弹性模量支撑材料在脉冲上升沿和峰值阶段均会产生波动性形变,但该波动性形变对电极间距不会造成太大的影响。     

高频原子波导中冷原子的磁导引

建立了高频原子波导模型,分析了铷冷原子在该波导内与磁场的相互作用势。高频波导线圈输入电流,在线圈中心轴线区域的势阱深度为mK量级,在线圈的径向能对温度为100 K左右的冷原子实现囚禁。通过分析可知改变输入波导线圈的输入电流大小,可改变势场的大小。计算了进入高频原子波导的冷原子和波导磁场产生相互作用束缚力的大小。在波导轴线中心区域,原子受到的束缚力较大,最大为1.710－23 N,为原子所受重力的10倍。