拉伸条件下双壁碳纳米管弹性性能的原子模拟

利用分子动力学方法，对双壁碳纳米管在拉伸条件下的弹性性能进行模拟，研究了直径在1 nm以上的4根双壁碳纳米管，模拟了它们的应力-应变关系以及泊松比.计算结果表明，在弹性范围内，双壁碳纳米管的应力与应变呈非线性关系，切线弹性模量大致从720 GPa减小至570 GPa，出现软化现象；随着拉伸应变的增大，泊松比从0.3变化到0.17，但结构尺寸对泊松比的影响不大. 关键词： 双壁碳纳米管 分子动力学 弹性模量 泊松比     

微腔旋转对耦合腔光波导群速度的影响

本文利用多重散射方法和时域有限差分方法,理论研究了微腔旋转对二维正方晶格光子晶体耦合腔光波导群速度的影响.研究结果表明,通过旋转微腔可以造成传播模的模式分裂,从而实现群速度的降低.当微腔旋转角度为45°时,传播模的群速度最小,两个传播模的群速度分别达到了0.0016倍和0.0009倍于真空光速,与微腔未旋转时相比降低了一个数量级.上述两种传播模群速度的差别是由传播模的空间对称性决定的. 关键词： 二维光子晶体 耦合腔光波导 群速度     

用星点法估值波面像差——Ⅰ.球差

比较了镜头的实测波面球差值与其星点像的图像,初步得到了波面球差值的大小与最佳像点前后衍射圈图像特征二者间的对应关系.从而有了用星点法估值波面球差的可能性.     

热惯性对热弹性行为影响的渐近分析

当热作用时间或受热器件结构尺寸呈现微尺度特征时, 热流运动的惯性效应将对热量的传递过程产生显著地影响. 基于热质的概念, 依据牛顿力学原理引入用于描述热质运动的热波方程, 结合各向同性材料的本构关系, 构建了计及热流运动惯性效应的广义热弹性动力学模型. 利用超常传热的微尺度特征, 采用解析的方法对半无限大体外表面受热冲击作用的一维问题进行了渐近求解. 通过对热波、热弹性波的传播和各物理场分布的分析以及与已有广义热弹性理论预测结果的对比, 揭示了热流运动的惯性效应对热弹性行为的影响. 结果表明：热量的传递除了受到热流加速的时间惯性影响之外, 热流运动的空间惯性也对传热行为产生影响, 当计及空间惯性时, 热波、热弹性波的波速、波前位置, 各物理场的建立时间、阶跃峰值及阶跃间隔均受到不同程度的影响. 关键词： 热惯性 热质运动 广义热弹性动力学模型 渐近分析     

弹性细杆弯曲的Kirchhoff方程的违约校正求解

采用Euler四元数表示的Kirchhoff方程来研究受力挤压作用下的弹性细杆的拓扑构形，进一 步研究弹性细杆的力学性质；将得到的微分方程与约束条件组成微分代数方程后再转化为微 分方程规范形式以便求解；为满足边界条件，应用数值打靶法求解边值条件，并将弹性细杆 在力作用下的拉压过程用Matlab仿真出来.同时对由于误差导致的违约现象进行处理，并针 对欧拉参数的特征，选取合适的修正系数以保持方程的稳定性. 关键词： DNA Euler四元数 Kirchhoff方程 弹性细杆 违约修正     

左手介质中电磁波的传播速度

在同向介质中,电磁波的群速度一般是能量传播的方向,并且电磁波的相速度和群速度在大部分情况下都满足瑞利关系.为了研究左手介质的电磁特性,本文从理论上导出了左手介质中电磁波的相速度、群速度及其关系,得出左手介质中电磁波的群速度为负,并介绍了左手介质的一些应用前景.     

化学机械抛光中纳米颗粒的作用分析

化学机械抛光（chemical mechanical polishing, CMP）是用于获取原子级平面度的有效手 段.目前，CMP的抛光液通常使用纳米级颗粒来加速切除和优化抛光质量.这类流体的流变性 能必须考虑微极性效应的影响.对考虑微极性效应的运动方程的求解，有助于了解CMP的作用 机理.数值模拟表明，微极性将提高抛光液的等效黏度从而在一定程度上提高其承载能力， 加速材料去除.这在低节距或低转速下尤为明显，体现出其具有尺寸依赖性.通过改变抛光液 中粒子的微极性，用实验研究了微极性效应对CMP中材料去除速率的影响，证明了分析的合 理性. 关键词： 化学机械抛光 微极流体 抛光液 流变特性 材料去除速率     

相对转动动力学方程的稳定性及在一类黏弹性系数下的解

建立圆柱体任意两个截面间的一般黏弹性转动力学方程，讨论了相对转角的稳定性，由于此方程为变系数的二阶线性的非齐次常微分方程组，没有统一的求解方法.因此，针对其中的一类黏弹性系数求得其解. 关键词： 变系数方程的解 相对转角 稳定性     

表面官能化碳纳米管^13C NMR参数的理论研究

碳纳米管表面化学修饰是当前研究的一大热点,修饰后由于极性基团的存在,碳纳米管在极性溶液环境中的分散度得到明显改善,这在很大程度上扩展了纳米管研究的应用范围.本文采用C80H20模型来表示(10,0)碳纳米管,基于此模型计算了一系列氮烯、卡宾和氟化的单壁纳米管的结构、偶极矩,以及核磁共振参数.研究表明高精度的密度泛函理论(DFT)计算能够用来预测纳米管的13C化学位移,理论研究的结果揭示了氮烯、卡宾以及1,2和1,4氟化的单壁纳米管的若干13C信号特征化学位移值,为实验NMR谱图的归属提供了一定的依据,并且可通过与实验相结合来监测表面官能化碳纳米管加成反应是否发生以及确认其加成方式.     

单壁碳纳米管晶格振动模及红外吸收光谱的研究

碳纳米管晶格动力学的研究可以提供碳纳米管结构和螺旋性等方面的相关信息。在室温下测量了单壁碳纳米管的红外吸收光谱,首次在透射法模式下观察到了其晶格振动模的红外吸收峰,通过与晶格动力学理论计算值对照,做出了振动模的初步归属。讨论了单壁碳纳米管高频振动模与管径的关系,并与高取向热解石墨振动模进行了对比。结果表明,红外吸收光谱包含有碳纳米管的许多信息,是研究其晶格动力学的有效方法。     

Longitudinal vibration and stability analysis of carbon nanotubes conveying viscous fluid

Nowadays, carbon nanotubes (CNT) play an important role in practical applications in fluidic devices. To this end, researchers have studied various aspects of vibration analysis of a behavior of CNT conveying fluid. In this paper, based on nonlocal elasticity theory, single-walled carbon nanotube (SWCNT) is simulated. To investigate and analyze the effect of internal fluid flow on the longitudinal vibration and stability of SWCNT, the equation of motion for longitudinal vibration is obtained by using Navier-Stokes equations. In the governing equation of motion, the interaction of fluid-structure, dynamic and fluid flow velocity along the axial coordinate of the nanotube and the nano-scale effect of the structure are considered. To solve the nonlocal longitudinal vibration equation, the approximate Galerkin method is employed and appropriate simply supported boundary conditions are applied. The results show that the axial vibrations of the nanotubesstrongly depend on the small-size effect. In addition, the fluid flowing in nanotube causes a decrease in the natural frequency of the system. It is obvious that the system natural frequencies reach zero at lower critical flow velocities as the wave number increases. Moreover, the critical flow velocity decreases as the nonlocal parameter increases.     

基于纳观域碳纳米管的太赫兹波天线研究

基于碳纳米管独特的结构特点建立了以其为基础的Pocklington积分方程,并设计了一种全新的碳纳米管太赫兹(THz)波天线.数值仿真和理论计算结果表明,碳纳米管能够产生高频THz电磁辐射,半波长为60μm、半径为2.712nm的单壁碳纳米管偶极天线在-10dB反射系数以下可以实现2.5THz与7.6THz的双频带工作,带宽分别为8.4%与2.7%,由其构成的纳米管天线阵可以获得10.3dB的高增益特性.所得结果有助于在纳观域开展高频THz波辐射源及天线的研究与设计. 关键词： 太赫兹波 碳纳米管 天线 辐射源     

轴向冲击载荷作用下双壁碳纳米管的动力屈曲

应用改进的有限元方法,建立考虑层间范德华力作用的壳-弹簧非线性有限元模型,基于B-R运动准则,系统地研究了双壁碳纳米管的动力屈曲问题,得到了轴向冲击载荷作用下双壁碳纳米管的临界动力屈曲载荷和临界动力失效载荷. 研究结果表明,在动力屈曲过程中,双壁碳纳米管层间距的变化非常小,各管的变形相互协调;碳纳米管中应力波的传播导致碳纳米管出现非对称屈曲模态,可明显观测到四个环向波瓣,沿着碳纳米管的轴线方向,四个波瓣的波峰和波谷交替变化. 对碳纳米管动力屈曲问题的研究表明,冲击载荷的大小和持续时间对碳纳米管的动力屈曲有 关键词： 碳纳米管 动力屈曲 冲击载荷     

The Radial Response of a Carbon Nanotube to Dynamic Pressure

Doklady Physics - The radial dynamics of a single-walled carbon nanotube under dynamic compression is considered in a linear formulation. The equation based on the Kirchoff hypotheses for the...     

Effect of temperature and geometrical nonlinearity on wave propagation characteristics of carbon nanotubes

Considering the effect of temperature and geometrical nonlinearity in the constitutive relation, the equation of motion for a carbon nanotube is obtained based on the Euler–Bernouli beam model. Also, the effect of van der Waals forces is taken into account in the formulation. The carbon nanotube is assumed to be under the application of a constant distributed external load. At any temperature, the equilibrium solutions of the governing equations for a single-walled carbon nanotube (SWCNT) and a double-walled carbon nanotube (DWCNT) are obtained. A small perturbation is assumed around the equilibrium solution. Using this perturbation, the nonlinear equations of motion are linearized. Using the linearized form of the equations of motion, the characteristic equations and dispersion relations are obtained. It is shown that in the linear case and for the case of high temperature there exists a temperature beyond which the phase velocity does not exist. It is shown that in the case of room or low temperature there is no critical value for temperature. Based on the dispersion equation, a relation for the critical value of temperature is obtained. It is found that when the large deformation effect is taken into account, the critical value for temperature does not exist. Also, the effect of large deformations on phase velocities and lateral deformations of single-walled and double-walled carbon nanotube beams are studied. It is found that unlike the linear theory, the nonlinear theory predicts a non-zero phase velocity at the temperature corresponding to linear critical temperature.     

碳纳米管吸收电磁波特性

本文研究碳纳米管阵列的介电谱函数与吸收电磁波的特性。应用等离激元和无规相近似方法给出碳纳米管的介电谱函数,进而求出吸收系数和反射功率比。介电函数随电磁波的频率变化,在光子能量与系统电子的能谱差相匹配时产生共振吸收,吸收系数出现多个大的吸收峰。反射功率比随薄层厚度的增加而指数衰减,其衰减速率和饱和值与电磁场的频率和碳纳米管的结构有密切的联系。     

Dependence of the electrical properties of defective single-walled carbon nanotubes on the vacancy density

The relationship between the electric properties and the vacancy density in single-walled carbon nanotubes has been investigated from first principles as well as the dependence of the influencing range of a vacancy in the nanotube on the nanotube chirality.Compared with the long-range interaction of the vacancies in a single-walled carbon nanotube with non-zero chiral angle,a much shorter interaction was found between vacancies in a zigzag single-walled carbon nanotube.In this study,we investigated the bandstructure fluctuations caused by the nanotube strain,which depends on both the vacancy density and the tube chirality.These theoretical results provide new insight to understand the relationship between the local deformation of a defective single-walled carbon nanotube and its measurable electronic properties.     

Wave characteristics of single-walled fluid-conveying carbon nanotubes subjected to multi-physical fields

Wave propagation in single-walled carbon nanotubes (SWCNTs) conveying fluids and placed in multi-physical fields (including magnetic and temperature fields) is studied in this paper. The nanotubes are modelled as Timoshenko beams. Based on the nonlocal beam theory, the governing equations of motion are derived using Hamilton's principle, and then solved by Galerkin approach, leading to two second-order ordinary differential equations (ODEs). Numerical simulations are carried out to verify the analytical model proposed in the present study, and determine the influences of the nonlocal parameter, the fluid velocity and flow density, the temperature and magnetic field flux change, and the surrounding elastic medium on the wave behaviour of SWCNTs. The results show that the nonlocal parameter has a considerable influence on dynamic behaviour of the nanotube and the fluid flow inside it. The results also show that the magnetic and temperature fields play an important role on the wave propagation characteristics of SWCNTs.     

An Approach for Solving Short-Wave Models for Camassa-Holm Equation and Degasperis-Procesi Equation

In this paper, to construct exact solution of nonlinear partial differential equation, an easy-to-use approach is proposed. By means of the transformation of the independent variables and the travelling wave transformation, the partial differential equation is reduced to an ordinary differential equation. To solve the ordinary differential equation, we assume the soliton solution in the explicit expression and obtain the travelling wave solution. By the transformation back to the original independent variables, the soliton solution of the original partial differential equation is derived. We investigate the short wave model for the Camassa-Holm equation and the Degasperis-Procesi equation respectively. One-cusp soliton solution of the Camassa-Holm equation is obtained. One-loop soliton solution of the Degasperis-Procesi equation is also obtained, the approximation of which in a closed form can be obtained firstly by the Adomian decomposition method. The obtained results in a parametric form coincide perfectly with those given in the present reference. This illustrates the efficiency and reliability of our approach.     

碳纳米管包裹的硅纳米线复合结构的热稳定性研究

采用经典分子动力学方法模拟一定直径[111]晶向的硅纳米线填充不同扶手椅型单壁碳纳米管复合结构的加热过程, 通过可视化和能量分析的方法判断复合结构中硅纳米线和碳纳米管的热稳定性. 通过讨论碳纳米管的空间限制作用和分子间相互作用力的关系, 对碳纳米管和硅纳米线的热稳定性变化进行初步解释. 研究发现碳纳米管中硅纳米线的热稳定性和碳纳米管的直径关系密切: 当管径较小时, 硅纳米线的热稳定性有所提高, 当管径增大到一定大小时, 硅纳米线的热稳定性会突然显著地下降, 直到硅纳米线与管壁不存在分子间相互作用力, 硅纳米线的热稳定性才会恢复. 而硅纳米线填充到碳纳米管中对碳纳米管的热稳定性有着明显的降低作用.