Collective diffusion in carbon nanotubes: Crossover between one dimension and three dimensions

Using non-equilibrium molecular dynamics and Monte Carlo methods, we study the collective diffusion of helium in carbon nanotubes. The results show that the collective diffusion coefficient(CDC) increases with the dimension of the channel. The collective diffusion coefficient has a linear relationship with the temperature and the concentration. There exist a ballistic transport in short carbon nanotubes and a diffusive transport in long carbon nanotubes. Fick's law has an invalid region in the nanoscale channel.     

随机外磁场作用下Ising自旋体系的随机共振

通过采用数字仿真手段，研究了经平均场处理的Ising自旋体系在弱确定性周期外场和随机外场（噪声场）混合驱动下的动态响应行为.着重考察了不同强度混合驱动外场作用下，Is ing自旋体系的非平衡动态转变所表现出区别于单纯确定性周期场作用下的新特征——随机 共振.选定体系非平衡动态转变的动态序参量Q为表征参量，系统模拟计算了混合驱动外场在多种参数组合下体系的动态响应特征，高场低温下的非连续动态转变和低场高温下的连续动态转变.模拟计算表明在适当混合驱动外场的作用下，Ising自旋体系具有随机共振现象，并诱发形成非 关键词： Ising自旋体系 随机共振 动态相变 对称性     

一道课本习题的探究

原题已知:△ABC中,∠ABC=45°,H是高AD和BE的交点. 求证:BH=AC(人教版初中《几何》P116B组第2题).     

Stochastic resonance and nonequilibrium dynamic phase transition of Ising spin system driven by a joint external field

The dynamic response and stochastic resonance of a kinetic Ising spin system （ISS） subject to the joint action of an external field of weak sinusoidal modulation and stochastic white-nolse are studied by solving the mean-field equation of motion based on Glauber dynamics. The periodically driven stochastic ISS shows that the characteristic stochastic resonance as well as nonequilibrium dynamic phase transition （NDPT） occurs when the frequency ω and amplitude h0 of driving field, the temperature t of the system and noise intensity D are all specifically in accordance with each other in quantity. There exist in the system two typical dynamic phases, referred to as dynamic disordered paramagnetic and ordered ferromagnetic phases respectively, corresponding to a zero- and a unit-dynamic order parameter. The NDPT boundary surface of the system which separates the dynamic paramagnetic phase from the dynamic ferromagnetic phase in the 3D parameter space of ho-t-D is also investigated. An interesting dynamical ferromagnetic phase with an intermediate order parameter of 0.66 is revealed for the first time in the ISS subject to the perturbation of a joint determinant and stochastic field. The intermediate order dynamical ferromagnetic phase is dynamically metastable in nature and owns a peculiar characteristic in its stability as well as the response to external driving field as compared with a fully order dynamic ferromagnetic phase.     

Enhancement effect of asymmetry on the thermal conductivity of double-stranded chain systems

Using nonequilibrium molecular dynamics simulations, we study the thermal conductivity of asymmetric double chains. We couple two different single chains through interchain coupling to build three kinds of asymmetric double-stranded chain system: intrachain interaction, external potential, and mass asymmetric double chains. It is reported that asymmetry is helpful in improving the thermal conductivity of the system. We first propose double-heat flux channels to explain the influence of asymmetric structures on the thermal conductivity. The phonon spectral behaviour and finite size effect are also included.     

Controlling Thermal Conductivity of Few-Layer Graphene Nanoribbons by Using the Transversal Pressure

We study the thermal transport of few-layer graphene nanoribbons in the presence of the transversal pressure by using molecular dynamics simulations.It is reported that the pressure can improve the thermal conductivity of few-layer graphene nanoribbons.This improvement can reach 37.5%in the low temperature region.The pressure dependence of thermal conductivity is also investigated for diferent length,width and thickness of few-layer graphene.Our results provide an alternative option to tuning thermal conductivity of few-layer graphene nanoribbons.Furthermore,it maybe indicate a so-called pressure-thermal efect in nanomaterials.     

Correlated Noises in a Prey-Predator Ecosystem

We investigate a Volterra ecosystem driven by correlated noises. The fluctuation in the death rate of the predator induces an increase of population density of the predators. The fluctuation in the growth rate of the prey, however, leads the predators to decay. It is reported that the predators undergo sensitivity to a random environment, whereas the preys exhibit a surprising endurance to the same stochastic factor. The predators are of better stability under strong correlation of noises.     

三维X-Y模型的滞后标度和动态相变行为

采用Monte Carlo方法对3DX-Y模型进行数值模拟计算，研究了在非线性外场驱动下3DX-Y模 型的滞后标度和动态相变.得出了滞后标度关系为Area～h^α₀ωβ(1-T/T_c)^γ， 其中α=0.57，β=0.34，γ=0.90.发现其动态相变行为在一定的临界参数条件下，初始短周 期(周期数PN≤10)内的结果具有与Ising模型类似的对称性破缺；但在长周期内(PN≥200)的 结果则明显区别于Ising模型而与Heisenberg模型相近，也即无稳定动态有序铁磁相的存在. 关键词： X-Y模型 滞后标度 动态相变 Monte Carlo方法     

Denaturation of DNA Double-Helix Characterized by Thermal Conductance

We deal with the thermal conductance and the denaturation of a three-dimensional DNA double helix based on the Peyrard-Bishop-Dauxois model by using non-equilibrium molecular dynamics simulations. It is reported that the thermal conductance of DNA has a substantial decrease near the denaturation where the DNA double helix separates into two single chains. We explain this phenomenon through the phonon spectra at different temperatures. It is suggested that the denaturation of DNA can also be characterized by the change of the thermal conductance.     

C60轰击石墨烯的瞬间动力学

采用非平衡分子动力学方法,通过分别控制温度和速度的方式研究了C60轰击石墨烯的瞬间动力学,研究表明,无论温度如何变化,C60在低速轰击石墨烯时都不能击穿石墨烯,但在高速轰击石墨烯时都能击穿石墨烯,并不受温度影响,对于在低速与高速的过渡段,发现C60击穿石墨烯的概率会随着温度的提升而呈现增加的趋势,导致此现象的原因是在高温时C60破坏石墨烯C—C键的概率更高,C60轰击石墨烯的动力学在石墨烯表面清理和纳米孔制备方面有潜在应用。