盐离子对双链DNA分子弹性影响的研究P

在DNA延伸过程中,考虑到氢键相互作用以及盐浓度(Na+)对氢键和堆积作用的影响,给出了修正的ZZO模型,得到了力-延伸曲线随盐浓度的变化规律.结果表明:随盐浓度的增加,延伸相变力非线性增加,并最终趋于稳定,理论计算结果与实验测量一致.     

盐离子对DNA延伸力的影响

在Ahsan等给出的描述DNA分子弹性的两状态虫链模型的基础上,考虑到盐离子浓度对静电自由能的影响,得到了延伸力随盐浓度的变化规律,结果表明:在低力和高力范围延伸力受盐浓度的影响较小,相变延伸范围随盐浓度的增加非线性增加,与实验测量一致.     

固定温度界面对相变波传播规律的影响

冲击载荷作用下,相变波的传播及相互作用是一热力耦合过程。采用理论和实验相结合的方法研究了固定温度界面对相变波传播特性的影响。首先基于形状记忆本构模型和一维特征线理论分析了各类间断面和温度界面的基本相互作用规律,发现温度界面对相变波的作用与相变波强度及界面两侧温度的相对高低有关;然后进行了相变波在具有固定温度界面的形状记忆TiNi杆中的传播实验,并实时测量了相变波传播过程中的温度变化。实验结果与理论分析基本一致,冲击载荷作用下相变波不仅是物质间断面,还是移动的温度界面。     

盐离子对B-DNA到Z-DNA结构转变影响的理论研究

在已给出的与溶液盐浓度有关的DNA弹性模型基础上, 考虑到Z-DNA的碱基堆积和氢键相互 作用, 给出了一个新的B-DNA到Z-DNA的结构转变模型. 研究了盐浓度对B—Z结构转变特性的影响, 得到了力延伸曲线、折叠角概率分布以及B—Z结构转变的临界扭矩随盐浓度的变化规律.结果表明: 当盐浓度达到2.4mol/L时, 松弛DNA的Z构象开始出现, 并且随盐浓度的增加, Z构象存在的概率增大, B—Z转变所需的扭转力矩减小. 关键词： DNA弹性 盐浓度 B—Z结构转变 堆积能     

格子Boltzmann方法在相变过程中的应用

提出了一种新的描述气液相变过程的单组分格子Boltzmann模型,利用该模型模拟水以及氨分别在R-K,RKS和P-R状态方程控制下的相变过程,发现相对于R-K和RKS状态方程,水以及氨在P-R状态方程控制下模拟结果均与实验值更接近;特别地,P-R状态方程更适合描述氨.为验证该模型处理两相问题的能力,利用该模型模拟不同温度下水以及氨在P-R状态方程控制下的界面密度梯度,所得的结果与经典的界面理论相符.为此,进一步探讨了气泡(液滴)与周围液体(气体)处于力平衡和热平衡时,气泡(液滴)内外压力差在不同温度下与其半径之间的关系,所得的结果满足Laplace定律,并得到了不同温度下水以及氨的表面张力,发现均与实验值符合得很好,且与表面张力临界理论甚为相符.     

DNA分子力学性质的测量

利用单分子实验技术测量了DNA分子的力学性质.通过生化手段将单根DNA分子连在顺磁小球与玻璃侧壁之间,利用磁铁对顺磁球施加力进而拉伸DNA.图像分析得到小球运动的轨迹以及DNA的长度,利用均分定理可以求得施加的外力.测量发现在外力作用下DNA分子的力学反应与高分子物理学的蠕虫状链模型符合良好.     

氘的气液界面及相变特性分子动力学仿真

氘作为重要的核聚变原料,其热物性数据是基础,而气液相界面特性和相变规律又是热物性的关键.国内外对氘的相界面特性研究甚少.本文基于分子动力学方法,采用截断移位Lennard-Jones 12-6势能函数模型描述原子间的相互作用,并考虑分子内部原子间键的谐振作用,对氘的气液界面特性及气液固相变过程进行了仿真研究,得到了氘在不同温度下气液界面过渡区域的厚度、表面张力值等;获得了氘的密度随相变过程的变化规律,并由此得出氘的熔沸点温度,上述计算结果与实验及文献值吻合良好.不仅从微观层面上揭示了氘的宏观热物性表征机理,而且所建立的仿真模型可直接用于预测缺乏实验工况下的氘热物性.     

铁磁形状记忆合金Ni52.5Mn23.5Ga24马氏体相变热滞后的研究

用相界面摩擦原理计算了Ni525Mn235Ga24单晶样品在马氏体相变过程中由于相界面摩擦所消耗的能量.计算结果表明,克服相界面摩擦所需要的能量为1314Jmol,仅占相变潜热的一小部分.另外,精细的交流磁化率测量样品的转变循环回线结果表明,相变热滞后的大小和马氏体的转变百分数成正比,从而进一步证明了热弹性马氏体相变的热滞后来源于相界面推移过程中的摩擦 关键词： 马氏体相变 Ni2MnGa     

Fe合金FCC-BCC原子尺度台阶型马氏体相界面迁移行为的分子动力学模拟研究

两相界面的原子尺度结构对相界面迁移行为具有重要影响.高分辨透射电子显微分析表明钢中马氏体相界面具有高度为若干原子层间距的台阶结构,然而目前Fe合金马氏体相变的模拟研究工作中绝大多数使用非台阶型相界面结构作为模拟初始模型.本文基于拓扑模型和相变位错理论构建了Fe合金FCC/BCC台阶型相界面初始模型,采用分子动力学模拟方法研究了Fe合金马氏体相界面的迁移行为.研究结果表明,当两相界面具有约束共格匹配关系及台阶结构时,体系发生FCC→BCC马氏体相变并呈现典型的非扩散切变特征;相变过程中FCC/BCC宏观尺度相界面沿其法线方向以(4.4±0.3)×10~2 m/s的速度迁移,且相界面在迁移过程中始终保持稳定的台阶结构和相对平直的宏观界面形貌特征;相变位错的滑移速度高达(2.8±0.2)×10~3 m/s,相变位错阵列沿台阶面的协同侧向滑移不仅是马氏体台阶结构宏观相界面迁移的微观机制,也是马氏体相变宏观形状应变的主要来源;采用分子动力学模拟方法获得的Fe合金马氏体相变晶体学特征参量与拓扑模型的解析解数值非常接近,相变产生的整体宏观形状应变由平行于相界面的剪切应变和垂直于相界面的法向应变两部分组成.     

双轴性向列相液晶的相变理论

假设一双轴性向列相液晶分子简单相互作用模型，利用平均场理论，得到从各向同性相至单轴向列相、单轴向列相至双轴向列相的相变. 结果表明，在一定温度范围内，分子形状的非轴对称性可导致系统双轴向列相的产生. 在核磁共振实验中，导出双轴向列相序参数与谱线分裂频率间的一般关系，并讨论序参数测量性的可能性. 关键词： 向列相液晶 相变     

Theoretical Study on Effects of Salt and Temperature on Denaturation Transition of Double-stranded DNA

We investigate the statistical mechanics properties of a nonlinear dynamics model of the denaturation of the DNA double-helix and study the effects of salt concentration and temperature on denaturation transition of DNA. The specific heat, entropy, and denaturation temperature of the system versus salt concentration are obtained. These results show that the denaturation of DNA not only depends on the temperature but also is influenced by the salt concentration in the solution of DNA, which are in agreement with experimental measurement.     

Nonlinear dynamics of an optical phase locked loop in presence of additional loop time delay

The dynamics of an optical phase locked loop (OPLL) with first order loop filter having inherent loop time delay is investigated. In the presence of delay, the system is modeled as a third order autonomous system. In the out of lock condition or during the process of locking, the dynamics of the system is highly nonlinear and different nonlinear phenomena, like limit cycle oscillation, period doubling, chaotic oscillations etc., may be observed with the variation of design parameters. Applying the techniques of the nonlinear dynamics, we have calculated the effects of the inherent loop time delay in determining the state of the loop. The analytical results predicting the parameter values for stable and unstable region of operation are obtained using the quasi-linear Routh–Hurwitz method. The parameter range required for the onset of chaotic oscillations is estimated by Melnikov's global perturbation method. The predicted results are in agreement with those obtained by numerical integration of system equations.     

Essay: Preheating and Turbulence: Echoes of a Not So Quiet Universe

We study the nonlinear decay of the inflaton which causes the reheating of the Universe in the transition from the inflationary phase to the radiation dominated phase, resulting in the creation of almost all matter constituting the present Universe. Our treatment allows us to follow the full dynamics of the system in a long time regime, and to describe not only the parametric resonance processes with nonlinear restructuring but also to characterize a final turbulent state in the dynamics by which the energy is nonlinearly transferred to all scales of the system with a consequent thermalization of the created matter.     

Nonlinear dynamics of a two-dimensional lattice

The dynamics of the nonlinear excitations in a two-dimensional (2D) φ⁴-diatomic lattice, with nonlinear on-site electron-phonon coupling at the polarizable ion site has been presented, without considering the self consistent phonon approximation. One of the major results obtained from our calculations is in the understanding of continuous structural phase transition, where we have obtained the minimum in soft mode frequency at a soft mode temperatureT _s (>T _c), not at critical temperatureT _c. This occurs due to the anisotropy of such 2D systems.     

First and second order non-equilibrium phase transition and evidence for non-extensive Tsallis statistics in Earth’s magnetosphere

In this paper strong evidence is provided for significant far from equilibrium phase transition processes in the Earth’s magnetosphere as revealed by the nonlinear analysis of in situ observations. These results constitute the solid base for the solution of the durable controversy about the chaotic or non-chaotic character of the magnetospheric dynamics. During the last two decades the concept of low dimensional chaos was supported by theoretical and experimental methods by our group in Thrace and others scientists, as an explicative paradigm of the magnetospheric dynamics including substorm processes. In parallel, the concept of self-organized criticality (SOC) and space-time intermittency was introduced as new and opposing to low dimensional chaos concepts for modeling the magnetospheric dynamics. Novel results concerning the nonlinear analysis of in situ space plasma data (magnetic-electric field, energetic particles and bulk plasma flow time series) obtained by the Geotail spacecraft presented in this paper for the first time reveal the following: (a) Coexistence of SOC and chaos states in the magnetospheric system and global phase transition from one state to the other during substorms. (b) Strong intermittent turbulent character of the magnetospheric system at the SOC or the low dimensional chaos states. (c) Clear indications for non-extensivity and q-Gaussian statistics during periods of low dimensional and chaotic dynamics of the magnetosphere. (d) Low dimensional and nonlinear space plasma dynamics in the day side magnetopause and bow shock dynamics. The dual character of the magnetospheric dynamics including low dimensional chaotic (coherent) and high dimensional turbulent states, as supported in this paper, is in agreement and verifies previous theoretical and experimental studies.     

Investigation of Phase Separation in a Partially Miscible Polymer Blend by Rheology

The phase boundary and phase‐separation dynamics of a binary poly(styrene‐co‐maleic anhydride)/poly(methyl methacrylate) blend have been investigated by rheological measurements and light scattering. The phase diagram was experimentally established by rheology, in which the binodal line was obtained by dynamic temperature ramps and the spinodal temperatures were quantitatively estimated on the basis of the theory developed by Ajji et al. The phase‐separation dynamics from rheological viewpoints have been further investigated on the basis of the obtained phase diagram. Rheological measurements can sensitively detect the rather early stages of phase separation compared with light scattering techniques. It was found that the dynamic storage modulus initially increases over time and subsequently decreases during nucleation and growth; on the other hand, it always decreased over time during spinodal decomposition. Compared with light scattering techniques, rheological measurements were found to be relatively reliable for probing phase‐separation mechanisms.     

Phase reduction approach to synchronisation of nonlinear oscillators

Systems of dynamical elements exhibiting spontaneous rhythms are found in various fields of science and engineering, including physics, chemistry, biology, physiology, and mechanical and electrical engineering. Such dynamical elements are often modelled as nonlinear limit-cycle oscillators. In this article, we briefly review phase reduction theory, which is a simple and powerful method for analysing the synchronisation properties of limit-cycle oscillators exhibiting rhythmic dynamics. Through phase reduction theory, we can systematically simplify the nonlinear multi-dimensional differential equations describing a limit-cycle oscillator to a one-dimensional phase equation, which is much easier to analyse. Classical applications of this theory, i.e. the phase locking of an oscillator to a periodic external forcing and the mutual synchronisation of interacting oscillators, are explained. Further, more recent applications of this theory to the synchronisation of non-interacting oscillators induced by common noise and the dynamics of coupled oscillators on complex networks are discussed. We also comment on some recent advances in phase reduction theory for noise-driven oscillators and rhythmic spatiotemporal patterns.     

Canard轨迹原理

为了精确的求出Canard轨迹的描述方程,提出了一个分段表达的非线性模型,能直接求出一个非线性二阶自治方程的相轨迹方程的解析解,能定量求出Canard轨迹的描述方程和参数条件,可以用两类方程简单描述所有的Canard轨迹. 关键词： 非线性系统 Canard轨迹 弛张振荡     

Dynamics of cubic–quintic nonlinear Schr?dinger equation with different parameters

We study the dynamics of the cubic–quintic nonlinear Schr?dinger equation by the symplectic method. The behaviors of the equation are discussed with harmonically modulated initial conditions, and the contributions from the quintic term are discussed. We observe the elliptic orbit, homoclinic orbit crossing, quasirecurrence, and stochastic motion with different nonlinear parameters in this system. Numerical simulations show that the changing processes of the motion of the system and the trajectories in the phase space are various for different cubic nonlinear parameters with the increase of the quintic nonlinear parameter.     

Phase Properties of Nonlinear Coherent States

Using the Pegg-Barnett fornalism we study the phase probability distributions and the squeezing effects ofmeasured phase operators in the nonlinear coherent states introduced by R.L. de Matos Filho and W. Vogel to describethe center-of mass motion of a trapped ion and the q-coherent states. Moreover, we have obtained the completenessrelation of nonlinear coherent states and proved that the q-Fock state |n>q introduced in many papers is, in fact, theusual Fock state.