【作者】 陈江星；

【导师】 李有泉； 张宏；

【作者基本信息】 浙江大学 ， 凝聚态物理， 2006， 博士

【摘要】 本论文主要研究了受外电场作用下螺旋波和胶体动力学性质。第一章概述性地介绍了在可激发系统和胶体系统的背景、斑图结构和相性质；第二章回顾了受外电场控制下螺旋波和胶体斑图结构、相性质的研究进展；从第三章至第七章,报告一些我们主要的研究工作：第三章研究了可激发介质当中螺旋波在偏振电场下的漂移性质；第四章研究了通过交变电场控制螺旋波的破碎；第五章研究了偏振电场下螺旋波与螺旋波的相同步效应；第六章研究了胶体在外电场驱动下的脱钉性质；第七章得出了基于外电场驱动力和无序强度的动力学相图；第八章研究了温度对胶体斑图结构的影响。螺旋波的研究在物理,化学,生物学等等自然科学当中引起了广泛的兴趣。特别由于螺旋波在心血管疾病,譬如心动过速和心颤,当中扮演了至关重要的角色。因此,怎样去消除和控制螺旋波有非常重要的实际价值。物理学上对螺旋波和湍流态的研究将极大的帮助心脏医学上得到关于预防和控制心率失常的重要方法和信息。胶体的研究一直是软凝聚态领域最受关注的课题之一,因为它提供了非常理想的模型去研究材料,物理,化学当中的许多问题。特别的,在外电场作用下胶体形成奇妙的斑图结构、相性质吸引了很多研究。我们研究了无序衬底上二维胶体在外场驱动下动力学性质。考虑到螺旋波和旋转电场都具有旋转对称性,我们首次研究了可激发介质当中螺旋波在旋转偏振电场下的漂移。第三章数值模拟结果显示：当电场的频率等于螺旋波频率两倍的时候,产生共振漂移。通过改变偏振模式,螺旋波漂移速度、方向能够被电场所调制。我们发现了一些非常有趣的现象。当电场与螺旋波的旋转方向一致而且是圆偏振的时候,螺旋波漂移速度达到最大。当电场与螺旋波的旋转方向相反且是圆偏振情况下,螺旋波被电场锁住,不能产生漂移。在相同偏振电场模式下,顺、逆时针旋转螺旋波产生的漂移角度之和等于kπ+π／2.基于弱形变近似下的解析分析很好的证实了数值模拟结果。因为一个实际的偏振电场在具体的实验当中(譬如BZ反应)容易实现,我们相信结果能在实验中得到证实。除了漂移,我们希望偏振电场的引起的其他效应,譬如图灵斑图等,能够在将来被研究。我们第一次发现了交变电场对螺旋波的一种新效应,并且应用这种新效应来控制螺旋波的破碎。生理实验表明,螺旋波的存在导致心动过速,演化成湍流态对应心颤的发生。因此,怎样控制螺旋波,使之不发生破碎引起了科学研究者很多的关注。然而到目前为止,控制的方法还很少。研究发展有效的具有实际意义的方法至关重要。电场对螺旋波的影响研究的比较多。一般来说,交流电场导致两个效应：螺旋波漂移和破碎。我们的研究表明,当外加交变电场的强度和频率恰当地时候,就能达到阻止螺旋波破碎的目的。这种方法的内在机理是因为交互电场有效的调制了螺旋波在低激发性时发生的漫游行为,导致多普勒效应被大大减弱。我们发现,圆偏振电场与螺旋波产生了相同步效应,成功的消除了二级霍普夫分岔。二级霍普夫分岔导致的螺旋波漫游行为,是系统失稳的主要原因。因此,消除二级霍普夫分岔对于稳定螺旋波具有十分重要的意义。我们给出了螺旋波激发性和圆偏振电场振幅的控制相图。考察偏振模式的影响得出：对称性更高的旋转偏振电场导致更高的临界破碎值。当电场旋转偏振方向同螺旋波相反的时候,螺旋波破碎后改变旋转方向重新出现稳定螺旋波。我们研究了受外电场驱动下了胶体的脱钉性质。首先就衬底上无序钉杂对动力学性质影响做了研究。当提高无序钉杂强度的时候,胶体系统发生了从弹性向塑性脱钉的转变,伴随着临界脱钉力的突然增大。在这个过程当中,系统从一个有序态转变到无序态。在弹性脱钉区域,在速度-驱动力微分曲线上没有发现峰值效应,而且胶体粒子横向运动被禁止。速度和驱动力呈现关联,指数大致等于1.0.在塑性脱钉区,速度-驱动力微分曲线在临界脱钉区域上发现峰值效应,并且产生历史关联,发生了横向扩散。胶体系统内部带电粒子间相互作用对胶体动力学影响的研究。我们发现当增大胶体粒子间相互作用力的时候,同样能发生从无序到有序,塑性到弹性脱钉的转变。这有可能在实验上实现带电强相互作用下胶体结晶化。上述转变以及一系列的动力学性质可以归结与机理：作用在胶体上的多个力相互竞争,当晶格软化和破裂后,单个胶体粒子调整到能量最低状态与位置,导致了有趣的动力学现象。我们研究得到了关于钉杂强度和驱动力的动力学相图。当钉杂力比较弱的时候,胶体系统形成有序晶格。模拟发现此时在驱动力作用下,胶体脱钉直接进入运动布洛赫玻璃相。当钉杂力提高到一定程度,伴随着弹性塑性脱钉的转变,胶体脱钉后先进入塑性流动区,然后随着驱动力提高进入运动布洛赫玻璃相。随着钉杂力的进一步提高,胶体在更高的外场下出现近晶相。因此在强钉杂下,随着驱动力的提高,依次出现蠕动无序相,塑性流动相,近晶相,运动布洛赫玻璃相。通过降低温度,我们发现了从流动液体相到运动近晶相的动力学相变。在这个相变上,动力学临界驱动力出现峰值效应,伴随着速度-驱动力曲线出现明显得交叠。胶体在高驱动力下的动力学性质研究较少,我们首次研究了在胶体高速运动区域动力学性质随温度的影响。更多还原

【Abstract】 In this thesis, we investigated spiral pattern and colloid dynamics under the influence of external electric field. There are seven chapters including a general introduction in chapter 1; a review of progress in chapter 2; From chapter 3 to 7, we report our main results:the investigation of drift behavior induced by polarized electric field in chapter 3; studies on controlling spiral breakup by ac electric field in chapter 4; Elimination of second Hopf Bifurcation by phase synchronization induced by polarized electric field in chapter 5; simulations of depinning properties in colloid systems in chapter 6; presentation of phase diagram depending on driving force and strength of pins in Chapter 7; investigation of dynamical phase transition induced by temperature in chapter 8.The topic of spiral waves has attracted wide interests in physics, chemistry, biology and other fields of natural science. In particular, they play an essential role in heart diseases such as arrhythmia and fibrillation. Thus, how to eliminate and control spiral waves is important for practical applications. Studies on spiral waves and turbulence in physics will greatly contribute to the development of cardiology in preventing and controlling the cardiac arrhythmias and fibrillation.There has been considerable interest in colloidal crystals during the past two decades, since they provide ideal model systems for studies of various problems in material science, physical chemistry, and condensed matter physics. Especially, it shows a rich variety of patterns and phases under the influence of electric field. Thus, it attracts widely attention. We studied the dynamics of two-dimensional colloids system on a disordered substrate using Langevin simulation.In the light that both the polarised electric field and the spiral waves possess rotation symmetry, we investigated the drift behavior of spiral waves under the influence of a polarized electric field for the first time. Numerical simulations show that the drift velocity of spiral tip can be controlled by changing the polarization-mode of the polarized electric field and some interesting drift phenomena are observed. When the electric field is circularly polarized and its rotation follows that of the spiral, the drift speed of spiral tip reaches its maximal value. On the contrary, opposite rotation between spiral and electric field locks the drift of spiral tip. The drift direction can also be tuned by changing the phase difference of the polarized electric field。The sum of drift angle of two opposite rotating spiral waves at fixed phase differences is equal to kπ+π/2. Analytical results based on the weak deformation approximation are consistent with the numerical results. Since a polarized electric field can be easily applied to practical systems, such as BZ reaction, we expect that our theoretical results will be observed in experiments. Besides the drift of spiral waves, we hope that other effects of the polarized electric field on spiral waves, Turing patterns, etc., will be studied in the future.A new effect induced by ac electric field on spiral is detected for the first time. We apply it as a method to control spiral breakup. The controlling of spiral wave breakup has attracted considerable attention. However, the controlling approach to prevent spiral wave breakup is still poor and open. It is necessary to develop some efficient and practical control schemes. Generally, the influence of electric field is studied widely. Ac field can induce two effects on spiral wave:drift and breakup (far deformation). With suitable amplitude and frequency of the ac electric field, spiral breakup can efficiently be suppressed. The underling mechanism is studied and presented:it is due to the efficient modulation of spiral meandering that prevent spiral breakup. We expect that our theoretical results will be observed in experiments.The phase synchronization between circular polarised electric and spiral eliminates the second Hopf bifurcation. We find the spiral is efficient modulated and become zero phase synchronization with the superimposed circular polarized electric field. The critical value of breakup is increased due to the vanishing of second Hopf bifurcation and tempering of meandering behavior. It is the rotating symmetry of the spiral that favoring the circular polarized electric field and leads to the striking behavior. Varying polarized modes shows that more ideal symmetry lead to higher critical value of breakup. Opposite rotation between spiral and electric field induces the spiral breakup and recover to rigid spiral again.We investigated depinning dynamics of 2D colloid system driven by external field in detail. At First, we studied the role of disorder on substrate. With increasing strength of disorder, we found a sharp crossover from elastic to plastic depinning associated with the order-disorder state transition and substantial increase of the depinning force. In the elastic regime, no peaks are found in the differential curves of the velocity-force dependence (VFD) and the transverse motion is forbidden. In addition, the scaling relationship between velocity and force is found to be valid with exponent about 1.0. In inhomogeneous depinning regimes, history dependence of depinning process is found. Peaks in the differential curves of VFD and transverse diffusion occur above depinning.We studied the influence of colloid-colloid interaction on depinning behavior. Through tuning the interparticle potential, we also can observe the disorder-order transition. Thus, it is possible to crystallize colloid system by strengthen interaction of colloid particles in experiments. The underlying mechanism of dynamics properties mentioned above is proposed:it is the competition of several types of force on colloid system that leads to the softness and fracture of colloid lattice which adjusts individual colloid particles to the lowest energy positions, inducing a series of interesting phenomena.We proposed the phase diagram depending on pinning strength and driving force. For weak disorder strength, the colloid systems form an ordered state and depin into moving Bragg glass phase by increasing driving force. Increasing the strength of pinning, a transition to a semtic flow phase occurs where longitudinal order is lost while transverse order remains. Four dynamic phases are found in strong pinning regime upon increasing applied driving force:creeping disordered, plastic flow, smectic flow, and moving Bragg glass phase.We found a dynamical phase transition from the moving liquid to the moving smectic at high drivingforces by decreasing the temperature. The dynamical properties in high driving force region are still less known. Thus, we considered influence of the temperature on the dynamical behavior of 2D colloids at high velocity for the first time. Across the observed dynamical transition, peak effect occurs in the dynamical critical driving force, accompanied by a clear crossing of velocity-force dependence curves.更多还原