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Dynamics of Rod like Particles in Supercooled Liquids -- Probing Dynamic Heterogeneity and Amorphous Order 过冷液体中棒状粒子的动力学——探究动态非均匀性和非晶态秩序
Pub Date : 2020-05-22 DOI: 10.1103/PhysRevApplied.16.034022
Anoop Mutneja, S. Karmakar
Probing dynamic and static correlation in glass-forming supercooled liquids has been a challenge for decades in spite of extensive research. Dynamic correlation which manifests itself as Dynamic Heterogeneity is ubiquitous in a vast variety of systems starting from molecular glass-forming liquids, dense colloidal systems to collections of cells. On the other hand, the mere concept of static correlation in these dense disordered systems remain somewhat elusive and its existence is still actively debated. We propose a novel method to extract both dynamic and static correlations using rod-like particles as probe. This method can be implemented in molecular glass-forming liquids in experiments as well as in other soft matter systems including biologically relevant systems. We also rationalize the observed log-normal like distribution of rotational decorrelation time of elongated probe molecules in reported experimental studies along with a proposal of a novel methodology to extract dynamic and static correlation lengths in experiments.
几十年来,尽管有广泛的研究,但探测玻璃形成过冷液体的动态和静态相关性一直是一个挑战。动态相关性表现为动态异质性,在从分子玻璃形成液体、致密胶体系统到细胞集合的各种系统中普遍存在。另一方面,在这些密集的无序系统中,静态相关的概念仍然有些难以捉摸,它的存在仍然是积极的争论。我们提出了一种新的方法来提取动态和静态的相关性使用棒状粒子作为探针。这种方法可以在实验中的分子玻璃形成液体中实现,也可以在其他软物质系统中实现,包括生物相关系统。我们还对实验研究中观察到的细长探针分子旋转去相关时间的对数正态分布进行了合理化,并提出了一种新的方法来提取实验中的动态和静态相关长度。
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引用次数: 1
A kinetic model for epidemic spread 流行病传播的动力学模型
Pub Date : 2020-05-20 DOI: 10.2140/memocs.2020.8.249
M. Pulvirenti, S. Simonella
We present a Boltzmann equation for mixtures of three species of particles reducing to the Kermack-McKendrick (SIR) equations for the time-evolution of the density of infected agents in an isolated population. The kinetic model is potentially more detailed and might provide information on space mixing of the agents.
我们提出了三种粒子混合物的玻尔兹曼方程,简化为Kermack-McKendrick (SIR)方程,用于隔离种群中感染因子密度的时间演化。动力学模型可能更详细,并可能提供有关介质空间混合的信息。
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引用次数: 12
Scalar Active Mixtures: The Nonreciprocal Cahn-Hilliard Model 标量活性混合:非互反Cahn-Hilliard模型
Pub Date : 2020-05-14 DOI: 10.1103/PHYSREVX.10.041009
Suropriya Saha, J. Agudo-Canalejo, R. Golestanian
Pair interactions between active particles need not follow Newton's third law. In this work we propose a continuum model of pattern formation due to non-reciprocal interaction between multiple species of scalar active matter. The classical Cahn-Hilliard model is minimally modified by supplementing the equilibrium Ginzburg-Landau dynamics with particle number conserving currents which cannot be derived from a free energy, reflecting the microscopic departure from action-reaction symmetry. The strength of the asymmetry in the interaction determines whether the steady state exhibits a macroscopic phase separation or a traveling density wave displaying global polar order. The latter structure, which is equivalent to an active self-propelled smectic phase, coarsens via annihilation of defects, whereas the former structure undergoes Ostwald ripening. The emergence of traveling density waves, which is a clear signature of broken time-reversal symmetry in this active system, is a generic feature of any multi-component mixture with microscopic non-reciprocal interactions.
活跃粒子之间的对相互作用不需要遵循牛顿第三定律。在这项工作中,我们提出了一个连续体模型,由于多种标量活性物质之间的非互反相互作用而形成图案。经典的Cahn-Hilliard模型通过用粒子数守恒电流(不能从自由能推导出来)补充平衡的金兹堡-朗道动力学来进行最小程度的修改,反映了微观上对作用-反应对称性的偏离。相互作用中不对称的强度决定了稳态是呈现宏观相分离还是呈现全局极性有序的行密度波。后一种结构相当于一个主动自推进的近晶相,通过缺陷的湮灭而变粗,而前一种结构则经历奥斯特瓦尔德成熟。行密度波的出现是任何具有微观非互反相互作用的多组分混合物的一般特征,是该有源系统中时间反转对称性破缺的明显标志。
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引用次数: 66
Sustaining a temperature difference 维持温差
Pub Date : 2020-05-13 DOI: 10.21468/SCIPOSTPHYS.9.3.030
M. Polettini, Alberto Garilli
We derive an expression for the minimal rate of entropy that sustains two reservoirs at different temperatures $T_0$ and $T_ell$. The law displays an intuitive $ell^{-1}$ dependency on the relative distance and a characterisic $log^2 (T_ell/T_0)$ dependency on the boundary temperatures. First we give a back-of-envelope argument based on the Fourier Law (FL) of conduction, showing that the least-dissipation profile is exponential. Then we revisit a model of a chain of oscillators, each coupled to a heat reservoir. In the limit of large damping we reobtain the exponential and squared-log behaviors, providing a self-consistent derivation of the FL. For small damping "equipartition frustration" leads to a well-known balistic behaviour, whose incompatibility with the FL posed a long-time challenge.
我们推导出在不同温度下维持两个热源的最小熵率表达式。该定律对相对距离具有直观的$ well ^{-1}$依赖性,对边界温度具有特征的$log^2 (T_ well /T_0)$依赖性。首先,我们给出了一个基于傅立叶定律(FL)的粗略论证,表明最小耗散曲线是指数型的。然后我们重新审视一个振子链的模型,每个振子都耦合到一个热源。在大阻尼的极限下,我们重新获得了指数和平方对数行为,提供了一个自一致的FL推导。对于小阻尼,“均分挫折”导致了众所周知的弹道行为,其与FL的不相容带来了长期的挑战。
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引用次数: 0
Kibble–Zurek Mechanism in a Dissipative Transverse Ising Chain 耗散横向Ising链中的Kibble-Zurek机制
Pub Date : 2020-05-12 DOI: 10.7566/JPSJ.89.104002
Hiroki Oshiyama, N. Shibata, S. Suzuki
We study the Kibble-Zurek mechanism in the transverse Ising chain coupled to a dissipative boson bath, making use of a new numerical method with the infinite time evolving block decimation combined with the discrete-time path integral. We first show the ground-state phase diagram and confirm that a quantum phase transition takes place in the presence of the system-bath coupling. Then we present the time dependence of the energy expectation value of the spin Hamiltonian and the scaling of the kink density with respect to the time period over which the spin Hamiltonian crosses a quantum phase transition. The energy of spins starts to grow from the energy at the ground state of the full system near a quantum phase transition. The kink density decays as a power law with respect to the time period. These results confirm that the Kibble-Zurek mechanism happens. We discuss the exponent for the decay of the kink density in comparison with a theoretical result with the quantum Monte-Carlo simulation. A comparison to an experimental study is also briefly mentioned.
本文利用无限时间演化的块抽取与离散时间路径积分相结合的一种新的数值方法,研究了耗散玻色子槽耦合的横向Ising链中的Kibble-Zurek机制。我们首先展示了基态相图,并证实了在系统浴耦合存在的情况下发生了量子相变。然后,我们给出了自旋哈密顿量的能量期望值的时间依赖性,以及扭结密度相对于自旋哈密顿量穿过量子相变的时间周期的标度。自旋的能量从接近量子相变的整个系统基态的能量开始增长。扭结密度随时间周期呈幂律衰减。这些结果证实了Kibble-Zurek机制的存在。我们讨论了扭结密度衰减的指数,并与量子蒙特卡罗模拟的理论结果进行了比较。并简要介绍了与实验研究的比较。
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引用次数: 8
Analysis of the Hopfield Model with Discrete Coupling 具有离散耦合的Hopfield模型分析
Pub Date : 2020-05-11 DOI: 10.7566/JPSJ.90.094602
Ryuta Sasaki, T. Aonishi
Growing demand for high-speed Ising-computing-specific hardware has prompted a need for determining how the accuracy depends on a hardware implementation with physically limited resources. For instance, in digital hardware such as field-programmable gate arrays, as the number of bits representing the coupling strength is reduced, the density of integrated Ising spins and the speed of computing can be increased while the calculation accuracy becomes lower. To optimize the accuracy-efficiency trade-off, we have to estimate the change in performance of the Ising computing machine depending on the number of bits representing the coupling strength. In this study, we tackle this issue by focusing on the Hopfield model with discrete coupling. The Hopfield model is a canonical Ising computing model. Previous studies have analyzed the effect of a few nonlinear functions (e.g. sign) for mapping the coupling strength on the Hopfield model with statistical mechanics methods, but not the effect of discretization of the coupling strength in detail. Here, we derived the order parameter equations of the Hopfield model with discrete coupling by using the replica method and clarified the relationship between the number of bits representing the coupling strength and the critical memory capacity.
对专用于高速isin计算的硬件日益增长的需求促使人们需要确定精度如何依赖于物理资源有限的硬件实现。例如,在诸如现场可编程门阵列之类的数字硬件中,随着表示耦合强度的比特数的减少,集成伊辛自旋的密度和计算速度可以增加,而计算精度却会降低。为了优化精度和效率之间的权衡,我们必须根据表示耦合强度的比特数来估计Ising计算机器的性能变化。在本研究中,我们通过关注具有离散耦合的Hopfield模型来解决这个问题。Hopfield模型是一个典型的Ising计算模型。以往的研究用统计力学方法分析了几种非线性函数(如符号)对Hopfield模型耦合强度映射的影响,但没有详细分析耦合强度离散化的影响。本文采用复制方法推导了离散耦合Hopfield模型的阶参数方程,阐明了表示耦合强度的位数与临界存储容量之间的关系。
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引用次数: 0
Coarse-grained second-order response theory 粗粒度二阶响应理论
Pub Date : 2020-05-11 DOI: 10.1103/physrevresearch.2.043123
Fenna Muller, U. Basu, Peter Sollich, M. Kruger
While linear response theory, manifested by the fluctuation dissipation theorem, can be applied on any length scale, nonlinear response theory is fundamentally of microscopic nature. We develop an exact theoretical framework for analyzing nonlinear (second order) response of coarse grained observables to time-dependent perturbations, using a path-integral formalism. The resulting expressions involve correlations of the observable with coarse grained path weights. The time symmetric part of these weights depends on paths and perturbation protocol in a complex manner, and, furthermore, the absence of Markovianity prevents slicing of the coarse grained path integral. Despite this, we show that the response function can be expressed in terms of path weights corresponding to a single-step perturbation. This formalism thus leads to an extrapolation scheme, which circumvents the mentioned difficulties, and where measuring linear responses of coarse-grained variables suffices to determine their second order response. We illustrate the validity of the formalism with the examples of an exactly solvable four-state model and the near-critical Ising model.
以波动耗散定理为代表的线性响应理论可以应用于任何长度尺度,而非线性响应理论本质上是微观性质的。我们开发了一个精确的理论框架来分析非线性(二阶)响应粗粒度观测到时间相关的扰动,使用路径积分形式。所得到的表达式涉及到可观察对象与粗粒度路径权重的相关性。这些权重的时间对称部分以复杂的方式依赖于路径和摄动协议,而且,马尔可夫性的缺失阻止了粗粒度路径积分的切片。尽管如此,我们证明了响应函数可以用对应于单步扰动的路径权重来表示。因此,这种形式导致了一种外推方案,它绕过了上述困难,并且测量粗粒度变量的线性响应足以确定它们的二阶响应。我们用一个完全可解的四态模型和近临界的伊辛模型的例子说明了形式主义的有效性。
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引用次数: 2
Apparent superballistic dynamics in one-dimensional random walks with biased detachment 有偏分离的一维随机行走的表观超弹道动力学
Pub Date : 2020-05-08 DOI: 10.1103/PHYSREVRESEARCH.2.033520
C. Korosec, David A. Sivak, N. R. Forde
The mean-squared displacement (MSD) is an averaged quantity widely used to assess anomalous diffusion. In many cases, such as molecular motors with finite processivity, dynamics of the system of interest produce trajectories of varying duration. Here we explore the effects of finite processivity on different measures of the MSD. We do so by investigating a deceptively simple dynamical system: a one-dimensional random walk (with equidistant jump lengths, symmetric move probabilities, and constant step duration) with an origin-directed detachment bias. By tuning the time dependence of the detachment bias, we find through analytical calculations and trajectory simulations that the system can exhibit a broad range of anomalous diffusion, extending beyond conventional diffusion to superdiffusion and even superballistic motion. We analytically determine that protocols with a time-increasing detachment lead to an ensemble-averaged velocity increasing in time, thereby providing the effective acceleration that is required to push the system above the ballistic threshold. MSD analysis of burnt-bridges ratchets similarly reveals superballistic behavior. Because superdiffusive MSDs are often used to infer biased, motor-like dynamics, these findings provide a cautionary tale for dynamical interpretation.
均方位移(MSD)是一个广泛用于评估异常扩散的平均量。在许多情况下,例如具有有限处理能力的分子马达,感兴趣系统的动力学产生不同持续时间的轨迹。在这里,我们探讨有限加工能力对MSD的不同措施的影响。我们通过研究一个看似简单的动力系统来做到这一点:一个一维随机行走(具有等距离跳跃长度,对称移动概率和恒定的步长),具有指向原点的分离偏差。通过调整分离偏差的时间依赖性,我们通过分析计算和轨迹模拟发现,该系统可以表现出大范围的异常扩散,从常规扩散扩展到超扩散甚至超弹道运动。我们通过分析确定,随时间增加的分离方案会导致整体平均速度随时间增加,从而提供将系统推到弹道阈值以上所需的有效加速度。MSD对烧桥棘轮的分析同样揭示了超弹道行为。由于超扩散msd经常被用来推断有偏差的运动动力学,这些发现为动力学解释提供了一个警示故事。
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引用次数: 8
Quantum quench dynamics in the transverse-field Ising model: A numerical expansion in linked rectangular clusters 横向场Ising模型中的量子猝灭动力学:连接矩形团簇中的数值展开
Pub Date : 2020-05-06 DOI: 10.21468/SCIPOSTPHYS.9.3.031
Jonas Richter, Tjark Heitmann, R. Steinigeweg
We study quantum quenches in the transverse-field Ising model defined on different lattice geometries such as chains, two- and three-leg ladders, and two-dimensional square lattices. Starting from fully polarized initial states, we consider the dynamics of the transverse and the longitudinal magnetization for quenches to weak, strong, and critical values of the transverse field. To this end, we rely on an efficient combination of numerical linked cluster expansions (NLCEs) and a forward propagation of pure states in real time. As a main result, we demonstrate that NLCEs comprising solely rectangular clusters provide a promising approach to study the real-time dynamics of two-dimensional quantum many-body systems directly in the thermodynamic limit. By comparing to existing data from the literature, we unveil that NLCEs yield converged results on time scales which are competitive to other state-of-the-art numerical methods.
我们研究了定义在不同晶格几何上的横场Ising模型中的量子猝灭,如链、两腿梯和三腿梯以及二维方形晶格。从完全极化的初始状态出发,我们考虑了横向和纵向磁场在弱、强、临界值淬火时的动态变化。为此,我们依赖于数值链接簇扩展(NLCEs)和纯状态实时前向传播的有效组合。作为主要结果,我们证明了仅由矩形团簇组成的NLCEs为直接在热力学极限下研究二维量子多体系统的实时动力学提供了一种很有前途的方法。通过与文献中的现有数据进行比较,我们揭示了NLCEs在时间尺度上的收敛结果与其他最先进的数值方法相比具有竞争力。
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引用次数: 8
Thermodynamically consistent gradient elasticity with an internal variable 具有内部变量的热力学一致梯度弹性
Pub Date : 2020-05-01 DOI: 10.2298/tam200204006v
P. V'an
The role of thermodynamics in continuum mechanics and the derivation of the proper constitutive relations is a discussed subject of Rational Mechanics. The classical literature did not use the accumulated knowledge of thermostatics and was very critical with the heuristic methods of irreversible thermodynamics. In this paper, a small strain gradient elasticity theory is constructed with memory effects and dissipation. The method is nonequilibrium thermodynamics with internal variables; therefore, the constitutive relations are compatible with thermodynamics by construction. Thermostatic Gibbs relation is introduced for elastic bodies with a single tensorial internal variable. The thermodynamic potentials are first-order weakly nonlocal, and the entropy production is calculated. Then the constitutive functions and the evolution equation of the internal variable is constructed. The second law analysis has shown a contribution of gradient terms to the stress, also without dissipation.
热力学在连续介质力学中的作用和适当的本构关系的推导是理性力学的一个讨论课题。经典文献没有运用积累的恒温学知识,对不可逆热力学的启发式方法持批判态度。本文建立了具有记忆效应和耗散效应的小应变梯度弹性理论。该方法是带内变量的非平衡热力学;因此,本构关系在构造上与热力学相容。引入了具有单张量内变量的弹性体的恒温吉布斯关系。热力学势是一阶弱非定域的,并计算了熵产。然后构造了本构函数和内变量的演化方程。第二定律分析表明梯度项对应力有贡献,但也没有耗散。
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引用次数: 3
期刊
arXiv: Statistical Mechanics
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