اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدSlow and Long-ranged Dynamical Heterogeneities in Dissipative Fluids
89
0
0.0
(
0
)
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
A two-dimensional bidisperse granular fluid is shown to exhibit pronounced long-ranged dynamical heterogeneities as dynamical arrest is approached. Here we focus on the most direct approach to study these heterogeneities: we identify clusters of slow particles and determine their size, $N_c$, and their radius of gyration, $R_G$. We show that $N_cpropto R_G^{d_f}$, providing direct evidence that the most immobile particles arrange in fractal objects with a fractal dimension, $d_f$, that is observed to increase with packing fraction $phi$. The cluster size distribution obeys scaling, approaching an algebraic decay in the limit of structural arrest, i.e., $phitophi_c$. Alternatively, dynamical heterogeneities are analyzed via the four-point structure factor $S_4(q,t)$ and the dynamical susceptibility $chi_4(t)$. $S_4(q,t)$ is shown to obey scaling in the full range of packing fractions, $0.6leqphileq 0.805$, and to become increasingly long-ranged as $phitophi_c$. Finite size scaling of $chi_4(t)$ provides a consistency check for the previously analyzed divergences of $chi_4(t)propto (phi-phi_c)^{-gamma_{chi}}$ and the correlation length $xipropto (phi-phi_c)^{-gamma_{xi}}$. We check the robustness of our results with respect to our definition of mobility. The divergences and the scaling for $phitophi_c$ suggest a non-equilibrium glass transition which seems qualitatively independent of the coefficient of restitution.
قيم البحث
اقرأ أيضاً
We study numerically spatio-temporal fluctuations during the out-of-equilibrium relaxation of the three-dimensional Edwards-Anderson model. We focus on two issues. (1) The evolution of a growing dynamical length scale in the glassy phase of the model
, and the consequent collapse of the distribution of local coarse-grained correlations measured at different pairs of times on a single function using {it two} scaling parameters, the value of the global correlation at the measuring times and the ratio of the coarse graining length to the dynamical length scale (in the thermodynamic limit). (2) The `triangular relation between coarse-grained local correlations at three pairs of times taken from the ordered instants $t_3 leq t_2 leq t_1$. Property (1) is consistent with the conjecture that the development of time-reparametrization invariance asymptotically is responsible for the main dynamic fluctuations in aging glassy systems as well as with other mechanisms proposed in the literature. Property (2), we stress, is a much stronger test of the relevance of the time-reparametrization invariance scenario.
We present an extensive numerical study of dynamical heterogeneities and their influence on diffusion in an athermal mesoscopic model for actively deformed amorphous solids. At low strain rates the stress dynamics are governed by cooperative regions
of plastic events. On the basis of scaling arguments as well as an extensive numerical study of an athermal elasto-plastic model, we show that there is a direct link between the self-diffusion coefficient and the size of cooperative regions at low strain rates. Both depend strongly on rate and on system size. A measure of the mean square displacement of passive tracers in deformed amorphous media thus gives information about the microscopic rheology, such as the geometry of the cooperative regions and their scaling with strain rate and system size.
The question of whether DNA conducts electric charges is intriguing to physicists and biologists alike. The suggestion that electron transfer/transport in DNA might be biologically important has triggered a series of experimental and theoretical inve
stigations. Here, we review recent theoretical progress by concentrating on quantum-chemical, molecular dynamics-based approaches to short DNA strands and physics-motivated tight-binding transport studies of long or even complete DNA sequences. In both cases, we observe small, but significant differences between specific DNA sequences such as periodic repetitions and aperiodic sequences of AT bases, lambda-DNA, centromeric DNA, promoter sequences as well as random-ATGC DNA.
We present numerical simulations of a model of cellulose consisting of long stiff rods, representing cellulose microfibrils, connected by stretchable crosslinks, representing xyloglucan molecules, hydrogen bonded to the microfibrils. Within a broad r
ange of temperature the competing interactions in the resulting network give rise to a slow glassy dynamics. In particular, the structural relaxation described by orientational correlation functions shows a logarithmic time dependence. The glassy dynamics is found to be due to the frustration introduced by the network of xyloglucan molecules. Weakening of interactions between rod and xyloglucan molecules results in a more marked reorientation of cellulose microfibrils, suggesting a possible mechanism to modify the dynamics of the plant cell wall.
In this topical review we discuss the nature of the low-temperature phase in both infinite-ranged and short-ranged spin glasses. We analyze the meaning of pure states in spin glasses, and distinguish between physical, or ``observable, states and (pro
bably) unphysical, ``invisible states. We review replica symmetry breaking, and describe what it would mean in short-ranged spin glasses. We introduce the notion of thermodynamic chaos, which leads to the metastate construct. We apply these tools to short-ranged spin glasses, and conclude that replica symmetry breaking, in any form, cannot describe the low-temperature spin glass phase in any finite dimension. We then discuss the remaining possible scenarios that_could_ describe the low-temperature phase, and the differences they exhibit in some of their physical properties -- in particular, the interfaces that separate them. We also present rigorous results on metastable states and discuss their connection to thermodynamic states. Finally, we discuss some of the differences between the statistical mechanics of homogeneous systems and those with quenched disorder and frustration.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
