Equilibrium and non-equilibrium fluctuations in a glass-forming liquid

Glass-forming liquids display strong fluctuations -- dynamical heterogeneities -- near their glass transition. By numerically simulating a binary Weeks-Chandler-Andersen liquid and varying both temperature and timescale, we investigate the probability distributions of two kinds of local fluctuations in the non-equilibrium (aging) regime and in the equilibrium regime; and find them to be very similar in the two regimes and across temperatures. We also observe that, when appropriately rescaled, the integrated dynamic susceptibility is very weakly dependent on temperature and very similar in both regimes.Comment: v1: 5 pages, 4 figures v2: 5 pages, 4 figures. Now includes results at three temperatures, two of them above T_{MCT} and one below T_{MCT}; and more extensive discussion of connections to experiment

Universal Scaling in the Aging of the Strong Glass Former SiO2_2

We show that the aging dynamics of a strong glass former displays a strikingly simple scaling behavior, connecting the average dynamics with its fluctuations, namely the dynamical heterogeneities. We perform molecular dynamics simulations of SiO$_2$ with BKS interactions, quenching the system from high to low temperature, and study the evolution of the system as a function of the waiting time $t_{\rm w}$ measured from the instant of the quench. We find that both the aging behavior of the dynamic susceptibility $\chi_4$ and the aging behavior of the probability distribution $P(f_{{\rm s},{\mathbf r}})$ of the local incoherent intermediate scattering function $f_{{\rm s},{\mathbf r}}$ can be described by simple scaling forms in terms of the global incoherent intermediate scattering function $C$. The scaling forms are the same that have been found to describe the aging of several fragile glass formers and that, in the case of $P(f_{{\rm s},{\mathbf r}})$, have been also predicted theoretically. A thorough study of the length scales involved highlights the importance of intermediate length scales. We also analyze directly the scaling dependence on particle type and on wavevector $q$, and find that both the average and the fluctuations of the slow aging dynamics are controlled by a unique aging clock, which is not only independent of the wavevector $q$, but is the same for O and Si atoms.Comment: 13 pages, 21 figures (postscript

Mapping dynamical heterogeneity in structural glasses to correlated fluctuations of the time variables

Dynamical heterogeneities -- strong fluctuations near the glass transition -- are believed to be crucial to explain much of the glass transition phenomenology. One possible hypothesis for their origin is that they emerge from soft (Goldstone) modes associated with a broken continuous symmetry under time reparametrizations. To test this hypothesis, we use numerical simulation data from four glass-forming models to construct coarse grained observables that probe the dynamical heterogeneity, and decompose the fluctuations of these observables into two transverse components associated with the postulated time-fluctuation soft modes and a longitudinal component unrelated to them. We find that as temperature is lowered and timescales are increased, the time reparametrization fluctuations become increasingly dominant, and that their correlation volumes grow together with the correlation volumes of the dynamical heterogeneities, while the correlation volumes for longitudinal fluctuations remain small.Comment: v4: Detailed analysis of transverse and longitudinal parts. One figure removed, two added. v3: Explicit decomposition into transverse and longitudinal parts, discussion of correlation volumes. One more figure v2: Modified introduction and forma

Anteproyecto de ley sobre el fideicomiso

Pelegrín Horacio Castillo Semán: Abogado y político dominicano nacido en San Francisco de Macorís y egresado de la Universidad Nacional Pedro Henríquez Ureña (UNPHU), donde, aparte de derecho, también estudió ciencias políticas. Realizó un diplomado en relaciones económicas internacionales e integración en el Instituto Tecnológico de Santo Domingo (INTEC) y un programa de posgrado en economía internacional y comercio exterior coordinado por la Universidad de Barcelona e INTEC. Asimismo, completó el Programa para Directivos en el Diseño y Gestión de Políticas, Programas y Proyectos Sociales, organizado por INDES-BID-INTEC. Fue diputado de la república por el partido Fuerza Nacional Progresista. Ha sido miembro de la Comisión Economía y Deuda Externa del Parlamento Latinoamericano y miembro de las comisiones interparlamentarias dominico-israelí, dominico-china, dominico-francesa y dominico-argentina. También se ha desempeñado como ministro de energía y minas. Como catedrático universitario que ha trabajado en la Universidad Iberoamericana (UNIBE), la UNPHU, la Pontificia Universidad Católica Madre y Maestra (PUCMM) y el Colegio Santísima Trinidad, ha impartido las siguientes asignaturas: Historia de las Ideas Políticas, Filosofía del Derecho, Derecho Constitucional, Derecho Administrativo, Economía Política y Relaciones Dominico-Haitianas.En este número 12 de la revista Coloquios Jurídicos se presentó un anteproyecto de ley de fideicomiso. La pieza establece la definición de la referida institución jurídica, las normas para su constitución, sus formatos para los casos en que tenga efecto luego de la muerte del fideicomitente o si se otorgan poderes discrecionales al fiduciario, así como el reconocimiento de la vigencia de las prohibiciones establecidas en el artículo 896 del Código Civil. Establece además, entre otros muchos puntos necesarios para su correcta estructuración, quiénes pueden ser los beneficiarios o fideicomisarios, a quiénes se les otorga capacidad para ser fiduciarios, las condiciones en que estos deberán ejercer sus facultades y prerrogativas y los casos de nulidad

Slow and Long-ranged Dynamical Heterogeneities in Dissipative Fluids

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 $N_c\propto R_G^{d_f}$, 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., $\phi\to\phi_c$. 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, $0.6\leq\phi\leq 0.805$, and to become increasingly long-ranged as $\phi\to\phi_c$. 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 $\xi\propto (\phi-\phi_c)^{-\gamma_{\xi}}$. We check the robustness of our results with respect to our definition of mobility. The divergences and the scaling for $\phi\to\phi_c$ suggest a non-equilibrium glass transition which seems qualitatively independent of the coefficient of restitution.Comment: 14 pages, 25 figure