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Register a new userAging and scaling laws in $beta$-hydroquinone-clathrate
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Added by
Maikel Rheinstaedter
Publication date
2003
fields
Physics
and research's language is
English
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The dielectric permittivity of the orientational glass methanol(x=0.73)-$beta$-hydroquinone-clathrate has been studied as function of temperature and waiting time using different temperature-time-protocols. We study aging, rejuvenation and memory effects in the glassy phase and discuss similarities and differences to aging in spin-glasses. We argue that the diluted methanol-clathrate, although conceptually close to its magnetic pendants, takes an intermediate character between a true spin-glass and a pure random field system.
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Methanol-$beta$-hydroquinone-clathrate has been established as a model system for dielectric ordering and fluctuations and is conceptually close to magnetic spin systems. In X-ray and neutron diffraction experiments, we investigated the ordered structure, the one-dimensional (1D) and the three-dimensional (3D) critical scattering in the paraelectric phase, and the temperature dependence of the lattice constants. Our results can be explained by microscopic models of the methanol pseudospin in the hydroquinone cage network, in consistency with previous dielectric investigations.
Impact induced attrition processes are, beyond being essential models of industrial ore processing, broadly regarded as the key to decipher the provenance of sedimentary particles. A detailed understanding of single impact phenomena of solid bodies has been obtained in physics and engineering, however, the description of gradual mass reduction and shape evolution in impact sequences relies on approximate mathematical models of mean field type, formulated as curvature-driven partial differential equations. Here we establish the first link between microscopic, particle-based material models and the mean field theory for these processes. Based on realistic computer simulations of particle-wall collision sequences, we first identify the well-known damage and fragmentation energy phases, then we show that the former is split into the abrasion phase with infinite sample lifetime, analogous to Sternbergs Law, at finite asymptotic mass and the cleavage phase with finite sample lifetime, decreasing as a power law of the impact velocity, analogous to Basquins Law. We demonstrate that only in the abrasion phase does shape evolution emerging in microscopic material models reproduce with startling accuracy the spatio-temporal patterns predicted by macroscopic mean field approaches. Our results substantially extend the phase diagram of impact phenomena and set the boundaries of the applicability of geometric mean field theories for geological shape evolution. Additionally, the scaling laws obtained can be exploited for quantitative predictions of evolution histories.
We derive exact expressions for a number of aging functions that are scaling limits of non-equilibrium correlations, R(tw,tw+t) as tw --> infinity with t/tw --> theta, in the 1D homogenous q-state Potts model for all q with T=0 dynamics following a quench from infinite temperature. One such quantity is (the two-point, two-time correlation function) <sigma(0,tw) sigma(n,tw+t)> when n/sqrt(tw) --> z. Exact, closed-form expressions are also obtained when one or more interludes of infinite temperature dynamics occur. Our derivations express the scaling limit via coalescing Brownian paths and a ``Brownian space-time spanning tree, which also yields other aging functions, such as the persistence probability of no spin flip at 0 between tw and tw+t.
Slow relaxation and aging of the conductance are experimental features of a range of materials, which are collectively known as electron glasses. We report dynamic Monte Carlo simulations of the standard electron glass lattice model. In a non-equilibrium state, the electrons will often form a Fermi distribution with an effective electron temperature higher than the phonon bath temperature. We study the effective temperature as a function of time in three different situations: relaxation after a quench from an initial random state, during driving by an external electric field and during relaxation after such driving. We observe logarithmic relaxation of the effective temperature after a quench from a random initial state as well as after driving the system for some time $t_w$ with a strong electric field. For not too strong electric field and not too long $t_w$ we observe that data for the effective temperature at different waiting times collapse when plotted as functions of $t/t_w$ -- the so-called simple aging. During the driving period we study how the effective temperature is established, separating the contributions from the sites involved in jumps from those that were not involved. It is found that the heating mainly affects the sites involved in jumps, but at strong driving, also the remaining sites are heated.
In this letter we announce rigorous results on the phenomenon of aging in the Glauber dynamics of the random energy model and their relation to Bouchauds REM-like trap model. We show that, below the critical temperature, if we consider a time-scale that diverges with the system size in such a way that equilibrium is almost, but not quite reached on that scale, a suitably defined autocorrelation function has the same asymptotic behaviour than its analog in the trap model.
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