Dynamic glass transition: bridging the gap between mode-coupling theory and the replica approach

We clarify the relation between the ergodicity breaking transition predicted by mode-coupling theory and the so-called dynamic transition predicted by the static replica approach. Following Franz and Parisi [Phys. Rev. Lett. 79, 2486 (1997)], we consider a system of particles in a metastable state characterized by non-trivial correlations with a quenched configuration. We show that the assumption that in a metastable state particle currents vanish leads to an expression for the replica off-diagonal direct correlation function in terms of a replica off-diagonal static four-point correlation function. A factorization approximation for this function results in an approximate closure for the replica off-diagonal direct correlation function. The replica off-diagonal Ornstein-Zernicke equation combined with this closure coincides with the equation for the non-ergodicity parameter derived using the mode-coupling theory.Comment: revised version; to be published in EP

Turbulent-like fluctuations in quasistatic flow of granular media

We analyze particle velocity fluctuations in a simulated granular system subjected to homogeneous quasistatic shearing. We show that these fluctuations share the following scaling characteristics of fluid turbulence in spite of their different physical origins: 1) Scale-dependent probability distribution with non-Guassian broadening at small time scales; 2) Power-law spectrum, reflecting long-range correlations and the self-affine nature of the fluctuations; 3) Superdiffusion with respect to the mean background flow

Die kernbetekenis van die mens se etiese bestaanswyse

Ethicists differ widely in their views on the field of investigation of ethics as a science. These differences underpinning various theories regarding the true nature of ethics, seriously inhibit collaboration between adherents of different stances in this respect. Consequently meaningful progress in the development of ethical sciences can largely be attributed to divergent views on the essence (the meaning kernel or modal nucleus) of the ethical mode of human existence. In this article an attempt is made at identifying the true meaning nucleus of the ethical aspect of reality. To achieve this, the meaning of the concept meaning nucleus as well as the characteristics of meaning nuclei as such and the way in which they should be formulated, are investigated. Finally some prevailing ideas on the nature of the ethical mode of human existence are judged against the findings of this investigation

Op weg na ’n opvoedkundige etiek: problematiek rondom die terme etiek. sede en moraal

One of the initial problems which not only ethics as an emerging science has to cope with, but also special sciences like education which have to employ ethical perspectives, is the lack of a unanimous scientific interpretation of the concepts ethics, mores and morals. A direct consequence of this state of affairs is that ethicists differ widely in respect of their views regarding the field of investigation of ethics as a science. What it really amounts to is that different ‘ethicists' are largely operating in dissimilar scientific fields. It stands to reason (hat it is hard to conduct a meaningful scientific discourse about ethical matters in this way and that the results of a great deal of research in ethics will be extremely confusing - not only to ethicists, but, amongst others, to educationists, parents, students and pupils as well, especially with regard to present day problems in respect of sexual relationships, drug abuse, protest art, political turmoil in educational (and other) matters, etc. In this article an account is given of some currcnt interpretations of the concepts ethics, mores and morals and an attempt is made at indicating possibilities which can be explored in the quest for solutions to this dilemma

Strain versus stress in a model granular material: a Devil's staircase

The series of equilibrium states reached by disordered packings of rigid, frictionless discs in two dimensions, under gradually varying stress, are studied by numerical simulations. Statistical properties of trajectories in configuration space are found to be independent of specific assumptions ruling granular dynamics, and determined by geometry only. A monotonic increase in some macroscopic loading parameter causes a discrete sequence of rearrangements. For a biaxial compression, we show that, due to the statistical importance of such events of large magnitudes, the dependence of the resulting strain on stress direction is a Levy flight in the thermodynamic limit.Comment: REVTeX, 4 pages, 5 included PostScript figures. New version altered throughout text, very close to published pape

Mobile particles in an immobile environment: Molecular Dynamics simulation of a binary Yukawa mixture

Molecular dynamics computer simulations are used to investigate thedynamics of a binary mixture of charged (Yukawa) particles with a size-ratio of 1:5. We find that the system undergoes a phase transition where the large particles crystallize while the small particles remain in a fluid-like (delocalized) phase. Upon decreasing temperature below the transition, the small particles become increasingly localized on intermediate time scales. This is reflected in the incoherent intermediate scattering functions by the appearance of a plateau with a growing height. At long times, the small particles show a diffusive hopping motion. We find that these transport properties are related to structural correlations and the single-particle potential energy distribution of the small particles.Comment: 7 pages, 5 figure

Equilibrium onions?

We demonstrate the possibility of a stable equilibrium multi-lamellar ("onion") phase in pure lamellar systems (no excess solvent) due to a sufficiently negative Gaussian curvature modulus. The onion phase is stabilized by non-linear elastic moduli coupled to a polydisperse size distribution (Apollonian packing) to allow space-filling without appreciable elastic distortion. This model is compared to experiments on copolymer-decorated lamellar surfactant systems, with reasonable qualitative agreement

Force distribution in a scalar model for non-cohesive granular material

We study a scalar lattice model for inter-grain forces in static, non-cohesive, granular materials, obtaining two primary results. (i) The applied stress as a function of overall strain shows a power law dependence with a nontrivial exponent, which moreover varies with system geometry. (ii) Probability distributions for forces on individual grains appear Gaussian at all stages of compression, showing no evidence of exponential tails. With regard to both results, we identify correlations responsible for deviations from previously suggested theories.Comment: 16 pages, 9 figures, Submitted to PR