298 research outputs found
Note: Scale-free center-of-mass displacement correlations in polymer films without topological constraints and momentum conservation
We present here computational work on the center-of-mass displacements in
thin polymer films of finite width without topological constraints and without
momentum conservation obtained using a well-known lattice Monte Carlo algorithm
with chain lengths ranging up to N=8192. Computing directly the center-of-mass
displacement correlation function C_N(t) allows to make manifest the existence
of scale-free colored forces acting on a reference chain. As suggested by the
scaling arguments put forward in a recent work on three-dimensional melts, we
obtain a negative algebraic decay C_N(t) \sim -1/(Nt) for times t << T_N with
T_N being the chain relaxation time. This implies a logarithmic correction to
the related center-of-mass mean square-displacement h_N(t) as has been checked
directly
The role of individual differences in understanding and enhancing intergroup contact
In a world characterized by divisive rhetoric, heightened xenophobia, and other forms of prejudice, it is increasingly important to find effective ways of promoting functional intergroup relations. Research on the relationship between intergroup contact and individual differences substantially contributes to achieving this goal. We review research considering the role played by individual differences in moderating the relationship between contact and prejudice and predicting contact, but also as an outcome of contact. We then outline potential directions for future research, including identifying underlying mechanisms, examining the role of context at an intergroup and societal level, and considering how positive – negative contact asymmetry may be influenced by individual differences. We then call for a broader range of individual difference and contact outcomes to be explored and encourage utilization of new methodological advances in the study of intergroup contact
From Equilibrium to Steady-State Dynamics after Switch-On of Shear
A relation between equilibrium, steady-state, and waiting-time dependent
dynamical two-time correlation functions in dense glass-forming liquids subject
to homogeneous steady shear flow is discussed. The systems under study show
pronounced shear thinning, i.e., a significant speedup in their steady-state
slow relaxation as compared to equilibrium. An approximate relation that
recovers the exact limit for small waiting times is derived following the
integration through transients (ITT) approach for the nonequilibrium
Smoluchowski dynamics, and is exemplified within a schematic model in the
framework of the mode-coupling theory of the glass transition (MCT). Computer
simulation results for the tagged-particle density correlation functions
corresponding to wave vectors in the shear-gradient directions from both
event-driven stochastic dynamics of a two-dimensional hard-disk system and from
previously published Newtonian-dynamics simulations of a three-dimensional
soft-sphere mixture are analyzed and compared with the predictions of the
ITT-based approximation. Good qualitative and semi-quantitative agreement is
found. Furthermore, for short waiting times, the theoretical description of the
waiting time dependence shows excellent quantitative agreement to the
simulations. This confirms the accuracy of the central approximation used
earlier to derive fluctuation dissipation ratios (Phys. Rev. Lett. 102,
135701). For intermediate waiting times, the correlation functions decay faster
at long times than the stationary ones. This behavior is predicted by our
theory and observed in simulations.Comment: 16 pages, 12 figures, submitted to Phys Rev
Depletion forces in non-equilibrium
The concept of effective depletion forces between two fixed big colloidal
particles in a bath of small particles is generalized to a non-equilibrium
situation where the bath of small Brownian particles is flowing around the big
particles with a prescribed velocity. In striking contrast to the equilibrium
case, the non-equilibrium forces violate Newton's third law, are
non-conservative and strongly anisotropic, featuring both strong attractive and
repulsive domains.Comment: 4 pages, 3 figure
Reentrance effect in the lane formation of driven colloids
Recently it has been shown that a strongly interacting colloidal mixture
consisting of oppositely driven particles, undergoes a nonequilibrium
transition towards lane formation provided the driving strength exceeds a
threshold value. We predict here a reentrance effect in lane formation: for
fixed high driving force and increasing particle densities, there is first a
transition towards lane formation which is followed by another transition back
to a state with no lanes. Our result is obtained both by Brownian dynamics
computer simulations and by a phenomenological dynamical density functional
theory.Comment: 4 pages, 2 figure
On the calculation of the self-diffusion coefficient of interacting Brownian particles
We consider two ways to calculate the self-diffusion coefficient of interacting Brownian particles. The first approach is based on the calculation of the mean square displacement of a Brownian particle starting from the Smoluchowski equation. In the second approach the self-diffusion
coefficient is obtained as the product of the thermodynamic driving force and the mobility. The advantages and limitations of the two methods are discussed
How Peclet number affects microstructure and transient cluster aggregation in sedimenting colloidal suspensions
We study how varying the P \'eclet number (Pe) affects the steady state
sedimentation of colloidal particles that interact through short-ranged
attractions. By employing a hybrid molecular dynamics simulation method we
demonstrate that the average sedimentation velocity changes from a non-
monotonic dependence on packing fraction {\phi} at low Pe numbers, to a
monotonic decrease with {\phi} at higher Pe numbers. At low Pe number the pair
correlation functions are close to their equilibrium values, but as the Pe
number increases, important deviations from equilibrium forms are observed.
Although the attractive forces we employ are not strong enough to form
permanent clusters, they do induce transient clusters whose behaviour is also
affected by Pe number. In particular, clusters are more likely to fragment and
less likely to aggregate at larger Pe numbers, and the probability of finding
larger clusters decreases with increasing Pe number. Interestingly, the
life-time of the clusters is more or less independent of Pe number in the range
we study. Instead, the change in cluster distribution occurs because larger
clusters are less likely to form with increasing Pe number. These results
illustrate some of the subtleties that occur in the crossover from equilibrium
like to purely non-equilibrium behaviour as the balance between convective and
thermal forces changes.Comment: 8 page
Non--Newtonian viscosity of interacting Brownian particles: comparison of theory and data
A recent first-principles approach to the non-linear rheology of dense
colloidal suspensions is evaluated and compared to simulation results of
sheared systems close to their glass transitions. The predicted scenario of a
universal transition of the structural dynamics between yielding of glasses and
non-Newtonian (shear-thinning) fluid flow appears well obeyed, and calculations
within simplified models rationalize the data over variations in shear rate and
viscosity of up to 3 decades.Comment: 6 pages, 2 figures; J. Phys. Condens. Matter to be published (Jan.
2003
Rotational Diffusion in a Chain of Particles
We study the coupled rotational diffusion in a two-particle chain on the
basis of a Smoluchowski equation and calculate time-correlation functions that
are measurable in an experiment. This might be used to explore hydrodynamic
interactions in the limit where lubrication theory is valid.Comment: 7 pages, 2 figures, to be published in J. Phys.: Condens. Matte
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