726 research outputs found
Entropy production in nonequilibrium steady states: A different approach and an exactly solvable canonical model
We discuss entropy production in nonequilibrium steady states by focusing on
paths obtained by sampling at regular (small) intervals, instead of sampling on
each change of the system's state. This allows us to study directly entropy
production in systems with microscopic irreversibility, for the first time. The
two sampling methods are equivalent, otherwise, and the fluctuation theorem
holds also for the novel paths. We focus on a fully irreversible three-state
loop, as a canonical model of microscopic irreversibility, finding its entropy
distribution, rate of entropy pr oduction, and large deviation function in
closed analytical form, and showing that the widely observed kink in the large
deviation function arises solely f rom microscopic irreversibility.Comment: 4 pages, 3 figures, submitted to Phys. Rev. Let
Crystallization in Glassy Suspensions of Hard Ellipsoids
We have carried out computer simulations of overcompressed suspensions of
hard monodisperse ellipsoids and observed their crystallization dynamics. The
system was compressed very rapidly in order to reach the regime of slow,
glass-like dynamics. We find that, although particle dynamics become
sub-diffusive and the intermediate scattering function clearly develops a
shoulder, crystallization proceeds via the usual scenario: nucleation and
growth for small supersaturations, spinodal decomposition for large
supersaturations.
In particular, we compared the mobility of the particles in the regions where
crystallization set in with the mobility in the rest of the system. We did not
find any signature in the dynamics of the melt that pointed towards the
imminent crystallization events
Strong Effect of Weak Charging in Suspensions of Anisotropic Colloids
Suspensions of hard colloidal particles frequently serve as model systems in
studies on fundamental aspects of phase transitions. But often colloidal
particles that are considered as ``hard'' are in fact weakly charged. If the
colloids are spherical, weak charging has a only a weak effect on the
structural properties of the suspension, which can be easily corrected for.
However, this does not hold for anisotropic particles.
We introduce a model for the interaction potential between charged ellipsoids
of revolution (spheroids) based on the Derjaguin approximation of
Debye--H\"uckel Theory and present a computer simulation study on aspects of
the system's structural properties and phase behaviour. In line with previous
experimental observations, we find that even a weak surface charge has a strong
impact on the correlation functions. A likewise strong impact is seen on the
phase behaviour, in particular, we find stable cubatic order in suspensions of
oblate ellipsoids
Lechoń’s ephemeral poems: people – issues – events in the New York period
English version. Original issue: “Archiwum Emigracji” 2023, no. 2 (32)https://apcz.umk.pl/AE/article/view/4969
The Early Crystal Nucleation Process in Hard Spheres shows Synchronised Ordering and Densification
We investigate the early part of the crystal nucleation process in the hard
sphere fluid using data produced by computer simulation. We find that hexagonal
order manifests continuously in the overcompressed liquid, beginning
approximately one diffusion time before the appearance of the first
`solid-like' particle of the nucleating cluster, and that a collective influx
of particles towards the nucleation site occurs simultaneously to the ordering
process: the density increases leading to nucleation are generated by the same
individual particle displacements as the increases in order. We rule out the
presence of qualitative differences in the early nucleation process between
medium and low overcompressions, and also provide evidence against any
separation of translational and orientational order on the relevant
lengthscales
Description of hard sphere crystals and crystal-fluid interfaces: a critical comparison between density functional approaches and a phase field crystal model
In materials science the phase field crystal approach has become popular to
model crystallization processes. Phase field crystal models are in essence
Landau-Ginzburg-type models, which should be derivable from the underlying
microscopic description of the system in question. We present a study on
classical density functional theory in three stages of approximation leading to
a specific phase field crystal model, and we discuss the limits of
applicability of the models that result from these approximations. As a test
system we have chosen the three--dimensional suspension of monodisperse hard
spheres. The levels of density functional theory that we discuss are
fundamental measure theory, a second-order Taylor expansion thereof, and a
minimal phase-field crystal model. We have computed coexistence densities,
vacancy concentrations in the crystalline phase, interfacial tensions and
interfacial order parameter profiles, and we compare these quantities to
simulation results. We also suggest a procedure to fit the free parameters of
the phase field crystal model.Comment: 21 page
On the influence of a patterned substrate on crystallization in suspensions of hard spheres
We present a computer simulation study on crystal nucleation and growth in
supersaturated suspensions of mono-disperse hard spheres induced by a
triangular lattice substrate. The main result is that compressed substrates are
wet by the crystalline phase (the crystalline phase directly appears without
any induction time), while for stretched substrates we observe heterogeneous
nucleation. The shapes of the nucleated crystallites fluctuate strongly. In the
case of homogeneous nucleation amorphous precursors have been observed (Phys.
Rev. Lett. {\bf 105}(2):025701 (2010)). For heterogeneous nucleation we do not
find such precursors. The fluid is directly transformed into highly ordered
crystallites.Comment: 14 pages, 13 figure
- …