3,720 research outputs found
Structural and dynamical heterogeneities in two-dimensional melting
Using molecular dynamics simulation, we study structural and dynamical
heterogeneities at melting in two-dimensional one-component systems with 36000
particles. Between crystal and liquid we find intermediate hexatic states,
where the density fluctuations are enhanced at small wave number k as well as
those of the six-fold orientational order parameter. Their structure factors
both grow up to the smallest wave number equal to the inverse system length.
The intermediate scattering function of the density S(k,t) is found to relax
exponentially with decay rate Gamma_k ~ k^z with z~2.6 at small k in the
hexatic phase.Comment: 6 pages, 8 figure
Belle time-dependent gamma measurements
The Belle experiment has measured the CKM angle in a variety of
ways. In this paper, we focused on the recent progress of time-dependent
analysis and the related measurements in Belle.Comment: 6th International Workshop on the CKM Unitary Triangle, University of
Warwick UK, 6-10 September 201
Quantifying Nonequilibrium Behavior with Varying Cooling Rates
We investigate nonequilibrium behavior in (1+1)-dimensional stochastic field
theories in the context of Ginzburg-Landau models at varying cooling rates. We
argue that a reliable measure of the departure from thermal equilibrium can be
obtained from the absolute value of the rate of change of the
momentum-integrated structure function, . We show that the
peak of scales with the cooling, or quench, time-scale,
, in agreement with the prediction by Laguna and Zurek for the scaling
of freeze-out time in both over and under-damped regimes. Furthermore, we show
that the amplitude of the peak scales as independent of the
viscosity.Comment: 4 pages, 4 figures, submitted to Phys. Rev. Let
Spatio-temporal structures in sheared polymer systems
We investigate spatio-temporal structures in sheared polymer systems by
solving a time-dependent Ginzburg-Landau model in two dimensions. (i) In
polymer solutions above the coexistence curve, crossover from linear to
nonlinear regimes occurs with increasing the shear rate. In the nonlinear
regime the solution behaves chaotically with large-amplitude composition
fluctuations. A characteristic heterogeneity length is calculated in the
nonlinear regime. (ii) We also study dynamics of shear-band structures in
wormlike micellar solutions under the condition of fixed stress. The average
shear rate exhibits large temporal fluctuations with occurrence of large
disturbances in the spatial structures.Comment: 16pages, 10figures, to be published in Physica
Spreading with evaporation and condensation in one-component fluids
We investigate the dynamics of spreading of a small liquid droplet in gas in
a one-component simple fluid, where the temperature is inhomogeneous around
0.9Tc and latent heat is released or generated at the interface upon
evaporation or condensation (with Tc being the critical temperature). In the
scheme of the dynamic van der Waals theory, the hydrodynamic equations
containing the gradient stress are solved in the axisymmetric geometry. We
assume that the substrate has a finite thickness and its temperature obeys the
thermal diffusion equation. A precursor film then spreads ahead of the bulk
droplet itself in the complete wetting condition. Cooling the substrate
enhances condensation of gas onto the advancing film, which mostly takes place
near the film edge and can be the dominant mechanism of the film growth in a
late stage. The generated latent heat produces a temperature peak or a hot spot
in the gas region near the film edge. On the other hand, heating the substrate
induces evaporation all over the interface. For weak heating, a steady-state
circular thin film can be formed on the substrate. For stronger heating,
evaporation dominates over condensation, leading to eventual disappearance of
the liquid region.Comment: 12 pages, 14 figure
Solvation Effects in Near-Critical Binary Mixtures
A Ginzburg-Landau theory is presented to investigate solvation effects in
near-critical polar fluid binary mixtures. Concentration-dependence of the
dielectric constant gives rise to a shell region around a charged particle
within which solvation occurs preferentially. As the critical point is
approached, the concentration has a long-range Ornstein-Zernike tail
representing strong critical electrostriction. If salt is added, strong
coupling arises among the critical fluctuations and the ions. The structure
factors of the critical fluctuations and the charge density are calculated and
the phase transition behavior is discussed.Comment: 12 pages, 8 figures, to be published in J. Chem. Phy
Plastic flow in polycrystal states in a binary mixture
Using molecular dynamics simulation we examine dynamics in sheared
polycrystal states in a binary mixture containing 10% larger particles in two
dimensions. We find large stress fluctuations arising from sliding motions of
the particles at the grain boundaries, which occur cooperatively to release the
elastic energy stored. These dynamic processes are visualized with the aid of a
sixfold angle representing the local crystal orientation and a
disorder variable representing a deviation from the hexagonal order
for particle .Comment: 3 pages, 3 figure
Rheology of a Supercooled Polymer Melt
Molecular dynamics simulations are performed for a polymer melt composed of
short chains in quiescent and sheared conditions. The stress relaxation
function exhibits a stretched exponential form in a relatively early
stage and ultimately follows the Rouse function in quiescent supercooled state.
Transient stress evolution after application of shear obeys the linear growth
for strain less than 0.1 and then saturates into a
non-Newtonian viscosity. In steady states, strong shear-thinning and elongation
of chains into ellipsoidal shapes are found at extremely small shear. A glassy
component of the stress is much enhanced in these examples.Comment: 4 pages, 5 figure
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