8,131 research outputs found
Coarsening Dynamics of a One-Dimensional Driven Cahn-Hilliard System
We study the one-dimensional Cahn-Hilliard equation with an additional
driving term representing, say, the effect of gravity. We find that the driving
field has an asymmetric effect on the solution for a single stationary
domain wall (or `kink'), the direction of the field determining whether the
analytic solutions found by Leung [J.Stat.Phys.{\bf 61}, 345 (1990)] are
unique. The dynamics of a kink-antikink pair (`bubble') is then studied. The
behaviour of a bubble is dependent on the relative sizes of a characteristic
length scale , where is the driving field, and the separation, ,
of the interfaces. For the velocities of the interfaces are
negligible, while in the opposite limit a travelling-wave solution is found
with a velocity . For this latter case () a set of
reduced equations, describing the evolution of the domain lengths, is obtained
for a system with a large number of interfaces, and implies a characteristic
length scale growing as . Numerical results for the domain-size
distribution and structure factor confirm this behavior, and show that the
system exhibits dynamical scaling from very early times.Comment: 20 pages, revtex, 10 figures, submitted to Phys. Rev.
The 3D structure of the Lagrangian acceleration in turbulent flows
We report experimental results on the three dimensional Lagrangian
acceleration in highly turbulent flows. Tracer particles are tracked optically
using four silicon strip detectors from high energy physics that provide high
temporal and spatial resolution. The components of the acceleration are shown
to be statistically dependent. The probability density function (PDF) of the
acceleration magnitude is comparable to a log-normal distribution. Assuming
isotropy, a log-normal distribution of the magnitude can account for the
observed dependency of the components. The time dynamics of the acceleration
components is found to be typical of the dissipation scales whereas the
magnitude evolves over longer times, possibly close to the integral time scale.Comment: accepted for publication in Physical Review Letter
Exquisite jade carving: figures, animals, ornaments
Exhibition held at the University Museum and Art Gallery, University of Hong Kong on Dec. 6, 1995-Feb. 6, 1996.published_or_final_versionFurther comments on flying deity/winged figure 17Foreword Lau, Michael W.M. Lau, Michael W.M. 4List of lenders 18借出展品的藏家和機構 18Chronology 19年表 19Works cited in the descriptions 20Plates 25Introduction Yeung, Chun-tong Yeung, Chun-tong 10展品圖版 25序言 楊春棠 楊春棠 12On Hongshan jade pendants So, Jenny F. So, Jenny F. 14Preface Fung, Sydney Fung, Sydney
Ordering dynamics of the driven lattice gas model
The evolution of a two-dimensional driven lattice-gas model is studied on an
L_x X L_y lattice. Scaling arguments and extensive numerical simulations are
used to show that starting from random initial configuration the model evolves
via two stages: (a) an early stage in which alternating stripes of particles
and vacancies are formed along the direction y of the driving field, and (b) a
stripe coarsening stage, in which the number of stripes is reduced and their
average width increases. The number of stripes formed at the end of the first
stage is shown to be a function of L_x/L_y^\phi, with \phi ~ 0.2. Thus,
depending on this parameter, the resulting state could be either single or
multi striped. In the second, stripe coarsening stage, the coarsening time is
found to be proportional to L_y, becoming infinitely long in the thermodynamic
limit. This implies that the multi striped state is thermodynamically stable.
The results put previous studies of the model in a more general framework
Dynamics of Ordering of Heisenberg Spins with Torque --- Nonconserved Case. I
We study the dynamics of ordering of a nonconserved Heisenberg magnet. The
dynamics consists of two parts --- an irreversible dissipation into a heat bath
and a reversible precession induced by a torque due to the local molecular
field. For quenches to zero temperature, we provide convincing arguments, both
numerically (Langevin simulation) and analytically (approximate closure scheme
due to Mazenko), that the torque is irrelevant at late times. We subject the
Mazenko closure scheme to systematic numerical tests. Such an analysis, carried
out for the first time on a vector order parameter, shows that the closure
scheme performs respectably well. For quenches to , we show, to , that the torque is irrelevant at the Wilson-Fisher fixed
point.Comment: 13 pages, REVTEX, and 19 .eps figures, compressed, Submitted to Phys.
Rev.
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