52,961 research outputs found
Intrinsic double-peak structure of the specific heat in low-dimensional quantum ferrimagnets
Motivated by recent magnetic measurements on A3Cu3(PO4)4 (A=Ca,Sr) and
Cu(3-Clpy)2(N3)2 (3-Clpy=3-Chloropyridine), both of which behave like
one-dimensional ferrimagnets, we extensively investigate the ferrimagnetic
specific heat with particular emphasis on its double-peak structure. Developing
a modified spin-wave theory, we reveal that ferromagnetic and antiferromagnetic
dual features of ferrimagnets may potentially induce an extra low-temperature
peak as well as a Schottky-type peak at mid temperatures in the specific heat.Comment: 5 pages, 6 figures embedded, Phys. Rev. B 65, 214418 (2002
Propagation of hydrodynamic interactions between particles in a compressible fluid
Hydrodynamic interactions are transmitted by viscous diffusion and sound
propagation: the temporal evolution of hydrodynamic interactions by both
mechanisms is studied by direct numerical simulation in this paper. The
hydrodynamic interactions for a system of two particles in a fluid are
estimated by the velocity correlation of the particles. In an incompressible
fluid, hydrodynamic interactions propagate instantaneously at the infinite
speed of sound, followed by the temporal evolution of viscous diffusion. On the
other hand, in a compressible fluid, sound propagates at a finite speed, which
affects the temporal evolution of the hydrodynamic interactions by the order of
magnitude relation between the time scales of viscous diffusion and sound
propagation. The hydrodynamic interactions are characterized by introducing the
ratio of these time scales as an interactive compressibility factor.Comment: 12 pages, 8 figure
Dynamical heterogeneity in a highly supercooled liquid: Consistent calculations of correlation length, intensity, and lifetime
We have investigated dynamical heterogeneity in a highly supercooled liquid
using molecular-dynamics simulations in three dimensions. Dynamical
heterogeneity can be characterized by three quantities: correlation length
, intensity , and lifetime . We evaluated
all three quantities consistently from a single order parameter. In a previous
study (H. Mizuno and R. Yamamoto, Phys. Rev. E {\bf 82}, 030501(R) (2010)), we
examined the lifetime in two time intervals
and , where is the
-relaxation time and is the time at which the
non-Gaussian parameter of the Van Hove self-correlation function is maximized.
In the present study, in addition to the lifetime , we
evaluated the correlation length and the intensity from
the same order parameter used for the lifetime . We
found that as the temperature decreases, the lifetime
grows dramatically, whereas the correlation length and the intensity
increase slowly compared to or plateaus.
Furthermore, we investigated the lifetime in more
detail. We examined the time-interval dependence of the lifetime
and found that as the time interval increases,
monotonically becomes longer and plateaus at the
relaxation time of the two-point density correlation function. At the large
time intervals for which plateaus, the heterogeneous
dynamics migrate in space with a diffusion mechanism, such as the particle
density.Comment: 12pages, 13figures, to appear in Physical Review
Thermal distortions of non-Gaussian beams in Fabry–Perot cavities
Thermal effects are already important in currently operating interferometric gravitational wave detectors. Planned upgrades of these detectors involve increasing optical power to combat quantum shot noise. We consider the ramifications of this increased power for one particular class of laser beams—wide, flat-topped, mesa beams. In particular we model a single mesa beam Fabry–Perot cavity having thermoelastically deformed mirrors. We calculate the intensity profile of the fundamental cavity eigenmode in the presence of thermal perturbations, and the associated changes in thermal noise. We also outline an idealized method of correcting for such effects. At each stage we contrast our results with those of a comparable Gaussian beam cavity. Although we focus on mesa beams the techniques described are applicable to any azimuthally symmetric system
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