1,442 research outputs found
Mesoscopic model for the fluctuating hydrodynamics of binary and ternary mixtures
A recently introduced particle-based model for fluid dynamics with continuous
velocities is generalized to model immiscible binary mixtures. Excluded volume
interactions between the two components are modeled by stochastic multiparticle
collisions which depend on the local velocities and densities. Momentum and
energy are conserved locally, and entropically driven phase separation occurs
for high collision rates. An explicit expression for the equation of state is
derived, and the concentration dependence of the bulk free energy is shown to
be the same as that of the Widom-Rowlinson model. Analytic results for the
phase diagram are in excellent agreement with simulation data. Results for the
line tension obtained from the analysis of the capillary wave spectrum of a
droplet agree with measurements based on the Laplace's equation. The
introduction of "amphiphilic" dimers makes it possible to model the phase
behavior and dynamics of ternary surfactant mixtures.Comment: 7 pages including 6 figure
Thermodynamics of the one-dimensional frustrated Heisenberg ferromagnet with arbitrary spin
The thermodynamic quantities (spin-spin correlation functions <{\bf S}_0{\bf
S}_n>, correlation length {\xi}, spin susceptibility {\chi}, and specific heat
C_V) of the frustrated one-dimensional J1-J2 Heisenberg ferromagnet with
arbitrary spin quantum number S below the quantum critical point, i.e. for J2<
|J1|/4, are calculated using a rotation-invariant Green-function formalism and
full diagonalization as well as a finite-temperature Lanczos technique for
finite chains of up to N=18 sites. The low-temperature behavior of the
susceptibility {\chi} and the correlation length {\xi} is well described by
\chi = (2/3)S^4 (|J1|-4J2) T^{-2} + A S^{5/2} (|J1|-4J2)^{1/2} T^{-3/2} and \xi
= S^2 (|J1|-4J2) T^{-1} + B S^{1/2} (|J1|-4J2)^{1/2} T^{-1/2} with A \approx
1.1 ... 1.2 and B \approx 0.84 ... 0.89. The vanishing of the factors in front
of the temperature at J2=|J1|/4 indicates a change of the critical behavior of
{\chi} and {\xi} at T \to 0. The specific heat may exhibit an additional
frustration-induced low-temperature maximum when approaching the quantum
critical point. This maximum appears for S=1/2 and S=1, but was not found for
S>1.Comment: 8 pages, 7 figure
Green's function theory of quasi-two-dimensional spin-half Heisenberg ferromagnets: stacked square versus stacked kagom\'e lattice
We consider the thermodynamic properties of the quasi-two-dimensional
spin-half Heisenberg ferromagnet on the stacked square and the stacked kagom\'e
lattices by using the spin-rotation-invariant Green's function method. We
calculate the critical temperature , the uniform static susceptibility
, the correlation lengths and the magnetization and
investigate the short-range order above . We find that and at
are smaller for the stacked kagom\'e lattice which we attribute to
frustration effects becoming relevant at finite temperatures.Comment: shortened version as published in PR
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Particle organization after viscous sedimentation in tilted containers
A series of sedimentation experiments and numerical simulations have been conducted
to understand the factors that control the final angle of a static sediment
layer formed by quasi-monodisperse particles settling in an inclined container. The
set of experiments includes several combinations of fluid viscosity, container angle,
and solids concentration. A comparison between the experiments and a set of twodimensional
numerical simulations shows that the physical mechanism responsible
for the energy dissipation in the system is the collision between the particles.
The results provide new insights into the mechanism that sets the morphology of
the sediment layer formed by the settling of quasi-monodisperse particles onto the
bottom of an inclined container. Tracking the interface between the suspension solids
and the clear fluid zone reveals that the final angle adopted by the sediment layer
shows strong dependencies on the initial particle concentration and the container
inclination, but not the fluid viscosity. It is concluded that (1) the hindrance function
plays an important role on the sediment bed angle, (2) the relation between the
friction effect and the slope may be explained as a quasi-linear function of the
projected velocity along the container bottom, and (3) prior to the end of settling
there is a significant interparticle interaction through the fluid affecting to the final
bed organization.We can express the sediment bed slope as a function of two dimensionless
numbers, a version of the inertial number and the particle concentration.
The present experiments confirm some previous results on the role of the interstitial
fluid on low Stokes number flows of particulate matter.The authors acknowledge the support of the National Commission for Scientific and Techno-
logical Research of Chile, CONICYT, Grant Nâ—¦ 21110766, Fondecyt Projects Nâ—¦ 11110201
and Nâ—¦ 1130910, the Department of Civil Engineering, the Department of Mining Engineering and the Advanced Mining Technology Center of the University of Chile, as well the staff
of the G.K. Batchelor Laboratory, Department of Applied Mathematics and Theoretical
Physics, University of Cambridge.This is the author accepted manuscript. The final version is available from AIP at http://dx.doi.org/10.1063/1.4958722
Quasiperiodic Tip Splitting in Directional Solidification
We report experimental results on the tip splitting dynamics of seaweed
growth in directional solidification of succinonitrile alloys with
poly(ethylene oxide) or acetone as solutes. The seaweed or dense branching
morphology was selected by solidifying grains which are oriented close to the
{111} plane. Despite the random appearance of the growth, a quasiperiodic tip
splitting morphology was observed in which the tip alternately splits to the
left and to the right. The tip splitting frequency f was found to be related to
the growth velocity V as a power law f V^{1.5}. This finding
is consistent with the predictions of a tip splitting model that is also
presented. Small anisotropies are shown to lead to different kinds of seaweed
morphologies.Comment: 4 pages, 7 figures, submitted to Physical Review Letter
Absence of long-range order in a spin-half Heisenberg antiferromagnet on the stacked kagome lattice
We study the ground state of a spin-half Heisenberg antiferromagnet on the
stacked kagome lattice by using a spin-rotation-invariant Green's-function
method. Since the pure two-dimensional kagome antiferromagnet is most likely a
magnetically disordered quantum spin liquid, we investigate the question
whether the coupling of kagome layers in a stacked three-dimensional system may
lead to a magnetically ordered ground state. We present spin-spin correlation
functions and correlation lengths. For comparison we apply also linear spin
wave theory. Our results provide strong evidence that the system remains
short-range ordered independent of the sign and the strength of the interlayer
coupling
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