5,637 research outputs found
Monte Carlo simulation results for critical Casimir forces
The confinement of critical fluctuations in soft media induces critical
Casimir forces acting on the confining surfaces. The temperature and geometry
dependences of such forces are characterized by universal scaling functions. A
novel approach is presented to determine them for films via Monte Carlo
simulations of lattice models. The method is based on an integration scheme of
free energy differences. Our results for the Ising and the XY universality
class compare favourably with corresponding experimental results for wetting
layers of classical binary liquid mixtures and of 4He, respectively.Comment: 14 pages, 5 figure
Derivation of a Non-Local Interfacial Hamiltonian for Short-Ranged Wetting II: General Diagrammatic Structure
In our first paper, we showed how a non-local effective Hamiltionian for
short-ranged wetting may be derived from an underlying Landau-Ginzburg-Wilson
model. Here, we combine the Green's function method with standard perturbation
theory to determine the general diagrammatic form of the binding potential
functional beyond the double-parabola approximation for the
Landau-Ginzburg-Wilson bulk potential. The main influence of cubic and quartic
interactions is simply to alter the coefficients of the double parabola-like
zig-zag diagrams and also to introduce curvature and tube-interaction
corrections (also represented diagrammatically), which are of minor importance.
Non-locality generates effective long-ranged many-body interfacial interactions
due to the reflection of tube-like fluctuations from the wall. Alternative wall
boundary conditions (with a surface field and enhancement) and the diagrammatic
description of tricritical wetting are also discussed.Comment: (14 pages, 2 figures) Submitted J. Phys. Condens. Matte
First Gale Western Butte Capping-Unit Compositions, and Relationships to Earlier Units Along Curiosity's Traverse
The Curiosity rover has been traversing through the clay-bearing unit (Glen Torridon; GT), approaching Greenheugh pediment, a large, fan-shaped surface surrounding the mouth of Gediz Vallis on the lower slope of Mt. Sharp. The pediment unconformably overlies the underlying bedrock, and is hence younger than units of the Mt. Sharp group. Orbital imaging of the pediment has shown it to have a slightly lower albedo and higher thermal inertia than neighboring units, to be relatively retentive of craters (e.g., erosion resistant), and to exhibit curved bedforms suggestive of lithified eolian bedforms. No diagnostic spectral signature has been observed from orbit. Recent rover positions allowed remote imaging of the contact between Greenheugh pediment and the eroded Murray formation strata below it, showing that the pediment capping material is cross-bedded and relatively thin (1-3 m), and suggesting that the pediment may have been much larger at one time. As Curiosity approached the edge of the pediment, the team investigated two buttes named Central and Western. The latter butte contains dark capping material that initially looked similar to the pediment cap, but close inspection revealed important physical differences. Here we report on compositions from ChemCam of two float rocks that appear to have rolled down from the capping unit, and on potential relation-ships to other targets along the traverse of the rover
Role of contrast-enhanced ultrasound (CEUS) in paediatric practice: an EFSUMB position statement
The use of contrast-enhanced ultrasound (CEUS) in adults is well established in many different areas, with a number of current applications deemed off-label, but the use supported by clinical experience and evidence. Paediatric CEUS is also an off-label application until recently with approval specifically for assessment of focal liver lesions. Nevertheless there is mounting evidence of the usefulness of CEUS in children in many areas, primarily as an imaging technique that reduces exposure to radiation, iodinated contrast medium and the patient-friendly circumstances of ultrasonography. This position statement of the European Federation of Societies in Ultrasound and Medicine (EFSUMB) assesses the current status of CEUS applications in children and makes suggestions for further development of this technique
Longitudinal magnetic excitations in classical spin systems
Using spin dynamics simulations we predict the splitting of the longitudinal
spin wave peak in all antiferromagnets with single site anisotropy into two
peaks separated by twice the energy gap at the Brillouin zone center. This
phenomenon has yet to be observed experimentally but can be easily investigated
through neutron scattering experiments on MnF and FeF. We have also
determined that for all classical Heisenberg models the longitudinal
propagative excitations are entirely multiple spin-wave in nature.Comment: four pages three figures, the last two postscript files are two parts
of the third figur
Universal scaling functions of critical Casimir forces obtained by Monte Carlo simulations
Effective Casimir forces induced by thermal fluctuations in the vicinity of
bulk critical points are studied by means of Monte Carlo simulations in
three-dimensional systems for film geometries and within the experimentally
relevant Ising and XY universality classes. Several surface universality
classes of the confining surfaces are considered, some of which are relevant
for recent experiments. A novel approach introduced previously EPL 80, 60009
(2007), based inter alia on an integration scheme of free energy differences,
is utilized to compute the universal scaling functions of the critical Casimir
forces in the critical range of temperatures above and below the bulk critical
temperature. The resulting predictions are compared with corresponding
experimental data for wetting films of fluids and with available theoretical
results.Comment: 21 pages, 17 figure
The Mass of the Black Hole in the Seyfert 1 Galaxy NGC 4593 from Reverberation Mapping
We present new observations leading to an improved black hole mass estimate
for the Seyfert 1 galaxy NGC 4593 as part of a reverberation-mapping campaign
conducted at the MDM Observatory. Cross-correlation analysis of the H_beta
emission-line light curve with the optical continuum light curve reveals an
emission-line time delay of 3.73 (+-0.75) days. By combining this time delay
with the H_beta line width, we derive a central black hole mass of M_BH =
9.8(+-2.1)x10^6 M_sun, an improvement in precision of a factor of several over
past results.Comment: 22 pages, 3 tables, 5 figures, accepted for publication in Ap
Normal and lateral critical Casimir forces between colloids and patterned substrates
We study the normal and lateral effective critical Casimir forces acting on a
spherical colloid immersed in a critical binary solvent and close to a
chemically structured substrate with alternating adsorption preference. We
calculate the universal scaling function for the corresponding potential and
compare our results with recent experimental data [Soyka F., Zvyagolskaya O.,
Hertlein C., Helden L., and Bechinger C., Phys. Rev. Lett., 101, 208301
(2008)]. The experimental potentials are properly captured by our predictions
only by accounting for geometrical details of the substrate pattern for which,
according to our theory, critical Casimir forces turn out to be a sensitive
probe.Comment: 6 pages, 3 figure
Universality for 2D Wedge Wetting
We study 2D wedge wetting using a continuum interfacial Hamiltonian model
which is solved by transfer-matrix methods. For arbitrary binding potentials,
we are able to exactly calculate the wedge free-energy and interface height
distribution function and, thus, can completely classify all types of critical
behaviour. We show that critical filling is characterized by strongly universal
fluctuation dominated critical exponents, whilst complete filling is determined
by the geometry rather than fluctuation effects. Related phenomena for
interface depinning from defect lines in the bulk are also considered.Comment: 4 pages, 1 figur
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