710 research outputs found
Disjoining Pressure and the Film-Height-Dependent Surface Tension of Thin Liquid Films: New Insight from Capillary Wave Fluctuations
In this paper we review simulation and experimental studies of thermal
capillary wave fluctuations as an ideal means for probing the underlying
disjoining pressure and surface tensions, and more generally, fine details of
the Interfacial Hamiltonian Model. We discuss recent simulation results that
reveal a film-height-dependent surface tension not accounted for in the
classical Interfacial Hamiltonian Model. We show how this observation may be
explained bottom-up from sound principles of statistical thermodynamics and
discuss some of its implications.Comment: File is accepted version with 70 pages and 13 figures. Submitted
23/08/2013; Accepted 06/11/2013; Online 17/11/201
Compressive Phase Contrast Tomography
When x-rays penetrate soft matter, their phase changes more rapidly than
their amplitude. In- terference effects visible with high brightness sources
creates higher contrast, edge enhanced images. When the object is piecewise
smooth (made of big blocks of a few components), such higher con- trast
datasets have a sparse solution. We apply basis pursuit solvers to improve SNR,
remove ring artifacts, reduce the number of views and radiation dose from phase
contrast datasets collected at the Hard X-Ray Micro Tomography Beamline at the
Advanced Light Source. We report a GPU code for the most computationally
intensive task, the gridding and inverse gridding algorithm (non uniform
sampled Fourier transform).Comment: 5 pages, "Image Reconstruction from Incomplete Data VI" conference
7800, SPIE Optical Engineering + Applications 1-5 August 2010 San Diego, CA
United State
A Relation Between Gravity in --Dimensions and Pontrjagin Topological Invariant
A relation between the MacDowell-Mansouri theory of gravity and the
Pontrjagin toplogical invariant in dimensions is discussed. This
relation may be of especial interest in the quest of finding a mechanism to go
from non-dynamical to dynamical gravity.Comment: 9 pages, Te
Riemann-Einstein Structure from Volume and Gauge Symmetry
It is shown how a metric structure can be induced in a simple way starting
with a gauge structure and a preferred volume, by spontaneous symmetry
breaking. A polynomial action, including coupling to matter, is constructed for
the symmetric phase. It is argued that assuming a preferred volume, in the
context of a metric theory, induces only a limited modification of the theory.Comment: LaTeX, 13 pages; Added additional reference in Reference
Gravity with de Sitter and Unitary Tangent Groups
Einstein Gravity can be formulated as a gauge theory with the tangent space
respecting the Lorentz symmetry. In this paper we show that the dimension of
the tangent space can be larger than the dimension of the manifold and by
requiring the invariance of the theory with respect to 5d Lorentz group (de
Sitter group) Einstein theory is reproduced unambiguously. The other
possibility is to have unitary symmetry on a complex tangent space of the same
dimension as the manifold. In this case the resultant theory is
Einstein-Strauss Hermitian gravity. The tangent group is important for matter
couplings. We show that in the de Sitter case the 4 dimensional space time
vector and scalar are naturally unified by a hidden symmetry being components
of a 5d vector in the tangent space. With a de Sitter tangent group spinors can
exist only when they are made complex or taken in doublets in a way similar to
N=2 supersymmetry.Comment: 23 pages, one reference added.To be published in JHE
Coupling of Gravity to Matter via SO(3,2) Gauge Fields
We consider gravity from the quantum field theory point of view and introduce
a natural way of coupling gravity to matter by following the gauge principle
for particle interactions. The energy-momentum tensor for the matter fields is
shown to be conserved and follows as a consequence of the dynamics in a
spontaneously broken SO(3,2) gauge theory of gravity. All known interactions
are described by the gauge principle at the microscopic level.Comment: 12 latex page
The geometric role of symmetry breaking in gravity
In gravity, breaking symmetry from a group G to a group H plays the role of
describing geometry in relation to the geometry the homogeneous space G/H. The
deep reason for this is Cartan's "method of equivalence," giving, in
particular, an exact correspondence between metrics and Cartan connections. I
argue that broken symmetry is thus implicit in any gravity theory, for purely
geometric reasons. As an application, I explain how this kind of thinking gives
a new approach to Hamiltonian gravity in which an observer field spontaneously
breaks Lorentz symmetry and gives a Cartan connection on space.Comment: 4 pages. Contribution written for proceedings of the conference
"Loops 11" (Madrid, May 2011
Semi-infinite boundary conditions for the simulation of interfaces: The Ar/CO2(s) model revisited
We propose a method to account for the long tail corrections of dispersive forces in inhomogeneous systems. This method deals separately with the two interfaces that are usually present in a simulation setup, effectively establishing semi-infinite boundary conditions that are appropriate for the study of the interface between two infinite bulk phases. Using the wandering interface method, we calculate surface free energies of vaporâliquid, wallâliquid, and wallâvapor interfaces for a model of Lennardâ Jones argon adsorbed on solid carbon dioxide. The results are employed as input to Youngâs equation, and the wetting temperature located. This estimate is compared with predictions from the method of effective interface potentials and good agreement is found. Our results show that truncating ArâAr interactions at two and a half molecular diameters results in a dramatic decrease of the wetting temperature of about 40%.We would like to thank Marcus MuÌller for suggesting us to describe the cutoff dependence of wetting properties by means of the sharp-kink approximation (cf., Sec. V). We also benefitted from helpful discussions with P. Bryk, A. Archer, and E. de Miguel. Generous financial support of Ministerio de Educacion y Ciencia through Project Nos. FIS2010- 22047-C05-05 and FIS2010-14866; Comunidad AutĂłnoma de Madrid through Project No. MODELICO-P2009/ESP- 1691; and Junta de AndalucĂa through Project No. P07- FQM02884 is gratefully acknowledged
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