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 (3+1)(3+1)--Dimensions and Pontrjagin Topological Invariant

A relation between the MacDowell-Mansouri theory of gravity and the Pontrjagin toplogical invariant in $(3+1)$ 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

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

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

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 vapor–liquid, wall–liquid, and wall–vapor interfaces for a model of Lennard– Jones argon adsorbed on solid carbon dioxide. The results are employed as input to Young’s 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 Ar–Ar 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 Müller 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 Autónoma de Madrid through Project No. MODELICO-P2009/ESP- 1691; and Junta de Andalucía through Project No. P07- FQM02884 is gratefully acknowledged