A Method To Remove Fringes From Images Using Wavelets

We have developed a new method that uses wavelet analysis to remove interference fringe patterns from images. This method is particularly useful for flat fields in the common case where fringes vary between the calibration and object data. We analyze the efficacy of this method by creating fake flats with fictitious fringes and removing the fringes. We find that the method removes 90% of the fringe pattern if its amplitude is equal to the random noise level and 60% if the fringe amplitude is $\approx 1/10$ of the noise level. We also present examples using real flat field frames. A routine written in the Interactive Data Language (IDL) that implements this algorithm is available from the authors and as an attachment to this paper.Comment: 7 pages, 14 figures. Accepted to the Astrophysical Journal. (The quality of the figures in this preprint has been downgraded in order to fulfill arXiv requirements. Check journal for the high-quality figures

Quantum Singularities in Spacetimes with Spherical and Cylindrical Topological Defects

Exact solutions of Einstein equations with null Riemman-Christoffel curvature tensor everywhere, except on a hypersurface, are studied using quantum particles obeying the Klein-Gordon equation. We consider the particular cases when the curvature is represented by a Dirac delta function with support either on a sphere or on a cylinder (spherical and cylindrical shells). In particular, we analyze the necessity of extra boundary conditions on the shells.Comment: 7 page,1 fig., Revtex, J. Math. Phys, in pres

Colloidal interactions in two dimensional nematics

The interaction between two disks immersed in a 2D nematic is investigated (i) analitically using the tensor order parameter formalism for the nematic configuration around isolated disks and (ii) numerically using finite element methods with adaptive meshing to minimize the corresponding Landau-de Gennes free energy. For strong homeotropic anchoring, each disk generates a pair of defects with one-half topological charge responsible for the 2D quadrupolar interaction between the disks at large distances. At short distance, the position of the defects may change, leading to unexpected complex interactions with the quadrupolar repulsive interactions becoming attractive. This short range attraction in all directions is still anisotropic. As the distance between the disks decreases their preferred relative orientation with respect to the far-field nematic director changes from oblique to perpendicular.Comment: 7 pages, 7 figure

Lorentz Violating Julia-Toulouse Mechanism

We propose a new Lorentz invariant violating extension for the pure photonic sector of the Standard Model due to the condensation of topological defects in the context of the Julia-Toulouse mechanism. Possible physical consequences leading to direct measurable effects over the confining properties of the elementary particles are explored.Comment: 4 page

Interaction of colloids with a nematic-isotropic interface

The Landau-de Gennes free energy is used to calculate the interaction between long cylindrical colloids and the nematic-isotropic (NI) interface. This interaction has two contributions: one is specific of liquid crystals and results from the deformation of the director field close to the particles or to the interface, while the other is generic and results from wetting and surface tension effects. Deep in the nematic phase the director field of long cylindrical colloids, with strong homeotropic anchoring, exhibits two half-integer defect lines. As the colloid moves towards the interface, the director configuration changes through a series of discontinuous transitions, where one or two of the defects are annihilated. In addition, the NI interface bends towards the colloid in order to minimize the elastic free energy in the nematic. In the isotropic phase, the colloid is surrounded by a thin nematic layer that reduces the surface free energy under favorable wetting conditions. The interaction has a well-defined minimum near the interface. In this region the director and interfacial structures are complex and cannot be described analytically. Using the numerical results for the Landau-de Gennes free energy in the harmonic region, we obtained simple scaling laws for the (linear) force on the colloid

On the integrability of halo dipoles in gravity

We stress that halo dipole components are nontrivial in core-halo systems in both Newton's gravity and General Relativity. To this end, we extend a recent exact relativistic model to include also a halo dipole component. Next, we consider orbits evolving in the inner vacuum between a monopolar core and a pure halo dipole and find that, while the Newtonian dynamics is integrable, its relativistic counterpart is chaotic. This shows that chaoticity due only to halo dipoles is an intrinsic relativistic gravitational effect.Comment: 9 pages, REVTEX, two postscript figures include