Checkerboard and stripe inhomogeneities in cuprates

We systematically investigate charge-ordering phases by means of a restricted and unrestricted Gutzwiller approximation to the single-band Hubbard model with nearest ($t$) and next-nearest neighbor hopping ($t'$). When $|t'/t|$ is small, as appropriate for ${\rm La_{2-x}Sr_xCuO_4}$, stripes are found, whereas in compounds with larger $|t'/t|$ (such as ${\rm Ca_{2-x}Na_x CuO_2Cl_2}$ and ${\rm Bi_2Sr_2CaCu_2O_{8+\delta}}$) checkerboard structures are favored. In contrast to the linear doping dependence found for stripes the charge periodicity of checkerboard textures is locked to 4 unit cells over a wide doping range. In addition we find that checkerboard structures are favored at surfaces.Comment: 5 pages, 3 figure

CONFINEMENT IN RELATIVISTIC POTENTIAL MODELS

In relativistic potential models of quarkonia based on a Dirac-type of equation with a local potential there is a sharp distinction between a linear potential V which is vector-like and one which is scalar-like: There are normalizable solutions for a scalar-like V but not for a vector-like V. It is pointed out that if instead one uses an equation of the no-pair type, which is more natural from the viewpoint of field theory, this somewhat bizarre difference disappears.Comment: LaTeX, 4 page

Black holes in extended gravity theories in Palatini formalism

We consider several physical scenarios where black holes within classical gravity theories including $R^2$ and Ricci-squared corrections and formulated \`a la Palatini can be analytically studied.Comment: 4 pages, contribution to the "Spanish Relativity Meeting in Portugal 2012 (Progress in Mathematical Relativity, Gravitation and Cosmology)", Springer Proceedings in Mathematics (to appear

Reduction of noise in gyro outputs

Technique is described to reduce extraneous gyro output signals by using relatively inexpensive shrouds which do not increase power comsumption. Shrouds reduce noise by minimizing mass of gas spinning with rotor, reducing Reynolds number near rotor, and inducing laminar flow

Tidal interaction of a rotating 1 Msun star with a binary companion

We calculate the tidal torque on a uniformly rotating 1 Msun star at various stages of core hydrogen burning by an orbiting companion. We apply the `traditional approximation' and solve the radial part of the tidal perturbations by matrix inversion of the set of finite difference equations on a very fine grid. We have identified resonances with gravity- and quasi-toroidal modes with up to 1000 radial nodes in the more evolved stellar models. For low forcing frequencies we find significant tidal response due to viscous damping of inertial modes in the convective envelope of the solar-type star. We conclude that effects due to stellar rotation (including resonance locking) may considerably enhance the speed of tidal evolution in solar-type stars.Comment: accepted for publ. in A&A, 11 pages, 6 figure

Feature-tailored spectroscopic analysis of the SNR Puppis A in X-rays

We introduce a distinct method to perform spatially-resolved spectral analysis of astronomical sources with highly structured X-ray emission. The method measures the surface brightness of neighbouring pixels to adaptively size and shape each region, thus the spectra from the bright and faint filamentary structures evident in the broadband images can be extracted. As a test case, we present the spectral analysis of the complete X-ray emitting plasma in the supernova remnant Puppis A observed with XMM-Newton and Chandra. Given the angular size of Puppis A, many pointings with different observational configurations have to be combined, presenting a challenge to any method of spatially-resolved spectroscopy. From the fit of a plane-parallel shocked plasma model we find that temperature, absorption column, ionization time scale, emission measure and elemental abundances of O, Ne, Mg, Si, S and Fe, are smoothly distributed in the remnant. Some regions with overabundances of O-Ne-Mg, previously characterized as ejecta material, were automatically selected by our method, proving the excellent response of the technique. This method is an advantageous tool for the exploitation of archival X-ray data.Comment: Accepted in Astronomy & Astrophysic