324 research outputs found
A new dissipation term for finite-difference simulations in Relativity
We present a new numerical dissipation algorithm, which can be efficiently
used in combination with centered finite-difference methods. We start from a
formulation of centered finite-volume methods for Numerical Relativity, in
which third-order space accuracy can be obtained by employing just
piecewise-linear reconstruction. We obtain a simplified version of the
algorithm, which can be viewed as a centered finite-difference method plus some
'adaptive dissipation'. The performance of this algorithm is confirmed by
numerical results obtained from 3D black hole simulations.Comment: Talk presented at the Spanish Relativity Meeting (Tenerife 2007
Robust evolution system for Numerical Relativity
The paper combines theoretical and applied ideas which have been previously
considered separately into a single set of evolution equations for Numerical
Relativity. New numerical ingredients are presented which avoid gauge
pathologies and allow one to perform robust 3D calculations. The potential of
the resulting numerical code is demonstrated by using the Schwarzschild black
hole as a test-bed. Its evolution can be followed up to times greater than one
hundred black hole masses.Comment: 11 pages, 4 figures; figure correcte
Influence of vulnerability factors in panic disorder severity
Background: We studied herein the predictive value for panic severity of three well-based vulnerability factors: personality traits (neuroticism and extraversion; NEO-PI-R), anxiety sensitivity (ASI), and perceived control (ACQ-R). Method: The sample was composed of 52 participants diagnosed with panic disorder, with or without agoraphobia, according to DSM-IV-TR criteria. Results: Our results revealed that the anxiety facet is a better predictor of panic severity than neuroticism. Anxiety sensitivity increases the predictive value for panic severity and, finally, perception of control of emotions is the only perception control subscale that increases the predictive value for panic severity more than the anxiety facet and anxiety sensitivity. Conclusions: This finding supports the assumption of the importance of taking into account the assessment of the lower order dimensions of the vulnerability factors in the field of psychopathology studies. Furthermore, the predictive value of perception of control of emotions indicates the importance of this specific vulnerability factor in the etiology of panic disorder (with or without agoraphobia) and, thus, shows the necessity to include emotion regulation strategies in the psychological treatments
The structure of Synechococcus elongatus enolase reveals key aspects of phosphoenolpyruvate binding
A structure-function characterization of Synechococcus elongatus enolase (SeEN) is presented, representing the first structural report on a cyanobacterial enolase. X-ray crystal structures of SeEN in its apoenzyme form and in complex with phosphoenolpyruvate are reported at 2.05 and 2.30 Å resolution, respectively. SeEN displays the typical fold of enolases, with a conformationally flexible loop that closes the active site upon substrate binding, assisted by two metal ions that stabilize the negatively charged groups. The enzyme exhibits a catalytic efficiency of 1.2 × 105 M -1s-1for the dehydration of 2-phospho-d-glycerate, which is comparable to the kinetic parameters of related enzymes. These results expand the understanding of the biophysical features of these enzymes, broadening the toolbox for metabolic engineering applications.Fil: Gonzalez, Javier Marcelo. Universidad Nacional de Santiago del Estero. Instituto de Bionanotecnología del Noa. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Instituto de Bionanotecnología del Noa; ArgentinaFil: Martí Arbona, Ricardo. Los Alamos National High Magnetic Field Laboratory; Estados UnidosFil: Chen, Julian C. H.. Los Alamos National High Magnetic Field Laboratory; Estados UnidosFil: Unkefer, Clifford. Los Alamos National High Magnetic Field Laboratory; Estados Unido
Strongly hyperbolic second order Einstein's evolution equations
BSSN-type evolution equations are discussed. The name refers to the
Baumgarte, Shapiro, Shibata, and Nakamura version of the Einstein evolution
equations, without introducing the conformal-traceless decomposition but
keeping the three connection functions and including a densitized lapse. It is
proved that a pseudo-differential first order reduction of these equations is
strongly hyperbolic. In the same way, densitized Arnowitt-Deser-Misner
evolution equations are found to be weakly hyperbolic. In both cases, the
positive densitized lapse function and the spacelike shift vector are arbitrary
given fields. This first order pseudodifferential reduction adds no extra
equations to the system and so no extra constraints.Comment: LaTeX, 16 pages, uses revtex4. Referee corections and new appendix
added. English grammar improved; typos correcte
Formulations of the 3+1 evolution equations in curvilinear coordinates
Following Brown, in this paper we give an overview of how to modify standard
hyperbolic formulations of the 3+1 evolution equations of General Relativity in
such a way that all auxiliary quantities are true tensors, thus allowing for
these formulations to be used with curvilinear sets of coordinates such as
spherical or cylindrical coordinates. After considering the general case for
both the Nagy-Ortiz-Reula (NOR) and the Baumgarte-Shapiro-Shibata-Nakamura
(BSSN) formulations, we specialize to the case of spherical symmetry and also
discuss the issue of regularity at the origin. Finally, we show some numerical
examples of the modified BSSN formulation at work in spherical symmetry.Comment: 19 pages, 12 figure
Stuffed Black Holes
Initial data corresponding to spacetimes containing black holes are
considered in the time symmetric case. The solutions are obtained by matching
across the apparent horizon different, conformally flat, spatial metrics. The
exterior metric is the vacuum solution obtained by the well known conformal
imaging method. The interior metric for every black hole is regular everywhere
and corresponds to a positive energy density. The resulting matched solutions
cover then the whole initial (Cauchy) hypersurface, without any singularity,
and can be useful for numerical applications. The simpler cases of one black
hole (Schwarzschild data) or two identical black holes (Misner data) are
explicitly solved. A procedure for extending this construction to the multiple
black hole case is also given, and it is shown to work for all time symmetric
vacuum solutions obtained by the conformal imaging method. The numerical
evolution of one such 'stuffed' black hole is compared with that of a pure
vacuum or 'plain' black hole in the spherically symmetric case.Comment: 12 pages, Latex, 4 postscript figures, corrected some typos, new
section about physical interpretatio
Hipocondría e información tranquilizadora.
Se revisa el rol de la información tranquilizadora como elemento definitorio y terapéutico de la hipocondría. Se indican algunas cuestiones a contemplar en la futura investigación sobre esta temática
- …