Criticality of inhomogeneous Nariai-like cosmological models

In this paper, we construct and study solutions of Einstein's equations in vacuum with a positive cosmological constant which can be considered as inhomogeneous generalizations of the Nariai cosmological model. Similar to this Nariai spacetime, our solutions are at the borderline between gravitational collapse and de-Sitter-like exponential expansion. Our studies focus in particular on the intriguing oscillatory dynamics which we discover. Our investigations are carried out both analytically (using heuristic mode analysis arguments) and numerically (using the numerical infrastructure recently introduced by us).Comment: 34 pages, 17 figure

Spectral-infinite element method approach for computing asymptotically flat initial data sets in general relativity

In this work, we introduce a spectral-infinite element method for solving Einstein's constraint equations in hyperbolic form. As an application of this, we use this method for computing asymptotically flat perturbations of a Kerr black hole with small angular momentum. Our numerical infrastructure is based on the use of a spin-weighted spherical harmonic transform combined with an infinite element method for solving partial differential equations in unbounded domains

Phase space analysis of quintessence fields trapped in a Randall-Sundrum Braneworld: anisotropic Bianchi I brane with a Positive Dark Radiation term

In this paper we investigate, from the dynamical systems perspective, the evolution of an scalar field with arbitrary potential trapped in a Randall-Sundrum's Braneworld of type 2. We consider an homogeneous but anisotropic Bianchi I (BI) brane filled also with a perfect fluid. We also consider the effect of the projection of the five-dimensional Weyl tensor onto the three-brane in the form of a positive Dark Radiation term. Using the center manifold theory we obtain sufficient conditions for the asymptotic stability of de Sitter solution with standard 4D behavior. We also prove that there are not late time de Sitter attractors with 5D-modifications since they are always saddle-like. This fact correlates with a transient primordial inflation. We present here sufficient conditions on the potential for the stability of the scalar field-matter scaling solution, the scalar field-dominated solution, and the scalar field-dark radiation scaling solution. We illustrate our analytical findings using a simple $f$-deviser as a toy model. All these results are generalizations of our previous results obtained for FRW branes.Comment: 14 pages, 11 figures, one affiliation added, matches the published version at CQG. arXiv admin note: substantial text overlap with arXiv:1110.173

Graceful exit from inflation for minimally coupled Bianchi A scalar field models

We consider the dynamics of Bianchi A scalar field models which undergo inflation. The main question is under which conditions does inflation come to an end and is succeeded by a decelerated epoch. This so-called "graceful exit" from inflation is an important ingredient in the standard model of cosmology, but is, at this stage, only understood for restricted classes of solutions. We present new results obtained by a combination of analytical and numerical techniques.Comment: 37 pages, 26 figures; matches the version published in CQ

Numerical Construction of initial data sets for inhomogeneous cosmological space-times with spatial topology of T3\mathbb{T}^3

In this work, we numerically construct initial data sets for cosmological space-times with a spatial topology of $\mathbb{T}^3$, which are generally inhomogeneous. To do so, we implement a pseudo-spectral approach based on the discrete Fourier transform for numerically solving Einstein's constraint equations in an algebraic-hyperbolic form. We explore the advantages and disadvantages of this method by comparing the numerical solutions with known analytical initial data sets. Furthermore, we obtain new families of initial data sets numerically for different configurations of the boundary values of certain geometric variables

Studies of spacetimes with spatial topologies S3 and S1 X S2

The purpose of this work is to introduce a new analytical and numerical approach to the treatment of the initial value problem for the vacuum Einstein field equations on spacetimes with spatial topologies S3 or S1 × S2 and symmetry groups U(1) or U(1)×U(1). The general idea consists of taking advantage of the action of the symmetry group U(1) to rewrite those spacetimes as a principal fiber bundle, which is trivial for S1 × S2 but not for S3. Thus, the initial value problem in four dimensions can be reduced to a three-dimensional initial value problem for a certain manifold with spatial topology S2. Furthermore, we avoid coordinate representations that suffer from coordinate singularities for S2 by expressing all the fields in terms of the spin-weighted spherical harmonics. We use the generalized wave map formalism to reduce the vacuum Einstein field equations on a manifold with three spatial dimensions to a system of quasilinear wave equations in terms of generalized gauge source functions with well-defined spin-weights. As a result, thanks to the fully tensorial character of these equations, the system of evolution equations can be solved numerically using a 2 + 1-pseudo-spectral approach based on a spin-weighted spherical harmonic transform. In this work, however, we apply our infrastructure to the study of Gowdy symmetric spacetimes, where thanks to the symmetry group U(1) × U(1), the system of hyperbolic equations obtained from the vacuum Einstein field equations can be reduced to a 1+1-system of partial differential equations. Therefore, we introduce an axial symmetric spin-weighted transform that provides an efficient treatment of axially symmetric functions in S2 by reducing the complexity of the general transform. To analyse the consistency, accuracy, and feasibility of our numerical infrastructure, we reproduce an inhomogeneous cosmological solution of the vacuum Einstein field quations with spatial topology S3 . In addition, we consider two applications of our infrastructure. In the first one, we numerically explore the behaviour of Gowdy S1 × S2 spacetimes using our infrastructure. In particular, we study the behaviour of some geometrical quantities to investigate the behaviour of those spacetimes when approach a future singularity. As a second application, we conduct a systematic investigation on the non-linear instability of the Nariai spacetime and the asymptotic behaviour of its perturbations

Caracterización bioquímica de proteasas de bacterias halotolerantes M3H1027, ML106512 y M4H153D

La presente investigación tiene como objeto de estudio a las bacterias halófilas que son microorganismos que crecen en ambientes con alto contenido de salinidad, capaces de producir proteasas importantes que han permitido el avance en la industria alimentaria, industria química y en biomedicina. El objetivo del trabajo fue caracterizar las proteasas intracelulares y extracelulares de bacterias halófilas obtenidas de los manantiales salinos de los distritos de Acos y Huanoquite de la región Cusco. Para conseguir el objetivo, a partir de cepas previamente aisladas, se realizó una selección de aquellas con actividad proteolítica, y se evaluó la actividad semicuantitativa en extractos crudos extracelulares e intracelulares en función a la concentración de proteínas totales correspondientes. El procedimiento de caracterización consistió en evaluar la actividad proteolítica bajo los efectos de temperatura, pH, iones metálicos y NaCl. La cepa M3H1027 presenta 5 proteasas cuyos tamaños moleculares son de 25 kDa, 29.4 kDa, 39.4 kDa, 54.2 kDa y 57.4 kDa, presentan metalo, serín y cisteín proteasas inhibidas por EDTA, leupeptín y E-64 respectivamente. Posee actividad termal óptima en amplios rangos de temperatura (4-70°C), pH (5.25-10.04), concentración de NaCl (0-20%) y mostró alta actividad proteolítica en presencia de Ca2+ y Mg2+. La cepa ML106512 presenta 3 proteasas extracelulares cuyos tamaños moleculares son de 17.3 kDa, 25 kDa y 30.5 kDa y una proteasa intracelular de 17.3 kDa. Las proteasas de 25 y 30.5 kDa no presentan inhibición, y la proteasa de 17.3 kDa es una cisteín proteasa.UNSAA