Can a Kasner Universe with a Viscous Cosmological Fluid be Anisotropic?

A Bianchi type -I metric of Kasner form is considered, when the space is filled with a viscous fluid. Whereas an ideal (nonviscous) fluid permits the Kasner metric to be anisotropic provided that the fluid satisfies the Zel'dovich equation of state, the viscous fluid does not permit the Kasner metric to be anisotropic at all. In the latter case, we calculate the Kasner (isotropic) metric expressed by the fluid's density, pressure, and bulk viscosity, at some chosen instant $t=t_0$. The equation of state is also calculated. The present paper is related to a recent Comment of Cataldo and del Campo [Phys. Rev. D, scheduled to April 15, 2000], on a previous work of the present authors [Phys. Rev. D {\bf 56}, 3322 (1997)].Comment: 8 pages, LaTeX, no figures. To appear in PR

Evolving Lorentzian wormholes supported by phantom matter with constant state parameters

In this paper we study the possibility of sustaining an evolving wormhole via exotic matter made out of phantom energy. We show that this exotic source can support the existence of evolving wormhole spacetimes. Explicitly, a family of evolving Lorentzian wormholes conformally related to another family of zero-tidal force static wormhole geometries is found in Einstein gravity. Contrary to the standard wormhole approach, where first a convenient geometry is fixed and then the matter distribution is derived, we follow the conventional approach for finding solutions in theoretical cosmology. We derive an analytical evolving wormhole geometry by supposing that the radial tension (which is negative to the radial pressure) and the pressure measured in the tangential directions have barotropic equations of state with constant state parameters. At spatial infinity this evolving wormhole, supported by this anisotropic matter, is asymptotically flat, and its slices $t=$ constant are spaces of constant curvature. During its evolution the shape of the wormhole expands with constant velocity, i.e without acceleration or deceleration, since the scale factor has strictly a linear evolution.Comment: 9 pages, 2 figures, Accepted for publication in Phys. Rev.

Viscous cosmologies in scalar-tensor theories for Kasner type metrics

In a viscous Bianchi type I metric of the Kasner form, it is well known that it is not possible to describe an anisotropic physical model of the universe, which satisfies the second law of thermodynamics and the dominant energy condition (DEC) in Einstein's theory of gravity. We examine this problem in scalar-tensor theories of gravity. In this theory we show that it is possible to describe the growth of entropy, keeping the thermodynamics and the dominant energy condition.Comment: 6 pages, Latex, accepted in Phys. Rev.

Casimir Effects Near the Big Rip Singularity in Viscous Cosmology

Analytical properties of the scalar expansion in the cosmic fluid are investigated, especially near the future singularity, when the fluid possesses a constant bulk viscosity \zeta. In addition, we assume that there is a Casimir-induced term in the fluid's energy-momentum tensor, in such a way that the Casimir contributions to the energy density and pressure are both proportional to 1/a^4, 'a' being the scale factor. A series expansion is worked out for the scalar expansion under the condition that the Casimir influence is small. Close to the Big Rip singularity the Casimir term has however to fade away and we obtain the same singular behavior for the scalar expansion, the scale factor, and the energy density, as in the Casimir-free viscous case.Comment: 7 pages RevTeX, no figures. Minor changes in discussion, some references added. To appear in Gen. Rel. Gra

Bianchi Type I Universes with Causal Bulk Viscous Cosmological Fluid

We consider the dynamics of a causal bulk viscous cosmological fluid filled constantly decelerating Bianchi type I space-time. The matter component of the Universe is assumed to satisfy a linear barotropic equation of state and the state equation of the small temperature Boltzmann gas. The resulting cosmological models satisfy the condition of smallness of the viscous stress. The time evolution of the relaxation time, temperature, bulk viscosity coefficient and comoving entropy of the dissipative fluid is also obtained.Comment: 11 pages, 5 figures, accepted for publication in International Journal of Modern Physics

Classification of HEp-2 staining patterns in ImmunoFluorescence images. Comparison of Support Vector Machines and Subclass Discriminant Analysis strategies

nti-nuclear antibodies test is based on the visual evaluation of the intensity and staining pattern in HEp-2 cell slides by means of indirect immunofluorescence (IIF) imaging, revealing the presence of autoantibodies responsible for important immune pathologies. In particular, the categorization of the staining pattern is crucial for differential diagnosis, because it provides information about autoantibodies type. Their manual classification is very time-consuming and not very reliable, since it depends on the subjectivity and on the experience of the specialist. This motivates the growing demand for computer-aided solutions able to perform staining pattern classification in a fully automated way. In this work we compare two classification techniques, based respectively on Support Vector Machines and Subclass Discriminant Analysis. A set of textural features characterizing the available samples are first extracted. Then, a feature selection scheme is applied in order to produce different datasets, containing a limited number of image attributes that are best suited to the classification purpose. Experiments on IIF images showed that our computer-aided method is able to identify staining patterns with an average accuracy of about 91% and demonstrate, in this specific problem, a better performance of Subclass Discriminant Analysis with respect to Support Vector Machine

Idiopathic Myenteric Ganglionitis Underlying Acute ‘Dramatic’ Intestinal Pseudoobstruction: Report of an Exceptional Case

Inflammation of the myenteric plexus of the gastrointestinal tract is a very rare pathological condition, with few reports in the medical literature. This pathological condition causes atonic gut motor dysfunction and is principally secondary to other diseases, being reported nearly solely as a paraneoplastic phenomenon in neuroendocrine lung tumors, including small cell carcinomas or neuroblastomas. In addition it can also be associated with disorders of the central nervous system, although it has rarely been described in Chagas disease. It has been named ‘idiopathic myenteric ganglionitis’ because no apparent causes can be demonstrated. We report the clinicopathologic findings of an exceptional case of a young woman affected by severe chronic constipation suddenly changing into acute intestinal pseudoobstruction with dramatic evolution. Relationships between ganglionitis, idiopathic constipation and acute intestinal pseudoobstruction as well as therapeutic implications are discussed

Proposition of a method based on mind maps to study changes in users’ perceptions during an IS/IT adoption process

Although knowledge about IS/IT adoption is very broad, it is fragmented, and we still do not understand well how users move dynamically from one stage to another during the adoption process, that is, from when a user knows a new technology until, if the process is successful, she/he incorporates it into her/his routine. One of the causes of this theoretical limitation relates to the lack of methodologies that help researchers analyze longitudinally collected data and distinguish changes that occur over time as participants experience the implementation of the new system. In this article, we present a method based on mind maps that allows researchers to graphically synthesize the mental processes experienced by individuals as they adopt a new system. The method allows comparing and measuring changes among mental models of an individual in different stages of the adoption. Findings show that this method better reflects user perceptions than others based on surveys and technical processing of textual data. Using mind maps is a novel contribution to researching and understanding technology adoption in a holistic way and with methods that include time as a contextual variable in the adoption process

Vortex pseudomomentum and dissipation in a superfluid vortex lattice

We propose an alternative approach to the dissipative vortex dynamics occurring in a superfluid vortex lattice at finite temperatures. Focusing upon the pseudomomentum of a vortex and its surrounding quasiparticles, we derive an equation of motion which, in spite of yielding the same evolution as the usual one for massless vortices, does not involve the vortex mass. This picture could provide further insights into the controversy about the nature of the vortex mass.Comment: 11 pages, no figures. Typo corrected in equation (28

Crossing of the w=-1 Barrier in Two-Fluid Viscous Modified Gravity

Singularities in the dark energy late universe are discussed, under the assumption that the Lagrangian contains the Einstein term R plus a modified gravity term of the form R^\alpha, where \alpha is a constant. It is found, similarly as in the case of pure Einstein gravity [I. Brevik and O. Gorbunova, Gen. Rel. Grav. 37 (2005), 2039], that the fluid can pass from the quintessence region (w>-1) into the phantom region (w<-1) as a consequence of a bulk viscosity varying with time. It becomes necessary now, however, to allow for a two-fluid model, since the viscosities for the two components vary differently with time. No scalar fields are needed for the description of the passage through the phantom barrier.Comment: 16 pages latex, no figure