Contribución al estudio de fluidos disipativos esféricamente simétricos

Se realiza un estudio de fluidos autogravitantes, esféricamentesimétricos, disipativos y localmente anisótropos en las presiones, discutiéndose la relación que existe entre el tensor de Weyl, el tensor de deformación, la anisotropía y la inhomogeneidad en la densidad de energía. Además, seanalizan distintos casos particulares de fluidos esféricamente simétricos, incluyendo el caso más general en el cual todas las variables mencionadas son distintas de cero. En el caso de fluidos perfectos, o fluidos disipativos, pero localmente anisótropos en el régimen de evolución cuasiestática, la inhomogeneidad en la densidad de energía depende exclusivamente del tensor de Weyl, lo cual refuerza la hipótesis de Penrose [1], la cual considera que los sistemas autogravitantes tienden a formar inhomogeneidades, definiéndose así una flecha gravitacional del tiempo. En el trabajo se concluye que en el caso más general, si se adopta el punto de vista de Penrose entonces esta flecha gravitacional depende tanto del tensor de Weyl como de la anisotropía y la disipación.  In this paper we study self-gravity, spherically symmetrical, dissipative and locally anisotropic in the pressure fluids; we discuss the relationship between the Weyl tensor, the deformation tensor, the anisotropy and inhomogeneities in the energy density. In addition, individual cases of spherically symmetric fluids, including the more general case in which all the variables above mentioned are different from zero, are studied. In the case of perfect fluids, or fluid dissipative but locally anisotropic in the regime of quasi-static evolution, the inhomogeneities in the energy density depends exclusively on the Weyl tensor, which reinforces the hypothesis of Penrose [1], which is based on the fact that the self-gravity systems tend to form inhomogeneities, defining so a gravitational time arrow. In the paper we conclude that in the more general case, if the perspective of Penrose is adopted, then this arrow is as dependent on the gravitational tensor of Weyl as on the anisotropy of the dissipation

Contribución al estudio de fluidos disipativos esféricamente simétricos

Se realiza un estudio de fluidos autogravitantes, esféricamentesimétricos, disipativos y localmente anisótropos en las presiones, discutiéndose la relación que existe entre el tensor de Weyl, el tensor de deformación, la anisotropía y la inhomogeneidad en la densidad de energía. Además, seanalizan distintos casos particulares de fluidos esféricamente simétricos, incluyendo el caso más general en el cual todas las variables mencionadas son distintas de cero. En el caso de fluidos perfectos, o fluidos disipativos, pero localmente anisótropos en el régimen de evolución cuasiestática, la inhomogeneidad en la densidad de energía depende exclusivamente del tensor de Weyl, lo cual refuerza la hipótesis de Penrose [1], la cual considera que los sistemas autogravitantes tienden a formar inhomogeneidades, definiéndose así una flecha gravitacional del tiempo. En el trabajo se concluye que en el caso más general, si se adopta el punto de vista de Penrose entonces esta flecha gravitacional depende tanto del tensor de Weyl como de la anisotropía y la disipación.  In this paper we study self-gravity, spherically symmetrical, dissipative and locally anisotropic in the pressure fluids; we discuss the relationship between the Weyl tensor, the deformation tensor, the anisotropy and inhomogeneities in the energy density. In addition, individual cases of spherically symmetric fluids, including the more general case in which all the variables above mentioned are different from zero, are studied. In the case of perfect fluids, or fluid dissipative but locally anisotropic in the regime of quasi-static evolution, the inhomogeneities in the energy density depends exclusively on the Weyl tensor, which reinforces the hypothesis of Penrose [1], which is based on the fact that the self-gravity systems tend to form inhomogeneities, defining so a gravitational time arrow. In the paper we conclude that in the more general case, if the perspective of Penrose is adopted, then this arrow is as dependent on the gravitational tensor of Weyl as on the anisotropy of the dissipation

Dynamics of viscous dissipative gravitational collapse: A full causal approach

The Misner and Sharp approach to the study of gravitational collapse is extended to the viscous dissipative case in, both, the streaming out and the diffusion approximations. The dynamical equation is then coupled to causal transport equations for the heat flux, the shear and the bulk viscosity, in the context of Israel--Stewart theory, without excluding the thermodynamics viscous/heat coupling coefficients. The result is compared with previous works where these later coefficients were neglected and viscosity variables were not assumed to satisfy causal transport equations. Prospective applications of this result to some astrophysical scenarios are discussed.Comment: 22 pages Latex. To appear in Int. J. Mod. Phys. D. Typos correcte

Contribución al estudio de fluidos disipativos esféricamente simétricos

Se realiza un estudio de fluidos autogravitantes, esféricamentesimétricos, disipativos y localmente anisótropos en las presiones, discutiéndose la relación que existe entre el tensor de Weyl, el tensor de deformación, la anisotropía y la inhomogeneidad en la densidad de energía. Además, seanalizan distintos casos particulares de fluidos esféricamente simétricos, incluyendo el caso más general en el cual todas las variables mencionadas son distintas de cero. En el caso de fluidos perfectos, o fluidos disipativos, pero localmente anisótropos en el régimen de evolución cuasiestática, la inhomogeneidad en la densidad de energía depende exclusivamente del tensor de Weyl, lo cual refuerza la hipótesis de Penrose [1], la cual considera que los sistemas autogravitantes tienden a formar inhomogeneidades, definiéndose así una flecha gravitacional del tiempo. En el trabajo se concluye que en el caso más general, si se adopta el punto de vista de Penrose entonces esta flecha gravitacional depende tanto del tensor de Weyl como de la anisotropía y la disipación.

Histopathological reaction in the vestibule after cochlear implantation in Macaca fascicularis.

Cochlear implantation surgery (CI) is considered a safe procedure and is the standard treatment for the auditory rehabilitation in patients with severe-to-profound sensorineural hearing loss. Although the development of minimally traumatic surgical concepts (MTSC) have enabled the preservation of residual hearing after the implantation, there is scarce literature regarding the vestibular affection following MTCS. The aim of the study is to analyze histopathologic changes in the vestibule after CI in an animal model (Macaca fascicularis). Cochlear implantation was performed successfully in 14 ears following MTCS. They were classified in two groups upon type of electrode array used. Group A (n = 6) with a FLEX 28 electrode array and Group B (n = 8) with HL14 array. A 6-month follow-up was carried out with periodic objective auditory testing. After their sacrifice, histological processing and subsequent analysis was carried out. Intracochlear findings, vestibular presence of fibrosis, obliteration or collapse is analyzed. Saccule and utricle dimensions and neuroepithelium width is measured. Cochlear implantation was performed successfully in all 14 ears through a round window approach. Mean angle of insertion was >270◦ for group A and 180–270◦ for group B. In group A auditory deterioration was observed in Mf 1A, Mf2A and Mf5A with histopathological signs of scala tympani ossification, saccule collapse (Mf1A and Mf2A) and cochlear aqueduct obliteration (Mf5A). Besides, signs of endolymphatic sinus dilatation was seen for Mf2B and Mf5A. Regarding group B, no auditory deterioration was observed. Histopathological signs of endolymphatic sinus dilatation were seen in Mf 2B and Mf 8B. In conclusion, the risk of histological damage of the vestibular organs following minimally traumatic surgical concepts and the soft surgery principles is very low. CI surgery is a safe procedure and it can be done preserving the vestibular structures

Structure and evolution of self-gravitating objects and the orthogonal splitting of the Riemann tensor

The full set of equations governing the structure and the evolution of self--gravitating spherically symmetric dissipative fluids with anisotropic stresses, is written down in terms of five scalar quantities obtained from the orthogonal splitting of the Riemann tensor, in the context of general relativity. It is shown that these scalars are directly related to fundamental properties of the fluid distribution, such as: energy density, energy density inhomogeneity, local anisotropy of pressure, dissipative flux and the active gravitational mass. It is also shown that in the static case, all possible solutions to Einstein equations may be expressed explicitly through these scalars. Some solutions are exhibited to illustrate this point.Comment: 32 pages, Late

Spherically symmetric dissipative anisotropic fluids: A general study

The full set of equations governing the evolution of self--gravitating spherically symmetric dissipative fluids with anisotropic stresses is deployed and used to carry out a general study on the behaviour of such systems, in the context of general relativity. Emphasis is given to the link between the Weyl tensor, the shear tensor, the anisotropy of the pressure and the density inhomogeneity. In particular we provide the general, necessary and sufficient, condition for the vanishing of the spatial gradients of energy density, which in turn suggests a possible definition of a gravitational arrow of time. Some solutions are also exhibited to illustrate the discussion.Comment: 28 pages Latex. To appear in Phys.Rev.

Identification and characterization of antibacterial compound(s) of cockroaches (Periplaneta americana)

Infectious diseases remain a significant threat to human health, contributing to more than 17 million deaths, annually. With the worsening trends of drug resistance, there is a need for newer and more powerful antimicrobial agents. We hypothesized that animals living in polluted environments are potential source of antimicrobials. Under polluted milieus, organisms such as cockroaches encounter different types of microbes, including superbugs. Such creatures survive the onslaught of superbugs and are able to ward off disease by producing antimicrobial substances. Here, we characterized antibacterial properties in extracts of various body organs of cockroaches (Periplaneta americana) and showed potent antibacterial activity in crude brain extract against methicillin-resistant Staphylococcus aureus and neuropathogenic E. coli K1. The size-exclusion spin columns revealed that the active compound(s) are less than 10 kDa in molecular mass. Using cytotoxicity assays, it was observed that pre-treatment of bacteria with lysates inhibited bacteria-mediated host cell cytotoxicity. Using spectra obtained with LC-MS on Agilent 1290 infinity liquid chromatograph, coupled with an Agilent 6460 triple quadruple mass spectrometer, tissues lysates were analyzed. Among hundreds of compounds, only a few homologous compounds were identified that contained isoquinoline group, chromene derivatives, thiazine groups, imidazoles, pyrrole containing analogs, sulfonamides, furanones, flavanones, and known to possess broad-spectrum antimicrobial properties, and possess anti-inflammatory, anti-tumour, and analgesic properties. Further identification, characterization and functional studies using individual compounds can act as a breakthrough in developing novel therapeutics against various pathogens including superbugs

Contribución al estudio de fluidos disipativos esféricamente simétricos

In this paper we study self-gravity, spherically symmetrical, dissipative and locally anisotropic in the pressure fluids; we discuss the relationship between the Weyl tensor, the deformation tensor, the anisotropy and inhomogeneities in the energy density. In addition, individual cases of spherically symmetric fluids, including the more general case in which all the variables above mentioned are different from zero, are studied. In the case of perfect fluids, or fluid dissipative but locally anisotropic in the regime of quasi-static evolution, the inhomogeneities in the energy density depends exclusively on the Weyl tensor, which reinforces the hypothesis of Penrose [1], which is based on the fact that the self-gravity systems tend to form inhomogeneities, defining so a gravitational time arrow. In the paper we conclude that in the more general case, if the perspective of Penrose is adopted, then this arrow is as dependent on the gravitational tensor of Weyl as on the anisotropy of the dissipation.Se realiza un estudio de fluidos autogravitantes, esféricamentesimétricos, disipativos y localmente anisótropos en las presiones, discutiéndose la relación que existe entre el tensor de Weyl, el tensor de deformación, la anisotropía y la inhomogeneidad en la densidad de energía. Además, seanalizan distintos casos particulares de fluidos esféricamente simétricos, incluyendo el caso más general en el cual todas las variables mencionadas son distintas de cero. En el caso de fluidos perfectos, o fluidos disipativos, pero localmente anisótropos en el régimen de evolución cuasiestática, la inhomogeneidad en la densidad de energía depende exclusivamente del tensor de Weyl, lo cual refuerza la hipótesis de Penrose [1], la cual considera que los sistemas autogravitantes tienden a formar inhomogeneidades, definiéndose así una flecha gravitacional del tiempo. En el trabajo se concluye que en el caso más general, si se adopta el punto de vista de Penrose entonces esta flecha gravitacional depende tanto del tensor de Weyl como de la anisotropía y la disipación.