Alkaline battery containing a separator of a cross-linked copolymer of vinyl alcohol and unsaturated carboxylic acid

A battery separator for an alkaline battery is described. The separator comprises a cross linked copolymer of vinyl alcohol units and unsaturated carboxylic acid units. The cross linked copolymer is insoluble in water, has excellent zincate diffusion and oxygen gas barrier properties and a low electrical resistivity. Cross linking with a polyaldehyde cross linking agent is preferred

Design principles for nickel-hydrogen cells and batteries

Nickel-hydrogen cells and, more recently, bipolar batteries have been built by a variety of organizations. The design principles that have been used by the technology group at the NASA Lewis Research Center draw upon their extensive background in separator technology, alkaline fuel cell technology, and several alkaline cell technology areas. These design principles have been incorporated into both the more contemporary individual pressure vessel (IPV) designs that were pioneered by other groups, as well as the more recent bipolar battery designs using active cooling that are being developed at NASA Lewis Research Center and under contract. These principles are rather straightforward applications of capillary force formalisms, coupled with the slowly developing data base resulting from careful post test analyses. The objective of this overall effort is directed towards the low-Earth-orbit (LEO) application where the cycle life requirements are much more severe than the geosynchronous-orbit (GEO) application. A summary of the design principles employed is presented along with a discussion of the recommendations for component pore sizes and pore size distributions, as well as suggested materials of construction. These will be made based on our experience in these areas to show how these design principles have been translated into operating hardware

Chaotic dynamics around astrophysical objects with nonisotropic stresses

The existence of chaotic behavior for the geodesics of the test particles orbiting compact objects is a subject of much current research. Some years ago, Gu\'eron and Letelier [Phys. Rev. E \textbf{66}, 046611 (2002)] reported the existence of chaotic behavior for the geodesics of the test particles orbiting compact objects like black holes induced by specific values of the quadrupolar deformation of the source using as models the Erez--Rosen solution and the Kerr black hole deformed by an internal multipole term. In this work, we are interesting in the study of the dynamic behavior of geodesics around astrophysical objects with intrinsic quadrupolar deformation or nonisotropic stresses, which induces nonvanishing quadrupolar deformation for the nonrotating limit. For our purpose, we use the Tomimatsu-Sato spacetime [Phys. Rev. Lett. \textbf{29} 1344 (1972)] and its arbitrary deformed generalization obtained as the particular vacuum case of the five parametric solution of Manko et al [Phys. Rev. D 62, 044048 (2000)], characterizing the geodesic dynamics throughout the Poincar\'e sections method. In contrast to the results by Gu\'eron and Letelier we find chaotic motion for oblate deformations instead of prolate deformations. It opens the possibility that the particles forming the accretion disk around a large variety of different astrophysical bodies (nonprolate, e.g., neutron stars) could exhibit chaotic dynamics. We also conjecture that the existence of an arbitrary deformation parameter is necessary for the existence of chaotic dynamics.Comment: 7 pages, 5 figure

Realistic Exact Solution for the Exterior Field of a Rotating Neutron Star

A new six-parametric, axisymmetric and asymptotically flat exact solution of Einstein-Maxwell field equations having reflection symmetry is presented. It has arbitrary physical parameters of mass, angular momentum, mass--quadrupole moment, current octupole moment, electric charge and magnetic dipole, so it can represent the exterior field of a rotating, deformed, magnetized and charged object; some properties of the closed-form analytic solution such as its multipolar structure, electromagnetic fields and singularities are also presented. In the vacuum case, this analytic solution is matched to some numerical interior solutions representing neutron stars, calculated by Berti & Stergioulas (Mon. Not. Roy. Astron. Soc. 350, 1416 (2004)), imposing that the multipole moments be the same. As an independent test of accuracy of the solution to describe exterior fields of neutron stars, we present an extensive comparison of the radii of innermost stable circular orbits (ISCOs) obtained from Berti & Stergioulas numerical solutions, Kerr solution (Phys. Rev. Lett. 11, 237 (1963)), Hartle & Thorne solution (Ap. J. 153, 807, (1968)), an analytic series expansion derived by Shibata & Sasaki (Phys. Rev. D. 58 104011 (1998)) and, our exact solution. We found that radii of ISCOs from our solution fits better than others with realistic numerical interior solutions.Comment: 13 pages, 13 figures, LaTeX documen

Photofission of heavy nuclei at energies up to 4 GeV

Total photofission cross sections for 238U, 235U, 233U, 237Np, 232Th, and natPb have been measured simultaneously, using tagged photons in the energy range Egamma=0.17-3.84 GeV. This was the first experiment performed using the Photon Tagging Facility in Hall B at Jefferson Lab. Our results show that the photofission cross section for 238U relative to that for 237Np is about 80%, implying the presence of important processes that compete with fission. We also observe that the relative photofission cross sections do not depend strongly on the incident photon energy over this entire energy range. If we assume that for 237Np the photofission probability is equal to unity, we observe a significant shadowing effect starting below 1.5 GeV.Comment: 4 pages of RevTex, 6 postscript figures, Submitted to Phys. Rev. Let

Colapso gravitacional radiativo esféricamente simétrico en relatividad general: introducción del factor de flujo, el factor de Eddington y la influencia de la relación de clausura entre ellos sobre la evolución del sistema

The H–J–Rs’ method [Phys. Rev. D22, 2305 (1980)] is extended to include the Eddington’s variable factor, the radiation flux factor and a closure relationship between them in order to show its influence on the behavior of density, pressure, fluid velocity and energy radiation flux, among others, of an object under gravitational collapse within the framework of general relativity. The post-quasistatic approximation of Herrera et al [Phys. Rev. D65, 104004 (2002)] along with the Tolman VI equation of state and the Lorentz–Eddington, Bowers–Wilson and Maximum Packing relationships were used to find that the choice of different closure relationships does not affect the global behavior of the system but only the instantaneous values of the different physical quantities.  Se extiende el método H–J–R [Phys. Rev. D22, 2305 (1980)] utilizando el factor variable de Eddington y el factor de flujo de radiación, y se presenta la influencia de la elección de la relación entre ellos sobre el comportamiento en el tiempo de la densidad, presión, velocidad del fluido y flujo de radiación, entre otras, de un objeto en fase de colapso gravitacional radiativo en el marco de la relatividad general. Para tal fin, se ha utilizado la aproximación poscuasiestática de Herrera et al [Phys. Rev. D65, 104004 (2002)] con la ecuación de estado Tolman VI y las relaciones de clausura de Lorentz–Eddington, Bowers–Wilson y Maximum Packing, encontrando que la elección de una relación de clausura particular no afecta el comportamiento General del colapso, pero sí afecta los valores instantáneos de las diferentes magnitudes físicas.         &nbsp

Frecuencia y sensibilidad antimicrobiana de agentes etiológicos de dacriocistitis

La dacriocistitis representa la infección más frecuente del sistema lagrimal. El estudio microbiológico de las dacriocistitis es importante para la adecuada selección de los antibióticos. El objetivo del estudio es determinar la frecuencia y sensibilidad antimicrobiana de los agentes causantes de dacriocistitis en pacientes que acudieron a laCátedra de Oftalmología del Hospital de Clínicas de mayo de 1998 a abril de 2007. Los pacientes no recibieron antibióticos por lo menos por una semana antes de la toma de muestra, que fueron tomadas por aspiración del contenido del saco lagrimal por el canalículo inferior o punción directa del saco lagrimal, y cultivadas en aerobiosis y anaerobiosis siguiendo métodos convencionales. De 41 pacientes (23 adultos y 18 niños), 30 (73,1%) presentaron cultivos positivos; 16 (53.4%) monomicrobianos y 14 (46,6%) polimicrobianos. Se aislaron 51 microorganismos, 37 en adultos y 14 en niños. El 54% de los microorganismos aislados en muestras de adultos correspondió a bacilos gramnegativos (enterobacterias, Haemophilus sp, anaerobios, y bacilos gramnegativos no fermentadores); 41% a cocos grampositivos (Staphylococcus aureus, Streptococcus pneumoniae, Streptococcus viridans, y estafilococo coagulasa negativo); el 72% de los micro-organismos aislados en niños correspondió a cocos grampositivos (Staphylococcus aureus y Streptococcus pneumoniae), y en una muestra se aisló Candida sp. La sensibilidad del Streptococcus pneumoniae a la penicilina y la del Staphylococcus aureus a la meticilina fue de 100%. Los microorganismos aislados presentaron buena sensibilidad a los antimicrobianos, pero por la gran variedad de microorganismos y la naturaleza polimicrobiana de los cultivos se debería ampliar el esquema inicial de tratamiento y de la profilaxis de la dacriocistorrinostomía y otros procedimientos intraoculares. Una opción es el uso de aminopenicilinas con un inhibidor de betalactamasa; asociado con colirio de tobramicina en niños y ciprofloxacina en adultos