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      A Compact Radio Counterpart to the Energetic X-ray Pulsar Associated with the TeV Gamma-Ray Source J1813-178

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          Abstract

          We report the detection of a time-variable, compact radio source coincident with CXOU J181335.1-174957, the X-ray pulsar near the center of the young radio supernova remnant G12.82-0.02, which overlaps the compact TeV source HESS J1813-178. The compact radio source, named VLA J181335.1-174957, was detected in 4.86 GHz VLA observations made in 2006. New VLA observations made in 2009 do not detect the source at a level 1.9±0.7 times (2.8σ) lower than that of 2006. We suggest that VLA J181335.1-174957 may be related to one of the recently detected classes of variable radio pulsars but cannot reach a firmer conclusion.

          Translated abstract

          Reportamos la detección de una fuente de radio compacta y variable coincidente con CXOU J181335.1-174957, el pulsar de rayos-X localizado cerca del centro de la remanente de supernova joven G12.82-0.02, la cual traslapa con la fuente TeV compacta HESS J1813-178. La fuente de radio compacta, que llamamos VLA J181335.1-174957, fue detectada en observaciones hechas a 4.86 GHz con el VLA en 2006. Nuevas observaciones hechas con el VLA en 2009 no detectan la fuente a un nivel 1.9±0.7 veces (2.8σ) más bajo que el de 2006. Sugerimos que VLA J181335.1-174957 podría estar relacionada con alguna de las recientemente detectadas clases de pulsares de radio variables, pero no podemos alcanzar una conclusión más sólida.

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          Rapid planetesimal formation in turbulent circumstellar discs

          The initial stages of planet formation in circumstellar gas discs proceed via dust grains that collide and build up larger and larger bodies (Safronov 1969). How this process continues from metre-sized boulders to kilometre-scale planetesimals is a major unsolved problem (Dominik et al. 2007): boulders stick together poorly (Benz 2000), and spiral into the protostar in a few hundred orbits due to a head wind from the slower rotating gas (Weidenschilling 1977). Gravitational collapse of the solid component has been suggested to overcome this barrier (Safronov 1969, Goldreich & Ward 1973, Youdin & Shu 2002). Even low levels of turbulence, however, inhibit sedimentation of solids to a sufficiently dense midplane layer (Weidenschilling & Cuzzi 1993, Dominik et al. 2007), but turbulence must be present to explain observed gas accretion in protostellar discs (Hartmann 1998). Here we report the discovery of efficient gravitational collapse of boulders in locally overdense regions in the midplane. The boulders concentrate initially in transient high pressures in the turbulent gas (Johansen, Klahr, & Henning 2006), and these concentrations are augmented a further order of magnitude by a streaming instability (Youdin & Goodman 2005, Johansen, Henning, & Klahr 2006, Johansen & Youdin 2007) driven by the relative flow of gas and solids. We find that gravitationally bound clusters form with masses comparable to dwarf planets and containing a distribution of boulder sizes. Gravitational collapse happens much faster than radial drift, offering a possible path to planetesimal formation in accreting circumstellar discs.
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            A perovskite oxide optimized for oxygen evolution catalysis from molecular orbital principles.

            The efficiency of many energy storage technologies, such as rechargeable metal-air batteries and hydrogen production from water splitting, is limited by the slow kinetics of the oxygen evolution reaction (OER). We found that Ba(0.5)Sr(0.5)Co(0.8)Fe(0.2)O(3-δ) (BSCF) catalyzes the OER with intrinsic activity that is at least an order of magnitude higher than that of the state-of-the-art iridium oxide catalyst in alkaline media. The high activity of BSCF was predicted from a design principle established by systematic examination of more than 10 transition metal oxides, which showed that the intrinsic OER activity exhibits a volcano-shaped dependence on the occupancy of the 3d electron with an e(g) symmetry of surface transition metal cations in an oxide. The peak OER activity was predicted to be at an e(g) occupancy close to unity, with high covalency of transition metal-oxygen bonds.
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              An optically stimulated superconducting-like phase in K3C60 far above equilibrium Tc

              The control of non-equilibrium phenomena in complex solids is an important research frontier, encompassing new effects like light induced superconductivity. Here, we show that coherent optical excitation of molecular vibrations in the organic conductor K3C60 can induce a non-equilibrium state with the optical properties of a superconductor. A transient gap in the real part of the optical conductivity and a low-frequency divergence of the imaginary part are measured for base temperatures far above equilibrium Tc=20 K. These findings underscore the role of coherent light fields in inducing emergent order.
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                Author and article information

                Journal
                rmaa
                Revista mexicana de astronomía y astrofísica
                Rev. mex. astron. astrofis
                Instituto de Astronomía, UNAM (México, DF, Mexico )
                0185-1101
                April 2010
                : 46
                : 1
                : 153-157
                Affiliations
                [01] Morelia Michoacán orgnameUniversidad Nacional Autónoma de México orgdiv1Centro de Radiostronomía y Astrofísica Mexico s.dzibcrya.unam.mx, l.loinardcrya.unam.mx, l.rodriguez@ 123456crya.unam.mx
                Article
                S0185-11012010000100014 S0185-1101(10)04600100014
                99b817db-4799-468e-9e12-8379e2c09e7e

                This work is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License.

                History
                : 04 November 2009
                : 04 February 2010
                Page count
                Figures: 0, Tables: 0, Equations: 0, References: 31, Pages: 5
                Product

                SciELO Mexico


                ISM: individual (G12.82-0.02),ISM: supernova remnants,pulsars: individual (CXOU J181335.1-174957)

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