874 research outputs found
Charged gravitational instantons in five-dimensional Einstein-Gauss-Bonnet-Maxwell theory
We study a solution of the Einstein-Gauus-Bonnet theory in 5 dimensions
coupled to a Maxwell field, whose euclidean continuation gives rise to an
instanton describing black hole pair production. We also discuss the dual
theory with a 3-form field coupled to gravity.Comment: 8 pages, plain Te
Robertson-Walker fluid sources endowed with rotation characterised by quadratic terms in angular velocity parameter
Einstein's equations for a Robertson-Walker fluid source endowed with
rotation Einstein's equations for a Robertson-Walker fluid source endowed with
rotation are presented upto and including quadratic terms in angular velocity
parameter. A family of analytic solutions are obtained for the case in which
the source angular velocity is purely time-dependent. A subclass of solutions
is presented which merge smoothly to homogeneous rotating and non-rotating
central sources. The particular solution for dust endowed with rotation is
presented. In all cases explicit expressions, depending sinusoidally on polar
angle, are given for the density and internal supporting pressure of the
rotating source. In addition to the non-zero axial velocity of the fluid
particles it is shown that there is also a radial component of velocity which
vanishes only at the poles. The velocity four-vector has a zero component
between poles
Asymptotic properties of black hole solutions in dimensionally reduced Einstein-Gauss-Bonnet gravity
We study the asymptotic behavior of the spherically symmetric solutions of
the system obtained from the dimensional reduction of the six-dimensional
Einstein- Gauss-Bonnet action. We show that in general the scalar field that
parametrizes the size of the internal space is not trivial, but nevertheless
the solutions depend on a single parameter. In analogy with other models
containing Gauss-Bonnet terms, naked singularities are avoided if a minimal
radius for the horizon is assumed.Comment: 9 pages, plain Te
Spherical Scalar Field Halo in Galaxies
We study a spherically symmetric fluctuation of scalar dark matter in the
cosmos and show that it could be the dark matter in galaxies, provided that the
scalar field has an exponential potential whose overall sign is negative and
whose exponent is constrained observationally by the rotation velocities of
galaxies. The local space-time of the fluctuation contains a three dimensional
space-like hypersurface with surplus of angle.Comment: 5 REVTeX pages, no figures. Contains important suggestions provided
by the referee. Final version, to appear in Phys. Rev.
S-adenosyl-L-methionine: (S)-scoulerine 9-O-methyltransferase, a highly stereo- and regio-specific enzyme in tetrahydroprotoberberine biosynthesis
Suspension cultures of Berberis species are useful sources for the detection and isolation of a new enzyme which transfers the methyl group from S-adenosyl-L-methionine specifically to the 9-position of the (S)-enantiomer of scoulerine, producing (S)-tetrahydrocolumbamine. The enzyme was enriched 27-fold; it is not particle bound, has a pH optimum of 8.9, a molecular weight of 63 000 and shows a high degree of substrate specificity
Black Hole Area in Brans-Dicke Theory
We have shown that the dynamics of the scalar field
in Brans-Dicke theories of gravity makes the surface area of the black hole
horizon {\it oscillatory} during its dynamical evolution. It explicitly
explains why the area theorem does not hold in Brans-Dicke theory. However, we
show that there exists a certain non-decreasing quantity defined on the event
horizon which is proportional to the black hole entropy for the case of
stationary solutions in Brans-Dicke theory. Some numerical simulations have
been demonstrated for Oppenheimer-Snyder collapse in Brans-Dicke theory.Comment: 12 pages, latex, 5 figures, epsfig.sty, some statements clarified and
two references added, to appear in Phys. Rev.
Study of direct versus orbital entry for Mars missions. Volume 6 - Appendix D - Subsystem studies and parametric data Final report
Subsystems analyses and parametric data on configurations for direct versus orbital entry for Mars mission
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Quantifying the relative importance of land cover change from climate and land use in the representative concentration pathways
Climate change is projected to cause substantial alterations in vegetation distribution, but these have been given little attention in comparison to land-use in the Representative Concentration Pathway (RCP) scenarios. Here we assess the climate-induced land cover changes (CILCC) in the RCPs, and compare them to land-use land cover change (LULCC). To do this, we use an ensemble of simulations with and without LULCC in earth system model HadGEM2-ES for RCP2.6, RCP4.5 and RCP8.5. We find that climate change causes an expansion poleward of vegetation that affects more land area than LULCC in all of the RCPs considered here. The terrestrial carbon changes from CILCC are also larger than for LULCC. When considering only forest, the LULCC is larger, but the CILCC is highly variable with the overall radiative forcing of the scenario. The CILCC forest increase compensates 90% of the global anthropogenic deforestation by 2100 in RCP8.5, but just 3% in RCP2.6. Overall, bigger land cover changes tend to originate from LULCC in the shorter term or lower radiative forcing scenarios, and from CILCC in the longer term and higher radiative forcing scenarios. The extent to which CILCC could compensate for LULCC raises difficult questions regarding global forest and biodiversity offsetting, especially at different timescales. This research shows the importance of considering the relative size of CILCC to LULCC, especially with regard to the ecological effects of the different RCPs
Twice Bitten, Thrice Shy: A Case of Recurrent Isolated Cardiac Sarcoidosis in the Transplanted Heart.
We present a case of recurrent isolated cardiac sarcoidosis, 3 years post-heart transplantation. The case highlights the scarcity of data on the utility of immunosuppression in cardiac sarcoidosis and, in particular, raises questions about the optimal immunosuppression regimen in transplant recipients. (Level of Difficulty: Advanced.)
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