3,024 research outputs found
Canonical Theory of 2+1 Gravity
Recently 2+1 dimensional gravity theory, especially has been
studied extensively. It was shown to be equivalent to the 2+1 Chern-Simon
theory and has been investigated to understand the black hole thermodynamics,
i.e. Hawking temperature and others. The purpose of this report is to
investigate the canonical formalism of the original 2+1 Einstein gravity theory
instead of the Chern-Simon theory. For the spherically symmetric space-time,
local conserved quantities(local mass and angular momentum) are introduced and
using them canonical quantum theory is defined. Constraints are imposed on
state vectors and solved analytically. The strategy to obtain the solution is
followed by our previous work.Comment: 6 pages, talk given at LLWI-2000: From Particles to Universe,
Alberta, 20-26 February 200
Global well-posedness of the Kirchhoff equation and Kirchhoff systems
This article is devoted to review the known results on global well-posedness
for the Cauchy problem to the Kirchhoff equation and Kirchhoff systems with
small data. Similar results will be obtained for the initial-boundary value
problems in exterior domains with compact boundary. Also, the known results on
large data problems will be reviewed together with open problems.Comment: arXiv admin note: text overlap with arXiv:1211.300
Does a black hole rotate in Chern-Simons modified gravity?
Rotating black hole solutions in the (3+1)-dimensional Chern-Simons modified
gravity theory are discussed by taking account of perturbation around the
Schwarzschild solution. The zenith-angle dependence of a metric function
related to the frame-dragging effect is determined from a constraint equation
independently of a choice of the embedding coordinate. We find that at least
within the framework of the first-order perturbation method, the black hole
cannot rotate for finite black hole mass if the embedding coordinate is taken
to be a timelike vector. However, the rotation can be permitted in the limit of
(where is the black hole mass and is the radius). For a
spacelike vector, the rotation can also be permitted for any value of the black
hole mass.Comment: 4 pages, Accepted for publication in Phys. Rev.
Conical Singular Solutions in (2+1)-Dimensional Gravity Employing the ADM Canonical Formalism
Topological solutions in the (2+1)-dimensional Einstein theory of gravity are
studied within the ADM canonical formalism. It is found that a conical
singularity appears in the closed de Sitter universe solution as a topological
defect in the case of the Einstein theory with a cosmological constant. Quantum
effects on the conical singularity are studied using the de Broglie-Bohm
interpretation. Finite quantum tunneling effects are obtained for the closed de
Sitter universe, while no quantum effects are obtained for an open universe.Comment: 15 pages, 3 figure
The role of the phosphopantetheinyltransferase enzyme, PswP, in the biosynthesis of antimicrobial secondary metabolites by <em>Serratia marcescens </em>Db10
Phosphopantetheinyltransferase (PPTase) enzymes fulfil essential roles in primary and secondary metabolism in prokaryotes, archaea and eukaryotes. PPTase enzymes catalyse the essential modification of the carrier protein domain of fatty acid synthases, polyketide synthases (PKSs) and non-ribosomal peptide synthetases (NRPSs). In bacteria and fungi, NRPS and PKS enzymes are often responsible for the biosynthesis of secondary metabolites with clinically relevant properties; these secondary metabolites include a variety of antimicrobial peptides. We have previously shown that in the Gram-negative bacterium Serratia marcescens Db10, the PPTase enzyme PswP is essential for the biosynthesis of an NRPS-PKS dependent antibiotic called althiomycin. In this work we utilize bioinformatic analyses to classify PswP as belonging to the F/KES subfamily of Sfp type PPTases and to putatively identify additional NRPS substrates of PswP, in addition to the althiomycin NRPS-PKS, in Ser. marcescens Db10. We show that PswP is required for the production of three diffusible metabolites by this organism, each possessing antimicrobial activity against Staphylococcus aureus. Genetic analyses identify the three metabolites as althiomycin, serrawettin W2 and an as-yet-uncharacterized siderophore, which may be related to enterobactin. Our results highlight the use of an individual PPTase enzyme in multiple biosynthetic pathways, each contributing to the ability of Ser. marcescens to inhibit competitor bacteria by the production of antimicrobial secondary metabolites
Spontaneous spin-polarized current in a nonuniform Rashba interaction system
We investigate the electron transport through a two-dimensional semiconductor
with a nonuniform Rashba spin-orbit interaction. Due to the combination of the
coherence effect and the Rashba interaction, a spontaneous spin-polarized
current emerges in the absence of any magnetic material and magnetic field. For
a two-terminal device, only the local current contains polarization; however,
with a four-terminal setup, a polarized total current is produced. This
phenomenon may offer a novel way for generating a spin-polarized current,
replacing the traditional spin-injection method.Comment: 4 pages, 4 figure
Viscous diffusion and photoevaporation of stellar disks
The evolution of a stellar disk under the influence of viscous evolution,
photoevaporation from the central source, and photoevaporation by external
stars is studied. We take the typical parameters of TTSs and the Trapezium
Cluster conditions. The photoionizing flux from the central source is assumed
to arise both from the quiescent star and accretion shocks at the base of
stellar magnetospheric columns, along which material from the disk accretes.
The accretion flux is calculated self-consistently from the accretion mass loss
rate. We find that the disk cannot be entirely removed using only viscous
evolution and photoionization from the disk-star accretion shock. However, when
FUV photoevaporation by external massive stars is included the disk is removed
in 10^6 -10^7yr; and when EUV photoevaporation by external massive stars is
included the disk is removed in 10^5 - 10^6yr.
An intriguing feature of photoevaporation by the central star is the
formation of a gap in the disk at late stages of the disk evolution. As the gap
starts forming, viscous spreading and photoevaporation work in resonance.
There is no gap formation for disks nearby external massive stars because the
outer annuli are quickly removed by the dominant EUV flux. On the other hand,
at larger, more typical distances (d>>0.03pc) from the external stars the flux
is FUV dominated. As a consequence, the disk is efficiently evaporated at two
different locations; forming a gap during the last stages of the disk
evolution.Comment: 27 pages, 11 figures, accepted for publication in Ap
Flat rotation curves in Chern-Simons modified gravity
We investigate the spacetime of a slowly rotating black hole in the
Chern-Simons modified gravity. The long range feature of frame-dragging effect
under the Chern-Simon gravity well explains the flat rotation curves of
galaxies which is a central evidence of dark matter. Our solution provides a
different scenario of rotating space from Goedel's solution.Comment: 4 pages, Accepted for publication in Phys. Rev.
Indications for grain growth and mass decrease in cold dust disks around Classical T Tauri stars in the MBM 12 young association
We report detection of continuum emission at 850 and 450 micron from disks
around four Classical T Tauri stars in the MBM 12 (L1457) young association.
Using a simple model we infer masses of 0.0014-0.012 M_sun for the disk of LkHa
263 ABC, 0.005-0.021 M_sun for S18 ABab, 0.03-0.18 M_sun for LkHa 264 A, and
0.023-0.23 M_sun for LkHa 262. The disk mass found for LkHa 263 ABC is
consistent with the 0.0018 M_sun inferred from the scattered light image of the
edge-on disk around component C. Comparison to earlier 13CO line observations
indicates CO depletion by up to a factor 300 with respect to dark-cloud values.
The spectral energy distributions (SED) suggest grain growth, possibly to sizes
of a few hundred micron, but our spatially unresolved data cannot rule out
opacity as an explanation for the SED shape. Our observations show that these T
Tauri stars are still surrounded by significant reservoirs of cold material at
an age of 1-5 Myr. We conclude that the observed differences in disk mass are
likely explained by binary separation affecting the initial value. With
available accretion rate estimates we find that our data are consistent with
theoretical expectations for viscously evolving disks having decreased their
masses by ~30%.Comment: 15 pages, 3 figures, uses aastex. ApJ Letters, in pres
On the induced gauge invariant mass
We derive a general expression for the gauge invariant mass (m_G) for an
Abelian gauge field, as induced by vacuum polarization, in 1+1 dimensions. From
its relation to the chiral anomaly, we show that m_G has to satisfy a certain
quantization condition. This quantization can be, on the other hand, explicitly
verified by using the exact general expression for the gauge invariant mass in
terms of the fermion propagator. This result is applied to some explicit
examples, exploring the possibility of having interesting physical situations
where the value of departs from its canonical value. We also study the
possibility of generalizing the results to the 2+1 dimensional case at finite
temperature, showing that there are indeed situations where a finite and
non-vanishing gauge invariant mass is induced.Comment: 18 pages, Latex, 3 figures (pstex
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