401 research outputs found
Electromagnetic field of a charge asymptotically approaching spherically symmetric black hole
We consider a test charged particle falling onto a Schwarzschild black hole
and evaluate its electromagnetic field. The Regge-Wheeler equation is solved
analytically by approximating the potential barrier with Dirac delta function
and rectangular barrier. We show that for asymptotically large time measured by
a distant observer the electromagnetic field approaches the spherically
symmetric electrostatic field exponentially fast. This implies that in the
region accessible to a distant observer the initial state of separated charge
and Schwarzschild black hole becomes asymptotically indistinguishable from the
Reisnner-Nordstr\"om solution. Implications of this result for models with
plasma accretion on black holes are discussed.7 aComment: 7 pages, 2 figure
Coordinate time dependence in Quantum Gravity
The intuitive classical space-time picture breaks down in quantum gravity,
which makes a comparison and the development of semiclassical techniques quite
complicated. Using ingredients of the group averaging method to solve
constraints one can nevertheless introduce a classical coordinate time into the
quantum theory, and use it to investigate the way a semiclassical continuous
description emerges from discrete quantum evolution. Applying this technique to
test effective classical equations of loop cosmology and their implications for
inflation and bounces, we show that the effective semiclassical theory is in
good agreement with the quantum description even at short scales.Comment: 35 pages, 17 figure. Revised version. To appear in Phys. Rev.
Electromagnetic radiation and electromagnetic self-force of a point charge in the vicinity of Schwarzschild black hole
Point charge, radially moving in the vicinity of a black hole is considered.
Electromagnetic field in wave zone and in the small neighbourhood of the charge
is calculated. Numerical results of the calculation of the spectrum of
electromagnetic radiation of the point charge are presented. Covariant approach
for the calculation of electromagnetic self-force is used for the case of the
slowly moving charge. Numerical results for the self-force in the case of slow
motion of the particle are obtained and compared to the results in literature.Comment: 5 pages, 3 figure
Effective State Metamorphosis in Semi-Classical Loop Quantum Cosmology
Modification to the behavior of geometrical density at short scales is a key
result of loop quantum cosmology, responsible for an interesting phenomenology
in the very early universe. We demonstrate the way matter with arbitrary scale
factor dependence in Hamiltonian incorporates this change in its effective
dynamics in the loop modified phase. For generic matter, the equation of state
starts varying near a critical scale factor, becomes negative below it and
violates strong energy condition. This opens a new avenue to generalize various
phenomenological applications in loop quantum cosmology. We show that different
ways to define energy density may yield radically different results, especially
for the case corresponding to classical dust. We also discuss implications for
frequency dispersion induced by modification to geometric density at small
scales.Comment: Revised version; includes expanded discussion of natural
trans-Planckian modifications to frequency dispersion and robustness to
quantization ambiguities. To appear in Class. Quant. Gra
Inflationary universe in loop quantum cosmology
Loop quantum cosmology provides a nice solution of avoiding the big bang
singularity through a big bounce mechanism in the high energy region. In loop
quantum cosmology an inflationary universe is emergent after the big bounce, no
matter what matter component is filled in the universe. A super-inflation phase
without phantom matter will appear in a certain way in the initial stage after
the bounce; then the universe will undergo a normal inflation stage. We discuss
the condition of inflation in detail in this framework. Also, for slow-roll
inflation, we expect the imprint from the effects of the loop quantum cosmology
should be left in the primordial perturbation power spectrum. However, we show
that this imprint is too weak to be observed.Comment: 21 pages, 4 figures; accepted for publication in JCA
The Early Universe in Loop Quantum Cosmology
Loop quantum cosmology applies techniques derived for a background
independent quantization of general relativity to cosmological situations and
draws conclusions for the very early universe. Direct implications for the
singularity problem as well as phenomenology in the context of inflation or
bouncing universes result, which will be reviewed here. The discussion focuses
on recent new results for structure formation and generalizations of the
methods.Comment: 10 pages, 3 figures, plenary talk at VI Mexican School on Gravitation
and Mathematical Physics, Nov 21-27, 200
C,N-chelated diaminocarbene platinum(II) complexes derived from 3,4-diaryl-1H-pyrrol-2,5-diimines and cis-dichlorobis(isonitrile)platinum(II):Synthesis, cytotoxicity, and catalytic activity in hydrosilylation reactions
The reaction of 3,4-diaryl-1H-pyrrol-2,5-diimines with cis-dichlorobis(isonitrile)platinum(II) affords the C,N-chelated diaminocarbene platinum(II) complexes, which have been fully characterized including molecular spectroscopy, single crystal X-ray diffraction and DFT calculations. The obtained platinum(II) complexes are effective catalysts for the hydrosilylation of alkynes and alkenes. Thus, the reaction of phenylacetylene with triethoxysilane leads to the formation of α- and β-(E)-vinylsilanes, generating TON's in the range of 103 to 104 and TOF's in the range of 102 to 103 h−1. Also, the cross-linked silicones, possessing the luminescence properties, were obtained by the hydrosilylation reaction of vinyl- and hydride-containing polysiloxanes. Additionally, the efficiency of diaminocarbene platinum(II) complexes against CH1/PA-1, SW480, and A549 cancer cell lines has been demonstrated by in vitro cytotoxicity studies.peerReviewe
Mathematical Modeling of a Solar Arrays Deploying Process at Ground Tests
This paper focuses on the creating of a mathematical model of a solar array deploying process during ground tests. Lagrange equation was used to obtain the math model. The distinctive feature of this mathematical model is the possibility of taking into account the gravity compensation system influence on the construction in the deploying process and the aerodynamic resistance during ground tests
Perturbative Degrees of Freedom in Loop Quantum Gravity: Anisotropies
The relation between an isotropic and an anisotropic model in loop quantum
cosmology is discussed in detail, comparing the strict symmetry reduction with
a perturbative implementation of symmetry. While the latter cannot be done in a
canonical manner, it allows to consider the dynamics including the role of
small non-symmetric degrees of freedom for the symmetric evolution. This serves
as a model for the general situation of perturbative degrees of freedom in a
background independent quantization such as loop quantum gravity, and for the
more complicated addition of perturbative inhomogeneities. While being crucial
for cosmological phenomenology, it is shown that perturbative non-symmetric
degrees of freedom do not allow definitive conclusions for the singularity
issue and in such a situation could even lead to wrong claims.Comment: 32 page
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