22,350 research outputs found
Analysis of the linearity characteristics, tape recorders and compensation effects in the FM/FM telemetry system
Linearity characteristics, tape recorder effects, and tape speed compensation effects in FM/FM TELEMETRY syste
Cosmological Supergravity from a Massive Superparticle and Super Cosmological Black Holes
We describe in superspace a classical theory of two dimensional
dilaton supergravity with a cosmological constant, both with and without
coupling to a massive superparticle. We give general exact non-trivial
superspace solutions for the compensator superfield that describes the
supergravity in both cases. We then use these compensator solutions to
construct models of two-dimensional supersymmetric cosmological black holes.Comment: 20 pages, Late
Evolution of the macromolecular structure of sporopollenin during thermal degradation
AbstractReconstructing the original biogeochemistry of organic microfossils requires quantifying the extent of the chemical transformations they experienced during burial and maturation processes. In the present study, fossilization experiments have been performed using modern sporopollenin chosen as an analogue for the resistant biocompounds possibly constituting the wall of many organic microfossils. Sporopollenin powder has been processed thermally under argon atmosphere at different temperatures (up to 1000 °C) for varying durations (up to 900 min). Solid residues of each experiment have been characterized using infrared, Raman and synchrotron-based XANES spectroscopies. Results indicate that significant defunctionalisation and aromatization affect the molecular structure of sporopollenin with increasing temperature. Two distinct stages of evolution with temperature are observed: in a first stage, sporopollenin experiences dehydrogenation and deoxygenation simultaneously (below 500 °C); in a second stage (above 500 °C) an increasing concentration in aromatic groups and a lateral growth of aromatic layers are observed. With increasing heating duration (up to 900 min) at a constant temperature (360 °C), oxygen is progressively lost and conjugated carbon–carbon chains or domains grow progressively, following a log-linear kinetic behavior. Based on the comparison with natural spores fossilized within metasediments which experienced intense metamorphism, we show that the present experimental simulations may not perfectly mimic natural diagenesis and metamorphism. Yet, performing such laboratory experiments provides key insights on the processes transforming biogenic molecules into molecular fossils
Supersymmetric spacetimes in 2+1 adS-supergravity models
We find a class of (2+1)-dimensional spacetimes admitting Killing spinors
appropriate to (2,0) adS-supergravity. The vacuum spacetimes include anti-de
Sitter (adS) space and charged extreme black holes, but there are many others,
including spacetimes of arbitrarily large negative energy that have only
conical singularities, and the spacetimes of fractionally charged point
particles. The non-vacuum spacetimes are those of self-gravitating solitons
obtained by coupling (2,0) adS supergravity to sigma-model matter. We show,
subject to a condition on the matter currents (satisfied by the sigma model),
and a conjecture concerning global obstructions to the existence of certain
types of spinor fields, that the mass of each supersymmetric spacetime
saturates a classical bound, in terms of the angular momentum and charge, on
the total energy of arbitrary field configurations with the same boundary
conditions, although these bounds may be violated quantum mechanically.Comment: 47 pages, phyzzx.tex, no figures
A Note on Flux Induced Superpotentials in String Theory
Non-vanishing fluxes in M-theory and string theory compactifications induce a
superpotential in the lower dimensional theory. Gukov has conjectured the
explicit form of this superpotential. We check this conjecture for the
heterotic string compactified on a Calabi-Yau three-fold as well as for warped
M-theory compactifications on Spin(7) holonomy manifolds, by performing a
Kaluza-Klein reduction.Comment: 19 pages, no figure
Quantum Cosmology of Kantowski-Sachs like Models
The Wheeler-DeWitt equation for a class of Kantowski-Sachs like models is
completely solved. The generalized models include the Kantowski-Sachs model
with cosmological constant and pressureless dust. Likewise contained is a
joined model which consists of a Kantowski-Sachs cylinder inserted between two
FRW half--spheres. The (second order) WKB approximation is exact for the wave
functions of the complete set and this facilitates the product structure of the
wave function for the joined model. In spite of the product structure the wave
function can not be interpreted as admitting no correlations between the
different regions. This problem is due to the joining procedure and may
therefore be present for all joined models. Finally, the {s}ymmetric {i}nitial
{c}ondition (SIC) for the wave function is analyzed and compared with the ``no
bouindary'' condition. The consequences of the different boundary conditions
for the arrow of time are briefly mentioned.Comment: 21 pages, uses LaTeX2e, epsf.sty and float.sty, three figures (50
kb); changes: one figure added, new interpretation of quantizing procedure
for the joined model and many minor change
Free Energy and Entropy for Semi-classical Black Holes in the Canonical Ensemble
We consider the thermodynamics of a black hole coupled to thermal radiation
in a spatially finite (spherical) region. Thermodynamic state functions are
derived in the canonical ensemble, defined by elements of radius and
boundary temperature . Using recent solutions of the semi-classical
back reaction problem, we compute the corrections to the mass of the
black hole, thermal energy, the entropy and free energy due to the presence of
hot conformal scalars, massless spinors and U(1) gauge quantum fields in the
vicinity of the hole. The free energy is particularly important for assessing
under what conditions the nucleation of black holes from hot flat space is
likely to occur.Comment: 25 pages, not including 10 Figures available upon request from the
author: LAEFF-94/08. Typed in LaTe
Plasma Physics
Contains research objectives and reports on three research projects.United States Atomic Energy Commission AT(30-1)-1842
Periodic harmonic functions on lattices and points count in positive characteristic
This survey addresses pluri-periodic harmonic functions on lattices with
values in a positive characteristic field. We mention, as a motivation, the
game "Lights Out" following the work of Sutner, Goldwasser-Klostermeyer-Ware,
Barua-Ramakrishnan-Sarkar, Hunzikel-Machiavello-Park e.a.; see also 2 previous
author's preprints for a more detailed account. Our approach explores harmonic
analysis and algebraic geometry over a positive characteristic field. The
Fourier transform allows us to interpret pluri-periods of harmonic functions on
lattices as torsion multi-orders of points on the corresponding affine
algebraic variety.Comment: These are notes on 13p. based on a talk presented during the meeting
"Analysis on Graphs and Fractals", the Cardiff University, 29 May-2 June 2007
(a sattelite meeting of the programme "Analysis on Graphs and its
Applications" at the Isaac Newton Institute from 8 January to 29 June 2007
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