23,495 research outputs found
Quantum Lattice Fluctuations and Luminescence in C_60
We consider luminescence in photo-excited neutral C_60 using the
Su-Schrieffer-Heeger model applied to a single C_60 molecule. To calculate the
luminescence we use a collective coordinate method where our collective
coordinate resembles the displacement of the carbon atoms of the Hg(8) phonon
mode and extrapolates between the ground state "dimerisation" and the exciton
polaron. There is good agreement for the existing luminescence peak spacing and
fair agreement for the relative intensity. We predict the existence of further
peaks not yet resolved in experiment. PACS Numbers : 78.65.Hc, 74.70.Kn,
36.90+
Effect of cessation of late-night landing noise on sleep electrophysiology in the home
Simultaneous measurements of noise exposure and sleep electrophysiology were made in homes before and after cessation of nighttime aircraft landing noise. Six people were tested, all of whom had been exposed to intense aircraft noise for at least two years. Noise measurements indicated a large reduction in the hourly noise level during nighttime hours, but no charge during the daytime hours. Sleep measures indicated no dramatic changes in sleep patterns either immediately after a marked change in nocturnal noise exposure or approximately a month thereafter. No strong relationship was observed between noise level and sleep disturbances over the range from 60 to 90 db(A)
Urban solar photovoltaics potential: An inventory and modelling study applied to the San Fernando Valley region of Los Angeles
Procedures for analyzing the potential of solar photovoltaic collectors to meet energy requirements in a metropolitan region are described and a modeling effort is applied to the San Fernando Valley region of Los Angeles. The procedure involves a series of steps designed to produce maps and tabulations revealing the amount of rooftop area available for establishing solar collectors and the proportion of energy requirement that could be potentially supplied by solar photovoltaics within each of the 533 mainline feeder service areas in the study area. For the sixty five square mile study area, the results showed that, with half the available flat and south facing roofs used and assuming the availability of energy storage, 52.7 percent of the actual kWh energy requirements could have been met in 1978 using photovoltaic collectors. Hourly, daily, weekly, and monthly fluctuations in potential supply and actual loads and recommendations of avenues for further research are discussed. Some further potential applications of the modeling technique are suggested
Computing Volume Bounds of Inclusions by EIT Measurements
The size estimates approach for Electrical Impedance Tomography (EIT) allows
for estimating the size (area or volume) of an unknown inclusion in an
electrical conductor by means of one pair of boundary measurements of voltage
and current. In this paper we show by numerical simulations how to obtain such
bounds for practical application of the method. The computations are carried
out both in a 2D and a 3D setting.Comment: 20 pages with figure
Content & Watkins's account of natural axiomatizations
This paper briefly recounts the importance of the notion of natural axiomatizations for explicating hypothetico-deductivism, empirical significance, theoretical reduction, and organic fertility. Problems for the account of natural axiomatizations developed by John Watkins in Science and Scepticism and the revised account developed by Elie Zahar are demonstrated. It is then shown that Watkins's account can be salvaged from various counter-examples in a principled way by adding the demand that every axiom of a natural axiomatization should be part of the content of the theory being axiomatized. The crucial point here is that content cannot simply be identified with the set of logical consequences of a theory, but must be restricted to a proper subset of the consequence set. It is concluded that the revised Watkins account has certain advantages over the account of natural axiomatizations offered in Gemes (1993)
Isotopic Scaling in Nuclear Reactions
A three parameter scaling relationship between isotopic distributions for
elements with Z has been observed that allows a simple description of
the dependence of such distributions on the overall isospin of the system. This
scaling law (termed iso-scaling) applies for a variety of reaction mechanisms
that are dominated by phase space, including evaporation, multifragmentation
and deeply inelastic scattering. The origins of this scaling behavior for the
various reaction mechanisms are explained. For multifragmentation processes,
the systematics is influenced by the density dependence of the asymmetry term
of the equation of state.Comment: 10 Pages, 2 Figure
Dual Fronts Propagating into an Unstable State
The interface between an unstable state and a stable state usually develops a
single confined front travelling with constant velocity into the unstable
state. Recently, the splitting of such an interface into {\em two} fronts
propagating with {\em different} velocities was observed numerically in a
magnetic system. The intermediate state is unstable and grows linearly in time.
We first establish rigorously the existence of this phenomenon, called ``dual
front,'' for a class of structurally unstable one-component models. Then we use
this insight to explain dual fronts for a generic two-component
reaction-diffusion system, and for the magnetic system.Comment: 19 pages, Postscript, A
- nucleus relativistic mean field potentials consistent with kaonic atoms
atomic data are used to test several models of the nucleus
interaction. The t() optical potential, due to coupled channel
models incorporating the (1405) dynamics, fails to reproduce these
data. A standard relativistic mean field (RMF) potential, disregarding the
(1405) dynamics at low densities, also fails. The only successful
model is a hybrid of a theoretically motivated RMF approach in the nuclear
interior and a completely phenomenological density dependent potential, which
respects the low density theorem in the nuclear surface region. This best-fit
optical potential is found to be strongly attractive, with a depth of 180
\pm 20 MeV at the nuclear interior, in agreement with previous phenomenological
analyses.Comment: revised, Phys. Rev. C in pres
Topological dilaton black holes
In four-dimensional spacetime, when the two-sphere of black hole event
horizons is replaced by a two-dimensional hypersurface with zero or negative
constant curvature, the black hole is referred to as a topological black hole.
In this paper we present some exact topological black hole solutions in the
Einstein-Maxwell-dilaton theory with a Liouville-type dilaton potential.Comment: 8 pages, Revtex, no figure
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