918 research outputs found
A Probabilistic Approach for the Optimal Sizing of Storage Devices to Increase the Penetration of Plug-in Electric Vehicles in Direct Current Networks
The growing diffusion of electric vehicles connected to distribution networks for charging purposes is an ongoing problem that utilities must deal with. Direct current networks and storage devices have emerged as a feasible means of satisfying the expected increases in the numbers of vehicles while preserving the effective operation of the network. In this paper, an innovative probabilistic methodology is proposed for the optimal sizing of electrical storage devices with the aim of maximizing the penetration of plug-in electric vehicles while preserving efficient and effective operation of the network. The proposed methodology is based on an analytical solution of the problem concerning the power losses minimization in distribution networks equipped with storage devices. The closed-form expression that was obtained is included in a Monte Carlo simulation procedure aimed at handling the uncertainties in loads and renewable generation units. The results of several numerical applications are reported and discussed to demonstrate the validity of the proposed solution. Also, different penetration levels of generation units were analyzed in order to focus on the importance of renewable generation
Stress Tensor from the Trace Anomaly in Reissner-Nordstrom Spacetimes
The effective action associated with the trace anomaly provides a general
algorithm for approximating the expectation value of the stress tensor of
conformal matter fields in arbitrary curved spacetimes. In static, spherically
symmetric spacetimes, the algorithm involves solving a fourth order linear
differential equation in the radial coordinate r for the two scalar auxiliary
fields appearing in the anomaly action, and its corresponding stress tensor. By
appropriate choice of the homogeneous solutions of the auxiliary field
equations, we show that it is possible to obtain finite stress tensors on all
Reissner-Nordstrom event horizons, including the extreme Q=M case. We compare
these finite results to previous analytic approximation methods, which yield
invariably an infinite stress-energy on charged black hole horizons, as well as
with detailed numerical calculations that indicate the contrary. The
approximation scheme based on the auxiliary field effective action reproduces
all physically allowed behaviors of the quantum stress tensor, in a variety of
quantum states, for fields of any spin, in the vicinity of the entire family (0
le Q le M) of RN horizons.Comment: 43 pages, 12 figure
Condensates and quasiparticles in inflationary cosmology: mass generation and decay widths
During de Sitter inflation massless particles of minimally coupled scalar
fields acquire a mass and a decay width thereby becoming \emph{quasiparticles}.
For bare massless particles non-perturbative infrared radiative corrections
lead to a self-consistent generation of mass, for a quartic self interaction , and for a cubic self-interaction the mass is induced
by the formation of a non-perturbative \emph{condensate} leading to . These radiatively generated masses restore de Sitter
invariance and result in anomalous scaling dimensions of superhorizon
fluctuations. We introduce a generalization of the non-perturbative
Wigner-Weisskopf method to obtain the time evolution of quantum states that
include the self-consistent generation of mass and regulate the infrared
behavior. The infrared divergences are manifest as poles in
in the single particle self-energies, leading to a re-arrangement of the
perturbative series non-analytic in the couplings. A set of simple rules that
yield the leading order infrared contributions to the decay width are obtained
and implemented. The lack of kinematic thresholds entail that all particle
states acquire a decay width, dominated by the emission and absorption of
superhorizon quanta for cubic and quartic couplings respectively to
leading order in . The decay of single particle quantum states hastens as
their wavevectors cross the Hubble radius and their width is related to the
highly squeezed limit of the bi- or tri-spectrum of scalar fluctuations
respectively.Comment: 31 pages, 7 figures. Comments and references, matches published
versio
Small crater populations on Vesta
The NASA Dawn mission has extensively examined the surface of asteroid Vesta,
the second most massive body in the main belt. The high quality of the gathered
data provides us with an unique opportunity to determine the surface and
internal properties of one of the most important and intriguing main belt
asteroids (MBAs). In this paper, we focus on the size frequency distributions
(SFDs) of sub-kilometer impact craters observed at high spatial resolution on
several selected young terrains on Vesta. These small crater populations offer
an excellent opportunity to determine the nature of their asteroidal precursors
(namely MBAs) at sizes that are not directly observable from ground-based
telescopes (i.e., below ~100 m diameter). Moreover, unlike many other MBA
surfaces observed by spacecraft thus far, the young terrains examined had
crater spatial densities that were far from empirical saturation. Overall, we
find that the cumulative power-law index (slope) of small crater SFDs on Vesta
is fairly consistent with predictions derived from current collisional and
dynamical models down to a projectile size of ~10 m diameter (Bottke et al.,
2005a,b). The shape of the impactor SFD for small projectile sizes does not
appear to have changed over the last several billions of years, and an argument
can be made that the absolute number of small MBAs has remained roughly
constant (within a factor of 2) over the same time period. The apparent steady
state nature of the main belt population potentially provides us with a set of
intriguing constraints that can be used to glean insights into the physical
evolution of individual MBAs as well as the main belt as an ensemble.Comment: Accepted by PSS, to appear on Vesta cratering special issu
Study of the Effects of Community Education on Citizens' Attitudes and Dropout Rates in Eight Oklahoma Communities
Educational Administratio
Optical observations of NEA 162173 (1999 JU3) during the 2011-2012 apparition
Near-Earth asteroid 162173 (1999 JU3) is a potential target of two asteroid
sample return missions, not only because of its accessibility but also because
of the first C-type asteroid for exploration missions. The lightcurve-related
physical properties of this object were investigated during the 2011-2012
apparition. We aim to confirm the physical parameters useful for JAXA's
Hayabusa 2 mission, such as rotational period, absolute magnitude, and phase
function. Our data complement previous studies that did not cover low phase
angles. With optical imagers and 1-2 m class telescopes, we acquired the
photometric data at different phase angles. We independently derived the
rotational lightcurve and the phase curve of the asteroid. We have analyzed the
lightcurve of 162173 (1999 JU3), and derived a synodic rotational period of
7.625 +/- 0.003 h, the axis ratio a/b = 1.12. The absolute magnitude H_R =
18.69 +/- 0.07 mag and the phase slope of G = -0.09 +/- 0.03 were also obtained
based on the observations made during the 2011-2012 apparition.Comment: 4 pages, 3 figure
Cosmological Dark Energy: Prospects for a Dynamical Theory
We present an approach to the problem of vacuum energy in cosmology, based on
dynamical screening of Lambda on the horizon scale. We review first the
physical basis of vacuum energy as a phenomenon connected with macroscopic
boundary conditions, and the origin of the idea of its screening by particle
creation and vacuum polarization effects. We discuss next the relevance of the
quantum trace anomaly to this issue. The trace anomaly implies additional terms
in the low energy effective theory of gravity, which amounts to a non-trivial
modification of the classical Einstein theory, fully consistent with the
Equivalence Principle. We show that the new dynamical degrees of freedom the
anomaly contains provide a natural mechanism for relaxing Lambda to zero on
cosmological scales. We consider possible signatures of the restoration of
conformal invariance predicted by the fluctuations of these new scalar degrees
of freedom on the spectrum and statistics of the CMB, in light of the latest
bounds from WMAP. Finally we assess the prospects for a new cosmological model
in which the dark energy adjusts itself dynamically to the cosmological horizon
boundary, and therefore remains naturally of order H^2 at all times without
fine tuning.Comment: 50 pages, Invited Contribution to New Journal of Physics Focus Issue
on Dark Energ
Comment on "Gravitationally Induced Neutrino-Oscillation Phases"
We critically examine the recent claim (gr-qc/9603008) of a ``new effect'' of
gravitationally induced quantum mechanical phases in neutrino oscillations. A
straightforward exercise in the Schwarzschild coordinates appropriate to a
spherically symmetric non-rotating star shows that, although there is a general
relativistic effect of the star's gravity on neutrino oscillations, it is not
of the form claimed, and is too small to be measured.Comment: Plain LaTeX, 7 pages, no figure
Quantum Diffeomorphisms and Conformal Symmetry
We analyze the constraints of general coordinate invariance for quantum
theories possessing conformal symmetry in four dimensions. The character of
these constraints simplifies enormously on the Einstein universe . The global conformal symmetry algebra of this space determines
uniquely a finite shift in the Hamiltonian constraint from its classical value.
In other words, the global Wheeler-De Witt equation is {\it modified} at the
quantum level in a well-defined way in this case. We argue that the higher
moments of should not be imposed on the physical states {\it a priori}
either, but only the weaker condition . We
present an explicit example of the quantization and diffeomorphism constraints
on for a free conformal scalar field.Comment: PlainTeX File, 37 page
Stable gravastars with generalised exteriors
New spherically symmetric gravastar solutions, stable to radial
perturbations, are found by utilising the construction of Visser and Wiltshire.
The solutions possess an anti--de Sitter or de Sitter interior and a
Schwarzschild--(anti)--de Sitter or Reissner--Nordstr\"{o}m exterior. We find a
wide range of parameters which allow stable gravastar solutions, and present
the different qualitative behaviours of the equation of state for these
parameters.Comment: 14 pages, 11 figures, to appear in Classical and Quantum Gravit
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