22,454 research outputs found
Planning in probabilistic domains using a deterministic numeric planner
In the probabilistic track of the IPC5 - the last International planning competitions - a probabilistic planner based on combining deterministic planning with replanning - FF-REPLAN - out performed the other competitors. This probabilistic planning paradigm discarded the probabilistic information of the domain, just considering for each action its nominal effect as a deterministic effect
Rejuvenation and Memory in model Spin Glasses in 3 and 4 dimensions
We numerically study aging for the Edwards-Anderson Model in 3 and 4
dimensions using different temperature-change protocols. In D=3, time scales a
thousand times larger than in previous work are reached with the SUE machine.
Deviations from cumulative aging are observed in the non monotonic time
behavior of the coherence length. Memory and rejuvenation effects are found in
a temperature-cycle protocol, revealed by vanishing effective waiting times.
Similar effects are reported for the D=3$site-diluted ferromagnetic Ising model
(without chaos). However, rejuvenation is reduced if off-equilibrium
corrections to the fluctuation-dissipation theorem are considered. Memory and
rejuvenation are quantitatively describable in terms of the growth regime of
the spin-glass coherence length.Comment: Extended protocols. Accepted in Phys. Rev. B. 10 postscript figure
Choosing policy instruments for pollution control : a review
This paper presents the design of cost effective interventions to protect the environment from excessive pollution in developing countries. The concept of intervention is motivated by the typical explanation for environmental problems in economic theory--external effects. The aim of the paper is to review the relevant theoretical and empirical economic literature in order: (a) to distill the principal lessons and evaluate general rules of thumb; and (b) to identify gaps that need to be filled in order to make them more accessible and relevant to developing countries. The paper defines broadly the range of policy instruments that can be used to address pollution problems in developing countries. It includes instruments that have traditionally been in the realm of public finance, such as taxes, prices and subsidies. But it also covers regulations and other instruments designed to affect the amount of pollution or to mitigate its damage. To limit the scope of this paper, the authors treat pollution control policies, but not policies to address other environmental problems, such as soil erosion, deforestation, desertification or other natural resource problems. Many of the principles presented, however, broadly relate to the problem of correcting for external effects, and can be applied to these other problems as well. It also focuses on domestic problems and does not deal explicitly with trans-national or global pollution externalities.Economic Theory&Research,Water and Industry,Health Monitoring&Evaluation,Pollution Management&Control,Environmental Economics&Policies
The Sun, stellar-population models, and the age estimation of high-redshift galaxies
Given sufficiently deep optical spectroscopy, the age estimation of
high-redshif t () galaxies has been claimed to be a relatively robust
process (e.g. Dunlop et al. 1996) due to the fact that, for ages Gyr, the
near-ultraviolet light of a stellar population is expected to be dominated by
`well-understood' main-sequence (MS) stars. Recently, however, the reliability
of this process has been called into question by Yi et al (2000), who claim to
have developed models in which the spectrum produced by the main sequence
reddens much more rapidly than in the models of Jimenez et al (2000a), leading
to much younger age estimates for the reddest known high-redshift ellipticals.
In support of their revised age estimates, Yi et al cite the fact that their
models can reproduce the spectrum of the Sun at an age of 5 Gyr, whereas the
solar spectrum is not reproduced by the Jimenez et al models until
Gyr. Here we confirm this discrepancy, but point out that this is in fact a
{\it strength} of the Jimenez et al models and indicative of some flaw in the
models of Yi et al (which, in effect, imply that the Sun will turn into a red
giant any minute now). We have also explored the models of Worthey (1994)
(which are known to differ greatly from those of Jimenez et al in the treatment
of post-MS evolution) and find that the main-sequence component of Worthey's
models also cannot reproduce the solar spectrum until an age of 9-10 Gyr. We
conclude that either the models of Yi et al are not as main-sequence dominated
at 4-5 Gyr as claimed, or that the stellar evolutionary timescale in these
models is in error by a factor possibly as high as two. (abridged)Comment: Submitted to MNRAS, final versio
Tiltrotor CFD part I: validation
This paper presents performance analyses of the model-scale ERICA and TILTAERO tiltrotors and of the full-scale XV-15 rotor with high-fidelity computational fluids dynamics. For the ERICA tiltrotor, the overall effect of the blades on the fuselage was well captured, as demonstrated by analysing surface pressure measurements. However, there was no available experimental data for the blade aerodynamic loads. A comparison of computed rotor loads with experiments was instead possible for the XV-15 rotor, where CFD results predicted the FoM within 1.05%. The method was also able to capture the differences in performance between hover and propeller modes. Good agreement was also found for the TILTAERO loads. The overall agreement with the experimental data and theory for the considered cases demonstrates the capability of the present CFD method to accurately predict tiltrotor flows. In a second part of this work, the validated method is used for blade shape optimisation
The Geometrical Trinity of Gravity
The geometrical nature of gravity emerges from the universality dictated by
the equivalence principle. In the usual formulation of General Relativity, the
geometrisation of the gravitational interaction is performed in terms of the
spacetime curvature, which is now the standard interpretation of gravity.
However, this is not the only possibility. In these notes we discuss two
alternative, though equivalent, formulations of General Relativity in flat
spacetimes, in which gravity is fully ascribed either to torsion or to
non-metricity, thus putting forward the existence of three seemingly unrelated
representations of the same underlying theory. Based on these three alternative
formulations of General Relativity, we then discuss some extensions.Comment: 22 pages, 2 figure
F stars, metallicity, and the ages of red galaxies at z > 1
We explore whether the rest-frame near-UV spectral region, observable in
high-redshift galaxies via optical spectroscopy, contains sufficient
information to allow the degeneracy between age and metallicity to be lifted.
We do this by testing the ability of evolutionary synthesis models to reclaim
the correct metallicity when fitted to the near-UV spectra of F stars of known
(sub-solar and super-solar) metallicity. F stars are of particular interest
because the rest-frame near-UV spectra of the oldest known elliptical galaxies
at z > 1 appear to be dominated by F stars near to the main-sequence turnoff.
We find that, in the case of the F stars, where the HST ultraviolet spectra
have high signal:noise, model-fitting with metallicity allowed to vary as a
free parameter is rather successful at deriving the correct metallicity. As a
result, the estimated turnoff ages of these stars yielded by the model fitting
are well constrained. Encouraged by this we have fitted these same variable-
metallicity models to the deep, optical spectra of the z \simeq 1.5 mJy radio
galaxies 53W091 and 53W069 obtained with the Keck telescope. While the
age-metallicity degeneracy is not so easily lifted for these galaxies, we find
that even when metallicity is allowed as a free parameter, the best estimates
of their ages are still \geq 3 Gyr, with ages younger than 2 Gyr now strongly
excluded. Furthermore, we find that a search of the entire parameter space of
metallicity and star formation history using MOPED (Heavens et al., 2000) leads
to the same conclusion. Our results therefore continue to argue strongly
against an Einstein-de Sitter universe, and favour a lambda-dominated universe
in which star formation in at least these particular elliptical galaxies was
completed somewhere in the redshift range z = 3 - 5.Comment: 10 pages, LaTeX, uses MNRAS style file, incorporates 14 postscript
figures, submitted to MNRAS. Changes include: inclusion of single stellar
atmosphere model fits; more rigorous calculation of confidence regions; some
re-structurin
Variations of the solar granulation motions with height using the GOLF/SoHO experiment
Below 1 mHz, the power spectrum of helioseismic velocity measurements is
dominated by the spectrum of convective motions (granulation and
supergranulation) making it difficult to detect the low-order acoustic modes
and the gravity modes. We want to better understand the behavior of solar
granulation as a function of the observing height in the solar atmosphere and
with magnetic activity during solar cycle 23. We analyze the Power Spectral
Density (PSD) of eleven years of GOLF/SOHO velocity-time series using a
Harvey-type model to characterize the properties of the convective motions in
the solar oscillation power spectrum. We study then the evolution of the
granulation with the altitude in the solar atmosphere and with the solar
activity. First, we show that the traditional use of a lorentzian profile to
fit the envelope of the p modes is not well suitable for GOLF data. Indeed, to
properly model the solar spectrum, we need a second lorentzian profile. Second,
we show that the granulation clearly evolves with the height in the photosphere
but does not present any significant variation with the activity cycle.Comment: Paper accepted in A&A. 7 pages, 4 figures, 2 table
Sensitivity analysis of the solar rotation to helioseismic data from GONG, GOLF and MDI observations
Accurate determination of the rotation rate in the radiative zone of the sun
from helioseismic observations requires rotational frequency splittings of
exceptional quality as well as reliable inversion techniques. We present here
inferences based on mode parameters calculated from 2088-days long MDI, GONG
and GOLF time series that were fitted to estimate very low frequency rotational
splittings (nu < 1.7 mHz). These low frequency modes provide data of
exceptional quality, since the width of the mode peaks is much smaller than the
rotational splitting and hence it is much easier to separate the rotational
splittings from the effects caused by the finite lifetime and the stochastic
excitation of the modes. We also have implemented a new inversion methodology
that allows us to infer the rotation rate of the radiative interior from mode
sets that span l=1 to 25. Our results are compatible with the sun rotating like
a rigid solid in most of the radiative zone and slowing down in the core (R_sun
< 0.2). A resolution analysis of the inversion was carried out for the solar
rotation inverse problem. This analysis effectively establishes a direct
relationship between the mode set included in the inversion and the sensitivity
and information content of the resulting inferences. We show that such an
approach allows us to determine the effect of adding low frequency and low
degree p-modes, high frequency and low degree p-modes, as well as some g-modes
on the derived rotation rate in the solar radiative zone, and in particular the
solar core. We conclude that the level of uncertainties that is needed to infer
the dynamical conditions in the core when only p-modes are included is unlikely
to be reached in the near future, and hence sustained efforts are needed
towards the detection and characterization of g-modes.Comment: Accepted for publication in Astrophysical journal. 15 pages, 19
figure
Zoo-FISH in the European mole (Talpa europaea) detects all ancestral Boreo-Eutherian human homologous chromosome associations
Zoo-FISH with human whole-chromosome paint probes delineated syntenic association of human homologous chromosome segments 3-21, 14-15, 16-19, 4-8, 7-16 and 12-22 (twice) in the European mole (Talpa europaea, Talpidae, Eulipotyphla, Mammalia). These segment associations represent shared ancestral Boreo-Eutherian traits, half of which were previously not described for Eulipotyphla. The karyotype of the European mole acquired a minimum of 19 translocations and six inversions compared to the presumed Boreo-Eutherian ancestor. Copyright (c) 2006 S. Karger AG, Basel
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