38,946 research outputs found
Longitudinal profiles of Extensive Air Showers with inclusion of charm and bottom particles
Charm and bottom particles are rare in Extensive Air Showers but the effect
of its presence can be radical in the development of the Extensive Air Showers
(EAS). If such particles arise with a large fraction of the primary energy,
they can reach large atmospheric depths, depositing its energy in deeper layers
of the atmosphere. As a consequence, the EAS observables (, and
) will be modified, as well as the shape of the longitudinal profile
of the energy deposited in the atmosphere. In this paper, we will modify the
CORSIKA Monte Carlo by the inclusion of charm and bottom production in the
first interaction of the primary cosmic ray. Results for different selections
of the typical values of the heavy particles and distinct production
models will be presented.Comment: Replacement of tex file by the correct versio
Discerning Elementary Particles
We extend the quantum-mechanical results of Muller & Saunders (2008)
establishing the weak discernibility of an arbitrary number of similar fermions
in finite-dimensional Hilbert-spaces in two ways: (a) from fermions to bosons
for all finite-dimensional Hilbert-spaces; and (b) from finite-dimensional to
infinite-dimensional Hilbert-spaces for all elementary particles. In both cases
this is performed using operators whose physical significance is beyond
doubt.This confutes the currently dominant view that (A) the quantum-mechanical
description of similar particles conflicts with Leibniz's Principle of the
Identity of Indiscernibles (PII); and that (B) the only way to save PII is by
adopting some pre-Kantian metaphysical notion such as Scotusian haecceittas or
Adamsian primitive thisness. We take sides with Muller & Saunders (2008)
against this currently dominant view, which has been expounded and defended by,
among others, Schr\"odinger, Margenau, Cortes, Dalla Chiara, Di Francia,
Redhead, French, Teller, Butterfield, Mittelstaedt, Giuntini, Castellani,
Krause and Huggett.Comment: Final Version. To appear in Philosophy of Science, July 200
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Gamma-Ray Light Curves and Spectra of Models for Type-Ia Supernovae
Based on detailed Monte Carlo calculations, we present gamma-ray energy deposition functions, gamma-ray light curves, and gamma-ray spectra for a large set of theoretical models of Type Ia supernovae including ''classical'' detonation and deflagration, delayed detonation, explosions of low mass white dwarfs, and tamped detonation scenarios. Our computations show that models for Type Ia supernovae can be discriminated and the absolute amount of Ni-56 synthesized in the event can be determined on the basis of the gamma-ray light curves and spectra if gamma-ray measurements are combined with observations at other wavelengths, e.g., in the optical band. We discuss at which times gamma-ray observations are most suitable and needed from the theoretical point of view. The implication of the upper limit in the gamma-ray flux by CGRO experiment for our understanding of SN 1991 T is discussed. We find that this limit is consistent with both the optical light curve and the implied distance (12.5 Mpc), i.e., several models can be ruled out by the gamma-ray observations.Astronom
On the gamma-ray emission of Type Ia Supernovae
A multi-dimension, time-dependent Monte Carlo code is used to compute sample
gamma-ray spectra to explore whether unambiguous constraints could be obtained
from gamma-ray observations of Type Ia supernovae. Both spherical and
aspherical geometries are considered and it is shown that moderate departures
from sphericity can produce viewing-angle effects that are at least as
significant as those caused by the variation of key parameters in
one-dimensional models. Thus gamma-ray data could in principle carry some
geometrical information, and caution should be applied when discussing the
value of gamma-ray data based only on one-dimensional explosion models. In
light of the limited sensitivity of current gamma-ray observatories, the
computed theoretical spectra are studied to revisit the issue of whether useful
constraints could be obtained for moderately nearby objects. The most useful
gamma-ray measurements are likely to be of the light curve and time-dependent
hardness ratios, but sensitivity higher than currently available, particularly
at relatively hard energies (~2-3 MeV), is desirable.Comment: 10 pages, 8 figures. Accepted by MNRAS. Minor changes to clarify
discussion in Section
An extended hybrid density functional (X3LYP) with improved descriptions of nonbond interactions and thermodynamic properties of molecular systems
We derive here the form for the exact exchange energy density for a density that decays with Gaussian-type behavior at long range. This functional is intermediate between the B88 and the PW91 exchange functionals. Using this modified functional to match the form expected for Gaussian densities, we propose the X3LYP extended functional. We find that X3LYP significantly outperforms Becke three parameter LeeâYangâParr (B3LYP) for describing van der Waals and hydrogen bond interactions, while performing slightly better than B3LYP for predicting heats of formation, ionization potentials, electron affinities, proton affinities, and total atomic energies as validated with the extended G2 set of atoms and molecules. Thus X3LYP greatly enlarges the field of applications for density functional theory. In particular the success of X3LYP in describing the water dimer (with Re and De within the error bars of the most accurate determinations) makes it an excellent candidate for predicting accurate ligandâprotein and ligandâDNA interactions
Assessment of MISR and MODIS cloud top heights through inter-comparison with a back-scattering lidar at SIRTA
One year of back-scattering lidar cloud boundaries and optical depth were analysed for coincident inter-comparison with the latest processed versions of the NASA-TERRA MISR stereo and MODIS CO2-slicing operational cloud top heights. Optically thin clouds were found to be accurately characterised by the MISR cloud top height product as long as no other cloud was present at lower altitude. MODIS cloud top heights were generally found within the cloud extent retrieved by lidar; agreement improved as cloud optical depth increased and when CO2-slicing was the only technique used for the retrieval. The difference between Lidar and MISR cloud top heights was found to lie between â0.1 and 0.4 km for low clouds and between 0.1 and 3.1 km for high clouds. The difference between Lidar and MODIS cloud top heights was found to lie between â1.2 and 1.5 km for low clouds and between â1.4 and 2.7 km for high clouds
Emission of Massive Scalar Fields by a Higher-Dimensional Rotating Black-Hole
We perform a comprehensive study of the emission of massive scalar fields by
a higher-dimensional, simply rotating black hole both in the bulk and on the
brane. We derive approximate, analytic results as well as exact numerical ones
for the absorption probability, and demonstrate that the two sets agree very
well in the low and intermediate-energy regime for scalar fields with mass
m_\Phi < 1 TeV in the bulk and m_\Phi < 0.5 TeV on the brane. The numerical
values of the absorption probability are then used to derive the Hawking
radiation power emission spectra in terms of the number of extra dimensions,
angular-momentum of the black hole and mass of the emitted field. We compute
the total emissivities in the bulk and on the brane, and demonstrate that,
although the brane channel remains the dominant one, the bulk-over-brane energy
ratio is considerably increased (up to 33%) when the mass of the emitted field
is taken into account.Comment: 28 pages, 18 figure
MISR stereoscopic image matchers: techniques and results
The Multi-angle Imaging SpectroRadiometer (MISR) instrument, launched in December 1999 on the NASA EOS Terra satellite, produces images in the red band at 275-m resolution, over a swath width of 360 km, for the nine camera angles 70.5/spl deg/, 60/spl deg/, 45.6/spl deg/, and 26.1/spl deg/ forward, nadir, and 26.1/spl deg/, 45.6/spl deg/, 60/spl deg/, and 70.5/spl deg/ aft. A set of accurate and fast algorithms was developed for automated stereo matching of cloud features to obtain cloud-top height and motion over the nominal six-year lifetime of the mission. Accuracy and speed requirements necessitated the use of a combination of area-based and feature-based stereo-matchers with only pixel-level acuity. Feature-based techniques are used for cloud motion retrieval with the off-nadir MISR camera views, and the motion is then used to provide a correction to the disparities used to measure cloud-top heights which are derived from the innermost three cameras. Intercomparison with a previously developed "superstereo" matcher shows that the results are very comparable in accuracy with much greater coverage and at ten times the speed. Intercomparison of feature-based and area-based techniques shows that the feature-based techniques are comparable in accuracy at a factor of eight times the speed. An assessment of the accuracy of the area-based matcher for cloud-free scenes demonstrates the accuracy and completeness of the stereo-matcher. This trade-off has resulted in the loss of a reliable quality metric to predict accuracy and a slightly high blunder rate. Examples are shown of the application of the MISR stereo-matchers on several difficult scenes which demonstrate the efficacy of the matching approach
Determination of anisotropic dipole moments in self-assembled quantum dots using Rabi oscillations
By investigating the polarization-dependent Rabi oscillations using
photoluminescence spectroscopy, we determined the respective transition dipole
moments of the two excited excitonic states |Ex> and |Ey> of a single
self-assembled quantum dot that are nondegenerate due to shape anisotropy. We
find that the ratio of the two dipole moments is close to the physical
elongation ratio of the quantum dot.Comment: 11 pages, 2 figures, MS Word generated PDF fil
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