27,721 research outputs found
Planetary investigation utilizing an imaging spectrometer system based upon charge injection technology
An intrinsic silicon charge injection device (CID) television sensor array has been used in conjunction with a CaMoO4 colinear tunable acousto optic filter, a 61 inch reflector, a sophisticated computer system, and a digital color TV scan converter/computer to produce near IR images of Saturn and Jupiter with 10A spectral resolution and approximately 3 inch spatial resolution. The CID camera has successfully obtained digitized 100 x 100 array images with 5 minutes of exposure time, and slow-scanned readout to a computer. Details of the equipment setup, innovations, problems, experience, data and final equipment performance limits are given
The Tactical and Strategic Value of Commodity Futures
Historically, commodity futures have had excess returns similar to those of equities. But what should we expect in the future? The usual risk factors are unable to explain the time-series variation in excess returns. In addition, our evidence suggests that commodity futures are an inconsistent, if not tenuous, hedge against unexpected inflation. Further, the historically high average returns to a commodity futures portfolio are largely driven by the choice of weighting schemes. Indeed, an equally weighted long-only portfolio of commodity futures returns has approximately a zero excess return over the past 25 years. Our portfolio analysis suggests that the a long-only strategic allocation to commodities as a general asset class is a bet on the future term structure of commodity prices, in general, and on specific portfolio weighting schemes, in particular. In contrast, we provide evidence that there are distinct benefits to an asset allocation overlay that tactically allocates using commodity futures exposures. We examine three trading strategies that use both momentum and the term structure of futures prices. We find that the tactical strategies provide higher average returns and lower risk than a long-only commodity futures exposure.
High-Precision Thermodynamics and Hagedorn Density of States
We compute the entropy density of the confined phase of QCD without quarks on
the lattice to very high accuracy. The results are compared to the entropy
density of free glueballs, where we include all the known glueball states below
the two-particle threshold. We find that an excellent, parameter-free
description of the entropy density between 0.7Tc and Tc is obtained by
extending the spectrum with the exponential spectrum of the closed bosonic
string.Comment: 4 pages, 3 figure
Dissociation dynamics of fluorinated ethene cations:\ud from time bombs on a molecular level to double-regime dissociators\ud
The dissociative photoionization mechanism of internal energy selected CHF, 1,1-CHF, CHF and CF cations have been studied in the 13â20 eV photon energy range using imaging photoelectron photoion coincidence spectroscopy. Five predominant channels have been found; HF loss, statistical and non-statistical F loss, cleavage of the CâC bond post H or F-atom migration, and cleavage of the C=C bond. By modelling the breakdown diagrams and ion time-of-flight distributions using statistical theory, experimental 0 K appearance energies, E, of the daughter ions have been determined. Both CHF and 1,1-CHF are veritable time bombs with respect to dissociation via HF loss, where slow dissociation over a reverse barrier is followed by an explosion with large kinetic energy release. The first dissociative ionization pathway for CHF and CF involves an atom migration across the C=C bond, giving CFâCHF and CFâCF, respectively, which then dissociate to form CHF and CF. The nature of the F-loss pathway has been found to be bimodal for CHF and 1,1-CHF, switching from statistical to non-statistical behaviour as the photon energy increases. The dissociative ionization of CF is found to be comprised of two regimes. At high internal energies, a long-lived excited electronic state is formed, which loses an F atom in a non-statistical process and undergoes statistical redistribution of energy among the nuclear degrees of freedom. This is followed by a subsequent dissociation. In other words only the ground electronic state phase space stays inaccessible. The accurate E of CF and CF formation from CF together with the now well established âHÂș of CF yield self-consistent enthalpies of formation for the CF, CF, CF, and CF species
Supersymmetric black rings and three-charge supertubes
We present supergravity solutions for 1/8-supersymmetric black supertubes
with three charges and three dipoles. Their reduction to five dimensions yields
supersymmetric black rings with regular horizons and two independent angular
momenta. The general solution contains seven independent parameters and
provides the first example of non-uniqueness of supersymmetric black holes. In
ten dimensions, the solutions can be realized as D1-D5-P black supertubes. We
also present a worldvolume construction of a supertube that exhibits three
dipoles explicitly. This description allows an arbitrary cross-section but
captures only one of the angular momenta.Comment: 59 pages, 6 figures; v2: minor correction
Globular Clusters in NGC 1275
We present the results of a deep photometric study of the outer halo of NGC
1275, the highly active cD galaxy at the center of the Perseus cluster. We find
a modest excess of faint () starlike objects in its halo, indicating
a population of old-halo globular clusters. However, the total estimated
cluster population corresponds to a specific frequency of ,
no larger than that of normal giant ellipticals and three times lower than that
of other central cD galaxies such as M87. We discuss several ideas for the
origin of this galaxy. Our results reinforce the view that high (ie:
highly efficient globular cluster formation) is not associated with cooling
flows, or with recent starburst or merger phenomena.Comment: 25 pages, latex, postscript figures, tarred, Unix compressed,
postscript version of paper and figures available at
http://www.physics.mcmaster.ca/Grads/DKaisler/office.htm
Simulation of the Burridge-Knopoff Model of Earthquakes with Variable Range Stress Transfer
Simple models of earthquake faults are important for understanding the
mechanisms for their observed behavior, such as Gutenberg-Richter scaling and
the relation between large and small events, which is the basis for various
forecasting methods. Although cellular automaton models have been studied
extensively in the long-range stress transfer limit, this limit has not been
studied for the Burridge-Knopoff model, which includes more realistic friction
forces and inertia. We find that the latter model with long-range stress
transfer exhibits qualitatively different behavior than both the long-range
cellular automaton models and the usual Burridge-Knopoff model with nearest
neighbor springs, depending on the nature of the velocity-weakening friction
force. This result has important implications for our understanding of
earthquakes and other driven dissipative systems.Comment: 4 pages, 5 figures, published on Phys. Rev. Let
Faint, moving objects in the Hubble Deep Field: components of the dark halo?
The deepest optical image of the sky, the Hubble Deep Field (HDF), obtained
with the Hubble Space Telescope (HST) in December 1995, has been compared to a
similar image taken in December 1997. Two very faint, blue, isolated and
unresolved objects are found to display a substantial apparent proper motion,
23+/-5 mas/yr and 26+/-5 mas/yr; a further three objects at the detection limit
of the second epoch observations may also be moving. Galactic structure models
predict a general absence of stars in the color-magnitude range in which these
objects are found. However, these observations are consistent with
recently-developed models of old white dwarfs with hydrogen atmospheres, whose
color, contrary to previous expectations, has been shown to be blue. If these
apparently moving objects are indeed old white dwarfs with hydrogen atmospheres
and masses near 0.5 M_Sun, they have ages of approximately 12 Gyr, and a local
mass density that is sufficient, within the large uncertainties arising from
the small size of the sample, to account for the entire missing Galactic
dynamical mass.Comment: 6 pages, using emulateapj, including 2 colour figures, accepted for
publication in ApJ Letter
Results of the Australian geodetic VLBI experiment
The 250-2500 km baseline vectors between radio telescopes located at Tidbinbilla (DSS43) near Canberra, Parkes, Fleurs (X3) near Sydney, Hobart and Alice Springs were determined from radio interferometric observations of extragalactic sources. The observations were made during two 24-hour sessions on 26 April and 3 May 1982, and one 12-hour night-time session on 28 April 1982. The 275 km Tidbinbilla - Parkes baseline was measured with an accuracy of plus or minus 6 cm. The remaining baselines were measured with accuracies ranging from 15 cm to 6 m. The higher accuracies were achieved for the better instrumented sites of Tidbinbilla, Parkes and Fleurs. The data reduction technique and results of the experiment are discussed
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