29,619 research outputs found
Gain, phase and frequency stability of DSS-42 and DSS-43 vor Voyage Uranus encounter
Theoretically rigorous definitions are derived of such parameters as RF signal path length, phase delay, and phase/frequency stability in a Cassegrainian antenna applicable to a narrow bandwidth channel, as well as algorithms for evaluating these parameters. This work was performed in support of the Voyager spacecraft encounter with Uranus in January 1986. The information was needed to provide Voyager/Uranus radio science researchers with a rotational basis for deciding the best strategy to operate the three antennas involved during the crucial 5-hour occultation period of the encounter. Such recommendations are made at the end of the article
The electron plasma - Experiment theory and applications
Production, stability, and control of pure electron and electron rich plasmas - crossed field electron bea
The search for extraterrestrial intelligence: Telecommunications technology
Efforts to discover evidence of intelligent extraterrestrial life have become not only feasible, but respectable. Fledgling observational projects have begun that will use state-of-the-art hardware to develop sophisticated receiving and data processing systems. The rationale behind the Search for Extraterrestrial Intelligence, the manner in which the program is taking shape, and the implications for telecommunications are described. It is concluded that the breadth of technological development required for the detection of signals from galactic brethren has particular relevance for the future of telecommunications in Earth oriented uses
How tight is the Lieb-Oxford bound?
Density-functional theory requires ever better exchange-correlation (xc)
functionals for the ever more precise description of many-body effects on
electronic structure. Universal constraints on the xc energy are important
ingredients in the construction of improved functionals. Here we investigate
one such universal property of xc functionals: the Lieb-Oxford lower bound on
the exchange-correlation energy, , where
. To this end, we perform a survey of available exact or
near-exact data on xc energies of atoms, ions, molecules, solids, and some
model Hamiltonians (the electron liquid, Hooke's atom and the Hubbard model).
All physically realistic density distributions investigated are consistent with
the tighter limit . For large classes of systems one can obtain
class-specific (but not fully universal) similar bounds. The Lieb-Oxford bound
with is a key ingredient in the construction of modern xc
functionals, and a substantial change in the prefactor will have
consequences for the performance of these functionals.Comment: 10 pages, 3 figure
Probabilistic Cross-Identification of Astronomical Sources
We present a general probabilistic formalism for cross-identifying
astronomical point sources in multiple observations. Our Bayesian approach,
symmetric in all observations, is the foundation of a unified framework for
object matching, where not only spatial information, but physical properties,
such as colors, redshift and luminosity, can also be considered in a natural
way. We provide a practical recipe to implement an efficient recursive
algorithm to evaluate the Bayes factor over a set of catalogs with known
circular errors in positions. This new methodology is crucial for studies
leveraging the synergy of today's multi-wavelength observations and to enter
the time-domain science of the upcoming survey telescopes.Comment: Accepted for publication in the Astrophysical Journal, 8 pages, 1
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The production of BeV potential wells
Production of billion electron volt potential wells by cloud of electrons suspended in magnetic fiel
Adiabatic connection at negative coupling strengths
The adiabatic connection of density functional theory (DFT) for electronic
systems is generalized here to negative values of the coupling strength
(with {\em attractive} electrons). In the extreme limit
a simple physical solution is presented and its implications
for DFT (as well as its limitations) are discussed. For two-electron systems (a
case in which the present solution can be calculated exactly), we find that an
interpolation between the limit and the opposite limit of
infinitely strong repulsion () yields a rather accurate
estimate of the second-order correlation energy E\cor\glt[\rho] for several
different densities , without using virtual orbitals. The same procedure
is also applied to the Be isoelectronic series, analyzing the effects of
near-degeneracy.Comment: 9 pages, submitted to PR
QUASAT: An orbiting very long baseline interferometer program using large space antenna systems
QUASAT, which stands for QUASAR SATELLITE, is the name given to a new mission being studied by NASA. The QUASAT mission concept involves a free flying Earth orbiting large radio telescope, which will observe astronomical radio sources simultaneously with ground radio telescopes. The primary goal of QUASAT is to provide a system capable of collecting radio frequency data which will lead to a better understanding of extremely high energy events taking place in a variety of celestial objects including quasars, galactic nuclei, interstellar masers, radio stars and pulsars. QUASAT's unique scientific contribution will be the increased resolution in the emission brightness profile maps of the celestial objects
Analysis of the feasibility of an experiment to measure carbon monoxide in the atmosphere
The feasibility of measuring atmospheric carbon monoxide from a remote platform using the correlation interferometry technique was considered. It has been determined that CO data can be obtained with an accuracy of 10 percent using this technique on the first overtone band of CO at 2.3 mu. That band has been found to be much more suitable than the stronger fundamental band at 4.6 mu. Calculations for both wavelengths are presented which illustrate the effects of atmospheric temperature profiles, inversion layers, ground temperature and emissivity, CO profile, reflectivity, and atmospheric pressure. The applicable radiative transfer theory on which these calculations are based is described together with the principles of the technique
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