20,053 research outputs found
International Ultraviolet Explorer (IUE) satellite mission analysis
The results are presented of the mission analysis performed by Computer Sciences Corporation (CSC) in support of the International Ultraviolet Explorer (IUE) satellite. The launch window is open for three separate periods (for a total time of 7 months) during the year extending from July 20, 1977, to July 20, 1978. The synchronous orbit shadow constraint limits the launch window to approximately 88 minutes per day. Apogee boost motor fuel was computed to be 455 pounds (206 kilograms) and on-station weight was 931 pounds (422 kilograms). The target orbit is elliptical synchronous, with eccentricity 0.272 and 24 hour period
S-band antenna phased array communications system
The development of an S-band antenna phased array for spacecraft to spacecraft communication is discussed. The system requirements, antenna array subsystem design, and hardware implementation are examined. It is stated that the phased array approach offers the greatest simplicity and lowest cost. The objectives of the development contract are defined as: (1) design of a medium gain active phased array S-band communications antenna, (2) development and test of a model of a seven element planar array of radiating elements mounted in the appropriate cavity matrix, and (3) development and test of a breadboard transmit/receive microelectronics module
The use of LANDSAT digital data and computer-implemented techniques for an agricultural application
Agricultural applications procedures are described for use of LANDSAT digital data and other digitalized data (e.g., soils). The results of having followed these procedures are shown in production estimates for cotton and soybeans in Washington County, Mississippi. Examples of output products in both line printer and map formats are included, and a product adequacy assessment is made
Quantum Fluctuations in Dipolar Bose Gases
We investigate the influence of quantum fluctuations upon dipolar Bose gases
by means of the Bogoliubov-de Gennes theory. Thereby, we make use of the local
density approximation to evaluate the dipolar exchange interaction between the
condensate and the excited particles. This allows to obtain the Bogoliubov
spectrum analytically in the limit of large particle numbers. After discussing
the condensate depletion and the ground-state energy correction, we derive
quantum corrected equations of motion for harmonically trapped dipolar Bose
gases by using superfluid hydrodynamics. These equations are subsequently
applied to analyze the equilibrium configuration, the low-lying oscillation
frequencies, and the time-of-flight dynamics. We find that both atomic magnetic
and molecular electric dipolar systems offer promising scenarios for detecting
beyond mean-field effects.Comment: Published in PR
Exciton Mott transition in Si Revealed by Terahertz Spectroscopy
Exciton Mott transition in Si is investigated by using terahertz time-domain
spectroscopy. The excitonic correlation as manifested by the 1s-2p resonance is
observed above the Mott density. The scattering rate of charge carriers is
prominently enhanced at the proximity of Mott density, which is attributed to
the non-vanishing exciton correlation in the metallic electron-hole plasma.
Concomitantly, the signature of plasmon-exciton coupling is observed in the
loss function spectra.Comment: 5 pages, 3 figure
Research and development in CdS photovoltaic cells Third quarterly report, 29 Dec. 1965 - 29 Mar. 1966
Barrier formation studies of copper sulfide and cadmium sulfide in photovoltaic cell
Spectral weight redistribution in strongly correlated bosons in optical lattices
We calculate the single-particle spectral function for the one-band
Bose-Hubbard model within the random phase approximation (RPA). In the strongly
correlated superfluid, in addition to the gapless phonon excitations, we find
extra gapped modes which become particularly relevant near the superfluid-Mott
quantum phase transition (QPT). The strength in one of the gapped modes, a
precursor of the Mott phase, grows as the QPT is approached and evolves into a
hole (particle) excitation in the Mott insulator depending on whether the
chemical potential is above (below) the tip of the lobe. The sound velocity of
the Goldstone modes remains finite when the transition is approached at a
constant density, otherwise, it vanishes at the transition. It agrees well with
Bogoliubov theory except close to the transition. We also calculate the spatial
correlations for bosons in an inhomogeneous trapping potential creating
alternating shells of Mott insulator and superfluid. Finally, we discuss the
capability of the RPA approximation to correctly account for quantum
fluctuations in the vicinity of the QPT.Comment: 14 pages, 12 figure
Quantum stochastic description of collisions in a canonical Bose gas
We derive a stochastic process that describes the kinetics of a
one-dimensional Bose gas in a regime where three body collisions are important.
In this situation the system becomes non integrable offering the possibility to
investigate dissipative phenomena more simply compared to higher dimensional
gases. Unlike the quantum Boltzmann equation describing the average momentum
distribution, the stochastic approach allows a description of higher-order
correlation functions in a canonical ensemble. As will be shown, this ensemble
differs drastically from the grand canonical one. We illustrate the use of this
method by determining the time evolution of the momentum mode particle number
distribution and the static structure factor during the evaporative cooling
process.Comment: 4 pages, 4 figure
Precision radial velocities of double-lined spectroscopic binaries with an iodine absorption cell
A spectroscopic technique employing an iodine absorption cell (I_2) to
superimpose a reference spectrum onto a stellar spectrum is currently the most
widely adopted approach to obtain precision radial velocities of solar-type
stars. It has been used to detect ~80 extrasolar planets out of ~130 know. Yet
in its original version, it only allows us to measure precise radial velocities
of single stars. In this paper, we present a novel method employing an I_2
absorption cell that enables us to accurately determine radial velocities of
both components of double-lined binaries. Our preliminary results based on the
data from the Keck I telescope and HIRES spectrograph demonstrate that 20-30
m/s radial velocity precision can be routinely obtained for "early" type
binaries (F3-F8). For later type binaries, the precision reaches ~10 m/s. We
discuss applications of the technique to stellar astronomy and searches for
extrasolar planets in binary systems. In particular, we combine the
interferometric data collected with the Palomar Testbed Interferometer with our
preliminary precision velocities of the spectroscopic double-lined binary HD
4676 to demonstrate that with such a combination one can routinely obtain
masses of the binary components accurate at least at the level of 1.0%.Comment: Accepted for publication in The Astrophysical Journa
- …