38,653 research outputs found
Contamination effects of GPS Navstar solar array performance
The solar arrays on Navstars 1 to 6 have been limiting the electrical power capabilities in the extended life (beyond the 5 year design life). The departure from predicted performance consists of an extra 2.5 percent per year degradation beyond the radiation model estimates. This degradation is unusual in showing a linear rather than exponential decay with time. The performance of the arrays on these satellites has been examined in order to predict future behavior and to make refined projections on the Navstar 7 to 11 solar arrays. Evidence obtained from flight experiments on Navstar 5 and 6, and from laboratory experiments, suggests that contamination of the solar arrays while on orbit may be responsible. The evidence for photo-induced contamination of spacecraft surfaces is presented, and the effect on solar array output in the case of the GPS satellites is shown to be consistent with the observed anomalies
Mounting technique for pressure transducers minimizes measurement interferences
Miniaturized transducers are fabricated from commercially available four-arm semiconductor gages; transducers are connected as bridge circuit and mounted on internal face of small diaphragm. Jacket made of conductive plastic may be needed to avoid buildup or static charges
Form Factors Calculated on the Light-Front
A consistent treatment of decay is given on the
light-front. The to transition form factors are calculated in the
entire physical range of momentum transfer for the first time. The
valence-quark contribution is obtained using relativistic light-front wave
functions. Higher quark-antiquark Fock-state of the -meson bound state is
represented effectively by the configuration, and its effect
is calculated in the chiral perturbation theory. Wave function renormalization
is taken into account consistently. The contribution dominates
near the zero-recoil point ( GeV), and decreases rapidly as
the recoil momentum increases. We find that the calculated form factor
follows approximately a dipole -dependence in the entire range
of momentum transfer.Comment: Revtex, 19 pages, 9 figure
Gauge-invariant gravitational wave modes in pre-big bang cosmology
The t<0 branch of pre-big bang cosmological scenarios is subject to a
gravitational wave instability. The unstable behaviour of tensor perturbations
is derived in a very simple way in Hwang's covariant and gauge-invariant
formalism developed for extended theories of gravity. A simple interpretation
of this instability as the effect of an "antifriction" is given, and it is
argued that a universe must eventually enter the expanding phase.Comment: 4 pages, latex, to appear in Eur. Phys. J.
Why Newton's gravity is practically reliable in the large-scale cosmological simulations
Until now, it has been common to use Newton's gravity to study the non-linear
clustering properties of the large-scale structures. Without confirmation from
Einstein's theory, however, it has been unclear whether we can rely on the
analysis, for example, near the horizon scale. In this work we will provide a
confirmation of using Newton's gravity in cosmology based on relativistic
analysis of weakly non-linear situations to the third order in perturbations.
We will show that, except for the gravitational wave contribution, the
relativistic zero-pressure fluid equations perturbed to the second order in a
flat Friedmann background coincide exactly with the Newtonian results. We will
also present the pure relativistic correction terms appearing in the third
order. The third-order correction terms show that these are the linear-order
curvature perturbation strength higher than the second-order
relativistic/Newtonian terms. Thus, the pure general relativistic corrections
in the third order are independent of the horizon scale and are small in the
large-scale due to the low-level temperature anisotropy of the cosmic microwave
background radiation. Since we include the cosmological constant, our results
are relevant to currently favoured cosmology. As we prove that the Newtonian
hydrodynamic equations are valid in all cosmological scales to the second
order, and that the third-order correction terms are small, our result has a
practically important implication that one can now use the large-scale
Newtonian numerical simulation more reliably as the simulation scale approaches
and even goes beyond the horizon.Comment: 8 pages, no figur
Evaluation of three analytical methods for structures under random acoustic excitation
Evaluation of three methods for determining response analysis of plate and shell structures under random acoustic excitatio
Development of a solar-powered residential air conditioner: System optimization preliminary specification
Investigations aimed at the optimization of a baseline Rankine cycle solar powered air conditioner and the development of a preliminary system specification were conducted. Efforts encompassed the following: (1) investigations of the use of recuperators/regenerators to enhance the performance of the baseline system, (2) development of an off-design computer program for system performance prediction, (3) optimization of the turbocompressor design to cover a broad range of conditions and permit operation at low heat source water temperatures, (4) generation of parametric data describing system performance (COP and capacity), (5) development and evaluation of candidate system augmentation concepts and selection of the optimum approach, (6) generation of auxiliary power requirement data, (7) development of a complete solar collector-thermal storage-air conditioner computer program, (8) evaluation of the baseline Rankine air conditioner over a five day period simulating the NASA solar house operation, and (9) evaluation of the air conditioner as a heat pump
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