21,422 research outputs found
Electricity from photovoltaic solar cells: Flat-Plate Solar Array Project final report. Volume VI: Engineering sciences and reliability
The Flat-Plate Solar Array (FSA) Project, funded by the U.S. Government and managed by the Jet Propulsion Laboratory, was formed in 1975 to develop the module/array technology needed to attain widespread terrestrial use of photovoltaics by 1985. To accomplish this, the FSA Project established and managed an Industry, University, and Federal Government Team to perform the needed research and development.
This volume of the series of final reports documenting the FSA Project deals with the Project's activities directed at developing the engineering technology base required to achieve modules that meet the functional, safety and reliability requirements of large-scale terrestrial photovoltaic systems applications. These activities included: (1) development of functional, safety, and reliability requirements for such applications; (2) development of the engineering analytical approaches, test techniques, and design solutions required to meet the requirements; (3) synthesis and procurement of candidate designs for test and evaluation; and (4) performance of extensive testing, evaluation, and failure analysis to define design shortfalls and, thus, areas requiring additional research and development.
During the life of the FSA Project, these activities were known by and included a variety of evolving organizational titles: Design and Test, Large-Scale Procurements, Engineering, Engineering Sciences, Operations, Module Performance and Failure Analysis, and at the end of the Project, Reliability and Engineering Sciences.
This volume provides both a summary of the approach and technical outcome of these activities and provides a complete Bibliography (Appendix A) of the published documentation covering the detailed accomplishments and technologies developed
Flat-plate solar array project. Volume 6: Engineering sciences and reliability
The Flat-Plate Solar Array (FSA) Project activities directed at developing the engineering technology base required to achieve modules that meet the functional, safety, and reliability requirements of large scale terrestrial photovoltaic systems applications are reported. These activities included: (1) development of functional, safety, and reliability requirements for such applications; (2) development of the engineering analytical approaches, test techniques, and design solutions required to meet the requirements; (3) synthesis and procurement of candidate designs for test and evaluation; and (4) performance of extensive testing, evaluation, and failure analysis of define design shortfalls and, thus, areas requiring additional research and development. A summary of the approach and technical outcome of these activities are provided along with a complete bibliography of the published documentation covering the detailed accomplishments and technologies developed
Multi-Brane Worlds and modification of gravity at large scales
We discuss the implications of multi-brane constructions involving
combinations of positive and negative tension brane and show how anomalously
light KK states emerge when negative tension ''-'' branes are sandwiched
between ''+'' branes. We present a detailed study of a ''+--+'' brane
assignment which interpolates between two models that have been previously
proposed in which gravity is modified at large scales due to the anomalously
light states. We show that it has the peculiar characteristic that gravity
changes from four dimensional (4D) to 5D at large distances and returns to 4D
at even larger scales. We also consider a crystalline universe which leads to a
similar structure for gravity. The problems associated with intermediate
negative tension branes are discussed and a possible resolution suggested.Comment: 28 pages, 6 figures,references adde
Brane Universe and Multigravity: Modification of gravity at large and small distances
We consider a modification of gravity at large distances in a Brane Universe
which was discussed recently. In these models the modification of gravity at
large distances is ultimately connected to existence of negative tension
brane(s) and exponentially small tunneling factor. We discuss a general model
which interpolates between Bi-gravity model and GRS model. We also discuss the
possible mechanism of stabilization for negative tension branes in AdS
background. Finally we show that extra degrees of freedom of massive gravitons
do not lead to disastrous contradiction with General Relativity if the
stabilization condition is
implemented.Comment: 12 pages, 4 eps figures, LaTe
X-ray Reflection from Inhomogeneous Accretion Disks: II. Emission Line Variability and Implications for Reverberation Mapping
One of the principal scientific objectives of the upcoming Constellation-X
mission is to attempt to map the inner regions of accretion disks around black
holes in Seyfert galaxies by reverberation mapping of the Fe K fluorescence
line. This area of the disk is likely radiation pressure dominated and subject
to various dynamical instabilities. Here, we show that density inhomogeneities
in the disk atmosphere resulting from the photon bubble instability (PBI) can
cause rapid changes in the X-ray reflection features, even when the
illuminating flux is constant. Using a simulation of the development of the
PBI, we find that, for the disk parameters chosen, the Fe K and O VIII Ly\alpha
lines vary on timescales as short as a few hundredths of an orbital time. In
response to the changes in accretion disk structure, the Fe K equivalent width
(EW) shows variations as large as ~100 eV. The magnitude and direction
(positive or negative) of the changes depends on the ionization state of the
atmosphere. The largest changes are found when the disk is moderately ionized.
The O VIII EW varies by tens of eV, as well as exhibiting plenty of rapid,
low-amplitude changes. This effect provides a natural explanation for some
observed instances of short timescale Fe K variability which was uncorrelated
with the continuum (e.g., Mrk 841). New predictions for Fe K reverberation
mapping should be made which include the effects of this accretion disk driven
line variability and a variable ionization state. Reflection spectra averaged
over the evolution of the instability are well fit by constant density models
in the 2-10 keV region.Comment: 20 pages, 3 figures. Accepted by Ap
Studies on the promotion of nickel—alumina coprecipitated catalysts: I. Titanium oxide
A series of TiO2-promoted nickel—alumina catalysts has been prepared and characterized. The promoter was added in various proportions to a calcined coprecipitated nickel—alumina material by adsorption of the acetylacetonate complex of titanium, followed by further calcination and reduction. The structure of the resultant materials was similar to that of the unpromoted coprecipitated nickel—alumina. The chemisorption properties of the catalyst and its behaviour in the CO/H2 reaction were characteristic of a strong metal-support interaction (SMSI) reported in the literature for Ni/TiO2. The strong adsorption of both carbon monoxide and hydrogen were suppressed while the activity for carbon monoxide hydrogenation was increased, the activation energy being lowered. The higher activity, however, was relatively unstable under reaction conditions
Electronic spectra of polyatomic molecules with resolved individual rotational transitions
The density of rotational transitions for a polyatomic molecule is so large that in general many such
transitions are hidden under the Doppler profile, this being a fundamental limit of conventional high
resolution electronic spectroscopy. We present here the first Doppler-free cw two-photon spectrum of a
polyatomic molecule. In the case of benzene, 400 lines are observed of which 300 are due to single rotational
transitions, their spacing being weil below the Doppler profile. The resolution so achieved is 1.5 X 10'.
Benzene is a prototype planar molecule taken to have D •• symmetry in the ground as weil as in the first
excited state. From our ultra-high resolution results it is found that benzene in the excited SI state i8 a
symmetrical rotor to a high degree. A negative inertial defect is found for the excited state. The origin of this
inertial defect is discused
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