11,278 research outputs found
Variation of solar-selective properties of black chrome with plating time
The spectral reflectance properties of a commercially prepared black chrome over dull nickel, both plated on steel, for various plating times of the black chrome were measured. The plating current was 180 amperes per square foot. Values of absorptance integrated over the solar spectrum, and of infrared emittance integrated over black-body radiation at 250 F were obtained. It is shown that plating between one and two minutes produces the optimum combination of highest heat absorbed and lowest heat lost by radiation
The effect of different solar simulators on the measurement of short-circuit current temperature coefficients
Gallium arsenide solar cells are considered for several high temperature missions in space. Both near-Sun and concentrator missions could involve cell temperatures on the order of 200 C. Performance measurements of cells at elevated temperatures are usually made using simulated sunlight and a matched reference cell. Due to the change in bandgap with increasing temperature at portions of the spectrum where considerable simulated irradiance is present, there are significant differences in measured short circuit current at elevated temperatures among different simulators. To illustrate this, both experimental and theoretical data are presented for gallium arsenide cells
Radiation performance of AlGaAs concentrator cells and expected performance of cascade structures
Aluminum gallium arsenide, GaAs, silicon and InGaAs cells have been irradiated with 1 MeV electrons and 37 MeV protons. These cells are candidates for individual cells in a cascade structure. Data is presented for both electron and proton irradiation studies for one sun and a concentration level of 100X AMO. Results of calculations on the radiation resistance of cascade cell structures based on the individual cell data are also presented. Both series connected and separately connected structures are investigated
NITROGEN CARRY-OVER IMPACTS IN IRRIGATED COTTON PRODUCTION, SOUTHERN HIGH PLAINS OF TEXAS
A dynamic optimization model which introduces an intertemporal nitrate-nitrogen residual function is used to derive and evaluate nitrogen fertilizer optimal decision rules for irrigated cotton production in the Southern High Plains of Texas. Results indicate that optimal nitrogen applications critically depend on initial nitrate-nitrogen levels and nitrogen-to-cotton price ratios. Also, the results indicate that single-year optimization leads to suboptimal nitrogen applications, which helps explain long-term cotton yield declines in the Southern High Plains of Texas; but single-year optimization does not significantly impact the net present value of returns of irrigated cotton operations.Crop Production/Industries,
Zeeman Slowers for Strontium based on Permanent Magnets
We present the design, construction, and characterisation of longitudinal-
and transverse-field Zeeman slowers, based on arrays of permanent magnets, for
slowing thermal beams of atomic Sr. The slowers are optimised for operation
with deceleration related to the local laser intensity (by the parameter
), which uses more effectively the available laser power, in contrast
to the usual constant deceleration mode. Slowing efficiencies of up to
are realised and compared to those predicted by modelling.
We highlight the transverse-field slower, which is compact, highly tunable,
light-weight, and requires no electrical power, as a simple solution to slowing
Sr, well-suited to spaceborne application. For Sr we achieve a slow-atom
flux of around atomss at ms, loading
approximately atoms in to a magneto-optical-trap (MOT), and
capture all isotopes in approximate relative natural abundances
Decay widths of large-spin mesons from the non-critical string/gauge duality
In this paper, we use the non-critical string/gauge duality to calculate the
decay widths of large-spin mesons. Since it is believed that the string theory
of QCD is not a ten dimensional theory, we expect that the non-critical
versions of ten dimensional black hole backgrounds lead to better results than
the critical ones. For this purpose we concentrate on the confining theories
and consider two different six dimensional black hole backgrounds. We choose
the near extremal AdS6 model and the near extremal KM model to compute the
decay widths of large-spin mesons. Then, we present our results from these two
non-critical backgrounds and compare them together with those from the critical
models and experimental data.Comment: 21 pages and 3 figure
Gauge covariance and the fermion-photon vertex in three- and four- dimensional, massless quantum electrodynamics
In the quenched approximation, the gauge covariance properties of three
vertex Ans\"{a}tze in the Schwinger-Dyson equation for the fermion self energy
are analysed in three- and four- dimensional quantum electrodynamics. Based on
the Cornwall-Jackiw-Tomboulis effective action, it is inferred that the
spectral representation used for the vertex in the gauge technique cannot
support dynamical chiral symmetry breaking. A criterion for establishing
whether a given Ansatz can confer gauge covariance upon the Schwinger-Dyson
equation is presented and the Curtis and Pennington Ansatz is shown to satisfy
this constraint. We obtain an analytic solution of the Schwinger-Dyson equation
for quenched, massless three-dimensional quantum electrodynamics for arbitrary
values of the gauge parameter in the absence of dynamical chiral symmetry
breaking.Comment: 17 pages, PHY-7143-TH-93, REVTE
ISM In-Space Manufacturing
Develop and enable the technologies, materials, and processes required to provide affordable, sustainable on-demand manufacturing, recycling, and repair during Exploration Missions
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