8,104 research outputs found
Effects of a simulated space environment on thermal radiation characteristics of selected black coatings
Simulated space environment effects on thermal radiation characteristics of black coating
Vacuum and ultraviolet radiation effects on binders and pigments for spacecraft thermal control coatings
An evaluation of several silicone resin binders and powdered inorganic pigments for potential use in spacecraft thermal-control paint formulations is presented. The pigments were selected on the basis of a hypothesis relating the heat of formation of a compound to the compound's resistance to ultra-radiation-induced degradation. Reflectance measurements were made in situ to determine degradation rates due to ultraviolet radiation. The tested polydimethylsiloxane resins were not significantly affected by long exposures to ultraviolet radiation. All the pigments, which were dispersed in a polydimethylsiloxane resin, were degraded by ultraviolet radiation as determined by an increase of solar absorptance. For the materials evaluated in this study, no evidence was found to indicate that pigments with high heats of formation were resistant to ultraviolet degradation
Study of wrap-rib antenna design
The results of a parametric design study conducted to develop the significant characteristics and technology limitations of space deployable antenna systems with aperture sizes ranging from 50 up to 300 m and F/D ratios between 0.5 and 3.0 are presented. Wrap/rib type reflectors of both the prime and offset fed geometry and associated feed support structures were considered. The significant constraints investigated as limitations on achievable aperture were inherent manufacturability, orbit dynamic and thermal stability, antenna weight, and antenna stowed volume. A data base, resulting in the defined maximum achievable aperture size as a function of diameter, frequency and estimated cost, was formed
Emergent behaviour in a chlorophenol-mineralising three-tiered microbial `food web'
Anaerobic digestion enables the water industry to treat wastewater as a
resource for generating energy and recovering valuable by-products. The
complexity of the anaerobic digestion process has motivated the development of
complex models. However, this complexity makes it intractable to pin-point
stability and emergent behaviour. Here, the widely used Anaerobic Digestion
Model No. 1 (ADM1) has been reduced to its very backbone, a syntrophic
two-tiered microbial food chain and a slightly more complex three-tiered
microbial food web, with their stability analysed as function of the inflowing
substrate concentration and dilution rate. Parameterised for phenol and
chlorophenol degradation, steady-states were always stable and non-oscillatory.
Low input concentrations of chlorophenol were sufficient to maintain
chlorophenol- and phenol-degrading populations but resulted in poor conversion
and a hydrogen flux that was too low to sustain hydrogenotrophic methanogens.
The addition of hydrogen and phenol boosted the populations of all three
organisms, resulting in the counterintuitive phenomena that (i) the phenol
degraders were stimulated by adding hydrogen, even though hydrogen inhibits
phenol degradation, and (ii) the dechlorinators indirectly benefitted from
measures that stimulated their hydrogenotrophic competitors; both phenomena
hint at emergent behaviour.Comment: 19 pages, 8 figure
IMPACTS OF PRICE VARIABILITY ON MARKETING MARGINS AND PRODUCER VIABILITY IN THE TEXAS WHEAT INDUSTRY
The effects on marketing margins and Texas what producers of shifting from a period with stable prices to a period without stable prices were investigated using both econometric and simulation techniques. Empirical evidence reveals wheat export firms are risk averse and that either futures markets were unable to absorb increased price risk or futures markets absorbed increased price risk at a cost of $0.054 per bushel. Increased variability in prices and reduced farm program benefits substantially reduced the probability of Texas wheat producers receiving a reasonable return on equity and a reasonable rate of asset accumulation.Crop Production/Industries, Marketing,
Discovery of the first tau Sco analogues: HD 66665 and HD 63425
The B0.2 V magnetic star tau Sco stands out from the larger population of
massive OB stars due to its high X-ray activity, peculiar wind diagnostics and
highly complex magnetic field. This paper presents the discovery of the first
two tau Sco analogues - HD 66665 and HD 63425, identified by the striking
similarity of their UV spectra to that of tau Sco. ESPaDOnS spectropolarimetric
observations were secured by the Magnetism in Massive Stars CFHT Large Program,
in order to characterize the stellar and magnetic properties of these stars.
CMFGEN modelling of optical ESPaDOnS spectra and archived IUE UV spectra showed
that these stars have stellar parameters similar to those of tau Sco. A
magnetic field of similar surface strength is found on both stars, reinforcing
the connection between the presence of a magnetic field and wind peculiarities.
However, additional phase-resolved observations will be required in order to
assess the potential complexity of the magnetic fields, and verify if the wind
anomalies are linked to this property.Comment: 6 pages, 2 tables, 3 figures. Accepted for publication in MNRAS. The
definitive version will be available at www.blackwel-synergy.co
The changing UV and X-ray properties of the Of?p star CPD -28 2561
The Of?p star CPD -28 2561 was monitored at high energies with XMM-Newton and
HST. In X-rays, this magnetic oblique rotator displays bright and hard emission
that varies by ~55% with rotational phase. These changes occur in phase with
optical variations, as expected for magnetically confined winds; there are two
maxima and two minima in X-rays during the 73d rotational period of CPD -28
2561. However, contrary to previously studied cases, no significant hardness
variation is detected between minima and maxima, with the exception of the
second minimum which is slightly distinct from the first one. In the UV domain,
broad-band fluxes remain stable while line profiles display large variations.
Stronger absorptions at low velocities are observed when the magnetic equator
is seen edge-on, which can be reproduced by a detailed 3D model. However, a
difference in absorption at high velocities in the CIV and NV lines is also
detected for the two phases where the confined wind is seen nearly pole-on.
This suggests the presence of strong asymmetries about the magnetic equator,
mostly in the free-flowing wind (rather than in the confined dynamical
magnetosphere).Comment: 14 pages, 11 figures, accepted for publication by MNRA
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