18,494 research outputs found
Ultraviolet radiation effects
Solar ultraviolet testing was not developed which will provide highly accelerated (20 to 50X) exposures that correlate to flight test data. Additional studies are required to develop an exposure methodology which will assure that accelerated testing can be used for qualification of materials and coatings for long duration space flight. Some conclusions are listed: Solar UV radiation is present in all orbital environments; Solar UV does not change in flux with orbital altitude; UV radiation can degrade most coatings and polymeric films; Laboratory UV simulation methodology is needed for accelerated testing to 20 UV solar constants; Simulation of extreme UV (below 200 nm) is needed to evaluate requirements for EUV in solar simulation
Working group written presentation: Solar radiation
The members of the Solar Radiation Working Group arrived at two major solar radiation technology needs: (1) generation of a long term flight data base; and (2) development of a standardized UV testing methodology. The flight data base should include 1 to 5 year exposure of optical filters, windows, thermal control coatings, hardened coatings, polymeric films, and structural composites. The UV flux and wavelength distribution, as well as particulate radiation flux and energy, should be measured during this flight exposure. A standard testing methodology is needed to establish techniques for highly accelerated UV exposure which will correlate well with flight test data. Currently, UV can only be accelerated to about 3 solar constants and can correlate well with flight exposure data. With space missions to 30 years, acceleration rates of 30 to 100X are needed for efficient laboratory testing
Semiparametric estimation of (constrained) ultrametric trees
This paper introduces a general, formal treatment of dynamic constraints, i.e., constraints on the state changes that are allowed in a given state space. Such dynamic constraints can be seen as representations of "real world" constraints in a managerial context. The notions of transition, reversible and irreversible transition, and transition relation will be introduced. The link with Kripke models (for modal logics) is also made explicit. Several (subtle) examples of dynamic constraints will be given. Some important classes of dynamic constraints in a database context will be identified, e.g. various forms of cumulativity, non-decreasing values, constraints on initial and final values, life cycles, changing life cycles, and transition and constant dependencies. Several properties of these dependencies will be treated. For instance, it turns out that functional dependencies can be considered as "degenerated" transition dependencies. Also, the distinction between primary keys and alternate keys is reexamined, from a dynamic point of view.
CMB Constraints on Principal Components of the Inflaton Potential
We place functional constraints on the shape of the inflaton potential from
the cosmic microwave background through a variant of the generalized slow roll
approximation that allows large amplitude, rapidly changing deviations from
scale-free conditions. Employing a principal component decomposition of the
source function G'~3(V'/V)^2 - 2V''/V and keeping only those measured to better
than 10% results in 5 nearly independent Gaussian constraints that maybe used
to test any single-field inflationary model where such deviations are expected.
The first component implies < 3% variations at the 100 Mpc scale. One component
shows a 95% CL preference for deviations around the 300 Mpc scale at the ~10%
level but the global significance is reduced considering the 5 components
examined. This deviation also requires a change in the cold dark matter density
which in a flat LCDM model is disfavored by current supernova and Hubble
constant data and can be tested with future polarization or high multipole
temperature data. Its impact resembles a local running of the tilt from
multipoles 30-800 but is only marginally consistent with a constant running
beyond this range. For this analysis, we have implemented a ~40x faster WMAP7
likelihood method which we have made publicly available.Comment: 12 pages, 14 figures, submitted to Phys.Rev.D. Optimized WMAP7
likelihood code and principal component functions of the GSR source function
available at http://background.uchicago.edu/wmap_fast
Cluster Abundance in f(R) Gravity Models
As one of the most powerful probes of cosmological structure formation, the
abundance of massive galaxy clusters is a sensitive probe of modifications to
gravity on cosmological scales. In this paper, we present results from N-body
simulations of a general class of f(R) models, which self-consistently solve
the non-linear field equation for the enhanced forces. Within this class we
vary the amplitude of the field, which controls the range of the enhanced
gravitational forces, both at the present epoch and as a function of redshift.
Most models in the literature can be mapped onto the parameter space of this
class. Focusing on the abundance of massive dark matter halos, we compare the
simulation results to a simple spherical collapse model. Current constraints
lie in the large-field regime, where the chameleon mechanism is not important.
In this regime, the spherical collapse model works equally well for a wide
range of models and can serve as a model-independent tool for placing
constraints on f(R) gravity from cluster abundance. Using these results, we
show how constraints from the observed local abundance of X-ray clusters on a
specific f(R) model can be mapped onto other members of this general class of
models.Comment: 8 pages, 6 figure
Removing sky contributions from SCUBA data
The Submillimetre Common-User Bolometer Array (SCUBA) is a new continuum
camera operating on the James Clerk Maxwell Telescope (JCMT) on Mauna Kea,
Hawaii. It consists of two arrays of bolometric detectors; a 91 pixel 350/450
micron array and a 37 pixel 750/850 micron array. Both arrays can be used
simultaneously and have a field-of-view of approximately 2.4 arcminutes in
diameter on the sky.
Ideally, performance should be limited solely by the photon noise from the
sky background at all wavelengths of operation. However, observations at
submillimetre wavelengths are hampered by ``sky-noise'' which is caused by
spatial and temporal fluctuations in the emissivity of the atmosphere above the
telescope. These variations occur in atmospheric cells that are larger than the
array diameter, and so it is expected that the resultant noise will be
correlated across the array and, possibly, at different wavelengths.
In this paper we describe our initial investigations into the presence of
sky-noise for all the SCUBA observing modes, and explain our current technique
for removing it from the data.Comment: 11 pages, 16 figures, Proc SPIE vol 335
An analysis of LDEF-exposed silvered FEP teflon thermal blanket material
The characterization of selected silvered fluorinated ethylene propylene (FEP) teflon thermal blanket material which received 5 years and 9 months of exposure to the LEO environment on the Long Duration Exposure Facility is reported. X-ray photoelectron spectroscopy, infrared, and thermal analyses did not detect a significant change at the molecular level as the result of this exposure. However, various microscopic analyses revealed a roughening of the coating surface due to atomic oxygen erosion which resulted in some materials changing from specular reflectors of visible radiation to diffuse reflectors. The potential effect of silicon-containing molecular contamination on these materials is addressed
LDEF thermal control coatings post-flight analysis
The NASA Long Duration Exposure Facility (LDEF) provided a unique flight opportunity for conducting experiments in space and return of these experiments to Earth for laboratory evaluation. The results of one of these experiments, S0010, Exposure of Spacecraft Coatings, in which selected spacecraft thermal control coatings were exposed to the low-Earth orbital (LEO) environment on LDEF are reported. The objective of the experiment is to evaluate the response of thermal control coatings to LEO exposure, which includes atomic oxygen, ultraviolet and particulate radiation, meteoroid and debris, vacuum, and temperature cycling
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