11,655 research outputs found
The mass and dynamical state of Abell 2218
Abell 2218 is one of a handful of clusters in which X-ray and lensing
analyses of the cluster mass are in strong disagreement. It is also a system
for which X-ray data and radio measurements of the Sunyaev-Zel'dovich decrement
have been combined in an attempt to constrain the Hubble constant. However, in
the absence of reliable information on the temperature structure of the
intracluster gas, most analyses have been carried out under the assumption of
isothermality. We combine X-ray data from the ROSAT PSPC and the ASCA GIS
instruments, enabling us to fit non-isothermal models, and investigate the
impact that this has on the X-ray derived mass and the predicted
Sunyaev-Zel'dovich effect.
We find that a strongly non-isothermal model for the intracluster gas, which
implies a central cusp in the cluster mass distribution, is consistent with the
available X-ray data and compatible with the lensing results. At r<1 arcmin,
there is strong evidence to suggest that the cluster departs from a simple
relaxed model. We analyse the dynamics of the galaxies and find that the
central galaxy velocity dispersion is too high to allow a physical solution for
the galaxy orbits. The quality of the radio and X-ray data do not at present
allow very restrictive constraints to be placed on H_0. It is apparent that
earlier analyses have under-estimated the uncertainties involved. However,
values greater than 50 km/s/Mpc are preferred when lensing constraints are
taken into account.Comment: 16 pages, 9 postscript figures, accepted for publication in MNRA
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The climate change double whammy: Flood damage and the determinants of flood insurance coverage, the case of post-Katrina New Orleans
This paper advances scholarly debate on the contradictions of environmental risk management measures by analyzing the determinants of flood insurance coverage among a sample of 403 residents in New Orleans, a city undergoing rapid transformation due to post-Katrina rebuilding efforts and anthropogenic modifications of climate, hydrology, and ecology. The paper focuses on several predictors including subjective flood risk perception, trust in government officials, sociodemographic characteristics, and experience with flood damage. Using binary logistic regression, the results show that the likelihood of having flood insurance coverage is associated with past flood damage and socioeconomic status. Older people (over age 65) are more likely to have flood insurance than younger residents. Race, gender, trust, and perceived flood risk are not statistically significant predictors of flood insurance. We connect our findings to the paradoxes and conflictual dynamics of flood insurance, a major risk mitigation measure. As we point out, in flood-prone cities like New Orleans, flood insurance operates as a double whammy: uninsured or underinsured homes face pervasive risk of both flooding and rising insurance premiums under the conditions of global climate change
On the engineering portion of a research program to develop a zero-g, drag-free satellite and to perform a gyro test of general relativity in a satellite Fourth semiannual status report
Zero gravity satellite concept feasibility and control system design evaluation using air cushion vehicl
Develop a zero-G drag-free satellite and perform a gyro test of general relativity in a satellite Semiannual status report, Nov. 1965 - Apr. 1966
Aeronomy experiment satellite polar orbit, control analysis, and control simulatio
On the engineering portion of a research program - To perform a gyro test of general relativity in a satellite and develop associated control technology
Satellite attitude control using gyro-telescope structure driven by superconducting actuato
Effects of Tornado Damage, Prescribed Fire, and Salvage Logging on Oak (Quercus Spp.) Saplings in Upland Oak Forests in Northern Mississippi
After European colonization and extensive logging folloby long periods of fire suppression, oak dominated forests, woodlands, and savannahs are being replaced by an unprecedented forest ecosystem. In Mississippi, these new forest systems are dominated in the mid- and understory by mesophytic species such as red maple (Acer rubrum L.) and sweetgum (Liquidambar styraciflua L.). Partial thinning of trees folloby prescribed fire can regenerate oaks in managed timber stands. A severe tornado occurred on a monitored oak stand in northern Mississippi. Of the damaged plots, some were treated with either prescribed fire or salvage logging or were left alone. I examined the effects of these treatments on oak regeneration. Species composition of saplings was measured to assess the impact of tornado damage and the treatments on sapling regeneration. All saplings, especially oaks, were reduced upon salvage logging which resulted in dominance by mesophytic species. Tornado damage increased all sapling densities, especially oaks, resulting in increased representation by upland oak species. In burned plots, oak saplings resisted and recovered from prescribed fire better than mesophytic saplings, but not enough to gain an overall height advantage. On poor soils, tornado damage alone may be enough to allow the regeneration of oak species without a prescribed fire. Results also indicate that natural regeneration of oaks may be incompatible with salvage logging, especially in areas that receive severe damage from high wind events
Surface finishing of intricate metal mould structures by large-area electron beam irradiation
The advancement of polymer moulding tools is increasingly focused on imparting not only form but also surface texture for functionality to the surfaces of parts that are created. Furthermore, the increasing demand for inexpensive and higher quality micro-components means that tools for replication processes must take advantage of advanced manufacturing techniques. Tools created by processes such as micro-investment casting, as in this case, may often suffer from excessive surface roughness, malformed edges and general deformation. This results in higher de-moulding forces and a reduction in fidelity of moulded parts to design intent. In this study, large-area electron beam irradiation (EB) is shown to be an effective technique for improving these metrics. For the first time, large population, high aspect ratio micro-features are subject to this process and the mechanisms of smoothing and key enhancement phenomena are demonstrated. The possibility of including EB irradiation in an integrated process chain for arriving at net shape is also discussed.
Surfaces of protruding features are shown to have surface roughness reduced significantly from 126 to 22 nm Ra value, with bottom substrate also similarly improving from 150 to 27 nm Ra. Bottoms of recessed features are also observed to have much improved surface finishes. ‘Doming’ of tops of column features is also demonstrated, further enhancing form. These features would be far too fragile to be polished by any other mechanical method
Scanning system, infrared noise equivalent temperature difference: Measurement procedure
A procedure is described for determining the noise equivalent difference temperature for infrared electro-optical instruments. The instrumentation required, proper measurements, and methods of calculation are included
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