33,876 research outputs found
Analyses of moisture in polymers and composites
A suitable method for the direct measurement of moisture concentrations after humidity/thermal exposure on state of the art epoxy and polyimide resins and their graphite and glass fiber reinforcements was investigated. Methods for the determination of moisture concentration profiles, moisture diffusion modeling and moisture induced chemical changes were examined. Carefully fabricated, precharacterized epoxy and polyimide neat resins and their AS graphite and S glass reinforced composites were exposed to humid conditions using heavy water (D20), at ambient and elevated temperatures. These specimens were fixtured to theoretically limit the D20 permeation to a unidirectional penetration axis. The analytical techniques evaluated were: (1) laser pyrolysis gas chromatography mass spectrometry; (2) solids probe mass spectrometry; (3) laser pyrolysis conventional infrared spectroscopy; and (4) infrared imaging thermovision. The most reproducible and sensitive technique was solids probe mass spectrometry. The fabricated exposed specimens were analyzed for D20 profiling after humidity/thermal conditioning at three exposure time durations
Mothering through Islam: narratives of religious identity in London
This paper draws upon research with mothers of diverse Muslim backgrounds in London to explore how these women use ‘conservative’ interpretations of Islamic beliefs and practices to underpin their parenting strategies. In particular the paper looks at how mothers use religion as a frame to make sense of and give meaning to their experiences and encounters in Britain. We suggest that the women use Islam in four key ways: (i) as a framework for teaching their children right and wrong, (ii) as a means of protecting children from the ‘moral’ dangers of British society, (iii) as an authoritative voice that reinforces parenting, and (iv) as a means of critiquing specific aspects of both the traditional and British culture in which they live and daily negotiate their different cultural and religious belonging. In attempting to instil religious values in their London-based children, these mothers have to negotiate the hostility that Islam increasingly provokes in British society’s public arenas
Cooperative catalysis by silica-supported organic functional groups
Hybrid inorganic–organic materials comprising organic functional groups tethered from silica surfaces are versatile, heterogeneous catalysts. Recent advances have led to the preparation of silica materials containing multiple, different functional groups that can show cooperative catalysis; that is, these functional groups can act together to provide catalytic activity and selectivity superior to what can be obtained from either monofunctional materials or homogeneous catalysts. This tutorial review discusses cooperative catalysis of silica-based catalytic materials, focusing on the cooperative action of acid–base, acid–thiol, amine–urea, and imidazole–alcohol–carboxylate groups. Particular attention is given to the effect of the spatial arrangement of these organic groups and recent developments in the spatial organization of multiple groups on the silica surface
Contamination control concepts for space station customer servicing
The customer servicing operations envisioned for the space station, which include instrument repair, orbital replacement unit (ORU) changeout, and fluid replenishment for free-flying and attached payloads, are expected to create requirements for a unique contamination control subsystem for the customer servicing facility (CSF). Both the core space station and the CSF users present unique requirements/sensitivities, not all of which are currently defined with common criteria. Preliminary results from an assessment of the effects of the CSF-induced contamination environment are reported. Strategies for a comprehensive contamination control approach and a description of specific hardware devices and their applicability are discussed
N=2 supersymmetric spin foams in three dimensions
We construct the spin foam model for N=2 supergravity in three dimensions.
Classically, it is a BF theory with gauge algebra osp(2|2). This algebra has
representations which are not completely reducible. This complicates the
procedure when building a state sum. Fortunately, one can and should excise
these representations. We show that the restricted subset of representations
form a subcategory closed under tensor product. The resulting state-sum is once
again a topological invariant. Furthermore, within this framework one can
identify positively and negatively charged fermions propagating on the spin
foam. These results on osp(2|2) representations and intertwiners apply more
generally to spin network states for N=2 loop quantum supergravity (in 3+1
dimensions) where it allows to define a notion of BPS states.Comment: 12 page
Biases in metallicity measurements from global galaxy spectra: the effects of flux-weighting and diffuse ionized gas contamination
Galaxy metallicity scaling relations provide a powerful tool for
understanding galaxy evolution, but obtaining unbiased global galaxy gas-phase
oxygen abundances requires proper treatment of the various line-emitting
sources within spectroscopic apertures. We present a model framework that
treats galaxies as ensembles of HII and diffuse ionized gas (DIG) regions of
varying metallicities. These models are based upon empirical relations between
line ratios and electron temperature for HII regions, and DIG strong-line ratio
relations from SDSS-IV MaNGA IFU data. Flux-weighting effects and DIG
contamination can significantly affect properties inferred from global galaxy
spectra, biasing metallicity estimates by more than 0.3 dex in some cases. We
use observationally-motivated inputs to construct a model matched to typical
local star-forming galaxies, and quantify the biases in strong-line ratios,
electron temperatures, and direct-method metallicities as inferred from global
galaxy spectra relative to the median values of the HII region distributions in
each galaxy. We also provide a generalized set of models that can be applied to
individual galaxies or galaxy samples in atypical regions of parameter space.
We use these models to correct for the effects of flux-weighting and DIG
contamination in the local direct-method mass-metallicity and fundamental
metallicity relations, and in the mass-metallicity relation based on
strong-line metallicities. Future photoionization models of galaxy line
emission need to include DIG emission and represent galaxies as ensembles of
emitting regions with varying metallicity, instead of as single HII regions
with effective properties, in order to obtain unbiased estimates of key
underlying physical properties.Comment: 37 pages, 29 figures, 4 tables. Accepted to ApJ. See Figures 15-17
for typical global galaxy biases in strong-line ratios, electron
temperatures, and direct-method metallicitie
Substitutability of Livestock Manure for Chemical Fertilizer: A Contingent Valuation Analysis of Crop Producers
The impact of new manure management regulations depends on the willingness of crop producers to accept manure. A contingent valuation analysis of crop producers was used to estimate the willingness of crop producers to accept or pay for manure. Results indicate that producers will pay a positive price on average, but some would require a payment before accepting manure.Farm Management,
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