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Sökning: WFRF:(Woodward C) > (2005-2009) > (2008) > Engelska

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1.
  • Lynch, David K., et al. (författare)
  • NOVA V2362 CYGNI (NOVA CYGNI 2006): SPITZER, SWIFT, AND GROUND-BASED SPECTRAL EVOLUTION
  • 2008
  • Ingår i: Astronomical Journal. - 1538-3881 .- 0004-6256. ; 136:number 5, 2008 November, s. 1815-1827
  • Tidskriftsartikel (refereegranskat)abstract
    • Nova V2362 Cygni has undergone a number of very unusual changes. Ground-based spectroscopy initially revealed a normal sequence of events: the object faded and its near-infrared emission lines gradually shifted to higher excitation conditions until about day 100 when the optical fading reversed and the object slowly brightened. This was accompanied by a rise in the Swift X-ray telescope flux and a sudden shift in excitation of the visible and IR spectrum back to low levels. The new lower excitation spectrum revealed broad line widths and many P-Cygni profiles, all indicative of the ejection of a second shell. Eventually, dust formed, the X-ray brightness—apparently unaffected by dust formation—peaked and then declined, and the object faded at all wavelengths. The Spitzer dust spectra revealed a number of solid-state emission features that, at this time, are not identified.
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2.
  • McKie, Brendan, et al. (författare)
  • Ecosystem functioning in stream assemblages from different regions : contrasting responses to variation in detritivore richness, evenness and density.
  • 2008
  • Ingår i: Journal of Animal Ecology. - : Wiley. - 1365-2656 .- 0021-8790. ; 77:3, s. 495-504
  • Tidskriftsartikel (refereegranskat)abstract
    • 1. The diversity of species traits characterising a biological assemblage reflects not only its species richness but also its species evenness and total density, which together influence the concentration of traits within functional guilds, and is ultimately constrained by the regional species pool. Implications of such variation for spatio-temporal variability in biodiversity-ecosystem functioning relationships are potentially complex, but poorly understood.2. In separate microcosm experiments maintained at laboratories in Sweden, Romania and Ireland, we investigated effects of the species richness, evenness and density of stream-living detritivores on two related processes: detritivore leaf processing efficiency (LPE) and growth. Assemblage composition varied among the laboratories, with only one taxonomic order (Plecoptera) investigated in Sweden, whereas two orders, encompassing wider trait variation, were studied in Romania (Trichoptera and Plecoptera) and Ireland (Trichoptera and Isopoda).3. Relationships between density and both LPE and growth ranged from negative to positive across all the study species, highlighting the potential for density-dependent variation in process rates to alter ecosystem functioning, but indicating that such effects vary with species identity.4. Increased diversity was associated with 25-50% higher LPE in the two more heterogeneous assemblages, but whereas LPE in the Romanian study was generally enhanced as richness increased, LPE in the Irish study only increased in less even species mixtures dominated by particular species. Mechanisms underlying these diversity effects also contrasted. The Romanian results were predominantly attributable to the selection effect, whereas there was evidence for positive complementarity among species in Ireland.5. Growth was elevated in Romanian species mixtures, reflecting positive complementarity among species, but lower than expected growth in some Swedish mixtures was associated with negative complementarity.6. Our results emphasize the potential importance of detritivore diversity for stream ecosystem functioning across multiple contrasting assemblages, but variability in both the effects of diversity on the studied processes, and the mechanisms underlying those effects, highlight challenges in generalizing impacts of diversity change for the functional integrity of naturally dynamic stream ecosystems in situ.
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3.
  • Woodward, C. E., et al. (författare)
  • Exact density functional theory for ideal polymer fluids with nearest neighbor bonding constraints
  • 2008
  • Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 129:5
  • Tidskriftsartikel (refereegranskat)abstract
    • We present a new density functional theory of ideal polymer fluids, assuming nearest-neighbor bonding constraints. The free energy functional is expressed in terms of end site densities of chain segments and thus has a simpler mathematical structure than previously used expressions using multipoint distributions. This work is based on a formalism proposed by Tripathi and Chapman [Phys. Rev. Lett. 94, 087801 (2005)]. Those authors obtain an approximate free energy functional for ideal polymers in terms of monomer site densities. Calculations on both repulsive and attractive surfaces show that their theory is reasonably accurate in some cases, but does differ significantly from the exact result for longer polymers with attractive surfaces. We suggest that segment end site densities, rather than monomer site densities, are the preferred choice of "site functions" for expressing the free energy functional of polymer fluids. We illustrate the application of our theory to derive an expression for the free energy of an ideal fluid of infinitely long polymers. (C) 2008 American Institute of Physics.
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  • Resultat 1-3 av 3

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