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Item The Dust Cloud Around The White Dwarf G 29-38. II. Spectrum From 5 To 40 Mu M And Mid-Infrared Photometric Variability(2009-03) Reach, William T.; Lisse, Carey; von Hippel, Ted; Mullally, Fergal; Mullally, FergalWe model the mineralogy and distribution of dust around the white dwarf G29-39 using the infrared spectrum from 1 to 35 mu m. The spectral model for G29-38 dust combines a wide range of materials based on spectral studies of comets and debris disks. In order of their contribution to the mid-infrared emission, the most abundant minerals around G29-38 are amorphous carbon (lambda < 8 mu m), amorphous and crystalline silicates (5-40 mu m), water ice (10-15 and 23-35 mu m), and metal sulfides (18-28 mu m). The amorphous C can be equivalently replaced by other materials (like metallic Fe) with featureless infrared spectra. The best-fitting crystalline silicate is Fe-rich pyroxene. In order to absorb enough starlight to power the observed emission, the disk must either be much thinner than the stellar radius (so that it can be heated from above and below) or it must have an opening angle wider than 2 degrees. A "moderately optically thick" torus model fits well if the dust extends inward to 50 times the white dwarf radius, all grains hotter than 1100 K are vaporized, the optical depth from the star through the disk is tau(parallel to) = 5, and the radial density profile alpha r(-2.7); the total mass of this model disk is 2 x 1019 g. A physically thin (less than the white dwarf radius) and optically thick disk can contribute to the near-infrared continuum only; such a disk cannot explain the longer-wavelength continuum or strong emission features. The combination of a physically thin, optically thick inner disk and an outer, physically thick and moderately optically thin cloud or disk produces a reasonably good fit to the spectrum and requires only silicates in the outer cloud. We discuss the mineralogical results in comparison to planetary materials. The silicate composition contains minerals found from cometary spectra and meteorites, but Fe-rich pyroxene is more abundant than enstatite (Mg-rich pyroxene) or forsterite (Mg-rich olivine) in G29-38 dust, in contrast to what is found in most comet or meteorite mineralogies. Enstatite meteorites may be the most similar solar system materials to G29-38 dust. Finally, we suggest the surviving core of a "hot Jupiter" as an alternative (neither cometary nor asteroidal) origin for the debris, though further theoretical work is needed to determine if this hypothesis is viable.Item Effects of Temperature on the Metabolic Stoichiometry of Arctic Zooplankton(2013) Alcaraz, M.; Almeda, R.; Saiz, E.; Calbet, A.; Duarte, C. M.; Agusti, S.; Santiago, R.; Alonso, A.; Almeda, R.We assessed the relationship between zooplankton metabolism (respiration and inorganic N and P excretion) and "in situ" temperature through a grid of stations representing a range of natural temperature variation during the ATOS-Arctic cruise (July 2007). The objective was to explore not only the direct effects of temperature on zooplankton carbon respiratory losses (hereafter C-R) and NH4-N and PO4-P excretion rates (hereafter N-E and P-E, respectively), but also to investigate whether these metabolic pathways responded similarly to temperature, and so how temperature could affect the stoichiometry of the metabolic products. Metabolic rates, normalised to per unit of zooplankton carbon biomass, increased with increasing temperature following the Arrhenius equation. However, the activation energy differed for the various metabolic processes considered. Respiration, C-R, was the metabolic activity least affected by temperature, followed by N-E and P-E, and as a consequence the values of the C-R : N-E, C-R : P-E and N-E : P-E atomic quotients were inversely related to temperature. The effects of temperature on the stoichiometry of the excreted N and P products would contribute to modifying the nutrient pool available for phytoplankton and induce qualitative and quantitative shifts in the size, community structure and chemical composition of primary producers that could possibly translate to the whole Arctic marine food web.