GALEX and Optical Light Curves of EF Eridanus During a Low State: the Puzzling Source of UV Light

Low state optical photometry of EF Eri during an extended low accretion state combined with GALEX near and far UV time-resolved photometry reveals a source of UV flux that is much larger than the underlying 9500K white dwarf, and that is highly modulated on the orbital period. The near UV and optical light curves can be modeled with a 20,000K spot but no spot model can explain both the large amplitude FUV variations and the SED. The limitations of limb darkening, cyclotron and magnetic white dwarf models in explaining the observations are discussed.Comment: 10 pages, 4 figures to be published in ApJ Letter

Nutrition and food limitation of deposit-feeders. II. Differential effects of Hydrobia totteni and Ilyanassa obsoleta on the microbial community

We examined the effects of the mud snails Hydrobia totteni and Ilyanassa obsoleta on microbial communities of sediments in microcosms. Varying density of Hydrobia, and the presence of Ilyanassa, exerted no effect on steady state bacterial standing stock. This is probably related to the rapid recovery rate of bacteria, despite efficient grazing...

Nutrition and food limitation of deposit-feeders. I. The role of microbes in the growth of mod snails (Hydrobiidae)

A series of laboratory microcosm experiments demonstrate that somatic growth of the deposit-feeding gastropod, Hydrobia totteni, is related strongly to microalgal standing stock. Microalgal standing stock is, in turn, determined by the relative rates of grazing and recovery...

The importance of microalgae, bacteria and particulate organic matter in the somatic growth of Hydrobia totteni

Laboratory microcosm experiments reveal that benthic microalgae (filamentous blue-green and diatoms) probably constitute the bulk of nutrition in the somatic growth of the deposit feeding mud snail Hydrobia totteni. Despite an apparent excess of nitrogen in the particulate fraction of the sediment, H. totteni grows only about 42% as much in the dark as in the light. Growth in the dark is probably explained by the utilization of filamentous blue greens and, to a lesser extent, bacteria. The additional growth in the light is probably explained by benthic diatoms, as shown in previous studies. Standing-stocks of micro-organisms (bacteria and microalgae) and snail densities (0.5 cm–2, 2.0 cm–2) in laboratory treatments lie within the range of field conditions. A comparison of snail growth in oxidized and nonoxidized sediments, shows that particulate organic matter typically found in salt marsh sediments does not contribute substantially to somatic growth in H. totteni. Added rations of the seaweed Ulva rotundata also did not affect snail growth. Much of the available nitrogen may have been mineralized into the water column because Ulva is readily decomposed

The 3-Dimensional Structure of NGC 891 and M51

We investigate the three-dimensional structure of the nearby edge-on spiral galaxy NGC 891 using 3D Monte Carlo radiative transfer models, with realistic spiral structure and fractally clumped dust. Using the spiral and clumpiness parameters found from recently completed scattered light models we produce lower resolution SED models which reproduce the global UV-to-FIR SED of NGC 891. Our models contain a color gradient across the major axis of the galaxy - similar to what is seen in images of the NGC 891. With minor adjustment our SED models are able to match the majority of M51's SED, a similar galaxy at a near face-on different inclination.Comment: 3 pages, 1 figure. To appear in the Conference Proceedings of IAU Symposium No. 284: The Spectral Energy Distribution of Galaxies, R.J. Tuffs & C.C. Popescu, ed

Cosmological constant in spinfoam cosmology

We consider a simple modification of the amplitude defining the dynamics of loop quantum gravity, corresponding to the introduction of the cosmological constant, and possibly related to the SL(2,C)q extension of the theory recently considered by Fairbairn-Meusburger and Han. We show that in the context of spinfoam cosmology, this modification yields the de Sitter cosmological solution.Comment: 4 pages, 2 figure

Dual Heterotic Black-Holes in Four and Two Dimensions

We consider a class of extremal and non-extremal four-dimensional black-hole solutions occuring in toroidally compactified heterotic string theory, whose ten-dimensional interpretation involves a Kaluza-Klein monopole and a five-brane. We show that these four-dimensional solutions can be connected to extremal and non-extremal two-dimensional heterotic black-hole solutions through a change in the asymptotic behaviour of the harmonic functions associated with the Kaluza-Klein monopole and with the five-brane. This change in the asymptotic behaviour can be achieved by a sequence of S and T-S-T duality transformations in four dimensions. These transformations are implemented by performing a reduction on a two-torus with Lorentzian signature. We argue that the same mechanism can be applied to extremal and non-extremal black-hole solutions in the FHSV model.Comment: 10 pages, latex, 1 reference adde

The role of terrestrially derived organic carbon in the coastal ocean: A changing paradigm and the priming effect

One of the major conundrums in oceanography for the past 20 y has been that, although the total flux of dissolved organic carbon (OC; DOC) discharged annually to the global ocean can account for the turnover time of all oceanic DOC (ca. 4,000–6,000 y), chemical biomarker and stable isotopic data indicate that there is very little terrestrially derived OC (TerrOC) in the global ocean. Similarly, it has been estimated that only 30% of the TerrOC buried in marine sediments is of terrestrial origin in muddy deltaic regions with high sedimentation rates. If vascular plant material—assumed to be highly resistant to decay—makes up much of the DOC and particulate OC of riverine OC (along with soil OC), why do we not see more TerrOC in coastal and oceanic waters and sediments? An explanation for this “missing” TerrOC in the ocean is critical in our understanding of the global carbon cycle. Here, I consider the origin of vascular plants, the major component of TerrOC, and how their appearance affected the overall cycling of OC on land. I also examine the role vascular plant material plays in soil OC, inland aquatic ecosystems, and the ocean, and how our understanding of TerrOC and “priming” processes in these natural systems has gained considerable interests in the terrestrial literature, but has largely been ignored in the aquatic sciences. Finally, I close by postulating that priming is in fact an important process that needs to be incorporated into global carbon models in the context of climate change