Search results for "Diss"
showing 10 items of 2500 documents
Analysis of hybrid silica materials with the aid of conventional NMR and GC/MS.
2009
Two simple and straightforward procedures for determining the organic content of hybrid silica materials by means of conventional NMR and GC/MS techniques are described. The methods involve dissolving the hybrid material either in a concentrated solution of sodium hydroxide in deuterated water containing a suitable reference or in a solution of hydrogen fluoride in water and extracting with methylene chloride. These methods constitute useful routine techniques for obtaining immediate information concerning both the amount and chemical composition of the organic compounds on the silica surface.
Aluminum Nanocrystals as a Plasmonic Photocatalyst for Hydrogen Dissociation
2016
Hydrogen dissociation is a critical step in many hydrogenation reactions central to industrial chemical production and pollutant removal. This step typically utilizes the favorable band structure of precious metal catalysts like platinum and palladium to achieve high efficiency under mild conditions. Here we demonstrate that aluminum nanocrystals (Al NCs), when illuminated, can be used as a photocatalyst for hydrogen dissociation at room temperature and atmospheric pressure, despite the high activation barrier toward hydrogen adsorption and dissociation. We show that hot electron transfer from Al NCs to the antibonding orbitals of hydrogen molecules facilitates their dissociation. Hot elect…
Mobilization of late-endosomal cholesterol is inhibited by Rab guanine nucleotide dissociation inhibitor
2000
AbstractCholesterol entering cells in low-density lipoproteins (LDL) via receptor-mediated endocytosis is transported to organelles of the late endocytic pathway for degradation of the lipoprotein particles. The fate of the free cholesterol released remains poorly understood, however. Recent observations suggest that late-endosomal cholesterol sequestration is regulated by the dynamics of lysobisphosphatidic acid (LBPA)-rich membranes [1]. Genetic studies have pinpointed a protein, Niemann–Pick C-1 (NPC-1), that is required for the mobilization of late-endosomal/lysosomal cholesterol by an unknown mechanism [2]. Here, we report the removal of accumulated cholesterol by overexpression of the…
Accumulation of low oxygen water in deep waters of ice-covered lakes cooled below 4 °C
2013
We studied vertical distribution of oxygen under the ice of 5 medium-sized, morphologically variable lakes that cooled well below 4 °C before freezing. In the upper part of the water column, dissolved oxygen and dissolved inorganic carbon concentrations generally remained vertically almost uniform, but in the deepest water, concentrations changed rapidly near the bottom. The coincidence of the changes with an increase in deep water temperature shows that they were due to advection of water made heavier by the heat flux from the sediment. Consequently, water with low concentrations of dissolved oxygen and high concentrations of dissolved inorganic carbon accumulated in the deepest part of th…
Linking nutrient limitation and water chemistry in upland lakes to catchment characteristics
2003
The relationship between catchment characteristics and lake water chemistry, phytoplankton and periphyton biomass, and phytoplankton and periphyton nutrient limitation was investigated for 30 upland lakes in the U.K. These catchment characteristics included the proportion of different land cover categories in the catchment and some hydrological information. Multiple regression models could predict alkalinity, pH, total dissolved phosphorus, dissolved inorganic nitrogen, dissolved organic nitrogen, dissolved organic carbon and phytoplankton chlorophyll a from the proportional contribution of between two and six land cover categories within the catchment and explain between 42 and 73% of the …
Contributions of autochthonous and allochthonous sources to dissolved organic matter in a large, shallow, eutrophic lake with a highly calcareous cat…
2013
We traced the origin of dissolved organic matter (DOM) in the large, shallow, eutrophic Lake Vortsjarv in Estonia. Allochthonous DOM (Al-DOM) had higher δ13C values than autochthonous DOM (Au-DOM). The δ13C of inflow DOM varied from −28.2‰ to −25.4‰ (mean −26.7‰) and in-lake DOM varied from −28.4‰ to −26.1‰ (mean −27.2‰). Low stable isotope (SI) signatures of Au-DOM were caused by relatively 13C-depleted values of its precursors (mainly phytoplankton) with mean δ13C of −28.9‰. SI signatures of dissolved inorganic carbon (DIC) in the inflows and in the lake were also relatively low (from −15.1‰ to −3.28‰). SI values of DOM were lower during the active growing season from May to September and…
Changes in Pore Water Quality After Peatland Restoration: Assessment of a Large-Scale, Replicated Before-After-Control-Impact Study in Finland
2017
Drainage is known to affect peatland natural hydrology and water quality, but peatland restoration is considered to ameliorate peatland degradation. Using a replicated BACIPS (Before-After-Control-Impact Paired Series) design, we investigated 24 peatlands, all drained for forestry and subsequently restored, and 19 pristine control boreal peatlands with high temporal and spatial resolution data on hydroclimate and pore water quality. In drained conditions, total nitrogen (Ntot), total phosphorus (Ptot), and dissolved organic carbon (DOC) in pore water were several-fold higher than observed at pristine control sites, highlighting the impacts of long-term drainage on pore water quality. In gen…
LONG TIME BEHAVIOR OF A SHALLOW WATER MODEL FOR A BASIN WITH VARYING BOTTOM TOPOGRAPHY
2002
We study the long time behavior of a shallow water model introduced by Levermore and Sammartino to describe the motion of a viscous incompressible fluid confined in a basin with topography. Here we prove the existence of a global attractor and give an estimate on its Hausdorff and fractal dimension.
Impacts of Climate on the Flux of Dissolved Organic Carbon from Catchments
2010
Recent increases in dissolved organic carbon (DOC) concentrations in surface waters across both Europe and North America have focused attention on the factors controlling the export of DOC compounds from catchments. Waters containing high concentrations of DOC generally have a characteristic brown colour and are associated with the presence of highly organic soils. Catchments dominated by these soils typically export between 10 and 300 kg DOC ha−1 year−1 (Billett et al., 2004; Laudon et al., 2004; Jonsson et al., 2006). A portion of this DOC is mineralised in streams and lakes to CO2, while the remainder is transported to the sea (Jonsson et al., 2006). Organic matter accumulates in soils w…
Carbon isotope exchange between gaseous CO2 and thin solution films: Artificial cave experiments and a complete diffusion-reaction model
2017
Abstract Speleothem stable carbon isotope (δ 13 C) records provide important paleoclimate and paleo-environmental information. However, the interpretation of these records in terms of past climate or environmental change remains challenging because of various processes affecting the δ 13 C signals. A process that has only been sparsely discussed so far is carbon isotope exchange between the gaseous CO 2 of the cave atmosphere and the dissolved inorganic carbon (DIC) contained in the thin solution film on the speleothem, which may be particularly important for strongly ventilated caves. Here we present a novel, complete reaction diffusion model describing carbon isotope exchange between gase…