نتایج جستجو برای: silicic acid
تعداد نتایج: 747990 فیلتر نتایج به سال:
Silicic acid uptake kinetics for a field population of benthic diatoms were examined using a radioisotope tracer over a concentration range of 0-300 μmol L. The microphytobenthos half saturation constant (54 μmol L) and specific uptake rates (0.096 h) for silicic acid were well above those usually found in the pelagic environment. Silicic acid kinetics were hyperbolic only at low concentrations...
Today's Sargasso Sea is nutrient starved, except for episodic upwelling events caused by wind-driven winter mixing and eddies. Enhanced diatom opal burial in Sargasso Sea sediments indicates that silicic acid, a limiting nutrient today, may have been more available in subsurface waters during Heinrich Stadials, millennial-scale climate perturbations of the last glacial and deglaciation. Here we...
The availability of iron is known to exert a controlling influence on biological productivity in surface waters over large areas of the ocean and may have been an important factor in the variation of the concentration of atmospheric carbon dioxide over glacial cycles. The effect of iron in the Southern Ocean is particularly important because of its large area and abundant nitrate, yet iron-enha...
The release of silicic acid from sediments is known to play a n important role in determining the silicic acid concentration in the water columns of estuaries, but factors controlling the rate of release are poorly understood. Silicic acid efflux from sandy Chesapeake Bay sediment cores that were maintained in the dark was strongly dependent on biogenic silica deposition, temperature and salini...
One theory which seeks to explain the production of fibrous tissue in silicosis postulates the interaction of collagen precursors with polysilicic acid. This stage has been questioned because it is doubtful whether polymerized silicic acid is normally formed when quartz dissolves in aqueous media. A mechanism by which silicic acid may be polymerized in vivo has been demonstrated by studying the...
Buchnericin LB produced by Lactobacillus buchneri LB was purified to homogeneity by a rapid and simple three-step purification procedure including freeze drying, silicic acid adsorption/desorption and cation-exchange chromatography. After the silicic acid and cation-exchange chromatography steps, the activity of buchnericin LB was recovered by 85 and 25%, and its purity increased about 111 and ...
1. Chromatography of rat-liver lipids on a column of silicic acid or a mixture of silicic acid and Hyflo Super-Cel, with chloroform-methanol mixtures, gave monophosphoinositide-containing fractions which were invariably contaminated by the presence of nitrogen-containing phospholipids. The behaviour of the inositide was extremely sensitive to column loading and the results with different batche...
Within the past several years the application of silicic acid to the chromatographic fractionation of simple and complex lipides has received increased attention. In particular this adsorbent has been used in the separation of phospholipides by McKibbin (I), Lea et aE. (Z), and Hanahan et al. (3). As shown by Borgstrom (4), who used model lipide compounds, and Fillerup and Mead (5), who employe...
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