Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Silicates”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 559 records · Page 31Linked to original sources
PubMed2000

X-ray diffraction study of K3NdSi7O17: a new framework silicate with a linear Si-O-Si bond.

Hydrothermal investigations in the high-silica region of the K(2)O-Nd(2)O(3)-SiO(2) system, carried out in a search for novel fast-ion conductors (FICs), yielded the new compound tripotassium neodymium heptasilicate, K(3)NdSi(7)O(17). Single-crystal X-ray methods revealed that K(3)NdSi(7)O(17) crystallizes in space group P3, has lattice constants a = 16.131 (2) and c = 7.7146 (19) A, Z = 4, and 22 atoms in the asymmetric unit. Refinement was carried out to a residual, R(F), of 0.0253 and a weighted residual, wR(F(2)), of 0.0702 using anisotropic displacement parameters for all atoms. The silicate anion forms an interrupted framework, within which both Nd octahedra and K polyhedra are situated. The structure is unusual in that it contains a symmetry-constrained Si-O-Si bond angle of 180 degrees. No isomorphs to K(3)NdSi(7)O(17) are known.

Journal Article↗
PubMed2003

A furnace design for XANES spectroscopy of silicate melts under controlled oxygen fugacities and temperatures to 1773 K.

A controlled-atmosphere furnace has been constructed for X-ray absorption spectroscopy experiments under imposed oxygen fugacities at temperatures up to 1773 K. The use of the furnace is demonstrated in a study of the oxidation state of Cr in a basaltic silicate melt (mid-ocean ridge basalt) by K-edge XANES spectroscopy. This is the first time the Cr(2+)/Cr(3+) ratio has been identified directly in an Fe-bearing melt. At typical terrestrial oxygen fugacities around half the Cr is present as Cr(2+), even though this oxidation state has never been identified in a terrestrial material and only Cr(3+) is observed after quenching to a glass. Cr(2+) oxidizes to Cr(3+) on cooling in the presence of Fe(3+) according to the electron exchange reaction Cr(2+) + Fe(3+) --> Cr(3+) + Fe(2+). This illustrates the importance of the in situ determination of metal oxidation states in melts.

Journal Article↗
PubMed2007

Impact of carbon metabolism on 13C signatures of cyanobacteria and green non-sulfur-like bacteria inhabiting a microbial mat from an alkaline siliceous hot spring in Yellowstone National Park (USA).

Alkaline siliceous hot spring microbial mats in Yellowstone National Park are composed of two dominant phototropic groups, cyanobacteria and green non-sulfur-like bacteria (GNSLB). While cyanobacteria are thought to cross-feed low-molecular-weight organic compounds to support photoheterotrophic metabolism in GNSLB, it is unclear how this could lead to the heavier stable carbon isotopic signatures in GNSLB lipids compared with cyanobacterial lipids found in previous studies. The two groups of phototrophs were separated using percoll density gradient centrifugation and subsequent lipid and stable carbon isotopic analysis revealed that we obtained fractions with a approximately 60-fold enrichment in cyanobacterial and an approximately twofold enrichment in GNSLB biomass, respectively, compared with the mat itself. This technique was used to study the diel cycling and 13C content of the glucose pools in and the uptake of 13C-bicarbonate by the cyanobacteria and GNSLB, as well as the transfer of incorporated 13C from cyanobacteria to GNSLB. The results show that cyanobacteria have the highest bicarbonate uptake rates and accumulate glucose during the afternoon in full light conditions. In contrast, GNSLB have relatively higher bicarbonate uptake rates compared with cyanobacteria in the morning at low light levels. During the night GNSLB take up carbon that is likely derived through fermentation of cyanobacterial glucose enriched in 13C. The assimilation of 13C-enriched cyanobacterial carbon may thus lead to enriched 13C-contents of GNSLB cell components.

Bicarbonates↗
PubMed1998

Siliceous tablets in the larval shells of apatitic discinid brachiopods

The marine bivalved Brachiopoda are abundant throughout the geological record and have apatitic (CaPO4-rich) or calcitic (CaCO3-rich) shells. Vesicles covering the larval valves of living apatitic-shelled discinids contain tablets of silica. The tablets are cemented into close-packed mosaics by spherular apatite in glycosaminoglycans. They are usually lost as vesicles degrade but leave imprints on the underlying apatitic shell. Similar imprints ornament larval surfaces of some of the earliest Paleozoic apatitic-shelled brachiopods and may also be indicators of siliceous biomineralization.

Journal Article↗
PubMed1998

The effect of alumina on the electrical conductivity of silicate perovskite

Measurements of the electrical conductivity of silicate perovskite at 25 gigapascals and 1400 degrees to 1600 degreesC show that the conductivity of (Mg,Fe)SiO3 perovskite containing 2.89 weight percent Al2O3 is about 3.5 times greater than that of aluminum-free (Mg0.915Fe0.085)SiO3 perovskite. The conduction mechanism in perovskite between 1400 degrees and 1600 degreesC is most likely by polarons, because Mossbauer studies show that the aluminum-bearing perovskite has about 3.5 times the amount of Fe3+ as the aluminum-free sample. A conductivity-depth profile from 660 to 2900 kilometers based on aluminum-bearing perovskite is consistent with geophysical models.

Journal Article↗
PubMed1999

A kuroko-type polymetallic sulfide deposit in a submarine silicic caldera

Manned submersible studies have delineated a large and actively growing Kuroko-type volcanogenic massive sulfide deposit 400 kilometers south of Tokyo in Myojin Knoll submarine caldera. The sulfide body is located on the caldera floor at a depth of 1210 to 1360 meters, has an area of 400 by 400 by 30 meters, and is notably rich in gold and silver. The discovery of a large Kuroko-type polymetallic sulfide deposit in this arc-front caldera raises the possibility that the numerous unexplored submarine silicic calderas elsewhere might have similar deposits.

Journal Article↗
PubMed1999

Thermal equation of state of aluminum-enriched silicate perovskite

Inferences of the chemical homogeneity of Earth's mantle depend on comparing laboratory-derived equations of state of mantle phases with seismically determined properties of the material in situ. A uniform chemical composition of the entire mantle has been found to be consistent with measurements, to date, of these properties for the end-member MgSiO3 perovskite phase. New pressure-volume-temperature data for silicate perovskite containing 5 mole percent Al2O3 has yielded different values of the equation of state parameters, with the bulk modulus being significantly smaller at lower mantle conditions than for aluminum-free perovskite, thus requiring adjustments in other components to match seismic observations.

Journal Article↗
PubMed1998

Rice hull ash and silicic acid as adsorbents for concentration of bacteriocins

A model procedure has been developed for the rapid extraction of five bacteriocins (nisin, pediocin RS2, leucocin BC2, lactocin GI3, and enterocin CS1) from concentrated freeze-dried crude culture supernatants by adsorption onto acid or alkaline rice hull ash (RHA) or silicic acid (SA). Bacteriocins were adsorbed onto RHA or SA by a pH-dependent method and desorbed by decreasing the pH to 2.5 or 3.0 and heating at 90 degreesC for 5 min. The maximum adsorption and optimal pH range for different bacteriocins were as follows: nisin, 97% at pH 7.0; lactocin GI3, 94% at pH 6.0; pediocin RS2, 97% at pH 8.0 to 9.0; leucocin BC2, 88% at pH 9.0; and enterocin CS1, 94% at pH 5.0. The desorption level of lactocin GI3 or enterocin CS1 from the surfaces of both RHA and SA was 94%, while the desorption level of pediocin RS2 and leucocin BC2 was 50% or less. Nisin was desorbed readily from SA (91%) but not from RHA (50% or less). The adsorption of bacteriocins onto RHA and SA increased with the increasing concentration of bacteriocins. Analysis of the desorbed bacteriocins after dialysis and sodium dodecyl sulfate-16% polyacrylamide gel electrophoresis showed a single band that gave a single inhibition zone when overlaid with Lactobacillus plantarum for detection of lactocin GI3, enterocin CS1, and nisin. RHA appears useful for extraction, concentration, and partial purification of the five bacteriocins.

Journal Article↗
PubMed1980

Radioactivity studies on 2 synovial specimens after radiation synovectomy with yttrium-90 silicate.

Synovial membranes surgically removed from the knees of 2 patients who had received radioactive yttrium-90 silicate have been examined. Autoradiographs showed that in both cases the activity was unevenly distributed over the synovium. One of the specimens, removed 7 weeks after administration of the isotope, was found to contain a slight degree of radioactivity, attributable in part to a long-lived radioactive contaminant.

Arthritis, Rheumatoid↗
PubMed1989

Treatment of pigmented villonodular synovitis of the knee with yttrium-90 silicate: prospective evaluations by arthroscopy, histology, and 99mTc pertechnetate uptake measurements.

The diffuse form of pigmented villonodular synovitis of eight knee joints of eight patients was treated by intra-articular injection of 185 MBq yttrium-90 silicate (90Y). Six patients had a recurrence of disease after one or two surgical synovectomies. After treatment with 90Y once or twice four knees showed clinical improvement with an accompanying decrease of the inflammatory activity as measured by the technetium-99m pertechnetate (99mTcO4-) uptake ratio and the severity of the diseased synovial tissue. Arthroscopy was performed before and six months after each 90Y treatment. The ratio of 99mTcO4- uptake in the inflamed compared with the normal knee joint correlated well with the macroscopical grading of pigmented villonodular synovitis. In all cases areas of persistent synovitis were found after the 90Y injection and this was confirmed both by histological examination and 99mTcO4- uptake measurements. Biopsy specimens taken from the diseased synovial areas showed histologically mostly less prominent and less numerous villi. The cartilage damage was slightly increased in only two cases. No radiological deterioration was found during follow up (mean 24 months, range 12-41). No complications of the radiosynoviortheses were noted.

Adolescent↗
PubMed2003

Modification of porous aminopropyl-silicate microcapsule membrane by electrically-bonded external anionic polymers.

Biocompatibility and permeability of a microcapsule membrane governs the function of a microcapsule-shaped bioartificial pancreas. We have previously developed an alginate/sol-gel-synthesized aminopropyl-silicate/alginate microcapsule (Alg/AS/Alg), which had insufficient biocompatibility. The purpose of this study was to investigate whether the biocompatibility could improve by modifying the external surface with other anionic polymers and to investigate an influence of the modification on the permeability of the membrane. Four kinds of anionic polymers, poly(oxyethylene)diglycolic acid (3 kDa), heparin (15 kDa), Alg (54 kDa) and carboxymethylcellulose (CMC, 60 kDa) were used as the external anionic polymers. The heparin-bonded gel bead had the largest resistance to the diffusion of small molecules. The molecular mass cut-off point of 150 kDa required for immunoisolation was maintained for all anionic polymers. Cellular overgrowth to the implanted islet-enclosing microcapsule, a sign of insufficient biocompatibility, was suppressed by altering the external surface material from Alg to CMC. These results suggest that the biocompatibility of the Alg/AS/anionic polymer membrane can be improved by using a biocompatible anionic polymer. At the same time, it is suggested the influence on the permeability has to be investigated to develop an optimal microcapsule for bioartificial pancreas.

Animals↗
PubMed2002

Refractive-index changes caused by proton radiation in silicate optical glasses.

We have studied experimentally, by using a differential interferometric technique, the effect of proton radiation on the refractive index of commercial (Schott) silicate crown glasses, BK7 and LaK9, and their radiation-resistant counterparts. The strongest effect was observed for the radiation-hard lanthanum crown LaK9G15: At a 0.65-Mrad dose the index change was approximately 3 x 10(-5). Radiation-hard glasses are used in optical systems operating in radiation environments because they prevent spectral transmission degradation in the visible. However, such glasses are not protected against radiation-induced refractive-index perturbations, and a diffraction-limited optical system based on such glasses may fail owing to radiation-induced aberrations.

Journal Article↗
PubMed2006

Dispersion and thermal properties of lithium aluminum silicate glasses doped with Cr3+ ions.

A series of new lithium aluminum silicate (LAS) glass systems doped with chromium ion is prepared. The reflectance and transmittance of the glass slabs are recorded. By means of an iteration procedure, the glass refractive index n and the extinction coefficient k and their dispersions are obtained. Across a wide spectral range of 0.2-1.6 microm, the dispersion curves are used to determine the atomic and quantum constants of the prepared glasses. These findings provide the average oscillator wavelength, the average oscillator strength, oscillator energy, dispersion energy, lattice energy, and material dispersion of the glass materials to be calculated. For optical waveguide applications, the wavelength for zero material dispersion is obtained. Dilatometric measurements are performed and the thermal expansion coefficient is calculated to throw some light on the thermo-optical properties of the present glasses correlating them with their structure and the presence of nonbridging oxygen ions.

Journal Article↗
PubMed2006

Two-photon-excited fluorescence from silicate glass containing tantalum ions pumped by a near-infrared femtosecond pulsed laser.

We report a novel phenomenon in sodium-calcium-silicate glass doped with Ta(5+). Under irradiation with a 780 nm femtosecond pulsed laser, strong blue emission centered at about 420 nm could be observed. The spectral characteristics are similar to those pumped by ultraviolet photons. The log-log correlation between integrated emission intensity and pump power reveals that a two-photon absorption process is involved in the phenomenon. It is suggested that the presence of localized Ta(5+)5d(0) energy levels is responsible for the appearance of the blue emission. The results indicate that transition metal ions without d electrons play an important role in fields of optics when embedded into glass hosts.

Journal Article↗
PubMed1986

Isolation of beef brain phosphonolipids by thin layer chromatography: their identification and silicic acid column chromatographic separation.

The isolation and identification of the phosphonolipids from beef brain--right lobe, left lobe and cerebellum--is herein reported. The phosphonolipids were isolated by preparative thin layer chromatography (TLC) using the solvent system methanol/water (2:1, v/v) and identified preliminarily by TLC. The isolated phosphonolipids were subjected to silicic acid column chromatographic separation and the thus separated phosphonolipids were identified by TLC, nitrogen-phosphorus determinations and IR spectroscopy.

Animals↗
PubMed2001

Comparison of different digestion methods for total decomposition of siliceous and organic environmental samples.

A comparison was made of different digestion methods for the total decomposition of siliceous and organically environmental samples prior to their analysis by inductively coupled plasma optical emission spectrometry (ICP-OES). In the present study, three different digestion methods, including microwave-assisted, hot plate heating and pressurized digestion (pressure bomb), were employed for the determination of nine heavy metals, i.e. Ag, Cd, Cr, Cu, Fe, Mn, Ni, Pb and Zn in sediment, soil, sludge and oil. The investigation of different combinations of acids through their analytical performance demonstrated that HCl plays a vital role in the determination of silver. The combination of HNO3 and HCl possesses more reactive ability in oxidizing organic matter. The recoveries of all elements of interest in sediment (NIST 2704) obtained by different digestion methods were found to be 86% to 113%, while microwave assisted digestion with various combinations of HNO3-HCl-HF and HNO3-HClO4-HF was considered to be a viable alternative to the conventional digestion systems because of its more intensive reaction conditions. The analytical results of four certified reference materials with different matrices, including sediment (GBW 07305), soil (GBW 07411), sludge (BCR R-143) and oil (NIST 1085a), by the microwave-assisted acid digestion method indicated that the recoveries of all elements of interest were more than 85% and the throughput of applied analytical method could be elevated significantly.

Journal Article↗
PubMed2002

[Evaluation of the usefulness of spectrophotometric method based on the reaction of formation of silic-molybdenum blue for determination of silica in hydrogenated fat].

The spectrophotometric method based on the reaction of formation of silic-molybdenum blue for determination of silica (silicon dioxide) in hydrogenated fat was developed. Determination limit of silica in this method was 15.6 mg/kg and average recovery 77.77%. Using this method the content of silica in the edible fat (margarine) taken from the market was determined. The samples of margarine before determination of silicon dioxide were mineralised and than the analyte was concentrated. The silica was not found in the margarine samples at levels above the determination limit of spectrophotometric method i.e. 15.6 mg/kg.

Humans↗
PubMed2003

[Colonization of silicate bacterium strain NBT in wheat roots].

The strain NBT of silicate bacterium was labelled with streptomycin, and a stable streptomycin resistance strain NBT was obtained. Its colonization dynamics and affecting factors in wheat rhizosphere were studied in agar plates and greenhouse pots were studied by counting the method with selective medium. The results of pot culture experiment showed that strain NBT could successfully colonize in the rhizosphere of wheat. In pot cultures of sterile soil, the highest colonization level (3.4 x 10(7) cfu.g-1 root soil) was reached on 9th day after seeds sown; at 54th day, the population of strain NBT tended to stable, and decreased to 1.4 x 10(4) cfu.g-1 root soil. In pot cultures of unsterile soil, the highest colonization level (3.8 x 10(7) cfu.g-1 root soil) was reached at 9th day, and the population of strain NBT tended to a stationary state at 60th day, with the numbers being 1.4 x 10(4) cfu.g-1 root soil. Some biological and abiotic factors could greatly influence the colonization of the beneficial microorganism.

Plant Roots↗