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The most extremely osmotolerant microbial isolates are fungi from high-sugar environments that tolerate the lowest water activity (0.61) for growth yet reported. Studies of osmotolerant bacteria have focused on halotolerance rather than sucretolerance (ability to grow in high sugar concentrations). A collection of salinotolerant (≥10% NaCl or ≥50% MgSO4) bacterial isolates from the Great Salt Plains of Oklahoma and Hot Lake in Washington were screened for sucretolerance in medium supplemented with ≥50% fructose, glucose or sucrose. Tolerances significantly differed between solutes, even though water activities for saline media (0.92 and 0.85 for 10 and 20% NaCl Salt Plains media, respectively) were comparable or lower than water activities for high-sugar media (0.93 and 0.90 for 50 and 70% sucrose artificial nectar media, respectively). These specific solute effects were differentially expressed among individual isolates. Extrapolating the results of earlier food science studies with yeasts at high sugar concentrations to bacteria in salty environments with low water activity should be done with caution. Furthermore, the discussion of habitable Special Regions on Mars and the icy worlds should reflect an understanding of specific solute effects.
The effects of fish oil (FO) supplementation on glycaemic control are unclear, and positive effects may occur only when the phospholipid content of tissue membranes exceeds 14 % as n-3 PUFA. Subjects (n 36, thirty-three completed) were paired based on metabolic parameters and allocated into a parallel double-blind randomised trial with one of each pair offered daily either 6 g of FO (3·9 g n-3 PUFA) or 6 g of maize oil (MO) for 9 months. Hyperinsulinaemic–euglycaemic–euaminoacidaemic (HIEGEAA) clamps (with [6,6 2H2 glucose]) were performed at the start and end of the intervention. Endogenous glucose production (EGP) and whole-body protein turnover (WBPT) were each measured after an overnight fast. The primary outcome involved the effect of oil type on insulin sensitivity related to glycaemic control. The secondary outcome involved the effect of oil type on WBPT. Subjects on FO (n 16) had increased erythrocyte n-3 PUFA concentrations >14 %, whereas subjects on MO (n 17) had unaltered n-3 PUFA concentrations at 9 %. Type of oil had no effect on fasting EGP, insulin sensitivity or total glucose disposal during the HIEGEAA clamp. In contrast, under insulin-stimulated conditions, total protein disposal (P=0·007) and endogenous WBPT (P=0·001) were both increased with FO. In an associated pilot study (n 4, three completed), although n-3 PUFA in erythrocyte membranes increased to >14 % with the FO supplement, the enrichment in muscle membranes remained lower (8 %; P<0·001). In conclusion, long-term supplementation with FO, at amounts near the safety limits set by regulatory authorities in Europe and the USA, did not alter glycaemic control but did have an impact on WBPT.
Avian diet selection is hypothesized to be sensitive to seasonal changes in breeding status, but few tests exist for frugivorous tropical birds. Frugivorous birds provide an interesting test case because fruits are relatively deficient in minerals critical for reproduction. Here, we quantify annual patterns of fruit availability and diet for two frugivorous hornbill (Bucerotidae) species over a 5.5-y period to test for patterns of diet selection. Data from the lowland tropical rain forest of the Dja Reserve, Cameroon, are used to generate two nutritional indices. One index estimates the nutrient concentration of the diet chosen by Ceratogymna atrata and Bycanistes albotibialis on a monthly basis using 3165 feeding observations combined with fruit pulp sample data. The second index is an estimate of nutrient concentration of a non-selective or neutral diet across the study area based on tree fruiting phenology, vegetation survey and fruit-pulp sample data. Fifty-nine fruit pulp samples representing 40 species were analysed for 16 nutrient categories to contribute to both indices. Pulp samples accounted for approximately 75% of the observed diets. The results support expected patterns of nutrient selection. The two hornbill species selected a diet rich in calcium during the early breeding season (significantly so for B. albotibialis in July and August). Through the brooding and fledging periods, they switched from a calcium-rich diet to one rich in iron and caloric content as well as supplemental protein in the form of invertebrates. Calcium, the calcium to phosphorus ratio and fat concentration were the strongest predictors of breeding success (significant for calcium and Ca:P for B. albotibialis in June). We conclude that hornbills actively select fruit based on nutritional concentration and mineral concentration and that the indices developed here are useful for assessing frugivore diet over time.
The freeze-drying method of synthesizing powders of the superconducting oxide YBa2Cu3O7-δ is described. This process produces homogeneous, submicron powders of high purity. The effects of salt selection, solution concentration and pH on the process are described. Some evaluation of the sintering behavior and the effects on critical current density are included.
Zirconia gels have been synthesized from zirconium butoxide in excess water with HNO3. The structure and characteristics of the gels have been studied as a function of the acid content, and the transformation during heat treatment has been followed up to 1150°C.
From the results of a previous similar study on aluminum hydroxide gels, a comparison is made between the sol-gel processes of zirconia and those of alumina. A discussion of the differences of the aqueous media chemistry of Al and Zr, and gelation mechanisms, is presented.
The structures of alumina gels made from aluminum sec butoxide have been studied by X-ray diffraction and scanning electron microscopy as a function of pH as well as of the temperature of peptization and gelling. The structures of these gels appear to be very sensitive to the conditions of preparation, and lead to a variety of gelled products and transformation behaviors on firing. Specific attention is directed to preferential orientation and to structures which are X-ray super-amorphous.
Coagulation of HLW feed slurry can result from the interaction between acid metal cations and soluble silicates/silica. Feed slurry viscosity depend on a number of factors: (a) concentration and composition of the waste slurry electrolytes, (b) type and concentration of silica and silicate constituents in the glass former, (c) pH of the slurry feed, and (d) degree and order of mixing of the glass former with the waste sludge. Coagulation can be avoided by mixing to achieve a good dispersal of glass former globules in the waste slurry even when pH and electrolyte content favor it.
Catalyst supports are required to meet a wide range of objectives, including chemical purity and composition, optimised surface area/porosity and thermal stability. Gel processing offers means by which many of these requirements can be achieved. In addition, the use of sols of controlled rheology allows the support material to be prepared in a form which facilitates its application to substrates (including metals) as a coating, thereby greatly improving its versatility for producing novel catalysts. The preparation of typical support materials will be discussed, together with examples of their use in catalysis.
The sol-gel method for the preparation of ceramics and glasses has frequently been mentioned as more advantageous as compared to conventional methods. However, there are few known examples of a direct comparison for the same material. In the present work both the processing and resultant properties for ferroelectrics such as BaTiO3, KTaO3, KNbO3 and K(Ta,Nb)O3 made by both methods are directly compared. The uniformity is evaluated by high-angle x-ray diffraction, electron microscopy and EDAX and the dielectric properties are compared. The advantages and disadvantages of the sol-gel method are discussed.
The use of sol-gel techniques to prepare glasses and crystalline ceramics offers outstanding opportunity for breakthroughs in technology. The areas of particular promise include novel glasses; crystallineceramics with exceptional microstructures; coatings for modification of electrical, optical, mechanical and chemical properties; porous media with high surface area and tailored chemistry; ceramic powders with high chemical homogeneity and narrow distributions of particle size; matrix materials in ceramicceramic composites; and a wide spectrum of specialty ceramic materials, ranging from abrasives and fibers to glass ceramics and films. Opportunities in each of these areas will be discussed and related to the advances in understanding and process technology required for their achievement. The theses will be advanced that creative chemistry provides the key to many of these advances, that ceramists simply MUST learn more chemistry, but that we dare not rest from our labors when the chemistry is done.
Diketonate aluminum alkoxides were prepared and allowed to react with acetoxyalkylsilanes. The conversion of the aluminosiloxanes thus obtained to aluminosilicates at 450°C was demonstrated. These aluminosiloxane ceramic precursors are glassy, oligomeric materials which readily dissolve in organic solvents to give viscous solutions ideal for casting films. Films of the metal-organic compounds prepared in this manner yield monolithic, crack-free aluminosilicate films directly on thermal curing, with a thickness limit of 3000Å for single crystal silicon wafer substrates. These aluminosilicate films have been found to be effective anticorrosion barriers for various metal substrates. The chemistry of this organoaluminosilane system and the nature of the aluminosilicate films obtained has been investigated using a variety of chemical and physical methods. The results of this investigation will be described and the possible advantages of this direct conversion process over the sol-gel method as a means of obtaining aluminosilicate films will be discussed.
High purity, fine-grain size, SrTiO3 ceramics were fabricated from powders which were chemically derived by the Pechini method. The preparation is based upon a thermally polymerizable water-ethylene glycol-citric acid system in which a wide range of metal alkoxides, carbonates, and metal salts are soluble. The process is a closed system, and lends itself to the preparation of complex oxides which can contain numerous additives and dopants. In this study, Wdoped SrTiO3 powders were prepared with various Sr:Ti ratios, and fine grain internal boundary layer capacitors were fabricated by controlled segregation in sintering. Characteristics of the resin, powder, microstructures, and electrical properties are reported. The advantages and disadvantages of this method of chemical preparation for ceramic materials are noted.
Transition metal oxide gels can be obtained, through a polycondensation process, by acidification of aqueous solutions. Thin layers can be easily deposited onto a substrate. Their electronic and ionic properties could lead to new developments of the sol-gel process. The semiconducting properties of V2O gels can be used for antistatic coatings or electrical switching devices. These gels exhibit a lamellar structure and can be described as particle hydrates. They are fast proton conductors and could behave as a host lattice for intercalation.
Gels with compositions Na2O-(1-x)SiO2 were prepared from tetraethylorthosilicate (TEOS) with sodium acetate and from tetramethylorthosilicate (TMOS) with sodium methoxide or TEOS with sodium ethoxide. After gelation (10 min.) the samples were slowly dried for about one month at room temperature. Thermogravimetric analysis (up to 500°C) in air and O2 atmosphere was performed. The electrical properties were studied in air by impedance spectroscopy during successive temperature cycles starting from room temperature dried gels of composition 0.10 Na2O 0.90 SiO2. Protonic conductivity appears to be eliminated after reaching the 2nd stage of the drying process (200°C). The activation energies for conduction and the conductivities show small discrepancies from known values for homogeneous glasses of equivalent compositions. Considering the effect of water on the conductivity of glasses prepared by the melting procedure, one can estimate the residual water content in the so-called dried gels to be close to 0.5 wt %.