Molecular orbital calculations have been successively applied to mineralogical studies of equilibrium molecular geometry, electronic charge distributions, electronic spectra and bulk modulus calculations. To date, these studies have modelled bonding at atmospheric pressure. With the ever increasing interest in high pressure phases and mantle mineralogy, bonding studies of molecular groups at simulated high pressure can be an invaluable aid to understanding high pressure crystal chemistry, bond energetics and electronic spectra. This investigation tests the feasibility of various models to simulate pressure in ab initio SCF MO calculations on common metal-oxygen polyhedra. Pressure is simulated in the cluster, H₆Si₂O₇, by systematically stepping helium atoms directed^ along the Si-O bridging vectors toward the bridging oxygen. Changes in the Si-0 bond lengths, SiOSi angles and Si-0 force constants are monitored with increasing pressure. For an increase of 60 kbar pressure, the Si-0 bond length and SiOSi angle decrease 0.30% and 4.5%, respectively, which compares well with the 0.30% and 6.6% decrease observed in c-quartz for a similar increment of pressure. The linear correlation of Si-0 bond length and -sec(SiOSi), known to occur at one bar, holds at elevated pressure. In addition, the Si-0 stretching and SiOSi bending force constants show a percentage increase in the ratio 1:6 up to an estimated pressure of 140 kbar. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

Não consta resumo na publicação. / Abstract not available.

The lack of falcilities for veterinary services, such as analytical laboratories, which are distant from the field and at immense distances are aggravated by the constraint of transporting and preserving the samples. A method where a certain amount of the urine sample is absorbed onto filter paper, but dried in the field and then sent to the laboratory (Dried Filter Paper Method, DFPM), has been used in human medicine, but never applied in the veterinary field. The practice of expressing various urinary minerals/electrolytes relative to till' concentration of creatinine has recently become generally accepted. A single sample obviates the need for collection of urine over a 24-hour period. Fractional excretion (FE) of minerals and electrolytes (which is the mineral or electrolyte to creatinine ratio), is a simple, inexpensive measurement and a reasonable indicator of the renal clearance of minerals/electrolytes, using a single urine sample. The investigation was divided into two phases, The first was conducted entirely in vitro, using simulated urine (artificial and goat urine) dried on filter paper, manipulated in various ways under laboratory conditions, and the second phase was conducted in vivo and in vitro, using urine (collected from water-deprived goats) dried on filter paper and manipulated in various ways under laboratory conditions. Determination of mineral/electrolyte to creatinine ratios using the dried filter paper method consisted of Impregnating a specific filter paper with a specific volume of artificial/goat urine, diluted in a specific eluent, and then analysed for the analytes (creatinine, phosphate, chloride, magnesium, calcium, sodium, and potassium). Due to the wide range of filter papers, which could have been used for the trial, it was necessary to run an experiment to identify the best for the purpose. The experiment used filter papers from :2 different brands (Whatman® and Scheicher&Schuel filter papers). The following filter paper were compared: Whatman® no 2, 3, 5, 6, 42, 43, 44, and 542 and 860, 593, 595. 597, 598 for Schleicher&Schuell (very high quality). There were few significant differences. Whatman filter paper number 6, was chosen, because of the constant and uniform mineral/electrolyte to creatinine ratios. The very high variability of urine mineral/electrolyte concentrations in ruminants, and the limited linearity range of routine analytical equipment, constrains the routine use of laboratory analysers in urine mineral and electrolyte assessment. One of the approaches is to use a diluent, with a particular mineral/electrolyte concentration near to the lower end of the linear/standardised range. Therefore, "mixing" a small volume of urine with the diluent will result in a final mineral/electrolyte concentration, that falls into a linear and controlled/standard range for the particular mineral and electrolyte. A diluent was tested and the results for analytes show a high interclass correlation (R1 >0.75) between the expected and the calculated values of this ratio. The stability of mineral/electrolyte to creatinine ratio (B/Cr) in artificial and goat urine specimens using the dried filter paper method stored at 2 different temperatures during ten days was also evaluated experimently. While it has been found that P/Cr ratio, Mg/Cr ratio, K/Cr ratio are stable for the 10 days, the Cl/Cr ratio, Ca/Cr ratio, and Na/Cr were found to be less stable during the same period of time. The average results do not differ significantly from the control in either the artificial urine or the goat urine. Experiments were conducted to evaluate the reproducibility of artificial urine and artificial urine diluted 1:5 to simulate reproducibility of mineral/electrolyte to creatinine ratios with higher and lower concentrations, respectively. The results indicate a relatively good reproducibility of the method, because the variation, as measured by standard deviation, is small relative to the mean, except for Cl/Cr ratio and Ca/Cr ratio, where the results presented showed a relatively low reproducibility. In theory, since ratios can be obtained, and should be unchanged by taking measurements at different dilutions even if the amount of specimen is unknown, there should be no need to absorb a fixed amount of urine onto the filter paper when urine is collected, using this method. However, there appear to be limits to this in reality, dilution of urine below a 1: 10 dilution and/or the volume impregnated onto the filter paper below 0.525 ml on Whatman® number 6 filter paper. An experiment with goats on the relationship between the influence of water deprivation on minerallelectrulvte to creatinine ratio over a period of time demonstrated that concentrations and excretion of electrolytes vary from animal to animal, but the mineral/electrolyte to creatinine ratios by DFPM hardly vary, even if the goat is deprived of water. Using goat urine to determe mineral/electrolyte to creatinine ratio with the dried filter paper method gives high interclass correlation for mineral/electrolyte to creatinine ratio between the control (fresh urine sample, preserved in freezer) and the dried filter paper method on goats given water ad libitum. Interclass correlation agreement for the two methods was R1 >0.75. On the basis of the results, the method is robust for use as a urine sample preservation and transportation method for the determination of mineral/electrolyte to creatinine ratio with an added advantage of not needing either preservative or refrigeration. / Dissertation (MSc (Veterinary Science))--University of Pretoria, 2000. / Companion Animal Clinical Studies / unrestricted

Mineral hydration is known to result in low flotation recoveries and grades within primary platinum group element ores worldwide. This is because the phyllosilicate minerals derived from hydration reactions of silicate minerals (i) form electrostatic coatings on valuable minerals that in turn hinders collector adsorption, (ii) alter the viscosity of the slurry leading to poor gas dispersion and (iii) decrease the concentrate grade due to naturally-floating gangue. Sodium metasilicate was investigated because its dispersant, rheology modifying, and depressant properties could prove promising in combating the problems associated with these ore types. Quantitative evaluation by scanning electron microscopy (QEMSCAN) analysis revealed large quantities of serpentine and talc present within the ore sample used in this study, which led to a poor flotation response, as indicated by batch flotation tests. Using sodium metasilicate improved the recoveries and grades at high dosages (>1000 g/t). A suite of techniques was chosen to decouple sodium metasilicates' effects to answer why an improved flotation performance occurred. The zeta potential experiments indicate that improved recoveries are, in part, as a result of the reversal of serpentines surface charge, creating electrostatic repulsion between serpentine and valuable minerals which prevents the coating of valuable minerals by serpentine slimes. This corresponded with improved recoveries of a PGM proxy in the presence of serpentine slimes and a high sodium metasilicate dosage. Ore dilution and rheology tests indicate that decreased viscosity at high dosages also improved recoveries. This was supported by slower particle settling rates at high sodium metasilicate dosages during particle settling measurements. Talc micro-flotation tests revealed that the depression of talc occurred at higher sodium metasilicate dosages, which improved concentrate grade. This was supported by a QEMSCAN concentrate analysis of the sodium metasilicate batch flotation concentrates, which confirmed that talc, and other associated silicate minerals, were depressed at high sodium metasilicate dosages. The processing of near-surface altered ores is becoming an increasing problem worldwide and the use of sodium metasilicate proved valuable in mitigating the problems associated with the altered ore investigated in this study.

A number of montane herbs in northern Utah typically form flower buds beneath the snow cover and flower either through it or immediately after its recession. Two of these species, one naturally occurring , Claytonia lanceolata, and one cultivated bulb, Galanthus nivalis, were investigated for their response to this stress environment. Snow depth patterns, chlorophyll content of tissues, and plants grown in light-tight boxes, suggest that light passing through the snow to reach plants growing underneath is not critically involved in the timing of their developmental cycles or in their ability to endure this low temperature environment. Ability to endure stress seems to be closely related in a number of ways to activity at the plant membranes. Plants were protected from low temperature damage by application of cytokinin or calcium, both of which probably acted at the membrane. Potassium calcium antagonisms were reflected in the internal distribution of the ions under natural stress conditions; and plants that differentiated at the meristem while growing through the snow accumulated calcium at the tip during this growth .

The chemical properties of guanidinium tris(catecholato)siliconate, (H2N)2C=NH2J2(Si(C6H402)j]-XH20 (0 This same compound was, upon addition of' (H2N)2C=NH.HC1, isolated from 0.2, M aqueous catechol solutions buffered at pH 10 and containing the silicate minerals albite, andradite, muscovite, pyrophyllite, talc, and wollastonite, and also from unbuffered catechol solutions containing wollastonite and andradite. It is concluded from this work that the formation of an anionic catechol-silicon complex, Si(C6H402)32~ is largely responsible for the dissolution of the minerals mentioned above. From this conclusion, it is proposed that naturally occurring members of the class of organic compounds to which catechol belongs, the aromatic vic-diols, may play a role in chemical weathering, in the development of certain soil profiles, and in the entry and accumulation of silica in plants.

This thesis examines the mineral suite of undeveloped heavy-mineral deposits in the Cretaceous of the Northern Mississippi Embayment and compares them to the developed deposits of the Atlantic Coastal Plain. The hypothesis presented here is that Cretaceous heavy-mineral deposits of the eastern Mississippi Embayment had the same provenance, the Appalachian Piedmont, as did the younger sediments of the U.S. Atlantic Coast. Kyanite/sillimanite and staurolite were recognized in all samples, and represent strong evidence for an Appalachian Provenance. Alternatively, the overall lack of epidote in the HM suite points away from a Mississippi River related provenance. The dominant heavy minerals found in the Mississippi Embayment samples are ilmenite, leucoxene, zircon, rutile, kyanite/sillimanite, staurolite, and monazite. This suite of heavy minerals compares favorably to those represented along the Atlantic Coastal Plane, and supports an Appalachian Provenance. Southwest trending Paleozoic paleovalleys were likely sedimentation pathways from the Appalachian region.

No description available.

<p> A coarse grained amphibolite from the metamorphosed rim of the Whitestone Anorthosite was prepared in several ways for the purpose of determining the modal abundance of the constituent minerals by calibrated X-ray diffraction. A simple two component amphibolite consisting of plagioclase and amphibole was chosen and five major methods of mounting the specimens for X-ray diffraction were employed.</p> <p> It was hoped that a method could be found which would produce randomly oriented, homogeneous samples. A series of such samples each of a different component ratio would then provide a calibration curve from which the mode of a whole rock specimen could be estimated.</p> <p> The calibrated X-ray charts were produced on Philips scanning X-ray diffractometers.</p> <p> The inconsistencies in the results indicate that better technical procedures are required.</p> / Thesis / Bachelor of Science (BSc)

Page 20 missing from the thesis. / <p> This work was undertaken to evaluate neutron activation analysis as a technique for simultaneous determination of Ru and Os in sulfide minerals by counting the γ radiation of 97Ru and 103Ru, and the β^-radiation of 191Os and 193Os. The samples studied were collected from the Strathcona and Frood-Stobie Cu-Ni sulfide deposits of Sudbury. Sulfide minerals, including pyrrhotite, chalcopyrite, pentlandite and cubanite were separated from samples including representatives of both ore grade and non-commercial material. The minerals were analysed for Ru and Os to determine their concentration ranges in these sulfides, the degree of geochemical coherence of the metals in sulfides from both high grade ore zones and weakly mineralized rocks and their distribution between coexisting sulfides.</p> / Thesis / Master of Science (MSc)