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Thesis (M.S.)--Oregon State University, 2000. / Typescript (photocopy). Includes bibliographical references (leaves 62-63). Also available on the World Wide Web.

The rectal intima of the desert locust was found to possess fixed negative charges, rather than fixed neutral sites. It was suggested that the molecular species responsible for the negative sites might be acidic amino acids. The selective permeability of the intima as estimated from diffusion potentials, for divalent cations was 3a⁺² > Ca⁺² > Sr⁺² > Mg⁺² > Mn⁺², for monovalent cations was NH₄⁺ > Rb⁺ > Cs⁺ > K⁺ > Na⁺ > Li⁺ > TEA⁺ and for monovalent anions was HCO₃⁻ > CN⁻ > F⁻ > NO₃⁻ > CL⁻ > CH₃COO⁻ > Br⁻ > H₂PO₄⁻ > I⁻. Cation affinity for the fixed charged site was found to be in the order of Ca⁺² > Mg⁺⁺ » K⁺ > Na⁺. Similarity of effects of pH and ion concentration on streaming and diffusion potentials indicated that ion movement and water flow might take place through the same route. The intima was found to act as an osmotic compartment such that at high external osmotic pressures, the rate of water flow was reduced due to a shrinkage of the effective pore size in the intima, however the relative permeability of ions did not seem effected by membrane dehydration. Unstirred layers at the membrane-solution interfaces were found to have a minimal effect on diffusion potentials, however half of the value for streaming potentials was found to be due to a diffusion potential caused by an ion concentration difference in opposing unstirred layers. Calcium -45 flux across the intima at pH 5.5 (i.e. possessing fixed charge) was found to be 81 times greater, at a concentration of 10 mM/l CaCl₂, than calcium flux at the same concentration across the uncharged membrane (pH 2.2). The same effect was not significant for rubidium. Conversely, the removal of fixed charge enhanced anion flux. Calcium permeation rate was found to be a function of its dissociation rate from the fixed charge and did not correlate in a simple manner with the membrane binding capacity for calcium. A trans effect on calcium flux was also found in the intima and is believed to be a function of the dissociation rate of calcium from the fixed negative site. It was concluded that electro-osmosis was not the mode of water movement across the rectum, however physiological advantage of electro-osmosis was discussed. Flux experiments possible indicate that the intima might be the rate limiting step for K⁺ reabsorption in a hydrated animal. / Science, Faculty of / Zoology, Department of / Graduate

An in vitro preparation of the rectum of the desert locust Schistocerca gregaria is described and characterized. The rectal epithelium was mounted as a flat sheet separating two well stirred chambers and the trans-membrane potential difference (PD), membrane resistance, and short circuit current (SCC) were monitored. The PD and membrane resistance remained relatively constant for at least six hours at 35 mV (lumen positive) and 6000 Ohms . cm ⁻², respectively. After an initial two hour transient period during which the SCC dropped from 8 uMoles of charge .cm⁻² .hr⁻¹ to 3.5 uMoles. cm⁻² .h⁻¹ an approximate steady-state condition was reached and maintained for at least another four hours. The SCC was consistant with either a net cation transport from the hemolymph to the lumen of the rectum or a net anion transport in the opposite direction. Since Cl⁻ was the only major anion in the bathing media some experiments were carried out to evaluate the contribution of active Cl⁻ transport to the SCC. Substitution of SO4⁻ of NO3⁻ during the third and fourth hours in vitro had no effect on the SCC, although they abolished the initial two hours transient. Similar experiments in which Cl⁻ was substituted by acetate had a complex stimulatory effect on the SCC. Measurements of ³⁶Cl⁻ fluxes under SCC conditions during the same time period demonstrated a mean net flux of 1.52 uMoles of Cl⁻ cm⁻².hr from the rectal lumen to the hemolymph. This value is equivalent to one half the simultaneous SCC. These experiments clearly demonstrate that the rectal epithelium actively transports Cl⁻ in a direction consistent with the observed SCC but that this active transport of Cl⁻ does not contribute to the SCC during the third and fourth hours in vitro. Since rectal Na+ and K+ transport reported by other workers is in the wrong direction to account for the observed SCC, it seems necessary to propose (1) a Cl⁻ exchange pump (probably with HCO3⁻) perhaps located on the luminal membrane to account for the fact that active Cl⁻ transport does not contribute to the SCC and (2) a H+ and/or HCO3⁻ pump to account for the SCC. These proposals are incorporated in a model for organization of ion transport processes in the locust rectum. / Science, Faculty of / Zoology, Department of / Graduate

Thesis (Ph. D.)--University of Wisconsin--Madiosn, 1982. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 365-376).

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M.Sc. / The Mamatwan mine is situated at the most southern end of the world’s largest landbased resource of manganese, the Kalahari manganese field. The mine is operated by South African Manganese Corporation Limited (SAMANCOR) and is the largest open pit manganese mine in the world. The sedimentary manganese ore bed is interbedded with iron-formation of the Hotazel Formation of the Early Paleoproterozoic Voëlwater Subgroup of the Transvaal Supergroup. The open pit Mamatwan mine has a proven economic ore reserve of between 300 and 400Mt and produces 1.2Mt of manganese ore annually, of which 0.5Mt of ore is beneficiated and shipped through the harbour at Port Elizabeth. The remaining ore is railed to ferro-alloy plants at Meyerton and Newcastle. Carbonate-rich manganese lutite mined at the Mamatwan Mine is widely known as Mamatwan-type ore. It has a manganese content ranging from 30 – 38%. Only a small portion (15m of a total thickness of 49m) of the ore bed, containing an average of 38% Mn, is being mined and processed at present. The larger portion of the ore bed is not utilized. This study focuses on the physical and chemical characteristics of the ore bed in more detail in order to make suggestions on how to a) reduce waste by upgrading the upper parts of the lower manganese ore bed, or b) to improve the current recovery from the present economic zone. A second part of this study pays special attention to the lithostratigraphy of the lower manganese ore bed. The focus is on the paragenetic sequence and the diagenetic evolution of the braunite lutite that constitutes the manganese ore. The Mamatwan-type ore can be described as diagenetic to very low-grade metamorphic carbonate-bearing braunite manganolutite. Based on geochemical and mineralogical data, the lower manganese ore body was previously subdivided into eleven lithogically distinct zones. Based on detailed diamond drill core logging and with the aid of geochemical and physical data of two selected drill cores, an additional thirteen subzones were identified in this study. These new subzones were found to be consistent across the entire study area, located to the west and north of the present Mamatwan open pit. The paragenetic sequence recognised in the ore of the lower manganese ore bed can be subdivided into four stages, namely: (a) sedimentation, which is represented by fine lamination and the presence of fine-grained “dusty hematite”. (b) early diagenesis as represented by micritic carbonate matrix and possibly braunite, (c) late diagenesis or low-grade metamorphism are represented by coarse grained hausmannite, specularitic hematite, partridgeite and Mn-calcite, and supergene alteration that occurs immdediately below the contact of the ore bed to the unconformably overlying Tertiary Kalahari Formation. This supergene altered zone is marked by the presence of Mn4+ oxides such as cryptomelane, manjiroite, romanechite and pyrolusite, in addition to barite. The results obtained in this study permit definition of two sedimentary cycles within the manganese ore bed at the Mamatwan mine. Both cycles are defined by a carbonate-rich finely laminated zone at the base, overlain by a central manganese-rich economic zone, capped by manganese lutite that is enriched in carbonate ovoids. The two manganeserich zones are known as the M (lower) and X (upper) zone, and are characterized by the replacement of carbonate ovoids by hausmannite. The two Mn-rich zones are chemically and physically almost identical, with the M zone 7.5m thick and the X zone 5.5m thick. However, in the present mining configuration only the M zone is being mined. The most important result arising from the present study is the recommendation to restructure the future mining operation in order to mine not only the M zone, but also the X zone.