The clay mineral composition of sediments deposited in the last six oxygen isotope stages in the Gulf of Mexico continental slope was characterized. Smectite and illite were found to be the two major clay minerals of the clay fraction while kaolinite, chlorite and quartz were present in the clay fraction but in less proportions. Variations in clay mineral abundances, especially in the relative abundances of smectite and illite, were identified in relation to climate changes. Smectite was the most abundant mineral in sediments of the current (stage 1) and last interglacial maxima (stage 5) while illite dominates the clay min-eralogy of sediments from the last glacial maximum (stage 2). Relationships between clay mineralogy and physical properties were investigated as well. Significant positive correla-tions were found between Atterberg limits with the smectite content of the bulk sediment and with clay content. However, the relationship with smectite yielded a significantly higher correlation coefficient. Smectite and clay content also affect the natural water con-tent of sediments and its changes with depth.

It is well documented that aflatoxin contamination in foods presents significant economic and public health burdens worldwide. Aflatoxins, particularly aflatoxin B1 (AFB1), have been implicated in the etiology of disease and death in many parts of the world, necessitating research initiatives for intervention strategies designed to diminish biological exposure. Calcium montmorillonite clays (e.g. NovaSil Plus, NSP) have been found to tightly bind and inactivate aflatoxins in the gastrointestinal tract of multiple animal species. In the future, the hypothesis is that this strategy may also be appropriate for humans. Thus, the overall research goal was to investigate NSP suitability for human use through in vitro characterization followed by in vivo evaluation of NSP-AFB1 sorption and most importantly, safety of the clay. The first objective was to characterize the in vitro and in vivo sorption efficiency of NSP-AFB1 sorption and determine potential interactions with vitamin A (VA). Isothermal analysis suggested that NSP binds AFB1 with high capacity, affinity, and specificity in aqueous solution and further indicated that NSP does not appear to interact with VA. Subsequent short-term studies in Sprague-Dawley (S-D) rats and broiler chicks indicated that dietary inclusion of NSP (0.25%) significantly reduced AFB1 bioavailability without exerting overt toxicity. The second objective was to evaluate potential adverse effects of chronic ingestion of dietary NSP using male and female S-D rats in the absence of aflatoxins. Although statistically significant changes to a few parameters were noted, the differences did not appear to be NSP- or dose-dependent, suggesting that NSP at dietary inclusion levels as great as 2.0% (w/w) does not produce overt toxicity. Thus, this information increases the feasibility for using NSP in human trials in populations at high risk for aflatoxicosis. The third objective was to establish representative baseline data on human exposure to aflatoxins by collecting and quantifying urinary AFM1 in volunteers living in four separate communities in Ejura district of Ghana. Results revealed that urinary AFM1 in the study population was substantially high (mean = 1,850.86 ± 274.59 pg/mg creatinine), indicating that this particular population was highly exposed to aflatoxins and could be used for future intervention trials.

The objective of this research is the development of a new constitutive model to describe the behavior of cohesive soils under time dependent loading. In the work presented here, the modified SIMPLE DSS model is expanded to account for the effects of strain rate on clays in simple shear conditions. The response of clay soils is highly dependent on the rate of strain for both effective stress path and stress-strain behavior. The undrained shear strength is strongly influenced by strain rate both in monotonic and cyclic simple shear tests. Nevertheless, the few available experimental results cover a very limited range of loading conditions and rates. The existing literature established that the soil response display a unique relationship between shear strength and log scale of strain rate. To include the effects of strain rate, the modified simple effective stress model starts with two assumptions: (1) a specific shear strength corresponds to a specific strain rate in a unique relation; and (2) the effect of strain rate does not change the failure envelope. The proposed model is developed from the original SIMPLE DSS model, based on an effective stress formulation in a reduced stress space, and utilizing concepts related to the framework of bounding surface plasticity. The proposed model evaluationwas carried out comparing model simulations with results of simple shear tests on Boston Blue Clay and San Francisco Young Bay Mud. The model capability is useful especially in strain rate dependent responses for both monotonic and cyclic behavior, including irregular loading and step-changed condition. It was found that undrained shear strength in simple shear is directly related to strain rate effects and the responses in cyclic test show the more rate dependent behavior than those in monotonic test. The proposed model is able to predict the increase in undrained shear strength for higher strain rate.

Thesis (M.S.)--West Virginia University, 2001. / Title from document title page. Document formatted into pages; contains xii, 147 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 97-100).

Thesis (M.S.)--Ohio State University, 1964. / Includes bibliographical references. Available online via OhioLINK's ETD Center

Includes 2 theses (M.S. in Engin.)--by E.L. DiBiagio and Jack Watkins. / Project no. NR-081-117, contract no. Nonr-100 9(00). Includes bibliographical references.

Thesis (Ph. D.)--University of Chicago, 1914. / "Private edition, distributed by the University of Chicago libraries, Chicago, Illinois." Reprinted from the Journal of geology, vol. xxviii, no. 2, February-March 1920.

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