<p> The processes that generated the distinctive landscape of the Iowa Erosion Surface (IES) of northeastern Iowa have been debated for over a century. A number of researchers have concluded that the IES experienced a periglacial environment and was underlain by continuous permafrost during the last glacial maximum. Ubiquitous throughout the IES is a stone zone that lies 60-100cm below the surface. Several explanations for the genesis of the stone zone have been proposed, including a lag concentrate, biomantle processes, and cryogenesis. We utilized a combination of coring and trenching, ground penetrating radar and resistivity to investigate the 3D distribution of the stone zone, overlying "pedisediment" and the underlying contact with dense till across a 100m2 area on a typical IES hillslope in east-central Iowa . Our preliminary results indicate that the stone zone occurs in the basal few decimeters of pedisediment that rests uncomformably and abruptly on eroded, dense till. Ice wedge casts extend from the stone zone into the underlying till. The depth of the stone zone below the modern surface increases downslope and the stone zone dissipates and eventually is replaced by relatively thick loamy sand beneath the footslope. These relationships argue against the stone zone being of biogenic origin. The occurrence of ice wedge casts associated with the stone zone and systematic changes in the thickness and texture of the pedisediment suggest to us that stone zone on the IES was formed by a combination of cryogenic and active zone erosive processes during the full glacial period.</p>

A fully coupled, effective stress based elasto-plastic model is presented for a rigorous analysis of flow and deformation in variably saturated porous media subjected to monotonic and cyclic loading. The governing equations are derived based on the effective stress concept, equations of equilibrium, and conservation equations of mass and momentum using a systematic macroscopic approach. Both elastic and elasto-plastic constitutive equations are developed. All model coefficients are identified in terms of measurable parameters. The governing equations presented are general in nature, embodying all previously presented formulations in the field. A unified bounding surface plasticity model is developed to describe the stress-strain behaviour of variably saturated soils subjected to monotonic and cyclic loading. The model is formulated incrementally within the critical state framework using the effective stress approach. The model takes into account the effects of both plastic volumetric strain and matric suction on the hardening of the bounding surface. Cyclic behaviour is captured through a new mapping rule in which the point of stress reversal is taken as the centre of projection. The effect of particle crushing at high stresses is considered through a three-segmented critical state and isotropic compression lines. A non-associative flow rule is employed to generalise application of the model to all soils. Solution to the governing equations is obtained numerically using the finite element approach, with the finite difference method employed for the time integration of the rate equations. The elasto-plastic constitutive equations are integrated explicitly using Euler???s forward and the modified Euler integration schemes. Yield surface correction schemes are adopted to improve accuracy of the solution. Essential elements of the proposed model are validated by comparing numerical predictions with experimental data from the literature for fully and partially saturated soils subjected to monotonic and cyclic loadings in drained, undrained, isotropic and deviatoric conditions. The results demonstrate capability of the coupled model to predict essential characteristics of variably saturated soils subjected to monotonic and cyclic loadings in a unified manner.

Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2006. / Source: Dissertation Abstracts International, Volume: 68-02, Section: B, page: 0861. Adviser: Robert J. M. Hudson. Includes bibliographical references. Available on microfilm from Pro Quest Information and Learning.

Thesis (Ph.D.) -- University of Adelaide, School of Agriculture, Food and Wine, Discipline of Plant and Food Science, 2008. / Includes bibliography (leaves 151-177) Also available in print form.

Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2008. / Source: Dissertation Abstracts International, Volume: 69-05, Section: B, page: 2678. Adviser: Emerson D. Nafziger. Includes bibliographical references. Available on microfilm from Pro Quest Information and Learning.

Thesis (Ph. D.)--University of Toronto, 2008. / Includes bibliographical references.

Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2009. / Source: Dissertation Abstracts International, Volume: 70-06, Section: B, page: 3245. Adviser: Michelle Wander. Includes bibliographical references. Available on microfilm from Pro Quest Information and Learning.

-20 m2 and the permeabilitycould be altered with the addition of different additives. Full analysis of the changes in permeability could be performed after a test time of one week compared with a test time of several months in a shale core experiment using the Hassler cell.

No description available.

This thesis reports the interactions of (poly)cations with a variety of clay minerals and the application of the resultant organoclays as both sorbents and catalysts. The behaviour of organoclays containing tetramethylammonium cations (TMA[+]), is compared to the behaviour of organoclays containing polycations of the formula [(Me[2]NCH[2]CHOHCH[2])[n]][n+] (Magnafloc 206), which are shown to form two distinct types of organoclay. To investigate the interactions of the (poly)cations with clay surfaces, several dry powder analysis techniques have been employed including Kjeldahl nitrogen analysis, variable temperature x-ray diffraction and thermogravimetric analysis. The studies have shown that the (poly)cations reside between the clay layers and that the nature of the clay and the resident exchange cation have a significant effect on the amount adsorbed. It is also shown that the polycations have a higher affinity than tetramethylammonium cations for all the clay minerals investigated. Sorbents exchanged with various amounts of (poly)cation are investigated for their ability to adsorb benzene and rho-nitrophenol from water. The adsorption by polycation containing sorbents is reduced compared to TMA[+] containing sorbents and the latter is comparable with that reported in the literature. The adsorption site in such sorbents is the siloxane surface in the clay interlayers, as shown by the observation that the uptake of both benzene and / rho-nitrophenol by TMA[+] exchanged SAz-1, a high charge montmorillonite, was reduced compared to TMA[+] exchanged SWy-1, a low charge montmorillonite. In SAz-1 there is closer packing of adsorbed TMA[+] cations resulting in less siloxane surface area being available. Hydration of the TMA[+] cations also increases steric constraints. High polycation loadings prevent the clay layers from expanding and thus accessibility of rho-nitrophenol to the clay surface is reduced. Partition into the organic carbon content of the polymer occurs but uptake does not increase with organic carbon content as expected. Also, TMA[+] exchanged Westone-L was expected to behave similarly to TMA[+] exchanged SWy-1 as Westone-L and SWy-1 have very similar cation exchange capacities. However, it is shown that TMA[+] exchanged Westone-L behaves more like TMA[+] exchanged SAz-1 which has a much higher cation exchange capacity. A range of organoclays containing either tetraalkylammonium cations or polycations at differing exchange levels have been subjected to acid leaching at either 25 or 90&deg;C. The activity of these acid-activated (poly)cation-exchanged clays for the conversion of alpha-pinene to camphene and limonene was determined and compared with those from clay samples (without (poly)cations), acid-treated in the same manner. The presence of the polycation had a more marked influence on the activity of samples derived from SAz-1 than for corresponding samples derived from SWy-2, which was attributed to the increased hydrophobicity of the polycation loaded clay. Comparable yields for SWy-2 in the absence and presence of polycation suggest that SWy-2 disperses well in the nonpolar alpha-pinene. Also, octadecyltrimethylammonium and dodecyltrimethylammonium exchanged clays were generally less active than TMA[+] exchanged clays which were comparable to the most active polymer containing catalysts. It has also been shown that the octahedral iron content of the clay affects its catalytic activity. Finally, a competitive adsorption method of catalyst preparation has been developed which may replace more conventional high temperature techniques.