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Generally, dielectrophoresis (DEP) analysis of biological cell samples relies on the differing electrical parameters between the cells and the surrounding fluid medium. To achieve effective positive DEP manipulation and sorting of mammalian cells in suspension, it is required to resuspend the cells into a low-conductivity fluid buffer. The use of a low conductivity buffer also aids in minimizing the effects of Joule heating, which can cause cell death and ineffective cell trapping. The common method to prepare the sample relies on centrifugation of sensitive cells, a time-consuming and tedious process that may result in decreased sample viability. Herein is presented a microfluidic device that passively moves cells from a high-conductivity growth media into a low-conductivity DEP buffer. It is comprised of con- verging rows of pillars and uses mechanical filtration to force cells into the new buffer while allowing for the old fluid to flow through the posts and out of separate outlets. Because this device is intended to be used upstream of a contactless dielectrophoresis (cDEP) device, the buffer exchange device must have an outlet flow rate that is within the range necessary for direct integration with the cDEP device, maintain a low shear stress that will not affect the integrity of the sample and achieve sufficiently high cell recovery. Methods of this project included optimizing the shape, size, and orientation of the posts, determining the flow rate for maintaining an ideal DEP buffer conductivity, numerical modeling of shear stress, and determining the cell recovery rate. It is anticipated that this device can be extended to physiological media sample processing such as for liquid biopsy. / Master of Science / In order to accomplish numerous biomedical experiments, cells must be transferred from their native fluid growth media into a different fluid solution, through a process referred to as buffer exchange. The current method for buffer exchange is time consuming, tedious, and affects the number of cells left alive for experimentation. In this work, we present a microfluidic device that can accomplish the buffer exchange process by simply flowing in the cells in their media in parallel with the new buffer solution. The results of this research work can be extended to aid in the process of buffer exchange for various biological experiments. The proposed device utilizes mechanical filtration to force cells into the new buffer while allowing for the old fluid to flow through the posts and out of separate outlets. The design of the device was optimized through computational analysis of the concentration and fluid shear stress in conjunction with experimental tests of devices for outlet conductivity and cell retention.

A common water quality issue is an excess of nutrients which can lead to problems such as eutrophication. Stream restoration is one method by which improvements in water quality may be attempted. One strategy is increasing hyporheic zone flow at baseflow by addition of instream structures. The hyporheic zone can be an area of increased biogeochemical activity, with potential enhancement of reactions such as denitrification. However, the comparative effects of various instream restoration techniques, as well as the role of watershed setting and corresponding environmental characteristics in which restoration occurs (e.g., hydraulic conductivity, stream slope), are still poorly understood. In this study we numerically modeled groundwater and surface water interaction in a 200 m second order stream reach in southwestern Virginia using MIKE SHE. We calibrated the model to hydrologic and tracer data available during field tests of restoration techniques. We then simulated different types of instream restoration techniques (e.g., fully and partially channel-spanning weirs and buried structures), and varied hydrologic and biogeochemical controlling factors driven by watershed setting. The measured effects for this sensitivity analysis were direction and magnitude of surface water-groundwater exchange and amount of denitrification. We found that factors related to watershed setting had the greatest effect on surface water-groundwater exchange and on denitrification, including streambed hydraulic conductivity, natural or background stream topography and slope, and groundwater levels. Type and number of instream structures also influenced surface water-groundwater exchange and denitrification, but to a lesser degree, and the effect of structures was in turn controlled by watershed setting. Watershed setting was thus the largest control, both on exchange overall, and the effectiveness of structures. Human effects on watersheds such as agriculture and urbanization therefore likely play a role in whether reach-scale restoration practices succeed in achieving water quality goals. More broadly, restoration efforts at the watershed scale itself, such as reducing fertilizer use or improving stormwater management, may be necessary to achieve ambitious water quality goals. Nevertheless, reach-scale restoration efforts such as in-stream structures may play a useful role in certain watershed settings. Furthermore, other reach-scale restoration techniques that affect streambed topography, such as addition of pool-riffle sequences, may be more effective, and bear investigation. / Master of Science / A common water quality issue is an excess of nutrients which can lead to problems such as algal blooms. Stream restoration is one method by which improvements in water quality may be attempted. One strategy is increasing hyporheic zone flow by addition of instream structures. The hyporheic zone is an area of the stream bed and banks where there is increased biogeochemical activity, with potential enhancement of reactions that may remove nutrients such as denitrification. However, the comparative effects of various instream restoration techniques, as well as the role of watershed setting and corresponding environmental characteristics in which restoration occurs (e.g., hydraulic conductivity, stream slope), are still poorly understood. In this study we numerically modeled groundwater and surface water interaction in a 200 m headwater stream reach in southwestern Virginia using MIKE SHE. We calibrated the model to hydrologic and tracer data available during field tests of restoration techniques. We then simulated different types of instream restoration techniques (e.g., fully and partially channel-spanning weirs and buried structures), and varied hydrologic and biogeochemical controlling factors driven by watershed setting. The measured effects for this sensitivity analysis were direction and magnitude of surface water-groundwater exchange and amount of denitrification. We found that factors related to watershed setting had the greatest effect on surface water-groundwater exchange and on denitrification, including streambed hydraulic conductivity, natural stream topography and slope, and groundwater levels. Type and number of instream structures also influenced surface water-groundwater exchange and denitrification, but to a lesser degree, and the effect of structures was in turn controlled by watershed setting. Watershed setting was thus the largest control, both on exchange overall, and the effectiveness of structures. Human effects on watersheds such as agriculture and urbanization therefore likely play a role in whether reach-scale restoration practices succeed in achieving water quality goals. More broadly, restoration efforts at the watershed scale itself, such as reducing fertilizer use or improving stormwater management, may be necessary to achieve ambitious water quality goals. Nevertheless, reach-scale restoration efforts such as instream structures may play a useful role in certain watershed settings. Furthermore, other reach-scale restoration techniques that affect streambed topography, such as addition of pool-riffle sequences, may be more effective, and bear investigation.

by Leung Wai-Lun, Ma Chuen. / Thesis (M.B.A.)--Chinese University of Hong Kong, 1989. / Bibliography: leaves 74-75.

Thesis (MSc)--University of Stellenbosch, 2003. / ENGLISH ABSTRACT: The equilibrium distribution coefficients of 42 elements [Li(I), Na(I), K(I), Rb(I), Cs(I), Sc(III), Ti(IV), V(IV), V(V), Mn(II), Fe(III), Ni(II), Zn(II), Al(III), Ga(III), As(V), Y(III), Zr(IV), Nb(V), Mo(VI), Cd(II), In(III), Sn(IV), Sb(V), Ta(V), W(VI), Pb(II), Bi(III), La(III), Ce(III), Th(IV), U(VI), Co(II), Ag(I), Ge(IV),Mg(II), Sr(II), Ba(II), Tb(III), Yb(III), Cr(III) and Cu(II)] on Bio Rad AG MP-50 macroporous cation exchange resin in varying citric acid – nitric acid mixtures were successfully determined. The equilibrium distribution coefficients of these selected elements were determined in 0.1 M and 0.25 M citric acid at various concentrations of nitric acid, namely, 0.2 M, 0.5 M, and 1.0M, respectively. Two component [Mo(VI)-Y(III); Zr(IV)-La(III) and As(V)-Zn(II)] and three component [Nb(V)-Ta(V)-V(V)] elemental separations on a 10 ml AG MP-50 resin column were successfully determined to illustrate how the results of the above equilibrium distribution coefficients can be utilised. From the equilibrium distribution coefficients obtained for magnesium(II) and sodium(I), a proposal was put forward to modify the current sodium-22 production performed at iThemba LABS. While the results did not predict a possible separation between the two elements, a theory concerning the use of citric acid in the production was proven not to hold under the chosen conditions. / AFRIKAANSE OPSOMMING: Die ewewig verdelingskoëffisiënte van 42 elemente [Li(I), Na(I), K(I), Rb(I), Cs(I), Sc(III), Ti(IV), V(IV), V(V), Mn(II), Fe(III), Ni(II), Zn(II), Al(III), Ga(III), As(V), Y(III), Zr(IV), Nb(V), Mo(VI), Cd(II), In(III), Sn(IV), Sb(V), Ta(V), W(VI), Pb(II), Bi(III), La(III), Ce(III), Th(IV), U(VI), Co(II), Ag(I), Ge(IV),Mg(II), Sr(II), Ba(II), Tb(III), Yb(III), Cr(III) en Cu(II)] is op Bio Rad se AG MP-50 makroporeuse kationiese uitruilerhars in verskillende sitroensuur – salpetersuur mengsels met sukses bepaal. Die verdelingskoëffisiënte is in 0.1 M en 0.25 M sitroensuur met verskillende konsentrasies van salpetersuur (0.2 M, 0.5 M en 1.0 M) bepaal. Twee-komponent [Mo(VI)-Y(III); Zr(IV)-La(III) en As(V)-Zn(II)] en drie-komponent [Nb(V)-Ta(V)-V(V)] skeidings op ’n 10 ml AG MP-50 harskolom is suksesvol bepaal om te demonstreer hoe die verdelingskoëffisiëntresultate gebruik kan word. As ’n uitvloeisel van die verdelingskoëffisiëntresultate vir Mg(II) en Na(I), is ’n voorstel ingedien om die huidige natrium-22 produksiemetode, tans in gebruik by iThemba LABS, te modifiseer. Die resultate het nie ’n skeiding tussen die twee elemente voorspel nie, maar het bewys dat ’n teorie oor die gebruik van sitroensuur in die produksie nie heeltemal korrek was onder die huidige toestande nie.

published_or_final_version / abstract / Real Estate and Construction / Doctoral / Doctor of Philosophy

In this thesis I describe Khmers negotiations of circumstances surrounding the disassembly, reconstruction, and redefinition of Khmer identity from their homeland in Cambodia to a traditional Khmer village recreated in the United States. Using a framework derived from a constructivist perspective, I have placed processes of negotiation and identity transformation within the lived context of Khmers lives. Thus, a holistic understanding of the interrelatedness of multiple changes in Khmerness is made possible. Ethnographic data collected between 1997 and 1999, through participant-observation and interviews, inform this study. Findings from this study reveal three levels of identity transformation as told by members of a small Khmer village established along the U. S. Gulf of Mexico. However, these three levels of transformation are not mutually exclusive nor are they necessarily sequential. Each transformation of Khmers identities constitutes permeable aggregates of other past and continuing disassemblies, reconstructions and redefinitions of Khmerness. Findings from this study demonstrate that Khmer identity shifts and is transformed by past and present experiences and with their changing circumstances, from endangered Cambodian, to refugees, to re-established Khmers in America.

The social exchange research tradition has examined the effects of structural factors on behavioral and psychological outcomes. Emerson's power-dependence perspective has driven many of these projects, and I follow this line of work. In spite of Emerson's suggestion that changes in the structure of networks should be a focus of investigation, power-dependence research to date has focused exclusively on networks as static, unchanging entities. I extend social exchange theory to consider the effects of structural change on actors within social exchange networks. I predict that dynamic networks and static networks produce different effects on behavioral commitment and on the psychological variables of trust, pleasure and interest. I test these hypotheses using a factorial experimental design. Support for the hypotheses is mixed, and examination of empirical results uncovers some unexpected findings with respect to the exchange behavior of actors in equal-power versus unequal-power networks. Actors in equal-power networks show indifference between potential exchange partners, while actors in unequal-power networks demonstrate unexpectedly high levels of behavioral commitment. Drawing on power-dependence theory, I also generate and test positionally-specific predictions for the psychological variables.

Approved for public release, distribution is unlimited / To achieve integration of the Naval Meteorology and Oceanography (METOC) community into the developing FORCEnet environment, transformational innovations must be researched and implemented. Agent based software is an example of technology that can be employed in this way by changing the method by which METOC data is distributed to end-users. This thesis documents the creation and implementation of a software agent that uses Internet connections to retrieve numerical model data, loads this output into array data containers, and then makes it available to the end-user in a machinereadable forecast object format. The impact of the importation of this forecast object into warfare commander command-and-control software is then assessed using the commercially available SEAWAY logistics tool. This assessment highlights the importance of defining the METOC functional requirements for the emerging FORCEnet environment, so that proper interfaces to exchange data freely, and visually depict it, are incorporated during next generation software development. Using these types of agents to automate the generation and delivery of weather parameters could also allow the importation of data into previously insular software, provide reach-back support to the warfighter, and be a means of reducing manpower and budgetary requirements during this time of fiscal constraint. / Lieutenant, United States Navy