Geomembranes are one of the most widely used geosynthetics in various civil engineering applications. Their primary function is as a barrier to liquid or vapour flow. Smooth Geomembranes are frequently used in combination with different soils, and due to their low surface roughness, are challenging to design to ensure adequate shear strength along the smooth geomembrane-soil interface. It is important to use the appropriate values of interface shear strength parameters in the design of slopes incorporating one or more geomembranes in contact with soils. The parameters are determined by conducting direct shear test on the geomembrane-soil interface. Laboratory tests of interface shear strength for geomembranes and soil are typically carried out with no provision for measurement of pore pressures at the soil/geomembrane interface. <p>This thesis deals with study of smooth geomembrane-soil interfaces, particularly under unsaturated conditions. The various factors that affect the interface shear behaviour are also studied. The tests were conducted using a modified direct shear box with a miniature pore pressure transducer installed adjacent to the surface of the geomembrane. Geomembranesoil interface shear tests were carried out with continuous measurement of suction in close proximity to the interface during the shearing process thus making it possible to analyze test results in terms of effective stresses. The method was found to be suitable for unsaturated soils at low values of matric suction. <p>Results of interface shear tests conducted using this method show that it is quite effective in evaluating interface shear behaviour between a geomembrane and an unsaturated soil. The results suggest that soil suction contributes to shearing resistance at low normal stress values. At lower normal stress values, the interface shear behaviour appears to be governed only by the magnitude of total normal stress. <p> At high normal stresses, the failure mechanism changed from soil particles sliding at the surface of geomembrane to soil particles getting embedded into the geomembrane and plowing trenches along the direction of shear. A plowing failure mechanism resulted in the mobilization of significantly higher shear strength at the geomembrane soil interface. It was found that placement water contents near saturated conditions results in lower effective stresses, a shallower plowing mechanism and lower values of mobilized interface shear strength.

To achieve efficient planarization with reduced device dimensions in integrated circuits, a better understanding of the physics, chemistry, and the complex interplay involved in chemical mechanical planarization (CMP) is needed. The CMP process takes place at the interface of the pad and wafer in the presence of the fluid slurry medium. The hardness of Cu is significantly less than the slurry abrasive particles which are usually alumina or silica. It has been accepted that a surface layer can protect the Cu surface from scratching during CMP. Four competing mechanisms in materials removal have been reported: the chemical dissolution of Cu, the mechanical removal through slurry abrasives, the formation of thin layer of Cu oxide and the sweeping surface material by slurry flow. Despite the previous investigation of Cu removal, the electrochemical properties of Cu surface layer is yet to be understood. The motivation of this research was to understand the fundamental aspects of removal mechanisms in terms of electrochemical interactions, chemical dissolution, mechanical wear, and factors affecting planarization. Since one of the major requirements in CMP is to have a high surface finish, i.e., low surface roughness, optimization of the surface finish in reference to various parameters was emphasized. Three approaches were used in this research: in situ measurement of material removal, exploration of the electropotential activation and passivation at the copper surface and modeling of the synergistic electrochemical-mechanical interactions on the copper surface. In this research, copper polishing experiments were conducted using a table top tribometer. A potentiostat was coupled with this tribometer. This combination enabled the evaluation of important variables such as applied pressure, polishing speed, slurry chemistry, pH, materials, and applied DC potential. Experiments were designed to understand the combined and individual effect of electrochemical interactions as well as mechanical impact during polishing. Extensive surface characterization was performed with AFM, SEM, TEM and XPS. An innovative method for direct material removal measurement on the nanometer scale was developed and used. Experimental observations were compared with the theoretically calculated material removal rate values. The synergistic effect of all of the components of the process, which result in a better quality surface finish was quantitatively evaluated for the first time. Impressed potential during CMP proved to be a controlling parameter in the material removal mechanism. Using the experimental results, a model was developed, which provided a practical insight into the CMP process. The research is expected to help with electrochemical material removal in copper planarization with low-k dielectrics.

Silicon is commonly used in infrared (IR) imaging systems. The surface quality is an important issue in optics manufacturing since surface roughness affects optical performance of imaging systems. Surface quality of an optical component is determined by number of factor, including cutting parameters / cutting speed, depth of cut and feed in radial direction. In this thesis, an experimental study has been performed to investigate the relation between cutting parameters and average roughness of the surface of silicon. In the experiments, silicon specimens, which have a diameter of 50 mm, were face turned by using a 2-axis CNC single point diamond turning machine. The specimens were machined by using either constant spindle speed or constant cutting speed. Two different tools with rake angles of -15 degrees and -25 degrees were used. The attained surfaces were measured by using a white light interferometer, which has a resolution of 0.1nm. The experiments were designed according to the factorial design method, considering cutting parameters. The effects of cutting parameters and tool rake angles on surface quality of silicon were observed. The best average surface roughness obtained was about 1 nm which is quite better than the acceptable average surface roughness level of 25 nm.

In this study, effect of surface roughness on convective heat transfer and fluid flow in two dimensional parallel plate microchannels is analyzed by numerically. For this purpose, single-phase, developing, laminar fluid flow at steady state and in the slip flow regime is considered. The continuity, momentum, and energy equations for Newtonian fluids are solved numerically for constant wall temperature boundary condition. Slip velocity and temperature jump at wall boundaries are imposed to observe the rarefaction effect. Effect of axial conduction inside the fluid and viscous dissipation also considered separately. Roughness elements on the surfaces are simulated by triangular geometrical obstructions. Then, the effect of these roughness elements on the velocity field and Nusselt number are compared to the results obtained from the analyses of flows in microchannels with smooth surfaces. It is found that increasing surface roughness reduces the heat transfer at continuum conditions. However in slip flow regime, increase in Nusselt number with increasing roughness height is observed. Moreover, this increase is found to be more obvious at low rarefied flows. It is also found that presence of axial conduction and viscous dissipation has increasing effect on heat transfer in smooth and rough channels.

Title from PDF of title page (University of Missouri--Columbia, viewed on Feb 17, 2010). The entire thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file; a non-technical public abstract appears in the public.pdf file. Thesis advisor: Dr. Kathleen M. Trauth. Includes bibliographical references.

Thesis (Ph. D.)--University of California, Riverside, 2009. / Includes abstract. Also issued in print. Includes bibliographical references. Available via ProQuest Digital Dissertations.

Synthetic Aperture Radar (SAR) has been identified as a good candidate to provide high-resolution soil moisture information over extended areas. SAR data could be used as observations within a global Data Assimilation (DA) approach to benefit applications such as hydrology and agriculture. Prior to developing an operational DA system, one must tackle the following challenges of soil moisture estimation with SAR: (1) the dependency of the measured radar signal on both soil moisture and soil surface roughness which leads to an ill-conditioned inverse problem, and (2) the difficulty in characterizing spatially/temporally surface roughness of natural soils and its scattering contribution. The objectives of this project are (1) to develop a roughness measurement method to improve the spatial/temporal characterization of soil surface roughness, and (2) to investigate to what extent the inverse problem can be solved by combining multipolarization, multi-incidence, and/or multi-frequency radar measurements. The first objective is achieved with a measurement method based on Structure from Motion (SfM). It is tailored to monitor natural surface roughness changes which have often been assumed negligible although without evidence. The measurement method is flexible, a.ordable, straightforward and generates Digital Elevation Models (DEMs) for a SAR-pixel-size plot with mm accuracy. A new processing method based on band-filtering of the DEM and its 2D Power Spectral Density (PSD) is proposed to compute the classical roughness parameters. Time series of DEMs show that non-negligible changes in surface roughness can happen within two months at scales relevant for microwave scattering. The second objective is achieved using maximum likelihood fitting of the Oh backscattering model to (1) full-polarimetric Radarsat-2 data and (2) simulated multi-polarization / multi-incidence / multi-frequency radar data. Model fitting with the Radarsat-2 images leads to poor soil moisture retrieval which is related to inaccuracy of the Oh model. Model fitting with the simulated data quantifies the amount of multilooking for di.erent combinations of measurements needed to mitigate the critical e.ect of speckle on soil moisture uncertainty. Results also suggest that dual-polarization measurements at L- and C-bands are a promising combination to achieve the observation requirements of soil moisture. In conclusion, the SfM method along with the recommended processing techniques are good candidates to improve the characterization of surface roughness. A combination of multi-polarization and multi-frequency radar measurements appears to be a robust basis for a future Data Assimilation system for global soil moisture monitoring.

This dissertation involved a theoretical and experimental investigation of the adhesive forces between spherical particles of four different diameters and two selected flooring materials under different air velocities. Previous theoretical work and experiments described in the literature tended to be conducted with idealized surfaces, and therefore have limited applicability to indoor environments. Controlled experiments were designed, constructed and executed to measure the air velocity required to overcome adhesion forces. The diameters of the particles investigated were 0.5, 3.0, 5.0 and 9.9 [mu]m, and the flooring materials were linoleum and wooden flooring. The critical velocity, the flow at which 50% of the particles detached, is presented as a function of particle diameter for each surface. The measured values were then compared to empirical and theoretical models as well as to a scaling analysis that considers component forces that act on a particle-surface system. The results suggest that critical velocity decreases with increasing particle diameter and that existing models have limited applicability to resuspension from flooring materials. / text

published_or_final_version / Electrical and Electronic Engineering / Doctoral / Doctor of Philosophy

The high-density integrated circuit (IC) gives rise to geometrically complex multiscale chip-package structures whose electromagnetic performance is difficult to predict. This motivates this dissertation to work on an efficient full-wave transient solver that is capable of capturing all the electromagnetic behaviors of such structures with high accuracy and reduced computational complexity compared to the existing methods. In this work, the unconditionally stable Laguerre-FDTD method is adopted as the core algorithm for the transient full-wave solver. As part of this research, skin-effect is rigorously incorporated into the solver which avoids dense meshing inside conductor structures and significantly increases computational efficiency. Moreover, as an alternative to typical planar interconnects for next generation high-speed ICs, substrate integrated waveguide, is investigated. Conductor surface roughness is efficiently modeled to accurately capture its high-frequency loss behavior. To further improve the computational performance of chip-package co-simulation, a novel transient non-conformal domain decomposition method has been proposed. Large-scale chip-package structure can be efficiently simulated by decomposing the computational domain into subdomains with independent meshing strategy. Numerical results demonstrate the capability, accuracy and efficiency of the proposed methods.