Esta Tesis presenta los resultados de la investigación desarrollada en el marco del proyecto Temperature Buffer Test (TBT). El objetivo general de este proyecto es investigar el desempeño de la bentonita usada en barreras de ingeniería bajo la acción de las altas temperaturas que se esperan alrededor de los contenedores con residuos vitrificados. Dentro del proyecto, se ha implementado un ensayo de campo a escala real que simula el almacenamiento de residuos radioactivos de alta actividad. Adicionalmente, se realizaron experimentos en laboratorio para evaluar la respuesta de la bentonita usada en el proyecto bajo diferentes acciones externas.Las formulaciones que se usan para analizar el comportamiento de barreras de ingeniería de arcillas se escriben en términos de las variables de estado usando relaciones constitutivas. Entre esas leyes la curva de retención define la relación constitutiva entre la cantidad de agua en el suelo y su nivel de energía. Tradicionalmente, la influencia de variables externas como la temperatura y la fábrica del suelo sobre la capacidad de retención de agua del suelo se analiza utilizando conceptos derivados del modelo capilar. Sin embargo, estos análisis sistemáticamente fallaron para explicar las observaciones experimentales. En esta Tesis, se han evaluado los datos experimentales obtenidos en muestras de bentonita ensayadas a diferentes temperaturas y densidades usando una aproximación derivada a partir de conceptos de termodinámica de adsorción. Esta aproximación también define una herramienta para introducir en una manera simple el efecto de temperatura y densidad de la muestra en las simulaciones numéricas.En general se supone que la interacción entre la esmectita, que es el principal mineral de la bentonita, y el agua cambia las propiedades del agua retenida en el suelo. En particular, experimentos a nivel mineralógico así como los datos obtenidos en muestras compactadas de arcilla expansiva sugieren valores de la densidad del agua mayores que 1.0 Mg/m3 (es decir, la densidad del agua libre). Desde un punto de vista práctico, este efecto se traduce en valores calculados del grado de saturación mayor que uno para valores bajos de succión. Este aspecto es importante cuando se realizan análisis numéricos, debido a que las ecuaciones de balance se basan en el grado de saturación como la principal variable para indicar el contenido de agua en el medio poroso. En esta Tesis se ha desarrollado una metodología que define la densidad del agua como una función de la energía del agua en los poros del suelo. Este método fue usado para analizar datos publicados de la capacidad de retención de agua de muestras compactadas de diferentes bentonitas.El análisis de la respuesta mecánica de arcillas expansivas bajo acciones externas como aquellas típicamente encontradas en barreras de ingeniería es una tarea compleja. Los modelos constitutivos usados en los cálculos numéricos deben ser capaces de simular los principales aspectos de la respuesta material. En esta Tesis se han adoptado modelos previamente desarrollados para simular el comportamiento de muestras compactadas de arcilla expansiva. Los parámetros de estos modelos se calibraron usando datos experimentales que corresponden a muestras compactadas de bentonita MX-80, el material adoptado como referencia en el proyecto TBT.Los conceptos desarrollados en esta Tesis se incorporaron en un código numérico capaz de resolver problemas acoplados en medios porosos deformables. Este código fue aplicado tanto para el análisis de un ensayo de maqueta como para la simulación del ensayo in situ, ambos desarrollados en el marco del proyecto TBT. Las simulaciones numéricas demostraron las capacidades del código para capturar la tendencia general de los datos experimentales. Además, el análisis de los resultados numéricos puso de manifiesto los diferentes fenómenos que tienen lugar en los procesos acoplados así como los mecanismos de interacción entre ellos. / This Thesis presents the results of the research carried out in the framework of the Temperature Buffer Test (TBT) project. The overall objective of this project is to investigate how well the bentonite used in engineered barriers can endure the high temperatures expected to be found around vitrified waste canisters. Within the project, a full-scale field test that simulates the deposition of high level radioactive waste has been implemented. Additionally, laboratory experiments were carried out to evaluate the response of the bentonite used in the project under different external actions.Coupled formulations used to analyse the behaviour of an engineered clay barrier are written in terms of the state variables by using constitutive relations. Among these laws the soil water retention curve (SWRC) defines the constitutive relationship between the amount of water in the soil and its energy status. Traditionally, the influence of external variables like temperature and soil fabric on the water retention capacity of soils has been analysed using concepts derived from the capillary model. However, theses analyses systematically failed to explain the experimental observations. In this Thesis, experimental data obtained on bentonite samples tested at different temperatures and densities were evaluated using an approach derived from concepts of thermodynamic of adsorption. This approach also gives a tool to introduce in a simple way the effect of temperature and sample porosity in numerical simulations.It is generally accepted that the interaction between smectite, which is the main mineral of bentonite, and water changes the properties of the water retained in the soil. In particular, values of the water density higher than 1.0 Mg/m3 (i.e. the density of the free water) have been suggested by experiments at mineralogical level as well as by data obtained on compacted samples of expansive clays. From a practical point of view this effect traduces in values of degree of saturation higher than one at lower values of suction. This is important when a numerical analysis is being performed, as balance equations are based on the degree of saturation as the main variable to indicate the water content within the porous medium. In this Thesis a methodology that defines the water density as a function of the energy of the water within the soil pores was developed. This method was applied to analyse published data about the water retention capacity for compacted samples of different bentonites.The analysis of the mechanical response of expansive clays under external actions as those typically found in engineered barriers is a complex task. Constitutive models used in numerical calculations have to be able to simulate the main aspects of the material response. Models previously developed to simulate the behaviour of compacted samples made up of expansive clay were adopted in this Thesis. Parameters in these models were calibrated using experimental data corresponding to compacted samples of MX-80 bentonite, the material adopted as reference in the TBT project.Concepts developed in the Thesis were included in a numerical code able to solve coupled problems in deformable porous media. This code was then applied to the analysis of a mock-up experiment and to the simulation of the in situ test carried out within the framework of the TBT project. Theses numerical simulations showed the capabilities of the code to capture the general tendency of the experimental data. Additionally, the analysis of numerical results enhanced the understanding of the different phenomena that take place in coupled processes as well as the interaction mechanisms between them.

This thesis focuses on designing Low-Density Parity-Check (LDPC) codes for forward-error-correction. The target application is real-time multimedia communications over packet networks. We investigate two code design issues, which are important in the target application scenarios, designing LDPC codes with low decoding latency, and constructing capacity-approaching LDPC codes with very low error probabilities. On designing LDPC codes with low decoding latency, we present a framework for optimizing the code parameters so that the decoding can be fulfilled after only a small number of iterative decoding iterations. The brute force approach for such optimization is numerical intractable, because it involves a difficult discrete optimization programming. In this thesis, we show an asymptotic approximation to the number of decoding iterations. Based on this asymptotic approximation, we propose an approximate optimization framework for finding near-optimal code parameters, so that the number of decoding iterations is minimized. The approximate optimization approach is numerically tractable. Numerical results confirm that the proposed optimization approach has excellent numerical properties, and codes with excellent performance in terms of number of decoding iterations can be obtained. Our results show that the numbers of decoding iterations of the codes by the proposed design approach can be as small as one-fifth of the numbers of decoding iterations of some previously well-known codes. The numerical results also show that the proposed asymptotic approximation is generally tight for even non-extremely limiting cases. On constructing capacity-approaching LDPC codes with very low error probabilities, we propose a new LDPC code construction scheme based on $2$-lifts. Based on stopping set distribution analysis, we propose design criteria for the resulting codes to have very low error floors. High error floors are the main problems of previously constructed capacity-approaching codes, which prevent them from achieving very low error probabilities. Numerical results confirm that codes with very low error floors can be obtained by the proposed code construction scheme and the design criteria. Compared with the codes by the previous standard construction schemes, which have error floors at the levels of $10^{-3}$ to $10^{-4}$, the codes by the proposed approach do not have observable error floors at the levels higher than $10^{-7}$. The error floors of the codes by the proposed approach are also significantly lower compared with the codes by the previous approaches to constructing codes with low error floors.

Introduction: The benefits of regular exercise on skeletal health have been well-documented in terms of stimulation of bone accrual and bone maintenance. Medium-impact sports activities such as running have been demonstrated to exert site-specific enhancement of bone mass in the lower appendicular skeleton. However, elite female runners engaged in high intensity training and sports activity may also be at risk of amenorrhea and low bone mineral density (BMD) resulting from inadequate caloric intake. Purpose: To investigate the effect of intensive exercise and maintenance of adequate caloric intake on BMD in a group of elite female runners. Methods: This study represents a secondary assessment of existing data that were obtained between 1994 and 2009. Using dual-energy X-ray absorptiometry, a group of elite runners (n=11) in this study was screened in the Laboratory for Elite Athlete Performance at Georgia State University. This was a longitudinal study in which three sequential measurements of BMD, as well as fat and lean tissue body composition of each athlete took place. The average interval between measurements was 1.1 years and 2.6 years respectively. Regional BMD measurements for head, arms, legs, trunk, ribs, pelvis, and spine were assessed, as well as the value for total body BMD. The study participants also received dietary counseling emphasizing daily caloric balance and adequate calcium intake. Results: The average age of the runners increased from 24.59 (±4.41) to 28.14 (±5.94) years over the study. This was accompanied by an increase in body mass (54.98±3.54 to 56.11±4.07 kg), while height remained constant. The average body mass index (BMI) of the subjects increased from 19.34 to 19.71 kg/m2, largely due to an increase in total per cent body fat (13.97±2.96% to 16.01±4.28%). Average regional and total BMD values increased over the study period and increases were between 2 and 4%. A majority of subjects (n=7) had a BMI>19 kg/m2, while a sub-group of runners (n=4) had a BMI˂19 kg/m2. Mean trunk, pelvis and spine BMD parameters for the two BMI groups were significantly different (p˂0.05), with reduced BMD values in the lower BMI sub-group. The average T-scores associated with arm BMD were considerably lower than T-scores associated with leg BMD values in the runners. The average T-scores for leg BMD values were almost two standard deviations higher than leg BMD values for a reference population at peak bone mass. Two subjects were osteopenic, resulting in an 18% prevalence rate of osteopenia in the group of runners. Conclusions: The majority of elite runners in this study exhibited a positive trend in BMD parameters. This was reflected as increased total as well as regional BMD values. Increased body mass in addition to the activity of running positively contributed to bone mass via a weight-bearing effect. Increased adipose tissue may also have been a source of endocrine hormones such as estrogen and leptin, which exert a positive effect on bone accrual.

This dissertation consists of two essays. The connecting theme for this body of work is social interaction. I define social interaction, for this dissertation, as non-market based face-to-face interaction between individuals where each is interested in a response. The first contribution investigates the relationship between social interaction and neighborhood population density. I use the exogenous variation in a set of geological instruments to predict the neighborhood population density. The results suggest that an increase in neighborhood population density increases some types of social interaction. The second contribution brings social interaction into a standard urban consumer theory model, the Alonso-Muth model.

This thesis studies two important carbon structures, graphene and carbon nanotubes, with the purpose of understanding how their three-dimensional electron density distribution affects the way fast ions interact with them. <br /><br /> A brief introduction to research in pure carbon structures is made. We then use different models to calculate the equilibrium electron density distribution in graphene and carbon nanotubes. <br /><br /> In the second part of the thesis we investigate fast ions moving parallel to a graphene sheet and experiencing forces due to the dynamic polarization of carbon valence electrons. Using the three-dimensional electron density distribution of graphene, we calculate the force directly opposing the ion's motion (stopping force), as well as the force which bends the ion's trajectory towards the sheet (image force). It is our purpose to compare these results with those based on a two-dimensional hydrodynamic model of graphene, which approximates the electron distribution of graphene by a charged fluid confined to the two-dimensional plane of the sheet. <br /><br /> The results obtained for interactions of ions with a single graphene sheet should be useful for a further analysis of ion channeling through carbon nanostructures.

This thesis focuses on designing Low-Density Parity-Check (LDPC) codes for forward-error-correction. The target application is real-time multimedia communications over packet networks. We investigate two code design issues, which are important in the target application scenarios, designing LDPC codes with low decoding latency, and constructing capacity-approaching LDPC codes with very low error probabilities. On designing LDPC codes with low decoding latency, we present a framework for optimizing the code parameters so that the decoding can be fulfilled after only a small number of iterative decoding iterations. The brute force approach for such optimization is numerical intractable, because it involves a difficult discrete optimization programming. In this thesis, we show an asymptotic approximation to the number of decoding iterations. Based on this asymptotic approximation, we propose an approximate optimization framework for finding near-optimal code parameters, so that the number of decoding iterations is minimized. The approximate optimization approach is numerically tractable. Numerical results confirm that the proposed optimization approach has excellent numerical properties, and codes with excellent performance in terms of number of decoding iterations can be obtained. Our results show that the numbers of decoding iterations of the codes by the proposed design approach can be as small as one-fifth of the numbers of decoding iterations of some previously well-known codes. The numerical results also show that the proposed asymptotic approximation is generally tight for even non-extremely limiting cases. On constructing capacity-approaching LDPC codes with very low error probabilities, we propose a new LDPC code construction scheme based on $2$-lifts. Based on stopping set distribution analysis, we propose design criteria for the resulting codes to have very low error floors. High error floors are the main problems of previously constructed capacity-approaching codes, which prevent them from achieving very low error probabilities. Numerical results confirm that codes with very low error floors can be obtained by the proposed code construction scheme and the design criteria. Compared with the codes by the previous standard construction schemes, which have error floors at the levels of $10^{-3}$ to $10^{-4}$, the codes by the proposed approach do not have observable error floors at the levels higher than $10^{-7}$. The error floors of the codes by the proposed approach are also significantly lower compared with the codes by the previous approaches to constructing codes with low error floors.

Density fluctuations in high temperature fusion plasmas have been a central challenge to the development of fusion power. They are the cause of excessive anomalous losses from the plasma and are still not fully understood. A microwave scattering experiment is performed on the Saskatchewan Torus-Modified (STOR-M) tokamak for the first time to study these density fluctuations with wave-numbers in the range <b><i>k</i></b> = 5 /cm to 10 /cm. The fluctuations are found to follow <i>k¦Ñ_s</i> scaling consistent with ion drift waves; signatures of the electron temperature gradient (ETG) mode connected with anomalous electron losses are not detected. The fluctuation level in the STOR-M is measured to be <i>n_tilda/n</i> ¡Ö 0.1 at a mean perpendicular wave-number of <b><i>k</b>_perp</b></i> ¡Ö 7 /cm and is reported for the first time. The fluctuation levels are inversely proportional to the energy confinement time suggesting that these fluctuations are driving anomalous particle and energy losses from the STOR-M. The system is now fully operational and this work paves the way for future experiments with this equipment.

<p>The pressure-density relationship and the pressure distribution inside the compression chamber of a newly designed New Holland BB960 large square baler were studied for the baling of alfalfa, whole green barley, barley straw, and wheat straw. An analytical model was developed for the pressure distribution inside the compression chamber of the large square baler in the x-, y-, and z-directions by assuming isotropic linear elastic properties for forage materials. In order to validate this model, a tri-axial sensor was designed and used to measure the forces inside the compression chamber when whole green barley, barley straw, and wheat straw were baled. The experimental results proved that the developed analytical model for each of the tested forage materials had a good correlation with the experimental data with a reasonable coefficient of determination (0.95) and standard error (20.0 kPa). Test data were also used to develop an empirical model for the pressure distribution inside the compression chamber of the baler for each of the tested forage materials using least square method in regression analysis. These empirical models were simple equations which were only functions of the distance from the full extension point of the plunger along the compression chamber length.</p><p>Analytical and empirical models were also developed for the pressure-density relationship of the baler for baling alfalfa and barley straw. Results showed that bale density initially decreased with distance from the plunger, and then remained almost constant up to the end of the compression chamber. The developed empirical model for both alfalfa and barley straw was a combination of a quadratic and an exponential equation. In order to validate the developed models, field tests were performed by baling alfalfa and barley straw of different moisture contents, flake sizes, and load settings. The forces on the plunger arms were recorded by a data acquisition system. The actual bale bulk density was calculated by measuring the bale dimensions and weight. Results showed that both load setting and flake size had a significant effect on the plunger force. The plunger force increased with increased load setting and flake size. Comparing analytical and empirical models for bale density as a function of the pressure on the plunger showed that the trend of variation of density with pressure in both models was similar, but the rate of change was different. The variation rate of density with pressure in the analytical model was higher than that of the empirical model. The analytical model underestimated the bale density at low plunger pressures but showed more accurate prediction at higher pressures, while the empirical model accurately predicted the bale density at both low and high pressures. Some crop properties such as coefficient of friction and modulus of elasticity were determined for the development of the pressure distribution model. Results showed that static coefficient of friction of alfalfa on a polished steel surface was a quadratic function of material moisture content, while the relationship between the coefficient of friction of barley straw on a polished steel surface and material moisture content was best expressed by a linear equation. Results of this study also proved that modulus of elasticity of alfalfa and barley straw was constant for the density range encountered in the large square baler.</p>

This study was undertaken to compare the effects of changing energy intake, either by restricting feed intake or by altering dietary energy concentration, on the growth performance of pigs. The relative abilities of the DE, ME and NE systems to predict pig growth performance were also evaluated. A total of 72 barrows, having initial body-weights of 30 ± 2 kg, were randomly assigned to one of nine dietary treatments. These treatments were organized in a 3 x 3 factorial arrangement consisting of three dietary energy concentrations (2.18, 2.29 and 2.40 Mcal NE/kg) and three levels of feed allowance (80, 90 and 100% of ad libitum). Actual feed allowances of 79, 91 and 100% of ad libitum were achieved. No interactive effects of feeding level and dietary energy concentration were observed (P > 0.10). Increases in feed allowance from 79 to 91 to 100% of ad libitum resulted in increases in daily intakes of feed (P < 0.0001) and energy (P < 0.0001). Improvements in the rate (P < 0.0001) and efficiency (P < 0.0001) of body-weight gain were also noted. Additionally, feeding level affected the amount of energy available for body-weight gain on a daily (P < 0.0001) but not on a total (P > 0.10) basis. The efficiency with which dietary energy was used for weight gain was unaffected by feeding level (P > 0.10). Increases in dietary energy concentration were accompanied by decreases in daily feed intakes (P = 0.0016); however, dietary energy concentration did not affect daily energy intakes (P > 0.10). Neither average daily gains nor feed conversion efficiencies were affected by changes in dietary energy concentration (P > 0.10). Additionally, there were no differences among energy concentration treatments in terms of the amount of dietary energy available for body-weight gain (P > 0.10) or the efficiency with which it was used (P > 0.10). No differences were observed between the DE, ME and NE systems in terms of their abilities to predict the growth performance of pigs. The present study demonstrates that the energy intake of pigs can be effectively manipulated via adjustments in feeding level and that changes in dietary energy density, over the range studied here, are unable to affect changes in energy intake. This finding indicates that extreme caution should be used when extrapolating data obtained from studies in which feed allowance was manipulated to scenarios (e.g. commercial practice) in which energy density is to be altered, and vice versa.

<p>Breast cancer is currently the most common non-skin cancer and the second leading cause of cancer-related death in women here in the United States. X-ray mammography is currently the standard clinical imaging modality for breast cancer screening and diagnosis due to its high sensitivity and resolution at a low patient dose. With the advancement of breast imaging from analog to digital, quantitative measurements rather than qualitative assessments can be made from these images. One such measurement, mammographic breast density (i.e. the percentage of the entire breast volume that is taken up by dense glandular tissue), has been shown to be a biomarker well correlated with cancer risk. However, a digital mammogram still suffers from its projective nature. The resulting overlap of normal breast tissue can obscure lesions, limit quantitative measurement accuracy, and present false alarms leading to unnecessary recall studies. To address this key limitation, several 3D imaging techniques have been developed such as breast magnetic resonance imaging (MRI), dedicated breast computed tomography (CT), and digital breast tomosynthesis (tomo). Perhaps the most recently developed modality is tomo, which is a limited-angle cone-beam CT of the breast compressed in the same geometry as mammography. Because tomo retains all the aforementioned advantages of mammography but adds depth information and can be built based on an existing digital mammography device, measuring breast density and extracting other quantitative features from tomo images was a major focus of this study.</p><p>Before attempting to measure breast density and other features from reconstructed tomo image volumes, the quantitative potential of this imaging modality was assessed. First, we explored a slice-by-slice technique that measures tissue density using only the information from a single slice from the reconstructed tomosynthesis volume with geometrically simple tissue-equivalent phantoms. Once this task has been satisfactorily performed, we studied a probabilistic approach toward quantitation of the entire 3D volume. Some work has been done previously in the realm of 2D hidden Markov random fields (HMRFs) to categorize mammograms according to their Wolf pattern, detect mammographic lesions, and segment satellite and mixed media (text/photograph) images. For this project, a 3D hidden Markov model (HMM) method was developed and applied to tomo images under the simplified assumption that the possible tissue type of each tomo voxel is either adipose (fatty) or glandular (dense). Because adipose and glandular tissue is easily distinguished in MR images, patient breast MRIs were used to train, validate, and finally to assess the accuracy of our HMM segmentation algorithm when applied to tomo images by comparing the volumetric breast density to the MRI breast density for the same patient. Because they are so often studied conjunctively, several image texture features were calculated and compared between MRI and tomo as well.</p><p>Another aim of our study was to investigate whether changes in macroscopic 3D imaging features (texture and density) can accurately predict the chemoprevention response that was measured with Random Periareolar Fine Needle Aspiration (RPFNA) cytology for a uniquely young high-risk cohort of women. This aim to investigate the potential of combining multi-modality macroscopic 3D imaging information with a cytological measure of risk and then investigating how response to tamoxifen and other chemoprevention treatment affects each of these risk biomarkers in young, high-risk women is completely novel in the fields of medical physics and biomedical engineering.</p> / Dissertation