Thesis (Ph.D.) -- Mississippi State University. Department of Mechanical Engineering. / Title from title screen. Includes bibliographical references.

Thesis (M.S.) -- Mississippi State University. Department of Physics and Astronomy. / Title from title screen. Includes bibliographical references.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1969. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliography.

Thesis (Ph.D.) -- McMaster University, 2001. / Includes bibliographical references (leaves 136-143). Also available via World Wide Web.

Thesis (Ph. D.)--Ohio State University, 2005. / Title from first page of PDF file. Includes bibliographical references (p. 121-127).

Thesis (Ph. D.)--University of Missouri-Columbia, 2000. / Typescript. Vita. Includes bibliographical references (leaves 182-188). Also available on the Internet.

Many aspects associated with conversion of lignocellulose to biofuels and other valuable products have been investigated to develop the most effective processes for biorefineries. The goal of this research was to improve the efficiency and effectiveness of the lignocellulose conversion process by achieving a more basic understanding of pretreatment and enzymatic hydrolysis at high solids, including kinetic modeling and separation and recovery of glucose. Effects of NaOH pretreatment conditions on saccharide yields from enzymatic hydrolysis were characterized in low- and high-solids systems. Factors associated with pretreatment and hydrolysis were investigated, including duration of pretreatment at different temperatures and NaOH loadings, as well as different solids and enzyme loadings. Under relatively mild pretreatment conditions, corn stover composition was essentially equivalent for all time and temperature combinations; however, components were likely affected by pretreatment, as differences in subsequent cellulose conversions were observed. Flushing the hydrolyzate and reusing the substrate was also studied as a method for inhibitor mitigation while increasing overall glucose yields. Flushing the PCS throughout the hydrolysis reaction eliminated the need to wash the pretreated biomass prior to enzymatic hydrolysis when supplementing with low doses of enzyme, thus reducing the amount of process water required. The robustness of an established kinetic model was examined for heterogeneous hydrolysis reactions in high-solids systems. Michaelis-Menten kinetics is the traditional approach to modeling enzymatic hydrolysis; however, high-solids reactions violate the main underlying assumption of the equation: that the reaction is homogeneous in nature. The ability to accurately predict product yields from enzymatic hydrolysis in high-solids systems will aid in optimizing the conversion process. Molecularly-imprinted materials were studied for use in both bulk adsorption and in column chromatography separations. Glucose-imprinted materials selectively adsorbed glucose compared xylose by nearly 4:1. Non-imprinted materials were neither selective in the type of sugar adsorbed, nor were they capable of adsorbing sugar at as high a capacity as the glucose-imprinted materials. Liquid chromatography with imprinted materials was not a suitable means for separating glucose from solution under the conditions investigated; however, many factors impact the effectiveness of such a separation process and warrant further investigation.

Since the Dust Bowl, conservation agriculture has become a common practice globally. Because of the rising interest in the use of corn biomass as a feedstock for biofuel production, the effects of corn stover removal on soil erosion were explored. It was hypothesized that selective harvesting strategies would impact soil erosion differently across a variety of slopes. Soil erosion boxes were constructed, and a rainfall simulator with an intensity of 30 mm hr-1 for 46 min was used to create runoff from slopes of 1, 5, and 10% and three cover factor treatments (no removal and two simulated corn stover removal strategies). Due to research time constraints, simulated corn roots were constructed to emulate actual corn roots in all experiments. The corn stover harvest strategies change the distribution of cobs, husks, leaves, and stalks in field; these changes were represented as the cover factor treatments. Changing the type of plant material on the soil surface impacted the predicted soil erosion from the Revised Universal Soil Loss Equation (RUSLE). Based on the results from this study, the effect of corn stover cover percentages had a significant impact on the predicted and observed soil loss.

Lignocellulosic biomass pretreatment is a fundamental step in the production of renewable fuels and chemicals. It is responsible for the disruption and removal of lignin and hemicellulose from the lignocellulosic matrix, improving the enzymatic hydrolysis of cellulose. Alkaline pretreatment has been shown to be successful on agricultural residues and dedicated energy crops. The objective of this study was to evaluate the pretreatment of switchgrass, wheat straw, corn stover, and miscanthus using calcium hydroxide, potassium hydroxide, and sodium hydroxide at the same hydroxyl concentration, 60% moisture content, and two temperatures for seven days. Enzymatic hydrolysis was also performed and the glucose produced measured. The composition of cellulose, hemicellulose, and lignin before and after pretreatment were quantified according to the standard procedures developed by the NREL for biomass. The hydrolysis was performed at 50°C and 150 rpm. The enzyme loading was 60 FPU/g cellulose. Overall, calcium hydroxide pretreatment resulted in the lowest delignification and structural carbohydrates after pretreatment, as well as lowest glucose yield; In addition to having a higher cost and carbon dioxide emission then sodium and potassium hydroxides. Sodium hydroxide and potassium hydroxide had similar performance in terms of composition changes due to pretreatment and glucose yield after enzymatic hydrolysis.

Cette thèse porte sur la compréhension des mécanismes de forming dans les mémoires à pont conducteur (CBRAM) à base d’oxydes métalliques. Pour cela nous avons admis que l’empilement mémoire est une cellule électrochimique à l’échelle du nanomètre et considéré que les principaux mécanismes de forming sont basés sur des effets électrochimiques. Nous avons débuté nos études à partir d’un couple de référence CuxTey/Oxyde, analysé par HAXPES et ToF-SIMS avant et après l’electro-forming, dans le but d’observer les diffusions et les modifications de l’environnement chimique durant le forming. Ensuite, la couche fournissant les ions, basée sur un alliage CuxTey, ainsi que le diélectrique (Ta2O5, GdOx, or Al2O3) ont été modifiés étape par étape. Les résultats de leurs analyses ont été comparés avec ceux de l’empilement de référence dans le but de comprendre le rôle de chaque couche et des éléments présents dans l’empilement.Nous avons vu que les propriétés du diélectrique, telles que la force des liaisons métal-oxygène, l’hygroscopicité, ou l’éventuelle présence de défauts comme les lacunes d’oxygène, peuvent favoriser un comportement mémoire plutôt OXRAM, CBRAM ou hybride OXRAM/CBRAM. De plus, quand le cuivre diffuse durant le forming, une contre diffusion d’oxygène apparaît également dans le diélectrique. Ensuite, la présence de tellure dans la couche fournissant les ions est nécessaire pour permettre l’effacement de la mémoire, car il permet la re-dissolution du filament de cuivre dans la couche fournissant les ions. Nous avons également vu que le germanium amorphise l’alliage de CuxTeyGez et donc permet son intégration tout en le protégeant de l’oxydation. De plus, il est possible de remplacer le germanium par du zirconium, réduisant ainsi le diélectrique, ce qui facilite le forming. / This thesis focuses on the understanding of forming mechanisms in oxide-based conductive bridge memories (CBRAM), based on metallic oxides. For this purpose, we compared the memory stack to an electrochemical cell at nanometer scale and consider that the main mechanisms occurring in the memory rely on electrochemical effects. We started our studies from a reference couple CuxTey/Oxide, analyzed by HAXPES and ToF-SIMS before and after electro-forming, in order to observe the diffusions and the modifications of the chemical environment occurring during forming. Then, the ion source layer based on CuxTey alloy and the dielectric (Ta2O5, GdOx or Al2O3) were sequentially modified and results of their analyses were compared to the reference stack, in order to understand the role of each layer and chemical elements present in the memory stack.We evidenced that the properties of the dielectric, such as the strength of its oxygen-metal bonds, its hygroscopicity or the eventual presence of defects such as oxygen vacancies, can promote a given memory behavior from OXRAM to CBRAM or hybrid OXRAM/CBRAM behavior. Moreover, when copper diffuses during the forming, an oxygen counter diffusion also takes place in the dielectric. Also, the presence of tellurium in the ion source layer is required to reset the memory as it enables the dissolution of the copper filament in the ion source layer. We also show that germanium amorphizes the CuxTeyGez alloy, thus enables its integration, and protects it from oxidation. Moreover, it is possible to substitute germanium by zirconium resulting in the dielectric reduction, which eases the forming.