Supported Ni and Rh catalysts were developed for the reforming of two greenhouse gases, methane and carbon dioxide to syngas (a mixture of hydrogen and carbon monoxide). This is an endothermic, equilibrium limited reaction. To overcome the thermodynamic limitations, a commercially available porous membrane (Vycor glass) was used in a combined reactor-separator configuration. This was to selectively remove one or more of the products from the reaction chamber, and consequently shift the equilibrium to the right. However, the separation mechanism in this membrane involved Knudsen diffusion, which provided only partial separations. Consequently, there was some transport of reactants across the membrane and this led to only marginal improvements in performance. To overcome this limitation, a new membrane was developed by modifying the Vycor substrate by the chemical vapor deposition of a silica precursor. This new membrane, termed Nanosil, provided high selectivity to hydrogen at permeabilities comparable to the support material. Application of this membrane in the combined reactor-separator unit provided higher conversions than that obtained using the Vycor membrane. / Ph. D.

Selective dissolution also known as dealloying is a corrosion process in which one component of a binary alloy system is selectively removed through an electrochemically controlled process which leads to the formation of a porous metal "sponge" with a porosity that is completely interconnected and random in direction. Nanoporous metals are desirable since they have larger surface areas than an equal volume of non-porous material. Because of their enormous surface area per volume, these highly porous metal electrodes are superior materials for high surface area applications such as in biomedical devices, microfilters and catalysts. Understanding the kinetic processes governing the development of porosity during dealloying and having ability to change the electrochemical conditions will allow us to better control over the average ligament size and distribution in porosity. The basic kinetic processes involved in the formation of these structures are related to such issues as environmental effects and electrochemical conditions on diffusion, microscopic coarsening phenomenon at room temperature and elevated temperatures, alloy passivation, and Gibbs-Thomson effects. The average pore size and distribution was found to depend on the electrolyte composition, dealloying rate, applied potential and time. The porosity was found to significantly coarsen at room temperature during the dealloying process and this coarsening was highly dependent on the applied potential. It is showed that the commonly accepted measurement of the critical potential for alloy dissolution calculated based on extrapolation of anodic polarization data results in an overestimation of this quantity. A series of constant applied potential experiments prove to be a more accurate method for critical potential determination. / Ph. D.

The goal of this research is developing a computational framework to study mechanical fatigue and fracture at different length scales for a broad range of materials. The developed multiscale framework is utilized to study the details of fracture and fatigue for the rolling contact in rails, additively manufactured alloys, and bio-inspired hierarchical materials. Rolling contact fatigue (RCF) is a major source of failure and a dominant cause of maintenance and replacements in many railways around the world. The highly-localized stress in a relatively small contact area at the wheel-rail interface promotes micro-crack initiation and propagation near the surface of the rail. 2D and 3D microstructural-based computational frameworks are developed for studying the rolling contact fatigue in rail materials. The method can predict RCF life and simulate crack initiation sites under various conditions. The results obtained from studying RCF behavior in different conditions will help better maintenance of the railways and increase the safety of trains. The developed framework is employed to study the fracture and fatigue behavior in 3D printed metallic alloys fabricated by selective laser melting (SLM) method. SLM method as a part of metal additive manufacturing (AM) technologies is revolutionizing the manufacturing sector and is being utilized across a diverse array of industries, including biomedical, automotive, aerospace, energy, consumer goods, and many others. Since experiments on 3D printed alloys are considerably time-consuming and expensive, computational analysis is a proper alternative to reduce cost and time. In this research, a computational framework is developed to study fracture and fatigue in different scales in 3D printed alloys fabricated by the SLM method. Our method for studying the fatigue at the microstructural level of 3D printed alloys is pioneering with no similar work being available in the literature. Our studies can be used as a first step toward establishing comprehensive numerical frameworks to investigate fracture and fatigue behavior of 3D metallic devices with complex geometries, fabricated by 3D printing. Composite materials are fabricated by combining the attractive mechanical properties of materials into one system. A combination of materials with different mechanical properties, size, geometry, and order of different phases can lead to fabricating a new material with a wide range of properties. A fundamental problem in engineering is how to find the design that exhibits the best combination of these properties. Biological composites like bone, nacre, and teeth attracted much attention among the researchers. These materials are constructed from simple building blocks and show an uncommon combination of high strength and toughness. By inspiring from simple building blocks in bio-inspired materials, we have simulated fracture behavior of a pre-designed composite material consisting of soft and stiff building blocks. The results show a better performance of bio-inspired composites compared to their building blocks. Furthermore, an optimization methodology is implemented into the designing the bio-inspired composites for the first time, which enables us to perform the bio-inspired material design with the target of finding the most efficient geometries that can resist defects in their structure. This study can be used as an effective reference for creating damage-tolerant structures with improved mechanical behavior. / Doctor of Philosophy / The goal of this research is developing a multiscale framework to study the details of fracture and fatigue for the rolling contact in rails, additively manufactured alloys, and bio-inspired hierarchical materials. Rolling contact fatigue (RCF) is a major source of failure and a dominant cause of maintenance and replacements in many railways around the world. Different computational models are developed for studying rolling contact fatigue in rail materials. The method can predict RCF life and simulate crack initiation sites under various conditions and the results will help better maintenance of the railways and increase the safety of trains. The developed model is employed to study the fracture and fatigue behavior in 3D printed metals created by the selective laser melting (SLM) method. SLM method as a part of metal additive manufacturing (AM) technologies is revolutionizing industries including biomedical, automotive, aerospace, energy, and many others. Since experiments on 3D printed metals are considerably time-consuming and expensive, computational analysis is a proper alternative to reduce cost and time. Our method for studying the fatigue at the microstructural level of 3D printed alloys can help to create more fatigue and fracture resistant materials. In the last section, we have studied fracture behavior in bio-inspired materials. A fundamental problem in engineering is how to find the design that exhibits the best combination of mechanical properties. Biological materials like bone, nacre, and teeth are constructed from simple building blocks and show a surprising combination of high strength and toughness. By inspiring from these materials, we have simulated fracture behavior of a pre-designed composite material consisting of soft and stiff building blocks. The results show a better performance of bio-inspired structure compared to its building blocks. Furthermore, an optimization method is implemented into the designing the bio-inspired structures for the first time, which enables us to perform the bio-inspired material design with the target of finding the most efficient geometries that can resist defects in their structure.

Space Time Trellis Coding (STTC) is a unique technique that combines the use of multiple transmit antennas with channel coding. This scheme provides capacity benefits in fading channels, and helps in improving the data rate and reliability of wireless communication. STTC schemes have been primarily designed assuming perfect channel estimates to be available at the receiver. However, in practical wireless systems, this is never the case. The noisy wireless channel precludes an exact characterization of channel coefficients. Even near-perfect channel estimates can necessitate huge overhead in terms of processing or spectral efficiency. This practical concern motivates the study of the impact of channel estimation errors on the design and performance of STTC. The design criteria for STTC are validated in the absence of perfect channel estimates at the receiver. Analytical results are presented that model the performance of STTC systems in the presence of channel estimation errors. Training based channel estimation schemes are the most popular choice for STTC systems. The amount of training however, increases with the number of transmit antennas used, the number of multi-path components in the channel and a decrease in the channel coherence time. This dependence is shown to decrease the performance gain obtained when increasing the number of transmit antennas in STTC systems, especially in channels with a large Doppler spread (low channel coherence time). In frequency selective channels, the training overhead associated with increasing the number of antennas can be so large that no benefit is shown to be obtained by using STTC. The amount of performance degradation due to channel estimation errors is shown to be influenced by system parameters such as the specific STTC code employed and the number of transmit and receive antennas in the system in addition to the magnitude of the estimation error. Hence inappropriate choice of system parameters is shown to significantly alter the performance pattern of STTC. The viability of STTC in practical wireless systems is thus addressed and it is shown that that channel estimation could offset benefits derived from this scheme. / Master of Science

A literature survey was performed to evaluate the state-of-the-art membrane systems for CO₂/CH₄ separation which is critical in the natural gas industry. The systems that were reviewed included zeolite, carbon, polymeric, mixed matrix, amorphous silica, and supported ionic liquid membranes. Supported ionic liquid CO₂/CH₄ selective membranes were synthesized in our laboratory by applying room temperature ionic liquids (RTILs) to porous inorganic α-alumina supports. The supported ionic liquid membranes (SILMs) displayed CO₂ permeance of 1x10⁻⁹ to 3x10⁻⁸ mol m⁻² s⁻¹ Pa⁻¹ and CO₂/CH₄ selectivity of up to 50 which is comparable with the current polymeric separation systems. It is concluded that, although the RTIL membranes showed good CO₂/CH₄ selectivity, the CO₂ permeance was too low for industrial applications. A new type of SILM was prepared by dissolving 1-aminopyridinium iodide which contained amine functionality in other ionic liquids which improved the CO₂ permeance and selectivity of these membranes. The H₂ gas separation is an important process because it has many industrial applications in petroleum processing and chemical synthesis. Amorphous silica membranes for H₂ separation were prepared on hollow fiber (HF) inorganic supports using chemical vapor deposition (CVD) of tetraethyl orthosilicate (TEOS). These membranes exhibited good H₂ permeance on the order of 10⁻⁷ mol m⁻² s⁻¹ Pa⁻¹ together with H₂/CO₂ selectivity of over 100. The separation was achieved using a new hybrid intermediate layer that was developed by depositing a mesoporous silica layer on top of γ-alumina. / Master of Science

The use of boron in the synthesis and development of asymmetric methodologies and various biological and medicinal compounds has increased significantly over the last decade. This thesis reports the development of a novel diastereoselective reaction for the α-alkylation of chiral β-borylated esters. We propose that standard deprotonation of chiral β-borylated esters with lithium diisopropylamide (LDA) leads to the formation of a boron"ate" intermediate that upon treatment with an alkylation reagent collapses to provide chiral α, β-substituted boronic esters with a high degree of diastereoselectivity. This reaction is powerful in that a wide range of chiral β-borylated ester substrates can be employed that possess varying degrees of substitution and steric bulk. Results show that the reaction is syn-selective and provides yields of up to 60%, with diastereomeric ratios as high as (9.7:1). Additionally, alkylation products from bulkier tert-butyl esters provide higher DR values compared to those of methyl esters that possess the same β-functional groups. Several techniques were utilized to elucidate the mechanism of this reaction including variations of reaction temperature and equivalents of base, and also real-time analysis of the reaction by ¹¹B NMR experiments. / Master of Science

Master of Science / This thesis concerns a predominantly white university, Western Carolina University, with historical links to the Cherokee people as well as contemporary links to the Eastern Band of Cherokee Indians. I chose to analyze WCU's student newspaper within a 50-year period before and during the beginning emergence of the American Indian Movement to determine in what ways, if any, do students engage with settler-colonial narratives to selectively remember events and express their student body collective identity. Within the analysis process, I determined the narratives of Ancient Peoples, Exoticism and Romanticism, and Civilized and Uncivilized Peoples most significantly impacted student identity formation. My results demonstrated how students' newspaper articles intertwined campus identity narratives with a perpetuation of settler-colonial beliefs.

Mitt i Europas växande beroende av extern antimonproduktion har Europeiska kommissionen konsekvent betonat ett växande gap mellan utbud och efterfrågan sedan 2014. Som svar på denna utmaning riktade sig denna studie mot sekundära antimonkällor från underutnyttjade rester av guld, koppar och blymalm, som för närvarande utgör ett miljöproblem. Genom noggranna experiment, fastställde vi att optimal antimonurlakning uppnås vid 120 °C inom 2 timmar med en 250 g/L Na2S och 60 g/L NaOH-blandning. Detta tillvägagångssätt accentuerar selektiv extraktion, förbättrar antimonåtervinningen och minimerar kopparinterferens. En innovativ aspekt av denna studie var användandet utav mikrovågsassisterad urlakning, vilket visar fördelar i både utvinningseffektivitet och bevarande av mineralstrukturer jämfört med traditionella metoder. Våra resultat stöds av flera analytiska verktyg och ger en första förståelse, även om detaljerna kring mikrovågsassisterad urlakning och dess skalbarhet motiverar ytterligare utforskning. Denna studie introducerar en metod för urlakning av antimon från koppargruvavfall och föreslår ett motsvarande återvinningssystem som kan vara ekonomiskt lönsamt. Sådana ansträngningar kan ge ett blygsamt bidrag till att lindra den nuvarande situationen. / Amid Europe's growing reliance on external antimony production, the European Commission has consistently emphasized an expanding supply-demand gap since 2014. Responding to this challenge, our research targeted secondary antimony sources from underutilized residues of gold, copper, and lead ore processing, which currently pose environmental concerns. Through meticulous experimentation, we determined that optimal antimony leaching is achieved at 120°C within 2 hours, using a 250 g/L Na2S and 60 g/L NaOH mixture. This approach accentuates selective extraction, enhancing antimony recovery and minimizing copper interference. An innovative facet of this study was the adoption of microwave-assisted leaching, demonstrating advantages in both extraction efficiency and mineral structure conservation over traditional methods. Our results, backed by multiple analytical tools, provide an initial understanding, though areas like the specifics of microwave-assisted leaching and its scalability warrant further exploration. This study introduces a method for leaching antimony from copper mining waste and suggests a corresponding recycling system that may be economically viable. Such endeavors might offer a modest contribution to alleviating the present situation.

While mutation testing is an effective fault-based testing technique, it has its challenges such as being computationally expensive and requiring a large amount of effort to review surviving mutants. These problems have resulted in mutation testing mostly being restricted to academic research and not as widely adopted in the industry. In the academic context, the focus has been on maximizing the mutation score and while a high mutation score might increase the quality of the software, it is not feasible to kill all the mutants. Moreover, all mutants are not as equally important, and some can not or should not be killed. Instead, the focus should be shifted to prioritizing the productive mutants, those that further improve the test suite or the source code. This thesis investigated if some mutation operators are more suitable for certain types of software by using selective mutation. The mutation operators were evaluated based on their ability to generate productive mutants. Moreover, the mutation operators were analyzed to identify how they could be improved to reduce the number of unproductive mutants generated by them. Dextool Mutate was used to conduct mutation testing on four open-source C/C++ software that were all different types of software. It was concluded that some mutation operators are more suitable for certain types of software resulting in the proposal of a set of mutation operators for each software type. Moreover, various improvements for the mutation operators were identified that reduce the number of unproductive mutants generated. Lastly, it may be helpful to customize the implementation of mutation operators for each type of software and some software types may require additional specialized mutation operators.

With increasing legislative demands to remove nitrogen oxides (NOx) from automotive diesel exhaust, new catalyst systems are investigated and intensely studied in industry as well in academia. The most prevailing catalytic method of choice is the selective catalytic reduction (SCR) where non-toxic urea is used as a reductant for practical reasons. Usually urea is stored in a separate tank and once injected into the exhaust system it hydrolyses into the more aggressive reductant NH3 and CO2. 4 NH3 + 4 NO + O2 -> 4 N2 + 6 H2O (NH3-SCR reaction) In regions where vanadium is not banned cost effective V2O5/WO3/TiO2 NH3-SCR catalyst systems can be used. Vanadium based are well understood, but they do however not provide stability above ca. 550 °C for longer periods of time. In exhaust treatment systems where the temperature is either high or where high temperature excursions are experienced from e.g. regeneration of particulate filters, zeolite based catalysts are therefore today the most promising candidates as high-temperature stable and non-toxic catalysts for the NH3-SCR reaction. Among the most promising candidates are the Cu- and Fe-based zeolites. Usually Fe based zeolites show good performance in the temperature range 250-500 °C and reasonable stability, whereas Cu-based zeolites show good low-temperature activity in the 180-400 °C range. The presence of copper does however also lead to a lower stability of the catalyst material. Since the low-temperature activity is of paramount importance it is necessary to improve this behavior. Therefore the purpose of this project is to investigate: - The deactivation mechanism of copper based zeolites - The influence of the zeolite framework on stability and activity These investigations should mostly be carried out on model systems such as Cu-ZSM-5 and Cu-IM-5. Recently it was found that zeolite materials with the CHA-type structure show increased hydrothermal stability, most likely originating from the small 8-MR window openings in the structure. Part of the project should therefore also include investigations on this type and other similar structures, and therefore entail: - Synthesis, in-depth characterization and catalytic testing of Cu-SSZ-13 and Cu-SAPO-34 (both structures having the CHA-type framework) - Theoretical DFT calculations on relevant parameters found by the in-depth investigation of the afore-mentioned materials - Synthesis and testing of similar materials with 8-MR windows to elucidate the influence of the zeolite sub-structure i.e. if different ring sizes in the structure influences the catalytic performance Relevant characterization techniques include, besides conventional methods, in situ methods such as: high resolution (transmission) electron microscopy, infrared (and raman) spectroscopy together with X-ray absorption spectroscopy. These are all techniques that will complement each other to produce invaluable results. Zeolites are today applied in many and diverse applications both within automotive and environmental catalysis, but also within the petrochemical and renewable chemistry. The findings of this project are therefore also believed to contribute to a more comprehensive understanding of this class of materials, relevant to many areas of heterogeneous catalysis, and therefore have the potential, to create research and business with very high impact. / Vennestrom, PNR. (2014). Selective catalytic reduction of nitrogen oxides with ammonia over microporous zeolite catalysts [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/43217