This thesis introduces lamina emergent mechanisms (LEMs) and presents components that can be used as building blocks to create LEMs capable of more complex motion. As the name suggests, lamina emergent mechanisms are fabricated out of planar materials (the lamina) but their motion is out of that plane (emergent). Lamina emergent mechanisms can provide benefits that include reduced manufacturing costs and minimal volume when in the planar state. The compact initial state of LEMs is beneficial in reducing shipping costs, especially in volume critical applications. LEMs also exhibit the potential benefits of compliant mechanisms, namely increased precision, reduced weight, reduced wear, and part count reduction. The LEM components presented in this thesis include flexible segments, fundamental mechanisms, and a new complaint joint, the lamina emergent torsional (LET) Joint. The flexible segments are developed through changes in geometry, boundary/loading conditions, and material. The fundamental mechanisms presented have motion similar to planar change-point four-bar and six-bar mechanisms, and spherical change-point mechanisms. The LET Joint is presented as a compliant joint suited for applications where large angular rotation is desired, but high off-axis stiffness is not as critical. The joint is introduced and the equations necessary for determining the force-deflection characteristics and stress are presented. Since the LET Joint can be fabricated from a single planar layer, it is well suited for macro and micro applications. Illustrative examples of the LET Joint are provided with devices fabricated from materials as diverse as steel, polypropylene, and polycrystalline silicon.

In this research a variable-stiffness compliant mechanism was developed to generate variable force-displacement profiles at the mechanisms coupler point. The mechanism is based on a compliant Roberts straight-line mechanism, and the stiffness is varied by changing the effective length of the compliant links with an actuated slider. The variable-stiffness mechanism was used in a one-degree-of-freedom haptic interface to demonstrate the effectiveness of varying the stiffness of a compliant mechanism. Unlike traditional haptic interfaces, in which the force is controlled using motors and rigid links, the haptic interface developed in this work displays haptic stiffness via the variable-stiffness compliant mechanism. The force-deflection behavior of the mechanismwas analyzed using the Pseudo-Rigid Body Model (PRBM), and two key parameters, KQ and g,were optimized using finite element analysis (FEA) to match the model with the behavior of the device. One of the key features of the mechanism is that the inherent return-to-zero behavior of the compliant mechanism was used to provide the stiffness feedback felt by the user. A prototype haptic interface was developed capable of simulating the force-displacement profile of Lachmans Test performed on an injured ACL knee. The compliant haptic interface was capable of displaying stiffnesses between 4200 N/m and 7200 N/m.

Call number: LD2668 .T4 1965 C53 / Master of Science

Anaerobic ammonium oxidizing (Anammox) bacteria are known to utilize ammonium and nitrite as electron donor and acceptor, respectively, to produce nitrogen gas as their main final product with by-product formation of nitrate. Anammox bacteria provide the advantages of significant saving in aeration, no requirement for external electron donor, reduction of greenhouse gas emission, lowered sludge production, and higher specific nitrogen-removing activity compared to the conventional nitrification-denitrification process used in nutritent-N removal. Therefore, the anammox process has recently been widely studied and applied as a state-of-the-art biotechnology to remove nutrient nitrogen from ammonium-rich wastewater. However, the inhibitory impact of nitrite (one of the two main substrates) on the anammox process has been reported in both lab- and full-scale anammox systems, which limits the application of anammox process. Based on the current knowledge, a wide range of nitrite concentrations causing anammmox inhibition was reported to be correlated to the pH and energy status of anammox bacteria, and the understanding of the mechanisms of nitrite inhibition to anammox bacteria is still not clear. Therefore, the purpose of this work is to investigate the mechanism of nitrite inhibition and develop a strategy for recovering nitrite inhibited anammox processes. The effects of pre-exposing anammox bacteria to nitrite alone on their subsequent activity and metabolism after ammonium has been added was evaluated in batch bioassays. The results showed that pre-exposure of anammox bacteria to nitrite without ammonium caused dramatic inhibition with observed 50% inhibition concentration (IC₅₀) of 52 mg NO₂⁻-N L⁻¹, compared to an IC₅₀ of 384 mg NO₂⁻-N L⁻¹ obtained in the control group with ammonium and nitrite added simultaneously. The accumulated nitric oxide (NO) found in the group with anammox bacteria pre-inhibited by nitrite indicated that pre-exposure to nitrite most likely caused disruption of the anammox biochemistry by interrupting the hydrazine synthesis step. Meanwhile, active metabolic status of anammox bacteria fueled by a strong proton gradient maintained by controlling pH in the optimal range of 7.2-7.8 enhanced the ability of anammox bacteria to tolerate nitrite inhibition. This was evaluated by depleting the proton gradient by utilizing two uncouplers of respiration, 2,4 dinitrophenol (24DNP) and carbonyl cyanide m-chlorophenyl hydrazine (CCCP). The results showed that presence of 0.28 mg CCCP L⁻¹ caused enhancement of nitrite inhibition to anammox bacteria, with a calculated IC₅₀ of 18.7 mg NO₂⁻-N L⁻¹ compared to an IC₅₀ greater than 150 mg NO₂⁻-N L⁻¹ in the control group lacking CCCP. Meanwhile, the sensitivity to NO₂⁻ was 3 times in anammox bacteria pre-exposed to 100 mg NO₂⁻ L⁻¹ for 24 h than in treatments lacking 37.8 mg 24DNP L⁻¹. A potential strategy of detoxifying the nitrite inhibition to anammox bacteria was proposed by using nitrate due to the finding of the presence of NarK, with potential function of NO₃⁻/NO₂⁻ antiporter, encoded in the anammox genome. Both batch- and continuous-experiments were carried out to test this hypothesis. The relative contribution of nitrate to nitrite detoxification was found to be pH dependent but the attenuation of nitrite inhibition is independent of the proton motive force which is supported by the result that nitrate caused almost complete attenuation of nitrite toxicity in cells exposed to the proton gradient disruptor, CCCP, at pH 7.5. Increase in nitrate concentration also improved the attenuation of nitrite inhibition to anammox process, with the maximum recovery being achieved at 0.85 mM in batch experiment and 2.0 mM for 3 days in continuous-fed bioreactor. Moreover, the timing of nitrate addition is significant because long-term nitrite inhibition of anammox biomass results in irreversible damage of the cells, under which condition addition of nitrate showed no positive impact on recovery of nitrite inhibition. This study also investigated the inhibitory effects of six metals (Cu²⁺, Cd²⁺, Ni²⁺, Zn²⁺, Pb²⁺, and molybdate) commonly found in landfill leachate on anammox activity. Results from batch bioassays indicated that precipitation reactions decreased considerably the soluble concentration of the cationic metals. Cu, Zn, Cd, and Ni were the most toxic metals with 50% inhibiting soluble concentrations of 4.2, 7.6, 11.2, and 48.6 mg L⁻¹, respectively. Molybdate and Pb²⁺ were not or only moderately inhibitory at the highest soluble concentrations tested (22.7 mg Mo L-1 and 6.0 mg Pb L⁻¹, respectively). Microbial inhibition was strongly correlated with both the added- and the dissolved metal concentration. These relationships could be described by a noncompetitive inhibition model for all inhibitory metals except for Pb. The results of this dissertation indicate that the resistance of anammox bacteria to nitrite inhibition could be enhanced by maintaining either an active metabolism in simultaneous presence of ammonium and nitrite, or sufficient proton gradient to enable relieving nitrite accumulation in sensitive regions of the anammox cells through an active nitrite transport system. An alternative nitrite detoxification mechanism was also demonstrated which relied on a secondary transport system facilitated by exogenous nitrate to avoid the accumulation of toxic intraorganelle nitrite concentration. Moreover, the results obtained in the study investigating the impact of heavy metals on anammox process provides new insights on the sensitivity of anammox bacteria to common metals and can be used to devise strategies to minimize inhibition of the anammox process when treating wastewater containing heavy metals.

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

published_or_final_version / abstract / Zoology / Master / Master of Philosophy

Escherichia coli phosphoenolpyruvate carboxykinase (ATP:oxaloacetate carboxylase (transphorsphorylating) EC 4.1.1.49) catalyzes the decarboxylation and subsequent phosphorylation of oxaloacetate (OAA) to phosphoenolpyruvate (PEP) in the presence of Mg2+ATP and synergistic catalysis has been observed in the presence of Ca2+ or Mn2+. Structural analyses have shown that active site residues Arg333, Ser250 and Tyr207 are coordinated differently in E. coli PCK structures complexed with Mg2+ATP-oxalate, Mg2+ATP-Mn2+-pyruvate and Mg2+ATP-Ca2+-pyruvate; hence, we hypothesize that the function of Arg333, Ser250 and Tyr207, depends on the absence or presence of Ca2+ or Mn2+ during catalysis by E. coli phosphoenolpyruvate carboxykinase (PCK). In order to verify this hypothesis, site directed mutagenesis of the pckA gene was used to convert Arg333 to Gln, Ser250 to Ala and Tyr207 to Phe, while 14CO2 exchange assay and x-ray crystallography were used to determine the effects of these mutations on catalysis by E. coli PCK in the presence of OAA and Mg2+ATP with Ca2+ or Mn2+ metal ions. Kinetic analysis showed that the Tyr207Phe mutation decrease kcat by 1.7 fold, while Ser250Ala and Arg333Gln reduced kcat by 10.8 and 4,555 fold respectively in the presence of Mg2+ATP and OAA. In the presence of Mg2+ATP, OAA and Ca2+, Arg333Gln, Ser250Ala and Tyr207Phe mutations reduced kcat by 11,688, 44 and 2 fold respectively. In the presence of Mg2+ATP, OAA and Mn2+ Arg333Gln, Ser250Ala and Tyr207Phe mutations reduced kcat by 2,880, 4 and 5.5 fold respectively. The crystal structure of Ser250Ala complexed with Mg2+ATP-Mn2+-pyruvate, showed that in the presence of Mn2+, Ser250Ala mutation reduced the angle between the γ-phosphate of ATP and residue 250 by 6.2 Å and increased the distance between the hydroxyl group of Tyr207 and the CH2 group of pyruvate by 0.5 Å. As a result we conclude that Arg333 is important for oxaloacetate decarboxylation and phosphorylation. During catalysis in the presence of Mg2+ATP with or without Ca2+ or Mn2+, Ser250 functions to maintain one γ-phosphate oxygen of ATP in an eclipsed conformation, while Tyr207 functions to drive oxaloacetate decarboxylation during catalysis in the presence of Mn2+ ion. Kinetic and structural studies of E. coli PCK have previously been used to show that Asp269 is involved in metal coordination, while Lys254 and Arg65 are important for Mg2+ATP and OAA binding to E. coli PCK respectively. In this study the E. coli PCK Asp269Asn-Mg2+ATP-Ca2+-pyruvate crystal structure showed that the Asp269Asn mutation reduced the number of ligands coordinating Ca2+ from seven to three, while no electron density was observed for Mg2+ATP and OAA in Lys254Ser and Arg65Gln crystal structures respectively.

This thesis explores the design development and experimental testing of a planar linkage for the Skiboard, a novel snowsports equipment device. The Skiboard, similar to a skateboard in appearance and style of use, combines two short skis with a bindingless board. Its aim is to fill a gap in the snowsports market for a product that offers a wide range of freestyle and trick riding possibilities, beyond those of a snowboard, while being as stable and easy to ride as a pair of skis. While the concept of the Skiboard in itself is simple, the task of designing a mechanism to link the skis to the board is complex. To translate a gradual lean of the rider into a gradual and equal tilting of the skis requires a multi-loop linkage mechanism. The synthesis and analysis of a mechanism for this application was the inspiration for the development of the synthesis-related design tools presented in this thesis. Design methodologies and design software concepts have been developed for use by designers faced with under-defined, “black-box” linkage synthesis problems similar to the Skiboard mechanism synthesis task. A software-based design of experiments setup, called SMAC, is introduced in this thesis and was used throughout the linkage synthesis process for the Skiboard. One promising candidate mechanism, developed and chosen using SMAC, is followed through to the pre-prototyping phase of the design process. PSEO, another, more advanced, software tool for complex and multi-loop linkage synthesis is also presented in the concept stage of development. This type of program has the potential to automate some of the most time-consuming portions of the synthesis and analysis process with the use of a genetic algorithm and curve-matching algorithm. Additionally, it keeps much of the user’s interaction with the design process and the design itself intact, which is something not offered by existing tools incorporating similar levels of automation. Overall, this thesis is an exploration into the field of linkage design, a topic with little crossover between theory and practical design helps. It includes a review of existing synthesis tools and the development of new tools to suit complex applications such as the Skiboard. The design process for the Skiboard linkage mechanism is also presented and illustrates the way in which the creative design process is iterative, progressively informing the designer’s understanding of the functional requirements of the linkage and how to best satisfy them.

No description available.

No description available.