In this thesis, we first show that the performance of ranking and selection (R&S) procedures in steady-state simulations depends highly on the quality of the variance estimates that are used. We study the performance of R&S procedures using three variance estimators --- overlapping area, overlapping Cramer--von Mises, and overlapping modified jackknifed Durbin--Watson estimators --- that show better long-run performance than other estimators previously used in conjunction with R&S procedures for steady-state simulations. We devote additional study to the development of the new overlapping modified jackknifed Durbin--Watson estimator and demonstrate some of its useful properties. Next, we consider the problem of finding the best simulated system under a primary performance measure, while also satisfying stochastic constraints on secondary performance measures, known as constrained ranking and selection. We first present a new framework that allows certain systems to become dormant, halting sampling for those systems as the procedure continues. We also develop general procedures for constrained R&S that guarantee a nominal probability of correct selection, under any number of constraints and correlation across systems. In addition, we address new topics critical to efficiency of the these procedures, namely the allocation of error between feasibility check and selection, the use of common random numbers, and the cost of switching between simulated systems.

All computer simulation models require some form of initialization before their outputs can be considered meaningful. Simulation models are typically initialized in a particular, often "empty" state and therefore must be "warmed-up" for an unknown amount of simulation time before reaching a "quasi-steady-state" representative of the systems' performance. The portion of the output series that is influenced by the arbitrary initialization is referred to as the initial transient and is a widely recognized problem in simulation analysis. Although several methods exist for removing the initial transient, there are no methods that perform well in all applications. This research evaluates the effectiveness of several techniques for reducing initialization bias from simulations using the commercial transportation simulation model VISSIM®. The three methods ultimately selected for evaluation are Welch's Method, the Marginal Standard Error Rule (MSER) and the Volume Balancing Method currently being used by the CORSIM model. Three model instances - a single intersection, a corridor, and a large network - were created to analyze the length of the initial transient for varying scenarios, under high and low demand scenarios. After presenting the results of each initialization method, advantages and criticisms of each are discussed as well as issues that arose during the implementation. The results for estimation of the extent of the initial transient are compared across each method and across the varying model sizes and volume levels. Based on the results of this study, Welch's Method is recommended based on is consistency and ease of implementation.

Most modern systems are equipped with very complex, expensive, and high technology components whose maintenance costs have become an increasingly large portion of the total operating cost of these systems. Thus, the efficacy of the maintenance policy for these and related systems has become a major concern to both manufacturing and design engineers. Different kinds of maintenance strategies have been proposed to solve the problem. While some of these have proven effective, there is yet no definitive approach that has been found that support the maintainability requirements of transient systems or systems that exhibit transient behavior. Transient behavior is the notion of non-steady state operation, which is the characteristic of system operation during its useful life. For designing convenience most of the maintenance strategies have assumed negligible maintenance or repair time which is not practical.In this research an opportunistic maintenance (OM) approach is implemented on a multi-unit system that exhibits transient behavior. Under OM policy, if a maintenance event has been scheduled for certain components and in the process of implementing the scheduled maintenance of these targeted components, the maintenance of other components whose maintenance times are in close proximity is also implemented at the same time. As a result, the time and cost of marshalling and staging maintenance resources are reduced. As part of the system effectiveness measure, the instantaneous system availability based on the transient nature of the system, is estimated using the renewal theory approach.

Spray cooling is a high heat removal technique which has been used widely in many industries, especially metallurgical, where the control of the temperatures of metals is an important factor to obtain the desired microstructure; and also in microelectronics where is very important to obtain high heat fluxes at relatively low surface temperatures. In this study, an open loop spray cooling system has been fabricated to provide an upward-facing spray over a 12 mm diameter test surface. A full cone spray nozzle was used to deliver deionized water to the test surface at five pressures (10, 15, 20, 25 and 30 psi), and at three different distances to the test surface (3, 7 and 12 mm). The volumetric flow rate at the surface used in the experiments depended on both the pressures and the distances. For a distance of 3 mm and 7 mm, the volumetric flow rate range from 336.6 to 627 ml/min while for 12 mm, the range was from 336.6 to 484.28 ml/min. Heat fluxes of 1.92 to 451 W/cm2, 2.1 to 417.3 W/cm2 and 1.9 to 409.5 W/cm2 for distances of 3, 7 and 12 mm respectively were registered at different input power levels. For all the three distances, the volumetric flow rate affects the heat flux, especially for 3 mm; and this effect decreases for higher distances. However, the distance between the nozzle and the test surface has little effect on the heat flux at low pressures but at higher pressures, the difference in heat flux is mainly due to the fact that part of the spray does not impinge the test surface.

The human mitochondrial DNA (mtDNA) genome must be faithfully maintained by the mitochondrial DNA replication machinery. Deficiencies in mtDNA maintenance result in the accumulation of mutations and deletions, which have been associated with a number of neuromuscular degenerative disorders including, mtDNA depletion syndrome, Alpers syndrome, progressive external opthalmoplegia (PEO), and sensory ataxic neuropathy, dysarthria, and opthalmoparesis (SANDO). The mtDNA replication machinery is comprised of a nuclearly-encoded DNA polymerase gamma (Pol γ), single-stranded DNA binding protein (mtSSB), and a hexameric mtDNA helicase. In this work, we employed quantitative pre-steady state kinetic techniques to establish the mechanisms responsible for the replication of the human mitochondrial DNA by Pol γ and explored the effects of point mutations that are observed in heritable diseases. With our biochemical characterization of mutants of Pol γ, we have shown unique characteristics that would lead to profound physiological consequences over time. Additionally, we have made significant progress towards reconstitution of the mitochondrial DNA replisome by monitoring DNA polymerization that is dependent on helicase unwinding of double stranded DNA. Overall, this work provides a better understanding of the mechanism of mtDNA replication and has important implications toward understanding the role of mitochondrial DNA replication in mitochondrial disease, ageing and cancer. In addition to the work on the mtDNA replisome, we have applied pre-steady state kinetic techniques to better understand the mechanism of RNA-dependent DNA polymerization by HIV reverse transcriptase (HIV-RT). This enzyme is responsible for the replication of the viral genome in HIV and is a common target for anti-HIV drugs. We have characterized the role of enzyme conformational changes in the kinetics of incorporation of correct nucleotide and the Nucleotide Reverse Transcriptase Inhibitor (NRTI) AZT by wild-type enzyme, as well as a mutant with clinical resistance to AZT. This work provides a better understanding of the complete mechanism of RNA-dependent DNA polymerization, the changes in the mechanism in the presence of inhibitor and the development of resistance to this nucleoside analog; and thereby this work contributes to the long-term goal of designing more effective drugs that can possibly deter resistance and be used successfully for treatment of HIV. / text

The flow structure and convective heat transfer behavior of a free liquid jet ejecting from a round nozzle impinging vertically on a hemispherical solid plate and a slot nozzle impinging vertically on a cylindrical curved plate have been studied using a numerical analysis approach. The simulation model incorporated the entire fluid region and the solid hemisphere or curved plate. Solution was done for both isothermal and constant heat flux boundary conditions at the inner surface of the hemispherical plate and the constant heat flux boundary condition at the inner surface of the cylindrical shaped plate. Computations for the round nozzle impinging jet on the hemispherical plate and cylindrical plate were done for jet Reynolds number (ReJ) ranging from 500 to 2000, dimensionless nozzle to target spacing ratio (β) from 0.75 to 3, and for various dimensionless plate thicknesses to diameter nozzle ratio (b/dn) from 0.083-1.5. Also, computations for the slot nozzle impinging jet on the cylindrical plate were done for inner plate radius of curvature to nozzle diameter ratio (Ri/dn) of 4.16-16.66, plate thickness to nozzle diameter ratio (b/dn) of 0.08-1.0, and different nozzle diameters (dn), Results are presented for dimensionless solid-fluid interface temperature, dimensionless maximum temperature in the solid, local and average Nusselt numbers using the following fluids: water (H2O), flouroinert (FC-77), and oil (MIL-7808) and the following solid materials: aluminum, copper, Constantan, silver, and silicon. Materials with higher thermal conductivity maintained a more uniform temperature distribution at the solid-fluid interface. A higher Reynolds number increased the Nusselt number over the entire solid-fluid interface. Local and average Nusselt number and heat transfer coefficient distributions showed a strong dependence on the impingement velocity or Reynolds number. As the velocity increases, the local Nusselt number increases over the entire solid-fluid interface. Decreasing the nozzle to target spacing favors the increasing of the Nusselt number. Increasing the nozzle diameter decreases the temperature at the curved plate outer surface and increases the local Nusselt number. Similarly, local and average Nusselt number was enhanced by decreasing plate thickness. Numerical simulation results are validated by comparing with experimental measurements and related correlations.

<p>Lipopolysaccharide, the physical barrier that protects Gram-negative bacteria from various antibiotics and environmental stressors, is anchored to the outer membrane by the phosphorylated, acylated disaccharide of glucosamine known as lipid A. Besides being necessary for the viability of most Gram-negative bacteria, lipid A interacts directly with specific mammalian immune cell receptors, causing an inflammatory response that can result in septic shock. The lipid A biosynthetic pathway contains nine enzymatic steps, the sixth being the phosphorylation of the tetraacyldisaccharide-1-phosphate (DSMP) precursor to form lipid IV_A by the inner membrane-bound kinase LpxK, a divergent member of the P-loop containing nucleotide triphosphate hydrolase superfamily. LpxK is the only known P-loop kinase to act on a lipid at the membrane interface.</p><p> We report herein multiple crystal structures of <italic>Aquifex aeolicus</italic> LpxK in apo as well as ATP, ADP/Mg<super>2+</super>, AMP-PCP, and chloride-bound forms. LpxK consists of two &alpha;/&beta;/&alpha; sandwich domains connected by a two-stranded &beta;-sheet linker. The N-terminal domain, which has most structural homology to other P-loop kinase family members, is responsible for catalysis at the P-loop and positioning of the DSMP substrate for phosphoryl transfer on the inner membrane. The smaller C-terminal domain, a substructure unique to LpxK, helps bind the nucleotide substrate using a 25º hinge motion about its base which also assembles the necessary catalytic residues at the active site.</p><p> Using a thin-layer chromatography-based radioassay, we have performed extensive kinetic characterization of the enzyme and demonstrate that LpxK activity <italic>in vitro</italic> is dependent on the presence of detergent micelles, the use of divalent cations, and formation of a ternary LpxK-ATP/Mg<super>2+</super>-DSMP complex. Implementing steady-state kinetic analysis of multiple point mutants, we identify crucial active site residues. We propose that the interaction of D99 with H261 acts to increase the pK_a of the imidazole group, which in turn serves as the catalytic base to deprotonate the 4&rsquo;-hydroxyl of DSMP. An analogous mechanism has not yet been reported for any member of the P-loop kinase family.</p><p> The membrane/lipid binding characteristics of LpxK have also been also investigated through a crystal structure of the LpxK-lipid IV_A product complex along with point mutagenesis of residues in the DSMP binding pocket. Critical contacts with the bound lipid include interactions along the glucosamine backbone and the 1-position phosphate group, especially through R171. Furthermore, analysis of truncation mutants of the N-terminal helix of LpxK demonstrates that this substructure is a critical hydrophobic contact point with the membrane, and that both charge-charge and hydrophobic interactions contribute to the localization of LpxK at the lipid bilayer. </p><p> Overall, this work has contributed significantly to the limited knowledge surrounding membrane-bound enzymes that act upon lipid substrates. It has also provided insight into the process of enzyme evolution as LpxK, while containing a similar core domain as other P-loop kinases, has developed multiple subdomains required for both cellular localization and recognition of novel substrates. Finally, the presence of multiple crystal structures and detailed understanding of the LpxK catalytic mechanism will improve the chances of successfully targeting this essential step in lipid A biosynthesis in the pursuit of novel antimicrobials.</p> / Dissertation

Iki ekonominės krizės visuomenėje vyravo vartotojiškas požiūris, gauti kuo didesnes pajamas, noras turėti kuo daugiau, tačiau toks besaikis vartojimas pasaulį privedė prie finansinės krizės ir sukrėtė vyraujantį ekonominį modelį iki pat pamatų. Nepaisant technologinių pasiekimų, keičiantis gamybos ir vartojimo tempams kinta ir išteklių naudojimas bei aplinkos tarša. Nacionalinėje darnaus vystymosi strategijoje (toliau NDVS) (2009) iškeltas tikslas, kad Lietuva pagal ekonomikos lygį ir išteklių naudojimo efektyvumo rodiklius iki 2020 m. turi pasiekti 2003 m. ES–15 šalių vidurkį, o pagal aplinkos taršos rodiklius – neviršyti ES leistinų normatyvų, todėl labai svarbu žinoti, kaip siekiant šių tikslų gali keistis aplinkos būklė ir, ar pasiseks įgyvendinti darnaus vystymosi strategijoje numatytus aplinkosauginius tikslus. Darbo tikslas – išanalizuoti pagrindinius aplinkos sektoriaus darnaus vystymosi rodiklius ir nustatyti jų priklausomybę nuo ekonomikos pokyčių 2000–2020 m. Lietuvoje. Darbe buvo analizuojami pagrindiniai Lietuvos darnaus vystymosi ekonominiai, socialiniai ir aplinkosauginiai rodikliai 2000–2010 m., taip pat nustatyta aplinkos kintamųjų priklausomybė nuo ekonomikos (ne)augimo ir įvertintos galimos aplinkos kintamųjų tendencijos bei galimybės įgyvendinti iškeltus tikslus, pagal tris galimus ekonomikos vystymosi scenarijus 2010–2020 m. laikotarpiu. Sudarius tris galimus ekonomikos vystymosi scenarijus rezultatai parodė, kad jei šalies ūkis vystytųsi pagal pirmą (16... [toliau žr. visą tekstą] / Consumeristic approach to maximize income, the desire to have more has dominated in societies before the economic crisis, but that excessive consumption of the world has led to the financial crisis witch has shaken dominant economic model to the foundation. Despite technological achievements, changing production and consumption rates influence use of resources and environment pollution. The main aim of the National Sustainable Development Strategy (2009) is to achieve the average development level of EU15 in year 2003 according to the indicators of economic and social developments as well as to the efficiency in consumption of resources and to stay within the EU’s allowable limits by 2020. The aim of the study is to examine main sustainability indicators of environmental sphere and to assess their dependence from economic (GDP) changes over 2000–2020 periods in Lithuania. The main changes of indicators of sustainable development over 2000–2010 period were assessed in Lithuania. Also dependence of environment variables from economic (de)growth was examined and possible tendencies of environmental variables and opportunities to achieve foreseen targets, according to three possible scenarios for economic development over 2000–2020 periods were evaluated. Three possible scenarios for economic development has shown that if country’s economy develops according to the first (16 % GDP growth) or second (zero GDP growth) scenario, the aim set by NSDS (2009) to decouple the... [to full text]

The control and protection system of early nuclear power plants (Generation II) have been designed and built on the then reliable analog system. Technology has evolved in recent times and digital system has replaced most analog technology in most industries. Due to safety precautions and robust licensing requirements in the nuclear industry, the analog and digital system works concurrent to each other in most control and protection systems of nuclear power plants. Due to the ageing, regular maintenance and intermittent operation, the analog plant system often gives faulty signals. The objective of this thesis is to simulate a transient using a simulator to reduce the effects of system faults on the nuclear plant control and protection system, by detecting the faults early. The following steps will be performed: • validating the simulator measurements by simulating a normal operation, • detecting faults early on in the system These can be performed by resorting to a model that generates estimates of the correct sensors signal values based on actual readings and correlations among them. The next step can be performed by a fault detection module which determines early whether or not the plant systems are behaving normally and detects the fault. (Baraldi P. et al, 2010.) / Thesis (MSc (Engineering Sciences in Nuclear Engineering))--North-West University, Potchefstroom Campus, 2013.

The control and protection system of early nuclear power plants (Generation II) have been designed and built on the then reliable analog system. Technology has evolved in recent times and digital system has replaced most analog technology in most industries. Due to safety precautions and robust licensing requirements in the nuclear industry, the analog and digital system works concurrent to each other in most control and protection systems of nuclear power plants. Due to the ageing, regular maintenance and intermittent operation, the analog plant system often gives faulty signals. The objective of this thesis is to simulate a transient using a simulator to reduce the effects of system faults on the nuclear plant control and protection system, by detecting the faults early. The following steps will be performed: • validating the simulator measurements by simulating a normal operation, • detecting faults early on in the system These can be performed by resorting to a model that generates estimates of the correct sensors signal values based on actual readings and correlations among them. The next step can be performed by a fault detection module which determines early whether or not the plant systems are behaving normally and detects the fault. (Baraldi P. et al, 2010.) / Thesis (MSc (Engineering Sciences in Nuclear Engineering))--North-West University, Potchefstroom Campus, 2013.