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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
341

Silicon-based organic and inorganic polymers

Spinu, Maria 05 February 2007 (has links)
The range of polymeric materials containing the Si-O bond spans from the three-dimensional inorganic networks of silica (SiO₂), to linear high molecular weight polysiloxanes which display properties of both organic and inorganic materials. Part 1 of this dissertation describes the synthesis of three-dimensional inorganic SiO₂ networks and organic-inorganic hybrid networks using a low temperature solution technique known as the sol-gel process. During this process, hydrolysis and subsequent condensation of inorganic alkoxides (most often tetraethylorthosilicate, TEOS) in the presence of catalysts leads to the formation of three-dimensional SiO₂ networks. However, the strong acid or base catalysts typically employed in sol-gel reactions would also cause undesirable degradation of many organic modifiers, especially at higher temperatures required for the drying of the gels. A catalyst-free sol-gel process, based on tetramethyl orthosilicate (TMOS), the most reactive silicon tetra alkoxide in the series, was developed. The catalyst-free route provides an optimum reaction environment for the synthesis of organic-inorganic materials through copolymerization reactions. This concept will be exemplified by two organic-inorganic systems in which TMOS was used as the inorganic component while poly(dimethylsiloxane) and polyimide oligomers respectively, were employed as the organic component. The effect of such modifications on the surface and bulk properties of the inorganic SiO₂ networks was also investigated. Part 2 of this dissertation describes specific aspects associated with the synthesis of amine containing polysiloxane oligomers. A new molecular design which allows for independent control of molecular weight and amine functionalities was developed. The new synthesis involves anionic ring opening equilibrium copolymerization of the cyclic siloxane tetramer D₄ with a new cyclic siloxane monomer containing amine functionalities as pendant groups on silicon atoms. The effect of the bulky substituent {-CH₂CH(CH₃)CH₂NHCH₂CH₂NH₂} of the silicon atom on the position of thermodynamic equilibrium, and the extent of molecular weight and composition control in the linear polysiloxane oligomers was studied. / Ph. D.
342

A study of factors affecting queen survival, nest initiation, and nest development in the baldfaced hornet Dolichovespula maculata (L.) (Hymenoptera:Vespidae)

Stein, Kenneth John 13 October 2005 (has links)
Mating success and nutrient reserve effects on queen survival and nest initiation were examined with respect to the reproductive fitness of queens of the baldfaced hornet, Dolichovespula maculata. The sperm content of the Spermatheca was examined in queens of this hornet species and in queens of 10 other yellowjacket species collected in spring and summer of 1987, 1988 and 1989. Queens of the baldfaced hornet, D. maculata, were also analyzed for sperm content prior to nest initiation and during colony development. A regression model was employed to determine sperm utilization. Based on total cell counts and adult census, the sperm use efficiency of this species changed from approximately 90-100 sperm released per egg in the initial stages of colony development, to 2-3 sperm released per egg after 1000 eggs had been laid. Near the end of the season the predicted number of sperm released per egg was 0-1. The number of sperm in D. maculata males ranged from 2-2.5 million; a value considerably greater than the mean sperm number (20,223; ±4,669) found in mated spring queens (n=15). Nineteen (18.4%) of 103 yellowjacket queens analyzed in the spring seasons of 1987 and 1988 were uninseminated. The effects of mating success and sperm utilization on colony development are discussed. A significant regression of sperm content on colony size was also found for 8 species of yellowjacket. Queens of D. maculata were collected for studies of nutrient reserves before hibernation in the fall, during nest initiation, and after colonies had produced more than 2 worker broods. Fresh and dry weights were determined for all queens and a seasonal comparison of the energy reserves of lipids, sugar, and glycogen was performed on the thoracic and abdominal tagmata. Total nitrogen was also quantified to estimate protein changes by season. The results show that lipids accounted for 35% of the weight lost during hibernation, sugars 12%, and glycogen 6%. Total thoracic nitrogen remained constant throughout the year, whereas abdominal nitrogen was the same in the fall and spring queens but increased in the summer queens. The results from this study suggest that most queens which survive the winter and successfully initiate nests have similar energy reserve quantities. The implications of these findings to solitary foraging behavior are discussed. The eggs of D. maculata were examined in the spring and summer to quantify the energetic contributions provided by the queen. Mean egg weight was highest in the spring and decreased with progressive nest development. Both egg weight and energy reserves were variable among and within nests. The nutrient reserves for eggs in embryo nests, in order of importance, were lipid (22%), glucose (9.5%), and glycogen (5%). A 10-day egg incubation experiment demonstrated a mean loss of 83 ug dry weight; lipids could not completely account for the weight loss, either quantitatively or qualitatively. A study on egg developmental time failed to provide sufficient data; all eggs eventually died although embryonic larval movement was detected in 2 eggs after 16 days. The energetic contributions which a queen provides to the eggs are discussed with respect to foraging behavior and environmental influences. / Ph. D.
343

The manager as a system's controller: an application of management systems engineering concepts

Mendes, Joao Pedro M. 19 October 2005 (has links)
This research is about technology transfer from engineering to management. According to Kerlinger’s (1979) terminology, most practical management problems are formulated as engineering problems. So, it is legitimate to adapt general engineering techniques to solve those problems. In Industrial Dynamics, Forrester (1961) says “the practice of medicine or of engineering began as an empirical art representing only the exercise of judgment based on experience. The development of the underlying sciences was motivated by the need to understand better the foundation on which the art is rested.” Engineering evolved from an art after practitioners applied relationships explained by basic laws of nature. Engineers design and predict the performance of the systems they work with. At most, managers hope for acceptable performance; management is still much an art, whose practitioners study relationships based on data and observation. Therefore, the objective of this research is twofold: to establish the groundwork for a discipline of management systems engineering, and to provide one example of its application. A management system is any organizational position, its scope of authority, and its management tools. The Management System Model (MSM) describes a management system as the interaction between the manager, the operation, and the management tools (Kurstedt, Mendes, & Lee, 1988). Management systems engineering involves the specification, design, implementation and maintenance of management systems. The specification of a management system identifies the required performance characteristics in response to given events. The design is the prediction, with the aid of mathematical models, of the actual responses (outputs) to those events (inputs). The conceptual part of this research involves the development of mathematical models as fundamental tools to specify and design engineering systems. One significant contribution is the development of the conceptual framework and the demonstration of a quantitative analog for the MSM. The applied part of this research draws upon an emergency exercise in an industrial plant (the United States Department of Energy’s Feed Materials Production Center at Fernald, Ohio). An emergency is any event that threatens the integrity of people, environment, or assets. In the context of this research, emergency response is the set of actions required to neutralize or reduce the effects of the threatening event. An emergency exercise is the live simulation of the response to a dangerous situation in an industrial setting. The management system is composed of the plant management, the industrial plant where a simulated accident occurs, and the management tools used during the emergency. Specifically, the objective of the applied part is to show we can use a mathematical model to describe the dynamics of the emergency management system and make short-term predictions. The mathematical model is a control theory-based system estimator. The data to compare the model against is time series data generated from information portrayed to the plant management during the unfolding of the exercise. Therefore, this research describes a longitudinal study. The similarity between the data and the model results is apparent in graphical representations and statistically demonstrated through spectral cross-correlation analysis. So, another significant contribution is revitalizing the formal application of control theory to the study of management situations. / Ph. D.
344

Packed capillary columns for liquid chromatography

Wilson, William Henry 11 May 2006 (has links)
The advantages and disadvantages of packed capillary columns for high performance liquid chromatography are examined. Historically, the advantages are smaller sample and phase consumption, enhancement in sensitivity, easy column synthesis, higher obtainable efficiency, and easier interfacing to other techniques. These points are explored through experiments in microbore ion chromatography, packed fused silica columns, and capillary zone electrophoresis. These studies also address the disadvantages of microscale HPLC which are stringent instrument design, brittle or weak columns, poor column stability, and the lack of commercial instrumentation. The results of these investigations indicate the following. First, the purported sensitivity enhancement is really attributable to solute focusing and not to column miniaturization. Second, column synthesis is still a difficult procedure that requires experience. Third, higher efficiencies are realized, especially when the column diameter to particle diameter ratio is optimized. Fourth, interfacing to other techniques is simplified because of the lower volumetric flow rates. Finally, the only real disadvantages are stringent instrument design and brittle columns in some instances. This thesis offers means for circumventing these difficulties. / Ph. D.
345

Interframe image coding with three-dimensional gradient motion estimation

Lee, Choon 25 August 2008 (has links)
Two new methods for coding image sequences in video conferencing systems are developed in this dissertation. A simple 3-D gradient operator is developed to estimate motion in an image sequence on a pixel-by-pixel basis. A stochastic 3-D gradient operator is also developed for a gradient calculation which is more robust to the noise effects of the image sequence. These gradient operators are used to estimate motion in the next frame using information from three previous frames. The concept of tangent plane, which is perpendicular to the gradient vector, is introduced to guide searching for the motion vector. The simplified 3-d gradient motion estimation (GME) technique is compared to Netravali's pixel-recursive method with scalar quantization. It was found that performance of the GME technique is very close to that of Netravali' s technique with less computational complexity. To adapt the motion estimation techniques to vector quantization, two new supplementary methods of motion estimation using the pixel motion vectors from the motion estimator were studied. The methods use either the pixel motion vectors directly on the moving block (pixel motion estimation) or calculate the block motion vector from the pixel motion vectors (block motion estimation). For both methods, the differences between the prediction block and the moving block are vector quantized. / Ph. D.
346

The effect of heat shock, growth atmosphere, and recovery atmosphere on the survival of Escherichia coli 0157:H7 to heat

Murano, Elsa Alina 25 August 2008 (has links)
E. coli 0157:H7 is an important foodborne pathogen, responsible for several outbreaks of hemorrhagic colitis where improperly cooked hamburger meat was thought to be the vehicle. Various time/temperature combinations were used to determine the optimum conditions of heat shock which would result in the greatest number of survivors to a 55°C heat treatment. The optimum conditions were 42°C for 5 minutes and were used throughout the study. Heat shock of aerobically grown cells resulted in an increase in the mean D value after a 55°C heat treatment by a factor of 2.1 over nonheat-shocked controls. Heat shock of anaerobically grown cells also resulted ina significant increase in mean D value over nonheat-shocked controls. Anaerobic growth itself resulted in an increase in the ability of the cells to survive the 55°C heat treatment when compared with aerobically grown cells. Both heat-shocked and anaerobically grown cells contained a protein corresponding to a sigma³² subunit of RNA polymerase which has been identified as the 71,000 Galton heat shock protein characteristic of E. coli cells. Anaerobic plating resulted in a significant increase in the mean D values of both aerobically grown and anaerobically grown cells. The largest increase in mean D values was observed in aerobically grown non-heat-shocked cells, which increased by a factor of 2.3 when plated anaerobically instead of aerobically. The activities of catalase and superoxide dismutase in aerobically grown and anaerobically grown cells were studied to determine the reason why anaerobic plating enhanced recovery of cells. The activities of both enzymes were eliminated after heat treatment at 55°C for 20 minutes, regardless of whether the cells were heat-shocked or not. The ability of heat shock and anaerobic growth to protect the cells from a subsequent heat treatment was tested by measuring the rate of release of cell materials during heating at 55°C. Heat-shocking and anaerobic growth resulted in even faster release of cell materials during heating than controls, suggesting that neither of these stresses protected the cells against the effects of heat. The effect of heat shock on cell injury was studied. Heat shock of aerobically grown cells resulted in the greatest difference in log number of cells between cells plated in nonselective medium vs. selective medium. Thus, more cells were injured if heat-shocked than if not heat-shocked. Heat-shocking of anaerobically grown cells also resulted in more injured cells than non-heat-shocked controls. / Ph. D.
347

Characterization and regulation of the speA gene in Escherichia coli

Moore, Robert C. 20 September 2005 (has links)
In Escherichia coli, the speA gene encodes biosynthetic arginine decarboxylase (ADC), the first enzyme in a putrescine biosynthetic pathway. ADC converts arginine to agmatine, which is hydrolyzed by agmatine ureohydrolase, encoded by the speB gene, to putrescine and urea. ADC is negatively regulated by mechanisms requiring either cAMP and cAMP receptor protein (CRP) or putrescine. A 3,236 base pair (bp) BalI-AccI restriction fragment derived from plasmid pKA5, which contains a 7.5 kilobase (kb) E. coli genomic fragment in pBR322, was subcloned into pGEM-3Z to produce plasmids pRM15 and pRM59. Both pRM15 and pRM59 overexpress ADC and the DNA sequence of the BalI-AccI fragment in each plasmid was determined. A 2,119 bp restriction fragment containing 730 bp 5’ to speA, the speA promoter, and 1,389 bp (463 amino acids) of the 5’-end of speA was used to construct transcriptional (pRM161 and pRM162) and translational (pRM65) speA-lacZ fusion plasmids. The presence of the predicted 160,000 and 157,000 dalton ADC / Ph. D.
348

Relation entre la satisfaction conjugale et la perception des attitudes : étude comparative entre deux populations

St-Gelais, Marie-Claude 23 February 2022 (has links)
Les difficultés conjugales sont de plus en plus ouvertement exprimées de nos jours. Elles constituent, en fait, un des problèmes majeurs en psychologie sociale. En se basant sur le schème d'interaction perceptuel découlant du modèle perceptivo-attitudinal de Pléchaty (1983), il s'agit dans ce présent travail de comparer les couples en difficulté conjugale qui demandent une évaluation clinique avec les couples satisfaits de leur situation. Il est postulé que les couples satisfaits présentent plus de congruence perceptuelle dans tous les domaines de la vie à deux. Cette étude comparative fait appel à 49 couples insatisfaits et à 34 couples satisfaits. Les résultats démontrent que les couples insatisfaits présentent plus de discordance perceptuelle dans les cinq domaines de la vie à deux que les couples satisfaits. A ce niveau l'hypothèse est confirmée. Mais, suite à l'obtention des résultats découlant d'une analyse factorielle, i 1 est constaté qu'entre les hommes et les femmes il n'y a que deux facteurs distincts sur quatre pour décrire la perception qu'ils ont de leur vie conjugale. A ce titre la théorie perceptivo-attitudinale est partiellement appuyée. La discussion soulève la perception que chacun des conjoints ont de la vie conjugale.
349

Between domestic constraints and multilateral obligations : the reform of the Bundeswehr in the context of a normalised German foreign and security policy

Nuyken, Mark E. January 2012 (has links)
This thesis seeks to understand the developments in Germany’s foreign and security policy since the end of the Cold War. Primarily, this thesis will centre on the question of whether Germany can now, after being re-unified for more than 20 years, be considered a normal actor in international relations. Although this subject has been debated extensively, the effects a possible change in foreign policy behaviour has on related fields of policy, have largely been left aside. This thesis therefore sets out to understand if there has in fact been a change in Germany’s foreign and security policy and will then apply the findings on the institution most affected by this change, i.e. Germany’s armed forces the Bundeswehr. It will therefore firstly discuss the perceived changes in German foreign policy since 1990 by analysing the academic debate on the process of normalisation and continuation. It will be argued that Germany has in fact become more normal and abandoned the constrained foreign policy of the Cold-War-era. The Bundeswehr will therefore have to be reformed accordingly to accommodate the new tasks set out by the changed foreign policy – most importantly peacekeeping and peace-enforcing out-of-area missions. This thesis will therefore analyse the reform efforts made over the last 20 years and apply them to the Bundeswehr’s large deployments in Kosovo and Afghanistan to determine how effective the reforms have been. Finally, this thesis will be able to contribute to the discussion on Germany’s status of a normal player in international relations with the added perspective from the Bundeswehr’s point of view.
350

Die betekenis van die oprigting van die Berlynse muur (1961) in die konteks van die Koue Oorlog

04 November 2014 (has links)
M.A. (Historical Studies) / Please refer to full text to view abstract

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