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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.
141

Carbon Dioxide as a Benign Solvent for Homogeneous Catalyst Recovery and Recycle

Jones, Rebecca S. 19 July 2005 (has links)
We have successfully investigated the use of CO2 as a miscibility switch to create an environment in which we can run a homogeneously catalyzed reaction while maintaining a heterogeneous separation. We explored the use of this technique with fluorous biphasic systems, a fluorous solid support, and aqueous biphasic systems. In the case of the fluorous systems, CO2 was added to induce solubility of the fluorous catalyst. When the reaction was completed, CO2 was vented and the system returned to a biphasic state, making the separation easy. For the aqueous biphasic systems, the organic phase is chosen such that it is fully miscible with water at ambient conditions. Examples include acetonitrile, THF, and dioxane. The addition of CO2 reduces the polarity of the solvent and causes a phase split. The recovery of the water-soluble catalyst is once again heterogeneous. The application to aqueous biphasic systems is the most exciting studied. Aqueous biphasic systems are used industrially in the hydroformylation of propylene. With our technique, these systems can be extended to more hydrophobic substrates. We have shown a rate increase of 65 fold and 99% product recovery at modest pressures for the hydroformylation of 1-octene. These aqueous biphasic systems also show much promise in the arena of enzyme catalyzed reactions. We can create an environment in which the enzyme kinetics will no longer be mass transfer limited.
142

A Mutual Construction of the International System and the Nation States within a Model of Level-of-Analysis¡ÐA Case Study of the September 11 and the War on Terrorism

Wu, Tien-lun 13 December 2004 (has links)
Since the mode of level-of-analysis has to be treated as an empirical tool for IR theories to make a claim to become a social science in its own right, this study attempts to explore the political process of a mutual construction of the international system and the nation states within the model in three parts. Firstly, this study examines how the international system and the national states be settled upon as pregiven scientific entities on the basis of objective spatiality of territory and borders. Secondly, this study shows that in order to merge all states¡¦ diversities and differences into the sameness and likeness, the mutual construction is linked to the plausible assumptions about the structural world of universal rationality among all states, and the unfolding history of linear and progressive evolution. Finally, this study takes the September 11 and the war on terrorism as an example to illustrate the mutual construction and its consequences.
143

Homogeneous Catalysts For The Hydrolysis Of Sodium Borohydride: Synthesis, Characterization And Catalytic Use

Masjedi, Mehdi 01 August 2010 (has links) (PDF)
Recent study has shown that ruthenium(III) acetylacetonate acts as a homogeneous catalyst in the hydrolysis of sodium borohydride. When two equivalents of trimethylphosphite per ruthenium is added to the reaction solution containing sodium borohydride and ruthenium(III) acetylacetonate in the mixture of water and tetrahydrofuran, the rate of hydrogen generation is practically stopped (or reduced to the level of self hydrolysis). However, the catalytic hydrogen evolution of sodium borohydride restarts at an unexpectedly high rate in a certain period of time (induction time) after addition of trimethylphosphite. Consequently, trimethylphosphite known to be a poison in the hydrolysis, is involved in the formation of a new active catalyst (ruthenium species containing trimethylphosphite ligands) which has much higher catalytic activity in comparison with sole ruthenium(III) acetylacetonate. The same rate enhancement is observed by addition of two equivalents of triphenylphosphite per ruthenium into the medium. Varying the phosphorus compound affects not only the life time of catalyst but also the kinetic and activation parameters of the hydrolysis of sodium borohydride. However, varying the mole ratio of phosphorus compound to ruthenium does not affect the rate of hydrolysis or in other words, the rate of hydrogen generation is independent of phosphite concentration. Trans- and cis-[Ru(acac)2{P(OMe)3}2] complexes do not show significant catalytic activity in hydrogen generation of sodium borohydride. However, catalytic activity of cis-isomer is highly increased in the presence of two equivalents of trimethylphosphite, showing that the active catalyst formed during hydrolysis of sodium borohydride starting with Ru(acac)3 or cis-[Ru(acac)2{P(OMe)3}2], has more than two phosphine ligands. For the first time, a ruthenium(I) complex was isolated from aqueous solution after finishing the catalytic hydrolysis of sodium borohydride starting with ruthenium(III) acetylacetonate and trimethylphosphite. Hydridotetrakis(trimethylphosphite)ruthenium(I), [Ru{P(OMe)3}4H] was isolated and characterized by single crystal X-ray diffraction, Mass, UV-visible, FTIR, 1H, 13C and 31PNMR spectroscopy. Following the catalytic reaction by UV-Visible spectroscopy shows in-situ formation of a Ru(II) species which is mostly converted back to ruthenium(III) acetylacetonate after hydrolysis reaction along with formation of [Ru{P(OMe)3}4H] complex as a minor product. Although Ru(II) species could not be isolated, adding 1 equivalent of 2,2&#039 / -bipyridine yielded [Ru(acac)(bipy){P(OMe)3}H] complex which could be isolated and characterized by Mass, UV-Visible, FTIR, 1H, 13C and 31PNMR spectroscopy. In-situ generated Ru(II) species has much higher catalytic activity in comparison with its stabilized form [Ru(acac)(bipy){P(OMe)3}H] or [Ru{P(OMe)3}4H] complex. Conclusively, the fac-[Ru(acac){P(OMe)3}3H] complex is believed to be the in-situ generated Ru(II) species and the active catalyst in the hydrolysis of sodium borohydride.
144

Ruthenium(iii) Acetylacetonate As Catalyst Precursor In The Dehydrogenation Of Dimethylamine-borane

Unel, Ebru 01 February 2011 (has links) (PDF)
Amine boranes have recently been considered as solid hydrogen storage materials with high capability of hydrogen storage. Dimethylamine borane is one of the promising amine boranes with high theoretical gravimetric capacity of 16.9 wt%. Dimethylamine borane can undergo dehydrogenation only in the presence of a suitable catalyst at moderate temperature. In this project, throughout the dehydrogenation of dimethylamine borane (DMAB), the catalytic activity of ruthenium(III) acetylacetonate was examined for the first time. During the catalytic reaction, formation of a new in-situ ruthenium(II) species, [Ru{N2Me4}3(acac)H], is observed. Mercury poisoning experiment indicates that the in-situ ruthenium(II) species is a homogeneous catalyst in the dehydrogenation of dimethylamine borane. Kinetics of catalytic dehydrogenation of dimethylamine borane starting with ruthenium(III) acetylacetonate was investigated depending on catalyst concentration, substrate concentration and temperature. As a result, the hydrogen generation rate was found to be first-order with respect to catalyst concentration and zero-order regarding the substrate concentration. Besides, evaluation of the kinetic data yielded that the activation parameters for dehydrogenation reaction: the activation energy, Ea = 85 &plusmn / 2 kJ&bull / mol-1 / the enthalpy of activation, DH# = 82 &plusmn / 2 kJ&bull / mol-1 and the entropy of activation / DS# = -85 &plusmn / 5 J&bull / mol-1&bull / K-1. Additionally, before deactivation, [Ru{N2Me4}3(acac)H] provides 1700 turnovers over 100 hours in hydrogen evolution from the dehydrogenation of dimethlyamine borane. [Ru{N2Me4}3(acac)H] complex formed during the dehydrogenation of dimethylamine borane was isolated and characterized by UV-Visible, FTIR, 1H NMR, and Mass Spectroscopy. The isolated ruthenium(II) species was also tested as homogeneous catalyst in the dehydrogenation of dimethylamine borane.
145

Dynamic Switching Times For Season And Single Tickets In Sports And Entertainment With Time Dependent Demand Rates

Pakyardim, Yusuf Kenan 01 August 2011 (has links) (PDF)
The most important market segmentation in sports and entertainment industry is the competition between customers that buy bundle and single tickets. A common selling practice is starting the selling season with bundle ticket sales and switching to selling single tickets later on. The aim of this practice is to increase the number of customers that buy bundles, to create a fund before the season starts and to increase the load factor of the games with low demand. In this thesis, we investigate the effect of time dependent demand on dynamic switching times and the potential revenue gain over the case where the demand rate is assumed to be constant with time.
146

Kusin Vitamin : En studie om vitaminförpackningars olika attribut / Your friend Vitamin : A study about the different attributes of vitamin packages

Kim Hansson, Anna, Barth, Johanna January 2015 (has links)
Syfte: Syftet med studien är att undersöka vilka förpackningsrelaterade attribut som utgör en tilltalande vitaminförpackning. Metod: Studien lutar sig på en kvalitativ metod och för att få fram material som svarar på syftet har intervjuer med åtta stycken respondenter genomförts. Slutsats: De slutsatser som dragits är att mellanstora rundade förpackningar medskruv/”plopp”-lock föredras samt att blått och grönt är attraktiva färger för vitaminförpackningar. Tydlig, både innehålls- och utformningsmässig, information är även av stor vikt. / Purpose: The purpose of this study is to investigate which packaging attributesthat make an appealing vitamin package Method: The study uses a qualitative method and eight in-depth interviews withconsumers have been made in order to gain knowledge about the subject. Conclusion: The conclusions that have been made are that rounded medium sizedpackages with screw cap or “plop-lids” are preferred and that the colours blue andgreen are attractive when it comes to vitamin packages. Distinct informationpresented in a clear manner is also important.
147

The effects of small-scale heterogeneities on aquifer storage recovery systems

Hutchings, William C 01 June 2005 (has links)
Aquifer Storage Recovery (ASR) is a recently developed (circa 1970) method (in the U.S.A.) to reduce groundwater-pumping stresses by injecting treated wastewater or surface water during periods of low demand into an aquifer followed by its recovery during periods of high demand. This method has been successfully implemented in numerous locations across the U.S.A. and worldwide, mainly due to the cost savings provided by the use of an unlimited reservoir (aquifer) in which to store water compared to the costs to construct surface impoundments and the inherent problems with storing such water for extended periods of time under evaporative atmospheric conditions. "This study describes the use of a highly discretized, three-dimensional, variable-density, numerical model (SEAWAT 2000) that incorporates the vertical variation of hydraulic conductivities, measured foot by foot, from a continuous core collected from the upper Floridan aquifer in southwest Florida, to evaluate the effects of small-scale heterogeneities on a hypothetical ASR system well. In order to compare these effects to the more general case in which average hydraulic parameters are used to characterize flow zones, a model is constructed with average parameters taken from the heterogeneous case. This study attempts to determine whether aquifer heterogeneities influence the performance of ASR systems, compared to assumed homogeneous conditions, by quantifying differences in recovery efficiency, horizontal and vertical flow due to advection and dispersion, plume dimensions, and storage periods. The results of this study indicate that 1) the geometry of the injectate plume under homogeneous and heterogeneous conditions differ significantly; 2) background formation total dissolved solids (TDS) concentrations significantly control the quantity of potable water available for recovery; 3) dispersion exhibits a strong control on vertical mixing; 4) multiple injection cycles are required to generate a plume of potable water for long term storage; and 5) the percent recoveries under homogeneous and heterogeneous conditions are generally similar only in low-salinity background concentrations, due to the absence of the effects of buoyancy. Although the percent recoveries of the systems modeled are similar, the success of an ASR well is strongly controlled by the existence of heterogeneities, which essentially determine the degree of horizontal and vertical mixing of the injectate with formation waters. Heterogeneities result in varying groundwater and mass transport paths during injection and recovery periods. Presumably these variations would need to be considered when evaluating potential variations in groundwater quality due to mixing between formation and injected water. Understanding potential variations in groundwater quality and treatment alternatives due to the presence of ASR-associated geochemical conditions, e.g., elevated arsenic concentrations, may also be improved with a detailed heterogeneous numerical model.
148

Resultants and height bounds for zeros of homogeneous polynomial systems

Rauh, Nikolas Marcel 26 July 2013 (has links)
In 1955, Cassels proved a now celebrated theorem giving a search bound algorithm for determining whether a quadratic form has a nontrivial zero over the rationals. Since then, his work has been greatly generalized, but most of these newer techniques do not follow his original method of proof. In this thesis, we revisit his 1955 proof, modernize his tools and language, and use this machinery to prove more general theorems regarding height bounds for the common zeros of a system of polynomials in terms of the heights of those polynomials. We then use these theorems to give a short proof of a more general (albeit, known) version of Cassels' Theorem and give some weaker results concerning the rational points of a cubic or a pair of quadratics. / text
149

Dendrimer-encapsulated metal nanoparticles: synthesis, characterization, and applications to catalysis

Niu, Yanhui 30 September 2004 (has links)
The research in this dissertation examines the chemistry and applications of dendrimers in homogeneous catalysis. We examined interactions between dendrimers and charged probe molecules, prepared dendrimer-encapsulated metal nanoparticles in organic solvents, studied size-selectivity of dendrimer-encapsulted catalysts, and designed molecular rulers as in-situ probes to measure the location of dendrimer-encapsulted metal nanoparticles. The intrinsic proton binding constant and a constant that characterizes the strength of electrostatic interactions among occupied binding sites in poly(amidoamine) (PAMAM) dendrimers have been obtained by studying the effect of solution pH on the protonation of the dendrimers. The significant finding is that these two factors are greatly modulated by the unique and hydrophobic microenvironment in the dendrimer interior. Hydrophilic poly(propylene imine) (PPI) dendrimers were modified with various hydrophobic alkyl chains through an amide linkage and were then used as templates for preparing intradendrimer copper nanoclusters. The main driving force for encapsulating metal-ions was found to be the differences in metal-ion solubility between the solvent and the interior of the dendrimer. Nanometer-sized metal particles are synthesized and encapsulated into the interior of dendrimers by first mixing together the dendrimer and metal ion solution and then reducing the composite chemically, and the resulting dendrimer-encapsulated metal nanoparticles can then be used as catalysts. By controlling the packing density on the dendrimer periphery using either different dendrimer generations or dendrimer surface functionalities, it is possible to control access of substrates to the encapsulated catalytic nanoparticle. Molecular rulers consisting of a large molecular "stopper", a reactive probe and a linker were designed as in-situ probes for determining the average distance between the surface of dendrimer-encapsulated palladium nanoparticles and the periphery of their fourth-generation, hydroxyl-terminated PAMAM dendrimer hosts. By doing so, we avoid having to make assumptions about the nanoparticle size and shape. The results suggest that the surface of the encapsulated nanoparticle is situated 0.7 ± 0.2 nm from the surface of the dendrimer.
150

Indium complexes and their role in the ring-opening polymerization of lactide

Douglas, Amy Frances 05 1900 (has links)
The synthesis and characterization of a series of chiral indium complexes bearing a tridentate NNO ligand are reported. The ligand 2-[[[(dimethylamino)cyclohexyl]amino]methyl]- 4,6-bis(tert-butyl) phenol (H₂NNO) was synthesized via a previously published procedure and bound to indium by both a protonolysis and salt metathesis route. A dimethylated indium complex (NNO)InMe₂ (1) was isolated by reaction of InMe₃ with H₂NNO. A one-pot saltmetathesis route was used to produce a unique mixed-bridge dinuclear indium complex [(NNO)InCl] ₂(μ-OEt)(μ-Cl) (3) from a mixture of indium trichloride, potassium ethoxide and the monopotassiated salt of the ligand, KH(NNO). Direct reaction of KH(NNO) and indium trichloride resulted in the formation of (NNO)InCl₂ (4) which was carried forward to 3 by reaction with sodium ethoxide. The complex 3 is active for the ROP of β-butyrolactone ε-caprolactone and lactide and is the first reported indium-based catalyst for lactide or β-butyrolactone ROP. Kinetic studies of 3 for ROP of LA revealed that catalyst was well-behaved, and that the rate was first order with regard to lactide and catalyst. The enthalpy and entropy of activation for the ROP were experimentally determined. Polymer produced by ROP by 3 has narrow molecular weight distribution and a good correlation is seen between the observed moleular weight and monomer loading. A mechanism was proposed for 3 acting as a catalyst for the ROP of lactide; however further experiments are required to confirm this mechanism. Polymer samples isolated from the ROP of rac-lactide by rac-3 show isotactic enrichment. It is postulated that the chiral catalyst 3 is exerting stereocontrol via an enantiomorphic site control mechanism.

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