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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.
171

In Situ Reinforced Polymers Using Low Molecular Weight Compounds

Yordem, Onur Sinan 01 September 2011 (has links)
The primary objective of this research is to generate reinforcing domains in situ during the processing of polymers by using phase separation techniques. Low molecular weight compounds were mixed with polymers where the process viscosity is reduced at process temperatures and mechanical properties are improved once the material system is cooled or reacted. Thermally induced phase separation and thermotropic phase transformation of low molar mass compounds were used in isotactic polypropylene (iPP) and poly(ether ether ketone) (PEEK) resins. Reaction induced phase separation was utilized in thermosets to generate anisotropic reinforcements. A new strategy to increase fracture toughness of materials was introduced. Simultaneously, enhancement in stiffness and reduction in process viscosity were also attained. Materials with improved rheological and mechanical properties were prepared by using thermotropic phase transformations of metal soaps in polymers (calcium stearate/iPP). Morphology and thermal properties were studied using WAXS, DSC and SEM. Mechanical and rheological investigation showed significant reduction in process viscosity and substantial improvement in fracture toughness were attained. Effects of molecular architecture of metal soaps were investigated in PEEK (calcium stearate/PEEK and sodium stearate/PEEK). The selected compounds reduced the process viscosity due to the high temperature co-continuous morphology of metal soaps. Unlike the iPP system that incorporates spherical particles, interaction between PEEK and metal soaps resulted in two discrete and co-continuous phases of PEEK and the metal stearates. DMA and melt rheology exhibited that sodium stearate/PEEK composites are stiffer. Effective moduli of secondary metal stearate phase were calculated using different composite theories, which suggested bicontinuous morphology to the metal soaps in PEEK. Use of low molecular weight crystallizable solvents was investigated in reactive systems. Formation of anisotropic reinforcements was evaluated using dimethyl sulfone (DMS) as the crystallizable diluent and diglycidyl ether of bisphenol-A (DGEBA)/m-phenylene diamine (mPDA) material system as the epoxy thermoset. Miscible blends of DMS and DGEBA/mPDA form homogenous mixtures that undergo polymerization induced phase separation, once the DGEBA oligomers react with mPDA. The effect of the competition between the crystallization and phase separation of DMS resulted in nano-wires to micro-scale fiber-like crystals that were generated by adjusting the reaction temperature and DMS concentration.
172

Profiling of Low-Molecular-Weight Carbonyls and Protein Modifications in Flavored Milk

Wölk, Michele, Schröter, Theres, Hoffmann, Ralf, Milkovska-Stamenova, Sanja 13 April 2023 (has links)
Thermal treatments of dairy products favor oxidations, Maillard reactions, and the formation of sugar or lipid oxidation products. Additives including flavorings might enhance these reactions or even induce further reactions. Here we aimed to characterize protein modifications in four flavored milk drinks using samples along the production chain—raw milk, pasteurization, mixing with flavorings, heat treatment, and the commercial product. Therefore, milk samples were analyzed using a bottom up proteomics approach and a combination of data-independent (MSE) and data-dependent acquisition methods (DDA). Twenty-one small carbonylated lipids were identified by shotgun lipidomics triggering 13 protein modifications. Additionally, two Amadori products, 12 advanced glycation end products (AGEs), and 12 oxidation-related modifications were targeted at the protein level. The most common modifications were lactosylation, formylation, and carboxymethylation. The numbers and distribution of modification sites present in raw milk remained stable after pasteurization and mixing with flavorings, while the final heat treatment significantly increased lactosylation and hexosylation in qualitative and quantitative terms. The processing steps did not significantly affect the numbers of AGE-modified, oxidized/carbonylated, and lipid-carbonylated sites in proteins.
173

Subcutaneous Injection Techniques of Anticoagulant Therapies

Morissette, Leah 01 May 2015 (has links)
Subcutaneous anticoagulant medications like Heparin and Low-Molecular Weight Heparin are injections that readily cause bruising, pain, induration, and hematoma formation at the injection site. It is known that these adverse reactions can be correlated to the technique used to administer these medications; however, there is no established technique that reduces bruising, pain, induration, and hematoma formation at the site. Currently, the only protocol for subcutaneous Heparin and Low-Molecular Weight Heparin is that it is to be administered subcutaneously in the abdomen and when using a prefilled syringe, the air bubble should not be removed. The purpose of this study was to identify current nursing practice for the administration of these medications and to compare the results to researched techniques that resulted in less adverse site reactions. A total of 33 participants were recruited. The survey targeted six researched techniques found, after a comprehensive literature review, to have reduced site adverse effects associated with subcutaneous Heparin and Low-Molecular Weight Heparin. After completing the survey, it was found that current practice does not reflect techniques researched to reduce bruising, pain, induration, and hematoma formation at the site. In fact, very few completed one of the six research techniques that were questioned, which included: a two minute application of a cold compress/pack before and/or after the injection, an injection duration lasting 30 seconds, slow removal of the needle over five seconds, application of pressure after the injection for a minimum of 30 seconds, use of a hot pack/compress after the injection, and the use of a3 mL syringe. It was also found that there were inconsistencies in techniques that have been previously established as current protocol for these medications.
174

Relationships between reduced sulfur and dissolved organic matter in prairie pothole wetlands

McAdams, Brandon C. 11 October 2017 (has links)
No description available.
175

HIGH MOLECULAR WEIGHT TEAR PROTEINS AND OCULAR SURFACE MUCINS IN CONTACT LENS-RELATED DRY EYE

Ramamoorthy, Padmapriya 21 October 2011 (has links)
No description available.
176

The Influence of Aromatic Disulfonated Random and Block Copolymers' Molecular Weight, Composition,and Microstructure on the Properties of Proton Exchange Membranes for Fuel Cells

Li, Yanxiang 27 September 2007 (has links)
The purity of the disulfonated monomer, such as 3,3"-disulfonated-4,4"-dichlorodiphenyl sulfone (SDCDPS), was very important for obtaining high molecular weight copolymers and accurate control of the oligomer's molecular weight. A novel method to characterize the purity of disulfonated monomer, SDCDPS, was developed by using UV-visible spectroscopy. This allowed for utiliziation of the crude SDCDPS directly in the copolymerization to save money, energy, and time. Three series of tert-butylphenyl terminated disulfonated poly(arylene ether sulfone) copolymers (BPSH35, 6FSH35, and 6FSH48) with controlled molecular weightsï¼ Mnï¼ , 20 to 50 kg·mol-1, were successfully prepared by the direct copolymerization method. The molecular weight of the copolymer was controlled by a monofunctional monomer tert-butylphenyl, and characterized by the combination of 1H NMR spectra and modified intrinsic viscosity measurements in NMP with 0.05 M LiBr, which was added to suppress the polyelectrolyte effect. The mechanical properties of the membranes, such as the modulus, strength and elongation at break, were improved by increasing the molecular weights, but water uptake and proton conductivities found insensitive to copolymers" molecular weights. Three series of disulfonated poly(arylene ether ketone) random copolymers have been synthesized and comparatively studied, according to their different chemical structures, for use as proton exchange membranes. The copolymers containing more flexible molecular structures had higher water uptake and proton conductivity than the rigid structures at the same ion exchange capacity. This may be due to the more flexible chemical structures being able to form better phase separated morphology and higher hydration levels. A new hydrophobic-hydrophilic multiblock copolymer has been successfully synthesized based on the careful coupling of a fluorine terminated poly(arylene ether ketone) (6FK) hydrophobic oligomer and a phenoxide terminated disulfonated poly(arylene ether sulfone) (BPSH) hydrophilic oligomer. AFM images and the water diffusion coefficient results confirmed that the multiblock copolymer formed better proton transport channels. This multiblock copolymer showed comparable proton conductivity and fuel cell performance to the Nafion® control and had much better proton transport properties than random ketone copolymers under partially hydrated conditions. This suggested that the multiblock copolymers are promising candidates for proton exchange membranes especially for applications at high temperatures and low relative humidity. / Ph. D.
177

Shear and extensional rheology of hydroxypropyl cellulose melt using capillary rheometry

Paradkar, Anant R, Kelly, Adrian L., Coates, Philip D., York, Peter January 2009 (has links)
No / With increasing interest in hot melt extrusion for preparing polymer-drug systems, knowledge of the shear and extensional rheology of polymers is required for the formulation and process design. Shear and extensional rheology of three commercial grades of hydroxypropyl cellulose (HPC) was examined at 140, 145 and 150 degrees C using twin bore capillary rheometry at range of processing rates. The power law model fitted for shear flow behaviour up to shear strain rates of approximately 1000s(-1), above which measured shear viscosities deviated from the power law and surface instabilities were observed in the extrudate, particularly for higher molecular weight grades. Shear thinning index was found to be relatively independent of temperature and molecular weight, whilst the consistency index, indicative of zero shear viscosity increased exponentially with increase in molecular weight. Extensional viscosity of all grades studied was found to decrease with increasing temperature and increasing processing rate. Foaming of the extrudate occurred especially at low temperatures and with the high molecular weight grade. An understanding of the relationships between shear and extensional flows with temperature, processing rate and molecular weight is a useful tool for process design; optimisation and troubleshooting of Hot melt extrusion (HME) of pharmaceutical formulations.
178

Extrapolation des bio-techniques RMN à la caractérisation des produits lourds du pétrole / Extrapolation of NMR techniques from biology to the study of heavy oil compounds

Durand, Emmanuelle 13 November 2009 (has links)
Dans un contexte où la demande énergétique ne cesse de croître et où les réserves pétrolières sont limitées, il est nécessaire de développer des sources énergétiques alternatives ainsi que de ransformer celles existantes afin de satisfaire les besoins croissants notamment dans les secteurs du transport et de la pétrochimie. Un des objectifs de l’IFP est de concevoir et d’améliorer des procédés de raffinages existants afin d’optimiser l’utilisation des ressources conventionnelles tout en les diversifiant afin de produire notamment du carburant à partir des produits lourds du pétrole. L'enjeu des prochaines décennies est de convertir efficacement des bruts lourds en produits légers valorisables tels que l'essence, le kérosène et le gazole. Pour cela, il est indispensable de disposer d'une connaissance précise des produits présents dans la charge, principalement des asphaltènes, afin d'adapter le catalyseur utilisé et obtenir les meilleurs résultats de conversion possibles. L’objectif de la thèse visait à obtenir une meilleure caractérisation physico-chimique des asphaltènes en solution. Le manuscrit décrit une nouvelle application de la technique RMN DOSY (Diffusion Ordered Spectroscopy) à la caractérisation des produits lourds du pétrole. Des asphaltenes de cinq origines différentes ont été analysées sur une large gamme de concentration afin d’étudier leur agrégation en solution. Les résultats révèlent l’existence de deux familles d’agrégats en régime semidilué : une famille diffusant rapidement appelée nanoagrégats et un type d’agrégats diffusant plus lentement nommée macroagrégats dans ce manuscrit. L’influence du solvant a été étudiée sur une charge analysée dans le toluène, le tetra-hydrofurane et le chloroforme. Des informations physiques moyennes sur la taille et la masse moléculaire des nanoagrégats des asphaltènes ont été calculées à partir de leur diffusion en solution. Il a ainsi été possible de mettre en évidence des familles de produits caractérisées par une structure et une masse moléculaire en une seule expérience. Le manuscrit propose également une discussion sur le caractère continental ou/et archipel des asphaltènes. L’hypothèse de départ est basée sur la co-existence des deux types d’asphaltènes avec un caractère archipel (ou continental) plus ou moins marqué suivant l’origine des échantillons / New energy supplies need to be developed to face the growing worldwide energy demand. Heavy oils have attracted attention since their represent an important energy reserve. The problem to deal with during their upgrading is the presence of asphaltenes, representing the heaviest and the most resistant fraction of the crude oil. It is worth getting a better understanding into the physico-chemistry of asphaltenes to develop new catalysts and new conversion processes. The manuscript describes a new application of Diffusion Ordered Spectroscopy (1H-DOSY) NMR experiment. It is evaluated as a potential tool to investigate the physico-chemistry of asphaltenes from five different origins in just one experiment. Asphaltenes were studied over a wide range of concentrations in different solvents to get a deeper insight into their aggregation behaviour. For the first time, two different aggregates were observed in the semi-dilute regime and reported in this manuscript. Average size and molecular weight are estimated from diffusion measurements at infinite dilution. Based on different results, a discussion about continental and archipelago type is also provided. Asphaltenes are expected to be a distribution of the two types of asphaltenes with a more pronounced archipelago (or continental) type depending on the origin of the sample
179

Přenos nabitých a nenabitých částic přes modelové biologické membrány / Transport of charged and neutral particles across the model biomembranes

Parisová, Martina January 2012 (has links)
This work was focused on the preparation of model stabilized phospholipid membranes formed on porous polycarbonate carrier. 1,2-dipalmitoyl-sn-glycero-3-phosphocholin was used for their formation in hydrophilic pores of polycarbonate carrier. For characterization of the formation of phospholipid layers, their changes and a study of transport processes, electrochemical impedance spectroscopy and voltammetry were used. Transport of cadmium and copper ions was studied in the presence and in the absence of ionophore calcimycin which was incorporated into the formed of phospholipid membrane. Because these ions are often bound in complexes with various substances, such as low molecular weight organic acids (LMWOAs), this work was also focused on the transport of copper and cadmium ions across the model phospholipid membranes in the presence of malic acid, citric acid and oxalic acid at different pH. Besides the use of ionophore, some pilot experiments were performed to realize the transfer of copper ions using two peptides, nisin and transportan 10. Formation of phospholipid membranes and the transport processes were characterized by two proposed electric equivalent circuits which correspond to the covered and to the uncovered polycarbobate carrier. Keywords: Phospholipids, Membranes, Ionophore, Peptid....
180

Hvězdicovité polymerní nosiče léčiv pro cílenou dopravu a pH-řízené uvolňování léčiva / Star polymeric carriers of drugs for targeting and pH-dependent release of drugs

Bittner, Matyáš January 2013 (has links)
This diploma thesis brings new data about design, synthesis, physico-chemical characterisation and biological efficacy of the novel star-like HPMA-based conjugates intended for treatment of solid tumors. Recently, many different water-soluble drug delivery systems based on N-(2- hydroxypropyl)methacrylamide (HPMA) copolymers have been described. Here, we report synthesis and physico-chemical characterisation of high molecular weight star-like HPMA- based polymer carriers with low polydispersity prepared by controlled grafting of HPMA copolymers onto PAMAM dendrimer core. With the aim to keep the polydispersity of drug delivery system as low as possible, reversible Addition-Fragmentation Chain Transfer (RAFT) polymerisation was used for HPMA-based polymer precursor preparation. The end groups of the polymer presursors was afterwards used for grafting using carbodidimide condensation reaction or copper free click chemistry on polyamidoamine (PAMAM) dendrimers resulting in a formation of star-like high-molecular-weight (HMW) drug carriers. Described synthetic procedure provided preparation of star-like HMW drug carriers with Mw between 1.105 - 3.105 g/mol and narrow distribution of Mw. The model drug, doxorubicin (Dox), was attached to the hydrazide group containing polymer cariers by pH- sensitive...

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