Ce mémoire porte sur l’étude de l’ignifugation d’une résine époxyde grâce à l’utilisation de nanoparticules. L’incorporation de Polyhedral Oligomeric Silsesquioxanes (POSS) ou de nanotubes de carbone seuls dans la matrice apporte une amélioration très limitée des propriétés feu. La fonctionnalisation covalente de nanotubes de carbone par des fonctions retardatrices de flamme a été réalisée et caractérisée, mais elle n’augmente pas les performances feu de la matrice chargée en nanotubes de carbone. La combinaison entre un retardateur de flamme phosphoré (APP) et les nanotubes de carbone révèle l’existence d’un effet antagoniste entre ces deux charges. Au contraire, l’utilisation de POSS en combinaison avec l’APP apporte une synergie. L’étude de la dégradation thermique de ces systèmes montre que les interactions entre ces constituants modifient la viscosité de la matrice dégradée. La capture des gaz de dégradation est améliorée dans le cas APP/POSS, ce qui résulte en la création d’une couche protectrice plus tôt qu’avec le système de référence contenant l’APP seul. De plus, la présence de POSS rend possible la création de silicophosphates renforçant le résidu. Au contraire, le résidu du système à base de nanotubes de carbone est très rigide et se fissure durant la combustion, ce qui empêche la bonne formation de la couche protectrice. / This thesis aims at flame-retarding an epoxy resin through the use of nanoparticles. Incorporation of Polyhedral Oligomeric Silsesquioxane (POSS) or carbon nanotubes alone in the matrix provides little enhancement of the reaction to fire. The covalent functionalization of carbon nanotubes by grafting fire-retardant moieties has been carried out and characterized, but it does not enhance the reaction to fire of the epoxy matrix filled with carbon nanotubes. The combination between a phosphorus-based flame-retardant (APP) and carbon nanotubes reveals an antagonistic effect between these two fillers. On the contrary, using POSS in combination with APP provides a synergy. The study of the thermal degradation of these systems shows that the interactions between these fillers modify the viscosity of the degraded matrix. The trapping of degradation gases is enhanced in the case of APP/POSS, which results in the creation of a protective layer earlier than with the reference system containing APP alone. Furthermore, the presence of POSS permits the creation of silicophosphates which reinforce the residue. On the contrary, the residue of the formulation containing carbon nanotubes is excessively stiff and it cracks during combustion, hindering the proper formation of the protective layer.

Typescript (Photocopy). / Digitized by Kansas Correctional Industries

Les protéines de la famille Mep/Amt/Rh sont largement conservées dans l’évolution. Cette famille comprend les facteurs Rhésus dont les antigènes Rh humains sont les membres les plus notoires. Le rôle des protéines de type Mep/Amt/Rh en tant que transporteurs d’ammonium a largement été décrit chez les bactéries, les champignons et les plantes. Néanmoins, leur mécanisme de fonctionnement demeure élusif et la régulation de leur activité a été peu abordée chez les organismes eucaryotes. En utilisant comme modèles de la famille Mep/Amt/Rh les trois transporteurs d’ammonium de la levure Saccharomyces cerevisiae, nous avons tenté de comprendre les mécanismes de fonctionnement et de régulation de cette famille de protéines membranaires. Nous montrons qu’un résidu aspartate, conservé dans la famille Mep/Amt/Rh et situé à proximité d’un vestibule cation-attractif, joue un rôle structural dans la reconnaissance de l’ammonium chez le transporteur Mep2. De plus, un résidu histidine très conservé dans le pore hydrophobe des protéines Mep/Amt/Rh est substitué par un aspartate chez un sous-groupe de transporteurs d’ammonium fongiques. Cette substitution permet de définir deux sous-familles fonctionnelles possédant des propriétés bien distinctes. Nous montrons également que la kinase Npr1 intervient dans la modulation de l’activité intrinsèque des trois protéines Mep qui demeurent inactives mais stables à la membrane plasmique en absence de la kinase. Hormis leur rôle dans le transport d’ammonium en tant que source d’azote, nous montrons que l’activité des protéines Mep est requise pour différentes réponses physiologiques. Une diminution d’entrée d’ammonium en absence des protéines Mep ou de leur régulateur positif Npr1 entraîne une dérépression des gènes soumis à la répression catabolique azotée ainsi qu’un défaut dans le repompage de l’ammonium catabolique excrété durant la croissance en présence d’autres sources azotées. Un rôle supplémentaire de senseur d’ammonium avait été attribué au transporteur Mep2 dans l’induction de la croissance filamenteuse en réponse à une limitation en ammonium. Nous montrons que l’état d’activité de la protéine Mep2 est étroitement lié à sa capacité à induire le développement filamenteux.

The work presented in this dissertation focuses on + 4 NH in marine sediments and attempts to elucidate some of the specific pathways and processes affecting + 4 NH in coastal marine regions. The majority of work was conducted in the Laguna Madre estuary. A major feature of the estuary is the Gulf Intracoastal Waterway (GIWW) connecting the Lower Laguna Madre to Baffin Bay. Establishment of the GIWW has altered the hydrodynamics of the estuary, reduced seagrass coverage and increased sediment mobility resulting in frequent maintenance by the U.S. Army Corp of Engineers. GIWW sediment relocation associated with dredging is investigated to determine potential influence of + 4 NH release during resuspension. GIWW sediments are characterized by extremely high concentrations of porewater and exchangeable + 4 NH as well as reducing ions (millimolar HS-), and significant release hours to days after resuspension was observed during laboratory experiments. Using sediment + 4 NH porewater and exchangeable quantities, release potentials are calculated for a dredging event conducted in 1989 and results indicate that potential release from the dredging event are comparable to monthly inputs from intact GIWW and seagrass sediments. Reducing condition influence on + 4 NH adsorption dynamics was tested through resuspension experiments over a wide range of initial bulk concentrations in laboratory determined redox conditions. Significant increase in + 4 NH adsorption was observed in anoxic conditions. Calculations of the apparent partition coefficient (K*) were determined to be affected as well and implications to diagenetic models is explored. Observations in the laboratory were tested in field monitoring. Analysis of wind measurements established strong potential for interaction with sediments over the collection period. Measurements of water column + 4 NH , total suspended solids, and chlorophyll exhibited highest concentrations and correlation in areas close to the GIWW. Concentration measurements were combined with flux measurements in a model system designed to integrate field observations. Several model cases were considered including and excluding sediment resuspension. Model simulations including sediment resuspension maintained water column concentrations similar to field observations.

The objective of this study was to evaluate the effect of orally administered ammonium chloride (NH4CL) on pH and specific gravity of urine, overall gain, and water consumption in mature wethers on a grower/finisher ration. Obstructive urolithiasis, or urinary calculi, is a common problem in sheep and goat production systems utilizing a high grain diet, particularly one high in magnesium. Maintaining animals on a 70 to 90% concentrate ration is most conducive to the formation of urinary calculi. Boer cross wethers (n = 24) were stratified by body weight and randomly assigned within strata to one of three treatment groups. Wethers were placed on a common diet containing 2% NH4Cl during the three week collection period. Treatment consisted of daily oral dosages of 0g NH4CL (CON), 5.85 g NH4CL (TRT 1), or 13.8g NH4CL (TRT 2). Urine collected from TRT2 tested more acidic on the second and fourth collections before coming back linear constant with both the control (CON) and TRT1 . There was no effect of treatment (P < 0.001) on specific gravity of urine. Weight gain was greater (P < 0.01) in TRT1 (4.15 kg) and TRT2 (4.48 kg) as compared to CON wethers (2.95 kg). Water consumption was the most variable of all investigated objectives; all groups began with a linear increase for the first 4 d. Treatment 2 (P < 0.001) then showed significant increase at collections 2 and 4. Treatment 1 stayed more linear with the control with minimal increases (P < 0.001) occurring at periods of more acidic urine. This study indicates that administration of NA4Cl had minimal effect on urine pH, water consumption, and overall gain, but no effect on specific gravity.

The work presented in this dissertation focuses on + 4 NH in marine sediments and attempts to elucidate some of the specific pathways and processes affecting + 4 NH in coastal marine regions. The majority of work was conducted in the Laguna Madre estuary. A major feature of the estuary is the Gulf Intracoastal Waterway (GIWW) connecting the Lower Laguna Madre to Baffin Bay. Establishment of the GIWW has altered the hydrodynamics of the estuary, reduced seagrass coverage and increased sediment mobility resulting in frequent maintenance by the U.S. Army Corp of Engineers. GIWW sediment relocation associated with dredging is investigated to determine potential influence of + 4 NH release during resuspension. GIWW sediments are characterized by extremely high concentrations of porewater and exchangeable + 4 NH as well as reducing ions (millimolar HS-), and significant release hours to days after resuspension was observed during laboratory experiments. Using sediment + 4 NH porewater and exchangeable quantities, release potentials are calculated for a dredging event conducted in 1989 and results indicate that potential release from the dredging event are comparable to monthly inputs from intact GIWW and seagrass sediments. Reducing condition influence on + 4 NH adsorption dynamics was tested through resuspension experiments over a wide range of initial bulk concentrations in laboratory determined redox conditions. Significant increase in + 4 NH adsorption was observed in anoxic conditions. Calculations of the apparent partition coefficient (K*) were determined to be affected as well and implications to diagenetic models is explored. Observations in the laboratory were tested in field monitoring. Analysis of wind measurements established strong potential for interaction with sediments over the collection period. Measurements of water column + 4 NH , total suspended solids, and chlorophyll exhibited highest concentrations and correlation in areas close to the GIWW. Concentration measurements were combined with flux measurements in a model system designed to integrate field observations. Several model cases were considered including and excluding sediment resuspension. Model simulations including sediment resuspension maintained water column concentrations similar to field observations.

Thèse de doctorat : Sciences et techniques de l'environnement : Paris 12 : 2005. / Titre provenant de l'écran-titre. Pagination : 336 f. Bibliogr. p. 231-245.

No description available.

Ammonium chloride (NH4Cl) has been the primary preventive modality for struvite urolithiasis in goats. This study investigated the effect of continuous and pulse dose NH4Cl therapeutic regimens on urine pH in ten goats. The initial regimen (feed additive) consisted of 0.007% NH4Cl as a feed additive. Following this week long regime, the two treatment regimens were designed as a standard ten goat cross-over design. The first treatment regimen (continuous) consisted of daily administration of a titrated dosage of NH4Cl for ten days, followed by four days without treatment. The third treatment regimen (pulse) used daily administration of a titrated dose of NH4Cl for three consecutive days followed by four days without treatment for three treatment periods. Ammonium chloride dosages were titrated to result in a urine pH of < 6.5 (target level) prior to commencing treatment regimens. Urine pH was evaluated once daily during feed additive regimen and twice daily during the treatment regimens. A Bayesian methodology was used to determine the daily odds ratios for production of target urine pH during treatment regimens. The odds ratios were also calculated between pulse dosages during the pulse regimen. The feed additive regimen did not result in target urine pH within 7 days. Treatment with the continuous regimen resulted in target pH, however, pH returned to >6.5 within five days, (odds ratio 0.23-1.56 at Treatment Time 10). The odds ratios for each pulse period of the pulse dose regimen were 2.20-7.45, 0.41-1.68 and 1.59-5.62 respectively. The results of this study indicate that variability in response to therapy warrants titrating individual dosages of NH4Cl, continuous therapy results in a loss of effectiveness, and pulse dosage is effective in repeatedly producing a urine pH of <6.5.

Thesis (M.S.)--University of Missouri, School of Mines and Metallurgy, 1920. / The entire thesis text is included in file. A.M. Howald determined to be Arthur Mark Howald from "1874-1999 MSM-UMR Alumni Directory." Typescript. Illustrated by author. Title from title screen of thesis/dissertation PDF file (viewed May 18, 2009). Includes bibliographical references.