Dissertations / Theses on the topic 'Nitrogen gas'

Thesis (M.S.)--West Virginia University, 2009.
Title from document title page. Document formatted into pages; contains vii, 40 p. : col. ill. Includes abstract. Includes bibliographical references (p. 39-40).

The diesel engine currently accounts for 32 per cent of the new passenger car sales in Europe. In the US, diesel-power is responsible for 94 per cent of all freight movement. Comparing European Stage III standard petrol and diesel passenger car emissions, diesel NOx emissions are still considered a concern. This thesis investigates the mechanisms by which oxides of nitrogen are formed during diesel combustion. It reviews the current methods of controlling NOx emissions, such as retarding fuel injection timing, exhaust gas re-circulation (EGR), water injection and exhaust after-treatment. Modelling using a phenomenological model, is used to demonstrate the extended Zeldovich mechanism and formation trends, the effects of EGR and the significance of the Zeldovich mechanism rate constants. Modified Zeldovich rate constants are proposed to improve the correlation to measured data. Clearly, EGR is currently the most effective method of reducing NOx emissions from passenger car diesel engines. The way EGR works in suppressing NOx formation is reviewed in detail. Experimentation on a 1.8 litre inline 4-cylinder 4-valve per cylinder DI diesel with a variable nozzle turbine (VNT) turbocharger was used to demonstrate the concept of "additional" EGR on this small automotive engine. "Additional" EGR is the concept whereby a proportion of the EGR is added to the total charge, so that the volumetric efficiency increases as EGR is introduced. By using "additional" EGR, the benefits of lower NOx emissions combined with reduced particulates emissions and improved fuel consumption were clearly demonstrated at two test conditions. The reasons for achieving lower NOx emissions when using a VNT turbocharger and EGR have been explained. Finally, several methods of calculating EGR proportion were used and compared against true mass flow. The use of a CO2 balance was found to be the most accurate method.

Thesis (M.S.)--West Virginia University, 2003.
Title from document title page. Document formatted into pages; contains x, 115 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 101-102).

The kinetics of the reaction of atomic sulfur and nitrogen dioxide have been investigated over the temperature range 298 to 650 K and pressures from 14 - 405 mbar using the laser flash photolysis - resonance fluorescence technique. The overall bimolecular rate expression k (T) = (1.88 ± 0.49) x10-11 exp-(4.14 ± 0.10 kJ mol-1)/RT cm3 molecule-1 s-1 is derived. Ab initio calculations were performed at the CCSD(T)/CBS level of theory and a potential energy surface has been derived. RRKM theory calculations were performed on the system. It is found that an initially formed SNO2 is vibrationally excited and the rate of collisional stabilization is slower than the rate of dissociation to SO + NO products by a factor of 100 - 1000, under the experimental conditions.

The use of Silicon Carbide Field Effect Transistor (SiC-FET) sensors in cyclic operation is a proven way to quantify different gases. The standard workflow involves extracting shape-defining features such as averages and slopes of the sensor signal. This work’s main goal is to verify if frequency modulation can be used to simultaneously quantify Nitric Oxide (NO), Nitrogen Dioxide (NO2) and Ammonia (NH3). Linear models were chosen, namely: Ordinary Least Squares (OLS), Principal Components Regression (PCR), Partial Least Squares Regression (PLSR) and Ridge regression. Results indicate that these models fail to predict concentrations completely for every gas. Analysis indicates that the features are not linear in terms of concentrations. This work is concluded by recommending a few other alternatives before discarding frequency cycling completely: non-parametric models of regression and different frequency regime, namely the use of triangular waves in future experiments.

Nitrogen-selective Carbon Molecular Sieve (CMS) membranes were developed for nitrogen/methane separation. Effects of pyrolysis conditions including pyrolysis temperature protocol and pyrolysis atmosphere were studied for Matrimid® and 6FDA:BPDA-DAM precursors. It was revealed that high pyrolysis temperature is essential to achieve attractive nitrogen/methane selectivity due to the subtle size difference between the two gas penetrants. Detailed study on one of the best performing CMS membranes showed that diffusion selection, more specifically, the entropic factor responsible for diffusion selection provides a significant contribution to the high selectivity. The effect of precursor was studied by considering nine carefully selected polymers. The structures and properties of these polymer precursors were compared and correlated with the separation performance of resulting CMS membranes. The translation of intrinsic CMS transport properties into the hollow fiber morphology was also explored. Substructure collapse and asymmetry lost during pyrolysis were observed, which resulted in significant increases of separation layer thickness and decreases in permeance. Vinyltrimethoxy silane (VTMS)-treatment was applied to polymer hollow fiber before pyrolysis to overcome the problem of substructure collapse. The effects of VTMS-treatment on both the substructure and skin layer are discussed.

The Nitrogen Phosphorus Detector is a sensitive, selective device used in gas chromatography. It responds selectively towards nitrogen and phosphorus containing organic compounds with detection limits in the picogram range. The detector is of great importance for the measurement of trace levels of drugs, pesticides and herbicides in biological matrices and the environment. There is, however, some dispute in the literature regarding the detector's response mechanism. The detector is based on a hydrogen-air diffusion flame. Two electrodes polarise the flame with a potential difference of about 200 V and the current through the flame is measured using an electrometer amplifier. The selectivity of the system relies on the presence of an alkali metal source, usually rubidium. In the presence of nitrogen- and phosphorus-containing organics, C~ and PO· anions are formed, yielding a current which is the measured response. It has been suggested that this selective response arises from a charge transfer reaction between the rubidium excited states and ~ or PO· and P02• radicals. Using an AlGaAs diode laser, the rubidium excited state population can be modulated and the influence on detector current monitored. Rubidium resonance-enhanced ionisation, laser-induced fluorescence and emission spectroscopy have all been used to further probe the response mechanism of the detector. Results have demonstrated that during response the C~ radical concentration increases. In addition the diode laser can modulate the excited state rubidium concentration altering it by a factor of 2. However despite more that doubling the Rubidium excited state concentration no increase in detector response is observed. From these observations it has been concluded that the above mentioned charge transfer reaction plays little if any role in detector response.

On-board hydrogen and syngas production is considered as a transition solution from fossil fuel to hydrogen powered vehicles until problems associated with hydrogen infrastructure, distribution and storage are resolved. A hydrogen- or syngas-rich stream, which substitutes part of the main hydrocarbon fuel, can be produced by supplying diesel fuel in a fuel-reforming reactor, integrated within the exhaust pipe of a diesel engine. The primary aim of this project was to investigate the effects of intake air enrichment with product gas on the performance, combustion and emissions of a diesel engine. The novelty of this study was the utilisation of the dilution effect of the reformate, combined with replacement of part of the hydrocarbon fuel in the engine cylinder by either hydrogen or syngas. The experiments were performed using a fully instrumented, prototype 2.0 litre Ford HSDI diesel engine. The engine was tested in four different operating conditions, representative for light- and medium-duty diesel engines. The product gas was simulated by bottled gases, the composition of which resembled that of typical diesel reformer product gas. In each operating condition, the percentage of the bottled gases and the start of diesel injection were varied in order to find the optimum operating points. The results showed that when the intake air was enriched with hydrogen, smoke and CO emissions decreased at the expense of NOx. Supply of nitrogen-rich combustion air into the engine resulted in a reduction in NOx emissions; nevertheless, this technique had a detrimental effect on smoke and CO emissions. Under low-speed low-load operation, enrichment of the intake air with a mixture of hydrogen and nitrogen led to simultaneous reductions in NOx, smoke and CO emissions. Introduction of a mixture of syngas and nitrogen into the engine resulted in simultaneous reductions in NOx and smoke emissions over a wide range of the engine operating window. Admission of bottled gases into the engine had a negative impact on brake thermal efficiency. Although there are many papers in the literature dealing with the effects of intake air enrichment with separate hydrogen, syngas and nitrogen, no studies were found examining how a mixture composed of hydrogen and nitrogen or syngas and nitrogen would affect a diesel engine. Apart from making a significant contribution to existing knowledge, it is 3 believed that this research work will benefit the development of an engine-reformer system since the product gas is mainly composed of either a mixture of hydrogen and nitrogen or a mixture of syngas and nitrogen.

Los pastos son el hábitat más extenso del mundo, siendo fundamentales para la mitigación del cambio climático. Sin embrago, las predicciones sobre emisiones de gases de efecto invernadero (GEI), ciclo del carbono (C) y del nitrógeno (N), todavía están marcadas por una alta incertidumbre, la cual subyace en gran medida en las interacciones entre suelo y vegetación. La presente tesis investiga cómo la vegetación influye sobre el intercambio de GEI y la dinámica del C y el N, en términos de fenología, estructura, composición y diversidad. Para este fin, se han seleccionado pastos a lo largo de un gradiente climático (desde pastos alpinos del Pirineo hasta dehesas en el suroeste de la Península Ibérica). El intercambio de GEI se determinó combinado medidas continuas (eddy covariance) y discretas (cámaras de suelo). La dinámica del C y el N, se aproximó mediante el contenido de C y N, y el ratio isotópico de 13C y 15N. Los resultados mostraron que la vegetación influyó sobre el intercambio de GEI y la dinámica del C y N a lo largo del gradiente climático y de gestión. En ambientes de montaña la fenología condicionó las interacciones entre intercambio de CO2 y vegetación, en función del estrato altitudinal. En dehesas, la estructura compuesta por árboles y pasto, condicionó las emisiones de CO2 y N2O, siendo importante la especie de árbol. El contenido de C y N, y la discriminación contra 13C y 15N incrementó bajo copa en comparación con el pasto abierto. Dicha estructura determinó la composición de grupos funcionales de plantas, éstos presentando particularidades en la adquisición y uso de C y N. Así mismo, la composición de la vegetación influyó sobre el intercambio de GEI. Las legumbres incrementaron la asimilación neta de CO2 y las emisiones de N2O; la composición de especies influyo sobre la respiración y el intercambio de N2O. La interacción entre cereales y legumbres incrementó la asimilación neta de CO2 en comparación con monocultivos de cereal, como resultado de una mayor asimilación bruta pero no mayor respiración. La inclusión de la vegetación mejoró la comprensión sobre los mecanismos que afectan al intercambio de GEI y la dinámica del C y el N.
Les pastures són l’hàbitat més extens del món, essent fonamentals per a la mitigació del canvi climàtic. Tot i així, les prediccions respecte a les emissions de gasos d’efecte hivernacle (GEH) i cicle del carboni (C) i del nitrogen (N), estan encara marcades per una gran incertesa, la qual recau en bona part en les interaccions entre el sòl i la vegetació. Aquesta tesi investiga com la vegetació influeix sobre el intercanvi de GEH i la dinàmica del C i el N, en termes de fenologia, estructura, composició i diversitat. Per a aquesta finalitat, es van seleccionar pastures al llarg d’un gradient climàtic (des de prats alpins del Pirineu fins a deveses al sud-oest de la Península Ibèrica). El intercanvi de GEH es va determinar mitjançant mesures continues (eddy covariance) i discretes (cambres de sòl). La dinàmica del C i el N, es va aproximar mitjançant el contingut de C i N, i el rati isotòpic de 13C i 15N. Els resultats mostraren que la vegetació va influir sobre el intercanvi de GEH i la dinàmica del C i N al llarg del gradient climàtic i de gestió. En ambients de muntanya la fenologia va condicionar les interacciones entre el intercanvi de CO2 i la vegetació, en funció del estrat altitudinal. A les deveses l’estructura composta per arbres i pastures, va condicionar les emissions de CO2 i N2O, essent important l’espècie d’arbre. El contingut de C i N, i la discriminació contra 13C i 15N va incrementar sota copa en comparació amb la pastura oberta. Aquesta estructura va determinar la composició de grups funcionals de plantes, els quals presentaren particularitats en l’adquisició i ús de C i N. Així mateix, la composició de la vegetació influí sobre el intercanvi de GEH. Les lleguminoses incrementaren l’assimilació neta de CO2 i las emissions de N2O; la composició d’espècies va influir sobre la respiració i el intercanvi de N2O. La interacció entre cereals i lleguminoses incrementà l’assimilació neta de CO2 en comparació amb monocultius de cereal, com a resultat d’una major assimilació bruta però no major respiració. En general, la inclusió de la vegetació va millorar la comprensió sobre els mecanismes que afecten al intercanvi de GEH i la dinàmica del C i el N.
Grasslands are the most widespread habitat in the world, and play a crucial role in climate change mitigation. However, predictions about greenhouse gas (GHG) fluxes, and carbon (C) and nitrogen (N) cycling, are still marked by great uncertainty, which in good part lies on soil – vegetation interactions. Accrdingly, this thesis investigates the role of vegetation, in terms of phenology, structure and diversity, as a driver of GHG exchange, C and N cycling in grasslands along a climatic gradient (mountain grasslands and dehesa ecosystems) and under diffrent management regimes. GHG recording was done combining continuous (eddy covariance) and discrete chamber based measurements. C and N cycling was assessed using C and N content, and 13C and 15N isotope ratios as a proxy. Our results showed that vegetation influenced GHG fluxes and C and N cycling along the climatic gradient and management regimes. In mountain environments, phenology determined interactions between CO2 exchange, vegetation and environmental variables, depending on the elevation belt. In dehesa ecosystems, the tree – open grassland structure drove CO2 and N2O fluxes, with some differences among tree species. Moreover, the different plant functional types, presented marked differences in their C and N acquisition and use strategies. Legumes enhanced net CO2 uptake and N2O emissions; as well as cereal – legume interactions enhanced net CO2 uptake compared to cereal monocultures. Overall, the inclusion of vegetation structure and diversity improved the understanding of mechanisms affecting GHG exchange, and C and N cycling.

Conselho Nacional de Desenvolvimento CientÃfico e TecnolÃgico
To evaluate the gas exchange, the biomass flow, the biomass components before and after grazing and the tillering dynamics in massai grass under increasing nitrogen fertilization levels (control - without nitrogen fertilizer; 400; 800 and 1200 kgâha-1âyear-1) under rotational stocking with sheeps in a completely randomized design with measurements repeated in time, this research was carried out. The level of nitrogen for each treatment was divided into two parcels, the first half applied immediately after the animals leave the paddock and the second half applied in rest period half, according to each level assessed. The rest period was set at approximately 1.5 new leaf blades per tiller, as determined in pre-testing when the starting of the experiment, providing a period of 22, 18, 16 and 13 days for the nitrogen levels of 0.0 - control, 400, 800 and 1200 kgâha-1âyear-1, respectively. The technique of "mob-grazing" was used for the realization of grazing, using groups of animals for rapid defoliation (duration from 7 to 11 hours). With the animals grazing, the sward height was monitored with a ruler until they reach the recommended residual canopy height of approximately 15 cm, corresponding to the residual LAI of approximately 1.5. The variables: stomatal conductance, leaf photosynthesis rate, leaf carbon dioxide concentration, photosynthesis/transpiration ratio, chlorophyll relative index and nitrogen sufficiency index revealed positive linear response to the nitrogen fertilization. The nitrogen level 1200 kgâha- 1 âyear-1 presented increment of 92.3% on leaf photosynthesis rate in relation to the control. The leaf temperature and photosynthesis / conductance ratio were reduced with increasing of N levels. The leaf transpiration and total herbage biomass revealed quadratic response with maximum point with increasing of levels N. The leaf elongation rate was increased with the nitrogen levels and the grazing cycle 4 showed lower value in relation to the others. The culm elongation rate was increased with N levels, however it was not influenced by the grazing cycles. The leaf senescence rates before and after grazing were not influenced by nitrogen and were not altered by the grazing cycles. The leaf appearance rate and phylochron showed increasing and decreasing linear response, respectively, with N levels. The leaf average length revealed quadratic response with maximum point with N levels and grazing cycle 4 showed the lowest value for that variable. For each kg Nâha-1âyear-1 was observed increments of 0.161 and 0.1604 kgâha-1âday-1 for the herbage production and herbage accumulation rates, respectively. There was quadratic response for green forage biomass, green leaf biomass, green culm biomass, forage total density, canopy height and alive/senescent material ratio reaching maximum values (5172.9, 4146.3, 1033.9 kgâha-1âcycle-1; 179.1 kgâha-1âcm-1, 36.8 cm, 4.0, respectively) for nitrogen levels of 896; 933.9; 797; 879.2; 751.4 and 1161 kgâha-1âyear-1, respectively. For such variables was observed differences between the grazing cycles studied. The N levels provided increment to the variables: residual tiller population density, residual total herbage biomass, residual green herbage biomass, senescent herbage biomass, residual total herbage density and residual green herbage density. It was observed quadratic response for residual green stem herbage biomass and residual green stem density, reaching maximum values (1,014.4 kgâha-1âcycle-1 and 67.9 kgâha-1âcm-1, respectively) for the N levels of 881 and 872.1 kgâha-1âyear-1, respectively. It was observed quadratic response for the leaf/culm residual ratio and residual biomass quality index, reaching minimum values (0.75; 23%, respectively) for the nitrogen fertilization levels of 707.6 and 679.3 kgâha-1âyear-1, respectively. The grazing cycles influenced the most variables analysed after grazing, except for the residual green herbage biomass, the residual alive/senescent relation and the residual green herbage density. The tiller appearance rate, survival rate and mortality rate, tiller biomass and vegetative tillers/senescent tillers relation was increased with the nitrogen fertilization levels, with the first two rates and tiller biomass ranging between the evaluation periods. There was quadratic response for tillers flowering rate, vegetative tillers population density and reproductive tillers population density reaching maximum values (0.051 tillersâ100 tillers-1âday-1; 4818 and 35 tillersâm-2, respectively) for nitrogen fertilization levels of 613.5; 993.5 and 623.9 kgâha-1âyear-1, respectively. For the flowering rate and reproductive tillers population density was observed zifferences between the evaluation periods. The nitrogen fertilization promotes positive responses on gas exchange and morphophysiology of massai grass, recomending aplication of this nutrient up to 934 kgâha-1âyear-1. The grazing cycles promote little changes in the morphophysiological traits of massai grass, when a rigorous grazing management is adopted.
Objetivou-se avaliar as trocas gasosas, o fluxo de biomassa, a estrutura e os componentes da biomassa no prà e pÃs-pastejo e a dinÃmica de perfilhamento em capim-massai submetido a crescentes doses de nitrogÃnio (controle - sem nitrogÃnio; 400; 800 e 1200 kgâha-1âano-1) e sob lotaÃÃo rotativa com ovinos, num delineamento inteiramente casualizado com medidas repetidas no tempo. A dose de nitrogÃnio para cada tratamento foi dividida em duas parcelas, sendo a primeira metade aplicada logo apÃs a saÃda dos animais do piquete e a segunda metade aplicada na metade do perÃodo de descanso, de acordo com cada dose avaliada. O perÃodo de descanso adotado foi de aproximadamente 1,5 novas folhas por perfilho, conforme determinaÃÃo em prÃ-ensaio quando do inÃcio da instalaÃÃo do experimento, propiciando um intervalo de 22; 18; 16 e 13 dias para as doses de nitrogÃnio de 0,0 â controle; 400; 800 e 1200 kgâha-1âano-1, respectivamente. A tÃcnica de âmob-grazingâ foi usada para a realizaÃÃo dos pastejos, empregando-se grupos de animais para desfolhaÃÃes rÃpidas (duraÃÃo de 7 a 11 horas). à medida que os animais pastejavam, a altura do pasto foi monitorada com auxÃlio de uma rÃgua, atà que o dossel atingisse a altura residual preconizada de aproximadamente 15 cm, correspondendo ao IAF residual de saÃda dos animais do piquete de aproximadamente 1,5. As variÃveis: condutÃncia estomÃtica, taxa de fotossÃntese foliar, concentraÃÃo interna de CO2, relaÃÃo fotossÃntese/transpiraÃÃo, Ãndice relativo de clorofila e Ãndice de suficiÃncia de nitrogÃnio responderam de forma linear crescente ao incremento nas doses de nitrogÃnio. Verificou-se aumento de 92,3% na taxa de fotossÃntese para a dose de nitrogÃnio de 1200 kgâha-1âano-1 em relaÃÃo à ausÃncia de nitrogÃnio. A temperatura da folha e a relaÃÃo fotossÃntese/condutÃncia foram reduzidas com o aumento nas doses de nitrogÃnio. A adubaÃÃo nitrogenada proporcionou resposta quadrÃtica com ponto de mÃxima sobre a taxa de transpiraÃÃo foliar e produÃÃo de biomassa de forragem total. A taxa de alongamento foliar respondeu crescentemente Ãs doses de nitrogÃnio (N) e o ciclo de pastejo 4 revelou valor inferior em relaÃÃo aos trÃs primeiros. A taxa de alongamento das hastes respondeu de forma linear crescente com as doses de N, porÃm nÃo foi influenciada pelos ciclos de pastejo. As taxas de senescÃncia foliar anterior e posterior nÃo foram influenciadas pela adubaÃÃo nitrogenada, nem tampouco foram alteradas com os ciclos sucessivos de pastejo. A taxa de aparecimento foliar e o filocrono foram influenciados somente pela adubaÃÃo nitrogenada, revelando resposta linear crescente e decrescente, respectivamente, com as doses de N. Constatou-se resposta quadrÃtica com ponto de mÃximo para o comprimento mÃdio das folhas com a elevaÃÃo nas doses de N e o ciclo de pastejo 4 apresentou menor valor para a referida variÃvel. Para cada quilograma de Nâha-1âano-1, observou-se incrementos de 0,161 e 0,1604 kgâha-1âdia-1 na taxa de produÃÃo de forragem e de acÃmulo de forragem, respectivamente. Constatou-se resposta quadrÃtica para as variÃveis: biomassa de forragem verde, de lÃmina foliar verde, de colmo verde, densidade total de forragem, altura do dossel e relaÃÃo material vivo/material morto, alcanÃando valores mÃximos (5172,9; 4146,3; 1033,9 kgâha-1âciclo-1; 179,1 kgâha-1âcm-1; 36,8 cm; 4,0; respectivamente) nas doses de N de 896; 933,9; 797; 879,2; 751,4 e 1161 kgâha-1âano-1, respectivamente. Para tais variÃveis, verificou-se oscilaÃÃo entre os ciclos de pastejo estudados. ElevaÃÃo nas doses de nitrogÃnio proporcionou resposta crescente sobre as variÃveis: densidade populacional de perfilhos residual, biomassa de forragem total residual, de forragem verde residual, de forragem morta residual, densidade total de forragem residual e densidade de forragem verde residual. Verficou-se resposta quadrÃtica para a biomassa de colmo verde residual e densidade de colmo verde residual, alcanÃando valores mÃximos (1.014,4 kgâha-1âciclo-1 e 67,9 kgâha-1âcm-1, respectivamente) nas doses de nitrogÃnio de 881 e 872,1 kg âha-1âano-1, respectivamente. Observou-se resposta quadrÃtica para a relaÃÃo lÃmina foliar/colmo residual e Ãndice de qualidade da biomassa residual, alcanÃando valores mÃnimos (0,75; 23%, respectivamente) nas doses de nitrogÃnio de 707,6 e 679,3 kgâha-1âano-1, respectivamente. Os ciclos de pastejo exerceram alteraÃÃes sobre a maioria das variÃveis analisadas no pÃs-pastejo, exceto para a biomassa de forragem verde residual, relaÃÃo material vivo/material morto residual e densidade de forragem verde residual. As taxas de aparecimento, sobrevivÃncia e mortalidade de perfilhos, biomassa do perfilho e relaÃÃo perfilhos vegetativos/perfilhos mortos responderam crescentemente Ãs doses de nitrogÃnio, com as duas primeiras taxas e a biomassa do perfilho variando entre os perÃodos de avaliaÃÃo. Constatou-se resposta quadrÃtica para a taxa de florescimento de perfilhos, densidade populacional de perfilhos vegetativos e densidade populacional de perfilhos reprodutivos, alcanÃando valores mÃximos (0,051 perfâ100 perf-1âdia-1; 4818 e 35 perfâm-2, respectivamente) nas doses de nitrogÃnio de 613,5; 993,5 e 623,9 kgâha-1âano-1, respectivamente. Para a taxa de florescimento e densidade populacional de perfilhos reprodutivos, verificou-se oscilaÃÃo entre os perÃodos de avaliaÃÃo. A adubaÃÃo nitrogenada proporciona respostas positivas sobre as trocas gasosas e morfofisiologia do capim-massai, podendo-se utilizar uma dose de nitrogÃnio de atà 934 kgâha-1âano-1. Os ciclos de pastejo modificam as caracterÃsticas morfofisiolÃgicas da referida forrageira em pequena magnitude, quando se adota um manejo rigoroso do pastejo.

Durant cette thèse, nous avons préparé par diffusion d'azote dans le niobium et par combustion auto-propagée sous atmosphère d'azote des poudres de nitrure de niobium de type δ-NbNx cubique avec des pourcentages atomiques x azote/niobium différents. Les paramètres de maille a de ces poudres ont été déterminés par diffraction des RX. Leurs températures de transition supraconductrice Tc ont été déterminées par des mesures de magnétisme. La détermination des valeurs exactes de x, a et Tc a permis de mettre en évidence un maximum pour le paramètre de maille et pour la température de transition pour une valeur de x = 0. 98 précisément. Une étude réalisée sur des particules de niobium de taille 100 µm a mis également en évidence la formation successive des phases α-Nb(N), β-Nb2N1±y, γ-Nb4N3±y, δ-NbN1±y ce qui est en total accord avec le diagramme de phases Nb-N référencé dans la littérature. Des expériences à basses pressions (P(N2) = 0. 12–10. 0 MPa) ont été réalisées pour étudier des modes différents de combustion par filtration avec “front concave” et “front plan”. Nous avons montré qu'un front concave se produisait dans un domaine de pression 0. 12−1. 0 MPa alors que dans le domaine 1−10 MPa, le front de combustion était plan, laissant donc présager d'une combustion stable. Dans les expériences à hautes pressions (P(N2) = 48−230 MPa) des conditions expérimentales bien spécifiques ont été choisies afin de limiter les pertes de chaleur. Pour les synthèses, les échantillons ont été entourés par une couche d'isolant de nitrure de bore poreux afin de réduire les pertes de chaleur pour obtenir ainsi une augmentation du coefficient “x” (jusqu'à 1. 015)
This PhD thesis was aimed at obtaining of δ-NbNx powders with various nitrogen/niobium ratio x (both below and above the unity) via reactive diffusion and SHS in nitrogen gas. Lattice parameter a of cubic niobium nitride powders was determined by means of XRD. Their critical temperatures Tc were determined using magnetic measurements. Simultaneous high-accuracy measurements of the x, a and Tc values allowed us to unambiguously reveal the maxima in the a(x) and Tc(x) curves which was found to happen at x = 0. 98. The mechanism of phase formations in the diffusion product with a particle size of about 100 m was investigated. According to EPMA data, it was found to proceed in the following order: Nb → α-Nb(N) → β-Nb2N1±y → γ-Nb4N3±y → δ-NbN1±y that is in agreement with the recent phase diagram. SHS experiments at lower pressures (P(N2) = 0. 12–10. 0 MPa) were aimed at investigation of different combustion modes such as “surface” and “layer-by-layer” modes experimentally and theoretically. Combustion with a concave front (“surface” mode) was found to occur within the pressure range 0. 12–1. 0 MPa while that with a planar front (“layer-by-layer” mode), in the range 1–10 MPa. SHS experiments at high pressures (P(N2) = 48–230 MPa) were mostly oriented on the investigation of influence of different heat conditions. It was shown that upon filtration combustion infiltration of nitrogen gas into the sample body is not the only parameter which limits the extent of nitriding of Nb powder. Gas permeable heat insulation is recommended in order to decrease heat loss from the sample into environment and thus to provide more favorable conditions for the achievement of higher extent of nitriding. Using heat insulation high extent of conversion (x = 1. 015) was obtained at lower pressures than in previous studies

In Anbetracht des Kompromisses zwischen der Erzielung des höchsten Gewinns und der geringsten Umweltbelastung ist ein tiefes Verständnis der ökonomischen Folgen der Stickstoff (N) Düngung erforderlich. Die vorliegende Doktorarbeit liefert umfassende Einblicke in (i) die Auswirkungen des standortspezifischen N-Managements (SSNM) auf die Rentabilität und Risikominderung, (ii) die Auswirkungen von Unsicherheiten und Risikoeinflüssen auf optimale N-Düngergaben und (iii) das Potenzial und die Kosten der Vermeidung von Treibhausgas (THG) Emissionen durch N-Düngereduktion. Ein Modellierungsansatz wurde entwickelt, um die Wirkung von Ertrag und Proteingehalt, Wirtschafts- und Risikoauswirkungen sowie THG-Emissionen auf die N-Düngung zu simulieren. Die Ergebnisse der Arbeit zeigen, dass SSNM die Wirtschaftlichkeit verbessert, indem es eine höhere Weizenqualität und damit Preisprämien erzielt. SSNM reduziert das Risiko, die Backqualität nicht zu erreichen, und es gibt keine wesentlichen Nachteile beim Verlustrisikomanagement im Vergleich zum einheitlichen Management. Preisprämien für eine höhere Weizenqualität bieten Anreize für höhere N-Düngergaben. Prämien verflachen die Gewinnfunktion weiter, was unzureichende Argumente für eine Absenkung des N-Inputs aus der Wirtschaftlichkeitssicht liefert, selbst bei einer hohen Risikoaversion der Landwirte. Eine moderate Reduzierung der mineralischen N-Düngung kann die THG-Emissionen bei moderaten Opportunitätskosten mindern. Die THG-Vermeidung durch N-Düngereduktion in einer bestimmten Region kann unter Berücksichtigung kultur- und ertragszonenspezifischer Ertragswirkungen optimiert werden. Insgesamt liefert diese Arbeit wichtige Erkenntnisse über die Chancen und Nachteile der Anpassung der N-Düngergaben. Darüber hinaus leistet sie einen direkten Beitrag zur Identifizierung von kosten- und risikoeffizienten N-Managementoptionen und bildet die Grundlage für effektive politische Ansätze zur THG-Vermeidung durch selektive N-Düngereduktion.
Considering the tradeoff between achieving the highest profit and causing the lowest environmental impact, there is a need for a profound understanding of the economic consequences of nitrogen (N) fertilizer application. The present doctoral research provides comprehensive insights into (i) effects of site-specific N management (SSNM) on profitability and risk mitigation; (ii) impacts of uncertainties and risk implications on optimal N fertilizer rates; and (iii) potential and costs of mitigating greenhouse gas (GHG) emissions by N fertilizer reduction. A modelling approach was developed to simulate the response of yield, protein, economic and risk implications, and GHG emissions to N fertilizer application. Findings of the thesis show that SSNM improves profitability by achieving higher grain quality, thus, price premiums. SSNM reduces the risk of not reaching the baking grain quality and poses no considerable disadvantage on downside risk management compared to uniform management. Price premiums for higher wheat quality provide incentives for higher N input rates. Premiums further flatten the profit function, giving insufficient arguments for lowering N input from a farm profitability perspective, even in presence of high risk aversion of farmers. Moderate reduction of mineral N fertilizer can mitigate GHG emissions at moderate opportunity costs. GHG mitigation by N fertilizer reduction in a given region can be optimized considering crop and yield-zone-specific yield responses. Overall, this thesis provides important insights on chances and drawbacks of adjusting N fertilizer rates. Moreover, it makes a direct contribution in identifying cost- and risk-efficient N management options and provides a basis for effective policy approaches to reduce GHG emissions by selective N fertilizer reduction.

Thesis (Ph. D.)--West Virginia University, 2005.
Title from document title page. Document formatted into pages; contains xv, 173 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 168-173).

Nitrous oxide (N2O) is a potent greenhouse gas (GHG) which is released naturally into the atmosphere as a by-product of the microbial processes of nitrification and denitrification. Agricultural activities are believed to account for up to 80% of anthropogenic N2O emissions at a global scale; however, these estimates are prone to large uncertainties due to the large temporal and spatial variability associated with flux measurements. This thesis contains five studies which aimed to improve the ability to measure and predict N2O emissions from agricultural activities. A closed loop dynamic chamber was developed using a quantum cascade laser (QCL). This method provided high precision chamber measurements of N2O flux from soils with a detection limit below 4 μg N2O-N m-2 h-1. Using the dynamic chamber method allowed for a detailed investigation of uncertainties in individual measurements including contributions from regression fitting, temperature and pressure. The lack of negative fluxes measured that were outwith the detection limits of the methodology (0.3% of all measurements) highlighted that the uptake of N2O reported in some previous literature is likely to have been the result of detection limits of measurement methods applied. Spatial variability of N2O flux was investigated at the plot, field and farm scale. Fluxes were measured from a grassland field plot before and after a tillage event. These measurements highlighted the large spatially variability present in N2O fluxes from agricultural soils. Fluxes varied by up to three orders of magnitude over distances less than 5 metres after the tillage event. A field scale experiment carried out on grazed grassland investigated relationships between soil properties and N2O flux. This study found that N2O emissions correlated strongly with available nitrogen content in the soil and that animal waste was likely responsible for the spatial variability of N2O flux observed at the field scale. A farm scale inventory of N2O emissions was carried out investigating several large point sources of N2O and emissions from the wider field coverage. The inventory estimates that nitrogen fertiliser application is the single largest N2O source from the livestock farm accounting for 49% of annual emissions.

Abstract In this research, a facilitated transport membrane was developed. The reactive membrane consisted of a carrier entrapped in poly(vinyl alcohol) "PVA" matrix cast on a polysulfone support. PVA was selected to hold the reactive carrier because of its hydrophilicity and compatibility with the carrier. Several reactive amines were examined for their suitability as carrier. Among the amines tested as a carrier for CO₂, diethanolamine "DEA" demonstrates a greater improvement in the permeation of CO₂ as well as selectivity over N₂. DEA is a secondary amine and one of the most commonly used amines for gas treating due to its favourable reaction kinetics with acid gases and because of its stability when regenerated. Initially, pure gas permeation was employed for materials selection and membrane preparation procedures. The effects of process conditions on the membrane performance, which involve carrier concentrations, feed pressures and operating temperatures were examined. Then the effects of membrane thickness and long-term stability tests were conducted. Once the appropriate membrane materials and preparation procedures were established, the next phase of the study involved the determination of the actual separation of CO₂/N₂ mixtures. These experiments were carried out by adjusting the feed gas composition, feed pressures and operating temperature. In general, the results obtained with CO₂/N₂ mixtures were in agreement with those obtained with pure gas permeation experiments. It was found that facilitation is more significant at lower CO₂ partial pressure differential across the membrane. At higher partial pressure differentials, the reactive membrane may no longer serve as a facilitating medium due to the saturation of the reactive part of the membrane. Under such conditions the permeance values and selectivity obtained were simply due to the solubility and diffusivity of the CO₂ and N₂ in the membrane matrix. Since it was not possible to analyze concentration profiles inside the thin membrane experimentally, it was decided to analyze the effects of various parameters through the analytical transport equations. The zwitterion mechanism was used to illustrate the kinetics of the CO₂-DEA systems. The mass transport equations were solved numerically. All relevant physicochemical properties needed to implement the mass transport equations were taken from the literatures. The calculated results support the experimental trends that were observed for the CO₂ permeance as a function of partial pressure differentials and carrier concentrations.

Atmospheric aerosols encapsulate a wide variety of particles with different compositions, sizes and sources of origin. They also directly and indirectly affect climate by their interactions with sunlight, clouds, atmospheric chemical species, and even other suspended particles. To understand the atmospheric aerosol processes and the effects they have in global and regional climate is of utmost importance for the future establishment of environmental regulations and emission policies that affect aerosol precursor compounds in an effective and beneficial manner. In particular, aerosols are known to be formed from emissions from human activities, such as fossil fuel burning, agriculture, or concentrated animal feeding operations (CAFOs). Secondary organic aerosols (SOA) constitute a type of atmospheric aerosols that are formed from the atmospheric oxidation of organic compounds that are released from various sources into the atmosphere. Due to the complexity of the atmosphere and variability of its conditions, the direct study of SOA formation is a challenging task, but the implementation of atmospheric chamber facilities to study aerosol formation and growth under controlled conditions has provided a way to study the formation and growth of SOA. However, chamber experiments cannot study specific reactions or individual compounds from the aerosol formation mechanisms in isolation, they can only provide insight on what is produced and what it is produced from, and under what conditions. Thus, kinetic modeling of the mechanisms of gas-phase atmospheric oxidation of the compounds of interest is used to develop reliable and accurate chemical models that will help have precise estimations and determine the mechanisms by which volatile organic compounds interact to produce aerosol particles. Dimethyl sulfide (DMS), dimethyl disulfide (DMDS) and trimethylamine (TMA) are three relevant atmospheric compounds, due to their emissions from many natural and anthropogenic sources and recent studies on emissions of these compounds from animal waste from CAFOs has triggered the interests on the study of SOA formation from these and other similar compounds. In this study, kinetic modeling of the atmospheric oxidation mechanisms of DMDS, DMS and TMA is used to simulate atmospheric chamber studies of aerosol formation to develop accurate models and help determine the mechanisms of aerosol formation.

The area of vegetable production is growing rapidly world-wide, as are efforts to increase production on existing lands in these labor- and input-intensive systems. Yet information on nutrient losses, greenhouse gas emissions, and input efficiency is lacking. Sustainable intensification of these systems requires knowing how to optimize nutrient and water inputs to improve yields while minimizing negative environmental consequences. This work characterizes soil nitrogen (N) dynamics, nitrate (NO3¯) leaching, greenhouse gas emissions, and crop yield in five diversified vegetable systems spanning a gradient of intensification that is characterized by inputs, tillage and rotational fallow periods. The study systems included a low input organic system (LI), a mechanized, medium scale organic system (CSA), an organic movable high tunnel system (MOV), a conventional system (CONV) and an organic stationary high tunnel system (HT). In a three-year vegetable crop rotation with three systems (LI, HT and CONV), key N loss pathways varied by system; marked N2O and CO2 losses were observed in the LI system and NO3– leaching was greatest in the CONV system. Yield-scaled global warming potential (GWP) was greater in the LI system compared to HT and CONV, driven by greater greenhouse gas flux and lower yields in the LI system. The field data from CONV system were used to calibrate the Root Zone Water Quality Model version 2 (RZWQM2) and HT and LI vegetable systems were used to validate the model. RZWQM2 simulated soil NO3¯-N content reasonably well in crops grown on bare ground and open field (e.g. beet, collard, bean). Despite use of simultaneous heat and water (SHAW) option in RZWQM2 to incorporate the use of plastic mulch, we were not able to successfully simulate NO3¯-N data. The model simulated cumulative N2O emissions from the CONV vegetable system reasonably well, while the model overestimated N2O emissions in HT and LI systems.

The commercial pressure frying has been limited to frying huge amount of products due to its dependence on the amount of moisture released from the food for generating the desired pressure. This study investigated the feasibility of using nitrogen gas as a substitute for steam in the pressure frying system. The effects of various process conditions (source of pressure, frying temperature and pressure) on fried product and frying oil qualities were evaluated. Frying experiments were performed on breaded/battered poultry products including chicken nuggets (homogenous) and chicken fillets (marinated, intact muscle). Efforts were also made to develop rapid methods to determine frying oil quality and discriminate among fresh, marginal and discarded oils using a chemosensory (also known as electronic nose) or Fourier transform infrared spectroscopy (FTIR-ATR). Frying temperature and pressure affected fried food quality. An increase in frying pressure resulted in tender, juicier products with less oil uptake due to high moisture retention. An increase in frying oil temperature resulted in an increased moisture loss, oil uptake resulting in less tender and juicier products. Compared with frying using steam released from food, using nitrogen provided similar or better quality fried products in terms of moisture retention, juiciness and texture. The reused oils from the fryer using nitrogen gas was better in quality than the system using steam as evidenced from the physical, chemical and chemosensory measurements.
Ph. D.

Thesis (M.S.)--West Virginia University, 2006.
Title from document title page. Document formatted into pages; contains x, 107 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 88-90).

River networks act as a link between components of the terrestrial landscape, such as soils and groundwater, with the atmosphere and oceans, and are now believed to contribute significantly to global budgets of carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O). The idea of rivers being an inert conduit for carbon and nitrogen to reach the coast has been challenged recently, with considerable processing of carbon and nitrogen occurring in both the water column and bed sediments in the various aquatic components that make up a river network, including lakes, streams, rivers and estuaries. Although understanding of the cycling of carbon and nitrogen has improved markedly in the last 20 years, there is still much uncertainty regarding the production and emission of greenhouse gases (GHGs) linked to this processing across river catchments and few studies have quantified GHG fluxes from source to sea. Therefore this study aimed to a) understand the spatial and temporal saturations and fluxes of GHGs from both the freshwater River Tay catchment (Scotland) and the River Tay estuary, and b) understand what controls the production of GHGs within both a freshwater lake and across multiple sites in the freshwater river using laboratory incubations of sediment. Hotspots of in-stream production and emission were evident both in the freshwater catchment and the estuary, with significant temporal and spatial variability in saturation and emission (density) for CH4, CO2 and N2O. CH4 emission densities, across the freshwater river sites, ranged from 1720 to 15500 μg C m-2 d-1 with a freshwater catchment wide mean of 4640 μg C m-2 d-1, and in general decreased from upland to lowland sites along the main river stem, with notable peaks of emission in a lowland tributary and at the outflow of a lowland loch. This corresponds well with the main drivers of spatial variability which include allochthonous inputs from gas rich soil waters and in-situ production in fine grained organic rich sediments. CH4 production was observed to be higher in the lowland tributaries (R. Isla 4500 μg C m-2 d- 1) compared to main-stem river sites both in the lowland river (129 μg C m-2 d-1) and upland river which displayed an uptake of CH4 (-1210 μg C m-2 d-1). The main driver of spatial variability in CH4 production rates was the quality of the sediment, as production was higher in fine grained sediments rich in carbon compared to sand and gravels with a low carbon content. CH4 production also varied seasonally, with temperature and seasonal variation in sediment quality as the predominant driving factors. CO2 emission densities across the freshwater catchment ranged from 517 to 2550 mg C m-2 d-1 with a catchment mean flux density of 1500 mg C m-2 d-1. Flux densities on the whole increased along the main river stem from upland sites to lowland sites, with higher fluxes in lowland tributaries. Seasonally, CO2 flux density was highest in late summer and autumn and lowest in winter at most sites, highlighting the importance in seasonal environmental controls such as temperature, light, and substrate availability. Production rates in the sediment increased from upland to lowland sites with highest production rates evident in the lowland tributaries, and in autumn sediment samples. N2O emission density also showed considerable spatial and seasonal variation across the catchment with flux densities ranging from 176 to 1850 μg N m-2 d-1 with a mean flux of 780 μg N m-2 d-1. Mean fluxes were highest in the lowland tributaries and lowest in the upland river with sediment experiments finding similar spatial variation in N2O production. On the whole, in-stream N2O production and emission across the freshwater catchment was driven by increases in nutrient concentration (NO3 -, NH4 +) which in turn was related to the proportion of agricultural landuse. The saturation and emission of GHGs also varied substantially both spatially and temporally in the River Tay estuary, with a mean emission density of 2790 μg CH4-C m-2 d-1, 990 mg CO2-C m-2 d-1 and 162 μg N2O-N m-2 d-1. The spatial variability of GHG concentrations and emission densities in the estuary were predominantly controlled by the balance between lateral inputs (from tidal flushing of surrounding intertidal areas), in-situ microbial production/consumption (both in the water column and bed sediments) and physical mixing/loss processes. Although emission densities of CH4, CO2 and N2O appear low compared to the freshwater river, this is because the estuary is emitting large quantities of gas in the middle and outer estuary, for example net annual emission of N2O increased from 84.7 kg N2O-N yr-1 in the upper freshwater section of the estuary to 888 kg N2O-N yr-1 in the middle estuary section, then decreased to 309 kg N2O-N yr-1 in the saltwater lower estuary. Overall, this study has shown that both dissolved and aerial fluxes of GHGs vary markedly both spatially and temporal from source to sea in a temperate river catchment, with hotspots of in-stream production and emission across the river catchment. The catchment (river, lake and estuary) was a smaller source of CO2, CH4 and N2O emission (total emission and by area) compared to other highly polluted aquatic systems both in the UK and globally.

Thesis (Ph. D.)--Virginia Polytechnic Institute and State University, 1993.
On t.p. "x̳" is subscript. Vita. Abstract. Includes bibliographical references (leaves 179-185). Also available via the Internet.

The initial physiological processes leading to enhanced growth of loblolly pine subsequent to fertilization are not clearly understood. Much of the debate revolves around the temporal response of photosynthesis (Pn) to fertilization or even if Pn increases at all due to enhanced nutrition. This study tracked loblolly pine light-saturated photosynthesis (Asat), dark respiration (Rd), volume, height, basal diameter, and leaf area responses in eight clones to fertilization (112 kg/ha N) over the course of a growing season in the field. Measurements were conducted intensively before and after fertilization in order to track the initial physiological changes prior to any changes in growth in the fertilized seedlings. The results showed that fertilization does increase Pn rates although there was no significant effect on Rd rates during the study. The fertilized seedlings mean Asat rates were significantly higher on three sampling dates and remained higher throughout most of the sampling period. At the end of the growing season, the fertilized seedlings had a 30.5% higher projected crown area than the controls and 48% greater mean volumes. Physiological and growth responses were significantly different among clones with some showing large and others showing little or no response to fertilization. These results support the hypothesis from Gough et al. (2004b) that post-fertilization increases in Pn create extra photoassimilate used in building larger leaf areas. These larger leaf areas contribute to higher canopy photosynthesis levels, which leads to an increase in dry matter production.
Master of Science

Thesis (M.S.)--West Virginia University, 1999.
Title from document title page. Document formatted into pages; contains xii, 120 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 102-107).

Ice recrystallization during cryopreservation results in cell death and decreased cell viabilities due to cellular damage. This is a significant problem particularly in regenerative medicine where decreased cell viabilities post-thaw affect the success of the therapy. Given the success of these therapies to treat various diseases, the development of novel cryprotectants which have the ability to inhibit ice recrystallization during freezing and thawing are urgently required. Current cryoprotectant such as dimethyl sulfoxide, is associated with cytotoxicity in the clinical settings and thus are not optimal cryoprotectants. Our laboratory is interested in the rational synthesis of non-cytotoxic small molecules which possess the property of ice recrystallization inhibition (IRI) activity. Previously, the Ben laboratory has demonstrated that simple monosaccharides possess moderate ice recrystallization inhibition activity and that this activity is linked to hydration. The “compatibility” of the carbohydrate within the three-dimensional hydrogen bonded network of water is inversely proportional to its IRI activity. Hydration has previously been directly linked to the stereochemical relationship of individual hydroxyl groups on the carbohydrate. Additionally, it has been proposed that intramolecular hydrogen bond formation and hydrogen bonding cooperativity has a large effect on the water structure thus impacting hydration. Structure-function work has suggested that the presence of an amine as a hydrogen donor at the endocyclic position within the pyranose ring maybe beneficial to IRI activity. Thus, the first part of this thesis describes the synthesis and IRI activity of D-glucose and D-galactose based azasugars and its analogues. These azasugars have replaced the endocyclic ring oxygen with an amine. These azasugars and their analogues were found to possess moderate to potent IRI activity suggesting that hydrogen bond donation may be important for hydration and thus, IRI activity at the endocyclic ring oxygen. During the development of these azasugars, the Ben laboratory developed carbohydrate-based surfactants and hydrogelators possessing unprecedented IRI activity. A potential use of molecules possessing IRI activity is towards the inhibition of gas hydrate formation. Gas hydrates are ice-like solids containing gases within a highly ordered network of water molecules. These gas hydrates tend to accumulate in oil and gas pipelines posing significant dangers as the build-up of solid material leads to blockages in the pipeline reducing flow. Previous work had demonstrated the use of antifreeze proteins possessing potent IRI activity in inhibiting gas hydrate formation. However, their complex structure limits commercial use. Thus, the second part of the thesis describes the use of the azasugars, carbohydrate-based surfactants and hydrogelators in inhibiting gas hydrate formation. The effectiveness of the small molecules is compared to a commercial inhibitor PVP 10. Some of these small molecules were significantly better inhibitors of gas hydrate formation than the currently utilized inhibitor PVP 10. The low molecular weights of these small molecules, easy synthesis and potency make them excellent alternatives to PVP 10. However it was found that while some of the structural features in the small molecules may be amenable to both activities, it seems that the ability to inhibit ice recrystallization is not a good indicator of a compounds ability to inhibit gas hydrate formation. In a continuing effort to develop novel small molecule IRIs, the Ben laboratory has develop three classes of compounds. These include: carbohydrate-based surfactants and hydrogelators, lysine-based surfactants and truncated C-linked glycopeptides. Structure-function work utilizing these compounds revealed that presence of long alkyl chains, an amide linkage and the presence of an open-alditol chain are all important to IRI activity. However, the surfactant-like nature limits their use in cryopreservation and thus prompted the discovery of phenoxyglycosides as IRI active molecules. The structural features of these recently developed small molecules were combined to generate novel small molecule IRIs which do not resemble surfactants. These novel small molecules included “disaccharides” which possessed an aryl group at the anomeric position of a pyranose ring and an open-alditol chain linked via an amide bond. Additionally, N-cycloalkyl-D-aldonamides and N-phenyl-D-aldonamides were also synthesized. Of these novel small molecules, two very potent IRI active molecules were discovered: a “disaccharide” possessing an aryl group at the anomeric position with the open-alditol chain of D-galactose linked via an amide bond at C3 and N-phenyl-D-arbonamide. Both of these small molecules were assessed for their ability to cryopreserve hematopoietic stem cells. Unfortunately, the additional of these compounds failed to improved percent cell viabilities as compared to DMSO.

Sheep grazing to control weeds during fallow may influence soil C and N and greenhouse gas emissions by consuming crop residue and returning feces and urine to the soil. An experiment was conducted to evaluate the effect of sheep grazing compared to tillage and herbicide application for weed control on soil total C, total N, NH â������-N, and NO â�����-N contents at the 0-120 cm depth from 2009 to 2011 and greenhouse gas (CO â������, N â������O, and CH â������) emissions from May to October, 2010 and 2011 under dryland cropping systems in western Montana. Treatments were three fallow management practices (sheep grazing [GRAZ), herbicide application [CHEM], and tillage [MECH]) and three cropping sequences (continuous alfalfa [CA], continuous spring wheat [CSW], and spring wheatpea/barley hay-fallow [W-P/B-F]). Soil samples were collected with a hydraulic probe after crop harvest and greenhouse gas samples at 3 to 14 d intervals with a static chamber. Soil total C was greater in CSW and W-P/B-F than in CA at 5-30 cm but was greater in CA and CSW than in W-P/B-F at 60-90 cm. Soil total N and NO â�����-N contents were greater in CSW and W-P/B-F than in CA at 5-120 cm. Soil NH â������-N content varied with treatments and years. Soil temperature and water content at 0-15 cm were greater in CHEM with W-P/B-F and GRAZ with CA than in other treatments. Greenhouse gas fluxes peaked immediately following substantial precipitation (>12 mm) and/or N fertilization, regardless of treatments. Total CO â������ flux from May to October was greater in GRAZ with CA but N â������O flux was greater in CHEM and GRAZ with CSW than in other treatments in 2010 and 2011. Total CH ₄ flux was greater in CA than in CSW and W-P/BF in 2011. Net global warming potential and greenhouse gas intensity were greater in CHEM with CSW than in other treatments. Continuous spring wheat increased soil C and N storage and available N at subsurface layers compared to other cropping sequences. Because of higher N â������O emissions and lower C sequestration rate, global warming potential and greenhouse gas intensity increased under continuous spring wheat with herbicide application for weed control.

Atmospheric deposition of nitrogen species represents an additional nutrient source to natural environments, and can alter the nitrogen cycle by increasing nutrient levels beyond the requirements of organisms. In Tampa Bay, atmospheric deposition of dissolved inorganic nitrogen species (DIN) has been found to be the second largest nitrogen source, but little is known about dissolved organic nitrogen species (DON). The research goal was to improve the dry and wet deposition estimates by inclusion of the DON contribution. In the atmospheric chemistry field a standard method to measure DON in atmospheric samples has not been agreed upon. This research proposes the use of the ultraviolet (UV)-photolysis method and presents the optimal settings for its application on atmospheric samples. Using a factorial design scheme, experiments on surrogate nitrogen compounds, typically found in the atmosphere, indicated that DON can be xviii measured with no biases if optimal settings are fixed to be solution pH 2 with a 24-hr irradiance period. DIN species (NH4 +, NO2 -, NO3 -) and DON concentrations were determined in fine (PM2.5) and coarse particles (PM10-2.5) as well as in rainwater samples collected at Tampa Bay. The estimates of wet deposition fluxes for NH4 +, NO3 - and DON were 1.40, 3.18 and 0.34 kg-N ha-1yr-1, respectively. Hourly-measured gas concentrations and 24-hr integrated PM10 concentrations were used in conjunction with a below-cloud scavenging model to explain DIN and DON concentration in rainwater samples. Scavenging of aerosol-phase DON contributed only 0.9 ± 0.2% to rainwater DON concentrations, and therefore gas scavenging should be responsible for 99%. These results confirmed the existence of negative biases in the dry and wet deposition fluxes over Tampa Bay. There is increasing interest in simulating wet deposition fluxes, and the proposed below-cloud scavenging model offers a new computational approach to the problem. It integrates the typical gas and particle collection functions and the concept of the deposition-weighted average concentrations. The model uses mass balance to describe the time-dependent cumulative contribution of all droplets in the rain spectrum to the rainwater concentration, giving predictions closer to experimental values and better estimations than those reported in the literature for similar cases.