Previously disturbed and regenerating forests make up a significant proportion of the North American land area, and therefore play an important role in the exchanges of heat and trace gases between the terrestrial biosphere and the atmosphere. Assessment of local to global variability in CO2 exchanges by forests requires a combination of CO2 measurements made by eddy covariance (EC), field measurements, remote sensing data, and ecosystem models. The integration of these is problematic because of a mis-match in scale between measurement techniques. Despite the importance of regenerating forests on the global carbon balance, the processes affecting the carbon cycle within these forests is not well understood. Airborne scanning light detection and ranging (lidar) instruments provide new opportunities to examine three-dimensional forest characteristics from the level of individual trees to ecosystems and beyond. Lidar is therefore an effective link between plot measurements, eddy covariance, and low resolution remote sensing pixels. This thesis dissertation presents new science on the use of airborne lidar for evaluating remote sensing products within heterogeneous and previously clearcut ecosystems. The goals of this thesis were to first understand the processes affecting CO2 exchanges within a previously disturbed boreal jack pine chronosequence located in Saskatchewan, Canada and then to apply this understanding to evaluate low resolution remote sensing data products from the Moderate Resolution Imaging Spectroradiometer (MODIS) using airborne lidar. The first objective of this dissertation examined the factors that control light use efficiency (LUE) within the jack pine chronosequence during dry and wet years. The second objective examined the importance of vegetation structure and ground surface elevation on CO2 fluxes within a mature jack pine forest. The third objective developed and tested a simple model of lidar fractional cover and related this to the fraction of photosynthetically active radiation absorbed by the canopy (fPAR). This was then used to evaluate the MODIS fPAR product across the lower part of a watershed. Finally, the fourth objective was to model gross primary production (GPP) from airborne lidar. Lidar estimates of GPP were then compared with those from the EC system at the jack pine chronosequence and with the MODIS GPP (Collection 5) product. / Thesis (Ph.D, Geography) -- Queen's University, 2008-08-22 08:50:51.44

No description available.

Mercury (Hg) has been recognized as a contaminant of global concern due to its high toxicity, as well as its ability to mobilize over long distances and biomagnify up through the food chain. The discovery of polar springtime atmospheric mercury depletion events (AMDEs) in the 1990s provides a new mechanism for enhanced atmospheric Hg deposition to the surface environment in the Arctic, yet questions remain on the process leading to AMDEs and the net contribution of AMDEs to Hg loadings to the Arctic marine ecosystem. Here we report the first systematic study of AMDEs over the open ocean conducted in the Amundsen Gulf flaw lead system from February to July 2008. A total of 31 AMDEs were observed which showed clear dependence on local sea ice environment and meteorological conditions. Enhanced concentrations of dissolved gaseous mercury were also measured in both under ice and open water conditions. Our results confirm that the sea ice environment plays a large role in Hg dynamics in the Arctic Ocean.

No description available.

Traditionally, agricultural nitrous oxide (N₂O) emission of New Zealand has been measured using chambers or lysimeters, and micrometeorological flux measurement experiments have been very few. Since micrometerological flux measurement systems have the advantage of measuring spatially integrated flux values for longer time periods compared to measurements made using chambers, development and verification of such a system was needed for New Zealand's agro-meteorological conditions. In this study, efficacy of such a combined flux gradient (FG) - eddy covariance (EC) micrometeorological flux measurement system is verified by continuously measuring N₂O fluxes from some control and mitigated agricultural plots of New Zealand. The control fields had natural N₂O emission, whereas, the mitigated plots were treated with chemicals to reduce N₂O emission. In this combined FG-EC method, the turbulent eddy diffusivities were estimated using the Monin-Obukhov (M-O) similarity theory based parameterization (where diffusion velocity `dhp' was used) and a thermal approach (where eddy diffusivity `kht' was used) from the EC measurements. These transfer coefficients (kht and dhp) along with the measured N₂O concentration differences were then fitted to the traditional FG equation to compute final flux values. As the primary objective of this study, measured fluxes from two different seasons and from two approaches were compared for consistency and then verified against published results. Under this wider objective of verification of the FG-EC micrometeorological method of N₂O flux estimation, this research thesis addresses three key issues: (i) assessment of error propagation in the measured flux through the eddy diffusivity - to understand the random error dynamics of the system and to estimate precision of the overall method, (ii) quantification and separation of N₂O source area emission rates from adjacent plots - to identify the contribution of an individual plot to the measured flux when multi-plot fluxes were measured from sources with different biogenic characters, and (iii) quantification of the effect of animal grazing and mitigation on the measured flux and actual emission rate of N₂O - to assess robustness of the FG-EC micrometeorological system. As a fourth objective of this study, (iv) new scaling properties of a turbulence surface layer model of a convective atmosphere is investigated as an alternative to the standard M-O similarity theory, as significant questioning of the M-O theory has been reported in some recent publications. Results from the verification experiment showed that the daily measured flux values obtained from this combined micrometeorlogical system for control plots varied between 0-191.9 and 0-491.8 gN₂O-N.ha⁻¹.day⁻¹ for autumn and spring experiments, respectively, for the parameterization method. Similarly, the daily mean flux values were found to be 10.9 ± 0.98 and 11.7 ± 0.57 gN₂O-N.ha⁻¹.day⁻¹ for the autumn and spring seasons, respectively. All these values were found to be of the same order of previously reported values in the literature and found to verifying that this FG-EC system works well under a range of meteorological conditions within a defined error range. Therefore, when the propagated random error was computed in the final flux value using kht and dhp, the mean relative error in kht was found to be higher than the mean relative error in dhp, irrespective of stability. From a Monte-Carlo type simulation of the random error, it was found that the maximum error can be up to 80% for kht irrespective of stability, and 49% and 35% for dhp respectively for stable (1/L ≥ 0, where L is Obukhov length) and unstable (1/L < 0) atmosphere. Errors in the concentration differences were estimated based on the minimum resolvable estimates from the gas analyzer and the associated random errors were found to be 6% and 8% for unstable and stable conditions. Finally, the total mean random error in the N2Oflux values was found to be approximately of the order of 9% and 12% for the parameterization method for unstable and stable conditions, respectively, and 16.5% for the thermal method, irrespective of stability. Objective (ii) of this research was addressed by developing a `footprint fraction' based inverse footprint method. Results of the footprint analysis method were assessed, first, by comparing footprint fractions obtained from both an analytical footprint model and a `forward' simulation of a backward Lagrangian stochastic (bLs) model; and second, by comparing the source area emission rates of a control plot obtained from the footprint analysis method and from the `backward' simulation of the bLs model. It was observed that the analytical footprint fractions were realistic as they compared well with the values obtain from the bLs model. The actual emission rates were found to be on average 2.1% higher than the measured flux values for the control plots. On average 4.3% of the measured fluxes were found to be contributed by source areas outside of the field domain. Again, the proposed footprint method of emission rate estimation was found to work well under a wider range of atmospheric stability, as the inverse footprint model and bLs model based emission rates were found to correlate well (0.70 and 0.61 for autumn and spring, respectively) with a 99% statistical significance. Similarly when the effect of grazing on the N₂O fluxes was considered, a 90% enhancement in the flux values was observed after grazing, followed by a decreasing trend in fluxes. However, contrary to existing knowledge of mitigation of N₂O flux by an inhibitor, this study found no statistically significant effect of mitigation in the pastoral emission of N₂O. Error accumulation, lesser soil N₂O production potential and/or inefficiency of the FG-EC method was conjectured to be reason/s for such discrepancy and some alternative convective boundary layer turbulence scaling was tested. Separate field measurement data, including the vertical profile measurements of the convective boundary layer and sonic anemometer measurements within the surface layer were used for this purpose. The spectral analysis of the vertical wind component, temperature and heat flux revealed that this new model of the convective boundary layer, which explains atmospheric boundary layer turbulence in terms of some nonlocal parameters, is more suitable than the traditional Monin-Obukhov similarity theory based model of atmospheric turbulence where the atmospheric flow properties are local. Therefore, it can be concluded that this new model of turbulence might provide the framework for a newer model of flux estimation in future. Overall, the FG-EC model of N₂O flux estimation method seems to work well within a certain error range. However, more field applications of this FG-EC method are needed for different agro-meteorological conditions of New Zealand before this method is accepted as a standard method of flux estimation, particularly, inefficiency in detecting the effect of mitigation should be tested. Development of an alternative flux gradient model which includes nonlocal atmospheric surface parameters might also be considered as a future research objective.

This dissertation examines the response of piezoelectric material strain to electron flux influence. A plate of PZT5h is prepared as the specimen. The positive electrode is removed, and the negative electrode is connected to a power amplifier. Sixteen strain gages are attached as the strain sensor. The specimen is placed in a vacuum chamber, then the positive side is illuminated by electron beam. The characteristic of the static strain response is predicted by deriving the equation strain/deflection of the plate. Two methods are used, the Electro-Mechanical Equations and numerical analysis using Finite Element Method. The settings of the electron gun system (energy and emission current), along with the electric potential of the negative electrode (back-pressure), are varied to examine piezoelectric material responses under various conditions. Several material characteristics are examined: current flow to and from the material, time response of material strain, charge and strain distribution, and blooming. Results from these experiments suggest several conditions control the strain development in piezoelectric material. The current flow and strain on the material is stable if the backpressure voltage is positive. As a comparison, the current flow is small and the strain drifts down if the backpressure voltage is significantly negative. The material needs only 1 second to follow a positive step in backpressure voltage, but needs almost 1 minute to respond to a negative step backpressure change. This phenomenon is a result of secondary electron emission change and the energy transfer from the primary electrons to the local electrons on the material. The time needed to achieve steady state condition is also a dependent of emission current. After a period of time the primary electron incidence induces strain throughout the 7.5-cm-by-5-cm plate despite the fact that the beam diameter is only 1 cm2. One possibility is blooming due to electron movement under intense electric fields in the dielectric material.

The work explains how the dynamics of the release of water vapors from flux during the Control Atmosphere Brazing influences the process conditions important for the quality of the brazed product. The process involves sequential events such as continuous ramp-up heating, flux and filler melting, reactive flow, isothermal dwell and rapid quench solidification performed under the controlled atmosphere. During this complex process effluents are released. Some effluents are detrimental for the product quality (water vapor) and some are harmful for the environment (HF). We selected to study water vapor emissions with an objective to quantify these emissions and to consider their influence on the manufacturing process. Experiments were conducted using different fluxes. Findings are presented to compare the vapors released in each case. The objective is not necessarily to develop a metric for sustainability, but to understand the kinetics of an effluent release. A simple predictive model has been devised to approximate experimental data behavior. The data from the TGA analysis obtained from other sources, and the dew point temperature history from the controlled atmosphere brazing experiments performed in course of this work, have been used for the purpose of comparison and analysis.

This thesis extends the work of Crimmins (1995) on the control of glycolytic flux in yeast by the enzymes 6-phosphofructo-1-kinase and pyruvate kinase (Pyk1p). This study also examines the influence of Pf1kp and Pyk1p upon yeast resistance to the weak acid preservative, benzoic acid. In <I>Saccharomyces cerevisiae</I>, Pyk1p is encoded by <I>PYK1</I>, and the α and β subunits of Pf1kp are encoded by <I>PFK1</I> and <I>PFK2</I>, respectively. To test the influence of these genes upon glycolytic control, an isogenic set of <I>S. cerevisiae</I> mutants were utilised in which <I>PYK1, PFK1</I> and <I>PFK2</I> expression is dependent on the <I>PGK1</I> promoter. Increased Pf1k levels had little effect upon rates of glucose utilisation or ethanol production during fermentative growth. However, overexpressing Pyk1p resulted in an increased growth rate and an increase in glycolytic flux. This suggests that Pyk1p, but not Pf1kp, exerts some degree of control over the glycolytic flux under these conditions. The effects of reducing Pf1kp and Pyk1p levels were also studied by placing <I>PYK1, PFK1</I> and <I>PFK2</I> under the control of the weak <I>PGK1Δuas</I> promoter. The double Pf1kp mutant showed no significant changes in doubling time, ethanol production or glucose consumption. However, a mutant with a 3-fold reduction ion Pyk1p levels displayed slower growth rates and reduced glycolytic flux. In addition, there was an imbalance in the carbon flow in this mutant, with reductions in ethanol and glycerol production evident, along with increased TCA cycle activity. Hence, while Pf1kp levels did not affect cell physiology significantly under the conditions studied, reduced Pyk1p levels seemed to disturb glycolytic flux and carbon flow. Decreased Pf1kp levels caused an increase in the sensitivity of yeast cells to benzoate, whereas the Pyk1p mutant was not affected. This confirmed that benzoic acid specifically inhibits Pf1kp rather than glycolysis in general.

Dans le monde du Web, on retrouve les formats RSS et Atom (feeds) qui sont, sans doute, les formats XML les plus populaires et les plus utilisés. Ces formats permettent aux, entre autres, communautés Web, industriels, et services web de publier et d'échanger des documents XML. En outre, ils permettent à un utilisateur de consulter librement des données/informations sans avoir à basculer d'un site à un autre, et cela à l'aide d'applications logicielles. Dans ce cas, l'utilisateur enregistre ses fournisseurs de flux favoris, chaque fournisseur diffuse la liste des nouveaux éléments qui ont été modifiés depuis le dernier téléchargement. Cependant, l'enregistrement d'un certain nombre de sources de flux dans un agrégateur de flux engendre à la fois des problèmes d'hétérogénéité (à cause des différences structurelles et de contenu) et des problèmes de surcharges d'information. Par ailleurs, aucun des agrégateurs de flux existants n'offre une approche qui intègre (ou fusionne) les flux en tenant compte de leurs similarités, du contexte de l'utilisateur et de ses préférences. Dans cette thèse, nous proposons un framework formel qui permet de traiter l'hétérogénéité, l'intégration et l'interrogation des flux d'actualités. Ce framework est fondé sur une représentation arborescente d'un flux et possède trois éléments principaux qui sont les suivants: comparateur de flux, intégrateur de flux, et processeur de requêtes. Le comparateur de flux permet de mesurer le degré de similarité entre deux éléments/flux en utilisant une base de connaissance intégrant une approche ascendante et progressive. Nous proposons une mesure de similarité à base de concept capable de calculer la similarité entre les flux selon le nombre de leurs concepts communs (et différents) et leurs proximités sémantiques. Nous montrons également comment définir et identifier la relation exclusive entre deux textes ou éléments. L'intégrateur de flux permet de fusionner plusieurs flux provenant de différentes sources tout en tenant compte du contexte de l'utilisateur. Nous montrons dans notre étude comment représenter le contexte d'utilisateur ainsi que ses préférences. Nous fournissons un ensemble prédéfini de règles de fusion qui peuvent être enrichies et adaptées par chaque utilisateur. Quant au processeur de requêtes, il se base sur une étude formelle et plus précisément sur une algèbre dédiée à la fusion des flux continus d'actualités que nous proposons ici. Les opérateurs proposés dans cette algèbre sont aidés par des fonctions à base de similarité. Nous catégorisons les opérateurs de flux selon trois catégories: opérateurs d'extraction, opérateurs ensemblistes et opérateur de fusion. Nous montrons que l'opérateur de fusion généralise l'opération de jointure et les opérateurs ensemblistes. Nous fournissons également un ensemble de règles de réécriture et d'équivalence de requêtes pour la simplification et l'optimisation des requêtes. Enfin, nous présentons un prototype nommé "Easy RSS Manager" (EasyRSSManager). Ce prototype est un lecteur sémantique de flux et un composant sémantique pour l'interrogation des fenêtres de flux. EasyRSSManager a été utilisé pour valider, démontrer et tester la faisabilité des différentes propositions de notre étude. En particulier, nous avons testé la complexité en temps et la pertinence de nos approches en utilisant à la fois des données réelles et syntaxiques.

Mercury (Hg) has been recognized as a contaminant of global concern due to its high toxicity, as well as its ability to mobilize over long distances and biomagnify up through the food chain. The discovery of polar springtime atmospheric mercury depletion events (AMDEs) in the 1990s provides a new mechanism for enhanced atmospheric Hg deposition to the surface environment in the Arctic, yet questions remain on the process leading to AMDEs and the net contribution of AMDEs to Hg loadings to the Arctic marine ecosystem. Here we report the first systematic study of AMDEs over the open ocean conducted in the Amundsen Gulf flaw lead system from February to July 2008. A total of 31 AMDEs were observed which showed clear dependence on local sea ice environment and meteorological conditions. Enhanced concentrations of dissolved gaseous mercury were also measured in both under ice and open water conditions. Our results confirm that the sea ice environment plays a large role in Hg dynamics in the Arctic Ocean.