Predicting contaminant transport pathways in the Caribou-Poker Creek Research Watershed

Thesis (M.S.) University of Alaska Fairbanks, 2002In order to evaluate the impact of natural organic matter (NOM) on drinking water, the hydrology of the Caribou-Poker Creeks Research Watershed (CPCRW) was considered. The CPCRW provided an excellent opportunity to investigate contaminant transport as it relates to hydrology in a well studied, discontinuous permafrost environment. The seasonal variation of organic chemistry of three different water sources (i.e. ground water, artesian spring and stream) was studied during the course of the year 2001. This thesis comprises three chapters, each of which seeks to gain a better understanding of the contaminant transport pathways in a boreal watershed, Caribou Poker Creeks Research Watershed. The hypothesis of Chapter One was that the heavy metal Cadmium (Cd) is strongly correlated to NOM. The objective was to establish the likely sources of cadmium mobility in organic rich soils. Cadmium was selected because of its tendency to be more mobile in soils than other heavy metals. The hypothesis of Chapter Two was as follows; the chemical nature of dissolved organic matter (DOM) changes during the course of a year in a boreal watershed. The objective of this study was to evaluate the seasonal character of DOM in the CPCRW. DOM was characterized using pyrolysis-gas chromatograph/mass spectrometry (Py-GC/MS), as well as ultraviolet absorbance at 254 nanometers (UV254) and dissolved organic carbon (DOC). Finally, Chapter Three had for central hypothesis that water could be traced to its origin through a correlation of NOM fingerprints. NOM was used as a natural tracer. One hypothesis was that the water appearing on the discharge areas (north-facing slopes) was derived from infiltration at higher elevation on recharging area (south-facing slopes). It was also expected to find that surface water in downstream segments could be correlated with an upstream source, and that this relationship would change during the course of the year. The main objective of this thesis was to establish the relationship of NOM type (chemical/physical characteristic) to Cd mobilization.Factors affecting cadmium mobility in a boreal soil -- Seasonal variation in organic matter chemistry in a boreal watershed -- Hydrology of the boreal watershed, Caribou-Poker Creeks Research Watershed

Strain superlattices and macroscale suspension of Graphene induced by corrugated substrates

We investigate the organized formation of strain, ripples and suspended features in macroscopic CVD-prepared graphene sheets transferred onto a corrugated substrate made of an ordered arrays of silica pillars of variable geometries. Depending on the aspect ratio and sharpness of the corrugated array, graphene can conformally coat the surface, partially collapse, or lay, fakir-like, fully suspended between pillars over tens of micrometers. Upon increase of pillar density, ripples in collapsed films display a transition from random oriented pleats emerging from pillars to ripples linking nearest neighboring pillars organized in domains of given orientation. Spatially-resolved Raman spectroscopy, atomic force microscopy and electronic microscopy reveal uniaxial strain domains in the transferred graphene, which are induced and controlled by the geometry. We propose a simple theoretical model to explain the transition between suspended and collapsed graphene. For the arrays with high aspect ratio pillars, graphene membranes stays suspended over macroscopic distances with minimal interaction with pillars tip apex. It offers a platform to tailor stress in graphene layers and open perspectives for electron transport and nanomechanical applications

Conception d'un moteur asynchrone adapté à une double alimentation (réduction des pertes supplémentaires induites par une alimentation de type M.L.I.)

Ce mémoire traite des pertes supplémentaires développées asynchrones de fortes puissances. Le premier chapitre est consacré à la modélisation de l'ensemble machine-convertisseurs en régime sinusoïdal et non sinusoïdal. L'auteur y développe un calcul analytique des diverses inductances des enroulements statoriques et rotoriques en fonction des différents paramètres géométriques de la machine. Il met en évidence quelques caractéristiques offertes par la double alimentation telle que la possibilité de réduire considérablement les pertes fer dans le cas d'une machine à champs rotorique et statorique inverses. Le second chapitre s'intéresse au choix des dimensions des conducteurs et de leur subdivision pour différentes configurations de bobinage ainsi que l'influence de la température sur les pertes supplémentaires. Les expressions analytiques sont calculées à partir d'un modèle monodirectionnel. L'auteur met en évidence pour chaque type d'enroulement et motif d'alimentation l'existence d'une hauteur critique des conducteurs qui minimise les pertes par effet Joule. Le troisième chapitre traite des pertes fer supplémentaires. L'auteur s'appuie sur une approche expérimentale et une modélisation thermique de la machine. L'étude est menée sur une macvhine asynchrone de 4kW équipée au stator de thermocouples. Des essais d'échauffements pour différents motifs d'alimentation ont permis de trouver une loi permettant de prédire les pertes de fer à partir de celles obtenues en régime sinusoïdal en fonction du taux de distorsion et de la fréquence de découpage du signal d'alimentation. Dans le quatrième chapitre l'auteur compare pour une machine connue, les pertes pour différents types de commande M.L.I. L'auteur montre que la commande à E/f=Cte suit le même profil que les pertes en régime sinusoïdal avec une majoration et que celles-ci sont largement inférieures à celles obtenues avec une M.L.I. sinus-triangle ou M.L.I calculée.This memory treats about additional losses developed in high power induction motors. The first chapter is devoted to the modelling of the machine-converters association with sinusoidal and nonsinusoidal wave forms. The author develops an analytical calculation of the different inductances of the stator and rotor windings according to the geometrical parameters of the machine. It underlines some characteristics offered by the double feeding such as the possibility of reducing considerably the iron losses in the case of opposite rotor and stator fields. The second chapter relates to the choice of the dimensions of the wires and of their subdivisions for different configurations of windings and discusses the temperature influence on the additional losses. The analytical expressions are calculated with a one-dimensional model. The author underlines that for each type of winding and current wave form, a critical height of the conductors which minimises the copper losses exists. The third chapter treats on additional iron losses. The author uses an experimental approach and a thermal modelling of the machine. The study is undertaken on an asynchronous machine of 4kW equipped at the stator with thermocouples. Temperature-rise tests for various voltage wave forms made it possible to find a law for predicting the iron losses from those obtained in sinusoidal mode according to the distortion rate and the sampling frequency of the signal. In the fourth chapter the author compares for a known machine, the losses for different type of PWM control. The author shows that the law with E/f=Constant follows the same profile as the losses in sinusoidal mode but with an increase and that they are largely lower than those obtained with a sine-triangle PWM or for a calculated PWM.BELFORT-BU L. FEBVRE (900102102) / SudocSudocFranceF

New expression to calculate quantity of recovered heat in the earth-pipe-air heat-exchanger operating in winter heating mode

A new expression is proposed to calculate the earth-energy of an earth-air-pipe heat exchanger during winter heating for three kinds of soil in France. An analytical model is obtained by using numerical computation developed in Scilab – a free open source software. The authors showed the comparison between their simple analytical model and experimental results. They showed the influence of different parameters to specify the size of the heat exchanger

Secondary calcite crystallization and oxidation processes of granite near the summit of Mt. McKinley, Alaska

Sur la montagne du Denali, Alaska (également connue sous le nom de Mont McKinley), les processus de désagrégation sont dominés par la cristallisation secondaire (calcite) et l’oxydation (vernis), avec une action limitée du gel. Pendant les étés de 2002 et 2003, deux sites d’étude (versants nord et sud d’une face rocheuse) situés à 5 710 m d’altitude sur le Denali ont montré un nombre limité de cycles gel-dégel actuels (30 et 63 cycles, respectivement) ; ces cycles peu fréquents sont semblables à ceux mesurés à l’intérieur des terres de l’Antarctique (46 cycles gel-dégel en 1994). Les conditions d’humidité de la roche ont été influencées par le rayonnement solaire et par la neige soufflée. La neige soufflée et sa fonte ont fourni une humidité abondante à la surface de la roche. Dans la tranche d’altitude de 3 000 à 3 500 m, la neige soufflée est la plus active sur les faces sud et sud-est où la température de la roche est la plus élevée. Le taux de saturation des fissures ou de surfaces poreuses est considéré comme minimal. La cristallisation secondaire et l’oxydation sont régies par l’évaporation de surface, l’apport d’humidité et les propriétés chimiques de la roche. Le paramètre le plus important dans le secteur d’étude est l’apport d’humidité, pour une même roche et un niveau de rayonnement solaire constant. Les particules de neige sont déplacées par les vents, apportant l’humidité à la surface de la roche où la neige s’entasse, principalement aux pieds des falaises et aux cols. La cristallisation secondaire et l’oxydation se sont ainsi plus développées aux pieds des falaises et au niveau des cols exposés au sud et au sud-est où la température est la plus élevée.On the mountain of Denali, Alaska (also known as Mt. McKinley), weathering processes are dominated by secondary crystallization (calcite) and oxidation (varnish), but frost action is limited. During the summer of 2002-2003, two study sites (a north-facing rock wall and a south-facing rock wall) on Denali showed limited numbers of effective freeze-thaw cycles (30 and 63 cycles, respectively) ; this infrequent cycling is similar to that found at sites in inland Antarctica (46 effective freeze-thaw cycles in 1994). Rock moisture conditions were influenced by solar radiation and snow blowing.  Blowing snow and subsequent melting provided abundant moisture to the rock wall. Elevation between 3000 and 3500 m experience the most active snow blowing, at the south to southeast facing rock wall. The saturation rate of the pore space or surface cracks is considered minimal. The secondary crystallization (calcite) and the varnish are controlled by surface evaporation, moisture supply, and the chemical properties of the rock. The most important control parameter in this study area was moisture availability, given the same bedrock and level of solar radiation. Snow particles are moved by jet stream winds, bringing moisture to the rock surface, where it collects mainly in lower cliffs and cols. Thus the secondary calcite crystallization and varnish developed severely in the lower cliffs and cols of high temperature at south-south west facing walls

Strain Superlattices and Macroscale Suspension of Graphene Induced by Corrugated Substrates

We investigate the organized formation of strain, ripples, and suspended features in macroscopic graphene sheets transferred onto corrugated substrates made of an ordered array of silica pillars with variable geometries. Depending on the pitch and sharpness of the corrugated array, graphene can conformally coat the surface, partially collapse, or lie fully suspended between pillars in a fakir-like fashion over tens of micrometers. With increasing pillar density, ripples in collapsed films display a transition from random oriented pleats emerging from pillars to organized domains of parallel ripples linking pillars, eventually leading to suspended tent-like features. Spatially resolved Raman spectroscopy, atomic force microscopy, and electronic microscopy reveal uniaxial strain domains in the transferred graphene, which are induced and controlled by the geometry. We propose a simple theoretical model to explain the structural transition between fully suspended and collapsed graphene. For the arrays of high density pillars, graphene membranes stay suspended over macroscopic distances with minimal interaction with the pillars’ apexes. It offers a platform to tailor stress in graphene layers and opens perspectives for electron transport and nanomechanical applications