Résumé : L’Arctique est particulièrement sensible aux changements climatiques et a récemment subi des modifications majeures incluant une diminution dramatique de l’extension de la glace de mer. Notre capacité́ à modéliser et à potentiellement réduire les changements climatiques est limitée, en partie, par les incertitudes associées au forçage radiatif induit par les effets directs et indirects des aérosols, qui dépendent de notre compréhension des processus impliquant les nuages et les aérosols. La charge des aérosols est caractérisée par l’épaisseur optique des aérosols (AOD) qui est le paramètre radiatif extensif le plus important et l’indicateur régional du comportement des aérosols sans doute le plus décisif. Une de nos lacunes majeures dans la compréhension des aérosols arctiques est leur comportement durant l’hiver polaire. Cela est principalement dû au manque de mesures nocturnes d’AOD. Dans ce travail, on utilise des instruments (lidar et photomètre stellaire) installés en Arctique pour mesurer, respectivement, les profils verticaux des aérosols et une valeur intégrée dans la colonne (AOD) de ces profils. En outre, les données d’un lidar spatial (CALIOP) sont utilisées pour fournir un contexte pan-arctique et des statistiques saisonnières pour supporter les mesures au sol. Ces dernières ont été obtenues aux stations arctiques d’Eureka (80◦ N, 86◦ W) et de Ny Ålesund (79◦ N, 12◦ E) durant les hivers polaires de 2010-2011 et 2011-2012. L’importance physique des pe- tites variations d’amplitude de l’AOD est typique de l’hiver polaire en Arctique, mais suppose une vérification pour s’assurer que des artefacts ne contribuent pas à ces variations (par exemple un masque de nuage insuffisant). Une analyse des processus basée sur des événements (avec une résolution temporelle ≈ une minute) est essentielle pour s’assurer que les paramètres optiques et microphysiques extensifs (grossiers) et intensifs (par particules) sont cohérents et physiquement conformes. La synergie photomètre stellaire-lidar nous permet de caractériser plusieurs événements distincts au cours des périodes de mesures, en particulier : des aérosols, des cristaux de glace, des nuages fins et des nuages polaires stratosphériques (PSC). Dans l’ensemble, les modes fin (<1μm) et grossier (>1μm) de l’AOD obtenus par photométrie stellaire (τ[indice inférieur f] et τ[indice inférieur c]) sont cohérents avec leurs analogues produits à partir des profils intégrés du lidar. Cependant certaines inconsistances causées par des facteurs instrumentaux et environnementaux ont aussi été trouvées. La division de l’AOD du photomètre stellaire τ[indice inférieur f] et τ[indice inférieur c] a été davantage exploitée afin d’éliminer les épaisseurs optiques du mode grossier (le filtrage spectral de nuages) et, par la suite, de comparer τ[indice inférieur]f avec les AODs obtenues par le filtrage de nuages traditionnel (temporel). Alors que les filtrages temporel et spectral des nuages des cas étudiés au niveau des processus ont conduit à des résultats bons à modérés en termes de cohérence entre les données filtrées spectralement et temporellement (les épaisseurs optiques des photomètres stellaires et lidars étant toutes deux filtrées temporellement), les résultats saisonniers semblent être encore contaminés par les nuages. En imposant un accord en utilisant un second filtre, plus restrictif, avec un critère de ciel clair ("enveloppe minimale du nuage"), les valeurs saisonnières moyennes obtenues étaient de 0.08 à Eureka et 0.04 à Ny Ålesund durant l’hiver 2010-2011. En 2011-2012, ces valeurs étaient, respectivement, de 0.12 et 0.09. En revanche les valeurs d’épaisseur optique de CALIOP (estimées entre 0 et 8 km) ont légèrement diminué de 2010-2011 à 2011-2012 (0.04 vs. 0.03). // Abstract : The Arctic region is particularly sensitive to climate change and has recently undergone major alterations including a dramatic decrease of sea-ice extent. Our ability to model and potentially mitigate climate change is limited, in part, by the uncertainties associated with radiative forcing due to direct and indirect aerosol effects which in turn are dependent on our understanding of aerosol and cloud processes. Aerosol loading can be characterized by aerosol optical depth (AOD) which is the most important (extensive or bulk) aerosol radiative parameter and arguably the most important regional indicator of aerosol behavior. One of the most important shortcomings in our understanding of Arctic aerosols is their behavior during the Polar winter. A major reason for this is the lack of night-time AOD measurements. In this work we use lidar and starphotometry instruments in the Arctic to obtain vertically resolved aerosol profiles and column integrated representations of those profiles (AODs) respectively. In addition, data from a space-borne lidar (CALIOP) is used to provide a pan-Arctic context and seasonal statistics in support of ground based measurements. The latter were obtained at the Eureka (80 ◦ N, 86 ◦ W) and Ny Ålesund (79 ◦ N, 12 ◦ E) high Arctic stations during the Polar Winters of 2010-11 and 2011-12. The physical significance of the variation of the small-amplitude AODs that are typical of the Arctic Polar Winter, requires verification to ensure that artifactual contributions (such as incomplete cloud screening) do not contribute to these variations. A process-level event-based analysis (with a time resolution of ≈ minutes), is essential to ensure that extracted extensive (bulk) and intensive (per particle) optical and microphysical indicators are coherent and physically consistent. Using the starphotometry-lidar synergy we characterized several distinct events throughout the measurement period: these included aerosol, ice crystal, thin cloud and polar stratospheric cloud (PSC) events. In general fine (<1 μm ) and coarse (>1 μm )modeAODs from starphotometry ( τ[subscript f] and τ [subscript c] ) were coherent with their lidar analogues produced from integrated profiles : however several inconsistencies related to instrumental and environmental factors were also found. The division of starphotometer AODs into τ[subscript ]f and τ [subscript c] components was further exploited to eliminate coarse mode cloud optical depths (spectral cloud screening) and subsequently compare τ [subscript f] with cloud-screened AODs using a traditional (temporal based) approach. While temporal and spectral cloud screening case studies at process level resolutions yielded good to moderate results in terms of the coherence between spectrally and temporally cloud screened data (both temporally screened starphotometer and lidar optical depths), seasonal results apparently still contained cloud contaminated data. Forcing an agreement using a more restrictive, second-pass, clear sky criterion ("minimal cloud envelope") produced mean 2010-11 AOD seasonal values of 0.08 and 0.04 for Eureka and Ny Ålesund respectively. In 2011-12 these values were 0.12 and 0.09. Conversely, CALIOP AODs (0 to 8 km) for the high Arctic showed a slight decrease from 2010-2011 to 2011-2012 (0.04 vs 0.03).

Newly released Imaging Ultraviolet Spectrograph/Mars Atmosphere and Volatile EvolutioN (IUVS/MAVEN) measurements of CO2 density in the Martian thermosphere have been used for comparison with the predictions of the Max Planck Institute Martian General Circulation Model (MPI-MGCM). The simulations reproduced (within one standard deviation) the available zonal mean density and derived temperature above 130 km. The MGCM replicated the observed dominant zonal wave number 3 nonmigrating tide and demonstrated that it represents a nonmoving imprint of the topography in the thermosphere. The comparison shows a great dependence of the simulated density and temperature to the prescribed solar flux, atomic oxygen abundances and gravity wave effects, with the former two being especially important in the thermosphere above 130 km and the latter playing a significant role both in the mesosphere and thermosphere.

The freezing kinetics of binary nitric acid/water aerosols is of fundamental importance to the modelling of polar stratospheric clouds and the role they in ozone depletion over the Arctic/Antarctic regions. Cirrus clouds are also often composed of nitric acid solutions, hence an understanding of freezing process in these aerosols also aids in modelling the earth's radiation budget and global warming. This thesis explores the kinetic phase diagram of nitric acid/water aerosols with sizes ranging between 0. 2 and 1. 5 mm in radius and concentrations ranging between pure water and 0. 45 mole fraction HNO3. Although the kinetic phase diagram has now been studied between 0. 46 mole fraction HNO3 and pure water, more data is needed in the region between 0. 18 and 0. 25 mole fraction HNO3 to confirm the results reported. The project described in this thesis are a continuation of a project begun by Allan Bertram. The measurements involving aerosols with compositions greater than 0. 25 mole fraction HNO3 were carried out as part of Allan Bertram's Ph. D. thesis (see ref. 20) These data were later examined using a more comprehensive data analysis method (as presented in this thesis) in an effort to obtain a more complete understanding of this system.

GaN-based HFETs demonstrate ubiquitous high power and high frequency performance and attract tremendous research efforts. Even though significant advances have been achieved, there still exist some critical issues needed to be investigated and solved. In particular, high defect densities due to inhomogeneous growth and operation under high power conditions bring many unique problems which are not so critical in the conventional Si and GaAs materials systems. In order to reduce the defect density and heat dissipation of GaN-based HFETs, research work on the realization of GaN-based HFETs on bulk GaN substrate has been carried out and the key problems have been identified and solved. Hot phonon scattering is the bottleneck which limits the enhancement of electron velocity in the GaN 2DEG channel. It is found that the plasmon-phonon coupling is the mechanism for converting of hot phonons into high group velocity acoustic phonons. In order to push more electrons into the GaN 2DEG channel in the plasmon-phonon coupling regime and to further reduce the hot phonon lifetime, a novel AlGaN/GaN dual channel HFET structure has been proposed. The growth, fabrication and characterization of such a AlGaN/GaN dual channel HFET structure has been carried out. Conventionally GaN-based light emitting diodes and laser diodes are grown and fabricated using the c-plane III-nitride expitaxy layers. In c-plane III-nitride epi-layers, the polarization-induced electric field introduces spatial separation of electron and hole wave functions in quantum wells (QW)s used LEDs and laser diodes LDs and degrades quantum efficiency. As well, blueshift in the emission wavelength becomes inevitable with increasing injection current unless very thin QWs are employed. The use of nonpolar orientations, namely, m-plane or a-plane GaN, would solve this problem. So far, m-plane GaN has been obtained on LiAlO2 (100), m-plane SiC substrates, and m-plane bulk GaN, which all have limited availability and/or high cost. Silicon substrates are very attractive for the growth of GaN due to their high quality, good thermal conductivity, low cost, availability in large size, and ease with which they can be selectively removed before packaging for better light extraction and heat transfer when needed To realize the low cost and improve the internal quantum efficiency of GaN based light emitting diodes, the process for m-plane GaN growth on Si (112) substrates has been studied and optimized. The continuous m-plane GaN film is successfully grown on Si (112) substrates.

The present thesis begins with a brief overview of some of the most important international, mainly global conventions relevant to the protection of biological diversity in its entierety. Subsequent chapters then deal with some species or higher taxons of marine mammals, in particular with cetaceans, polar bears and pinnipeds. The aim was not only to analyse relevant international conventions, but also to discuss some interesting and precise questions that complete and form the conservation regime.

The poles of Mars, much like Earth's polar regions, are covered by kilometer-thick sheets of ice that interact with the Martian atmosphere and can record climatic changes in their stratigraphy. These polar caps are composed of several icy sections that interact with the Martian environment over different timescales. This dissertation describes my investigation of two of these units: The South Polar Residual Cap (SPRC), and the North Polar Layered Deposits (NPLD). The overarching theme of my work is to explore the connections between these caps and the current (SPRC) and past (NPLD) climate of Mars using a wide variety of data from spacecraft missions, and applying numerical models of surface properties and processes to interpret the observations. The SPRC is a ~10 meter thick slab of bright carbon dioxide ice that is covered by pits and scarps formed by differential sublimation. It is unclear whether this cap is in a state of net accumulation or net ablation. During the summer of Mars Year 28 (2006/2007), The High Resolution Imaging Science Experiment (HiRISE) observed an apparent increase in brightness near the edges of these pits that had not been seen before, and was not seen in the few years following. I analyzed hundreds of images from HiRISE and the Mars Orbiter Camera (MOC), as well as data from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) to search for compositional and/or grain-size changes in the ice that could explain these "halos". I coupled my observations with numerical modeling of the spectral reflectance of the ice, to explore the effects of different ice grain sizes and minuscule dust inclusions on the observed brightness. I concluded that the features were caused by the occurrence of a global dust storm, after which the depositing dust actually acted to darken the SPRC. The halos were thus areas that had been kept relatively "clean" of the depositing dust, thanks to winds driven by enhanced sublimation from the pit walls. The fact that the halos did not show up in subsequent years means that they had not been exhumed, and that flat areas of the SPRC are in a state of net accumulation. It is likely that events like these result in new flat surfaces formed by snowfall driven by the depositing dust, which could explain the persistence of the cap throughout history. The polar layered deposits (PLD) are kilometer-thick stratified dome structures composed of dusty water ice that make up the bulk of the polar caps. The layers that make up the PLD are thought to record climatic variations over timescales of millions of years, in a similar way to Earth's ice caps. These caps are dissected by deep troughs that allow us to observe outcrops of their internal layers and map the stratigraphy. In the past, researchers have done this using layer brightness. However, remotely observed brightness has been shown to be affected by many external factors and may not represent an intrinsic property of the layers. Using Digital Terrain Models (DTM) made from HiRISE stereo images of NPLD outcrops, I mapped the change with depth of each layer's topographic protrusion from the scarp slope, defining the stratigraphy with a property related to the layers' resistance to erosion. I mapped the protrusion stratigraphy of 16 sites throughout the NPLD, and correlated the stratigraphic profiles from a subset of these sites, with Context Camera (CTX) images and signal-matching algorithms. This correlation combined topographic information with brightness information, resulting in an improvement of the current state of stratigraphic mapping of the NPLD, providing further evidence that layer sequences are continuous across the NPLD, and setting lower limits on relative accumulation rates for large sections of the cap.In order to search for a connection between the Martian paleoclimate and the NPLD stratigraphic record, I identified overlapping periodicities in the stratigraphic structure and compared them to periodicities in the climatic history, represented by the change in insolation with time at the North Pole over the last 5 Myr. I found that the ratio of stratigraphic wavelengths is systematically lower than the ratio between dominant modes of oscillation of the north polar insolation. However, a similar wavelet analysis of synthetic stratigraphic profiles created with a simple climate-driven model of accumulation revealed that a detectable non-linear relationship exists between the variation of insolation on the North Polar region of Mars and the stratigraphic record preserved in the NPLD. The dissertation is organized into four principal chapters and one final chapter with concluding remarks and future directions. Chapter 1 gives an introduction to Mars' polar regions and to the history of research in astronomically forced climate change through cyclostratigraphy, along with a short summary of the scope and main questions of this study. Chapter 2 details my study of the SPRC halos. Chapter 3 deals with the stratigraphic mapping of the NPLD through high-resolution topography, and Chapter 4 presents the results of my search for an astronomical forcing signal in the NPLD stratigraphy. Chapter 2 was published in the journal Icarus, in a special issue on the dynamic geologic processes of Mars and the science learned from continuous monitoring of these processes through remote sensing. Chapter 3 has been accepted for publication in the Journal of Geophysical Research. A modified version of Chapter 4 will be submitted to Nature Geoscience.

In this series of essays about professional burnout, a veteran teacher seeks a way to continue her work and enthusiasm in it, for the sake of both her and her students. To that end, she explores her relationships with her father and mother, and how the practices of teaching and learning she brought from home have affected her present classroom experiences. A complicating factor is the presence of chronic illness and its demands both primary and secondary: her father's Alzheimer's, her mother's bi-polar disorder, and the demands of eldercare for her mother. She also explores her own habitual practice of being a student, in a reflective inquiry into the mind and situation of students from inside her own experiences. Interleaved vignettes of student interaction illustrate the kinds of difficulty that the speaker has with her teaching. They appear chronologically to suggest a developmental movement.

In today’s society the ability to communicate with one another has grown, were a lot of focus is aimed towards speed in the telecommunication industry. For transmissions to become even faster, there are many ways to enhance transmission speeds of which error correction is one. Padding messages such that they are protected from noise, while using as few bits as possible and ensuring safe transmit is handled by error correction codes. Short codes with low complexity is a solution to faster transmission speeds. An error correction code which has gained a lot of attention since its first appearance in 2009 is Polar Codes. Polar Codes was chosen as the 3GPP standard for 5G control channel. The goal of the thesis is to develop and implement Polar Codes and rate matching according to the 3GPP standard 38.212. Polar Codes are then to be evaluated with different block sizes and rate matching settings. Finally Polar Code is compared with Convolutional code in a LTE-simulation environment. The performance evaluations are presented using BLER/(Eb/N0)-graphs. In this thesis a Polar encoder, rate matching and a Polar decoder (with Successive Cancellation algorithm) were successfully implemented. The simulation results show that Polar Codes performs better with longer block sizes and also has a better BLER-performance than Convolutional Codes when given the same message lengths.

The wintertime North-Atlantic exhibits enhanced circulation variability relative to other areas of the globe and is a key determinant of weather and climate in the highly populated regions of Europe and Eastern North America. Previous work has linked extreme stratospheric polar vortex and planetary wave heat flux events with variability of the North-Atlantic circulation. To elucidate the role of the stratosphere in driving variability of the North-Atlantic circulation, the goal of this thesis is to clarify the relationship between extreme planetary wave heat flux and vortex events and understand the dynamical mechanisms driving extreme stratospheric planetary wave heat flux events using an idealized model. The relationship between extreme stratospheric planetary wave heat flux and polar vortex events is clarified by comparing and contrasting their composite lifecycles using reanalysis data. Extreme negative heat flux events, defined as those less than the 5th percentile of the wintertime wave-1 distribution, involve stratospheric EP-flux divergence producing an acceleration of the vortex whereas extreme positive heat flux events, defined as those greater than the 95th percentile, involve stratospheric EP-flux convergence producing a deceleration of the vortex. Similar but smaller magnitude heat flux (22th and 78th percentile) events contribute to the development of longer-timescale vortex events. Negative heat flux events precede strong vortex events, showing that strong vortex events are true dynamical events involving wave-mean flow interaction. Conversely, positive heat flux events precede weak vortex events. The tropospheric jet shifts in the North-Atlantic that occur almost simultaneously with extreme stratospheric heat flux events are shown to be comparable if not larger than those that follow extreme vortex events for several weeks. Next, a dry-dynamical core model is configured to capture the lifecycle of extreme positive and negative heat flux events seen in reanalysis. The events are not captured using the standard model setup with idealized wave-1 topography. A modified control simulation captures the key ingredients of the events: 1) the extremes of the stratospheric eddy heat flux distribution, 2) the cross-spectral correlation and phase between the stratosphere and troposphere, 3) the evolution of the eddy heat flux and EP-flux divergence, 4) the stratospheric evolution of the zonal-mean flow, including the NAM, NAM time-tendency, potential temperature time-tendency and stratospheric wave geometry, and 5) the tropospheric evolution, including the high-latitude wave-1 geopotential height pattern and mid-latitude jet shift. Comparison between the model and reanalysis reveals that higher-order planetary wavenumbers play a role prior to the events. Finally, the dry-dynamical core model is used to examine the large-scale dynamical mechanisms driving extreme stratospheric negative heat flux events and their coupling with the tropospheric circulation. An ensemble spectral nudging methodology is used to isolate the role of: 1) the tropospheric wave-1 precursor, 2) the stratospheric zonal-mean flow and 3) the higher-order wavenumbers. The events are partially reproduced when nudging the wave-1 precursor and the zonal-mean flow whereas they are not reproduced when nudging either separately. In contrast, nudging the wave-1 precursor and the higher-order waves reproduces the events, including the evolution of the zonal-mean flow. Mechanism denial experiments show that the higher-order planetary wavenumbers drive the events by modifying the zonal-mean flow and through wave-wave interaction. Nudging all tropospheric wave precursors confirms they are the source of the stratospheric waves. Nudging all stratospheric waves reproduces the coupling with the tropospheric circulation. Taken together, the experiments show that extreme stratospheric negative heat flux events are consistent with downward wave coupling from the stratosphere to the troposphere.

La littérature gabonaise, forte de son dynamisme, voit davantage d’écrivains faire le choix de décrire les réalités sociales dans une langue française réappropriée. Ce qui consiste pour eux à réinventer le français, à l’image de leur société, et à en faire leur propre langue d’écriture. Notre thèse se propose d’étudier ce phénomène dans le polar gabonais, ce genre en plein essor représenté par Janis Otsiémi, et de démontrer que la créativité du point de vue de la langue reste indissociable de l’engagement et de la conviction de l’écrivain gabonais, et afro-subsaharien par extension. En premier abord, il est question de distinguer la langue d’écriture de l’écriture de la langue. Pour cela, étudier les stratégies d’écriture de l’écrivain, relever les divers gabonismes et africanismes présents dans le roman d’Otsiémi et les fonctions propres à chacune des particularités linguistiques, nous permet de faire état de l’esthétique littéraire et des pratiques langagières gabonaises. En second lieu, l’objectif est pour nous de procéder à une herméneutique de l’oeuvre d’Otsiémi pour dégager grâce à la subversion de l’écriture la poétique subversive de son oeuvre. Pour ce faire, situer le style de l’auteur revient à évaluerl’engagement de l’auteur vis-à-vis de la langue et de l’écriture, à faire face à une écriture hybride résultant du foisonnement des intertextes, et à aborder l’identité à la fois revalorisée et déconstruite par l’auteur, respectant ainsi le principe élémentaire du polar qu’est celui d’écrire le noir. / The Gabonese literature, strong in its dynamism, sees more writers make the choice to describe social realities in a French language reappropriated. What is for them to reinvent the French, in the image of their society, and to make their own language of writing. Our thesis proposes to study this phenomenon in the Gabonese crime novel, this booming genre represented by Janis Otsiemi, and to demonstrate that creativity from the point of view of language remains inseparable fromthe commitment and conviction of the Gabonese writer, and afro-sub-Saharan by extension. At first, it is a question of distinguishing the language of writing from the writing of the language. To do this, to study the writer's writing strategies, to identify the various gabonisms and Africanisms present in Otsiemi's novel and the functions proper to each linguistic peculiarity, allows us to describe literary aesthetics and Gabonese languages practices. In the second place, the objective is for us to proceed with a hermeneutic of the work of Otsiemi to free, thanks to the subversion of writing, the subversive poetics of his work. To do this, situating the author's style amounts to evaluating the author's commitment to language and writing, to coping with a hybrid writing resulting from the proliferation of intertexts, and to approach the identity both revalorized and deconstructed by the author, thus respecting the elementary principle of the crime novel that is to write black.