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La couronne solaire est un milieu très dynamique : instabilités du champ magnétique, qui structure le plasma, conduit à l'accélération et le chauffage des particules chargées et à l'éjection de grandes structures dans l'héliosphère, les émissions de masse coronale (CME, selon ces sigles en anglais). Ces structures magnétiques éjectées peuvent interagir avec le champ magnétique de la Terre et affecter le plasma de l'environnement. Ces structures conduisent également à l'induction des courants électriques dans le sol à des latitudes élevées. L'étude de l'origine et de la propagation de ces émissions est d'intérêt pour l’astrophysique dans l’encadre des applications générales et pour la météorologie de l’espace. La compréhension des processus de base est une condition importante pour l'élaboration des méthodes de prévision des arrivées de ces perturbations en utilisant des observations de la couronne solaire. Les CMEs sont observées et étudiées à travers des images coronographiques. La limitation fondamentale du coronographe est qu'il montre la couronne seulement dans le plan du ciel, donc il bloque, forcément, la vue sur le disque solaire. Mais le geoefficacité d'une CME dépend essentiellement de la proximité à la ligne Soleil- Terre et de l'évolution dans la basse couronne que ne sont pas visibles à travers des observations coronographiques. Un des problèmes est la difficulté d’estimer l'arrivée d'une CME à la Terre, parce que les mesures avec coronographes directes de la vitesse de propagation des CMEs qui est dirigée vers la Terre ne sont pas possibles dans la ligne Soleil-Terre. Cette thèse présente l'étude des CMEs en trois étapes : (1) une étude de cas de l'évolution CME dans la bassecouronne et son rôle dans l'accélération des particules, (2) la relation entre la polarisation de l'émission de sursauts radio de type IV associées à CMEs dans la couronne et l'orientation du champ magnétique observé quand les CMEs arrivent à la Terre, et (3) des estimations radiatives de la vitesse des CMEs pour les prévisions des temps d’arrivée des CMEs à la Terre. Imagerie en utilisant des émissions radio dans la basse couronna peut montrer les signatures des CMEs sur le disque solaire. Des études précédentes avec le Radiohéliographe de Nançay (NRH) suggèrent, en fait, que les images de radio aux longueurs d'onde métriques peuvent suivre l'évolution des CMEs bien avant qu'ils deviennent visibles dans la couronne. Le diagnostic de l'évolution CME dans la basse couronne développée dans ce travail a été illustrée par l'étude de l'événement éruptif du 26 Avril 2008, qui a offert une occasion unique d'étudier le lien physique entre une seule CME bien identifiée, l'accélération des électrons tracé par émission radio, ainsi que la production des particules énergétiques solaires (SEP, selon ces sigles en anglais) observées dans l'espace. Nous effectuons une analyse détaillée en combinant les observations radio (NRH et DAM, Wind / WAVES spectrographe) et les observations de la couronne avec des satellites dans EUV et lumière blanche, ainsi que des mesures ‘in situ’ des particules énergétiques près de 1UA (satellites SoHO et STEREO). En combinant des images prises à partir de plusieurs points de vue, nous avons pu déduire l'évolution 3D en fonction du temps du front de l’éjection de mass qui s’est développée autour de l’éruption de la CME. Enfin, nous avons identifié, à partir des observations radio et SEP, trois régions différentes d'accélération des particules associées à l'évolution de la même CME, séparés en longitude environ 140°. / The solar corona is a highly dynamical medium: instabilities of the magnetic field, which structure the plasma, lead to the acceleration and heating ofcharged particles and to the ejection of large structures into the heliosphere, the Coronal Mass Ejections (CMEs). These ejected magnetic structures can interact with the Earth's magnetic field and thereby affect the plasma environment and the high atmosphere of the Earth. Studying the origin and propagation of CMEs is of interest for both astrophysics in general and space weather applications. The understanding of the basic processes is indeed a pre-requisite for developing prediction methods of potentially geo-effective disturbances based on observations of the solar corona.The CMEs are observed and studied primarily through coronographic images. The basic limitation of the coronagraph is that it shows the corona only in the plane of the sky, and blocks by necessity the view on the solar disk. But the geoeffectiveness of a CME depends crucially on the proximity to the Sun-Earth line and the measurements of the propagation speed, onset and early evolution of CMEs in the low corona are not accessible to coronographic observations. This thesis presents the study of CMEs in three different stages: (1) a case study of the CME evolution in the low corona and of its role in particle acceleration, (2) the relationship between the polarisation of the type IV radio emission associated with Earth-directed CMEs in the corona and the orientation of the magnetic field observed as the CMEs arrive at the Earth, and (3) the estimation of the travel times of CMEs to the Earth. Radio imaging with the Nancay Radioheliograph (NRH) suggest that radio images at metric wavelengths track the early evolution of CMEs well before they become visible in the corona. The examination of the CME evolution in the low corona developed in this work was illustrated through the study of the eruptive event on 26 April 2008, which offered a unique opportunity to investigate the physical link between a single well-identified CME, electron acceleration as traced by radio emission, and the production of solar energetic particles (SEPs) observed in space. We conduct a detailed analysis combining radio observations (NRH and Decameter Array, Wind/WAVES spectrograph) with remote-sensing observations of the corona in extreme ultraviolet (EUV) and white light as well as in-situ measurements of energetic particles near 1AU (SoHO and STEREO spacecraft). By combining images taken from multiple vantage points we were able to derive the time-dependent evolution of the 3D pressure front developing around the erupting CME. Finally, we identified, from the radio and SEP observations, three different particle acceleration regions associated to the evolution of the same CME, separated in longitude by about 140$^\circ$. The observations for this event showed that it is misleading to interpret multi-spacecraft SEP measurements in terms of one acceleration region in the corona.

Le Radiohéliographe de Nançay, rénové en 1996, est un instrument dédié à l'étude de l'activité sporadique de la couronne solaire, dans le domaine métrique et décimétrique. Les structures calmes de la couronne peuvent être également observées par l'utilisation de la synthèse d'ouverture, qui autorise la cartographie de structures à faible contraste.<br /><br />Je présente dans cette thèse les premiers résultats de synthèse d'ouverture pour l'instrument rénové, en m'intéressant tout particulièrement à la contrepartie radio des filaments solaires, jamais étudiée auparavant dans cette gamme de longueur d'onde. Je montre que les observations sont explicables par la présence d'une cavité coronale autour des filaments, et que la radio permet son observation directe sur le disque.<br /><br />Je décris enfin trois cas de Disparitions Brusques de filament montrant, pour la première fois en radio, les stades initiaux du développement d'éruptions de filaments et de CMEs sur le disque, sous l'aspect des émissions thermiques. Ce travail s'appuie fortement sur les observations multi longueurs d'onde, rendues possibles par l'existence du satellite SOHO sur toute la période, et notamment son télescope EIT, et son coronographe LASCO.

Thesis (Ph.D.)--Boston University / The formation, evolution and eruption of solar active regions is a main theme in solar physics. Ultimately the goal is predicting when, where and how an eruption will occur, which will greatly aid space weather forecasting. Special kinds of S-shaped active regions (sigmoids) facilitate this line of research, since they provide conditions that are easier to disentangle and have a high probability for erupting as flares and/or coronal mass ejections (CME). Several theories have been proposed for the formation, evolution, and eruption of solar active regions. Testing these against detailed models of sigmoidal regions can provide insight into the dominant mechanisms and conditions required for eruption. This thesis explores the behavior of solar sigmoids via both observational and magnetic modeling studies. Data from the most modern space-based solar observatories are utilized in addition to state-of-the-art three-dimensional data-driven magnetic field modeling to gain insight into the physical processes controlling the evolution and eruption of solar sigmoids. We use X-ray observations and the magnetic field models to introduce the reader to the underlying magnetic and plasma structure defining these regions. By means of a large comprehensive observational study we investigate the formation and evolution mechanism. Specifically, we show that flux cancellation is a major mechanism for building the underlying magnetic structure associated with sigmoids, namely magnetic flux ropes. We make use of topological analysis to describe the complicated magnetic field structure of the sigmoids. We show that when data-driven models are used in sync with MHD simulations and observations we can arrive at a consistent picture of the scenario for CME onset, namely the positive feedback between reconnection at a generalized X-line and the torus instability. In addition we show that topological analysis is of great use in analyzing the post-eruption flare- and CME-associated observational features. Such analysis is used to extend the standard 2D flare/CME models to 3D and to find potentially large implications of topology to understanding 3D reconnection and the seed populations of energetic particles in CMEs.

Novel sol-gel titania-poly(dimethylsiloxane) (TiO2-PDMS) and titania-silica-N-(triethoxysilylpropyl)-O-polyethylene oxide urethane (TiO2-SiO2-TESP-PEO) coatings were developed for capillary microextraction (CME) to perform on-line preconcentration and HPLC analysis of trace impurities in aqueous samples. Due to chemical inertness of titania, effective covalent binding of a suitable organic ligand to its surface is difficult via conventional surface modification methods. In this research, sol-gel chemistry was employed to chemically bind hydroxy-terminated poly(dimethylsiloxane) (PDMS) and N-(triethoxysilylpropyl)-O-polyethylene oxide urethane (TESP-PEO) to sol-gel titania and sol-gel titania-silica network, respectively. A method is presented describing in situ preparation of the titania-based sol-gel PDMS and TESP-PEO coatings and their immobilization on the inner surface of a fused-silica microextraction capillary. To perform on-line CME-HPLC, the sol-gel TiO2-PDMS or TiO2-SiO2-TESP-PEO capillarywas installed in the HPLC injection port as an external sampling loop, and a conventionalHPLC separation column was used for the liquid chromatographic separation. The sol-gel TiO2-PDMS-coated microextraction capillary was used for on-line CME-HPLC analysis of non-polar and moderately polar analytes, and the sol-gel coatings showed excellent pH (1-13), and solvent (acetonitrile and methanol) stabilities under elevated temperatures (150 C) over analogous non-sol-gel silica-based coatings. Extraction of highly polar analytes, especially from aqueous phases is not an easy task. However, the sol-gel TiO2-SiO2-TESP-PEO-coated capillaries showed excellent capability of extracting underivatized highly polar analytes from aqueous samples. This opens the possibility to employ sol-gel titania-based polar coatings for solvent-free extraction and trace analysis of target analytes in environmental and biomedical matrices. To our knowledge, this is the first research on the use of sol-gel titania (or titania-silica)-based organic-inorganic materials as a sorbent in capillary microextraction. The newly developed sol-gel titania (or titania-silica)-based organic-inorganic hybrid extraction media provides an effective solution to coupling CME with HPLC (CME-HPLC), and this can be expected to become a powerful analytical tool in environmental investigations, proteomic research, early disease diagnosis and biomarker research. Being a combination of a highly efficient solvent free sample preconcentration technique (CME) and a powerful separation method (HPLC), CME-HPLC poses to become a key analytical tool in solving complex chemical, environmental, and biomedical problems involving complex matrices.

A case study which examines the agreement between prediction and data is performed for three, complex interplanetary shocks which were detected at the Sun-Earth Lagrange point L1 and induced moderate to intense geomagnetic storms. We use model output from previous runs of the coupled coronal-heliosphere WSA-Enlil+Cone model, available through the Community Coordinated Modeling Center (CCMC), and in-situ data from the OMNI data set. Code written in MATLAB is used to compare the model output with the in-situ measurements of the interplanetary magnetic field as well as the density, speed and temperature of the solar wind. In addition, the difference between the predicted and actual shock arrival time is computed and regions of potential temperature depression are identified. A considerable discrepancy is found between data and model for the studied events. The main reason is deemed to be an inadequate representation of the ambient solar wind as well as the complex interactions between interplanetary coronal mass ejections and corotating interaction regions. We suggest future steps to be taken for the further development of the model as well as for the general understanding of space weather and the Sun-Earth connection. / Denna fallstudie undersöker överensstämmelsen mellan modell och data för tre interplanetära chockvågor, som kunde detekteras vid jordens Lagrangepunkt 1, och som orsakade geomagnetiska stormar av måttlig till kraftig styrka. Vi använder oss av tidigare genomförda körningar av den sammansatta WSA-Enlil+Cone modellen, som avbildar fortplantningen av temporära störningar med ursprung i solens korona, såsom koronamassutkastningar, ut i heliosfären. Modellen gjordes tillgänglig av Community Coordinated Modeling Center (CCMC) och datan inhämtades från OMNI. Kod skriven i MATLAB nyttjades för att göra en jämförelse mellan modell och faktiska mätningar av det interplanetära magnetfältet samt solvindens hastighet, densitet och temperatur. Utöver detta, beräknas också skillnaden mellan förväntad och faktisk ankomsttid av respektive interplanetär chock, och tidsperioder med en temperatursänkning utöver det normala identifieras. Vi finner en omfattande avvikelse mellan modell och data, i synnerhet för de fall där på varandra följande koronamassutkastningar förväntas interagera eller rent av slås ihop samt för uppskattningen av den omgivande solvindens egenskaper och det interplanetära fältet under pågående geomagnetisk störning. Interaktionen mellan koronamassutkastningar och närliggande ko-roterande interaktionsregioner har ej heller återskapats väl av modellen ifråga. Slutligen ger vi förslag på möjliga, framtida åtgärder som kan bör tas i åtanke vid konstruerandet av framtida versioner av nämnda modell, liksom för den allmänna förståelsen för rymdvädrets inverkan på Jorden.

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The development of the central nervous system is dysregulated in neurodevelopmental disorders such as intellectual disability, autism spectrum disorder, and epilepsy. These three disorders have different clinical features, yet there is high comorbidity between them. They can be difficult to study due to their highly complex aetiologies, however there are various monogenic diseases that can cause all of them, including SYNGAP1 haploinsufficiency where the synaptic guanosine triphosphatase (GTPase)-activating protein (SYNGAP) protein levels are highly reduced; Fragile X syndrome where the fragile X mental retardation protein (FMRP) is no longer translated; and DNM1 epileptic encephalopathy where mutations in the Dynamin1 gene alter the protein function. These monogenic conditions are synaptopathies as the proteins affected play important roles in synapse stability and neurotransmission. Because of the high comorbidity between these disorders, it is hypothesised that there may be a common mechanism underlying them. We hypothesise that a deficit in presynaptic vesicle recycling may be part of a common mechanism underlying intellectual disability, autism spectrum disorder, and epilepsy especially in SYNGAP1 haploinsufficiency, Fragile X syndrome, and DNM1 epileptic encephalopathy. Using various fluorescent presynaptic activity reporters including synaptic pHluorins, tetramethylrhodamine dextran and calcium dyes to compare presynaptic activity in in vitro models of these monogenic conditions, we found differences in synaptic vesicle (SV) endocytosis in the genetically altered conditions compared to wildtype controls. We observed various SV endocytosis defects in clathrin-mediated endocytosis (CME) or activity-dependent bulk endocytosis (ADBE) in our models. We observed enhanced CME in SynGAP1 KO mouse hippocampal neurons. This enhanced SV endocytosis was accompanied by decreased SV cargo on the plasma membrane. Rat SynGAP1 KO hippocampal neurons did not display enhanced SV endocytosis, nor did neurons with the GTPase-activating (GAP) domain of SynGAP deleted. This was perhaps due to the altered time course of development between these rodent species. In mouse and rat models of Fragile X syndrome, CME was not altered compared to wildtype controls. However, in a rat model, we observed fewer nerve terminals undergoing ADBE which is the dominant SV endocytosis mode during elevated neuronal activity. De novo epileptic encephalopathy-associated mutations in DNM1 had differential effects on SV recycling through both CME and ADBE. Mouse hippocampal neurons overexpressing Dyn1R237W, Dyn1I289F and Dyn1H396D all showed less CME compared to overexpression of Dyn1WT. Moreover, fewer nerve terminals overexpressing Dyn1H396D were found to undergo ADBE. We also found that a large-conductance potassium (BK) channel opener can accelerate clathrin-mediated endocytosis and thus may be able to rescue the impaired SV endocytosis caused by these mutants. Although there is not yet a common underlying pathway at the presynaptic level between these conditions, SV recycling dysfunction is present across all of these models. Furthermore, we propose an axis of pathophysiology model where optimal SV endocytosis is required for optimised neural performance. We propose that either decreased or increased SV endocytosis can lead to the synaptic dysfunction observed in these models.

Master of Science / Department of Agricultural Economics / Ted C. Schroeder / With volatile cattle markets, comes substantial amounts of price risk for all parties involved in the industry. Hedging with futures markets to mitigate risk is a common practice performed by commercial producers. For this to be an effective risk management tool, the futures contract must function correctly by accurately representing the price and quality of the underlying product. Often times, commodity futures contracts are settled by physical delivery. However, two livestock contracts transitioned to a cash settled index, feeder cattle in 1986 and lean hogs in 1997, to enhance the performance of the contract and promote participation by commercial users. Eliminating high delivery costs, reducing any issues with the grading process when the product is delivered, and portraying a truer commercial value, are some of the benefits of a cash settlement index. There has been some speculation that dates back to the 1980’s regarding whether the live cattle futures contract should switch to cash settlement rather than physical delivery. This study was done to measure the impact the change to cash settlement had on the hedging ability of the feeder cattle futures contract. Even though the feeder cattle contract represents a different sector of the industry, the results still provide some insight as to whether cash settlement can be advantageous for a futures contract. The ability to forecast basis is critical when hedging with futures to manage risk. The magnitude of basis prediction error (BPE), or the difference between expected basis and actual basis, is a common method used to measure the hedging ability of a futures contract. This procedure was utilized to analyze the effects the change to cash settlement had on BPE in six different regions: Kansas, Missouri, Nebraska, North/South Dakota, Oklahoma, and Texas. Expected basis was calculated using a two, three, and four year historical average technique for each respective week to contract expiration. Other market factors were also included in the models to ensure the cash settlement adjustment was not the sole reason for BPE variations over time. To estimate the impact the different elements have on basis predictability, Ordinary Least Squares regression was used for each of the three stacked models. For the two-year historical basis prediction error model, Kansas was the only area with a statistically significant value indicating cash settlement reduced BPE by $0.18. Three states, Kansas (-$0.24/cwt.), Missouri (-$0.17/cwt.), and Texas (-$0.16/cwt.), showed a statistically significant decrease in BPE due to cash settlement for the three-year historical basis prediction error model. Also, the coefficient for Oklahoma was just slightly above the statistically significant level. However, the four-year model had moderately different results. The estimate for Kansas was statistically significant at -$0.18/cwt. meaning cash settlement reduced BPE, while the Dakotas region actually showed a statistically significant increase in BPE by $0.18/cwt. This research provides evidence that cash settlement can improve the basis predictability of a futures contract depending on the region and technique used to calculate expected basis.

Present-day Mars is a cold and dry planet with a thin CO2-dominated atmosphere comprising only a few ­­­mbar pressure at low altitudes. However, the Martian surface is marked with valley networks, hydrated mineral clays, carbonates and the remains of deltas and meandering rivers, i.e. traces of an active hydrological cycle present early in the planet's geological history. A strong greenhouse effect, and thus a thicker atmosphere, would have been required to sustain a sufficiently warm environment, particularly under the weaker luminosity of the early Sun. The fate of this early atmosphere is currently unknown. While several mechanisms can remove atmospheric mass over time, a prominent hypothesis suggests that the lack of an intrinsic Earth-like global magnetic dipole has allowed the solar wind to erode the early Martian atmosphere by imparting energy to the planet's ionosphere which subsequently flows out as ion escape, over time depleting the greenhouse gasses and collapsing the ancient hydrological cycle. Previous studies have found insignificant ion escape rates under present-day conditions, however, the young Sun emitted significantly stronger solar wind and photoionizing radiation flux compared to the present. The geological record establishes the time of collapse of the hydrological cycle, estimated to have occurred in the mid-late Hesperian period (~3.3 billion years ago) at latest. To constrain the amount of atmosphere lost through ion escape since, we use the extensive database of ion flux measurements from the Analyzer of Space Plasmas and Energetic Atoms (ASPERA-3) particles package on the Mars Express orbiter (2004-present) to quantify the ion escape rate dependence on upstream solar wind and solar radiation conditions. The Martian ion escape rate is shown to be insensitive to solar wind parameters with a weak inverse dependence on solar wind dynamic pressure, and linearly dependent on solar ionizing photon flux, indicating efficient screening of the bulk ionosphere by the induced magnetic fields. The impact of an extreme coronal mass ejection is studied and found to have no significant effect on the ion escape rate. Instead, intense solar wind is shown to only increase the escaping energy flux, i.e. total power of escaping ions, without increasing the rate by accelerating already escaping ions. The orientation of the strongest magnetized crustal fields are shown to modulate the ion escape rate, though to have no significant time-averaged effect. We also study the influence of solar wind and solar radiation on the major Martian plasma boundaries and discuss factors that might limit the ion escape rate, including solar wind-ion escape coupling, which is found to be ≲1% and decreasing with increased solar wind dynamic pressure. The significant escape rate dependencies found are extrapolated back in time, considering the evolution of solar wind and ionizing radiation, and shown to account for only 4.8 ± 1.1 mbar equivalent surface pressure loss since the time of collapse of the Martian hydrosphere in the Hesperian, with ~6 mbar as an upper estimate. Extended to the late Noachian period (3.9 billion years ago), the found dependencies can only account for ≲10 mbar removed through ion escape, an insignificant amount compared to the ≳1 bar surface pressure required to sustain a warm climate on early Mars.