Complex magnetosphere-ionosphere coupling mechanisms result in high latitude irregularities that are difficult to characterize. Until recently, the polar and auroral irregularities remained largely unexplored. Inadequate infrastructures to deploy and maintain advanced dual frequency Global Navigation Satellite System (GNSS) receivers at high latitudes, especially in the Southern hemisphere, makes such an investigation a formidable task. Additionally, the complicated geometry of the magnetic field lines in these regions pose challenges in designing global scintillation models. This dissertation takes some steps towards bridging these gaps while advancing the state-of-the-art high latitude irregularity studies. In the first part of this dissertation, we briefly describe the Autonomous Adaptive Low-Power Instrument Platforms (AAL-PIP) experimental setup. These space science instrument platforms are being deployed in remote locations in Antarctica, improving the coverage of GNSS data availability. We explain in detail the method developed for analyzing high rate (typically 50 Hz) data from a novel dual-frequency Global Positioning System (GPS) receiver called Connected Autonomous Space Environment Sensor (CASES). We also report first observations from CASES at high latitudes. From this study, we established that CASES can be reliably used as a science grade GPS scintillation monitor. Following this, a novel three dimensional (3D) electromagnetic (EM) wave propagation model called "Satellite-beacon Ionospheric-scintillation Global Model of the upper Atmosphere" (SIGMA) was developed to simulate GNSS scintillations on ground. GPS scintillation simulations of significantly high fidelity are now possible with this model. While the model is global, it is the first such model which accounts for the complicated geometry of magnetic field lines at high latitudes. Using SIGMA, a sensitivity study is presented to understand the effect of geographical, propagation and irregularity parameters on the phase scintillations. This allows us to reduce the dimensionality of the design space while solving the inverse problem described next. In the final part, we utilize the tools developed for GPS measurement analysis and SIGMA to characterize the high latitude irregularities. We propose an inverse modeling technique to derive irregularity parameters by comparing the high rate (50 Hz) GNSS observations to the modeled outputs. We consider interhemispheric high latitude datasets for this investigation. We also implement SIGMA for analyzing a substorm event observed by AAL-PIP stations. One of the unique contributions of this research is to demonstrate that such an inverse modeling technique can form a basis in the investigation of the ionospheric irregularities. Moreover, availability of ample auxiliary data from multi-instrument observations can assist in this quest of understanding the physics of high latitude irregularities and their generation mechanisms. / Ph. D.

The earth's ionosphere-thermosphere region is a coupled environment which is governed by interactions between the overlapping neutral constituents and ionospheric plasma. The mid-latitude thermosphere-ionosphere system is very complex owing to its sensitivity to both the polar and equatorial processes. The mid-latitudes is also a relatively unexplored and less understood region primarily due to the paucity of observing instruments that have traditionally been available. However, the past 9 years of mid-latitude expansion of the Super Dual Auroral Radar Network (SuperDARN) has provided new access to continuous large-scale observations of the sub-auroral ionosphere. On the other hand, the past 3 years of mid-latitude expansion of the North American Thermosphere Ionosphere Observation Network (NATION) Fabry-Perot interferometer array, has created a critical resource for measuring the thermospheric neutral winds. The overlap of these two observing networks in the mid-east North American sector has resulted in a strong ground-based large-scale platform for co-located study of mid-latitude thermosphere-ionosphere dynamics for the first time. The coupling between ions and neutrals is a very important process for controlling the thermospheric dynamics. Ion-neutral coupling at high latitudes has been studied in many previous papers, but there have been very few studies focused on the mid-latitude region. Hence, in this work we have studied the ion-neutral coupling mechanisms and timescales at mid-latitudes during disturbed geomagnetic conditions by using the co-located observations from the SuperDARN-NATION array. The study has focused on the main phase as well as the late recovery phase of a geomagnetic storm which occurred on October 2-3, 2013. Ion drag is known to drive the neutral circulation during the main phase of storm at auroral latitudes, while the neutral wind disturbance dynamo mechanism is known to generate ionospheric electric fields and currents during the recovery phase. By using the methods of ion-neutral momentum exchange theory and time lagged correlation analysis, we analyzed the timescales at which the ion-neutral coupling operates. The ions are observed to drive the neutral winds on a timescale of ~ 84 minutes in the storm main phase which is significantly faster than expected from the driving due to local ion-drag alone (~ 124 minutes). This suggests that along with ion-drag, other local and non-local storm-time influences like Joule heating are also playing an important part in driving the neutral winds. On the other hand, in the late recovery phase, the neutral winds are found to be strongly coupled with the ions and maintain the ion convection without any significant time delay which is consistent with effect of the 'disturbance dynamo' or 'neutral-flywheel' persisting well into the late recovery phase. The timescales and underlying physics understood through this work serve as an important contribution to our knowledge of ion-neutral coupling processes at the middle latitudes. Looking forward, the expansion of co-located SuperDARN-NATION coverage at mid-latitudes, and developments in the tools of large-scale visualization through FPI wind field mapping and SuperDARN convection maps, has created a very strong basis for using the results and analysis tools developed in this work for large-scale ion-neutral coupling characterization in future. / Master of Science

Thesis advisor: Christopher Kenaley / Bergmann’s rule predicts a change in body size with latitude, with larger members of a taxonomic group occurring further from the equator. This pattern has been described for many groups of organisms; however, no study has assessed this relationship across a substantial number of ray-finned fish species, the largest group of vertebrates. I performed Bayesian phylogenetic modeling using maximum length and latitude data for 3021 species of actinopterygians to assess Bergmann’s rule in the group. The impact of salinity tolerance on the relationship between length and latitude was also considered. Maximum length and salinity tolerance data were obtained from FishBase, and latitude data were obtained from museum records. I found that, overall, Bergmann’s rule holds and is not significantly affected by salinity tolerance except when not considering phylogeny, in which case only marine species show the trend. / Thesis (BA) — Boston College, 2023. / Submitted to: Boston College. College of Arts and Sciences. / Discipline: Departmental Honors. / Discipline: Biology.

The data from the new mid-latitude radars of the Super Dual Auroral Radar Network (SuperDARN) provide new types of challenges and observations. We have developed a method for identifying periods of ionospheric backscatter that increase the number of data and reduce the average velocity in agreement with previous incoherent scatter radar (ISR) studies. Analysis of the data identified by this method clearly shows that different types of ionospheric irregularities are being observed in the mid-latitude region. One type of irregularity is clearly subauroral and equatorward of the plasmapause. Fitting a convection pattern to the Doppler velocities associated with subauroral ionospheric scatter reveals some interesting features. Subauroral convection is shown to be westward thought most of the night, with an eastward turning near dawn. The rotation factor of the ionosphere relative to the rotation of the earth is shown to be ~0.95, which is in good agreement with previous studies of plasmaspheric corotation. / Master of Science

Orientador: Fernando Roberto Martins / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Biologia / Made available in DSpace on 2018-08-19T15:38:55Z (GMT). No. of bitstreams: 1 Cerqueira_RobertaMacedo_D.pdf: 10307758 bytes, checksum: 977436429d0c6254aef3b745b653e89d (MD5) Previous issue date: 2011 / Resumo: Padrões de diversidade de espécies existem e são estudados em uma variedade de sistemas e escalas espaciais. Diferentes fatores geográficos e ambientais têm sido associados à variação na de diversidade em áreas florestadas, entretanto, ainda não existe um consenso na comunidade científica quanto à importância e à influência destes fatores em relação ao aumento ou diminuição da diversidade. Estudos pontuais de florística e fitossociologia no Brasil têm possibilitado o estabelecimento de alguns padrões e inferências sobre os fatores que afetam diretamente a diversidade dos sítios. A Floresta Ombrófila Densa ou Floresta Pluvial Atlântica (FPA) distribui-se ao longo de toda a costa brasileira. Apresenta elevada riqueza de espécies e um grande número de espécies endêmicas. Suas fitofisionomias são classificadas de acordo com a latitude e altitude em que ocorrem. Propomos neste estudo investigar os padrões de distribuição da diversidade alfa em sítios localizados em toda área de ocorrência da Floresta Pluvial Atlântica, procurando identificar centros de diversidade, a relação entre a distribuição da diversidade alfa e variáveis ambientais e a padrões de distribuição dos táxons (família, gêneros e espécies) ao longo da FPA. Utilizamos como medida de diversidade o índice de Shannon (H') e separamos as tabelas fitossociológicas por região geográfica. Os resultados apontaram para uma maior diversidade alfa na região sudeste brasileira, principalmente nos estados do Espírito Santo, São Paulo e Rio de Janeiro. Utilizamos regressões múltiplas e análises de correspondência canônica (CCA) para verificarmos correlações entre variáveis ambientais e índices de diversidade (H', ChaoI e C de Simpson). Nossos resultados demonstraram uma relação positiva entre latitude, altitude e longitude e os índices H' e ChaoI e uma relação negativa para C, em ambas as análises. Considerando os níveis taxonômicos analisados (família, gêneros e espécies), predominou o padrão de distribuição geográfica restrita. Myrtaceae apresentou a maior diversidade hierárquica e a maior constância relativa entre todas as famílias analisadas. Ocotea e Eugenia foram os dois únicos gêneros que apresentaram constância relativa acima de 80%. Dentre as espécies analisadas, nenhuma apresentou constância relativa >80% / Abstract: Patterns of species diversity exist and are studied within a variety of systems and spatial scales. Different geographical and environmental factors have been associated to the range of diversity in forest areas; however, there is of yet no consensus in the scientific community regarding the importance and the influence of these factors in relation to the increase or the decrease in diversity. Specific studies on floristics and phytosociology in Brazil have enabled establishing some patterns and inferences on the factors which directly affect the diversity in a particular site. The Atlantic Ombrophilous Dense Forest or the Atlantic Rain Forest (ARF) is distributed along the entire Brazilian coastline. It presents an abundance of species and an elevated number of endemic species. Its phytophysiognomies are classified according to the latitude and the altitude in which they occur. In this study we propose to investigate the patterns of distribution of the alpha diversity in sites located throughout the Atlantic Rain Forest, aiming at identifying centers of diversity, the relationship between the distribution of the alpha diversity and environmental variables and the patterns of distribution of taxons (family, genus and species) along the ARF. As a measurement of diversity, we used the Shannon Index (H') and we separated the sites according to geographical area. Results have shown a larger alpha diversity in the Southeast of Brazil, especially in the Espírito Santo, São Paulo e Rio de Janeiro states. We have used multiple regressions and Canonical Correspondence Analysis (CCA) to observe the correlation between environmental variables and diversity indices (H', Chao I and Simpson's C). Our results showed a positive relationship between latitude, altitude, longitude, and the H' and Chao I index and a negative relationship to C, in both analysis Considering the taxonomic levels that were analyzed (family, genus and species), a pattern of restricted geographical distribution was predominant. Myrtaceae presented larger hierarchical diversity and the highest relative constancy among all the families analyzed Ocotea and Eugenia were the only two genus which presented relative constancy higher than 80 %. Among the species analyzed, none presented relative constancy >80% / Doutorado / Biologia Vegetal / Doutor em Biologia Vegetal

No description available.

The Juno Waves instrument detected new broadband plasma wave emissions on the first three successful passes over the low altitude polar regions of Jupiter on Days 240 and 346 of 2016 and Day 033 of 2017. This study investigated the characteristics of these emissions and found similarities to whistler-mode auroral hiss observed at Earth, including the funnel-shaped frequency-time features. The electron cyclotron frequency was much higher than both the emission frequencies for all three days and the local plasma frequency, which was assumed to be 20 – 40 kHz. The electric to magnetic field (E/cB) ratio was around three near the start of each event and then decreased to one for the remaining duration of each pass. Spin modulation phase shifts were found on two of the three days (Day 240 and Day 033), indicating wave propagation up to the assumed plasma frequency. A correlation of the electric field spectral densities with the flux of up-going 20 to 800 keV electron beams on all three days were found, with correlation coefficients of 0.59, 0.72, and 0.34 for Day 240, Day 346, and Day 033 respectively. We conclude that the emissions are propagating in the whistler-mode and are driven by energetic up-going electron beams along the polar cap magnetic field lines.

One of the intriguing features of the F-region ionosphere are anomalous evening enhancements of the electron density over certain mid-latitude sites. The most prominent example of this enhancement is the Weddell Sea Anomaly. Although the evening anomalies have been known for several decades, their generation mechanisms are still under debate and their accurate modeling remains a challenge. In this dissertation, the role of thermospheric neutral winds in the generation of these anomalies is investigated. Thermospheric winds play an important role in the dynamics of the F-region ionosphere, and, as it will be shown, in the generation of the evening anomalies. However, to date, their reliable estimation remains a challenge. To mitigate this shortcoming, data assimilation models were employed. First, seasonal global maps of F-region peak parameters (NmF2 and hmF2) from COSMIC radio occultation measurements were assimilated into the Global Assimilation of Ionospheric Measurements Full Physics (GAIM-FP) model. The model estimates magnetic meridional winds at low and mid-latitudes. GAIM-FP estimated winds were shown to be in good agreement with independent ground-based wind observations. Next, in order to address the role of neutral wind components in the generation of anomalies, a separate, 3-D physics-based Thermosphere Wind Assimilation Model (TWAM) was developed. TWAM is based on an implicit Kalman filter technique, and combines GAIM-FP magnetic meridional wind data with the equation of motion of the neutral gas to provide the climatology of the thermospheric wind components. The neutral wind components estimated by TWAM were also found to be in close quantitative agreement with independent ground-based wind observations, and were shown to accurately reproduce NmF2 and hmF2 over the anomalies. To understand the physical mechanism behind the anomalies, the plasma production, loss, and transport processes were analyzed. It was found that, due to the action of the equatorward wind, the evening density maximum forms at altitudes where the recombination rate is relatively small. It was revealed that at this time and altitude, plasma loss due to transport also weakens. As a consequence, the relative role of solar production increases over the net loss process and the electron density enhancement occurs.

Biodiversity is a fundamental part of the functioning of ecosystems and their ability to provide ecosystem services. It has been shown that a high biodiversity increases the robustness of an ecosystem according to the insurance hypothesis. I propose that a similar effect can be seen on a higher scale, where a high diversity of ecosystem types might stabilize the ecological functionality of a region. By comparing eleven network characters in 70 tropical and temperate ecosystems, their diversity was measured as Euclidean distance between the systems in the 11-dimensional room defined by these characters.  The diversity of ecosystems was shown to be significantly higher in tropical latitudes than in temperate. A possible explanation to this result could be that the higher species diversity in the tropics allows for more types of ecosystems. A higher diversity of ecosystems in a region might indicate a larger amount and variation of possible ecosystem goods and services as well as provide the region with an increased robustness. The measurement of ecosystem diversity between regions might also be of importance in a conservation perspective, where unique and vulnerable ecosystems can be discovered and protected.

L'influence des dirigeants sur la performance (ou contre-performance) de la firme fait l'objet de nombreux débats. Selon la vision déterministe, les pressions internes et externes qui s'exercent sur le dirigeant sont si importantes que ce dernier dispose de très peu de marge de manoeuvre pour influencer les résultats de la firme. D'un autre côté, selon les partisans de l'école du leadership, le dirigeant est l'unique architecte de l'entreprise et c'est à lui qu'incombe la performance de l'entreprise. Ces deux points de vue sont nuancés par le concept de latitude managériale qui mesure la marge de manoeuvre dont le dirigeant qui lui permet de se démarquer significativement des autres entreprises du secteur. Cette thèse s'intéresse à la responsabilité du dirigeant sur la performance de la firme ainsi que sur les décisions qui y sont opérées. Elle porte sur les grands patrons français qui ont, notamment, la particularité de former de puissants réseaux sociaux. Le premier chapitre dresse un portrait des grands dirigeants français et met en évidence les principales caractéristiques des décideurs hexagonaux. Le deuxième chapitre étudie le phénomène d'endogamie observé lors des successions de dirigeants ainsi que l'impact sur la performance de la firme. Le troisième chapitre propose une évaluation de l'effet du dirigeant sur la performance de la firme. Enfin le quatrième chapitre mesure l'impact du pouvoir du dirigeant sur les décisions de de croissance externe de la firme. Cette thèse corrobore l'idée que le pouvoir économique demeure au sein d'une castedirigeante fermée