The several million years preceding the Cretaceous/Paleogene (K/Pg) boundary has been the focus of many studies. Changes in ocean circulation and sea level, extinctions, and major volcanic events have all been documented for this interval. Important research questions these changes raise include the climate dynamics during the warm, but not hot, time after the decay of the Late Cretaceous greenhouse interval and the stability of ecosystems prior to the mass extinctions at the end-Cretaceous. I document several biotic perturbations as well as changes in ocean circulation during the Maastrichtian stage of the latest Cretaceous that question whether the biosphere was being preconditioned for the end-Cretaceous extinction. The first event at Shatsky Rise in the tropical North Pacific was the brief acme of inoceramid clams at ~71 Ma, followed by their abrupt extinction during the “mid-Maastrichtian event” at 70.1 Ma. The second is an intriguing dissolution event that began ~67.8 Ma at Ocean Drilling Program Site 1209 (2387 m). The dissolution event is marked by very poor planktic foraminiferal preservation and sharply reduced calcareous plankton diversity. The shift into the dissolution interval was initially gradual, then rapid. Within the late Maastrichtian dissolution interval, the planktic/benthic (P/B) ratio is low, planktic foraminifera are highly fragmented, larger taxa are mostly absent, small taxa are relatively abundant, and planktic foraminifera and nannofossil species richness are low. The event is followed by an abrupt recovery in carbonate preservation ~300 kyr prior to the K/Pg boundary. Was the dissolution event caused by a change in deep water circulation, migration of the site out of the high productivity tropical belt, or ocean acidification associated with Deccan Traps volcanism? Our data show that changing deep water masses, coupled with reduced productivity and associated decrease in pelagic carbonate flux was responsible for the dissolution interval, while Deccan Traps volcanism may have caused surface ocean acidification ~200-kyr prior to the K/Pg mass extinction event.

No description available.

Gallium Nitride (GaN) high electron mobility transistors (HEMT) have superior performance characteristics compared to Silicon (Si) and Gallium Arsenide (GaAs) based transistors. GaN is a wide bandgap semiconductor which allows it to operate at higher breakdown voltages and power. Unlike traditional semiconductor devices, the GaN HEMT channel region is undoped and relies on the piezoelectric effect created at the GaN and Aluminum Gallium Nitride (AlGaN) heterojunction to create a conduction channel in the form of a quantum well known as the two dimensional electron gas (2DEG). Because the GaN HEMTs are undoped, these devices have higher electron mobility crucial for high frequency operation. However, over time and use these devices degrade in a manner that is not well understood. This research utilizes low frequency noise (LFN) as a method for analyzing changes and degradation mechanisms in GaN-on-Si devices due to gate stress. LFN is a useful tool for probing different regions of the device that cannot be measured through direct means. LFN generation in GaN HEMTs is based on the carrier fluctuation theory of 1/f noise generation which states fluctuations in the number of charge carriers results in conductance fluctuations that produce a Lorentzian noise spectrum. The summing Lorentzian noise spectra from multiple traps leads to 1/f and random telegraph signal (RTS) noise. The primary cause of carrier fluctuations are electron traps near the 2DEG and in the AlGaN bulk. These traps occur naturally due to dislocations and impurities in the manufacturing process, but new traps can be generated by the inverse-piezoelectric effect during gate stress. This thesis introduces noise and presents a circuit to bias the devices and measure gate and drain LFN simultaneously. Three measurements are performed before and after gate DC stress at three different temperatures: DC characterization, capacitance-voltage (C-V) measurements, and LFN measurements. The DC characteristics show an increase in gate leakage after stress caused by an increase in traps after degradation consistent with trap assisted tunneling. However, the leakage current on the drain and source side differ before and after stress leading to the conclusion that the source side of the gate is more sensitive to gate stress. Gate leakage current on the drain side is also sensitive to temperature due to thermionic trap assisted tunneling. Hooge parameter calculations agree with previous research. The LFN results show an increase in gate and drain noise power, SIg(f) and SId(f), in accordance with increased gate leakage current under cutoff bias. RTS noise is also observed to increase in frequency with increased temperature. Activation energies for RTS noise are extracted and qualitatively linked to trap depth based on the McWhorter trap model.

<p>  </p> <p>In recent decades, wildlife studies have begun to incorporate more structural characteristics into studies of habitat. However, most still collect habitat data primarily from field measurements, which are limited in spatial extent and force researchers to extrapolate from small-scale, ground-based measures. LiDAR offers the opportunity to objectively measure habitat features across landscape-level extents. I mapped and measured forest canopy structural diversity at 181 plots across Indiana at a series of three (25-m, 50-m, and 100-m) radii to quantify landscape heterogeneity across space, utilizing new 2016–2020 aerial LiDAR in tandem with high-resolution camera traps. I aimed to quantify the relationship between use of forest sites by seven wildlife species and habitat structural characteristics, specifically predicting species occupancy as a function of LiDAR-derived metrics. I predicted that habitat generalists like raccoons (<em>Procyon lotor</em>) and Virginia opossum (<em>Didelphis virginiana</em>) would be best predicted by the null hypothesis and that measures of gap fraction would best predict edge species such as coyote (<em>Canis latrans</em>), white-tailed deer (<em>Odocoileus virginianus</em>), and wild turkey (<em>Meleagris gallopavo</em>). Additionally, I predicted a positive relationship between vegetation area and both eastern cottontail rabbit (<em>Sylvilagus floridanus</em>) and tree squirrels (Sciuridae spp.). I expected that measures of habitat heterogeneity would be included in best models for tree squirrels and white-tailed deer, and that models for squirrels would have lower root mean square error (RMSE) values. Ultimately, structural metrics varied across radii, and best models depended on plot radius size. Measures of vertical heterogeneity were the best predictors for species like raccoon, wild turkey, and coyote, with a higher probability of occupancy for all three with increased heterogeneity. Additionally, models for eastern cottontail rabbit incorporating vegetation area indices, Gini diversity, and gap fraction demonstrated significance and low predictive error. Habitat generalists, such as white-tailed deer and Virginia opossum did not select for specific structural metrics and were best predicted by the null model. Ultimately, these results indicated that LiDAR is a promising potential tool for measuring ecologically meaningful variables at scales large enough to properly represent home range and resource use at the home-range level, filling an important gap in our understanding. </p>

In South Africa, the majority of youth entering emerging adulthood find themselves in a protracted struggle to access further education, training or to secure their first decent job. The purpose of this multi-case study is to deepen the understanding of how capability measurement approaches and tools can empower marginalized youth to better understand their aspirations and map their way through emerging adulthood and out of poverty. This research aims to deepen the understanding of youth's experience utilizing 'Poverty Stoplight'; a poverty measurement and capability building instrument that utilizes a self-assessment survey and mentorship methodology. The researcher utilized a youth-focused participatory approach in conducting focus groups and in-depth one-on-one interviews across five marginalized communities in the Western Cape to gain insight into their experience using the tool, their ability to envision their future selves and develop their aspirations. What emerged from the data were insights into the youth's aspirations, the perceived enabling factors and impediments towards their aspirations and their experiences utilizing Poverty Stoplight. This process enabled youth to genuinely reflect and assess their situation, and have the opportunity to define their aspirations. Overall the Poverty Stoplight programme was experienced as empowering by participants, with several implications for the programme pertaining to data accessibility, communication, mentorship and solution sharing, as well as the importance of youth-specific participatory approaches. Aligned to this, the findings yielded several recommendations pertaining to providing support and enabling opportunities for emerging adults to realise their aspirations. Despite the limitations of this research, this study is relevant for stakeholders in South Africa and globally as it examines the critical issue of youth development, with a focus on the ability of young people to attain their aspirations. Further, it analyses the capability measurement approach as a means to ensuring young people can better understand and plot their way out of poverty, making the most of their individual capabilities and attributes within the broader structural and systemic challenges they face. This exploration of practical tools and methodologies being developed and utilized by pioneering organisations in the South African context provides empirical evidence of the merit of such approaches, with recommendations on how tools and approaches can even better serve the needs of youth. Further, longitudinal research is merited into the use of such capability measurement approaches to empower youth and the further use of participatory methodologies.

L'Afrique de l'Ouest se caractérise par de forts taux de pauvreté et par une protection sociale et des marchés financiers formels défaillants. Dans un tel contexte, les familles remplissent des rôles importants qui façonnent la vie économique et sociale de leurs membres. Cependant, l'efficacité de cette institution fait débat, notamment lorsqu'elle est analysée du point de vue individuel. Ainsi, un nombre croissant d'études en économie du développement se penchent sur les coûts individuels induits par les fonctions familiales. Ma thèse de doctorat s'appuie sur cette littérature et y contribue en analysant la façon dont les décisions économiques individuelles sont prises au sein de la famille au Sénégal, et illustre des cas où la famille ne parvient pas à assurer le bien-être individuel de ses membres.Le premier chapitre s'attache à mesurer les coûts individuels de la redistribution informelle qui a lieu au sein des réseaux sociaux et entre ces derniers, et en particulier au sein de la famille élargie. En effet, en tant que mécanisme d'assurance, de fortes pressions redistributives modifient les choix économiques individuels. En s'appuyant sur des données expérimentales, nous estimons une taxe sociale d'environ 9% et nos résultats indiquent l'existence de fortes distorsions dans les choix d'allocation individuels. Par ailleurs nos résultats montrent que la pression à la redistribution est du fait, principalement, de famille élargie et non du ménage, des cercles amicaux ou du voisinage. Le deuxième chapitre examine comment l'environnement sanitaire contraint les investissements parentaux en termes de santé des enfants. Son objectif est de déterminer si les risques concurrents en mortalité réduisent les investissements des parents dans la santé de leurs enfants. Pour cela nous faisons, dans cet article, l'hypothèse qu'il existe des complémentarités entre les investissements en santé spécifiques à certaines maladies ; et testons celle-ci en nous appuyant sur une intervention récente visant à éradiquer le paludisme au Sénégal. Nos résultats soutiennent ce modèle de risques concurrents et impliquent que les comportements privés d'investissement en santé des parents et les politiques publiques de santé sont complémentaires. Enfin, le troisième chapitre explore comment une stratégie de gestion des risques ex-post, le mariage d'enfants, est lié aux chocs de mortalité au sein des familles. En particulier, j'examine si les décès paternels ont des conséquences néfastes en termes de transition sur le marché du mariage des jeunes orphelines. Mes résultats mettent en évidence la grande vulnérabilité de ce groupe d'enfants en termes de mariages précoces. / In the West Africa subregion, poverty is pervasive and social protection at the state-level, as well as formal financial markets poorly function. In such a context, families fulfill important roles, which shape the economic and social life of its members and are key drivers of economic development. How this private institution performs is, however, quite a debate and a growing body of the literature in development economics has focused on the question of the economic inefficiencies of the family institution. My PhD thesis builds upon this literature and contributes to it by shedding light on how individual economic decisions are taken within the family in Senegal, and in which cases the family fails to ensure individual welfare of its members.The first chapter focuses on the individual costs of the informal redistribution that take place within and between social networks, and in particular within the extended family. Using a lab-in the field experiment, we aim at identifying the hidden costs of social obligations for redistribution on individual resource allocation choices. Our results are threefold: (i) we estimate a social tax of about 9\%; (ii) we provide evidence on strong distortions in individual allocation choices; (iii) our results point at people fearing redistributive pressure from the extended family members, but not from within the household or from friends and neighbors. We expand on prior literature by both identifying the individual cost of informal redistribution and then relating it to postexperiment resource-allocation decisions, and by disentangling intra- and interhousehold redistributive pressure. The second chapter investigates how the health environment prevents parents from investing in child health. Its main objective is to investigate whether the health risks faced by children, and in particular their competing nature as mortality risks, depress parental investment in child health. We argue that there are complementarities between disease-specific investments and we test this hypothesis by exploiting recent interventions that made anti-malaria products suddenly affordable to most households in 2009 in Senegal. Our first contribution is to be the first to use data on private health expenditures to validate a model with complementarities between disease-specific investments. Our second contribution is to show that parental behavioral responses clearly complement anti-malaria campaigns, whereby they magnify their impact on all-cause mortality for children. Finally, the third chapter explores how a quite harmful ex-post risk management strategy, child marriage, relates to changes in family structures (mortality shocks). In particular, I investigate whether paternal death induces adverse marriage outcomes for young orphans. I also discuss the channel that could induce such effects. My results underpinned the high vulnerability of this group of children: when the father dies, the young girls are more likely to marry as child brides and to be child mothers than their non-orphan counterparts. Those girls have more frequently broken marital trajectories, in particular due to divorce. This paper builds upon the existing demographic literature and provides at least two contributions. First, it is, to my knowledge, the first to study jointly the timing of the father's death and other dimensions of well-being such as fertility, marital dissolution and consumption. Second, it discusses the extent to which selection on unobservables might bias the analysis, an issue that is discarded in most studies.

Dans ce mémoire, nous nous penchons sur des résultats de localisation pour les marches biaisées en milieux aléatoires. Plus précisément, nous allons revisiter la démarche que David Croydon a fait afin de prouver un résultat de localisation pour la marche aléatoire biaisée sur la trace d’une marche aléatoire simple dans Z^d. Ensuite, nous allons débuter la généralisation de son résultat au cas où l’environnement sous-jacent est la marche aléatoire branchante par l’élaboration d’un résultat de localisation pour la marche biaisée sur la trace d’une bonne approximation des marches branchantes, leur K-squelette. / In this thesis, we will look at localization results for random walks on random environnements. More precisely, we will go through the techniques used by David Croydon to prove a localization result for the biased random walk on the trace of a simple random walk in Z^d. Then, we will begin the generalization of his result to the case where the underlying environnement is a branching random walk. To do this, we will prove a version of the localization result for the biased random walk on the trace of a K-skeleton in Z^d, which is a good approximation of the branching random walk.

AlGaN/GaN metal–insulator–semiconductor high electron mobility transistors (MIS-HEMTs) are promising candidates for next generation high-efficiency and high-voltage power applications. The excellent physical properties of GaN-based materials, featuring high critical electric field and large carrier saturation velocity, combined to the high carrier density and large mobility of the two-dimensional electron gas confined at the AlGaN/GaN interface, enable higher power density minimizing power losses and self-heating of the device. However, the advent of the GaN-based MIS-HEMT to the industrial production is still hindered by technological challenges that are being faced in parallel. Among them, one of the biggest challenge is represented by the insertion of a gate dielectric in MIS-HEMTs compared to Schottky-gate HEMTs, which causes operational instability due to the presence of high-density trap states located at the dielectric/III-nitride interface or within the dielectric. The development of a gold-free ohmic contact technology is another important concern since the high-volume and cost-effective production of GaN-based transistors also depends on the cooperative manufacturing of GaN-based devices in Si production facilities, where gold represents an undesidered source of contamination. In fact, even though over the past years there have been multiple attemps to develop gold-free ohmic contacts, there is still no full understanding of the contact formation and current transport mechanism. The first objective of this work was the investigation of a gold-free and low-resistive ohmic contact technology to AlGaN/GaN based on sputtered Ta/Al-based metal stacks annealed at low temperatures. A low contact resistance below 1 Ω mm was obtained using Ta/Al-based metal stacks annealed at temperatures below 600 °C. The ohmic behavior and the contact properties of contact resistance, optimum annealing temperature and thermal stability of Ta/Al-based contacts were studied. The nature of the current transport was also investigated indicating a contact mechanism governed by thermionic field emission tunneling through the AlGaN barrier. Finally, gold-free Ta/Al-based ohmic contacts were integrated in MIS-HEMTs fabricated on a 150 mm GaN-on- Si substrate, demonstrating to be a promising contact technology for AlGaN/GaN devices and revealing to be beneficial for devices operating at high temperatures. The optimization of the MIS-gate structure in terms of trap states at the dielectric/III-nitride interface and inside the dielectric in MIS-HEMTs using atomic layer deposited (ALD) Al2O3 as gate insulator was the second focus of this work. First, the MIS-gate structure was improved by an O2 plasma surface preconditioning applied before the Al2O3 deposition and by an N2 postmetallization anneal applied after gate metallization, which significantly reduced trap states at the Al2O3/GaN interface and within the dielectric. Afterwards, the effectiveness of these treatments was demonstrated in Al2O3-AlGaN/GaN MIS-HEMTs by pulsed current–voltage measurements revealing improved threshold voltage stability. Lastly, it was shown that also the lower annealing temperatures used for the formation of Ta/Al-based ohmic contacts, processed before gate dielectric deposition, are beneficial in terms of trap states at the ALD-Al2O3/GaN interface, representing a new aspect to be considered when using an ohmic first fabrication approach.

Three different habitats: secondary forest, acacia plantation, and mixed forests on limestone, were chosen to determine and compare the ant species diversity in these habitats. A total of 24 identified species and 11 morphology species belonging to 20 genera in seven subfamilies were collected using pitfall traps from June 2014 to May 2015. The Shannon-Wiener’s species diversity index indicated that the diversity was the highest in the acacia plantation (2.08), followed by the secondary forest (1.99) and lowest in the mixed forests on limestone (1.83). There are three dominant species in the habitat (I), Pheidole noda, Odontomachus cf. monticola, and Odontoponera denticulate; four dominant species in the habitat (II), Odontoponera denticulata, Carebara diversa, Technomyrmex brunneus and Anoplolepis gracilipes; and only one dominant species in the habitat (III), Anoplolepis gracilipes. The species similarity (S) relatively low may be because of the difference vegetation and condition in the three habitats. / Đa dạng loài kiến trong ba môi trường sống khác nhau: rừng rậm thường xanh nhiệt đới, rừng keo và rừng hỗn giao trên núi đá vôi, được nghiên cứu để xác định và so sánh sự đa dạng các loài kiến trong những môi trường sống. Phương pháp nghiên cứu: sử dụng bẫy hố từ tháng 6 năm 2014 đến tháng 5 năm 2015. Đã ghi nhận được 35 loài, thuộc 20 giống, 7 phân họ. Chỉ số đa dạng loài Shannon-Wiener cho thấy rừng keo có chỉ số đa dạng cao nhất (2,08), tiếp theo là rừng rậm thường xanh nhiệt đới (1,99) và cuối cùng là rừng hỗn giao trên núi đá vôi (1,83). Có 3 loài ưu thế ở sinh cảnh (I) là Pheidole noda, Odontomachus cf. monticola và Odontoponera denticulata, bốn loài ưu thế ở sinh cảnh (II) là Carebara diversa, Technomyrmex brunneus, Odontoponera denticulate và Anoplolepis gracilipes. Ở sinh cảnh (III) chỉ có duy nhất một loài chiếm ưu thế là loài Anoplolepis gracilipes. Chỉ số tương đồng (S) tương đối thấp có thể là do sự khác nhau ở các thảm thực vật và điều kiện sống trong ba sinh cảnh.

No description available.