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1
Rhod, Eduardo Luis. "Quaternary CLB a falul tolerant quaternary FPGA". reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2012. http://hdl.handle.net/10183/72925.
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A diminuição no tamanho dos transistores vem aumentando cada vez mais o número de funções que os dispositivos eletrônicos podem realizar. Apesar da diminuição do tamanho mínimo dos transistores, a velocidade máxima dos circuitos não consegue seguir a mesma taxa de aumento. Um dos grandes culpados apontados pelos pesquisadores são as interconexões entre os transistores e também entre os componentes. O aumento no número de interconexões dos circuitos traz consigo um significativo aumento do cosumo de energia, aumento do atraso de propagação dos sinais, além de um aumento da complexidade e custo do projeto dos circuitos integrados. Como uma possível solução a este problema é proposta a utilização de lógica multivalorada, mais especificamente, a lógica quaternária. Os dispositivos FPGAs são caracterizados principalmente pela grande flexibilidade que oferecem aos projetistas de sistemas digitais. Entretanto, com o avanço nas tecnologias de fabricação de circuitos integrados e diminuição das dimensões de fabricação, os problemas relacionados ao grande número de interconexões são uma preocupação para as próximas tecnologias de FPGAs. As tecnologias menores que 90nm possuem um grande aumento na taxa de erros dos circuitos, na lógica combinacional e sequencial. Apesar de algumas potenciais soluções começara a ser investigadas pela comunidade, a busca por circuitos tolerantes a erros induzidos por radiação, sem penalidades no desempenho, área ou potência, ainda é um assunto de pesquisa em aberto. Este trabalho propõe o uso de circuitos quaternários com modificações para tolerar falhas provenientes de eventos transientes. Como principal contribuição deste trabalho destaca-se o desenvolvimento de uma CLB (do inglês Configurable Logic Block) quaternária capaz de suportar eventos transientes e, na possibilidade de um erro, evitá-lo ou corrigi-lo.The decrease in transistor size is increasing the number of functions that can be performed by the electronic devices. Despite this reduction in the transistors minimum size, the circuit’s speed does not follow the same rate. One of the major reasons pointed out by researchers are the interconnections between the transistors and between the components. The increase in the number of circuit interconnections brings a significant increase in energy consumption, propagation delay of signals, and an increase in the complexity and cost of new technologies IC designs. As a possible solution to this problem the use of multivalued logic is being proposed, more specifically, the quaternary logic. FPGA devices are characterized mainly by offering greater flexibility to designers of digital systems. However, with the advance in IC manufacturing technologies and the reduced size of the minimum fabricated dimensions, the problems related to the large number of interconnections are a concern for future technologies of FPGAs. The sub 90nm technologies have a large increase in the error rate of its functions for the combinational and sequential logic. Although potential solutions are being investigated by the community, the search for circuits tolerant to radiation induced errors, without performance, area, or power penalties, is still an open research issue. This work proposes the use of quaternary circuits with modifications to tolerate faults from transient events. The main contribution of this work is the development of a quaternary CLB (Configurable Logic Block) able to withstand transient events and the occurrence of soft errors.
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Lizak, Pawel. "Optimal quaternary linear codes". Thesis, University of Salford, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.308200.
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Grandin, Henrik. "Hybrid Quaternary/Binary Computing". Thesis, Uppsala universitet, Institutionen för informationsteknologi, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-305243.
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Due to scaling limitations and the end of Dennard scaling, energy efficiency has become a primary design goal. Approximate computing aims to solve this problem by sacrificing accuracy for efficiency. This project have evaluated a dual mode architecture that gives accuracy when needed and energy efficiency when it is possible. By combining binary and quaternary logic, up to half of the logic could be deactivated whenever absolute correctness is not critical. This project also proposes a hybrid mode, which aims to increase the number of cases where a more energy efficient representation could be used. By combining the two modes through using the more stable binary logic for the bits with higher significance, while at the same time using the energy efficient quaternary logic for the bits with the least significance, energy can still be saved while at the same time drastically limiting the potential size of the error. Simulations have shown that the hybrid mode not only succeeds in decreasing the maximum size of errors, but also reduces the total number of errors, compared to the quaternary mode. Results show increased energy efficiency of 10% without altering the perceived result at all. If we allow for some degradation of the result, the energy efficiency would improve with almost 40%.
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Cattley, Christopher Andrew. "Quaternary nanocrystal solar cells". Thesis, University of Oxford, 2016. http://ora.ox.ac.uk/objects/uuid:977e0f75-e597-4c7a-8f72-6a26031f8f0b.
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This thesis studies quaternary chalcogenide nanocrystals and their photovoltaic applications. A temperature-dependent phase change between two distinct crystallographic phases of stoichiometric Cu2ZnSnS4 is investigated through the development of a one pot synthesis method. Characterisation of the Cu2ZnSnS4 nanocrystals was performed using absorption spectroscopy, transmission electron microscopy (TEM) and powder X-ray diffraction (XRD). An investigation was conducted into the effects of using hexamethyldisilathiane (a volatile sulphur precursor) in the nucleation of small (<7nm), mono-dispersed and solution-stable quaternary Cu2ZnSnS4 nanocrystals. A strategy to synthesize high quality thermodynamically stable kesterite Cu2ZnSnS4 nanocrystals is established, which subsequently enabled the systematic study of Cu2ZnSnS4 nanocrystal formation mechanisms, using optical characterization, XRD, TEM and Raman spectroscopy. Further studies employed scanning transmission electron microscopy (STEM) energy dispersive x-ray (EDX) mapping to examine the elemental spatial distributions of Cu2ZnSnS4 nanocrystals, in order to analyse their compositional uniformity. In addition, the stability of nanocrystals synthesised using alternative ligands is investigated using Fourier transform infrared spectroscopy, without solution based ligand substitution protocol is used to replace aliphatic reaction ligands with short, aromatic pyridine ligands in order to further improve Cu2ZnSnS4 colloid stability. A layer-by-layer spin coating method is developed to fabricate a semiconductor heterojunction, using CdS as an n-type window, which is utilised to investigate the photovoltaic properties of Cu2ZnSnS4 nanocrystals. Finally, three novel passivation techniques are investigated, in order to optimise the optoelectronic properties of the solar cells to the point where a power conversion efficiency (PCE) of 1.00±0.04% is achieved. Although seemingly modest when compared to the performance of leading devices (PCE>12%) this represents one of the highest obtained for a Cu2ZnSnS4 nanocrystal solar cell, fabricated completely under ambient conditions at low temperatures.
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Grun, Rainer Wolfgang. "Contributions to quaternary geochronology". Phd thesis, Canberra, ACT : The Australian National University, 1995. http://hdl.handle.net/1885/145307.
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Hardiman, J. C. "Quaternary volcanism on Nisyros, Greece". Thesis, University of Cambridge, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.603684.
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This thesis describes the volcanic deposits on Nisyros, Aegean sea, Greece and uses them to understand volcanic processes and the evolution of the island. Nisyros is a small (42 km2 in area) symmetric stratovolcano which has evolved on the eastern end of the Aegean volcanic arc over the last 200 ka of the Quaternary. The first volcanic activity was submarine. This left a layer of pillow larvas of basaltic-andesite composition overlying the Tertiary sedimentary basement of the Aegean. Subsequent volcanic activity was subaerial, and over 20 lava and pyroclastic eruptions of basaltic-andesite to rhyolite composition led to the formation of a stratovolcano. The younger eruptions were rhyolitic and the magma emitted is estimated to be of the order of a few km3 in volume. These eruptions led to the formation of a 10 km2 in area caldera which now dominates the centre of the island. A suite of domes were extruded progressively on western side of the caldera floor with field appearances suggesting activity continuing into the Holocene. The activity documented in historical records and seen at the present day is entirely phreatic and is the expression of a geothermal reservoir at a shallow depth below the caldera floor. The aims of this project were to describe the volcanic stratigraphy, to use the xenolith suite to understand magmatic and vent erosion processes, and to use the deposits from the three rhyolite eruptions to understand the youngest volcanic history of the island and timing of the caldera formation. Fieldwork was used to deduce the stratigraphy of the island. The stratocone succession consists of 3 cycles that start with basaltic-andesite to andesite lavas (BA&AI, BA&AII. BA&AIII) and pyroclastic deposits (SPI, SPII, SPIII) and proceed to dacite to rhyolite lava extrusions (DI, DII and RI, DIII) and pyroclastics (MSP, PK, LP).
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Franke, Jasper Gideon. "Networks of the late Quaternary". Doctoral thesis, Humboldt-Universität zu Berlin, 2019. http://dx.doi.org/10.18452/19994.
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In den letzten Jahren erfreuen sich komplexe Netzwerke einer zunehmenden Beliebtheit, um Zusammenhänge und Strukturen in hoch-dimensionalen Datensätzen zu analysieren. Im Unterschied zu vielen anderen Forschungsgebieten wurden sie jedoch selten auf Paläoklima-Daten angewandt, obwohl die steigende Anzahl an veröffentlichen Zeitreihen die Nutzung effizienter Methoden multivariater Analyse ermöglicht. Die Resultate der wenigen Studien, in denen Netzwerkmethoden und Paläoklima-Daten kombiniert wurden, sind außerdem geprägt von niedriger Robustheit und hohen Unsicherheiten. Dies steht im Zusammenhang zu der niedrigen Anzahl und Auflösung der Zeitreihen als auch den Unsicherheiten, die den meisten Paläoklima-Rekonstruktionen zu eigen sind.
In dieser Doktorarbeit schlage ich verschiedene Wege vor, um diese Probleme zu überwinden, indem verlässlichere, quantitative Resultate ermöglicht werden, unter anderem indem die Datenunsicherheiten explizit in die Analyse mit einbezogen werden. Zu diesem Zweck präsentiere ich vier Fallstudien mit einem Fokus auf zwei Zeiträume, das späte Holozän (die letzten zweitausend Jahre) und den Übergang von der letzten Kaltzeit zur aktuellen Warmzeit, die letzte glaziale Termination. Alle diese Studien legen einen räumlichen Fokus auf den Nordatlantik, eine Schlüsselregion globaler Klimavariabilität. Ich beschränke mich hierbei auf zwei Methoden, eine der netzwerkbasierten Zeitreihenanalyse, Sichtbarkeitsgraphen genannt, und eine der räumlichen Analyse, sogenannte Klimanetzwerke.
Neben Erweiterungen von existierende Methoden, schlage ich auch neue Wege vor, um verlässliche Resultate auch für Zeitreihen mit hohen Unsicherheiten zu erhalten. Diese Fallstudien demonstrieren, dass Netzwerkmethoden auch für die Analyse von Paläoklima-Daten nützlich sein können. Sie sind daher ein weiterer Schritt hin zu einer künftigen Anwendung durch eine größere Anzahl an Forschenden.In recent years, complex networks have become an increasingly popular tool to analyse relationships and structures in high-dimensional data sets in a variety of research fields. They have, however, rarely been applied to paleoclimate data sets, even though the growing number of published records demands efficient tools of multivariate analysis. The few published results that combine network methods and paleoclimate proxies are often not robust or have high uncertainty levels, linked tothe low dimensionality, resolution and the large uncertainties of most particulate time series. In this thesis, I propose several ways to overcome these issues in order to obtain reliable and quantitative results from network based tools by taking the particularities of paleoclimate data into account. For this purpose, I present four case studies, focusing on two time periods, the late Holocene (last two millennia) and the transition from the last ice age to the recent warm period, the last deglaciation. These studies are all related to the North Atlantic, a key region in multi-decadal to millennial scale climate variability. I primarily use two methods, one of network based time series analysis named visibility graphs and one of spatial analysis, so called limate networks. I have both further developed existing methods, but also propose new ways to yield reliable results when dealing with highly uncertain paleoclimate data. The case studies demonstrate the usefulness of network based data analysis to study patterns of regional climate variability. Hence, this work is another step in bringing network based approaches to a larger audience and towards a wider application of these methods.
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Souza, Melina Mara de 1984. "Palinologia em sedimentos quaternários, localizados na Estação do Instituto Florestal de Jataí, SP". [s.n.], 2010. http://repositorio.unicamp.br/jspui/handle/REPOSIP/287276.
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Orientadores: Frésia Soledad Ricardi Torres Branco, André JasperDissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Geociências
Made available in DSpace on 2018-08-16T07:38:35Z (GMT). No. of bitstreams: 1 Souza_MelinaMarade_M.pdf: 2503896 bytes, checksum: 9cde6f27f9a424cade3629e5e8b1b0b2 (MD5) Previous issue date: 2010
Resumo: O estudo de uma trincheira coletada em um meandro abandonado, as margens do Rio Mogi-Guaçú, em uma área coberta por Cerrado, na Estação do Instituto Florestal de Jataí, Município de Luís Antônio (SP), permitiu realizar estudos pertinentes a evolução paleoambiental e, possíveis inferências paleoclimáticas, ao longo dos últimos 10.251 anos A.P. As interpretações paleoecológicas foram baseadas nas análises dos fragmentos de carvão, assembléias de palinomorfos, e análises isotópicas. A partir das análises isotópicas foi possível estabelecer a cronologia dos eventos ocorridos no local, por meio de análises de 14C, e a distinção dos valores isotópicos de ? 13C, que possibilitou a interpretação e diferenciação das variações da vegetação de plantas C3 (árvore) e C4 (gramínea). A análise palinológica, foi baseada em diagrama de perfil de porcentagem e concentração dos palinomorfos preservados no depósito estudado, o que permitiu estabelecer, através de dados estatísticos a determinação e distribuição da vegetação durante o Holoceno na área de estudo. Para análise dos fragmentos de carvão, foi feita á identificação e separação dos fragmentos encontrados em cada nível, em estereomicroscópio e fotografados no MEV, estabelecendo inferências e informações importantes tanto no domínio das variações paleoambientais, como paleoclimáticas e paleoincêndios. Os resultados das análises palinológicas, isotópicas e fragmentos de charcoals apontaram para um clima mais seco que o atual entre 10.251 e 10.186 anos A.P. com altas taxas de fragmentos de carvão, indicando períodos de ocorrência de paleoincêndios e de abertura florestal, onde valores de ? 13C em torno de -14,26¿, mostram a presença de plantas C4 (gramíneas), uma vegetação mais aberta que a atual. Entre 10.186 e 2.096 anos A.P. onde ocorreu um empobrecimento isotópico e uma mistura de plantas C3 e C4, com o aumento da freqüência de grãos de pólen indicadores de Cerrado como Byrsonima e Dydimopanax, podemos inferir que nesta fase o clima esteve mais úmido, e a vegetação mais fechada. Após 2.096 anos A.P. até os dias atuais as condições paleoclimáticas seriam as mesmas, caracterizada como cerradão, que possui formações florestais com espécies de Cerrado sentido restrito, sem nenhum registro de fragmentos de carvão e o aparecimento de grãos de pólens de Cerrado
Abstract: The study collected a trench in an abandoned meander on the banks of Mogi-Guaçú River in an area covered by Cerrado at the Station of the Instituto Florestal de Jataí, in Municipality of Luis Antonio (SP). It was allowed to conduct relevant studies and palaeoenvironmental evollution, possible paleoclimatic inferences, over the past 10.251 years A.P. The paleoecological interpretations were based on analysis of charcoal fragments, palynomorph assemblages, and isotopic analysis. From the isotopic analysis it was possible to establish the chronology of events on site, by analysis of 14C, and the distinction of the isotopic values of ? 13C, which facilitated the interpretation and differentiation of changes in vegetation from C3 plants (trees) and C4 ( grass). Pollen analysis were based on census profile of the percentage and concentration of the palynomorphs preserved in the deposit studied allowing to establish, through statistical data, the determination and distribution of vegetation during the Holocene in the study area. To analyze the charcoals, it was made the identification and the fragments found in each level were separated by a stereomicroscope and photographed in the MEV, establishing inferences and important information, both in the field of palaeoenvironmental variations, as paleoclimate and paleofires. The results of pollen analysis, isotopic and charcoals fragments pointed to a drier climate than nowadays, from 10.251 to 10.186 years A.P. with high rates of charcoals fragments, indicating periods of paleofires occurrence and open forest where values around ? 13C -14,26 ¿, indicated the presence of C4 plants (grasses), more open vegetation than at present. From 10.186 to 2.096 years A.P. occurred an isotopic depletion and a mixture of C3 and C4 plants, increasing pollen frequency indicators of Cerrado and Byrsonima Dydimopanax. At this stage the climate was wetter and the vegetation closer. After 2.096 years A.P. until nowadays, the paleoclimatic conditions have been the same, characterized as Cerrado, which has forest with species of Cerrado sensu stricto with no record of charcoals and the appearance of pollen of Cerrado
Mestrado
Geologia e Recursos Naturais
Mestre em Geociências
9
Ghazoui, Zakaria. "Late Quaternary Seismicity and Climate in the Western Nepal : Himalaya". Thesis, Université Grenoble Alpes (ComUE), 2018. http://www.theses.fr/2018GREAU026/document.
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L'Himalaya résultant de la collision indo-asiatique, dans laquelle l'Inde plonge sous le Tibet, initie régulièrement des tremblements de terre destructeurs dont la plupart sont mortel pour les communautés népalaises et limitrophes. Telle une muraille séparant les plaines d’Inde et le haut plateau du Tibet, l’Himalaya façonne la circulation atmosphérique, affectant tant le climat régional que global. Cette thèse vise à se pencher sur l'histoire et l'évolution peu connue du climat et de la sismicité de l'Himalaya, dans une des régions les moins peuplées et la plus reculées du Népal occidental. Dans le contexte de changements climatiques et environnementaux, l'un des aspects les moins bien élucidés de l'histoire de l'Himalaya au cours du Quaternaire supérieur est celui de l'extension des glaciers ainsi que leurs impacts sur l'évolution du paysage. En nous appuyant sur des observations de terrain, sur des datations par nucléides cosmogéniques (10Be) ainsi que des observations satellitaires, nous avons pu estimer l'étendue maximale des glaciers durant le dernier maximum glaciaire. Soutenant ainsi l'hypothèse suivant laquelle la présence de glacier fut relativement plus étendue à l'échelle du Népal occidental mais pas de l’ordre d’une calotte glaciaire. Sur le plan sismologique, l’enjeu à la fois sociale, économique et politique de l’occurrence d’un séisme de magnitude plus élevée que le récent séisme de 2015 dont l’épicentre se situe près de la ville de Gorkha constitue une préoccupation majeure et motive en grande partie cette thèse. Le dernier séisme majeur ayant rompu le Main Frontal Thrust de magnitude supérieure à 8 (Mb) s’est déroulé le 6 juin 1505 et a considérablement impacté la population népalaise et environnante. Le caractère singulier du Népal occidental s’exprimant ainsi par l’hypothèse de la présence d’un hiatus sismique s’étendant sur plus de 500 ans sur base d’archives historiques et d’études paléosismologiques. Dans cette perspective, cette thèse se penche sur deux questions majeures relatives au comportement sismique de l'Himalaya : d'une part, l'hypothèse d'une lacune sismique dans l'Himalaya central et, d'autre part, de la distribution temporelle des séismes au cours de la fin du Quaternaire. A cette fin, une nouvelle approche de recherche, indépendamment du recours aux tranchées paléosismiques, a été mise en œuvre en Himalaya. En utilisant les lacs comme paleoseismomètre, au travers de la collecte de carottes sédimentaires, nous avons pu affiner la résolution temporelle et déceler des séismes à ce jours non répertorié dans les basses de données accessible et ce sur une échelle de 700 ans. La mise en évidence de séismes important (Mw>6.5) non répertorié indique que le Népal occidental connait une activité sismique comparable au centre du Népal et remet en question l’hypothèse d’un gap sismique au centre de l’Himalaya. Sur base d'une carotte sédimentaire plus longue provenant du même lac, nous avons étudié la distribution temporelle des séismes sur une période de 6000 ans, permettant ainsi de mettre en évidence le caractère aléatoire de l’occurrence des séismes constituant un changement de paradigme là où notion de cycle sismique est encore prépondérante. La mise en évidence du caractère aléatoire de l’occurrence des séismes tant à courte échelle de temps (instrumentale) qu’à l’échelle du Quaternaire infirme l’hypothèse du gap sismique au centre de l’Himalaya et mets en évidence le risque permanent pour le million de personnes concernées. Cette thèse s’achève en se penchant sur une possible relation à l’échelle globale entre la variation de taux de séismicité et les changements climatiques au cours de l’Holocène. Nous constatons ainsi que la sismicité globale connu des périodes de séismes accrue sur 7000 ans. Ces périodes de plus fortes activités semblent être synchrone avec la somme des avancées glaciaires de l'Holocène moyen et supérieurThe Himalayan collision, in which India underthrusts below Tibet, regularly produces major destructive earthquakes in Nepal and its neighboring countries, most of which are fatal to nearby communities. As a wall dividing the Indian plains and the Tibetan plateau, the Himalaya also significantly modifies the atmospheric circulation, affecting both the local and global climate. This thesis explores the poorly known Quaternary history and evolution of Himalayan climate and seismicity, more particularly in the least populated and most remote region of Western Nepal. In terms of climate and environmental change, one of the least understood aspects of Himalayan history during the late Quaternary is the extension of glaciers and their impacts on landscape evolution. Based on field observations, cosmogenic nuclide dating (10Be) and satellite observations, we estimated the maximum extent of glaciers during the Last Glacial Maximum, which supports the hypothesis of a relatively large glacier cover, but not of an extended ice cap, at the scale of Western Nepal. In terms of seismology, the social, economic and political implications of the occurrence of an earthquake of higher magnitude than the recent earthquake of 2015, whose epicenter is located near the city of Gorkha, is a major concern and largely motivates this thesis. The last major earthquake of magnitude greater than 8 (Mb) took place on 6 June 1505 and had a profound impact on the Nepalese population and the surrounding area. In Western Nepal the 1505 event was the last earthquake that ruptured the Main Frontal Thrust according to historical archives and paleoseismological studies, which gave rise to the concept of a seismic gap in western Nepal and adjacent areas in northern India. With this in mind, this thesis addresses two major issues on the Himalayan seismic behavior: on the first hand is the hypothesis of a seismic gap in the central Himalaya and on the second the temporal distribution of earthquakes during the late Quaternary. For this purpose, a new research approach independent of paleoseismic trenches was applied in the Himalaya. By using lakes as paleoseismometers, we were able to refine the temporal resolution and identify earthquakes that had not yet been documented in the accessible databases on a 700-year scale. Our results from Lake Rara highlight significant previously-unknown earthquakes (Mw>6.5) and they reveal that Western Nepal is seismically as active as central Nepal. Furthermore, they call into question the hypothesis of a seismic gap in the central Himalaya. Based on a longer sediment core from the same lake, we studied the temporal distribution of earthquakes over a period of 6000 years, which has highlighted the random nature of the occurrence of earthquakes, constituting a paradigm shift where the notion of seismic cycle is still prevalent. The random nature of the occurrence of earthquakes both on short (instrumental) and Quaternary time scales disproves the hypothesis of the seismic gap in the central Himalaya and underlines the permanent risk for the million people of concern. The final part of this thesis addresses the possible global relationship between seismic rate fluctuations and climate change during the Holocene. Our results show that the global seismicity clustered over 7000 years and appears to be synchronous with the sum of glacial advances through the Mid and Late Holocene
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Pernas, Vallès Jaume. "On Quaternary Linear Reed-Muller Codes". Doctoral thesis, Universitat Autònoma de Barcelona, 2012. http://hdl.handle.net/10803/96434.
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A la literatura recent hi podem trobar la introducció de noves famílies de codis de Reed-
Muller quaternaris lineals RMs. Les imatges d’aquests nous codis a través del mapa de
Gray són codis binaris Z4-lineals que comparteixen els paràmetres i les propietats (longitud, dimensió, distància mínima, inclusió, i relació de dualitat) amb la família de codis de Reed-
Muller binaris lineals. El kernel d’un codi binari C es defineix com K(C) = {x 2 Zn2
:
C + x = C}. La dimensió del kernel és un invariant estructural per els codis binaris
equivalents. Part d’aquesta tesi consisteix en establir els valors de la dimensió del kernel
per aquestes noves famílies de codis de Reed-Muller Z4-lineals. Tot i que dos codis Z4-
lineals no equivalents poden compartir el mateix valor de la dimensió del kernel, en el cas
dels codis de Reed-Muller RMs aquest resultat es suficient per donar-ne una classificació
completa.
Per altra banda, un codi quaternari lineal de Hadamard C, és un codi que un cop li
hem aplicat el mapa de Gray obtenim un codi binari de Hadamard. És conegut que els
codis de Hadamard quaternaris formen part de les famílies de codis quaternaris de Reed-
MullerRMs. Definim el grup de permutacions d’un codi quaternari lineal com PAut(C) =
{ 2 Sn : (C) = C}. Com a resultat d’aquesta tesi també s’estableix l’ordre dels grups de
permutacions de les famílies de codis de Hadamard quaternaris. A més a més, aquests grups
són caracteritzats proporcionant la forma dels seus generadors i la forma de les òrbites del
grup PAut(C) actuant sobre el codi C. Sabem que el codi dual, en el sentit quaternari, d’un
codi de Hadamard és un codi 1-perfecte estès. D’aquesta manera els resultats obtinguts
sobre el grup de permutacions es poden transportar a una família de codis quaternaris 1-
perfectes estesosRecently, new families of quaternary linear Reed-Muller codes RMs have been introduced. They satisfy that, under the Gray map, the corresponding Z4-linear codes have the same parameters and properties (length, dimension, minimum distance, inclusion, and duality relation) as the codes of the binary linear Reed-Muller family. The kernel of a binary code C is K(C) = {x 2 Zn2 : C + x = C}. The dimension of the kernel is a structural invariant for equivalent binary codes. In this work, the dimension of the kernel for these new families of Z4-linear Reed-Muller codes is established. This result is sufficient to give a full classification of these new families of Z4-linear Reed-Muller codes up to equivalence. A quaternary linear Hadamard code C is a code over Z4 that under the Gray map, the corresponding Z4-linear code is a binary Hadamard code. It is well known that quaternary linear Hadamard codes are included in the RMs families of codes. The permutation automorphism group of a quaternary linear code C of length n is defined as PAut(C) = { 2 Sn : (C) = C}. In this dissertation, the order of the permutation automorphism group of all quaternary linear Hadamard codes is established. Moreover, these groups are completely characterized by providing their generators and also by computing the orbits of their action on C. Since the dual of a Hadamard code is an extended 1-perfect code in the quaternary sense, the permutation automorphism group of the quaternary linear extended 1-perfect codes is also established.
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Walock, Michael. "Nanocomposite coatings based on quaternary metalnitrogen". Phd thesis, Paris, ENSAM, 2012. http://pastel.archives-ouvertes.fr/pastel-00843104.
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Lors de ce projet, des revêtements de CrN-WC ont été étudiés en temps que matériaux hybrides durs et résistants. L'association d'un carbure et d'un nitrure résistants bien à la corrosion et obtenus dans des conditions optimales de dépôt permettra d'avoir des matériaux de protection contre l'usure, la corrosion mais aussi des dépôts servant de couches tampon à du diamant nanocristallin dont l'adhérence est mauvaise. Tout d'abord nous avons déterminé la faisabilité du système de CrN-WC et son utilisation comme couche intermédiaire pour du diamant nanocristallin. En faisant varier les paramètres de dépôt, nous avons optimisé la microstructure, les caractéristiques chimiques, mécaniques et tribologiques de nos couches. Si le système CrN-WC adhère relativement bien sur silicium, ce ne fut pas le cas sur acier. Les propriétés mécaniques de ces dépôts ont été par ailleurs plus faibles que celles que nous attendions. Nous avons ensuite étudié l'influence de la température sur nos dépôts de CrN-WC. En effet, le fait de chauffer lors du dépôt permet d'augmenter l'adhérence des couches et d'améliorer leurs propriétés mécaniques. Les revêtements obtenus à haute température ont bien montré une amélioration marquée de leurs diverses caractéristiques par rapport aux dépôts obtenus sans chauff.
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Ashton, Richard James. "On indefinite diagonal quaternary quadratic forms". Thesis, Imperial College London, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.434827.
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Klimaschewski, A. "Late quaternary environmental change of Kamchatka". Thesis, Queen's University Belfast, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.557656.
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Holocene vegetational developments in Russia are relatively unknown, and among the least studied areas of the country is the peninsula of Kamchatka. Late Quaternary research has focussed on aspects such as volcanology, tephrochronology, glacier fluctuations and prehistoric archaeology. The present study is a interdisciplinary enquiry into the late-Quaternary environmental change of Karnchatka. Four sediment cores from three lakes and a peat bog, located in different parts of the peninsula, were investigated. They provide a survey of environmental change in diverse landscapes in Kamchatka. All cores were analysed for pollen and loss-on-ignition and were dated by the radiocarbon method using an AMS machine. The pollen diagrams of Pechora Lake, Lifebuoy Lake and Olive-backed Lake display low frequencies of herbaceous and aquatic taxa. Wet and moist areas surrounding the lakes are primarily represented by Betula, Alnus viridis and Cyperaceae. Pinus pumila dominates the vegetation of the well-drained soils of the hill slopes. The vegetation at Utka is, after a strong decrease of grasses, sedges and ferns, mainly dominated by Betula, Alnus viridis and Thalictrum. Upper parts of the pollen diagram are characterised by higher frequencies of Filipendula and Myrica. Alrthree lake sites illustrate a relatively simultaneous spread of Pinus pumila between 4100 to 4300 cal yr BP. At Utka, evidence of Pinus pumila is rare. Pollen grains of Picea and Larix, identified at Olive-backed Lake, support the concept of existence of local retreat areas in Kamchatka during glacial time. This study gives new insights into the late Quaternary vegetation and landscape development of Kamchatka. The composition of the forests and the way in which they were assembled over time is examined, as well as whether plants survived within the peninsula, or if they migrated in from elsewhere in east Asia following the last glaciation.
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Rae, Alaric Campbell. "Late Quaternary glaciation in Southwest Ireland". Thesis, Coventry University, 2004. http://curve.coventry.ac.uk/open/items/03055be6-aad0-4313-d72e-1dac2156f221/1.
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During the last main phase of glaciations (26-13kaBP) an ice cap developed in south west Ireland and ice, from a dispersal centre in the vicinity of Kenmare, flowed north and diverged on the southern slopes of the Macgillycuddy’s Reeks. On these slopes, a weathering limit separates ice-moulded bedrock, on low ground, from frost-weathered terrain above. Assessment of bedrock dilation joint characteristics, Schmidt hammer R-value data, clay-sized mineral contents and magnetic properties of basal soil samples confirms significant contrasts in the degree of weathering above and below this limit. The weathering limit declines in altitude along former ice flow-lines and is confluent with morainic deposits on the eastern side of the Gap of Dunloe and on the western slopes of Skregbeg. This evidence supports the assertion that the high-level weathering limit is a periglacial trimline that marks the former maximum upper limit of the body of ice, which occupied this area of southwest Ireland during the LGM. This evidence, however, does not confute the notion that cold based, non-erosive plateau ice may have covered some or all of the upland surfaces that occur above the recorded weathering limits. Reconstruction of the former ice surface profile from periglacial trimline limits along three former flow lines yielded mean estimates for basal shear stress that ranged from 104.2 to 125.9 kPa. Although these values are high, they are within the range deemed normal for glaciers and ice sheets. The values suggest that the reconstructed areas of the ice cap were warm based and flowing on a bedrock substrate. This is supported by the geomorphological evidence of these areas, which shows that a landform – sediment association has developed consisting of zones of glacial scour and a thin, discontinuous drift cover. This contrasts with the glacial geomorphology of northern parts of the study area, where drift cover is largely continuous, and extensive in valley bottoms and on surrounding hillsides, and is associated with large lateral moraines.
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Cronin, Sean Peter. "Quaternary sedimentation in Welsh lacustrine environments". Thesis, Aberystwyth University, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.321621.
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Chalmers, Rhona Mary Lindsay. "Neotectonic fracturing associated with Quaternary Travertines". Thesis, University of Bristol, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.265417.
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Al, Kharoosi Fatma Salim Ali. "Describing quaternary codes using binary codes". Thesis, Queen Mary, University of London, 2011. http://qmro.qmul.ac.uk/xmlui/handle/123456789/1312.
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For a quaternary code C of length n, de ne a pair of binary codes fC1;C2g as: -C1 = C mod 2 -C2 = h(C \ 2Zn 4 ) where h is a bijection from 2Z4 to Z2 mapping 0 to 0 and 2 to 1 and for the extension to a map acting coordinatewise. Here C1 C2. For a pair of binary codes fC1;C2g with C1 C2, let C(C1;C2) be the set of Z4-codes giving rise to this binary pair as de ned above. Our main goal is to describe the set C(C1;C2) using the binary pair of codes fC1;C2g. In Chapter 1, we give some preliminaries. In Chapter 2, we start with a general description of codes fC1;C2g which give cardinality of C(C1;C2). Then we show that C(C1;C2) ' C 1 Zn 2 =C2. The cohomology of C(C1;C2) is given in Section (2:2). Then we end chapter 2 with a description of dual codes of C(C1;C2). Chapter 3 is about weight enumerators of codes in C(C1;C2). The average swe is given in terms of weight enumerators of C1 and C2 in Section(3:1) as swe(x; y; z) = jC2j 2n (weC1(x + z; 2y) (x + z)n) + weC2(x; z) Detailed computations of swe's of codes in C(C1;C2) using codes fC1;C2g is then given. Information about di erent weight enumerators of codes in C(C1;C2) is given in Section (3:2). These weight enumerators are included in an a ne space of polynomials. Then we end chapter 3 with a description of weight enumerators of self dual codes. Chapter 4 deals with actions of 2 the automorphism group G = Aut(C1) \ Aut(C2) Sn on C(C1;C2) which preserves cwe of codes. Corresponding action on C 1 Zn 2 =C2 is explained in this chapter. Changing signs of coordinates can be de ned as an action of Zn 2 on C(C1;C2). This action preserves swe of codes. Corresponding action on C 1 Zn 2 =C2 is provided in this chapter. In the appendix, we give a complete description of Z4-codes in C(C1;C2) with C1 = C2 = Extended Hamming Code of length 8. A programming code in GAP for computing derivations is given. And a description of the a ne space containing the swe's of Z4-codes is given with examples of di erent C1 = C2 having same weight enumerator.
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Fu, Tiantian. "Quaternary amine metabolism in gut microbiota". Thesis, University of Warwick, 2017. http://wrap.warwick.ac.uk/95877/.
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Quaternary amines such as choline and carnitine are essential nutrients for humans supplied from daily food; however, quaternary amines metabolism by gut microbiota can lead to the development of various diseases, including non-alcoholic fatty liver disease and cardiovascular disease. It is hypothesized that both diseases are promoted by microbial catabolism of choline and carnitine to trimethylamine (TMA). Proteus mirabilis is a Gram-negative gut proteobacterium, which can metabolize choline anaerobically to form TMA. I demonstrated that the identified cutC gene is essential for choline degradation and subsequent TMA production in this bacterium. Using P. mirabilis as the model, I investigated the physiological role of quaternary amine metabolism from the bacterial perspective and demonstrated that P. mirabilis can rapidly uptake and degrade choline to enhance growth rate, cell yield and swarming speed under anaerobic and microaerophilic conditions. I also provide the first evidence of a novel choline-metabolizing microcompartment, which is present in both vegetative and swarming cells supplemented with choline. Another important dietary source of TMA in human gut is carnitine. I used two model proteobacteria Acinetobacter baumannii and Escherichia coli in this project to investigate the role of carnitine metabolism to TMA in health and disease. A. baumannii and E. coli can use carnitine as a growth substrate to produce TMA. To better understand the role of quaternary amine metabolism in host health and disease, I used Caenorhabditis elegans model to investigate carnitine metabolism on the life span of the worm. My data suggest that malate, the degradation product of carnitine, extends the life span of C. elegans fed on A. baumannii or E. coli. Together, my study reveals that choline and carnitine metabolism as an adaptation strategy for gut proteobacteria and contributes to better understand the ecology of these TMA-forming gut bacteria in health and disease.
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Maddison, Eleanor Jane. "Seasonally laminated late Quaternary Antarctic sediments". Thesis, Cardiff University, 2005. http://orca.cf.ac.uk/56054/.
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Quaternary diatom-rich laminated sediments, found in Antarctic inner shelf depressions, contain high-resolution records of climate change. Diatom assemblages and sediment fabric of four laminated intervals were examined with a scanning electron microscope (using backscattered and secondary electron imagery) and light microscope in this study. Deglacial Palmer Deep laminated sediments (western Antarctic Peninsula) are composed of alternating biogenic diatom ooze and diatom-bearing terrigenous laminae. These laminae are interpreted as spring and summer signals respectively, with negligible winter deposition. Sub-seasonal species specific sub-laminae are observed repeatedly through the summer laminae. Tidal cycles, high storm intensities and / or intrusion of Circumpolar Deep Water onto the continental shelf create variation in shelf waters, enhancing species specific productivity through the summer. Post-glacial Mertz Ninnis Trough laminated sediments (East Antarctic Margin) are composed of five lamina and one sub-lamina types. During deposition the Mertz Glacier Polynya was active and Adelie Land Bottom Water formation was strong. Mid-Holocene Mertz Ninnis Trough laminated sediments are composed of five lamina types. Sea ice cover and sea ice formation was reduced relative to post-glacial times. The Mertz Glacier Polynya was not as active as in the post-glacial and Adelie Land Bottom Water formation was lower. Late-Holocene Durmont d'Urville Trough laminated sediments (East Antarctic Margin) are composed of eight lamina and one sub-lamina types. Sea ice cover was extensive and persistent in the late-Holocene. Warmer periods occurred during the transition from mid-Holocene Climatic Optimum to cooler late-Holocene climatic conditions. The types of lamina and sub-lamina formed in all four laminated intervals are controlled by seasonal sea ice cover, nutrient levels and light levels, which are in turn influenced by climate and oceanography. The Western Antarctic Peninsula and East Antarctic Margin laminated sediments give an insight into oceanographic responses to climatic change and variation through the Quaternary around the Antarctic margin.
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McDonald, Valerie Alexandra. "Evaluating Immunotoxicity of Quaternary Ammonium Compounds". Thesis, Virginia Tech, 2017. http://hdl.handle.net/10919/79723.
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Alkyl dimethyl benzyl ammonium chloride (ADBAC) and didecyl dimethyl ammonium chloride (DDAC) are common quaternary ammonium compounds used as disinfectants in households, medical, and restaurant settings. They cause occupational skin and respiratory hazards in humans, and developmental and reproductive toxicity in mice. They also cause increased secretions of proinflammatory cytokines in cell lines and vaginal inflammation in porcine models; but have not been evaluated for developmental immunotoxicity. We assessed immunotoxicity in-vitro with J774A.1 murine macrophage cell line by analyzing cytokine production and phagocytosis; and evaluated developmental immunotoxicity in CD-1 mice by analyzing antibody production. Additionally, because of the associations between gut microbiome dysbiosis and immune disease, we monitored changes in the microbiome as a result of ADBAC+DDAC exposure. Production of cytokines TNF-alpha and IL-6 increased at low ADBAC+DDAC concentrations, and IL-10 decreased in the murine macrophages with ADBAC+DDAC exposure. The phagocytic function of macrophages was also severely decreased. ADBAC+DDAC altered the mouse microbiome by decreasing the relative abundance of Bacteroides and increases in Clostridia in F0 and F1 generations. IgG primary and secondary responses were altered in F1 male mice; and IgA and IgM production were decreased in secondary response in F2 male mice. Since ADBAC+DDAC show signs of immunotoxicity in mice, further studies are needed to reassess risk for human exposure as ADBAC+DDAC may be contributing to immune disease.Master of Science
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LOCATELLI, Elisa. "Insular small mammals from Quaternary deposits of Sicily and Flores". Doctoral thesis, Università degli studi di Ferrara, 2011. http://hdl.handle.net/11392/2389231.
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This PhD thesis deals with fossil small mammals from Quaternary deposits from Sicily (Italy) and Flores (Indonesia). It is well known that evolutionary dynamics on islands are quite different than on mainland, because of, amongst the others, the shortage of resources, the reduced interspecific competition and predation, the difficultness in reaching/leaving the island. Therefore many species undergo strong size variation, giving rise to phenomena of gigantism (small mammals) or dwarfism, and a variation in the structure of mammalian communities takes place.
In this thesis faunal associations of two very different islands have been taken into account, in order to record the difference in the effects that distance from the mainland, area of the island, introduction of new species and time have on small mammals community.
Sicily is in fact the largest Mediterranean island and is very close to the mainland, so close that periodically, during low-standing phases of sea level it was connected to Southern Italy and mammals could reach it. Thus the analysis of the material from Isolidda 3 (Trapani), a Middle - Late Pleistocene paleontological site, could record phases of isolation from the mainland, with a very impoverished (only three rodents and one insectivore) and unbalanced fauna, whilst Oriente Cave (Favignana Island) (Late Pleistocene – Holocene) and Cala Mancina Cave (Trapani) (Holocene), two archeological sites, provided evidence of the arrival of small mammals during the LGM or with man. The abundance of the fossil remains collected allowed also the taxonomical and phylogenetical study of the Microtus (Terricola) and Crocidura in Sicily. The study of small mammals of these archeological deposits facilitates, in conjunction with other disciplines, the reconstruction of the palaeo-environment in which Late Paleolithic and Mesolithic people lived .
On the other hand, Liang Bua (Flores, Indonesia) (Late Pleistocene – Holocene), the well-known site for the discovery of Homo floresiensis, is located on an oceanic island. It has never been connected to the mainland and the faunal association displays high degrees of endemism, with the presence of three giants rats (Papagomys armandvillei, Papagomys theodorverhoeveni and Spelaeomys florensis), two middle size rats (Paulamys naso and Komodomys rintjanus) and two small rats (Rattus hainaldi and Rattus exulans). Despite the apparent high number of species, the great part of them is strictly related, confirming the long period of isolation. Since Liang Bua represents the richest deposit for many of these species, it was possible to provide an accurate morphometrical description of upper and lower toothrow of the murids. Moreover, it was possible to record the extinction of Spelaeomys florensis, the severe diminution of the other giant rats (P. armandvillei and P. theodorverhoeveni), Paulamys naso and Rattus hainaldi, and the introduction (intentional or accidental) by Neolithic agriculturists of Rattus exulans.
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Azaza, Mohamed. "Changes in animal husbandry, diet and animal trade in Tunisia from the Iron Age to the Roman period: an archeozoological approach". Doctoral thesis, Universitat Rovira i Virgili, 2020. http://hdl.handle.net/10803/669870.
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L'objectiu general d'aquesta tesi és utilitzar un enfocament arqueozoològic per avançar Comprendre els canvis que la
colonització romana de Tunísia va provocar en els animals. pràctiques de cria, patrons de dieta i comerç
d'animals.Per aconseguir aquest objectiu, hem emprès un estudi comparatiu de encaixos faunístics.Hem analitzat les
restes de fauna de Ghizen i Zama, i els resultats han estatcontextualitzat amb tota la informació arqueozoológica de
Tunísia.Vam desenvolupar una metodologia específica per comparar dades de fauna . La nostraLes anàlisis es van
concentrar a la quantificació taxonòmica de les principals espècies domèstiques.(Bovins, ovins, caprins i porcins) per
establir la importància econòmica de cada
tàxon Es van examinar els elements esquelètics per determinar els efectes de alteració tafonòmica i humana en cada
acoblament. L'edat a el morir es va estimar en per fer llum sobre l'ús i l'explotació d'animals. Els nostres resultats
proporcionen una major comprensió dels canvis en les pràctiques de cria d'animals, la dieta de carn i el comerç
d'animals a Tunísia des de l'Edat del Ferro fins al període romàEl objetivo general de esta tesis es utilizar un enfoque arqueozoológico para avanzar Comprender los cambios que la colonización romana de Túnez provocó en los animales. prácticas de cría, patrones de dieta y comercio de animales. Para lograr este objetivo, hemos emprendido un estudio comparativo de ensambles faunísticos. Hemos analizado los restos de fauna de Ghizen y Zama, y los resultados han sido contextualizado con toda la información arqueozoológica disponible de Túnez. Desarrollamos una metodología específica para comparar datos de fauna publicados. Los análisis se concentraron en la cuantificación taxonómica de las principales especies domésticas. (bovinos, ovinos, caprinos y porcinos) para establecer la importancia económica de cada taxón Se examinaron los elementos esqueléticos para determinar los efectos de alteración tafonómica y humana en cada ensamblaje. La edad al morir se estimó en para arrojar luz sobre el uso y la explotación de animales. Nuestros resultados proporcionan una mayor comprensión de los cambios en las prácticas de cría de animales, la dieta de carne y el comercio de animales en Túnez desde la Edad del Hierro hasta el período romano
aumentó: el primero fueron explotados en gran medida por su lana, mientras que este último se convirtió en una importante fuente de carne. Al mismo tiempo, especies como el gato, la rata negra, el ratón doméstico, el conejo, la liebre y el barbecho los ciervos fueron introducidos en Túnez durante el período romano, lo que demuestra que los animales fueron otro producto comercializado en los puertos del norte de África. El comercio de animales fue una importante actividad económica para Túnez, no solo para la exportación de bestias salvajes sino También para la importación de animales salvajes y domésticos. La dieta de la carne también fue modificada, particularmente en las provincias del norte de Túnez, donde hubo un aumento en el consumo de carne de cerdo. Por lo tanto, proponemos que la carne dietética El patrón documentado en Túnez durante el período romano estuvo influenciado no solo por factores culturales, pero también por factores económicos y quizás ambientales, todos los c The broad aim of this thesis is to use an archeozoological approach to further understand the changes that the Roman colonization of Tunisia brought about in animal husbandry practices, diet patterns and the animal trade. To achieve this aim, we have undertaken a comparative study of faunal assemblages. We have analyzed the faunal remains from Ghizen and Zama, and the results have been contextualized with all the archaeozoological information available from Tunisia. We developed a specific methodology for comparing published faunal data. Our analyses concentrated on the taxonomical quantification of the main domestic species (cattle, sheep, goat and pig) in order to establish the economic importance of each taxon. The skeletal elements were examined in order to determine the effects of taphonomic and human alteration on each assemblage. Age at death was estimated in order to shed light on animal use and exploitation. Our results provide greater insight into changes in animal husbandry practices, meat diet and animal trade in Tunisia from the Iron Age to the Roman period
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Bisbal, Chinesta José Francisco. "Biogeografía e impacto humano en las comunidades de anfibios y reptiles del Cuaternario final en la Península ibérica: la Cueva del Mirador (Atapuerca, Burgos) y la población de Chalcides ocellatus (Scincidae) de la Serra del Molar (Alicante)". Doctoral thesis, Universitat Rovira i Virgili, 2020. http://hdl.handle.net/10803/670225.
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Aquesta tesi doctoral presenta la primera aproximació a la paleobiogeografia dels amfibis i rèptils de la Península Ibèrica durant el Quaternari final, basada en una síntesi comparativa del registre conegut fins ara. S'han establert dues regions biòtiques durant el Plistocè tardà: la primera localitzada en el sud i centre ibèrics, amb espècies termòfiles com les més representatives, i la segona en el terç nord ibèric, dominat per espècies generalistes-eurosiberianes. Després de l'Últim Màxim Glacial i al llarg de l'Holocè es va produir la concurrència en el nord d'espècies generalistes-eurosiberians i termòfiles, per l'expansió de les espècies mediterrànies, i la possible introducció humana d'espècies magrebines. Amb aquest marc general, la importància del clima i de la influència humana en la composició de les associacions d’herpetofauna s'analitzen en dos casos d'estudi. El primer són les egagròpiles de la Cueva del Mirador (Atapuerca), vint acumulacions de microvertebrados del Calcolític-Bronze inicial. L'estudi taxonòmic ha permès identificar 350 individus de 20 tàxons diferents, majoritàriament herpetofauna. L'anàlisi tafonòmic ha postulat com a agent acumulador un depredador de categoria 2, possiblement un mussol. L'anàlisi estadística mostra l'existència de diferències quantitatives i qualitatives en la seva composició, interpretades com a variacions estacionals entre el final de l'hivern i l'estiu. La singular composició faunística de les egagròpiles s'interpreta com un efecte secundari de l'impacte humà. La composició herpetofaunística relaciona aquestes associacions amb l'expansió postglacial de les espècies termòfiles. El segon cas d'estudi és la població de Chalcides ocellatus de la Serra del Molar, el seu primer registre ibèric. L'estudi molecular ha determinat el seu origen en el nord d'Egipte i la seva possible translocació a través del comerç marítim, antic o modern, segons els diversos vincles històrics el sud-est ibèric i el mediterrani oriental.Esta tesis doctoral presenta la primera aproximación a la paleobiogeografía de los anfibios y reptiles de la Península Ibérica durante el Cuaternario final, basada en una síntesis comparativa del registro conocido hasta ahora. Se han establecido dos regiones bióticas durante el Pleistoceno tardío: la primera localizada en el sur y centro ibéricos, con especies termófilas como las más representativas, y la segunda en el tercio norte ibérico, dominado por especies generalistas- eurosiberianas. Después del Último Máximo Glacial y a lo largo del Holoceno se produjo la concurrencia en el norte de especies generalistas-eurosiberianos y termófilas, por la expansión de las especies mediterráneas, y la posible introducción humana de especies magrebíes. Con este marco general, la importancia del clima y de la influencia humana en la composición de las asociaciones de herpetofauna se analizan en dos casos de estudio. El primero son las egagrópilas de la Cueva del Mirador (Atapuerca), veinte acumulaciones de microvertebrados del Calcolítico-Bronce inicial. El estudio taxonómico ha permitido identificar 350 individuos de 20 taxones diferentes, mayoritariamente herpetofauna. El análisis tafonómico ha postulado como agente acumulador un depredador categoría 2, posiblemente un búho. El análisis estadístico muestra la existencia de diferencias cuantitativas y cualitativas en su composición, interpretadas como variaciones estacionales entre el final del invierno y el verano. La singular composición faunística de las egagrópilas se interpreta como un efecto secundario del impacto humano. La composición herpetofaunística relaciona estas asociaciones con la expansión posglacial de las especies termófilas. El segundo caso de estudio es la población de Chalcides ocellatus de la Serra del Molar, su primer registro ibérico. El estudio molecular ha determinado su origen en el norte de Egipto y su posible translocación a través del comercio marítimo, antiguo o moderno, según los diversos vínculos históricos entre el sureste ibérico y el Mediterráneo oriental.
This doctoral thesis presents the first approach to the paleobiogeography of the amphibians and reptiles of the Iberian Peninsula during the final Quaternary, based on a comparative synthesis of the known record until now. Two biotic regions have been established during the late Pleistocene: the first one located in the south and central Iberia, with thermophilic species as the most representative, and the second one in the northern third, dominated by generalist-Eurosiberian species. After the Last Glacial Maximum and throughout the Holocene, the concurrence of generalist-Eurosiberian and thermophilic species occurred in the north, due to the expansion of Mediterranean species, and the possible human introduction of Maghreb species. Within this general context, the importance of climate and human influence on the composition of herpetofauna associations are analyzed in two case studies. The first is the pellets from Cueva del Mirador (Atapuerca), twenty microvertebrate accumulations from the Chalcolithic-Early Bronze period. The taxonomic study has identified 350 individuals from 20 different taxa, mostly herpetofauna. Taphonomic analysis has postulated a category 2 predator, possibly an owl, as the accumulating agent. The statistical analysis shows the existence of quantitative and qualitative differences in their composition, interpreted as seasonal variations between the end of winter and summer. The unique faunistic composition of the pellets is interpreted as a secondary effect of human impact. The herpetofaunistic composition relates these associations to the post-glacial expansion of thermophilic species. The second case study is the population of Chalcides ocellatus from the Serra del Molar, its first Iberian record. The molecular study has determined its origin in northern Egypt and its possible translocation through maritime trade, either ancient or modern, according to the various historical links between the Iberian southeast and the eastern Mediterranean.
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Cruz, Erick Antal. "Fósseis de vertebrados pleistocênicos dos setores central e Sul da planície costeira do Rio Grande do Sul, Brasil: descrição e controles na distribuição". reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2016. http://hdl.handle.net/10183/133661.
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A presença de depósitos fossilíferos na antepraia e plataforma continental interna foi atribuída às oscilações do nível do mar durante o Quaternário. Hoje em dia, esses depósitos estão sendo erodidos por ondas e correntes e transportados para a praia. O presente trabalho teve como objetivo comparar o setor central e sul da Planície Costeira do Rio Grande do Sul, quantificando e qualificando quanto sua tafonomia, taxonomia e representatividade dos restos esqueletais. Foi coletado um total de 2.820 fósseis, dentre os quais 95% foram coletados no setor sul e apenas 5% foram coletados no setor central. A principal hipótese para essa diferença é a disponibilidade de fósseis na antepraia e plataforma interna. A presença de vários parceis e elevações e depressões submersas na antepraia e plataforma interna do setor sul indica, provavelmente as áreas-fonte de onde os fósseis são erodidos. Em ambos os setores foram identificados duas populações de bioclastos: fósseis nãoidentificados (85%) e fósseis identificados (15%), indicando maior e menor retrabalhamento pelas ondas, respectivamente. As mesmas ordens e restos esqueletais foram identificados em ambos os setores, com exceção de alguns que foram encontrados somente no setor sul. Na fauna marinha, a ordem mais comum foi a Perciformes representada principalmente por tumores ósseos da espécie Pogonias cromis. Dentes de tubarões (Lamniformes e Carcharhiniformes) e raias (Myliobatiformes) foram encontrados apenas no setor sul, devido à presença da espessa konzentrat-lagerstätte de conchas marinhas fósseis, chamada de "Concheiros". Na fauna terrestre, a ordem mais comum foi a Cingulata (principalmente gliptodontídeos do gênero Glyptodon). Os elementos acessórios representados por osteoderms de cingulados foram os restos esqueletais mais abundantes, devido ao grande número de osteodermos que cobre o esqueleto de cingulates e ao pequeno tamanho e forma compacta das osteodermos que favorecem o transporte. Elementos de tamanho pequeno (32-64 mm) e de forma compacta, como osteoderms, dentes e vértebras, são encontrados em maior quantidade e são facilmente transportados. Elementos de tamanho grande (maior que 128 mm) e de forma de lâmina/disco, como ossos longos e elementos cranianos, são encontrados em menor quantidade e são dificilmente transportados.The presence of fossiliferous deposits in the shoreface and inner continental shelf was attributed to the sea-level oscillations during the Quaternary. Nowadays, these deposits are being eroded by waves and currents and transported onto the beach. The present work aimed to compare the central and southern sectors of the Coastal Plain of Rio Grande do Sul, quantifying and qualifying as its taphonomy, taxonomy and skeletal remains representativeness. A total of 2.820 fossils was collected, among which 95% were collected in the southern sector and only 5% were collected in the central sector. The hypothesis for this difference is the availability of fossils in the shoreface and inner continental shelf. The presence of several sedimentary submerged rocks and submerged elevations and depressions in the shoreface and inner continental shelf of the southern sector indicates probably the source-areas where the fossils are eroded from. In both sectors were identified two populations of bioclasts: non-identified fossils (85%) and identified fossils (15%), indicating greater and less waves reworking, respectively. The same orders and skeletal remains were identified in both sectors, except for some that were only found in the southern sector. In the marine fauna, the most common order was the Perciformes represented mainly by bone tumors of the species Pogonias cromis. Teeth of sharks (Lamniformes and Carcharhiniformes) and rays (Myliobatiformes) were only found in the southern sector due to the presence of the thick konzentrat-lagerstätte of fossil marine shells, called “Concheiros”. In the terrestrial fauna, the most common order was the Cingulata (mostly glyptodontids especially the genre Glyptodon). The accessory elements represented by osteoderms of cingulates were the most abundant skeletal remains, due to the large number of osteoderms that covers the skeleton of cingulates and the small size and compact shape of the osteoderms which favour the transport. Small-size (32-64 mm) and compact-shape elements such as osteoderms, teeth and vertebrae are found in greater quantity and are easily transported. Bigger-sizes (exceeding 128 mm) and blade/disc-shape elements such as long bones and cranial elements are found in less quantity and are hardly transported.
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Fernández, Córdoba Cristina. "On Reed-Muller and related quaternary codes". Doctoral thesis, Universitat Autònoma de Barcelona, 2004. http://hdl.handle.net/10803/5805.
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Goksen, Kadir. "Optical Properties Of Some Quaternary Thallium Chalcogenides". Phd thesis, METU, 2008. http://etd.lib.metu.edu.tr/upload/12609442/index.pdf.
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Optical properties of Tl4In3GaSe8, Tl4InGa3Se8, Tl4In3GaS8, Tl2InGaS4 and Tl4InGa3S8 chain and layered crystals were studied by means of photoluminescence (PL) and transmission-reflection experiments. Several emission bands were observed in the PL spectra within the 475-800 nm wavelength region. The results of the temperature- and excitation intensity-dependent PL measurements in 15-300 K and 0.13×10-3-110.34 W cm-2 ranges, respectively, suggested that the observed bands were originated from the recombination of electrons with the holes by realization of donor-acceptor or free-to-bound type transitions. Transmission-reflection measurements in the wavelength range of 400-1100 nm revealed the values of indirect and direct band gap energies of the crystals studied. By the temperature-dependent transmission measurements in 10-300 K range, the rates of change of the indirect band gap of the samples with temperature were found to be negative. The oscillator and dispersion energies, and zero-frequency refractive indices were determined by the analysis of the refractive index dispersion data using the Wemple&ndash
DiDomenico single-effective-oscillator model. Furthermore, the structural parameters of all crystals were defined by the analysis of X-ray powder diffraction data. The determination of the compositional parameters of the studied crystals was done by energy dispersive spectral analysis experiments.
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Todd, Claire E. "Late quaternary evolution of Reedy Glacier, Antarctica /". Thesis, Connect to this title online; UW restricted, 2007. http://hdl.handle.net/1773/6712.
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Mitchell, A. "Asymmetric synthesis of quaternary centres using organocatalysis". Thesis, University of Edinburgh, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.657854.
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The task of creating an all carbon quaternary centre, bearing an alkyl moiety with differentiated functionalities and substituents is a desired key step in organic synthesis. A variety of endeavours by research groups have lead to the construction of stereogenic quaternary centres, albeit with narrow scope of substrate. Despite the repertoire of transition metals/ligand, chiral auxiliaries and reagents available at hand, efficient enantioselective and organocatalytic methodologies for the construction of all carbon quaternary centres still remains a daunting challenge for synthetic chemists. One of the most popular methods to install a quaternary centre is via a conjugate addition, the addition of a chiral tertiary enolate to an electron deficient alkene or carbonyl compound has led to high levels of synthetic accomplishment over generations. Our strategy to assemble such quaternary centres focused on an organocatalytic tandem. Michael-aldol reaction, as an efficient one-pot strategy to install vicinal quaternary centres with good levels of enantioselective induction. Initial 1, 4-conjugate addition of the nucleophile with a-acrolein type Michael acceptors generates the enolate, which is now set up to undergo an intramolecular aldol reaction providing the desired molecules. Molecular complexes of this class are also amenable to further catalytic transformations and synthetic elaborations. This thesis presents our investigations towards organocatalytic enantioselective strategies for the assembly of fully substituted quaternary centres.
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Davies, Heather Louise. "Quaternary palaeolimnology of a Mexican crater lake". Thesis, Kingston University, 1995. http://eprints.kingston.ac.uk/20583/.
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La Piscina de Yuriria is a small (0.75 Km2), hydrologically closed crater lake situated in the Neovolcanic Axis of Central Mexico (20013'N, 100008'W, 1740m a.s.l.). The water level has fluctuated markedly over the last decade and, at present, has a chemical composition of Na-C03-CI type. It represents a highly evolved water body modified by evaporative concentration and dissolution of the salt crust produced during desiccation in 1987. Water reappeared in the basin during 1991 and was very shallow and anoxic. The lake basin is known to have been occupied by man since -3,100 yr BP and so provides an excellent opportunity to examine the nature and relative importance of anthropogenic disturbance and naturally induced climatic change. The record for a single 14.3m core (YC2) from La Piscina de Yuriria extends back -26,600 yr BP with the dating control provided by 16 radiocarbon dates. The project used a variety of techniques to reconstruct the palaeolimnology of the lake including: (i) ostracods; faunal assemblage analyses; trace-element and stable oxygen and carbon isotope analyses; (ii) Sedimentological analyses; mineralogical analyses; grain-size analyses; X-Ray diffraction; stable oxygen and carbonisotope analyses of fine-grained carbonate; Laser ablation lCP-MS; (iii) Sediment geochemistry. A number of moist and dry phases have been identified, through the core, which are controlled primarily by variations in precipitation/evaporation (PIE) ratios over La Piscina de Yuriria. A number of periods of catchment disturbance have also been identified which occured under both moist and dry conditions. The base of the core (-26,600 yr BP) reflects the most arid phase with stable conditions within the catchment. At 25,000 yr BP freshwater flowed into a salt filled basin with a second phase of moist conditions at 22,200 yr BP. The onset of drier conditions at 20,000 yr BP resulted in a pronounced phase of catchment erosion. The dry period continued and intensified between 19,000 and 14,700 yr BP. During this period two wet events were identified at 17,000 and 15,000 yr BP. Dry conditions resumed between -12,100 and 11,500 yr BP and were then replaced by moist conditions. Between -12,000 and -7,000 yr BP conditions appeared to be generally unstable, alternating between dry and wet phases. Between 8,000 and -3,000 yr BP conditions were more moist. A short-lived dry event occurred at -3,300 yr BP, which resulted in renewed catchment disturbance. Dry conditions were identified between-2,500 yr BP and -900 yr BP where a short-lived wet event produced: stable catchment conditions. Catchment disturbance resumed and continued toward the top of the core reflecting slightly drier conditions than during the moist event. The record is dominated by a strong climatic signal which does not appear to have been masked by anthropogenic effects during the last 3,100 yr BP. Comparison of the events identified in the core, with other sites within the Neotropics, suggests that many of the climatic changes occurred on a regional scale.
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Mehrshahi, Daryoush. "Late Quaternary palaeoenvironments, Ardakan Playa, central Iran". Thesis, University of Sheffield, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.301016.
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Redda, Araya. "Quaternary geomorphology of the Vale of Edale". Thesis, University of Sheffield, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.392762.
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Parr, J. A. "Antimicrobial properties of silicone quaternary ammonium compounds". Thesis, Bucks New University, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.375600.
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McLaren, Susan Janet. "Vadose diagenesis of late Quaternary coastal sediments". Thesis, King's College London (University of London), 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.389061.
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King, Stephen Charles. "Late Quaternary palaeoceanography of the Peru Margin". Thesis, University of Southampton, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.239459.
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Fenton, Mia. "Late Quaternary history of Red Sea outflow". Thesis, University of Southampton, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.264851.
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Frimpong, Kwame. "Synthesis of Quaternary Carbon Centers via Hydroformylation". Thesis, Boston College, 2011. http://hdl.handle.net/2345/2413.
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Thesis advisor: Kian L. TanUtilization of directing groups in a general and efficient manner for highly regioselective hydroformylation of 1,1-disubstituted olefins
Thesis (MS) — Boston College, 2011
Submitted to: Boston College. Graduate School of Arts and Sciences
Discipline: Chemistry
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Pawley, Steven Michael. "Quaternary Glaciations of North and West Norfolk". Thesis, Royal Holloway, University of London, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.430784.
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Lacey, Jack H. "Late Quaternary palaeoenvironmental reconstruction from Lake Ohrid". Thesis, University of Nottingham, 2016. http://eprints.nottingham.ac.uk/31993/.
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Lake Ohrid is a large, deep, ancient lake located on the Balkan Peninsula and has an extraordinary degree of endemic biodiversity. A deep drilling campaign was carried out in 2013 as part of the Scientific Collaboration on Past Speciation Conditions in Lake Ohrid (SCOPSCO) project to better understand the influence of climate and environmental change on evolutionary patterns and endemism. Initial results from a 569 m sediment succession drilled in the centre of the basin indicate continuous lacustrine conditions over the past ca. 1.2 Ma. This thesis presents new stable isotope data from carbonate within the upper 248 m of the composite profile, covering the last ca. 640 ka at a millennial-scale resolution (≈ 0.5 ka). Isotope data are used to provide a long-term palaeoenvironmental reconstruction, which is supported by a quantitative model of modern lake water isotope composition and a detailed multi-proxy investigation of climate evolution since the last glacial period. Water balance calculations confirm Ohrid to be an evaporative system with a complex hydrology. Variations in the isotope composition of modern lake water are suggested to represent long-term fluctuations in water balance. A trend from wetter to drier conditions through the Holocene is consistent with regional and hemispheric processes related to changes in insolation. Over the last ca. 640 ka, endogenic calcite is precipitated in abundance during warm stages, however carbonate is negligible during glacial periods with the exception of discrete horizons comprising early diagenetic authigenic siderite. The oxygen isotope composition of lake water, calculated using calcite and siderite, indicates more evaporated conditions during warm stages and fresher lake water in glacial phases. Low frequency variability shown by calcite isotope data suggests relatively stable conditions before ca. 450 ka, a transition to a wetter climate between ca. 400-250 ka, and a trend to drier climate conditions after ca. 250 ka. Higher frequency millennial-scale oscillations and abrupt climate events observed during warm stages are likely associated with regional climate change as a function of orbital forcing. This study emphasises the potential of Lake Ohrid as a valuable archive of climate change in the central Mediterranean region and demonstrates the efficacy of isotope data for palaeoenvironmental reconstruction at Lake Ohrid.
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Farrant, Andrew Roger. "Long-term Quaternary chronologies from cave deposits". Thesis, University of Bristol, 1995. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.294897.
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Zhao, Hongli. "Quaternary distal tephra studies of Northeastern China". Thesis, Queen's University Belfast, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.534593.
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Sinka, Katharine Jane. "Developing the Mutual Climatic Range method of palaeoclimatic reconstruction". Thesis, University of East Anglia, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.359332.
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Codron, Daryl Mark. "Dietary ecology of Chacma baboons (Papio Ursinus (Kerr, 1972) and Pleistocene Cercopithecoidea in Savanna environments of South Africa". Master's thesis, University of Cape Town, 2003. http://hdl.handle.net/11427/4190.
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Bibliography: leaves 124-140.This dissertation deals with the dietary ecology of savanna-dwelling chacma baboons (Papio ursinus), and a number of fossil cercopithecoids, from modern and Pleistocene environments of South Africa, respectively, using principles of stable light isotope ecology. Previous studies of baboon ecology, based largely on direct observations, have not quantified spatial and temporal dietary variability. The dietary ecology of fossil cercopithecoids is even less clear.
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Dorendorf, Frank. "Genesis of Quaternary volcanic rocks from Kamchatka/Russia". Doctoral thesis, [S.l. : s.n.], 1999. http://deposit.ddb.de/cgi-bin/dokserv?idn=963613448.
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Sawada, Michael Charles. "Late quaternary paleoclimates and biogeography of North America". Thesis, University of Ottawa (Canada), 2001. http://hdl.handle.net/10393/9031.
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Pollen, spores, and dinoflagellate cysts are used with the modern analog technique (MAT) to provide paleoclimate reconstructions for terrestrial and marine environments in northeastern North America. Multivariate analysis of marine and nearby terrestrial pollen sequences from Hudson Bay, Labrador and the St. Lawrence, differentiate tundra, boreal and deciduous forest assemblages in time and space. These three regions had differing climate histories with respect to deglaciation and air mass boundaries. Prior to 6000 14C yr BP, cooler temperatures reconstructed along the Labrador margins agree with climate simulations indicating a persistent anticyclone over the Quebec-Labrador ice sheet. A late Holocene cooling at forest-tundra sites suggests a recent southern movement in the mean position of the polar front. The degree to which those critical thresholds of dissimilarity, that are used to identify non-analog pollen assemblages, are due to limitations of the modern pollen database or critical decisions within the MAT are explored by means of stochastic simulation, spatial statistics and graphical techniques. Critical thresholds of SQD, as derived by the expected value under randomization, become greater as the number of taxa in the pollen set increases. Larger pollen sets, with continentally infrequent but regionally abundant taxa, better distinguish between continental vegetation zones. Global and local spatial autocorrelation within climate anomalies indicate where the modern sample network induces biases in the climate reconstruction using the MAT. The spatial scale of terrestrial climate or vegetation reconstructions from pollen in lake-sediments is investigated through the study of pollen source area in southern Quebec. Despite the different regional vegetation, estimated pollen source areas and relevant pollen productivity for Pinus, Picea, Abies, Fagus, Quercus and Tsuga are consistent with studies from Michigan, Wisconsin and Sweden. These estimates are robust with respect to various plant abundance distance-weighting schemes and imply that the same inferences can be made regarding plant abundance from pollen throughout a lake-derived fossil pollen sequence. Stochastic simulations illustrate that the definition of relevant pollen source area requires consistent within-site vegetation heterogeneity within a network of pollen sites. Underutilized proxy-climate data from wetland taxa are demonstrated to contain climate signals at the continental scale and have the potential to further our climatic and biogeographic picture of North America over the past 21,000 years. Pollen and spores from modern wetland taxa conform to their geographic ranges and allow interpretations of their past range changes. The climatic tolerances that govern their geographic distributions are used to interpret past range changes in climatic terns. Sphagnum spore distributions suggest major peatland developments after 9 ka and 5 ka. Sphagnum, Potamogeton, Isoetes, Myriophyllum Typha/Sparganium, and Menyanthes trifoliata were in Alaska during the last glacial maximum (LGM) and moved into the ice-free corridor by 13 ka. Since the LGM, four migration routes for aquatic taxa are identified in response to the climate changes of the late Quaternary.
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Saeidi, Shayan. "Nonlinear Optics in III-V Quaternary Semiconductor Waveguides". Thesis, Université d'Ottawa / University of Ottawa, 2018. http://hdl.handle.net/10393/37300.
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The fundamental limits of electronic systems in communication networks motivated scholars to think of an alternative approach to overcome problems such as demand for wider bandwidths and heat dissipation. All-optical signal processing is demonstrated as a potential solution. A major improvement in cost and speed of networking systems is expected through replacing microelectronics by photonic chips. However, the variety of operations essential to perform all-optical signal processing cannot be handled by a single material platform yet. Several III-V semiconductors, such as AlGaAs, have demonstrated potentials for photonic integration; nevertheless, there is still lack of data in literature on nonlinear optical properties of these materials. In this thesis, we extend the quest to evaluate more candidates from this class of semiconductors. Moreover, we are aiming for demonstrating the potentials of various III-V compounds for nonlinear photonics on-a-chip.
In this thesis, we propose several optical waveguide designs based on quaternary III-V semiconductors AlGaAsSb and InGaAsP. We present modal analysis for waveguide designs and show that effective mode area much less than 1 $\mu m^{2}$ can be obtained. We also report specific waveguide designs that display zero-dispersion points at the specific wavelength ranges of interest. The designed waveguides are thus expected to demonstrate efficient nonlinear optical interactions. Next step is the fabrication of these devices with the goal to experimentally assess their nonlinear optical performance. The fabrication process of InGaAsP/InP strip-loaded waveguide is briefly reviewed. Following that, we report on the first, to the best of our knowledge, demonstration of third-order nonlinear optical interactions in InGaAsP/InP strip-loaded waveguides. We have performed self-phase modulation, nonlinear absorption measurements, and four-wave mixing experiments at the telecom wavelength range. The nonlinear phase shift up to 2.5 $\pi$ has been observed.
Following that, we use Monte-Carlo method for design optimization and tolerance analysis of a multi-step lateral taper Spot-Size Converter in indium phosphide. An exemplary four-step lateral taper design featuring 0.35 dB coupling loss at optimal alignment of a standard single-mode fiber, $>$7 $\mu m$ 1-dB displacement tolerance in any direction of in a facet plane, and a great stability against manufacturing variances demonstrated.
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Roberts, Stephen J. "Quaternary tephrochronology in Iceland dating principles & applications". Thesis, University of Edinburgh, 2002. http://hdl.handle.net/1842/27282.
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Multi-method dating of the previously undated Óþoli Tephra of the Vestfírðir Peninsular, NW Iceland provides a unique chronological constraint for Quaternary landscape evolution, ice sheet extent, ice-sheet thickness and ice-free area hypotheses in Iceland. For the first time, a major age constraint has been placed on the glacially driven, macroscale landscape evolution processes of fjord network formation on the Vestfíröir Peninsula. The pre-14C. Quaternary era is a vital period in which current glacial/interglacial cycles developed and caused widespread environmental change. Dating controls for this era are limited because of widespread glacial erosion, but in Iceland certain tephra deposits have survived glacial overriding and can provide accurate age constraints and precise spatial correlation for stratigraphic sequences. This study focuses on two tephra deposits of great palaeoenvironmental significance: the aforementioned Óþoli Tephra and the þörsmórk Ignimbrite. The Óþoli Tephra rest unconformably 580-600 m.a.s.l. near the plateau surface of Skagafjall (NW Iceland). The 100-160 m thick sequence of ice-damned lake deposits beneath it were thought to have formed during the Last Glacial Maximum (LGM), 20-17 ka. The þörsmórk Ignimbrite þIG; S. Iceland) is the largest Quaternary-age ignimbrite deposit in Iceland and glass compositions have been geochemically linked with the highly silicic (SiO2 >68 wt %) ignimbrite deposit in Iceland and glass compositions have been geochemically linked with the highly silicic (SiO2 >68 wt %) component of North Atlantic Ash Zone-2 (NAAZ-2), 48-58 ka. Correlation fission-track (FT) and thermoluminescence (TL) methods were used to produce ages from the glass shards that overwhelmingly dominate the highly silicic airfall and/or surge ash components of these deposits. Dating glass shards is advantageous because they form during the magma-quenching phase of an eruption and nearly always reflect the ‘true’ eruption age. They are also the most far-travelled and geochemically diagnostic phase of Icelandic tephra.
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Balzer, Solweig A. "Quaternary geology and dispersal patterns, Winagami region, Alberta". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp02/NQ59928.pdf.
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Olago, Daniel Ochieng. "Late Quaternary lake sediments of Mount Kenya, Kenya". Thesis, University of Oxford, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.296036.
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Bray, Helen E. "Late Quaternary palaeoenvironmental reconstruction of the Arabian Peninsula". Thesis, University of Oxford, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.399406.
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Griffiths, S. J. "Late Quaternary palaeoclimatology of Lake Kopais, central Greece". Thesis, Swansea University, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.507951.
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