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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
11

Method of Micro-Sampling Human Dentine Collagen for Stable Isotope Analysis

Curtis, Mandi J., Beaumont, Julia, Elamin, F., Wilson, Andrew S., Koon, Hannah E.C. 12 April 2022 (has links)
Yes / Sampling of dentine for stable carbon (δ13 C) and nitrogen (δ15 N) isotope ratios in the direction of tooth growth allows the study of temporal changes to the diet and physiological stress of an individual during tooth formation. Current methods of sampling permanent teeth using 1mm increments provide temporal resolution of six - nine months at best depending on the tooth chosen. While this gives sufficient sample sizes for reliable analysis by mass spectrometry, sectioning the dentine across the incremental structures results in a rolling average of the isotope ratios. A novel method of incremental dentine collagen sampling has been developed to decrease the collagen increment size to 0.35mm along the incremental structures thus reducing averaging and improving the temporal resolution of short-term changes within the δ13 C and δ15 N values. This study presents data for a MicroMill-assisted sampling method that allows for sampling at 0.35mm width x 1mm depth increments following the incremental growth pattern of dentine. A NewWave MicroMill was used to sample the demineralised dentine section of modern donated human third molars from Sudan and compared to data from the same teeth using the 1mm incremental sectioning method 2 from Beaumont et al. (2013). The δ13 C and δ15 N isotopic data showed an increased temporal resolution, with each increment providing data for two-four months of dentine formation. The data show the potential of this method for studying dietary reconstruction, nutritional stress, and physiological change with greater temporal resolution potentially to seasonal level and with less attenuation of the δ13 C and δ15 N values than was previously possible from human dentine.
12

Changes in Alcoholic Beverage Choice and Risky Drinking among Adolescents in Europe 1999–2019

Loy, Johanna K., Seitz, Nicki-Nils, Bye, Elin K., Dietze, Paul, Kilian, Carolin, Manthey, Jakob, Raitasalo, Kirsimarja, Soellner, Renate, Trolldal, Björn, Törrönen, Jukka, Kraus, Ludwig 04 May 2023 (has links)
This paper explores trends in beverage preference in adolescents, identifies related regional differences, and examines cluster differences in key drinking measures. Data were obtained from the European School Survey Project on Alcohol and Other Drugs (ESPAD), covering 24 European countries between 1999 and 2019. Trends in the distribution of alcoholic beverages on the participants’ most recent drinking occasion were analysed by sex and country using fractional multinomial logit regression. Clusters of countries based on trends and predicted beverage proportions were compared regarding the prevalence of drinkers, mean alcohol volume and prevalence of heavy drinking. Four distinct clusters each among girls and boys emerged. Among girls, there was not one type of beverage that was preferred across clusters, but the proportion of cider/alcopops strongly increased over time in most clusters. Among boys, the proportion of beer decreased, but was dominant across time in all clusters. Only northern European countries formed a geographically defined region with the highest prevalence of heavy drinking and average alcohol volume in both genders. Adolescent beverage preferences are associated with mean alcohol volume and heavy drinking at a country-level. Future approaches to drinking cultures need to take subpopulations such as adolescents into account.
13

Seismic velocity contrasts and temporal changes of strike-slip faults in central California

Zhao, Peng 27 August 2010 (has links)
The spatial patterns of bimaterial interfaces along the Parkfield section of the San Andreas Fault (SAF) and central section of the Calaveras Fault are systematically investigated with large data sets of near-fault waveforms. Different from the usage of direct P and S waves in traditional tomographic studies, a particular seismic phase named fault zone head wave (FZHW) is used to image the bimaterial fault interfaces. The results show clear variations of seismic velocities contrast both along-strike and along-depth directions in both regions, which is in general consistent with local geological setting at surface and existing 3D tomography results. In the Parkfield section of SAF, the result of velocity contrast is used to test the relationship between preferred rupture directions of M6 Parkfield earthquakes and bimaterial interface. Strong velocity contrast (~5-10%) near Middle Mountain (MM) could control the rupture directions of nearby earthquakes to SE, such as the case for 1966 M6 Parkfield earthquake. In comparison, weak velocity contrast (~0-2%) near the epicenter of the 2004 Parkfield M6 earthquake (i.e., Gold Hill) probably has no influence on controlling its rupture direction, which is consistent with the bilateral rupture of the 2004 Parkfield earthquake. In the central Calaveras Fault, a detailed analysis of the moveout between FZHWs and direct P waves revealed the existence of a complicated fault structure with velocity contrast increasing from NW to SE of station CCO. The high velocity contrast SE of station CCO could be caused by a low-velocity zone SE of station CCO. The spatio-temporal variations of seismic velocity around the central Calaveras Fault and its nearby region are investigated based on the waveform analysis of 333 repeating clusters following the 1984 ML6.2 Morgan Hill earthquake. Clear reduction of seismic velocity is shown for all repeating clusters immediately after the mainshock, followed by a logarithmic recovery. The coseismic change mostly occurs at shallow layers (top few hundred meters) for the region away from the rupture area of the mainshock, but extends much deeper around the rupture zone of the Morgan Hill earthquake. The estimated depth of the damage zone is up to 6 km in the fault based on the repeating clusters directly beneath station CCO. Finally, temporal changes around the Parkfield section of SAF are studied using recently developed ambient noise cross-correlation technique. The extracted daily empirical Green functions (EGFs) from 0.4-1.3 Hz noise records are used to estimate subtle temporal changes associated with large earthquakes from local to teleseismic distances. The results show clear coseismic reduction of seismic velocities after the 2004 M6 Parkfield earthquake, similar to the previous observation based on repeating earthquakes. However, no systematic changes have been detected for other four regional/teleseismic events that have triggered clear tremor activity in the same region. These results suggest that temporal changes associated with distance sources are very subtle or localized so that they could not be detected within the resolution of the current technique (~0.2%).
14

Mudan?as a longo prazo na comunidade de peixes de uma ba?a tropical do sudeste do Brasil (1987-2013): perda gradativa da biodiversidade da zona interna para zona externa / Long-term changes in fish communities of a tropical bay in Southeastern Brazil (1987-2013): gradative losses of biodiversity from the inner to the outer zone

Pinto, Samara Macedo 28 May 2015 (has links)
Submitted by Celso Magalhaes (celsomagalhaes@ufrrj.br) on 2017-06-08T13:33:20Z No. of bitstreams: 1 2015 - Samara Macedo Pinto.pdf: 970121 bytes, checksum: f69dfd12be8357633a632969c91a1d3a (MD5) / Made available in DSpace on 2017-06-08T13:33:20Z (GMT). No. of bitstreams: 1 2015 - Samara Macedo Pinto.pdf: 970121 bytes, checksum: f69dfd12be8357633a632969c91a1d3a (MD5) Previous issue date: 2015-05-28 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior - CAPES / Fish communities in developing countries have, in many cases, showed a decrease in the species richness and abundance over time as a result of anthropogenic impacts. We analyzed fish communities of three zones (inner, middle and outer) of the Sepetiba Bay (Southeastern Brazil) using identical sampling methods (bottom trawl) during four different time periods: 1987?1988; 1993?1995; 1998?2001 and 2012?2013. A total of 33,140 fish representing 127 species in 88 genera and 41 families were recorded. Our results revealed highly significant and consistent differences in the fish community structure among the bay zones, and a decreased in the fish richness and abundance over the time period. Changes in fish richness and abundance were related mostly to a sharp decrease that occurred in the inner bay zone, the most impacted bay area, and, to a lesser extent, in the middle zone between the two first (1987?1988 and 1993?1995) and the two latter time periods (1998?2001 and 2012?2013), whereas the outer zone remained comparatively stable over time. Spatial changes in the fish community structure among the bay zones were related to differences in salinity, transparency and depth with this latter variable, together with other factors, acting as a buffer for stabalizing community changes; however, these environmental variables explained little of the variation in the temporal changes. The most important changes over time in abundant species were the numerical decreases of the Ariid Cathorops spixii, the serranid Diplectrum radiale and sciaenid Cynoscion leiarchus, and increases of the sciaenid Micropogonias furnieri and the marine catfish Genidens genidens, with this latter species restricted to the inner and middle zones. This study adds long-term information on gradual fish community changes along spatial gradients of environmental and anthropogenic influences in embayment systems. It is perhaps timely to link conservation and management planning with historical information to protect fish biodiversity in tropical developing countries / As comunidades de peixes em pa?ses em desenvolvimento, em muitos casos, mostram uma diminui??o na riqueza e abund?ncia das esp?cies ao longo do tempo como resultado das evid?ncias dos impactos antropog?nicos. N?s analisamos as comunidades de peixes ao longo de tr?s zonas (interna, central e externa) da Ba?a de Sepetiba (Sudeste do Brasil), utilizando m?todos id?nticos de amostragem (bottom trawl) de peixes durante quatro per?odos temporais diferentes: 1987?1988; 1993?1995; 1998?2001 e 2012?2013. Registrou-se um total de 33.140 peixes representando 127 esp?cies em 88 g?neros e 41 fam?lias. Nossos resultados revelaram diferen?as altamente significativas e consistentes na estrutura da comunidade de peixes entre as zonas da ba?a e uma diminui??o na riqueza de esp?cies e abund?ncia ao longo do per?odo de estudo. As mudan?as na riqueza de esp?cies e abund?ncia foram relacionadas, principalmente, ? uma forte queda que ocorreu na zona interna da ba?a, ?rea esta mais afetada e, em menor medida, na zona central entre os dois primeiros (1987?1988 e 1993?1995) e os ?ltimos dois per?odos temporais (1998?2001 e 2012?2013), enquanto a zona exterior permaneceu relativamente est?vel ao longo do tempo. Mudan?as espaciais na estrutura da comunidade de peixes entre as zonas da ba?a foram relacionadas ?s diferen?as de salinidade, transpar?ncia e profundidade com este ?ltima vari?vel, em conjunto com outros fatores, atuando como um ?buffer? estabilizando mudan?as na comunidade; no entanto, essas vari?veis ambientais explicaram pouco a varia??o nas mudan?as temporais. As mudan?as mais importantes ao longo do tempo em esp?cies abundantes foi a diminui??o num?rica do Ariideo Cathorops spixii, do Serran?deo Diplectrum radiale e do Sciaen?deo Cynoscion leiarchus, e o aumento do Sciaen?deo Micropogonias furnieri e o bagre marinho Genidens genidens, com esta ?ltima esp?cie restrita ?s zonas interna e central. Este estudo acrescenta informa??o de longo prazo sobre mudan?as graduais nas comunidades de peixes ao longo de gradientes espaciais com influ?ncias ambientais e antr?picas no sistema de ba?a. Talvez seja oportuno vincular conserva??o e planejamento de gest?o com informa??es hist?ricas para proteger a biodiversidade de peixes em pa?ses tropicais em desenvolvimento.
15

Processus d’assemblage des communautés végétales dans les zones humides de Gironde : du diagnostic aux services écosystémiques / Assembly rules in wetlands plant communities : from diagnosis to ecosystemic services

Alfonsi, Elsa 06 December 2016 (has links)
Les zones humides sont des écosystèmes dynamiques en perpétuel changement, dans le temps et dans l'espace et demeurent parmi les plus menacés au monde. Ce travail de thèse est une contribution à la connaissance et la conservation des zones humides. Nous avons étudié la végétation de différents milieux, appartenant à un réseau de zones humides de Gironde, allant des landes humides aux prairies alluviales. Nous les avons choisies pour leur intérêt patrimonial et les enjeux de gestion qu'elles représentent dans le département. Nous avons utilisé plusieurs approches descriptives et expérimentales. La première partie vise à étudier l’organisation des communautés des deux grands systèmes, les landes humides et les prairies alluviales, le long de gradients environnementaux. Dans un deuxième temps, une approche combinant données anciennes et récentes, nous a permis de caractériser les changements de végétation à long terme selon différentes stratégies d’étude de la végétation. La troisième partie, par une approche expérimentale a été conduite sur une communauté végétale à fort enjeu patrimonial : les prairies à Molinie (code 6410 de la Directive Natura 2000). Cette troisième partie a permis de mettre en évidence la part respective des filtres stochastiques (dispersion de graines) et déterministes (compétition) dans une communauté soumise à de fortes contraintes environnementales (inondation). Enfin, dans une analyse prospective, nous avons considéré les enjeux de biodiversité ainsi que les services écosystémiques, cette fois, à l'échelle du département. Cette analyse envisage les outils à développer pour une approche multi-taxon et multi-services sur l'ensemble des zones humides de Gironde. L’ensemble de ce travail a permis de construire un dispositif de suivi de la biodiversité végétale au niveau départemental. Les résultats de ce travail contribuent aujourd’hui à considérer la gestion de ces communautés végétales de façon intégrée et proposent des outils d’aide à la décision pour la gestion de ces espaces. / Wetlands are dynamic ecosystems, constantly changing in time and space, and remaining among the most threatened ecosystems in the world. This thesis contribute to wetland knowledge and conservation. We studied the vegetation of different communities belonging to a network of wetlands in Gironde and ranging from wet heathlands to alluvial meadows. Wetlands were selected from the department council historical interest and management issues. We used several descriptive and experimental approaches. The first part aims to study the organization of the communities of the two major systems, heathlands and alluvial grasslands, along environmental gradients. Then, in a second time, an approach combining old and recent data allowed us to characterize long-term vegetation changes according to different strategies of vegetation study. The third part was conducted on a plant community with a strong conservation issue: Molinia caerulea wet meadow (Code 6410 of the Natura 2000 Directive) with an experimental approach. We highlight here the importance of stochastic filters (seed dispersion) and deterministic filters (competition) in a community controlled by environmental constraints (flooding). Finally, within a prospective analysis, we considered biodiversity issues and supply in ecosystems services at the departmental level. This analysis investigate tools to develop for a multi-taxon and multi-service approach in any Gironde wetlands. This work allowed us to create a monitoring device for plant biodiversity in the department. These results lead to consider nowadays the management of these plant communities in an integrated way and offer tools of decision support for the management of these communities.
16

Riparian vegetation patterns according to hydrogeomorphological factors at different spatial and temporal scales in Mediterranean rivers

Garófano Gómez, Virginia 03 June 2013 (has links)
Los corredores riparios en ambientes semiáridos mediterráneos son ecosistemas de gran biodiversidad y complejidad. En ellos confluyen una gran variedad de perturbaciones naturales capaces de crear un mosaico espacial y temporal con pocos paralelos en otros ecosistemas. Sin embargo, a pesar de su valor, los ecosistemas riparios están amenazados debido a los altos niveles de intervención humana. La construcción de presas (y la consecuente manipulación del caudal) está considerada como la perturbación humana más importante que se cierne sobre ellos. Esta tesis ha tenido como objetivo analizar el ecosistema ripario, abarcando diferentes escalas espaciales y temporales, y centrándose en los factores que influyen en la distribución, estructura, composición, calidad y dinámica de su vegetación, tanto en tramos naturales como hidrológicamente alterados de ríos mediterráneos, concretamente de la Demarcación Hidrográfica del Júcar (Este de España). Para lograr este objetivo, se han hecho los siguientes aportes a la investigación: A) Determinar los patrones de distribución de especies leñosas riparias en el gradiente transversal de la ribera y definir grupos de especies con respuesta similar a las condiciones físicas del hábitat; B) Comparar la respuesta de dichas especies en tramos naturales y alterados hidrológicamente; C) Definir curvas de respuesta y gremios hidrológicos de especies en tramos con régimen natural; D) Establecer los principales factores que determinan la calidad del hábitat ripario y fluvial y los patrones longitudinales de la composición florística, así como de las características del hábitat fluvial en un segmento hidrológicamente alterado; E) Describir los cambios espacio-temporales en la estructura y complejidad de la vegetación, y los cambios temporales en el régimen de caudales del corredor ripario de un tramo hidrológicamente alterado. Los objetivos anteriores fueron abordados con diferentes metodologías que implicaron la combinación de diversas fuentes de información y un esfuerzo importante en la toma de datos en varios lugares de estudio de los ríos Cabriel, Mijares y Serpis. Para cumplir con los objetivos A y B, se llevaron a cabo un muestreo de suelos y un muestreo georreferenciado de vegetación a través de transectos transversales al cauce en dos tramos naturales y tres regulados. Los datos fueron analizados con estadística robusta y multivariante. Para cumplir el objetivo C, el muestreo georreferenciado anterior (junto con un muestreo dendrocronológico) fue acoplado con un modelo hidráulico en los dos tramos naturales, con el fin de obtener la serie temporal de cotas del agua a la que habían estado expuestas cada una de las plantas durante su vida. La respuesta de las especies y su posible agregación en gremios hidrológicos fue comparada mediante estadística robusta en relación a la duración de la inundación, duración de la inundación durante el período de crecimiento, duración continua de la inundación, frecuencia de inundación y elevación de la planta respecto al caudal base. Para lograr el objetivo D, toda la sección regulada del río Serpis (desde la presa Beniarrés - hasta la desembocadura; 40 km) se dividió en segmentos. En cada uno de ellos se llevó a cabo un inventario de flora y se aplicaron índices hidromorfológicos. Los segmentos fueron agrupados de acuerdo a su composición florística y características del hábitat fluvial utilizando diferentes técnicas de estadística multivariante. Finalmente se discutieron los factores principales que controlan los patrones espaciales de la composición florística, las características del hábitat fluvial, la calidad del hábitat ribereño y la heterogeneidad del hábitat fluvial. Para alcanzar el objetivo E, se combinaron series históricas de caudales y su manipulación humana con imágenes aéreas históricas (reveladoras de cambios en la cubierta vegetal) y observaciones de campo de la distribución de edades de la vegetación y morfología del corredor ripario del río Mijares en los últimos 60 años. De esta información, se extrajeron métricas del paisaje e índices hidrológicos para identificar y resumir los cambios espacio-temporales en la estructura de la ribera y en el régimen de caudales. El estudio a escala transversal nos ayudó a comprender en cada uno de los tramos la zonación de las especies leñosas riparias en función de la morfología y características del suelo, revelando que la alteración del caudal puede influir en la modificación de los patrones posicionales de las especies. Se definieron tres gremios hidrológicos: ¿altamente tolerante a la inundación¿, ¿tolerante intermedio¿ y ¿de transición entre ripario y terrestre¿. El estudio a escala longitudinal sugirió que la respuesta de la vegetación a un cambio hidrológico es altamente dependiente de la geomorfología local. Se constató que los factores principales que determinan los patrones hidromorfológicos y florísticos son un régimen de caudales artificial y altamente variable (identificado en los segmentos con peor calidad del hábitat ripario y fluvial), la presencia de estructuras laterales en el cauce y las características geomorfológicas. Como efectos importantes de la regulación del caudal a largo plazo, el estudio a escala espacio-temporal reveló un aumento en la cobertura y densidad de la vegetación leñosa, una deriva en la composición de especies y una disminución en las áreas de sedimento desnudo (esencial para el reclutamiento de las especies riparias pioneras), junto con una reducción sincrónica en la complejidad de la ribera. Estos cambios estarían relacionados con la disminución de la magnitud y variabilidad de los caudales en las últimas seis décadas. Solo una mejor comprensión de los procesos ecohidrológicos y de las implicaciones de la alteración hidrológica sobre los ecosistemas riparios mediterráneos podrá apoyar la integración eficaz de estos sistemas en las decisiones de gestión del agua. / Garófano Gómez, V. (2013). Riparian vegetation patterns according to hydrogeomorphological factors at different spatial and temporal scales in Mediterranean rivers [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/29395

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