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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.
1

Quantification et caractérisation des mouvements verticaux aux courtes échelles de temps dans les zones dites stables

Biessy, Guillaume 07 December 2009 (has links) (PDF)
Les déformations de la surface de la Terre résultent de plusieurs processus géologiques, très étudiés aux frontières de plaques en raison de leurs fortes amplitudes. Leurs caractéristiques sont variées : amplitude, durée, périodicité et variabilité spatiale. Il existe cependant des zones dites stables où les déformations localisées ou diffuses sont moins importantes en amplitude mais non négligeables une fois cumulées sur de longues périodes de temps. L'objectif principal de cette étude est la quantification et la caractérisation des mouvements verticaux au sein de zones à faible taux de déformation aux courtes échelles de temps, avec plusieurs questions sous-jacentes. Quelle stratégie adopter pour mesurer précisément ces faibles déformations ? Comment extraire et filtrer les effets des différents processus dans un signal GPS de déformation? Comment prendre en compte la surcharge océanique et ses effets locaux dans les traitements GPS ? Dans quelle mesure peut-on relier mouvements verticaux et variations hydrogéologiques ? Cette étude tente de répondre à ces questions tant du point de vue des processus étudiés que de la méthodologie employée. Afin de répondre à ces questions, nous nous sommes intéressés à deux zones : la Bretagne (France) et la plaine du Saïs (Maroc). Le site breton est situé sur une marge passive, à sismicité modérée, sujette à de fortes amplitudes de marées océaniques, et à l'aplomb d'un aquifère cristallin fracturé. La zone d'étude au Maroc est située entre les rides pré-rifaines et le Moyen Atlas, sismiquement actifs, et à l'aplomb d'un vaste aquifère profond et calcaire.
2

Uso da Pistia stratiotes como fitorremediadora de recursos hídricos contaminados por clomazone

Escoto, Dandara Fidélis 20 March 2017 (has links)
Submitted by Marcos Anselmo (marcos.anselmo@unipampa.edu.br) on 2017-06-05T13:54:36Z No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) DANDARA FIDÉLIS ESCOTO.pdf: 2090171 bytes, checksum: 1c4b35661ab0654fc646af3838138cf9 (MD5) / Approved for entry into archive by Marcos Anselmo (marcos.anselmo@unipampa.edu.br) on 2017-06-05T13:54:50Z (GMT) No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) DANDARA FIDÉLIS ESCOTO.pdf: 2090171 bytes, checksum: 1c4b35661ab0654fc646af3838138cf9 (MD5) / Made available in DSpace on 2017-06-05T13:54:50Z (GMT). No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) DANDARA FIDÉLIS ESCOTO.pdf: 2090171 bytes, checksum: 1c4b35661ab0654fc646af3838138cf9 (MD5) Previous issue date: 2017-03-20 / With the growth of world population and the advent of industrialization, the demand for abundant and profitable food production worldwide is increasing. There is then a need for strategies that minimize loss and changes in food products, especially those that are grown for long periods of time like grains and vegetables. In this bias arise the pesticides, marketed since the nineteenth century, increasingly specialized and chemically modified to achieve greater efficiency in pest elimination and a shorter period of time. When pesticides are used correctly, they minimize grain losses by over 40%, but when used improperly or above the recommended dosage, they can lead to environmental and public health impacts. In this context, Clomazone (2 - (2-chlorobenzyl) -4,4-dimethyl-1,2-oxazolidin-3-one), active principle of the commercial herbicide Gamit®, of the Isoxazolidinone family and belonging to toxicological class III is Of broad spectrum used for the control of annual grasses and broadleaf weeds in cotton, peas, squash, soybeans, sweet potatoes, tobacco, wheat and rice. However, this herbicide has a series of physico-chemical characteristics and distinct behavior depending on the environment where it is inserted which can cause the increase of its permanence in the environment and contamination of organisms that are not its origin targets. An alternative to reduce the environmental impact caused by herbicides is phytoremediation. Phytoremediation consists of a technique of removal and / or pollutants from environments using plants as environmental remediation agents. This study aimed to evaluate the ability of the Pistia Stratiotes plant species in phytoremediation of the herbicide clomazone in its commercial form of water resources. The assay lasted 24 days and counted on two herbicidal concentrations that were determined from the one hundred fold multiplication of the dose recommended for use in crops, setting up an acute exposure to the herbicide. The clomazone degradation kinetics analyzes were performed by analytical methods by high performance liquid chromatography coupled to a detector with CLAE-DAD diode array. After 24 days of experiment, it was possible to identify that the plant species was able to reduce the presence of the herbicide clomazone in water by 90% and also that despite the water exposure to P. stratiotes does not undergo morphological changes due to sensitivity to the compound. Thus, the results indicate that Pistia Straiotes is capable of phytoremediation of the herbicide clomazone of water resources. / Com o crescimento da população mundial e o advento da industrialização cada vez mais aumenta a demanda pela produção abundante e rentável de alimentos pelo mundo todo. Existe então a necessidade de estratégias que minimizem a perda e as alterações nos produtos alimentares, sobretudo os que são cultivados por longos períodos de tempo como grãos e hortaliças. Neste viés surgem os pesticidas, comercializados desde o século XIX, cada vez mais especializados e modificados quimicamente para atingir uma maior eficiência na eliminação de pragas e um menor período de tempo. Quando os pesticidas são usados corretamente, eles minimizam acima de 40% as perdas de grãos, mas quando usados de maneira incorreta ou acima da dosagem recomendada, podem conduzir a impactos no ambiente e na saúde pública. Neste contexto, o Clomazone (2 - (2-clorobenzil) -4,4-dimetil-1,2-oxazolidin-3-ona), princípio ativo do herbicida comercial Gamit®, da família das Isoxazolidinona e pertencente a classe toxicológica III é de amplo espectro usado para o controle de gramíneas anuais e plantas daninhas de folha larga em algodão, ervilhas, abóbora, soja, batata-doce, tabaco, trigo e arroz. Porém, este herbicida possui uma série de características físico-químicas e comportamento distinto dependentemente do ambiente onde for inserido o que pode causar o aumento de sua permanência no ambiente e contaminação de organismos que não são os seus alvos de origem. Uma alternativa para reduzir o impacto ambiental causado pelos herbicidas é a fitorremediação. A fitorremediação consiste em uma técnica de remoção e/ou de poluentes dos ambientes utilizando plantas como agentes de remediação ambiental. Este estudo teve como objetivo avaliar a capacidade a espécie vegetal Pistia stratiotes em fitorremediar o herbicida clomazone em sua forma comercial de recursos hídricos. O ensaio teve a duração de 24 dias e contou com duas concentrações o herbicida que foram determinadas a partir da multiplicação em cem vezes da dose recomendada para uso em lavouras, configurando uma exposição aguda ao herbicida. As análises da cinética de degradação do clomazone foram realizadas através de métodos analíticos por cromatográfica líquida de alta eficiência acoplada a detector com arranjo de diodos CLAE-DAD. Após os 24 dias de experimento foi possível identificar que a espécie vegetal foi capaz de reduzir em 90% a presença do herbicida clomazone na água e também que apesar da exposição agua a P. Stratiotes não sofre alterações morfológicas em decorrência de sensibilidade ao composto. Dessa maneira, os resultados indicam que a Pistia Straiotes é capaz de fitorremediar o herbicida clomazone de recursos hídricos.
3

Determination of geodetic velocity field parameters for the African tectonic plate using the technique of Global Navigation Satellite Systems

Munghemezulu, Cilence January 2013 (has links)
Space geodesy is one of the disciplines that contributes uniquely to the global society; its applications have grown to such an extent that system Earth is better understood today. The current accuracy of the Global Navigation Satellite Systems (GNSS) technique is below centimetre level and this allows very accurate determination of velocity field parameters. This study focused on utilizing GNSS to determine the inter-continental plate velocity field for Africa in support of the African Geodetic Reference Frame (AFREF). Data spanning 12.4 years were processed in the International Terrestrial Reference Frame (ITRF2008) using GAMIT/GLOBK 10.4 (developed at the Massachusetts Institute of Technology). Primarily, processing of data focused on International GNSS Service (IGS) stations with a few non-IGS stations (which are of geodetic quality) included, such as Hamburg (HAMB) and Matjiesfontein (MATJ). The same data set was analysed using the Combination and Analyses of Terrestrial Reference Frame (CATREF) software developed at Institut National de l’Information Géographique et Forestière (IGN). Validation of the results was achieved through comparison of the velocity solution from this study with a solution obtained from a core of IGS GNSS stations processed by the Jet Propulsion Laboratory (JPL). No significant differences were evident between the GAMIT/GLOBK 10.4, CATREF and JPL solutions. The results from the Matjiesfontein station indicated that the proposed Matjiesfontein Observatory site shows no significant vertical or horizontal local motion; this information is valuable in that there is no obvious local site instability. The velocity field as derived by GNSS displays no unexpected deviations and supports current understanding of the motion of the Nubian, Somalian and Arabian plates. Furthermore, the comparison of the velocity vectors derived from the IGS station HRAO, Satellite Laser Ranging (SLR) MOBLAS-6 station and 26 m Very Long Baseline Interferometry (VLBI) telescope, which are collocated at the Hartebeesthoek Radio Astronomy Observatory (HartRAO) indicated good agreement and both techniques exhibit no significant vertical motion. This study also contributed to the first computation of the AFREF solution. It is envisaged that as more stations are added to the sparsely distributed current network, more accurate results and better tectonic models can be derived. The availability of station velocities will facilitate adjustments within the AFREF. / Dissertation (MSc)--University of Pretoria, 2013. / gm2014 / Geography, Geoinformatics and Meteorology / unrestricted
4

Near-Real-Time GPS Sensing of Atmospheric Water Vapour

Bai, Zhengdong January 2005 (has links)
An important goal in modern weather prediction is to improve short-term weather forecasts, especially of severe weather and precipitation. However, the ability to achieve this goal is hindered by the lack of timely and accurate observations of atmospheric water vapour, which is one of the most poorly measured and least understood constituents of the Earth's atmosphere due to its high temporal and spatial variability. This situation is being addressed by the Global Positioning System (GPS) technology. GPS radio signals are slowed and bent by changes in temperature, pressure and water vapour in the atmosphere. Traditionally, the GPS signal propagation delay is considered a nuisance parameter that is an impediment to obtaining precise coordinates using GPS. Recent development in GPS precise positioning and orbit determination has enabled the atmospheric parameters to be determined to a high degree of accuracy on a routine basis, using continuous tracking data from ground-based GPS receivers. The aim of this research is to address several critical scientific challenges in estimating the atmospheric water vapour content in near-real-time (NRT) in Australia. Contributions are made to the field of GPS meteorology in the following five areas: First of all, research efforts were made to develop a technical platform for the ground-based GPS meteorology studies and demonstration of GPS Precipitable Water Vapour (PWV) estimation using observations from Australian Regional GPS Networks (ARGN). Methods of estimation of water vapour from GPS and radiosonde data have been developed and tested. GAMIT-based GPS data processing strategies and compare analysis with radiosonde water vapour solutions from the Australia Upper Air Network (AUAN) were undertaken, providing an effective technical basis for further studies. Secondly, the research has developed techniques to allow estimation of atmospheric water vapour from GPS data and surface meteorological observations collected around the GPS sites. Ideally a dedicated meteorological sensor is installed adjacent to the GPS antenna. However, meteorological sensors are normally not installed at most Australian GPS stations. Installing a new meteorological sensor at each GPS station would involve additional cost at the level of one-third or half of the geodetic GPS receiver cost. We have experimentally developed and demonstrated interpolation methods for making use of hourly collected surface meteorological data from the Australian Automatic Weather Station (AWS) network operated by the Bureau of Meteorology (BOM) to estimate atmospheric water vapour. Thirdly, the research has studied ocean tidal loading and its effects on GPS derived precipitable water vapour estimates. The periodic motion of the Earth's surface due to ocean loading is one of the largest periodic motions. However, very little work has been done to quantify their effects on GPS-derived solutions at the GPS sites in the Australian region surrounded by ocean waters. The research presents the theoretical analysis and experimental results from the ARGN network, focusing on ocean loading and its effects on GPS derived precipitable water vapour estimates. The fourth important effort was the development of techniques for estimating highrate Slant Water Vapour (SWV) values for future operational meteorological applications in Australia, including addressing such issues as slant-path delay recovery from post-fit double-difference residuals, and overcoming site multipath effects. The experimental results have demonstrated the efficiency of the proposed methods. Finally, in order to address the meteorological applications with the existing and anticipated GPS reference stations in the Australian region, and measure the atmospheric water vapour content in near-real-time, the technical issues to implement NRT GPS water vapour estimation were identified and discussed, including the data requirements for meteorological and climate applications, NRT data processing and quality control procedures for GPS orbits. The experimental GPS PWV results from NRT and post data processing are compared and presented.

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