• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 120
  • 59
  • 27
  • 18
  • 17
  • 11
  • 7
  • 4
  • 3
  • 2
  • 2
  • 1
  • 1
  • 1
  • 1
  • Tagged with
  • 332
  • 98
  • 42
  • 32
  • 31
  • 28
  • 26
  • 26
  • 22
  • 21
  • 20
  • 20
  • 20
  • 19
  • 19
  • 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.
181

Quantitative determination of quinone chromophore changes during ECF bleaching of kraft pulp

Zawadzki, Michael A. 08 1900 (has links)
No description available.
182

Análisis de la participación en deporte en edad escolar en la Región de Murcia 2005-2010

Morales Baños, Vicente 03 November 2015 (has links)
El objeto de estudio de esta Tesis Doctoral analiza la participación en el programa de Deporte Escolar de la Región de Murcia durante cinco años (2005-2010) y teniendo en cuenta diferentes variables (categoría, género, grupo intermunicipal, curso, tipo de deporte, tipo de centro). Se ha realizado un recorrido conceptual alrededor de términos relacionados con el deporte y hemos observado la realidad del deporte escolar en las diferentes comunidades autónomas, así como aspectos relacionados con esta actividad como: competición, valores, centros de enseñanza, etc. A partir de la problemática observada a lo largo del marco teórico del Deporte en Edad Escolar, se han establecido los objetivos siguientes: Objetivos: 1. Detectar si la participación femenina aumenta con el paso del tiempo. 2. Constatar la evolución en la participación, en el paso de la enseñanza primaria a la secundaria (de la categoría alevín a infantil) del alumnado en el programa de Deporte Escolar. 3. Diferenciar la participación del alumnado de centros privados-concertados en las competiciones del programa de Deporte Escolar, respecto a los de centros públicos. 4. Comparar las preferencias en cuanto al género, respecto a los deportes colectivos e individuales. 5. Discriminar si la participación por categorías depende de la zona geográfica donde se desarrolle el programa de Deporte Escolar. 6. Destacar que tipo de deporte se realiza más según la zona geográfica donde se practica. 7. Determinar qué tipo de deporte se practica más según el tipo de centro. 8. Comprobar si la participación en deporte escolar de cada grupo intermunicipal durante el período de estudio no es directamente proporcional a la población escolar de estos. Población La Población de estudio corresponde a todos los sujetos en Edad Escolar de la Región de Murcia, 741.728, con una edad comprendida entre los 8 y los 18 años (Benjamín-Juvenil) durante los 5 cursos académicos objeto de esta investigación. Muestra La muestra seleccionada corresponde a todas las participaciones que han realizado los sujetos en el Campeonato de Promoción Deportiva del programa de “Deporte Escolar” de la Región de Murcia, Un total de 249.326 participaciones de alumnos durante las cinco temporadas objeto de estudio. Material e Instrumentos La inscripción de los alumnos de cada centro escolar se realiza desde el propio centro a través de la página web de la Comunidad Autónoma de la Región de Murcia, en una Aplicación Informática de la Dirección General de Deportes, de la que se extrajeron los datos de participación. Con estos datos se ha programado una base de datos en el Programa de Análisis estadístico SPSS versión 15.0. CONCLUSIONES Las participaciones femeninas en el Campeonato de Promoción Deportiva aumentan con el paso del tiempo, sin embargo las masculinas son superiores a las femeninas en todas las categorías, grupos intermunicipales y tipos de centro. Las participaciones son mayores en categoría Alevín y aumentan durante el período de estudio. Se produce un mayor porcentaje de participaciones en los centros públicos que en los privados-concertados. Las mayores participaciones se producen en los deportes individuales de forma global y con un porcentaje más alto en las chicas. El mayor ratio de participación por individuo de población se produce en el grupo intermunicipal uno, donde se ubican, entre otros, los municipios de Librilla y Lorca. La participación en deportes individuales y/o colectivos es similar en los centros privados-concertados, mientras que en los públicos, los deportes individuales aventajan en un pequeño porcentaje a los colectivos. El ratio de participación por individuo de la población en deporte escolar de cada grupo intermunicipal no es directamente proporcional a la población escolar de los mismos en ninguna zona y en ningún curso. / The purpose of this thesis is to analyze the participation to the School Sports programme in the Region of Murcia during five years (2005-2010), taking into account several variables (category, genre, intermunicipal group, course, type of sport, type of centre). Different concepts about sports have been studied, therefore, we have been able to notice the reality of School Sports in the different Autonomous Regions and some features related to this activity such as: competition, values, educational institution, etc. Based on the problems discerned along the theoretical frame of sport in school age, some objectives have been established: Objectives: 1. Detect if female participation is increasing along time. 2. Verify the development in participation of students in the programme of School Sports when they start Secondary School and leave behind Primary school (from alevin to infantil category). 3. Distinguish between state-subsidised or private students participation and public students participation in competitions in the School Sport programme. 4. Compare the genre preferences related to individual and group sports. 5. Establish if the participation by categories depends on the geographical area. 6. Specify what sport is played the most on each geographical area. 7. Determine what sport is played most depending on the type of the educational centre. 8. Corroborate if the participation of each intermunicipal group in School Sports is not directly proportional to their student population. Population The target population corresponds to all the school-age individuals in the Region of Murcia (741,728) aged between 8 to 18 years old (Benjamín-Juvenil categories) during five academic years. Sample The chosen sample corresponds to all the participations the individuals have made in the Sport Promotion Championship of the School Sport programme of the Region of Murcia (a total of 249,326 participations during the five target seasons). Materials and Resources Student’s registration in each educational centre is performed at their own centre through Region of Murcia’s web page in the Dirección General de Deportes’ App from which the data participation was taken. A database has been programmed with this data in the Statistic Analysis Programme SPSS version 15.0. CONCLUSIONS Female participations in the Sport Promotion Championship are increasing over time, however male participations are still superior to female ones in each category of the intermunicipal groups and types of educational centre. Female participants are superior in Alevín category and are increasing during the study period. A greater percentage of participants are set in public centres than in state-subsidised centres. The greatest number of participants is in individual sports and with a higher percentage in female participation. The biggest ratio of participations per individual is set in the intermunicipal group number one, where local governments of Librilla and Lorca are located. Participation in individual/group sports is similar in state-subsidised or private educational centres, whereas in public centres individual sports lead the group ones by a small percentage. The ratio of participations per individual in School Sports of each intermunicipal group is not directly proportional to the student population in any area and any school year.
183

Lichen thermal sensitivities, moisture interception and elemental accumulation in an arid South African ecosystem

Maphangwa, Khumbudzo Walter January 2010 (has links)
<p>Elevated temperatures accompanying climate warming are expected to have adverse effects on sensitive lichen species. This premise was examined by measuring the sensitivity of different lichen species to elevated temperatures in the laboratory and in the field. Laboratory studies involved the exposure of nine hydrated lichen species (Xanthoparmelia austro-africana, X. hyporhytida, Xanthoparmelia sp., Xanthomaculina hottentotta, Teloschistes capensis, Ramalina sp., Flavopuntelia caperata, Lasallia papulosa, Parmotrema austrosinensis) collected from sites of different aridity and mean annual temperature for 2 hourly intervals to temperatures ranging from 24&ordm / C to 48&ordm / C in a forced daft oven and measuring their respiration rates and maximum quantum yield of PSII. Field studies involved simultaneous hourly measurements of ground surface air temperatures and Lichen effective quantum yield of PSII of hydrated lichen species populations under ambient and artificially modified environmental conditions.</p>
184

Constraining sources of atmospheric trace constituents with Lagrangian particle dispersion modeling

Benmergui, Joshua January 2013 (has links)
This manuscript based thesis examines and advances methods for constraining sources of atmospheric trace constituents with a Lagrangian particle dispersion model. The method of Bayesian inversion is demonstrated, and a new method is introduced to a class of similar problems where established methods are not applicable. First, A new regression based methodology was developed and applied to observations of atmospheric methanesulfonic acid mass concentrations at Alert, Nunavut. The methodology was used to compare the importance of phytoplankton blooms vs. the ice-free ocean as sources of the dimethylsulfide precursor, and to compare the importance of bromine monoxide vs. hydroxyl as agents oxidizing dimethylsul de to methanesulfonic acid. These issues are relevant to the application of methanesulfonic acid concentrations in ice cores to determine historic sea ice properties. The analysis indicated that source regions to Alert during the spring are primarily ice-free ocean with a significant contribution from ice edge blooms, and during the summer to be dominated by the ice-free ocean. The model also indicated that oxidation of DMS by BrO was the dominant source of MSA in the spring, while DMS oxidation by OH was the dominant source in the summer. Secondly, Bayesian inversion was applied to observations of atmospheric elemental carbon mass concentrations at Tsinghua University in Beijing, China. The analysis provided evidence that current bottom-up elemental carbon emissions estimates in northern China are likely underpredicted. Global chemical transport models show ubiquitous underestimates of the atmospheric burden of elemental carbon, especially near large sources of emissions. Northern China is among the regions with the most intensive elemental carbon emissions in the world, and an underestimate of emissions in this region may be partially responsible for the global chemical transport model underestimates.
185

Early Archaean crustal evolution: evidence from ~3.5million year old greenstone successions in the Pilgangoora Belt, Pilbara Craton, Australia

Green, Michael Godfrey January 2001 (has links)
In the Pilgangoora Belt of the Pilbara Craton, Australia, the 3517 Ma Coonterunah Group and 3484-3468 Ma Carlindi granitoids underlie the 3458 Ma Warrawoona Group beneath an erosional unconformity, thus providing evidence for ancient emergent continental crust. The basalts either side of the unconformity are remarkably similar, with N-MORB-normalised enrichment factors for LILE, Th, U and LREE greater than those for Ta, Nb, P, Zr, Ti, Y and M-HREE, and initial e(Nd, Hf) compositions which systematically vary with Sm/Nd, Nb/U and Nb/La ratios. Geological and geochemical evidence shows that the Warrawoona Group was erupted onto continental basement, and that these basalts assimilated small amounts of Carlindi granitoid. As the Coonterunah basalts have similar compositions, they probably formed likewise, although they were deposited >60 myr before. Indeed, such a model may be applicable to most other early Pilbara greenstone successions, and so an older continental basement was probably critical for early Pilbara evolution. The geochemical, geological and geophysical characteristics of the Pilbara greenstone successions can be best explained as flood basalt successions deposited onto thin, submerged continental basement. This magmatism was induced by thermal upwelling in the mantle, although the basalts themselves do not have compositions which reflect derivation from an anomalously hot mantle. The Carlindi granitoids probably formed by fusion of young garnet-hornblende-rich sialic crust induced by basaltic volcanism. Early Archaean rocks have Nd-Hf isotope compositions which indicate that the young mantle had differentiated into distinct isotopic domains before 4.0 Ga. Such ancient depletion was associated with an increase of mantle Nb/U ratios to modern values, and hence this event probably reflects the extraction of an amount of continental crust equivalent to its modern mass from the primitive mantle before 3.5 Ga. Thus, a steady-state model of crustal growth is favoured whereby post ~4.0 Ga continental additions have been balanced by recycling back into the mantle, with no net global flux of continental crust at modern subduction zones. It is also proposed that the decoupling of initial e(Nd) and e(Hf) from its typical covariant behaviour was related to the formation of continental crust, perhaps by widespread formation of TTG magmas.
186

Influência da queima da palha de cana de açúcar na constituição do material particulado atmosférico (MP2,5 e MP10) e as suas implicações potenciais sobre a saúde humana /

Silva, Flavio Soares. January 2011 (has links)
Orientador: Mary Rosa Rodrigues de Marchi / Banca: Christine Laure Marie Bourote / Banca: Annibal Duarte Pereira Netto / Banca: Nilva Ré Poppi / Banca: Roma Tauler / Resumo: No Brasil, a queima da cana de açúcar é utilizada para facilitar a colheita, mas este procedimento causa grande poluição ambiental devido a quantidade de fuligem lançada na atmosfera. O material particulado (MP) emitido contém inúmeros contaminantes, tais como: hidrocarbonetos policíclicos aromáticos (HPAs) e elementos. A cidade de Araraquara/SP possui cerca de 200.000 habitantes e é cercada por plantações de cana de açúcar, sendo que a prática de queimada é constante no período da safra (abril-novembro, todos os anos). Neste trabalho, determinou-se a concentração elementar e de HPAs em MP na cidade de Araraquara durante o período da safra (S) e da entre safra (E) da cana de açúcar. Foram coletadas 60 amostras (E) e 220 amostras (S) para a análise de HPAs, e 10 amostras (E) e 10 amostras (S) para a análise elementar. As amostras foram coletadas utilizando um amostrador dicotômico (vazão: 10 L min-1, 24 h) com filtros de PTFE (37 mm, 2 μm de tamanho de poro). Para a análise de HPAs, dez filtros de PTFE contendo o MP foram extraídos em banho de ultrassom com acetona/n-hexano (1:1 v/v), sendo que as análises foram efetuadas por HPLC/FLD. A análise elementar foi efetuada por fluorescência de raios X por energia dispersiva (EDXRF), sem tratamento prévio das amostras. A concentração mediana de HPAs totais foi de 1,9 ng m-3 (E) e 6,2 ng m-3 (S). A concentração mediana de benzo[a]pireno, HPA considerado carcinogênico, foi de 0,026 ng m-3 e 0,15 ng m-3 para os períodos de E e S, respectivamente. O risco potencial de câncer associado à exposição a HPAs por inalação, foi estimado com base na concentração de benzo[a]pireno equivalente (BaPeq), onde a toxicidade de uma mistura de HPAs é definida pela concentração de cada substância multiplicada pelo seu fator de equivalência de toxicidade relativa (FET). Os valores medianos encontrados para... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: In Brazil, the sugar cane crops are burned to facilitate the harvesting, this procedure causes environmental pollution from the large amounts of soot that are released into the atmosphere. This particulate matter (MP) contains numerous contaminants such as polycyclic aromatic hydrocarbons (PAHs) and metals. The city of Araraquara, located at central area from São Paulo State, has around 200,000 inhabitants and is surrounded by sugarcane plantations (46,994 ha of total cultivated area, in the harvest 2008/2009). In this study, PAHs concentrations and elemental composition in the MP were determined in Araraquara city during the sugarcane harvesting (HV) and non-harvesting (NHV) seasons. 60 samples were collected during the NHV and 220 samples during the HV seasons for the analysis of PAHs. 10 samples were collected during the NHV and 10 samples during the HV season for the analysis of Si, K, Ca, Ti, V, Fe, Sr, Cr, Ni, Mn, Cu, Zn, As, Cd, Pb, Sb, Al, S and Cl. The samples were collected using a dichotomous sampler (10 L min-1, 24 h) with PTFE filters. Ten filters sets were extracted (ultrasonic bath with hexane/acetone (1:1 v/v)) and analyzed by HPLC/FLD for the analysis of PAHs. Information concerning the bulk elemental concentration was provided by energy-dispersive x-ray fluorescence (EDXRF). The median concentration for total PAHs was 1.9 ng m-3 (NHV) and 6.2 ng m-3 (HV). Benzo[a]pyrene median concentration was 0.026 ng m-3 and 0.15 ng m-3 for the NHV and HV seasons, respectively. The potential cancer risk associated to inhalation exposure was estimated based on the benzo[a]pyrene toxic equivalence (BaPeq), where the overall toxicity of a PAH mixture is defined by the concentration of each compound multiplied... (Complete abstract click electronic access below) / Doutor
187

Modulární systém pro prvkovou analýzu metodou laserové spektroskopie / Modular System for Elemental Analysis using Laser Spectroscopy

Klempa, Tomáš January 2015 (has links)
This diploma thesis is solved for AtomTrace Company and describes mechanical design of modular system for elemental analysis using laser spectroscopy. Object of this thesis is to create at once compact and modular system, with addition of liquid analysis module. System described in this work came out from current solution and is capable of interaction of new and previous modules. New solution is more economical both in budget and mass, whole system is fully functional and liquid analysis module with flat jet has 40 % stability, as described in experiments. The benefit of this work is possible future integration of system or separate modules into the AtomTrace portfolio and industry applications.
188

Etnomatemáticas y el grado de Razonamiento Lógico Matemático en los estudiantes de cuarto grado del nivel primario de la I.E. Nº 38142/ V-P Inca Pachacútec del distrito de Vilcas Huamán – Ayacucho

Romaní Castro, Natalia January 2015 (has links)
El documento digital no refiere asesor / Publicación a texto completo no autorizada por el autor / Estudia el problema de la relación entre el nivel de conocimiento de la Etnomatemática y el grado de Razonamiento Lógico Matemático en el proceso de enseñanza –aprendizaje en la EIB, de los alumnos del cuarto grado de la I.E. N° 38142/ V-P Inca Pachacútec del distrito de Vilcas Huamán. La hipótesis que se ha formulado es que existe una relación positiva entre el nivel de conocimiento de la Etnomatemática y el grado de Razonamiento Lógico. Se aplicaron tres exámenes a los niños a fin de recoger información, relacionar y medir las variables de estudio para efectuar las correlaciones. Los resultados fueron analizados en el nivel descriptivo y en el nivel inferencial, según los objetivos y las hipótesis, siguiendo el modelo de investigación. En el nivel descriptivo, se han utilizado, las medidas de tendencia central y de dispersión para determinar los niveles predominantes del conocimiento de la etnomatemática y el grado de razonamiento lógico matemática en el nivel inferencial, se ha hecho uso de la estadística paramétrica, utilizando los modelos matemáticos, coeficiente de correlación de Pearson Los resultados encontrados indican que el nivel de conocimiento de la Etnomatemática y el grado de Razonamiento Lógico Matemático muestran una correlación positiva débil dentro del proceso de enseñanza –aprendizaje en la población de nuestra investigación. / Tesis
189

Analysis of three wetland medicinal plants: Centella asiatica, Cyperus longus and Typha capensis found in the Western Cape Province of South Africa.

Saibu, Olusola Surajudeen January 2017 (has links)
Magister Scientiae (Biodiversity and Conservation Biology) / South Africa is recognised worldwide for its rich diversity of plants, many of which have been used in ethno-medicine. However, the use of wetland plant species in ethno-medicine required further investigations. This research is aimed at investigating three wetland medicinal, plant species, Centella asiatica, Cyperus longus and Typha capensis based on their geographical, seasonal, mineral nutrient (Fe, Mn, Ca, Mg, K and Na) and secondary metabolite characteristics. Samples of each species were collected from Grabouw, Kelderhoff, Kenilworth, Pringle Bay, University of the Western Cape (UWC) and Worcester within the Western Cape Province of South Africa. Specimen and soil collections were carried out during autumn, spring, summer and winter of 2014. Both plant and soil samples were acid digested and mineral nutrient concentrations in the samples were analysed using an atomic absorption spectrometer (AAS). Secondary metabolites were determined using analytical TLC on normal phase Merck-Silva gel coated aluminium plates as well as by using HPLC separation from crude extracts of C. asiatica, C. longus and T. capensis using LC-MS hardware from Agilent. The elemental analysis of soil samples showed that Ca, K, Mg, Mn and Zn concentrations were predominantly low. Soil mineral concentrations increased progressively from inland (Worcester) towards the coastland in the south (Pringle Bay). Calcium and sodium concentrations, in particular, were higher in soil samples obtained from Grabouw (inland south) and decreased northward towards Worcester. Comparatively, plant mineral concentrations were generally higher than soil concentrations. The high concentration of some of these essential elements, in selected plants is an indication that these plant species could be a good source of essential elements. High concentrations of phytochemicals were found in Centella asiatica during winter, while Cyperus longus and Typha capensis exhibited high concentrations during autumn indicating variation in respect of season. Consequently, harvesting of the studied plants should be done at the season with a relatively high phytochemical concentration. Studies are needed to investigate the extent of pesticide or herbicide contamination in wetland plants to protect the health of users. The LC-MS analyses of the three study species showed that seasonal variation affects metabolite constituents and moreover that these metabolite constituents differ from one locality to another. The seasonal variation of the elements in the studied medicinal plants justified the importance of harvesting seasons in the optimal utilization of the studied plants for medicinal purpose. s, for C. asiatica, anti-bacterial treatments for C. longus and fertility enhancement and birth control for T. capensis.
190

Uso de descontinuidades fortes na simulação de problemas de fratura

Silva, Cristiane Zuffo da January 2015 (has links)
A formação e propagação de fissuras é um fenômeno observado em diversos materiais utilizados na engenharia, como concreto, metais, cerâmicas e rochas. Tendo em vista a grande influência que fissuras têm no comportamento global da estrutura o objetivo deste trabalho consiste na implementação de um modelo de fissura com descontinuidades fortes incorporadas a fim de analisar o processo de fratura em materiais quase-frágeis. A descontinuidade no campo de deslocamentos (descontinuidade forte) é representada através da introdução de graus de liberdade adicionais no interior do elemento finito, sendo esta abordagem denominada enriquecimento elementar (E-FEM). Nestes modelos a fissura pode se propagar em qualquer direção dentro do elemento finito, evitando a necessidade de redefinição da malha em cada etapa, além de fornecer resultados relativamente independentes da malha de elementos finitos utilizada. Por serem internos a cada elemento finito, os graus de liberdade adicionais podem ser eliminados da solução global por condensação estática. Desta forma as descontinuidades são definidas em nível de elemento e o modelo pode ser facilmente implementado em códigos computacionais existentes. O modelo implementado foi proposto por Dvorkin, Cuitiño e Gioia (1990), o qual pertence à classe de modelos com formulação assimétrica estaticamente e cinematicamente consistente (SKON). Esta formulação é caracterizada por garantir o movimento de corpo rígido entre as partes do elemento além de assegurar a continuidade de tensões na linha de fissura, resultando numa matriz de rigidez assimétrica. Diferentes relações constitutivas podem ser utilizadas para descrever o comportamento das regiões com e sem fissura. Portanto, para a região não fissurada, utilizouse um modelo constitutivo elástico linear e para a região fissurada foi analisada a performance de dois modelos constitutivos distintos: linear e exponencial. A capacidade de representar o comportamento de elementos estruturais fissurados foi ilustrada através de exemplos de tração e flexão comparados com outros modelos de fissura existentes e com resultados experimentais. Em relação aos modelos constitutivos para a linha da fissura, o modelo linear não se mostrou adequado por superestimar as tensões de pico além de apresentar um ramo de amolecimento mais frágil. Já o modelo exponencial mostrou-se bastante eficiente representando de forma correta o comportamento de materiais quase-frágeis. / The formation and propagation of cracks is a phenomenon observed in many materials used in engineering, such as concrete, metals, ceramics and rocks. In view of the influence of cracks in the global behavior of the structure, the aim of this work is the implementation of an embedded strong discontinuity model in order to analyze the fracture process in quasi-brittle materials. The discontinuity in the displacement field (strong discontinuity) is represented by the introduction of additional degrees of freedom within the finite element. This approach is called elemental enrichment (E-FEM). The embedded models allow the propagation of crack in any direction within the finite element, avoiding the need of remeshing and providing objective results (mesh independent). The additional degrees of freedom are introduced into the finite element, then these degrees can be eliminated from the global solution by static condensation and the model can be easily implemented in existent computational codes. The model used here was proposed by Dvorkin, Cuitiño and Gioia (1990), which belongs to the statically and kinematically optimal non-symmetric (SKON) formulation. In this formulation, the kinematics that allows for relative rigid body motion and the enforcement of the traction continuity are introduced at element level, resulting a non-symmetric formulation. Different constitutive relations can be used to describe the behavior of the zones with and without cracks. For the zone without cracks it was used a linear elastic model and for the cracked zone it was analyzed the behavior of two different constitutive models: linear and exponential. The ability of the model to represent the behavior of cracked structural elements was illustrated by bending and tensile tests and the results were compared with numerical and experimental data. Regarding the constitutive models for the fracture zone, it was concluded that the linear model was not suitable because it overestimated the maximum stress and promoted a britller softening. In contrast, the exponential model proved to be very efficient to represent the behavior of quasi-brittle materials.

Page generated in 0.8812 seconds