136 research outputs found
Experimental and analytical investigation of radiation-induced natural convection in the near shore regions of lakes and reservoirs
Radiation-induced natural convection can play an important role in developing mixing and flow exchange within lakes and reservoirs that are well-protected from wind and have a long residence time. In the daytime, although incoming solar radiation transfers the radiative energy uniformly across the water surface, the bathymetry variation between the near shore and deep water regions creates a horizontal temperature gradient, leading to a horizontal convective motion. In addition, as the incoming light penetrates, its intensity attenuates with increasing depth according to Beer’s law. In near shore regions where the water depth is less than the light penetration depth, there exists residual radiation that is absorbed by the bed and re-emitted back to the water body as a heat flux. Therefore, a relatively warmer water layer is formed near the bottom and may become unstable leading to a vertical convective flow. Thus, net transport and mixing in such water bodies in daytime is promoted by these flows, the characterisation of which is the aim of this thesis. In Chapter 2, the vertical convective flow alone is studied on a laboratory scale using concurrent shadowgraph and Particle Image Velocimetry (PIV) measurements and experimental results are compared with previously developed scales. The 3D linear stability of this flow is investigated using a frozen time model in Chapter 3. The effect of different parameters on the critical conditions and the resulting flow pattern are evaluated. Further, the numerical and laboratory experimental determinations of critical wave numbers are compared. In Chapter 4, the coupled convective flow is examined on a laboratory scale using the same concurrent visualisation technique. The flow development, flow structure and its dependency on off-shore distance are quantified and compared with previously developed scales. Chapter 5 concludes the present study through reviewing the main results and providing suggestions for future work
The Afghan Women’s Writing Project: A Critical Discourse Analysis of Poetry and Narrative as Conflict Resolution Tools
The Afghan Women’s Writing Project (AWWP) emerged in 2009 as a platform through which Afghan women could express their lived experiences and perspectives on a range of culturally relevant issues while retaining their anonymity. The purpose of this research was to understand poetry as a conflict resolution tool that Afghan women are using to be active participants in the social, political and cultural dialogue that is determining their rights. This research focused on three questions: 1) How do Afghan women describe the state of womanhood in Afghanistan? 2) How do Afghan women describe the conflict they experience in their everyday lives? 3) How might poetry and narrative be used to manage the conflict that Afghan women are facing? This research presents a critical discourse analysis (CDA) of one hundred published poems from the AWWP poetry database. Data analysis included open coding, thematic analysis, and the use of van Dijk’s six-step CDA model to evaluate the semantic macrostructures, local meanings, linguistic markers, global and local discourse forms, linguistic realizations, analysis of context, and the researcher’s own interpretive analysis. The findings identify and explain the major themes derived from the study as well as describe how Afghan women feel about womanhood and conflict. The major themes included: child brides/forced marriage, hijab/burqa/niqab, women’s resistance, parents as protectors and/or perpetrators, the power of writing and stress as a result of conflict. This dissertation concludes with a discussion of implications for sustainable norm change using poetry, directions for future research, and recommendations for policy and programming
SYNTHESIS AND CHARACTERIZATION OF HYDROXYAPATITECALCIUM HYDROXIDE FOR DENTAL COMPOSITES
In this work hydroxyapatite was precipitated from calcium hydroxide and phosphoric acid. Calcium hydroxide forms in addition to hydroxyapatite in samples with calcium to phosphorus ratio more than the stoichiometric one (Ca/P = 1.67). The effect of changing the pH of the precipitation solution was investigated. Changing the pH of solution had no effect on the amount of compounds formed in the structure. In contrast, an increase in Ca/P ratio increases the total amount of calcium hydroxide which is suitable for dental composite application
Mesh Requirement Investigation for 2D and 3D Aerodynamic Simulation of Vertical Axis Wind Turbines
The accuracy of a Computational Fluid Dynamics (CFD) model to capture the complex flow around a small vertical axis wind turbine (VAWT) on 2D and 3D grids is investigated. The aerodynamic complexity of the flow is mostly due to rapid variation of the angle of attack of the rotating blades. The resulting flow includes large separation flows over the blades, dynamic stall, and wake-blade interaction. These features are sensitive to the grid resolution and turbulence models. In the present research, a grid convergence study is conducted on 2D grids to examine the CFD model sensitivity to mesh resolution and to identify when grid convergence is obtained. An averaged-grid size of y^+>30 is employed along the wall to capture the near-wall region flow structures. Moreover, a parallel OpenFOAM solver is used to investigate the numerical solution of Unsteady Reynolds-Averaged Navier-Stokes (URANS) equations coupled with Spalart-Allmaras (SA) turbulence model. As a result, it is seen that the Power Coefficient (C_p), in 2D investigations, increases with the mesh size until it achieves grid convergence. For a 3D simulation, only a coarse mesh can be used due to large computational requirements. It is found that the 3D coarse mesh significantly under-predicts the Power Coefficient but is able to predict tip vortices
Icarus op de Kinder Intensive Care. Een theoretische studie naar aanleiding van de ICK-praktijken en praktijkscènes.
Preparation and characterization of magnetic nanoparticles immobilized in acrylamide based hydrogels for metal extraction
In recent years, smart hydrogel has attracted great attention especially in biomedical and pharmaceutical fields. Hydrogel has polymeric chain structure with a three-dimensional network that is able to swell significantly in aqueous environments. This study involves the development of magnetic hydrogel with nanoparticles for absorption of toxic metal ions (Cu (II), Ni (II), and Co (II)). The nanoparticles with magnetic properties were synthesized in poly acrylamide based hydrogels (method A-C). An in situ preparation process was employed to synthesize the nanoparticles with magnetic properties in hydrogel structure. The differences in rate of absorption between native and magnetic hydrogel was investigated in this study. Compared with native ones, apparently magnetic hydrogels can absorb higher amount of toxic metal ions due to the presence of magnetic nano particles. On the other hand, magnetic nanoparticles also provide large surface area which make them capable of absorbing more toxic metal ions. The highest percentage of absorbtion is attributed to AAm-co-AAc (0.6 gr) while the lowest one is for AAm-co-PEG (0.2 gr) (494 % and 23 % respectively). In absorption of toxic metal ions, AAm-co-AAc (0.6 gr) shows the best performance comparing to other types of hydrogels. This investigation shows that hydrogels and magnetic nano particles are applicable in waste water treatment and metal extraction application. The formation of magnetic nanoparticles in the polymer networks was determined by X-ray Diffraction (XRD), Fourier Transform Infrared (FTIR) spectroscopy and observed using Field Emission Scanning Electron Microscope (FESEM)
Del istmo de Fitzcarrald a La Pampa: análisis del sistema de redes de ciudades mineras de la región de Madre de Dios en el área de influencia de la carretera Interoceánica (1980-2018)
Tanto la geografía como la historia han permitido aproximarnos al estudio de la memoria del
proceso de configuración del espacio minero del departamento de Madre de Dios. El análisis
territorial de esta región de la Amazonía ha evidenciado la evolución del modelo centroperiferia
como resultado de la transformación de esta margen territorial y de frontera gracias
al avance de las dinámicas territoriales a múltiples escalas. La multiescaralidad de estas
dinámicas ha influenciado en construir nuevas relaciones desiguales de tipo flujos y de poder
sobre esta periferia modificando el grado de dominación.
En la actualidad, la actividad minera se ha convertido en un problema coyuntural social y
ambiental; no obstante, la consolidación de la economía del oro en la región representa el
arraigo territorial de los frentes extractivos desde inicios de la ocupación occidental como la
avanzada cauchera liderada por Carlos Fermin Fitzcarrald. Él facilitó la articulación fluvial
con las principales urbes caucheras (Iquitos y Manaos) mediante la implementación de un
puente fluvial denominado istmo de Fitzcarrald. Después de más de un siglo, “La Pampa”
significa la consolidación de una red de vías terrestres y centros poblados los cuales son
componentes esenciales del sistema de redes de ciudades mineras del departamento. No
obstante, tanto la pavimentación del principal eje vial mediante la construcción de la carretera
Interoceánica Sur en el marco de los cinco tramos del Corredor Vial Interoceánico Sur (IIRSASur)
como la expansión de la minería hacia las zonas de conservación (Reserva Nacional de
Tambopata y Reserva Comunal de Amarakaeri) desencadenó en la configuración de una red
urbana en constante dinamismo. A partir de este momento, esta carretera provocó cambios
económicos, tecnológicos y estructurales sostenedores del proceso de urbanización vinculado
a la economía del oro.
El propósito de esta tesis es visibilizar el origen de “La Pampa”. Para ello es necesario
comprender el proceso de consolidación del frente extractivo minero a causa del predominio
de la red vial y el crecimiento urbano y demográfico de los principales centros poblados
surgidos en la década del 80’. La interacción de estos elementos con las dinámicas mundiales
de la economía del oro (precio internacional) determinó la formación de dos subsistemas
urbano (1) Puerto Maldonado-Laberinto y 2) Mazuko-Huepetuhe) y este gran campamento
ilegal (“La Pampa”)Both geography and history have enabled an approach to research on the memory of the
shaping process of the mining activity space in the Madre de Dios region. The territorial
analysis of this region of the Amazon has demonstrated the evolution of the center-periphery
model as a result of the transformation of this territorial margin and border due to the advance
of territorial dynamics at multiple scales. The multiscarality of these dynamics has influenced
the development of new unequal flow and power relations over this periphery by modifying
the degree of domination.
Nowadays, mining activity has become a social and environmental contextual problem;
however, the consolidation of gold economy in the region represents the territorial roots
towards extractive activities that took place since the beginning of the western occupation as
the rubber exploitation led by Carlos Fermin Fitzcarrald. He facilitated river connections with
the main rubber-producing cities (Iquitos and Manaos) by implementing a river bridge called
“istmo de Fitzcarrald”. Over a century later, "La Pampa" represents a land networks and towns
which are essential components of a system of networked mining cities in the region. However,
both the paving of the main road axis through the construction of the South Interoceanic
Highway in five sections of the South Interoceanic Road Corridor (IIRSA-South) and the
expansion of mining within the conservation areas (Tambopata National Reserve and
Amarakaeri Communal Reserve) triggered the conformation of a constantly dynamic urban
network. From that moment on, the highway caused economic, technological and structural
changes that support the urbanization process linked to the gold economy.
The purpose of this thesis is to make the origin of "La Pampa" visible. For this, it is necessary
to understand the mining extractive activity consolidation process caused by the predominance
of the road network and the urban and demographic growth of the main towns that appeared
in the 80's. The interaction of these elements with the global dynamics of gold economy
(international price) determined the formation of two urban subsystems (1) “Puerto
Maldonado-Laberinto” and (2) “Mazuko-Huepetuhe” and the large illegal camp called “La
Pampa
Niedrig-sinternde Kondensatorwerkstoffe auf der Basis von Bariumtitanat
The main objective of this work was the development of new barium titanate capacitor materials, which fully densified at a sintering temperature of 900 °C, exhibiting a high and almost temperature-independent dielectric constant as well as low dielectric loss. In order to decrease the sintering temperature of barium titanate from ca. 1300 °C to 900 °C, addition of various types of sintering aids have been tested. Li-containing sintering additives show the best result concerning densification and dielectric properties. By addition of 2 to 3 wt% (SrO-B2O3-Li2O) -, (ZnO-B2O3-Li2O) - or (LiF-SrCO3)-additive combinations to commercially available barium titanate powder 95 % of the theoretical density was achieved after sintering at 900 °C. The sintered capacitor materials with the above mentioned additive combinations possess high dielectric constants from 1800 to 3590. It is well known that for a high temperature stability of dielectric constant the formation of core-shell structure in a fine-grained microstructure is required (average grain size < 1 micron). For BaTiO3 sample contained 2 wt% LiF-SrCO3 is temperature coefficient of capacitance (TCC) relatively low. The TCC in temperature range between 0 °C and 80 °C is less than ± 15%. The significantly higher TCC for the BaTiO3 sample contained 3 wt% SrO-B2O3-Li2O is due to the strong grain growth during sintering. To reduce the TCC in this sample Nb2O5-Co2O3 was added. By addition of 1.5 wt% Nb2O5-Co2O3 the temperature stability of the dielectric constant could be significantly improved as a result of the grain growth inhibition during sintering. For BaTiO3 sample contained ZnO-B2O3-Li2O a fine-grained microstructure was formed which caused the relatively low TCC of this sample. However, the influence of Nb2O5-Co2O3-addition on dielectric properties of ZnO-B2O3-Li2O containing BaTiO3 sample was also investigated. The BaTiO3 sample contained ZnO-B2O3-Li2O-Nb2O5-Co2O3 shows a high dielectric constant up to 2370. The Co2O3-Nb2O5-addition would not cause further lowering of TCC because of a strong grain growth during sintering. To reduce the TCC, the grain growth during sintering must be controlled. For this goal the composition of ZnO-B2O3-Li2O was modified. It was found that an increase of B2O3 content or a decrease of Li2O and ZnO content in ZnO-B2O3-Li2O additive composition improves the temperature stability of the dielectric constant. The BaTiO3 ceramics contained modified ZnO-Li2O-B2O3 composition and 1.5 wt% Nb2O5-Co2O3 showed TCC of less than ± 15 % over the measured temperature range from - 40 °C to +125 °C. However, the room temperature dielectric constant also reduced and amounted to 1280. The formation of the core-shell structure in a fine-grained microstructure has been proved in TEM/SEM studies of this sample and it is responsible for the high temperature stability of the dielectric constant. The further objective of this work was manufacturing of ceramic tapes from the new capacitor materials and integration of these tapes into multi component LTCC moduls, i.e. a combination with ferritic tapes and standard low dielectric constant tapes (Basis LTCC). Tapes and laminates from five favoured capacitor materials have been produced. The sintered laminates show significantly higher dielectric constant (up to 3350) and lower dielectric loss (less than 0,025) in comparison to pressed samples. This is because of lower porosity of the laminates after sintering. The results of the temperature stability of the dielectric constant in powder compacts could be reproduced in multilayer capacitors. Due to very low capacity changes in the frequency range between 1 kHz and 1 MHz all five capacitor materials are applicable at this frequency range. Furthermore the capacitor tapes exhibit high breakdown strength significantly above 20 kV / mm (except one sample). To reach a defect free co-firing of sandwiched LTCC laminates consisting of capacitor tapes and standard low dielectric constant tapes the shrinkage behaviour and the coefficient of thermal expansion of two components were matched. The embedded capacitor tapes into standard low dielectric constant tapes can be sufficiently densified during co-firing process at 900 °C and the dielectric properties are comparable with those of separate sintered capacitor tapes. The co-firing of multi component LTCC laminates consisting of ferritic tapes, low dielectric constant tapes and capacitor tapes with different shrinkage curves was also investigated. It was found that the Manufacturing of such a multi-component module is only possible when a uniaxial pressure (1.25 MPa) is carried out during co-firing. However, because of the difference in the coefficient of thermal expansion of different components, a quite defect free multi-component module could not be manufactured but by stacking the tapes in the correct order defects like cracks can be strongly minimized. For this purpose the capacitor tapes that have larger coefficient of thermal expansion must be inserted in the middle of the multi component laminates. The results obtained in this work are very useful for the integration of passive components into compacted LTCC module and the further miniaturization of electronic devices based on ceramic multilayer. The new low fired high dielectric constant materials can be used both as ceramic tapes, as well as screen-printable pastes for integration of capacitors into LTCC modules.Das Hauptziel dieser Arbeit bestand in der Entwicklung neuer Bariumtitanat-Kondensatorwerkstoffe, die bereits bei 900°C dichtsintern, eine hohe Dielektrizitätskonstante mit geringer Temperaturabhängigkeit sowie geringe dielektrische Verluste und eine hohe Durchschlagfestigkeit aufweisen. Um die Sintertemperatur von Bariumtitanatpulver von ca. 1300 °C auf 900 °C herabzusetzen, wurden Additivkombinationen entwickelt. Als besonders geeignet haben sich Li-haltige Sinteradditivkombinationen herausgestellt. Durch Zugabe von 2 bis 3 Ma.-% einer Additivkombination aus (LiF-SrCO3), (SrO-B2O3-Li2O) oder (ZnO-B2O3-Li2O) verdichtet das Bariumtitanat bereits bei Temperaturen von 900 °C auf mehr als 95 % der Reindichte. Die gesinterten Kondensatorwerkstoffe weisen hohe Dielektrizitätskonstanten zwischen 1800 und 3590 auf. Für eine geringe Temperaturabhängigkeit der Dielektrizitätskonstante ist die Bildung von core-shell Strukturen in einem feinkörnigen (mittlere Korngröße ≤ 1 ikron) und homogenen Gefüge erforderlich. Bei der BaTiO3-Probe mit 2 Ma.-% (LiF-SrCO3)-Additivsystem ist die Temperaturabhängigkeit der Dielektrizitätskonstante relativ gering. Die Kapazitätsänderung im Temperaturbereich zwischen 0 °C und +80 °C ist kleiner als ±15 %. Die deutlich größere Temperaturabhängigkeit der Dielektrizitätskonstante bei BaTiO3-Werkstoffen mit (SrO-B2O3-Li2O)-Additiven resultiert aus dem starken Kornwachstums während des Sinterns. Zur Verringerung wurden ergänzend (Nb2O5-Co2O3)-Additive zugesetzt. Durch Zugabe von 1,5 Ma.-% (Nb2O5-Co2O3) konnte die Temperaturstabilität der Dielektrizitätskonstante erheblich verbessert werden, weil das starke Kornwachstum während des Sinterns gehemmt wurde. Die BaTiO3-Werkstoffe mit (ZnO-B2O3-Li2O)-Additiven besitzen ein feinkörniges Gefüge, weswegen die Temperaturabhängigkeit der Dielektrizitätskonstante von vornherein relativ gering ist. Trotzdem wurde auch hier der Einfluss des (Nb2O5-Co2O3)-Zusatzes auf die dielektrischen Eigenschaften untersucht. Die BaTiO3-Probe mit (ZnO-B2O3-Li2O-Nb2O5-Co2O3)-Additiven weist eine hohe Dielektrizitätskonstante von 2370 auf. Der Nb2O5-Co2O3-Zusatz führte allerdings nicht zu weiterer Absenkung der Temperaturabhängigkeit der Dielektrizitätskonstante, da hier während des Sinterns ein starkes Kornwachstum stattfand. Um dieses zu reduzieren, wurden die Masseanteile der ZnO-B2O3-Li2O-Additivkomponente modifiziert. Eine Erhöhung des B2O3-Gehalts bzw. eine Reduzierung des Li2O- und ZnO-Gehalts im ZnO-B2O3-Li2O-Additivsystem verbessert durch das Verhindern eines starken Kornwachstums beim Sintern die Temperaturstabilität der Dielektrizitätskonstante (Kapazitätsänderung von < ±15 % im gemessenen Temperaturbereich zwischen -40 °C und +125 °C), senkt aber gleichzeitig die Dielektrizitätskonstante selbst auf 1280. Auch hier zeigten TEM/REM-Untersuchungen das entstandene homogene und feinkörnige Gefüge mit core-shell Strukturen. Aufbauend auf die neuentwickelten LTCC-kompatiblen Kondensatorwerkstoffe bestand ein weiteres Ziel dieser Arbeit in der Herstellung von keramischen Folien aus den neuen Werkstoffen und der Integration dieser Folien in Multikomponenten-LTCC-Module, d. h. einer Kombination mit ferritischen Folien und Folien mit niedriger Permittivität (Basis-LTCC). Es wurden aus fünf ausgewählten Kondensatorwerkstoffen Folien und Laminate hergestellt. Die gesinterten Laminate weisen aufgrund geringer Porosität wesentlich höhere Dielektrizitätskonstanten von 1220 bis 3350 und geringere dielektrische Verluste von 0,008 bis 0,024 im Vergleich zu den gesinterten Presslingen auf. Das Temperaturverhalten der Dielektrizitätskonstante der über das Foliengießen hergestellten Werkstoffe unterscheidet sich nur sehr geringfügig vom Temperaturverhalten der trockengepressten Proben. Aufgrund sehr geringer Kapazitätsschwankungen im Frequenzbereich zwischen 1 kHz und 1 MHz können alle fünf Kondensatorwerkstoffe in diesem Frequenzbereich eingesetzt werden. Außerdem weisen die Kondensatorfolien (mit einer Ausnahme) hohe Durchschlagfestigkeiten deutlich oberhalb von 20 kV/mm auf. Um ein fehlerfreies Co-firing der niedrig sinternden Kondensatorfolien in Kombination mit LTCC-Basisfolien zu ermöglichen, wurden der thermische Ausdehnungskoeffizient und das Sinterverhalten des Basiswerkstoffs an die Eigenschaften des Kondensatorwerkstoffs angepasst. Kondensatorfolien mit auflaminierten Außenlagen aus den an der BAM entwickelten Basisfolien konnten im Co-firing Prozess ausreichend verdichten und erzielten dielektrische Parameter vergleichbar denen vom separat gesinterten Kondensatorwerkstoff. Es wurde versucht, Multikomponenten-Laminate aus Ferrit-, Basis- und Kondensatorfolie mit unterschiedlichem Schwindungsverhalten herzustellen. Dies gelang jedoch nur unter Ausübung eines uniaxialen Drucks von 1,25 MPa während des Co-firings. Aufgrund unterschiedlicher Ausdehnungskoeffizienten der verschiedenen Komponenten konnte ein völlig fehlerfreies Multikomponenten-Modul nicht hergestellt werden. Anordnung und Größe der Gefügefehler wie Risse werden durch die Anordnung der verschiedenen Folientypen im Laminat bestimmt. Die im Rahmen dieser Arbeit erzielten Ergebnisse sind für die Integration passiver Bauelemente in kompakte LTCC-Module und die weitere Miniaturisierung elektronischer Bauteile auf Multilayerbasis von großem Nutzen. Die neuen niedrig sinternden hochdielektrischen Kondensatormaterialien können sowohl als Folie als auch als siebdruckfähige Pasten zur Integration von Kondensatoren in LTCC-Module verwendet werden
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