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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.
71

Estudo comparativo da degradação de poliestireno e de poliestireno de alto impacto por envelhecimentos natural e artificial. / Comparative study of natural and artificial weathering of polystyrene and high impact polystyrene.

Daniel Fernandes Borrelly 27 March 2002 (has links)
O estudo do comportamento de materiais em relação a intempérie, esforços, tempo, temperatura é fundamental para a escolha de materiais para uma dada aplicação. O poliestireno é uma resina polimérica muito aplicada no mercado, pois é transparente e relativamente econômica, mas não é indicada para aplicações com muita exposição a radiações luminosas, já que é muito susceptível a intemperismos, não sendo recomendada para aplicações com excessiva exposição. A adição de borracha (copolímero de estireno e butadieno) melhora algumas de suas propriedades, como resistência ao impacto e ductilidade, mas piora outras características, como a resistência à tração. Em relação ao intemperismo, apesar da borracha degradar-se rapidamente, ela protege o poliestireno da radiação ultravioleta. Este estudo visa comparar as conseqüências da degradação por envelhecimento natural com o envelhecimento artificial acelerado do poliestireno e do poliestireno de alto impacto e a determinação da possível correlação entre eles. Foram utilizados equipamentos de envelhecimento artificial, de ensaio de tração, impacto IZOD, índice de fluidez, uma estação de envelhecimento natural e equipamento de análise térmica (DSC). Os resultados obtidos permitiram correlacionar os envelhecimentos natural e artificial em relação às propriedades medidas, sendo que para o poliestireno comum, o envelhecimento artificial acelerou a degradação em cerca de 4 vezes, enquanto que para o poliestireno de alto impacto, o fator de aceleração foi de cerca de 2 vezes. / The study of weathering materials regarding to climate, stresses, time, temperature, is essential to choose the materials for a purpose. Polystyrene is a polymeric resin with much usage in the market as it is transparent and relatively cheap, but it is not indicated for outdoor purposes with much actinic radiation exposure, as it is very sensitive to weathering, tough not recommended to purposes with much exposure. The addition of rubber (styrene-butadiene copolymer) improves some of its properties, like impact resistance and ductility, but decreases other properties, like tensile strength. Regarding the weathering, although the rubber degrades very quickly, it protects the polystyrene from the ultraviolet radiation. This study aims to compare the consequences of the degradation by natural weathering and accelerated artificial weathering and try to correlate their results. Equipments for artificial weathering, tensile strength, IZOD impact, melt flow, a natural weathering station and DSC thermal analysis equipment were used. The results allowed the correlation between the natural and artificial weathering regarding the measured properties, as for the common polystyrene the artificial weathering accelerated the degradation in approximately 4 times, while for the high impact polystyrene the acceleration factor resulted in approximately 2 times.
72

Geoquímica e proveniência do Grupo Bauru no Oeste de Minas Gerais / Geochemistry and provenance of Bauru Group on West Minas Gerais State

Mattos, Nathália Helena Secol, 1988- 08 August 2014 (has links)
Orientador: Alessandro Batezelli / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Geociências / Made available in DSpace on 2018-08-25T21:40:30Z (GMT). No. of bitstreams: 1 Mattos_NathaliaHelenaSecol_M.pdf: 5195246 bytes, checksum: 2551186b0e4a53abcac203b4227922a3 (MD5) Previous issue date: 2014 / Resumo: Estudos geoquímicos e mineralógicos de arenitos e argilitos da Bacia Bauru (Cretáceo Superior), localizada na região do Triângulo Mineiro (Minas Gerais) foram realizados visando à determinação da proveniência, tectônica da rocha fonte, o papel de processos como intemperismo e reciclagem sedimentar na assinatura geoquímica da rocha fonte e à proposição de um modelo de evolução paleoambiental para a área de estudo. As amostras tem sua mineralogia principal composta por quartzo, microclínio, calcita, albita, dolomita e hematita. Illita, montmorillonita e paligorsquita são os argilominerais identificados. Elementos maiores, traços e terras raras e as razões elementares entre eles foram utilizadas para determinar a composição da rocha fonte. Valores do Índice Químico de Alteração e do Índice de Intemperismo Químico variando de 64 a 92 e de 84 a 98, respectivamente, e a ocorrência de feldspatos nas rochas sedimentares indicam intemperismo químico moderado na área fonte. Gráficos de elementos maiores e traços e valores para razões como La/Sc (1,47-4,86), (La/Yb)c (3,86-20,44) e a anomalia de Eu (Eu/Eu* = 0,62-0,92) comparados com dados da literatura sugerem que os sedimentos da Bacia Bauru na área de estudo tenham sido originados de rochas de composição quartzítica a granítico-gnáissica, derivadas de áreas continentais estáveis e depositados em ambientes de bacias intracratônica. A possível área-fonte para as rochas estudadas localiza-se a NE da Bacia Bauru, consistindo em rochas graníticas e metassedimentares do embasamento pré-cambriano. A deposição sedimentar na Bacia Bauru reflete a interação de processos aluviais e lacustres / Abstract: Geochemical and mineralogical studies of sandstones and mudstones from the Late Cretaceous Bauru Basin of Triângulo Mineiro region (Minas Gerais State) were undertaken to determine the provenance, tectonic setting, the role of weathering, sorting and recycling on the source rock geochemical signature and to propose a palaeoenvironmental evolution model to the study area. The analysed samples are mainly composed by quartz, microcline, calcite, albite, dolomite and hematite. Illite, montmorillonite and palygorskite are the identified clay minerals. Major elements were used to determine the source rock composition, as well as trace and rare earth elements and the ratios among them. Chemical Index of Alteration and Chemical Index of Weathering ranging from 64.83 to 92.3 and from 84 to 98.2, respectively, along with the feldspar occurrence on sedimentary rocks indicate a moderate weathering in the source area. Plots of major and trace elements and values for the ratios such as La/Sc (1.47-4.86), (La/Yb)c (3.86-20.44) and the Eu anomaly (Eu/Eu*= 0.62-0.92), compared to data from the literature indicate source rock was located into a continental passive margin tectonic setting and sediments were derived from quartzitic to granitic-gneissic rocks of stable continental areas and deposited in an intracratonic basin. Probable source area to the studied rocks is located at NE of Bauru Basin and consists in granitic and metassedimentary rocks from the Precambrian basement. Sedimentary deposition in Bauru Basin reflects an interaction of alluvial and processes / Mestrado / Geologia e Recursos Naturais / Mestra em Geociências
73

Geochemistry in the Critical Zone: limestone-shale and kimberlite weathering in the Flint Hills, Kansas, USA

Gura, Colleen Marie January 1900 (has links)
Master of Science / Department of Geology / Saugata Datta / Pamela Kempton / The Critical Zone is the realm where rocks meet life. This study examines the physicochemical interactions that occur when interbedded limestone-shale systems and kimberlitic rocks weather to form soils. Fast weathering processes with extensive soil loss have been a major environmental concern in the Flint Hills for decades. Knowledge of soil formation processes, rates of formation and subsequent loss, and understanding how these processes differ in different systems are critical for managing soil as a resource. Kimberlites are CO₂-rich igneous rocks that are high in Mg and Fe; they are compositionally distinct from the Paleozoic limestones and shales found throughout the rest of the region. This study will compare the geochemistry and mineralogy of the Stockdale Kimberlite in Riley county to that of interbedded limestone-shale system typical of the Flint Hills as sampled from Konza Prairie LTER. Bulk composition and mineralogy of the soils overlying these different bedrock types have been analyzed using X-Ray Fluorescence (XRF), X-Ray Diffraction (XRD), bulk elemental extractions, and particle size analyses. Results show that the kimberlitic soils have higher concentrations of Fe, Mg, Ca, K and some trace elements in greater proportions (e.g. Ti, Ni, Cu). The weathering products differ mineralogically as well, e.g. lizardite is abundant in kimberlitic soils and absent from the limestone terranes. Kimberlite derived soils also contain minerals as well such as kleberite (an alteration product of illminite), phlogopite, and magnetite. Kimberlite-sourced soils have different physical properties than the thin limestone-sourced soils surrounding them. Particle size analysis shows that the limestone-shale soils have different proportions of the clay size fraction in different core locations (~47% in highlands, ~51% at watershed base, ~41% in lowlands) whereas kimberlitic soils have a larger sand fraction than Konza (~19% vs. 10%). Clay minerals from the limestone-shale system reveals clay micas, kaolinite, and some expandable 2:1 layer silicates. Clay minerals from kimberlite-sourced soils are identified as primarily smectites with clay micas and kaolinites. Similarities between the kimberlite and limestone-shale soils are primarily seen in the shallower portions of the soil profile, suggesting that loess/wind-blown dust make a significant contribution to the soils in both areas. It could be concluded that kimberlite-sourced and limestone-shale-sourced soils produce weathering products that differ both chemically and mineralogically and could potentially have agricultural significance in terms of water retention as well as ionic and nutrient mobilities in these soils.
74

Surface preparation and the effects on rock art deterioration

Venter, Gerda 05 July 2011 (has links)
The Drakensberg is the highest part of a 1000-km long escarpment that also forms a natural border between South Africa and eastern Lesotho. The uKhahlamba-Drakensberg Park was declared a World Heritage site in 2000 and is globally significant, in particular due to the rock art painted by San hunter-gatherers who inhabited the area from about 8 000 years ago until the late 19th Century. Approximately 30 000 painted images can be found in nearly 600 rock shelters in the area. Rock art heritage in the Drakensberg is unfortunately being lost through a variety of processes, some natural and others resulting from human impacts. Previous research on the weathering of San paintings has focused largely on either monitoring processes causing weathering in rock shelters or investigating rock surfaces that are adjacent to the rock paintings. Recent findings indicate that some of the San art has been painted onto surfaces that were prepared by smoothing the rock surface with a “grinding stone” and coated with a clay (“ground”) layer prior to the application of pigments. This new information may have important implications for rock art conservation as smoothing of a rock surface could significantly modify the physical and chemical characteristics of the surface, thereby influencing the deterioration of the art. In this study two classification systems are developed from data collected in four rock shelters situated in the Park. The first, a Type of Surface Classification System, is developed for the purpose of identifying different types of rock surfaces within rock shelters. The second, a State of Deterioration Classification System, is developed with the purpose of establishing, through visual inspection, how deteriorated the rock art on different types of rock surfaces is. Linkages between the type of surface and the state of deterioration are also explored. Findings show that it is not only possible to determine which surface type a painting has been painted on, but that different rock surface types can deteriorate through different weathering mechanisms and to a different degree. One type of rock surface, acknowledged but not yet recorded, was found amongst the rock art paintings selected for the purpose of this study. More importantly, the alteration of rock surfaces through human action in the past is found to cause rock surfaces to deteriorate either at an accelerated or a retarded rate as opposed to rock paintings that were made on surfaces that have only been altered by natural weathering mechanisms. For example, if a rock surface has only been smoothed with a grinding stone, results show that weathering mechanisms did not deteriorate the surface as quickly as in the case where a clay ground layer has been applied to the rock surface. Different types of rock surfaces deteriorating through different weathering mechanisms (as a result of surface preparation) might have significant implications in terms of rock art conservation as the strategies implemented to conserve rock art should be adapted to consider surface type. In terms of rock art studies aiming to conserve this precious heritage, the two classification systems presented could, therefore, be useful non-destructive tools in assessing rock art deterioration. Copyright / Dissertation (MA)--University of Pretoria, 2011. / Geography, Geoinformatics and Meteorology / MA / Unrestricted
75

Fragmented Cities and the Potential of Fallow Spaces: Finding Connectivity Through Architecture

Kryspin, Kelsey M. 15 July 2021 (has links)
No description available.
76

White-Black Disparity in Maternal Mortality and Morbidity: An Exploration of Risk Factors

Gilbert, Ann, Harmeyer, Dr. Erin 04 April 2020 (has links)
Black expectant mothers are more likely to die from pregnancy-related complications than white expectant mothers. While researchers have long documented this disparity, the gap persists. The purpose of this literature review is to describe the white-black disparity in maternal mortality and morbidity, identify racism and discrimination across multiple ecological systems as a primary driver of this disparity, and suggest implications of this for social work practice. This review presents basic statistics and means of data collection regarding this disparity, acknowledges known risk factors for pregnancy-related deaths, and identifies the association between racism and discrimination in healthcare settings and this white-black disparity. A bioecological framework will be used to further analyze the implications of racism on multiple ecological systems. The conclusion presents existing interventions and provides recommendations for social workers regarding this healthcare disparity.
77

An Anchoring Urban Cemetery, Memphis, Tennessee

Ricks, Lauren Mackenzie 23 June 2011 (has links)
This thesis proposes an urban infill cemetery in Memphis, Tennessee. By infilling seven blocks within the arts district of downtown Memphis with a new urban cemetery, further significance is given to both the city and the cemetery. Because it would be a newly built cemetery, it could initially function as an urban park and become a cemetery over time as the space is needed to remember the dead. The same elements of the cemetery would compose the park, but by allowing a slow transformation from park to cemetery, the resulting public space will carry much more meaning than either space could do alone. The cemetery connects the continuing evolution of the city with the lives of its citizens. Each block is different yet linked and intertwined, just like Memphis residents. The blocks are multi-use and as such, share the history and legacy of those who have died with those who live in and visit the city. / Master of Architecture
78

The Silver Fraction - A Weathered Inebriation: Plans, Elevations, Sections, Details, Models and Texts for a Brewery and a Biergarten on the bank of the Potomac River, Alexandria, Virginia

Zellweger, Jon Robert 15 April 2004 (has links)
Architecture is an exhaustive act. With the Herculean efforts of the patron, the architect and the builder, a building comes into being. Materials are collected and transformed in order to create a place for Man to dwell. That is, materials occurring in their natural state are transformed by the Hand of Man and thereby enter it His realm. In turn, the Manmade becomes situated in and a part of the natural world. This relationship is a Material Reciprocity. In the Timaeus, a concept of a world soul is outlined in which all elements that compose the physical world (the "ten-thousand things" of the Tao-Te Ching) are endowed with consciousness: the Anima Mundi. How does architecture become part of Place? What role does Weathering play in this act? How does Man's understanding of Weathering's accretions enoble architecture? Sun Moon Earth BREW / Master of Architecture
79

Magazine Hill : a weathered continuum

Gouws, Cliff 30 November 2011 (has links)
NDLTD Innovative ETD Award 2012. This dissertation is rooted within a process of unification, a personal struggle to understand the fragile relationship that exists between architecture and time. The project focuses on architecture’s potential to adapt according to the passage of time, through the process of aging and weathering. This study is founded in the aim to re-establish a connection between the continuum of time and architecture. The project places contemporary commemorative architecture under the limelight, criticising the static notion of heritage commemoration through the typologies of museums and memorials. These typologies often evolve into static monuments, where the relevance to contemporary society can be questioned. The architectural response of this dissertation is thus focused on commemoration through everyday use. The proposed historical site (Magazine Hill) forms a comprehensive construct of different layers of time and influence. This mysterious, abandoned and isolated site consists of two ammunition magazines, five bomb shelters and ammunition factories, all structures that represent an era of unrest in South Africa. In 1945 a mysterious explosion of the Central Magazine scarred the face of Magazine Hill, leading the activities on the site to an early death, trapping architecture in time and abandonment. The proposed programme forms part of the conceptual premise of mediation, unifying different opposites inherent in both Magazine Hill and the South African context. A brass foundry is proposed to recycle the spent ammunition shells of the South African National Defence Force (SANDF), thereby introducing brass artists as a public interface to Magazine Hill. Where ammunition was once produced, ammunition is now reduced. This programme could form mediation between the public and the military; exposing different layers of the past by reinstating a connection between architecture and time. View Clifford Gouw's video on <a href="http://www.youtube.com/watch?v=MVnn-sDfR_U ">YouTube</a>. Copyright 2011, University of Pretoria. All rights reserved. The copyright in this work vests in the University of Pretoria. No part of this work may be reproduced or transmitted in any form or by any means, without the prior written permission of the University of Pretoria. Please cite as follows: Gouws, C 2011, Magazine Hill : a weathered continuum, MArch(Prof) dissertation, University of Pretoria, Pretoria, viewed yymmdd < http://upetd.up.ac.za/thesis/available/etd-11302011-195515 / > C12/4/86/gm / Dissertation (MArch(Prof))--University of Pretoria, 2011. / Architecture / unrestricted
80

Weathering of wood surfaces: characteristics, mechanisms, and prevention

Chang, Shang-Tzen January 1982 (has links)
Photodegradation of southern yellow pine, its mechanisms and means of prevention were studied. Changes in brightness and color were recognized when wood was exposed outdoors or to ultraviolet light. Scanning electron micrographs showed that most of the cell walls on irradiated transverse surface were separated at the middle lamella region. Half-bordered pits and bordered pits on irradiated longitudinal surf aces were found to be readily destroyed by ultraviolet light. It was also noted that progressively granular surfaces formed on the cell walls of latewood in response to irradiation with ultraviolet light. Spectrophotometric studies on the chemical changes of exposed wood, lignin, and cellulose revealed that photochemical reactions primarily took place in lignin, leading to the generation of carbonyl- and carboxylic-containing degradation products of low molecular weight. Formation of hydroperoxides, one of the mechanisms attributed to the photodegradation of wood, was illustrated from iodometry UV absorption studies. The hydroperoxide concentration at the wood surface increased when wood was irradiated in the presence of singlet oxygen generators. The hydroperoxide concentration decreased when wood was irradiated in the presence of singlet oxygen quenchers. These findings imply the participation of singlet oxygen and the formation of hydroperoxides at the photo-irradiated wood surfaces. It was found that the photodegradative effects on wood surfaces were mitigated by treating wood surfaces with aqueous solutions of chromic acid or ferric chloride, by treating with penetrating chemical agents such as trial, glycol and 1-octadecanol, or by coating with clear polymeric ultraviolet stabilizers such as homo- and copolymer of 2-hydroxy-4(3-methacryloxy-2-hydroxypropoxy)benzophenone. Experimental results showed that the polymeric ultraviolet stabilizers provided the best protection of the treatments tried, and were themselves stable and resistant to photodegradation. Possible chemistry and mechanisms of protection provided by organic and inorganic chemical agents are discussed. / Ph. D.

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