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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

Response of 7075 and 7050 aluminium alloys to high temperature pre-precipitation heat treatment

Tehinse, Olayinka 26 August 2014 (has links)
Al-Zn-Mg-Cu (7xxx series) aluminium alloys are widely used for aircraft structures. It is difficult to obtain a combination of optimal strength and stress corrosion cracking (SCC) resistance for these alloys. It appears that SCC resistance of these alloys is related to grain boundary precipitate morphology. One technique to control the grain boundary precipitate morphology is to introduce a controlled cooling procedure referred to as High Temperature Pre-precipitation (HTPP) treatment following the solution heat treatment. There is need for a detailed study of the effect of HTPP on the properties of commercial Al-Zn-Mg-Cu alloys using different intermediate temperatures. In this thesis research, the results of ten HTPP processes applied to 7075 and 7050 commercial 7xxx series alloys are presented in terms of hardness, electrical conductivity, corrosion resistance, TEM analysis of grain boundary precipitate morphology and EDS analysis of solute concentration profile at the grain boundary. Results indicate that subsequent to HTPP processing, the 7050 alloy can be precipitation aged to a higher hardness compared to 7075; this result is associated with the modification of 7050 alloy by zirconium versus chromium in 7075 alloy. HTPP heat treatment achieves better SCC resistance compared to standard T6 temper. However, it does not appear that HTPP can achieve a combination of hardness, electrical conductivity and corrosion resistance superior to standard T6 and T7X tempers. / October 2014
2

OS PASSERIFORMES DA MATA ATLÂNTICA SEGUEM A REGRA DE BERGMANN? / PASSERIFORMES OF THE ATLANTIC FOLLOW BERGMANN RULE?

Silva Neto, Edvaldo Nunes da 31 March 2015 (has links)
Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / The main goal of this research is to test the Bergmann Rule in its levels - order, suborder and parvordem - in contrast with the leading families (Furnariidae, Thamnophilidae, Tyrannidae e Thraupidae) passerines of the Atlantic Forest. I intended to identify whether the pattern of body size distribution in these groups follow this rule. To reach the goal, the Atlantic Forest was divided into 123 squares (110km x110km). So, I calculated the average body size and the passerines richness in each square. Environmental variables employed as predictors were temperature, precipitation and space. The analysis of Linear Regression and, MantelCorrelationwere used. I observed that passerines are positively correlated to temperature and precipitation. On the other hand, latitude is not correlated to Passeri nor to Tyrannidae. I concluded that, in general, all Atlantic Forest passerines follow the Bergmann Rule are in consonance with the Bergmann Rule. In general, researches test/employ the Bergman Rule in more global patterns for passerines. So, we found no previous researches focusing specifically on the Atlantic Forest. In this light, this research is meaningful to this geographic scale, especially because of the uniqueness of this South America ancient ecosystem, the Atlantic Forest. / O objetivo deste estudo foi testar a Regra de Bergmann a nível de ordem, subordem, e principais famílias (Furnariidae, Thamnophilidae, Tyrannidae e Thraupidae) de Passeriformes florestais da Mata Atlântica a fim de identificar se os padrões de distribuição do tamanho corporal nesses grupos seguem essa regra. A Mata Atlântica foi dividida em 123 quadrículas (110km x 110km) e foi calculado o tamanho corporal médio e a riqueza dos Passeriformes em cada quadrícula. As variáveis ambientais utilizadas como preditoras foram a temperatura, a precipitação e o espaço geográfico. Utilizamos as análises de Regressão linear e correlação de Mantel. Desta forma encontramos que os Passeriformes são correlacionados positivamente com a temperatura e a precipitação. A latitude não se correlacionou com Passeri e Tyrannidae.Ao final concluímos que em geral todos os Passeriformes florestais da Mata Atlântica seguem a Regra de Bergmann. Em geral as pesquisas voltadas para a Regra de Bergmann tratam de padrões mais globais para aves. E, maisregionalmente, como na Mata Atlântica, nada foi testado quanto a isto e, assim, este estudo se torna relevante para essa escala geográfica. Ainda mais devido a singularidade da Mata Atlântica, que é um ecossistema antigo na América do Sul.
3

Časová a prostorová variabilita v globálních a regionálních klimatických modelech / Spatiotemporal variability of global and regional climate models

Crhová, Lenka January 2019 (has links)
Title: Spatiotemporal variability of global and regional climate models Author: RNDr. Lenka Crhová Department: Department of Atmospheric Physics Supervisor: RNDr. Eva Holtanová, Ph.D., Department of Atmospheric Physics Abstract: This thesis deals with variability of basic meteorological variables in global and regional climate models (GCMs and RCMs) outputs. Three different approaches were used in order to analyse climate models' ability to represent different aspects of variability of meteorological variables. The temporal variability with focus on its changes during a time and temporal scale components were studied. The relationship between air temperature and precipitation were employed in order to investigate the representation of spatiotemporal variability in climate models. Moreover, the influence of different characteristics of climate model simulations, such as the size of the RCM integration domain or differences between RCM and GCM simulations, were also considered. Two simulations of RCM ALADIN-Climate/CZ with different sizes of integration domain and their driving simulation of GCM ARPÉGE-Climat were used for analysis of the temporal changes in temperature mean and variability and selected simulations of RCMs and GCMs from the EURO-CORDEX and CMIP5 projects were employed for analyses of...
4

Correlation Analysis of Climatic Variables, Migration and Dengue Cases in Southeast Florida

Lugo, Brunilda 01 January 2015 (has links)
Dengue fever is a debilitating, viral, mosquito-borne disease occurring in tropical and subtropical areas in the world. The majority of dengue cases in the United States were acquired in endemic areas by travelers or immigrants. However, in recent years, autochthonous (locally acquired) dengue cases have been diagnosed in Florida. The purpose of this study was to find an association between potential risk factors and the expansion of dengue fever in the United States. Guided by the eco-bio-social framework, which offers a broad assessment of risk factors for the illness, a retrospective design was used with archival data to correlate changes in climatic variables and imported dengue cases with autochthonous dengue cases in Southeast Florida from 1980 to 2013. A Spearman correlation indicated weak correlations between temperature and autochthonous dengue cases (rs = .999, p = 000) and imported dengue cases with autochthonous dengue cases (rs = .162, p = 000). A negative binomial multivariate regression was used to analyze the expansion of dengue to each monthly unit of temperature, rainfall, and imported dengue cases over 34 years. The results indicated that temperature (IRR = 2.198; 95% CI [1.903, 2.538]) and precipitation (IRR = .991; 95% CI [.988, .994]) were predictors for the geographic expansion of dengue fever in Southeast Florida. The positive social changes include the use of the results to develop an understanding of how climatic variables and migration may influence the expansion of dengue fever to nonendemic regions. The results can be used by public health authorities to address risk factors and to formulate evidence-based decisions in regard to prevention and education concerning dengue fever.
5

Correlation Analysis of Climatic Variables, Migration and Dengue Cases in Southeast Florida

Lugo, Brunilda 01 January 2015 (has links)
Dengue fever is a debilitating, viral, mosquito-borne disease occurring in tropical and subtropical areas in the world. The majority of dengue cases in the United States were acquired in endemic areas by travelers or immigrants. However, in recent years, autochthonous (locally acquired) dengue cases have been diagnosed in Florida. The purpose of this study was to find an association between potential risk factors and the expansion of dengue fever in the United States. Guided by the eco-bio-social framework, which offers a broad assessment of risk factors for the illness, a retrospective design was used with archival data to correlate changes in climatic variables and imported dengue cases with autochthonous dengue cases in Southeast Florida from 1980 to 2013. A Spearman correlation indicated weak correlations between temperature and autochthonous dengue cases (rs = .999, p = 000) and imported dengue cases with autochthonous dengue cases (rs = .162, p = 000). A negative binomial multivariate regression was used to analyze the expansion of dengue to each monthly unit of temperature, rainfall, and imported dengue cases over 34 years. The results indicated that temperature (IRR = 2.198; 95% CI [1.903, 2.538]) and precipitation (IRR = .991; 95% CI [.988, .994]) were predictors for the geographic expansion of dengue fever in Southeast Florida. The positive social changes include the use of the results to develop an understanding of how climatic variables and migration may influence the expansion of dengue fever to nonendemic regions. The results can be used by public health authorities to address risk factors and to formulate evidence-based decisions in regard to prevention and education concerning dengue fever.

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