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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.
291

Experiments and analyses for flow through partially solidified alloys.

Ganesan, Sankaranarayanan January 1990 (has links)
The equation for the conservation of momentum in the mushy zone during solidification is derived using the volume averaging technique. The conditions under which the momentum equation reduces to Darcy's law are elucidated. Permeabilities for flow of interdendritic liquid in Al-Cu alloys with equiaxial structures are measured using a simple, cost-effective permeameter. Center-to-center distance between grains (180 μm to 450 μm), specific surface (3.21 x 10⁻² μm⁻¹ to 3.095 x 10⁻¹ μm⁻¹), and volume fraction liquid (0.166 to 0.434) are the structural parameters studied in this investigation. Permeability in Al-Cu alloys with equiaxial grains is structure sensitive. For example, permeabilities for globular structures (nondendritic) are approximately one order of magnitude greater than permeabilities for the dendritic-globular structures, when the volume fraction liquid is approximately 0.3. To better understand the dependence of permeability on structure morphology, structure evolution during the permeability testing was studied in isothermal coarsening experiments. Dimensionless permeabilities based on specific surface, and center-to-center distance between grains are presented along with the theoretical results for flow through different arrays (simple cubic, body-centered cubic and face-centered cubic) of uniform spheres. With dimensionless permeability defined as KSᵥ², where Sᵥ is the specific surface of the solid, the empirical data compare reasonably well with theoretical curves for flow through arrays of uniform spheres. Numerical experiments are performed to obtain permeabilities for flow parallel to primary dendrites in columnar structures with high volume-fraction liquid where physical experiments may fail. The results of numerical experiments are presented along with the analytical results for flow parallel to cylinders arranged in square and triangular packing, analytical results for flow through periodically constricted tubes and the available empirical data. The results indicate that there is a transition in the behavior of permeability in the neighborhood of volume fraction liquid equal to 0.65.
292

Magnesium alloy strip produced by a melt-conditioned twin roll casting process

Bayandorian, Iman January 2010 (has links)
Twin roll casting (TRC) offers a promising route for the economic production of Mg sheet, but unfortunately, it produces strip with coarse and non-uniform microstructures and severe centre line segregation. Recently, a novel magnesium strip casting process termed melt conditioned twin roll casting (MC-TRC) was developed that, compared with the conventional TRC process, emphasizes solidification control at the casting stage rather than hot rolling. This was achieved by melt conditioning under intensive forced convection prior to twin roll casting resulting in enhanced heterogeneous nucleation followed by equiaxed growth. In this study the development of TRC and MC-TRC processes and a microstructural comparison of the MC-TRC Mg-alloy strip with that of conventional TRC strip, have been investigated. Emphasis has been focused on the solidification behaviour of the intensively sheared liquid metal, and on the mechanisms for microstructural refinement and compositional uniformity in the MCTRC process. The results of the process development indicate that the MC-TRC process reduces considerably or eliminates defects such as the centre line segregation, voids and cracks at or near the strip surface that are always present in conventional TRC strip. The newly-designed homogenization treatment investigated for TRC and MC-TRC magnesium alloy strips was based on microstructural evolution obtained during heat treatment. The results of the MC-TRC strips showed a much faster recrystallization rate with finer recrystallized grains, which are due to more homogeneous and a finer grain size of the as-cast MC-TRC strips compared with the as-cast TRC strips. During down-stream processing, the effects of MC-TRC process on microstructural evolution of hot-rolled magnesium strips have been understood thoroughly by accurate control of the hot-rolling procedure during each step of strip thickness reduction. This study indicates that the MC-TRC strip requires fewer rolling steps when compared to TRC strip, thus offering reduced processing cost and carbon footprint. Mechanical properties at room temperature of MC-TRC as-cast and rolled sheets are much improved when compared with the conventional TRC as-cast and rolled sheets which can result in a higher quality of final components. The mechanical properties at elevated temperature shows for the first time that the higher elongation and lower yield strength of MC-TRC as-cast strips at a temperature close to its optimised hot-rolling temperature results in better ability for rolling and higher ductility of MC-TRC Mg strip compared with the TRC Mg strip.
293

Vem slår på djungeltrumman? : En studie om vilka som syns i public service-mediers artiklar om Järvaområdet

Tanha, Sophie January 2017 (has links)
Vilka syns i public services artiklar om en av Sveriges mest (ö)kända förorter? Hur skildras de, och har detta något att göra med hur invandrare behandlats utifrån ett postkolonialt perspektiv? Genom att göra en kvantitativ innehållsanalys och sedan en framinganalys på sju utvalda artiklar från de första 15 veckorna år 2017 ska denna studie ta reda på vem som får uttala sig om det omdiskuterade Järvaområdet. Resultatet av innehållsanalysen blev tre diagram som visar hur vita myndighetsmän och politiker dominerar i samtalen kring Järva.   Textanalysen visar att rättsväsendet ofta målas upp som en viktig del för att åtgärda problemen i området. Artiklarna nämner problem i områden generellt, men utan en närmare definition för vilka problem som syftas på eller vilka som drabbas utav dem. Lösningen enligt framingmetodens uppdelning av artikeln är alltid fler poliser eller bättre resurser för rättsväsendet. Även om ord som kan ge läsaren postkoloniala kopplingar inte används av artikelns skribent i brödtexten kan de förekomma i citat som skribenten valt att lyfta fram. Eftersom framingteorin menar att artikeln målar upp en ram för mottagaren att ta del av innebär även ordval som citeras från någon annan som en stor del av hur mottagaren uppfattar artikeln.   Slutsatsen är därför att SVT och SR som redaktioner inte medvetet tycks reproducera postkoloniala bilder av förorten, men att detta ändå blir effekten av en ojämn representation där vita män får tala för den socioekonomiskt svaga invandraren som något som ska lösas eller åtgärdas. Effekten av detta kan bli att läsaren ser på dessa personer som problem i samhället, vilket kan öka stigmatiseringen kring förorter som de i Järvaområdet.
294

Högskolans effekt på gymnasieelevers studieresultat : En kvantitativ undersökning om en högskolas effekt på gymnasieelevers betyg i olika socioekonomiska områdestyper

Hachem, Maéva January 2017 (has links)
A university has been shown to have a positive effect on society and has led to greater awareness of the social problems found in our towns today and a willingness to openly discuss and resolve them. Universities have a social and civic role that improves the social living conditions in the areas surrounding them. A university also improves the local economy by creating jobs and attracting new businesses which in turn lead to an improved infrastructure and a subsequent decrease in residence segregation. Residential segregation is a growing phenomenon in Sweden where students living in disadvantaged areas are less likely to succeed in school than students living in more advantaged areas, as is often shown by their school results. The purpose of this study is to analyze a university’s effects on high school student’s grades in different socioeconomic living areas in Sweden. Is there a correlation between the student’s grades in these areas and the presence of a university in the region? To analyze these effects, a multilevel regression model in two scales has been used. his thesis shows that a direct correlation exists between high school students’ grades and the presence of a university in the region. A university has a strong improving effect on the grades of students from highly resourceful areas. The study further illustrates that although a new university will lead to an improvement of the general standard of education of a region, the introduction of more universities does not result in an increase in the number of people with a university education.
295

”En av grunderna i demokrati är alla människors lika värde, det spelar ingen roll var vi kommer ifrån” : En kvalitativ studie om islamundervisningen med fokus på ”vi” och ”dem”, ur ett lärarperspektiv.

Liridona, Xhemaili, Mavraj, Floriana January 2016 (has links)
I denna studie undersöker vi utifrån ett lärarperspektiv islamundervisningen på tre kommunala grundskolor, i en mångkulturell stad, Landskrona. Studiens fokus ligger vid att undersöka om ett ”vi” och ”dem” tänkande präglas i undervisningen om islam. Den utvalda metoden är semistrukturerade intervjuer med sex grundskolelärare, vilka är verksamma på tre olika skolor. Eftersom att media idag är en viktig informationskälla, som bidrar till att forma uppfattningar har studien även behandlat hur media tillämpas i islamundervisningen. Efter de genomförda intervjuerna har lärarna indikerat att media framförallt är den källa som kan ge en kontroversiell bild av islam. Vidare framkom det i studien att samtliga intervjuade lärare på ett varierande sätt upplevt en ”vi” och ”dem” känsla i såväl skolan som islamundervisningen. De intervjuade religionslärarna hävdar dessutom att religionen har en väsentlig roll i skapandet av ”vi” och ”dem”. Detta eftersom religionen förknippas med ens identitet, enligt de intervjuade lärarna.
296

Contexts Matter: The Relationship Between School Wide Student Demographics and Graduation Rates

Riddle, Philip 22 April 2013 (has links)
Nearly 60 years after the Supreme Court Decision in Brown, segregation is still an ingrained facet of American public education. This study investigated the extent to which these continued patterns of segregation influenced graduation rates from high school. The study used data provided by the Virginia Department of Education (VDOE) on the 2011 graduating cohorts in 302 public high schools across the state. The results indicate that graduation rates for all students vary significantly as a function of the overall socioeconomic and racial composition of high schools. In addition, low-income students are significantly more likely to graduate in low-poverty high schools and minorities are significantly more likely to graduate in high schools that are not highly segregated by race. Finally, school level demographic variables explain a significant, independent share of the variance in graduation rates among high schools. These results lend weight to policies designed to integrate high schools as a way to equalize educational opportunity.
297

Occupational gender segregation across functional fields

Nilsen, Nadia 22 May 2009 (has links)
The purpose of this study is to investigate the nature and degree of occupational gender segregation across the functional fields in South Africa and to determine if existing “supply-side” explanations serve to explain the phenomenon through an attitudinal survey of the females in the sample. The UNISA first year MBL students were requested to complete the survey during their August Centre Visit at the SBL Sasol auditorium in Midrand. The survey consists of two sections. Section A determined the gender of the sample element and subsequently their functional field of occupation, which enabled the calculation of the Karmel and MacLachlan Index per functional field. The Finance, General Management, Information Technology, Operations and Production and Procurement, Buying and Logistics fields showed high levels of integration, while the Marketing, Sales and Customer Service field showed low levels of segregation in favour of women. Human Resources was strongly female dominant, while Research and Development was strongly male dominant. The “Other” field showed the highest level of segregation in favour of women. Section B contains the attitudinal Likert scale questions to measure the extent to which the various supply-side explanations determine the women’s career decisions. There seem to be certain explanation types, such as Exchange Utility and Reward, which serve as strong selection criteria and other factors that play a lesser role, such as Teaching Styles and Self-Image. Based on the averages the Occupational Sex-Typing, Self-Efficacy and Parental Influence explanations showed no agreement from any of the sample elements. / Graduate School of Business Leadership / MBL
298

Accessing Health: Examining Racial and Geographic Disparities in Diabetes Prevalence as a Result of the Built Environment

Powell, Amanda 10 May 2017 (has links)
Diabetes is a leading cause of premature death and disability in the United States and vulnerable populations may be at increased risk. Racial residential segregation, population density, and other factors influence the built environment, which in turn affects access to health-related facilities. Using the theory of fundamental causes, this study aims to determine whether neighborhood-level sociodemographic factors, the built environment, and subsequent access to health-related facilities are associated with diabetes prevalence in Georgia’s population. A built environment assessment of all health facilities located in the state of Georgia was conducted using health data from the 2014 Behavioral Risk Factor Surveillance System and demographic data from the 2010 US Census. Geospatial techniques, including hot-spot analyses and the two-step floating catchment area method were used to determine the effect of racial concentration, socioeconomic status, and population density on access to health-related facilities and thus on diabetes prevalence. Linear and spatial regression analyses were conducted to determine the significance of the association between access to facilities and diabetes prevalence. The results of the geospatial and regression analyses show that socioeconomic factors significantly affect the built environment, which in turn significantly influence diabetes prevalence. This interdisciplinary study contributes to the literature by providing a comprehensive analysis of the relationship between sociodemographic factors, the built environment, and diabetes prevalence in a southeastern state. Keywords: Diabetes, Disparities, Access, Racial Segregation, Urban/Rural, Built Environment Diabetes is a leading cause of premature death and disability in the United States and vulnerable populations may be at increased risk. Racial residential segregation, population density, and other factors influence the built environment, which in turn affects access to health-related facilities. Using the theory of fundamental causes, this study aims to determine whether neighborhood-level sociodemographic factors, the built environment, and subsequent access to health-related facilities are associated with diabetes prevalence in Georgia’s population. A built environment assessment of all health facilities located in the state of Georgia was conducted using health data from the 2014 Behavioral Risk Factor Surveillance System and demographic data from the 2010 US Census. Geospatial techniques, including hot-spot analyses and the two-step floating catchment area method were used to determine the effect of racial concentration, socioeconomic status, and population density on access to health-related facilities and thus on diabetes prevalence. Linear and spatial regression analyses were conducted to determine the significance of the association between access to facilities and diabetes prevalence. The results of the geospatial and regression analyses show that socioeconomic factors significantly affect the built environment, which in turn significantly influence diabetes prevalence. This interdisciplinary study contributes to the literature by providing a comprehensive analysis of the relationship between sociodemographic factors, the built environment, and diabetes prevalence in a southeastern state.
299

A behavioral task sets an upper bound on the time required to access object memories before object segregation

Sanguinetti, Joseph L., Peterson, Mary A. 22 December 2016 (has links)
Traditional theories of vision assume that object segregation occurs before access to object memories. Yet, behavioral evidence shows that familiar configuration is a prior for segregation, and electrophysiological experiments demonstrate these memories are accessed rapidly. A behavioral index of the speed of access is lacking, however. Here we asked how quickly behavior is influenced by object memories that are accessed in the course of object segregation. We investigated whether access to object memories on the groundside of a border can slow behavior during a rapid categorization task. Participants viewed two silhouettes that depicted a real-world and a novel object. Their task was to saccade toward the real-world object as quickly as possible. Half of the nontarget novel objects were ambiguous in that a portion of a real-world object was suggested, but not consciously perceived, on the groundside of their borders. The rest of the nontargets were unambiguous. We tested whether saccadic reaction times were perturbed by the real-world objects suggested on the groundside of ambiguous novel silhouettes. In Experiments 1 and 2, saccadic reaction times were slowed when nontargets were ambiguous rather than unambiguous. Experiment 2 set an upper limit of 190 ms on the time required for object memories in grounds to influence behavior. Experiment 3 ruled out factors that could have produced longer latencies other than access to object memories. These results provide the first behavioral index of how quickly memories of objects suggested in grounds can influence behavior, placing the upper limit at 190 ms.
300

The Impacts of Exclusionary Zoning Practices and Gentrification on Low-Income and Minority Populations in America's Inner Cities

Jackson, Tanjanesia 21 May 2004 (has links)
This thesis will examine the effects of residential segregation, exclusionary zoning, and gentrification on low-income minorities in inner cities. The research will show the relationship between housing inequalities and institutional classism and racism. In addition, the research will examine the use of public policies and regulations that maintain the existing isolation and concentration of minorities and low-income families through disinvestment.

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