Ce travail expérimental analyse le mélange de deux fluides miscibles associé à un écoulement induit par gravité dans la géométrie confinée d'un tube incliné. L'étude de la vitesse du front en fonction des paramètres de contrôle (contraste de densité entre les fluides \Delta\rho/\rho <

Educational attainment is a key component of occupational attainment and social mobility in America. Special education is a policy intervention geared toward ensuring equal educational opportunities for students distinctive from the majority. Students labeled with learning disabilities (LDs) comprise about half of the special education population, and are typically assigned the LD label for achievement levels that are lower than would be expected given their IQ. Although they have average or high IQs, students labeled with an LD continue to experience disparities in educational outcomes. In this dissertation, I use sociological perspectives and a large nationally representative dataset, The Education Longitudinal Study of 2002, to investigate the social and structural roots of the LD label, and to explore ways in which the LD label produces stigma or stratification during high school. In general, I find that (1) the disproportionate labeling of various status groups is indicative of the social and structural roots of the LD label, and that the process of assigning the LD label may not be uniform across schools; (2) labeled students have poorer educational outcomes than even unlabeled students who achieved at similar levels in early high school; (3) stigma related to the LD label is suggested by parents’ and particularly teachers’ much lower educational expectations for labeled students than for similar students not labeled with disability; (4) stratification related to the LD label is suggested by the placement of labeled students into lower levels of coursework than unlabeled students who performed similarly in a comparable level of coursework during the prior year; and (5) stigma and stratification related to the LD label are magnified among labeled students who are more socially advantaged, or who are higher achieving. Overall, the results suggest that the experiences of students labeled with an LD can be improved by addressing these social and structural factors that differentiate the likelihood of carrying the LD label, and have negative implications for labeled students’ social and academic experiences during high school. / text

Hypoxia is frequently detected during summer in Corpus Christi Bay, Texas, and causes significant harm to benthic organism population and diversity. Hypoxia is associated with the density stratification in the Bay but the cause of stratification is uncertain. To support the study of hypoxia and stratification, a cyberinfrastructure based on the CUAHSI (Consortium of Universities for the Advancement of Hydrologic Science, Inc) Hydrologic Information System (HIS) is implemented. HIS unites the sensor networks in the Bay by providing a standard data language and protocol for transferring data. Thus hypoxia-related data from multiple sources can be compiled into a structured database. In Corpus Christi Bay, salinity data collected from many locations and times are synthesized into a three-dimensional space-time continuum using geostatistical methods. The three dimensions are the depth, the distance along a transect line, and time. The kriged salinity concentration in space and time illuminates the pattern of movement of a saline gravity current along the bottom of the Bay. The travel time of a gravity current in the Bay is estimated to be on the order of one week and the speed is on the order of 1 km per day. Statistical study of high-resolution wind data shows that the stratification pattern in the Bay is related to the occurrence of strong, southeasterly winds in the 5 days prior to the observation. This relationship supports the hypothesis that stratification is caused by the wind initiating hypersaline gravity currents which flow from Laguna Madre into Corpus Christi Bay. An empirical physical hypoxia model is created that tracks the fate and transport of the gravity currents. The model uses wind and water quality data from real-time sensors published by HIS to predict the extent and duration of hypoxic regions in the Bay. Comparison of model results with historical data from 2005 to 2008 shows that wind-driven gravity currents can explain the spatially heterogeneous patterns of hypoxic zones in Corpus Christi Bay. / text

The purpose of this study was to examine the relative contribution of socioeconomic status and student perceptions of school effectiveness to academic achievement in engineering students. The variables representing the general factor of socioeconomic status were 1) father’s occupation, 2) father’s schooling, 3) mother’s schooling, 4) family income, and 5) family’s community population. The variables representing student perceptions of school effectiveness were: 1) help seeking factor, 2) professional preparation factor, 3) experience factor, 4) outside classroom activity factor, 5) personal encouragement factor, and 6) delivery factor. A question was developed for this specific study and was completed by 110 senior engineering students from the Durango Institute of Technology in Durango, Mexico. Data were analyzed by means of a truncated component regression. The results of the data analysis indicated that the compounded set of socioeconomic and school factors was significantly related to student achievement, although all factors together explained only 18 percent of the total variance in student achievement. Socioeconomic status by itself did not have a significant relationship with academic achievement of engineering students. Also, the results of the data analysis indicated that professional preparation and personal encouragement had the greatest degree of relationship with student achievement of the six school factors representing student perceptions of school effectiveness. The other school factors – help seeking, experience, outside classroom activity, and delivery – were not significantly associated with academic achievement.

When attempting to explain the economics of occupational structure, income servies as the apex of discrimination. Women earn only 60% of what men earn. This statistic does not offend enough people since efforts to change the situation have provided only further resistance by women and men for improvement in the earnings split. Women tend to receive lower wage and salary earnings than men because of differences in types of jobs held, job training and continuity of work experience. Large numbers of women work in traditionally low-paying occupations and low-wage industries. Women tend to respond to their cultural up-bringing. My hypothesis rests on the foundation that women feel compelled to move into low-income areas. I utilized occupational and georaphic categories in order to provide a more selected example of wage discrimination.

The "college-for-all" norm encourages all students to attend college, and while rising college ambitions point to the effectiveness of this encouragement, differences by race and income in who goes to the most selective institutions and who actually graduates from those institutions point to persistent inequalities. With few exceptions, the majority of research on college access has focused more on documenting these inequalities and less on explaining how students end up in their respective institutions. In particular, we lack in-depth examinations of how students navigate the college admissions process, which represents one of the last hurdles between students and college attendance. Considering the increasingly complex nature of college admissions, especially for the most elite schools, the application process is a key gate-keeping mechanism in the reproduction of inequality in higher education, both in terms of who attends college and whether or not they finish (vertical stratification) and what kind of school they enroll in (horizontal stratification). My dissertation delves into this process and finds that institutions such as universities and high schools tend to reinforce disadvantages by failing to adjust their messages for different student populations. All students in my study are fed high college aspirations, but not all have the same "college knowledge." When less advantaged students attempt to pursue the dominant college pathway, like they see so many of their peers successfully navigating, they meet with unrealized aspirations and college "under-matching." Though interest in under-matching and horizontal stratification in higher education is growing, we know very little about the processes that lead to these outcomes. Drawing on extensive field research at two high schools and interviews with 137 respondents, I examine the three stages of the college-choice process – aspirations, search, and choice. I examine how institutional forces, such as high school organization and culture and higher educational marketing, lead students to engage in the college application process in very different ways during each of the three stages. I argue that the first step towards understanding more about why low-income and minority students struggle to graduate college is to look at the circumstances under which they made their college choices. / Sociology

Phytoplankton mirrors changes in the environment and plays an important role in biogeochemical processes. Phytoplankton dynamics is the outcome of both autogenic succession and external disturbances. This thesis focused on the seasonal variation of water column stability and its effects on phytoplankton, particularly considering the influence of mixing events on phytoplankton development. Lake Erken is a dimictic lake with weak and often interrupted summer stratification, which represents an intermediate case between a polymictic lake and a lake with strong summer stratification. There are two diatom phases annually. The spring bloom is caused by pioneer centric diatoms, and the autumn diatom phase is dominated by meroplanktonic diatoms induced by turnover. A summer Cyanobacteria bloom – mainly Gloeotrichia echinulata, depended on the length and stability of stratification. Winter and spring air temperature is found to play an important role in the annual succession of phytoplankton by initiating changes in ice/snow-cover and lake thermal stability and setting the basic status. Instead of starting from zero, the vernal phytoplankton piles up on the overwintering community, this trans-annual ecological memory influences both the composition and diversity and taxonomic distinctness of spring phytoplankton. Water column stability during summer in Lake Erken is mainly influenced by wind-induced turbulence and internal seiches. As thermal stratification develops from early until late summer, variations in stability and gradual deepening of the thermocline depth influence phytoplankton dynamics directly by changing its distribution, and also indirectly by altering the nutrient and light availability. A new disturbance index (DI) was defined to quantify environmental stability/disturbance and tested well to indicate phytoplankton equilibrium status in two summer stratification periods. The concept of species and functional groups was generally used in this study. However, a next generation sequencing based approach was also tested and proved to provide an excellent candidate for revealing distribution patterns of phytoplankton in inland waters.

The topic of this papework for master degree is „Teacher‘s social status in our society (In Kazlu Ruda municipality)“. The object of the research – problems of teachers‘ social status in province. The purpose of the research – to analyse social status and its changes (Kazlu Ruda municipality). Hypothesis of the research – since 1990 the teachers‘ status has lowered in province. It was caused by new social – economical conditions and the change of values in our sodiety, also by the teachers‘ behavior in these conditions. The goals: o to introduce the concept of social status and stratification. o to show the teachers‘ status during the process of changes in education system since Lithuania has become independent. o to introduce the teachers‘, who work in Kazlu Ruda municipality schools, attitude to their profession. o to discuss the attitude of different social groups in Kazlu Ruda municipality to teachers‘ prosession. We have been using two methods in the empirical part of of the research: a questionnaire and an interview. There hasn‘t been any probability in selecting the interviewees. We have questioned 117 teachers in Kazlu Ruda municipality (it makes 50%) and we have got all the questionnaires back. A number of different social groups took part in the quality interviewing: 4 doctors, 4 priests, 5 policemen, 8 businessmen, 7 municipality workes, 5 farmes, 8 unemployed, 5 homeless people. All these people were interviewed separately in their homes, offices or in the... [to full text]

In an unpublished study in Toronto it was observed that cases were in Hardy-Weinberg Equilibrium at a locus whereas their family members were in Hardy-Weinberg Disequilibrium (HWD). This led to an investigation of relatives of affected individuals to see whether the multiplicative model could be revealed by a nonzero HWD coefficient in relatives. Genotypic frequencies and HWD coefficients were derived for affected individuals and their affected and unaffected relatives. Methods were also developed to test for association using data from affected individuals and their relatives. In addition, a model was developed to assess whether the HWD observed in a data set from a stratified population can be explained by both genetic association and stratification. Parameter estimates for these models can be obtained using maximum likelihood methods, and used to deduce the mode of inheritance of the disease. / Departure from HWE (HWD) in a sample may indicate genotyping error, population stratification, selection bias, or some combination thereof. Therefore, loci exhibiting HWD are often excluded from association studies. However, it has been shown that in case-control studies HWD can result from a genetic effect at the locus, and HWD at a marker locus can be interpreted as evidence for association with a disease. In an unpublished study in Toronto it was observed that cases were in Hardy- Weinberg equilibrium at a locus whereas their family members were in HWD. It has been shown that the HWD coefficient for a multiplicative genetic model is zero. This led to an investigation of relatives of affected individuals to see whether the multiplicative model could be revealed by a nonzero HWD coefficient in relatives. Genotypic frequencies and HWD coefficients were derived for affected individuals and their affected and unaffected relatives. A substantial HWD was found in both individuals in dominant and recessive genetic models but HWD is only slightly nonzero for additive and multiplicative models. Methods were also developed to test for association using data from affected individuals and their relatives. Parameter estimates for these models can be obtained using maximum likelihood methods, and estimates provide valuable information regarding the mode of inheritance of the disease. The methods were applied to 112 discordant sib pairs with Alzheimer’s disease typed for the ApoE polymorphism and a significant association was observed between the "4 ApoE allele and Alzheimer’s disease. Case-control studies may indicate spurious association with a marker locus in a stratified population. Methods were developed to determine if the HWD observed in a data set from a stratified population can be explained by both genetic association and stratification. Parameter estimates for these models can be obtained using maximum likelihood methods, and used to deduce the mode of inheritance of the disease. Applying the model to the R990G SNP of the CASR gene, it was found that the HWD was adequately explained by a recessive genetic association and a stratification proportion of 10%, consistent with the population of Toronto.

Solar domestic hot water (SDHW) systems collect energy with a solar collector, transfer the energy to the water through a heat exchanger, and store it in a storage tank. The water in the tank should be thermally stratified to the highest possible degree to maximize system efficiency because a stratified tank has higher availability than a mixed tank temperature. The objective of this research is to develop a manifold that will enhance thermal stratification in the SDHW tank. In this work a new immersion shell-and-coil heat exchanger with a perforated manifold that extends from the heat exchanger to the top of the tank was used to enhance the thermal stratification. The purpose of the perforated manifold is to deliver the water heated by the heat exchanger to the tank at the level where the temperature of the water in the tank matches the temperature of the heated water, thereby enhancing stratification. The effectiveness of the perforated manifold was determined experimentally. An experimental set-up was designed and constructed. The experimental results were analyzed for each manifold design then compared to determine the most effective manifold. The experimental work included testing and comparing different manifold designs. To simulate an actual system, experiments were conducted on three initial tank conditions, namely cold, hot, and mixed tank conditions. The thermal performance of the system in terms of tank availability and entropy, maximum tank temperature, and thermal stratification were studied. A method to determine and design a perforated manifold that works with the standard Canadian SDHW system was established and evaluated experimentally. An availability analysis approach was developed to evaluate the thermal performance of manifolds, which have been operated at different times of the year. Theoretically, gradually increasing the diameter of the holes in the manifold from the bottom into the top should reduce the unwanted flow of cold water from the bottom of the tank to the manifold and enhance the thermal performance of the manifold. However, the experimental did not confirm this.