8 resultados para second harmonic generation

em Digital Commons at Florida International University


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The rise in diversity and numbers of U.S. immigrants since 1965 has spawned a number of studies about the education of these immigrants and their children. Most of this research finds that school-age immigrants arriving in the last 20 years have the highest drop-out rates, lowest test scores, and are less likely than their native born peers to go to college. This dissertation examines the experiences of Nicaraguan immigrant youth living in Miami and the factors that make some of these adolescents feel positive about education, while others have negative attitudes about education. The method for this study combined structured and unstructured interviews, participant observation, focus groups, and data collected from a larger data set to understand the academic orientation of 25 Nicaraguan youths over a 4-year period. One of the independent variables is length of time in the United States. During the time of my initial contact with the subjects, 6 had been living in the United States for less than 3 years, 14 had been living in the United States between 6 and 12 years, and 6 had been living in the in the United States most or all of their lives (either they were born in the United States or had resided here for over 12 years). ^ Results are based on the students' particular experiences, which influence the dependent variable, academic orientation. Besides length of time, the independent variables also include ethnic self-identity, perceived discrimination, social capital in Miami, and peer influence. The study finds that those who are very recent arrivals have a “dual frame of reference,” that is, they directly compare their educational opportunities here in the United States, with their prior, often less favorable, situation in their homeland. Many of those who were born in Nicaragua, but have been residing in Miami most of their lives, have a less favorable view of education based on a higher degree of perceived discrimination. However, those who are second generation Nicaraguans deliberately take advantage of the strength inherent in their co-ethnic community unique to Miami. Recognition of this ethnic community prompts them to perceive education as worthwhile. ^

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Prices of U.S. Treasury securities vary over time and across maturities. When the market in Treasurys is sufficiently complete and frictionless, these prices may be modeled by a function time and maturity. A cross-section of this function for time held fixed is called the yield curve; the aggregate of these sections is the evolution of the yield curve. This dissertation studies aspects of this evolution. ^ There are two complementary approaches to the study of yield curve evolution here. The first is principal components analysis; the second is wavelet analysis. In both approaches both the time and maturity variables are discretized. In principal components analysis the vectors of yield curve shifts are viewed as observations of a multivariate normal distribution. The resulting covariance matrix is diagonalized; the resulting eigenvalues and eigenvectors (the principal components) are used to draw inferences about the yield curve evolution. ^ In wavelet analysis, the vectors of shifts are resolved into hierarchies of localized fundamental shifts (wavelets) that leave specified global properties invariant (average change and duration change). The hierarchies relate to the degree of localization with movements restricted to a single maturity at the base and general movements at the apex. Second generation wavelet techniques allow better adaptation of the model to economic observables. Statistically, the wavelet approach is inherently nonparametric while the wavelets themselves are better adapted to describing a complete market. ^ Principal components analysis provides information on the dimension of the yield curve process. While there is no clear demarkation between operative factors and noise, the top six principal components pick up 99% of total interest rate variation 95% of the time. An economically justified basis of this process is hard to find; for example a simple linear model will not suffice for the first principal component and the shape of this component is nonstationary. ^ Wavelet analysis works more directly with yield curve observations than principal components analysis. In fact the complete process from bond data to multiresolution is presented, including the dedicated Perl programs and the details of the portfolio metrics and specially adapted wavelet construction. The result is more robust statistics which provide balance to the more fragile principal components analysis. ^

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Immigrants from Jamaica represent the largest number of migrants to the United States from the English speaking Caribbean. Research indicates that of all Caribbean immigrants they are most likely to retain the ethnic identity of their home country for the longest period of time. This dissertation explored the nature of ethnic identity and sought to determine its impact upon the additional variables of self-esteem and academic factors. A secondary analysis was carried out using data collected in the Spring of 1992 by Portes and Rumbaut on the children of immigrants attending the eighth and ninth grades in local schools in San Diego and southern Florida. A sample of 151 second-generation Jamaican immigrants was selected from the data set. ^ Six hypotheses yielded mixed results. Both parents who have a Jamaican ethnic identity present in the household are the best predictor Jamaican youth who retain a Jamaican ethnic identity. It was expected that ethnic identity would be a predictor of positive academic factors. The study showed that ethnic identity was not associated with one of the academic factors which were examined: help given with homework. ^ Neither family economic status nor parents' level of education played a significant role in the retention of Jamaican identity. Other findings were that there was no mean difference in the self-esteem scores of respondents who had similar ethnic identities to their parents and those who did not. There was also no difference found in the academic factors of either group. The study also showed that there was a small correlation between parent-child conflict and self-esteem. Specifically, the study found that the higher the conflict between youth and their parents, the lower the self-esteem of the youth. Finally it found that time lived in the U.S. was the best predictor of a higher GPA and it was also related to lower self-esteem. ^ Surprisingly, the study found that the relationship between ethnic identity and SES was the opposite of what was expected in that it found that SES was higher when there was no Jamaican identity. ^

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The purpose of this dissertation was to determine the interactions of sexuality and education among low socioeconomic status first and second generation Mexican immigrant adolescent girls. Much of the existing research differentiates between immigrant generations with little examination of the differences within a particular immigrant generation. This study utilized qualitative methods to examine how various social institutions intersected to influence the young women's decisions about education and sexuality. The methodology included more than three years of participant observation in a South Florida high school and surrounding community; structured and unstructured interviews with twenty young women, their family members, school personnel, and community activists; and surveys conducted with the young women and their parent or guardian. ^ Moving beyond the limits of essentialist immigration theories, this project revealed within group (i.e. immigrant generation) complexities as well as between group similarities. The data included in this dissertation delineate how relationships of power and control permeated the lives of first and second generation Mexican immigrant adolescent girls. The lens of this dissertation is focused on the salient issues of sexuality and education: two dominant forces in many adolescent lives. ^ I found the young women represented a variety of positions on the academic orientation and sexuality continuums and engaged in activities that both reinforced and countered their stated positions on each of these issues. Specifically, first and second generation immigrants are often viewed as maintaining opposing viewpoints about both education and female sexuality however, for these young women the within group variation was larger than the between group variation. While all the young women in this study expressed a belief in the value of education, they engaged in activities that both fortified and contradicted that expressed position. Additionally, although acculturation can lead to increased sexual activity and decreased engagement with education, the first generation immigrant young women in this study became pregnant and/or withdrew from school in equal proportions to their second generation counterparts. In summary, structural forces combined, often inadvertently, and contributed to these young women's spiraling negative academic orientation and/or rational choice of motherhood. Finally, the findings are linked to policy implications. ^

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The purpose of this qualitative study was to explore the academic and nonacademic experiences of self-identified first-generation college students who left college before their second year. The study sought to find how the experiences might have affected the students' decision to depart. The case study method was used to investigate these college students who attended Florida International University. Semi-structured interviews were conducted with six ex-students who identified themselves as first-generation college students. The narrative data from the interviews were transcribed, coded, and analyzed. Analysis was informed by Pascarella, Pierson, Wolniak, and Terenzini's (2004) theoretical framework of important college academic and nonacademic experiences. An audit trail was kept and the data was triangulated by using multiple sources to establish certain findings. The most critical tool for enhancing trustworthiness was the use of member checking. I also received ongoing feedback from my major professor and committee throughout the dissertation process. The participants reported the following academic experiences: (a) patterns of coursework; (b) course-related interactions with peers; (c) relationships with faculty; (d) class size; (e) academic advisement; (f) orientation and peer advisors; and (e) financial aid. The participants reported the following nonacademic experiences; (f) on- or off- campus employment; (g) on- or off-campus residence; (h) participation in extracurricular activities; (i) noncourse-related peer relationships; (j) commuting and parking; and (k) FIU as an HSI. Isolationism and poor fit with the university were the most prevalent reasons for departure. The reported experiences of these first-generation college students shed light on those experiences that contributed to their departure. University administrators should give additional attention to these stories in an effort to improve retention strategies for this population. All but two of the participants went on to enroll in other institutions and reported good experiences with their new institutions. Recommendations are provided for continued research concerning how to best meet the needs of college students like the participants; students who have not learned from their parents about higher education financial aid, academic advisement, and orientation.

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Hispanic Generation 1.5 students are foreign-born, U.S. high school graduates who are socialized in the English dominant K-12 school system while still maintaining the native language and culture at home (Allison, 2006; Blumenthal, 2002; Harklau, Siegal, & Losey, 1999; Rumbault & Ima, 1988). When transitioning from high school to college, these students sometimes assess into ESL courses based on their English language abilities, and because of this ESL placement, Hispanic Generation 1.5 students might have different engagement experiences than their mainstream peers. Engagement is a critical factor in student success and long-term retention because students’ positive and negative engagement experiences affect their membership and sense of belonging at the institution. The purpose of this study was to describe the engagement and membership experiences of Hispanic Generation 1.5 students’ at a Massachusetts community college. This study employed naturalistic inquiry within an embedded descriptive case study design that included three units of analysis: the students’ engagement experiences in (a) ESL courses, (b) developmental courses, and (c) mainstream courses. The main source of data was in-depth interviews with Hispanic Generation 1.5 students at Commonwealth of Massachusetts Community College. Criterion sampling was used to select the interview participants, ensuring that all participants were native Spanish speakers and were taking or had taken at least one ESL course at the institution. The study findings show that these Hispanic Generation 1.5 students at the college did not perceive peer engagement as critical to academic success. Most times the participants avoided peer engagement outside of the classroom, especially with fellow Hispanic students, who they felt would deter them from their English language development and general academic work. Engagement with ESL faculty and ESL academic support staff played the most critical role in the participants’ sense of belonging and success, and students who were required to engage with faculty and academic support staff outside of the classroom were the most satisfied with their educational experiences. While the participants were all disappointed with some aspect of their ESL placement, they valued the ESL engagement experiences more than the engagement experiences while completing developmental and credit coursework.

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The economic development of any region involves some consequences to the environment. The choice of a socially optimal development plan must consider a measure of the strategy's environmental impact. This dissertation tackles this problem by examining environmental impacts of new production activities. The study uses the experience of the Carajás region in the north of Brazil. This region, which prior to the 1960's was an isolated outpost of the Amazon area, was integrated to the rest of the country with a non-sophisticated but strategic road system and eventually became the second largest iron ore mining area in the world. Finally, in the 1980's, the area was linked, by way of a railroad, to the nearest seaport along the Atlantic Ocean. The consequence of such changes was a burst of economic growth along the railroad Corridor and neighboring areas. In this work, a Social Accounting Matrix (SAM) is used to construct a 2-region (Corridor and surrounding area), fixed price, Computable General Equilibrium (CGE) Model to examine the relationship between production and pollution by measuring the different pollution effects of alternative growth strategies. SAMs are a very useful tool to examine the environmental impacts of development by linking production activities to measurable indices of natural resource degradation. The simulation results suggest that the strategies leading to faster economic growth in the short run are also those that lead to faster rates of environmental degradation. The simulations also show that the strategies that leads to faster rates of short run growth do so at the price of a rate of environmental depletion that is unsustainable from a long run perspective. These results, therefore, support the concern expressed by environmental economists and policy makers regarding the possible trade-offs between economic growth and environmental preservation. This stresses the need for a careful analysis of the environmental impacts of alternative growth strategies. ^

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Personalized recommender systems aim to assist users in retrieving and accessing interesting items by automatically acquiring user preferences from the historical data and matching items with the preferences. In the last decade, recommendation services have gained great attention due to the problem of information overload. However, despite recent advances of personalization techniques, several critical issues in modern recommender systems have not been well studied. These issues include: (1) understanding the accessing patterns of users (i.e., how to effectively model users' accessing behaviors); (2) understanding the relations between users and other objects (i.e., how to comprehensively assess the complex correlations between users and entities in recommender systems); and (3) understanding the interest change of users (i.e., how to adaptively capture users' preference drift over time). To meet the needs of users in modern recommender systems, it is imperative to provide solutions to address the aforementioned issues and apply the solutions to real-world applications. ^ The major goal of this dissertation is to provide integrated recommendation approaches to tackle the challenges of the current generation of recommender systems. In particular, three user-oriented aspects of recommendation techniques were studied, including understanding accessing patterns, understanding complex relations and understanding temporal dynamics. To this end, we made three research contributions. First, we presented various personalized user profiling algorithms to capture click behaviors of users from both coarse- and fine-grained granularities; second, we proposed graph-based recommendation models to describe the complex correlations in a recommender system; third, we studied temporal recommendation approaches in order to capture the preference changes of users, by considering both long-term and short-term user profiles. In addition, a versatile recommendation framework was proposed, in which the proposed recommendation techniques were seamlessly integrated. Different evaluation criteria were implemented in this framework for evaluating recommendation techniques in real-world recommendation applications. ^ In summary, the frequent changes of user interests and item repository lead to a series of user-centric challenges that are not well addressed in the current generation of recommender systems. My work proposed reasonable solutions to these challenges and provided insights on how to address these challenges using a simple yet effective recommendation framework.^