Ces travaux concernent l'étude d'un procédé de vapogazéification de biomasse en lit fluidisé circulant. En résultent un ensemble d'outils théoriques (modèles de simulation et de dimensionnement) et expérimentaux (pilote de vapogazéification en lit fluidisé circulant) dans le but de permettre la construction d'un procédé à dimension industrielle. Le dimensionnement, la conception et la construction d'un pilote de vapogazéification de 20 kg/h de biomasse en lit fluidisé circulant ont été réalisés. L'hydrodynamique de ce pilote a été étudiée de manière à isoler les paramètres clés permettant d'en assurer le contrôle. Les résultats obtenus lors de l'opération de pilote ont en outre permis de mieux comprendre les mécanismes d'attrition de particules polydisperses (olivine et char) en lit fluidisé circulant. Pour compléter cette étude, les phénomènes de mélange et de ségrégation des particules ont été étudiés par voie expérimentale et numérique (CFD-3D MFIX). Enfin, un certain nombre de modèles numériques (0D, 1D bulle-émulsion, bilan de population) ont été proposés pour répondre aux besoins techniques d'aide à la conception des lits fluidisés circulants appliqués à la vapogazéification de biomasse. / The vapogasification of biomass in a Circulating Fluidized Bed has been studied in order to enable the design and the erection of an industrial process. Theoretical and experimental tools have been designed to allow an engineering approach. In order to understand the hydrodynamic behaviour of the reactor, a pilot plant has been designed and erected to feed 20 kg/h of biomass. An exhaustive study of process parameters has been carried out, to determine predominant parameters for the process global control. Operating the built system has also permit to understand attrition phenomenon of polydisperse particles (olivine and char) in the Circulating Fluidized Bed. In order to complete those results, a study of mixing and segregation of those polydisperse particles has been carried out in fluidized bed with both experimental and numerical (CFD-3D MFIX) approaches. A significant contribution has also been done to numerical models assisting biomass vapogasification in Circulating Fluidized Beds design: 0D, 1D, bubble-emulsion, population balance).

Cette thèse se compose de quatre travaux indépendants. Le premier concerne les modèles partiellement identifiés, c'est-à-dire des modèles dans lesquels la valeur du paramètre d’intérêt ne peut pas être déduite de la distribution des données et des hypothèses du modèle. Dans certaines situations, aucune ou au contraire plusieurs valeurs du paramètre d’intérêt sont compatibles avec les données et les hypothèses du modèle. Ce travail démontre entre autre que si l’ensemble des distributions de probabilités compatibles avec le modèle est convexe, alors les parties extrêmes de ce convexe caractérise l’ensemble des distributions compatibles avec le modèle. Le deuxième travail propose une méthode basée sur une condition d’exclusion pour corriger de l’attrition endogène dans les panels. Nous appliquons cette méthode pour estimer les transitions sur le marché du travail à partir de l’enquête emploi française. Le troisième travail propose une méthode simple pour estimer un modèle logistique avec effets fixes et dépendance d’état tel qu’étudié par Honoré et Kiriazidou. Il propose également un nouvel estimateur des écarts-types qui semble avoir de meilleures propriétés à distance finie. Le quatrième travail est une évaluation sur les collèges de la politique éducative des Réseaux-Ambition-Réussite lancée en 2006. Nous exploitons une discontinuité dans la sélection des collèges pour comparer entre eux certains collèges « identiques » avant la mise en place de la politique. Les résultats de cette évaluation laissent place à peu d’optimisme concernant l’efficacité de cette politique. / This work consists of four independent chapters. The first deals with partially identified models, i.e. models in which the parameter of interest is not uniquely identified from the data and the model’s assumptions. In some cases, no value of the parameter of interest is compatible with the data and the model’s assumption. And conversely in some cases, many values are compatible with the data and the model’s assumptions. This work demonstrates among other things that if the set of probability distributions compatible with the model is convex, then this set is characterized by its the extreme parts. The second paper proposes a method based on an exclusion restriction to correct endogenous attrition in panels. We apply this method to estimate the transitions on the labor market from the French Labour Force Survey. The third paper proposes a simple method to estimate a Logit model with fixed effects and state dependence as studied by Honoré and Kiriazidou. It also proposes a new method for inference. The fourth work is an evaluation of a French educational policy, implemented in 2006 whose objective is to provide extra resource to a subset of junior high schools. We exploit a discontinuity in treatment selection to build a credible counterfactual. Our results indicate some adverse treatment effects.

The purpose of this exploratory, retrospective study was to determine if student demographics and academic variables predicted student persistence and success in an associate degree nursing program in Florida and to investigate the variables in Tinto's Longitudinal Model of Dropout (1975).The sample population (N=304) for this study was students enrolled in one of the initial courses of the associate degree nursing program at Daytona Beach Community College (DBCC) in Daytona Beach, FL from August 2002 through August 2003. Students were assigned to one of three groups (a) passing group, (b) failing group, or (c) withdrawing group. The convenience sample of (N=304) included: 242 students who successfully completed the nursing program, 32 students who failed a nursing course, and 38 students who withdrew from a course prior to successful completion. Demographic variables, admission and college science course grade point averages, and Nurse Entrance Test (NET) scores were collected on the sample population. Descriptive statistics were used to identify any unique differences that may have existed between the three groups, and multinomial logistic regression was used to determine the variables that best predicted success in the associate degree nursing program. Students in the passing group were found to be slightly older than students in the failing and withdrawing groups. The passing group had a higher percentage of females; the failing and withdrawing groups had higher percentages of males. The failing and withdrawing groups also contained higher percentages of minority students and students with English as a second language. Ethnicity was considered a significant predictor for student success in this study. Grade point average (GPA) score at the time of admission to the nursing program and college mean science course GPA scores were significant predictors. Students in the passing group had higher mean admission grade point averages than the failing and withdrawing groups. Students in the passing group also had noticeably higher mean grade point averages in all college science courses. NET scores were not considered significant predictors, at least for students who met the requirements for admission, and minimal differences were noted between the three groups in the study. The results of the study supported the use of variables identified in Tinto's Longitudinal Model of Dropout (1975) for predicting program success with nursing students. Individual attributes and pre-college experiences were predictors of student success for this sample, and demographic differences were identified between successful and unsuccessful students. Based on the results, the nursing department should consider placing more emphasis on admission and college science course grade point averages during the application process. A future conceptual model should include college science course GPAs, specifically anatomy and physiology and microbiology, and admission grade point average. Remedial or support services should be emphasized for minority students and students with English as a second language. Strategies should be implemented to retain men in the nursing program.

Retaining quality teachers is critical to the success of America's schools. How to retain quality teachers, especially in high needs schools, is a question of fervent debate among educational researchers, policy makers, administrators, parents, and students. This study examines the issue of teacher retention from an emic perspective, focused on understanding the perspective of those closest to the retention decision, teachers in hard-to-staff schools. This study examines the lived experiences of four teachers at a hard-to-staff, urban, secondary school as these experiences impact their decisions to remain in teaching and at their current campus. Research methods adopted an existential phenomenological perspective and focused on understanding deeply the perspective of participants and how participants make meaning of their lived experiences as they relate to the retention decision. Three hour-long interviews were conducted with each of the four participants utilizing methodology laid out by Seidman (1991). Data were analyzed using NVIVO 10 to apply a series of coding and recoding procedures to interview transcripts. Conclusions suggest four factors motivated these teachers to teach and remain in their current hard-to-staff, urban, secondary school. These factors include: belief in the power of education, relationships with students, mentoring and professional partnering, and remaining professionally challenged. Findings suggest factors that drive teachers out of teaching and out of hard-to-staff schools include: inconsistent administrative support, low student motivation, and lack of resources.

Approved for public release; distribution is unlimited / This thesis was conducted to analyze certain factors affecting first-term attrition from U.S. Naval ships. The Survival Tracking File (STF) was used as the primary data source, and from it files were constructed that permitted three areas of study. First, the overall cohort of a year's worth of enlistees was examined. The survival curve for the cohort was generated and individual monthly cohorts were examined for attrition patterns. Secondly, overall attrition percentages were calculated for individual ships and for classes of ships and these attrition percentages were then examined for differences using statistical techniques. An ANOVA model using transformed data proved accurate in explaining attrition variance. Lastly, a comparison between attrition per month and underway hours per month was made for classes of ships and for individual ships of three specific classes. A rough relationship was observed, between peaks of high underway hours and peaks of attrition. In looking at individual aircraft carriers, the attrition percentage seemed to be inversely proportional to underway hours per month. Several of these findings warrant further investigation so that the Navy may more fully understand its attrition problem and thereby take steps to alleviate it. / http://archive.org/details/descriptiveanaly00carl / Lieutenant, United States Navy

This report addresses the lack of progress in the field of Second Language Attrition (L2A). Review of L2A history and literature show this to be cause by lack of appropriate data. Five criteria for appropriate data are suggested and a corpus of L2A data (57,000 words, spoken Spanish) which meets the criteria is presented. The history of the corpus is explained in detail, including subject selection, instruments and methods of collection, and markup -- XML was used to annotate the corpus with nineteen categories of speech errors, adapted from Nation's (2001) "Learning Vocabulary in Another Language." An example analysis of how the corpus can be used for L2A research is provided with step-by-step instructions on writing scripts for data extraction and post-processing in the Perl language. Source code is included in the text. Complete beginners tutorials on the XML and Perl languages are included in the appendices. The report also introduces a website, developed specifically to host the corpus, where researchers may register, download the corpus and share work they have done with the corpus. All files used in the example project, as well as this report, are available for download at the website. Findings from the example analysis support Plateau Phases, the Regression Hypothesis and suggest the Threshold Hypothesis does not apply to marked forms. This shows the corpus to be of great value to the L2A research community.

<p>Longitudinal surveys have revolutionized empirical research and our understanding of the dynamic processes that affect the economic prosperity, health and well-being of the population. This dissertation explores and provides evidence, through three empirical applications, on the costs and benefits of designing, implementing and using data from a new, innovative longitudinal survey, the Mexican Family Life Survey (MxFLS). The survey, which is representative of the Mexican population living in Mexico in 2002, is designed to follow movers within Mexico and also those who move to the United States. This design lies at the center of the contributions of my research to the scientific literature.</p><p>Attrition is the Achilles heel of longitudinal surveys. The first essay of the dissertation focuses on the cost of attrition for scientific knowledge. Following the same individual through time allows a researcher to trace the evolution of a respondent's behaviors and outcomes in a dynamic framework; however, if attrition is selected on unobserved characteristics, the advantage of using panel data could be severely hindered. Exploring different methods to adjust for attrition, this essay provides evidence of limitations of standard post-survey adjustments strategies that are the standard in the literature. These approaches, exploit only baseline characteristics of the respondents and, conditional on those characteristics, treat attriters as missing at random. I provide evidence that this assumption is substantively important and rejected in the MxFLS in spite of the fact that attrition in that survey is low relative to other nationally-representative surveys conducted in the United States and abroad. </p><p>The second essay in this dissertation exploits the fact that MxFLS follows movers within Mexico and those who move across the Mexico-US border to provide new insights into the mechanisms that underlie the selectivity of migrants within Mexico, how they differ from migrants who move from Mexico to the U.S. and how those who return contrast with the migrants who remain in the U.S. more permanently. The results provide evidence that human capital is predictive of migration within Mexico and to the United States, but that there is little indication that the decision to stay in the United States is highly correlated with education. In contrast, having relatives in the United States is not only a powerful predictor of migration to the United States, but it is also predictive of successful economic assimilation. </p><p>The third essay exploits a different dimension of the longitudinal survey in order to address an important question regarding the impact of unanticipated crime and violence on population well-being. To wit, the essay rigorously examines the impact of the recent surge in violent crime in Mexico on the labor market outcomes, migration, and wealth of the Mexican population. The timing of the last two waves of the MxFLS paired with the panel nature of the survey, allows the comparison of outcomes of the same individual in periods of low and high violence, which removes the potentially endogenous time-invariant unobserved heterogeneity between respondents. Moreover, due to the fact that the MxFLS was designed to follow migrant respondents, this study is able to directly test whether there is a systematic migratory response to crime. The results from this analysis find that crime predicts migration and it negatively affects the labor outcomes of self-employed individuals. In addition, the negative effects on the labor outcomes have translated into reductions in per capita expenditure at the household level, which suggests that the recent wave of violence in Mexico may have long-term consequences on the wealth and well-being of Mexican households.</p> / Dissertation

Previous research has shown L1 attrition to be selective (Gürel 2004) and often restricted to structures at the interfaces between syntax and context/pragmatics, but not to occur with syntactic properties that do not involve such interfaces (Interface Hypothesis, Sorace & Filiaci 2006). This is supported by many studies exploring cross-linguistic influence effects in interface structures, such as the production and/or interpretation of null versus overt pronominal subjects, not only in L1 attriters (Tsimpli et al. 2004, Montrul 2004) but also in other bilingual groups with different language combinations, such as early bilinguals (Paradis & Navarro 2003, Sorace et al. 2009), and advanced late bilinguals (Belletti et al. 2007, Rothman 2009). The current hypothesis is that individual L1 attrition affects only the ability to process interface structures but not knowledge representations themselves (Sorace 2011). In this thesis, we first compared a well-studied syntax-pragmatics interface phenomenon (pronominal subjects in Spanish) with a non-interface structure (the Spanish personal preposition a, also known as Differential Object Marking, DOM). In Spanish, the distribution of null and overt subject pronouns is pragmatically constrained, whereas the presence of the preposition just depends on the animacy and specificity of the direct object. Participants included a group of attrited speakers of L1 Spanish who had been living in the UK for a minimum of 5 years, and a group of Spanish monolinguals. Using a naturalness judgment task and eye tracking while reading, participants were presented with anaphoric sentences in which number cues matched or mismatched predicted antecedent preferences (i.e. null pronoun: subject preference; overt pronoun: object preference). The DOM study also used a mismatch paradigm, crossing preposition presence (al vs. el) with animacy, where an animate object requires the prepositional form al and an inanimate object requires the article el. Offline ratings revealed equal mismatch sensitivity for both groups of participants with both structures. However, eye-tracking measures showed that monolinguals were reliably more sensitive than attriters to the pronoun mismatch, while both groups showed equal on-line sensitivity to the DOM mismatch, which reveals that attrition affects interface structures, but not non-interface structures. Second, we investigated the effects of recent (re)exposure to L1 input on attrition. A second group of attriters carried out the same experiment after having been exposed exclusively to Spanish in a monolingual Spanish-speaking environment for a minimum of a week. Their eye-tracking results patterned with the monolingual group. This novel manipulation shows that attrition effects decrease as a result of L1 exposure, which reveals that bilinguals are sensitive to input changes and that attrition affects online sensitivity rather than causing a permanent change in speakers’ L1 grammatical representations.

Philosophiae Doctor - PhD / Academic success, which is measured by continuous assessment and examination results, is one of the major goals of higher education. However, Higher Education institutions worldwide are faced with a challenge on how to improve the academic performance, success and ultimately the retention of students during their studies. Aim: The aim of this study was to develop an intervention towards the improvement of academic performance, success and retention among undergraduate nursing students at a university in the Western Cape, South Africa. Methods: A multi-method research approach was employed to meet the study aim and objectives. The study was conducted in three phases that were guided by the adapted phases of the Design and Development (D&D) model by Rothman and Thomas (2013). Phase one (Study 1– 4) was the problem analysis and information gathering phase. Phase two was the design and early development during which designing observational elements and specifying procedural elements were applied. Phase three (Study 5) was the validation phase. Results: This thesis comprised of five interdependent studies. Study 1: A systematic review of literature was conducted encompassing previous literature from 2006 to 2016 regarding the predictors of academic performance and success among undergraduate nursing students. It was found that satisfactory academic performance among nursing students is associated with older age, female gender, English language proficiency, majority ethnic status, pre-admission academic achievements, selecting nursing as first choice for study, participating in organised music programmes, active academic engagement, as well as psychological and emotional factors. Study 2: Undergraduate nursing students’ (n =232) perceptions regarding their educational environment were explored. This study showed that generally the nursing students were positive about their educational environment. However, the findings indicated that enhancements are required to improve the conditions of the educational environment. Study 3: The study explored the challenges experienced by undergraduate nursing students (6 - focus group discussions) regarding their academic performance and success and the measures implemented to overcome these challenges. The findings revealed that students’ academic performance is influenced by the students’ economic background, place of residence, inadequate theoretical and clinical support and the unfavorable educational environment. However, the findings also indicated that students employ a surface approach to learning, maintain a positive attitude and remain academically engaged in response to these challenges. Study 4: The study explored the challenges experienced by nurse educators (n = 8) regarding the academic performance, success and retention of undergraduate nursing students and the measures implemented to overcome these challenges. The findings revealed that students’ academic performance is influenced by poor class attendance, lack of academic readiness, socioeconomic backgrounds, English language proficiency, structure of the programme, the educational environment and the working conditions for nurse educators. Study 5: A three round Delphi study was conducted to validate an intervention towards improving the academic performance, success and retention among nursing students. The intervention was structured into eleven categories that emerged from phase 2: (1) Select high quality prospective nursing students; (2) Provide English language support; (3) Promote class attendance; 4) providing financial support to deserving students; (5) Provide university residence to undergraduate nursing students; (6) Encourage family support and involvement; (7) Make the undergraduate nursing programme student-friendly; (8) Ensure a conducive teaching and learning environment; (9) Enhance theoretical and clinical support to undergraduate nursing students at all times; (10) Ensure uniformity and consistency in the process of teaching and learning as well as; (11) Provide support to nurse educators and clinical supervisors. Conclusion: The findings of this study have several implications for the education of nursing students. The developed intervention may help promote better understanding of the academic performance, success and retention of nursing students.

A satisfação dos clientes é fundamental para a manutenção do relacionamento com a empresa. Quando eles precisam resolver algum problema, a empresa necessita proporcionar bom atendimento e ter capacidade de resolutividade. No entanto, o atendimento massificado, muitas vezes, impossibilita soluções sensíveis às necessidades dos clientes. A metodologia estatística pode ajudar a empresa na priorização de clientes com perfil a reclamar em um órgão de defesa ao consumidor (ODC), evitando assim uma situação de atrito. Neste projeto, foi realizada a modelagem do comportamento do cliente com relação à propensão ao atrito. Foram testadas as técnicas de Regressão Logística, Random Forest e Algoritmos Genéticos. Os resultados mostraram que os Algoritmos Genéticos são uma boa opção para tornar o modelo mais simples (parcimonioso), sem perda de performance, e que o Random Forest possibilitou ganho de performance, porém torna o modelo mais complexo, tanto do ponto de vista computacional quanto prático no que tange à implantação em sistemas de produção da empresa. / Customer satisfaction is key to maintaining the relationship with the company. When these need to solve some problem, the company needs to provide good service and have resolving capacity. However, the mass service often makes it impossible. The statistical methodology can help the company in the prioritization of clients with profile to complain in ODC, thus avoiding a situation of attrition. In this project was carried out the modeling of the behavior of the client in relation to the propensity to attrition. Logistic Regression, Random Forest and Genetic Algorithms were tested. The results showed that the Genetic Algorithms are a good option to make the model simpler (parsimonious) without loss of performance and that Random Forest allowed performance gain, but it makes the model more complex, both from the point of view computational and practical in relation to the implantation in production systems of the company.