La modélisation et l’optimisation des procédés de polymérisation d’oléfines en prenant en compte les caractéristiques de la polymérisation et du procédé mis en jeu peuvent aider à améliorer les procédés de polymérisation industriels. Dans cette étude, un modèle a été développé et ses paramètres déterminés afin de calculer des propriétés thermodynamiques et physiques du système de polymérisation de l’éthylène. Des modèles en régime permanent et transitoire sont élaborés pour les procédés de polymérisation industriels en suspension ou en phase gazeuse, basés sur les cinétiques de polymérisation en présence de catalyseur Ziegler-Natta. La conduite des réacteurs a été analysée et le changement de grade simulé / Modeling and optimization of olefin polymerization processes based on polymerization and process characteristics provide guidance to plants and improve industrial processes. In this work, a model is proposed and its parameters determined to calculate thermodynamic and physical properties of the ethylene polymerization system. Based on industrial Zigler-Natta catalyzed multi-active sites ethylene polymerization kinetics, both steady and transient state plant-scale models are developed for industrial slurry and gas phase ethylene polymerization processes. The operating conditions of the reactors are analyzed; the grade transition and process optimization simulated

Thesis advisor: Irwin Blumer / The transition from eighth grade to ninth grade is a critical time in a young person's educational career. Ninth grade programs and separate buildings for ninth graders have grown over the last ten years in an effort to meet their distinct needs. Research in this area reveals very little documentation of the teachers' voices on this subject. This researcher sought to add their perspective in identifying the salient features of effective ninth grade programs which make for a smooth transition to high school. More specifically, the researcher wanted to learn if teachers of only ninth graders believed that a separate facility eased the transition to high school. / Thesis (PhD) — Boston College, 2004. / Submitted to: Boston College. Lynch School of Education. / Discipline: Educational Administration.

The purpose of this study was to determine if a transition program had an effect on the academic and social issues that at-risk ninth graders face as they transition to high school. A case study approach based on archival data was used to explore differences in the treatment and control groups. These groups were measured by grade point average (GPA), absences, tardies to school, course failures, discipline referrals, verified credits, and dropouts. Freshman retention, poor attendance, high failure rates, Standards of Learning (SOL) failures, and discipline problems are some of the issues facing at-risk ninth graders as they transition to high school. These issues can contribute to higher dropout rates, therefore making it more difficult to compete in today's workforce. As we prepare our students to compete in today's global economy, it is necessary to examine the current practices that high schools are utilizing to improve student outcomes, and to prepare more effectively for the higher expectations of today's workforce and educational institutions. This quantitative study examined the success of the Academic Careers and Technology (A.C.T.) class at Stuarts Draft High School , a yearlong ninth-grade transition program designed for at-risk students that was first implemented in 2003. The A.C.T. program was designed to provide ninth-grade at-risk students with the skills necessary for making a successful transition from middle school to high school and for continued success in their remaining high school career. The curriculum included extended time on reading comprehension, writing, and organizational and study skills. Additionally, technology integration, conflict resolution, and an adult mentor program were included in the curriculum. / Ed. D.

The movement from middle school to high school is a crucial period as adolescents frequently have a difficult time acclimating to the high school environment and often experience a decline in their academic achievement from middle school to ninth grade (DeLamar and Brown, 2016; Ellerbrock and Kiefer, 2014; Fulk, 2003; Mizelle and Irvin, 2000; Neild, 2009). Many students who drop out of school do so in ninth grade and do not graduate on time with their classmates (Asplaugh, 1998; Bottoms, 2002; Fulk, 2003; Neild, Stoner-Eby, and Furstenberg, 2008). The components of a successful middle school to high school transition program address the academic, procedural, and social challenges students face during this time (Akos and Galassi, 2004; Anderson et al., 2000; Block, 2016; Cauley and Jovanovich, 2006; Ellerbrock et al., 2015; Smith et al., 2006). Richard Samuel School (RSS), a stand-alone ninth-grade center, has addressed transition challenges for over 25 years. This single case study research examined the reasons for development of this unique school configuration, as well as the programmatic structures created to address students' academic, procedural, and social concerns, through the perceptions of former students, staff, and administrators. This study identifies the effectiveness, benefits, and drawbacks of the program design which addressed the middle school to high school transition for all students at RSS. The study analyzes the program during the first ten years of its existence, from its inception in 1993 until 2003. As a result of this study, themes around responsive and supportive accountability among staff and students were evident. Through transition structures, such as development of a school support team, core content teachers planning for and teaching advanced and standard level curriculum coupled with student placement on an interdisciplinary team and every student assigned a teacher advisor, students at RSS experienced a positive transition to high school. As a result, a decline in student retention occurred and after year three of implementation, there was a 0% dropout rate. The results of this case study will contribute to research regarding impactful transition programming from middle school to high school. / Doctor of Education / The movement from middle school to high school is a crucial period as students frequently have a difficult time adjusting to the high school environment and often experience a decline in their grades once they leave middle school and enter ninth grade (DeLamar & Brown, 2016; Ellerbrock & Kiefer, 2014; Fulk, 2003; Mizelle & Irvin, 2000; Neild, 2009). Many students who drop out of school do so in ninth grade and do not graduate on time with their classmates (Asplaugh, 1998; Bottoms, 2002; Fulk, 2003; Neild, Stoner-Eby, & Furstenberg, 2008). The transition from middle school to high school involves communication between school personnel, students, and their parents to ensure it is successful. The components of a successful middle school to high school transition program address the academic, procedural, and social challenges students face during this time (Akos & Galassi, 2004; Anderson, Jacobs, Schramm, & Splittgerber, 2000; Block, 2016; Cauley & Jovanovich, 2006; Ellerbrock, Denmon, & Owens, 2015; Smith, Feldwisch, & Abell, 2006). Richard Samuel School (RSS), a stand-alone ninth-grade center, has addressed transition challenges for over 25 years. The focus in this single case study research was to examine the reasons for the development of this unique school configuration, as well as the programmatic structures created to address students’ academic, procedural, and social concerns, through the perceptions of former students, staff, and administrators. An additional focus was to identify the effectiveness, benefits, and drawbacks of the program design which addressed the middle school to high school transition for all students at RSS. The study covered the program during the first 10 years of its existence, from its inception in 1993 until 2003. The results of this study contribute to the research regarding impactful transition programming from middle school to high school.

The transition to high school is a critical juncture of a student's educational career. The type of ninth grade transition program a high school has in place can be a deciding factor regarding whether students 'make it or break it' during their first year and, ultimately, have success throughout all of high school. Currently, resources are available about different aspects of the ninth grade transition, but nothing provides principals with a research-based and practitioner-endorsed comprehensive approach to designing and implementing a ninth grade transition program. A comprehensive approach starts with proper goals and objectives, includes essential specific components and ingredients needed in a ninth grade transition program, and requires data or measures to judge the effectiveness of the program. Therefore, a Delphi study was undertaken to answer the following research question: What should be the goals/objectives of a comprehensive ninth grade transition program (i.e., academic success alone or are there other things that also are important)? The secondary questions focused on the components or ingredients that are essential and how to evaluate the success of a ninth grade transition program. This Delphi study included three rounds during which data were gathered from a 20-member panel of experts that included both national leaders and education practitioners. The panel produced 21 consensus items on goals/objectives of a ninth grade transition program, 10 consensus items on essential components of a ninth grade transition program, and 15 consensus items on the data/measures to evaluate the success of a ninth grade transition program. Results indicated that transition programs need to address both academic and social/emotional needs of students. The data provided evidence that principals need to take great care in teacher quality, instructional practices, and a systematic approach to monitoring the performance of ninth grade students as well as ensuring students make a positive connection with an adult in the school. / Ed. D.

As unidades industriais de produção de poliolefinas operam de maneira contínua, mas precisam produzir diferentes tipos de grades poliméricos (polímeros com diferentes especificações, para diferentes aplicações). As condições de operação do reator são mantidas por um certo período de tempo para produzir um determinado grade, e periodicamente as condições são alteradas para produzir lotes de outros grades. Estas transições permitem produzir diferentes grades usando o mesmo reator, mas exige mudanças nas condições operacionais e, como consequência, o polímero produzido durante uma transição fica fora da especificação. Assim, é desejável que as transições sejam realizadas no menor tempo possível, de maneira a produzir a menor quantidade de polímero fora da especificação. Estratégias mais eficientes de operar a transição podem ser obtidas através da solução de um problema de otimização dinâmica. Neste trabalho uma função objetivo integral quadrática foi minimizada, utilizando técnicas sequenciais dinâmicas para resolução da otimização. Os resultados foram primeiramente simulados e depois otimizados para a homopolimerização e copolimerização. No caso da homopolimerização, as otimizações mostraram que para aumentar o MI é preciso aumentar a concentração de hidrogênio na alimentação. Já na copolimerização, para aumentar o MI foi preciso diminuir a concentração de hidrogênio na alimentação e aumentar a vazão de comonômero; e para diminuir a densidade foi preciso aumentar a vazão de comonômero. Observou-se que as propriedades instantâneas têm dinâmica mais rápida e agressiva que as cumulativas. Os resultados mostraram que quando a parametrização não era adequada a solução se afastava do ótimo. Foi possível notar que atuar durante 2 tempos de residência já traz uma redução significativa do tempo para o término da transição e da massa de produto fora da especificação. O perfil das propriedades da transição no sentido grade 1 - grade 2 se mostrou diferente do grade 2 - grade 1, concluindo que o perfil de uma transição depende fortemente da direção da mudança nas propriedades. / Polyolefin plants operate under continuous production, but they need to supply many types of polymer grades (polymer with different specification, used in different applications). The operating conditions are maintained constant during the production of a certain grade and need to change periodically to produce another grade. Grade transitions allow the production of different polymer grades in a single reactor, but as they require changes in the operating conditions, there is a large production of off-specification polymer. Therefore, a desired transition drives the polymer properties to the new grade in a short period of time, producing a small amount of off-specification polymer. Efficient strategies to operate the transition can be obtained by solving a problem of dynamic optimization. In this work, a quadratic integral objective function was minimized by using dynamic sequential techniques for solving optimization. The results were first simulated and then optimized for the homopolymerization and copolymerization. In the case of homopolymerization, optimizations showed that to increase the MI is necessary to increase the hydrogen concentration in the feed. In the copolymerization, to increase the MI was necessary to reduce the concentration of hydrogen in the feed and increase the comonomer flow rate; and to decrease the density was necessary to increase the comonomer flow rate. It was observed that the instantaneous properties have faster and aggressive dynamics compared to the cumulative properties. The results showed that when the parameterization was not adequate the solution moves away from the optimum. It was observed that to act for 2 residence times makes a significant reduction in the transition time completion and in the mass of product out of specification. The trajectories of the transition properties towards grade 1 - grade 2 showed different behavior compared to grade 2 - grade 1 transition, concluding that the profile of a transition depends strongly on the direction of change in the properties.

As unidades industriais de produção de poliolefinas operam de maneira contínua, mas precisam produzir diferentes tipos de grades poliméricos (polímeros com diferentes especificações, para diferentes aplicações). As condições de operação do reator são mantidas por um certo período de tempo para produzir um determinado grade, e periodicamente as condições são alteradas para produzir lotes de outros grades. Estas transições permitem produzir diferentes grades usando o mesmo reator, mas exige mudanças nas condições operacionais e, como consequência, o polímero produzido durante uma transição fica fora da especificação. Assim, é desejável que as transições sejam realizadas no menor tempo possível, de maneira a produzir a menor quantidade de polímero fora da especificação. Estratégias mais eficientes de operar a transição podem ser obtidas através da solução de um problema de otimização dinâmica. Neste trabalho uma função objetivo integral quadrática foi minimizada, utilizando técnicas sequenciais dinâmicas para resolução da otimização. Os resultados foram primeiramente simulados e depois otimizados para a homopolimerização e copolimerização. No caso da homopolimerização, as otimizações mostraram que para aumentar o MI é preciso aumentar a concentração de hidrogênio na alimentação. Já na copolimerização, para aumentar o MI foi preciso diminuir a concentração de hidrogênio na alimentação e aumentar a vazão de comonômero; e para diminuir a densidade foi preciso aumentar a vazão de comonômero. Observou-se que as propriedades instantâneas têm dinâmica mais rápida e agressiva que as cumulativas. Os resultados mostraram que quando a parametrização não era adequada a solução se afastava do ótimo. Foi possível notar que atuar durante 2 tempos de residência já traz uma redução significativa do tempo para o término da transição e da massa de produto fora da especificação. O perfil das propriedades da transição no sentido grade 1 - grade 2 se mostrou diferente do grade 2 - grade 1, concluindo que o perfil de uma transição depende fortemente da direção da mudança nas propriedades. / Polyolefin plants operate under continuous production, but they need to supply many types of polymer grades (polymer with different specification, used in different applications). The operating conditions are maintained constant during the production of a certain grade and need to change periodically to produce another grade. Grade transitions allow the production of different polymer grades in a single reactor, but as they require changes in the operating conditions, there is a large production of off-specification polymer. Therefore, a desired transition drives the polymer properties to the new grade in a short period of time, producing a small amount of off-specification polymer. Efficient strategies to operate the transition can be obtained by solving a problem of dynamic optimization. In this work, a quadratic integral objective function was minimized by using dynamic sequential techniques for solving optimization. The results were first simulated and then optimized for the homopolymerization and copolymerization. In the case of homopolymerization, optimizations showed that to increase the MI is necessary to increase the hydrogen concentration in the feed. In the copolymerization, to increase the MI was necessary to reduce the concentration of hydrogen in the feed and increase the comonomer flow rate; and to decrease the density was necessary to increase the comonomer flow rate. It was observed that the instantaneous properties have faster and aggressive dynamics compared to the cumulative properties. The results showed that when the parameterization was not adequate the solution moves away from the optimum. It was observed that to act for 2 residence times makes a significant reduction in the transition time completion and in the mass of product out of specification. The trajectories of the transition properties towards grade 1 - grade 2 showed different behavior compared to grade 2 - grade 1 transition, concluding that the profile of a transition depends strongly on the direction of change in the properties.

A Freshman Academy's Influence on Student Connectivity, Attendance, and Academic Achievement by Nancy O. LoPresti MA, Montclair State University 2005 MAT, Marygrove College, 2002 BA, Kean University 1981 Doctoral Study Submitted in Partial Fulfillment of the Requirements for the Degree of Doctor of Education Walden University June 2017