Thesis - Technische hogeschool Delft. / Bibliography: p. 108.

Thesis (M.S.)--Oregon State University, 2008. / Printout. Includes bibliographical references (leaves 68-70). Also available on the World Wide Web.

Acceleration spelar en viktig roll i att ta sig från punkt A till punkt B i en personbil. Eftersom förare själva har full kontroll över hur de väljer att accelerera finns det potential för variation i accelerationsbeteenden mellan förare. Något som kan påverka ett givet fordon och dess omgivning i olika grad. Detta projekt syftade till att mäta det genomsnittliga accelerationsbeteendet hos förare i normal trafik. Mätningar utfördes vid fyra korsningar i Stockholm, Sverige. Två i de närliggande förorterna och två i stadskärnan. Accelerationerna beräknades från stillastående och över ett förutbestämt avstånd på 20 meter. En statistisk analys av resultaten utfördes sedan för att ta reda på om det finns ett samband mellan fordonstyp, korsningsläge samt fordonsmotortyp och accelerationshastigheter. Förare kategoriserades också efter milda, normala eller aggressiva beteenden. 20 fordon mättes per korsning vilket gav totalt 80 fordon som ingick i mätningen. Av dessa fordon observerades att 58 följde ett normalt accelerationsbeteende, 14 ett aggressivt och 8 ett milt. En maximal acceleration på 4,92 m/s2och en minimiacceleration på 1,03 m/s2observerades över samtligakorsningar. Resultaten från den statistiska analysen fann inget samband mellan korsningens geografiska plats och accelerationsbeteenden. Dessutom hittades inget samband mellan accelerationsbeteenden och vilken typ av fordon som kördes. Däremot observerades det att fordonsmotortyp har en märkbar effekt på accelerationshastigheter oberoende av vald korsning. Utifrån dessa resultat gjordes även en hållbarhetsanalys avseende miljöpåverkan från bränsleförbrukning och däckslitage. Däremot fastslogs det att mer forskning behöver göras i ämnet för att få mer konkreta resultat som bättre representerar helheten.

This study was designed to identify factors that might influence Pennsylvania public school superintendents in the decision regarding the potential use of single-subject acceleration as a practice for meeting the needs of students in the elementary setting. The research targeted public school superintendents in the Commonwealth of Pennsylvania. In Pennsylvania, gifted education is mandated by Chapter 16 of the Pennsylvania School Code, yet acceleration policy is left to the local education agency (LEA), the school district. Since use of single-subject acceleration is not consistent across districts, this study sought to understand how administrators make decisions about using this tool. Previous research identified teacher and counselor perception of acceleration. Because the superintendent is instrumental in developing district policy, this research focused on their perceptions of this one specific acceleration tool. The research survey was delivered electronically to district superintendents via email using publically available district email addresses. Of the four hundred and ninety- nine (499) state superintendents, 96 returned the survey for a response rate of 20%. The survey included questions for the superintendent about the district’s size and its designation as urban, suburban, or rural. The survey also included questions about the superintendent’s background in regards to receiving gifted services or training in acceleration as well as the superintendent’s perceptions of gifted education. The survey was intended to address three research questions. 1. What factors impact Pennsylvania superintendents in adopting the practice of single-subject acceleration in their districts? 2. How might the personal and professional background of Pennsylvania superintendents, including experience and training, affect decisions in regard to use of single-subject acceleration? 3. What are superintendent’s attitudes about gifted education? Of the respondents, there were 46 each from suburban and rural districts and 4 from urban districts. The majority of the respondents had under six years of experience and under 250 annual graduates in their districts. Fewer than 20% identified as having been trained in single-subject acceleration, and 51% expressed utilizing single-subject acceleration. Quantitative survey research results revealed that superintendents in larger districts and suburban districts – characteristics that are confounded – are more likely to utilize single-subject acceleration. Further, superintendents expressed concern with transportation issues and logistical, scheduling, and coordination issues associated with single-subject acceleration. The quantitative survey results showed few correlations with superintendents’ background and utilization of the practice of single subject acceleration. The results, identified, however, indicate that the more training or life exposure regarding gifted education, the greater the support and the lower the concerns with gifted education. Further, those trained in single-subject acceleration were more likely to anticipate support from their boards regarding single-subject acceleration. Pennsylvania public school superintendents expressed support generally for gifted education even if it were not mandated under Chapter 16. The superintendents overwhelmingly agreed that the gifted need special attention to develop talents. More than a quarter of the superintendents disagreed, however, that a greater number of children should be allowed to skip a grade however while over forty percent of superintendents express neutrality on that topic. Yet, superintendents responded with disagreement about supporting gifted education in their districts; only 15 superintendents expressed agreeing or strongly agreeing with supporting gifted education in their district. This result, seemingly contradictory with other findings, is worthy of deeper investigation. Follow-up qualitative research utilized an interview format and targeted survey respondent volunteers. The follow-up interviews were used to gain deeper insight on the survey questions than binary or Likert-scale questions could reveal. The qualitative interviews revealed tremendous weight on organizational dynamics among the superintendent, school board, teachers, parents, and community at large. In regards to single-subject acceleration, interviews highlighted that culture needed to support single-subject acceleration or student need for acceleration must be strongly evident. / Educational Administration

As many as 1.9 million sports-related concussions occur annually in youth sports in the United States (U.S.). Often considered a transient injury, research has begun to relate sports-related concussions to long-term neurodegeneration. Youth athletes are considered to be more vulnerable to concussion than their adult counterparts. The research presented in this dissertation was aimed at promoting player safety in youth football as it relates to concussion. Balance dysfunction is often cited as one of the most common symptoms associated with a concussion. Several postural control assessments were assessed in order to develop a youth-specific testing protocol. A cognitive, dual-task assessment was presented for clinician use in the management of sports-related concussion. On-field data collected from youth football players wearing instrumented helmets allowed for characterization of the biomechanics of head impacts and concussions for this population. A youth concussion risk function was developed using head impact data collected from youth football players with medically diagnosed concussions. The proposed testing standard for youth football helmets was assessed in the laboratory and related to on-field head impact data to determine how representative the standard is of youth football head impacts. Helmet safety standards and certifications operate on a pass-fail threshold that does not allow consumers to weigh the relative performance of helmets. A modification of the Summation of Tests for the Analysis of Risk (STAR) evaluation system was developed for youth football helmets. Data presented in this dissertation have direct application to the development of future helmet safety standards and potentially other safety applications as well. / Doctor of Philosophy / As many as 1.9 million sports-related concussions occur annually in youth sports in the United States (U.S.). Often considered a short-term injury, research has begun to relate sports-related concussions to long-term breakdowns in neurological processes. Youth athletes are considered to be more vulnerable to concussion than their adult counterparts. The research presented in this dissertation was aimed at informing player safety in youth football as it relates to concussion. Abnormal balance is often cited as one of the most common symptoms associated with a concussion. Several balance assessments were assessed in order to develop a youth-specific testing protocol. An assessment involving quiet standing while being subjected to a cognitive task was presented for clinician use in the management of sports-related concussion. On-field data collected from youth football players wearing instrumented helmets allowed for characterization of the biomechanics of head impacts and concussions for this youth population. A youth concussion risk function was developed that related linear and rotational head acceleration to risk of concussion. The proposed testing standard for youth football helmets was assessed in the laboratory and observed to assess the most severe head impacts a youth player may experience during participation in football. A modification of the Summation of Tests for the Analysis of Risk (STAR) evaluation system was developed for youth football helmets in order to give consumers more information about helmet performance beyond the pass-fail criteria of the helmet standards. Data presented in this dissertation have direct application to the development of future helmet safety standards and potentially other safety applications as well.

The research presented in this thesis focuses on head impact exposure in youth football. The on-field portion of this research investigated high magnitude head impacts that youth football players experience in games and practices. With previously validated data collection methods, linear and rotational head accelerations from head impacts were collected. Over the course of two seasons, 79 total player-seasons resulted in over 13,000 impacts. A small subset of these, 979 impacts exceeding 40 g, represented the focus of this research as these impacts pose the greatest risk of injury to individuals. Some tackling drills in practice were found to have higher acceleration severities than those observed in games. How practice activities are conducted also contributes towards the overall high magnitude head impact exposure for practice, not just the practice drill itself. Within games, players who are running backs and linebackers played most frequently and experienced higher magnitude impacts more often than their teammates. Data were also collected from all players off the field. Each player completed balance assessments at the beginning and end of the season to allow for comparison, even in absence of a clinically-diagnosed concussion. Current balance assessments were observed to fall short for detecting postural control differences in this youth population. Modifications to these assessments were recommended that might allow for further insights. Research presented in this thesis will inform youth football organizations as they continue to develop strategies to enhance player safety and mitigate head impact exposure. / Master of Science / The research presented in this thesis focuses on head impact exposure in youth football. The on-field portion of this research investigated high magnitude head impacts, which are associated with heightened risk of concussion, that youth football players experience in games and practices. With previously validated data collection methods, the specific causation for high risk head impacts in youth football practices and games was determined for the first time. In some practice drills, players were observed to hit harder and more frequently than they would in games. As youth practices occur more often than games do, limiting the time spent in these types of practice drills is recommended. How practice activities are conducted also contributes towards the overall high magnitude head impact exposure for practice, not just the practice drill itself. Events where players had the opportunity to get up to speed prior to impact were more likely to be high risk than events where players essentially impacted from a standstill. Data were also collected from all players off the field. Each player completed balance assessments at the beginning and end of the season to allow for comparison, even in absence of a clinically-diagnosed concussion. Current balance assessments were observed to fall short for detecting balance differences in this youth population. Modifications to these assessments were recommended that might allow for further insights. Research presented in this thesis will inform youth football organizations as they continue to develop strategies to enhance player safety and mitigate head impact exposure.

Laser plasma wakefield accelerators have seen tremendous progress in the last years, now capable of producing electron beams in the GeV energy range. The inherent few-femtoseconds short bunch duration of these accelerators leads to ultra-high peak-currents. Reducing the energy spread found in these accelerators, while scaling their output to hundreds of kiloampere peak current would stimulate the next generation of radiation sources covering high-field THz, high-brightness X-ray and -ray sources, compact free-electron lasers and laboratory-size beam-driven plasma accelerators. At such high currents, an accelerator operates in the beam loaded regime where the accelerating field is strongly modified by the self-fields of the injected bunch, potentially deteriorating key beam parameters. However, if appropriately controlled, the beam loading effect can be employed to improve the accelerator’s performance, specifically to reduce the energy spread. In this thesis the beam-loading effect is systematically studied at a quasi-monoenergetic nanocoulomb-class laser wakefield accelerator. For this purpose, a tailored scheme of the self-truncated ionisation injection process is introduced for the non-linear bubble regime. This scheme facilitates stable and tunable injection of high-charge electron bunches within a short and limited time-frame, ensuring low energy spread right after injection. Employing a three millimetres gas-jet acceleration medium and a moderate 150 TW short pulse laser system as driver, unprecedented charges of up to 0.5 nC within a quasi-monoenergetic peak and energies of ~0.5 GeV are achieved. Studying the beam loading mechanism, it is demonstrated that at the optimal loading condition, i.e. at a specific amount of injected charge, performance of the accelerator is optimised with a minimisation of the energy spread. At a relative energy spread of only 15%, the associated peak current is around 10 kA, while scaling this scheme to operate with a petawatt driver laser promises peak-currents up to 100 kA.

We report the status of two-color high intensity laser-plasma interaction experiments on the UT³ laser system at the University of Texas at Austin. After an outline of the experimental apparatus, an overview of the motivating theoretical work, and a characterization of the performance of our Chirped Pulse Raman Amplification system (CPRA) we report the status of our most recent experiment. We have attempted to seed the growth of the Raman Forward Scattering (RFS) instability in order to produce electrons at lower driving pulse power than is conventionally needed. We have been unsuccessful, and provide reasons why and recommendations for future modifications to the experimental apparatus. The most significant conclusion is that the CPRA system as it is now is not appropriate for this experiment because the observed RFS spectrum is at higher wavelength than our system. Possible future changes include either amplifying a separate barium nitrate sideband at 938 nm through the CPRA system or using a different Raman active medium after the main 800 nm UT³ pulse is compressed. The feasibility study of these possible modifications is not yet complete. / text

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