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- Genre: Masters Thesis
- Creators: Arizona State University
- Creators: Chakraborty, Bijeta
- Member of: ASU Electronic Theses and Dissertations
Description
Efficiency of components is an ever increasing area of importance to portable applications, where a finite battery means finite operating time. Higher efficiency devices need to be designed that don't compromise on the performance that the consumer has come to expect. Class D amplifiers deliver on the goal of increased efficiency, but at the cost of distortion. Class AB amplifiers have low efficiency, but high linearity. By modulating the supply voltage of a Class AB amplifier to make a Class H amplifier, the efficiency can increase while still maintaining the Class AB level of linearity. A 92dB Power Supply Rejection Ratio (PSRR) Class AB amplifier and a Class H amplifier were designed in a 0.24um process for portable audio applications. Using a multiphase buck converter increased the efficiency of the Class H amplifier while still maintaining a fast response time to respond to audio frequencies. The Class H amplifier had an efficiency above the Class AB amplifier by 5-7% from 5-30mW of output power without affecting the total harmonic distortion (THD) at the design specifications. The Class H amplifier design met all design specifications and showed performance comparable to the designed Class AB amplifier across 1kHz-20kHz and 0.01mW-30mW. The Class H design was able to output 30mW into 16Ohms without any increase in THD. This design shows that Class H amplifiers merit more research into their potential for increasing efficiency of audio amplifiers and that even simple designs can give significant increases in efficiency without compromising linearity.
ContributorsPeterson, Cory (Author) / Bakkaloglu, Bertan (Thesis advisor) / Barnaby, Hugh (Committee member) / Kiaei, Sayfe (Committee member) / Arizona State University (Publisher)
Created2013
Description
Although many studies have looked into the benefits and consequences of consuming breakfast, most have not looked into the unintended consequences of breakfast being served at school; specifically the consumption of an additional breakfast. This cross-sectional study investigated the prevalence and health related outcomes of the consumption of an additional breakfast at school amongst youth using a survey assessing possible predictors (i.e. parental education, morning activities, race), the ASA-kids 24-hr dietary recall, and height and weight measurements. A total of fifty-eight participants (aged 13.5±1.6 years; 55.2% male) were recruited at after school library programs and Boys and Girls Clubs in the Phoenix, Arizona Metro Area during 2014. The main outcomes measured were BMI percentile, total calories, iron, sodium, carbohydrates, added sugar, and fiber. In the study, the prevalence of consumption of an additional breakfast at school at least once a week or more was 32.7%. There were no significant differences between the consumption of an additional breakfast and not an additional breakfast amongst the main outcomes measures. The directionality of the relationship between the consumption of an additional breakfast and overweight/obesity amongst youth was inverse (OR = 0.309; p-value = 0.121), but this was not significant. This study found that the consumption of an additional breakfast at school is not contributing to overweight/obesity in youth, nor does it alter overall caloric and nutrient intake. School breakfast programs are important for providing breakfast and key nutrients to youth.
ContributorsSimpson, Julie (Author) / Bruening, Meg (Committee member) / Ohri-Vachaspati, Punam (Committee member) / Rider, Linda (Committee member) / Arizona State University (Publisher)
Created2015
Description
Thousands of children are being injured every day in bicycling accidents. Interventions, like Safe Routes to School, are currently in place to combat injury rates by providing programs to teach children safe biking behaviors. In order to develop effective behavioral change programs, behavior and the components of which it is composed must be understood. Attitudes, subjective norms, and self-efficacy are important predictors of intention to perform a behavior. The purpose of this study was to ascertain the extent to which attitude, subjective norms, self-efficacy, and bike rodeo participation explain third through eighth graders' intentions to bike safely. These constructs were tested using a survey research design in a purposive sample of fifty-seven third through eighth grade students in Safe Routes to School schools in the Southwest. Students took an online survey in the computer lab at their respective schools supervised by a teacher. The study found attitudes to be comprised of three factors: happy/safe, not afraid, and calm. Overall, the model explained approximately 71% of the variance in children's intentions to bike safely, R2=.749, Adjusted R2=.713, F(7, 49)=20.854, p<.01. The significant predictors were happy/safe attitudes, subjective norms, self-efficacy, and a quadratic self-efficacy term explaining 10% (p=.019), 28% (p<.01), 18% (p<.01), and 15% (p<.01) respectively. The results of the study can be used to create future and improve current bike safety interventions for children.
ContributorsPayton, Kayla G (Author) / Rodriguez, Ariel (Thesis advisor) / Tyrrell, Timothy (Committee member) / Maruyama, Kenichi (Committee member) / Arizona State University (Publisher)
Created2011
Description
Few measurement tools provide reliable, valid data on both children's emotional and behavioral engagement in school. The School Liking and Avoidance Questionnaire (SLAQ) is one such self-report measure developed to evaluate a child's degree of engagement in the school setting as it is manifest in a child's school liking and school avoidance. This study evaluated the SLAQ's dimensionality, reliability, and validity. Data were gathered on children from kindergarten through 6th grade (n=396). Participants reported on their school liking and avoidance in the spring of each school year. Scores consistently represented two distinct, yet related subscales (i.e., school liking and school avoidance) that were reliable and stable over time. Validation analyses provided some corroboration of the construct validity of the SLAQ subscales, but evidence of predictive validity was inconsistent with the hypothesized relations (i.e., early report of school liking and school avoidance did not predict later achievement outcomes). In sum, the findings from this study provide some support for the dimensionality, reliability, and validity of the SLAQ and suggest that it can be used for the assessment of young children's behavioral and emotional engagement in school.
ContributorsSmith, Jillian (Author) / Ladd, Gary W. (Thesis advisor) / Ladd, Becky (Committee member) / Thompson, Marilyn (Committee member) / Arizona State University (Publisher)
Created2011
Description
Class D Amplifiers are widely used in portable systems such as mobile phones to achieve high efficiency. The demands of portable electronics for low power consumption to extend battery life and reduce heat dissipation mandate efficient, high-performance audio amplifiers. The high efficiency of Class D amplifiers (CDAs) makes them particularly attractive for portable applications. The Digital class D amplifier is an interesting solution to increase the efficiency of embedded systems. However, this solution is not good enough in terms of PWM stage linearity and power supply rejection. An efficient control is needed to correct the error sources in order to get a high fidelity sound quality in the whole audio range of frequencies. A fundamental analysis on various error sources due to non idealities in the power stage have been discussed here with key focus on Power supply perturbations driving the Power stage of a Class D Audio Amplifier. Two types of closed loop Digital Class D architecture for PSRR improvement have been proposed and modeled. Double sided uniform sampling modulation has been used. One of the architecture uses feedback around the power stage and the second architecture uses feedback into digital domain. Simulation & experimental results confirm that the closed loop PSRR & PS-IMD improve by around 30-40 dB and 25 dB respectively.
ContributorsChakraborty, Bijeta (Author) / Bakkaloglu, Bertan (Thesis advisor) / Garrity, Douglas (Committee member) / Ozev, Sule (Committee member) / Arizona State University (Publisher)
Created2012
Description
Salad bars are promoted as a means to increase fruit and vegetable consumption among school-age children; however, no study has assessed barriers to having salad bars. Further, it is not known if barriers differ across school level. This cross-sectional study investigated the barriers to having salad bars across school level among schools without salad bars in Arizona (n=177). Multivariate binominal regression models were used to determine differences between the barriers and school level, adjusting for years at current job, enrollment of school, free-reduced eligibility rate and district level clustering. The top five barriers were not enough staff (51.4%), lack of space for salad bars (49.7%), food waste concerns (37.9%), sanitation/food safety concerns (31.3%), and time to get through the lines (28.3%) Adjusted analyses indicated two significant differences between barriers across school level: time to get through lines (p=0.040) and outside caterer/vendor (p=0.018) with time to get through lines reported more often by elementary and middle school nutrition managers and outside caterer/vendor reported most often by high school nutrition managers. There were several key barriers reported and results indicate that having an outside vendor/caterer for their meal programs and time to get through the service lines varied across school level. High schools report a higher percent of the barrier outside caterer/vendors and elementary and middle schools report a higher percent of the barrier time to get through the lines. Results indicate that research determining the approximate time it takes students to get through salad bar lines will need to be considered. More research is needed to determine if the barrier time to get through the service lines is due to selection of food items or if it is due to the enrollment size of the lunch period. Future research interventions may consider investigating food safety and sanitation concerns of middle school nutrition managers. Findings may be used to guide ways to decrease barriers in schools without salad bars.
ContributorsKebric, Kelsey (Author) / Bruening, Meg (Thesis advisor) / Ohri-Vachaspati, Punam (Committee member) / Adams, Marc (Committee member) / Arizona State University (Publisher)
Created2016
Description
Despite the literature suggesting that fruits and vegetables (F&V) can have a protective outcome against overweight, obesity and chronic diseases, consumption is still inadequate. In order to address under consumption of F&V among children, schools have become a platform for a variety of food programs. The Fresh Fruit and Vegetable Program (FFVP), a United States Department of Agriculture (USDA) initiative, aims to increase exposure and consumption of F&V in low-income school children by providing F&V snacks. Participation in FFVP has been associated with higher preference and consumption of F&V and research also suggests that the program has the potential to decrease rates of overweight and obesity. The benefits of this program have been found to extend outside of the school setting, with higher requests for F&V at home and at the grocery store. This study aims to explore how children’s participation in the FFVP influences home food environments and shopping practices through qualitative analysis focus group data. Four focus groups were held with parents (n=25) from three FFVP participating schools. The data was analyzed using an inductive thematic analysis approach to find themes within the discussions. The findings were grouped into three categories: General Perceptions of FFVP, Impact of FFVP on the Home Food Environment, and Impact of FFVP on Shopping Practices. For General Perceptions of FFVP, themes were: Children learn about and enjoy F&V, awareness of farm to school programs, and children make healthier choices. Impact of FFVP on the Home Food Environment included the themes: Choosing heathier foods and snacks, parent F&V behaviors, children request F&V at home, and children talk about or bring F&V home. Finally, Impact of FFVP on Shopping Practices included the themes: children’s involvement in shopping, children request to buy F&V, children request non-produce items, and parents decline or limit unhealthy requests. This qualitative study provides valuable insights about how FFVP participation influences child and family behaviors towards F&V at home and in the grocery store. School food programs, such as the FFVP, have a positive influence on F&V related behaviors among children and should be continued and expanded.
ContributorsAcosta Ortiz, Marina (Author) / Ohri-Vachaspati, Punam (Thesis advisor) / DeWeese, Robin (Thesis advisor) / Gruner, Jessie (Committee member) / Arizona State University (Publisher)
Created2018
Description
Background: Healthy eating plays critical roles in the prevention of many chronic diseases, but there are many barriers in life that prevent people from adopting and maintaining healthy diets. Thus, identifications of barriers that people perceive they have in trying to eat healthy can guide the strategies for dietary behavior change interventions by taking account of the barriers. Objective: The purpose of this study was to identify and quantify the perceived barriers to healthy eating (PBHE), to investigate the relationship between socioeconomic factors and PBHE, and to explore the associations between PBHE and dietary intake among parents of elementary-school aged children living in South Phoenix, AZ. Methods: Socioeconomic factors and PBHEs were obtained via survey and diet was assessed by two interviewer-assisted 24 h diet recalls. The associations between employment and PBHEs, education and PBHEs, and household monthly income and PBHEs were analyzed by Mann-Whitney Test, Kruskal Wallis Test, and Spearman’s correlation test, respectively. The relationship between PBHEs and dietary intake were analyzed by Spearman’s correlation test. Linear regression was used to assess the associations between total PBHE, and dietary intake (including added sugar, fruit and vegetable), adjusted by covariates (including socioeconomic status, birth country, age and gender). Results: Of 149 participants who completed the survey (mean age = 38.47±7.08 y), 136 completed the 24 h diet recalls. The mean reported total, social support, emotions and daily mechanics PBHE scores were 2.63±0.91, 2.52±1.16, 2.71±1.06, and 2.58±0.95, respectively, out of a 5-point scale. Daily fruit, vegetable, sugar-sweetened beverage, sweetened foods, and added sugar intake were reported as 1.66±1.56 servings, 2.45±1.43 servings, 1.19±1.30 servings, 2.02±2.12 servings and 49.93±31.17 g, respectively. Employment status was significantly associated with total PBHE (Z = -2.28, p=0.023), and support PBHE (Z = -2.623, p=0.009). Education was significantly related to total PBHE (χ2 = -7.987, p=0.046), and daily mechanics PBHE (χ2= 11.735, p=0.008). Household monthly income levels were significantly correlated to daily mechanics PBHE (r = -0.265, p=0.005). Added sugar was positively correlated with total PBHE (r=0.202, p=0.020), emotions PBHE (r=0.239, p=0.006), and daily mechanics PBHE (r=0.179, p=0.040). Sugar sweetened beverage intake was significantly related to emotions PBHE (r=0.183, p=0.035). When adjusting for socioeconomic factors in the regression analysis, there was no significant association between PBHE and diet intake. Conclusion: Overall, results suggest PBHEs listed in this study are mainly associated with socioeconomic factors, but they are not related to diet intake. Future studies will focus on the precise role of overcoming some identified barriers in improving healthy eating behaviors, and the causality between barriers and healthy eating.
ContributorsQiu, Chongying (Author) / Vega-Lopez, Sonia (Thesis advisor) / Crespo, Noe (Committee member) / Shepard, Christina (Committee member) / Arizona State University (Publisher)
Created2018
Description
In this thesis, a digital input class D audio amplifier system which has the ability
to reject the power supply noise and nonlinearly of the output stage is presented. The main digital class D feed-forward path is using the fully-digital sigma-delta PWM open loop topology. Feedback loop is used to suppress the power supply noise and harmonic distortions. The design is using global foundry 0.18um technology.
Based on simulation, the power supply rejection at 200Hz is about -49dB with
81dB dynamic range and -70dB THD+N. The full scale output power can reach as high as 27mW and still keep minimum -68dB THD+N. The system efficiency at full scale is about 82%.
to reject the power supply noise and nonlinearly of the output stage is presented. The main digital class D feed-forward path is using the fully-digital sigma-delta PWM open loop topology. Feedback loop is used to suppress the power supply noise and harmonic distortions. The design is using global foundry 0.18um technology.
Based on simulation, the power supply rejection at 200Hz is about -49dB with
81dB dynamic range and -70dB THD+N. The full scale output power can reach as high as 27mW and still keep minimum -68dB THD+N. The system efficiency at full scale is about 82%.
ContributorsBai, Jing (Author) / Bakkaloglu, Bertan (Thesis advisor) / Arizona State University (Publisher)
Created2015
Description
The purpose of this study was to investigate the role teacher-relational bullying schemas may have in influencing the likelihood of youth seeking teachers' assistance. The first goal of the study was to assess whether supportive and helpful teacher-responses to bullying schemas (TRBS) were associated with greater likelihood of involving teachers, and unhelpful TRBSs was related to lower likelihood of teacher seeking coping. The second goal was to examine possible differences in TRBS and likelihood of seeking help based on sex, grade, personal behavioral blame, personal aggression, and victimization. Towards these aims, data were gathered from 320 fourth and sixth grade students (152 boys; 168 girls) in the fall and spring of the academic year. MANOVA analyses revealed sex and grade differences, such as sixth grade boys were least likely to tell their teacher and most likely to blame their own behavior for being bullied than any other group. Results from a series of regression analyses found personal behavior blame and peer-directed aggression was related with less likelihood of telling. In addition, the association between parents or principal TRBS and telling the teacher was moderated by personal behavioral blame. Moreover, punishment predicted lower probability of telling concurrently and longitudinally.
ContributorsCortes, Khaerannisa (Author) / Kochenderfer-Ladd, Becky (Thesis advisor) / Ladd, Gary W. (Committee member) / Eggum, Natalie D. (Committee member) / Arizona State University (Publisher)
Created2013