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Tesi sul tema "Multilevel analysis"
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1
Venkatasubramanian, S. "Illiteracy in India : a multilevel analysis". Thesis, University of Portsmouth, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.302445.
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Sy, Oumar Sekou. "Multilevel mediation analysis estimation and applications /". Search for this dissertation online, 2004. http://wwwlib.umi.com/cr/ksu/main.
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Woodhouse, Geoffrey M. "Adjustment for measurement error in multilevel analysis". Thesis, University College London (University of London), 1998. http://discovery.ucl.ac.uk/10019113/.
Testo completoAbstract (sommario):
Measurements in educational research are often subject to error. Where it is desired to base conclusions on underlying characteristics rather than on the raw measurements of them, it is necessary to adjust for measurement error in the modelling process. In this thesis it is shown how the classical model for measurement error may be extended to model the more complex structures of error variance and covariance that typically occur in multilevel models, particularly multivariate multilevel models, with continuous response. For these models parameter estimators are derived, with adjustment based on prior values of the measurement error variances and covariances among the response and explanatory variables. A straightforward method of specifring these prior values is presented. In simulations using data with known characteristics the new procedure is shown to be effective in reducing the biases in parameter estimates that result from unadjusted estimation. Improved estimates of the standard errors also are demonstrated. In particular, random coefficients of variables with error are successfully estimated. The estimation procedure is then used in a two-level analysis of an educational data set. It is shown how estimates and conclusions can vary, depending on the degree of measurement error that is assumed to exist in explanatory variables at level 1 and level 2. The importance of obtaining satisfactory prior estimates of measurement error variances and covariances, and of correctly adjusting for them during analysis, is demonstrated.
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Wong, Chun-mei May. "Multilevel models for survival analysis in dental research". Click to view the E-thesis via HKUTO, 2005. http://sunzi.lib.hku.hk/hkuto/record/B3637216X.
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Pham, Thanh Vinh. "The performance of Multilevel Structural Equation Modeling (MSEM) in comparison to Multilevel Modeling (MLM) in multilevel mediation analysis with non-normal data". Scholar Commons, 2017. http://scholarcommons.usf.edu/etd/7077.
Testo completoAbstract (sommario):
The mediation analysis has been used to test if the effect of one variable on another variable is mediated by the third variable. The mediation analysis answers a question of how a predictor influences an outcome variable. Such information helps to gain understanding of mechanism underlying the variation of the outcome. When the mediation analysis is conducted on hierarchical data, the structure of data needs to be taken into account. Krull and MacKinnon (1999) recommended using Multilevel Modeling (MLM) with nested data and showed that the MLM approach has more power and flexibility over the standard Ordinary Least Squares (OLS) approach in multilevel data. However the MLM mediation model still has some limitations such as incapability of analyzing outcome variables measured at the upper level. Preacher, Zyphur, and Zhang (2010) proposed that the Multilevel Structural Equation Modeling (MSEM) will overcome the limitation of MLM approach in multilevel mediation analysis. The purpose of this study was to examine the performance of the MSEM approach on non-normal hierarchical data. This study also aimed to compare the MSEM method with the MLM method proposed by MacKinnon (2008) and Zhang, Zyphur, and Preacher (2009). The study focused on the null hypothesis testing which were presented by Type I error, statistical power, and convergence rate. Using Monte Carlo method, this study systematically investigates the effect of several factors on the performance of the MSEM and MLM methods. Designed factors considered were: the magnitude of the population indirect effect, the population distribution shape, sample size at level 1 and level 2, and the intra-class correlation (ICC) level. The results of this study showed no significant effect of the degree of non-normality on any performance criteria of either MSEM or MLM models. While the Type I error rates of the MLM model reached the expected alpha level as the group number was 300 or higher, the MSEM model showed very conservative performance in term of controlling for the Type I error with the rejection rates of null conditions were zero or closed to zero across all conditions. It was evident that the MLM model outperformed the MSEM model in term of power for most simulated conditions. Among the simulation factors examined in this dissertation, the mediation effect size emerged as the most important one since it is highly associated with each of the considered performance criteria. This study also supported the finding of previous studies (Preacher, Zhang, & Zyphur, 2011; Zhang, 2005) about the relationship between sample size, especially the number of group, and the performance of either the MLM or MSEM models. The accuracy and precision of the MLM and MSEM methods were also investigated partially in this study in term of relative bias and confidence interval (CI) width. The MSEM model outperformed the MLM model in term of relative bias while the MLM model had better CI width than the MSEM model. Sample size, effect size, and ICC value were the factors that significantly associate with the performance of these methods in term of relative bias and CI width.
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Feng, Yuanjian. "Detection and Characterization of Multilevel Genomic Patterns". Diss., Virginia Tech, 2010. http://hdl.handle.net/10919/38577.
Testo completoAbstract (sommario):
DNA microarray has become a powerful tool in genetics, molecular biology, and biomedical research. DNA microarray can be used for measuring the genotypes, structural changes, and gene expressions of human genomes. Detection and characterization of multilevel, high-throughput microarray genomic data pose new challenges to statistical pattern recognition and machine learning research. In this dissertation, we propose novel computational methods for analyzing DNA copy number changes and learning the trees of phenotypes using DNA microarray data.
DNA copy number change is an important form of structural variations in human genomes. The copy number signals measured by high-density DNA microarrays usually have low signal-to-noise ratios and complex patterns due to inhomogeneous composition of tissue samples. We propose a robust detection method for extracting copy number changes in a single signal profile and consensus copy number changes in the signal profiles of a population. We adapt a solution-path algorithm to efficiently solve the optimization problems associated with the proposed method. We tested the proposed method on both simulation and real CGH and SNP microarray datasets, and observed competitively improved performance as compared to several widely-adopted copy number change detection methods. We also propose a chromosome instability measure to summarize the extracted copy number changes for assessing chromosomal instabilities of tumor genomes. The proposed measure demonstrates distinct patterns between different subtypes of ovarian serous carcinomas and normal samples.
Among active research on complex human diseases using genomic data, little effort and progress have been made in discovering the relational structural information embedded in the molecular data. We propose two stability analysis based methods to learn stable and highly resolved trees of phenotypes using microarray gene expression data of heterogeneous diseases. In the first method, we use a hierarchical, divisive visualization approach to explore the tree of phenotypes and a leave-one-out cross validation to select stable tree structures. In the second method, we propose a node bandwidth constraint to construct stable trees that can balance the descriptive power and reproducibility of tree structures. Using a top-down merging procedure, we modify the binary tree structures learned by hierarchical group clustering methods to achieve a given node bandwidth. We use a bootstrap based stability analysis to select stable tree structures under different node bandwidth constraints. The experimental results on two microarray gene expression datasets of human diseases show that the proposed methods can discover stable trees of phenotypes that reveal the relationships between multiple diseases with biological plausibility.Ph. D.
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Neilson, Lisa Anne. "Social capital and political consumerism: a multilevel analysis". Connect to resource, 2006. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1156951934.
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Hesari, Saeed Aroni. "A multilevel superelement substructuring for boxlike caisson analysis". Thesis, University of Ottawa (Canada), 1994. http://hdl.handle.net/10393/6540.
Testo completoAbstract (sommario):
A multilevel superelement substructuring approach for linear-static analysis of rectangular boxlike caissons is developed. The structure is considered as an assemblage of superelements in three substructural levels. These are panel, layer, and caisson superelements. Each superelement substructure is derived by applying the principle of static condensation. Rectangular 9-node flat shell elements, which are composed of membrane stress and Mindlin plate bending elements, are assembled together to make the stiffness and load matrices of each panel substructure. Every panel substructure is condensed to a panel superelement. Then all of them in a layer are assembled together and condensed to layer superelement. Finally, the later superelement(s) are assembled and condensed to yield to caisson superelement. After the assembling process, equilibrium equations are solved for the caisson superelement. Then a multilevel recovery process, with an inverse sequence of assembling one, gives the internal degrees of freedom for caisson, layer, and panel superelements, respectively. Finding all displacements, one can finally compute internal forces for every individual flat shell element. This special purpose superelement substructure method provides considerable efficiency in practical analysis and design of boxlike caissons. Based on this approach, a computer program is developed which takes the most advantage from the repetition of similar individual elements and panels. Several numerical examples are solved indicating good agreement with other analytical or numerical methods and proper convergency for design purposes.
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Shumka, Ellen. "The social facilitation of bullying : a multilevel analysis". Thesis, University of British Columbia, 2012. http://hdl.handle.net/2429/43517.
Testo completoAbstract (sommario):
It is well documented that bullying is harmful and relatively common among children and adolescents. Children report understanding that bullying is wrong, yet bullying continues to be a persistent problem in schools. The goal of the present study was to examine whether children’s bullying behaviours were socially facilitated by group norms and beliefs. Children’s justifications and rationalizations for engaging in wrongful behaviour, a phenomenon referred to as moral disengagement (MD), have been linked to bullying behaviour at the individual level. Specifically, children who report engaging in bulling tend to report more MD than those who do not. Only one study to date, however, has examined MD at the group level and results indicated that group levels of MD, over and above individual levels, predicted engagement in bullying. Group level processes, especially group norms supporting aggression and bullying, have also been linked to greater bullying perpetration. The current investigation extended this research by examining how group levels of MD and normative beliefs about deviancy influenced bullying using two unique samples of schoolchildren. The first study examined the influence of two group level variables (MD and normative beliefs about deviancy) on bullying over a school year in a sample of 376 students (surveyed in Grade 5 and 6) from 38 schools in Southern Ontario. The second study examined the influence of group MD on 1128 students across 74 classrooms in Vancouver, British Columbia. Results across both studies did not support the hypothesis that group levels of MD (Study 1 & 2) and normative beliefs about deviancy (Study 1 only) influenced engagement in bullying. The findings suggest that further investigations are required in order to better understand the effects group level MD and normative beliefs on bullying behaviour.
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Wong, Chun-mei May, e 王春美. "Multilevel models for survival analysis in dental research". Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2005. http://hub.hku.hk/bib/B3637216X.
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Steele, Fiona Alison. "Multilevel analysis of health and family planning data". Thesis, University of Southampton, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.319290.
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Johns, Robert. "Therapist effects over time : a multilevel modelling analysis". Thesis, University of Sheffield, 2017. http://etheses.whiterose.ac.uk/18214/.
Testo completoAbstract (sommario):
Therapists are differentially effective, a concept that has been termed ‘therapist effects’. Research has shown that therapist effects account for around 5% of the variability in outcomes of psychological therapy. However, there has been little research investigating whether such therapist effects are stable over time. A systematic review was conducted to provide a contemporary synopsis of therapist effects research. The review comprised 21 studies that focussed on therapist effects for outcomes, extending the most recent review of Baldwin and Imel (2013). Results found an average therapist effect of 5% which was in common with previous findings. New research areas included low intensity treatment settings and comparisons of different outcome measures. In order to investigate the stability of therapist effects over time, the research report analysed data from steps 2 (low intensity) and 3 (high intensity) of an Improving Access to Psychological Therapies service, comprising 12,949 patients and 141 therapists. Multilevel modelling was used to determine the therapist effect of the whole service over 40 months. Then, for five equal time periods, Markov chain Monte Carlo procedures compared therapist effects over time. Results found an overall therapist effect of 4.9% with no statistical difference between time periods. Therapist effects for step 2 of 2.9% and for step 3 of 4.9% were found. However, such effects were not statistically stable over time. Further studies with higher patient and therapist sample sizes are recommended.
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Steffens, Niklas K., Meir Shemla, Jürgen Wegge e Stefan Diestel. "Organizational Tenure and Employee Performance: A Multilevel Analysis". Sage, 2014. https://tud.qucosa.de/id/qucosa%3A35549.
Testo completoAbstract (sommario):
Previous research has investigated the relationship between organizational tenure and performance by focusing primarily on organizational tenure of the individual employee. We propose that this approach is limited because organizational tenure should be conceptualized as relating to multiple entities including teams and their leaders. As predicted, analysis of two objective performance indicators of 1,753 employees working with 250 leaders of natural work teams in a financial services company revealed that, beyond employee organizational tenure, team leader organizational tenure and team organizational tenure diversity had positive incremental effects on employee performance. Moreover, the positive impact of employee organizational tenure was less pronounced in teams with high rather than low tenure diversity. Our findings suggest that organizations’ capacity to promote performance will be limited if they focus on organizational tenure of an individual, while neglecting the ways in which performance is shaped by organizational tenure related to multiple entities within a team.
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Lee, Ji-Youn. "A Multilevel Analysis of Young Adult Migration, 1980-1998". DigitalCommons@USU, 2002. https://digitalcommons.usu.edu/etd/4289.
Testo completoAbstract (sommario):
The primary objective of this research was to investigate the propensity to migrate the destination choices of young adults, and the importance of individual, household, and community characteristics in these migration choices. Using cohort data from the National Longitudinal Survey ofYouth79 from 1980 to 1998, this study specifies the set of individual-, household-, and community-level of determinants on migrat ion and then incorporates these variables in multivariate analyses to test their direct and relative effects on the migratory behavior of young adult groups. A Cox proportional hazard analysis suggests that among three levels of factors, individual characteristics are the most important determinants of migration, but the migratory behavior is more fully explained by multilevel variables rather than a single-level variable.
This research had three foci within the primary objective. First, at the individual level, this study is tbe first step in research that intended to suggest the usefulness of status inconsistency arguments on migration studies. Findings of tbe research indicate that underrewarded individuals are more likely to migrate than those who have balanced status, while overrewarded individuals are less likely to migrate than those who have balanced status.
Second, at the household-level investigation, this research focused on the effects of relative conjugal power between husbands and wives on migration. Results suggest that differences in relative power between husbands and wives has only minor effects on migration and the direction of migration, but the quantitative effects of relative power variables are greater for wives than for husbands.
Third, at the community-level investigation, this study focused on analyzing the interaction between the residential mobility of individuals and characteristics of the residential areas where they are located. The migration propensity of the most mobile types of people (the more educated whites) has responded more to differences in community characteristics than that of the least mobile types of people (the less educated blacks).
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Xia, Yuan. "Multilevel Monte Carlo for jump processes". Thesis, University of Oxford, 2013. http://ora.ox.ac.uk/objects/uuid:7bc8e98a-0216-4551-a1f3-1b318e514ee8.
Testo completoAbstract (sommario):
This thesis consists of two parts. The first part (Chapters 2-4) considers multilevel Monte Carlo for option pricing in finite activity jump-diffusion models. We use a jump-adapted Milstein discretisation for constant rate cases and with the thinning method for bounded state-dependent rate cases. Multilevel Monte Carlo estimators are constructed for Asian, lookback, barrier and digital options. The computational efficiency is numerically demonstrated and analytically justified. The second part (Chapter 5) deals with option pricing problems in exponential Lévy models where the increments of the underlying process can be directly simulated. We discuss several examples: Variance Gamma, Normal Inverse Gaussian and alpha-stable processes and present numerical experiments of multilevel Monte Carlo for Asian, lookback, barrier options, where the running maximum of the Lévy process involved in lookback and barrier payoffs is approximated using discretely monitored maximum. To analytically verify the computational complexity of multilevel method, we also prove some upper bounds on Lp convergence rate of discretely monitored error for a broad class of Lévy processes.
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Galliat, Tobias. "Adaptive multilevel cluster analysis by self organizing box maps". [S.l.] : [s.n.], 2002. http://www.diss.fu-berlin.de/2002/125/index.html.
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Sanders, Elizabeth A. "Multilevel Analysis Methods for Partially Nested Cluster Randomized Trials". UNIVERSITY OF WASHINGTON, 2012. http://pqdtopen.proquest.com/#viewpdf?dispub=3452760.
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Xi, Guoliang. "Income inequality and health in Ontario: A multilevel analysis". Thesis, University of Ottawa (Canada), 2003. http://hdl.handle.net/10393/26350.
Testo completoAbstract (sommario):
Objectives. To examine the association of income inequality at the public health unit level with individual health in Ontario.
Design. Cross sectional multilevel study. Individual-level data drawn from 30,939 respondents in Ontario Health Survey 1996--1997. Median area income and income inequality calculated from 1996 census data, the latter using Gini coefficient. Setting. 37 public health units in Ontario.
Subjects. Ontario residents aged 25 years or older.
Main outcome measures. Self-rated health status and the Health Utility Index. Results Controlling for individual-level factors, respondents living in public health units in the highest income inequality tercile had odds ratios of 1.25 (95% CI 1.10--1.42) for fair/poor self-rated health, and 1.14 (95% CI 1.04--1.25) for a Health Utility Index score <1, compared with people living in public health units in the lowest tercile. Controlling further for median area income had little effect on the association.
Conclusions. Income inequality was significantly associated with individual health status independent of individual income at public health unit level in Ontario.
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Driscoll, Ira, e University of Lethbridge Faculty of Arts and Science. "The aging hippocampus : a multilevel analysis in the rat". Thesis, Lethbridge, Alta. : University of Lethbridge, Faculty of Arts and Science, 2005, 2005. http://hdl.handle.net/10133/12.
Testo completoAbstract (sommario):
The purpose of the current thesis was twofold: (1) to examine various factors that might be contributing to age-related learning and memory deficits specifically related to the hippocampus, and (2) to validate our rat model of aging, employing a multilevel analysis. We found age-related deficits on both spatial and non-spatial hippocampus-dependent taks that were accompanied by structural alterations observed in vivo (volune, but not neuronal metabolic function) and post mortem (neuronal density and neurogenesis, but not synaptic or mitochondrial density). Furthermore, our results suggest that the observed hippocampal structural changes, named decreased volume and neurogenesis, predict learning and memory deficits, and both can be accounted for by neurogenic reduction. In addition, the above-mentioned pattern of age-related deficits closely resembles that seen in humans, suggesting the present rat version of aging to be a very useful model for investigating hippocampal aging in humans.iii, 236 leaves : ill. (some col.) ; 29 cm.
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Cheung, Ka-yan, e 張嘉茵. "Multilevel modeling for the analysis of longitudinal periodontal data". Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2011. http://hub.hku.hk/bib/B46605496.
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Ruiz, Amador Dolly Natalia. "Multilevel aging phenomena analysis in complex ultimate CMOS designs". Thesis, Grenoble, 2012. http://www.theses.fr/2012GRENT002/document.
Testo completoAbstract (sommario):
L'auteur n'a pas fourni de résumé en françaisIntegrated circuits evolution is driven by the trend of increasing operating frequencies and downscaling of the device size, while embedding more and more complex functionalities in a single chip. However, the continuation of the device-scaling race generates a number of technology challenges. For instance, the downscaling of transistor channel lengths induce short-channel effects (drain-induced barrier lowering and punch-through phenomena); high electric field in the devices tend to increase Hot electron effect (or Hot Carrier) and Oxide Dielectric Breakdown; higher temperatures in IC products generates an increase of the Negative Bias Temperature Instability (NBTI) effect on pMOS devices. Today, it is considered that the above reliability mechanisms are ones of the main causes of circuit degradation performance in the field. This dissertation will address the Hot Carrier (HC) and NBTI impacts on CMOS product electrical performances. A CAD bottom-up approach will be proposed and analyzed, based on the Design–in Reliability (DiR) methodology. With this purpose, a detailed analysis of the NBTI and the HC behaviours and their impact at different abstraction level is provided throughout this thesis. First, a physical framework presenting the NBTI and the HC mechanisms is given, focusing on electrical parameters weakening of nMOS and pMOS transistors. Moreover, the main analytical HC and NBTI degradation models are treated in details. In the second part, the delay degradation of digital standard cells due to NBTI, HCI is shown; an in-depth electrical CAD analysis illustrates the combined effects of design parameters and HCI/NBTI on the timing performance of standard cells. Additionally, a gate level approach is developed, in which HC and NBTI mechanisms are individually addressed. The consequences of the degradation at system level are presented in the third part of the thesis. With this objective, data extracted from silicon measures are compared against CAD estimations on two complexes IPs fabricated on STCMOS 45nm technologies. It is expected that the findings of this thesis highly contribute to the understanding of the NBTI and HC reliability wearout mechanisms at the system level.STAR
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Mahoe, Rochelle A. "A multilevel analysis of student persistence in high school". Thesis, University of Hawaii at Manoa, 2003. http://proquest.umi.com/pqdweb?index=0&did=765033461&SrchMode=1&sid=2&Fmt=2&VInst=PROD&VType=PQD&RQT=309&VName=PQD&TS=1233163560&clientId=23440.
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Farrell, Patricio. "Multilevel collocation with radial basis functions". Thesis, University of Oxford, 2014. https://ora.ox.ac.uk/objects/uuid:9fd99f0f-2556-41eb-8bcd-5b9256296a17.
Testo completoAbstract (sommario):
In this thesis, we analyse multilevel collocation methods involving compactly supported radial basis functions. We focus on linear second-order elliptic bound- ary value problems as well as Darcy's problem. While in the former case we use scalar-valued positive definite functions for constructing multilevel approximants, in the latter case we use matrix-valued functions that are automatically divergence-free. A similar result is presented for interpolating divergence-free vector fields. Even though it had been observed more than a decade ago that the stationary setting, i.e. when the support radii shrink as fast as the mesh norm, does not lead to convergence, it was up to now an open question how the support radii should depend on the mesh norm to ensure convergence. For each case above, we answer this question here thoroughly. Furthermore, we analyse and improve the stability of the linear systems. And lastly, we examine the case when the approximant does not lie in the same space as the solution to the PDE.
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Patil, Sandeep. "Analysis and Loss Estimation of Different Multilevel DC-DC Converter Modulesand Different Proposed Multilevel DC-DC Converter Systems". University of Toledo / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1396628125.
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Khatiwada, Aastha. "Multilevel Models for Longitudinal Data". Digital Commons @ East Tennessee State University, 2016. https://dc.etsu.edu/etd/3090.
Testo completoAbstract (sommario):
Longitudinal data arise when individuals are measured several times during an ob- servation period and thus the data for each individual are not independent. There are several ways of analyzing longitudinal data when different treatments are com- pared. Multilevel models are used to analyze data that are clustered in some way. In this work, multilevel models are used to analyze longitudinal data from a case study. Results from other more commonly used methods are compared to multilevel models. Also, comparison in output between two software, SAS and R, is done. Finally a method consisting of fitting individual models for each individual and then doing ANOVA type analysis on the estimated parameters of the individual models is proposed and its power for different sample sizes and effect sizes is studied by simulation.
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Marquez, Damian Jose Ignacio. "Multilevel acceleration of neutron transport calculations". Thesis, Atlanta, Ga. : Georgia Institute of Technology, 2007. http://hdl.handle.net/1853/19731.
Testo completoAbstract (sommario):
Thesis (M.S.)--Nuclear and Radiological Engineering, Georgia Institute of Technology, 2008.Committee Chair: Stacey, Weston M.; Committee Co-Chair: de Oliveira, Cassiano R.E.; Committee Member: Hertel, Nolan; Committee Member: van Rooijen, Wilfred F.G.
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Bråthen, Eystein Widar. "Multilevel Analysis Applied to Fetal Growth Data with Missing Values". Thesis, Norwegian University of Science and Technology, Department of Mathematical Sciences, 2006. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-9306.
Testo completoAbstract (sommario):
Intrauterine growth retardation means that the growth of a fetus is restricted as compared with its biological growth potential. This contributes to an increased risk for illnesses or death of the newborn. Therefore it is important to characterize, detect and to follow up clinically any suspected or confirmed growth restriction of the fetus. In this master thesis we aim to describe the course of growth during the pregnancy based on repeated ultrasound measurements and study how the growth depends on different background variables of the mother in analyzing the data from the SGA (small-for-getational age) - project. The SGA-project contains data from 5722 pregnancies that took place in Trondheim, Bergen and Uppsala from 1986-1988, named The Scandinavian SGA-studies. In this thesis we have confined ourselves to a random sample of 561 pregnancies. A problem with many studies of this kind is that the data set contain missing values. In the SGA data set under study there were missing values from one or more of the ultrasound measurements for approximately 40% of the women. Until recently, the most popular used missing-data method available has been complete case analysis, where only subjects with a complete set of data are being analysed. There exist a number of alternative ways of dealing with missing data. Bayesian multiple imputation (MI) has become a highly useful paradigm for handling missing values in many settings. In this paper we compare 2 general approaches that come highly recommended: Bayesian MI and maximum likelihood (ML), and point out some of its unique features. One aspect of MI is the separation of the imputation phase from the analysis phase. It can be advantageous in settings where the models underlying the two phases are different. We have used a multilevel analysis for the course of fetal growth. Multilevel analysis has a hierarchic structure with two levels of variation: variation between points in time for the same fetus (level 1) and variation between fetuses (level 2). Level 1 is modeled by regression analysis with gestational age as the independent variable and level 2 is modeled by regarding the regression coefficients as stochastic with a set of (non directly observed) values for individual fetuses and some background variables of the mother. The model we ended up with describes the devolopment in time of the abdominal diameter (MAD) of the fetus. It had several ``significant'' covariates (p-value < 0.05), they were gestational age (Time-variable), the body-mass index (BMI), age of the mother, an index varible wich tells if a mother has given birth to a low-weight child in an earlier pregnancy and the gender of the fetus. The last covariate was not significant in a strictly mathematical way, but since it is well known that the gender of the fetus has an important effect we included gender in the model as well. When we used the MI-method on the random sample (561) with missing values, the estimated standard deviations of the parameters have been reduced compared to those obtained from the complete case analysis. There were not a significant change in the parameter estimates except for the coefficient for the age of the mother. We also have found a procedure to verify if the MI-method gives us reasonable imputed values for the missing values by following the MCAR-procedure defined in Section 6. Another interesting observation from a simulation study is that estimates of the coefficients for variables used to generate the MAR and MNAR missing mechanism are ``suffering'' because they tend to be more biased compared to the values from the complete case analysis on the random sample (320) than the other variables. According to the MAR assumption such a procedure should give unbiased parameter estimates. {Key Words: Longitudinal data, multilevel analysis, missing data, multiple imputation (MI), Gibbs sampling, linear mixed-effects model and maximum likelihood (ML)-procedure.
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Högberg, Björn. "Ageing, health inequalities and welfare state regimes – a multilevel analysis". Thesis, Umeå universitet, Sociologiska institutionen, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-100401.
Testo completoAbstract (sommario):
The paper studies class inequalities in health over the ageing process in a comparative perspective. It investigates if health inequalities among the elderly vary between European welfare state regimes, and if this variation is age-dependent. Previous comparative research on health inequalities have largely failed to take age and ageing into account, and have not investigated whether cross-country variation in health inequalities might differ for different age categories. Since the elderly belong to the demographic category most dependent on welfare policies, an ageing perspective is warranted. The study combines fives data rounds (2002 to 2010) from the European Social Survey. Multilevel techniques are used, and the analysis is stratified by age, comparing the 50-64 year olds with those aged 65-80 years. Health is measured by self-assessed general health and disability status. Two results stand out. First, class differences in health are strongly reduced or vanish completely for the 65-80 year olds in the Social democratic welfare states, while they remain stable or are in some cases even intensified in almost all other welfare states. Second, the cross-country variation in health inequalities is much larger for the oldest (aged 65-80 years) than is the case for the 50-64 year olds. It is concluded that welfare policies seem to influence the magnitude of health inequalities, and that the importance of welfare state context is greater for the elderly, who are more fragile and more reliant on welfare policies such as public pensions and elderly care.
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Sica, Edgardo. "Eco-innovations and companies' financial constraints : a multilevel-perspective analysis". Thesis, University of Sussex, 2016. http://sro.sussex.ac.uk/id/eprint/63974/.
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Riddell, Abby Rubin. "School effectiveness in secondary education in Zimbabwe : a multilevel analysis". Thesis, University College London (University of London), 1988. http://discovery.ucl.ac.uk/10018436/.
Testo completoAbstract (sommario):
Survey data was collected in 1985 covering information on 3,1100 Form IV students in Zimbabwe, their teachers, their classes and the 32 schools from which they were drawn - spread across six different school types. This data is analysed using a multilevel regression programme to evaluate the effectiveness of different schools in terms of '0' level results in English Language, English Literature and Mathematics. In Chapter One, the historical background to education in Zimbabwe is presented, together with an overview of the main policy changes since Independence. The study itself is situated in Chapter Two against the backdrop of a review of the literature and a discussion of the methodology which distinguishes this study as part of the third wave of research into school effectiveness. Chapter Three describes the study itself, the sample, the variables, and an overview of the school type differences. Chapter Four details the construction of the index variables at the student, the class and the school level. In Chapter Five the results of the progression of linear models are presented, substantiating the choice of 'final' models for each eub3ect. Chapter Six presents an analysis of the different costs at different types of schools, and Chapter Seven draws the threads through the arguments presented in Chapters Two. Five and Six, presenting the implications for Zimbabwe of the stud y 's findings as well as the implications for further research in this field. Whereas much of the literature on school effectiveness has assumed that family background influences on educational achievement operate differently in Third World countries relative to industrialised countries and that school-based factors predominate, this study demonstrates the inadequacy of the models on which such conclusions have been based and concludes that such a distinct pattern of educational achievement for the Third World may indeed be a fallacy.
31
Yu, Jianghui. "DC Fault Current Analysis and Control for Modular Multilevel Converters". Thesis, Virginia Tech, 2016. http://hdl.handle.net/10919/78054.
Testo completoAbstract (sommario):
Recent research into industrial applications of electric power conversion shows an increase in the use of renewable energy sources and an increase in the need for electric power by the loads. The Medium-Voltage DC (MVDC) concept can be an optimal solution. On the other hand, the Modular Multilevel Converter (MMC) is an attractive converter topology choice, as it has advantages such as excellent harmonic performance, distributed energy storage, and near ideal current and voltage scalability.
The fault response, on the other hand, is a big challenge for the MVDC distribution systems and the traditional MMCs with the Half-Bridge submodule configuration, especially when a DC short circuit fault happens. In this study, the fault current behavior is analyzed. An alternative submodule topology and a fault operation control are explored to achieve the fault current limiting capability of the converter.
A three-phase SiC-based MMC prototype with the Full-Bridge configuration is designed and built. The SiC devices can be readily adopted to take advantage of the wide-bandgap devices in MVDC applications. The Full-Bridge configuration provides additional control and energy storage capabilities. The full in-depth design, controls, and testing of the MMC prototype are presented, including among others: component selection, control algorithms, control hardware implementation, pre-charge and discharge circuits, and protection scheme.
Systematical tests are conducted to verify the function of the converter. The fault current behavior and the performance of the proposed control are verified by both simulation and experiment. Fast fault current clearing and fault ride-through capability are achieved.Master of Science
32
Powell, Marvin. "A Multilevel Multitrait-Multimethod Analysis of the Child Behavior Checklist". Thesis, University of North Texas, 2016. https://digital.library.unt.edu/ark:/67531/metadc862789/.
Testo completoAbstract (sommario):
Behavioral and emotional problems (BEPs) are known to affect children's ability to shape and maintain effective social relationships. BEPs are typically categorized into two main factors: internalizing and externalizing behaviors. Internalizing behaviors represent introverted problems, directed inwardly to the individual. While externalizing behavior patterns represent behaviors that are directed outwardly. Behaviors, emotions and thoughts are experienced by all people but on a continuum rather than in terms of absence versus presence of the behavior. The child behavior checklist (CBCL) is used to measure BEPs. The system of CBCL (parent form) measures also includes a teacher rating form and a youth self-report. Using 62 teachers and 311 students, the present study assessed convergent and discriminant validity using a correlated trait, correlated method minus one [CT-C(M-1)] model. The results showed low to moderate teacher-student agreement on the traits. To extend the theoretical structure of the teacher and self-report forms, the present study assessed the nested structure of the data using a multilevel model. Results revealed the nested structure of the data should not be ignored.
33
Li, Chen. "State Space Modeling and Power Flow Analysis of Modular Multilevel Converters". Thesis, Virginia Tech, 2016. http://hdl.handle.net/10919/71811.
Testo completoAbstract (sommario):
For the future of sustainable energy, renewable energy will need to significantly penetrate existing utility grids. While various renewable energy sources are networked with high-voltage DC grids, integration between these high-voltage DC grids and the existing AC grids is a significant technical challenge. Among the limited choices available, the modular multi-level converter (MMC) is the most prominent interface converter used between the DC and AC grids. This subject has been widely pursued in recent years. One of the important design challenges when using an MMC is to reduce the capacitor size associated with each module. Currently, a rather large capacitor bank is required to store a certain amount of line-frequency related circulating energy. Several control strategies have been introduced to reduce the capacitor voltage ripples by injecting certain harmonic current. Most of these strategies were developed using trial and error and there is a lack of a systematic means to address this issue. Most recently, Yadong Lyu has proposed to control the modulation index in order to reduce capacitor ripples. The total elimination of the unwanted circulating power associated with both the fundamental line frequency and the second-order harmonic was demonstrated, and this resulted in a dramatic reduction in capacitor size. To gain a better understanding of the intricate operation of the MMC, this thesis proposes a state-space analysis technique in the present paper. Combining the power flow analysis with the state trajectory portrayed on a set of two-dimensional state plans, it clearly delineates the desired power transfer from the unwanted circulating energy, thus leading to an ultimate reduction in the circulation energy and therefore the required capacitor volume.Master of Science
34
Kaplan, Matthew Frederick. "Implementation of automated multilevel substructuring for frequency response analysis of structures". Access restricted to users with UT Austin EID Full text (PDF) from UMI/Dissertation Abstracts International, 2001. http://wwwlib.umi.com/cr/utexas/fullcit?p3037508.
Testo completo
35
Ozdil, Utkun. "A Multilevel Structural Model Of Mathematical Thinking In Derivative Concept". Phd thesis, METU, 2012. http://etd.lib.metu.edu.tr/upload/12614000/index.pdf.
Testo completoAbstract (sommario):
The purpose of the study was threefold: (1) to determine the factor structure of mathematical thinking at the within-classroom and at the between-classroom level(2) to investigate the extent of variation in the relationships among different mathematical thinking constructs at the within- and between-classroom levels
and (3) to examine the cross-level interactions among different types of mathematical thinking. Previous research was extended by investigating the factor structure of mathematical thinking in derivative at the within- and between-classroom levels, and further examining the direct, indirect, and cross-level relations among different types of mathematical thinking. Multilevel analyses of a cross-sectional dataset containing two independent samples of undergraduate students nested within classrooms showed that the within-structure of mathematical thinking includes enactive, iconic, algorithmic, algebraic, formal, and axiomatic thinking, whereas the between-structure contains formal-axiomatic, proceptual-symbolic, and conceptual-embodied thinking. Major findings from the two-level mathematical thinking model revealed that: (1) enactive, iconic, algebraic, and axiomatic thinking varied primarily as a function of formal and algorithmic thinking
(2) the strongest direct effect of formal-axiomatic thinking was on proceptual-symbolic thinking
(3) the nature of the relationships was cyclic at the between-classroom level
(4) the within-classroom mathematical thinking constructs significantly moderate the relationships among conceptual-embodied, proceptual-symbolic, and formal-axiomatic thinking
and (5) the between-classroom mathematical thinking constructs moderate the relationships among enactive, iconic, algorithmic, algebraic, formal, and axiomatic thinking. The challenges when using multilevel exploratory factor analysis, multilevel confirmatory factor analysis, and multilevel structural equation modeling with categorical variables are emphasized. Methodological and educational implications of findings are discussed.
36
Romaniuk, Helena. "Analysis of product usage panel data". Thesis, University of Southampton, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.326798.
Testo completo
37
Sun, Yue. "A Multilevel Analysis of Student Engagement, Teacher Quality, and Math Achievement". Diss., Virginia Tech, 2016. http://hdl.handle.net/10919/82721.
Testo completoAbstract (sommario):
This study examined the relationships between math engagement, teacher quality, school factors, and math achievement in middle school students. This study used the Trends in International Mathematics and Science Study (TIMSS) data from the 2007 wave. The data were analyzed using exploratory factor analysis (EFA), confirmatory factor analysis (CFA), and hierarchical linear modeling (HLM). The results EFA and CFA showed that students’ engagement in math classrooms consists of three dimensions: behavior, cognition, and emotion. The results provided evidence in supporting the multidimensional theory of student engagement, and provided a well-developed instrument that could measure students’ math engagement. The findings of HLM analysis indicated that students’ emotional engagement had a positive association with math achievement. In addition, teacher content knowledge displayed a positive effect on achievement, and teacher subject knowledge preparation and students’ emotional engagement showed an interactional effect on achievement. What’s more, school SES was a significant factor that influences math achievement. The findings suggested that students’ math achievement was not only related to students’ engagement, but also varied across class and school level factors. The study had both theoretical and practical significance, providing valuable insights for math education and math learning.Ph. D.
38
鄧沛權 e Pui-kuen Tang. "Business network: network marketing : analysis of network marketing using business network theories". Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1997. http://hub.hku.hk/bib/B31268316.
Testo completo
39
Tang, Pui-kuen. "Business network : network marketing : analysis of network marketing using business network theories /". Hong Kong : University of Hong Kong, 1997. http://sunzi.lib.hku.hk/hkuto/record.jsp?B18840127.
Testo completo
40
Nicolás, Apruzzese Joan. "Design and analysis of a novel multilevel active-clamped power-converter". Doctoral thesis, Universitat Politècnica de Catalunya, 2013. http://hdl.handle.net/10803/134933.
Testo completoAbstract (sommario):
Multilevel converter technology has been receiving increasing attention during the last years due to its important advantages compared to conventional two-level conversion. Multilevel converters reduce the voltage across each semiconductor. These converters also synthesize waveforms with better harmonic spectrum, and in most cases, increasing the efficiency of the power conversion system. However, a larger quantity of semiconductors is needed and the modulation strategy to control them becomes more complex. There are three basic multilevel converter topologies: diode clamped, flying capacitor, and cascaded H-bridge with separate dc sources. Numerous hybrid configurations combining them and other multilevel topologies have also been presented in the literature.
A novel multilevel active-clamped (MAC) topology is the subject of study of the present thesis. This topology is derived from the generalized multilevel topology by simply removing all flying capacitors. The topology can also be seen as an extension into an arbitrary number of levels of the three-level active neutral-point-clamped (ANPC) topology. The novel converter is controlled using a proper set of switching states and a switching state transition strategy, which permits to obtain the maximum benefits from the converter.
In this thesis, the performance and operating capabilities of the MAC topology are studied through comprehensive efficiency and fault-tolerance analyses.
The efficiency analysis comprises a study of power-device conduction and switching losses in the topology, followed by analytical and experimental efficiency comparisons between the MAC converter and conventional two-level converters.
In the analysis of the fault-tolerance capacity of the MAC topology both open- and short-circuit faults are considered and the analysis is carried out under single-device and two-simultaneous-device faults. Switching strategies to overcome the limitations caused by faults and topology variations to increment the fault-tolerance ability of the MAC converter are proposed.
The thesis also proposes guidelines to guarantee a proper MAC converter design and improve its performance.
41
Chang, Chiung-Fang. "Fertility patterns among the minority populations of China: A multilevel analysis". Texas A&M University, 2003. http://hdl.handle.net/1969.1/1186.
Testo completoAbstract (sommario):
Sociological and demographic analyses of minority fertility in the United States have suggested that the processes of socioeconomic, cultural, marital, and structural assimilation will lead to convergence in fertility. So far, little research has used the assimilation approach to study the fertility of the minority populations of China, and also, no research has taken both individual-level and group-level characteristics as predictors.
Using micro-data from the One Percent 1990 Census of China, this dissertation performs multilevel analyses, hierarchical generalized linear modeling, to examine the effects of assimilation and the one-child policy at both the individual level and the group level on minority women's fertility.
Several patterns are found in the multilevel analyses. First, the contextual characteristics of minority groups have strong correlations with fertility across thirty major minority groups in China. It suggests that community power and subculture have strong influences on women's decisions regarding their number of children. Second, the effect of the one-child policy is positive and highly significant on minority women's fertility. However, the strong policy effect does not cover the effect of assimilation. After controlling for policy, the impact of all the assimilation predictors, at both the individual and group level, still remains statistically significant. At the individual level, minority women's educational level, occupational status, status of intermarriage, and migration status have significant and positive impacts on their fertility. At the group level, the levels of minority groups' residential segregation, educational segregation, illiteracy, intermarriage rate, and their Moslem group culture have significant and negative impacts on individual women's fertility. Third, several cross-level interactions in the rural models are not consistent with the complete models, which suggests that some indirect effects of assimilation on minority fertility may come from the urban minorities. Finally, in addition to the direct impacts of socioeconomic, marital, and cultural assimilation on minority fertility, several cross-level interactions are significant and indirectly affect women's fertility. Findings reported in this dissertation indicate a successful integration of individual and contextual variables in analyses of minority fertility. The results contribute to the understanding of the assimilation impacts on minority fertility in China.
42
Novosel, Lorraine Marie. "Depressive symptomatology, patient-provider communication, and patient satisfaction : a multilevel analysis". [Tampa, Fla] : University of South Florida, 2007. http://purl.fcla.edu/usf/dc/et/SFE0001866.
Testo completo
43
Stornes, Per. "Working Conditions and Wellbeing : A multilevel analysis of 34 European countries". Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for sosiologi og statsvitenskap, 2014. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-25735.
Testo completoAbstract (sommario):
This paper studies the effects of working conditions on wellbeing in 34 European countries. The background for the study is an interest in work as a social determinant of health, in this case mental health as captured in the concept of wellbeing. Working conditions are theorized at three levels. At the micro level, the psychosocial theories on stress and the work environment are reviewed; the demand-control-support model, effort-reward imbalance, organizational justice and emotional labour. The physical environment is also covered. At the meso level, social class is theorized as relational versus positional, and its relationship to the social gradient is discussed. At the macro level, two alternative typologies are compared. First, the typology of welfare state regimes based on Esping-Andersen (1990). Second, the typology of what I refer to as working conditions regimes, based on the Work Security Index (Rosskam 2009). The thesis uses data from the European Working Conditions Survey. The technique of multilevel analysis is applied using a random intercept model, showing that around 5.7% of the variation in wellbeing stems from the national level. The results show that psychosocial theories such as the demand-control-support model, effort-reward imbalance, organizational justice, as well as the physical environment all have a significant influence on wellbeing, while emotional labour does not. Occupational class has a significant effect for lower classes. At the national level, there are more significant differences between the working conditions regimes than among the welfare states regimes. In terms of effects sizes, the psychosocial models are about as influential as the working conditions regimes, while class appears to have relatively modest influence on wellbeing. Working conditions regimes thus emerge as a viable alternative to welfare regimes when studying health related inequalities in the field of working conditions. The theoretical basis for the working conditions regimes is discussed, and there appears to be need for further theorizing and empirical research on this relatively new concept. Justice is proposed as a key framework influencing wellbeing at an institutional level, beyond the psychosocial. The thesis also argues that structural explanations to national differences in wellbeing are in need of further research.
44
Velasquez, Beatriz Caicedo. "Individual and neighbourhood determinants of adolescent aggressive behaviour : a multilevel analysis". Thesis, University of Bristol, 2012. http://hdl.handle.net/1983/5906ebe6-e711-4d84-b649-2bb0997be40b.
Testo completoAbstract (sommario):
This research examines the extent to which, individual and neighbourhood characteristics contribute to the risk of two different types of adolescent aggressive behaviour: aggression and delinquency. In addition, it explores potential mechanisms explaining the influence of neighbourhood conditions on adolescent aggressive behaviour. Data regarding adolescent behaviour is taken from self-reported surveys, applied to 1,686 Colombian adolescents, residing in 103 neighbourhoods. Data regarding neighbourhoods is taken from official government datasets, as well as two community surveys that are independent of the individual aggression survey. A range of statistical approaches is used to develop reliable valid measures of both adolescent aggressive behaviour and neighbourhood characteristics: multilevel Rasch models, multilevel factor analysis, ecometrics, spatial multiple membership models, Geographic Information Systems and hierarchical Bayes procedures. For the analysis, the research develops an explicit conceptual framework and uses multi level modelling and multilevel structural equation modelling to obtain unbiased estimates of overall effects, cross-level interactions, direct and indirect effects. Results indicate that individual and neighbourhood-level factors are not only directly and indirectly associated with adolescent aggressive behaviour, but also interact with one another to shape adolescent behaviour. By identifying the processes through which neighbourhoods constrain, enhance or modify adolescent behaviours, these results may be used to inform community based programs, aiming to reduce adolescent aggressive behaviour.
45
Harling, Guy. "The social epidemiology of tuberculosis in South Africa : a multilevel analysis". Master's thesis, University of Cape Town, 2006. http://hdl.handle.net/11427/9326.
Testo completoAbstract (sommario):
Includes bibliographical references (leaves 95-105).Tuberculosis has long been considered a disease of poverty but there has been little research into the pathways through which low socio-economic status leads to increased risk of disease. This study reviews the existing literature on risk factors for tuberculosis disease with a particular focus on those variables that reflect the social setting in which an individual lives. It then conducts a multilevel analysis of South African data from the 1998 South African Demographic and Health Survey and the 1996 national census to evaluate individual-, household -and community-level risk factors for tuberculosis disease using a hierarchical regression model.
46
Benbrook, Jimmie Glen 1943. "A SYSTEM ANALYSIS OF A MULTILEVEL SECURE LOCAL AREA NETWORK (COMPUTER)". Thesis, The University of Arizona, 1986. http://hdl.handle.net/10150/275531.
Testo completo
47
Padmanaban, Sanjeevikumar <1978>. "Analysis and Implementation of Multiphase-Multilevel Inverter for Open-Winding Loads". Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2012. http://amsdottorato.unibo.it/4351/4/padmanaban_sanjeevikumar_thesis.pdf.
Testo completoAbstract (sommario):
Research work carried out in focusing a novel multiphase-multilevel ac motor drive system much suitable for low-voltage high-current power applications. In specific, six-phase asymmetrical induction motor with open-end stator winding configuration, fed from four standard two-level three-phase voltage source inverters (VSIs). Proposed synchronous reference frame control algorithm shares the total dc source power among the 4 VSIs in each switching cycle with three degree of freedom. Precisely, first degree of freedom concerns with the current sharing between two three-phase stator windings. Based on modified multilevel space vector pulse width modulation shares the voltage between each single VSIs of two three-phase stator windings with second and third degree of freedom, having proper multilevel output waveforms.
Complete model of whole ac motor drive based on three-phase space vector decomposition approach was developed in PLECS - numerical simulation software working in MATLAB environment. Proposed synchronous reference control algorithm was framed in MATLAB with modified multilevel space vector pulse width modulator. The effectiveness of the entire ac motor drives system was tested. Simulation results are given in detail to show symmetrical and asymmetrical, power sharing conditions. Furthermore, the three degree of freedom are exploited to investigate fault tolerant capabilities in post-fault conditions. Complete set of simulation results are provided when one, two and three VSIs are faulty.
Hardware prototype model of quad-inverter was implemented with two passive three-phase open-winding loads using two TMS320F2812 DSP controllers. Developed McBSP (multi-channel buffered serial port) communication algorithm able to control the four VSIs for PWM communication and synchronization. Open-loop control scheme based on inverse three-phase decomposition approach was developed to control entire quad-inverter configuration and tested with balanced and unbalanced operating conditions with simplified PWM techniques.
Both simulation and experimental results are always in good agreement with theoretical developments.
48
Padmanaban, Sanjeevikumar <1978>. "Analysis and Implementation of Multiphase-Multilevel Inverter for Open-Winding Loads". Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2012. http://amsdottorato.unibo.it/4351/.
Testo completoAbstract (sommario):
Research work carried out in focusing a novel multiphase-multilevel ac motor drive system much suitable for low-voltage high-current power applications. In specific, six-phase asymmetrical induction motor with open-end stator winding configuration, fed from four standard two-level three-phase voltage source inverters (VSIs). Proposed synchronous reference frame control algorithm shares the total dc source power among the 4 VSIs in each switching cycle with three degree of freedom. Precisely, first degree of freedom concerns with the current sharing between two three-phase stator windings. Based on modified multilevel space vector pulse width modulation shares the voltage between each single VSIs of two three-phase stator windings with second and third degree of freedom, having proper multilevel output waveforms.
Complete model of whole ac motor drive based on three-phase space vector decomposition approach was developed in PLECS - numerical simulation software working in MATLAB environment. Proposed synchronous reference control algorithm was framed in MATLAB with modified multilevel space vector pulse width modulator. The effectiveness of the entire ac motor drives system was tested. Simulation results are given in detail to show symmetrical and asymmetrical, power sharing conditions. Furthermore, the three degree of freedom are exploited to investigate fault tolerant capabilities in post-fault conditions. Complete set of simulation results are provided when one, two and three VSIs are faulty.
Hardware prototype model of quad-inverter was implemented with two passive three-phase open-winding loads using two TMS320F2812 DSP controllers. Developed McBSP (multi-channel buffered serial port) communication algorithm able to control the four VSIs for PWM communication and synchronization. Open-loop control scheme based on inverse three-phase decomposition approach was developed to control entire quad-inverter configuration and tested with balanced and unbalanced operating conditions with simplified PWM techniques.
Both simulation and experimental results are always in good agreement with theoretical developments.
49
Piombo, Sara <1969>. "Multilevel Analysis in Household Survey: An Application to Health Condition Data". Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2013. http://amsdottorato.unibo.it/5220/1/piombo_sara_tesi.pdf.
Testo completoAbstract (sommario):
The aim of this thesis is to apply multilevel regression model in context of household surveys. Hierarchical structure in this type of data is characterized by many small groups. In last years comparative and multilevel analysis in the field of perceived health have grown in size. The purpose of this thesis is to develop a multilevel analysis with three level of hierarchy for Physical Component Summary outcome to: evaluate magnitude of within and between variance at each level (individual, household and municipality); explore which covariates affect on perceived physical health at each level; compare model-based and design-based approach in order to establish informativeness of sampling design; estimate a quantile regression for hierarchical data. The target population are the Italian residents aged 18 years and older. Our study shows a high degree of homogeneity within level 1 units belonging from the same group, with an intraclass correlation of 27% in a level-2 null model. Almost all variance is explained by level 1 covariates. In
fact, in our model the explanatory variables having more impact on the outcome
are disability, unable to work, age and chronic diseases (18 pathologies). An additional analysis are performed by using novel procedure of analysis :"Linear Quantile Mixed Model", named "Multilevel Linear Quantile Regression", estimate. This give us the possibility to describe more generally the conditional distribution of the response through the estimation of its quantiles, while accounting for the dependence among the observations. This has represented a great advantage of our models with respect to classic multilevel regression. The median regression with random effects reveals to be more efficient than the mean regression in representation of the outcome central tendency. A more detailed analysis of the conditional distribution of the response on other quantiles highlighted a differential effect of some covariate along the distribution.Lo scopo di questa tesi è quello di applicare il modello di regressione multilivello nel contesto di indagini sulle famiglie. La struttura gerarchica in questo tipo di dati è caratterizzato da numerosi piccoli gruppi. Negli ultimi anni analisi comparative e multilivello sullo stato di salute percepito sono aumentate molto. L’obiettivo di questa tesi è di applicare un'analisi multilivello a tre livelli per la variabile risposta Physical Component Summary allo scopo di: valutare entità all'interno e tra varianza ad ogni livello (individuale, familiare e comune); indagare quali covariate influiscono sulla percezione dello stato di salute fisica ogni livello; confrontare le analisi model-based e di design-based al fine di stabilire se i pesi campionari siano informativiti per il modello di interesse; stimare una regressione quantile per i dati gerarchici. La popolazione target sono i residenti italiani di età compresa tra 18 anni. Il nostro studio rileva un’elevata omogeneità tra le unità di livello 1 e una correlazione intraclasse del 27% nel modello nullo a 2livelli. Quasi tutta la varianza è spiegata dalle covariate di livello. Nel nostro modello le variabili esplicative hanno un impatto maggiore sulla variabile risposta sono la disabilità, inabilità al lavoro, l’età e le malattie croniche (18 patologie). Un'ulteriore analisi viene eseguita utilizzando una nuova procedura di analisi: "Regressione lineare quantile multilivello”. Questa analisi ci dà la possibilità di descrivere più in generale la distribuzione condizionata della variabile risposta attraverso la stima dei suoi quantili. Questo ha portato un grande vantaggio nei nostri modelli rispetto al classico modello di regressione multilivello. La regressione mediana con effetti casuali si rivela più efficiente del regressione media nella rappresentazione della tendenza centrale. Un'analisi più dettagliata della distribuzione condizionata della variabile risposta in corrispondenza di altri quantili ha evidenziato che certe covariate hanno un effetto diverso lungo la distribuzione.
50
Piombo, Sara <1969>. "Multilevel Analysis in Household Survey: An Application to Health Condition Data". Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2013. http://amsdottorato.unibo.it/5220/.
Testo completoAbstract (sommario):
The aim of this thesis is to apply multilevel regression model in context of household surveys. Hierarchical structure in this type of data is characterized by many small groups. In last years comparative and multilevel analysis in the field of perceived health have grown in size. The purpose of this thesis is to develop a multilevel analysis with three level of hierarchy for Physical Component Summary outcome to: evaluate magnitude of within and between variance at each level (individual, household and municipality); explore which covariates affect on perceived physical health at each level; compare model-based and design-based approach in order to establish informativeness of sampling design; estimate a quantile regression for hierarchical data. The target population are the Italian residents aged 18 years and older. Our study shows a high degree of homogeneity within level 1 units belonging from the same group, with an intraclass correlation of 27% in a level-2 null model. Almost all variance is explained by level 1 covariates. In
fact, in our model the explanatory variables having more impact on the outcome
are disability, unable to work, age and chronic diseases (18 pathologies). An additional analysis are performed by using novel procedure of analysis :"Linear Quantile Mixed Model", named "Multilevel Linear Quantile Regression", estimate. This give us the possibility to describe more generally the conditional distribution of the response through the estimation of its quantiles, while accounting for the dependence among the observations. This has represented a great advantage of our models with respect to classic multilevel regression. The median regression with random effects reveals to be more efficient than the mean regression in representation of the outcome central tendency. A more detailed analysis of the conditional distribution of the response on other quantiles highlighted a differential effect of some covariate along the distribution.Lo scopo di questa tesi è quello di applicare il modello di regressione multilivello nel contesto di indagini sulle famiglie. La struttura gerarchica in questo tipo di dati è caratterizzato da numerosi piccoli gruppi. Negli ultimi anni analisi comparative e multilivello sullo stato di salute percepito sono aumentate molto. L’obiettivo di questa tesi è di applicare un'analisi multilivello a tre livelli per la variabile risposta Physical Component Summary allo scopo di: valutare entità all'interno e tra varianza ad ogni livello (individuale, familiare e comune); indagare quali covariate influiscono sulla percezione dello stato di salute fisica ogni livello; confrontare le analisi model-based e di design-based al fine di stabilire se i pesi campionari siano informativiti per il modello di interesse; stimare una regressione quantile per i dati gerarchici. La popolazione target sono i residenti italiani di età compresa tra 18 anni. Il nostro studio rileva un’elevata omogeneità tra le unità di livello 1 e una correlazione intraclasse del 27% nel modello nullo a 2livelli. Quasi tutta la varianza è spiegata dalle covariate di livello. Nel nostro modello le variabili esplicative hanno un impatto maggiore sulla variabile risposta sono la disabilità, inabilità al lavoro, l’età e le malattie croniche (18 patologie). Un'ulteriore analisi viene eseguita utilizzando una nuova procedura di analisi: "Regressione lineare quantile multilivello”. Questa analisi ci dà la possibilità di descrivere più in generale la distribuzione condizionata della variabile risposta attraverso la stima dei suoi quantili. Questo ha portato un grande vantaggio nei nostri modelli rispetto al classico modello di regressione multilivello. La regressione mediana con effetti casuali si rivela più efficiente del regressione media nella rappresentazione della tendenza centrale. Un'analisi più dettagliata della distribuzione condizionata della variabile risposta in corrispondenza di altri quantili ha evidenziato che certe covariate hanno un effetto diverso lungo la distribuzione.