• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 487
  • 115
  • 115
  • 61
  • 38
  • 30
  • 24
  • 22
  • 8
  • 6
  • 5
  • 5
  • 4
  • 4
  • 3
  • Tagged with
  • 1089
  • 164
  • 164
  • 139
  • 135
  • 119
  • 108
  • 101
  • 93
  • 91
  • 85
  • 80
  • 78
  • 76
  • 74
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
511

Leucemias e proximidade de residência a linhas de energia elétrica na cidade de São Paulo / Leukemia and proximity the residence to electric power lines in Sao Paulo city

Sollitto, Ciliane Matilde 03 April 2009 (has links)
O objetivo deste estudo foi o de investigar a relação de casos notificados de leucemias na faixa etária de 0 a 19 anos e proximidade de residência com linhas de energia elétrica na cidade de São Paulo, entre os anos de 1997 e 2004. Para este propósito, foram geocodificados os casos notificados de leucemias em crianças e adolescentes com idade entre 0 e 19 anos, registrados na cidade de São Paulo por meio de banco de dados fornecido pelo Registro de Câncer de Base Populacional (RCBP-SP); os casos da doença na faixa etária especificada foram georreferenciados em relação às linhas de energia elétrica, aos distritos administrativos da cidade e aos setores censitários. Assim pode-se calcular a incidência dos casos georreferenciados para o município de São Paulo utilizando como base os dados demográficos do censo de 2000, publicados pelo Instituto Brasileiro de Geografia e Estatística (IBGE) e calcular a incidência dos casos georreferenciados de acordo com o local de residência e a distância das linhas de energia elétrica, construindo mapas temáticos a partir de instrumentos disponíveis nos Sistemas de Informação Geográfica (SIG) da cidade. Desta forma foi demonstrado que os casos georreferenciados de leucemia em crianças e adolescentes com idade entre 0 e 19 anos, registrados no RCBP-SP, no período de 1997 a 2004, têm uma distribuição homogênea, quando observados em relação ao município como um todo, porém ao especificar-se a distribuição pelas distâncias das residências em relação às linhas de energia elétrica, denota-se que a incidência revela-se maior à distância de 200 metros (22,46/100.000 hab.), do que às distâncias de 400 (14,97/100.000 hab.), 600 (16,08/100.000 hab.), 800 (21,17/100.000 hab.) e 1000 metros (20,07/100.000 hab.) e que esta incidência também é maior quando comparada com a incidência geral do município (19,34/100.000 hab.). / The aim of this study was to investigate the relationship of reported cases of leukemia at the age from 0 to 19 years old and their residence proximity to power lines in the city of Sao Paulo, between the years 1997 and 2004. For this purpose, the leukemia childhood cases notified by Cancer Register Population Base of Sao Paulo city were geocoded and georreferenced in relation to the electric power lines, administrative districts and census sector of the city. Thus, we could calculate the incidence that cases utilizing the demographic bases from 2000 Brazilian census and the incidence according to the distances of electric power lines, producing the thematic layer maps from Geographical Information Systems - GIS. Our results demonstrated that childhood leukemia cases, notified by RCBP-SP from 1997 to 2004 in Sao Paulo city, have homogeneous distribution when observed all the territory, however, the highest value of incidence occurred in a 200 meters of distance the electric power lines (22,46/100.000 inhab.), when compared with 400 (14,97/100.000 inhab.), 600 (16,08/100.000 inhab.), 800 (21,17/100.000 inhab.) and 1000 meters (20,07/100.000 inhab.), and it is also biggest when compared with entire territory (19,34/100.000 inhab.).
512

Dispersão de sementes e processos de limitação demográfica de plantas em ambientes com e sem bambus na Floresta Pluvial Atlântica

Rother, Débora Cristina [UNESP] 30 November 2010 (has links) (PDF)
Made available in DSpace on 2014-06-11T19:30:58Z (GMT). No. of bitstreams: 0 Previous issue date: 2010-11-30Bitstream added on 2014-06-13T20:21:33Z : No. of bitstreams: 1 rother_dc_dr_rcla.pdf: 2462027 bytes, checksum: c33bd50a18fd50beab5b4f95e4d965a4 (MD5) / Em florestas tropicais, ainda são incipientes os estudos que tratam da influência dos bambus na dinâmica da vegetação. Pela grande capacidade de se expandir rapidamente no ambiente seja por crescimento vegetativo ou por produção massiva de sementes, os bambus promovem alterações significativas na estrutura das comunidades vegetais. Desta forma, esse estudo teve como objetivo avaliar o ciclo de vida das plantas em ambientes com (B) e sem bambus (SB) em uma área de floresta Atlântica densamente ocupada pelo bambu nativo Guadua tagoara. Os objetivos específicos deste estudo foram separados em capítulos. Para o capítulo 1, conhecer a composição de aves associadas aos ambientes com e sem bambus, identificar as aves que compõem a guilda de dispersores de sementes de Euterpe edulis, Sloanea guianensis e Virola bicuhyba e avaliar o potencial de dispersão das aves registradas em censos. Para o capítulo 2, avaliar o padrão espacial dos estágios iniciais da regeneração da comunidade de plantas nos ambientes B e SB. Finalmente para o capítulo 3, quantificar as perdas de propágulos e as probabilidades de transição entre cada etapa demográfica das três espécies de plantas selecionadas, e identificar os gargalos demográficos do recrutamento que podem colapsar a regeneração natural das três espécies de plantas nos ambientes B e SB. Verificamos que nos ambientes B foi registrado maior número de espécies de aves do que em ambientes SB. A maioria das aves registradas em censos nos dois ambientes foi insetívora, seguida por espécies frugívoras. A efetividade da dispersão de Euterpe, Sloanea e Virola, esteve restrita a um pequeno grupo de dispersores efetivos. As aves que mais contribuíram para a dispersão de Virola ocorreram mais freqüentemente em B. Este padrão foi similar para Sloanea, enquanto Euterpe apresentou um padrão misto, com algumas espécies de aves... / Studies about the bamboo influence in the plant dynamic process are still incipient. Given that bamboos are able to quickly expand in environment by either vegetative growth or massive seed production, bamboos promote significant changes in plant community structure. Thus, this work aimed at assessing the plant life cycles in bamboo (B) and non bamboo stands (NB) in an Atlantic forest area where the native bamboo Guadua tagoara occurs at high densities. The specific goals of this study were showed in chapters. For chapter 1, to know bird species associated with bamboo and non bamboo stands, identify the birds which belong to seed dispersers guild of Euterpe edulis, Sloanea guianensis and Virola bicuhyba and evaluate dispersal effectiveness and potential contribution to seed dispersal for the three plant species. For chapter 2, assess the spatial pattern of early regeneration stages of plant communities in B and NB stands. Finally, for chapter 3, quantify propagule losses as well as the probabilities of transition between each stage for all three plant species, and identify the demographic bottlenecks in recruitment that could collapse natural regeneration of the three plant species in B and NB stands. We verified that a higher number of bird species was registered in B stands than in NB. Most of registered birds in both B and NB stands were insectivorous followed by frugivorous species. The dispersal effectiveness of Euterpe, Sloanea and Virola depended on a restricted subset of effective bird dispersers. Birds which mostly contributed to the seed dispersal of Virola occurred more frequently in B. This pattern was similar for Sloanea while Euterpe exhibited a mixed pattern with some bird species contributing to the dispersal in the B stands and other species contributing in NB stands. We conclude that a substantial number of frugivorous bird species can favor borders of bamboo patches... (Complete abstract click electronic access below)
513

Stabilita důchodového systému České republiky v souvislosti s důchodovou reformou / Stability of pension system in the Czech Republic in coherence with pension reform

Möstl, David January 2012 (has links)
Hardly anyone doubt about the necessity of pension reform nowadays. Opinions how to process the reform differs considerably. The main point of my work is to evaluate preferability of so called opt-out (partial release of financial sources from system based on continuous contribution into fund system) for various income and age groups in order to find out that such measures will not fundamentally threaten stability of pension system in the Czech Republic. Reform changes of pension reform of chosen EU countries are to be characterized in my thesis. I will also evaluate possibilities of aplication of foreign experience in the Czech Republic. The basic methods will be above all the analysis of questionnaire results, mathematical and statistical methods and method of international comparation.
514

Statistical inference in population genetics using microsatellites

Csilléry, Katalin January 2009 (has links)
Statistical inference from molecular population genetic data is currently a very active area of research for two main reasons. First, in the past two decades an enormous amount of molecular genetic data have been produced and the amount of data is expected to grow even more in the future. Second, drawing inferences about complex population genetics problems, for example understanding the demographic and genetic factors that shaped modern populations, poses a serious statistical challenge. Amongst the many different kinds of genetic data that have appeared in the past two decades, the highly polymorphic microsatellites have played an important role. Microsatellites revolutionized the population genetics of natural populations, and were the initial tool for linkage mapping in humans and other model organisms. Despite their important role, and extensive use, the evolutionary dynamics of microsatellites are still not fully understood, and their statistical methods are often underdeveloped and do not adequately model microsatellite evolution. In this thesis, I address some aspects of this problem by assessing the performance of existing statistical tools, and developing some new ones. My work encompasses a range of statistical methods from simple hypothesis testing to more recent, complex computational statistical tools. This thesis consists of four main topics. First, I review the statistical methods that have been developed for microsatellites in population genetics applications. I review the different models of the microsatellite mutation process, and ask which models are the most supported by data, and how models were incorporated into statistical methods. I also present estimates of mutation parameters for several species based on published data. Second, I evaluate the performance of estimators of genetic relatedness using real data from five vertebrate populations. I demonstrate that the overall performance of marker-based pairwise relatedness estimators mainly depends on the population relatedness composition and may only be improved by the marker data quality within the limits of the population relatedness composition. Third, I investigate the different null hypotheses that may be used to test for independence between loci. Using simulations I show that testing for statistical independence (i.e. zero linkage disequilibrium, LD) is difficult to interpret in most cases, and instead a null hypothesis should be tested, which accounts for the “background LD” due to finite population size. I investigate the utility of a novel approximate testing procedure to circumvent this problem, and illustrate its use on a real data set from red deer. Fourth, I explore the utility of Approximate Bayesian Computation, inference based on summary statistics, to estimate demographic parameters from admixed populations. Assuming a simple demographic model, I show that the choice of summary statistics greatly influences the quality of the estimation, and that different parameters are better estimated with different summary statistics. Most importantly, I show how the estimation of most admixture parameters can be considerably improved via the use of linkage disequilibrium statistics from microsatellite data.
515

Inferring population history from genealogies

Lohse, Konrad R. January 2010 (has links)
This thesis investigates a range of genealogical approaches to making quantitative inferences about the spatial and demographic history of populations with application to two insect systems: A local radiation of high alpine ground beetles (Carabidae) in the genus Trechus and major refugial populations of the oak gall parasitoid Cecidostiba fungosa (Pteromalidae). i) Summary statistics, which make explicit use of genealogical information are developed. Using simulations their power to detect a history of population growth is shown to be higher than that of standard measures such as Tajima’s D for single and multilocus data. The improvement arises from the fact that in contrast to pairwise measures, the new statistics are minimally confounded with the topology. ii) A Bayesian method to reconstructing character states is used to infer the Pleistocene history of populations of high alpine Trechus sampled along a singlemountain range frommitochondrial and nuclear data. Despite evidence for some incomplete lineage sorting, a simple model of a series of extreme founder events out of two refugia during or before the last glacial maximum provides a good fit to the data. iii) A large set of exon-primed, intron-spanning (EPIC) loci is developed for Hymenoptera from EST and genomic data. Amplification success is screened on a range of Hymenopteran species associated with two insect-plant interactions: Oak galls and figs. iv) Borrowing model-based approaches developed to quantify species divergence, the new EPIC loci are used to investigate the relationships between three major European refugia in the oak gall parasitoid C. fungosa. These analyses reveal strong support for an eastern origin, effective ancestral population sizes comparable to insect model species and evidence for recent population divergence during the last interglacial. The results also suggest that there is significant information in minimal samples provided a large number of loci are available. v) Results for the probability of gene tree topologies are derived for a model of divergence with gene flow between three populations. I outline how the asymmetries in the frequency of gene tree topologies may be used to distinguish incomplete lineage sorting from migration and discuss the results in the context of next generation sequence data from D. melanogaster and humans and Neanderthals.
516

Factors Influencing Student Achievement in Texas

Pickering, Sarah Kelley 05 1900 (has links)
This study examines the relationships among student socioeconomic status, school district enrollment, minority enrollment, district expenditure per pupil, and the teaching experience of faculty as these variables influence the achievement scores of secondary students in Texas. Data from a total of 1,061 Texas school districts were used to determine the effects of the indicated district-level predictor variables on three criterion variables: reading, mathematics, and writing scores for the 11th-grade Texas Education Assessment of Minimum Skills (TEAMS). The study led to the following conclusions: 1. Low socioeconomic status of students in Texas, as in the rest of the United States, insures that test scores will be lower if all other variables are held constant. 2. Large minority populations are strong predictors of low test scores, especially in mathematics and reading. 3. Students in districts whose faculty had a high average of years of teaching experience also scored high in achievement tests, especially in mathematics and writing. 4. High average district expenditure per pupil predicts high test scores, especially in reading. 5. School district size or enrollment has low predictive value of test scores. Among several specific recommendations, this study advises that further study be done concerning the most effective ways to educate minority and socioeconomically disadvantaged student populations. The study also recommends that better ways be found to retain experienced teachers in the classroom, including monetary compensation, extra allowances for staff development, and additional resources. The study cautions against simply adding money to a district's budget to increase student achievement scores, asserting that districts should make thorough studies before higher expenditures per pupil are alone used to increase test scores.
517

Parental Involvement Typologies as Related to Student Achievement.

Derrick-Lewis, Stacia Maria 01 May 2001 (has links)
The purpose of this study was to examine specific parenting practices in four East Tennessee counties to determine their relationships, if any, to student achievement among various demographic groups. The investigation included status variables, such as parents' educational level, annual income level, and family structure. Students' Normal Curve Equivalent scores on the Terra Nova Standardized Test were used to measure student achievement. The Epstein (1987) typologies were used to classify parent involvement modalities. The analysis consisted of four research questions and were tested at the .05 level of significance. Pearson's product-moment, Spearman's rho, and Kendall's Tau B correlation coefficients were used to analyze the degree of relationship between Epstein's six typologies and student achievement. A t-test was used to describe the relationship between student achievement and the number of parents in the home. One-way Analyses of Variance were used to describe the relationships between student achievement and parents' educational and income levels. Kruskal Wallis tests were used to analyze differences in parental involvement by the number of parents in the home, parental income, and education levels. A Hierarchical Regression Analysis was also used to determine the extent to which parents' income, educational levels, and family structure assist in predicting student achievement. The sample consisted of 413 students in grade 4 in four counties in East Tennessee. Two schools were selected from each county as a representative sample of the population. The results of this study indicate significant relationships between student achievement and the parental involvement typologies of volunteering, learning at home, decision-making, and collaborating with the community. The relationships between student achievement and parental involvement in conjunction with parents' educational and income levels were also significant. Both parental involvement typologies and family demographics emphasize goals which are achieved most effectively when families and schools work together.
518

A Comparison of Weekend and Weekday Travel Behavior Characteristics in Urban Areas

Agarwal, Ashish 27 May 2004 (has links)
Travel demand analysis has traditionally focused on exploring and modeling travel behavior on weekdays. This emphasis on weekday travel behavior analysis was largely motivated by the presence of well-defined peak periods, primarily associated with the journey to and from work. Most travel demand models are based on weekday travel characteristics and purport to estimate traffic volumes for daily or peak weekday conditions. Much of the planning and policy making that occurs in transportation arena in response to weekday travel behavior and forecasts. More recently, there had been a growing interest in exploring, understanding, and quantifying weekend travel characteristics. The ability to do this has been limited due to the non-availability of travel survey data that includes weekend trip information. Most travel surveys collect information about weekday travel behavior and ignore weekend days. However, the 2001 National Household Travel Survey includes a substantial sample that provided detailed trip information for weekend days and therefore this dataset offers a key opportunity to explore in-depth weekend travel characteristics. Weekend travel behavior is expected to be substantially different from the weekday travel behavior for difference in several spatial and temporal constraints. The difference in constraints can also lead to a change in trip chaining patterns on weekdays and weekends. Differences in constraints coupled with socio-economic changes characterized by greater disposable income, time-constrained lives, and greater discretionary activity opportunities point towards the growing role that weekend travel behavior is going to play in transportation planning and policy-making. This thesis provides a comprehensive analysis of weekend travel behavior using the 2001 NHTS. Differences and similarities between weekday and weekend travel behavior are identified and presented for different urban areas sizes varying according to Metropolitan Statistical Area (MSA) size. Models of weekend and weekday travel behavior are developed to capture the structural relationship of socio-demographics, activity durations, and travel duration are developed using structural equations modeling approaches to better understand the relationships among these aspects of travel behavior on weekdays and weekends. This report is supposed to act as an updated data guide to the National Cooperative Highway Research Program's (NCHRP) Report 365 titled "Travel Estimation Techniques for Urban Planning" aims at studying the changes in behavioral characteristics between two categories of the day of week - a weekday and a weekend based on personal, household and trip characteristics.
519

A Comparative Analysis of Travel Time Expenditures in the United States

Toole-Holt, Lavenia Anne 06 July 2004 (has links)
Literature on transportation planning and modeling is replete with the concept of a travel time budget. According to this concept, average daily travel times tend to be relatively constant. However, evidence from the 1983 Nationwide Personal Transportation Survey and the 2001 National Household Travel Survey suggest that the average daily travel time has increased by 1.9 minutes per year. Understanding travel time expenditures is important for forecasting travel demand, especially future vehicle miles of travel. Historically, travel demand models considered vehicle availability and income as limiting factors for travel, but going forward time may be the constraint. As individuals spend more time devoted to travel, less time will be available for other activities. Therefore, future travel demand is dependent on people's willingness to spend time traveling. Growth of travel demand has been per capita based not just population based. This has been enabled by several cultural trends, including fewer children to care for; specialization of activities; multitasking during travel, for example, cell phone use can add value to travel time; seeking socialization away from home; and increases in real income enabling more activity participation. This study will report the increase in average daily travel time expenditures and analyze the increase by various demographic segments of the population. Travel time expenditures are also related to activity participation, the characteristics of the area, and many other interrelated factors at the person level. Aggregate values will be used to investigate the general relationships between daily travel time expenditures and socio-demographic characteristics. Careful consideration of the implications of the increase in travel time, as well as the changes in society that have contributed to these changes will be explored. The increase in travel time expenditures is likely to play a significant role in future travel demand growth in the United States and will impact the performance of the transportation system going forward. If travel time expenditures continue to grow, the hope for slowing VMT growth may not materialize. Understanding the mechanics of why people are traveling more will aid planners and modelers in estimating future travel demand.
520

An Analysis of Characteristics of Long and Short Commuters in the United States

Vaddepalli, Srikanth 30 March 2004 (has links)
An in-depth-analysis was carried out on short, medium and long commuters using the National Household Travel Survey (NHTS) of 2001 and American Community Survey (ACS) of 2000 to determine the role of individual,household, trip and area related characteristics on commute length. The individuals with commute time less than or equal to 15 min were considered as short commuters and individuals with commute time greater than 15 min but less than 60 min were considered as medium commuters and the individuals with commute time 60 min or more were considered as long commuters. The commute time is considered as a link joining the residence and workplace locations. The availability of the desired mode used is considered as flexibility in moving the location of these points in the area. As the jobs get dispersed the lower income people face more and more transportation problems in linking the residence and workplace. There is a potential threat in their social, physical and economic isolation in the society. The individual, household, and area related characteristics are assumed to influence both the commute time and location of these points. The descriptive analysis using NHTS 2001 and ACS 2000 revealed that the characteristics of short and long commuters are different in nature. A commuter type choice model and commute length measurement models were used to estimate the influence of socio-demographic characteristics on the residential and workplace separation. Multinomial Logit Model (MNL) methodology was adopted to develop the commuter type choice model and Structural Equations Model methodology (SEM) was adopted with commute time and commute distance as endogenous variables to estimate the commute length on a continuous scale. The models confirmed the importance of demographic variables in explaining commuter length.

Page generated in 0.0709 seconds