• Refine Query
• Source
• Publication year
• to
• Language
• 59
• 43
• 3
• 3
• 3
• 2
• 2
• 2
• 1
• 1
• 1
• 1
• 1
• 1
• 1
• Tagged with
• 126
• 126
• 39
• 25
• 22
• 21
• 21
• 19
• 17
• 17
• 14
• 14
• 13
• 13
• 12
• 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.
31

Test of Treatment Effect with Zero-Inflated Over-Dispersed Count Data from Randomized Single Factor Experiments

Fan, Huihao 12 September 2014 (has links)
No description available.
32

Limit theorems for integer partitions and their generalisations

Ralaivaosaona, Dimbinaina 03 1900 (has links)
Thesis (PhD)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: Various properties of integer partitions are studied in this work, in particular the number of summands, the number of ascents and the multiplicities of parts. We work on random partitions, where all partitions from a certain family are equally likely, and determine moments and limiting distributions of the different parameters. The thesis focuses on three main problems: the first of these problems is concerned with the length of prime partitions (i.e., partitions whose parts are all prime numbers), in particular restricted partitions (i.e., partitions where all parts are distinct). We prove a central limit theorem for this parameter and obtain very precise asymptotic formulas for the mean and variance. The second main focus is on the distribution of the number of parts of a given multiplicity, where we obtain a very interesting phase transition from a Gaussian distribution to a Poisson distribution and further to a degenerate distribution, not only in the classical case, but in the more general context of ⋋-partitions: partitions where all the summands have to be elements of a given sequence ⋋ of integers. Finally, we look into another phase transition from restricted to unrestricted partitions (and from Gaussian to Gumbel-distribution) as we study the number of summands in partitions with bounded multiplicities. / AFRIKAANSE OPSOMMING: Verskillende eienskappe van heelgetal-partisies word in hierdie tesis bestudeer, in die besonder die aantal terme, die aantal stygings en die veelvoudighede van terme. Ons werk met stogastiese partisies, waar al die partisies in ’n sekere familie ewekansig is, en ons bepaal momente en limietverdelings van die verskillende parameters. Die teses fokusseer op drie hoofprobleme: die eerste van hierdie probleme gaan oor die lengte van priemgetal-partisies (d.w.s., partisies waar al die terme priemgetalle is), in die besonder beperkte partisies (d.w.s., partisies waar al die terme verskillend is). Ons bewys ’n sentrale limietstelling vir hierdie parameter en verkry baie presiese asimptotiese formules vir die gemiddelde en die variansie. Die tweede hooffokus is op die verdeling van die aantal terme van ’n gegewe veelvoudigheid, waar ons ’n baie interessante fase-oorgang van ’n normaalverdeling na ’n Poisson-verdeling en verder na ’n ontaarde verdeling verkry, nie net in die klassieke geval nie, maar ook in die meer algemene konteks van sogenaamde ⋋-partities: partisies waar al die terme elemente van ’n gegewe ry ⋋ van heelgetalle moet wees.
33

Distribuições em série de potências modificadas inflacionadas e distribuição Weibull binominal negativa / Inflated modified power serie distribution and Weibull negative binomial

Rodrigues, Cristiane 03 June 2011 (has links)
34

Spatial and temporal dynamics of the microbial communities in soils cultivated with sugarcane / Dinâmica espaço-temporal da comunidade microbiana de solos cultivados com cana-de-açúcar

Gumiere, Thiago 23 February 2017 (has links)
The environmental conditions driving the microbial community dynamics in crop soils remain unclear. Here, we focused on the spatial and temporal dynamics of microbial communities in soils cultivated with sugarcane under different soil managements, during two years. Our work was divided into three essential parts, where i) we discuss ecological models and theories for the microbial exploration in crop soils, arguing that those ecological models, which partitioned the microbial communities, may increase the resolution of the environmental and the microbial interactions; ii) we developed a probabilistic model based on the occurrence frequency of microorganisms across systems identifying the core microbial community. The model is based on the Poisson distribution, and it was tested in four datasets available in the Earth Microbiome Project; iii) we identified the core bacterial and fungal communities across soils cultivated with sugarcane, verifying which abiotic components could drive the composition of groups. We increased the resolution of the environmental and the microbial interactions, showing that the core and the variable microbial communities are driven by distinct abiotic components. We also observed that the core and variable microbial communities harbor distinct potential functionality, as nitrogen fixation being more predicted to the core bacterial commmunity, and nitrification process for the variable bacterial community. Our finds increase the knowledge of microbial dynamics and functionality, helping to reveal and explore the crop system microbiome. / As condições ambientais que podem modular a dinâmica da comunidade microbiana em solos de culturas são pouco conhecidas. O presente trabalho foi dividido em três partes essenciais, onde i) discutiu-se modelos e teorias ecológicas para a exploração microbiana em solo agrícolas, argumentando-se que os modelos ecológicos que particionam as comunidades microbianas, poderiam aumentar a resolução entre interações microbianas e o ambiente, ii) desenvolveu-se um modelo probabilístico baseado na freqüência de ocorrência de microorganismos através de sistema identificando a comunidade microbiana \"core\". O modelo baseou-se na distribuição de Poisson, sendo este testado em quatro conjuntos de dados disponíveis no Projeto \"Earth Microbiome\", e iii) identificou-se as comunidades bacterianas e fúngicas core em solos cultivados com cana-de-açúcar, verificando-se quais componentes abióticos poderiam modular a composição dos grupos. Com isso, elevou-se a resolução das interações ambiental e microbiana, indicando que o core microbiano e as comunidades microbianas variáveis são moduladas por componentes abióticos distintos. Observou-se também que as comunidades core e variável possuem funcionalidade potencial distinta, como fixação de nitrogênio mais predita para o core bacteriano e processo de nitrificação para a comunidade variável de bactérias. Os resultados do presente trabalho elevam o conhecimento da dinâmica e funcionalidade microbiana, ajudando a revelar e explorar o microbioma do sistema de cultivo.
35

On the regression model with count data: with application in air pollution data.

by Kwok-Fai Mo. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1999. / Includes bibliographical references (leaves 74-79). / Abstracts in English and Chinese. / Chapter 1 --- Introduction --- p.1 / Chapter 2 --- Statistical Modeling --- p.5 / Chapter 2.1 --- Poisson Regression --- p.5 / Chapter 2.2 --- Overdispersion and Autorrelation --- p.7 / Chapter 2.3 --- Generalized Estimating Equation --- p.9 / Chapter 2.4 --- Zeger's Mehthod --- p.12 / Chapter 2.5 --- Multicollinearity --- p.18 / Chapter 2.5.1 --- The Modified Generalized Estimating Equation --- p.18 / Chapter 2.6 --- Bootstrapping Method --- p.21 / Chapter 2.7 --- The Bootstrap Choice of Ridge Parameter --- p.23 / Chapter 3 --- The Robustness of Zeger's Approach to the Specification of ηt - Simulation Study --- p.26 / Chapter 3.1 --- Introduction --- p.26 / Chapter 3.2 --- Zeger's Algorithm with Varoious Time Series Data --- p.27 / Chapter 3.2.1 --- Data without Multicollinearity --- p.27 / Chapter 3.2.1 --- Data with Multicollinearity --- p.34 / Chapter 3.3 --- Modified Generalized Estimating Equation Approach --- p.40 / Chapter 3.3 --- The Choice of Ridge Paramter in Bootstrap --- p.42 / Chapter 4 --- Real Example --- p.46 / Chapter 4.1 --- Data Structure --- p.46 / Chapter 4.2 --- Model Building --- p.49 / Chapter 4.3 --- Single Pollutant Model --- p.57 / Chapter 4.4 --- Multiple Pollutant Model --- p.62 / Chapter 5 --- Conclusion and Discussion --- p.64 / Appendix --- p.69 / References --- p.74
36

Análise de contagens multivariadas. / Multivariate count analysis.

Ho, Linda Lee 15 September 1995 (has links)
Este trabalho apresenta uma análise estatística de contagens multivariadas proveniente de várias populações através de modelos de regressão. Foram considerados casos onde os vetores respostas obedeçam às distribuições Poisson multivariada e Poisson log-normal multivariada. Esta distribuição admite correlação de ambos sinais entre componentes do vetor resposta, enquanto que as distribuições mais usuais para dados de contagens (como a Poisson multivariada) admitem apenas correlação positiva entre as componentes do vetor resposta. São discutidos métodos de estimação e testes de hipóteses sobre os parâmetros do modelo para o caso bivariado. Estes modelos de regressão foram aplicados a um conjunto de dados referentes a contagens de dois tipos de defeitos em 100 gramas de fibras têxteis de quatro máquinas craqueadeiras, sendo duas de um fabricante e as outras de um segundo fabricante. Os resultados obtidos nos diferentes modelos de regressão foram comparados. Para estudar o comportamento das estimativas dos parâmetros de uma distribuição Poisson Log-Normal, amostras foram simuladas segundo esta distribuição. / Regression models are presented to analyse multivariate counts from many populations. Due to the random vector characteristic, we consider two classes of probability models: Multivariate Poisson distribution and Multivariate Poisson Log-Normal distribution. The last distribution admits negative and positive correlations between two components of a random vector under study, while other distributions (as Multivariate Poisson) admit only positive correlation. Estimation methods and test of hypothese on the parameters in bivariate case are discussed. The proposed techniques are illustrated by numerical examples, considering counts of two types of defects in 100g of textile fibers produced by four machines, two from one manufacturer and the other two from another one. The results from different regression models are compared. The empirical distribution of Poisson Log-Normal parameter estimations are studied by simulated samples.
37

Spatial and temporal dynamics of the microbial communities in soils cultivated with sugarcane / Dinâmica espaço-temporal da comunidade microbiana de solos cultivados com cana-de-açúcar

Thiago Gumiere 23 February 2017 (has links)
The environmental conditions driving the microbial community dynamics in crop soils remain unclear. Here, we focused on the spatial and temporal dynamics of microbial communities in soils cultivated with sugarcane under different soil managements, during two years. Our work was divided into three essential parts, where i) we discuss ecological models and theories for the microbial exploration in crop soils, arguing that those ecological models, which partitioned the microbial communities, may increase the resolution of the environmental and the microbial interactions; ii) we developed a probabilistic model based on the occurrence frequency of microorganisms across systems identifying the core microbial community. The model is based on the Poisson distribution, and it was tested in four datasets available in the Earth Microbiome Project; iii) we identified the core bacterial and fungal communities across soils cultivated with sugarcane, verifying which abiotic components could drive the composition of groups. We increased the resolution of the environmental and the microbial interactions, showing that the core and the variable microbial communities are driven by distinct abiotic components. We also observed that the core and variable microbial communities harbor distinct potential functionality, as nitrogen fixation being more predicted to the core bacterial commmunity, and nitrification process for the variable bacterial community. Our finds increase the knowledge of microbial dynamics and functionality, helping to reveal and explore the crop system microbiome. / As condições ambientais que podem modular a dinâmica da comunidade microbiana em solos de culturas são pouco conhecidas. O presente trabalho foi dividido em três partes essenciais, onde i) discutiu-se modelos e teorias ecológicas para a exploração microbiana em solo agrícolas, argumentando-se que os modelos ecológicos que particionam as comunidades microbianas, poderiam aumentar a resolução entre interações microbianas e o ambiente, ii) desenvolveu-se um modelo probabilístico baseado na freqüência de ocorrência de microorganismos através de sistema identificando a comunidade microbiana \"core\". O modelo baseou-se na distribuição de Poisson, sendo este testado em quatro conjuntos de dados disponíveis no Projeto \"Earth Microbiome\", e iii) identificou-se as comunidades bacterianas e fúngicas core em solos cultivados com cana-de-açúcar, verificando-se quais componentes abióticos poderiam modular a composição dos grupos. Com isso, elevou-se a resolução das interações ambiental e microbiana, indicando que o core microbiano e as comunidades microbianas variáveis são moduladas por componentes abióticos distintos. Observou-se também que as comunidades core e variável possuem funcionalidade potencial distinta, como fixação de nitrogênio mais predita para o core bacteriano e processo de nitrificação para a comunidade variável de bactérias. Os resultados do presente trabalho elevam o conhecimento da dinâmica e funcionalidade microbiana, ajudando a revelar e explorar o microbioma do sistema de cultivo.
38

Review of Reliability Techniques

Doherty, Eugene Richard 01 May 1966 (has links)
In the development of any product to perform a specific function the first concern of the engineer is to design for satisfactory operation. Engineers originally approached the reliability problem by using excessive safety factors to be assured the structure or material would withstand the calculated loads and stresses. The engineer also learned from operating or testing the equipment until failures occurred and then redesigning as mistakes became apparent. These methods were time consuming and often resulted in bulky over designed products. These approaches became impractical with the advent of new technological advancements. The accelerated industrial development of aircraft, missiles, and modern electronics coupled with a need for a drastic reduction in weight and size magnified the problem. As products became more complex the problem of building a reliable product was intensified. An appreciation for the increase in complexity can be gained from considering that in a period of fifteen years the requirements for electronic tubes on a U.S. Navy destroyer changed from sixty to thirty-six hundred (14). During World War II new equipment was developed that had to be operational for extended period of time if the military mission was to be accomplished. The addition of a time requirement added to the already difficult problem caused by the increasing complexity of equipment. It soon became obvious that new techniques had to be developed that would assist the manufacturer in designing a reliable product.
39

Incorporating discontinuities in value-at-risk via the poisson jump diffusion model and variance gamma model

Lee, Brendan Chee-Seng, Banking & Finance, Australian School of Business, UNSW January 2007 (has links)
We utilise several asset pricing models that allow for discontinuities in the returns and volatility time series in order to obtain estimates of Value-at-Risk (VaR). The first class of model that we use mixes a continuous diffusion process with discrete jumps at random points in time (Poisson Jump Diffusion Model). We also apply a purely discontinuous model that does not contain any continuous component at all in the underlying distribution (Variance Gamma Model). These models have been shown to have some success in capturing certain characteristics of return distributions, a few being leptokurtosis and skewness. Calibrating these models onto the returns of an index of Australian stocks (All Ordinaries Index), we then use the resulting parameters to obtain daily estimates of VaR. In order to obtain the VaR estimates for the Poisson Jump Diffusion Model and the Variance Gamma Model, we introduce the use of an innovation from option pricing techniques, which concentrates on the more tractable characteristic functions of the models. Having then obtained a series of VaR estimates, we then apply a variety of criteria to assess how each model performs and also evaluate these models against the traditional approaches to calculating VaR, such as that suggested by J.P. Morgan???s RiskMetrics. Our results show that whilst the Poisson Jump Diffusion model proved the most accurate at the 95% VaR level, neither the Poisson Jump Diffusion or Variance Gamma models were dominant in the other performance criteria examined. Overall, no model was clearly superior according to all the performance criteria analysed, and it seems that the extra computational time required to calibrate the Poisson Jump Diffusion and Variance Gamma models for the purposes of VaR estimation do not provide sufficient reward for the additional effort than that currently employed by Riskmetrics.
40

Multivariate Poisson hidden Markov models for analysis of spatial counts

Karunanayake, Chandima Piyadharshani 08 June 2007
Multivariate count data are found in a variety of fields. For modeling such data, one may consider the multivariate Poisson distribution. Overdispersion is a problem when modeling the data with the multivariate Poisson distribution. Therefore, in this thesis we propose a new multivariate Poisson hidden Markov model based on the extension of independent multivariate Poisson finite mixture models, as a solution to this problem. This model, which can take into account the spatial nature of weed counts, is applied to weed species counts in an agricultural field. The distribution of counts depends on the underlying sequence of states, which are unobserved or hidden. These hidden states represent the regions where weed counts are relatively homogeneous. Analysis of these data involves the estimation of the number of hidden states, Poisson means and covariances. Parameter estimation is done using a modified EM algorithm for maximum likelihood estimation. <p>We extend the univariate Markov-dependent Poisson finite mixture model to the multivariate Poisson case (bivariate and trivariate) to model counts of two or three species. Also, we contribute to the hidden Markov model research area by developing Splus/R codes for the analysis of the multivariate Poisson hidden Markov model. Splus/R codes are written for the estimation of multivariate Poisson hidden Markov model using the EM algorithm and the forward-backward procedure and the bootstrap estimation of standard errors. The estimated parameters are used to calculate the goodness of fit measures of the models.<p>Results suggest that the multivariate Poisson hidden Markov model, with five states and an independent covariance structure, gives a reasonable fit to this dataset. Since this model deals with overdispersion and spatial information, it will help to get an insight about weed distribution for herbicide applications. This model may lead researchers to find other factors such as soil moisture, fertilizer level, etc., to determine the states, which govern the distribution of the weed counts.

Page generated in 0.1364 seconds