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  • 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.
91

Clause linkage in southeastern Tepehuan, : a Uto-Aztecan language of Northern Mexico

García Salido, Gabriela 06 November 2014 (has links)
Linguistics / This dissertation examines the complexity of complementation in O’dam, also known as Southeastern Tepehuan (SET), based on a corpus of twenty-seven hours of naturally recorded speech (105 texts). This complexity is due in part to the fact that the same subordinate marker, na, encodes complements, adverbial and relative clauses, and, in some instances, non-embedded clauses. That is, distributional patterns indicate that na is a polyfunctional marker in SET. In addition to using the na marker, SET conveys adverbial and complement clauses through using non-embedded clauses (i.e., juxtaposition), supporting the notion that subordination does not always involve an embedded association (Cristofaro 2003). Crucially, juxtaposition is used as a coordination strategy. Therefore, investigating clause linkage in SET highlights the formal and semantic categories in which SET differentiates embedded clauses. It further suggests that SET has a continuum of features that distinguish these dependent relationships (e.g., aspect, second position clitics, inherent control, an overt subordinate marker, negation, and focus); thus, this research contributes to recent work on the typology of complementation. All embedded clauses in SET can be distinguished by means of a second position clitic and by the morphology attached to the embedded predicate or to the subordinate marker. More specifically, complements and relative clauses require second position clitics, but adverbials only use them if they are marking switch-reference. This behavior is unique, because adverbials use second position clitics as an indicator of thematic continuity for subjects, suggesting that the development of these clitics evolved independently with the function of marking switch reference. Also, ‘when’ clauses do not have a fixed order compared to locative and manner adverbial clauses, because locative and manner adverbial clauses, along with complements and relatives, always follow the main clause. As for the morphology encoded in complement clauses, SET distinguishes between embedded clauses with or without a complementizer, and on the basis of internal aspectual morphology and inherent control. As a result, it is not the form, but the interface of morphosyntactic, semantic and pragmatic information that helps us identify the type of embedded clause we are facing. / text
92

Structure-function analysis of the bacteriophage PRD1 DNA terminal protein: Nucleotide sequence, overexpression, and site-directed mutagenesis of the terminal protein gene.

Hsieh, Jui-Cheng. January 1990 (has links)
The nucleotide sequence of the PRD1 terminal protein gene has been determined. The coding region for PRD1 terminal protein is 777 base pairs long and encodes 259 amino acid residues (29,326 daltons). The deduced amino acid sequence of PRD1 terminal protein reveals no overall homology with other known terminal proteins or related proteins. A closer examination revealed a highly conserved amino acid sequence, YSRLRT, exist among all identified DNA terminal proteins including PRD1, PZA, Nf, φ29 and adenovirus. This is the first conserved amino acid sequence that has been found in all identified DNA terminal proteins. Not only is the YSRLRT sequence conserved, but its spatial location is similar as well. Therefore, the significance of the YSRLRT conserved sequence is suggested by both its conservative spatial location and high degree of homology across species. To study the structure-function relationship of the YSRLRT sequence of PRD1 terminal protein, in vitro site-directed mutagenesis was performed to determine the role of each amino acid in this conserved region. The PRD1 terminal protein and DNA polymerase genes were cloned into phagemid pEMBLex3, and the recombinant plasmid used for constructing mutants. Eleven PRD1 terminal protein mutant clones were examined for their priming complex formation activities. Our results have strongly demonstrated that the positive charge residue of arginine-174 plays an important role for PRD1 terminal protein function. There are 13 tyrosine residues in the predicted PRD1 terminal protein. It was of interest to known which tyrosine is actually linked to terminal nucleotide of the PRD1 DNA. We used a new approach involving replacing the tyrosine residues with phenylalanine residues in the carboxyl terminal portion of the protein. From analyses, the tyrosine-190 has been determined to be the most likely linkage site between terminal protein and PRD1 DNA.
93

Behavioural case linkage : generalisability, ecological validity, and methodology

Tonkin, Matthew James January 2012 (has links)
Behavioural case linkage (BCL) is a procedure that can be used to identify linked crime series, which contain two or more crimes committed by the same person, thereby helping the police to detect and prosecute repeat offenders who are responsible for a disproportionate amount of crime. However, despite the potential benefits of BCL, there are also damaging consequences if crimes are incorrectly linked. Consequently, research has started to test if and how this procedure can work in the most efficient and reliable way. But, the extant literature has a number of important limitations, particularly in terms of (1) generalisability (i.e., there have been few attempts to replicate findings across geographical locations and time periods), (2) ecological validity (i.e., the methodology used to test BCL is not representative of how the procedure is used in practice), and (3) methodology (i.e., there is a lack of research to systematically compare the various methodological/statistical approaches to BCL). The primary aim of this thesis was to address these three important limitations. In terms of generalisability, this thesis has tested the extent to which previous BCL research on residential burglary, commercial robbery, and car theft can be replicated in new geographical locations and time periods. In terms of ecological validity, a number of new methodologies have been developed and tested that reduce the gap between research and practice in BCL by allowing both non-serial and unsolved offences (as well as solved, serial offences) to be included when testing the principles of BCL, and also for these principles to be tested with crime series that contain several different types of offence. In terms of methodology, novel methodological approaches have been compared with the ‘traditional’, status quo methodology for researching the BCL principles, thereby ensuring that the findings reported in this thesis can be compared with previous work. This thesis, therefore, has important implications for theory, research, and practice and the findings are discussed in the context of these. Future research directions are also outlined.
94

Characterisation of five GH16 glycanase and transglycanase activities and of their hemicellulosic substrates

Simmons, Thomas J. January 2014 (has links)
Plant primary cell walls are hydrated extracellular complexes composed largely of polysaccharides: cellulose, hemicellulose and pectin. Cell wall constituents and composition vary in cell-, environment-, and species-dependent manners. For example, within land plant hemicelluloses xyloglucan is ubiquitous while mixedlinkage (1→3),(1→4)-β-D-glucan (MLG) is found only in the Poales and Equisetum. Glycosyl hydrolase 16 (GH16) enzyme family members include numerous enzymes with pertinence to the understanding of the ‘lives’ of cell wall hemicelluloses. However, despite this, the details of the interactions between GH16 enzymes and their substrates have often not been elucidated. Likewise, the true preferences of many of these enzymes and the range of substrates which they can utilise remain to be fully explored. By providing a greater wealth of information for the correlation of enzyme structure with reaction catalysed, such an understanding would enable better predictions of the activities of novel enzymes. Crucially, this would also allow better identification of roles performed by these enzymes in planta as well as of the potential applications of these enzymes. This work sought to further our understanding of the interactions between GH16 enzymes and their substrates by the study of five activities exhibited by GH16 enzymes – xyloglucan endotransglucosylase (XET), xyloglucan endoglucanase/hydrolase (XEG/XEH), mixed-linkage glucan : xyloglucan endotransglucosylase (MXE), lichenase and cellulose : xyloglucan endotransglucosylase (CXE). All of the analysed activities act on xyloglucan and/or MLG. Of particular focus is the novel enzyme MXE from the evolutionarily isolated genus Equisetum (horsetail), which acts on both. Notable findings include: identification of MXE/CXE gene; determination of the substrate specificity of MXE; defining of the sites of attack of lichenase, XEG, XET and MXE; discovery of novel xyloglucan structures and discrepancies between the xyloglucan present in different barley organs.
95

Investigation of genetic factors causing asthma and associated traits

Haghighi Kakhki, Alireza January 2011 (has links)
Asthma is a common complex disease that affects millions of people around the world. Studies indicate the increase in prevalence of asthma worldwide during the past century and report asthma as an important cause of morbidity and mortality. Asthma can be considered as an important health condition in the UK that ranks amongst the countries with the highest rate of asthma prevalence, hospital admissions and mortality due to asthma. Asthma is caused by a combination of genetic and environmental factors. Genetics has an important role in development of asthma with the heritability of around 70% in most studies. To date, more than 100 asthma . associated genes have been identified but they account for only a small proportion of the heritability of asthma. The centerpiece of this thesis is the investigation of genetic association of cystatin and cathepsin genes with asthma and associated phenotypes including atopy and IgE levels. Cathepsinsl cystatins, as proteases and the related antiproteases have been suggested to have a role in airway remodeling. The investigation included three phases; initial association study, replication study in two independent samples sets and complementary analyses. Three sample panels were used in the studies; AUS1/UK1, MRC- AlMRC-E and DLM-4264. The results of this work identified CSTL 1 (cystatin like-1) associated with asthma and IgE levels.
96

On Descriptive and Predictive Models for Serial Crime Analysis

Borg, Anton January 2014 (has links)
Law enforcement agencies regularly collect crime scene information. There exists, however, no detailed, systematic procedure for this. The data collected is affected by the experience or current condition of law enforcement officers. Consequently, the data collected might differ vastly between crime scenes. This is especially problematic when investigating volume crimes. Law enforcement officers regularly do manual comparison on crimes based on the collected data. This is a time-consuming process; especially as the collected crime scene information might not always be comparable. The structuring of data and introduction of automatic comparison systems could benefit the investigation process. This thesis investigates descriptive and predictive models for automatic comparison of crime scene data with the purpose of aiding law enforcement investigations. The thesis first investigates predictive and descriptive methods, with a focus on data structuring, comparison, and evaluation of methods. The knowledge is then applied to the domain of crime scene analysis, with a focus on detecting serial residential burglaries. This thesis introduces a procedure for systematic collection of crime scene information. The thesis also investigates impact and relationship between crime scene characteristics and how to evaluate the descriptive model results. The results suggest that the use of descriptive and predictive models can provide feedback for crime scene analysis that allows a more effective use of law enforcement resources. Using descriptive models based on crime characteristics, including Modus Operandi, allows law enforcement agents to filter cases intelligently. Further, by estimating the link probability between cases, law enforcement agents can focus on cases with higher link likelihood. This would allow a more effective use of law enforcement resources, potentially allowing an increase in clear-up rates.
97

Aplicação de ferramentas moleculares e convencionais no melhoramento genético da soja /

Espindola, Sybelli Magda Coelho Gonçalves. January 2013 (has links)
Orientador: Antônio Orlando Di Mauro / Coorientador: Sandra Helena Unêda-Trevisoli / Banca: Luís Fernando Alliprandini / Banca: Vanoli Fronza / Banca: Gustavo Vitti Moro / Banca: João Carlos de Oliveira / Resumo: Atualmente, a soja destaca-se como a mais importante oleaginosa cultivada no mundo. Os investimentos em pesquisa levaram à "tropicalização" da soja, permitindo, pela primeira vez na história, que o grão fosse plantado com sucesso, em regiões de baixas latitudes, entre o Trópico de Capricórnio e a linha do Equador. Em função disso tem-se buscado o desenvolvimento de genótipos com ampla adaptabilidade, o que implica em uma baixa interação genótipo x ambiente. O entendimento do tipo de interação permite um melhor posicionamento e indicação de regiões de plantio da cultivar em questão facilitando o trabalho do melhorista. A presença desse fenômeno pode acarretar uma redução da produtividade global de uma área para a qual se faça uma indicação geral de uma dada cultivar. Por outro lado, pode-se tirar proveito de sua existência usando-se procedimentos estatísticos que identifiquem o padrão dessa interação, e gerem informações que possibilitem o agrupamento de locais em zonas dentro das quais a magnitude da interação não seja significativa, permitindo indicações específicas de cultivares para tais zonas. O uso de ferramentas moleculares tem se apresentado como uma opção para seleção de características com base no genótipo e eliminando assim o efeito do ambiente na expressão da característica em questão. O melhoramento assistido por marcadores moleculares tem sido tema de inúmeros trabalhos de seleção assistida, cujos resultados variam de concretos e positivos a controversos e pouco significativos em termos de ganhos genéticos, econômicos e eficiência, quando comparados com a seleção fenotípica. Os capítulos seguintes permitem apresentar resultados de metodologias moleculares e convencionais aplicadas em um programa de melhoramento para seleção de genótipos superiores de soja. / Abstract: Nowadays, soybean highlights as the most important oilseed cultivated in the world. The investments in research led to soybean "tropicalization", allowing, for the first time in history, that the grain was seeded with success, in low latitudes, between the tropic of Capricorn and the Equator. Due to this, researchers have tried to develop wide adaptability genotypes, which implies in a low genotype x environment interaction. The comprehension of the type of interaction allows a better placement and indications of cultivar planting regions, facilitating the breeder's work. The presence of this phenomenon may result in a global productivity decrease of an area that make up an overall indication of a given cultivar. On the other hand, it is possible to take advantage of their existence using statistical procedures to identify the pattern of this interaction, and generate information that allow the grouping of local areas within which the magnitude of the interaction is not significant. Specific cultivar indication for these zones. The use o molecular tools have shown as an option for characteristics selection base on genotype and then eliminating the environment effect in the expression of the characteristic in question. The molecular marker-assisted breeding has been the subject of numerous works assisted selection, whose results varies from concrete and positive to controversial and little significant in terms of genetic gains, and economic efficiency compared to phenotypic selection. The following chapters present results provide molecular and conventional methodologies applied in a breeding program for superior genotypes selection. / Doutor
98

Construção do mapa genético integrado em uma progênie de irmâos-completos proveniente do cruzamento entre Eucalyptus grandis e Eucalyptus urophylla / Development of an integrated genetic map for a full-sib progeny from crossing between Eucalyptus grandis and Eucalyptus urophylla

Taniguti, Cristiane Hayumi 26 January 2017 (has links)
O eucalipto é amplamente cultivado em diversos países, dentre os quais, o Brasil se destaca pela sua alta produção. A cultura tem grande importância comercial e atende à uma ampla variedade de setores do mercado, entre eles o de celulose. Apesar disso, a cultura ainda está nas fases iniciais de domesticação devido, principalmente, ao seu longo ciclo reprodutivo e tempo de rotação, uma vez que os cortes são feitos entre 5 e 15 anos. A aplicação de tecnologias de marcadores moleculares é uma proposta promissora para acelerar o melhoramento do eucalipto. Com o desenvolvimento de metodologias modernas de sequenciamento tornou-se acessível a obtenção de grande quantidade de marcadores a baixo custo. Uma das aplicações de tais marcadores é a construção de mapas genéticos de ligação, os quais permitem a caracterização genética de caracteres quantitativos, além de estudos comparativos entre populações e o auxílio na montagem de genomas. No presente trabalho, objetivou-se a construção de um mapa genético integrado em uma progênie F1 segregante com 200 indivíduos, proveniente do cruzamento entre Eucalyptus grandis e Eucalyptus urophylla. Para identificação dos marcadores, foi realizado o ressequenciamento do genoma completo (WGS) dos genitores e a genotipagem por sequenciamento (GBS) da progênie. A metodologia de construção de mapa foi adaptada para o conjunto de dados obtido, que apresenta grande quantidade de marcadores do tipo SNP, pouco informativos e com maior probabilidade de erro comparado com os marcadores tradicionais mais utilizados nos últimos anos. Para isso foram propostas duas estratégias: i) utilização da posição dos marcadores no genoma de referência para auxílio na ordenação dos marcadores no mapa; ii) alteração do parâmetro de probabilidade de erro da abordagem implementada no software Onemap. O mapa obtido apresentou padrão de taxa de recombinação semelhante a outros mapas construídos para eucalipto. O mapa apresentou tamanho total de 1471.91 cM e 1512 marcadores, com distância média entre eles de 1.85 cM. Os marcadores formaram 11 grupos de ligação, que corresponderam aos cromossomos do genoma de referência. Em média, foram cobertos 96.8% dos cromossomos. Também foram agrupados, junto aos 11 grupos, 61 marcadores localizados em outros scaffolds no genoma de referência, os quais podem servir para elucidação na montagem destes. Utilizando as estratégias propostas, foi obtido um mapa integrado adequado para o experimento em questão, considerando o tamanho da população de mapeamento. / The eucalyptus is widely cultivated in several countries, among which Brazil is highlighted by its high production. This culture has great comercial importance and supplies a wide variety of markets, including cellulose. However, the culture is still in the early stages of domestication due, mainly, to its long reproductive cycle and rotation time, since cuts are made between 5 and 15 years. The application of molecular marker technologies is a promising proposal to accelerate the improvement of eucalyptus. By the development of modern sequencing methodologies it was possible to obtain a large quantity of markers at low cost. One of the applications of such markers is the construction of genetic linkage maps, which allow the genetic characterization of quantitative traits, as well as comparative studies between populations and the support in the assembly of genomes. In the present work, the aim was to construct an integrated genetic map in a segregating F1 progeny with 200 individuals, derived from the cross between Eucalyptus grandis and Eucalyptus urophylla. For the identification of the markers, it was performed a complete genome re-sequencing (WGS) of the parents and genotyping-by-sequencing (GBS) of the progeny. The mapping methodology was adapted to the obtained data set, which presents a large amount of SNP-type markers, with little information and with a greater probability of error compared to the most used traditional markers in the last years. For this, two strategies were proposed: i) use of the position of the markers in the reference genome to aid in the ordering of the markers on the map; ii) change of the error probability parameter in the approach implemented in the software Onemap. The obtained map showed recombination rate pattern similar to other maps constructed for eucalyptus. The map presented a total size of 1471.91 cM and 1512 markers, with a mean distance between them of 1.85 cM. The markers formed 11 linkage groups, which corresponded to chromosomes of the reference genome. On average, 96.8 % of chromosomes were covered. 61 markers located in other scaffolds in the reference genome were grouped with the 11 groups. They may serve to elucidate the assembly of these. Using the proposed strategies, a suitable integrated map was obtained for the present experiment, considering the size of the mapping population.
99

Uso da técnica de linkage nos sistemas de informação em saúde: aplicação na base de dados do Registro de Câncer de base populacional do município de São Paulo / The use of the linkage technique in health information systems: application in the database of the São Paulo Population-based Cancer Registry

Peres, Stela Verzinhasse 07 December 2011 (has links)
A disponibilidade de grandes bases de dados informatizadas em saúde tornou a técnica de relacionamento de fontes de dados, também conhecida como linkage, uma alternativa para diferentes tipos de estudos. Esta técnica proporciona a geração de uma base de dados mais completa e de baixo custo operacional. Objetivo- Investigar a possibilidade de completar/aperfeiçoar as informações da base de dados do RCBP-SP, no período de 1997 a 2005, utilizando o processo de linkage com três outras bases, a saber: Programa de Aprimoramento de Mortalidade (PRO-AIM), Autorização e Procedimentos de Alta Complexidade (APAC-SIA/SUS) e Fundação Sistema Estadual de Análise de Dados (FSeade). Métodos- Neste estudo foi utilizada a base de dados do RCBP-SP, composta por 343.306 com casos incidentes de câncer do município de São Paulo, registrados no período de 1997 a 2005, com idades que variaram de menos de um a 106 anos, de ambos os sexos. Para a completitude das informações do RCBP-SP foram utilizadas as bases de dados, a saber: PRO-AIM, APAC-SIA/SUS e FSeade. Foram utilizadas as técnicas de linkage probabilística e determinística. O linkage probabilístico foi realizado pelo programa Reclink III versão 3.1.6. Quanto ao linkage determinístico as rotinas foram realizadas em Visual Basic, com as bases hospedadas em SQL Server. Foram calculados os coeficientes brutos de incidência (CBI) e mortalidade (CBM) antes e após o linkage. A análise de sobrevida global foi realizada pela técnica de Kaplan-Meier e para na comparação entre as curvas, utilizou-se o teste de log rank. Foram calculados os valores da área sob a curva, sensibilidade e especificidade para determinar o ponto de corte do escore de maior precisão na identificação dos pares verdadeiros. Resultados- Após o linkage, verificou-se um ganho de 101,5 por cento para a variável endereço e 31,5 por cento para a data do óbito e 80,0 por cento para a data da última informação. Quanto à variável nome da mãe, na base de dados do RCBP-SP antes do linkage esta informação representava somente 0,5 por cento , tendo sido complementada, no geral, em 76.332 registros. A análise de sobrevida global mostrou que antes do processo de linkage havia uma subestimação na probabilidade de estar vivo em todos os períodos analisados. No geral, para a análise de sobrevida truncada em sete anos, a probabilidade de estar vivo no primeiro ano de seguimento antes do linkage foi menor quando comparada a probabilidade de estar vivo ao primeiro ano de seguimento após o linkage (48,8 por cento x 61,1 por cento ; p< 0,001). Conclusão- A técnica de linkage tanto probabilística quanto determinística foi efetiva para completar/aperfeiçoar as informações da base de dados do RCBP-SP. Além do mais, o CBI apresentou um ganho de 3,4 por cento . Quanto ao CBM houve um ganho de 25,8 por cento . Após o uso da técnica de linkage, foi verificado que os valores para a sobrevida global estavam subestimados para ambos os sexos, faixas etárias e para as topografias de câncer / The availability of large computerized databases on health has enabled the record linkage technique, an alternative for different study designs. This technique provides the generation of a more complete database, at low operational cost. Objective to investigate the possibility of completing/improving information from the database of the RCBP-SP, in the period between 1997 and 2005, using the record linkage technique with other three databases, namely: Mortality Improvement Program (PRO-AIM), Authorization of Highly Complex Procedures (APAC-SIA/SUS) and State System of Data Analysis (FSeade), comparing different strategies. Methods In this study we used the database of the RCBP-SP composed of 343,306 incident cancer cases in the Municipality of São Paulo registered in the period between 1997 and 2005 with ages raging from under one to 106 years, from both sexes. To complete the database of the RCBP-SP three databases were used, namely: PRO-AIM, APAC-SIA/SUS and FSeade. Both probabilistic and deterministic record linkage were used. Probabilistic linkage was performed using the Reclink III software, version 3.1.6. As for the the deterministic record linkage, the routines were run in the Visual Basic and databases hosted on a SQL Server. Before and after record linkage, crude incidence (CIR) and mortality rates (CMR) were calculated. The overall survival analysis was performed using the Kaplan-Meier technique and for the comparison between curves, the log rank test was employed. In order to determine the most precise cut-off scores in identifying true matches, we calculated the area under the curve, as well as, sensitivity and specificity. Results After record linkage, it was verified a gain of 101.5 per cent for the variable address, 31.5 per cent for death date and 80,0 per cent for the date of latest information. As for the variable mother´s name, in the database of the RCBP-SP before record linkage, this information represented only 0.5 per cent , having been completed, in general, in 76,332 registries. The overall survival analysis showed that before the record linkage there was an underestimation of the probability of being alive for all periods assessed. In general, for the truncated survival at seven years, the probability of being alive at the first year of follow up before record linkage was lower when compared to the probability of being alive at the first year of follow up after record linkage (48.8 per cent x 61.1 per cent ; p< 0.001). Conclusion Both the probabilistic and deterministic record linkage were effective to complete/improve information from the database of the RCBP-SP. Moreover, the CIR had a gain of de 3.4 per cent . As for the CMR, there was a gain of 25.8 per cent . After using the record linkage technique, it was verified that values for overall survival were underestimated for both sexes, all age groups, and cancer sites
100

Análise da aprendizagem de ligações em otimização evolutiva / Analysis of linkage learning in evolutionary optimization

Martins, Jean Paulo 13 May 2015 (has links)
A suposta ubiquidade de sistemas decomponíveis foi interpretada por Holland (1975) como o principal motivo para o desempenho dos algoritmos genéticos (Genetic Algorithms (GAs)). A hipótese de Building Blocks (BBs) sugere que algoritmos genéticos mais eficientes poderiam ser implementados, contudo, apenas anos depois essas ideias puderam ser avaliadas experimentalmente no contexto de algoritmos de estimação de distribuição (Estimation of Distribution Algorithms (EDAs)). EDAs utilizam modelos probabilísticos, estimados a partir da população, para inferir características do espaço de busca que poderiam ser utilizadas para implementar operadores de reprodução mais eficazes. Tanto em problemas mono- quanto multi-objetivo, EDAs emergiram sob a premissa de que a eficácia dos operadores de reprodução seria proporcional à representatividade dos modelos probabilísticos utilizados. No entanto, estudos recentes tem demonstrado que a dificuldade em se construir modelos confiáveis pode tornar essa premissa inviável. Ou seja, para certos problemas de otimização os modelos probabilísticos utilizados seriam, em geral, de baixa qualidade e, portanto, não produziriam operadores eficazes. Esta tese trata das limitações encontradas na construção de modelos probabilísticos (linkage learning) sob a perspectiva da multimodalidade dos problemas em questão. A análise teórica considerou problemas aditivamente separáveis, enquanto a generalização das conclusões foi investigada em instâncias do modelo NK-landscapes e do problema da mochila multidimensional (Multidimensional Knapsack Problem (MKP)). Os resultados indicaram que a acurácia dos modelos probabilísticos é se relaciona inversamente ao grau de multimodalidade da função objetivo e que, em casos de extrema multimodalidade a construção de modelos probabilísticos confiáveis pode ser tornar infactível. Este resultado poderia inviabilizar o uso de EDAs no contexto multiobjetivo, devido a intrínseca multimodalidade de tais problemas. No entanto, observou-se que apesar da ausência de estatísticas confiáveis sobre cada uma das funções objetivo, a correlação entre elas se torna estatisticamente observável e útil aos operadores de reprodução na manutenção da diversidade e controle convergência da população. / The supposed ubiquity of nearly-decomposable systems was interpreted by Holland (1975) as the rationale for the performance of Genetic Algorithms (GAs), the Building Block (BB) hypothesis. His seminal studies suggest more efficient GAs as viable, but only later on his ideas have become practically tangible in the context of Estimation of Distribution Algorithms (EDAs). EDAs employ probabilistic modeling so as to infer properties of the search space (BBs) that could be useful for the effectiveness of reproduction operators. In both, single- and multi-objective contexts, EDAs have emerged on the assumption there is a correlation between how much information a model can conceive and how effective reproduction operators can be. However, more recent results suggest the difficulties in producing accurate linkage models can prevent such a relation to be true. In other words, for some optimization problems linkage learning might not be able to produce accurate linkage models, hence EDAs would not outperform GAs. This thesis addresses the limits of linkage learning in the context of single- and bi-objective problems, regarding the influence of multimodality on the accuracy of the linkage models and the efficiency of EDAs. A theoretical analysis was performed in terms of additively separable functions and general conclusions are assessed through experimentation with instances of the NK-model and the Multidimensional Knapsack Problem (MKP). The results indicated that the accuracy of the linkage models tends to decrease as a result of increasing multimodality, which weakens pairwise dependencies and might lead to pairwise independence in extreme cases. Since most EDAs rely on bivariate statistics to estimate multivariate distributions, their applicability is limited to optimization problems within a certain range of multimodality. In multi-objective problems, on the other hand, some EDAs have shown better performance than GAs, which seemed as a contradiction since multi-objective problems are inherently multimodal. Our results suggest that in such cases the correlation among the objective functions becomes statistically evident, as a consequence, linkage learning models such correlation instead of problems substructures, which is useful to obtain a better exploration of extreme regions of the objective space.

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