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Numerical Simulation of Bloch Equations for Dynamic Magnetic Resonance ImagingHazra, Arijit 07 October 2016 (has links)
No description available.
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De la coexistence de l’orientation stratégique et de l’orientation marché en entreprise : une quête de performance / On matching strategic orientation and market orientation : Implications on the firm performanceAbarar, Ibtissam 12 March 2012 (has links)
La contribution du marketing management à la stratégie est une problématique qui a suscité un grand intérêt, aussi bien dans la communauté des chercheurs que celle des praticiens. L’orientation marché a été un sujet d’investigation fertile dans ce courant de recherche et des débats ont été lancés sur sa capacité à influencer le design stratégique de l’entreprise. Toutefois, peu d’études empiriques ont analysé la relation entre l’orientation stratégique et les comportements orientés marché. Le présent travail tente de contribuer à la théorie de l’interface en examinant cette relation et son impact sur la performance de l’entreprise. Il intègre par ailleurs l’analyse du poids de certains modérateurs qui influencent cette association. Cette recherche doctorale présente une étude empirique qui répond à ces questionnements. Nous avons menée une étude qui a testé notre modèle auprès de 254 senior managers et nous avons opté pour une modélisation en équations structurelles. Nos résultats débouchent sur de nombreuses implications managériales. / Recognized as a topic with important implications for executive practice, the contribution of marketing to business strategy management is a fertile topic of investigation. Within this research stream the role of market orientation has deserved special attention. Prior research raised a substantial debate regarding the market orientation capability to influence strategy design. However, few have investigated this interaction effect and little is understood of the business performance implications of market orientation‘s contribution to business strategy formation. This research addresses theseshortfalls in the literature by examining relationships between market orientation and strategic orientation, their interaction effect on performance, and some factors that moderate their effects on performance. In an attempt to address these key issues, this doctoral research presents an empirical investigation. We conducted a survey of 254 senior executives about their practices adopted in their respective firms. We next performed a structural equation modeling analysis. The results highlight many managerial implications for the practitioners.
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An Approach to Effectively Identify Insider Attacks within an OrganizationDoss, Gary 01 January 2012 (has links)
The purpose of this research is to identify the factors that influence organizational insiders to violate information security policies. There are numerous accounts of successful malicious activities conducted by employees and internal users of organizations. Researchers and organizations have begun looking at methods to reduce or mitigate the insider threat problem. Few proposed methods and models to identify, deter, and prevent the insider threat are based on empirical data. Additionally, few studies have focused on the targets or goals of the insider with organizational control as a foundation. From a target perspective, an organization might be able to control the outcome of a malicious insider threat attack.
This research applied a criminology lens as an organization policy violation is, or resembles, a criminal activity. This research uses the Routine Activities Theory (RAT) as a guide to develop a theoretical model. The adoption of RAT was for its focus on the target and the protective controls, while still taking into account the motivated offender. The study identified the components of the model concerning insider threats, espionage, and illicit behavior related to information systems through literature. This led to the development of 10 hypotheses regarding the relationships of key factors that influence malicious insider activity. Data was collected using a scenario-based survey, which allowed for impartial responses from a third-person perspective. This technique has become popular in the field of criminology, as the effects of social desirability, acceptance, or repudiation will not be a concern. A pilot test verified the survey's ability to collect the appropriate data. The research employed Structural Equation Modeling (SEM) and Confirmatory Factor Analysis (CFA) techniques to analyze and evaluate the data. SEM and CFA techniques identified the fit of the model and the factors that influence information security policy violations. The result of the analysis provided criteria to accept the hypotheses and to identify key factors that influence insider Information System policy violations. This research identified the relationships and the level of influence between each factor.
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Selection during Early Life Stages and Local Adaptation in Arabidopsis thalianaPostma, Froukje M. January 2016 (has links)
Organisms are often adapted to their local environment, but the role of early life stages in adaptive differentiation among populations remains poorly known. The aim of my thesis was to investigate the contribution of early life stages to the magnitude and genetic basis of local adaptation, and to identify the underlying adaptive traits. For this, I used two natural populations of the annual plant Arabidopsis thaliana from Italy and Sweden, and a Recombinant Inbred Line (RIL) population derived from a cross between these populations. By combining greenhouse and field experiments, Quantitative Trait Loci (QTL) mapping, and path analysis, I examined (1) the genetic basis of seed dormancy, (2) the contribution of differential seedling establishment to local adaptation, (3) among-year variation in selection during seedling establishment, (4) direct and indirect effects of seed dormancy and timing of germination on fitness, and (5) the adaptive value of the seed bank. I found that both the level and the genetic basis of seed dormancy were affected by the maternal environment. One major-effect QTL was identified in all maternal environments, which overlaps with the dormancy gene DELAY OF GERMINATION 1 (DOG1). Selection through seedling establishment success contributed strongly to local adaptation and genetic tradeoffs, and varied among years. Variation in seedling establishment and overall fitness among RILs could be explained by genetically based differences in seed dormancy and timing of germination. Seed dormancy affected fitness throughout the life cycle, by affecting the proportion of germinated seeds, and indirectly via effects on timing of germination, plant size and flowering time. My results suggest that a considerable portion of A. thaliana seeds enter the seed bank. I found genetic differences in dormancy cycling behaviour between the two populations, which could contribute to local adaptation. The value of a seed bank should be higher at the Swedish study site than at the Italian study site due to lower rate of seed mortality in the soil. Overall, the results of this thesis demonstrate that early life stages contribute strongly to both the magnitude and the genetics of local adaptation.
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Consumer adoption of audiobook streaming servicesNyström Müller, Jonathan, Engström, Casper January 2019 (has links)
The streaming of audiobooks is a new and fast-growing phenomenon amongst Swedish consumers. There exists a lack of knowledge on this topic as it is previously unexplored within academia. As the audiobook streaming services are growing it is important for providers and competitors to understand the key factors determining usage intention from an end-user’s perspective. This thesis therefore examines what factors influence end-user’s adoption of audiobook streaming-services, the examination extends both for consumers intention to begin using as well as continue using the service. Factors related to the end-user’s usage intention were explored and identified in a Swedish context. A theoretical model consisting of eight hypotheses was constructed to examine the relationships between five variables. The model is based on previous literature of technology adoption and in particular the technology acceptance model (TAM). Additional theory was gathered on previous research on similar technologies such consumers adoption of E-books and E-readers. To achieve the research purpose of the thesis, a quantitative method was used and data was gathered through an online questionnaire with 935 (769 valid) responses. Structural equation modeling (SEM) was used with RStudio to test the collected data on our theoretical model. The results showcased that our model was successful in explaining key factors influencing usage intention. The findings indicate that perceived usefulness and perceived ease of use influence usage intention positively, while end-user’s attachment to paper books and reading impact usage intention negatively. Further results and the implications of these results are discussed.
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[en] ANTECEDENTS AND CONSEQUENCES OF THE LEVELS OF MALE INVOLVEMENT WITH APPAREL: AN EMPIRICAL STUDY WITH MALES FROM RIO DE JANEIRO / [pt] ANTECEDENTES E CONSEQÜÊNCIAS DOS NÍVEIS DE ENVOLVIMENTO MASCULINO COM VESTUÁRIO: UMA PESQUISA EMPÍRICA COM HOMENS DO RIO DE JANEIROLIA DAVIDOVITSCH 13 September 2007 (has links)
[pt] Observam-se, na atualidade, novas formas de identidades
masculinas
sendo ofertadas a partir da ênfase na estética do corpo e
da moda. Visando
contribuir com os múltiplos agentes do setor de moda
masculina para um maior
conhecimento de seus consumidores, este estudo utilizou o
conceito de
envolvimento com vestuário como principal ferramenta para
explorar a relação
dos homens do Rio de Janeiro com os assuntos ligados ao
vestuário. As seguintes
questões centrais foram lançadas: Quais os atuais níveis
de envolvimento dos
homens com o vestuário? Quais fatores podem exercer
influências em tais níveis?
Quais as possíveis conseqüências desses níveis no
comportamento de consumo
masculino? Assim, foi proposto um modelo teórico
relacionando os níveis de
envolvimento dos homens com vestuário a três antecedentes
(percepção dos
valores simbólicos, hedônicos e utilitários do vestuário)
e três conseqüentes
(busca de informação, percepção da importância dos
diferentes atributos da roupa
e percepção de diferenças entre as marcas de roupa
masculina). Tal modelo foi
testado, através da técnica da Modelagem de Equações
Estruturais, alcançando
índices de ajuste satisfatórios. A análise do modelo
indicou quais antecedentes e
conseqüentes obtiveram apoio empírico. / [en] Nowadays, it can be observed that new forms of male
identity have been
created stemming from the emphasis placed on physical
fitness and fashion. With
the aim of providing the multiple agents in the male
fashion sector with data that
could help them learn more about their customers, this
study has made use of the
concept of apparel involvement as its main tool in
examining how males from
Rio de Janeiro relate to matters concerning apparel. The
following are the central
questions guiding this study: What are the present levels
of male involvement
with apparel? What are the factors that may influence
these levels? How could
these levels possibly affect the behavior of male
consumers? Thus, a theoretical
model has been proposed that links the levels of apparel
involvement of males
with three antecedents, namely perception of the symbolic,
hedonic and utilitarian
values of apparel, and with three consequences, namely
search for information,
perception of the relevance of the different attributes of
clothes, and perception of
differences among male clothing brands. The model has been
tested through the
Structural Equation Modeling technique and it has reached
satisfactory fit
indexes. The analysis of the model has indicated which
antecedents and
consequences of apparel involvement received empirical
support.
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Estudo empírico da relação entre qualidade da informação e impacto individual no contexto organizacional / An empirical investigation of the relationship between information quality and individual impact in organizationsSantos, Gilson Ditzel 17 December 2009 (has links)
A falta da qualidade da informação resulta em prejuízos para as organizações. No entanto, a mensuração desses prejuízos é uma tarefa complexa e, muitas vezes, não é do interesse das organizações. Apesar de várias pesquisas de abrangência global sobre qualidade da informação confirmarem seu impacto sobre o desempenho organizacional, muitas das organizações que atuam no Brasil parecem não estar interessadas na gestão da qualidade da informação de maneira formal. Do ponto de vista acadêmico, há que se definir indicadores apropriados para a mensuração dos impactos da qualidade da informação sobre as organizações, bem como, contextualizar essas medidas de forma a propiciar sua generalização. O objetivo desta pesquisa é, portanto, evidenciar que a qualidade da informação impacta o desempenho de organizações que atuam no Brasil e indicar parâmetros que possam moderar essa relação. A medida de impacto organizacional foca o nível individual, para que seja possível avaliar quais características do knowledge worker e de seu ambiente de trabalho interferem na sua percepção da qualidade da informação e do desempenho de seu trabalho. O estudo é de natureza descritiva, portanto, os construtos utilizados são conhecidos e anteriormente validados. No entanto, o arranjo desses construtos e a utilização de variáveis externas, que podem influenciar na relação entre qualidade da informação e impacto individual percebidos são o diferencial desta pesquisa. A unidade de pesquisa é o indivíduo que trabalha em uma organização e utiliza, no mínimo, um sistema de informação para realizar o seu trabalho. Foi realizada pesquisa de levantamento social, por meio de questionário eletrônico autoaplicado, em duas organizações atuantes no Estado do Paraná. A análise dos dados se deu por modelamento de equações estruturais, com a utilização de análise multigrupos. Os resultados confirmam a relação positiva direta da qualidade da informação sobre os impactos individuais e apontam para possíveis variáveis moderadoras dessa relação. A complementação futura desta pesquisa pode-se dar com a avaliação de organizações de diferentes setores econômicos e com a inclusão de outras variáveis externas que diferenciem melhor os indivíduos que atuam nas organizações. / Low-quality information negatively impacts organizational performance. However, the measurement of such impacts is a complex task which not all the organizations perceive as worthwhile accomplishing. Although many worldwide researches about information quality confirm its impact over organizational performance, many organizations that operate in Brazil seem not to be interested in managing information quality. Concerning academic research, it is necessary to define proper indicators to measure the organizational impacts of information quality, considering contextual characteristics. The aim of this research is to confirm that information quality impacts organizational performance of organizations operating in Brazil and show which external variables may moderate this relationship. In this research organizational impact is measured at the individual level, in order that it is possible to define which personal and workplace characteristics influence knowledge workers perception of information quality and individual performance. This research is descriptive and the constructs used are known and previously validated. However, the research model, that includes external variables that may influence the relationship between perceived information quality and individual impact, has never been proposed nor validated by other researchers. The research unit is the individual that work in organizations and use at least one information system to do his job. A survey using self employed electronic questionnaire was applied to two large organizations that operate in Paraná State. Structural Equation Modeling was used to analyze the data. The results confirmed the positive influence of information quality over individual impacts and suggested possible moderators of that relationship. Future studies could include the evaluation of organizations operating in different industries and could test other external variables tha differentiate the individuals better.
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Fatores de risco para nascimento pré-termo - uma análise com modelagem de equações estruturais / Risk factors of preterm birth - an analysis with structural equation modelingOliveira, Adelaide Alves de 20 October 2014 (has links)
Introdução: Um dos principais fatores associados à mortalidade e morbidade no período perinatal é o nascimento pré-termo. Sua prevalência está aumentando em diversas localidades e os motivos para tal envolve complexa inter-relação de fatores que incluem aspectos biológicos, de assistência, psicológicos, sociais e econômicos, entre diversos outros associados ao nascimento pré-termo. Objetivo: O presente estudo objetiva analisar os efeitos de variáveis associadas ao nascimento pré-termo, via modelagem de equações estruturais (MEE), com a construção de variáveis latentes de vulnerabilidade socioeconômica, familiar, psicossocial, condições maternas e intercorrências. Outros objetivos são analisar as diversas fontes de obtenção da idade gestacional (IG) visando gerar uma variável latente para a idade gestacional e comparar modelos com diferentes tipos de variável de desfecho (contínuo, ordinal, binário e latente). Métodos: Esse estudo foi baseado na pesquisa do tipo caso-controle populacional sobre nascidos vivos hospitalares de mães residentes na cidade de Londrina, estado do Paraná, realizado entre junho de 2006 e março de 2007. A partir de um modelo conceitual, foi empregada a MEE para construir modelos com variáveis latentes e compostas com utilização de medidas de ajustes. Resultados: O Modelo final apontou os seguintes efeitos diretos sobre IG: intercorrências, atenção de pré-natal inadequada, gestação múltipla, condição reprodutiva, IMC, consumo de bebida alcoólica, prática de caminhadas e esforço físico. Além do efeito direto da atenção pré-natal, foi encontrado seu papel de variável de mediação entre as variáveis latentes: Vulnerabilidade Socioeconômica, Não Aceitação da Gravidez e Vulnerabilidade Familiar e o desfecho IG. Conclusões: Para a utilização de MEE, foi necessário rediscutir o papel das variáveis propostas no estudo original, o que sugere que, para a aplicação da metodologia, já seja considerada a formulação de variáveis latentes à priori na fase de planejamento de uma pesquisa. A aplicação do MEE permitiu construir variáveis latentes e variáveis compostas a partir do estudo original e identificar efeitos diretos, indiretos e de mediação sobre IG. Ademais, foi possível construir e utilizar a variável latente IG a partir das fontes de registro. / Introduction: One of the main factors associated with mortality and morbidity in the perinatal period is preterm birth. Its prevalence is increasing in many locations and the reasons for such involves a complex interplay of factors associated with preterm birth including biological aspects, assistance, psychological, social and economic factors birth, among many others associated with preterm birth. Objective: This study aims to analyze the effects of variables associated with preterm birth via structural equation modeling (SEM), with the construction of latent variables of socioeconomic vulnerability, family, psychosocial, and maternal complications. Other objectives are to analyze the use of various sources of registering gestational age in order to generate a latent variable for gestational age (GA) and compare models with different types of outcome (continuous, ordinal, binary and latent variable). Methods - This study was based on research in population case-control over hospital births to mothers resident in the city of Londrina, Paraná, conducted between June 2006 and March 2007. From a conceptual model it was used SEM to build models with latent and composite variables with use of adjustment measures. Results: The final model showed the following direct effects on GA: complications, prenatal care inadequate, multiple gestation, reproductive condition, BMI, alcohol consumption, going for walks and effort. Besides the direct effect of prenatal care, found their role of mediating variable between latent variables: Socioeconomic Vulnerability, Not Acceptance of Pregnancy, Vulnerability and Family and the outcome GA. Conclusions: For the use of SEM it was necessary to revisit the role of the variables proposed in the original study, which suggests that, for the application of the methodology, it is already considered the formulation of a priori latent variables in the planning phase of a research. The application allowed SEM to build latent variables and composite variables from the original study and identify direct, indirect and mediating effects on GA. Furthermore, it was possible to build and use the GA latent variable from the recording sources.
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Segmentação de mercado aplicada ao varejo online / Market segmentation applied to online retailVeríssimo, Henrique Urubatã Dias Silva 31 October 2011 (has links)
O canal online de vendas de varejo por meio da Internet tem mostrado impressionante crescimento em termos de uso por parte dos consumidores desde o início dos anos 2000 até 2011, com boas perspectivas de trajetória ascendente para os próximos anos. Essa evolução realça a importância de se realizar planejamento estratégico de negócios que leve em conta o advento da era digital. A segmentação de mercado, tema central deste estudo, é o primeiro requisito para a formulação das estratégias de marketing das empresas, segundo Lambin (2000). Wedel e Kamakura (2000) e Kotler e Keller (2006) são as principais referências para os conceitos de segmentação utilizados neste estudo. Com uma amostra por conveniência formada por 743 consumidores do Brasil, procurou-se investigar, em uma primeira etapa, de caráter exploratório, aspectos ou fatores relacionados ao comportamento de aquisição de produtos no contexto do varejo online. Foi encontrada, principalmente, uma significante relação positiva entre o tempo desde a primeira compra online e maiores frequências de compra anuais pela Internet, o que sugere a importância da familiaridade e confiança para uso mais frequente do canal. A segunda e a terceira etapas foram baseadas principalmente em um modelo proposto por Overby e Lee (2006), que sugere a existência de relações de dependência entre \"intenção de compra\" versus \"valores associados à utilização do canal online\" e \"preferência por determinado site\". Na segunda etapa, de caráter correlacional, foi verificado que os dados coletados se ajustaram adequadamente ao modelo em questão por meio do uso de modelagem de equações estruturais. O objetivo da terceira etapa era verificar a existência de diferenças nas relações de dependência entre os fatores quando são considerados diferentes grupos de consumidores. Conforme recomendações de Hahn et al. (2002), isto foi feito por meio do uso das técnicas de mistura finita em PLS (FIMIX-PLS) e posteriormente por análise de multigrupos em PLS (PLS-MGA) (Henseler et al., 2009). Foram encontradas diferenças significantes para a importância de fatores ao se considerarem os seguintes segmentos: \"feminino\" (as mulheres deram mais importância para o \"valor utilitário\" do que o observado para a amostra total), \"pessoas que dão pouca importância à familiaridade com a loja online\" e \"pessoas que compram online 1 ou 2 vezes ao ano\" (essas pessoas deram mais importância ao \"valor hedônico\" que o observado para a amostra total) e \"compradores de livros\" (que deram menos importância para a preferência que o observado para a amostra total). A análise das diferenças nas relações entre os fatores contribuiu para a atribuição de avaliações de \"grau de resposta\" para cada segmento em relação aos fatores estudados. O grau de resposta é um dos critérios mais críticos para uma segmentação de mercado eficaz e consequentemente pode gerar subsídios importantes para o planejamento estratégico de marketing no contexto do varejo online. / The online retail channel has shown impressive growth in terms of its use by consumers since the beginning of years 2000 up to 2011, with good perspectives of growth for the next years. This growth enhances the business-oriented importance of carrying through strategic planning that takes into account the advent of the digital age. Market segmentation, a central theme of this study, is the first requisite for the formulation of marketing strategies by companies according to Lambin (2000). Wedel and Kamakura (2000) and Kotler and Keller (2006) are the main references for the concepts of segmentation mentioned in this study. With a convenience sample formed by 743 Brazilian consumers, the purpose was to investigate, with an exploratory character at a first stage, aspects or factors related to consumer behavior when purchasing products in the context of online retailing. The main finding of this stage was a significant positive relation between \"the time since the first online purchase\"(time since adoption of the channel) and greater annual frequencies of purchase on the Internet. This suggests the importance of familiarity and confidence for generating more frequent use of the online retail channel by consumers. Second and third stages of this study were mainly based on a model proposed by Overby and Lee (2006) which suggests the existence of dependence relationships between \"purchase intention\" versus \"values associated to the use of online channel\" and \"preference for determined online site\". The second stage had correlacional character, and it was verified that the collected data were adjusted adequately to the model in question by means of using structural equation modeling. The objective of the third stage was to verify the existence of differences in dependence relationships among the studied factors when different groups of consumers were considered. Finite mixtures in PLS (FIMIX-PLS procedures) and multi-group analysis in PLS (MGA-PLS) were made following recommendations of Hahn et al. (2002) and Henseler et al. (2009) respectively. Significant differences for the importance of factors for different segments were found: \"feminine\" (women gave more importance to the \"utilitarian value\" when compared the total sample), \"people who give little importance to the familiarity with the online store\" and \"people who buy online 1 or 2 times per year\" (these groups gave more importance to hedonic value when compared to total sample) and finally \"book purchasers\" (who gave less importance to preference when compared to total sample\"). Analysis of the differences in the relationships among the studied factors contributed for evaluating the \"responsiveness\" criterion for each segment. Responsiveness is one of the most critical criteria for effectiveness of any market segmentation and consequently this contribution can generate important subsidies for strategic marketing planning in the context of online retailing.
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Desenvolvimento de modelos de causalidade com informações de QTLs para estudo do relacionamento de caracteres fenotípicos relativos à absorção de fósforo em milho / Development of causal models with QTL information to the study of relationship among traits associated with phosphorus uptake in maizeGianotto, Adriana Cheavegatti 26 March 2015 (has links)
Metodologias de mapeamento de QTLs modernas empregam abordagem multivariada e se beneficiam da matriz de covariâncias fenotípicas para melhorar as estimativas de localização e efeitos de QTLs. No entanto, a correlação fenotípica pode ser em parte atribuída às relações de causalidade entre os fenótipos e mesmo as abordagens de mapeamento de QTLs multivariadas atuais têm desconsiderado tais relacionamentos. Dentre as metodologias científicas desenvolvidas para o estudo da causalidade em dados observacionais, destacam-se os modelos de equações estruturais e os modelos gráficos. Neste trabalho, foi estudado um conjunto de caracteres fenotípicos relacionados à morfologia de raízes, absorção de fósforo e acúmulo de biomassa em uma população composta de 145 linhagens endogâmicas recombinantes (RILs) do programa de melhoramento de milho da EMBRAPA Milho e Sorgo. O mapeamento de QTLs para os caracteres fenotípicos foi realizado utilizando mapeamento de múltiplos intervalos univariado (MIM) e multivariado (MT-MIM). A análise MIM revelou QTLs afetando diâmetro de raízes, área de superfície de raízes finas, peso seco da parte aérea e concentração de fósforo na parte aérea e nas raízes. A análise MT-MIM revelou 12 QTLs, com diferentes padrões de pleiotropia, com efeitos marginais para as sete variáveis analisadas. Um modelo de relacionamento causal entre os caracteres fenotípicos foi desenvolvido utilizando conhecimento prévio e modelagem de equações estruturais. O modelo de equações estruturais apresentou fluxo unidirecional de causalidade entre as variáveis, com as variáveis de morfologia de raízes exercendo efeito sobre as variáveis de acúmulo de biomassa, que por sua vez, têm efeito sobre as variáveis de absorção de fósforo. A aplicação do algoritmo PC para a descoberta de causalidade automatizada baseada nos padrões de independências condicionais não foi capaz de orientar todas as relações de causalidade descobertas, porém revelou um relacionamento mais complexo que o modelo de equações estruturais, com potenciais ciclos de retroalimentação causais. O emprego de algoritmos de descoberta de causalidade baseados em informações de QTLs, chamados QDG e QPSO, permitiu a orientação de todos os relacionamentos de causalidade encontrados pelo algoritmo PC e confirmou a existência de dois ciclos vizinhos de relacionamento causais entre as variáveis estudadas. Como regra geral, os QTLs pleiotrópicos detectados pela metodologia MT-MIM apresentaram efeitos sobre caracteres fenotípicos alinhados causalmente nos modelos propostos pelos algoritmos PC e QDG, sugerindo que alguns dos QTLs detectados são na realidade efeitos indiretos de QTLs situados em posição mais elevada no modelo causal. O emprego da abordagem MT-MIM aliada à análise de causalidade permitiu melhor compreensão da arquitetura genética dos caracteres de morfologia de raiz, acumulação de biomassa e aquisição de fósforo em milho. / Modern QTL mapping approaches are multivariate and take advantage of the phenotypic covariance matrix to improve estimates of QTL positions and effects. However, phenotypic correlation can also be assigned to the causal relationship among phenotypes, and even modern multivariate QTL analysis does not take these relationships into account. Structural equation models and graphical models are the main methodologies to study causality from observational data. We studied a set of phenotypes related to root morphology, biomass accumulation and phosphorus acquisition in maize. These phenotypes were measured in a maize population from the EMBRAPA breeding program composed of 145 recombinant inbred lines (RILs) derived from the crossing of two divergent lines for phosphorus acquisition efficiency. QTL mapping for the traits was performed using univariate (MIM) and multivariate (MT-MIM) multiple interval mapping. MIM analysis revealed QTL affecting root diameter, fine root surface area, shoot dry weight and root dry weight. MT-MIM analysis revealed 12 QTL with different pleiotropy patterns and QTL with marginal effects affecting all seven studied characters. A causal model for phenotype characters was developed using a priori knowledge and structural equation model techniques. The structural equation model presented an unidirectional causal flow among the variables, with root morphological traits exerting causal effects over biomass traits, which in turn cause phosphorus acquisition traits. Using PC algorithm for an automatic search of causal models based on conditional independence was not able to orient all discovered causal relationships among traits but revealed a more intricated relationship than the structural equation model, with potential causal feedback loops among the traits. Employing causal search algorithms based on QTL information (named QDG and QPSO) allowed the orientation of all causal relationships detected by PC algorithm and it has also confirmed the presence of two neighbor causal cycles among the studied traits. As a general rule, pleiotropic QTL detected by MT-MIM approach exerted effects over traits according to the causal model discovered by PC and QDG algorithms, suggesting that some of the QTL detected effects were indirect effects of QTL located upstream at the proposed causal model. Employing MT-MIM approach and causal analysis has allowed a better comprehension of genetic architecture underlying root morphology, biomass accumulation and phosphorus acquisition traits in maize.
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