• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 8
  • 2
  • 2
  • Tagged with
  • 12
  • 12
  • 5
  • 4
  • 4
  • 3
  • 3
  • 3
  • 3
  • 3
  • 3
  • 3
  • 3
  • 3
  • 3
  • 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.
1

Online Market Monitoring

Walchhofer, Norbert 22 February 2017 (has links) (PDF)
This thesis conceptualizes a generic monitoring framework for online markets, which has also been implemented in a prototypic fashion. Thereby identifying a set of arising challenges for which solutions have been developed. An introductory section gives a short overview of the field of research, states identified scientfic challenges and derives research questions thereof. The following articles describe (i) the general approach of an online market monitor, (ii) how to encapsulate domain-dependent configurations & functionalities from monitoring core modules to facilitate a generic approach, (iii) change frequency estimation for observational units in a dynamic and fuzzy population setting, (iv) the development of an adaptive harvest heuristic scheduling new observations by utilizing the change frequency estimator, (v) how to make use of collected market information in form of business intelligence reports and finally (vi) an exemplary meta-analysis showing how to draw further conclusions about market mechanisms.
2

Dinâmica estocástica de populações biológicas / Stochastic Dynamics of Biological Poupulations

Hirata, Flávia Mayumi Ruziska 15 August 2017 (has links)
Nesta tese investigamos modelos irreversíveis dentro do contexto da mecânica estatística de não-equilíbrio motivados por alguns problemas de dinâmicas de populações biológicas. Procuramos identificar a existência de transições de fase e as classes de universalidade às quais os modelos pertencem. Além disso, buscamos modelos que capturem as principais características dos sistemas biológicos que procuramos descrever. Encontramos a solução analítica exata para o modelo suscetível-infectado-recuperado (SIR) em uma rede unidimensional. Investigamos o modelo suscetível-infectado-recuperado com infecção recorrente. Mostramos que o modelo pertence à classe de universalidade da percolação isotrópica, salvo pelos parâmetros em que se torna o processo de contato. Obtivemos também a linha de transição entre as fases em que há e não há propagação da epidemia, através de aproximações de campo médio e por simulações de Monte Carlo do modelo na rede quadrada. Investigamos uma dinâmica para duas espécies biológicas e dois nichos ecológicos; para tanto introduzimos um modelo estocástico irreversível de quatro estados. Concluímos que o modelo oferece uma descrição para as oscilações temporais das populações das espécies e para a alternância de dominância entre estas. Para chegar a esta conclusão, utilizamos simulações de Monte Carlo do modelo na rede quadrada, aproximações de campo médio e a abordagem da equação mestra de nascimento e morte, a qual, para grandes populações, pode ser aproximada por uma equação de Fokker-Planck que é associada a um conjunto de equações de Langevin. Por fim, usando simulações de Monte Carlo, analisamos a dinâmica de duas espécies biológicas e dois nichos ecológicos incluindo difusão. Novamente verificamos que o modelo gera cenários com oscilações temporais das populações das espécies e alternância de dominância entre estas. Ademais, concluímos que modelo pertence à classe de universalidade da percolação direcionada e obtivemos o diagrama de fase. / In this thesis we investigate irreversible models within the context of nonequilibrium statistical mechanics motivated by some problems of biological population dynamics. We look for dentifying the existence of phase transition and the universality classes to which the models belong. In addition to that, we look for models that capture the main characteristics of the biological systems which we are interested in describing. We found the exact analytic solution of the susceptible-infected-recovered (SIR) model on one-dimensional lattice. We investigated the susceptible-infected-recovered model with recurrent infection. We showed that the model belongs to the isotropic percolation universality class, except for the parameters that make the model become a contact process. We obtained the transition line between the phases in which there is propagation of the epidemic and in which there is not, by means of mean-field approximations and Monte Carlo simulations on a square lattice. Furthermore, we investigated a dynamic for two biological species and ecological niches; for this purpose we introduced an irreversible stochastic model with four states. We conclude that the modoffers a description of time oscillations of the species populations and of the alternating dominance between them. To achieve this conclusion we used Monte Carlo simulations of this model on a square lattice, mean-field approximation, and the birth and death master equation approach, which for large populations can be approximated by a Fokker-Planck equation that is associated to a set of Langevin equations. Finally, using Monte Carlo simulations, we analyzed a dynamic for two biological species and ecological niches including diffusion. Again, we verified that the model generates scenarios with time oscillations of the species populations and with alternating dominance between them. Also, we conclude that the model belongs to the directed percolation universality class and we found the phase diagram.
3

Dinâmica estocástica de populações biológicas / Stochastic Dynamics of Biological Poupulations

Flávia Mayumi Ruziska Hirata 15 August 2017 (has links)
Nesta tese investigamos modelos irreversíveis dentro do contexto da mecânica estatística de não-equilíbrio motivados por alguns problemas de dinâmicas de populações biológicas. Procuramos identificar a existência de transições de fase e as classes de universalidade às quais os modelos pertencem. Além disso, buscamos modelos que capturem as principais características dos sistemas biológicos que procuramos descrever. Encontramos a solução analítica exata para o modelo suscetível-infectado-recuperado (SIR) em uma rede unidimensional. Investigamos o modelo suscetível-infectado-recuperado com infecção recorrente. Mostramos que o modelo pertence à classe de universalidade da percolação isotrópica, salvo pelos parâmetros em que se torna o processo de contato. Obtivemos também a linha de transição entre as fases em que há e não há propagação da epidemia, através de aproximações de campo médio e por simulações de Monte Carlo do modelo na rede quadrada. Investigamos uma dinâmica para duas espécies biológicas e dois nichos ecológicos; para tanto introduzimos um modelo estocástico irreversível de quatro estados. Concluímos que o modelo oferece uma descrição para as oscilações temporais das populações das espécies e para a alternância de dominância entre estas. Para chegar a esta conclusão, utilizamos simulações de Monte Carlo do modelo na rede quadrada, aproximações de campo médio e a abordagem da equação mestra de nascimento e morte, a qual, para grandes populações, pode ser aproximada por uma equação de Fokker-Planck que é associada a um conjunto de equações de Langevin. Por fim, usando simulações de Monte Carlo, analisamos a dinâmica de duas espécies biológicas e dois nichos ecológicos incluindo difusão. Novamente verificamos que o modelo gera cenários com oscilações temporais das populações das espécies e alternância de dominância entre estas. Ademais, concluímos que modelo pertence à classe de universalidade da percolação direcionada e obtivemos o diagrama de fase. / In this thesis we investigate irreversible models within the context of nonequilibrium statistical mechanics motivated by some problems of biological population dynamics. We look for dentifying the existence of phase transition and the universality classes to which the models belong. In addition to that, we look for models that capture the main characteristics of the biological systems which we are interested in describing. We found the exact analytic solution of the susceptible-infected-recovered (SIR) model on one-dimensional lattice. We investigated the susceptible-infected-recovered model with recurrent infection. We showed that the model belongs to the isotropic percolation universality class, except for the parameters that make the model become a contact process. We obtained the transition line between the phases in which there is propagation of the epidemic and in which there is not, by means of mean-field approximations and Monte Carlo simulations on a square lattice. Furthermore, we investigated a dynamic for two biological species and ecological niches; for this purpose we introduced an irreversible stochastic model with four states. We conclude that the modoffers a description of time oscillations of the species populations and of the alternating dominance between them. To achieve this conclusion we used Monte Carlo simulations of this model on a square lattice, mean-field approximation, and the birth and death master equation approach, which for large populations can be approximated by a Fokker-Planck equation that is associated to a set of Langevin equations. Finally, using Monte Carlo simulations, we analyzed a dynamic for two biological species and ecological niches including diffusion. Again, we verified that the model generates scenarios with time oscillations of the species populations and with alternating dominance between them. Also, we conclude that the model belongs to the directed percolation universality class and we found the phase diagram.
4

Dinâmica de populações: modelo predador-presa estocástico e difusivo em um reticulado / Dynamic population: Predator-prey stochastic and difusive model on a lattice

Rodrigues, Áttila Leães 29 January 2009 (has links)
Estudamos o modelo predador-presa estocástico definido em uma rede com interações entre os primeiros vizinhos, cada sítio podendo assumir três estados: vazio, ocupado por presa e ocupado por predador. Introduzimos ainda um parâmetro que controla a possibilidade de difuãao dos estados, a difusão é permitida entre quaisquer estados. O modelo exibe uma fase oscilante, uma fase não-oscilante e uma fase absorvente. As duas primeiras fases possibilitam a coexistência entre as espécies biológicas enquanto na fase absorvente a rede é totalmente preenchida por presas e o sistema fica preso nessa configuração. Determinamos a linha de transição da fase não-oscilante para a fase absorvente por meio de simulações dependentes do tempo. Também, determinamos a linha de transição da fase oscilante para a fase não-oscilante através da análise das funções de autocorrelação das séries temporais de presas e predadores. Além disso, estudamos o modelo por meio de aproximações de campo médio dinâmico. Concluímos que a inclusão da difusão no modelo predador-presa leva a uma maior região de coexistência das espécies no diagrama de fases. Nossos resultados sugerem que o componente difusivo é irrevelevante quanto ao comportamento crítico, pois ele não exclui o modelo da classe de universalidade da percolação direcionada. / We have studied the predator-prey stochastic model defined on a lattice with first neighbour interactions. Each site of the lattice may assume one of three states: vacant, occupied by prey and occupied by predator. We have introduced a parameter that controls the possibility of difusion among sites. The model shows an oscilating phase, a non-oscilating phase and an absorbing phase. In the first two phases the system exhibits coexistence of biological species while in the absorbing phase the lattice is filled with prey and the system becomes trapped. We have determined the transition line between the non-oscilating and absorbing phases using time-dependent simulations. We have also determined the transition lines between oscilating and non-oscilating phases using time-autocorrelation functions of the prey time-series. In addition, we have studied the model by means of dynamical mean-field aproximations. We conclude that the introduction of diffusion in the predator-prey model leads to a larger region of coexistence in the phase diagram. Our results suggest that difusion is irrelevant for the critical behavior since it does not change the universatility class of the model.
5

Integrating dynamic and statistical modelling approaches in order to improve predictions for scenarios of environmental change

Zurell, Damaris January 2011 (has links)
Species respond to environmental change by dynamically adjusting their geographical ranges. Robust predictions of these changes are prerequisites to inform dynamic and sustainable conservation strategies. Correlative species distribution models (SDMs) relate species’ occurrence records to prevailing environmental factors to describe the environmental niche. They have been widely applied in global change context as they have comparably low data requirements and allow for rapid assessments of potential future species’ distributions. However, due to their static nature, transient responses to environmental change are essentially ignored in SDMs. Furthermore, neither dispersal nor demographic processes and biotic interactions are explicitly incorporated. Therefore, it has often been suggested to link statistical and mechanistic modelling approaches in order to make more realistic predictions of species’ distributions for scenarios of environmental change. In this thesis, I present two different ways of such linkage. (i) Mechanistic modelling can act as virtual playground for testing statistical models and allows extensive exploration of specific questions. I promote this ‘virtual ecologist’ approach as a powerful evaluation framework for testing sampling protocols, analyses and modelling tools. Also, I employ such an approach to systematically assess the effects of transient dynamics and ecological properties and processes on the prediction accuracy of SDMs for climate change projections. That way, relevant mechanisms are identified that shape the species’ response to altered environmental conditions and which should hence be considered when trying to project species’ distribution through time. (ii) I supplement SDM projections of potential future habitat for black grouse in Switzerland with an individual-based population model. By explicitly considering complex interactions between habitat availability and demographic processes, this allows for a more direct assessment of expected population response to environmental change and associated extinction risks. However, predictions were highly variable across simulations emphasising the need for principal evaluation tools like sensitivity analysis to assess uncertainty and robustness in dynamic range predictions. Furthermore, I identify data coverage of the environmental niche as a likely cause for contrasted range predictions between SDM algorithms. SDMs may fail to make reliable predictions for truncated and edge niches, meaning that portions of the niche are not represented in the data or niche edges coincide with data limits. Overall, my thesis contributes to an improved understanding of uncertainty factors in predictions of range dynamics and presents ways how to deal with these. Finally I provide preliminary guidelines for predictive modelling of dynamic species’ response to environmental change, identify key challenges for future research and discuss emerging developments. / Das Vorkommen von Arten wird zunehmend bedroht durch Klima- und Landnutzungswandel. Robuste Vorhersagen der damit verbundenen Arealveränderungen sind ausschlaggebend für die Erarbeitung dynamischer und nachhaltiger Naturschutzstrategien. Habitateignungsmodelle erstellen statistische Zusammenhänge zwischen dem Vorkommen einer Art und relevanten Umweltvariablen und erlauben zügige Einschätzungen potentieller Arealveränderungen. Dabei werden jedoch transiente Dynamiken weitgehend ignoriert sowie demographische Prozesse und biotische Interaktionen. Daher wurden Vorschläge laut, diese statistischen Modelle mit mechanistischeren Ansätzen zu koppeln. In der vorliegenden Arbeit zeige ich zwei verschiedene Möglichkeiten solcher Kopplung auf. (i) Ich beschreibe den sogenannten ‚Virtuellen Ökologen’-Ansatz als mächtiges Validierungswerkzeug, in dem mechanistische Modelle virtuelle Testflächen bieten zur Erforschung verschiedener Probenahmedesigns oder statistischer Methoden sowie spezifischer Fragestellungen. Auch verwende ich diesen Ansatz, um systematisch zu untersuchen wie sich transiente Dynamiken sowie Arteigenschaften und ökologische Prozesse auf die Vorhersagegüte von Habitateignungsmodellen auswirken. So kann ich entscheidende Prozesse identifizieren welche in zukünftigen Modellen Berücksichtigung finden sollten. (ii) Darauf aufbauend koppele ich Vorhersagen von Habitateignungsmodellen mit einem individuen-basierten Populationsmodell, um die Entwicklung des Schweizer Birkhuhnbestandes unter Klimawandel vorherzusagen. Durch die explizite Berücksichtigung der Wechselwirkungen zwischen Habitat und demographischer Prozesse lassen sich direktere Aussagen über Populationsentwicklung und damit verbundener Extinktionsrisiken treffen. Allerdings führen verschiedene Simulationen auch zu hoher Variabilität zwischen Vorhersagen, was die Bedeutung von Sensitivitätsanalysen unterstreicht, um Unsicherheiten und Robustheit von Vorhersagen einzuschätzen. Außerdem identifiziere ich Restriktionen in der Datenabdeckung des Umweltraumes als möglichen Grund für kontrastierende Vorhersagen verschiedener Habitateignungsmodelle. Wenn die Nische einer Art nicht vollständig durch Daten beschrieben ist, kann dies zu unrealistischen Vorhersagen der Art-Habitat-Beziehung führen. Insgesamt trägt meine Arbeit erheblich bei zu einem besseren Verständnis der Auswirkung verschiedenster Unsicherheitsfaktoren auf Vorhersagen von Arealveränderungen und zeigt Wege auf, mit diesen umzugehen. Abschließend erstelle ich einen vorläufigen Leitfaden für Vorhersagemodelle und identifiziere Kernpunkte für weitere Forschung auf diesem Gebiet.
6

Dinâmica de populações: modelo predador-presa estocástico e difusivo em um reticulado / Dynamic population: Predator-prey stochastic and difusive model on a lattice

Áttila Leães Rodrigues 29 January 2009 (has links)
Estudamos o modelo predador-presa estocástico definido em uma rede com interações entre os primeiros vizinhos, cada sítio podendo assumir três estados: vazio, ocupado por presa e ocupado por predador. Introduzimos ainda um parâmetro que controla a possibilidade de difuãao dos estados, a difusão é permitida entre quaisquer estados. O modelo exibe uma fase oscilante, uma fase não-oscilante e uma fase absorvente. As duas primeiras fases possibilitam a coexistência entre as espécies biológicas enquanto na fase absorvente a rede é totalmente preenchida por presas e o sistema fica preso nessa configuração. Determinamos a linha de transição da fase não-oscilante para a fase absorvente por meio de simulações dependentes do tempo. Também, determinamos a linha de transição da fase oscilante para a fase não-oscilante através da análise das funções de autocorrelação das séries temporais de presas e predadores. Além disso, estudamos o modelo por meio de aproximações de campo médio dinâmico. Concluímos que a inclusão da difusão no modelo predador-presa leva a uma maior região de coexistência das espécies no diagrama de fases. Nossos resultados sugerem que o componente difusivo é irrevelevante quanto ao comportamento crítico, pois ele não exclui o modelo da classe de universalidade da percolação direcionada. / We have studied the predator-prey stochastic model defined on a lattice with first neighbour interactions. Each site of the lattice may assume one of three states: vacant, occupied by prey and occupied by predator. We have introduced a parameter that controls the possibility of difusion among sites. The model shows an oscilating phase, a non-oscilating phase and an absorbing phase. In the first two phases the system exhibits coexistence of biological species while in the absorbing phase the lattice is filled with prey and the system becomes trapped. We have determined the transition line between the non-oscilating and absorbing phases using time-dependent simulations. We have also determined the transition lines between oscilating and non-oscilating phases using time-autocorrelation functions of the prey time-series. In addition, we have studied the model by means of dynamical mean-field aproximations. We conclude that the introduction of diffusion in the predator-prey model leads to a larger region of coexistence in the phase diagram. Our results suggest that difusion is irrelevant for the critical behavior since it does not change the universatility class of the model.
7

Stochastic Control of Time-varying Wireless Networks

Lotfinezhad, Mahdi 19 February 2010 (has links)
One critical step to successfully integrate wireless data networks to the high-speed wired backbone is the design of network control policies that efficiently utilize resources to provide Quality of Service (QoS) to the users in the integrated networks. Such a design has remained a challenge since wireless networks are time-varying in nature, not only in terms of user/packet arrivals but also in terms of physical channel conditions and access opportunities. In this thesis, we study the stochastic control of time-varying networks to design efficient scheduling and resource allocation policies. In particular, in Chapter 3, we focus on a broad class of control policies that work based on a pick-and-compare principle for networks with time-varying channels. By trading the throughput for complexity and memory requirement, these policies require less complexity compared to the well-investigated throughput-optimal Generalized Maximum Weight Matching (GMWM) policy and also require only linear-memory storage with the number of data-flows. Through Lyapunov analysis tools, we characterize the stability region and delay performance of the studied policies and show how they vary in response to the channel variations. In Chapter 4, we go into further detail and consider the problem of network control from a new perspective through which we carefully incorporate the time-efficiency of underlying scheduling algorithms. Specifically, we develop a policy that dynamically adjusts the time given to the available scheduling algorithms according to queue-backlog and channel correlations. We study the resulting stability region of developed policy and show that the region is at least as large as the one for any static policy. Finally, motivated by the current under-utilization of wireless spectrum, in Chapter 5, we investigate the control of cognitive radio networks as a special example of networks that provide time-varying access opportunities. We assume that users dynamically join and leave the network and may have different utility functions, or could collaborate for a common purpose. We develop a policy that performs joint admission and resource control and works for any user load, either inside or outside the capacity region. Through Lyapunov Optimization techniques, we show that the developed policy can achieve a utility performance arbitrarily close to the optimality with a tradeoff in the average service delay of admitted users.
8

Stochastic Control of Time-varying Wireless Networks

Lotfinezhad, Mahdi 19 February 2010 (has links)
One critical step to successfully integrate wireless data networks to the high-speed wired backbone is the design of network control policies that efficiently utilize resources to provide Quality of Service (QoS) to the users in the integrated networks. Such a design has remained a challenge since wireless networks are time-varying in nature, not only in terms of user/packet arrivals but also in terms of physical channel conditions and access opportunities. In this thesis, we study the stochastic control of time-varying networks to design efficient scheduling and resource allocation policies. In particular, in Chapter 3, we focus on a broad class of control policies that work based on a pick-and-compare principle for networks with time-varying channels. By trading the throughput for complexity and memory requirement, these policies require less complexity compared to the well-investigated throughput-optimal Generalized Maximum Weight Matching (GMWM) policy and also require only linear-memory storage with the number of data-flows. Through Lyapunov analysis tools, we characterize the stability region and delay performance of the studied policies and show how they vary in response to the channel variations. In Chapter 4, we go into further detail and consider the problem of network control from a new perspective through which we carefully incorporate the time-efficiency of underlying scheduling algorithms. Specifically, we develop a policy that dynamically adjusts the time given to the available scheduling algorithms according to queue-backlog and channel correlations. We study the resulting stability region of developed policy and show that the region is at least as large as the one for any static policy. Finally, motivated by the current under-utilization of wireless spectrum, in Chapter 5, we investigate the control of cognitive radio networks as a special example of networks that provide time-varying access opportunities. We assume that users dynamically join and leave the network and may have different utility functions, or could collaborate for a common purpose. We develop a policy that performs joint admission and resource control and works for any user load, either inside or outside the capacity region. Through Lyapunov Optimization techniques, we show that the developed policy can achieve a utility performance arbitrarily close to the optimality with a tradeoff in the average service delay of admitted users.
9

Dinâmica de população de Tapirira guianensis AUBL. (Anacardiaceae), em áreas de restinga e cerradão do Estado de São Paulo

Baldoni, Raquel Negrão 03 March 2010 (has links)
Made available in DSpace on 2016-06-02T19:31:50Z (GMT). No. of bitstreams: 1 3006.pdf: 1341440 bytes, checksum: fae98217cd72e30df97045d459945022 (MD5) Previous issue date: 2010-03-03 / Universidade Federal de Minas Gerais / The situation of a population can only be assessed through demographic studies, considering its dynamics in terms of changes on fecundity, recruitment and mortality of individuals. Considering the peculiarities of the vegetation in State of Sao Paulo and the ability that some plant species have to occupy some of these different ecosystems, this study aims to assess the ecology of two populations of Tapirira guianensis Aubl. (Anacardiaceae), in the restinga located at the Parque Estadual da Ilha do Cardoso and in the cerrado at the Estação Ecológica de Assis. This project was carried out within the permanent plots of the project funded by Biota. There, were randomly allocated 50 plots of 20m x 20m (total area of 2 ha/environment) and all individuals of Tapirira guianensis found within these plots were identified and measured. Individuals were classified into ontogenetic stages in accordance with the Troll´s Model. We found allometric differences between the populations that might be related to the phenotypic plasticity to environmental variations. The population structure of T. guianensis was significantly different between restinga and cerrado (t-test, p <0.001). In the restinga, the structure shows the form of "j" reverse while in the cerrado, the population does not present this form of distribution. The difference between the populations is mainly due to the absence of seedlings in the cerrado. We found no differences between plant density and soil types, which suggest that T. guianensis is indifferent to soil caracteristics. The population growth rate indicated that both populations from restinga (&#955; = 0.96) and from cerrado (&#955; = 0.91) are close to 1.0, so these two populations seems to be in equilíbrium. However, we verified differences on demographic parameters between these populations. We suggest that variation between populations is related to phytogeographic conditions in restinga and cerrado, and to the interaction between various environmental factors. / A ecologia de uma população pode ser avaliada substancialmente por meio de um estudo demográfico, principalmente quando são realizados estudos da sua dinâmica, incluindo o acompanhamento da fecundidade dos indivíduos, recrutamento e taxa de mortalidade. Diante da peculiaridade das formações vegetais no Estado de São Paulo e do interessante ponto de vista de distribuição de ochloespecies, este trabalho tem o objetivo de avaliar a ecologia de duas populações de Tapirira guianensis Aubl. (Anacardiaceae), uma ocorrente em área de restinga, no Parque Estadual da Ilha do Cardoso e outra em área de cerradão, na Estação Ecológica de Assis. Este projeto foi desenvolvido dentro das parcelas do projeto temático Parcelas Permanentes - BIOTA/FAPESP. Foram sorteadas 50 parcelas de 20m x 20m (totalizando uma área de 2 ha/ambiente), dentro das quais todos os indivíduos foram individualizados e medidos trimestralmente. Estabelecemos a estrutura da população por estádios ontogenéticos de acordo com o Modelo de Troll. Encontramos diferenças nas relações alométricas das populações, relacionadas com plasticidade fenotípica nos diferentes ambientes. Encontramos diferenças para a estrutura de população de T. guianensis na restinga e cerradão (t-test, p<0.001). A população de T. guianensis da restinga apresenta forma de j invertido , diferentemente da população de cerradão, que não apresenta esta distribuição na forma de j invertido . A diferença entre as populações está principalmente na ausência de plântulas no cerradão. A taxa de crescimento populacional indicou que tanto as populações da restinga (&#955; = 0.96) quanto as do cerradão (&#955; =0.91) apresentam valores próximos de 1, portanto, estando as duas populações em estase. A dinâmica das populações de T. guianensis apresenta diferenças na restinga e cerradão estudados. Embora as taxas de crescimento populacionais sejam similares para as duas populações, as estratégias de crescimento são diferentes nos dois ambientes. Enquanto a população de T. guianensis que ocorre na restinga prioriza a sobrevivência, a população de T. guianensis no cerradão investe mais em crescimento. Portanto, podemos reconhecer diferenças nos parâmetros demográficos que compõem a dinâmica das populações de T. guianensis em diferentes ambientes. Este resultado, assim, pode demostrar a ocorrencia de plasticidade fenotipica em nível populacional para esta espécie, á partir do uso de estratégias diferenciadas de crescimento em ambientes diferentes de forma a alcançar estabilidade.
10

Ensaios em economia regional e urbana

Amarante, Adriano de January 2011 (has links)
Nesta tese propõe-se responder a três principais questões: No primeiro ensaio estuda-se o impacto dos investimentos privados de multinacionais do setor automobilístico no Brasil sobre o crescimento da atividade econômica dos municípios. Os resultados obtidos sugerem que as cidades onde se instalam este tipo de investimentos alcançam um desempenho superior aos outros grupos de municípios sem este recurso. Estes resultados apontam para uma subprovisão de bens públicos esperada em todo agrupamento de cidades, e um crescimento da atividade industrial no grupo de municípios de domicílio dos investimentos em detrimento a um crescimento abaixo da média do grupo de controle dos municípios adjacentes. No segundo ensaio proposto nesta tese, levanta-se a questão sobre qual o impacto do investimento em infraestrutura viária sobre a economia dos municípios do estado de Santa Catarina. Para responder esta questão, o método de regressão de dados em painel foi utilizado para identificar e mensurar o efeito do investimento público em rodovias interestaduais sobre o crescimento econômico municipal. Os resultados apontam para um efeito positivo sobre os municípios adjacentes e aqueles cortados pela rodovia federal. O setor agropecuário tende a perder valor agregado dado uma possível realocação de recursos para o setor de serviços e indústria de transformação. No terceiro e último ensaio, sobre a dinâmica da distribuição espacial da população no Brasil, tem-se como ideia central testar a Lei de Zipf tendo por base as estimativas da dinâmica populacional dos municípios brasileiros e seus limites populacionais (K). Recentes trabalhos na área de economia regional e urbana, e da nova geografia econômica (NGE), retomam o tema sobre a distribuição espacial da população entre as cidades. A principal questão neste ensaio é descobrir sobre a existência de uma tendência na distribuição do tamanho dos municípios brasileiros a atender a Lei de Zipf. Após as estimativas para um estado estacionário na dinâmica populacional dos municípios brasileiros e as estimativas por regressão quantílica da lei de potência, rejeitou-se em quase a totalidade das amostras a existência de um expoente igual a -1. / In this thesis propose to reply three principals’ questions. In the first essay examines the impact of private investment of multinational automobile industry in Brazil about the growth of economic activity of municipalities. The results obtained suggest that the municipalities that settle the investments reach a performance superior to other groups of municipalities. These results point to a underprovision expected of public goods in all groups of municipalities and increasing industrial activity in the municipalities of domicile of the investment over a growth below the average of the control group of adjacent municipalities. In the second essay proposed in this thesis, the question is about what the impact of highway infrastructure investment on the economy of the municipalities in the State of Santa Catarina. To answer this question makes use of panel date regression method to identify and measure the effect of public investment on the municipal economic growth. The results does are positive on the neighbouring and crossways interstate highway, the agriculture sector loses added value due a possible relocation of resources to service and manufacture sector. In the third essay, on the dynamics of spatial distribution of population in the Brazil, the core insight this is to test the Zipf’s Law from estimates of population dynamics of Brazilian municipalities and their population limits (K). Lately, studies on the approach of urban and regional economy and of new economic geography (NEG) recovers’ theme on the spatial distribution of population among cities. The central question in this essay, is whether there is a trend in the distribution of sizes of municipalities meet Zipf's law? After estimates for a steady state in the population dynamics of Brazilian municipalities and estimates for regression quantiles power law rejected in almost all of the samples the presence of an exponent equal to-1.

Page generated in 0.1157 seconds