Página 1 dos resultados de 19176 itens digitais encontrados em 0.049 segundos

Funções generalizadas, modelos de crescimento contínuos e discretos e caminhadas estocásticas em meios desordenados; Generalized functions, discrete and continuous growth models and stochastic walks on disordered media

Gonzalez, Rodrigo Silva
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 06/07/2011 PT
Relevância na Pesquisa
65.82%
Este trabalho está divido em duas partes. Na primeira apresentamos as funções logaritmo e exponencial generalizadas. A partir delas uma grande variedade de outras funções generalizadas pode ser obtida, permitindo uma formulação única dos comportamentos oscilatório, exponencial e lei de potência, característicos dos principais fenômenos físicos. Também mostramos que é possível generalizar a função densidade de probabilidade (pdf) exponencial estendida (stretched exponential) e, a partir dela, uma vasta gama de outras pdfs, que caracterizam os sistemas complexos em Física. As funções logaritmo e exponencial generalizadas também são úteis na generalização de vários modelos contínuos de crescimento em uma formulação única: o modelo de crescimento generalizado de Tsoullaris e Wallace. O mesmo pode ser feito para modelos discretos de crescimento, obtendo, como modelo mais geral, o -Ricker generalizado. Encerrando a primeira parte, mostramos que a pdf gaussiana generalizada (um caso particular da exponencial estendida generalizada) é a solução da equação de difusão não-linear, que caracteriza a caminhada determinista do turista. Na segunda parte deste trabalho é apresentada a caminhada do turista e suas duas versões originais: a determinista (CDT) e a estocástica (CET). A primeira delas é uma caminhada parcialmente autorrepulsiva...

Uma abordagem bayesiana para modelos não lineares na presença de assimetria e heteroscedasticidade; A bayesian approach for nonlinear models in the presence of asymmetry

Campos, Aline Minniti de
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 22/08/2011 PT
Relevância na Pesquisa
55.78%
Esta dissertação flexibiliza a suposição de normalidade, dispondo de distribuições assimétricas em modelos de crescimento. Propõe uma abordagem bayesiana para ajuste de modelos não lineares quando a suposição de normalidade para os erros não é razoável e/ou apresentam heteroscedasticidade. Assim, adota-se as distribuições skew-normal e skew-t para as situações em que é necessário modelar dados com caudas mais pesadas ou mais leves que a normal e assimétricos; sendo que é considerado também a presença de heteroscedasticidade. Diferentes funções são utilizadas na estrutura multiplicativa para modelar a variância. Com esse objetivo, métodos de inferência na abordagem bayesiana são desenvolvidos para estimar os parâmetros dos modelos de regressão não linear com os erros seguindo as distribuições citadas anteriormente. A metodologia visa aplicação à curvas de crescimento para dados de árvores; This paper relaxes the assumption of normality, featuring asymmetric distributions in growth models. Proposes a Bayesian approach to fit nonlinear models when the assumption of normality for the errors is not reasonable and/or exhibit heteroscedasticity. Thus, we adopt the skew-normal and skew-t distributions for situations where it is necessary to model data with tails heavier or lighter than normal and asymmetric...

Modelos aplicados ao crescimento e tratamento de tumores e à disseminação da dengue e tuberculose; Models applied to tumors growth and treatment and the spread of dengue and tuberculosis.

Cabella, Brenno Caetano Troca
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 31/05/2012 PT
Relevância na Pesquisa
55.79%
A generalização de modelos de crescimento por meio de um parâmetro de controle foi primeiramente proposta por Richards, em 1959. Em nosso trabalho, propomos uma forma alternativa de generalização obtendo uma interpretação emp rica e outra microscopica do parâmetro de controle. Mais especificamente, quando consideramos a proliferacão de c elulas, o parâmetro est a relacionado ao alcance da interação e a dimensão fractal da estrutura celular. Obtemos a solucão anal ítica para esta equação diferencial. Mostramos que, atrav és da escolha apropriada da escala conseguimos o colapso de dados representando a independência em relacão aos parâmetros e as condições iniciais. Al ém disso, ao considerarmos a taxa de esforco como a retirada de indiví duos de uma população, podemos associ á-la ao tratamento visando extinguir uma populacãoo de c élulas cancerosas. Em modelos epidemiol ogicos, propomos modelar a dinâmica de transmissão da dengue utilizando equacões diferenciais ordin árias. Em nosso modelo, levamos em conta tanto a dinâmica do hospedeiro quanto a do vetor, assim temos o controle da dinâmica de ambas as populações. Inclu ímos tamb ém no modelo o efeito "enhancing" com intuito de verificar sua influência na dinâmica de disseminacão da doença. O efeito "enhancing" é considerado uma das principais hipóteses para explicar a dengue hemorr ágica que pode levar a morte. Fizemos o estudo de um modelo epidemiol ógico da dengue com o objetivo de revelar quais são os fatores que levam a disseminação desse caso mais severo da doenca e...

Modelos de efeito Allee e epidemiológicos de tuberculose; Allee effect and epidemiological models for tuberculosis

Santos, Lindomar Soares dos
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 04/07/2013 PT
Relevância na Pesquisa
55.88%
A dinâmica de crescimento populacional de uma espécie é permeada pela relação entre as desvantagens da competição intraespecífica e os benefícios da presença de conspecíficos. Para muitas espécies, os benefícios da cooperação podem superar as desvantagens da competição. A correlação positiva entre tamanho populacional e adaptabilidade em populações muito pequenas é conhecida como efeito Allee demográfico. Apesar de haver modelos matemáticos isolados para os diferentes tipos de efeitos Allee, não há um modelo simples que os abranja e os conecte a modelos de crescimento mais gerais (como o de Richards). Propomos unificar modelos de efeitos Allee e o de crescimento de Richards em um modelo que permita um novo ponto de vista sobre o efeito Allee demográfico. Um exemplo do aumento das possibilidades descritivas de tal generalização é a emergência de mais de uma transição cooperação-competição quando considerado um caso particular desse novo modelo (Allee-Gompertz). Apesar da importância do crescimento populacional, a maioria dos modelos básicos de transmissão de doenças infecciosas considera o tamanho populacional constante ou adota simplificações pouco plausíveis. Nesta tese, mostramos as deficiências de um modelo compartimental dinâmico de tuberculose já consagrado e propomos um novo modelo com crescimento populacional logístico. Quando comparados...

Stochastic Differential Equations General Models of Individual Growth in Uncertain Environments and Application to Profit Optimization in Livestock Production

Braumann, Carlos A.; Filipe, Patrícia A.; Carlos, Clara; Roquete, Carlos J.
Fonte: ISI Publications Publicador: ISI Publications
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
55.89%
Individual animal growth in a randomly varying environment is modeled using stochastic differential equation models. These models are generalizations of the classical deterministic growth models used in regression methods, but incorporate a random dynamical term describing the effects of environmental and other random fluctuations on the growth process. We describe parameter estimation and prediction methods, illustrating with data on cow growth of the Mertolengo breed raised in Alentejo (Portugal) under natural conditions; see models, their properties and statistical techniques in the references below. We first show that these models outperform the traditional regression models in predictive power for they take into account the dynamical nature of the growth process and its interaction with environmental fluctuations. We then apply the models to profit optimization in livestock production, taking into account production costs and sales revenues. Assuming the animal is to be sold when it reaches some prescribed age, we determine the optimal age at which an animal should be sold in order to maximize profit. Another possibility is to sell the animal when it reaches a prescribed size. The first passage time distribution through a prescribed size is studied and used to determine the optimal size at which the animal should be sold. We then determine which policy (selling at a fixed age or selling at a fixed size) is preferable in terms of profit and compare results with the deterministic case.

Individual tree growth models for eucalyptus in northern Brazil

Martins,Fabrina Bolzan; Soares,Carlos Pedro Boechat; Silva,Gilson Fernandes da
Fonte: São Paulo - Escola Superior de Agricultura "Luiz de Queiroz" Publicador: São Paulo - Escola Superior de Agricultura "Luiz de Queiroz"
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/06/2014 EN
Relevância na Pesquisa
55.88%
The diameter and height growth model is one of three submodels used for simulating individual tree growth. In Brazil, there are few studies on the dimensional growth of individual trees be they native or exotic species, despite their potential. This study aimed to evaluate diameter and height growth models for individual trees for eucalyptus stands and to validate the best fitting model. Tree diameter and height data were obtained from 48 permanent plots of unthinned stands of Eucalyptus grandis × Eucalyptus urophylla hybrid located in northern Brazil. The evaluation of the diameter and height growth models was based on adjusted coefficient of determination, standard error of estimate as a percentage, trend, root mean square error and Akaike Information Criterion. Analysis also included distribution of residual percentage, statistical significance and signs of the coefficients. The Lundqvist-Korf model provided the most accurate estimates for diameter and height growth, in comparison with the other models, providing better statistical values, greater proximity to observed values and better distribution of residual percentages. The use of this type of model is feasible and can result in significant improvements in the accuracy of yield estimates.

An investigation on the role of institutions for income and growth models

Vieira,Flávio Vilela; Damasceno,Aderbal Oliveira
Fonte: Faculdade de Economia, Administração e Contabilidade de Ribeirão Preto da Universidade de São Paulo Publicador: Faculdade de Economia, Administração e Contabilidade de Ribeirão Preto da Universidade de São Paulo
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/09/2011 EN
Relevância na Pesquisa
65.82%
This work evaluates the role of institutions on per capita income levels (cross-section) and growth models (panel data). The cross-section results suggest that there is some evidence regarding the role of institutions since all the estimated coefficients are positive and statistically significant but there is evidence of weak instruments. The results from the panel growth models suggest that there is scarce evidence for the role of institutions in fostering long-run growth. In one word, there is no indication of an empirical consensus to claim that institutions have a primary role, meaning that institutions cause growth and difference in income levels.

How Might Climate Change Affect Economic Growth in Developing Countries? A Review of the Growth Literature with a Climate Lens

Lecocq, Franck; Shalizi, Zmarak
Fonte: World Bank, Washington, DC Publicador: World Bank, Washington, DC
Relevância na Pesquisa
55.92%
This paper reviews the empirical and theoretical literature on economic growth to examine how the four components of the climate change bill, namely mitigation, proactive (ex ante) adaptation, reactive (ex post) adaptation, and ultimate damages of climate change affect growth, especially in developing countries. The authors consider successively the Cass-Koopmans growth model and three major strands of the subsequent literature on growth: with multiple sectors, with rigidities, and with increasing returns. The paper finds that although the growth literature rarely addresses climate change per se, some issues discussed in the growth literature are directly relevant for climate change analysis. Notably, destruction of production factors, or decrease in factor productivity may strongly affect long-run equilibrium growth even in one-sector neoclassical growth models; climatic shocks have had large impacts on growth in developing countries because of rigidities; and the introducing increasing returns has a major impact on growth dynamics...

A Model on Knowledge and Endogenous Growth

Chen, Derek H. C.; Looi Kee, Hiau
Fonte: World Bank, Washington, DC Publicador: World Bank, Washington, DC
Relevância na Pesquisa
55.79%
The authors present a model of endogenous growth in which the main engine of economic development is knowledge. Using a two-sector closed economy model that comprises of a conventional goods-producing sector and a research and development sector, their model incorporates two key aspects of knowledge: technology and human capital. Steady-state equilibrium conditions show that the growth rate of per capita income hinges on the growth rate of human capital. While the growth rate of human capital has been previously shown to affect the growth of the economy in transition between steady states or balanced growth paths, the authors are the first to link the growth rate of human capital to the steady-state growth rate of productivity and output per worker. Furthermore, this result does not exhibit scale effects or policy invariance, both of which have been longstanding concerns with the predictions of endogenous growth models developed in the 1990s.

Poverty Traps, Aid, and Growth

Kraay, Aart; Raddatz, Claudio
Fonte: World Bank, Washington, DC Publicador: World Bank, Washington, DC
Relevância na Pesquisa
55.89%
The authors examine the empirical evidence in support of the poverty trap view of underdevelopment. They calibrate simple aggregate growth models in which poverty traps can arise due to either low saving or low technology at low levels of development. They then use these models to assess the empirical relevance of poverty traps and their consequences for policy. The authors find little evidence of the existence of poverty traps based on these two broad mechanisms. When put to the task of explaining the persistence of low income in African countries, the models require either unreasonable values for key parameters, or else generate counterfactual predictions regarding the relations between key variables. These results call into question the view that a large scaling-up of aid to the poorest countries is a necessary condition for sharp and sustained increases in growth.

The Refoundation of the Symmetric Equilibrium in Schumpeterian Growth Models

COZZI, Guido; GIORDANI, Paolo; ZAMPARELLI, Luca
Fonte: Academic Press Inc Elsevier Science Publicador: Academic Press Inc Elsevier Science
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
65.79%
We provide a refoundation of the symmetric growth equilibrium characterizing the research sector of vertical R&D-driven growth models. We argue that the usual assumptions made in this class of models leave the agents indifferent as to where targeting research: hence, the problem of the allocation of R&D investment across sectors is indeterminate. By introducing an ,-contamination of confidence in the expected distribution of R&D investment, we prove that the symmetric structure of R&D investment is the unique rational expectations equilibrium compatible with ambiguity-averse agents adopting a maxmin strategy. (C) 2006 Elsevier Inc. All rights reserved.

On convergence in endogenous growth models

Ortigueira, Salvador; Santos, Manuel S.
Fonte: Universidade Carlos III de Madrid Publicador: Universidade Carlos III de Madrid
Tipo: Trabalho em Andamento Formato: application/pdf
Publicado em /12/1994 ENG
Relevância na Pesquisa
65.78%
In this paper we analyze the rate of convergence to a balanced path in a class of endogenous growth models with physical and human capital. We show that such rate depends locally on the technological parameters of the model. but does not depend on those parameters related to preferences. These results stand in sharp contrast with those of the one-sector neoclassical growth model where both preferences and technologies determine the speed of convergence toward a steady state.

Differential-difference equations in economics: on the numerical solution of vintage capital growth models

Boucekkine, Raouf; Licandro, Omar; Paul, Christopher
Fonte: Universidade Carlos III de Madrid Publicador: Universidade Carlos III de Madrid
Tipo: Trabalho em Andamento Formato: application/pdf
Publicado em /12/1995 ENG
Relevância na Pesquisa
55.81%
In this papel, we examine techniques for the analytical and numerical solution of statedependent differential-difference equations. Such equations occur in the continuous time modelling of vintage capital growth models, which form a particularly important class of models in modern economic growth theory. The theoretical treatment of non-statedependent differential-difference equations in economics has already been discussed by Benhabib and Rustichini (1991). In general, though, the state-dependence of a model prevents its analytical solution in all but the simplest of cases. We review a numerical method for solving state-dependent models, using sorne simple examples to illustrate our discussion. In addition, we analyse the Solow vintage capital growth model. We conclude by mentioning a crucial unresolved issue related to this topic.

Bayesian hierarchical modelling of bacteria growth

Palacios, Ana P.; Marín, J. Miguel; Wiper, Michael P.
Fonte: Universidade Carlos III de Madrid Publicador: Universidade Carlos III de Madrid
Tipo: Trabalho em Andamento Formato: application/pdf
Publicado em /04/2010 ENG
Relevância na Pesquisa
55.83%
Bacterial growth models are commonly used in food safety. Such models permit the prediction of microbial safety and the shelf life of perishable foods. In this paper, we study the problem of modelling bacterial growth when we observe multiple experimental results under identical environmental conditions. We develop a hierarchical version of the Gompertz equation to take into account the possibility of replicated experiments and we show how it can be fitted using a fully Bayesian approach. This approach is illustrated using experimental data from Listeria monocytogenes growth and the results are compared with alternative models. Model selection is undertaken throughout using an appropriate version of the deviance information criterion and the posterior predictive loss criterion. Models are fitted using WinBUGS via R2WinBUGS.

It's Not Factor Accumulation : Stylized Facts and Growth Models

Easterly, William; Levine, Ross
Fonte: Washington, DC: World Bank Publicador: Washington, DC: World Bank
Tipo: Journal Article; Publications & Research :: Journal Article
ENGLISH; EN_US
Relevância na Pesquisa
55.86%
The article documents five stylized facts of economic growth: (1) the 'residual' (total factor productivity, tfp) rather than factor accumulation accounts for most of the income and growth differences across countries; (2) income diverges over the long run; (3) factor accumulation is persistent while growth is not, and the growth path of countries exhibits remarkable variation; (4) economic activity is highly concentrated, with all factors of production flowing to the richest areas; and (5) national policies are closely associated with long-run economic growth rates. These facts do not support models with diminishing returns, constant returns to scale, some fixed factor of production, or an emphasis on factor accumulation. However, empirical work does not yet decisively distinguish among the different theoretical conceptions of tfp growth. Economists should devote more effort toward modeling and quantifying tfp.

Comment on 'It's Not Factor Accumulation : Stylized Facts and Growth Models,' by William Easterly and Ross Levine

Romer, Paul
Fonte: Washington, DC: World Bank Publicador: Washington, DC: World Bank
Tipo: Journal Article; Publications & Research :: Journal Article
ENGLISH; EN_US
Relevância na Pesquisa
65.78%
When economists in the 1950s and 1960s used growth models to understand the experience of developing countries, they allowed for the possibility of technology differences between developing countries and the United States. But because they did not have a good theory for talking about the forces that determined the level of the technology-in the United States any more than in developing countries-technology factors tended to be pushed into the background in policy discussions. The new growth theory of the 1980s generated a counter reaction in the 1990s that Pete Klenow and Andres Rodriguez-Clare have called the 'neoclassical revival.' The article by William Easterly and Ross Levine is part of the next swing in the scholarly pendulum. It moves away from the critical assumption in the neoclassical revival that the level of technology is the same in all countries.

The Growth Report : Strategies for Sustained Growth and Inclusive Development; Informe sobre el crecimiento : estrategias para el crecimiento sostenido y el desarrollo incluyente

Commission on Growth and Development
Fonte: Washington, DC : World Bank Publicador: Washington, DC : World Bank
Tipo: Publications & Research :: Publication; Publications & Research :: Publication
ENGLISH; EN_US
Relevância na Pesquisa
65.81%
The report has four main parts. In the first, the commission reviews the 13 economies that have sustained, high growth in the postwar period. Their growth models had some common flavors: the strategic integration with the world economy; the mobility of resources, particularly labor; the high savings and investment rates; and a capable government committed to growth. The report goes on to describe the cast of mind and techniques of policy making that leaders will need if they are to emulate such a growth model. It concludes that their policy making will need to be patient, pragmatic, and experimental. In the second part, the commission lays out the ingredients a growth strategy might include. These range from public investment and exchange rate policies to land sales and redistribution. A list of ingredients is not enough to make a dish, of course, as Bob Solow, a Nobel Prize-winning economist and a member of the Commission, points out. The commission, however, refrains from offering policy makers a recipe...

Human Capital and Growth : The Recovered Role of Education Systems

Dessus, Sebastien
Fonte: World Bank, Washington, DC Publicador: World Bank, Washington, DC
Tipo: Publications & Research :: Policy Research Working Paper; Publications & Research
ENGLISH; EN_US
Relevância na Pesquisa
55.85%
Recent empirical studies question conventional wisdom about the importance of education to growth. These results partly reflect how international differences in the quality of education systems--defined by the systems' ability to produce one marginal unit of productive human capital--are not taken into account. The author estimates neoclassical growth models on panel data in which the elasticity of human capital depends stochastically on different characteristics of the education system. Among characteristics that explain differences in quality are education infrastructure, the initial endowment of human capital, and the ability to distribute educational services equally among potential students. Giving priority to primary education for all rather than secondary education to a few is more likely to foster growth (for the same fiscal burden). But parallel actions are also probably needed--for example, promoting institutions that motivate skilled workers to spend time on growth-promoting activities and encouraging the inflow of foreign technologies to maximize the social return to public investment in education.

An investigation on the role of institutions for income and growth models

Vieira, Flávio Vilela; Damasceno, Aderbal Oliveira
Fonte: Universidade de São Paulo. Faculdade de Economia, Administração e Contabilidade de RP Publicador: Universidade de São Paulo. Faculdade de Economia, Administração e Contabilidade de RP
Tipo: info:eu-repo/semantics/article; info:eu-repo/semantics/publishedVersion; ; ; Formato: application/pdf
Publicado em 01/09/2011 ENG
Relevância na Pesquisa
65.82%
This work evaluates the role of institutions on per capita income levels (cross-section) and growth models (panel data). The cross-section results suggest that there is some evidence regarding the role of institutions since all the estimated coefficients are positive and statistically significant but there is evidence of weak instruments. The results from the panel growth models suggest that there is scarce evidence for the role of institutions in fostering long-run growth. In one word, there is no indication of an empirical consensus to claim that institutions have a primary role, meaning that institutions cause growth and difference in income levels.; O presente trabalho examina o papel das instituições em modelos de renda per capita (corte transversal) e de crescimento (painel). Os resultados das estimações de corte transversal sugerem que há alguma evidência quanto ao papel das instituições dado que os coeficientes estimados são positivos e estatisticamente significativos, mas existem evidências de que os instrumentos utilizados são fracos. Os resultados para os modelos de crescimento sugerem que há poucas evidências quanto arelevância das instituições para estimular o crescimento. Sumarizando, não há indicação de um consenso empírico capaz de sustentar o argumento do papel primordial das instituições...

I(0) in, integration and cointegration out: Time series properties of endogenous growth models

Lau, Sau-him (Paul)
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
55.88%
To complement empirical growth studies applying unit root and cointegration methods, this paper shows that integration and cointegration properties arise intrinsically in stochastic endogenous growth models under fairly general conditions. It shows that a unit root has to be present in the autoregressive polynomial of the variables generated by an endogenous growth model, so as to produce steady-state growth in the absence of exogenous growth-generating element. This endogenous-growth-generating mechanism induces difference stationarity of the variables even though the external impulses are stationary, and it leads to the phenomenon of cointegration if the variables satisfy a state space representation. The 'unit root propagation mechanism' is the time series analogue of the 'constant returns' (to reproducible inputs) condition in the theoretical endogenous growth literature. The time series properties of endogenous growth models, when combined with their counterparts for exogenous growth models, lead to testable implications for distinguishing between these two classes of models.