A mixture theory based method for three-dimensional modeling of reinforce concrete members with embedded crack finite elements

The paper presents a methodology to model three-dimensional reinforced concrete members by means of embedded discontinuity elements based on the Continuum Strong Discontinuous Approach (CSDA). Mixture theory concepts are used to model reinforced concrete as a 31) composite material constituted of concrete with long fibers (rebars) bundles oriented in different directions embedded in it. The effects of the rebars are modeled by phenomenological constitutive models devised to reproduce the axial non-linear behavior, as well as the bond-slip and dowel action. The paper presents the constitutive models assumed for the components and the compatibility conditions chosen to constitute the composite. Numerical analyses of existing experimental reinforced concrete members are presented, illustrating the applicability of the proposed methodology.

A novel intelligent system to nitrogen content prediction in plants using indirect chlorophyll measurements

The accurate identification of the nitrogen content in plants is extremely important since it involves economic aspects and environmental impacts, Several experimental tests have been carried out to obtain characteristics and parameters associated with the health of plants and its growing. The nitrogen content identification in plants involves a lot of non-linear parameters and complexes mathematical models. This paper describes a novel approach for identification of nitrogen content thought SPAD index using artificial neural networks (ANN). The network acts as identifier of relationships among, crop varieties, fertilizer treatments, type of leaf and nitrogen content in the plants (target). So, nitrogen content can be generalized and estimated and from an input parameter set. This approach can form the basis for development of an accurate real time system to predict nitrogen content in plants.

An efficient Hopfield network to solve economic dispatch problems with transmission system representation

Economic dispatch (ED) problems have recently been solved by artificial neural network approaches. Systems based on artificial neural networks have high computational rates due to the use of a massive number of simple processing elements and the high degree of connectivity between these elements. The ability of neural networks to realize some complex non-linear function makes them attractive for system optimization. All ED models solved by neural approaches described in the literature fail to represent the transmission system. Therefore, such procedures may calculate dispatch policies, which do not take into account important active power constraints. Another drawback pointed out in the literature is that some of the neural approaches fail to converge efficiently toward feasible equilibrium points. A modified Hopfield approach designed to solve ED problems with transmission system representation is presented in this paper. The transmission system is represented through linear load flow equations and constraints on active power flows. The internal parameters of such modified Hopfield networks are computed using the valid-subspace technique. These parameters guarantee the network convergence to feasible equilibrium points, which represent the solution for the ED problem. Simulation results and a sensitivity analysis involving IEEE 14-bus test system are presented to illustrate efficiency of the proposed approach. (C) 2004 Elsevier Ltd. All rights reserved.

Conventional and microwave sintering of CaCu(3)Ti(4)O(12)/CaTiO(3) ceramic composites: non-ohmic and dielectric properties

The non-ohmic and dielectric properties as well as the dependence on the microstructural features of CaCu(3)Ti(4)O(12)/CaTiO(3) ceramic composites obtained by conventional and microwave sintering were investigated. It was demonstrated that the non-ohmic and dielectric properties depend strongly on the sintering conditions. It was found that the non-linear coefficient reaches values of 65 for microwave-sintered samples and 42 for samples sintered in a conventional furnace when a current density interval of 1-10 mA cm(-2) is considered. The non-linear coefficient value of 65 is equivalent to 1500 for samples sintered in the microwave if a current interval of 5-30 mA is considered as is shortly discussed by Chung et al (2004 Nature Mater. 3 774). Due to a high non-linear coefficient and a low leakage current (90 mu A) under both processing conditions, these samples are promising for varistor applications. The conventionally sintered samples exhibit a higher relative dielectric constant at 1 kHz (2960) compared with the samples sintered in the microwave furnace (2100). At high frequencies, the dielectric constant is also larger in the samples sintered in the conventional furnace. Depending on the application, one or another synthesis methodology is recommended, that is, for varistor applications sintered in a microwave furnace and for dielectric application sintered in a conventional furnace.

Comparative degradation of ZnO- and SnO(2)-based polycrystalline non-ohmic devices by current pulse stress

The degradation behaviour of SnO(2)-based varistors (SCNCr) due to current pulses (8/20 mu s) is reported here for the first time in comparison with the ZnO-based commercial varistors (ZnO). Puncturing and/or cracking failures were observed in ZnO-based varistors possessing inferior thermo-mechanical properties in comparison with that found in a SCNCr system free of failures. Both systems presented electric degradation related to the increase in the leakage current and decrease in the electric breakdown field, non-linear coefficient and average value of the potential barrier height. However, it was found that a more severe degradation occurred in the ZnO-based varistors concerning their non-ohmic behaviour, while in the SCNCr system, a strong non-ohmic behaviour remained after the degradation. These results indicate that the degradation in the metal oxide varistors is controlled by a defect diffusion process whose rate depends on the mobility, the concentration of meta-stable defects and the amount of electrically active interfaces. The improved behaviour of the SCNCr system is then inferred to be associated with the higher amount of electrically active interfaces (85%) and to a higher energy necessary to activate the diffusion of the specific defects.

On relaxed LMI-based design for fuzzy controllers

Relaxed conditions for stability of nonlinear continuous-time systems given by fuzzy models axe presented. A theoretical analysis shows that the proposed method provides better or at least the same results of the methods presented in the literature. Digital simulations exemplify this fact. This result is also used for fuzzy regulators design. The nonlinear systems are represented by fuzzy models proposed by Takagi and Sugeno. The stability analysis and the design of controllers axe described by LMIs (Linear Matrix Inequalities), that can be solved efficiently using convex programming techniques.

Análise de barreiras e o modelo de ressonância funcional de acidentes de Erik Hollnagel

Partindo de apresentação da proposta de análise de acidentes baseada no modelo sistêmico e não linear de acidentes, dito de ressonância funcional, desenvolvido por Erik Hollnagel, este texto discute críticas às concepções deterministas de acidente e aos modelos lineares de representação desses eventos. Aspectos do modelo de ressonância funcional são usados como eixo definidor de proposta de agenda de discussões a ser desenvolvida pelos interessados no tema da análise de acidentes, destacando-se: a) a defesa do abandono da idéia de causas de acidentes e sua substituição pela de explicação desses eventos; b) apresentação dos conceitos de variabilidade de desempenhos e adaptações locais e a proposta de sua utilização como bases para a identificação de perfis ou aspectos típicos de acidentes. Por fim, discute-se a necessidade de incorporação dos conceitos apresentados no debate sobre novos caminhos para as práticas de análises e de prevenção de acidentes em nosso país.

Choosing between Cox proportional hazards and logistic models for interval-censored data via bootstrap

This work develops a new methodology in order to discriminate models for interval-censored data based on bootstrap residual simulation by observing the deviance difference from one model in relation to another, according to Hinde (1992). Generally, this sort of data can generate a large number of tied observations and, in this case, survival time can be regarded as discrete. Therefore, the Cox proportional hazards model for grouped data (Prentice & Gloeckler, 1978) and the logistic model (Lawless, 1982) can befitted by means of generalized linear models. Whitehead (1989) considered censoring to be an indicative variable with a binomial distribution and fitted the Cox proportional hazards model using complementary log-log as a link function. In addition, a logistic model can be fitted using logit as a link function. The proposed methodology arises as an alternative to the score tests developed by Colosimo et al. (2000), where such models can be obtained for discrete binary data as particular cases from the Aranda-Ordaz distribution asymmetric family. These tests are thus developed with a basis on link functions to generate such a fit. The example that motivates this study was the dataset from an experiment carried out on a flax cultivar planted on four substrata susceptible to the pathogen Fusarium oxysoprum. The response variable, which is the time until blighting, was observed in intervals during 52 days. The results were compared with the model fit and the AIC values.

Utilização da relação potência-tempo até exaustão em testes de caminhada para avaliação da aptidão aeróbia

O objetivo do presente estudo foi avaliar a aptidão aeróbia em testes de caminhada com carga externa aplicada por meio da inclinação da esteira, a partir da relação não linear entre inclinação da esteira e tempo até a exaustão em velocidade fixa. Doze indivíduos do gênero masculino com 23,2 ± 2,7 anos de idade, 74,0 ± 7,9kg de massa corporal e 23,7 ± 2,5kg·(m²)-1 de IMC, realizaram duas etapas de testes de caminhada em esteira ergométrica com velocidade fixa de 5,5km·h-1 em todos os testes e sobrecarga de intensidade aplicada por meio de inclinação da esteira (%). A etapa 1 consistiu de três testes retangulares até a exaustão voluntária, nas intensidades de 18%, 20% e 22% de inclinação, para determinação dos parâmetros do modelo de potência crítica por dois modelos lineares e um hiperbólico. A etapa 2 consistiu na determinação da intensidade correspondente ao máximo estado estável de lactato sanguíneo (MEEL). ANOVA demonstrou que o modelo hiperbólico (15,4 ± 1,1%) resultou em estimativa significativamente menor que os outros dois modelos lineares inclinação-tempo-1 (16,0 ± 1,0%) e hiperbólico linearizado tempo-1-inclinação (15,9 ± 1,0%), porém, houve alta correlação entre os modelos. Os dois modelos lineares superestimaram a intensidade do MEEL (14,1 ± 1,4%), e o modelo hiperbólico, mesmo sem diferença estatística, apresentou fraca correlação, com baixa concordância em relação ao MEEL. Conclui-se que a relação inclinação-tempo até a exaustão, em testes de caminhada, não permitem a estimativa de intensidade de exercício suportável por longo período de tempo.

The use of artificial neural networks in analysing the nutritional ecology of Chrysomya megacephala (F.) (Diptera: Calliphoridae), compared with a statistical model

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Influência da temperatura e da concentração do cloreto de sódio (NaCl) nas isotermas de sorção da carne de tambaqui (Colossoma macroparum)

As isotermas de sorção da carne de tambaqui desidratada osmoticamente foram determinadas a três temperaturas (5, 17 e 29ºC) e com duas concentrações de solução osmótica (10 e 30% de NaCl), pelo método gravimétrico. Quatro modelos de sorção foram testados para verificar o melhor ajuste; GAB, Oswin, BET e PELEG. Os dados experimentais se ajustaram satisfatoriamente aos modelos. O modelo escolhido para este trabalho foi o de PELEG. Para o ajuste nas curvas de sorção, foi feita a análise de regressão não-linear, usada o programa estatístico ORIGIN 4.0 para estimar as constantes dos modelos. A avaliação do melhor ajuste foi feita pela análise do coeficiente de determinação do ajuste (r²) e teste de Qui-quadrado (x²). Foram analisadas as influências da variação da temperatura e concentração de NaCl na atividade de água da carne do tambaqui. À medida que decresce a temperatura há um decréscimo na atividade de água. Um aumento na concentração do NaCl diminui a atividade de água. A propriedade termodinâmica estudada foi o calor isostérico de sorção. A medida que aumenta a concentração da solução osmótica aumenta o valor do calor isostérico de sorção.

Structure formation in the presence of dark energy perturbations

We study non-linear structure formation in the presence of dark energy. The influence of dark energy on the growth of large-scale cosmological structures is exerted both through its background effect on the expansion rate, and through its perturbations. In order to compute the rate of formation of massive objects we employ the spherical collapse formalism, which we generalize to include fluids with pressure. We show that the resulting non-linear evolution equations are identical to the ones obtained in the pseudo-Newtonian approach to cosmological perturbations, in the regime where an equation of state serves to describe both the background pressure relative to density, and the pressure perturbations relative to the density perturbations. We then consider a wide range of constant and time-dependent equations of state (including phantom models) parametrized in a standard way, and study their impact on the non-linear growth of structure. The main effect is the formation of dark energy structure associated with the dark matter halo: non-phantom equations of state induce the formation of a dark energy halo, damping the growth of structures; phantom models, on the other hand, generate dark energy voids, enhancing structure growth. Finally, we employ the Press-Schechter formalism to compute how dark energy affects the number of massive objects as a function of redshift (number counts).

Multifractal regime transition in a modified minority game model

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Signatures of primordial non-Gaussianities in the matter power-spectrum and bispectrum: the time-RG approach

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Short comments on self-synchronization of two non-ideal sources supported by a flexible portal frame structure

A practical problem of synchronization of a non-ideal (i.e. when the excitation is influenced by the response of the system) and non-linear vibrating system was posed and investigated by means of numerical simulations. Two rotating unbalanced motors compose the mathematical model considered here with limited power supply mounted on the horizontal beam of a simple portal frame. As a starting point, the problem is reduced to a four-degrees-of-freedom model and its equations of motion, derived elsewhere via a Lagrangian approach, are presented. The numerical results show the expected phenomena associated with the passage through resonance with limited power. Further, for a two-to-one relationship between the frequencies associated with the first symmetric mode and the sway mode, by using the variation of torque constants, the control of the self-synchronization and synchronization (in the system) are observed at certain levels of excitations.