Effect of different ferrule designs on the fracture resistance and failure pattern of endodontically treated teeth restored with fiber posts and all-ceramic crowns

OBJECTIVE: This study investigated the effect of different ferrule heights on endodontically treated premolars. MATERIAL AND METHODS: Fifty sound mandibular first premolars were endodontically treated and then restored with 7-mm fiber post (FRC Postec Plus #1 Ivoclar-Vivadent) luted with self-polymerized resin cement (Multilink, Ivoclar Vivadent) while the coronal section was restored with hybrid composite core build-up material (Tetric Ceram, Ivoclar-Vivadent), which received all-ceramic crown. Different ferrule heights were investigated: 1-mm circumferential ferrule without post and core (group 1 used as control), a circumferential 1-mm ferrule (group 2), non-uniform ferrule 2-mm buccally and 1-mm lingually (group 3), non-uniform ferrule 3-mm buccally and 2-mm lingually (group 4), and finally no ferrule preparation (group 5). The fracture load and failure pattern of the tested groups were investigated by applying axial load to the ceramic crowns (n=10). Data were analyzed statistically by one-way ANOVA and Tukey's post-hoc test was used for pair-wise comparisons (α=0.05). RESULTS: There were no significant differences among the failure load of all tested groups (P<0.780). The control group had the lowest fracture resistance (891.43±202.22 N) and the highest catastrophic failure rate (P<0.05). Compared to the control group, the use of fiber post reduced the percentage of catastrophic failure while increasing the ferrule height did not influence the fracture resistance of the restored specimens. CONCLUSIONS: Within the limitations of this study, increasing the ferrule length did not influence the fracture resistance of endodontically treated teeth restored with glass ceramic crowns. Insertion of a fiber post could reduce the percentage of catastrophic failure of these restorations under function.

Influence of separate and mixed experimental designs on reaction times to two simple visual stimuli

Testing contexts have been shown to critically influence experimental results in psychophysical studies. One of these contexts that show important modulation of the behavioral effects of different stimulatory conditions is the separate (blocked) or mixed presentation of these stimulatory conditions. The study presents evidence that the apparent discriminabilities of two target stimuli can change according to which of these two testing contexts is used. A cross inside a ring and a vertical line inside a ring were presented as go stimuli in a go/no-go reaction time task. In one experiment, each of these stimuli was presented to a different group of volunteers and in another experiment they were presented to the same group of volunteers, randomly mixed in the blocks of trials. Similar reaction times were obtained for the two stimuli in the first experiment, and different reaction times (faster for the cross) in the second experiment. The latter result indicates that the two stimuli have different discriminabilities from the no-go stimulus; the cross having greater discriminability. This difference is however masked, presumably by the adoption of specific compensatory attentional sets, in a separate testing context.

Social interaction as a heuristic for combinatorial optimization problems

We investigate the performance of a variant of Axelrod's model for dissemination of culture-the Adaptive Culture Heuristic (ACH)-on solving an NP-Complete optimization problem, namely, the classification of binary input patterns of size F by a Boolean Binary Perceptron. In this heuristic, N agents, characterized by binary strings of length F which represent possible solutions to the optimization problem, are fixed at the sites of a square lattice and interact with their nearest neighbors only. The interactions are such that the agents' strings (or cultures) become more similar to the low-cost strings of their neighbors resulting in the dissemination of these strings across the lattice. Eventually the dynamics freezes into a homogeneous absorbing configuration in which all agents exhibit identical solutions to the optimization problem. We find through extensive simulations that the probability of finding the optimal solution is a function of the reduced variable F/N(1/4) so that the number of agents must increase with the fourth power of the problem size, N proportional to F(4), to guarantee a fixed probability of success. In this case, we find that the relaxation time to reach an absorbing configuration scales with F(6) which can be interpreted as the overall computational cost of the ACH to find an optimal set of weights for a Boolean binary perceptron, given a fixed probability of success.

Experimental investigation on adaptive robust controller designs applied to a free-floating space manipulator

This paper aims to formulate and investigate the application of various nonlinear H(infinity) control methods to a fiee-floating space manipulator subject to parametric uncertainties and external disturbances. From a tutorial perspective, a model-based approach and adaptive procedures based on linear parametrization, neural networks and fuzzy systems are covered by this work. A comparative study is conducted based on experimental implementations performed with an actual underactuated fixed-base planar manipulator which is, following the DEM concept, dynamically equivalent to a free-floating space manipulator. (C) 2011 Elsevier Ltd. All rights reserved.

Effects of the preventive and corrective adjustments in economical designs for online process control for attributes with misclassification errors

The procedure for online process control by attributes consists of inspecting a single item at every m produced items. It is decided on the basis of the inspection result whether the process is in-control (the conforming fraction is stable) or out-of-control (the conforming fraction is decreased, for example). Most articles about online process control have cited the stoppage of the production process for an adjustment when the inspected item is non-conforming (then the production is restarted in-control, here denominated as corrective adjustment). Moreover, the articles related to this subject do not present semi-economical designs (which may yield high quantities of non-conforming items), as they do not include a policy of preventive adjustments (in such case no item is inspected), which can be more economical, mainly if the inspected item can be misclassified. In this article, the possibility of preventive or corrective adjustments in the process is decided at every m produced item. If a preventive adjustment is decided upon, then no item is inspected. On the contrary, the m-th item is inspected; if it conforms, the production goes on, otherwise, an adjustment takes place and the process restarts in-control. This approach is economically feasible for some practical situations and the parameters of the proposed procedure are determined minimizing an average cost function subject to some statistical restrictions (for example, to assure a minimal levelfixed in advanceof conforming items in the production process). Numerical examples illustrate the proposal.

Photoelastic Stress Analysis of Different Designs of Cement-Retained Fixed Partial Dentures on Morse Taper Oral Implants

There is no consensus in literature regarding the best plan for prosthetic rehabilitation with partial multiple adjacent implants to minimize stress generated in the bone-implant interface. The aim of this study was to evaluate the biomechanical behavior of cemented fixed partial dentures, splinted and nonsplinted, on Morse taper implants and with different types of coating material (ceramic and resin), using photoelastic stress analysis. A photoelastic model of an interposed edentulous space, missing a second premolar and a first molar, and rehabilitated with 4 different types of cemented crowns and supported by 2 adjacent implants was used. Groups were as follows: UC, splinted ceramic crowns; IC, nonsplinted ceramic crowns; UR, splinted resin crowns; and IR, nonsplinted resin crowns. Different vertical static loading conditions were performed: balanced occlusal load, 10 kgf; simultaneous punctiform load on the implanted premolar and molar, 10 kgf; and alternate punctiform load on the implanted premolar and molar, 5 kgf. Changes in stress distribution were analyzed in a polariscope, and digital photographs were taken of each condition to allow comparison of stress pattern distribution around the implants. Cementation of the fixed partial dentures generated stresses between implants. Splinted restorations distributed the stresses more evenly between the implants than nonsplinted when force was applied. Ceramic restorations presented better distribution of stresses than resin restorations. Based on the results obtained, it was concluded that splinted ceramic restorations promote better stress distribution around osseointegrated implants when compared with nonsplinted crowns; metal-ceramic restorations present less stress concentration and magnitude than metal-plastic restorations.

Approximating a class of combinatorial problems with rational objective function

In the late seventies, Megiddo proposed a way to use an algorithm for the problem of minimizing a linear function a(0) + a(1)x(1) + ... + a(n)x(n) subject to certain constraints to solve the problem of minimizing a rational function of the form (a(0) + a(1)x(1) + ... + a(n)x(n))/(b(0) + b(1)x(1) + ... + b(n)x(n)) subject to the same set of constraints, assuming that the denominator is always positive. Using a rather strong assumption, Hashizume et al. extended Megiddo`s result to include approximation algorithms. Their assumption essentially asks for the existence of good approximation algorithms for optimization problems with possibly negative coefficients in the (linear) objective function, which is rather unusual for most combinatorial problems. In this paper, we present an alternative extension of Megiddo`s result for approximations that avoids this issue and applies to a large class of optimization problems. Specifically, we show that, if there is an alpha-approximation for the problem of minimizing a nonnegative linear function subject to constraints satisfying a certain increasing property then there is an alpha-approximation (1 1/alpha-approximation) for the problem of minimizing (maximizing) a nonnegative rational function subject to the same constraints. Our framework applies to covering problems and network design problems, among others.

Incidências da hermenêutica para a metodologia da pesquisa teórica em psicanálise

O artigo traz uma breve revisão das principais abordagens hermenêuticas envolvidas na interpretação de textos e discursos a fim de delimitar a incidência dessa problemática no campo da pesquisa teórica em psicanálise. Define as diferentes formas de pesquisa em psicanálise e indica como as mudanças na compreensão da hermenêutica incidem também sobre a compreensão do estatuto epistemológico do saber psicanalítico. Apresenta e discute as propostas de metodologia de investigação teórica de Laplanche e Figueiredo. Ao concluir, indica a aproximação do método psicanalítico aplicado a textos e discursos com as perspectivas contemporâneas da hermenêutica e propõe uma abordagem própria para pesquisas de cunho histórico-conceitual e epistemológico em psicanálise.

Perspectivas da investigação sobre determinantes sociais em câncer

As diferenças socioeconômicas têm reflexos no perfil epidemiológico de câncer, no que diz respeito a incidência, mortalidade, sobrevida e qualidade de vida após o diagnóstico. Neste artigo examinam-se as disparidades da ocorrência de câncer na população brasileira e sintetizam-se evidências das investigações sobre determinantes sociais em câncer. Foram considerados os principais fatores que modulam a influência das condições socioeconômicas na ocorrência do câncer, como tabagismo, consumo de álcool, hábitos alimentares e obesidade, ocupação e acesso aos serviços de saúde. Modificações nas condições sociais dependem de mudanças estruturais na sociedade, a exemplo de melhorias do nível educacional; no entanto, investigações epidemiológicas bem conduzidas podem contribuir para o planejamento de intervenções visando a reduzir o impacto dos determinantes sociais em câncer. Esses estudos devem prover estratégias para promoção da qualidade das informações de incidência e mortalidade; realização periódica de inquéritos populacionais sobre prevalência de fatores de risco para câncer; desenvolver desenhos epidemiológicos mais eficientes para avaliar o efeito de fatores etiológicos em câncer e suas relações com o status social; análise de programas de rastreamento para tumores passíveis de detecção precoce; e avaliações do acesso da população ao diagnóstico e tratamento. Essas pesquisas devem contemplar populações em distintas regiões do mundo, em particular aquelas vivendo em regiões marginalizadas da dinâmica do atual sistema econômico global.

Tendência temporal e desigualdades na mortalidade por diarreias em menores de 5 anos

OBJETIVO: Analisar a tendência da mortalidade por diarreia entre menores de 5 anos, no município de Osasco (SP), entre 1980 e 2000. MÉTODOS: Trata-se de estudo observacional com dois delineamentos. Um descritivo, que toma o indivíduo como unidade do estudo, e outro ecológico, analisando agregado populacional que incluiu análise de séries temporais. A fonte de dados foi o sistema de informação de mortalidade do Estado de São Paulo e censos de 1980, 1991 e 2000. Descreveu-se a variação sazonal e para a análise de tendência aplicaram-se modelos log lineares de regressão polinomiais, utilizando-se variáveis sociodemográficas da criança e da mãe. Foram analisadas a evolução de indicadores sociodemográficos do município de 1980 a 2000, as taxas médias de mortalidade por diarreia nos menores de 5 anos e seus diferenciais por distrito nos anos 90. RESULTADOS: Dos 1.360 óbitos, 94,3 e 75,3% atingiram, respectivamente, menores de 1 ano e de 6 meses. O declínio da mortalidade foi de 98,3%, com deslocamento da sazonalidade do verão para o outono. A mediana da idade elevou-se de 2 meses nos primeiros períodos para 3 meses no último. O resíduo de óbitos manteve-se entre filhos de mães de 20 a 29 anos e escolaridade < 8 anos. O risco relativo entre o distrito mais atingido e a taxa média do município diminuiu de 3,4 para 1,3 do primeiro para o segundo quinquênio dos anos 90. CONCLUSÃO: Nossos resultados apontam uma elevação da idade mais vulnerável e a provável mudança do agente mais frequentemente associado ao óbito por diarreia.

Utilização de técnicas estatísticas em duas revistas de fruticultura

Neste trabalho são descritas as técnicas de análise estatística utilizadas e a acessibilidade estatística em uma amostra dos artigos originais publicados no período 1996-2006 em duas revistas de pesquisa na área de fruticultura: a Revista Brasileira de Fruticultura (RBF) e a revista francesa Fruits. No total foram classificados 986 artigos em 16 categorias de análise estatística, ordenadas em grau ascendente de complexidade. No período analisado, foi constatado um aumento no uso de análises mais sofisticadas ao longo do tempo em ambos as revistas. Os trabalhos publicados pela RBF aplicaram com maior freqüência técnicas estatísticas mais complexas, com maior utilização de delineamentos em blocos aleatorizados, arranjos fatoriais, parcelas subdivididas e modelos hierárquicos, e do teste de Tukey para comparações múltiplas de médias. Nos trabalhos publicados pela revista Fruits, predominou o uso de outros testes paramétricos e do teste de Duncan. O pacote estatístico SAS foi o mais utilizado nos artigos publicados em ambas as revistas. Os leitores da revista RBF precisaram de um nível de conhecimento estatístico mais elevado para ter acesso à maior parte dos artigos publicados no período, em comparação com os leitores da revista francesa.

Características agronômicas do Panicum maximum cv. "Mombaça" submetido a níveis crescentes de fósforo

O objetivo deste experimento foi avaliar o efeito da adição de doses crescentes de P2O5 sobre a altura do dossel, o número de perfilhos e a produção de matéria seca de folhas e de colmos do capim-Mombaça, em diferentes idades. Foi conduzido um experimento implantado em um Nitossolo Vermelho Eutrófico. O delineamento experimental usado foi o de blocos completos casualizados, com quatro repetições, cinco doses de P2O5 (30, 60, 90, 120 e 150kg ha-1) e uma testemunha. Para a primeira e segunda coletas, observou-se o efeito linear do fósforo sobre o perfilhamento. Para a terceira e quarta coletas, os dados ajustaram-se ao modelo quadrático. A participação das lâminas foliares na matéria seca da parte aérea diminuiu com as doses de P2O5. Por outro lado, a participação de colmos aumentou com as doses de P2O5. A produção de matéria seca (MS) da parte aérea para primeira, segunda e terceira coletas respondeu de forma linear à aplicação de P2O5 observando-se um aumento estimado de 7, 15 e 19kg ha-1 de MS por kg ha-1 de P2O5, respectivamente. Para a quarta coleta, os dados ajustaram-se ao modelo quadrático de regressão, sendo a máxima produção, 8,3Mg ha-1 de MS, obtida com a aplicação de 103kg ha-1 de P2O5.

Tendência temporal e desigualdades na mortalidade por diarreias em

Objetivo: Analisar a tendência da mortalidade por diarreia entre menores de 5 anos, no município de Osasco (SP), entre 1980 e 2000. Métodos: Trata-se de estudo observacional com dois delineamentos. Um descritivo, que toma o indivíduo como unidade do estudo, e outro ecológico, analisando agregado populacional que incluiu análise de séries temporais. A fonte de dados foi o sistema de informação de mortalidade do Estado de São Paulo e censos de 1980, 1991 e 2000. Descreveu-se a variação sazonal e para a análise de tendência aplicaram-se modelos log lineares de regressão polinomiais, utilizando-se variáveis sociodemográficas da criança e da mãe. Foram analisadas a evolução de indicadores sociodemográficos do município de 1980 a 2000, as taxas médias de mortalidade por diarreia nos menores de 5 anos e seus diferenciais por distrito nos anos 90. Resultados: Dos 1.360 óbitos, 94,3 e 75,3% atingiram, respectivamente, menores de 1 ano e de 6 meses. O declínio da mortalidade foi de 98,3%, com deslocamento da sazonalidade do verão para o outono. A mediana da idade elevou-se de 2 meses nos primeiros períodos para 3 meses no último. O resíduo de óbitos manteve-se entre filhos de mães de 20 a 29 anos e escolaridade < 8 anos. O risco relativo entre o distrito mais atingido e a taxa média do município diminuiu de 3,4 para 1,3 do primeiro para o segundo quinquênio dos anos 90. Conclusão: Nossos resultados apontam uma elevação da idade mais vulnerável e a provável mudança do agente mais frequentemente associado ao óbito por diarreia

Risk optimization of a steel frame communications tower subject to tornado winds

The structural engineering community in Brazil faces new challenges with the recent occurrence of high intensity tornados. Satellite surveillance data shows that the area covering the south-east of Brazil, Uruguay and some of Argentina is one of the world most tornado-prone areas, second only to the infamous tornado alley in central United States. The design of structures subject to tornado winds is a typical example of decision making in the presence of uncertainty. Structural design involves finding a good balance between the competing goals of safety and economy. This paper presents a methodology to find the optimum balance between these goals in the presence of uncertainty. In this paper, reliability-based risk optimization is used to find the optimal safety coefficient that minimizes the total expected cost of a steel frame communications tower, subject to extreme storm and tornado wind loads. The technique is not new, but it is applied to a practical problem of increasing interest to Brazilian structural engineers. The problem is formulated in the partial safety factor format used in current design codes, with all additional partial factor introduced to serve as optimization variable. The expected cost of failure (or risk) is defined as the product of a. limit state exceedance probability by a limit state exceedance cost. These costs include costs of repairing, rebuilding, and paying compensation for injury and loss of life. The total expected failure cost is the sum of individual expected costs over all failure modes. The steel frame communications, tower subject of this study has become very common in Brazil due to increasing mobile phone coverage. The study shows that optimum reliability is strongly dependent on the cost (or consequences) of failure. Since failure consequences depend oil actual tower location, it turn,,; out that different optimum designs should be used in different locations. Failure consequences are also different for the different parties involved in the design, construction and operation of the tower. Hence, it is important that risk is well understood by the parties involved, so that proper contracts call be made. The investigation shows that when non-structural terms dominate design costs (e.g, in residential or office buildings) it is not too costly to over-design; this observation is in agreement with the observed practice for non-optimized structural systems. In this situation, is much easier to loose money by under-design. When by under-design. When structural material cost is a significant part of design cost (e.g. concrete dam or bridge), one is likely to lose significantmoney by over-design. In this situation, a cost-risk-benefit optimization analysis is highly recommended. Finally, the study also shows that under time-varying loads like tornados, the optimum reliability is strongly dependent on the selected design life.

Influence of memory in deterministic walks in random media: Analytical calculation within a mean-field approximation

Consider a random medium consisting of N points randomly distributed so that there is no correlation among the distances separating them. This is the random link model, which is the high dimensionality limit (mean-field approximation) for the Euclidean random point structure. In the random link model, at discrete time steps, a walker moves to the nearest point, which has not been visited in the last mu steps (memory), producing a deterministic partially self-avoiding walk (the tourist walk). We have analytically obtained the distribution of the number n of points explored by the walker with memory mu=2, as well as the transient and period joint distribution. This result enables us to explain the abrupt change in the exploratory behavior between the cases mu=1 (memoryless walker, driven by extreme value statistics) and mu=2 (walker with memory, driven by combinatorial statistics). In the mu=1 case, the mean newly visited points in the thermodynamic limit (N >> 1) is just < n >=e=2.72... while in the mu=2 case, the mean number < n > of visited points grows proportionally to N(1/2). Also, this result allows us to establish an equivalence between the random link model with mu=2 and random map (uncorrelated back and forth distances) with mu=0 and the abrupt change between the probabilities for null transient time and subsequent ones.