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Search Results: 1 - 10 of 367240 matches for " S;Silva "
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Optimal Aggregate Production Plans via a Constrained LQG Model  [PDF]
Oscar S. Silva Filho
Engineering (ENG) , 2014, DOI: 10.4236/eng.2014.612075
Abstract: In this paper, a single product, multi-period, aggregate production planning problem is formulated as a linear-quadratic Gaussian (LQG) optimal control model with chance constraints on state and control variables. Such formulation is based on a classical production planning model developed in 1960 by Holt, Modigliani, Muth and Simon, and known, since then, as the HMMS model [1]. The proposed LQG model extends the HMMS model, taking into account both chance-constraints on the decision variables and data generating process, based on ARMA model, to represent the fluctuation of demand. Using the certainty-equivalence principle, the constrained LQG model can be transformed into an equivalent, but deterministic model, which is called here as Mean Value Problem (MVP). This problem preserves the main properties of the original model such as convexity and some statistical moments. Besides, it is easier to be implemented and solved numerically than its stochastic version. In addition, two very simple suboptimal procedures from stochastic control theory are briefly discussed. Finally, an illustrative example is introduced to show how the extended HMMS model can be used to develop plans and to generate production scenarios.
Revista GEINTEC : Gest?o, Inova??o e Tecnologias , 2012,
Abstract: O avan o dos recursos tecnológicos, aliado às facilidades de acesso a informa o e aos meios decomunica o, est o promovendo mudan as na forma de ensinar e aprender. Gra as ás ferramentas disponibilizadas na web, a internet passou de um ambiente somente de leitura, para um ambiente em que o usuário participa ativamente tornando-se leitor e autor de conteúdos. Dessa forma, o usuário, busca informa es, interage com amigos, profissionais, especialistas e cria um ambiente pessoal de aprendizagem. Passa a ser o condutor de seu processo de aprendizagem.Este artigo tem por objetivo refletir sobre o Ambiente Pessoal de Aprendizagem como recurso de aprendizagem para o professor.
Revista GEINTEC : Gest?o, Inova??o e Tecnologias , 2012,
Abstract: Estamos passando de um modelo de sociedade industrial para um modelo de sociedade da informa o, que se caracteriza pela globaliza o da economia, da cultura, o surgimento de novos setores de trabalho, a interatividade e a interdependência entre as tecnologias, sendo um dos elementos mais significativos a sociedade girar em torno das Tecnologias da Informa o e Comunica o.A incorpora o desses recursos na área educacional, tem facilitado o acesso a informa o, ao lazer e ao aprendizado. Para que as tecnologias sejam elementos de inclus o social e profissional, precisam ser acessíveis. A proposta deste artigo é refletir sobre a incorpora o da acessibilidade digital em ambientes virtuais de aprendizagem para que pessoas com deficiências visuais parcial ou total possam acompanhar os cursos a distancia, participandoativamente na constru o do seu aprendizado.
Revista GEINTEC : Gest?o, Inova??o e Tecnologias , 2011,
Abstract: Os recursos da Web 2.0 est o sendo empregados em várias áreas do conhecimento humano, possibilitando o contato entre as pessoas, o acesso a informa o e o aprendizado. Quando tais recursos s o empregados na área da saúde, denomina-se Health 2.0. Atualmente, a utiliza o de blogs, redes sociais, acesso a portais de informa o sobre saúde, tem se intensificado, pois as pessoas buscam informa es sobre qualidade de vida, procedimentos médicos, e tratamentos de saúde. Este artigo tem como proposta refletir sobre a Web 2.0 como fonte de informa o, bem como os benefícios e limita es que o emprego destes recursos pode propiciar ao usuário.
On Superpotentials and Charge Algebras of Gauge Theories
S. Silva
Physics , 1998, DOI: 10.1016/S0550-3213(99)00392-2
Abstract: We propose a new "Hamiltonian inspired" covariant formula to define (without harmful ambiguities) the superpotential and the physical charges associated to a gauge symmetry. The criterion requires the variation of the Noether current not to contain any derivative terms in $\partial_{\mu}\delta \f$. The examples of Yang-Mills (in its first order formulation) and 3-dimensional Chern-Simons theories are revisited and the corresponding charge algebras (with their central extensions in the Chern-Simons case) are computed in a straightforward way. We then generalize the previous results to any (2n+1)-dimensional non-abelian Chern-Simons theory for a particular choice of boundary conditions. We compute explicitly the superpotential associated to the non-abelian gauge symmetry which is nothing but the Chern-Simons Lagrangian in (2n-1) dimensions. The corresponding charge algebra is also computed. However, no associated central charge is found for $n \geq 2$. Finally, we treat the abelian p-form Chern-Simons theory in a similar way.
An Exploratory Study of Batch Splitting through Combined Control of Release and Dispatching  [PDF]
Nuno O. Fernandes, S. Carmo -Silva
Creative Education (CE) , 2012, DOI: 10.4236/ce.2012.37B006

Workload Control (WLC) has been developed as a production planning and control approach for make-to-order manufacturing. Previous studies on WLC often assume a simplified shop where released batches are treated as independent jobs, which proceed through the different stages of processing without being split. Batch splitting allows released batches to be split into a number of smaller sub-batches so that its operations at work centres can be overlapped and its progress accelerated. This paper investigates how WLC performs under batch splitting. Evaluating the performance of WLC in this context is an important step towards the alignment between WLC theory and practice. Thus, assuming a production situation with unbalanced utilizations of manufacturing resources, the effectiveness of different dispatching rules and job release strategies are examined using simulation. Results highlight the importance of controlled release of jobs to the shop floor and the importance of differentiating between bottleneck and non-bottleneck work centres for purpose of dispatching.

Model of Three-Phase Transmission Line with the Theory of Modal Decomposition Implied  [PDF]
Rodrigo Cleber da Silva, Sérgio Kurokawa
Energy and Power Engineering (EPE) , 2013, DOI: 10.4236/epe.2013.54B217

This paper shows the development of transmission line model, based on lumped element circuit that provides answers directly in the time and phase domain. This model is valid to represent the ideally transposed line, the phases of each of the small line segments are separated in their modes of propagation and the voltage and current are calculated at the modal domain. However, the conversion phase-mode-phase is inserted in the state equations which describe the currents and voltages along the line of which there is no need to know the user of the model representation of the theory in the line modal domain.

Aluminium Toxicity Targets in Plants
Sónia Silva
Journal of Botany , 2012, DOI: 10.1155/2012/219462
Abstract: Aluminium (Al) is the third most abundant metallic element in soil but becomes available to plants only when the soil pH drops below 5.5. At those conditions, plants present several signals of Al toxicity. As reported by literature, major consequences of Al exposure are the decrease of plant production and the inhibition of root growth. The root growth inhibition may be directly/indirectly responsible for the loss of plant production. In this paper the most remarkable symptoms of Al toxicity in plants and the latest findings in this area are addressed. Root growth inhibition, ROS production, alterations on root cell wall and plasma membrane, nutrient unbalances, callose accumulation, and disturbance of cytoplasmic Ca2+ homeostasis, among other signals of Al toxicity are discussed, and, when possible, the behavior of Al-tolerant versus Al-sensitive genotypes under Al is compared. 1. Introduction Aluminium (Al) ranks third in abundance among the Earth’s crust elements, after oxygen and silicon, and is the most abundant metallic element. A large amount of Al is incorporated into aluminosilicate soil minerals, and very small quantities appear in the soluble form, capable of influencing biological systems [1]. Al bioavailability, and in consequence, toxicity, is mainly restricted to acid environments. Acid soils (with a pH of 5.5 or lower) are among the most important limitations to agricultural production. The production of staple food crops, in particular grain crops, is negatively influenced by acid soils [2]. Some agricultural practices, as removal of products from the farm, leaching of nitrogen below the plant root zone, inappropriate use of nitrogenous fertilizers, and build-up in organic matter, are causing further acidification of agricultural soils. When pH drops below 5.5, aluminosilicate clays and aluminium hydroxide minerals begin to dissolve, releasing aluminium-hydroxy cations and A l ( H 2 O ) 6 3 + ( A l 3 + ), that then exchange with other cations. On that conditions, A l 3 + also forms the mononuclear species A l O H 2 + , A l ( O H ) 2 + , Al(OH)3, and Al(OH)4 [3]. The mononuclear A l 3 + species and Al13 are considered as the most toxic forms [4, 5]. Although some crops (e.g., pineapple, tea) are considered tolerant to high levels of exchangeable Al, for most crops it is a serious constraint. Species and genotypes within species greatly differ in their tolerance to Al. For most crops, fertilization and attempts of soil correction (e.g., liming) may not be enough per se to reduce Al toxicity (e.g., as the soil reaction remains strongly
Estratégias seqüenciais subótimas para planejamento agregado da produ??o sob incertezas
Filho, Oscar S. Silva;
Gest?o & Produ??o , 2000, DOI: 10.1590/S0104-530X2000000300005
Abstract: within a hierarchical decision chain, a major part of problems is dependent on the time component and strongly sensitive to endogenous and exogenous components. these problems can be related to an important class of stochastic optimal control. difficulties to provide a closed-loop policy for them, lead to look for sub-optimal alternatives. in this paper, four different sub-optimal procedures are investigated in relation to their structural properties. a case study, based on an aggregated production planning problem, is considered with the purpose of comparing the different procedures. the best one is used to provide managerial scenarios about the future use of material resources of the firm.
A procura do turismo em espa?o rural
Etnográfica , 2007,
Abstract: this article deals with the demand for tourism in rural areas (tra) in portugal, presenting the results of research developed in continental portugal and, particularly, in three village contexts. we conclude that the demand is mainly performed by middle class urbanites with two main goals: to break free from everyday life and to reenergize in the countryside. the countryside is, for these urban dwellers, a kind of paradise on earth that incorporates many of the virtues believed to be inexistent in the cities: tranquillity, nature, tradition and authenticity. lodging in tra houses is a decisive step for their desired immersion in rural idyll, wether in rustic houses, manor-houses or palace-like houses.
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