A Laplace transform method for energy multigroup hybrid discrete ordinates slab lattice calculations

In typical lattice cells where a highly absorbing, small fuel element is embedded in the moderator, a large weakly absorbing medium, high-order transport methods become unnecessary. In this work we describe a hybrid discrete ordinates (SN) method for energy multigroup slab lattice calculations. This hybrid SN method combines the convenience of a low-order SN method in the moderator with a high-order SN method in the fuel. The idea is based on the fact that in weakly absorbing media whose physical size is several neutron mean free paths in extent, even the S2 method (P1 approximation), leads to an accurate result. We use special fuel-moderator interface conditions and the Laplace transform (LTSN) analytical numerical method to calculate the two-energy group neutron flux distributions and the thermal disadvantage factor. We present numerical results for a range of typical model problems

A Laplace transform method for energy multigroup hybrid discrete ordinates slab lattice calculations

In typical lattice cells where a highly absorbing, small fuel element is embedded in the moderator, a large weakly absorbing medium, high-order transport methods become unnecessary. In this work we describe a hybrid discrete ordinates (SN) method for energy multigroup slab lattice calculations. This hybrid SN method combines the convenience of a low-order SN method in the moderator with a high-order SN method in the fuel. The idea is based on the fact that in weakly absorbing media whose physical size is several neutron mean free paths in extent, even the S2 method (P1 approximation), leads to an accurate result. We use special fuel-moderator interface conditions and the Laplace transform (LTSN) analytical numerical method to calculate the two-energy group neutron flux distributions and the thermal disadvantage factor. We present numerical results for a range of typical model problems

An analytical solver for the multi-group two-dimensional neutron-diffusion equation by integral transform techniques

In this work, we present an analytical solver for neutron diffusion in a rectangular two-dimensional geometry by a two-step integral transform procedure. To this end, we consider a regionwise homogeneous problem for two energy groups, i.e. fast and thermal neutrons, respectively. Each region has its specific physical properties, specified by cross-sections and diffusion constants. The problem is set up by two coupled bi-dimensional diffusion equations in agreement with general perturbation theory. These are solved by integral transforms Laplace transform and generalized integral transform technique yielding analytical expressions for the scalar neutron fluxes. The solutions for neutron fluxes are presented for fast and thermal neutrons in the four regions

Uma Solução Analítica para a Equação que descreve o Decaimento da Turbulência na Camada Limite Convectiva

Uma solução analítica para a equação que descreve odecaimento da turbulência na camada limite convectiva:uma aproximação isotrópic

Mangal communities of the "Salgado Paraense": Ecological heterogeneity along the Bragança peninsula assessed through soil and leaf analyses

Mangroves in the Bragança peninsula occur in a variety of environmental settings differing in tidal influence and fresh water run-off. The construction of a paved road running through the middle of the peninsula modified the transversal flow of water. Five sites were sampled along this road: I. Coastal site near the village of Ajuruteua, II. Tidal creeks flowing into the lower Caeté river, III. Central lagoons, IV. Avicennia basin forest, and V. Upper Caeté estuary near the village of Acarajó. All but site III, harbored the three common mangroves species Rhizophora mangle, Laguncularia racemosa and Avicennia germinans. Monospecific communities of shrub-like Avicennia germinans stands characterized site III. Soils were highly organic therefore bulk density was inversely correlated to the concentrations of C and N. Sites I and V had the lowest salinity values. The highest salinity was measured ii the Avicennia dominated sites III and IV. Nitrogen showed similar values in all sites, but S was clearly more abundant in sites II and V. Leaf dimensions varied significantly between sites. Considering leaf area expansion as indicator ofstress and δ 13C values as indicator of water use efficiency, site V was more favorable for Rhizophora and Laguncularia while site IV was so for Avicennia. Leaf shape measured as the length/width ratio was more variable in Avicennia and least variable in Rhizophora. Leaf nutrients were not correlated with soil nutrient content. Sodium and Mg were more concentrated in Avicennia leaves while Fe was more concentrated in Laguncularia and Mn in Rhizophora leaves. Avicennia showed the highest N and the lowest Ca concentrations as expected for being a glycinbetaine accumulator and an oxalate-former. δ 15N values indicate that N source for mangroves is essentially the mineralization of organic matter

Solução Analítica da Equação de Advecção-difusão Considerando Fechamento não-local da Turbulência e Condições de Vento Fraco

Neste trabalho consideramos o fechamento não-local da difusãoturbulenta na equação de advecção-difusão. Obtemos uma solução analíticapara a equação de advecção-difusão usando o método GILTT (GeneralizedIntegral Laplace Transform Technique). Para testar a nova solução analítica,as concentrações máximas obtidas são comparadas com os dados experimentaisdo experimento de ITT Delhi para condições de vento fraco

Aspetos bioecológicos de flebotomíneos (Diptera, Psychodidae), vetores de Leishmania sp., capturados no Velho e no Novo Mundo: Alentejo, Portugal e Volta Redonda, Brasil, 2016-2017

Aspectos bioecológicos de flebotomíneos no Novo e Velho mundo: Brasil e POrtuga

Simulação da Dispersão de Poluentes Usando um Modelo Lagrangeano em Condições de Vento Fraco

Neste trabalho, utilizamos o modelo de partícula Lagrangeanosemi-analítico ILS-LW (Iterative Langevin Solution for Low Wind) parainvestigar o processo de dispersão atmosférica em condições de vento fracodurante o experimento OLAD (Over Land Atmospheric Dispersion).A partir da análise estatística constatamos que o modelo reproduz satisfatoriamenteo conjunto de dados observados no experimento

Modelo euleriano semi-analítico para a dispersão de contaminantes na Camada Limite Planetária

An analytical air quality dispersion model based on a discretization of the planetary boundary layer in N sub-layers is presented. In each sub-layer the diffusion-advection equation is solved by the Laplace Transform techniques, considering an average value for the vertical exchange coefficient and the wind speed. As a consequence, the present approach allows to employ realistic semi-empirical profiles for the eddy diffusivity and wind speed, in such manner that the inhomogeneous turbulence can be handle. The model performance have been evaluated using the well-known Copenhagen and Prairie Grass datasets. Then, the application of the statistical evalution procedure (Hanna, 1989) over the out coming results has show that the proposed analytical dispersion model produces a good fitting of the observational data.Um modelo de dispersão analítico baseado na discretização da Camada Limite Planetária em N subcamadas é apresentado. Em cada subcamada a equação de difusão-adevcção é resolvida pelo emprego da transformada de Laplace, considerando um valor médio para o coeficiente de difusão e para a velocidade do vento. O presente modelo emprega perfis realísticos semi-empíricos para o coeficiente de difusão e velocidade do vento, de modo que a turbulência não homogênea pode ser utilizada. A performance do modelo é testada confrontando as simulações com os dados experimentais de Prairie Grass e Copenhagen. A aplicação de índices estatísticos (Hanna, 1989) mostra que o modelo analítico de dispersão proposto produz bons resultados