An investigation on the mechanics of homogeneous expansion in gas-fluidized beds

The Richardson and Zaki (1954, Sedimentation and fluidization. Trans. Inst. Chem. Eng. 32, pp. 35–53.) equation has been used extensively to investigate the expansion profiles of homogeneous gas-fluidized beds. The experimental value of the parameter n appearing in the equation indicates how significantly interparticle forces affect the expansion of these beds, revealing the relative importance of these forces with respect to the fluid dynamic ones. In this work, we modeled the stable expansion of gas-fluidized beds of different diameter, accounting for enduring contacts among particles and wall effects. We solved the model numerically to obtain the bed expansion profiles, back-calculating from them the values of the parameter n. For all the cases considered, we observed that the values of n are higher than those obtained by purely fluid dynamic correlations, such as those advanced by Richardson and Zaki, and Rowe (1987, A convenient empirical equation for estimation of the Richardson and Zaki exponent. Chem. Eng. Sci. 42, pp. 2795.). This effect was more pronounced in beds of smaller diameter. To validate our model, we carried out fluidization and defluidization experiments, analyzing the results by means of the Richardson and Zaki equation. We obtained a reasonable agreement between numerical and experimental findings; this suggests that enduring contacts among particles, which are manifestations of cohesiveness, affect homogeneous bed expansion. This effect is amplified by wall friction

Eulerian modelling and computational fluid dynamics simulation of mono and polydisperse fluidized suspension

This research project is concerned with the Eulerian-Eulerian mathematical modelling of fluidized suspensions. We first derive new averaged equations of motion for particulate systems made up of a finite number of monodisperse particle classes; this clarifies the mathematical origin and physical meaning of the terms featuring in the equations and allows to attain a well-posed multiphase model. We then tackle the closure problem of the fluid-particle interaction force in monodisperse fluidized suspensions, laying emphasis on the buoyancy, drag and elastic forces. We analyze critically several constitutive relations used to express these forces, we identify their shortcomings and we advance new, and more accurate, closure equations. To validate them we study, analytically and computationally, the expansion and collapse of homogeneous fluidized beds and their transition to the bubbling regime, comparing the result with experimental data. We then address the mathematical modelling of polydisperse fluidized suspensions, which are characterized by a continuous distribution of the particle properties, such as size or velocity. Here we adopt a more powerful modelling approach based on the generalized population balance equation (GPBE). Whereas the classical transport equations of continuum mechanics are three-dimensional, the GPBE is usually higher-dimensional and incompatible with customary computational schemes. To solve it, we use the method of moments (MOM), which resorts to a limited number of GPBE moments to derive three-dimensional transport equations that can be handled by normal CFD codes. The limited set of equations, which replaces the single multidimensional GPBE, keeps the problem tractable when applied to complicated multiphase flows; the main obstacle to the method is that the moment transport equations are mathematically unclosed. To overcome the problem, we present two very efficient methods, the direct quadrature method of moments (DQMOM) and the quadrature method of moments (QMOM). Both approximate the volume density function (VDF) featuring in the GPBE by using a quadrature formula. The methods are very flexible: the number of nodes in the quadrature corresponds to the number of disperse phases simulated. The more the nodes, the better the quadrature approximation; more nodes, however, entail also more complexity and more computational effort. For monovariate systems, i.e., systems with only one internal coordinate in the generalized sense, the methods are entirely equivalent from a theoretical standpoint; computationally, however, they differ substantially. To conclude the work, we use DQMOM to simulate the dynamics of two polydisperse powders initially arranged as two superposed, perfectly-segregated packed systems. As fluidization occurs, the simulation tracks the evolution in time and physical space of the quadrature nodes and weights and predicts the mixing attained by the system. To validate the method, we compare computational predictions with experimental results

Galaxy evolution in groups. USGC U268 and USGC U376 in the Leo cloud

With the aim of investigating galaxy evolution in nearby galaxy groups, we analysed the spectral energy distribution of 24 galaxies, members of two groups in the Leo cloud, USGC U268 and USGC U376. We estimated the ages and stellar masses of the galaxies by fitting their total apparent magnitudes from far-ultraviolet to near-infrared with population synthesis models. The comparison of the results for a subsample of galaxies with smooth particle hydrodynamic (SPH) simulations with chemo-photometric implementation, shows that in most cases the estimated stellar masses obtained with the two different approaches are in good agreement. The kinematical and dynamical analysis indicates that USGC U268 is in a pre-virial collapse phase while USGC U376 is likely in a more evolved phase towards virialization.Comment: 16 pages, 6 figures; accepted for publication in Advances in Space Research, Special Issue: Ultraviolet Astrophysic

Estoque comercial para o segundo ciclo de corte na Floresta Nacional do Tapajós - área experimental KM 67 - Embrapa.

O estudo apresenta o estoque comercial para o segundo ciclo de corte do experimento km 67 da Embrapa Amazônia Oriental. Este volume é de 69,7 m³/ha para o grupo de espécies comerciais colhidas em 1979, considerando diâmetro mínimo de corte de 50 cm. A média de produtividade em volume comercial para este grupo de espécies comerciais foi de 1,47 m³/ha/ano no período de 31 anos de monitoramento. Logo após a exploração de 1979, as espécies comerciais iniciaram a recuperação de sua estrutura, na comparação entre o volume após a exploração (1981) e o volume disponível 31 anos depois, houve um acréscimo de 45,5 m³/ha em árvores dessas espécies com diâmetro acima do DMC

Extragalactic Source Counts and Contributions to the Anisotropies of the Cosmic Microwave Background. Predictions for the Planck Surveyor mission

We present predictions for the counts of extragalactic sources, the contributions to fluctuations and their spatial power spectrum in each channel foreseen for the Planck Surveyor (formerly COBRAS/SAMBA) mission. The contribution to fluctuations due to clustering of both radio and far--IR sources is found to be generally small in comparison with the Poisson term; however the relative importance of the clustering contribution increases and may eventually become dominant if sources are identified and subtracted down to faint flux limits. The central Planck frequency bands are expected to be ``clean'': at high galactic latitude (|b|>20), where the reduced galactic noise does not prevent the detection of the extragalactic signal, only a tiny fraction of pixels is found to be contaminated by discrete extragalactic sources. Moreover, removal of contaminating signals is eased by the substantial difference between their power spectrum and that of primordial fluctuations.Comment: 10 pages, Latex, mn.sty, 8 figures included, MNRAS, in the press. Minor changes in the text. Sections 3.1 and 3.2 have been expanded. Source counts in Table 2 have been slightly changed. Figure 1,2,7 and 8 have been replaced by new version

New quadrature-based moment method for the mixing of inert polydisperse fluidized powders in commercial CFD codes

To describe the behavior of polydisperse multiphase systems in an Eulerian framework, we solved the population balance equation (PBE), letting it account only for particle size dependencies. To integrate the PBE within a commercial computational fluid dynamics code, we formulated and implemented a novel version of the quadrature method of moments (QMOM). This no longer assumes that the particles move with the same velocity, allowing the latter to be size-dependent. To verify and test the model, we simulated the mixing of inert polydisperse fluidized suspensions initially segregated, validating the results experimentally. Because the accuracy of QMOM increases with the number of moments tracked, we ran three classes of simulations, preserving the first four, six, and eight integer moments of the particle density function. We found that in some cases the numerics corrupts the higher-order moments and a corrective algorithm, designed to restore the validity of the moment set, has to be implemented

Patrón génico de fibrosis y apoptosis en nefropatía obstructiva experimental : : modulación por rosuvastatina

La nefropatía obstructiva puede ser un desorden renal complejo de tratar debido al severo cuadro inflamatorio, desbalance oxidativo, apoptosis y fibrosis. Estudios previos sostienen que rosuvastatina (Ros) podría tener utilidad como una opción terapéutica en enfermedades renales que cursarían con apoptosis y fibrosis. Objetivo: Evaluar los posibles efectos antiapoptóticos y antifibróticos de Ros durante la obstrucción ureteral unilateral en ratas neonatas. Materiales y Métodos: Ratas Wistar neonatas de 48 hs. de vida fueron intervenidas quirúrgicamente (grupo experimental) o no (grupo control). Ambos grupos fueron subdivididos en tratadas o no tratadas con Ros (10mg / kg por día) vía oral durante 14 días. Posteriormente se procedió a nefrectomizar y procesar las cortezas renales para determinar por RT-PCR las expresiones de genes: óxido nítrico sintasa inducible (iNOS), factor promotor génico de chaperonas (hsf1), proteína de shock térmico (hsp70), bax, bcL2, wt1, p53, snail, proteína morfogénica del hueso (bmp7), caderina E, factor transformador de crecimiento (tgf-β) y factor de necrosis tumoral (tnf-α). Resultados: La obstrucción ureteral unilateral neonatal indujo una marcada fibrosis y apoptosis, mientras que el tratamiento con Ros moduló el patrón de genes fibróticos y apoptóticos mediante disminución de la expresión de bmp7, caderina E, wt1, p53 y bcl2; además indujo una caída en la expresión de los genes profibróticos y proapoptóticos (bax, tnf-α y tgf-β). El análisis de los resultados presentados, permiten sugerir que la protección renal de rosuvastatina durante nefropatía obstructiva de ratas neonatas estaría asociado a la interacción entre hsp70 y la biodisponibilidad del óxido nítrico con el concomitante descenso en genes pro-apoptóticos.Fibrosis and apoptosis gene pattern in experimental obstructive nephropathy: Rosuvastatin modulation Obstructive nephropathy renal disorder can be complex to treat due to the severe apoptosis and fibrosis. Previous studies shown that rosuvastatin (Ros), may have potential utility as a therapeutic option in kidney diseases which lead to apoptosis and fibrosis. Objective: to evaluate the possible antifibrotic and antiapoptotic effects of Ros during experimental neonatal rats unilateral ureteral obstruction (UUO). Materials and Methods: Neonatal rats were surgically obstructed (experimental group) or not (control group), which were Ros treated or not (10 mg/kg per day) during 14 days. Subsequent nephrectomy and processing of the renal cortex to determinate by RT-PCR technique, genes expression of inducible nitric oxide synthase (iNOS), heat shock factor 1 (hsf1), heat shock protein 70 (hsp70), bax, bcl2, wt1, p53, snail, bone morphogenetic protein (bmp7), E-cadherin, transforming growth factor (tgf-β) and tumor necrosis factor (tnf-α). Results: neonatal UUO induced fibrosis and apoptosis, while Ros treatment modulated the fibrotic and apoptotic genes pattern and increased the bmp7, Ecadherin, wt1, p53 and bcl2 expression as well as decreased the profibrotic and proapoptotic genes expression (bax, tnf-α y tgf-β). Our results allow us to suggest that Ros renal protection during UUO is linked to hsp70 and nitric oxide bioavailability interaction, with concomitant decrease in pro apoptotic gene pattern.Fil: Mazzei, L.. Universidad Nacional de Cuyo. Facultad de Ciencias Médicas. Área de FisiopatologíaFil: García, M.. Universidad Nacional de Cuyo. Facultad de Ciencias Médicas. Área de FisiopatologíaFil: Manucha, W.. Universidad Nacional de Cuyo. Facultad de Ciencias Médicas. Área de Fisiopatologí

Controlled photon transfer between two individual nanoemitters via shared high-Q modes of a microsphere resonator

We realize controlled cavity-mediated photon transfer between two single nanoparticles over a distance of several tens of micrometers. First, we show how a single nanoscopic emitter attached to a near-field probe can be coupled to high-Q whispering-gallery modes of a silica microsphere at will. Then we demonstrate transfer of energy between this and a second nanoparticle deposited on the sphere surface. We estimate the photon transfer efficiency to be about six orders of magnitude higher than that via free space propagation at comparable separations.Comment: accepted for publication in Nano Letter