1,631 research outputs found
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
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