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Radial Variations (radial + variation)

Distribution by Scientific Domains

Chemistry	57%

Selected Abstracts

Radial variation of optical and near-infrared colours in luminous early-type galaxies in A2199

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2004
Naoyuki Tamura
ABSTRACT We performed K -band surface photometry for luminous early-type galaxies in a nearby rich cluster A2199. Combining it with B - and R -band surface photometry, radial variations of B,R and R,K colours in the galaxies were investigated. It is found that the inner regions of the galaxies are redder in both B,R and R,K colours. Comparing the radial variations of both colours with predictions of simple stellar population models for a range of ages and metallicities, it is suggested that the cluster ellipticals have negative metallicity gradients, but their age gradients are consistent with zero, although our sample is small; the typical metallicity gradient is estimated to be ,0.16 ± 0.09 in d log Z/d log r, while the age gradient is estimated to be ,0.10 ± 0.14 in d log (age)/d log r. Considering that similar results have also been derived in the other recent studies using samples of ellipticals in the Coma cluster and less dense environments, it seems that there is no strong dependence on galaxy environment in the radial gradient of stellar population in an elliptical galaxy. [source]

Iron K, line profiles and the inner boundary condition of accretion flows

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2003
A. Merloni
ABSTRACT Recent X-ray observations have shown evidence for exceptionally broad and skewed iron K, emission lines from several accreting black hole systems. The lines are assumed to be due to fluorescence of the accretion disc illuminated by a surrounding corona and require a steep emissivity profile increasing into the innermost radius. This appears to question both standard accretion disc theory and the zero-torque assumption for the inner boundary condition, both of which predict a much less extreme profile. Instead it argues that a torque may be present due to magnetic coupling with matter in the plunging region or even to the spinning black hole itself. Discussion so far has centred on the torque acting on the disc. However, the crucial determinant of the iron line profile is the radial variation of the power radiated in the corona. Here we study the effects of different inner boundary conditions on the coronal emissivity and on the profiles of the observable Fe K, lines. We argue that in the extreme case where a prominent highly redshifted component of the iron line is detected, requiring a steep emissivity profile in the innermost part and a flatter one outside, energy from the gas plunging into the black hole is being fed directly to the corona. [source]

Radial nonuniformity index (RNI) in fluidized beds and other multiphase flow systems

THE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 2 2001
Jing-Xu (Jesse) Zhu
Abstract The radial nonuniformity index (RNI) is a new non-dimensional index recently devised to quantify the extent of radial variations of flow parameters in fluidized beds and other multiphase flow systems. The index, defined as the ratio of the standard deviation of the given flow parameter in the radial direction to the maximum practically possible standard deviation of that particular parameter, is shown to be an excellent measure of the radial flow structure. This index allows the use of a single value to summarize the radial variation of a given flow parameter. The higher the value of the RNI the less uniform is the flow, and vice versa. Using this technique, radial distributions of local solids concentration and particle velocities from different circulating fluidized bed systems (gas-solid and liquid-solid, upflow and downflow) were examined. It has been found that the RNI can be confidently related to the flow conditions in the circulating fluidized beds, and more insight understanding has been achieved. L'indice de non-uniformité radiale (RNI) est un nouvel indice adimensionnel introduit récemment pour quantifier l'étendue des variations radiales des paramètres d'écoulement dans les lits fluidisés et autres systèmes d'écoulement multiphasiques. On montre que cet indice, défini comme le rapport entre I'écart type du paramètre d'écoulement donné dans la direction radiale et I'écart type maximum pratiquement possible de ce paramètre particulier, est une excellente mesure de la structure d'écoulement radial. Il permet I'utilisation d'une valeur unique pour décrire la variation radiale d'un paramètre d'écoulement donné. Plus la valeur de RNI est élevée, moins I'écoulement est uniforme, et vice-versa. À I'aide de cette technique, on a examiné les distributions radiales des concentrations de solides locales et des vitesses de particules pour différents systèmes de lits fluidisés circulants (gaz-solide et liquide-solide, ascendant et descendant). On a trouvé que le RNI pouvait ,tre relié en toute confiance aux conditions d'écoulement dans les lits fluidisés circulants, ce qui permet de mieux comprendre ce problème. [source]

The effect of gas-liquid counter-current operation on gas hold-up in bubble columns using electrical resistance tomography,

JOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 9 2010
Haibo Jin
Abstract BACKGROUND: In order to improve the performance of a counter-current bubble column, radial variations of the gas hold-ups and mean hold-ups were investigated in a 0.160 m i.d. bubble column using electrical resistance tomography with two axial locations (Plane 1 and Plane 2). In all experiments the liquid phase was tap water and the gas phase air. The superficial gas velocity was varied from 0.02 to 0.25 m s,1, and the liquid velocity varied from 0 to 0.01 m s,1. The effect of liquid velocity on the distribution of mean hold-ups and radial gas hold-ups is discussed. RESULTS: The gas hold-up profile in a gas,liquid counter-current bubble column was determined by electrical resistance tomography. The liquid velocity slightly influences the mean hold-up and radial hold-up distribution under the selected operating conditions and the liquid flow improves the transition gas velocity from a homogeneous regime to a heterogeneous regime. Meanwhile, the radial gas hold-up profiles are steeper at the central region of the column with increasing gas velocity. Moreover, the gas hold-up in the centre of the column becomes steeper with increasing liquid velocity. CONCLUSIONS: The value of mean gas hold-ups slightly increases with increasing downward liquid velocity, and more than mean gas hold-ups in batch and co-current operation. According to the experimental results, an empirical correlation for the centreline gas hold-up is obtained based on the effects of gas velocity, liquid velocity, and ratio of axial height to column diameter. The values calculated in this way are in close agreement with experimental data, and compare with literature data on gas hold-ups at the centre of the column. Copyright © 2010 Society of Chemical Industry [source]

Mechanics of column beds: I. Acquisition of the relevant parameters

AICHE JOURNAL, Issue 3 2003
Bee Gaik Yew
The efficiency of chromatographic columns is adversely affected by large-scale radial variations of the packing density or void ratio of the material used to prepare the bed. This heterogeneity is due to wall friction effects that take place during the preparation of the column and to seepage effects operating during the packing process and the subsequent operation of the column. The dependence of the bed's void fraction on the stress applied during its consolidation was determined, as well as its permeability at various stages of the consolidation process and the coefficient of friction between typical packing materials and the stainless steel wall of chromatographic columns. These results are required to develop and use numerical models of the volumetric response to axial compression of the bed and models of the coupled mechanical-seepage rheology of particulate materials. [source]