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Bulk Flow (bulk + flow)
Selected AbstractsFat Migration in Chocolate: Diffusion or Capillary Flow in a Particulate Solid?,A Hypothesis PaperJOURNAL OF FOOD SCIENCE, Issue 7 2004J. M. Aguilera ABSTRACT: The exact mechanism of fat and oil migration in chocolate and chocolate coatings is still unknown. Nevertheless, the so-called "diffusion equation" derived from Fick's 2nd law has been extensively used to model the phenomenon, giving the impression that molecular diffusion is the single transport mechanism. We propose that chocolate may be microstructurally regarded as a particulate medium formed by an assembly of fat-coated particles (for example, cocoa solids, sugars crystals, and milk powder). Within this matrix the liquid fraction of cocoa fat (which increases with temperature) is likely to move under capillary forces through interparticle passages and connected pores. Based on available evidence (microstructure, kinetic data, temperature dependence of liquid fat fraction, and so on) we demonstrate that capillary forces may have an important role to play in bulk flow of liquid fat and oils. The Lucas-Washburn equation for capillary rise fits available data under most reported experimental conditions. Detailed microstructural analysis in actual products as well as data on key parameters (surface tension, contact angle, viscosity) is necessary to confirm this hypothesis. Bulk flow due to capillary effects, highly disregarded in structured foods, should be considered as a mass transfer mechanism in liquid-filled porous or particulate foods. [source] Three-dimensional study of the pressure field and advantages of hemispherical crucible in silicon Czochralski crystal growthCRYSTAL RESEARCH AND TECHNOLOGY, Issue 6 2010F. Mokhtari Abstract The effects of several growth parameters in cylindrical and spherical Czochralski crystal process are studied numerically and particularly, we focus on the influence of the pressure field. We present a set of three-dimensional computational simulations using the finite volume package Fluent in two different geometries, a new geometry as cylindro-spherical and the traditional configuration as cylindro-cylindrical. We found that the evolution of pressure which is has not been studied before; this important function is strongly related to the vorticity in the bulk flow, the free surface and the growth interface. It seems that the pressure is more sensitive to the breaking of symmetry than the other properties that characterize the crystal growth as temperature or velocity fields. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] An in vitro investigation of the bulk flow of fluid through apical foramina during simulated tooth extraction: a potential confounder in microbiological studies?INTERNATIONAL ENDODONTIC JOURNAL, Issue 4 2001A. Kapalas Aim,The ,pumping action' induced during tooth extraction may cause bacteria suspended in tissue fluids to be transposed from one anatomical compartment to another. Apart from causing bacteraemia, this may lead to inaccuracies in studies evaluating the presence and distribution of bacteria in and around tooth apices. The aim was to investigate the bulk flow of fluid through apical foramina during simulated extraction of teeth in an in vitro model. The influence of the presence or absence of a coronal restoration was also evaluated. Methodology,Twenty extracted single-rooted, human, mature, permanent teeth were used. Standard access cavities were prepared and the root canals located. Standardized micrographs of the apical foramina were obtained and their area (µm2) was calculated by image analysis software. The teeth were then set and sealed into polyvinylsiloxane (rubber base) impression material. Crystal violet dye was inoculated into the coronal half of the root canal system. Tooth extraction movements were simulated in the impression matrix and the leakage of dyes with and without the presence of a coronal restoration was examined. The procedure was repeated, following application of safranin dye in a coronal trough within the simulated rubber base gingival margin at the CEJ. The results were analysed statistically with the independent-samples t -test and the McNemar test. Results,In the absence of a coronal restoration crystal violet leaked out of the apical foramina in 18/20 teeth; conversely safranin leaked into the teeth through the apical foramina in 11/20 cases when applied to the external root surface. In the presence of an intact coronal restoration crystal violet dye leaked out in 6/20 teeth and conversely safranin leaked into 7/20 teeth. The presence of a coronal restoration significantly reduced (P = 0.002) dye leakage out of the root canal system. No associations were found for leakage of dye into the root canal system when applied externally. In addition, the amount of dye leakage was positively correlated with the area of the apical foramen in the presence of a coronal restoration (P = 0.009). Conclusion,The presence of a coronal restoration significantly reduced leakage of dye out of the apical foramen. Microbiological studies on root canals and periapical lesions using extracted teeth should take potential contamination from this source into account. [source] Fat Migration in Chocolate: Diffusion or Capillary Flow in a Particulate Solid?,A Hypothesis PaperJOURNAL OF FOOD SCIENCE, Issue 7 2004J. M. Aguilera ABSTRACT: The exact mechanism of fat and oil migration in chocolate and chocolate coatings is still unknown. Nevertheless, the so-called "diffusion equation" derived from Fick's 2nd law has been extensively used to model the phenomenon, giving the impression that molecular diffusion is the single transport mechanism. We propose that chocolate may be microstructurally regarded as a particulate medium formed by an assembly of fat-coated particles (for example, cocoa solids, sugars crystals, and milk powder). Within this matrix the liquid fraction of cocoa fat (which increases with temperature) is likely to move under capillary forces through interparticle passages and connected pores. Based on available evidence (microstructure, kinetic data, temperature dependence of liquid fat fraction, and so on) we demonstrate that capillary forces may have an important role to play in bulk flow of liquid fat and oils. The Lucas-Washburn equation for capillary rise fits available data under most reported experimental conditions. Detailed microstructural analysis in actual products as well as data on key parameters (surface tension, contact angle, viscosity) is necessary to confirm this hypothesis. Bulk flow due to capillary effects, highly disregarded in structured foods, should be considered as a mass transfer mechanism in liquid-filled porous or particulate foods. [source] Mesomixing in semi-batch reaction crystallization and influence of reactor sizeAICHE JOURNAL, Issue 12 2004Marika Torbacke Abstract Experiments on semibatch reaction crystallization of benzoic acid are reported, in which hydrochloric acid was fed into an agitated solution of sodium benzoate. The influence of mixing and the influence of reactor size are examined on the product crystal mean size. The product mean size increases with increasing stirring rate and with decreasing feed rate. At low feed rates, the mean size increases at decreasing feed pipe diameter. At high feed rates the influence of the feed pipe diameter is more complex. Micromixing is of some importance in most experiments, but the rate of mesomixing especially governs the process. Mesomixing seems to be adequately described by the inertial-convective disintegration mechanism. In many aspects experimental results cannot be described by the turbulent-dispersion mechanism. The product mean size does not exhibit a clear dependence on reactor size, but depends more strongly on other parameters. Results from experiments from 1 L scale to 200 L scale can be correlated fairly well against a dimensionless number defined as the ratio of the total time of reactant feeding to the time constant of mixing. The best representation of the mixing time constant is obtained by making it directly proportional to the ratio of the feed pipe diameter and the linear velocity of the bulk flow passing the feed pipe. The proportionality constant can be calculated from turbulence data over the bulk flow at the feed point. © 2004 American Institute of Chemical Engineers AIChE J, 50: 3107,3119, 2004 [source] Cosmic flows on 100 h,1 Mpc scales: standardized minimum variance bulk flow, shear and octupole momentsMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2010Hume A. Feldman ABSTRACT The low-order moments, such as the bulk flow and shear, of the large-scale peculiar velocity field are sensitive probes of the matter density fluctuations on very large scales. In practice, however, peculiar velocity surveys are usually sparse and noisy, which can lead to the aliasing of small-scale power into what is meant to be a probe of the largest scales. Previously, we developed an optimal ,minimum variance' (MV) weighting scheme, designed to overcome this problem by minimizing the difference between the measured bulk flow (BF) and that which would be measured by an ideal survey. Here we extend this MV analysis to include the shear and octupole moments, which are designed to have almost no correlations between them so that they are virtually orthogonal. We apply this MV analysis to a compilation of all major peculiar velocity surveys, consisting of 4536 measurements. Our estimate of the BF on scales of ,100 h,1 Mpc has a magnitude of |v| = 416 ± 78 km s ,1 towards Galactic l= 282°± 11° and b= 6°± 6°. This result is in disagreement with , cold dark matter with Wilkinson Microwave Anisotropy Probe 5 (WMAP5) cosmological parameters at a high confidence level, but is in good agreement with our previous MV result without an orthogonality constraint, showing that the shear and octupole moments did not contaminate the previous BF measurement. The shear and octupole moments are consistent with WMAP5 power spectrum, although the measurement noise is larger for these moments than for the BF. The relatively low shear moments suggest that the sources responsible for the BF are at large distances. [source] Compton scattering of Fe K, lines in magnetic cataclysmic variablesMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2008A. L. McNamara ABSTRACT Compton scattering of X-rays in the bulk flow of the accretion column in magnetic cataclysmic variables (mCVs) can significantly shift photon energies. We present Monte Carlo simulations based on a non-linear algorithm demonstrating the effects of Compton scattering on the H-, He-like and neutral Fe K, lines produced in the post-shock region of the accretion column. The peak line emissivities of the photons in the post-shock flow are taken into consideration and frequency shifts due to Doppler effects are also included. We find that line profiles are most distorted by Compton scattering effects in strongly magnetized mCVs with a low white dwarf mass and high mass accretion rate and which are viewed at an oblique angle with respect to the accretion column. The resulting line profiles are most sensitive to the inclination angle. We have also explored the effects of modifying the accretion column width and using a realistic emissivity profile. We find that these do not have a significant overall effect on the resulting line profiles. A comparison of our simulated line spectra with high-resolution Chandra/HETGS observations of the mCV GK Per indicates that a wing feature redward of the 6.4-keV line may result from Compton recoil near the base of the accretion column. [source] | |||||||||||||