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Size Distribution (size + distribution)
Kinds of Size Distribution Selected AbstractsINEQUALITY, INCOMPLETE CONTRACTS, AND THE SIZE DISTRIBUTION OF BUSINESS FIRMS,INTERNATIONAL ECONOMIC REVIEW, Issue 2 2010Thomas Gall This article analyzes the effects of intrafirm bargaining on the formation of firms in an economy with imperfect capital markets and contracting constraints. In equilibrium, wealth inequality induces a heterogeneous distribution of firm sizes, allowing for firms both too small and too large in terms of technical efficiency. The findings connect well to empirical facts such as the missing middle of firm-size distributions in developing countries. The model can encompass a nonmonotonic relationship between aggregate output and inequality. It turns out that an inflow of capital may indeed decrease output in absolute terms. [source] QUALITY AND CONSUMER ACCEPTANCE OF AKARA (FRIED COWPEA PASTE) PROCESSED FROM WET- AND DRY-MILLED COWPEA (VIGNA UNGUICULATA) MEAL WITH SPECIFIED PARTICLE SIZE DISTRIBUTIONJOURNAL OF FOOD QUALITY, Issue 3 2007MELISSA A. VANCHINA ABSTRACT Direct quality indicators of cowpea paste and akara produced from traditionally wet-milled peas, and hammer-milled (dry-milled) and freeze-dried (wet-milled) meals were examined in this study. Both meal samples studied were formulated to consist of 65% medium-sized particles and 35% large particles by weight. Particle volume mean diameters (µm) of the three paste samples were not significantly different from one another at the various stages during akara production. Scanning electron micrographs of akara crumb were converted to threshold images and analyzed. There was no significant difference in the amount of air found in the akara samples. Akara produced from both meals was found acceptable by sensory panelists with no significant difference in any of the attributes or overall liking among the three samples. [source] Particle Size Distribution (Texture) of Eroded Soil MaterialJOURNAL OF AGRONOMY AND CROP SCIENCE, Issue 5 2002F. Basic Abstract The total quantity of erosional drift on a Stagnic Luvisol on which six tillage methods were used was measured over 5 years of investigation. The texture of the tilled soil and the erosional drift for each trial method was recorded in the same plots. The results obtained suggested that erosional drift was generally richer in silt and clay particles. The standard deviations of coarse sand indicated that approximately the same quantity of coarse sand was found in plot soil and in erosional drift for all tillage methods. Sometimes more and sometimes fewer fine sand particles were found in erosional drift than in plot soil. In most cases, more silt particles were found in erosional drift than in plot soil. The standard deviation and coefficient of variation for clay and silt were higher in erosional drift than in plot soil for all methods. The highest content of clay particles was recorded in erosional drift from the no-tillage treatment in all investigation years. The results suggest that the correct choice of tillage method (no-tillage and ploughing across the slope) on a Stagnic Luvisol can protect the soil on a slope. [source] Air Inclusion Into a Model Cake Batter Using a Pressure Whisk: Development of Gas Hold-up and Bubble Size DistributionJOURNAL OF FOOD SCIENCE, Issue 8 2001A.H. Massey ABSTRACT: This paper investigates the development of gas hold-up (that is, gas volume fraction) and bubble size distribution in a model cake batter, which is aerated in a pressure whisk. With increasing aeration time, the hold-up was found to pass through a maximum before approaching a uniform steady state value. A mathematical model that describes this profile has been developed. Bubble size distribution was found to be adequately described by a log normal distribution function with mean size varying between 20 and 50 ,m. Higher pressures were found to increase hold-up and mean bubble size, whereas higher whisk speeds reduced the time required to achieve a given hold-up and the final mean bubble size. [source] Measurement based modeling and control of bimodal particle size distribution in batch emulsion polymerizationAICHE JOURNAL, Issue 8 2010Mazen Alamir Abstract In this article, a novel modeling approach is proposed for bimodal Particle Size Distribution (PSD) control in batch emulsion polymerization. The modeling approach is based on a behavioral model structure that captures the dynamics of PSD. The parameters of the resulting model can be easily identified using a limited number of experiments. The resulting model can then be incorporated in a simple learning scheme to produce a desired bimodal PSD while compensating for model mismatch and/or physical parameters variations using very simple updating rules. © 2010 American Institute of Chemical Engineers AIChE J, 2010 [source] Coupled Single-Particle and Population Balance Modeling for Particle Size Distribution of Poly(propylene) Produced in Loop ReactorsMACROMOLECULAR REACTION ENGINEERING, Issue 2 2010Zheng-Hong Luo Abstract A comprehensive model was developed for the PSD of PP produced in loop reactors. The polymeric multilayer model (PMLM) was first applied to calculate the single particle growth rate under intraparticle transfer limitations. In order to obtain the comprehensive model, the PMLM was solved together with a steady-state particle population equation to predict the PSD in the loop reactors. The simulated PSD data obtained under steady-state polymerization conditions agreed with the actual data collected from industrial scale plant. The comprehensive model was also used to predict the effects of some critical factors, including the intraparticle mass and heat transfer limitations, the feed catalyst particle size and the catalyst deactivation, etc., on the PSD. [source] Experimental Study on Particle Size Distribution and Concentration Using Transmission Fluctuation Spectrometry with the Autocorrelation TechniquePARTICLE & PARTICLE SYSTEMS CHARACTERIZATION, Issue 3 2005Xiaoai Guo Abstract Based on the statistical characteristics of the transmission fluctuations in the particle suspension, transmission fluctuation spectrometry with autocorrelation (TFS-AC) is described theoretically, with the assumptions of geometric ray propagation and completely absorbent particles in the suspension. The experiments presented here are realized in a focused Gaussian beam with the TFS-AC technique. The acquisition of transmission fluctuation signals is achieved by using a high-resolution digital oscilloscope. The transition function of TFS-AC is obtained by varying the autocorrelation time. With a modified iterative Chahine inversion algorithm, solving a linear equation retrieves information on the particle size distribution and particle concentration. Some experimental results on spherical and non-spherical particles are presented and discussed. The experiments cover a particle size range from 1,m to 1000,,m and a particle concentration of up to 12,%. [source] Analysis of Particle Size Distribution by Particle TrackingPARTICLE & PARTICLE SYSTEMS CHARACTERIZATION, Issue 5 2004Christiane Finder Abstract Particle tracking is performed using a combination of dark field or fluorescence video microscopy with automatic image analysis. The optical detection together with the image analysis software allows for the time resolved localization of individual particles with diameters between 100 and 1000,nm. Observation of their Brownian motion over a set of time intervals leads to the determination of their mean square displacements under the given room temperature and viscosity. Hereby, the radii of a set of particles visible within a given optical frame are derived simultaneously. Rapid data analysis leads to reliable particle size histograms. The applicability of this method is demonstrated on polystyrene latices and PMMA nanospheres with radii between 51,nm and 202,nm. [source] Size Distribution of Dispersed Luteal Cells During Oestrous Cycle in Angora GoatsREPRODUCTION IN DOMESTIC ANIMALS, Issue 5 2007H Kalender Contents The present study examines the size distribution of the goat steroidogenic luteal cells throughout the oestrous cycle. Corpora lutea (CL) were collected after laparatomy on days 5, 10 and 16 of the oestrous cycle. Luteal cells were isolated from CL by collagenase digestion. Steriodogenic luteal cells were identified by staining of the cells for 3, -hydroxysteroid dehydrogenase activity, a marker for steroidogenic cells. Luteal cells having steroidogenic capacity covered a wide spectrum of sizes, ranging from 5 to 37.5 ,m in diameter. There was a significant increase in mean cell diameters (p < 0.01) as CL aged. The mean cell diameter on day 5 was 11.55 ± 0.12 ,m, which was significantly increased and reached up to 19.18 ± 0.24 ,m by day 16 of the oestrous cycle. The ratio of large to small luteal cells was 0.06:1.0 on day 5 of the oestrous cycle. This ratio increased to 0.78:1.0 by day 16 of the oestrous cycle. Luteal cell size on days 5, 10 and 16 of the oestrous cycle reached its maximum at 7.5, 10 and 35 ,m in diameter, respectively. Development of CL is associated with an increase in luteal cell size in goats. It is likely that small luteal cells could develop into large luteal cells as CL becomes older during oestrous cycle in goats. [source] The Effect of Particle Size Distribution on Pressure Drop through Packed Beds of Cooked Wood ChipsTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 4 2005Quak Foo Lee Abstract The pressure drop of process liquors through columns of wood chips determines the operability, efficiency and control of both batch and continuous pulp digesters and the quality of the pulp produced from them. Pressure drop was measured through columns of industrial white spruce chips (produced with a chipping head-rig) as a function of the chip size distribution and the extent of delignification. Flow resistance depended on the porosity of the chip bed which was affected by the kappa number of the chips (which affected their flexibility) and chip size distribution, the compaction forces applied to the column, and the liquid superficial velocity. The chip beds were compressible and inelastic. Previous work from the literature using the Ergun equation to characterize pressure losses through chip beds is examined and compared with results of this work. La perte de charge des liqueurs de procédés dans des colonnes de copeaux de bois détermine l'opérabilité, l'efficacité et le contrôle des digesteurs de pâtes discontinus et continus, ainsi que la qualité de la pâte produite. La perte de charge a été mesurée dans des colonnes de copeaux d'épinette (produits avec une machine de fabrication de copeaux) en fonction de la distribution de taille des copeaux et du degré de délignification. La résistance à l'écoulement dépend de la porosité du lit de copeaux qui est influencée par le nombre de kappa des copeaux (qui influe sur leur flexibilité) et la distribution de taille des copeaux, les forces de compaction appliquées à la colonne ainsi que la vitesse de liquide superficielle. Les lits de copeaux sont compressibles et inélastiques. Un travail antérieur de la littérature scientifique faisant appel à l'équation d'Ergun pour caractériser les pertes de charge dans les lits de copeaux est examiné et comparé aux résultats du présent travail. [source] Factors Controlling the Abundance and Size Distribution of the Phototrophic Ciliate Myrionecta rubra in Open Waters of the North AtlanticTHE JOURNAL OF EUKARYOTIC MICROBIOLOGY, Issue 5 2008DAVID J. S. MONTAGNES ABSTRACT. Myrionecta rubra, a ubiquitous planktonic ciliate, has received much attention due to its wide distribution, occurrence as a red tide organism, and unusual cryptophyte endosymbiont. Although well studied in coastal waters, M. rubra is poorly examined in the open ocean. In the Irminger Basin, North Atlantic, the abundance of M. rubra was 0,5 cells/ml, which is low compared with that found in coastal areas. Distinct patchiness (100 km) was revealed by geostatistical analysis. Multiple regression indicated there was little relationship between M. rubra abundance and a number of environmental factors, with the exception of temperature and phytoplankton biomass, which influenced abundance in the spring. We also improve on studies that indicate distinct size classes of M. rubra; we statistically recognise four significantly distinct width classes (5,16, 12,23, 18,27, 21,33 ,m), which decrease in abundance with increasing size. A multinomial logistic regression revealed the main variable correlated with this size distribution was ambient nitrate concentration. Finally, we propose a hypothesis for the distribution of sizes, involving nutrients, feeding, and dividing of the endosymbiont. [source] Nutrient Content and Substrate Effect on Fine Root Density and Size Distribution in a Nicaraguan Rain Forest,BIOTROPICA, Issue 4 2001Brent C. Blair First page of article [source] Firm Size Distribution in Small SamplesBULLETIN OF ECONOMIC RESEARCH, Issue 4 2004Luigi Buzzacchi D40; L11; G22 Abstract Sutton (1998) has recently proposed a theoretical lower bound to firm size inequality when a market is made of several independent submarkets. His results are valid asymptotically, as the number of submarkets becomes arbitrarily large. We show that, in small samples, his results can be interpreted as a positive relationship between an index of firm size inequality and the number of submarkets. We also test this relationship in the Italian motor insurance market. [source] Drop Size Distribution in a Standard Twin-Impeller Batch Mixer at High Dispersed-Phase Volume FractionCHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 8 2009A. EL-Hamouz Abstract The preparation of concentrated aqueous silicone oil emulsions has been investigated with particular attention to the effect of the dispersed-phase volume fraction , from 0.01 to 0.5 for a wide range of oil viscosities (50 to 1000 cSt). Oil was added on the top surface of a 6-L vessel. Drop size distribution and Sauter mean diameter, d32, measurements were carried out over 24 h mixing time. Emulsification was found to be relatively sensitive to the oil phase viscosity, ,d, for the same , yielding a narrower drop size distribution for low oil viscosity (50 cSt) and a wider drop size distribution for the highly viscous oil (1000 cSt). For the same ,, increasing ,d resulted in increasing d32. The equilibrium d32 was found to be well correlated to the viscosity number by for , = 0.5. For the same oil viscosity, d32 was found to increase with increasing ,. A multiregression of d32 with both , and Vi for various silicone oil viscosity grades was successfully correlated by with a regression coefficient (R2) of 0.975. This shows a very weak dependence of the equilibrium d32 on ,. [source] Bubble Size Distribution in Oil-Based Bubble ColumnsCHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 11 2008S.-S. Homayouni Abstract A practical population balance model was used to evaluate the bubble size distribution in a bubble column. In addition, the bubble size distribution in the bubble column was measured at different gas velocities by photography and analysis of the pictures. Four types of liquid, i.e., water and three petroleum-based liquids, were used in the experiments. The gas phase was air. It was found that the existing models in the literature are not able to satisfactorily predict the experimentally measured bubble size distribution. The model can be corrected by applying a correction factor to the energy dissipation rate. The corrected model fits the experimental bubble size distribution considerably better than the existing models. The variation of this correction factor is reported for different systems at different gas velocities. [source] Utilization of Focused Beam Reflectance Measurement in the Control of Crystal Size Distribution in a Batch Cooled CrystallizerCHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 2 2006S. Barthe Abstract Controlling crystal size distribution (CSD) is important to downstream processing and to product quality. The distribution can be characterized by a mean or dominant size and the spread about the mean or dominant size. The development of tools leading to the control of the distribution in a batch crystallizer is the main topic of the present study. An experimentally based control scheme was implemented for batch cooling crystallization of paracetamol from ethanol solutions. Estimates of the CSD in the batch crystallizer were obtained by applying a model of the octahedral paracetamol crystals to a chord length distribution (CLD) obtained from focused beam reflectance measurement (FBRM) and Lasentec software. The model estimates showed reasonably good agreement with results obtained from sieve analyses performed at the end of the runs. [source] Microwave-Assisted Synthesis of Water-Dispersed CdTe Nanocrystals with High Luminescent Efficiency and Narrow Size Distribution.CHEMINFORM, Issue 18 2007Yao He Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] Crystallization of Silicate Magmas Deciphered Using Crystal Size DistributionsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 3 2007Bruce D. Marsh The remoteness and inhospitable nature of natural silicate magma make it exceedingly difficult to study in its natural setting deep beneath volcanoes. Although laboratory experiments involving molten rock are routinely performed, it is the style and nature of crystallization under natural conditions that is important to understand. This is where the crystal size distributions (CSD) method becomes fundamentally valuable. Just as chemical thermodynamics offers a quantitative macroscopic means of investigating chemical processes that occur at the atomic level, crystal size distribution theory quantitatively relates the overall observed spectrum of crystal sizes to both the kinetics of crystallization and the physical processes affecting the population of crystals themselves. Petrography, which is the qualitative study of rock textures, is the oldest, most comprehensively developed, and perhaps most beautiful aspect of studying magmatic rocks. It is the ultimate link to the kinetics of crystallization and the integrated space,time history of evolution of every magma. CSD analysis offers a quantitative inroad to unlocking and quantifying the observed textures of magmatic rocks. Perhaps the most stunning feature of crystal-rich magmatic rocks is that the constituent crystal populations show smooth and often quasi-linear log-normal distributions of negative slope when plotted as population density against crystal size. These patterns are decipherable using CSD theory, and this method has proven uniquely valuable in deciphering the kinetics of crystallization of magma. The CSD method has been largely developed in chemical engineering by Randolph and Larson,1,2 among many others, for use in understanding industrial crystallization processes, and its introduction to natural magmatic systems began in 1988. The CSD approach is particularly valuable in its ease of application to complex systems. It is an aid to classical kinetic theory by being, in its purest form, free of any atomistic assumptions regarding crystal nucleation and growth. Yet the CSD method provides kinetic information valuable to understanding the connection between crystal nucleation and growth and the overall cooling and dynamics of magma. It offers a means of investigating crystallization in dynamic systems, involving both physical and chemical processes, independent of an exact kinetic theory. The CSD method applied to rocks shows a systematic and detailed history of crystal nucleation and growth that forms the foundation of a comprehensive and general model of magma solidification. [source] Growth, Survival, Yield, and Size Distributions of Freshwater Prawn Macrobrachium rosenbergii and Tilapia Oreochromis niloticus in Polyculture and Monoculture Systems in Puerto RicoJOURNAL OF THE WORLD AQUACULTURE SOCIETY, Issue 3 2000Alfredo Garcia-Pérez The experiment consisted of three treatments with three replicates each. The stocking rates for the prawn monoculture, fish monoculture and polyculture treatments were respectively: 7 prawns/m2, 1 tilapia/M2, and 7 prawns with 1 tilapia/ m2. The mean stocking size for tilapia and prawn were respectively, 7,8 g and 1,1.3 g. After 145 d of culture, yields and mean weight of tilapia in monoculture and polyculture system were not significantly different. Total yields were 2,942 and 2,769 kg/ha, respectively. Mean weights were 348 g in monoculture and 331 g in polyculture. Yields and mean weight of prawns in monoculture and polyculture were significantly different. Total yields were 1,367 and 951 kg/ha, respectively. Mean weights were 55 g in monoculture and 31 g in polyculture. Total yield in polyculture was 3,720 kg/ha showing an increase over the production separately obtained in prawn and fish monoculture. [source] Matrix Representation of Polymer Chain Size Distributions, 3 , Case Studies for Linear Polymerization Mechanisms at Transient ConditionsMACROMOLECULAR THEORY AND SIMULATIONS, Issue 4-5 2008Heloísa L. Sanches Abstract The mass balance equations used to describe different polymerization systems are represented and analyzed with the help of a general matrix framework previously developed. Some of its properties were presented in previous works and are illustrated here in three examples. The first example regards the dynamics of a copolymerization reactor. It is shown that terminal and penultimate models may predict qualitatively different responses in batch reactions. The second example also regards the dynamics of copolymerization reactions. It is shown how manipulation of initial conditions and monomer feed rates can be used to keep copolymer composition constant throughout the batch. The third example concerns the existence of oscillating chain size distributions when there are multiple monomer insertion steps. [source] Matrix Representation of Polymer Chain Size Distributions, 2,MACROMOLECULAR THEORY AND SIMULATIONS, Issue 2 2007Fundamental Analysis of Linear Polymerization Mechanisms at Transient Conditions Abstract Analysis of the mass balance equations that describe a reaction system may be useful to provide information about its dynamics, such as the restricted set of compositions that can be achieved from a given set of initial compositions and the effect of feeding reactants to the reaction environment along the reaction course. Since these results may be important for the formulation of reaction policies, this work presents the properties of a matrix polymerization model previously developed and extended to describe transient conditions. This model is based on the definitions of two matrices: the consumption matrix (A,,,Kt), which contains information about chemical transformations among the many active polymer species in the system, and the propagation matrix Kp, which contains information about chain growth. It is shown that the set of mass balance equations that describes the dynamics of active chemical species in polymerization reactions has a stable and unique solution, which is bounded if feed rates are also bounded. It is also shown that the set of compositions that may be reached through manipulation of the feed rates is restricted and may not include all possible chemical compositions. Finally, it is shown that the obtained molecular weight distributions are special multiple time convolutions of the initiation rates. [source] Determination of Size Distributions of Concentrated Polymer Particles Embedded in a Solid Polymer MatrixPARTICLE & PARTICLE SYSTEMS CHARACTERIZATION, Issue 1 2008Ezequiel R. Soulé Abstract In this work we present the results obtained from the size characterization of polymer particles embedded in a solid polymer matrix using Static Light Scattering (SLS) and Scanning Electron Microscopy (SEM). The analyzed samples are the result of the solution polymerization of isobornyl methacrylate (IBoMA) in polyisobutylene (PIB) at complete conversion. Induced by polymerization, the system undergoes phase separation. As a result, spherical micron sized particles rich in PIB are formed. At the end of the polymerization, the particles become trapped in a solid polymer matrix rich in Poly-IBoMA. Size, concentration, and refractive index, make the resulting particle system scatter light under the Rayleigh-Debye-Gans (RDG) regime with interparticle interference. For Light Scattering (LS) characterization the samples are measured with a Flat Cell Static Light Scattering (FCSLS) apparatus, in which the reaction takes place. The resulting SLS spectra are analyzed using the Percus-Yevick approximation to model the interference effects. The local monodisperse approximation is used to consider polydispersity in the particle sizes. The estimated particle size distributions agree well with the measurements from SEM. In this work a concentrated particle system that naturally scatters light according to the RDG regime has been fully characterized in terms of its particle size distribution. This work, against the opinion of other authors, shows the feasibility of measuring still particles using a one dimensional array of light detectors. [source] Particle Size Distributions from Static Light Scattering with Regularized Non-Negative Least Squares ConstraintsPARTICLE & PARTICLE SYSTEMS CHARACTERIZATION, Issue 6 2006Alejandro R. Roig Abstract Simulated data from static light scattering produced by several particle size distributions (PSD) of spherical particles in dilute solution is analyzed with a regularized non-negative least squares method (r-NNLS). Strong fluctuations in broad PSD's obtained from direct application of NNLS are supressed through an averaging procedure, as introduced long ago in the inversion problem in dynamic light scattering. A positive correlation between the best PSD obtained from several averaging schemes and the condition number of the respective data transfer matrices was obtained. The performance of the method is found to be similar to that of constrained regularization (CONTIN), which uses also NNLS as a starting solution, but incorporates another regularizing strategy. [source] Shape and Size Determination by Laser Diffraction: Average Aspect Ratio and Size Distributions by Volume; Feasibility of Data Analysis by Neural NetworksPARTICLE & PARTICLE SYSTEMS CHARACTERIZATION, Issue 1 2005Luc Deriemaeker Abstract A new strategy for the recovery of the average shape factor and the volume weighted size distribution from laser diffraction data using neural networks is presented. The method yields reliable estimates for both the shape factor and the volume weighted size distribution. [source] Inference for Constrained Estimation of Tumor Size DistributionsBIOMETRICS, Issue 4 2008Debashis Ghosh Summary In order to develop better treatment and screening programs for cancer prevention programs, it is important to be able to understand the natural history of the disease and what factors affect its progression. We focus on a particular framework first outlined by Kimmel and Flehinger (1991, Biometrics, 47, 987,1004) and in particular one of their limiting scenarios for analysis. Using an equivalence with a binary regression model, we characterize the nonparametric maximum likelihood estimation procedure for estimation of the tumor size distribution function and give associated asymptotic results. Extensions to semiparametric models and missing data are also described. Application to data from two cancer studies is used to illustrate the finite-sample behavior of the procedure. [source] Experiments, Modeling and Simulation of Drop Size Distributions in Stirred Liquid/ Liquid SystemsCHEMIE-INGENIEUR-TECHNIK (CIT), Issue 8 2005A. Gäbler No abstract is available for this article. [source] Size distribution and genetic structure in relation to clonal growth within a population of Magnolia tomentosa Thunb. (Magnoliaceae)MOLECULAR ECOLOGY, Issue 9 2004S. SETSUKO Abstract To establish a baseline for conservation of a threatened clonal tree, Magnolia tomentosa, we investigated size distribution and genetic structure within a population, using six microsatellite markers. Within the study site, 1044 living ramets (stems) were distinguished into 175 genets (individuals). The mean number of ramets per genet was 5.97, and 76% of all genets had multiple ramets. Genets, which apparently produced new ramets through sprouting and layering, were generally composed of several large ramets and many small ramets. Spatial autocorrelation analysis of microsatellite alleles revealed positive autocorrelation over short distances for both ramets and genets. The Moran's I -value of ramets in the shortest distance class was 3.8 times larger than that of genets, reflecting the effect of clonal growth. To analyse the size-class differences in genetic structure, the 175 genets were separated into two size classes, small and large. The correlogram for the small genets exhibited positive spatial autocorrelation in the shortest distance class, but this was not the case for the correlogram for the large genets, indicating that genetic structure is weakened or lost through self-thinning as the genets grow. The FIS value over all loci for the small genets was positive and deviated significantly from zero, while the corresponding value for the large genets was close to zero. The excess homozygotes in the small genets may be the result of genetic substructuring and/or inbreeding, and the reduction in homozygote frequency from the small to large genets may be because of loss of genetic structure and/or inbreeding depression. [source] Size distributions of suspended particles in open channel flow over bed materialsENVIRONMETRICS, Issue 2 2005B. S. Mazumder Controlled experiments have shown that the grain-size distribution of suspended sediments is related to bed material, flow velocity and height of suspension above the sand bed in an open channel flow. A theoretical model has been developed for computation of suspended grain-size distribution on the basis of continuity equations of sediment and water, using the computed bed-layer concentration as a reference. The proposed model includes the effect of suspension concentration into the mean velocity, turbulent and viscous shear stresses owing to the dynamic coupling between the flow and sediments in suspension. The effect of hindered settling due to the increased concentration in suspension is also taken into account. The model is considered to be a more general one than the existing models, and the results of the present model compare well with the experimental data. Copyright © 2004 John Wiley & Sons, Ltd. [source] Effects of sand and process water pH on toluene diluted heavy oil in water emulsions in turbulent flowAICHE JOURNAL, Issue 1 2009Chandra W. Angle Abstract The presence of sand in heavy oil production is known to enhance oil recovery. Sand can also be detrimental depending on the properties of the sand,water interface. In this process, the water soluble material interacts with both sand and oil droplets and affects emulsion stability. The formation and stability of heavy oil-in-water emulsions during turbulent flow using batch process stirred-tank mixing of oil, sand, and water were investigated at three pH. Size distributions were measured by laser diffraction. High-speed video photomicrography was used to observe the process during mixing. Results showed that the presence of sand enhanced formation of stable, fine emulsion at basic pH 8.5. When the pH of the water was reduced below 6.5 both sand and droplets surface properties changed, the emulsions became less stable and coalescence was apparent. The sand grains acted as coalescers at low pH and enhanced breakage at high pH. © Her Majesty the Queen in Right of Canada, as represented by the Minister of Natural Resources, 2008 AIChE J, 2009 [source] Size distributions and stability of toluene diluted heavy oil emulsionsAICHE JOURNAL, Issue 3 2006Chandra W. Angle Abstract The sizes and stability of oil droplets created from various concentrations of heavy oil-in-toluene at a fixed oil:water ratio were investigated during turbulent flow in model process water. The Reynolds number (Re) ranged from 17,000 to 34,500 and was obtained by stirred tank mixing with a Rushton turbine. The droplet sizes were monitored using laser light scattering. Results showed that at high Re and low oil concentrations (that is, low drop-surface coverage), breakage of the droplets was the dominant process, but as Re was reduced, coalescence was dominant. Droplets were less prone to breakage as the oil concentrations in toluene increased, and droplet sizes approached a steady state quickly during mixing. Their size distributions broadened and stability increased as heavy oil in toluene increased. Stability was attributed to a surface coverage by asphaltenes and the consequent interfacial elasticity that provided resilience to breakage. Equilibrium interfacial tension ,E was determined by fitting a diffusion-limited kinetic mathematical model to the data. The Gibbs adsorption model gave a monolayer surface coverage of 3 nm2/mol asphaltenes, consistent with other published results. High zeta potential of the droplets also hindered coalescence. © 2005 American Institute of Chemical Engineers AIChE J, 2006 [source] | |||||||||||||||||||||||||||||||||||||||||||||||||