Home About us Contact
|
Home About us Contact | ||
|
|
||
Large Particles (large + particle)
Selected AbstractsEvaluation of double-crystal SANS data influenced by multiple scatteringJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 3-1 2000aroun Evaluation of small-angle neutron scattering (SANS) data is often complicated by multiple scattering effects if large particles of relatively high volume fraction have to be studied and dilution or contrast reduction is impossible. The use of pin-hole SANS instruments is often limited due to the contradictory requirements of high resolution and short wavelength needed to keep scattering contrast as low as possible. Double crystal (DC) SANS diffractometers of Bonse-Hart and bent-crystal type are useful alternatives in such cases, as they permit reaching very high resolution with thermal neutrons. A method for SANS data evaluation suited to DC instruments is presented. It includes the common scheme of the indirect Fourier transformation method, but takes multiple scattering into account. The scattering medium is described by the frequency function g(x) defined as the cosine Fourier transform of slit-smeared data. Although a simplistic model of polydisperse spheres is used to represent g(x), resulting g(x) function and some integral parameters are independent of this model. Tests on simulated data show, that the method reproduce well true values of microstructural parameters, though systematic errors are observed in the cases when the unscattered part of incident beam completely disappears. If the scattering power 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] Chemical Characteristics of Low-Fat Soymilk Prepared by Low-Speed Centrifugal Fractionation of the Raw SoymilkJOURNAL OF FOOD SCIENCE, Issue 5 2010Zhi-Sheng Liu Abstract:, Large oil,protein particles (2 to 60 ,m) were found in raw soymilk (or water extract of soybean), which was prepared in specific conditions. The large particles could be separated by sedimentation by centrifuging raw soymilk for 5 to 30 min at a low gravitational force ranging from 96 to 2410 ×,g. Chemical analysis showed that 80% to 90% of the total lipids and 30% to 40% of the total proteins were located in the precipitated fraction. The supernatant fraction had a dramatically higher protein-to-lipid ratio than the whole soymilk. The ratio of 11S/7S proteins and the ratio of 11S acidic/basic subunits were significantly (P,< 0.05) higher in the precipitate than that either in the whole soymilk or in the supernatant. Besides centrifuging conditions, other factors, including soymilk concentration, grinding method, soybean variety, and soybean storage, also significantly (P,< 0.05) affected the centrifugal fractionation. This study showed that low-speed centrifugation facilitated the separation of oil-protein particles from raw soymilk, and can be used as an innovative method for preparing low-fat soymilk and 11S protein-enriched ingredients. The findings also increased our understanding of the association or aggregation between proteins and lipids in raw soymilk after grinding. Practical Application:, Soymilk has become a popular beverage in the Western world due to its health benefits. Consumer demands for low-fat and organic foods have been increasing in the recent years. Currently, there are no alternative methods for manufacturing low-fat soymilk from whole soybeans. We found that most, if not all, of lipids in the raw soymilk were located in large particles, which could be separated by low-speed centrifugation. This centrifugal fractionation was investigated by varying processing parameters, soybean varieties, and soybean storage conditions. The approach has potential to be used for manufacturing low-fat soymilk. This study also has increased our understanding of the interactions between lipid and protein in raw soymilk. [source] Mechanisms of particle dispersion in a turbulent, square duct flowAICHE JOURNAL, Issue 7 2009Michael Fairweather Abstract Particle dispersion in a square duct flow is studied using large eddy simulation combined with Lagrangian particle tracking under conditions of one-way coupling. The flow has a bulk Re = 250 k, with six particle sizes ranging from 5 to 1000 ,m. Results obtained for the fluid phase show good agreement with experimental data. For particles, predictions demonstrate that secondary flows within the duct dominate small particle dispersion and result in a uniform distribution, whereas gravity promotes the deposition of large particles on the duct floor. For the largest particles, the secondary flows contribute to particle concentration in corners on the duct floor, with these particles also clustering in low-velocity regions close to the floor. A detailed analysis of the influence of the flow on particle distribution is provided through consideration of the particle dispersion function, with the mechanisms of particle dispersion elucidated using a dynamical analysis. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] Agglomeration modeling of small and large particles by a diffusion theory approachAICHE JOURNAL, Issue 5 2009Alvaro Realpe Abstract The interaction particle-binder during the wet granulation process plays a major role in the agglomeration of particles. This interaction has been modeled by a force balance acting on the particle where the binder's viscous force increases the strength of liquid bridge and facilitates the particle agglomeration. In this work, agglomeration kernels based on Brownian movement approach of small particles in the binder layer, the size ratio between particles (monodispersed and polydispersed), and binder's viscous forces were considered to model the wet granulation process of pharmaceutical powders in a laboratory-scale high shear mixer. The assumptions of no-stationary and pseudostationary behavior were suitable to describe the growth kinetics of the two stages (fast and slow) observed. A volume ratio of 150 between large and small particles produces the most effective granulation growth. The developed kernels were tested simulating experimental data obtained from a high shear mixer. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] Factors affecting the deposition of inhaled porous drug particlesJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 7 2002Cynthia J. Musante Abstract Recent findings indicate that the inhalation of large manufactured porous particles may be particularly effective for drug delivery. In this study, a mathematical model was employed to systematically investigate the effects of particle size, particle density, aerosol polydispersity, and patient ventilatory parameters on deposition patterns of inhaled drugs in healthy human lungs. Aerodynamically similar particles with densities of 0.1, 1.0, and 2.0 g/cm3 were considered. Particle size distributions were defined with mass median aerodynamic diameters (MMADs) ranging from 1 to 3 ,m and geometric standard deviations ranging from 1.5 to 2.5, representing particles in the respirable size range. Breathing rates of 30 and 60 L/min with tidal volumes of 500 to 3000 mL were assumed, simulating shallow to deep breaths from a dry powder inhaler. Particles with a high density and a small geometric diameter had slightly greater deposition fractions than particles that were aerodynamically similar, but had lower density and larger geometric size (typical of manufactured porous particles). This can be explained by the fact that particles with a small geometric diameter deposit primarily by diffusion, which is a function of geometric size but is independent of density. As MMAD increased, the effect of density on deposition was less pronounced because of the decreased efficiency of diffusion for large particles. These data suggest that polydisperse aerosols containing a significant proportion of submicron particles will deposit in the pulmonary airways with greater efficiency than aerodynamically similar aerosols comprised of geometrically larger porous particles. © 2002 Wiley-Liss Inc. and the American Pharmaceutical Association J Pharm Sci 91:1590,1600, 2002 [source] Dispersion Behavior of ZrB2 Powder in Aqueous SolutionJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 11 2007Sea-Hoon Lee Dispersion conditions of ZrB2 powder in water were investigated using poly(ethyleneimine) (PEI) as a dispersant. Pulverization of ZrB2 powder to submicrometer size was difficult and a substantial amount of large particles remained after an intensive planatery milling for 72 h. The isoelectric point (IEP) of ZrB2 powder was measured to be pH 5.8 by electrophoresis, which shifted to pH 6.2 after milling. The application of PEI changed the IEP of the boride slurry to ,pH 11. Well-dispersed aqueous ZrB2 slurries with a high solid loading (up to 45 vol%) were fabricated at pH 6.5,7.5 by the application of 1.5 wt% PEI. [source] Starch and fibre distribution in maize silages in relation to particle sizeJOURNAL OF THE SCIENCE OF FOOD AND AGRICULTURE, Issue 3 2003I Fernandez Abstract In a first trial the particle size distribution of four maize silages was measured by two different sieving methods, dry and wet sieving. Particle size distribution was quantified by three values, mean particle size, extent of dispersion, and proportion of large particles. Wet sieving separated particles better than dry sieving and was more suitable for measuring maize silage particle size. In a second trial the particle size distribution of 10 maize hybrids grown in the same conditions was measured by wet sieving. Starch proportion in large particles varied widely between maize hybrids, from 39.7 to 82.4%, against a variation from 75.4 to 100% for cell wall proportion in the same class of particles, and these variations might be predicted by dry matter distribution. © 2003 Society of Chemical Industry [source] Convergence in the macroscopic anatomy of the reticulum in wild ruminant species of different feeding types and a new resulting hypothesis on reticular functionJOURNAL OF ZOOLOGY, Issue 1 2010M. Clauss Abstract The reticulum is the second part of the ruminant forestomach, located between the rumen and the omasum and characterized by honeycomb-like internal mucosa. With its fluid contents, it plays a decisive role in particle separation. Differences among species have been linked to their feeding style. We investigated whether reticulum size (absolute and in relation to rumen size) and size of the crests that form the mucosal honeycomb pattern differ among over 60 ruminant species of various body sizes and feeding type, controlling for phylogeny. Linear dimensions generally scaled allometrically, that is to body mass0.33. With or without controlling for phylogeny, species that ingest a higher proportion of grass in their natural diet had both significantly larger (higher) rumens and higher reticular mucosa crests, but neither reticulum height nor reticulum width varied with feeding type. The height of the reticular mucosa crests represents a dietary adaptation in ruminants. We suggest that the reticular honeycomb structures do not separate particles by acting as traps (neither for small nor for large particles), but that the structures reduce the lumen of the reticulum during contractions , at varying degrees of completeness in the different feeding types. In browsing species with rumen contents that may be less fluid and more viscous than those of the reticulum, incomplete closure of the lumen may allow the reticulum to retain the fluid necessary for particle separation. In grazing species, whose rumen contents are more stratified with a larger distinct fluid pool, a more complete closure of the reticular lumen due to higher crests may be beneficial as the reticulum can quickly re-fill with fluid rumen contents that contain pre-sorted particles. [source] Stable Free Radical Polymerization in Emulsion: Modeling the Thermodynamics of Monomer Transfer between Droplets and ParticlesMACROMOLECULAR THEORY AND SIMULATIONS, Issue 2-3 2008Jordan Pohn Abstract A mathematical model is developed from polymer solution thermodynamics and stable free radical polymerization kinetics to predict the monomer swelling behavior of large droplets and small particles that coexist during the seeded polymerization of styrene in emulsion. This model is used to predict the sensitivity of polymerized latex stability (based on the persistence of large particles) to changes in seed particle size and final latex target molecular weight. Simulation results show that the use of small seed particles (diameter,,,50 nm) in recipe formulation will lead to polymerization occurring preferentially in the large droplets, and offers theoretical evidence that TEMPO-mediated ab initio emulsion polymerizations will not be feasible. Our predictions are consistent with experimental evidence suggesting that the presence of large particles leads to the formation of undesirable coagulum in the final product. [source] Gas Classification of Particles Using a Packed BedPARTICLE & PARTICLE SYSTEMS CHARACTERIZATION, Issue 4 2008Wei Yang Abstract Gas classification of particles using a packed bed is, for the first time, proposed and tested for two materials, i.e., glass ballotini and microcrystalline cellulose (MCC). A 2,m long column with 9.5,mm diameter is packed with 2,mm spherical particles. The particles to be classified are injected into the inlet of the packed bed by a carrier gas. Measurements of the breakthrough curves of the particles are carried out at the outlet of the packed bed. The results show that the particle elution order is particle size dependent with large particles elutriated faster than small ones. Taking the particle size into account, the retention time of irregular MCC particles is much longer than that of spherical glass beads and the difference is attributed to the particle shape and cohesiveness. Based on the findings, binary mixtures of both, glass and MCC beads are injected into the packed bed for the classification experiments. The results show different dependence on the superficial gas velocity of the particle classification efficiency. The particle classification efficiency of glass particles increases with decreasing superficial gas velocity, whereas that of MCC particles increases with increasing superficial gas velocity. [source] Morphology development of PC/PE blends during compounding in a twin-screw extruderPOLYMER ENGINEERING & SCIENCE, Issue 1 2007Bo Yin The morphological development of a polycarbonate/polyethylene (PC/PE) blend in a twin-screw extruder was studied using a scanning electron microscope (SEM). The effects of extrusion temperature, viscosity ratio (the ratio of the viscosity of the dispersed phase to that of the matrix), and the screw configuration on the morphology of the PC/PE blend during the extrusion were discussed in detail. It was found that the morphology of the dispersed particles and the interfacial adhesion between the dispersed phase and matrix were both influenced by the extrusion temperature. The dispersed phase had a spheroidal shape and a small size during the high temperature processing, and an irregular shape and a large size when it was processed at low temperature. The PC phase with a lower viscosity was easier to disperse and also to coalesce. Therefore, the deformation of the low-viscosity dispersed phase during the processing was more intense than that of the high-viscosity dispersed phase. By comparing the effects of the different screw configurations on the morphology development of the PC/PE blend, it was found that the melting and breaking up of the dispersed phase were mainly affected in the initial blending stages by the number of the kneading blocks. While a kneading block with a 90 degree staggering angle was used, the size of the dispersed particles decreased and the long fibers were shortened, the large particles were drawn by the additional kneading zone. Finally, all of these structures were completely changed to the short fibers. POLYM. ENG. SCI., 47:14,25, 2007. © 2006 Society of Plastics Engineers [source] Digestion in the common marmoset (Callithrix jacchus), a gummivore,frugivoreAMERICAN JOURNAL OF PRIMATOLOGY, Issue 12 2009Michael L. Power Abstract Wild common marmosets (Callithrix jacchus) feed on fruits, insects, and gums, all of which provide different digestive challenges. Much of the ingested mass of fruits consists of seeds. In general, seeds represent indigestible bulk to marmosets and could inhibit feeding if they are not eliminated rapidly. In contrast, gums are ,-linked polysaccharides that require microbial fermentation. Their digestion would benefit from an extended residence time within the gut. Earlier research found that mean retention time (MRT) for a liquid digestive marker (cobalt EDTA) was significantly longer than MRT for a particulate marker (chromium-mordanted fiber), suggesting that common marmosets preferentially retain liquid digesta. We conducted two four-day-long digestion trials on 13 individually housed adult common marmosets fed a single-item, purified diet in order to examine the relations among MRT of cobalt EDTA and chromium-mordanted fiber, food dry matter intake (DMI), and apparent digestibility of dry matter (ADDM). We compared the MRT values with the data from the previous study mentioned above and a study using polystyrene beads. There were no significant correlations among MRT, ADDM, or DMI, although increases in DMI between trials were associated with decreases in MRT. ADDM was consistent within individuals between trials; but the mean values ranged from 75.0 to 83.4% among individuals. We found no difference in MRT between the liquid (17.5±1.6,hr) and particulate (17.9±1.4 hr) markers. Although these values were not significantly different than found previously, the MRT for chromium-mordanted fiber tended to be longer. This probably reflects the relatively small size of the chromium-mordanted fiber particles used in this study. An inverse relationship between particle size and MRT was evident; the mean MRT of polysterene beads, the largest marker, was only 8.3±1.5,hr. Marmosets appear to retain liquids and small particles within the gut longer than large particles. Am. J. Primatol. 71:957,963, 2009. © 2009 Wiley-Liss, Inc. [source] Superparamagnetic iron oxide particles: contrast media for magnetic resonance imaging,APPLIED ORGANOMETALLIC CHEMISTRY, Issue 10 2004Rüdiger Lawaczeck Abstract The mainstream magnetic iron oxide particles used as contrast media for magnetic resonance (MR) imaging are composed of a magnetic iron oxide core surrounded by a dextran or carboxydextran coat. The core size ranges from 2 nm to less than 10 nm, and the hydrodynamic diameter ranges from 20 nm to about 120 nm. The coat prevents aggregation and sedimentation of the particles in aqueous solutions, achieves high biological tolerance, and prevents toxic side effects. Two kinds of particles are considered: (i) large particles (>30 nm), called superparamagnetic iron oxide particles (SPIOs) for liver imaging; (ii) smaller particles (<30 nm hydrodynamic diameter), called ultrasmall SPIOs (USPIOs), e.g. for MR angiography. To characterize the particles, Mössbauer spectra are presented for the two particle ensembles. These spectra allow insight into the magnetic coupling, the valency of the iron ions and a rough estimate of the core size to be deduced. On the basis of the concentration dependence of the MR signal intensities, two applications are discussed together with two representative clinical examples. Future indications for MR diagnostics, e.g. the labeling and tracking of stem cells during stem-cell therapy control, are outlined. Copyright © 2004 John Wiley & Sons, Ltd. [source] Macromolecular crystal data phased by negative-stained electron-microscopy reconstructionsACTA CRYSTALLOGRAPHICA SECTION D, Issue 5 2010Stefano Trapani The combination of transmission electron microscopy with X-ray diffraction data is usually limited to relatively large particles. Here, the approach is continued one step further by utilizing negative staining, a technique that is of wider applicability than cryo-electron microscopy, to produce models of medium-size proteins suitable for molecular replacement. The technique was used to solve the crystal structure of the dodecameric type II dehydroquinase enzyme from Candida albicans (,190,kDa) and that of the orthologous Streptomyces coelicolor protein. [source] Analysis of the effect of particle size distributions on the fluid dynamic behavior and segregation patterns of fluidized, vibrated and vibrofluidized bedsASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 1 2007Roger Valeri Daleffe Abstract In this work, the effects of particle size distribution on the dynamics and segregation patterns in fluidized, vibrated and vibrofluidized beds were investigated. Four particle size distributions composed of glass spheres were tested: binary, flat, Gaussian and a reference one, all of them with a mean Sauter diameter equal to 2.18 × 10,3 m. The experimental setup consisted basically of a circular glass chamber with a height of 0.50 m and diameter of 0.114 m and was operated in different modes: as a fluidized bed (, = 0), or either as vibrated or vibrofluidized beds (, = 2). The pressure drops in the fluidized and vibrofluidized beds were not significantly affected by the particle size distributions. Well-defined segregation patterns were observed in fluidized and vibrated beds, with the small particles concentrated at the top and the large particles at the bottom in the fluidized bed, and with a reversed pattern in the vibrated bed. Segregation patterns in the vibrofluidized bed depended on the values of the vibration parameters. Segregation in vibrofluidized and vibrated beds was minimized by operating at high amplitudes of vibration. Copyright © 2007 Curtin University of Technology and John Wiley & Sons, Ltd. [source] Clathrin-mediated endocytosis: What works for small, also works for bigBIOESSAYS, Issue 6 2010Javier Pizarro-Cerdį Abstract Clathrin and the endocytosis machinery has recently been described as being required in mammalian cells for the internalization of large particles including pathogenic bacteria, fungi, and large viruses. These apparently unexpected observations, within the framework of the classical mechanisms for the formation of clathrin-coated vesicles, are now considered as examples of a new non-classical function of clathrin, which can promote the internalization of membrane domains associated to planar clathrin lattices. The role of actin downstream of clathrin seems to be critical for this still poorly characterized process. The historical frontier between endocytosis and phagocytosis is vanishing in the light of this new role for clathrin. [source] 3422: Sources of straylight in the human eyeACTA OPHTHALMOLOGICA, Issue 2010D DE BROUWERE Purpose Besides refractive aberrations, ocular light scattering is a major parameter affecting image quality on the retina in healthy eyes. Several pathologies in the anterior segment such as corneal scarring and cataract cause significant increase of straylight in the eye. In this study, we link morphologic changes addressed to corneal scarring to a scattering function. Methods Excised rabbit corneas with different grades of scarring following photorefractive keratectomy were optically evaluated for their forward light scattering distribution and consecutively prepared for histology. An absolute parameter for forward scattering was calculated based on the readings in the optical device. We compared this parameter to the relative thickness of the scar tissue observed in the histological data. Results The histological data showed a wide variation of thickness a scar tissue layer in the anterior stroma. The scattering ratio measured using the optical device measuring forward light scattering correlated strongly with the relative thickness of the scar tissue layer with (0.63, Pearson's coefficient), as well as a standard haze exam (measuring backscattered light) (0.51, Pearson's coefficient). The light scattering distribution is narrowly forward peaked (FWHM 30 arcmin), suggesting this light scattering is caused by large particles such as myofibroblasts, oedema or irregular scar tissue in the ablated zone. Conclusion Corneal light scattering associated with the increased amount of haze after excimer laser ablation has a narrowly forward distribution that can be attributed to the subepithelial structures observed in treated corneas. This is in contrast to the origin of scatterers linked to cataract, as small protein aggregates and multilamellar bodies that are scattering over wider angles. [source] Study of the Electroless Silver Seed Formation on Silicon SurfaceCHINESE JOURNAL OF CHEMISTRY, Issue 2 2007Hao Tong Abstract The silver seed on silicon was prepared through aqueous HF and AgNO3 solution at room temperature. In order to explore the formation process of silver seed on silicon, the methods of open circuit potential with time (OCP- t), anodic stripping sweep voltammetry (ASV) and scanning tunneling microscope (STM) were used in this work. The procedure of silver nucleus growing into large particles was explained by electro-negativity. The growth mechanism of silver seed on silicon has been presented: at first, the silver monolayer and multilayer firstly grows onto silicon without fully covering the surface at the expense of silicon etching due to the silver seed attracting the electron from silicon, after that, the monolayer coalesces together, forming continuous grain film with some silver atoms diffusing into the silicon and the multilayer still grows thick simultaneously. [source]
| | |||||||||||||||||||||||||||