Showing papers on "Particle published in 1984"

Excitation of internal kink modes by trapped energetic beam ions

Abstract: Energetic trapped particles are shown to have a destabilizing effect on the internal kink mode in tokamaks. The plasma pressure threshold for the mode is lowered by the particles. The growth rate is near the ideal magnetohydrodynamic value, but the frequency is comparable to the trapped particle precission frequency. A model for the instability cycle gives stability properties, associated particle losses, and neutron emissivity consistent with the fishbone events observed in PDX.

Formation of monodispersed spindle-type hematite particles

Abstract: Procedures have been developed which yield spindle-type colloidal hematite particles of narrow size distribution by forced hydrolysis of ferric chloride solutions at elevated temperatures. It was shown that small additions of phosphate or hypophosphite ions to such systems before aging had a significant effect on the resulting particle shape. Specifically, the axial ratio of the precipitated solids depended on the concentration of these anions in the original solutions.

Crack propagation in a glass particle-filled epoxy resin

Abstract: The investigation outlined in the preceding paper has been extended to cover the effect of particle/matrix adhesion upon crack propagation in an epoxy resin reinforced with spherical glass particles. The behaviour has again been interpreted in terms of crack pinning and blunting. It has again been shown that in the absence of blunting a critical crack opening displacement criterion can be applied. The strength of the particle/matrix interface is found to affect both the crack propagation behaviour and the appearance of the fracture surface. It is also found to have a profound effect upon the fracture strength of the composites. The best overall mechanical properties are obtained for composites containing particles treated with coupling agent.

Feeding Currents and Particle Capture Mechanisms in Suspension Feeding Animals

Abstract: The apparent diversity of suspension feeding animals is, in one sense, more apparent than real. Virtually all suspension feeders capture particles from the water at low Reynolds numbers with cylindrical filtering elements, so, at the level of the filtering elements, flow patterns are identical and viscous forces dominate the situation. Six particle capture mechanisms are likely to be operating alone or in combination: (1) scan and trap (isolation of a parcel of fluid containing the particle), (2) sieving, (3) direct interception, (4) inertial impaction, (5) gravitational deposition, and (6) diffusive deposition. To insure that all variables relevant to the suspension feeding process are recorded, future work on suspension feeding should report the diameter and spacing of the filtering elements, flow speeds, diameter of particles available and captured, particle settling velocities, particle mobility (active or passive), and particle surface properties.

Visible light induced generation of hydrogen from H2S in mixed semiconductor dispersions; improved efficiency through inter-particle electron transfer

Abstract: Electron transfer from the conduction band of CdS to that of TiO2 particles occurs in alkaline suspensions containing SH– ions and is exploited to improve the performance of a system that decomposes H2S with visible light.

Modern methods of particle size analysis

Abstract: Commercial Instrumentation for Particle Size Analysis. The Application of Particle Characterization Methods to Submicron Dispersions and Emulsions. Particle Size Using Photon Correlation Spectroscopy. Application of Photon Correlation Function Profile Analysis to Molecular Weight Distributions of Polymers in Solution. Particle and Droplet Sizing Using Fraunhofer Diffraction. Particle Size Measurements from 0.l to l,000 um Based on Light Scattering and Diffraction. Field--Flow Fractionation of Particles. Detection Systems for Particle Chromatography. Hydrodynamic Chromatography of High Molecular Weight Water--Soluble Polymers. Appendix----Manufacturers of Instruments for Particle Size Analysis. Index.

Filter mesh size and food particle uptake by Daphnia

Abstract: Food size selection of four Daphnia, species (D. magna, D. hyalina, D. galeata, D. pulicaria) was investigated using spherical plastic beads as artificial food and with small bacteria. The size of the particles ranged from 0.1 to 35 μm with special emphasis to the particle diameters between 0.1 and 1 μm. In one set of experiments a mixture of differently sized particles was offered as food suspension and the selectivity of filtering was determined by comparing the size spectrum of the particles found in the gut contents with the spectrum in the food suspension. In a second series of experiments suspensions of uniformly sized particles were offered to single animals and their feeding activity was observed directly. In both types of experiments the mesh sizes of the filtering apparatus of the respective animals studied were measured after the experiments by, scanning electron microscopy. The mean sizes of the filter meshes were about 0.4–0.7 μm. In all experiments the size of the particles found in the gut or those which caused high feeding activities were larger than the smallest mesh sizes of the filters. As a consequence simple mechanical sieving provides a sufficient explanation for the mechanism of particle retention of the filtering process in Daphnia. D. magna was found to feed with high efficiency on suspended freshwater bacteria, the residual species investigated showed low filtering efficiencies when bacteria were offered as food.

Apparatus and method for the detection and classification of articles using flow cytometry techniques

Abstract: This invention concerns a flow apparatus and method for the detection of particles in a sample. Particles are moved, substantially one at a time, in a fluid flow stream. An incident beam of illumination is provided so as to be directed at the particles in the flow stream. Data associated with each moving particle as it passes through the beam of illumination is detected. A class of particles is established, these particles having common characteristics based on the data detected from such class of particles. The data is then stored. Such stored data is compared to data detected from sample particles of an unknown class. A determination is then made that particles from the unknown class belong to the established class as a result of matching respective data.

The adhesion of particles undergoing an elastic-plastic impact with a surface

Abstract: A new model is presented which describes the adhesion of a particle to a surface following an elastic-plastic impact. The experimental testing of the model is described and it is shown that use of the model leads to values of the adhesive surface energy between the particle and the surface which are in good agreement with values obtained by other means. A method for determining the adhesive energy from the measurement of impacts involving only elastic deformations is also presented.

Photochemistry of Colloidal Metal Sulfides. 7. Absorption and Fluorescence of Extremely Small ZnS Particles (The World of the Neglected Dimensions)

Abstract: Extremely small colloidal ZnS particles (diameter ∼ 1.7 nm) were made by either photo-degradation of 3 nm particles or rapid precipitation in phosphate containing solution at pH = 7-−8. The absorption spectra of these particles are different from that of macrocrystalline ZnS, and the changes are regarded as an indication for the transition from semiconductor ZnS to polymolecular ZnS with decreasing particle size. – The dependence of the intensity of the fluorescence on particle size, temperature, photoanodic corrosion and the quenching of fluorescence were investigated for colloids on a silicon dioxide carrier, in phosphate solution, and without a stabilizer. Photo-anodic corrosion strongly improves the fluorescence properties. – One adsorbed Cd2+ ion per colloidal particle is sufficient for efficient quenching of the fluorescence. However, a new fluorescence band appears which is explained by the formation of a layer of 1:1 co-colloid at the surface of the ZnS particles. – Methylviologen was also found to be a very efficient quencher. The decay of the fluorescence is wavelength dependent, i.e. the fraction of long-lived fluorescence is greater at longer wavelengths. – A mechanism is discussed, where the fluorescence centers are anion vacancies, and fluorescence is emitted when electrons trapped in states of different energies and exhibiting different life-times tunnel to the localized positive holes.

Monte Carlo shock-like solutions to the Boltzmann equation with collective scattering

Abstract: The results of Monte Carlo simulations of steady state shocks generated by a collision operator that isotropizes the particles by means of elastic scattering in some locally defined frame of reference are presented. The simulations include both the back reaction of accelerated particles on the inflowing plasma and the free escape of high-energy particles from finite shocks. Energetic particles are found to be naturally extracted out of the background plasma by the shock process with an efficiency in good quantitative agreement with an earlier analytic approximation (Eichler, 1983 and 1984) and observations (Gosling et al., 1981) of the entire particle spectrum at a quasi-parallel interplanetary shock. The analytic approximation, which allows a self-consistent determination of the effective adiabatic index of the shocked gas, is used to calculate the overall acceleration efficiency and particle spectrum for cases where ultrarelativistic energies are obtained. It is found that shocks of the strength necessary to produce galactic cosmic rays put approximately 15 percent of the shock energy into relativistic particles.

Electrically and thermally conductive adhesive transfer tape

Abstract: The adhesive layer of the novel transfer tape contains electrically and thermally conductive particles such as silver which are preferably spherical and are larger than the thickness of the adhesive between particles. When used to bond two rigid substrates together, pressure is applied to the substrates to flatten the particles to the thickness of the adhesive between particles, thus making good electrical and thermal connection between the substrates through each particle.

Manipulation of particles

Abstract: Separation of particles types from a mixed population of particles in a liquid is obtained in an ultrasonic wave produced by interference between the outputs from spaced ultrasonic sources (115,118). One or more selected particle types may be separated by displacement axially along the standing wave or may be carried transversely through the standing wave or by combining both methods. The described separation can be achieved by control of flow of the liquid or giving the standing wave a drift, or by controlling the intensity or the frequency of the standing wave or by any combination of these factors. The preferred ultrasonic frequency range is between 100 kHz and 100 MHz. The process is particularly suitable for the separation of biological particles, from macromolecules to plant cells.

Diffusiophoresis: Migration of Colloidal Particles in Gradients of Solute Concentration

Abstract: When a rigid colloidal particle is placed in a solution which is not uniform in the concentration of some solute that interacts with the particle, the particle will be propelled in the direction of higher or lower concentration of the solute. The resulting locomotion is called diffusiophoresis. Experimental observations and theoretical predictions of the migration velocity of hydrosoIs are reviewed. Present commercial applications include the formation of rubber gloves and the deposition of paint films onto a steel surface. New applications to the analysis of colloidal mixtures and solid-liquid separation are suggested.

Method for making hollow porous microspheres

Abstract: Hollow microspheres are made by a process which comprises forming a film of a dispersed particle film-forming composition (containing dispersed particles, a binder, a film stabilizing agent and a continuous liquid phase) across a coaxial blowing nozzle, applying a blowing gas at a positive pressure on the inner surface of the dispersed particle composition film to blow the film and form, in the region of the coaxial blowing nozzle orifice, hollow dispersed particle microspheres having stable film walls, removing the hollow microspheres, treating them to bring dispersed particles into point to point contact and harden them to obtain hollow green microspheres, and subsequently subjecting them to a sufficiently high temperature for a sufficient period of time to remove the continuous liquid phase and to sinter the dispersed particles at their points of contact to form within the walls of said hollow microspheres interconnecting voids that are continuous from the outer wall surface to the inner wall surface of the hollow microspheres, and to obtain hollow porous microspheres having substantially uniform void content and substantially uniform distribution of the voids in their walls.

The Transport and Kinetics of Photogenerated Carriers in Colloidal Semiconductor Electrode Particles

Abstract: The transport and kinetics of photogenerated majority and minority carriers in a spherical semiconductor particle of colloidal size are considered. The Poisson-Boltzmann equation is solved for the sphere, and the potential distribution in the particle is obtained. The recombination of the carriers according to Hall-Shockley-Read kinetics gives rise to a number of different cases, for which equations describing the flux of photogenerated species in the external solution are obtained. Kinetic case diagrams show how the different cases are related to each other and how they depend upon such variables as the irradiance, the Fermi level in the electrolyte, the surface rate constants, and the radius of the particle. Three different strategies which could lead to devices for efficient solar energy conversion are found and discussed.

Condensational Growth of Ultrafine Aerosol Particles in a New Particle Size Magnifier

Abstract: A new particle size magnifier (PSM) has been manufactured. In order to evaluate the performance of the PSM, the condensational growth of ultrafine aerosol particles in a supersaturated dibutyl phthalate vapor-air mixture is investigated theoretically and experimentally. First, the supersaturation ratio, the condensable DBP vapor content, and the critical size of the particle that will grow in the PSM are calculated for the mixing of hot air containing the DBP vapor with normal-temperature vapor-free air. Then the time dependence of the droplet radius during condensational growth is evaluated by numerically solving the basic equation under various conditions. From the results it is found that at higher particle number concentrations, the final droplet radii can be determined by the particle number concentration and the condensable DBP vapor content, but that at lower concentrations the particle growth can be approximated by the growth of the isolated droplet. Finally, size distributions of grown DBP drople...

The role of flocculation in the filtering of particulate matter in estuaries

Abstract: The structuring of suspended particulate matter in estuaries into flocculated settling entities is described and discussed. A hierarchy of three particle distribution types is described: In situ distributions contain abundant large low density fragile aggregates(macro-flocs) with high settling rates, the formation of which is promoted by low turbulence and high particulate concentrations. During periods of high currents in nature and during shipboard and laboratory sample handling, these macro-flocs break up into more stable distributions of smaller flocs which are the basic building blocs of the larger units. Laboratory oxidation of organic matter and disaggregation of aggregates allow the size analysis of individual single mineral grain distributions for purposes of direct comparison between bottom and suspended sediment spectra. The constituent grain-size distribution of the inorganic component of a floc replicates the grain size of the suspension as a whole. The diverse grain size and chemical nature of the organic matter makes its flocculation kinetics more complicated. Past laboratory experiments have indicated the existence of organic-inorganic proportions optimum for flocculation. This is substantiated by ash-loss data from three estuaries with different relative inputs of organic and inorganic matter. The particulate matter in each was dominated by similar organic-inorganic proportions (65-75% organic matter by volume) indicating that the component in excess of this value had been preferentially exported from the estuary. Settling of suspended sediment as macro-flocs and near bottom break-up and resuspension of floc fragments control the very dynamic equilibrium between particle trapping and particle flushing in estuaries.

Small angle neutron scattering studies on non-aqueous dispersions of calcium carbonate

Abstract: Colloidal dispersions of calcium carbonate in toluene, with the particles stabilised by an alkyl aryl sulphonic acid, have been examined by small angle neutron scattering. On the basis of the assumption that the adsorbed layer of stabilising surface active agent formed a concentric shell around a spherical calcium carbonate core particle, a method was developed to determine both the radius of the core particle and the thickness of the adsorbed layer. For the two series of particles examined the calcium carbonate core particles were found to have radii of 22 and 67 a respectively and in both cases the adsorbed layer thickness was found to be 19.0±1 a. The method provides a means of obtaining adsorbed layer thicknesses under conditions where particle and layer cannot be separated.