Showing papers on "Particle published in 1979"

Drag coefficient and relative velocity in bubbly, droplet or particulate flows

Abstract: Drag coefficient and relative motion correlations for dispersed two-phase flows of bubbles, drops, and particles were developed from simple similarity criteria and a mixture viscosity model. The results are compared with a number of experimental data, and satisfactory agreements are obtained at wide ranges of the particle concentration and Reynolds number. Characteristics differences between fluid particle systems and solid particle systems at higher Reynolds numbers or at higher concentration regimes were successfully predicted by the model. Results showed that the drag law in various dispersed two-phase flows could be put on a general and unified base by the present method.

Long-range correlations in smoke-particle aggregates

Abstract: Ultrafine smoke particles stick together to form chain-like aggregates. We find that the particle density has long-range correlations of the same form in iron, zinc or silicon dioxide aggregates. The correlation data suggest a power-law spatial dependence giving a Hausdorff dimension between 1.7 and 1.9. We discuss the consistency of these results with a model based on percolation. We also compare our results with a random-walk model, which has a nominal Hausdorff dimension of 2.

Plasma etching—A discussion of mechanisms

Abstract: The purpose of the present paper is to review the salient features of our understanding of phenomena which occur in plasma etching situations. The etching process is discussed in terms of three basic steps: adsorption, product formation, and product desorption. Experiments performed in well‐defined (nonplasma) environments are discussed with the goal of clarifying the relative importance of these three steps in the etching process. An attempt is made to relate the resulting concepts to several phenomena generally observed in plasma situations (e.g. etching anisotropy, selective etching, the loading effect, and the role of additive gases). Moreover, the glow discharge, in addition to generating active species which initiate the chemical reactions, also causes the etched surface to be subjected to energetic particle (ions, electrons) bombardment. The role of this radiation in the etching process is emphasized. Speculative comments relating to plasma etching parameters and apparatus are also given.

The interpretation of real-space information from small-angle scattering experiments

Abstract: The distance distribution function contains all the accessible information about the scattering medium. It is possible to determine the following particle parameters from this function: maximum dimension of the particle, radius of gyration, and zero-angle intensity (molecular weight). The shape of the distance distribution function enables one to distinguish and to recognize directly and rationally the following types of particles: compact globular particles; particles elongated in one dimension, with constant and with variable cross-section; spherical vesicles. The thickness of flat particles as well as the inner and outer diameter of spherical vesicles can be determined from the distance distribution function. Inhomogeneous particles with at least two regions of electron densities differing in their signs show typical features in the distance distribution. These characteristics can be found without further assumptions, independently of the shape of the particle. For concentric shells with different electron densities it is possible to obtain some general information about their structure. Residual concentration effects cannot be overlooked in real space. The formation of dimers can be analyzed with the aid of the distance distribution function.

Size Distributions of Precipitation Particles in Frontal Clouds.

Abstract: Measurements of the size spectra of precipitation particles have been made with Particle Measuring Systems probes aboard an aircraft flying through frontal clouds as part of the CYCLES (Cyclonic Extra-tropical Storms) PROJECT These measurements were obtained while the aircraft flew through the clouds associated with mesoscale rainbands at temperatures ranging from −42 to +6°C Particles ≳15 mm in diameter closely follow an exponential size distribution Above the melting level precipitation occurs mainly in the form of ice particles In this region the mean particle size of the exponential distribution increases with increasing temperature, indicating that the ice particles grow as they drift downward The variance of the exponential distribution also increases with increasing temperature above the melting level, indicating that the particles grow particularly well by collection as they fall at various speeds Passage of the failing particles through the melting level is accompanied by a sudden

In Situ Electron Microscopy Studies of Catalyst Particle Behavior

Abstract: Although transmission electron microscopy (TEM) has been in routine operation for over 25 years, it is somewhat surprising to find that there has only been limited use of the technique by workers in the field of catalysis. Turkevich and his co-workers [1] were among the first investigators to use the electron microscope to study catalytic substances. In general, most applications have centered around the determination of particle size distributions in supported metal catalyst systems [2]. More recently, however, it has been recognized that the technique can yield much more fundamental information on such aspects as the morphology of small particles and the nature of their interaction with a support medium. This advance is the result of the achievement of high resolution TEM (0.25 nm resolution).

Calculated deposition of inhaled particles in the airway generations of normal subjects.

Abstract: Detailed regional deposition of inhaled particles in the human lung is calculated for individual airway generations. The calculations are based on Landahl's deposition model as applied to the morphometric lung model of Weibel. We consider primarily deposition patterns of iron oxide particles with diameters ranging between 1 and 10 micrometers, but we also calculate patterns of deposition for bis(2-ethylhexyl) sebacate particles with diameters as small as 0.2 micrometers. We obtain good agreement between predicted values and observed values for alveolar retention of inhaled iron oxide particles with 64 and 20% of total deposition predicted to occur in nonciliated airways for 2- and 5-micrometer particles, respectively. This is compared with 48 +/- 9 and 27 +/- 10% for the measured values. Calculated values for total lung deposition of small bis(2-ethylhexyl) sebacate particles agree well with experimental data. The calculations show a minimum in deposition occurring for particle diameters of 0.5 micrometers, which is in agreement with observations. A calculation of surface concentration of deposited 7.9-micrometer aerodynamic particles reveals a very large concentration occurring at airway generation four. This observation is considered in light of observations that bronchial carcinomas occur in this vicinity of the lung.

Biological particles of given size, shape, and density for use in biological reactors

Abstract: Novel biomass support particles containing growing cells have been developed for use in large-scale fermentation processes. The characteristic size of the entrapped biomass is identical to that of the physical structure of the support particle, and particles can be produced of any size, shape, and density with a wide variety of microorganisms. Use of the particles in fermentors leads to high biomass concentration independent of throughput, predetermined biomass concentrations, the use of novel types of fermentor with advantageous performance characteristics, possibilities for the optimization of advantageous diffusion effects, and new procedures for biomass recovery.

Extinction by a spherical particle in an absorbing medium

Abstract: The extinction cross section for an arbitrary spherical particle that is embedded in an absorbing medium is derived by considering that which is measured in an actual extinction experiment. The resultant “optical theorem” is similar in form to the optical theorem for particles in a nonabsorbing medium. Calculations of extinction by germanium particles that are embedded in a polyethylene medium at room temperature have been performed for far-infrared frequencies (50–200 cm−1). If the imaginary part of the medium refractive index is ignored, then particulate extinction is underestimated by factors of between 2 and 4 over the frequency range of interest for 0.02-μm-radius spheres. In addition, there is a significant shift of a bulk germanium absorption maximum, which is not predicted when the medium is assumed to be nonabsorbing. For larger particles, the relative error decreases but still may be significant.

Efficiency of Particle Retention and Filtration Rate in Four Species of Ascidians

Abstract: Particle retention in Ascidiella aspersa, Molgula manhattensis, Clavelina lepadiformis and Ciona intestinalis was determined from comparisons of particle-size distributions in the inhaled and exhaled water. Particles down to 2-3 jun were completely retained and the retention efficiency of smaller particles decreased to about 70 \"/o for 1 ~ u n particles. There was no indication that the ascidians were able to adjust their retention efficiency. Filtration rates (F, m1 min-l) as a function of total dry weight (W,,,,,, g) could be expressed as F = 54.4 W,0,,,'-05 in A. aspersa and F = 46.4 Wr0r,P-84 in C. intestinalis. It is concluded that undisturbed ascidians filter the water continuously at constant rates.

An electrophoretic display, its properties, model, and addressing

Abstract: A model to describe the optical behavior of an electrophoretic display (EPD) device is developed. The model involves the particle size and mobility as well as the time of removal of particles from an electrode. The most important aspect of this model is the treatment of the dynamics of removing particle layers from an electrode. This process plays a significant role in controlling the optical off-response rate. The optical on-response is governed by the particle mobility or the spatial distribution of the particles through the cell. Various schemes for addressing the electrophoretic device are discussed. Only a display employing assisted array addressing appears capable of giving a large-area graphics quality display with short response time. Fringing field particle migration was found to seriously degrade image quality. A cell subdivision structure is used to overcome fringing field migration, particle settling, and electrohydrodynamic effects.

The effect of polytetrafluoroethylene particles on the foamability of aqueous surfactant solutions

Abstract: It has been shown that the presence of PTFE particles may reduce the amount of foam which can be generated by vigorous shaking of surfactant solutions. PTFE is an inert and hydrophobic material. The experiments have therefore demonstrated that the formation of destabilizing surface tension gradients is not a necessary condition for antifoam behavior. Simple calculations have demonstrated that particles of hydrophobic material present in thin films may in principle spontaneously dewet to form a hole which would necessarily lead to film rupture. The critical condition for hole formation is shown to be dependent upon contact angle and particle shape. Particle size is an implicit consideration in that the smallest dimension of the particle must be approximately equal to the film thickness before hole formation can occur. This antifoam mechanism is shown to be consistent with all the experimental observations concerning the effect of PTFE particles on the foamability of surfactant solutions.

Coal-water slurry and method for its preparation

Abstract: A pipeline pumpable coal-water slurry having a novel combination of coal particles and carrier water is prepared by a method wherein the particle sizes and their distribution are controlled in accordance with a particle size distribution formula which is especially beneficial for providing a novel coal compact with a minimum amount of void space between particles and a maximum amount of particle surface area with an advantageous amount of colloidal sized particles present. These features combine to enhance the dispersing effects generated by electrolytes and/or dispersing agents selected and added to the coal compact and/or slurry to provide a near maximum zeta potential to the particles in the slurry and to provide low viscosity to the resulting yield pseudoplastic coal-water slurry. Brookfield viscosities obtained, e.g. 1000 cps, or less, at 60 rpm with 75 wt. % coal, dry basis, make the coal-water slurry especially advantageous for transport by pipeline over long distances. The coal-water slurry can be provided at a high coal content so that the slurry can be burned directly without need for dewatering at its destination.

Stability and immunogenicity of empty particles of foot-and-mouth disease virus

Abstract: Three strains of foot-and-mouth disease virus were shown to contain significant amounts of naturally occurring 75 S, empty particles as well as the infectious, 140 S full particles. One of these strains — A Pando (1970) — was studied in detail. The empty particles from this virus strain were shown to have an observed sedimentation coefficient of 67S in 0.04m phosphate buffer; they were labile in SDS, non-infectious and probably RNA-free and, on heating, they broke down to 12 S subunits as did the 140 S particles. The empty particles differed from the full particles in their polypeptide composition since they contained VP0, but there was no evidence for a diminished content of VP4. The 75 S particles were shown to be present in significant amounts and to be stable to AEI inactivation. At 4° C they were stable for at least two years. In guinea pigs they were as immunogenic as the 140 S particles. The antisera raised against the 75 S particles had the same serological specificity in neutralization tests as sera prepared against the 140 S particle. It was concluded that the 75 S particles from the A Pando (1970) strain of FMD virus may provide as important a contribution as 140 S particles to the immunogenicity of inactivated vaccines prepared from this virus strain.

The mechanism of whisker growth in the reduction of wüstite

Abstract: The growth of iron whiskers on wustite is explained on the basis of C. Wagner’s mechanism for the reduction of nonstoichiometric oxides. The first metal nucleus develops into a whisker if the iron accumulation in the supersaturated wustite particle is nearly uniform, a condition which is favored by chemical control. A mathematical model is proposed in which the “filling ratio” of wustite by iron prior to nucleation is expressed in terms of the reaction constant, the chemical diffusion coefficient of iron, the particle radius, the Fe/o ratio at equilibrium with the gas, and the critical Fe/o ratio for nucleation at the most favorable site. The morphology of iron in the early stages of reduction, which goes from a single cylindrical whisker, through sponge iron to a smooth layer, can be predicted by comparing at all times the map of the actual Fe/o ratio at the surface with the map of the local Fe/O ratio for nucleation. A satisfactory test of the theory is obtained through a survey of the experimental evidence available about the effect of several physico-chemical factors of reduction on the iron morphology,e.g. surface characteristics, particle size, composition of the reducing gas, solute cations in wustite, temperature, and gas transport.

Light scattering and fluorescence by small particles having internal structure.

Abstract: Two related, yet distinct queries are considered: 1. How does the internal morphology of a small particle affect the elastic light scattering signals. An algorithm was devised, accurate for particles comparable only to small biological spheres (diameter less than 1 ..mu..m), which suggests that light scattering is sensitive to internal morphology only in the backward directions. Accordingly, observations should be obtained in these directions when probing for internal morphology. 2. How are fluorescent signals affected when the active molecules are variously distributed within small particles. One cannot assume that the fluorescent signals are simply proportional to the number of active molecules contained in the particle because there may also be a dependence upon the geometrical and optical properties of the particle and upon the particular spatial distribution of these molecules within the particle. Indeed, even the measured emission spectrum may be affected by such morphological features. Here, too, these calculations are mainly restricted to small particles (diameter less than 1 ..mu..m) in which the fluorescent molecules are isotropic and immobile. Under these conditions the effects are quite dramatic. These effects should be considered in quantitative procedures which utilize fluorescence for determining the concentration of specific molecules in small particles suchmore » as biological cells. They may provide a clue for discriminating among cells which differ morphologically or in which the spatial distribution of the fluorescent moiety differs. These effects may be minimized by utilizing a light source which is polarized perpendicularly to the scattering plane.« less