Showing papers on "Particle published in 1972"

An investigation of particle trajectories in two-phase flow systems

Abstract: This paper describes a theoretical investigation into (i) the response of a spherical particle to a one-dimensional fluid flow, (ii) the motion of a spherical particle in a uniform two-dimensional fluid flow about a circular cylinder and (iii) the motion of a particle about a lifting aerofoil section. In all three cases the drag of the particle is allowed to vary with (instantaneous) Reynolds number by using an analytical approximation to the standard experimental drag-Reynolds-number relationship for spherical particles.

Light Scattering by a Spheroidal Particle

Abstract: The solution of electromagnetic scattering by a homogeneous prolate (or oblate) spheroidal particle with an arbitrary size and refractive index is obtained for any angle of incidence by solving Maxwell's equations under given boundary conditions. The method used is that of separating the vector wave equations in the spheroidal coordinates and expanding them in terms of the spheroidal wavefunctions. The unknown coefficients for the expansion are determined by a system of equations derived from the boundary conditions regarding the continuity of tangential components of the electric and magnetic vectors across the surface of the spheroid. The solutions both in the prolate and oblate spheroidal coordinate systems result in a same form, and the equations for the oblate spheroidal system can be obtained from those for the prolate one by replacing the prolate spheroidal wavefunctions with the oblate ones and vice versa. For an oblique incidence, the polarized incident wave is resolved into two components, the TM mode for which the magnetic vector vibrates perpendicularly to the incident plane and the TE mode for which the electric vector vibrates perpendicularly to this plane. For the incidence along the rotation axis the resultant equations are given in the form similar to the one for a sphere given by the Mie theory. The physical parameters involved are the following five quantities: the size parameter defined by the product of the semifocal distance of the spheroid and the propagation constant of the incident wave, the eccentricity, the refractive index of the spheroid relative to the surrounding medium, the incident angle between the direction of the incident wave and the rotation axis, and the angles that specify the direction of the scattered wave.

Thermal fluctuation aftereffect model for some systems with ferromagnetic‐antiferromagnetic coupling

Abstract: A theoretical model is developed for, and applied to, some coupled‐film systems consisting of an underlying ferromagnetic thin film and a surface layer of antiferromagnetic material viewed as an assembly of uniaxial small particles. The magnetization of the film biases, and is in turn biased by, the particles through an interfacial exchange coupling. Above a blocking temperature, dependent on size, particles are able to reverse rapidly due to thermal fluctuation, thus exhibiting superparamagnetic response. By assuming a physically reasonable distribution of particle sizes, good agreement is obtained between computed curves for temperature and frequency dependence of hysteresis loop displacement and coercivity based on this model and corresponding experimental results for oxidized Permalloy films, reported in a companion paper. This thermal fluctuation model is also applied successfully to the case of oxidized cobalt films as studied by Schlenker. In this case it is necessary to include in the analysis the...

Interaction of solar and galactic cosmic-ray particles with the Moon

Abstract: Calculation of the rates of formation of radionuclides as a function of depth in the moon for bombardments by galactic-cosmic-ray particles and by solar protons. The fluxes and spectra of galactic-cosmic-ray particles and of solar protons as a function of depth in the moon are first determined semiempirically. For galactic cosmic rays, the model emphasizes the production of secondary particles and the attenuation of particles by nuclear interactions. Solar proton calculations cover a range of observed spectral parameters, and only ionization energy losses need be considered. The excitation functions for the nuclear reactions used in these calculations are presented. The calculated production rates are given for a range of depths in the moon and are compared with experimental results and with earlier calculations. The model can also be applied to other effects of particle bombardment.

Size separation of marine seston by membrane and glass‐fiber filters1

Abstract: The average minimum sizes of particles retained by metal membranes (Selas Flotronics) and perforated polycarbonate membranes (General Electric Nuclepore) were similar to the stated pore sizes when relatively small seawater samples with moderate concentrations of particles were filtered. When large samples or high concentrations were filtered, the average retention size was less than the stated pore size. All cellulose ester membranes (Millipore) retained particles much smaller than the stated pore size, even from small samples with low particle concentrations. Glass-fiber filters had retention characteristics similar to membrane filters.

Electrical resistivity of conducting particles in an insulating matrix

Abstract: When conducting particles are added to a nonconducting matrix, conductivity increases abruptly at a critical concentration. The theory of infinite chains is used to predict the variation of conductivity with particle concentration. Factors which determine the critical concentration are discussed.

Apparatuses for trapping and accelerating neutral particles

Abstract: There is disclosed a variety of apparatuses for controlling by radiation pressure the motion of a particle free to move with respect to its environment, based on the discovery that one or more beams of coherent optical radiation can overpower gravity and thermally induced reaction (photophoresis) forces on a small particle. The disclosed results of the effect of the radiation pressure on the motion of the particle include controllably heating the particle to provide a black-body point light source, bombardment of a sample target with small particles, very high-energy particle acceleration, strong-focusing acceleration of a neutral particle, vacuum deposition of thin films from ultrapure particles controllably vaporized while held by radiation pressure, tensile-strength testing of materials based on the radiation-pressure effect of circularly polarized light, and acceleration measurement for inertial guidance and measurement of very low gas pressures.

Turbulent fluid and particle interaction

Abstract: Main attention will be paid to the more basic aspects following from the interaction between fluid and discrete particles. First we will consider a single particle in a turbulent-flow field. The basic equation describing the motion of a particle has a number of terms which can either be given in a formal way only, or which contain parameters that depend strongly on the nature of both the particle and the fluid, and on the turbulent fluid motion. A description of the behaviour of the particle depending on the magnitude of those parameters and in the light of the ratio between response time and the many characteristic times of the turbulence will be given. The study of the long-time behaviour of the particle following the Lagrangian description leads to considering the turbulent diffusion of the particle relative to that of the fluid. Some attention will be paid to the effect of spatial inhomogeneity of the mean flow field. In the case of many discrete particles in a turbulent-flow field, an additional important parameter is the concentration by volume of the particles. Direct and indirect interaction of particles will be considered and their effects on the dynamic behaviour of the particulate phase and on the turbulence of the fluid. The merits and shortcomings of the continuum concept for the particulate phase, and of the concept of an eddy diffusion coefficient, will be discussed.

Efficiency of particle retention in Mytilus edulis L.

Abstract: It is shown that Mytilus edulis is capable of retaining particles at least as small as 2 µ with great efficiency. This probably means that particles smaller than 5 µ play an important role in the nutrition of the mussel, as particles of this size are an important fraction of the total organic particulate matter.

Variation of single particle mid-infrared emission spectrum with particle size.

Abstract: The emission spectra of single particles of inorganic solids as a function of particle size have been recorded from 6 μ to 11.8 μ. For small optically thin particles, an emission maximum is produced in the reststrahlen region. The emission behavior is dominated by scattering and can be adequately described in terms of Mie absorption efficiency factors. As the particle size is increased, the emission band reverses its polarity, and the spectrum approaches that of a polished plate. The data provide source functions necessary for determining the emission behavior of particulate samples in which temperature gradients exist, such as on the lunar surface. The data are of particular interest for interpreting the spectral behavior of circumstellar silicate particles.

Total Binding Energies of Nuclei, and Particle-Removal Experiments

Abstract: Under the assumptions of the impulse approximation, there is a relation between the cross section for removing a particle from a system and the total binding energy of the system, if it is bound by two-body forces. This relation is established and applied to the ($p,2p$) reaction on nuclear targets. Data from recent experiments are used to obtain values for the total binding energy of the protons in various nuclei, which are then compared with the measured values.

Behavior of dispersed particles in turbulent liquid flow

Abstract: Turbulent motion of particles suspended in water in a stirred tank and that of drops supplied to turbulent pipe flow of water are studied with emphasis on their scales. The scales considered are 1) sampling time scale : the very small time interval in which the displacement of a particle is measured, 2) measuring time scale : the time-duration during which a continuous measurement is run, and 3) sampling spatial scale : the width of a location in which the displacement of a particle is followed. The effects of these scales on the magnitude of turbulence velocity components are examined, and the magnitudes are evaluated with a set of values of scales which seem most appropriate to each particle motion. The magnitudes are correlated uniformly in both dispersions with particle diameters and energy dissipation rates of surrounding liquid.

The role of particle interactions in the rheology of dispersed systems

Abstract: Certain aspects of the rheological behaviour of dispersions cannot be understood unless attractive forces between the particles are assumed, resulting in the building-up of a network structure.

Neutral particle accelerator utilizing radiation pressure

Abstract: There are disclosed apparatuses for generating plasmas at thermonuclear temperatures by employing radiation pressure to accelerate suitable reactant particles to a relative velocity at which their mutual collision can generate the required temperature of the nuclei within the time that one particle passes through the other. The orbital electrons and the nuclei will be heated essentially equally rapidly, so that, even with a relatively simple magnetic confinement field, electronic instabilities prior to thermonuclear fusion may be avoided.

The Size of Suspended Particulate Matter in Air Size distributions of ambient aerosols must be studied in order to determine their effects on the environment

Abstract: By means of the NASN cascade impactor the particle sizes of ambient aerosols can be measured by fractionating the particles according to their aerodynamic dimensions, and the fractions can be quantified gravimetrically. Data obtained with this instrument show that particulate matter suspended in urban air in the United States and Great Britain is remarkably uniform in distribution and that the particles are predominantly less than 1 µm in diameter. In Ankara, Turkey, the high proportion of particles larger than 1 µm in diameter are associated with the incomplete combustion of lignite; particulate concentrations in Ankara, however, are considerably higher than those measured elsewhere. The growth of particles in air during temperature inversions occurs in Cincinnati; the greater proportion of large particles found there during inversion periods can account for the reduction in visibility. Aerosols in the vicinity of highways are composed of particles larger than those found some distance away because of the reentrainment of debris by the traffic-induced turbulence. On the other hand, highway configuration and traffic volume have little effect on the size distribution of aerosols in samples collected away from the turbulence area of the roadway. Aerosols measured inside buildings are predominantly smaller in size and exhibit a narrower range of sizes than aerosols outside buildings.

Molecular and ultrastructural studies of non-crystalline calcium phosphates.

Abstract: Five non-crystalline calcium phosphate precipitates prepared from solutions varying in pH, degree of supersaturation and carbonate content were examined by physicochemical and morphological methods. X-ray diffraction, infrared spectrophotometry and electron diffraction measurements confirmed the amorphous nature of each precipitate. Both transmission and scanning electron microscopy demonstrated that the native elemental particles of all 5 synthetic products were spherical in shape and independent of the preparative procedures employed. Four of the precipitates contained spherules of similar sizes (200–1200 A in diameter) while the one relatively rich in carbonate exhibited much larger particles (700–2000 A in diameter). The spherules were uniformly dense to the electron beam when viewed with the current density at its lowest useful level. Exposure to higher electron currents immediately resulted in the development of numerous electron-lucent centers in each particle. Heating in vacuum to temperatures up to 600° did not change the amorphous nature of the precipitates or the morphology and size of their elemental particles even though almost all of the water contained in the original precipitates was removed by this process. Heat treatment did not induce formation of electron-lucent centers. On the contrary it, made the spherules increasingly resistant to beam damage. These findings suggest that the beam electrons interact with the oxygen or hydrogen atoms of the aqueous constituent of the amorphous calcium phosphate and that this initial reaction is followed by displacement and/or loss of other atoms.