Showing papers on "Particle published in 1969"

The limitation of electron mean free path in small silver particles

Abstract: By evaluating, with help of Mie's theory, absorption measurements of spherical silver particles — (between 24 and 210 A in diameter) — suspended as colloid in photosensitive glasses we found that the absorption coefficient at the wavelength of absorption peak (λ=0.405 μ) remains constant, whereas the refractive index increases by about a factor of 5 when the particle size decreases. Within accuracy of measurements and the differences of bulk optical constants of various authors this deviation from the bulk values can be described by the “free path effect”, the influence of conduction electron collisions with particle surfaces. The results are compared with the quantum mechanical theory ofKawabata andKubo.

The scaled particle theory for particles of arbitrary shape

Abstract: The scaled particle theory of Reiss et al. has been extended to hard non-spherical particles and equations analogous to the Percus-Yevick equation have been obtained for mixtures of particles of the same shape but different sizes. The resulting equation of state produces exact second and third virial coefficients which are functions of the average radius, the surface area and the volume of the particle. The equations of state for several systems of hard non-spherical particles are compared with that for a system of hard spheres.

Cell Sizing: A Light Scattering Photometer for Rapid Volume Determination

Abstract: Theory predicts that small angle light scattering by spherical particles of 5 to 20 μ diam is nearly proportional to volume and insensitive to particle refractive index. A flow system photometer with helium‐neon laser light source measures the scattering between 0.5 and 2.0° from individual particles at 104 to 105/min. Volume distributions of mammalian cells and plastic microspheres agree with other independent determinations.

Active Sites and Ice Crystal Nucleation.

Abstract: The concept of active nucleation sites is examined in the light of standard nucleation theory and it is suggested that these sites are probably small re-entrant corners or jogs in growth steps on the surface of the nucleating particle. The nucleation behavior of a spherical particle with a conical pit on its surface is examined in detail and the activity of a population of particles having a log-normal distribution of such pits is worked out. The parameters involved in the theory can be evaluated within acceptable limits and the resulting curves exhibit the phenomena observed experimentally. Generalized activity curves are given in parametric form for more detailed comparison with experiment.

Alternative‐Current Field‐Induced Forces and Their Biological Implications

Abstract: Steady‐state, field‐induced forces on particles of microscopic size become significant at field strength values of the order of 100 v/cm. They include "pearl‐chain formation," i.e. the alignment of particles in the direction of the imposed field, and the orientation of nonspherical particles. The time constant, which describes the speed of these phenomena, depends on field strength, and particle and other parameters. For pulsed fields, a lower level of applied average power can suffice to evoke the phenomena mentioned. Biological implications include the possibility of nonthermal effects of biological significance.

Optical efficiencies of large particles of arbitrary shape and orientation

Abstract: The “anomalous diffraction” approximation of van de Hulst is extended to new particles and orientations thereof. It predicts the extinction and absorption efficiencies, Kext and Kabs, of particles larger than the wavelength and of refractive index not too different from that of the medium. Existing expressions for the normally oriented thin disc and long thin cylinder are found to be equally applicable to the same particles when arbitrarily oriented if the particle parameters are redefined. Geometrical relations are used to prove that van de Hulst's expressions for the homogeneous sphere also describe the ellipsoid of revolution of arbitrary axial ratio and orientation if the particle size parameter is suitably redefined. Numerical solutions of the basic relations for Kext are outlined and illustrated. They are applicable to particles of almost any shape, gross internal structure, and orientation. To support the extension of this “large particle” approximation, its domain is re-examined in terms of the conditions needed for ray propagation within the particle. These conditions can define how sophisticated an optical model of the particle should be. If the particle used is not too large, they can also justify the representation of a nonspherical particle by a spherical model. New expressions and methods are used to determine the effects of random particle orientation on effective K values of various particles. Random orientation is found to cause many nonspherical particles to behave optically almost like spherical particles of equal volumes.

Process for the preparation of pigmented polymer powders of controlled particle shape and size and size distribution and product

Abstract: Pigmented polymer powders of average particle size less than 30 microns, which can be of uniform shape and in a narrow size distribution, are prepared by controlled heating, melting and agitation of a liquid dispersion of pigmented polymer in bulk or particle form in the presence of a surfactant or by controlled heating and agitating a liquid containing surfactant to which molten polymer is added. Pigmented powders can thus be obtained having spherical particles of very narrow size distribution approaching uniformity.

The frequency dependence of the Kerr effect for suspensions of rigid particles

Abstract: Measurements have been carried out in the frequency range from 1 Hz to 10 6 Hz of the Kerr effect for suspension of rigid particles in moderately conducting media. The measurements are for tobacco mosaic virus, bentonite, Baymal, and Avicel and are of the steady component and the magnitude and phase of the alternating component of the optical birefringence. By comparison of measurements with the theory for the Kerr effect for a suspension of rigid ellipsoidal particles it is possible to determine the rotary diffusion coefficient and the relative significance of permanent and induced electric dipole moment and to obtain information on the direction of the permanent moment with respect to the particle axis. Tobacco mosaic virus is found to possess a permanent moment which is not aligned with the particle axis. In the high-frequency region processes become evident which are not associated with permanent moment or rotary diffusion effects but are probably related to the frequency dependence of the induced moment.

Process for the preparation of polymer powders of controlled particle shape,size and size distribution and product

Abstract: POLYMER POWDERS ARE PREPARED BY CONTROLLED MELTING, HEATING AND AGITATION OF A LIQUID DISPERSION OF POLYMER PARTICLES IN THE PRESENCE OF A SURFACTANT. POWDERS CAN THUS BE OBTAINED COMPOSED OF SPERICAL PARTICLES OF CONTROLLED AVERAGE SIZE AND SIZE DISTRIBUTION, THE SAME, LARGER OR SMALLER THAN THE STARTING PARTICLES. PARTICLES CAN ALSO BE PRODUCED FROM MOLTEN POLYMER MASSES, IN A LIQUID WITH ADDED SURFACTANT AND THEN MODIFIED IN SHAPE, SIZE AND SIZE DISTRIBUTION BY ADDITIONAL CONTROLLED HEATING AND AGITATION OF THE LIQUID DISPERSION.

Particles and Sources

Abstract: It is proposed that the phenomenological theory of particles be based on the source concept, which is abstracted from the physical possibility of creating or annihilating any particle in a suitable collision. The source representation displays both the momentum and the space-time characteristics of particle behavior. Topics discussed include: spin and statistics, charge and the Euclidean postulate, massless particles, and $S{U}_{3}$ and spin. It is emphasized that the source description is logically independent of hypotheses concerning the fundamental nature of particles.

Flow properties of suspensions with high solids concentration

Abstract: Equations were developed for evaluating the laminar flow behavior of high-solids suspensions from the physical properties of the liquid and solid components. A technique was developed for calculating suspension flow rates as a function of pressure drop. The technique is applicable to the design of pipe lines. Flow measurements were made in pipe-line viscometers of a unique design that minimized entrance and exit effects. Experimental flow data were obtained for suspensions consisting of nickel, alumina, copper, or glass solids in sodium, xylene, or glycerine vehicles with solids concentrations of 28 to 55 vol. %. The basis for the correlation of the data was an analytical investigation of the flow behavior that considered the particle-particle interaction that takes place in a settled suspension. The correlation equations fit all systems investigated. They take into account the effects of liquid viscosity, liquid and solid densities, particle size, size distribution, particle surface area, volume fraction of solids in the suspension, and volume fraction of solids at maximum settled conditions.

Apparatus and method of measurement of particulate mass

Abstract: A PARTICLE MEASUREMENT APPARATUS HAVING AN OSCILLATOR CIRCUIT WITH A QUARTZ CRYSTAL CARRYING ELECTRODE FILMS TO DETECT PARTICLE MASS FORCE COLLECTED ON A SURFACE OF A FILM BY READING THE CHANGE IN THE RESONANT FREQUENCY OF THE QUARTZ CRYSTAL. THE OSCILLATOR CIRCUIT IS COMBINED WITH A DEVICE FOR FORCE-COLLECTING PARTICKLES ON THE ELECTRICALLY- DRIVEN FILM. THE ELECTRICAL SIGNAL OF THE OSCILLATOR CIRCUIT IS MONITORED BY A FREQUENCY-COUNTING DEVICE.

Observations of magnetization reversal in cobalt-rare-earth particles

Abstract: A new technique for the separation of strongly magnetic powders by particle size has led to observations of discontinuous magnetization changes in samples of cobalt-rare-earth particles. These magnetization jumps were investigated in a single particle, and it was found that they occurred at various reproducible and strongly quantized fields, whose value depended on the value of the field previously applied to saturate the sample. This suggested that the coercive force of these materials might be very sensitive to the nature of the surface, which was verified experimentally. These results add support to the interpretation of the magnetic properties of high-crystal-anisotropy permanent magnet materials in terms of domain boundary nucleation and motion.

Device which separates minute particles according to electronically sensed volume.

Abstract: A device has been developed that is able to fractionate a mixture of microscopic particles according to small differences in their volume. A dilute suspension of the particles passes through a sensor within which the volume of each particle is electronically measured. Subsequently the suspension emerges into the air as a liquid jet. This jet is caused to break into a large number of individual droplets, thereby isolating the suspended particles. Droplets containing particles of the desired volume ranges are electronically charged and electrostatically deflected into suitable receptacles. The apparatus is described in considerable detail with illustrative application to polystyrene spheres and to human white blood cells.

Particle size and molecular weight effects on the melt flow of emulsion PVC

Abstract: The melt flow behavior of straight emulsion-polymerized PVC in a capillary extrusion rheometer has been found to depend upon both the molecular weight and the particle size of the sample. Observations of flow-rate, post-extrusion swell, and extrudate appearance, as functions of extrusion temperature and pressure, suggest that both molecular deformation and particle slippage are involved in the flow mechanism. The relative importance of these two modes of flow varies with extrusion conditions and with the PVC molecular weight and particle size. Particle slippage is favored by large particle size, high molecular weight, and low temperature and by a shear stress above a critical yield value. Apparent melt viscosity, swelling, and roughness are minimized under conditions corresponding to the maximum contribution of particle slippage. In the proper range of temperature and shear rate, straight emulsion PVC yields smooth, low-swell extrudates of excellent physical properties.

Electric field phenomena in fluidized and fixed beds

Abstract: Stabilization of a bed of dielectric particles against fluidization by an electric field (≥ 103 volts/cm) is described. Glass bead and silica gel particle beds have been observed to behave as packed beds with flow rates (and pressure drops) of the fluidizing gas up to 15 times the normal incipient fluidization rate. The pressure drop at the breakup of this fixed bed was dependent on the second power of voltage, the particular bed material, and geometry of the system. Under suitable conditions 100% bed expansion without diffusive particle motion or bubble formation was obtained using silica gel particles. Comparison with iron particle bed-magnetic field effects are presented. Surface polarization charge effects are the simplest explanation of the phenomena. Several of the possible applications are suggested, such as precipitation enhancement in an aerosol filter or as a new tool for investigating aggregative fluidization.

Carbon Black Morphology: I. Particle Microstructure. II. Automated EM Analysis of Aggregate Size and Shape

Abstract: Carbon black particle and aggregate microstructure were studied in detail by means of high resolution electron microscopy. Improved instrumental and environmental conditions have enabled more detailed studies on the size, orientation, and spacing of graphite layers in carbon black particles than heretofore possible. The layers form continuous networks about particle growth centers and between adjoining particles and show a paracrystalline orientation rather than individual crystallites. Based on this type of orientation carbon black primary aggregates are now defined as single graphite paracrystals exhibiting either a fibrous (furnace and channel blacks) or spheroidal (thermal blacks) shape.

A comparison of two methods of measuring particle size of Al2O3 produced by a small rocket motor

Abstract: The size of aluminum oxide particles produced by small rocket motors is determined by tank collection and spectrophotometry. The size of the particulate determines loss in thrust due to particle lag, particulate radiant heat transfer, acoustic attenuation and impingement and rocket plume structure and properties.

Electroexcitation of Particle-Hole States in O 16

Abstract: : The paper presents experimental data and theoretical results for electroexcitation of T=1 particle-hole states in 016.

The production of low scattering dielectric mirrors using rotating vane particle filtration

Abstract: Some of the problems involving the production of high efficiency laser mirror coatings are discussed. Gross scattering losses caused by dielectric particles becoming embedded in the multilayers present a major problem. An apparatus is described which was successfully used to reduce this effect to a very low level on one inch diameter, 23-layer mirrors.