Electromagnetic-field calculations for irregularly shaped, axisymmetric layered particles with focused illumination

Theoretical procedures are presented for the determination of the internal and the near-surface electromagnetic fields for an arbitrary monochromatic field (e.g., a focused laser beam) incident upon an irregulary shaped, axisymmetric layered particle. The layered spherical particle solution is also given as a special case of the general solution. Systematic calculations are presented that demonstrate the effects of particle shape and incident focused-beam orientation on the electromagnetic-field distributions.     

Electromagnetic field calculations for an irregularly shaped,near-spheroidal particle with arbitrary illumination

A spheroidal coordinate separation-of-variables solution has been developed for the determination of the internal, near-surface, and far-scattered electromagnetic fields for irregularly shaped elongated (prolatelike) and irregularly shaped flattened (oblatelike) particles with arbitrary monochromatic illumination. Calculated results are presented, for both plane-wave and focused-Gaussian-beam illumination, which demonstrate the effects of particle geometry on the internal, near-surface, and far-scattered-field distributions.     

Large-scale GPU based DEM modeling of mixing using irregularly shaped particles

Mixing of particulate systems is an important process to achieve uniformity, in particular pharmaceutical processes that requires the same amount of active ingredient per tablet. Several mixing processes exist, this study is concerned with mechanical mixing of crystalline particles using a four-blade mixer. Although numerical investigations of mixing using four-blades have been conducted, the simplification of particle shape to spherical or rounded superquadric particle systems is universal across these studies. Consequently, we quantify the effect of particle shape, that include round shapes and sharp edged polyhedral shapes, on the mixing kinematics (Lacey Mixing Index bounded by 0 and 1) that include radial and axial mixing as well as the inter-particle force chain network in a numerical study. We consider six 100 000 particles systems that include spheres, cubes, scaled hexagonal prism, bilunabirotunda, truncated tetrahedra, and a mixed particle system. This is in addition to two six million particle systems consisting of sphere and truncated tetrahedra particles that we can simulate within a realistic time frame due to GPU computing. We found that spherical particles mixed the fastest with Lacey mixing indices of up to 0.9, while polyhedral shaped particle systems mixing indexes varied between 0.65 and 0.87, for the same mixing times. In general, to obtain a similar mixing index (of 0.7), polyhedral shaped particle systems needed to be mixed for 50% longer than a spherical particle system which is concerning given the predominant use of spherical particles in mixing studies.     

Quantitative evaluation of the effect of irregularly shaped particles in sheared granular assemblies

Assemblies of irregularly shaped particles exhibit higher shear strengths than assemblies of circular particles. We performed a series of 2D discrete element simulations to demonstrate that this particle shape effect is related to the induced moment and the additional dilation at the contacts between particles. We proposed a mechanically based particle shape index that is closely related to such contact behavior. A simple structural model is also investigated to clarify the micromechanical role of the particle shape.     

Highly filled particulate thermoplastic composites: Part I Packing density of irregularly shaped particles

The packing density of irregular shaped particles greatly affects the properties of highly filled particulate composite materials. The effects of particle size distribution parameters on the packing density of fused silica powder and cristobalite flour powder of different size ranges is reported. Various size distributions, according to the log-normal function, were prepared by sieving and characterized by light scattering, using a Malvern 2600 light scattering instrument. The apparent and tap density of the various powders was used to characterize the packing density. The size distribution width was found to have a major effect on the packing density. In addition, the particle size was found to affect the packing density however, its significance depends on the size range and shape of the particles. Mixtures of powders, each having a different size distribution, behave differently. This revised version was published online in November 2006 with corrections to the Cover Date.     

Effective elastic properties of solids with irregularly shaped inclusions

A unit rectangular cell is usually cut out from a medium for investigating fracture mechanism and elastic properties of the medium containing an array of irregularly shaped inclusions. It is desirable to clarify the geometrical parameters controlling the elastic properties of heterogeneous materials because they are usually embedded with randomly distributed particulate. The stress and strain relationship of the rectangular cell is obtained by an ad hoc hybrid-stress finite element method. By matching the boundary condition requirements, the effective elastic properties of composite materials are then calculated, and the effect of shape and arrangement of inclusions on the effective elastic properties is subsequently considered by the application of the ad hoc hybrid-stress finite element method through examining three types of rectangular cell models assuming rectangular arrays of rectangular or diamond inclusions. It is found that the area fraction (the ratio of the inclusion area over the rectangular cell area) is one dominant parameter controlling the effective elastic properties.     

Fracture mechanics transfer function for irregularly shaped two dimensional flaws

In an elastic medium, transfer functions converting a two-dimensional nondrcular flaw to a circular flaw with equivalent fatigue properties are developed for the simple case of uniaxial stress applied normal to the flaw plane. Elliptical and rectangular flaws are specifically discussed. The method outlined may have important applications in predicting the kinetics of growth of irregularly shaped flaws in conjunction with nondestructive measurements.     

Internal, near-surface, and scattered electromagnetic fields for a layered spheroid with arbitrary illumination

A spheroidal coordinate separation-of-variables solution has been developed for the determination of internal, near-surface, and scattered electromagnetic fields of a layered spheroid (either prolate or oblate) with arbitrary monochromatic illumination (e.g., plane wave or focused Gaussian beam). Calculated results are presented for layered 2:1 axis ratio prolate and oblate spheroids with an equivalent sphere size parameter of 20.     

Subwavelength-resolvable focused non-gaussian beam shaped with a binary diffractive optical element.

The diffraction-limited spot size limits the optical disk storage capacity and microscopic resolution. We describe a technique to shape a focused Gaussian beam into a superresolving beam by using a diffractive optical element fabricated by laser-assisted chemical etching. The focused shaped beam has a smaller width and a longer depth of focus than a similarly focused Gaussian beam. Using the diffraction-limited shaped beam along with threshold writing, we achieved a written pit size of less than 0.33 mum at a 695-nm laser wavelength, compared with a 0.7-mum focused Gaussian spot size (full width at e(-2) of the peak) with the same focusing lens. The energy conversion efficiency for the beam shaping was ~81%.     

Electromagnetic-field calculations for a sphere illuminated by a higher-order Gaussian beam. I. Internal and near-field effects

A theoretical procedure has been developed for the determination of internal and external electromagnetic fields that result from the interaction of a higher-order Gaussian beam with a homogeneous sphere. Specific calculations are performed for (1, 0), (0, 1), and (1, 1) mode Hermite-Gaussian beams and for doughnut mode beams of four different polarizations (radial, angular, arced, and helix). The effects of incident beam type on resonance excitation, and on the spatial distribution of the internal and near-surface electromagnetic fields, are examined.     

Measurement of cylindrical particles with phase Doppler anemometry

Light scattering from cylindrical particles has been described with geometric optics. The feasibility of determining the particle diameter with a planar phase Doppler anemometer has been examined by simulations and experiments. In particular, the influence of particle orientation on measurability and measurement accuracy has been investigated. Some recommendations for realizing a practical-measurement instrument have been presented.     

Pulsed-high-voltage-supplied variable cross-section cylindrical electrostatic precipitators for fly-ash particles

The article evaluates the effect of pulsed-high-voltage energization upon three types of cylindrical electrostatic precipitators that might be installed on the exhaust pipe of household boilers. The three models are similar in that the corona discharge is generated between a thin copper wire (diameter 0.16?mm), coaxial with a 354?mm long aluminum cylinder (inner diameter: 40?mm) that is the collecting electrode. The first model is a “standard” constant cross-section precipitator. The other two models are characterized by the presence of a 17?mm long, reduced cross-section (diameter: 23 or 30?mm) intermediate sector, located at about 1/3 of the precipitator length, from the inlet. The reduced cross-section was achieved by a sleeve made of either aluminum or polyvinylchloride, so that to create, in the latter case, a dielectric-barrier discharge. Pulsed energization of the three models of electrostatic precipitators was provided by positive or negative DC high-voltage supplies and a mechanical rotary spark-gap. The frequency of the high-voltage pulses ranged between 120 and 280?Hz. The experimental results show that the collection efficiency was better for both negative and positive high-voltage pulses. The best collection performances were obtained with the hybrid corona and dielectric-barrier discharge precipitator.     

Bridging technique for calculating the extinction efficiency of arbitrary shaped particles

A general bridging technique is developed to calculate the extinction efficiency of particles by combining the extended Rayleigh-Debye approximation and the modified anomalous diffraction theory. Comparisons with the exact methods are performed for spheres, spheroids, infinite cylinders, and finite cylinders. The overall features of the extinction efficiencies calculated from the new, to our knowledge, bridging method are in agreement with those calculated from the exact methods. Also discussed are accuracy of the new method and its domain of applicability. The new technique can be potentially applied to particles of virtually any shapes and sizes.     

Polyarc discrete element for efficiently simulating arbitrarily shaped 2D particles

A new two‐dimensional discrete element type, termed the ‘polyarc’ element is presented in this paper. Compared to other discrete element types, the new element is capable of representing any two‐dimensional convex particle shape with arbitrary angularity and elongation using a small number of shape parameters. Contact resolution between polyarc elements, which is the most computation‐extensive task in DEM simulation only involves simple closed‐form solutions. Two undesirable contact scenarios common for polygon elements can be avoided by the polyarc element, so the contact resolution algorithm for polyarc elements is simpler than that for polygon elements. The extra flexibility in particle shape representation induces little or no additional computational cost. The key algorithmic aspects of the new element, including the particle shape representation scheme, the quick neighbor search algorithm, the contact resolution algorithm, and the contact law are presented. The recommended contact law for the polyarc model was formulated on the basis of an evaluation of various contact law schemes for polygon type discrete elements. The capability and efficiency of the new element type were demonstrated through an investigation of strength anisotropy of a virtual sand consisting of a random mix of angular and smooth elongated particles subjected to biaxial compression tests. Copyright © 2011 John Wiley & Sons, Ltd.     

Dose distribution measurements and calculations for Dounreay hot particles

Discrete fragments of irradiated nuclear fuel have been discovered on the foreshore at the Dounreay nuclear site in Scotland, offshore on the seabed and at nearby beaches which have public access. The fragments contain mainly (137)Cs and (90)Sr/(90)Y and for particles recovered to date, (137)Cs activities are within the range of 10(3) to 10(8) Bq. The most active particles found at Sandside Beach contain approximately 3 x 10(5)Bq (137)Cs. Direct measurements of the spatial dose distributions from 37 fuel fragments were measured in detail for the first time using radiochromic dye film as part of a national evaluation of the associated potential radiological hazard. Monte Carlo code calculations of the doses are in good agreement with measurements, taking into account variations to be expected due to differences in shape and the increasing importance of self-absorption for the larger, more active fragments. Dose measurements provide little evidence for wide variations in the (137)Cs:(90)Sr/(90)Y ratio between fragments. Specific attention is given to the evaluation of skin dose, averaged over an area of 1 cm(2) at a depth of 0.07 mm, since this is of major radiological concern. There is no obvious dependence of skin dose on the site of origin of the fragments (foreshore, seabed or beaches) for a given (137)Cs activity level. A dose rate survey instrument (SmartION) was shown to provide a rapid and convenient method for skin dose assessment from fuel fragments in the (137)Cs activity range measured (2 x 10(5) to 2 x 10(7) Bq). A conversion factor multiplier of 240 can be applied to the open window SmartION scale reading to estimate the skin dose rate within +/-25%.     

Contact models based on experimental characterization of irregular shaped,micrometer-sized particles

The goal of this study is to investigate experimentally the mechanical contact properties of fine particles ( \(<\) 120  \(\upmu \) m) using of a novel experimental setup. On the basis of deformation curves from compression tests, particle behaviour under mechanical stress can be approximated with theoretical contact models. Models examined in this study include Walton and Braun, Tomas and Antonyuk, Zener and Thornton. Influence of climatic conditions on particle behaviour as well as hardening effects related to cyclic loading were also considered. Maltodextrin was used as a model substance for primary particles, while irregular shaped titanium dioxide granules were used to study the behaviour of agglomerates. In both cases, results are in good agreement with the established theories.     

Discrete-dipole-approximation-based light-scattering calculations for particles with a real refractive index smaller than unity

To assess the efficiency and accuracy of light-scattering calculations based on the discrete dipole approximation (DDA) for particles with a real relative refractive index smaller than unity, differential scattering cross sections and scattering efficiency factors were calculated for spherical particles. We performed the calculations for oxide particles and voids embedded in glass and silicon, using the exact scattering theory (Mie scattering) and the DDA. A comparison of the results shows that the DDA is applicable in the above refractive-index regime, and the conditions under which DDA-based calculations can provide scattering data with good accuracy are discussed.     

Growth of needle and plate shaped particles: theory for small supersaturations,maximum velocity hypothesis

Abstract

A solution to the diffusion controlled growth of needle and plate shaped particles is presented as their shape approaches respectively a paraboloid of revolution or a parabolic cylinder, under small supersaturation values, when capillarity and interface kinetic effects are present. The solutions show that as supersaturation decreases, the growth rate and needle tip radius approach a common value regardless of interfacial kinetics effects as capillarity is the main factor that retards particle growth. Simple asymptotic expressions are thus obtained to predict the growth rate and tip radius at low supersaturations, assuming a maximum velocity hypothesis. These represent the circumstances during solid state precipitation reactions which lead to secondary hardening in steels.     

Equiphase-sphere approximation for analysis of light scattering by arbitrarily shaped nonspherical particles

We extend the previously proposed concept of equiphase sphere (EPS) to analyze light-scattering properties of arbitrarily shaped particles. Our analyses based on the Wentzel-Kramers-Brillouin technique and numerical studies based on the finite-difference time-domain method demonstrate that a wide range of irregularly shaped particles can be approximated as their equivalent equiphase ellipsoids to determine their total scattering cross-section (TSCS) spectra. As a result, a simple expression given by the EPS approximation can be used to calculate the TSCS spectra of these particles. We find that the accuracy of the EPS approximation is influenced by both the magnitude and the geometric scale of the surface perturbation of the particle, and we derive validity conditions of the EPS approximation to guide the practical application of this method.     

Jamming in granular shear flows of frictional,polydisperse cylindrical particles

In this work, frictional, cylindrical particle shear flows with different size distributions (monodisperse, binary, Gaussian, uniform) are simulated using the Discrete Element Method (DEM). The influences of particle size distribution and interparticle friction coefficient on the solid phase stresses, bulk friction coefficient, and jamming transition are investigated. In frictional dense flows, shear stresses rise rapidly with the increasing solid volume fraction when jamming occurs. The results suggest that at the jamming volume fraction, stress fluctuation and granular temperature achieve the maximum values, and the rate of the stress increase with increasing solid volume fraction approaches the peak value. Meanwhile, the degree of cylindrical particle alignment approaches a valley value. In the polydisperse flows, the jamming volume fraction exhibits significant dependences on the fraction of the longer particles and the particle size distribution. Two models considering the effect of particle size distribution are discussed for predicting the jamming volume fractions of polydisperse flows with frictional, cylindrical particles.