Particle Perimeter Research Articles

A statistical model for the simulation of adsorption from a mixture of deformable particles

Competitive and cooperative adsorption from a mixture of deformable particles has been investigated by Monte Carlo simulation on a two-dimensional square lattice. Compact macromolecules (globular proteins) are modeled as soft particles made from connected subunits whose average configuration is determined by a potential that is coupled to the particle perimeter length and controls its deformability. Highly deformable macromolecules (disordered proteins and polysaccharides) are modeled as so-called fractal polymers of high conformational entropy. Numerical results show the dependence of the surface coverage and composition on the relative adsorption energies of the species and the strength of attractive interparticle subunit interactions. The importance of particle deformability and macromolecular interactions in relation to the structure of adsorbed layers is demonstrated by this model.

Image analysis and nonlinear modeling to determine dimensions of wet-sieved, masticated forage particles2

A procedure to estimate dimensions of digesta particles was developed and evaluated. After wet sieving, particles of masticated switchgrass and bermudagrass hays retained on sieves with apertures of 1.0 mm2 or larger were placed on moist white filter paper, separated manually, and photographed. Photographs were scanned with a flat-bed scanner, scaled to size, and digitized. Projected area, perimeter, length, and width of particles were determined by a microcomputer system. Variables derived for each particle included the form factor, which was defined as (4 x pi x area)/perimeter2, and each particle's length: width ratio. Ninety-three percent of data from two trials with steers had significant lack of fit (P less than .05 to P less than .0001) to normal, lognormal, Weibull, or gamma distributions. As an alternative, individual particle measurements were summed on a cumulative percentage basis for each variable and were fit to an inverted Gompertz function to estimate median, mode, and mean dimensions of scanned particles. Estimates from the equation fit the distribution well; asymptotic SE averaged 3.5 and 1.4% of parameter means for dimensions of masticated switchgrass and bermudagrass hay particles, respectively. No analytic solution exists for the mean, which must be estimated numerically, but analytic solutions are available for the median and mode. Use of this equation will prevent bias caused by lack of fit to a particular distribution and yield more accurate estimates of mean particle dimensions than arithmetic means.

Population-balance model of physical transformations of ash during char oxidation

A population-balance model, involving a set of coupled rate equations, is formulated to represent the agglomeration of fused ash droplets on the surface of an oxidizing char particle. Numerical solutions reproduce several features and trends obtained previously by Monte Carlo simulation. The present formulation identifies the key aspect of this phenomenology, namely the competition between the relaxation to a steady-state surface-droplet distribution and the departure from this steady state due to the increasing curvature of the particle perimeter. A principal consequence of this competition is that the mean surface-droplet diameter is predicted to exhibit an inflection point when plotted as a function of particle radius or fractional conversion.

Dynamic consolidation of type 304 stainless-steel powders in gas gun experiments

Specimens of type 304 stainless-steel powder consolidated using projectile impacts from a 10.2-cm gas gun have been recovered intact and the microstructures have been characterized. Variables for the study included two types of 304 stainless-steel powder, cavity depth, and peak stresses ranging from 11.7 to 21.1 GPa. All specimens exhibited three-dimensional contractions with approximately one-half of the densification associated with thickness. Some porosity from entrapped gas as a result of not evacuating the powder-filled cavities and microcracks due to the recovery method were observed. In the regions free of these defects, full densification was observed. The 11.7-GPa experiment produced considerable work hardening. The bonding around the particle perimeters ranged from melted regions to mechanical abutment. The 21.1-GPa experiment resulted in lower hardness, reduced metastable bcc phase, and more extensive bonding around the particle perimeters. These observations suggest that very high localized, and relatively high bulk temperatures were achieved for this peak stress. A two-dimensional numerical simulation, with the powder region considered as a two-component mixture, was used to examine the overall response of the powder-filled cavities and surrounding target to the stress wave. The calculations predicted the observed density change and the observed final shape for the compacted powder. Two-dimensional numerical simulations, in which the particles were individually modeled, were also performed to assess the behavior at the particle level. The deformation of the particles necessary to fill the interstitial regions along with the corresponding temperatures around the perimeters of the particles and their interiors were calculated. The deformation varies markedly around the particle periphery and the corresponding computed temperature rise ranges from slightly above ambient to above melting in regions of maximum particle extrusion. The nonuniform temperature rise around the particles correlates with the heterogeneous nature of the bonding observed experimentally. The model also predicts higher and broader temperature zones with increasing dynamic stress, in agreement with the experimental inferences.

The nature and stability of aluminum hydroxide precipitated on wyoming montmorillonite

A freeze—fracture technique was used to prepare replicas of interlayer surfaces of a hydroxy-aluminum montmorillonite (OH-Al-SWy-1), synthesized by titrating an Al-clay with NaOH. Aqueous suspensions containing 0.01 M NaClO 4 and 4% OH-Al-SWy-1 were frozen rapidly with Freon 22 to vitrify the solution phase and stored in liquid N 2. The frozen samples were fractured at 10 −6 Torr and 158K and C-Pt replicas were made of the exposed surface. Transmission electron microscopy (TEM) of the replicas showed a randomly distributed surface precipitate. The precipitate was flat and angular, resembling gibbsite morphologically. Gibbsite crystals were observed outside the interlayer when the suspension was air-dried on microscope grids, underscoring the value of the freeze—fracture technique in minimizing alteration of the OH-Al-SWy-1 complex. Using the mass of Al(OH) 3 fixed by the clay and the average particle perimeter observed by TEM (49.3 nm), we estimated the maximum Al(OH) 3 surface charge density and site density available for phosphate adsorption. The range of surface charge density for the Al(OH) 3, estimated from crystallographic data, was very close to the range of surface charge density for montmorillonite, suggesting that the latter may influence the maximum particle size of the precipitate. The total charge and edge [-Al(OH)(H 2O)] site density were less than the observed CEC reduction on SWy-1 and maximum phosphate retention on OH-Al-SWy-1 at pH 5.3, respectively. Interlayer Al(OH) 3 is known to be unstable with respect to gibbsite and it is possible that a relatively high specific surface area was responsible for the high solubility.

Quantitative analysis of soil structure with the microcomputer system

The present structure estimation methods are rather long-termed and expensive; moreover, they are sometimes impossible to use in reason of difficulty of sampling large sized specimens. The soil structure estimation in SEM enabling to obtain quick and reliable quantitative structure characteristics of small size samples (≈0,5 cm3) are becoming very important at present. SEM investigation of identical areas on both conjugated surfaces of sample fracture, total binary SEM image with real structure of undisturbed sample, discrimination and digitization of the image and its processing by computer with specially designed algorithms is the core of this method. The quantitative structure analysis is made practically instantly and the following data may be obtained: the number of pores and particles, average perimeter, square and radius of pores and particles, porosity, specific surface, pore shape index, the number of contacts between particles, pore and particle distribution according to the sizes. The quickness and reliability of the results obtained as well as the application which enables to cover all kinds of soils is an evident advantage of the method. The most important factor is the tracing of soil genesis and the nature of the strengths.

Image analysis of particle perimeters

The results of Quantimet measurements of particle perimeter and cross-sectional area are reported. The objective was to determine whether increasing magnification would reveal enough additional detail to cause a significant increase in the measured perimeter. Measurements on particles having simple and relatively complex shapes were compared. Increased perimeters of both particle types were found with increasing magnification, while cross-sectional area estimates remained constant. These curious results are shown to be analogous to the behavior of certain mathematical curves.

Cereal chlorotic mottle virus — a rhabdovirus of Gramineae in Australia transmitted by Nesoclutha pallida (Evans)

An undescribed rhabdovirus was found in eight species of Gramineae at locations extending over 1000 km of the tropical and subtropical Australian east coast. The incidence in maize was usually low but sometimes reached 50% in susceptible hybrids. Cereal chlorotic mottle virus (CCMV) was shown experimentally to infect Avena sativa L., Digitaria ciliaris (Retz.) Koeler, Dinebra retroflexa (Fahl.) Panz., Echinochloa colona (L.) Link., Eleusine coracana (L.) Gaertn., Eleusine indica (L.) Gaertn., Hordeum vulgare L., Triticum aestivum L. and Zea mays L. Symptoms in all hosts began as chlorotic striations, but were often reduced to a fine chlorotic mottle in subsequent growth. After a 3-day acquisition, 50% of individuals of the cicadellid Nesoclutha pallida (Evans) transmitted CCMV in consecutive test feeds with only occasional failures, but some insects then failed to transmit for up to 30 days before death. The time between acquisition and first transmission was 11–24 days and the time for symptom development in the plant was 11–21 days. The virus was acquired and transmitted by both nymphs and adults and by males and females. Transmission continued through the moult to adult. In negative stain the particles were bullet-shaped, 214 by 75 nm, with a net-like surface pattern and core width of 28 nm. There were c. 48 helix cross-striations and 52 surface projections around the full perimeter of bacilliform particles when viewed after brief fixing with glutaraldehyde before staining.

フォールアウト粒子に関する研究, (I)

Highly radioactive fall-out particles were found throughout Japan, resulting from the series of large scale nuclear test explosions carried out by U.S.S.R. during September and October, 1961. Fig. 1 shows the change of radioactivity in air-borne dusts since the beginning of these explosions and Plates 1 (a)-(h) and Table 1 show autoradiographically the changing aspect of fall-out particles in the atmosphere during this period. Many highly radioactive particles were collected and isolated from among numerous non-radioactive dust particles after elaborate procedures. Photomicrographs of them were taken and are shown in Plates 3-24 and Table 2. Plates designated by (P) were taken focussing at the perimeter of particles, showing the shape of the particle contour clearly, but the front side only vaguely. Plates designated by (F) and (M) were taken in order to show the change in depth of the surface state of particles, focussing at the front side of particles and at the middle part between the front side and the perimeter, respectively. We observed microscopically more than fifty highly radioactive particles. Most of them were quite, or nearly, spherical. There were, however, a few particles which deviated appreciably from sphere, as shown in Plates 13 and 16. The surface of some particles was irregular and creased. Several particles were coated with colorless amorphous materials like frosting, as shown in Plates 10 and 11. These materials were assumed to be non-radioactive because they had the same appearance as that of non-radioactive dust particles which were found numerously in air-borne dusts. Several particles had a few small particles of the same color attached on their surface, as shown in Plates 8-11. Almost all of the particles were yellowish, or reddish brown, however, there were some colorless, golden, or black particles. All the highly radioactive particles that we could isolate from among dust particles seemed to be so hard that only an impact of a needle could not crack them into two or more particles. It was found that radioactivity is roughly proportional to volume, as shown in Fig. 2. It seems that particles of light color have larger specific activity than those of dense color and that their conditions of particle formation were different from each other.