Cent Of Particles Research Articles

APOPHIS – effects of the 2029 Earth’s encounter on the surface and nearby dynamics

ABSTRACT The 99942 Apophis close encounter with Earth in 2029 may provide information about asteroid’s physical characteristics and measurements of Earth’s effects on the asteroid surface. In this work, we analysed the surface and the nearby dynamics of Apophis. The possible effects of its 2029 encounter on the surface and environment vicinity are also analysed. We consider a 340 m polyhedron with a uniform density (1.29, 2.2, and 3.5 g cm−3). The slope angles are computed, as well their variation that arises during the close approach. Such variation reaches 4° when low densities are used in our simulations and reaches 2° when the density is high. The zero-velocity curves, the equilibrium points, and their topological classification are obtained. We found four external equilibrium points and two of them are linearly stable. We also perform numerical simulations of bodies orbiting the asteroid, taking into account the irregular gravitational field of Apophis and two extra scenarios of perturbations: the solar radiation pressure and the Earth’s perturbation during the close approach. The radiation pressure plays an important role in the vicinity of the asteroid, only cm-sized particles survived for the time of integration. For densities of 2.2 and 3.5 g cm−3, a region of 5 cm radius particles survived for 30 yr of the simulation, and for 1.29 g cm−3, only particles with 15 cm of radius survived. The ejections and collisions are about 30–50 times larger when the close encounter effect is added but around 56–59 per cent of particles still survive the encounter.

Multi-blade milling from log to powder in one step – Experimental design and results

This study investigated a new technique for obtaining wood powders from whole logs (Pinus sylvestris L.) in a single-step operation. The performance of a prototype multi-blade shaft mill (MBSM) was evaluated using a designed series of experiments including three input parameters, i.e., the moisture content of the log, milling blade speed and log feeding speed, combined with multilinear regression (MLR) analysis. The milling performance was characterised by specific milling energy, particle size distribution and bulk density of powder. For MBSM powders (80 to 95% particles <1.0 mm), the specific milling energy ranged from 99 to 232 kWh t−1 DM. The mass per cent of particles <0.5 mm in MBSM powders ranged from 55 to 80% compared to 41% from hammer-milled powders. Powder bulk density varied from 138 to 264 kg m−3 DM and the moisture content of the milled log was the only significant (p < 0.05) factor affecting the bulk density of resulting powders (dried). MLR models show that the milling energy is inversely proportional to the moisture content, which indicates that moisture influences MBSM milling in a similar way as in the sawing of wood and opposite to that of impact-based mills (i.e. hammer mills).

Adenovirus aggregation and preservation in extracellular environment.

The conditions of adenovirus aggregations are analyzed. Adenovirus type 2 was propagated on Hep2 cells; virion aggregation analysis was performed by sedimentation velocity on sucrose gradients. The results show that aggregation depends on: 1) Ionic strength: aggregate formation was verified between 0.005 M and 0.05 M NaCl; 2) pH: at pH 7.1 virus particles are dispersed, 90 per cent of particles are aggregated at pH 4--5; at pH lower than 4 aggregation is not reversible; 3) Particle concentration: the dilution of a stock containing 5 X 10(11) particles/ml decrease rate of aggregate formation until all aggregation is inhibited; 4) Temperature: the degree of aggregation in the 25 to 37 degrees C range is constant but decreases when the temperature falls below 20 degrees, at +4 C there is no aggregation. The aggregation reaction presents a positive deltaH of 17.9 Kcal/mol and a deltaG of --1.32 Kcal/mol.

High collection efficiency of the aerotec-3 cyclone for submicron particles

The Aerotec-3 cyclone, a widely used instrument for the removal of coarse particulates from airstreams, has been calibrated with micron and submicron diameter aerosols. Fifty per cent of particles having an aerodynamic diameter of 0.6 μm were removed by the cyclone operating at 60ft 3 min −1. Thus this cyclone is much more efficient than heretofore supposed.

A simplified application of the Andersen sampler to the study of airborne fungus particles

An application of the Andersen sampler to the study of potentially allergenic, culturable, airborne fungus particles is described. For this purpose, a highly modified technique with a single culture plate beneath stage 6 (S 6 arrangement) was evaluated and found to produce a “telescoped” collection qualitatively comparable with growth obtained by conventional 6 plate arrays. The S 6 arrangement also appeared to yield quantitatively valid results if optimally short sampling periods were chosen. Up to 3 per cent of particles, capable of growth on the media used, were noted to bypass the S 6 plate after entering the intake orifice; however, these losses were not necessarily related to particle size. Significant impaction of particles upon sampler hardware was not suggested, and withdrawal of plates from the upper stages appeared to obviate adventitious deposition at those points. Increased particle recoveries were obtained when the sampler was made wind oriented, with the advantages being shown most clearly for genera having relatively large spores. Qualitative comparisons between collections made simultaneously by the open-culture plate method and by the wind-oriented Andersen sampler confirmed the latter's major theoretical advantage in recovering small-spored genera.

Effects of Pulverized Fuel Ash on the Moisture Characteristics of Soils

THE available water capacity (AWC) of a soil has been shown to be positively correlated with the percentage of fine sand (0.2–0.02 mm) and organic carbon present, and negatively correlated with the percentage of coarse sand (2.0–0.2 mm)1. Pulverized fuel ash, produced from the combustion of finely ground coal, is a dust containing between 50 and 70 per cent of “fine sand” size particles2. It occurred to us that pulverized fuel ash could be applied to increase the AWC of coarse textured soils. To test this hypothesis a field experiment was carried out on a coarse sandy loam of the Newport Series. Rates of ash, equivalent to 0, 50, 100 and 200 tons/acre, and containing 65 per cent of particles of size 0.2–0.02 mm, were incorporated into the top 12 in. of soil in small plots by putting soil and ash through a concrete mixer. There were five replications of each treatment. A satisfactory crop of red beet was grown on all plots, but there was a reduction of 9 per cent in the yield of roots with the highest rate of ash applied, which was probably caused by the presence of toxic quantities of boron. After harvest the various moisture characteristics of the soil were determined3: the upper limit of available water by the gravimetric method on samples taken 48 h after rewetting and the lower limit by the 15 atm. percentage method.

On the reproduction of influenza virus; quantitative studies with procedures which enumerate infective and hemagglutinating virus particles.

Procedures which make possible the enumeration of both infective and hemagglutinating influenza A virus particles have been developed and used in a quantitative investigation on the reproduction of the agent. Infective particles were found to be highly unstable and their half-life was only 147 minutes in allantoic fluid at 35 degrees C. both in vitro and in vivo. The instability of infective particles provides an explanation for the rapid accumulation of non-infective particles which retained the hemagglutinating property. The number of non-infective (N) particles was determined from the difference between the number of hemagglutinating (H) particles and the number of infective (I) particles as indicated by the relation: [N] = [H]- [1]. When the half-life of infective particles was taken into account, both infective and hemagglutinating particles were found to disappear from the allantoic fluid; i.e., were adsorbed by the allantoic membrane, at the same logarithmic rate after inoculation. Inoculation of any number of particles up to 3 x 10(7) was followed by a constant and progressive decrease in the proportion of unadsorbed particles from 0 to 4 hours. Approximately 20 per cent of particles were unadsorbed at 2 hours and about 5 per cent at 4 hours. Inoculation of 3 x 10(8) or more particles led to a larger proportion of unadsorbed particles at 4 hours. The maximum number of particles adsorbed was computed to be about 1.6 x 10(9). The concentration of both infective and hemagglutinating particles increased rapidly in the allantoic fluid after 4 hours when any number of infective particles up to 3 x 10(7) was inoculated. With such inocula, the rate of increase during the logarithmic period was constant and the time to double the concentration of infective or hemagglutinating particles was 46 minutes. With larger inocula, i.e. 3 x 10(8) particles, the concentrations of infective and hemagglutinating particles did not increase until after 8 hours and the rate of increase was much slower. The time to double the concentration of either then became 92 minutes. The number of infective particles was approximately equal to the number of hemagglutinating particles during the logarithmic increase period when any number of infective particles up to 3 x 10(6) was inoculated and no more than 10(6) non-infective particles were included in the inoculum. This finding was taken to indicate that all or almost all particles produced and released under these conditions were infective. That such particles became inactivated rapidly and led to the accumulation of an increasing number of non-infective particles after the logarithmic period can be explained by the short half-life of infective particles. The number of infective particles was no larger than one-tenth the number of hemagglutinating particles during the logarithmic increase period after 3 x 10(7) or more infective particles had been inoculated or when smaller inocula were used which also contained 3 x 10(7) or more non-infective particles. Non-infective particles prepared in vitro at 35 degrees or 22 degrees C. were as effective as those which accumulated in vivo in diminishing the proportion of infective particles in the yield. The extent of the reduction in the proportion of infective particles was directly related to the number of non-infective particles included in the inoculum. The yield of hemagglutinating particles was diminished when the inoculum contained 3 x 10(7) or more non-infective particles. The rate of increase was reduced so that the time to double the concentration became 92 minutes when the inoculum contained 3 x 10(8) non-infective particles. It appears from these findings that the single condition which will lead to the emergence of non-infective particles during the logarithmic period is a high initial particle-cell ratio. Because non-infective particles are equally as effective as infective particles in producing this result, it seems probable that the appearance of non-infective but hemagglutinating particles is not a necessary accompaniment of the reproductive process.