867,285 research outputs found
Soil Particle Size Distribution Protocol
The purpose of this resource is to sure the distribution of different sizes of soil particles in each horizon of a soil profile. Using dry, sieved soil from a horizon, students mix the soil with water and a dispersing solution to completely separate the particles from each other. Students shake the mixture to fully suspend the soil in the water. The soil particles are then allowed to settle out of suspension, and the specific gravity and temperature of the suspension are measured using a hydrometer and thermometer. These measurements are taken after 2 minutes and 24 hours. Educational levels: Middle school, High school
Particle Size Distribution in Aluminum Manufacturing Facilities.
As part of exposure assessment for an ongoing epidemiologic study of heart disease and fine particle exposures in aluminum industry, area particle samples were collected in production facilities to assess instrument reliability and particle size distribution at different process areas. Personal modular impactors (PMI) and Minimicro-orifice uniform deposition impactors (MiniMOUDI) were used. The coefficient of variation (CV) of co-located samples was used to evaluate the reproducibility of the samplers. PM2.5 measured by PMI was compared to PM2.5 calculated from MiniMOUDI data. Mass median aerodynamic diameter (MMAD) and concentrations of sub-micrometer (PM1.0) and quasi-ultrafine (PM0.56) particles were evaluated to characterize particle size distribution. Most of CVs were less than 30%. The slope of the linear regression of PMI_PM2.5 versus MiniMOUDI_PM2.5 was 1.03 mg/m3 per mg/m3 (± 0.05), with correlation coefficient of 0.97 (± 0.01). Particle size distribution varied substantively in smelters, whereas it was less variable in fabrication units with significantly smaller MMADs (arithmetic mean of MMADs: 2.59 μm in smelters vs. 1.31 μm in fabrication units, p = 0.001). Although the total particle concentration was more than two times higher in the smelters than in the fabrication units, the fraction of PM10 which was PM1.0 or PM0.56 was significantly lower in the smelters than in the fabrication units (p < 0.001). Consequently, the concentrations of sub-micrometer and quasi-ultrafine particles were similar in these two types of facilities. It would appear, studies evaluating ultrafine particle exposure in aluminum industry should focus on not only the smelters, but also the fabrication facilities
Direct indication of particle size in fluidized beds
Differential pressure measurements indicate particle size and particle size distribution in fluidized beds. The technique is based on the relationship between bed particle size and the intensity and frequency of fluctuations. By measuring the fluctuations, an estimate of average particle size of the fluid-bed material can be made
Size-dependent bandgap and particle size distribution of colloidal semiconductor nanocrystals
A new analytical expression for the size-dependent bandgap of colloidal
semiconductor nanocrystals is proposed within the framework of the finite-depth
square-well effective mass approximation in order to provide a quantitative
description of the quantum confinement effect. This allows one to convert
optical spectroscopic data (photoluminescence spectrum and absorbance edge)
into accurate estimates for the particle size distributions of colloidal
systems even if the traditional effective mass model is expected to fail, which
occurs typically for very small particles belonging to the so-called strong
confinement limit. By applying the reported theoretical methodologies to CdTe
nanocrystals synthesized through wet chemical routes, size distributions are
inferred and compared directly to those obtained from atomic force microscopy
and transmission electron microscopy. This analysis can be used as a
complementary tool for the characterization of nanocrystal samples of many
other systems such as the II-VI and III-V semiconductor materials.Comment: 9 pages, 5 figure
Modeling radiation in particle clouds: On the importance of inter-particle radiation for pulverized solid fuel combustion
The importance of inter-particle radiation for clusters of gray and diffuse
particles is investigated. The radiative cooling of each individual particle is
found to vary strongly with its position in the cluster, and a mean radiative
particle cooling term is proposed for single particle simulations of particle
clusters or for high detail simulation, like Direct Numerical Simulations of
small sub-volumes of large clusters of particles. Radiative cooling is shown to
be important both for furnaces for coal gasification and coal combustion.
Broadening the particle size distribution is found to have just a minor effect
on the radiative particle cooling. This is particularly the case for large and
dense particle clusters where there is essentially no effect of size
distribution broadening at all. For smaller and more dilute particle clusters,
the effect of distribution broadening is clear but still not dominant
Pair distribution function and structure factor of spherical particles
The availability of neutron spallation-source instruments that provide total
scattering powder diffraction has led to an increased application of real-space
structure analysis using the pair distribution function. Currently, the
analytical treatment of finite size effects within pair distribution refinement
procedures is limited. To that end, an envelope function is derived which
transforms the pair distribution function of an infinite solid into that of a
spherical particle with the same crystal structure. Distributions of particle
sizes are then considered, and the associated envelope function is used to
predict the particle size distribution of an experimental sample of gold
nanoparticles from its pair distribution function alone. Finally, complementing
the wealth of existing diffraction analysis, the peak broadening for the
structure factor of spherical particles, expressed as a convolution derived
from the envelope functions, is calculated exactly for all particle size
distributions considered, and peak maxima, offsets, and asymmetries are
discussed.Comment: 7 pages, 6 figure
The Smallest Particles in Saturn's A and C Rings
Radio occultations of Saturn's main rings by spacecraft suggest a power law
particle size-distribution down to sizes of the order of 1 cm (Marouf et al.,
1983), (Zebker et al., 1985). The lack of optical depth variations between
ultraviolet and near-IR wavelengths indicate a lack of micron-sized particles.
Between these two regimes, the particle-size distribution is largely unknown. A
cutoff where the particle-size distribution turns over must exist, but the
position and shape of it is not clear from existing studies.
Using a series of solar occultations performed by the VIMS instrument
on-board Cassini in the near-infrared, we are able to measure light forward
scattered by particles in the A and C rings. With a model of diffraction by
ring particles, and the previous radio work as a constraint on the slope of the
particle size distribution, we estimate the minimum particle size using a
truncated power-law size distribution. The C Ring shows a minimum particle size
of mm, with an assumed power law index of q=3.1 and a
maximum particle size of 10 m.
The A Ring signal shows a similar level of scattered flux, but modeling is
complicated by the presence of self-gravity wakes and higher optical depths. If
q<3, our A Ring model requires a minimum particle size below one millimeter (<
0.34 mm for an assumed q=2.75, or mm for a steeper
q=2.9) to be consistent with VIMS observations. These results might seem to
contradict previous optical(Dones et al., 1993) and infrared (French and
Nicholson, 2000) work, which implied that there were few particles in the A
Ring smaller than 1 cm. But, because of the shallow power law, relatively
little optical depth (between 0.03 and 0.16 in extinction, or 0.015 - 0.08 in
absorption) is provided by these particles.Comment: 47 pages, 16 figures, 3 Table
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