Stratospheric Aerosol Determinations

1974 ◽  
Vol 52 (8) ◽  
pp. 1519-1526 ◽  
Author(s):  
D. J. Hofmann
Keyword(s):  
Particle Size ◽  
Light Scattering ◽  
Stratospheric Aerosol ◽  
Small Particles ◽  
Particle Detectors ◽  
The Past ◽  
Body Of Knowledge ◽  
Large Particles ◽  
Comparison Of The Results ◽  
Lidar Observations

This review consists of a summary and comparison of the results of ongoing programs to study the stratospheric aerosol by a variety of techniques. In view of the considerable degree of disagreement among various experimental techniques in the past, the importance of comparative studies is emphasized. Many of the results are still in preliminary form, and only relatively new results are presented.Both remote and insitu measurements are discussed; the former consist mainly of lidar observations while the latter comprise impactor sampling and light-scattering particle detectors. Discussion is divided along traditional lines, i.e., by particle size, with "small" particles those of radii ≤0.1 µm and "large" particles those of radii ≥ 0.1 µm, with emphasis on the latter because of the considerably greater body of knowledge available for these particles.

scholarly journals Origin and Evolution of Recent Leonid Meteor Showers

1971 ◽  
Vol 13 ◽  
pp. 193-198 ◽  
Author(s):  
Bruce A. McIntosh
Keyword(s):  
Radiation Pressure ◽  
Ejection Velocity ◽  
Meteor Showers ◽  
Small Particles ◽  
Origin And Evolution ◽  
The Past ◽  
Long Duration ◽  
Large Particles ◽  
Particle Orbits ◽  
Perihelion Passage

The four most prominent returns of the Leonid shoiver in the past decade fall into two broad classes. The 1966 and 1969 showers were of short duration, had a high proportion of small particles, and occurred with the longest apparent delay after the perihelion passage of the parent comet Temple-Tuttle. By contrast, the 1961 and 1965 returns were of long duration, and had more large particles. The 1961 return preceded the comet.There are three major influences on particle orbits: ejection velocity, radiation pressure, and close encounters with planets. The observations are explainable in a qualitative way on the basis of the first two. But some speculation concerning the results of planetary perturbations must be invoked.

Studies of cattle and sheep eating leaf and stem fractions of grasses. 3. The retention time in the rumen of large feed particles

1981 ◽  
Vol 32 (1) ◽  
pp. 123 ◽  
Author(s):  
DP Poppi ◽  
DJ Minson ◽  
JH Ternouth
Keyword(s):  
Particle Size ◽  
Retention Time ◽  
Dry Matter ◽  
Simulation Studies ◽  
Small Particles ◽  
Dry Matter Distribution ◽  
Rhodes Grass ◽  
Large Particles ◽  
Voluntary Intake ◽  
Cattle And Sheep

Pangola grass (Digitavia decumbens) and Rhodes grass (Chlovis gayana) cut as 6 and 12 week regrowths were separated into leaf and stem fractions and fed ad libitum to four cattle and eight sheep fitted with ruminal fistulae to determine the importance of particle size in controlling the retention time of feed in the rumeno-reticulum (rumen). Particle size was determined by using a wet sieving technique, and based on the cumulative dry matter distribution on the sieves of faeces from cattle and sheep; all particles >1.18 mm were described as large particles. The proportion of large particles was measured in the chopped diet offered, the masticated diet, the ruminal contents and the faeces. Chopped leaf and stem fractions contained 0.85 and 0.86 g/g large particles respectively. Mastication by cattle reduced the proportion of large particles in leaf and stem to 0.58 and 0.76 (P < 0.01), and mastication by sheep to 0.56 and 0.67 (P < 0.01). The proportion of large particles in the rumen of sheep was 0.236 and 0.249 for leaf and stem respectively (P > 0.05) and in cattle 0.272 and 0.345 (P < 0.05). The faeces contained relatively few large feed particles (< 0.045 for cattle and <0.018 for sheep). Cattle eating leaf and stem produced faeces containing 0.027 and 0.040 (g/g) large particles (P <0.05), compared with only 0,008 and 0.013 (P < 0.05) in sheep. Most of the large particles entering the rumen in the masticated feed disappeared in the rumen by breakdown to smaller particles or by digestion. In cattle the proportions that disappeared were 0.978 and 0.976 (P > 0.05) for leaf and stem, and in sheep 0.993 and 0.991 (P > 0.05). Large particles in leaf and stem were retained in the rumen of the sheep for 11.0 and 11.7 h (P > 0.05). Cattle retained large particles in all diets for a longer time (P < 0.01); 16.1 h for leaf and 20,2 h for stem (P > 0.05). Differences in retention time of large particles in the rumen did not appear to be the only factor controlling the retention of dry matter in the rumen and voluntary intake. A model was developed to describe the flow of large and small particles through the rumen. Intake simulation studies indicated that the most important factor influencing dry matter retention time in the rumen was the retention time of small particles (> 1.18 mm). Changes in the rate of breakdown of large particles had a small effect on dry matter retention time.

The Infrared Analysis of Polyethylene Terephthalate Fibers and of Their Strength as Related to Sample Preparation and to Particle Size

1989 ◽  
Vol 43 (5) ◽  
pp. 791-794 ◽  
Author(s):  
R. O. Carter ◽  
K. R. Carduner ◽  
M. C. Paputa Peck ◽  
D. H. Motry
Keyword(s):  
Particle Size ◽  
Sample Preparation ◽  
Polyethylene Terephthalate ◽  
Infrared Analysis ◽  
Spectral Features ◽  
Band Broadening ◽  
Small Particles ◽  
Large Particles ◽  
Local Sample ◽  
Infrared Microscope

An explanation is presented for the broadening of intense spectral features observed in the infrared spectra of polyethylene terephthalate fibers prepared as KBr pellets. Since band broadening occurs in the spectra of stronger, undegraded fiber, it is proposed that, the stronger the fiber, the more the difficulty one has in pulverizing the sample. Larger particles result from undegraded polyester, which lead to broader bands for intense features. The local sample pathlength in the region of the large particles is greater than that for small particles, which can be more homogeneously mixed. Fiber samples can also be presented to an infrared microscope either “as is” or flattened. Striking differences exist between spectra for flattened and round fibers that were otherwise similar.

scholarly journals Stable solutions of a scalar conservation law for particle-size segregation in dense granular avalanches

2008 ◽  
Vol 19 (1) ◽  
pp. 61-86 ◽  
Author(s):  
M. SHEARER ◽  
J. M. N. T. GRAY ◽  
A. R. THORNTON
Keyword(s):  
Particle Size ◽  
Free Surface ◽  
Shear Flow ◽  
Free Surface Flows ◽  
Size Segregation ◽  
Small Particles ◽  
Surface Flows ◽  
Scalar Conservation Law ◽  
Large Particles ◽  
Scalar Conservation

Dense, dry granular avalanches are very efficient at sorting the larger particles towards the free surface of the flow, and finer grains towards the base, through the combined processes of kinetic sieving and squeeze expulsion. This generates an inversely graded particle-size distribution, which is fundamental to a variety of pattern formation mechanisms, as well as subtle size-mobility feedback effects, leading to the formation of coarse-grained lateral levees that create channels in geophysical flows, enhancing their run-out. In this paper we investigate some of the properties of a recent model [Gray, J. M. N. T. & Thornton, A. R. (2005) A theory for particle size segregation in shallow granular free-surface flows. Proc. R. Soc. 461, 1447–1473]; [Thornton, A. R., Gray, J. M. N. T. & Hogg, A. J. (2006) A three-phase mixture theory for particle size segregation in shallow granular free-surface flows. J. Fluid. Mech. 550, 1–25] for the segregation of particles of two sizes but the same density in a shear flow typical of shallow avalanches. The model is a scalar conservation law in space and time, for the volume fraction of smaller particles, with non-constant coefficients depending on depth within the avalanche. It is proved that for steady flow from an inlet, complete segregation occurs beyond a certain finite distance down the slope, no matter what the mixture at the inlet. In time-dependent flow, dynamic shock waves can develop; they are interfaces separating different mixes of particles. Shock waves are shown to be stable if and only if there is a greater concentration of large particles above the interface than below. Constructions with shocks and rarefaction waves are demonstrated on a pair of physically relevant initial boundary value problems, in which a region of all small particles is penetrated from the inlet by either a uniform mixture of particles or by a layer of small particles over a layer of large particles. In both cases, and under a linear shear flow, solutions are constructed for all time and shown to have similar structure for all choices of parameters.

Influence of Oxide Particle Size on the Erosion of the Control Stage Nozzle in a Supercritical Steam Turbine

2013 ◽  
Author(s):  
Liu-xi Cai ◽  
Shun-sen Wang ◽  
Lei Zhang ◽  
Jing-ru Mao ◽  
Zhen-ping Feng ◽  
...  
Keyword(s):  
Particle Size ◽  
Steam Turbine ◽  
Erosion Resistance ◽  
Size Range ◽  
Small Particles ◽  
Suction Surface ◽  
Erosion Damage ◽  
Pressure Surface ◽  
Control Stage ◽  
Large Particles

Reducing the solid particle erosion (SPE) of blades is one of the most important problems for high-parameter steam turbine. Based on the erosion rate models and the particle rebound models of blade materials obtained through the accelerated erosion test under high temperature, a lot of three dimension numerical simulations were conducted in this paper. The influence of particle size on the impingement point distribution on the nozzle surface and the erosion characteristics of control stage nozzle in a supercritical steam turbine were analyzed quantitatively. The size range of the oxide scale particles participating in the erosion damage were extended to 500μm, and some special anti-erosion measures corresponding to different size particles were proposed to reduce the erosion of nozzle. Results show that the erosion of pressure surface in the trailing edge of nozzle is mainly from the high-intensity impingement of particles smaller than 160μm, especially those with the size range from 20μm to 60μm. For the impingement of these small particles, optimizing the profile and cascade structure as well as coating the hard coating on the surface of nozzle can improve the erosion resistance of nozzle. However, these small particles do not impinge the nozzle trailing edge suction surface. The severe erosion damage of suction surface of nozzle was from the impingement again of the particles with the size range from 200μm to 500μm after rebounding from nozzle pressure surface. It is very difficult to resist the erosion damage of these large particles for the hard coating, and separating large particles from main steam before entering the nozzle chamber should be a good choice for improving the erosion resistance of turbine. These studies will provide a technical basis for selecting anti-erosion measures of control stage nozzle.

Inkjet printable silver dispersions: Effect of bimodal particle-size distribution on film formation and electrical conductivity

2010 ◽  
Vol 25 (5) ◽  
pp. 821-827 ◽  
Author(s):  
Krishna Balantrapu ◽  
Meaghan McMurran ◽  
Dan V. Goia
Keyword(s):  
Electrical Conductivity ◽  
Particle Size ◽  
Size Distribution ◽  
Film Formation ◽  
Small Particles ◽  
Silver Films ◽  
On Demand ◽  
Drop On Demand ◽  
Large Particles ◽  
Effect Of Particle Size

Inks containing silver nanoparticles of 12 nm, 80 nm, and a 15%/85% mixture of the two sizes were used to evaluate the effect of particle size and size distribution on the electrical properties of sintered films. The silver layers deposited with a “drop-on-demand” inkjet printer were heated at temperatures ranging from 125 to 200 °C. The small particles formed less resistive films at 125 °C, while the larger ones provided better electrical conductivity above 150 °C. The inks containing mixed small and large particles yielded the most conductive silver films over the entire investigated temperature range. A mechanism explaining these results is proposed based on the evolution of film microstructure with temperature.

Angle-dependent effects in Dynamic Light Scattering measurements of polydisperse particles

2021 ◽  
Author(s):  
Lin Jin ◽  
Curtis W Jarand ◽  
Mark L Brader ◽  
Wayne F Reed
Keyword(s):  
Particle Size ◽  
Light Scattering ◽  
Dynamic Light Scattering ◽  
Laser Wavelength ◽  
Recent Emergence ◽  
Large Particles ◽  
Average Diffusion ◽  
Biological Polymers ◽  
Average Size ◽  
The Relationship

Abstract Dynamic light scattering (DLS) is widely used for analyzing biological polymers and colloids. Its application to nanoparticles in medicine is becoming increasingly important with the recent emergence of prominent lipid nanoparticle-(LNP)based products, such as the SARS-CoV-2 vaccines from Pfizer, Inc.-BioNTech (BNT162b2) and Moderna, Inc. (mRNA-1273). DLS plays an important role in the characterization and quality control of nanoparticle-based therapeutics and vaccines. However, most DLS instruments have a single detection angle ,and the amplitude of the scattering vector, q, varies among them according to the relationship q=(n/sin(/2) where 0 is the laser wavelength. Results for identical, polydisperse samples among instruments of varying q yield different hydrodynamic diameters, because, as particles become larger they scatter less light at higher angles, so that higher-q instruments will under-sample large particles in polydisperse populations, and report higher z-average diffusion coefficients, and hence smaller effective hydrodynamic diameters than lower-q instruments. As particle size reaches the Mie regime the scattering envelope manifests angular maxima and minima, and the monotonic decrease of average size versus q is lost. This work examines results for different q-value instruments, using mixtures of monodisperse latex sphere standards, for which experimental measurements agree well with computations, and also polydisperse solutions of LNP, for which results follow expected trends. Mie effects on broad unimodal populations are also considered. There is no way to predict results between two instruments with different q for samples of unknown particle size distributions.

Flow-induced segregation in confined multicomponent suspensions: effects of particle size and rigidity

2013 ◽  
Vol 738 ◽  
pp. 423-462 ◽  
Author(s):  
Amit Kumar ◽  
Rafael G. Henríquez Rivera ◽  
Michael D. Graham
Keyword(s):  
Particle Size ◽  
Master Equation ◽  
Migration Velocity ◽  
Equation Model ◽  
Simple Shear Flow ◽  
Small Particles ◽  
Large Particles ◽  
Dilute Suspensions ◽  
Normal Particle ◽  
Non Local

AbstractThe effects of particle size and rigidity on segregation behaviour in confined simple shear flow of binary suspensions of fluid-filled elastic capsules are investigated in a model system that resembles blood. We study this problem with direct simulations as well as with a master equation model that incorporates two key sources of wall-normal particle transport: wall-induced migration and hydrodynamic pair collisions. The simulation results indicate that, in a mixture of large and small particles with equal capillary numbers, the small particles marginate, while the large particles antimarginate in their respective dilute suspensions. Here margination refers to localization of particles near walls, while antimargination refers to the opposite. In a mixture of particles with equal size and unequal capillary number, the stiffer particles marginate while the flexible particles antimarginate. The master equation model traces the origins of the segregation behaviour to the size and rigidity dependence of the wall-induced migration velocity and of the cross-stream particle displacements in various types of collisions. In particular, segregation by rigidity, especially at low volume fractions, is driven in large part by heterogeneous collisions, in which the stiff particle undergoes larger displacement. In contrast, segregation by size is driven mostly by the larger wall-induced migration velocity of larger particles. Additionally, a non-local drift-diffusion equation is derived from the master equation model, which provides further insights into the segregation behaviour.

scholarly journals Studies on respiratory infection: II. The influence of aerosol particle size on infection of the guinea-pig with Pasteurella pestis

1956 ◽  
Vol 54 (1) ◽  
pp. 37-48 ◽  
Author(s):  
H. A. Druett ◽  
J. M. Robinson ◽  
D. W. Henderson ◽  
L. Packman ◽  
S. Peacock
Keyword(s):  
Particle Size ◽  
Guinea Pig ◽  
Respiratory Tract ◽  
Respiratory Infection ◽  
Cross Infection ◽  
Airborne Particles ◽  
Small Particles ◽  
Large Particles ◽  
Aerosol Particle Size ◽  
Disease Characteristic

The LD50 dose of Past. pestis is much greater when tested by the respiratory route than by subcutaneous challenge. This is probably due to trauma inflicted on the airborne particles.Two forms of plague, both originating in the respiratory tract of the guinea-pig, can develop according to the size of the particle containing Past. pestis presented to the host. Small particles initiate a broncho-pneumonia which leads to septicaemia and death. Large particles establish a septicaemia, and death results more quickly without the development of a pneumonia.Cross-infection to normal animals occurs irregularly when they are exposed to others developing plague by the respiratory route. Such incident is rare when the initially infected animals are exposed to large particles. Cross-infected animals suffer from the disease characteristic of exposure to large particles. Attempts to establish an epizootic by cross-respiratory infection were abortive, probably due, in some measure, to the type of disease developing in first cross-infections.

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