Other Particles (other + particle)

Distribution by Scientific Domains

Selected Abstracts

Ritz finite elements for curvilinear particles

Paul R. Heyliger
Abstract A general finite element is presented for the representation of fields in curvilinear particles in two and three dimensions. The formulation of this element shares many similarities with usual finite element approximations, but differs in that nodal points are defined in part by contact points with other particles. Power series in the geometric coordinates are used as the starting basis functions, but are recast in terms of the field variables within the particle interior and the points of contact with other elements. There is no discretization error and the elements of the finite element matrices can all be evaluated in closed form. This approach is applicable to shapes in two and three dimensions, including discs, ellipses, spheres, spheroids, and potatoes. Examples are included for two-dimensional applications of steady-state heat transfer and elastostatics. Copyright 2005 John Wiley & Sons, Ltd. [source]

Morphology Change of Undoped and Sulfate-Ion-Doped Yttria Powders during Firing

Ikegami Takayasu
Morphologic changes that occurred during firing in undoped and sulfate-ion-doped yttria powders were examined in the present study. Clear scanning electron microscopy (SEM) images of uncoated insulators were achieved and charging of electrons was avoided by observing small samples, throughout which most of the electrons of the incident beam penetrated. SEM observation and firing of the samples were repeated several times. Searching the observed areas or particles started at low magnification, with the aid of photographs taken earlier. The sulfate-ion dopant inhibited volume diffusion and/or grain-boundary diffusion, and then particle growth of the sulfate-ion-doped yttria proceeded by surface diffusion or evaporation,condensation along with pore growth, which resulted in collapse of the agglomerates of primary particles. Although most of the other particles exhibited slight pore growth along with particle growth at temperatures as low as 800C, a hardening of the agglomerated particles, because of pore elimination by volume diffusion and/or grain-boundary diffusion, occurred at temperatures >850C. [source]

Noble gas compositions of Antarctic micrometeorites collected at the Dome Fuji Station in 1996 and 1997

Takahito Osawa
Eleven of the AMMs were collected in 1996 (F96 series) and 16 were collected in 1997 (F97 series). One of the F97 AMMs is a totally melted spherule, whereas all other particles are irregular in shape. Noble gases were extracted using a Nd-YAG continuous wave laser with an output power of 2.5-3.5 W for ,5 min. Most particles released measurable amounts of noble gases. 3He/4He ratios are determined for 26 AMMs ((0.85-9.65) 10,4). Solar energetic particles (SEP) are the dominant source of helium in most AMMs rather than solar wind (SW) and cosmogenic He. Three samples had higher 3He/4He ratios compared to that of SW, showing the presence of spallogenic 3He. The Ne isotopic composition of most AMMs resembled that of SEP as in the case of helium. Spallogenic 21Ne was detected in three samples, two of which had extremely long cosmic-ray exposure ages (> 100 Ma), calculated by assuming solar cosmic-ray (SCR) + galactic cosmic-ray (GCR) production. These two particles may have come to Earth directly from the Kuiper Belt. Most AMMs had negligible amounts of cosmogenic 21 Ne and exposure ages of <1 Ma. 40Ar/36Ar ratios for all particles (3.9,289) were lower than that of the terrestrial atmosphere (296), indicating an extraterrestrial origin of part of the Ar with a very low 40Ar/36Ar ratio plus some atmospheric contamination. Indeed, 40Ar/36Ar ratios for the AMMs are higher than SW, SEP, and Q-Ar values, which is explained by the presence of atmospheric 40Ar. The average 38Ar/36Ar ratio of 24 AMMs (0.194) is slightly higher than the value of atmospheric or Q-Ar, suggesting the presence of SEP-Ar which has a relatively high 38Ar/36Ar ratio. According to the elemental compositions of the heavy noble gases, Dome Fuji AMMs can be classified into three groups: chondritic (eight particles), air-affected (nine particles), and solar-affected (eight particles). The eight AMMs classified as chondritic preserve the heavy noble gas composition of primordial trapped component due to lack of atmospheric adsorption and solar implantation. The average of 129Xe/132Xe ratio for the 16 AMMs not affected by atmospheric contamination (1.05) corresponds to the values in matrices of carbonaceous chondrites (,1.04). One AMM, F96DK038, has high 129Xe/132Xe in excess of this ratio. Our results imply that most Dome Fuji AMMs originally had chondritic heavy noble gas compositions, and carbonaceous chondrite-like objects are appropriate candidate sources for most AMMs. [source]

Development of a Method for the Measurement of Particle Size and Velocity based on Projection onto a Variable Frequency Grating

Abstract Irregular particles down to approximately 3.8,,m have been sized by imaging them onto a variable frequency grating using laser illumination. Velocity can also be determined. The method was successful for certain particle types that were rough or irregular, partly absorbing or translucent. It was not successful for transparent spheres that display glare spots in the image, or other particles that produce localised regions of high brightness. [source]

A system of grabbing particles related to Galton-Watson trees

Jean Bertoin
Abstract We consider a system of particles with arms that are activated randomly to grab other particles as a toy model for polymerization. We assume that the following two rules are fulfilled: once a particle has been grabbed then it cannot be grabbed again, and an arm cannot grab a particle that belongs to its own cluster. We are interested in the shape of a typical polymer in the situation when the initial number of monomers is large and the numbers of arms of monomers are given by i.i.d. random variables. Our main result is a limit theorem for the empirical distribution of polymers, where limit is expressed in terms of a Galton-Watson tree. 2010 Wiley Periodicals, Inc. Random Struct. Alg., 2010 [source]