نتایج جستجو برای: grains
تعداد نتایج: 27038 فیلتر نتایج به سال:
The year of 2005 marks the 75th anniversary since Trumpler (1930) provided the first definitive proof of interstellar grains by demonstrating the existence of general absorption and reddening of starlight in the galactic plane. This article reviews our progressive understanding of the nature of interstellar dust.
We study number density distribution and the behavior of time correlation functions in the density of grains for a quasi-two dimensional system of vibrated grains. We study the system at various packing fractions, from low to high. At low densities we recover usual gas like behavior, reflected in a Poissonian statistics for the number density distribution. At higher densities we notice effects ...
A composite dust grain model which is consistent with the observed interstellar extinction and linear polarization is presented. The composite grain is made up of a host silicate spheroid and graphite inclusions. The extinction efficiencies of the composite spheroidal grains for three axial ratios are computed using the discrete dipole approximation (DDA). The interstellar extinction curve is e...
Wheat plants (Triticum aestivum L., cv. Warigal) were subjected to 20 d of water deficit during the period of endosperm cell division. Drought accentuated the differences in final grain weight between spikelets and between grains within spikelets. The distal grains of top spikelets were most affected by drought. The maximum number of endosperm cells was, respectively, 30 and 40 per cent lower i...
The study of nucleation mechanism of new grains during severe plastic deformation of magnesium alloys is of great importance to control the characteristics of final microstructures. To investigate the role of discontinuous recrystallization, a wrought AZ31 magnesium alloy was deformed by accumulative back extrusion process at 330 °C. The obtained microstructures were studied using optical and...
This review surveys the observed properties of interstellar dust grains: the wavelength-dependent extinction of starlight, including absorption features, from UV to infrared; optical luminescence; infrared emission; microwave emission; optical, UV, and X-ray scattering by dust; and polarization of starlight and of infrared emission. The relationship between presolar grains in meteorites and the...
Introduction: Presolar grains undergo a long jour ney through interstellar space before being incorporat ed into primitive meteorites from which they are recov ered [1]. During this journey they are exposed to parti cle impacts and UV-radiation which might lead to al teration, accretion or sputtering effects leading to changes in structure and formation of coatings on the original refracto...
Introduction: Carbonate is a minor phase in hydrous meteorites and hydrous interplanetary dust particles (IDPs), where it is believed to have formed by aqueous processing on asteroidal parent bodies [1]. Carbonate has been reported in the dust shells around evolved stars [2] and in other interstellar and circumstel-lar environments [3] where liquid water is unlikely to have been present. Toppan...
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