Thermal emission from grains in the galactic center
Galactic nucleus thermal emission due to dirty ice or silicate grains, explaining far IR radiation power output and spectral dependence
Krishna Swamy, K. S.↗
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The effect of methane, ammonia, and silicates on the 3.07-micron ice absorption in interstellar grains
Methane, ammonia and silicate effects on 3.07 micron ice absorption in interstellar grains, using cesium iodide window deposited sample measurements
Donn, B.↗
Attenuation of seismic waves by grain boundary relaxation
Elastic seismic waves attenuation in polycrystalline ceramics and rocks by grain boundary relaxation, noting strong frequency dependence of earth mantle internal friction
Jackson, D. D.↗
Composition and grain-size characteristics of fines from the Apollo 12 double-core tube
Petrography, mineral composition and grain size distribution of Apollo 12 lunar fines
Bird, M. L.↗
Variability of radiation from circumstellar grains surrounding R Coronae Borealis.
Radiation at IR wavelengths from circumstellar grains surrounding R CrB has been observed for approximately three years. Variations of flux with time have been larger at a wavelength of 3.5 microns than at 11 microns. Observations at IR and visual wavelengths of R CrB are presented in a graph. Another graph shows the change in the shape of the excess radiaton between two observations spaced by a period of about one year.
Forrest, W. J.↗
Absorbing ice model of interstellar grains.
Extinction curves have been calculated for Mie scattering by grains with a refractive index m equals to n - ik, where n was between 1.3 and 2.0 and k varied from 0 to 0.5. A good fit for the observed interstellar extinction in the wavelength region of 0.1 to 2.0 microns was obtained for particles with a radius of 0.1 micron and m equal to 1.3 - 0.2i. Inclusion of the changes in the refractive index in the vacuum ultraviolet region due to the strong absorptions of methane, ammonia and water does not appreciably alter these results. Theoretical extinction curves for the composite medium of H2O, NH3, CH4, and graphite show a general agreement with the observed interstellar reddening curve over the whole spectral range, in addition to producing kinks in the far-ultraviolet region.
Swamy, K. S. K.↗
Grain refinement control in gas-shielded arc welding of aluminum tubing
When sections are being welded, operator varies pulse rate of power supply and simultaneously monitors signal on oscilloscope until rate is found which produces maximum arc gas voltage. Remainder of welding is performed with power supply set at this pulse rate, producing desired maximum weld puddle agitation and fine uniform weld of grain structure.
Iceland, W. F.↗
An observation of the effect of grain structure on the appearance of Kirkendall porosity.
Study of substitutional diffusion in thoriated and nonthoriated nickel alloys, particularly in several nominally Ni-20Cr-2ThO2:Ni type diffusion couples diffused at 1530 K. Upon metallographic examination, one DS-NiCr:Ni couple had negligible Kirkendall pore formation while the other couples contained significant porosity. It is believed that the difference in Kirkendall porosity is related to the unique grain structure of the particular lot of DS-NiCr used in this diffusion couple.
Whittenberger, J. D.↗
Inert gases in a terra sample - Measurements in six grain-size fractions and two single particles from Lunar 20.
Review of the results of inert gas measurements performed on six grain-size fractions and two single particles from four samples of Luna 20 material. Presented and discussed data include the inert gas contents, element and isotope systematics, radiation ages, and Ar-36/Ar-40 systematics.
Heymann, D.↗
The effect of grain boundaries on the resistivity of polycrystalline silicon
The electrical resistivity of polycrystalline silicon films was investigated. The films were grown by the chemical vapor decomposition of silane on oxidized silicon wafers. The resistivity was found to be independent of dopant atom concentration in the lightly doped regions but was a strong function of dopant levels in the more heavily doped regions. A model, based on high dopant atom segregation in the grain boundaries, is proposed to explain the results.
Fripp, A. L., Jr.↗
Evolution of lunar soil grain-size and shape parameters
Substrates at the Apollo 15 and 16 sites were analyzed and showed essentially the same graphic mean, graphic standard deviation, and graphic skewness. The graphic kurtosis of Apollo 16 soils is slightly smaller than that of Apollo 15. In Apollo 15 soil samples, grain size and graphic standard deviation increase with depth, while the trend is reversed in Apollo 16 soil samples. Lower sphericity values for Apollo 15 samples coincide with concentrations of highly irregularly shaped glass particles. Two-dimensional sphericity of Apollo 15 samples is contoured as a function of particle size and depth below lunar surface. The results are consistent with an overall model for soil development in which samples closer to the surface are more mature in response to more prolonged reworking of meteorite impact.
Lindsay, J. F.↗
Grain size analysis and high frequency electrical properties of Apollo 15 and 16 samples
The particle size distribution of eleven surface fines samples collected by Apollo 15 and 16 was determined by the method of measuring the sedimentation rate in a column of water. The fact that the grain size distribution in the core samples shows significant differences within a few centimeters variation of depth is important for the understanding of the surface transportation processes which are responsible for the deposition of thin layers of different physical and/or chemical origin. The variation with density of the absorption length is plotted, and results would indicate that for the case of meter wavelength radar waves, reflections from depths of more than 100 meters generally contribute significantly to the radar echoes obtained.
Gold, T.↗
Some scattering problems of interstellar grains
Consideration of the general effects of size, shape, chemical composition, index of refraction, temperature, and other physical parameters of small particles upon their scattering properties. A determination of the relative importance of these effects to interstellar dust interpretations is attempted with the ultimate aim of a full definition of interstellar grain optics.
Greenberg, J. M.↗
Interstellar grains in museums
It is argued that carbonaceous chondrites, particularly of type I, are probably collections of interstellar grains which have been mildly transformed through exposure to higher than normal temperatures, resulting in a loss of volatile materials.
Cameron, A. G. W.↗
Interstellar CH and CH+ from the evaporation of grain mantles
Reexamination of a model originally suggested by Bates and Spitzer (1951) for interstellar molecule production by evaporation of grain mantles. It is shown that allowance for reactions involving CH(+), formerly ignored, remove the difficulties experienced by Bates and Spitzer. The essential features of CH and CH(+) observations in the directions of certain stars can be understood on the basis of this model.
Stecher, T. P.↗
Single-domain grain size limits for metallic iron
The theory of superparamagnetic (SP) threshold calculations and single-domain (SD) to nonuniform spin threshold calculations is considered. The SD upper grain size limit and the SP-to-SD threshold size are calculated. The size and shape criteria for the stable SD behavior of metallic iron have implications for lunar magnetism and the mechanism of iron-silicate fractionation in the solar nebula.
Butler, R. F.↗
Microwave resonance thermomagnetic analysis - A new method for characterizing fine-grained ferromagnetic constituents in lunar materials
Microwave resonance thermomagnetic analysis (MRTA) is the name given to a newly evolved technique for inferring the natures of fine-grained ferromagnetic constituents in lunar materials. Based on standard ferromagnetic resonance (FMR) procedures, the method makes use of the microwave skin effect for diagnosing the presence of metallic iron. Modelling experiments carried out on well-characterized iron and magnetitelike precipitates produced independently in simulated lunar glasses, coupled with published data for magnetite, provide a potential basis for detecting and discriminating between iron metal and ferric iron spinel, even when both are present in an unknown sample. Application of the technique to the lunar samples indicates the possible existence of magnetitelike phases in amounts up to about 0.3 wt% in soils from seven samples regions of the moon. These findings do not require any special geologic processes for their explanation, although some evidence supports the suggestion that fumarolic activity may have occurred in the lunar highlands.
Griscom, D. L.↗
Observation of iron-rich coating on lunar grains and a relation to low albedo
The outermost few atomic layers of lunar soil samples were studied by Auger spectroscopy and were found to contain in each case two to three times more iron than the mean bulk composition of the sample. The amount of excess iron is found to be closely correlated with the optical albedo in the manner that would be theoretically expected if the iron provided absorption centers. Crushed lunar rocks of similar mean composition, but lacking the extra iron coating of the soil grains, have a much higher albedo than most lunar soils sampled or observed on the lunar surface.
Gold, T.↗