18,558 research outputs found
Artificial meteor ablation studies
Artificial meteor ablation was performed on natural minerals, composed predominately of magnetite and hematite, using an arc heated plasma stream of air. Analysis of the ablated debris indicated most was composed of two or more minerals. The more volatile elements were depleted and the relative abundance of Fe increased as a result of both volatile depletion and a reduction in its oxidation state. Hematite was converted to magnetite in the ablation zone, and quartz and apatite minerals were converted to an Fe-rich glass consisting of varying amounts of Si, P, Cl, and Ca, depending upon the accessory minerals available at the time of melting. Artificially created ablation products from iron oxides exhibited unique properties depending on the composition of the original material and the environmental conditions of formation. In addition to the accepted elemental criteria, these properties were morphologic characteristics, textural parameters, and the existence of metastable minerals
Remote estimation of soil moisture
Two methods under consideration for making remote estimates of soil moisture involve measurements made in electromagnetic spectral region of 0.4 to 14.0 micrometers: (1) spectral reflectance, (2) soil temperature
An Approximation to the Likelihood Function for Band-Power Estimates of CMB Anisotropies
Band-power estimates of cosmic microwave background fluctuations are now
routinely used to place constraints on cosmological parameters. For this to be
done in a rigorous fashion, the full likelihood function of band-power
estimates must be employed. Even for Gaussian theories, this likelihood
function is not itself Gaussian, for the simple reason that band-powers measure
the {\em variance} of the random sky fluctuations. In the context of Gaussian
sky fluctuations, we use an ideal situation to motivate a general form for the
full likelihood function from a given experiment. This form contains only two
free parameters, which can be determined if the 68% and 95% confidence
intervals of the true likelihood function are known. The ansatz works
remarkably well when compared to the complete likelihood function for a number
of experiments. For application of this kind of approach, we suggest that in
the future both 68% and 95% (and perhaps also the 99.7%) confidence intervals
be given when reporting experimental results.Comment: Published versio
Problems associated with operations and measurement in cryogenic wind tunnels
Cryogenic wind tunnel T'3 under continuous blower operation has been the object of improvements and the installation of auxiliary equipment, dealing in particular with the enlargement of the liquid nitrogen injection reservoir and the hook-up to a fast data acquisition system. Following a brief description of the installation and its functioning, we present the main experimental techniques and the instrumentation used in the cryogenic environment
Artificial meteor ablation studies: Olivine
Artificial meteor ablation was performed on a Mg-rich olivine sample using an arc-heated plasma of ionized air. Experimental conditions simulated a meteor traveling about 12 km/sec at an altitude of 70 km. The mineral content of the original olivine sample was 98% olivine (including traces of olivine alteration products) and 2% chromite. Forsterite content of the original olivine was Fo-89. After ablation, the forsterite content had increased to Fo-94 in the recrystallized olivine. In addition, lamella-like intergrowths of magnetite were prevalent constituents. Wherever magnetite occurred, there was an increase in Mg and a corresponding decrease in Fe for the recrystallized olivine. The Allende fusion crust consisted of a recrystallized olivine, which was more Mg-rich and Fe-deficient than the original meteorite's olivine, and abundant magnetite grains. Although troilite and pentlandite were the common opaque mineral constituents in this meteorite, magnetite was the principal opaque mineral found in the fusion crust
Are the stratospheric dust particles meteor ablation debris or interplanetary dust?
Natural and laboratory created fusion crusts and debris from artificial meteor samples were used to develop criteria for recognizing meteor ablation debris in a collection of 5 to 50 micron particles from the stratosphere. These laboratory studies indicate that meteor ablation debris from nickel-iron meteoroids produce spherules containing taenite, wuestite, magnetite, and hematite. These same studies also indicate that ablation debris from chondritic meteoroids produce spheres and fragmentary debris. The spheres may be either silicate rich, containing zoned olivine, magnetite, and glass, or sulfide rich, containing iron oxides (e.g., magnetite, wuestite) and iron sulfides (e.g., pyrrhotite, pentlandite). The fragmentary debris may be either fine-grained aggregates of olivine, magnetite, pyroxene, and occasionally pyrrhotite (derived from the meteorite matrix) or individual olivine and pyroxene grains (derived from meteorite inclusions)
Case records of the Massachusetts General Hospital. Case 1-2014. A 32-year-old man with loss of vision and a rash
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