Measurement of the lunar neutron density profile

An in situ measurement of the lunar neutron density from 20 to 400 g/sq cm depth between the lunar surface was made by the Apollo 17 Lunar Neutron Probe Experiment using particle tracks produced by the B10(n, alpha)Li7 reaction. Both the absolute magnitude and depth profile of the neutron density are in good agreement with past theoretical calculations. The effect of cadmium absorption on the neutron density and in the relative Sm149 to Gd157 capture rates obtained experimentally implies that the true lunar Gd157 capture rate is about one half of that calculated theoretically

Simultaneous dual-element analyses of refractory metals in naturally occurring matrices using resonance ionization of sputtered atoms

The combination of secondary neutral mass spectrometry (SNMS) and resonance ionization spectroscopy (RIS) has been shown to be a powerful tool for the detection of low levels of elemental impurities in solids. Drawbacks of the technique have been the laser-repetition-rate-limited, low duty cycle of the analysis and the fact that RIS schemes are limited to determinations of a single element. These problems have been addressed as part of an ongoing program to explore the usefulness of RIS/SNMS instruments for the analysis of naturally occurring samples. Efficient two-color, two-photon (1+1) resonance ionization schemes were identified for Mo and for four platinum-group elements (Ru, Os, Ir, and Re). Careful selection of the ionization schemes allowed Mo or Ru to be measured simultaneously with Re, Os, or Ir, using two tunable dye lasers and an XeCl excimer laser. Resonance frequencies could be switched easily under computer control, so that all five elements can be rapidly analyzed. In situ measurements of these elements in metal grains from five meteorites were conducted. From the analyses, estimates of the precision and the detection limit of the instrument were made. The trade-off between lower detection limits and rapid multielement RIS analyses is discussed

Origin of Thorium/Uranium Variations in Carbonaceous Chondrites

Thorium-, U-, and Pb-isotopic analyses of a wide variety of planetary materials show that Th/U ratio (by weight) varies from 3.5 to 4.2. It is generally believed that chondritic meteorites contain refractory lithophile elements in a relative proportions close to solar, i.e., CI chondrites [1]. Surprisingly, a number of analyses of different types of carbonaceous chondrites show a large (at least a factor of 3) scatter in Th/U measurements [2]. The widest spread in Th/U is observed in the most primitive materials, CI-type chondrites. Cosmochronological models rely on the precise knowledge of the average solar system Th/U, therefore it is important to achieve a better understanding of the actinide chemistry in chondrites, e.g., what causes the variations in Th/U ratio

Apatite Control of Choncritic Actinide Chemistry?

The solar system Th/U is regarded as about 3.7, and ratios close to this are directly measured in a wide variety of planetary materials. Consequently, given that chondritic composition is regarded as solar for refractory lithophile elements, it is surprising that some ordinary chondrites show high ratios (6-6.5). We set out to understand the origin and implications of these anomalies, first by establishing that we had samples of the anomalous material using high accuracy isotope dilution, ICPMS measurements ofTh/U. Our three samples of Glatton (L6) were not anomalous (Th/U from 3.71 to 3.84), but for 12, typically gram-sized, samples of Harleton (L6) we find a range of Th/U from 2.5 to 6, a greater range of Th/U in one meteorite than in all previous ordinary chondrite analyses. Moreover, Fig. 1 shows (l) the Th/U variations linearly correlate with 11 U, suggesting two component mixing; (2) other literature analyses follow the Harleton trend

An analysis of the limitations of blind signal separation application with speech

Blind Signal Separation (BSS) techniques are commonly employed in the separation of speech signals, using Independent Component Analysis (ICA) as the criterion for separation. This paper investigates the viability of employing ICA for real-time speech separation (where short frame sizes are the norm). The relationship between the statistics of speech and the assumption of statistical independence (at the core of ICA) is examined over a range of frame sizes. The investigation confirms that statistical independence is not a valid assumption for speech when divided into the short frames appropriate to real-time separation. This is primarily due to the quasi-stationary nature of speech over the temporal short term. We conclude that employing ICA for real-time speech separation will always result in limited performance due to a fundamental failure to meet the strict assumptions of ICA

The Knudsen temperature jump and the Navier-Stokes hydrodynamics of granular gases driven by thermal walls

Thermal wall is a convenient idealization of a rapidly vibrating plate used for vibrofluidization of granular materials. The objective of this work is to incorporate the Knudsen temperature jump at thermal wall in the Navier-Stokes hydrodynamic modeling of dilute granular gases of monodisperse particles that collide nearly elastically. The Knudsen temperature jump manifests itself as an additional term, proportional to the temperature gradient, in the boundary condition for the temperature. Up to a numerical pre-factor of order unity, this term is known from kinetic theory of elastic gases. We determine the previously unknown numerical pre-factor by measuring, in a series of molecular dynamics (MD) simulations, steady-state temperature profiles of a gas of elastically colliding hard disks, confined between two thermal walls kept at different temperatures, and comparing the results with the predictions of a hydrodynamic calculation employing the modified boundary condition. The modified boundary condition is then applied, without any adjustable parameters, to a hydrodynamic calculation of the temperature profile of a gas of inelastic hard disks driven by a thermal wall. We find the hydrodynamic prediction to be in very good agreement with MD simulations of the same system. The results of this work pave the way to a more accurate hydrodynamic modeling of driven granular gases.Comment: 7 pages, 3 figure

Zoning patterns of Fe and V in spinel from a type B Ca-Al-rich inclusion: Constraints on subsolidus thermal history

We obtained two-dimensional concentration maps for the minor elements Fe and V in 21 spinel crystals in the Allende type B1 inclusion TS-34 with a 4–5 μm resolution. Locally high concentrations of Fe occur along at least one edge of the spinels and decrease toward the center of the grains. Enrichment in V can also occur along edges or at corners. In general, there is no overall correlation of the Fe and V distributions, but in local regions of two grains, the V and Fe distributions are correlated, strongly suggesting a local source for both elements. In these two grains, opaque assemblages are present that appear to locally control the V distributions. This, coupled with previous work, suggests that prior to alteration, TS-34 contained V-rich metal. Oxidation of this metal during alteration can account for the edge/corner V enrichments, but provide only minor FeO contributions, explaining the overall lack of correlation between Fe and V. Most of the FeO appears to have been externally introduced along spinel boundaries during alteration. These alteration phases served as sources for diffusion of FeO into spinel. FeO distributions in spinel lead to a mean attenuation length of ~8 μm and, using literature diffusion coefficients in isothermal and exponential cooling approximations for peak temperatures in the range 600–700°C, this leads to a time scale for calcium-aluminum-rich inclusion (CAI) alteration in the range of decades to centuries

Blow-up of the hyperbolic Burgers equation

The memory effects on microscopic kinetic systems have been sometimes modelled by means of the introduction of second order time derivatives in the macroscopic hydrodynamic equations. One prototypical example is the hyperbolic modification of the Burgers equation, that has been introduced to clarify the interplay of hyperbolicity and nonlinear hydrodynamic evolution. Previous studies suggested the finite time blow-up of this equation, and here we present a rigorous proof of this fact