5,569 research outputs found
Isobar-free neon isotope measurements of flux-fused potential reference minerals on a Helix-MC-Plus^(10K) mass spectrometer
This work presents new analytical techniques for extraction and analysis of neon from a suite of different mineral phases, including quartz, pyroxene, hematite, apatite, zircon, topaz, and fluorite. Neon was quantitatively extracted at 1100 °C from all of these minerals using an in-vacuum lithium borate-flux fusion technique. Evolved neon was purified using a cryogenic method capable of separating Ne from He present in abundances ~8 orders of magnitude higher, typical of samples carrying nucleogenic/radiogenic noble gases. The purified neon was measured on a Helix-MC-Plus^(10K) mass spectrometer that permits isobar-free measurement of all three neon isotopes. When operated at its highest mass resolving power (MRP) of ~10,300, the shoulder representing solely ²²Ne on the low mass-side of the ²²Ne-CO₂⁺² doublet is wide enough to permit measurement of isobar free ²²Ne. Operating in this mode comes with the penalty of a 50% reduction in neon sensitivity. Coupled with a mathematical isobar-stripping method, this approach excludes 99.5% of the CO₂⁺² while still collecting >99% of the ²²Ne beam. Routine edge-centering on the dynamic CO₂⁺² peak prior to introduction of a sample permits rapid and robust relocation of the desired measure point in the mass spectrum.
Cosmogenic ²¹Ne and ²²Ne concentrations obtained using these methods on the Cronus-A quartz and Cronus-P pyroxene international reference materials are in excellent agreement with previous work or expectations. Similarly, the concentration of nucleogenic ²¹Ne and ²²Ne in Durango apatite and the CIT hematite standard agree well with previous work. Durango apatite has notable heterogeneity in neon concentrations, consistent with previous observations of heterogeneous He, U and Th concentrations in this apatite. Nucleogenic neon concentrations are also presented for previously unstudied minerals including a Sri Lanka zircon (SLC), a topaz from the Imperial Topaz mine in Brazil (ITP1), and a fluorite (W-90) from New Hampshire. Taken together this set of potential reference minerals and the associated dataset provide a starting point for intercalibration among multiple mineral phases carrying ²¹Ne and ²²Ne of cosmogenic or nucleogenic origin
Graphics and composite material computer program enhancements for SPAR
User documentation is provided for additional computer programs developed for use in conjunction with SPAR. These programs plot digital data, simplify input for composite material section properties, and compute lamina stresses and strains. Sample problems are presented including execution procedures, program input, and graphical output
Ionospheric E-region Irregularities Produced by Non-linear Coupling of Unstable Plasma Waves
Ionospheric E region irregularities produced by nonlinear coupling of unstable plasma wave
Spin-2 Amplitudes in Black-Hole Evaporation
Quantum amplitudes for gravitational-wave perturbations of
Einstein/scalar collapse to a black hole are treated by analogy with
Maxwell perturbations. The spin-2 perturbations split into parts with odd and
even parity. We use the Regge-Wheeler gauge; at a certain point we make a gauge
transformation to an asymptotically-flat gauge, such that the metric
perturbations have the expected falloff behaviour at large radii. By analogy
with , for natural 'coordinate' variables are given by the magnetic
part of the Weyl tensor, which can be taken as boundary
data on a final space-like hypersurface . For simplicity, we take the
data on the initial surface to be exactly spherically-symmetric. The
(large) Lorentzian proper-time interval between and ,
measured at spatial infinity, is denoted by . We follow Feynman's
prescription and rotate into the complex: , for . The corresponding complexified {\it
classical} boundary-value problem is expected to be well-posed. The Lorentzian
quantum amplitude is recovered by taking the limit as . For
boundary data well below the Planck scale, and for a locally supersymmetric
theory, this involves only the semi-classical amplitude , where denotes the second-variation classical
action. The relations between the and natural boundary data,
involving supersymmetry, are investigated using 2-component spinor language in
terms of the Maxwell field strength and the Weyl spinor
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