7,797 research outputs found
Radioactive Iron Rain: Transporting Fe in Supernova Dust to the Ocean Floor
Several searches have found evidence of Fe deposition, presumably from
a near-Earth supernova (SN), with concentrations that vary in different
locations on Earth. This paper examines various influences on the path of
interstellar dust carrying Fe from a SN through the heliosphere, with
the aim of estimating the final global distribution on the ocean floor. We
study the influences of magnetic fields, angle of arrival, wind and ocean
cycling of SN material on the concentrations at different locations. We find
that the passage of SN material through the mesosphere/lower thermosphere (MLT)
is the greatest influence on the final global distribution, with ocean cycling
causing lesser alteration as the SN material sinks to the ocean floor. SN
distance estimates in previous works that assumed a uniform distribution are a
good approximation. Including the effects on surface distributions, we estimate
a distance of pc for a SN progenitor. This
is consistent with a SN occurring within the Tuc-Hor stellar group 2.8
Myr ago with SN material arriving on Earth 2.2 Myr ago. We note that the
SN dust retains directional information to within through its
arrival in the inner Solar System, so that SN debris deposition on inert bodies
such as the Moon will be anisotropic, and thus could in principle be used to
infer directional information. In particular, we predict that existing lunar
samples should show measurable Fe differences.Comment: 18 pages, 8 figures. Comments welcom
Astrophysical Shrapnel: Discriminating Among Near-Earth Stellar Explosion Sources of Live Radioactive Isotopes
We consider the production and deposition on Earth of isotopes with
half-lives in the range 10 to 10 years that might provide
signatures of nearby stellar explosions, extending previous analyses of
Core-Collapse Supernovae (CCSNe) to include Electron-Capture Supernovae
(ECSNe), Super-Asymptotic Giant Branch (SAGBs) stars, Thermonuclear/Type Ia
Supernovae (TNSNe), and Kilonovae/Neutron Star Mergers (KNe). We revisit
previous estimates of the Fe and Al signatures, and extend these
estimates to include Pu and Mn. We discuss interpretations of
the Fe signals in terrestrial and lunar reservoirs in terms of a nearby
stellar ejection ~2.2 Myr ago, showing that (i) the Fe yield rules out
the TNSN and KN interpretations, (ii) the Fe signals highly constrain a
SAGB interpretation but do not completely them rule out, (iii) are consistent
with a CCSN origin, and (iv) are highly compatible with an ECSN interpretation.
Future measurements could resolve the radioisotope deposition over time, and we
use the Sedov blast wave solution to illustrate possible time-resolved
profiles. Measuring such profiles would independently probe the blast
properties including distance, and would provide additional constraints the
nature of the explosion.Comment: 38 pages, 6 figures. Comments welcom
Bell's Theorem from Moore's Theorem
It is shown that the restrictions of what can be inferred from
classically-recorded observational outcomes that are imposed by the no-cloning
theorem, the Kochen-Specker theorem and Bell's theorem also follow from
restrictions on inferences from observations formulated within classical
automata theory. Similarities between the assumptions underlying classical
automata theory and those underlying universally-unitary quantum theory are
discussed.Comment: 12 pages; to appear in Int. J. General System
A model-theoretic interpretation of environmentally-induced superselection
Environmentally-induced superselection or "einselection" has been proposed as
an observer-independent mechanism by which apparently classical systems
"emerge" from physical interactions between degrees of freedom described
completely quantum-mechanically. It is shown that einselection can only
generate classical systems if the "environment" is assumed \textit{a priori} to
be classical; einselection therefore does not provide an observer-independent
mechanism by which classicality can emerge from quantum dynamics. Einselection
is then reformulated in terms of positive operator-valued measures (POVMs)
acting on a global quantum state. It is shown that this re-formulation enables
a natural interpretation of apparently-classical systems as virtual machines
that requires no assumptions beyond those of classical computer science.Comment: 15 pages, 1 figure; minor correction
Can Galactic Cosmic Rays Account for Solar 6Li Without Overproducing Gamma Rays?
Cosmic-ray interactions with interstellar gas produces both 6Li, which
accumulates in the interstellar medium (ISM), and mesons, which decay
to gamma-rays which propagate throughout the cosmos. Local 6Li abundances and
extragalactic gamma-rays thus have a common origin which tightly links them. We
exploit this connection to use gamma-ray observations to infer the contribution
to 6Li nucleosynthesis by standard Galactic cosmic-ray (GCR) interactions with
the ISM. Our calculation uses a carefully propagated cosmic-ray spectrum and
accounts for 6Li production from both fusion reactions () as well as from spallation channels ({p,\alpha+CNO \to ^6Li). We find
that although extreme assumptions yield a consistent picture, more realistic
ones indicate that solar 6Li cannot be produced by standard GCRs alone without
overproducing the hadronic gamma rays. Implications for the primordial 6Li
production by decaying dark matter and cosmic rays from cosmological structure
formation are discussed. Upcoming gamma-ray observations by GLAST will be
crucial for determining the resolution of this problem.Comment: 4 pages, 1 figure To be published in ApJ
PRODUCER VALUATION OF HERD BULL CHARACTERISTICS
This study evaluates the importance of certain bull characteristics (disposition, EPD's, conformation, etc.) on a cow-calf producer's herd bull purchase decision. Data were collected from the Auburn University Bull Test Sale from 1997 to 2004. A total of 260 buyers purchased a total of 370 bulls during this six-year period. These buyers will be surveyed to determine demographics, farm characteristics, and the importance of factors influencing their bull purchase decision. A hedonic pricing model will be utilized to determine the value that individual buyers place on various factors or bull characteristics when purchasing a bull.Livestock Production/Industries,
Chemical Abundance Constraints on White Dwarfs as Halo Dark Matter
We examine the chemical abundance constraints on a population of white dwarfs
in the Halo of our Galaxy. We are motivated by microlensing evidence for
massive compact halo objects (Machos) in the Galactic Halo, but our work
constrains white dwarfs in the Halo regardless of what the Machos are. We focus
on the composition of the material that would be ejected as the white dwarfs
are formed; abundance patterns in the ejecta strongly constrain white dwarf
production scenarios. Using both analytical and numerical chemical evolution
models, we confirm that very strong constraints come from Galactic Pop II and
extragalactic carbon abundances. We also point out that depending on the
stellar model, significant nitrogen is produced rather than carbon. The
combined constraints from C and N give from
comparison with the low C and N abundances in the Ly forest. We note,
however, that these results are subject to uncertainties regarding the
nucleosynthesis of low-metallicity stars. We thus investigate additional
constraints from D and He, finding that these light elements can be kept
within observational limits only for \Omega_{WD} \la 0.003 and for a white
dwarf progenitor initial mass function sharply peaked at low mass (2).
Finally, we consider a Galactic wind, which is required to remove the ejecta
accompanying white dwarf production from the galaxy. We show that such a wind
can be driven by Type Ia supernovae arising from the white dwarfs themselves,
but these supernovae also lead to unacceptably large abundances of iron. We
conclude that abundance constraints exclude white dwarfs as Machos. (abridged)Comment: Written in AASTeX, 26 pages plus 4 ps figure
Neutron activation analysis traces copper artifacts to geographical point of origin
Impurities remaining in the metallic copper are identified and quantified by spectrographic and neutron activation analysis. Determination of the type of ore used for the copper artifact places the geographic point of origin of the artifact
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