45,427 research outputs found
Antarctic iron meteorites: An unexpectedly high proportion of falls of unusual interest
The inhabited and explored areas of Earth have contributed 725 iron meteorites, accounting for 28% of the 2611 authenticated meteorites known of all types. Observed fall statistics give a much different view of relative abundance. The 42 historic iron meteorite falls spanning 230 years suggests a frequency of one fall per 5.6 years and represents only 4.9% of the total 853 known falls. Antarctic iron meteorite recoveries offer promise of providing a new perspective on the influx problem. At least 42 iron meteorite specimens were found during the last 25 years by various field teams working in Antarctica. Most of these specimens were not described in detail, but the available data indicates that 21 separate falls are represented, 50% of the number of recovered specimens. Twelve of the 21 falls were both structurally classified and placed into chemical groups. They are listed in order of increasing structural complexity and/or Ni content
A Bayesian test for the appropriateness of a model in the biomagnetic inverse problem
This paper extends the work of Clarke [1] on the Bayesian foundations of the
biomagnetic inverse problem. It derives expressions for the expectation and
variance of the a posteriori source current probability distribution given a
prior source current probability distribution, a source space weight function
and a data set. The calculation of the variance enables the construction of a
Bayesian test for the appropriateness of any source model that is chosen as the
a priori infomation. The test is illustrated using both simulated
(multi-dipole) data and the results of a study of early latency processing of
images of human faces.
[1] C.J.S. Clarke. Error estimates in the biomagnetic inverse problem.
Inverse Problems, 10:77--86, 1994.Comment: 13 pages, 16 figures. Submitted to Inverse Problem
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Free healthy breakfasts in primary schools: A cluster randomised controlled trial of a policy intervention in Wales, UK
Objective: The present study evaluated the impact of a national school programme of universal free healthy breakfast provision in Wales, UK.
Design: A cluster randomised controlled trial with repeated cross-sectional design and a 12-month follow-up. Primary outcomes were breakfast skipping, breakfast diet and episodic memory. Secondary outcomes were frequency of eating breakfast at home and at school, breakfast attitudes, rest-of-day diet and class behaviour.
Setting: Primary schools in nine local education authority areas.
Subjects: A total of 4350 students (aged 9–11 years) at baseline and 4472 at follow-up in 111 schools.
Results: Students in intervention schools reported significantly higher numbers of healthy food items consumed at breakfast and more positive attitudes towards breakfast eating at 12 months. Parents in intervention schools reported significantly higher rates of consumption of breakfast at school and correspondingly lower rates of breakfast consumption at home. No other significant differences were found.
Conclusions: The intervention did not reduce breakfast skipping; rather, pupils substituted breakfast at home for breakfast at school. However, there were improvements in children’s nutritional intake at breakfast time, if not the rest of the day, and more positive attitudes to breakfast, which may have implications for life-course dietary behaviours. There was no impact on episodic memory or classroom behaviour, which may require targeting breakfast skippers
Inhomogeneous Dust Collapse in 5D Einstein-Gauss-Bonnet Gravity
We consider a Lemaitre - Tolman - Bondi type space-time in Einstein gravity
with the Gauss-Bonnet combination of quadratic curvature terms, and present
exact solution in closed form. It turns out that the presence of the coupling
constant of the Gauss-Bonnet terms alpha > 0 completely changes the causal
structure of the singularities from the analogous general relativistic case.
The gravitational collapse of inhomogeneous dust in the five-dimensional
Gauss-Bonnet extended Einstein equations leads to formation of a massive, but
weak, timelike singularity which is forbidden in general relativity.
Interestingly, this is a counterexample to three conjecture viz. cosmic
censorship conjecture, hoop conjecture and Seifert's conjecture.Comment: 8 Latex Pages, 2 EPS figure
Cauchy-characteristic Evolution of Einstein-Klein-Gordon Systems: The Black Hole Regime
The Cauchy+characteristic matching (CCM) problem for the scalar wave equation
is investigated in the background geometry of a Schwarzschild black hole.
Previously reported work developed the CCM framework for the coupled
Einstein-Klein-Gordon system of equations, assuming a regular center of
symmetry. Here, the time evolution after the formation of a black hole is
pursued, using a CCM formulation of the governing equations perturbed around
the Schwarzschild background. An extension of the matching scheme allows for
arbitrary matching boundary motion across the coordinate grid. As a proof of
concept, the late time behavior of the dynamics of the scalar field is
explored. The power-law tails in both the time-like and null infinity limits
are verified.Comment: To appear in Phys. Rev. D, 9 pages, revtex, 5 figures available at
http://www.astro.psu.edu/users/nr/preprints.htm
Non-spherical collapse of a two fluid star
We obtain the analogue of collapsing Vaidya-like solution to include both a
null fluid and a string fluid, with a linear equation of state (), in non-spherical (plane symmetric and cylindrically symmetric) anti-de
Sitter space-timess. It turns out that the non-spherical collapse of two fluid
in anti-de Sitter space-times, in accordance with cosmic censorship, proceed to
form black holes, i.e., on naked singularity ever forms, violating hoop
conjecture.Comment: 7 pages, RevTeX 4, minor correction
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