29,724 research outputs found
The fifth international radiocarbon intercomparison (VIRI): An assessment of laboratory performance in stage 3
Proficiency testing is a widely used, international procedure common within the analytical chemistry community.
A proficiency trial (which VIRI is) often follows a standard protocol, including analysis that is typically based on zscores, with one key quantity, σp. From a laboratory intercomparison (sometimes called a proficiency trial), we hope to gain an assessment of accuracy (in this case, from dendro-dated samples), laboratory precision (from any duplicate samples), and generally, an overall measure of performance, including measurement variability and hence realistic estimates of uncertainty.
In addition, given our stated aim of creating an archive of reference materials, we also gain a determination of consensus values for new reference materials.
VIRI samples have been chosen to deliver these objectives and the sample ages included in the different stages, by design, spanned modern to background. With regard to pretreatment, some samples required intensive pretreatment (e.g. bone), while others required none (e.g. cellulose and humic acid). Sample size was not optimized, and indeed some samples were provided solely for accelerator mass spectrometry (AMS) measurement. In this sense, VIRI presented a more challenging exercise than previous intercomparisons, since by its design in stages, one can explore improvements (or deteriorations) over time in laboratory performance. At each stage, more than 50 laboratories have participated, with an increasing demographic shift towards more AMS and fewer radiometric laboratories
Metric of a tidally distorted, nonrotating black hole
The metric of a tidally distorted, nonrotating black hole is presented in a
light-cone coordinate system that penetrates the event horizon and possesses a
clear geometrical meaning. The metric is expressed as an expansion in powers of
r/R << 1, where r is a measure of distance from the black hole and R is the
local radius of curvature of the external spacetime; this is assumed to be much
larger than M, the mass of the black hole. The metric is calculated up to a
remainder of order (r/R)^4, and it depends on a family of tidal gravitational
fields which characterize the hole's local environment. The coordinate system
allows an easy identification of the event horizon, and expressions are derived
for its surface gravity and the rates at which the tidal interaction transfers
mass and angular momentum to the black hole.Comment: 4 pages. Final version, as it will appear in Physical Review Letter
Testing a Simplified Version of Einstein's Equations for Numerical Relativity
Solving dynamical problems in general relativity requires the full machinery
of numerical relativity. Wilson has proposed a simpler but approximate scheme
for systems near equilibrium, like binary neutron stars. We test the scheme on
isolated, rapidly rotating, relativistic stars. Since these objects are in
equilibrium, it is crucial that the approximation work well if we are to
believe its predictions for more complicated systems like binaries. Our results
are very encouraging.Comment: 9 pages (RevTeX 3.0 with 6 uuencoded figures), CRSR-107
Low Frequency Gravitational Waves from Black Hole MACHO Binaries
Nakamura, Sasaki, Tanaka, and Thorne have recently estimated the initial
distribution of binary MACHOs in the galactic halo assuming that the MACHOs are
primordial half solar mass black holes, and considered their coalescence as a
possible source for ground-based interferometer gravitational wave detectors
such as LIGO. Evolving their binary distribution forward in time to the
present, the low-frequency (10^{-5} < f < 10^{-1} Hz) spectrum of gravitational
waves associated with such a population of compact binaries is calculated. The
resulting gravitational waves would form a strong stochastic background in
proposed space interferometers such as LISA and OMEGA. Low frequency
gravitational waves are likely to become a key tool for determining the
properties of binaries within the dark MACHO population.Comment: 8 pages + 2 ps figures; AASTe
Explicating the role of partnerships in changing the health and well-being of local communities: a profile of neighbourhood renewal activity focused on promoting health and well-being in Salford and the north west region and the north east of England
This scoping and mapping report is one of three outputs from a project: Explicating the role of partnerships in
changing the health and well-being of local communities, one of a number of projects in a larger Higher Education Funding Council Strategic Development Fund project ( HEFCE )
entitled: Urban Regeneration: Making a Difference. This was a collaborative venture between Manchester Metropolitan University, Northumbria University, University of Salford and
University of Central Lancashire. Bradford University was an affiliated partner
Sellafield-derived anthropogenic C-14 in the marine intertidal environment of the NE Irish Sea
The intertidal biota from Parton beach, close to the Sellafield nuclear fuel reprocessing plant, were all found to be enriched in radiocarbon relative to ambient background. The degree of enrichment appears to reflect the positions of the biota in the food chain once the dilution in seaweed from atmospheric uptake is taken into account. Close to the low-water mark, the order was mussels gt limpets gt anemones congruent to winkles gt seaweed. The same order was observed close to the high-water mark, except that anemones were absent from this area. The activities in the biogeochemical fractions of the water column reflect the fact that discharges are primarily in the form of dissolved inorganic carbon (DIC), which is subsequently transferred to the particulate organic carbon (POC) and, to a lesser extent, the dissolved organic carbon (DOC), and finally, the particulate inorganic carbon (PIC). Analysis of intertidal sediment suggests that there is likely to be a gradual increase in the specific activity of C-14 in the inorganic component of this material as Sellafield contaminated organisms die and their shells are ground down by natural processes
Quasi-circular Orbits for Spinning Binary Black Holes
Using an effective potential method we examine binary black holes where the
individual holes carry spin. We trace out sequences of quasi-circular orbits
and locate the innermost stable circular orbit as a function of spin. At large
separations, the sequences of quasi-circular orbits match well with
post-Newtonian expansions, although a clear signature of the simplifying
assumption of conformal flatness is seen. The position of the ISCO is found to
be strongly dependent on the magnitude of the spin on each black hole. At close
separations of the holes, the effective potential method breaks down. In all
cases where an ISCO could be determined, we found that an apparent horizon
encompassing both holes forms for separations well inside the ISCO.
Nevertheless, we argue that the formation of a common horizon is still
associated with the breakdown of the effective potential method.Comment: 13 pages, 10 figures, submitted to PR
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