67,619 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
Fully Constrained Majorana Neutrino Mass Matrices Using
In 2002, two neutrino mixing ansatze having trimaximally-mixed middle
() columns, namely tri-chi-maximal mixing () and
tri-phi-maximal mixing (), were proposed. In 2012, it was
shown that with as well as
with leads to the solution,
, consistent with the
latest measurements of the reactor mixing angle, . To obtain
and
, the type~I see-saw
framework with fully constrained Majorana neutrino mass matrices was utilised.
These mass matrices also resulted in the neutrino mass ratios,
.
In this paper we construct a flavour model based on the discrete group
and obtain the aforementioned results. A Majorana neutrino
mass matrix (a symmetric matrix with 6 complex degrees of freedom)
is conveniently mapped into a flavon field transforming as the complex 6
dimensional representation of . Specific vacuum alignments
of the flavons are used to arrive at the desired mass matrices.Comment: 20 pages, 1 figure. arXiv admin note: substantial text overlap with
arXiv:1402.085
Deviations from Tribimaximal Neutrino Mixing using a Model with Symmetry
We present a model of neutrino mixing based on the flavour group
in order to account for the observation of a non-zero reactor mixing angle
(). The model provides a common flavour structure for the
charged-lepton and the neutrino sectors, giving their mass matrices a
`circulant-plus-diagonal' form. Mass matrices of this form readily lead to
mixing patterns with realistic deviations from tribimaximal mixing, including
non-zero . With the parameters constrained by existing
measurements, our model predicts an inverted neutrino mass hierarchy. We obtain
two distinct sets of solutions in which the atmospheric mixing angle lies in
the first and the second octants. The first (second) octant solution predicts
the lightest neutrino mass, ()
and the phase, (), offering the possibility of large observable violating
effects in future experiments.Comment: 9 pages, 3 figure
Unifying metastasis--Integrating intravasation, circulation and end organ colonization
Recent technological advances that have enabled the measurement of circulating tumour cells (CTCs) in patients have spurred interest in the circulatory phase of metastasis. Techniques that do not solely rely on a blood sample allow substantial biological interrogation beyond simply counting CTCs
Examining the inherent variability in ΔR: New methods of presenting ΔR values and implications for MRE studies
The dynamics of dark solitons in a trapped superfluid Fermi gas
We study soliton oscillations in a trapped superfluid Fermi gas across the
Bose-Einstein condensate to Bardeen-Cooper-Schrieffer (BEC-BCS) crossover. We
derive an exact equation relating the phase jump across the soliton to its
energy, and hence obtain an expression for the soliton period. Our analytic
approach is supported by simulations of the time-dependent Bogoliubov-de Gennes
equations, which show that the period dramatically increases as the soliton
becomes shallower on the BCS side of the resonance. Finally, we propose an
experimental protocol to test our predictions.Comment: 5 pages, 4 figure
Gamma rays from ultracompact primordial dark matter minihalos
Ultracompact minihalos have recently been proposed as a new class of dark
matter structure. These minihalos would be produced by phase transitions in the
early Universe or features in the inflaton potential, and constitute
non-baryonic massive compact halo objects (MACHOs) today. We examine the
prospect of detecting ultracompact minihalos in gamma-rays if dark matter
consists of self-annihilating particles. We compute present-day fluxes from
minihalos produced in the electron-positron annihilation epoch, and the QCD and
electroweak phase transitions in the early Universe. Even at a distance of 100
pc, minihalos produced during the electron-positron annihilation epoch should
be eminently detectable today, either by the Fermi satellite, current Air
Cherenkov telescopes, or even in archival EGRET data. Within ~1 pc, minihalos
formed in the QCD phase transition would have similar predicted fluxes to the
dwarf spheroidal galaxies targeted by current indirect dark matter searches, so
might also be detectable by present or upcoming experiments.Comment: 5 pages, 3 figures. Minor update to match published version of
erratu
Active damping application to the shuttle RMS
Control Structure Interaction (CSI) is a relatively new technology developed over the last 10 to 15 years for application to large flexible space vehicles. The central issue is recognition that high performance control systems necessary for good spacecraft performance may adversely interact with the dynamics of the spacecraft structures, a problem increasingly aggravated by the large size and reduced stiffness of modern spacecraft structural designs. The CSI analysis and design methods were developed to avoid interactions while maintaining spacecraft performance without exceeding structural capabilities, but they remain largely unvalidated by hardware experiments or demonstrations, particularly in-space flight demonstrations. One recent proposal for a low cost flight validation of CSI technology is to demonstrate active damping augmentation of the Space Shuttle Remote Manipulator System (RMS). An analytical effort to define the potential for such an active damping augmentation demonstration to improve the structural dynamic response of the RMS following payload maneuvers is described. It is hoped that this study will lead to an actual inflight CSI test with the RMS using existing shuttle hardware to the maximum extent possible. By using the existing hardware, the flight demonstration results may eventually be of direct benefit to actual Space Shuttle RMS operations, especially during the construction of the Space Station Freedom
JPL Ephemeris Tapes E9510, E9511, and E9512
The first issue of JPL Ephemeris Tapes is described. These tapes carry the positions and velocities of the planets and of the Moon, plus nutations and nutation rates in longitude and obliquity, together with second and fourth modified differences, for the interval December 30, 1949, to January 5, 2000
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