2,383 research outputs found
Real-time video correlator
Device provides two-dimensional correlation of video data. Operation is reliable, accurate, and predictable
Optimal Image Reconstruction in Radio Interferometry
We introduce a method for analyzing radio interferometry data which produces
maps which are optimal in the Bayesian sense of maximum posterior probability
density, given certain prior assumptions. It is similar to maximum entropy
techniques, but with an exact accounting of the multiplicity instead of the
usual approximation involving Stirling's formula. It also incorporates an Occam
factor, automatically limiting the effective amount of detail in the map to
that justified by the data. We use Gibbs sampling to determine, to any desired
degree of accuracy, the multi-dimensional posterior density distribution. From
this we can construct a mean posterior map and other measures of the posterior
density, including confidence limits on any well-defined function of the
posterior map.Comment: 41 pages, 11 figures. High resolution figures 8 and 9 available at
http://www.astro.uiuc.edu/~bwandelt/SuttonWandelt200
Environmental science in Lincolnshire primary schools: a case study and survey
(1) An historical overview traces the start of concern for the
environment in the latter part of the 19th century through to
recent international conferences to discuss the importance and
implementation of environmental education at all levels. The
case is then put for the importance of a structured environmental
science scheme in primary education tailored to children's
development.
(2) A case study of a Lincolnshire primary school follows the
planning, building and utilisation of a school environmental
science area. It includes the development of an environmental
science curriculum and the production of suitable interpretative
materials and teaching aids. This is followed by an attempt
at a summative evaluation of its effect.
(3) The results of a questionnaire survey of Lincolnshire primary
schools to determine the present situation with regard to
environmental science practice, facilities, and provision are
presented. These are compared with a similar survey carried out
ten years previously. Minor differences are revealed but the
overall pattern of results indicates that there has been little
improvement in the intervening decade, and that a great deal of
work still needs to be done if environmental science in primary
schools is to be accorded its rightful position and importance
in the curriculum
Evaluation of matrix-assisted laser desorption ionisation time-of-flight mass spectrometry (MALDI-TOF MS) for the Identification of Group B Streptococcus.
Objective
Group B Streptococcus (GBS) is a leading cause of neonatal meningitis and sepsis worldwide. Intrapartum antibiotics given to women carrying GBS are an effective means of reducing disease in the first week of life. Rapid and reliable tests are needed to accurately identify GBS from these women for timely intrapartum antibiotic administration to prevent neonatal disease. Many laboratories now use matrix-assisted laser desorption ionisation time-of-flight mass spectrometry (MALDI-TOF MS) by direct plating or cell lysis for the identification of GBS isolates. The cell lysis step increases time to results for clinical samples and is more complex to perform. Therefore, we seek to evaluate the sensitivity and specificity of the quicker and more rapid direct plating method in identifying GBS.
Results
We directly compared swab isolates analysed by both direct plating and cell lysis method and demonstrated that direct plating has a sensitivity and specificity of 0.97 and 1, respectively, compared to an additional cell lysis step. We demonstrated that MALDI-TOF MS can be successfully used for batch processing by the direct plating method which saves time. These results are reassuring for laboratories worldwide who seek to identify GBS from swabs samples as quickly as possible
S and D-wave phase shifts in isospin-2 pi pi scattering from lattice QCD
The isospin-2 pi pi system provides a useful testing ground for determining
elastic hadron scattering parameters from finite-volume spectra obtained using
lattice QCD computations. A reliable determination of the excited state
spectrum of two pions in a cubic box follows from variational analysis of
correlator matrices constructed using a large basis of operators. A general
operator construction is presented which respects the symmetries of a
multi-hadron system in flight. This is applied to the case of pi pi and allows
for the determination of the scattering phase-shifts at a large number of
kinematic points, in both S-wave and D-wave, within the elastic region. The
technique is demonstrated with a calculation at a pion mass of 396 MeV, where
the elastic scattering is found to be well described by a scattering length
parameterisation.Comment: Tables of little-group CGCs in ancillary file; v2: minor changes to
reflect published versio
Entanglement assisted alignment of reference frames using a dense covariant coding
We present a procedure inspired by dense coding, which enables a highly
efficient transmission of information of a continuous nature. The procedure
requires the sender and the recipient to share a maximally entangled state. We
deal with the concrete problem of aligning reference frames or trihedra by
means of a quantum system. We find the optimal covariant measurement and
compute the corresponding average error, which has a remarkably simple close
form. The connection of this procedure with that of estimating unitary
transformations on qubits is briefly discussed.Comment: 4 pages, RevTeX, Version to appear in PR
Representations of celestial coordinates in FITS
In Paper I, Greisen & Calabretta (2002) describe a generalized method for
assigning physical coordinates to FITS image pixels. This paper implements this
method for all spherical map projections likely to be of interest in astronomy.
The new methods encompass existing informal FITS spherical coordinate
conventions and translations from them are described. Detailed examples of
header interpretation and construction are given.Comment: Consequent to Paper I: "Representations of world coordinates in
FITS". 45 pages, 38 figures, 13 tables, aa macros v5.2 (2002/Jun). Both
papers submitted to Astronomy & Astrophysics (2002/07/19). Replaced to try to
get figure and table placement right (no textual changes
Ionospheric Power-Spectrum Tomography in Radio Interferometry
A tomographic method is described to quantify the three-dimensional
power-spectrum of the ionospheric electron-density fluctuations based on
radio-interferometric observations by a two-dimensional planar array. The
method is valid to first-order Born approximation and might be applicable to
correct observed visibilities for phase variations due to the imprint of the
full three-dimensional ionosphere. It is shown that not the ionospheric
electron density distribution is the primary structure to model in
interferometry, but its autocorrelation function or equivalent its
power-spectrum. An exact mathematical expression is derived that provides the
three dimensional power-spectrum of the ionospheric electron-density
fluctuations directly from a rescaled scattered intensity field and an incident
intensity field convolved with a complex unit phasor that depends on the w-term
and is defined on the full sky pupil plane. In the limit of a small field of
view, the method reduces to the single phase screen approximation. Tomographic
self-calibration can become important in high-dynamic range observations at low
radio frequencies with wide-field antenna interferometers, because a
three-dimensional ionosphere causes a spatially varying convolution of the sky,
whereas a single phase screen results in a spatially invariant convolution. A
thick ionosphere can therefore not be approximated by a single phase screen
without introducing errors in the calibration process. By applying a Radon
projection and the Fourier projection-slice theorem, it is shown that the
phase-screen approach in three dimensions is identical to the tomographic
method. Finally we suggest that residual speckle can cause a diffuse intensity
halo around sources, due to uncorrectable ionospheric phase fluctuations in the
short integrations, which could pose a fundamental limit on the dynamic range
in long-integration images.Comment: 8 pages; Accepted for publication in Ap
Romantic Partnerships and the Dispersion of Social Ties: A Network Analysis of Relationship Status on Facebook
A crucial task in the analysis of on-line social-networking systems is to
identify important people --- those linked by strong social ties --- within an
individual's network neighborhood. Here we investigate this question for a
particular category of strong ties, those involving spouses or romantic
partners. We organize our analysis around a basic question: given all the
connections among a person's friends, can you recognize his or her romantic
partner from the network structure alone? Using data from a large sample of
Facebook users, we find that this task can be accomplished with high accuracy,
but doing so requires the development of a new measure of tie strength that we
term `dispersion' --- the extent to which two people's mutual friends are not
themselves well-connected. The results offer methods for identifying types of
structurally significant people in on-line applications, and suggest a
potential expansion of existing theories of tie strength.Comment: Proc. 17th ACM Conference on Computer Supported Cooperative Work and
Social Computing (CSCW), 201
Bases in Lie and Quantum Algebras
Applications of algebras in physics are related to the connection of
measurable observables to relevant elements of the algebras, usually the
generators. However, in the determination of the generators in Lie algebras
there is place for some arbitrary conventions. The situation is much more
involved in the context of quantum algebras, where inside the quantum universal
enveloping algebra, we have not enough primitive elements that allow for a
privileged set of generators and all basic sets are equivalent. In this paper
we discuss how the Drinfeld double structure underlying every simple Lie
bialgebra characterizes uniquely a particular basis without any freedom,
completing the Cartan program on simple algebras. By means of a perturbative
construction, a distinguished deformed basis (we call it the analytical basis)
is obtained for every quantum group as the analytical prolongation of the above
defined Lie basis of the corresponding Lie bialgebra. It turns out that the
whole construction is unique, so to each quantum universal enveloping algebra
is associated one and only one bialgebra. In this way the problem of the
classification of quantum algebras is moved to the classification of
bialgebras. In order to make this procedure more clear, we discuss in detail
the simple cases of su(2) and su_q(2).Comment: 16 pages, Proceedings of the 5th International Symposium on Quantum
Theory and Symmetries QTS5 (July 22-28, 2007, Valladolid (Spain)
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