1,251 research outputs found
Fast algorithms for matching CCD images to a stellar catalogue
Two new algorithms are described for matching two dimensional coordinate
lists of point sources that are signifcantly faster than previous methods. By
matching rarely occurring triangles (or more complex shapes) in the two lists,
and by ordering searches by decreasing probability of success, it is
demonstrated that very few candidates need be considered to find a successful
match. Moreover, by immediately testing the suitability of a potential match
using an efficient mechanism, the need to process the entire candidate set is
avoided, yielding considerable performance improvements. Triangles are
described by a cosine metric that reduces the density of triangle space,
permitting efficient searches. An alternative shape characterization method
that reduces computational overhead in the construction phase is discussed. The
algorithms are tested on a set of 10 063 wide-field survey images, with
fields-of-view up to 4.8 x 3.6 deg, successfully matching 100% of the images in
a mean elapsed time of 6 ms (2.4 GHz Athlon CPU). The elapsed time of the
searching phase is shown to vary by less than 1 ms for list sizes between 10
and 200 points, demonstrating that fast, robust searches may be completed in
nearly constant time, independent of list size.Comment: Accepted for publication in Publications of the Astronomical Society
of Australi
CDM afforestation and reforestation baseline methodologies: An analysis of the submission and approval process
Afforestation and Reforestation (A/R), also widely termed LULUCF have been an important field of conflict in the Clean Development Mechanism (CDM) of the Kyoto Protocol. The first methodology for A/R projects has been submitted only by October 2004 and the first project was registered only in November 2006, two years after the first project in the energy sector. Like energy efficiency and transportation methodologies, A/R methodologies also suffer high rejection rate. 20 A/R CDM methodologies evaluated by the CDM Executive Board have been analyzed in this paper with respect to their approval history. On an average it took 4-5 months for approval of A/R methodologies in contrast to the long approval time taken in case of other methodologies (9-10 months). Most methodologies has been rejected because of not properly defining land eligibility, incomplete baseline scenario selection, lack of methods to prove additionality and insufficient treatment of uncertainties. --
Evolution of a metastable phase with a magnetic phase coexistence phenomenon and its unusual sensitivity to magnetic field cycling in the alloys Tb5-xLuxSi3 (x <= 0.7)
Recently, we reported an anomalous enhancement of the positive
magnetoresistance beyond a critical magnetic field in Tb5Si3 in the
magnetically ordered state, attributable to 'inverse metamagnetism'. This
results in unusual magnetic hysteresis loops for the pressurized specimens,
which are relevant to the topic of 'electronic phase separation'. In this
paper, we report the influence of small substitutions of Lu for Tb, to show the
evolution of these magnetic anomalies. We find that, at low temperatures, the
high-field high-resistivity phase could be partially stabilized on returning
the magnetic field to zero in many of these Lu substituted alloys, as measured
through the electrical resistivity ({\rho}). Also, the relative fractions of
this phase and the virgin phase appear to be controlled by a small tuning of
the composition and temperature. Interestingly, at 1.8 K a sudden 'switch-over'
of the value of {\rho} for this mixed phase to that for the virgin phase for
some compositions is observed at low fields after a few field cycles,
indicating metastability of this mixed phase
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