144 research outputs found
Short proofs of the Kneser-Lovász coloring principle
We prove that propositional translations of the Kneser–Lovász theorem have polynomial size extended Frege proofs and quasi-polynomial size Frege proofs for all fixed values of k.
We present a new counting-based combinatorial proof of the K neser–Lovász theorem based on the Hilton–Milner theorem; this avoids the topological arguments of prior proofs for all but finitely many base cases. We introduce new “truncated Tucker lemma” principles, which are miniaturizations of the octahedral Tucker lemma. The truncated Tucker lemma implies the Kneser–Lovász theorem. We show that the
k=1 case of the truncated Tucker lemma has polynomial size extended Frege proofs.Peer ReviewedPostprint (author's final draft
First Study of Combined Blazar Light Curves with FACT and HAWC
For studying variable sources like blazars, it is crucial to achieve unbiased
monitoring, either with dedicated telescopes in pointing mode or survey
instruments. At TeV energies, the High Altitude Water Cherenkov (HAWC)
observatory monitors approximately two thirds of the sky every day. It uses the
water Cherenkov technique, which provides an excellent duty cycle independent
of weather and season. The First G-APD Cherenkov Telescope (FACT) monitors a
small sample of sources with better sensitivity, using the imaging air
Cherenkov technique. Thanks to its camera with silicon-based photosensors, FACT
features an excellent detector performance and stability and extends its
observations to times with strong moonlight, increasing the duty cycle compared
to other imaging air Cherenkov telescopes. As FACT and HAWC have overlapping
energy ranges, a joint study can exploit the longer daily coverage given that
the observatories' locations are offset by 5.3 hours. Furthermore, the better
sensitivity of FACT adds a finer resolution of features on hour-long time
scales, while the continuous duty cycle of HAWC ensures evenly sampled
long-term coverage. Thus, the two instruments complement each other to provide
a more complete picture of blazar variability. In this presentation, the first
joint study of light curves from the two instruments will be shown, correlating
long-term measurements with daily sampling between air and water Cherenkov
telescopes. The presented results focus on the study of the variability of the
bright blazars Mrk 421 and Mrk 501 during the last two years featuring various
flaring activities.Comment: 6 pages, 2 figures. Contribution to the 6th International Symposium
on High Energy Gamma-Ray Astronomy (Gamma2016), Heidelberg, Germany. To be
published in the AIP Conference Proceeding
Terrestrial mammal three-dimensional photogrammetry : multispecies mass estimation
Assessing body mass in mammals is of importance as it influences virtually all aspects of
mammal physiology, behavior and ecological parameters. However, the assessment of body mass of large
mammals is potentially dangerous and logistically challenging. Photogrammetry (measurements through
the use of photographs) is a well-established science. In zoology it has been used with varying success to
estimate the size and mass of some marine and terrestrial mammal species. However, photogrammetric
body mass estimation of terrestrial mammals has received comparatively little attention. This is largely due
to species’ variable morphological attributes which complicates measurement especially if, for 3D
orientation, photogrammetric models are dependent on identifiable features on the animals themselves.
Ninety-two individuals belonging to 16 terrestrial mammalian species were weighed and photographed
for body mass estimation using a volumetric photogrammetry method, purposely applied with
commercially available software. This method is not dependent on identifiable body features for 3D
orientation. Measured body mass ranged from 25 kg to 4060 kg. Photogrammetric mass estimates versus
physically weighed mass was plotted and the goodness of fit assessed for each species. Body size, shape
and physiological attributes influence the accuracy of body mass estimation between species (although
consistent within species), largely attributed to morphological features (e.g., hair length and posture). This
photogrammetric method accurately estimated the body mass of several terrestrial mammal species. It
represents innovative use of photographs to create calibrated three-dimensional imagery for accurate
quantification of mammalian metrics, specifically body volume and mass. Advances of a method that is not
subject to species, sex or age is advantageous and suitable for wide application in our effort to model
population demography.The Department of Science
and Technology via the National Research Foundation
(NRF) and the University of Pretoria.http://www.esajournals.orgam2016Mammal Research Institut
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