78 research outputs found
Supermassive Binaries and Extragalactic Jets
Some quasars show Doppler shifted broad emission line peaks. I give new
statistics of the occurrence of these peaks and show that, while the most
spectacular cases are in quasars with strong radio jets inclined to the line of
sight, they are also almost as common in radio-quiet quasars. Theories of the
origin of the peaks are reviewed and it is argued that the displaced peaks are
most likely produced by the supermassive binary model. The separations of the
peaks in the 3C 390.3-type objects are consistent with orientation-dependent
"unified models" of quasar activity. If the supermassive binary model is
correct, all members of "the jet set" (astrophysical objects showing jets)
could be binaries.Comment: 31 pages, PostScript, missing figure is in ApJ 464, L105 (see
http://www.aas.org/ApJ/v464n2/5736/5736.html
Measurement of the lifetime of the meson using the decay mode
The difference in total widths between the and mesons is
measured using 3.0fb of data collected by the LHCb experiment in 7 and 8
TeV centre-of-mass energy proton-proton collisions at the LHC. Through the
study of the time evolution of and
decays, the width difference is measured to be
where the first uncertainty is statistical and the second
systematic. The known lifetime of the meson is used to convert this to a
precise measurement of the lifetime,
where the first uncertainty is
statistical and the second systematic.Comment: 19 pagers, 3 figure
Distribution-based fuzzy clustering of electrical resistivity tomography images for interface detection
A novel method for the effective identification of bedrock subsurface elevation from electrical resistivity tomography images is described. Identifying subsurface boundaries in the topographic data can be difficult due to smoothness constraints used in inversion, so a statistical population-based approach is used that extends previous work in calculating isoresistivity surfaces. The analysis framework involves a procedure for guiding a clustering approach based on the fuzzy c-means algorithm. An approximation of resistivity distributions, found using kernel density estimation, was utilized as a means of guiding the cluster centroids used to classify data. A fuzzy method was chosen over hard clustering due to uncertainty in hard edges in the topography data, and a measure of clustering uncertainty was identified based on the reciprocal of cluster membership. The algorithm was validated using a direct comparison of known observed bedrock depths at two 3-D survey sites, using real-time GPS information of exposed bedrock by quarrying on one site, and borehole logs at the other. Results show similarly accurate detection as a leading isosurface estimation method, and the proposed algorithm requires significantly less user input and prior site knowledge. Furthermore, the method is effectively dimension-independent and will scale to data of increased spatial dimensions without a significant effect on the runtime. A discussion on the results by automated versus supervised analysis is also presented
ESPaCE, European Satellite PArtnership for Computing Ephemerides
International audienceThe EC FP7 project entitled European Satellite PArtnership for Computing Ephemerides (ESPaCE) aims at strengthening the collaborative activities in the domain of the development of ephemerides and reference systems for natural satellites and spacecraft. An important part of the project addresses the extraction and analysis of astrometric data from observations by spacecraft not yet applied to dynamical solutions. They will be combined with ground-based astrometry in order to improve constraints on the dynamics and the physics of the objects. We will use all these data to provide improved ephemerides for natural satellites and spacecraft and to characterize the rotation properties of selected satellites. We also intend to investigate new technologies relevant to our aims, in particular Very Long Baseline Interferometry (VLBI) and Laser Ranging (LR) techniques. Another important part of the project will include merging (for the first time in Europe) the natural satellite astrometry data with spacecraft data in a global inversion. All the results and documents will be made available using standard formats (VO standard, SPICE kernels) for the use by space agencies and scientific community
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