29,244 research outputs found
LLAGN and jet-scaling probed with the EVN
Accreting black holes on all mass scales (from stellar to supermassive)
appear to follow a nonlinear relation between X-ray luminosity, radio
luminosity and BH mass, indicating that similar physical processes drive the
central engines in X-ray binaries and active galactic nuclei (AGN). However, in
recent years an increasing number of BH systems have been identified that do
not fit into this scheme. These outliers may be the key to understand how BH
systems are powered by accretion. Here we present results from EVN observations
of a sample of low-luminosity AGN (LLAGN) with known mass that have unusually
high radio powers when compared with their X-ray luminosity.Comment: Presented at the 11th EVN Symposium, Bordeaux, France, 2012 October
9-12. Six pages, including a figure and a table. Final, accepted versio
Space Charge Effect and Mirror Charge Effect in Photoemission Spectroscopy
We report the observation and systematic investigation of the space charge
effect and mirror charge effect in photoemission spectroscopy. When pulsed
light is incident on a sample, the photoemitted electrons experience energy
redistribution after escaping from the surface because of the Coulomb
interaction between them (space charge effect) and between photoemitted
electrons and the distribution of mirror charges in the sample (mirror charge
effect). These combined Coulomb interaction effects give rise to an energy
shift and a broadening which can be on the order of 10 meV for a typical
third-generation synchrotron light source. This value is comparable to many
fundamental physical parameters actively studied by photoemission spectroscopy
and should be taken seriously in interpreting photoemission data and in
designing next generation experiments.Comment: Journal of Electron Spectroscopy and Related Phenomena 142(2004)27-3
Approximate least trimmed sum of squares fitting and applications in image analysis
The least trimmed sum of squares (LTS) regression estimation criterion is a robust statistical method for model fitting in the presence of outliers. Compared with the classical least squares estimator, which uses the entire data set for regression and is consequently sensitive to outliers, LTS identifies the outliers and fits to the remaining data points for improved accuracy. Exactly solving an LTS problem is NP-hard, but as we show here, LTS can be formulated as a concave minimization problem. Since it is usually tractable to globally solve a convex minimization or concave maximization problem in polynomial time, inspired by [1], we instead solve LTS’ approximate complementary problem, which is convex minimization. We show that this complementary problem can be efficiently solved as a second order cone program. We thus propose an iterative procedure to approximately solve the original LTS problem. Our extensive experiments demonstrate that the proposed method is robust, efficient and scalable in dealing with problems where data are contaminated with outliers. We show several applications of our method in image analysis.Fumin Shen, Chunhua Shen, Anton van den Hengel and Zhenmin Tan
Strain engineering in graphene by laser irradiation
We demonstrate that the Raman spectrum of graphene on lithium niobate can be controlled locally by continuous exposure to laser irradiation. We interpret our results in terms of changes to doping and mechanical strain and show that our observations are consistent with light-induced gradual strain relaxation in the graphene layer
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