5,723 research outputs found
Extending and Exploring the 2 cm Survey Sample
We present new results from the VLBA 2 cm Survey, an imaging survey of active
galactic nuclei (AGN) at sub-milliarcsecond resolution. We extend the
structural variability monitoring program of more than 130 extragalactic
parsec-scale radio jets from over 170 AGN to a total of eight years. The sample
is explored further in time for all sources, and intensively for individual
objects. We report new detailed results on the compact sources III Zw 2, AO
0235+16, and NRAO 512.Comment: Proceedings of the 7th European VLBI Network Symposium (October 12-15
2004, Toledo, Spain), eds. Bachiller, R., Colomer, F., Desmurs, J. F., & de
Vicente, P., 2 tables, 3 figures, needs evn2004.cl
The VLBA 2cm Survey: Kinematics of pc-Scale Structures in Active Galactic Nuclei
The kinematics of jets in active galactic nuclei (QSOs, BL Lacs, Radio
Galaxies and Empty Field objects) on parsec scales is being studied with Very
Long Baseline Array observations at 15 GHz of a sample of more than 170 radio
sources. More than 1000 images have been taken since 1994. Here we present an
overview of the results of our study, including the proper motions of
components in the jets, and their relationship with other source properties.Comment: To be published in the volume "Highlights of Spanish Astrophysics
(III), Proceedings of the 5th Scientific Meeting of the Spanish Astronomical
Society" of the Astrophysics and Space Science Library (Kluwer), J. Gallego,
J. Zamorano, N. Cardiel (eds.), 4 pages, 2 figures, needs kapproc.st
Social and Political Dimensions of Identity
We study the interior regularity of solutions to the Dirichlet problem Lu = g in Omega, u = 0 in R-nOmega, for anisotropic operators of fractional type Lu(x) = integral(+infinity)(0) dp integral(Sn-1) da(w) 2u(x) - u(x + rho w) - u(x - rho w)/rho(1+2s). Here, a is any measure on Sn-1 (a prototype example for L is given by the sum of one-dimensional fractional Laplacians in fixed, given directions). When a is an element of C-infinity(Sn-1) and g is c(infinity)(Omega), solutions are known to be C-infinity inside Omega (but not up to the boundary). However, when a is a general measure, or even when a is L-infinity(s(n-1)), solutions are only known to be C-3s inside Omega. We prove here that, for general measures a, solutions are C1+3s-epsilon inside Omega for all epsilon > 0 whenever Omega is convex. When a is an element of L-infinity(Sn-1), we show that the same holds in all C-1,C-1 domains. In particular, solutions always possess a classical first derivative. The assumptions on the domain are sharp, since if the domain is not convex and the measure a is singular, we construct an explicit counterexample for which u is not C3s+epsilon for any epsilon > 0 - even if g and Omega are C-infinity
Multiband polarimetric and total intensity imaging of 3C345
We monitored the superluminal QSO 3C 345 at three epochs during a one-year
period in 1995--1996, observing with the VLBA at 22, 15, 8.4, and 5 GHz. We
imaged the radio source both in total and in polarized intensity. In the images
at 5 and 8.4 GHz, the jet emission is traced up to 20 milliarcseconds (mas)
from the jet core. In the 15 and 22 GHz images, we identify several enhanced
emission regions moving at apparent speeds of 5c. Images of the linear
polarized emission show predominantly an alignment of the electric vector with
the extremely curved jet along the inner part of the high frequency jet. At 5
GHz, the jet shows remarkably strong fractional polarization (m~15%) with the
electric vector perpendicular to the jet orientation.Comment: LaTeX file, 6 pages, 2 figures, needs "elsart" style package To be
published in New Astronomy Reviews, special issue: Proceedings of the 4th
EVN/JIVE VLBI Symposium, Eds. Garrett, M.A., Campbell, R.M., & Gurvits, L.
Absolute kinematics of radio source components in the complete S5 polar cap sample. III. First wide-field high-precision astrometry at 15.4 GHz
We report on the first wide-field, high-precision astrometric analysis of the
13 extragalactic radio sources of the complete S5 polar cap sample at 15.4 GHz.
We describe new algorithms developed to enable the use of differenced phase
delays in wide-field astrometric observations and discuss the impact of using
differenced phase delays on the precision of the wide-field astrometric
analysis. From this global fit, we obtained estimates of the relative source
positions with precisions ranging from 14 to 200 as at 15.4 GHz, depending
on the angular separation of the sources (from 1.6 to 20.8
degrees). These precisions are 10 times higher than the achievable
precisions using the phase-reference mapping technique.Comment: 9 pages, 7 figure
Use of spectral kurtosis for improving signal to noise ratio of acoustic emission signal from defective bearings
The use of Acoustic Emission (AE) to monitor the condition of roller bearings in rotating
machinery is growing in popularity. This investigation is centred on the application of
Spectral Kurtosis (SK) as a denoising tool able to enhance the bearing fault features from an
AE signal. This methodology was applied to AE signals acquired from an experimental
investigation where different size defects were seeded on a roller bearing. The results suggest
that the signal to noise ratio can be significantly improved using SK
- âŠ