96 research outputs found
The FFX Correlator
We established a new algorithm for correlation process in radio astronomy.
This scheme consists of the 1st-stage Fourier Transform as a filter and the
2nd-stage Fourier Transform for spectroscopy. The "FFX" correlator stands for
Filter and FX architecture, since the 1st-stage Fourier Transform is performed
as a digital filter, and the 2nd-stage Fourier Transform is performed as a
conventional FX scheme. We developed the FFX correlator hardware not only for
the verification of the FFX scheme algorithm but also for the application to
the Atacama Submillimeter Telescope Experiment (ASTE) telescope toward
high-dispersion and wideband radio observation at submillimeter wavelengths. In
this paper, we present the principle of the FFX correlator and its properties,
as well as the evaluation results with the production version.Comment: 20 figure
Multi-epoch, multi-frequency VLBI study of the parsec-scale jet in the blazar 3C 66A
We present the observational results of the Gamma-ray blazar, 3C 66A, at 2.3,
8.4, and 22 GHz at 4 epochs during 2004-05 with the VLBA. The resulting images
show an overall core-jet structure extending roughly to the south with two
intermediate breaks occurring in the region near the core. By model-fitting to
the visibility data, the northmost component, which is also the brightest, is
identified as the core according to its relatively flat spectrum and its
compactness. As combined with some previous results to investigate the proper
motions of the jet components, it is found the kinematics of 3C 66A is quite
complicated with components of inward and outward, subluminal and superluminal
motions all detected in the radio structure. The superluminal motions indicate
strong Doppler boosting exists in the jet. The apparent inward motions of the
innermost components last for at least 10 years and could not be caused by
new-born components. The possible reason could be non-stationarity of the core
due to opacity change.Comment: 24 pages, 4 figure
Boundary Scattering in Ballistic Graphene
We report magnetotransport measurements in ballistic graphene/hexagonal boron
nitride mesoscopic wires where the charge carrier mean free path is comparable
to wire width . Magnetoresistance curves show characteristic peak structures
where the peak field scales with the ratio of cyclotron radius
and wire width as , due to diffusive boundary
scattering. The obtained proportionality constant between and
differs from that of a classical semiconductor 2D electron system where
.Comment: 14 pages, 4 figure
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