9,668 research outputs found
Advances in Calibration and Imaging Techniques in Radio Interferometry
This paper summarizes some of the major calibration and image reconstruction
techniques used in radio interferometry and describes them in a common
mathematical framework. The use of this framework has a number of benefits,
ranging from clarification of the fundamentals, use of standard numerical
optimization techniques, and generalization or specialization to new
algorithms
Opportunities for optics in integrated circuits applications
Optics potentially addresses two key problems in electronic chips and systems: interconnects and timing. Short optical pulses (e.g., picoseconds or shorter) offer particularly precise timing. Results are shown for optical and electrical four-phase clocking, with <1 ps rms jitter for the optical case
A lattice Boltzmann model with random dynamical constraints
In this paper we introduce a modified lattice Boltzmann model (LBM) with the
capability of mimicking a fluid system with dynamic heterogeneities. The
physical system is modeled as a one-dimensional fluid, interacting with
finite-lifetime moving obstacles. Fluid motion is described by a lattice
Boltzmann equation and obstacles are randomly distributed semi-permeable
barriers which constrain the motion of the fluid particles. After a lifetime
delay, obstacles move to new random positions. It is found that the
non-linearly coupled dynamics of the fluid and obstacles produces heterogeneous
patterns in fluid density and non-exponential relaxation of two-time
autocorrelation function.Comment: 10 pages, 9 figures, to be published in Eur. Phys. J.
Synchrotron aging and the radio spectrum of SN 1993J
We combine the GMRT low frequency radio observations of SN 1993J with the VLA
high frequency radio data to get a near simultaneous spectrum around day 3200
since explosion. The low frequency measurements of the supernova determine the
turnover frequency and flux scale of the composite spectrum and help reveal a
steepening in the spectral index, , in the optically
thin part of the spectrum. This is the first observational evidence of a break
in the radio spectrum of a young supernova. We associate this break with the
phenomenon of synchrotron aging of radiating electrons. From the break in the
spectrum we calculate the magnetic field in the shocked region independent of
the equipartition assumption between energy density of relativistic particles
and magnetic energy density. We determine the ratio of these two energy
densities and find that this ratio is in the range: . We also predict the nature of the evolution of the synchrotron break
frequency with time, with competing effects due to diffusive Fermi acceleration
and adiabatic expansion of the radiative electron plasma.Comment: 12 pages, 2 figures. Accepted for publication in ApJ
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