19,899 research outputs found
Searches for radio transients
Exploration of the transient Universe is an exciting and fast-emerging area
within radio astronomy. Known transient phenomena range in time scales from
sub-nanoseconds to years or longer, thus spanning a huge range in time domain
and hinting a rich diversity in their underlying physical processes. Transient
phenomena are likely locations of explosive or dynamic events and they offer
tremendous potential to uncover new physics and astrophysics. A number of
upcoming next-generation radio facilities and recent advances in computing and
instrumentation have provided a much needed impetus for this field which has
remained a relatively uncharted territory for the past several decades. In this
paper we focus mainly on the class of phenomena that occur on very short time
scales (i.e. from milliseconds to nanoseconds), known as {\it
fast transients}, the detections of which involve considerable signal
processing and data management challenges, given the high time and frequency
resolutions required in their explorations, the role of propagation effects to
be considered and a multitude of deleterious effects due to radio frequency
interference. We will describe the techniques, strategies and challenges
involved in their detections and review the world-wide efforts currently under
way, both through scientific discoveries enabled by the ongoing large-scale
surveys at Parkes and Arecibo, as well as technical developments involving the
exploratory use of multi-element array instruments such as VLBA and GMRT. Such
developments will undoubtedly provide valuable inputs as next-generation arrays
such as LOFAR and ASKAP are designed and commissioned. With their wider fields
of view and higher sensitivities, these instruments, and eventually the SKA,
hold great potential to revolutionise this relatively nascent field, thereby
opening up exciting new science avenues in astrophysics.Comment: To appear in the special issue of the Bulletin of the Astronomical
Society of India on Transients at different wavelengths, eds D.J. Saikia and
D.A. Green. 21 pages, 5 figures. http://www.ncra.tifr.res.in/~bas
The visible touch: in planta visualization of protein-protein interactions by fluorophore-based methods
Experimental investigations on the impedance behavior of a short, cylindrical antenna in a lossy magnetoplasma
Impedance of cylindrical antennas in lossy magnetoplasmas and interpretations of maxima in cosmic noise intensities and ionogram
Experimental on-stream elimination of resonant whirl in a large centrifugal compressor
Resonant whirl condition during operation of a multi-stage centrifugal compressor at higher than anticipated speeds and loads was reported. The condition was diagnosed by a large scale computerized Machinery Condition Monitoring System (MACMOS). This computerized system verified that the predominant subsynchronous whirl frequency locked in on the first resonant frequency of the compressor rotor and did not vary with compressor speed. Compressor stability calculations showed the rotor system had excessive hearing stiffness and inadequate effective damping. An optimum bearing design which was developed to minimize the unbalance response and to maximize the stability threshold is presented
A theoretical investigation of noise reduction through the cylindrical fuselage of a twin-engine, propeller-driven aircraft
Interior noise in the fuselage of a twin-engine, propeller-driven aircraft with two propellers rotating in opposite directions is studied analytically. The fuselage was modeled as a stiffened cylindrical shell with simply supported ends, and the effects of stringers and frames were averaged over the shell surface. An approximate mathematical model of the propeller noise excitation was formulated which includes some of the propeller noise characteristics such as sweeping pressure waves around the sidewalls due to propeller rotation and the localized nature of the excitation with the highest levels near the propeller plane. Results are presented in the form of noise reduction, which is the difference between the levels of external and interior noise. The influence of propeller noise characteristics on the noise reduction was studied. The results indicate that the sweep velocity of the excitation around the fuselage sidewalls is critical to noise reduction
Densification and Structural Transitions in Networks that Grow by Node Copying
We introduce a growing network model---the copying model---in which a new
node attaches to a randomly selected target node and, in addition,
independently to each of the neighbors of the target with copying probability
. When , this algorithm generates sparse networks, in which
the average node degree is finite. A power-law degree distribution also arises,
with a non-universal exponent whose value is determined by a transcendental
equation in . In the sparse regime, the network is "normal", e.g., the
relative fluctuations in the number of links are asymptotically negligible. For
, the emergent networks are dense (the average degree
increases with the number of nodes ) and they exhibit intriguing structural
behaviors. In particular, the -dependence of the number of -cliques
(complete subgraphs of nodes) undergoes transitions from normal to
progressively more anomalous behavior at a -dependent critical values of
. Different realizations of the network, which start from the same initial
state, exhibit macroscopic fluctuations in the thermodynamic limit---absence of
self averaging. When linking to second neighbors of the target node can occur,
the number of links asymptotically grows as as , so that the
network is effectively complete as .Comment: 15 pages, 12 figure
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