284 research outputs found
Simultaneous dual-frequency radio observations of S5 0716+714: A search for intraday variability with the Korean VLBI Network
This study aims to search for the existence of intraday variability (IDV) of
BL Lac object S5 0716+714 at high radio frequencies for which the interstellar
scintillation effect is not significant. Using the 21-meter radio telescope of
the Korean VLBI Network (KVN), we present results of multi-epoch simultaneous
dual-frequency radio observations. Single-dish observations of S5 0716+714 were
simultaneously conducted at 21.7 GHz (K-band) and 42.4 GHz (Q-band), with a
high cadence of 30-60 minute intervals.We observed four epochs between December
2009 and June 2010. Over the whole set of observation epochs, S5 0716+714
showed significant inter-month variations in flux density at both the K- and
Q-bands, with modulation indices of approximately 19% for the K-band and
approximately 36% for the Q-band. In all epochs, no clear intraday variability
was detected at either frequency. The source shows monotonic flux density
increase in epochs 1 and 3 and monotonic flux density decrease in epochs 2 and
4. In the flux density increasing phases, the flux densities at the Q-band
increase more rapidly. In the decreasing phase, no significant flux density
difference is seen at the two frequencies. The situation could be different
close to flux density peaks that we did not witness in our observations. We
find an inverted spectrum with mean spectral indices of -0.57+-0.13 in epoch 1
and -0.15+-0.11 in epoch 3. On the other hand, we find relatively steep indices
of +0.24+-0.14 and +0.17+-0.18 in epochs 2 and 4, respectively. We conclude
that the frequency dependence of the variability and the change of the spectral
index are caused by source-intrinsic effects rather than by any extrinsic
scintillation effect.Comment: 6 pages and 4 figures and 4 table
Integration between WSNs and Internet based on Address Internetworking for Web Services
There has been an increasing interest in wireless sensor networks as a new technology to realize ubiquitous computing, and demands for internetworking technology between the wireless sensor networks and the Internet which is based on IP address. For this purpose, this paper proposes and implements the internetworking scheme which assigns IP addresses to the sensor nodes and internetworks based on the gateway-based integration for internetworking between the wireless sensor networks and the Internet. That is, the proposed scheme makes the access to the wireless sensor networks be serviced as like the Web service with internetworking Internet IP address and ZigBee address which is allocated to the sensor node in wireless sensor networks. For validating the proposed scheme, we made experiments using Berkeley TinyOS, Mica Motes, dual protocol stack based on ZigBee and IP, and showed the service result using browser (IE) and IPv6 address based on DNS
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