544 research outputs found
Two-way satellite time transfer using low power CW tones
In the search for an economical means of precise time transfer, the NRC Time Laboratory decided to adapt the techniques used by radio astronomers in an experiment to compare the phases of the local oscillators at widely separated VLBI stations. The objective is to design a system which would use commercial satellites, and which would be of reasonable cost for the ground stations and for operations. Two satellite ground stations were installed at NRC about 100 m from the Time Laboratory. For the preliminary experiment, a channel on the Anik Al 6/4 GHz satellite was made available by TELESAT Canada. Two tones were transmitted + or - MHz from the suppressed carrier. The difference frequency of 32 MHz was recorded using narrow band receivers. A low level 1 MHz phase modulation was added to identify the 32 MHz cycle, giving 1 microsec ambiguity in the time transfer. With less than 1/4 W in each tone, the EIRP is 43 dB below that of a normal TV Earth station, and no frequency dispersion is required. The measurements taken each second for the 32 MHz have an rms scatter of 1 ns
The radio emission from the Galaxy at 22 MHz
We present maps of the 22MHz radio emission between declinations -28d and
+80d, covering ~73% of the sky, derived from observations with the 22MHz
radiotelescope at the Dominion Radio Astrophysical Observatory (DRAO). The
resolution of the telescopt (EWxNS) is 1.1d x 1.7d secant(zenith angle). The
maps show the large scale features of the emission from the Galaxy including
the thick non-thermal disk, the North Polar Spur (NPS) and absorption due to
discrete HII regions and to an extended band of thermal electrons within 40d of
the Galactic centre. We give the flux densities of nine extended supernova
remnants shown on the maps
Two-way time transfers between NRC/NBS and NRC/USNO via the Hermes (CTS) satellite
At each station the differences were measured between the local UTC seconds pulse and the remote UTC pulse received by satellite. The difference between the readings, if station delays are assumed to be symmetrical, is two times the difference between the clocks at the two ground station sites. Over a 20-minute period, the precision over the satellite is better than 1 ns. The time transfer from NRC to the CRC satellite terminal near Ottawa and from NBS to the Denver HEW terminal was examined
Radio Halo and Relic Candidates from the Westerbork Northern Sky Survey
We have undertaken a systematic search for diffuse radio halos and relics in
all of the Abell clusters that are visible in the Westerbork Northern Sky
Survey (WENSS). In this survey we found 18 candidates, 11 of which are already
known from the literature, and 7 for which we provide the first evidence of
diffuse radio emission. All the clusters in this sample show other evidence for
a recent or ongoing merger. We also investigate the correlation between cluster
X-ray luminosity and radio power of halos. We develop a very simple model for
merger shocks that reproduces the sense of this correlation, although it is
probably not as steep as the correlation in the data. We discuss the
implications of X-ray--radio correlations for future detections of radio halos.Comment: Accepted for publication in the Astrophysical Journal. 12 pages with
9 embedded Postscript figures in emulateapj5.sty. A higher resolution version
of the paper is available at
http://www.astro.virginia.edu/~jck7k/research/papers/WENSS.ps.g
Understanding consumer demand for new transport technologies and services, and implications for the future of mobility
The transport sector is witnessing unprecedented levels of disruption.
Privately owned cars that operate on internal combustion engines have been the
dominant modes of passenger transport for much of the last century. However,
recent advances in transport technologies and services, such as the development
of autonomous vehicles, the emergence of shared mobility services, and the
commercialization of alternative fuel vehicle technologies, promise to
revolutionise how humans travel. The implications are profound: some have
predicted the end of private car dependent Western societies, others have
portended greater suburbanization than has ever been observed before. If
transport systems are to fulfil current and future needs of different
subpopulations, and satisfy short and long-term societal objectives, it is
imperative that we comprehend the many factors that shape individual behaviour.
This chapter introduces the technologies and services most likely to disrupt
prevailing practices in the transport sector. We review past studies that have
examined current and future demand for these new technologies and services, and
their likely short and long-term impacts on extant mobility patterns. We
conclude with a summary of what these new technologies and services might mean
for the future of mobility.Comment: 15 pages, 0 figures, book chapte
Dynamics of Host Immune Response Development During Schistosoma mansoni Infection
Schistosomiasis is a disease of global significance, with severity and pathology directly related to how the host responds to infection. The immunological narrative of schistosomiasis has been constructed through decades of study, with researchers often focussing on isolated time points, cell types and tissue sites of interest. However, the field currently lacks a comprehensive and up-to-date understanding of the immune trajectory of schistosomiasis over infection and across multiple tissue sites. We have defined schistosome-elicited immune responses at several distinct stages of the parasite lifecycle, in three tissue sites affected by infection: the liver, spleen, and mesenteric lymph nodes. Additionally, by performing RNA-seq on the livers of schistosome infected mice, we have generated novel transcriptomic insight into the development of schistosome-associated liver pathology and fibrosis across the breadth of infection. Through depletion of CD11c+ cells during peak stages of schistosome-driven inflammation, we have revealed a critical role for CD11c+ cells in the co-ordination and regulation of Th2 inflammation during infection. Our data provide an updated and high-resolution account of how host immune responses evolve over the course of murine schistosomiasis, underscoring the significance of CD11c+ cells in dictating host immunopathology against this important helminth infection
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