9,342 research outputs found
Experimental prediction of performance by superconducting cables
Broken superconductor method of short sample testing makes possible the prediction of the performance of well cooled, stabilized, superconducting cable coils. It yields a field-versus-current curve for a short sample of cable. Plots are given for the superconductor and copper currents at various magnetic field strengths
New ammonia masers towards NGC6334I
We report the detection of new ammonia masers in the non-metastable (8,6) and
(11,9) transitions towards the massive star forming region NGC6334I.
Observations were made with the ATCA interferometer and the emitting region
appears unresolved in the 2.7" x 0.8" beam, with deconvolved sizes less than an
arcsecond. We estimate peak brightness temperatures of 7.8 x 10^5 and 1.2 x
10^5 K for the (8,6) and (11,9) transitions, respectively. The masers appear
coincident both spatially and in velocity with a previously detected ammonia
(6,6) maser. We also suggest that emission in the (10,9), (9,9) and (7,6)
transitions may also be masers, based on their narrow line widths and
overlapping velocity ranges with the above masers, as observed with the
single-dish Mopra radiotelescope
A survey for redshifted molecular and atomic absorption lines - II. Associated HI, OH and millimetre lines in the z >~ 3 Parkes quarter-Jansky flat-spectrum sample
We present the results of a z>2.9 survey for HI 21-cm and molecular
absorption in the hosts of radio quasars using the GMRT and the Tidbinbilla
70-m telescope. Previously published searches, which are overwhelmingly at
redshifts of z<1, exhibit a 42% detection rate (31 out of 73 sources), and the
inclusion of our survey yields a 17% detection rate (2 out of 12 sources) at
z>2.5. We therefore believe that our high redshift selection is responsible for
our exclusive non-detections, and find that at ultra-violet luminosities of
>10e23 W/Hz, 21-cm absorption has never been detected. We also find this to not
only apply to our targets, but also those at low redshift exhibiting similar
luminosities, giving zero detections out of a total of 16 sources over z=0.24
to 3.8. This is in contrast to the < 10e23 W/Hz sources where there is a near
50% detection rate of 21-cm absorption.
The mix of 21-cm detections and non-detections is currently attributed to
orientation effects, where according to unified schemes of active galactic
nuclei, 21-cm absorption is more likely to occur in sources designated as radio
galaxies (type-2 objects, where the nucleus is viewed through dense obscuring
circumnuclear gas) than in quasars(type-1 objects, where we have a direct view
to the nucleus). However, due to the exclusively high ultra-violet luminosities
of our targets it is not clear whether orientation effects alone can wholly
account for the distribution, although there exists the possibility that the
large luminosities are indicative of a changing demographic of galaxy types. We
also find that below luminosities of ~10e23 W/Hz, both type-1 and type-2
objects have a 50% likelihood of exhibiting 21-cm absorption.Comment: 21 pages, accepted by MNRA
The molecular environment of massive star forming cores associated with Class II methanol maser emission
Methanol maser emission has proven to be an excellent signpost of regions
undergoing massive star formation (MSF). To investigate their role as an
evolutionary tracer, we have recently completed a large observing program with
the ATCA to derive the dynamical and physical properties of molecular/ionised
gas towards a sample of MSF regions traced by 6.7 GHz methanol maser emission.
We find that the molecular gas in many of these regions breaks up into multiple
sub-clumps which we separate into groups based on their association
with/without methanol maser and cm continuum emission. The temperature and
dynamic state of the molecular gas is markedly different between the groups.
Based on these differences, we attempt to assess the evolutionary state of the
cores in the groups and thus investigate the role of class II methanol masers
as a tracer of MSF.Comment: 5 pages, 1 figure, IAU Symposium 242 Conference Proceeding
Electrostatic internal energy using the method of images
For several configurations of charges in the presence of conductors, the
method of images permits us to obtain some observables associated with such a
configuration by replacing the conductors with some image charges. However,
simple inspection shows that the potential energy associated with both systems
does not coincide. Nevertheless, it can be shown that for a system of a
grounded or neutral conductor and a distribution of charges outside, the
external potential energy associated with the real charge distribution embedded
in the field generated by the set of image charges is twice the value of the
internal potential energy associated with the original system. This assertion
is valid for any size and shape of the conductor, and regardless of the
configuration of images required. In addition, even in the case in which the
conductor is not grounded nor neutral, it is still possible to calculate the
internal potential energy of the original configuration through the method of
images. These results show that the method of images could also be useful for
calculations of the internal potential energy of the original system.Comment: 5 pages, 3 figures. New discussions added. Minor change
Recent Extreme Ultraviolet Solar Spectra and Spectroheliograms
Extreme ultraviolet solar spectra and spectroheliogram analyse
Broadband, radio spectro-polarimetric study of 100 radiative-mode and jet-mode AGN
We present the results from a broadband (1 to 3 GHz), spectro-polarimetry
study of the integrated emission from 100 extragalactic radio sources with the
ATCA, selected to be highly linearly polarized at 1.4 GHz. We use a general
purpose, polarization model-fitting procedure that describes the Faraday
rotation measure (RM) and intrinsic polarization structure of up to three
distinct polarized emission regions or 'RM components' of a source. Overall,
37%/52%/11% of sources are best fit by one/two/three RM components. However,
these fractions are dependent on the signal-to-noise ratio (S/N) in
polarization (more RM components more likely at higher S/N). In general, our
analysis shows that sources with high integrated degrees of polarization at 1.4
GHz have low Faraday depolarization, are typically dominated by a single RM
component, have a steep spectral index, and a high intrinsic degree of
polarization. After classifying our sample into radiative-mode and jet-mode
AGN, we find no significant difference between the Faraday rotation or Faraday
depolarization properties of jet-mode and radiative-mode AGN. However, there is
a statistically significant difference in the intrinsic degree of polarization
between the two types, with the jet-mode sources having more intrinsically
ordered magnetic field structures than the radiative-mode sources. We also find
a preferred perpendicular orientation of the intrinsic magnetic field structure
of jet-mode AGN with respect to the jet direction, while no clear preference is
found for the radiative-mode sources.Comment: 29 pages (including Appendix), 28 figures, 7 tables. Accepted for
publication in MNRA
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