1,453 research outputs found
New class I methanol masers
We review properties of all known collisionally pumped (class I) methanol
maser series based on observations with the Australia Telescope Compact Array
(ATCA) and the Mopra radio telescope. Masers at 36, 84, 44 and 95 GHz are most
widespread, while 9.9, 25, 23.4 and 104 GHz masers are much rarer, tracing the
most energetic shocks. A survey of many southern masers at 36 and 44 GHz
suggests that these two transitions are highly complementary. The 23.4 GHz
maser is a new type of rare class I methanol maser, detected only in two
high-mass star-forming regions, G357.97-0.16 and G343.12-0.06, and showing a
behaviour similar to 9.9, 25 and 104 GHz masers. Interferometric positions
suggest that shocks responsible for class I masers could arise from a range of
phenomena, not merely an outflow scenario. For example, some masers might be
caused by interaction of an expanding HII region with its surrounding molecular
cloud. This has implications for evolutionary sequences incorporating class I
methanol masers if they appear more than once during the evolution of the
star-forming region. We also make predictions for candidate maser transitions
at the ALMA frequency range.Comment: 8 pages, 2 figures, to appear in proceedings for IAUS 287: Cosmic
Masers - from OH to H
The Australia Telescope campaign to study southern class I methanol masers
The Australia Telescope Compact Array (ATCA) and the Mopra facility have been
used to search for new southern class I methanol masers at 9.9, 25 (J=5) and
104 GHz, which are thought to trace more energetic conditions in the interface
regions of molecular outflows, than the widespread class I masers at 44 and 95
GHz. One source shows a clear outflow association.Comment: 2 pages, 1 figure (composed from 3 files), to appear in proceedings
of IAU Symposium 242 "Astrophysical masers and their environment" (eds. J.
Chapman and W. Baan
Some Aspects of the Application of Analytical Techniques in U.S. Governmental Program Management
During recent years developed countries have paid increasingly more attention to the development and implementation of complex, large-scale programs in different spheres of public policy: space, investigation, exploration of new territories, rational use of natural resources, environmental protection, etc. Some of the more remarkable examples of such programs are: the formation of the Bratsk-Ilimsk Territorial Production Complex; the construction of the Baikal-Amur Railway; and the development of the Nechernoziernnaja zone of the RSFSR in the USSR; the TVA experience; the construction of the Trans-Alaska pipeline in the USA; construction of the Shinkansen Railway in Japan.
The programs were developed and implemented by countries with different socio-economic systems, and in diverse spheres of governmental activity. They are also characterized by different scales, goals, degree of government involvement and other features. However, in spite of existing differences, one can find some common methodological and organizational aspects in the management of large-scale programs. Analysis of these aspects along with the generalization of experiences, both positive and negative, gained by different countries could provide a basis for improving public management. In this respect IIASA, with its ability to organize international and multidisciplinary scientific teams to tackle problems of program management, plays a role that can hardly be over-estimated.
This paper attempts to elucidate the integration of some analytical approaches into U.S. government program management
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
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