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171.
A. Frank E. G. Blackman A. Cunningham S. V. Lebedev D. Ampleford A. Ciardi S. N. Bland J. P. Chittenden M. G. Haines 《Astrophysics and Space Science》2005,298(1-2):107-114
We present new data from High-Energy Density (HED) laboratory experiments designed to explore the interaction of a heavy hypersonic
radiative jet with a cross wind. The jets are generated with the MAGPIE pulsed power machine where converging conical plasma
flows are produced from a cylindrically symmetric array of inclined wires. Radiative hypersonic jets emerge from the convergence
point. The cross wind is generated by ablation of a plastic foil via soft-X-rays from the plasma convergence region. Our experiments
show that the jets are deflected by the action of the cross wind with the angle of deflection dependent on the proximity of
the foil. Shocks within the jet beam are apparent in the data. Analysis of the data shows that the interaction of the jet
and cross wind is collisional and therefore in the hydrodynamic regime. We consider the astrophysical relevance of these experiments
applying published models of jet deflection developed for AGN and YSOs. We also present results of 3-D numerical simulations
of jet deflection using a new astrophysical Adaptive Mesh Refinement code. These simulations show highly structured shocks
occurring within the beam similar to what was observed in the experiments. 相似文献
172.
J. Mclelland J. Morrison B. Selleck B. Cunningham C. Olson K. Schmidt 《Journal of Metamorphic Geology》2002,20(1):175-190
Quartz–sillimanite segregations, quartz–albite lithologies (Ab95–98), and Kiruna‐type low‐Ti iron‐oxide deposits are associated with late‐ to post‐tectonic (c. 1055 Ma) leucogranites of Lyon Mountain Gneiss (LMG) in the Adirondack Mountains, New York State. Most recent interpretations of these controversial features, which are global in occurrence, favour hydrothermal origins in agreement with results presented here. Field relations document that quartz–sillimanite veins and nodules cut, and therefore post‐date, emplacement of host LMG leucogranites. Veins occur in oriented fracture networks, and aligned trains of nodules are interpreted as disrupted early veins. Late dykes of leucogranite cut veins and nodules demonstrating formation prior to terminal magmatism. Veins and nodules consist of sillimanite surrounded by quartz that commonly embays wall‐rock feldspar indicating leaching of Na and K from LMG feldspar by acidic hydrothermal fluids. Subsequent, and repeated, ductile flow disrupted earlier veins into nodular fragments but produced little grain shape fabric. Geochemical and petrographic studies of quartz–albite rock indicate that it formed through metasomatic replacement (albitization) of LMG microperthite by sodic hydrothermal fluids that resulted in diagnostic checkerboard albite. Low‐Ti iron‐oxide ores are commonly associated with the quartz–albite sub‐unit, and it is proposed that hydrothermal fluids related to albitization transported Fe as well. The regional extent of sodic alteration suggests large quantities of surface‐derived hydrothermal fluids. Fluid inclusion and oxygen isotope data are consistent with high temperature, regionally extensive fluids consisting primarily of evolved surface‐derived brines enriched in Na and Cl. Quartz–sillimanite veins and nodules, which are significantly more localised phenomena and require acidic fluids, were most likely formed from local magmatic fluids in the crystallizing carapaces of LMG plutons. 相似文献
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177.
T. Hill M. A. Thompson M. G. Burton A. J. Walsh V. Minier M. R. Cunningham D. Pierce-Price 《Monthly notices of the Royal Astronomical Society》2006,368(3):1223-1268
We report the results of a submillimetre continuum emission survey targeted towards 78 star formation regions, 72 of which are devoid of methanol maser and UC H ii regions, identified in the Swedish ESO Submillimetre Telescope (SEST)/SEST IMaging Bolometer Array (SIMBA) millimetre continuum survey of Hill et al. At least 45 per cent of the latter sources, dubbed 'mm-only', detected in this survey are also devoid of the mid-infrared MSX emission. The 450- and 850-μm continuum emission was mapped using the Submillimetre Common User Bolometer Array (SCUBA) instrument on the James Clerk Maxwell Telescope (JCMT). Emission is detected towards 97 per cent of the 78 sources targeted as well as towards 28 other SIMBA sources lying in the SCUBA fields.
In total, we have identified 212 cores in this submillimetre survey, including 106 previously known from the SIMBA survey. Of the remaining 106 sources, 53 result from resolving a SIMBA source into multiple submillimetre components, whilst the other 53 sources are submillimetre cores, not seen in the SIMBA. Additionally, we have identified two further mm-only sources in the SIMBA images. Of the total 405 sources identified in the SIMBA survey, 255 are only seen at millimetre wavelengths.
We concatenate the results from four (sub)millimetre continuum surveys of massive star formation, together with the Galactic plane map of Pierce-Price et al. in order to determine the dust grain emissivity index β for each of the sources in the SIMBA source list. We examine the value of β with respect to temperature, as well as for the source classes identified in the SIMBA survey, for variation of this index. Our results indicate that β is typically 2, which is consistent with previous determinations in the literature, but for a considerably larger sample than previous work. 相似文献
In total, we have identified 212 cores in this submillimetre survey, including 106 previously known from the SIMBA survey. Of the remaining 106 sources, 53 result from resolving a SIMBA source into multiple submillimetre components, whilst the other 53 sources are submillimetre cores, not seen in the SIMBA. Additionally, we have identified two further mm-only sources in the SIMBA images. Of the total 405 sources identified in the SIMBA survey, 255 are only seen at millimetre wavelengths.
We concatenate the results from four (sub)millimetre continuum surveys of massive star formation, together with the Galactic plane map of Pierce-Price et al. in order to determine the dust grain emissivity index β for each of the sources in the SIMBA source list. We examine the value of β with respect to temperature, as well as for the source classes identified in the SIMBA survey, for variation of this index. Our results indicate that β is typically 2, which is consistent with previous determinations in the literature, but for a considerably larger sample than previous work. 相似文献
178.
S. L. Breen S. P. Ellingsen M. Johnston-Hollitt S. Wotherspoon I. Bains M. G. Burton M. Cunningham N. Lo C. E. Senkbeil T. Wong 《Monthly notices of the Royal Astronomical Society》2007,377(2):491-506
We report the results of a blind search for 22-GHz water masers in two regions, covering approximately half a square degree, within the giant molecular cloud associated with RCW 106. The complete search of the two regions was carried out with the 26-m Mount Pleasant radio telescope and resulted in the detection of nine water masers, five of which are new detections. Australia Telescope Compact Array (ATCA) observations of these detections have allowed us to obtain positions with arcsecond accuracy, allowing meaningful comparison with infrared and molecular data for the region. We find that for the regions surveyed there are more water masers than either 6.7-GHz methanol, or main-line OH masers. The water masers are concentrated towards the central axis of the star formation region, in contrast to the 6.7-GHz methanol masers which tend to be located near the periphery. The colours of the GLIMPSE point sources associated with the water masers are similar to those of 6.7-GHz methanol masers, but slightly less red. We have made a statistical investigation of the properties of the 13 CO and 1.2-mm dust clumps with and without associated water masers. We find that the water masers are associated with the more massive, denser and brighter 13 CO and 1.2-mm dust clumps. We present statistical models that are able to predict those 13 CO and 1.2-mm dust clumps that are likely to have associated water masers, with a low misclassification rate. 相似文献
179.
Andrew Cunningham Adam Frank Peggy Varnière Alexei Poludnenko Sorin Mitran Lee Hartmann 《Astrophysics and Space Science》2005,298(1-2):317-322
We present two dimensional cylindrically symmetric hydrodynamic simulations and synthetic emission maps of a stellar wind
propagating into an infalling, rotating environment. The resulting outflow morphology, collimation and stability observed
in these simulations have relevance to the study of young stellar objects, Herbig-Haro jets and molecular outflows. Our code
follows hydrogen gas with molecular, atomic and ionic components tracking the associated time dependent molecular chemistry
and ionization dynamics with radiative cooling appropriate for a dense molecular gas. We present tests of the code as well
as new simulations which indicate the presence of instabilities in the wind-blown bubble’s swept-up shell. 相似文献
180.
Martin D. Robards Michael L. SchoonChanda L. Meek Nathan L. Engle 《Global Environmental Change》2011,21(2):522-529
While a sustained flow of ecosystem services brings tangible benefits to humans, some ecosystem states and suites of services may be more desired by some people than others. Allocating or using the flow of services is loaded with asymmetries, complex power dynamics and political struggles between groups of people. We argue that the issues associated with such allocation and use questions are poorly integrated into the literatures of resilience, sustainability, and vulnerability. To illustrate this, we focus on three socially constructed factors that inhibit a fuller understanding about how to sustain the flow of ecosystem services: (1) rigidity/poverty traps; (2) power asymmetries; and (3) scientization of policy/politicization of science. These factors limit our ability to assess the sustainable flows of ecosystem services, and in particular to better understand the trade-offs and limits to aggregate human activity. We demonstrate that an improved understanding of the allocation trade-offs and limits to the flows of ecosystem services could result from more applied research that integrates the developing fields of deliberative democracy, pragmatic environmental philosophy, and legitimacy and rule compliance. Without the understanding that such integration would bring, researchers and policy makers risk underestimating the limits on flows of ecosystem services and how to accomplish their provision toward the greater collective - rather than individual - good. 相似文献