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Mordecai-Mark MacLow 《Astrophysics and Space Science》2004,289(3-4):323-331
Interstellar turbulence is expected to dissipate quickly in theabsence of continuous energy input. I examine the energy availablefor driving the turbulence from six likely mechanisms:magnetorotational instability, gravitational instability, protostellaroutflows, HII region expansion, stellar winds, and supernovae.I conclude that supernovae contribute far more energy than the othermechanisms, and so form the most likely drving mechanism. 相似文献
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Mordecai-Mark Mac Low Michael D. Smith Ralf S. Klessen Andreas Burkert 《Astrophysics and Space Science》1998,261(1-4):195-196
Supersonic and super-Alfvénic turbulent motions generate an intricate pattern of shock waves through which the turbulence
decays. We here illustrate the spatial structure during shock formation and decay.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
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The magnetic field plays a crucial role in star formation. It is involved in rotational braking, collapse braking, outflow
formation and jet collimation. Direct observations of the field are difficult. However, the field can be indirectly estimated
through the field-cushioned C-shocks which produce strong infrared molecular emission lines. In particular, a high field in
the outflows will generate the ‘shock absorber’ signature: very broad H2lines. Such lines are indeed observed.
Here we summarise recent progress in C-shock formation and stability. We demonstrate numerically that the Shock Absorbers
are evolutionary and stable. The widths of H2lines then limit the magnetic field strength. A field of 6 mG is suggested for HH 212.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
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We compare high-resolution 2D and 3D numerical hydrocode simulations of asteroids striking the atmosphere of Venus. Our focus is on aerobraking and its effect on the size of impact craters. We consider impacts both by spheres and by the real asteroid 4769 Castalia, a severely nonspherical body in a Venus-crossing orbit. We compute mass and momentum fluxes as functions of altitude as global measures of the asteroid's progress. We find that, on average, the 2D and 3D simulations are in broad agreement over how quickly an asteroid slows down, but that the scatter about the average is much larger for the 2D models than for the 3D models. The 2D models appear to be rather strongly susceptible to the “butterfly effect,” in which tiny changes in initial conditions (e.g., 0.05% change in the impact velocity) produce quite different chaotic evolutions. By contrast, the global properties of the 3D models appear more reproducible despite seemingly large differences in initial conditions. We argue that this difference between 2D and 3D models has its root in the greater geometrical constraints present in any 2D model, and in particular in the global conservation of enstrophy in 2D that forces energy to pool in large-scale structures. It is the interaction of these artificial large-scale structures that causes slightly different 2D models to diverge so greatly. These constraints do not apply in 3D and large scale structures are not observed to form. A one-parameter modified pancake model reproduces the expected crater diameters of the 3D Castalias reasonably well. 相似文献
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Mordecai-Mark Mac Low 《Astrophysics and Space Science》2002,281(1-2):429-438
Summary of the third discussion of the conference. Topics covered include the mechanisms controlling the star formation rate
ingalaxies, the source of the driving energy for interstellar turbulence, and the reasons for different star formation rates
ingalaxies with similar masses.
This revised version was published online in September 2006 with corrections to the Cover Date. 相似文献
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Alexander Hubbard Mordecai-Mark Mac Low Denton S. Ebel 《Meteoritics & planetary science》2018,53(7):1507-1515
Meteoritical and astrophysical models of planet formation make contradictory predictions for dust concentration factors in chondrule-forming regions of the solar nebula. Meteoritical and cosmochemical models strongly suggest that chondrules, a key component of the meteoritical record, formed in regions with solids-to-gas mass ratios orders above the solar nebula average. However, models of dust grain dynamics in protoplanetary disks struggle to surpass concentration factors of a few except during very short-lived stages in a dust grain's life. Worse, those models do not predict significant concentration factors for dust grains the size of chondrule precursors. We briefly develop the difficulty in concentrating dust particles in the context of nebular chondrule formation and show that the disagreement is sufficiently stark that cosmochemists should explore ideas that might revise the concentration factor requirements downward. 相似文献
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Guillermo García-Segura Mordecai-Mark Mac Low Norbert Langer 《Astrophysics and Space Science》1995,224(1-2):459-460
We follow the interaction of massive stars with their circumstellar gas over their entire life-times by combining hydrodynamic stellar evolution calculations for 35 and 60M
stars and one- and two-dimensional gas dynamical calculations for the circumstellar medium. 相似文献
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