ner_tags: O O O O O O O O O O O O O O B-Citation I-Citation I-Citation O O O O O O O O O O O B-CelestialObject B-CelestialObject O O B-CelestialObject O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Citation I-Citation I-Citation I-Citation I-Citation I-Citation O O O O O O O O O O B-CelestialObject I-CelestialObject O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Wavelength O O O O O B-Wavelength I-Wavelength O O O O O O O O O O O O O O O O O O O O B-Citation I-Citation I-Citation I-Citation I-Citation I-Citation O O O O O O O B-CelestialObjectRegion I-CelestialObjectRegion O O O O B-CelestialObject B-CelestialObject B-CelestialObject O O B-CelestialObject I-CelestialObject B-CelestialObject O B-CelestialObject O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-CelestialObject O B-CelestialObject O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Formula I-Formula I-Formula I-Formula O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Citation I-Citation I-Citation I-Citation I-Citation I-Citation O O O O O O O O O O O O O O O O O O
tokens: flows merely graze past each other appear qualitatively similar to the fits provided by Lombardi et al. to the N-PDFs deduced by them for clouds such as the Perseus, Pipe or the California. All of these latter clouds exhibit little star-forming activity. The potential star-forming ability of a cloud can also be quantitatively assessed by investigating into the fraction of gas cycled into the dense phase. The latter realization, realization 4, is most inefficient in transforming gas into the dense phase as is reflected by the relatively small dense-gas fraction in the plot on the upper panel of Fig. 6 . Similarly, the SFF shown on the lower panel of Fig. 6 , for this latter case declines rapidly to less than a percent while that for the remaining three realizations, can be seen to rise steadily. In fact, Orkisz et al. ( 2017 ) attribute the observed poor efficiency of star formation in the Orion B cloud to the impact of large-scale differential motion causing the gas within the cloud to shear. The next set of plots in Fig. 7 showing the cumulative distribution of gas mass as a function of visual extinction (actually calculation for the K -band extinction), is also quite revealing from the perspective of the star-forming ability of a cloud. Similar plots were deduced by Lada, Lombardi Alvés ( 2010 ) for an ensemble of MCs in the Solar neighbourhood. Clouds such as the Pipe, Perseus, California and the Lupus 1, 3 and 4 known for their poverty in forming stars, showed mass distribution very similar to that for clouds assembled via collisions having a large impact parameter (realization 4 here), where there is very little mass at large extinction. By contrast, the mass distribution for the cloud assembled in realization 1, where the collision was almost head-on is similar to that for MCs such as the Orion or Ophiuchus that form stars more efficiently. It is of course true that stellar feedback in these latter clouds must also contribute to star formation in these latter clouds. We therefore restrict ourselves to the inference that a pristine cloud assembled via head-on or near head-on collision is likely to cycle a larger fraction of gas to higher extinctions ( A K > 1), which could then possibly become future birth-sites for stars. It is indeed interesting that a relatively simple self-gravitating, hydrodynamic model such as the one discussed here can possibly reconcile the observed variations in the distribution of gas mass as a function of visual extinction in nearby MCs. Finally, we examined the possible correlation between the fraction of gas cycled into the dense phase and the relative strength of compressional/solenoidal modes in the velocity field induced in the assembled cloud. The propensity of compressional modes towards assembling putative star-forming gas was demonstrated by Federrath, Klessen Schmidt ( 2008 ). They showed numerically that gas dominated by compressional turbulence, as indicated by the strength of the so-called driving