A Simple Perspective on the Mass-Area Relationship in Molecular Clouds

Despite over 30 years of study, the mass-area relationship within and among clouds is still poorly understood both observationally and theoretically. Modern extinction datasets should have sufficient resolution and dynamic range to characterize this relationship for nearby molecular clouds, although recent papers using extinction data seem to yield different interpretations regarding the nature and universality of this aspect of cloud structure. In this paper we try to unify these various results and interpretations by accounting for the different ways cloud properties are measured and analyzed. We interpret the mass-area relationship in terms of the column density distribution function and its possible variation within and among clouds. We quantitatively characterize regional variations in the column density PDF. We show that structures both within and among clouds possess the same degree of "universality", in that their PDF means do not systematically scale with structure size. Because of this, mass scales linearly with area.Comment: 10 pages, 8 figures, MNRAS in pres

Routine use of Hemospray for gastrointestinal bleeding: prospective two-center experience in Switzerland

Hemospray (Cook Medical, Winston-Salem, North Carolina, USA) is a hemostatic agent recently introduced for the management of upper gastrointestinal bleeding (GIB). To date, there is little experience with this fairly new hemostatic tool. The aim of this case series was to reflect the use and effectiveness of Hemospray as a treatment option in GIB in everyday clinical practice at two tertiary referral centers. Consecutive patients (n = 16) with active GIB of various origins were treated with Hemospray. The rate of successful initial hemostasis was 93.75 % (15 /16; salvage therapy 92.85 % [13/14]; monotherapy 100 % [2 /2]). The rebleeding rate within 7 days was 12.5 % (2/16). One patient, in whom interventional radiology also failed, had to undergo surgery as salvage therapy. The effectiveness of Hemospray in the management of GIB in various clinical situations is promising. Future multicenter randomized prospective trials for clearly defined bleeding situations are needed for greater generalizability of case series findings

Radiation-magnetohydrodynamic simulations of the photoionisation of magnetised globules

We present the first three-dimensional radiation-magnetohydrodynamic simulations of the photoionisation of a dense, magnetised molecular globule by an external source of ultraviolet radiation. We find that, for the case of a strong ionising field, significant deviations from the non-magnetic evolution are seen when the initial magnetic field threading the globule has an associated magnetic pressure that is greater than one hundred times the gas pressure. In such a strong-field case, the photoevaporating globule will adopt a flattened or "curled up" shape, depending on the initial field orientation, and magnetic confinement of the ionised photoevaporation flow can lead to recombination and subsequent fragmentation during advanced stages of the globule evolution. We find suggestive evidence that such magnetic effects may be important in the formation of bright, bar-like emission features in H II regions. We include simple but realistic fits to heating and cooling rates in the neutral and molecular gas in the vicinity of a high-mass star cluster and show that the frequently used isothermal approximation can lead to an overestimate of the importance of gravitational instability in the radiatively imploded globule. For globules within 2 parsecs of a high-mass star cluster, we find that heating by stellar x rays prevents the molecular gas from cooling below 50 K.Comment: 19 pages, 16 figures, many in full color. Accepted by MNRAS. Updated to reflect the accepted version. Significantly expanded and improved with respect to the first version. Well worth downloading agai