Probing the massive star forming environment - a multiwavelength investigation of the filamentary IRDC G333.73+0.37

We present a multiwavelength study of the filamentary infrared dark cloud (IRDC) G333.73+0.37. The region contains two distinct mid-infrared sources S1 and S2 connected by dark lanes of gas and dust. Cold dust emission from the IRDC is detected at seven wavelength bands and we have identified 10 high density clumps in the region. The physical properties of the clumps such as temperature: 14.3-22.3 K and mass: 87-1530 M_sun are determined by fitting a modified blackbody to the spectral energy distribution of each clump between 160 micron and 1.2 mm. The total mass of the IRDC is estimated to be $~4700 M_sun. The molecular line emission towards S1 reveals signatures of protostellar activity. Low frequency radio emission at 1300 and 610 MHz is detected towards S1 (shell-like) and S2 (compact morphology), confirming the presence of newly formed massive stars in the IRDC. Photometric analysis of near and mid-infrared point sources unveil the young stellar object population associated with the cloud. Fragmentation analysis indicates that the filament is supercritical. We observe a velocity gradient along the filament, that is likely to be associated with accretion flows within the filament rather than rotation. Based on various age estimates obtained for objects in different evolutionary stages, we attempt to set a limit to the current age of this cloud.Comment: 26 pages, 20 figures, accepted by Ap

Evolution and excitation conditions of outflows in high-mass star-forming regions

Theoretical models suggest that massive stars form via disk-mediated accretion, with bipolar outflows playing a fundamental role. A recent study toward massive molecular outflows has revealed a decrease of the SiO line intensity as the object evolves. The present study aims at characterizing the variation of the molecular outflow properties with time, and at studying the SiO excitation conditions in outflows associated with massive YSOs. We used the IRAM30m telescope to map 14 massive star-forming regions in the SiO(2-1), SiO(5-4) and HCO+(1-0) outflow lines, and in several dense gas and hot core tracers. Hi-GAL data was used to improve the spectral energy distributions and the L/M ratio, which is believed to be a good indicator of the evolutionary stage of the YSO. We detect SiO and HCO+ outflow emission in all the sources, and bipolar structures in six of them. The outflow parameters are similar to those found toward other massive YSOs. We find an increase of the HCO+ outflow energetics as the object evolve, and a decrease of the SiO abundance with time, from 10^(-8) to 10^(-9). The SiO(5-4) to (2-1) line ratio is found to be low at the ambient gas velocity, and increases as we move to high velocities, indicating that the excitation conditions of the SiO change with the velocity of the gas (with larger densities and/or temperatures for the high-velocity gas component). The properties of the SiO and HCO+ outflow emission suggest a scenario in which SiO is largely enhanced in the first evolutionary stages, probably due to strong shocks produced by the protostellar jet. As the object evolves, the power of the jet would decrease and so does the SiO abundance. During this process, however, the material surrounding the protostar would have been been swept up by the jet, and the outflow activity, traced by entrained molecular material (HCO+), would increase with time.Comment: 31 pages, 10 figures and 5 tables (plus 2 figures and 3 tables in the appendix). Accepted for publication in A&A. [Abstract modified to fit the arXiv requirements.

A study on subarcsecond scales of the ammonia and continuum emission toward the G16.59-0.05 high-mass star-forming region

We wish to investigate the structure, velocity field, and stellar content of the G16.59-0.05 high-mass star-forming region, where previous studies have established the presence of two almost perpendicular (NE-SW and SE-NW), massive outflows, and a rotating disk traced by methanol maser emission. We performed Very Large Array observations of the radio continuum and ammonia line emission, complemented by COMICS/Subaru and Hi-GAL/Herschel images in the mid- and far-infrared (IR). Our centimeter continuum maps reveal a collimated radio jet that is oriented E-W and centered on the methanol maser disk, placed at the SE border of a compact molecular core. The spectral index of the jet is negative, indicating non-thermal emission over most of the jet, except the peak close to the maser disk, where thermal free-free emission is observed. We find that the ammonia emission presents a bipolar structure consistent (on a smaller scale) in direction and velocity with that of the NE-SW bipolar outflow detected in previous CO observations. After analyzing our previous N2H+(1-0) observations again, we conclude that two scenarios are possible. In one case both the radio jet and the ammonia emission would trace the root of the large-scale CO bipolar outflow. The different orientation of the jet and the ammonia flow could be explained by precession and/or a non-isotropic density distribution around the star. In the other case, the N2H+(1-0) and ammonia bipolarity is interpreted as two overlapping clumps moving with different velocities along the line of sight. The ammonia gas also seems to undergo rotation consistent with the maser disk. Our IR images complemented by archival data allow us to derive a bolometric luminosity of about 10^4 L_sun and to conclude that most of the luminosity is due to the young stellar object associated with the maser disk.Comment: 11 pages, 12 figures, published in Astronomy and Astrophysic

Designability of alpha-helical Proteins

A typical protein structure is a compact packing of connected alpha-helices and/or beta-strands. We have developed a method for generating the ensemble of compact structures a given set of helices and strands can form. The method is tested on structures composed of four alpha-helices connected by short turns. All such natural four-helix bundles that are connected by short turns seen in nature are reproduced to closer than 3.6 Angstroms per residue within the ensemble. Since structures with no natural counterpart may be targets for ab initio structure design, the designability of each structure in the ensemble -- defined as the number of sequences with that structure as their lowest energy state -- is evaluated using a hydrophobic energy. For the case of four alpha-helices, a small set of highly designable structures emerges, most of which have an analog among the known four-helix fold families, however several novel packings and topologies are identified.Comment: 21 pages, 6 figures, to appear in PNA

Cell adhesion in free-standing multilayer films made of chitosan and alginate

The method for preparing multilayer ultrathin films by the consecu- tive deposition of oppositely charged polyelectrolytes has gained tre- mendous recognition due the user friendly preparation, capability of incorporating high loads of different types of biomolecules in the films, fine control over the materials’ structure, and robustness of the products under ambient and physiological conditions. However the preparation of such films needs the assembly on a substrate and, sometimes, cannot be detached from it, which has limited the appli- cation of such films in areas as tissue engineering and regenerative medicine (TERM).Thus, the production of free-standing films is of extreme importance once it allows the direct experimental determi- nation of many physical properties of fundamental significance such as ion permeation and mechanical properties that can be tuned for real-world applications. In this work, we investigated the elaboration of free-standing multilayer films made of chitosan (CHI) and alginate (ALG), by detaching a polyelectrolyte multilayer film from its under- lying substrate without any postprocessing step. The conditions for optimized film growth were investigated. The adhesion of C2C12 myoblast cells on the CHI/ALG membrane was assessed by cytoskele- tal and nuclear staining. A good cell adhesion and spreading was observed all over the surface. The results demonstrate the potential of such biocompatible free standing membranes made of CHI and ALG for applications in TERM

Kinematics of the ionized-to-neutral interfaces in Monoceros R2

Context. Monoceros R2 (Mon R2), at a distance of 830 pc, is the only ultra-compact H ii region (UC H ii) where its associated photon-dominated region (PDR) can be resolved with the Herschel Space Observatory. Aims. Our aim is to investigate observationally the kinematical patterns in the interface regions (i.e., the transition from atomic to molecular gas) associated with Mon R2. Methods. We used the HIFI instrument onboard Herschel to observe the line profiles of the reactive ions CH+, OH+ and H2O+ toward different positions in Mon R2. We derive the column density of these molecules and compare them with gas-phase chemistry models. Results. The reactive ion CH+ is detected both in emission (at central and red-shifted velocities) and in absorption (at blue-shifted velocities). OH+ is detected in absorption at both blue- and red-shifted velocities, with similar column densities. H2O+ is not detected at any of the positions, down to a rms of 40 mK toward the molecular peak. At this position, we find that the OH+ absorption originates in a mainly atomic medium, and therefore is associated with the most exposed layers of the PDR. These results are consistent with the predictions from photo-chemical models. The line profiles are consistent with the atomic gas being entrained in the ionized gas flow along the walls of the cavity of the H ii region. Based on this evidence, we are able to propose a new geometrical model for this region. Conclusions. The kinematical patterns of the OH+ and CH+ absorption indicate the existence of a layer of mainly atomic gas for which we have derived, for the first time, some physical parameters and its dynamics.Comment: 6 pages, 5 figures. Accepted for publication in A&

Candida albicans pathogenicity mechanisms

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