107 research outputs found
Enhanced thermal stability and fracture toughness of TiAlN coatings by Cr, Nb and V-alloying
The effect of metal alloying on mechanical properties including hardness and fracture toughness were investigated in three alloys, Ti~0.33Al0.50(Me)~0.17N (Me¿=¿Cr, Nb and V), and compared to Ti0.50Al0.50N, in the as-deposited state and after annealing. All studied alloys display similar as-deposited hardness while the hardness evolution during annealing is found to be connected to phase transformations, related to the alloy's thermal stability. The most pronounced hardening was observed in Ti0.50Al0.50N, while all the coatings with additional metal elements sustain their hardness better and they are harder than Ti0.50Al0.50N after annealing at 1100¿°C. Fracture toughness properties were extracted from scratch tests. In all tested conditions, as-deposited and annealed at 900 and 1100¿°C, Ti0.33Al0.50Nb0.17N show the least surface and sub-surface damage when scratched despite the differences in decomposition behavior and h-AlN formation. Theoretically estimated ductility of phases existing in the coatings correlates well with their crack resistance. In summary, Ti0.33Al0.50Nb0.17N is the toughest alloy in both as-deposited and post-annealed states.Peer ReviewedPostprint (author's final draft
Investigating particle acceleration in Protostellar Jets: The triple radio continuum source in serpens
While most protostellar jets present free-free emission at radio wavelengths, synchrotron emission has also been proposed to be present in a handful of these objects. The presence of nonthermal emission has been inferred by negative spectral indices at centimeter wavelengths. In one case (the HH 80-81 jet arising from a massive protostar), its synchrotron nature was confirmed by the detection of linearly polarized radio emission. One of the main consequences of these results is that synchrotron emission implies the presence of relativistic particles among the nonrelativistic material of these jets. Therefore, an acceleration mechanism should be taking place. The most probable scenario is that particles are accelerated when the jets strongly impact against the dense envelope surrounding the protostar. Here we present an analysis of radio observations obtained with the Very Large Array of the triple radio source in the Serpens star-forming region. This object is known to be a radio jet arising from an intermediate-mass protostar. It is also one of the first protostellar jets where the presence of nonthermal emission was proposed. We analyze the dynamics of the jet and the nature of the emission and discuss these issues in the context of the physical parameters of the jet and the particle acceleration phenomenon.Fil: RodrÃguez Kamenetzky, Adriana Raquel. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Centro CientÃfico Tecnológico Conicet - Córdoba. Instituto de AstronomÃa Teórica y Experimental. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba. Instituto de AstronomÃa Teórica y Experimental; ArgentinaFil: Carrasco Gonzalez, Carlos Eugenio. Universidad Nacional Autónoma de México; MéxicoFil: Araudo, Anabella Teresa. University of Oxford. Department of Physics; Reino Unido. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones CientÃficas. Instituto Argentino de RadioastronomÃa. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Centro CientÃfico Tecnológico Conicet - La Plata. Instituto Argentino de RadioastronomÃa; ArgentinaFil: Torrelles, Jose M.. Universidad de Barcelona; EspañaFil: Anglada, Guillem. Instituto de Astrofisica Andalucia; EspañaFil: Marti, Josep. Universidad de Jaén; EspañaFil: Luis Felipe Rodriguez. Universidad Nacional Autónoma de México; MéxicoFil: Valotto, Carlos Alberto. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Centro CientÃfico Tecnológico Conicet - Córdoba. Instituto de AstronomÃa Teórica y Experimental. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba. Instituto de AstronomÃa Teórica y Experimental; Argentin
Infrared and optical polarimetry around the low-mass star-forming region NGC 1333 IRAS 4A
We performed J- and R-band linear polarimetry with the 4.2 m William Herschel
Telescope at the Observatorio del Roque de los Muchachos and with the 1.6 m
telescope at the Observat\'orio do Pico dos Dias, respectively, to derive the
magnetic field geometry of the diffuse molecular cloud surrounding the embedded
protostellar system NGC 1333 IRAS 4A. We obtained interstellar polarization
data for about two dozen stars. The distribution of polarization position
angles has low dispersion and suggests the existence of an ordered magnetic
field component at physical scales larger than the protostar. Some of the
observed stars present intrinsic polarization and evidence of being young
stellar objects. The estimated mean orientation of the interstellar magnetic
field as derived from these data is almost perpendicular to the main direction
of the magnetic field associated with the dense molecular envelope around IRAS
4A. Since the distribution of the CO emission in NGC 1333 indicates that the
diffuse molecular gas has a multi-layered structure, we suggest that the
observed polarization position angles are caused by the superposed projection
along the line of sight of different magnetic field components.Comment: 37 pages, 9 figures, 5 tables, accepted for publication in A
An SiO Toroid and Wide-angle Outflow associated with the Massive Protostar W75N(B)-VLA2
We have carried out ALMA observations of the massive star-forming region
W75N(B), which contains the massive protostars VLA1, VLA2, and VLA3.
Particularly, VLA2 is an enigmatic protostar associated with a wind-driven
HO maser shell, which has evolved from an almost isotropic outflow to a
collimated one in just 20 years. The shell expansion seemed to be halted by an
obstacle located to the northeast of VLA2. Here we present our findings from
observing the 1.3 mm continuum and HCO and SiO emission lines. Within a
region of ( au) diameter, we have detected 40 compact
mm-continuum sources, three of them coinciding with VLA1, VLA2, and VLA3. While
the HCO emission is mainly distributed in a fragmented structure around the
three massive protostars, but without any of the main HCO clumps spatially
coinciding with them, the SiO is highly concentrated on VLA2, indicating the
presence of very strong shocks generated near this protostar. The SiO emission
is clearly resolved into an elongated structure (; au390 au) perpendicular to the major axis of the wind-driven maser
shell. The structure and kinematics of the SiO emission are consistent with a
toroid and a wide-angle outflow surrounding a central mass of
M, thus supporting previous theoretical predictions regarding the
evolution of the outflow. Additionally, we have identified the expected
location and estimated the gas density of the obstacle that is hindering the
expansion of the maser shell.Comment: To be published in The Astrophysical Journal Letters. Sixteen pages,
seven figures. Updated metadat
Understanding variations in the use of hypofractionated radiotherapy and its specific indications for breast cancer: A mixed-methods study
Background and purpose: Radiation oncology guidelines favour hypofractionated whole-breast radiotherapy (HWBRT) over more conventional schemes in the conservative treatment of breast cancer, but its adoption still varies in clinical practice. This study assessed the patterns of HWBRT adoption in Catalonia (Spain). Material and methods: We used a mixed-methods approach based on an explanatory sequential design, first collecting and analysing quantitative data on HWBRT use (>2.5 Gy per fraction) in 11 public radiotherapy centres (2005-2015) and then performing 25 semi-structured interviews with all department heads and reference radiation oncologist/s. Results: Of the 34,859 patients fulfiling the study criteria over the study period, just 12% were hypofractionated, reaching a percentage of 29% in 2015 (p < 0.001). Our analysis showed a narrowing age gap between patients receiving conventional fractionation and hypofractionation in centres leading adoption. However, there were important differences in clinicians' interpretation of evidence (e.g. regarding the perceived risk of long-term toxicity) and selection of patients for specific indications, both within and between departments. Conclusions: Differences observed in the rate of adoption of HWBRT could not be tackled only using a rational, evidence-based approach. Factors related to the management of radiotherapy departments play a major role in the diffusion of therapeutic strategies
- …