Maria Beltrán | UAP - Academia.edu (original) (raw)
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University of the Basque Country, Euskal Herriko Unibertsitatea
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Papers by Maria Beltrán
Multiple independent communications are studied on optical bus parallel computing models. These m... more Multiple independent communications are studied on optical bus parallel computing models. These models make use of an optical bus interconnect to provide for communication in a multi-processor system. The communication traffic studied in this paper results in potential frequent bus collisions. The well known collision detect mechanism is ineffective however due to the communication pipelining aspect of the optical bus. An analysis of the conditions necessary for bus collision and the subsequent communications model that represents the necessary information to determine potential bus collisions are presented. A simulation based on this model as well as results from the simulation are discussed. The results indicate collision patterns and trends in sequences of general communications. The model and simulation considered in this paper establishes a mechanism that enables future analysis of general communication usage of optical buses.
Nature, 2006
Theory predicts and observations confirm that low-mass stars (like the Sun) in their early life g... more Theory predicts and observations confirm that low-mass stars (like the Sun) in their early life grow by accreting gas from the surrounding material. But for stars ~ 10 times more massive than the Sun (~10 M_sun), the powerful stellar radiation is expected to inhibit accretion and thus limit the growth of their mass. Clearly, stars with masses >10 M_sun exist, so there must be a way for them to form. The problem may be solved by non-spherical accretion, which allows some of the stellar photons to escape along the symmetry axis where the density is lower. The recent detection of rotating disks and toroids around very young massive stars has lent support to the idea that high-mass (> 8 M_sun) stars could form in this way. Here we report observations of an ammonia line towards a high-mass star forming region. We conclude from the data that the gas is falling inwards towards a very young star of ~20 M_sun, in line with theoretical predictions of non-spherical accretion.
Astronomy & Astrophysics, 2009
Context: L1157-mm is a low-mass protostar driving an outflow which is considered the proto-type o... more Context: L1157-mm is a low-mass protostar driving an outflow which is considered the proto-type of the so-called chemically active outflows. In particular, the blue-shifted lobe B1 stands out for its rich mm-wave spectrum. Aims: Our aim is to infer the physical conditions of the molecular gas within L1157-B1. Methods: We carried out CH3CN(8{K}-7{K}) observations at 2 mm with the IRAM
Astronomy & Astrophysics, 2004
We present high angular resolution interferometric observations of the dust continuum at 2.7 and ... more We present high angular resolution interferometric observations of the dust continuum at 2.7 and 1.3 mm, and of the HC3N (12-11) and C18O (2-1) emission around L1157-mm, a Class~0 object that drives a spectacular molecular outflow. The millimeter dust emission is clearly resolved into two components, a flattened compact source of ~450 x 250 AU at 1.3 mm, and mass ~0.1 Msun, plus an extended envelope of ~3000 AU at 1.3 mm, and mass ~1.1 Msun. The millimeter spectral index varies throughout the region, with the lower value found toward the compact protostar, possibly indicating grain growth in the denser regions. A strong interaction between the molecular outflow and the close protostellar environment is taking place and affects the structure of the innermost parts of the envelope. This is shown by the spatial coincidence between the molecular outflow and the dust (1.3 mm continuum) and HC3N emission: both tracers show structures associated to the edges of the outflow lobes. Basically, the global picture sketched for the Class 0 object L1157-mm by Gueth et al. (1997) is supported. We find possible evidence of infall, but we do not detect any velocity gradient indicative of a rotating circumstellar disk.
Multiple independent communications are studied on optical bus parallel computing models. These m... more Multiple independent communications are studied on optical bus parallel computing models. These models make use of an optical bus interconnect to provide for communication in a multi-processor system. The communication traffic studied in this paper results in potential frequent bus collisions. The well known collision detect mechanism is ineffective however due to the communication pipelining aspect of the optical bus. An analysis of the conditions necessary for bus collision and the subsequent communications model that represents the necessary information to determine potential bus collisions are presented. A simulation based on this model as well as results from the simulation are discussed. The results indicate collision patterns and trends in sequences of general communications. The model and simulation considered in this paper establishes a mechanism that enables future analysis of general communication usage of optical buses.
Nature, 2006
Theory predicts and observations confirm that low-mass stars (like the Sun) in their early life g... more Theory predicts and observations confirm that low-mass stars (like the Sun) in their early life grow by accreting gas from the surrounding material. But for stars ~ 10 times more massive than the Sun (~10 M_sun), the powerful stellar radiation is expected to inhibit accretion and thus limit the growth of their mass. Clearly, stars with masses >10 M_sun exist, so there must be a way for them to form. The problem may be solved by non-spherical accretion, which allows some of the stellar photons to escape along the symmetry axis where the density is lower. The recent detection of rotating disks and toroids around very young massive stars has lent support to the idea that high-mass (> 8 M_sun) stars could form in this way. Here we report observations of an ammonia line towards a high-mass star forming region. We conclude from the data that the gas is falling inwards towards a very young star of ~20 M_sun, in line with theoretical predictions of non-spherical accretion.
Astronomy & Astrophysics, 2009
Context: L1157-mm is a low-mass protostar driving an outflow which is considered the proto-type o... more Context: L1157-mm is a low-mass protostar driving an outflow which is considered the proto-type of the so-called chemically active outflows. In particular, the blue-shifted lobe B1 stands out for its rich mm-wave spectrum. Aims: Our aim is to infer the physical conditions of the molecular gas within L1157-B1. Methods: We carried out CH3CN(8{K}-7{K}) observations at 2 mm with the IRAM
Astronomy & Astrophysics, 2004
We present high angular resolution interferometric observations of the dust continuum at 2.7 and ... more We present high angular resolution interferometric observations of the dust continuum at 2.7 and 1.3 mm, and of the HC3N (12-11) and C18O (2-1) emission around L1157-mm, a Class~0 object that drives a spectacular molecular outflow. The millimeter dust emission is clearly resolved into two components, a flattened compact source of ~450 x 250 AU at 1.3 mm, and mass ~0.1 Msun, plus an extended envelope of ~3000 AU at 1.3 mm, and mass ~1.1 Msun. The millimeter spectral index varies throughout the region, with the lower value found toward the compact protostar, possibly indicating grain growth in the denser regions. A strong interaction between the molecular outflow and the close protostellar environment is taking place and affects the structure of the innermost parts of the envelope. This is shown by the spatial coincidence between the molecular outflow and the dust (1.3 mm continuum) and HC3N emission: both tracers show structures associated to the edges of the outflow lobes. Basically, the global picture sketched for the Class 0 object L1157-mm by Gueth et al. (1997) is supported. We find possible evidence of infall, but we do not detect any velocity gradient indicative of a rotating circumstellar disk.