6,854 research outputs found
QCD and Hadronic Interactions - Experimental Summary of Moriond 03
The broad progress in QCD studies during the last years is summarise
Young Clusters in the Magellanic Clouds II
We present the results of a quantitative study of the degree of extension to
the boundary of the classical convective core within intermediate mass stars.
The basis of our empirical study is the stellar population of four young
populous clusters in the Magellanic Clouds which has been detailed in Keller,
Bessell & Da Costa (2000). The sample affords a meaningful comparison with
theoretical scenarios with varying degrees of convective core overshoot and
binary star fraction. Two critical properties of the population, the
main-sequence luminosity function and the number of evolved stars, form the
basis of our comparison between the observed data set and that simulated from
the stellar evolutionary models. On the basis of this comparison we conclude
that the case of no convective core overshoot is excluded at a 2 sigma level.Comment: 27 pages, 12 figures, AJ accepte
A comparison of evolutionary tracks for single Galactic massive stars
In this paper, we compare the currently available evolutionary tracks for
Galactic massive stars. Our main goal is to highlight the uncertainties on the
predicted evolutionary paths. We compute stellar evolution models with the
codes MESA and STAREVOL. We compare our results with those of four published
grids of massive stellar evolution models (Geneva, STERN, Padova and FRANEC
codes). We first investigate the effects of overshooting, mass loss,
metallicity, chemical composition. We subsequently focus on rotation. Finally,
we compare the predictions of published evolutionary models with the observed
properties of a large sample of Galactic stars. We find that all models agree
well for the main sequence evolution. Large differences in luminosity and
temperatures appear for the post main sequence evolution, especially in the
cool part of the HR diagram. Depending on the physical ingredients, tracks of
different initial masses can overlap, rendering any mass estimate doubtful. For
masses between 7 and 20 Msun, we find that the main sequence width is slightly
too narrow in the Geneva models including rotation. It is (much) too wide for
the (STERN) FRANEC models. This conclusion is reached from the investigation of
the HR diagram and from the evolution of the surface velocity as a function of
surface gravity. An overshooting parameter alpha between 0.1 and 0.2 in models
with rotation is preferred to reproduce the main sequence width. Determinations
of surface abundances of carbon and nitrogen are partly inconsistent and cannot
be used at present to discriminate between the predictions of published tracks.
For stars with initial masses larger than about 60 Msun, the FRANEC models with
rotation can reproduce the observations of luminous O supergiants and WNh
stars, while the Geneva models remain too hot.Comment: 17 pages, 12 figures. Accepted by Astronomy & Astrophysic
A New, Efficient Stellar Evolution Code for Calculating Complete Evolutionary Tracks
We present a new stellar evolution code and a set of results, demonstrating
its capability at calculating full evolutionary tracks for a wide range of
masses and metallicities. The code is fast and efficient, and is capable of
following through all evolutionary phases, without interruption or human
intervention. It is meant to be used also in the context of modeling the
evolution of dense stellar systems, for performing live calculations for both
normal star models and merger-products.
The code is based on a fully implicit, adaptive-grid numerical scheme that
solves simultaneously for structure, mesh and chemical composition. Full
details are given for the treatment of convection, equation of state, opacity,
nuclear reactions and mass loss.
Results of evolutionary calculations are shown for a solar model that matches
the characteristics of the present sun to an accuracy of better than 1%; a 1
Msun model for a wide range of metallicities; a series of models of stellar
populations I and II, for the mass range 0.25 to 64 Msun, followed from
pre-main-sequence to a cool white dwarf or core collapse. An initial final-mass
relationship is derived and compared with previous studies. Finally, we briefly
address the evolution of non-canonical configurations, merger-products of
low-mass main-sequence parents.Comment: MNRAS, in press; several sections and figures revise
A Systematic Review
The use of smart technology, specifically inertial sensors (accelerometers, gyroscopes, and magnetometers), to analyze swimming kinematics is being reported in the literature. However, little is known about the usage/application of such sensors in other human aquatic exercises. As the sensors are getting smaller, less expensive, and simple to deal with (regarding data acquisition), one might consider that its application to a broader range of exercises should be a reality. The aim of this systematic review was to update the state of the art about the framework related to the use of sensors assessing human movement in an aquatic environment, besides swimming. The following databases were used: IEEE Xplore, Pubmed, Science Direct, Scopus, and Web of Science. Five articles published in indexed journals, aiming to assess human exercises/movements in the aquatic environment were reviewed. The data from the five articles was categorized and summarized based on the aim, purpose, participants, sensor's specifications, body area and variables analyzed, and data analysis and statistics. The analyzed studies aimed to compare the movement/exercise kinematics between environments (i.e., dry land versus aquatic), and in some cases compared healthy to pathological participants. The use of sensors in a rehabilitation/hydrotherapy perspective may provide major advantages for therapists.Bolsa BIPD/ICIFCSH-Santander Universidades—UBI/2017info:eu-repo/semantics/publishedVersio
1995, Spatial and temporal variability of late Neogene equatorial Pacific carbonate
High-resolution, continuous records of GRAPE wet bulk density (a carbonate proxy) from Ocean Drilling Program Leg 138 provide one the opportunity for a detailed study of eastern equatorial Pacific Ocean carbonate sedimentation during the last 6 m.y. The transect of sites drilled spans both latitude and longitude in the eastern equatorial Pacific from 90° to 110°W and from 5°S to 10°N. Two modes of variability are resolved through the use of Empirical Orthogonal Function (EOF) analysis. In the presence of large tectonic and climatic boundary condition changes over the last 6 m.y., the dominant mode of spatial variability in carbonate sedimentation is remarkably constant. The first mode accounts for over 50% of the variance in the data, and is consistent with forcing by equatorial divergence. This mode characterizes both carbonate concentration and carbonate mass accumulation rate time series. Variability in the first mode is highly coherent with insolation, indicating a strong linear relationship between equatorial Pacific car bonate sedimentation and Milankovitch variability. Frequency domain analysis indicates that the coupling to equatorial divergence in carbonate sedimentation is strongest in the precession band (19-23 k.y.) and weakest though present at lower frequencies. The second mode of variability has a consistent spatial pattern of east-west asymmetry over the past 4 m.y. only; prior to 4 Ma, a different mode of spatial variability may have been present, possibly suggesting influence by closure of the Isthmus of Panama or other tectonic changes. The second mode of variability may indicate influence by CaCO3 dissolution. The second mode of variability is not highly coherent with insolation. Comparison of the modes of carbonate variability to a 4 m.y. record of benthic δ 1 8 indicates that although overall correlation between carbonate and δ 1 8 is low, both modes of variability in carbonate sedimentation are coherent with δ 1 8 changes at some frequencies. The first mode of carbonate variability is coherent with Sites 846/849 δ 1 8 at the dominant insolation periods, and the second mode is coherent at 100 k.y. during the last 2 m.y. The coherence between carbonate sedimentation and δ 1 8 in both EOF modes suggests that multiple uncorrelated modes of variability operated within the climate system during the late Neogene
The MIG Framework: Enabling Transparent Process Migration in Open MPI
This paper introduces the mig framework: an Open MPI extension to transparently support the migration of application processes, over different nodes of a distributed High-Performance Computing (HPC) system. The framework provides mechanism on top of which suitable resource managers can implement policies to react to hardware faults, address performance variability, improve resource utilization, perform a fine-grained load balancing and power thermal management.
Compared to other state-of-the-art approaches, the mig framework does not require changes in the application code. Moreover, it is highly maintainable, since it is mainly a self-contained solution that has required a very few changes in other already existing Open MPI frameworks. Experimental results have shown that the proposed extension does not introduce significant overhead in the application execution, while the penalty due to performing a migration can be properly taken into account by a resource manager
- …