1,774 research outputs found
Shape, spin and baryon fraction of clusters in the MareNostrum Universe
The MareNostrum Universe is one of the largest cosmological
SPH simulation done so far. It consists of dark and
gas particles in a box of 500 Mpc on a side. Here we study
the shapes and spins of the dark matter and gas components of the 10,000 most
massive objects extracted from the simulation as well as the gas fraction in
those objects. We find that the shapes of objects tend to be prolate both in
the dark matter and gas. There is a clear dependence of shape on halo mass, the
more massive ones being less spherical than the less massive objects. The gas
distribution is nevertheless much more spherical than the dark matter, although
the triaxiality parameters of gas and dark matter differ only by a few percent
and it increases with cluster mass. The spin parameters of gas and dark matter
can be well fitted by a lognormal distribution function. On average, the spin
of gas is 1.4 larger than the spin of dark matter. We find a similar behavior
for the spins at higher redshifts, with a slightly decrease of the spin ratios
to 1.16 at The cosmic normalized baryon fraction in the entire cluster
sample ranges from , at to at . At both
redshifts we find a slightly, but statistically significant decrease of
with cluster mass.Comment: 7 pages, 6 figures. Accepted for publication in The Astrophysical
Journa
SIG et évaluation des risques naturels : application aux risques sismiques de Quito
L'article retrace rapidement les principales étapes de la réalisation d'un scénario sismique sur la ville de Quito. Les croisements nécessaires entre les données provenant de domaines variés (sciences de la terre, ingénierie civile, et sociodémographie) ont pu être effectués rapidement grâce à l'utilisation du SIG SAVANE. LE SIG a permis l'édition de documents graphiques décrivant de façon concrète la vulnérabilité sismique de la ville, facilitant ainsi la prise de conscience des responsables politiques et économiques. (Résumé d'auteur
Aplicaciones comerciales de Pride en el litoral atlántico para el control de coquito (Cyperus rotundus)
Por invitación especial de la compañía Banco, efectuamos una comisión los primeros días de diciembre de 1980, a las áreas algodoneras de Codazzi, Valledupar, Bosconia, El Copey, Algarrobo, Luruaco e Hibacharo, para observar la action del producto Pride 50% sobre el "coquito" (Cyperus rotundus).
En esta comisión participaron activamente, además del autor, los ingenieros agr6nomos José Ignacio Giraldo, Arturo Cuervo, Fernando Garcia, Gustavo Villegas y Jaime Visbal, técnicos de la compañía Banco.Arroz-Oryza sativ
High-Redshift Galaxies in Cold Dark Matter Models
We use hydrodynamic cosmological simulations to predict the star formation
properties of high-redshift galaxies (z=2-6) in five variants of the
inflationary cold dark matter scenario, paying particular attention to z=3, the
redshift of the largest "Lyman-break galaxy" (LBG) samples. Because we link the
star formation timescale to the local gas density, the rate at which a galaxy
forms stars is governed mainly by the rate at which it accretes cooled gas from
the surrounding medium. At z=3, star formation in most of the simulated
galaxies is steady on 200 Myr timescales, and the instantaneous star formation
rate (SFR) is correlated with total stellar mass. However, there is enough
scatter in this correlation that a sample selected above a given SFR threshold
may contain galaxies with a fairly wide range of masses. The redshift history
and global density of star formation in the simulations depend mainly on the
amplitude of mass fluctuations in the underlying cosmological model. The three
models whose mass fluctuation amplitudes agree with recent analyses of the
Lyman-alpha forest also reproduce the observed luminosity function of LBGs
reasonably well, though the dynamic range of the comparison is small and the
theoretical and observational uncertainties are large. The models with higher
and lower amplitudes appear to predict too much and too little star formation,
respectively, though they are not clearly ruled out. The intermediate amplitude
models predict SFR ~ 30-40 Msun/yr for galaxies with a surface density 1 per
arcmin^2 per unit redshift at z=3. They predict much higher surface densities
at lower SFR, and significant numbers of galaxies with SFR > 10 Msun/yr at z >=
5.Comment: Submitted to ApJ. 31 pages including 10 ps figures. Full resolution
version of Fig 2 available at
http://www.astronomy.ohio-state.edu/~dhw/Sph/zgal.fig2.ps.g
Collocation analysis for UMLS knowledge-based word sense disambiguation
BACKGROUND: The effectiveness of knowledge-based word sense disambiguation (WSD) approaches depends in part on the information available in the reference knowledge resource. Off the shelf, these resources are not optimized for WSD and might lack terms to model the context properly. In addition, they might include noisy terms which contribute to false positives in the disambiguation results. METHODS: We analyzed some collocation types which could improve the performance of knowledge-based disambiguation methods. Collocations are obtained by extracting candidate collocations from MEDLINE and then assigning them to one of the senses of an ambiguous word. We performed this assignment either using semantic group profiles or a knowledge-based disambiguation method. In addition to collocations, we used second-order features from a previously implemented approach.Specifically, we measured the effect of these collocations in two knowledge-based WSD methods. The first method, AEC, uses the knowledge from the UMLS to collect examples from MEDLINE which are used to train a Naïve Bayes approach. The second method, MRD, builds a profile for each candidate sense based on the UMLS and compares the profile to the context of the ambiguous word.We have used two WSD test sets which contain disambiguation cases which are mapped to UMLS concepts. The first one, the NLM WSD set, was developed manually by several domain experts and contains words with high frequency occurrence in MEDLINE. The second one, the MSH WSD set, was developed automatically using the MeSH indexing in MEDLINE. It contains a larger set of words and covers a larger number of UMLS semantic types. RESULTS: The results indicate an improvement after the use of collocations, although the approaches have different performance depending on the data set. In the NLM WSD set, the improvement is larger for the MRD disambiguation method using second-order features. Assignment of collocations to a candidate sense based on UMLS semantic group profiles is more effective in the AEC method.In the MSH WSD set, the increment in performance is modest for all the methods. Collocations combined with the MRD disambiguation method have the best performance. The MRD disambiguation method and second-order features provide an insignificant change in performance. The AEC disambiguation method gives a modest improvement in performance. Assignment of collocations to a candidate sense based on knowledge-based methods has better performance. CONCLUSIONS: Collocations improve the performance of knowledge-based disambiguation methods, although results vary depending on the test set and method used. Generally, the AEC method is sensitive to query drift. Using AEC, just a few selected terms provide a large improvement in disambiguation performance. The MRD method handles noisy terms better but requires a larger set of terms to improve performance
The Global Earthquake Model Physical Vulnerability Database
There are almost 50 years of research on fragility and vulnerability assessment, both key
elements in seismic risk or loss estimation. This paper presents the online database of
physical vulnerability models that has been created as part of the Global Earthquake Model
(GEM) initiative. The database comprises fragility and vulnerability curves, damage-to-loss
models, and capacity curves for various types of structures. The attributes that have been
selected to characterize each function, the constraints of setting up a usable database, the
challenges in collecting these models, and the current trends in the development of
vulnerability models are discussed in this study. The current collection of models leverages
upon the outputs of several initiatives, such as GEM’s Global Vulnerability Consortium and
the European Syner-G project. This database is publicly available through the web-based
GEM OpenQuake-platform http://doi.org/10.13117/GEM.DATASET.VULN.WEB-V1.
Hot Topics in Ultra-Peripheral Collisions
Ultra-peripheral collisions of relativistic heavy ions involve long-ranged
electromagnetic interactions at impact parameters too large for hadronic
interactions to occur. The nuclear charges are large; with the coherent
enhancement, the cross sections are also large. Many types of photonuclear and
purely electromagnetic interactions are possible. We present here an
introduction to ultra-peripheral collisions, and present four of the most
compelling physics topics. This note developed from a discussion at a workshop
on ``Electromagnetic Probes of Fundamental Physics,'' in Erice, Italy, Oct.
16-21, 2001.Comment: 7 pages, with 3 figures. This developed from a discussion at the
workshop on "Electromagnetic Probes of Fundamental Physics," Oct. 16-21,
Erice, Ital
Evaluación del gramoxone en post-emergencia en el cultivo del algodonero
En el cultivo del algodón en Colombia el control de malezas va dirigido principalmente a librar las plantas de la competencia en los primeros 50 días, recurriendo para ello a la utilización de herbicidas en complemento con la aplicación de las desyerbas y el control mecanizado. En las épocas medianas y tar- días se contrarrestan las malezas para impedir su libre crecimiento y evitar la pudrición de cápsulas, los altos costos de recolección y la demeritación del algodón por la presencia de malezas.Algodó
Volcanic eruptions, lightning, and a waterfall: Differentiating the menagerie of infrasound in the Ecuadorian jungle
In northeastern Ecuador, near Reventador Volcano, the airwaves are filled with infrasound. Here we identify the locations and characterize three distinct sources of local infrasound, including two types of infrasonic sources, which are not commonly discussed in the literature. The first of these novel sources is an intense and continuous radiator with a fixed location corresponding to San Rafael Waterfall. The signal from the river exhibits a tremor-like envelope that is well correlated across the 3-element infrasound network. Beyond the river, we also observe and map spatially variable sources corresponding to thunder. These transient signals have impulsive onsets, but are not well correlated across the network and are attributable to spatially-distributed source regions. Finally, we identify plentiful infrasound corresponding to Reventador's volcanic vent that is associated with unrest. This study demonstrates the utility of dispersed infrasound networks for distinguishing variable sources and improving interpretation of mechanisms of infrasound radiators
- …