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Search Results: 1 - 10 of 982 matches for " Ribas "
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Gene frequencies in the blood group systems of the Cuban Charolais
Ribas Miriam
Genetics Selection Evolution , 1981, DOI: 10.1186/1297-9686-13-3-293
Caty Ribas
Coolabah , 2007,
The Sun and stars as the primary energy input in planetary atmospheres
I. Ribas
Physics , 2009, DOI: 10.1017/S1743921309992298
Abstract: Proper characterization of the host star to a planet is a key element to the understanding of its overall properties. The star has a direct impact through the modification of the structure and evolution of the planet atmosphere by being the overwhelmingly larger source of energy. The star plays a central role in shaping the structure, evolution, and even determining the mere existence of planetary atmospheres. The vast majority of the stellar flux is well understood thanks to the impressive progress made in the modeling of stellar atmospheres. At short wavelengths (X-rays to UV), however, the information is scarcer since the stellar emission does not originate in the photosphere but in the chromospheric and coronal regions, which are much less understood. The same can be said about particle emissions, with a strong impact on planetary atmospheres, because a detailed description of the time-evolution of stellar wind is still lacking. Here we review our current understanding of the flux and particle emissions of the Sun and low-mass stars and briefly address their impact in the context of planetary atmospheres.
The field brown dwarf LP 944-20 and the Castor moving group
I. Ribas
Physics , 2003, DOI: 10.1051/0004-6361:20030006
Abstract: A reliable age estimation for the field brown dwarf LP 944-20 is accomplished through the analysis of its kinematic properties. The space velocities of this star strongly suggest its membership in the so-called Castor moving group. LP 944-20 can be sensibly assumed to have the group's age, which is estimated to be ~320 Myr, and metal content, which is found to be roughly solar. With these new constrains and the available photometry and lithium abundance, current brown dwarf models are put to a test. Using the IR magnitudes and the lithium diagnostics, the models are able to provide a reasonable description of the brown dwarf's properties (to within a few sigma) but yield an age which is roughly 50% larger than our estimate. Possible reasons for this discrepancy are discussed.
The 0.4-Mo Eclipsing Binary CU Cancri: Absolute Dimensions, Comparison with Evolutionary Models and Possible Evidence for a Circumstellar Dust Disk
I. Ribas
Physics , 2002, DOI: 10.1051/0004-6361:20021609
Abstract: Photometric observations in the R and I bands of the detached M-type double-lined eclipsing binary CU Cnc have been acquired and analysed. The photometric elements obtained from the analysis of the light curves have been combined with an existing spectroscopic solution to yield high-precision (errors<2%) absolute dimensions: M_A=0.4333+/-0.0017 Mo, M_B=0.3980+/-0.0014 Mo, R_A=0.4317+/-0.0052 Ro, and R_B=0.3908+/-0.0094 Ro. The mean effective temperature of the system has been estimated to be Teff=3140+/-150 K by comparing multi-band photometry with synthetic colors computed from model atmospheres. Additionally, we have been able to obtain an estimate for the age (~320 Myr) and chemical composition ([Fe/H]~0.0) of the binary system through its membership of the Castor moving group. With all these observational constraints, we have carried out a critical test of recent stellar models for low-mass stars. The comparison reveals that most evolutionary models underestimate the radius of the stars by as much as 10%, thus confirming the trend observed by Torres & Ribas (2002) for YY Gem and V818 Tau. In the mass-absolute magnitude diagram, CU Cnc is observed to be dimmer than other stars of the same mass. After ruling out a number of different scenarios, the apparent faintness of CU Cnc can be explained if its components are some 10% cooler than similar-mass stars or if there is some source of circumstellar dust absorption. The latter could be a tantalizing indirect evidence for a coplanar (Vega-like) dusty disk around this relatively young M-type binary.
On Learning More Appropriate Selectional Restrictions
Francesc Ribas
Computer Science , 1995,
Abstract: We present some variations affecting the association measure and thresholding on a technique for learning Selectional Restrictions from on-line corpora. It uses a wide-coverage noun taxonomy and a statistical measure to generalize the appropriate semantic classes. Evaluation measures for the Selectional Restrictions learning task are discussed. Finally, an experimental evaluation of these variations is reported.
An Experiment on Learning Appropriate Selectional Restrictions from a Parsed Corpus
Francesc Ribas
Computer Science , 1994,
Abstract: We present a methodology to extract Selectional Restrictions at a variable level of abstraction from phrasally analyzed corpora. The method relays in the use of a wide-coverage noun taxonomy and a statistical measure of the co-occurrence of linguistic items. Some experimental results about the performance of the method are provided.
Como os economistas discordam: um ensaio metodológico sobre o "contexto da descoberta" em economia
Cavalieri, Marco Antonio Ribas;
Estudos Econ?micos (S?o Paulo) , 2007, DOI: 10.1590/S0101-41612007000200006
Abstract: this article concerns the methodology of investigations about the history of economic thought from a plural perspective, considering the variety of approaches as the strongest feature in the knowledge of economic phenomena. here it is presented a suggestive methodology to study the birth of schools of thought, what we call the "context of discovery" in economics. we argue about the relations between the social reality, which is historically and geographically specific, and the theories and new approaches that appear in these contexts. the methodology suggested ranges from the schools of thought characterization, by the means of kuhn and lakatos categories, to the treatment of anachronism, which is embedded in all intellectual historiography work. as a result, an interpretative model is designed, to be used in future studies about authors and schools of economic thought.
Comportamento de videiras Seibel na regi?o de S?o Roque, no Estado de S?o Paulo
Ribas, Wilson Corrêa;
Bragantia , 1967, DOI: 10.1590/S0006-87051967000100020
Abstract: for the ecological conditions of the state of s?o paulo, the most important group of grapevines qualified for wine is represented by hybrids seibel. in s?o roque, 79 cultivars were studied, of which 7 were separated, considered superior. although none of them might produce by itself, isolatedly, harmonic and well balanced wines, except in years of special vintage conditions, their association allows to correct characteristics of acidity, sugar percentage and dyeing substances in-order to obtain good wines.
A caracteriza??o da pobreza urbana ao longo do tempo: aplica??o do modelo idade-período-coorte na estima??o das tendências de priva??es cr?nica e transitória no Brasil
Ribas, Rafael Perez;
Revista Brasileira de Estudos de Popula??o , 2007, DOI: 10.1590/S0102-30982007000100009
Abstract: the profile of poverty in brazil has changed in recent decades, partially due to alterations in the reproduction and mortality standards of the population. during this same period, the designs of social policies, especially those for reducing poverty, have also undergone changes. it must be emphasized that the effectiveness of these policies depends on the type of poverty that is being dealt with. destitution can be a permanent or temporary phenomenon, and this transient-chronic (t-c) composition may show a temporal trend. the objective of this paper is to analyze this trend as well as the temporal evolution of poverty rates in urban areas. the result may make it possible to predict future income and destitution. to this end, an age-period-cohort (apc) model was applied to absolute and relative poverty measures and to the t-c composition, based on data from the pnads between 1995 and 2003. the results indicate that the cohort-effect is more expressive than the period effect for the recent reduction in poverty rates, especially for the chronic component. in contrast, the transient component showed a relative temporal tendency to increase.
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