Claro Americas is part of América Móvil, a Mexican telecom group serving clients in Argentina, Brazil, Chile, Colombia, Costa Rica, the Dominican Republic, Ecuador, El Salvador, Guatemala, Honduras, Nicaragua, Panama, Paraguay, Peru, Uruguay. The company's name means "bright", "clear" or "of course" in Portuguese and Spanish. Wikipedia.
Frouard J.,Claro |
Compere A.,University of Namur
Icarus | Year: 2012
The stability of the (87) Sylvia system and of the neighborhood of its two satellites is investigated. We use numerical integrations considering the non-sphericity of Sylvia, as well as the mutual perturbation of the satellites and the solar perturbation. Two numerical models have been used, which describe respectively the short and long-term evolution of the system. We show that the actual system is in a deeply stable zone, but surrounded by both fast and secular chaotic regions due to mean-motion and evection resonances. We then investigate how tidal and BYORP effects modify the location of the system over time with respect to the instability zones. The conclusion is that the system will cross the evection resonance before 1. Gyr.We generalize this study to other known triple systems, investigate possible evolutions of the systems under tidal and BYORP effects, and discuss their distance from instability regions. In particular, it is possible to show how systems in a joint opposing evolution can be destroyed depending on the masses of the satellites and their dissipative parameters. © 2012 Elsevier Inc..
Applied Radiation and Isotopes | Year: 2011
This paper describes the natural radioactivity of groundwater occurring in sedimentary (Bauru and Guarani) and fractured rock (Serra Geral) aquifer systems in the Paraná sedimentary basin, South America that is extensively used for drinking purposes, among others. The measurements of gross alpha and gross beta radioactivity as well the activity concentration of the natural dissolved radionuclides 40K, 238U, 234U, 226Ra, 222Rn, 210Po and 210Pb were held in 80 tubular wells drilled in 21 municipalities located at São Paulo State and its border with Mato Grosso do Sul State in Brazil. Most of the gross alpha radioactivity data were below 1mBq/L, whereas values exceeding the gross beta radioactivity detection limit of 30mBq/L were found. The radioelement solubility in the studied systems varied according to the sequence radon>radium>other radionuclides and the higher porosity of sandstones relatively to basalts and diabases could justify the enhanced presence of dissolved radon in the porous aquifer. The implications of the data obtained in terms of standards established for defining the drinking water quality have also been discussed. The population-weighted average activity concentration for these radionuclides was compared to the guideline value of 0.1mSv/yr for the total effective dose and discussed in terms of the choice of the dose conversion factors. © 2011 Elsevier Ltd.
Environmental Earth Sciences | Year: 2013
The radioactivity due to 238U and 234U in three aquifer systems occurring within the Paraná sedimentary basin, South America, has been investigated. Uranium is much less dissolved from fractured igneous rocks than from the porous sedimentary rocks as indicated by the U-mobility coefficients between 7. 6 × 10-6 and 1. 2 × 10-3 g cm-3. These values are also compatible with the U preference ratios relative to Na, K, Ca, Mg and SiO2, which showed that U is never preferentially mobilized in the liquid phase during the flow occurring in cracks, fissures, fractures and faults of the igneous basaltic rocks. Experimental dissolution of diabase grains on a time-scale laboratory has demonstrated that the U dissolution appeared to be a two-stage process characterized by linear and second-order kinetics. The U dissolution rate was 8 × 10-16 mol m-2 s-1 that is within the range of 4 × 10-16-3 × 10-14 mol m-2 s-1 estimated for other rock types. The 234U/238U activity ratio of dissolved U in solutions was higher than unity, a typical result expected during the water-rock interactions when preferential 234U-leach from the rock surfaces takes place. Some U-isotopes data allowed estimating 320 ka for the groundwater residence time in a sector of a transect in São Paulo State. A modeling has been also realized considering all U-isotopes data obtained in Bauru (35 samples), Serra Geral (16 samples) and Guarani (29 samples) aquifers. The results indicated that the Bauru aquifer waters may result from the admixture of waters from Guarani (1. 5 %) and Serra Geral (98. 5 %) aquifers. © 2012 Springer-Verlag.
Barreiro L.A.,Claro |
Barreiro L.A.,Federal University of Itajuba |
Medina R.,Federal University of Itajuba
Nuclear Physics B | Year: 2014
Recently, in  we proposed a revisited S-matrix approach to efficiently find the bosonic terms of the open superstring low energy effective lagrangian (OSLEEL). This approach allows to compute the α'N terms of the OSLEEL using open superstring n-point amplitudes in which n is considerably lower than (N+2) (which is the order of the required amplitude to obtain those α'N terms by means of the conventional S-matrix approach). In this work we use our revisited S-matrix approach to examine the structure of the scattering amplitudes, arriving at a closed form for them. This is a RNS derivation of the formula first found by Mafra, Schlotterer and Stieberger , using the pure spinor formalism. We have succeeded doing this for the 5, 6 and 7-point amplitudes. In order to achieve these results we have done a careful analysis of the kinematical structure of the amplitudes, finding as a by-product a purely kinematical derivation of the BCJ relations (for N=4, 5, 6 and 7). Also, following the spirit of the revisited S-matrix approach, we have found the α' expansions for these amplitudes up to α'6 order in some cases, by only using the well known open superstring 4-point amplitude, cyclic symmetry and tree level unitarity: we have not needed to compute any numerical series or any integral involving polylogarithms, at any moment. © 2014 The Authors.
Barreiroa L.A.,Claro |
Medina R.,Federal University of Itajuba
Journal of High Energy Physics | Year: 2012
The conventional S-matrix approach to the (tree level) open string low energy effective lagrangian assumes that, in order to obtain all its bosonic α' N order terms, it is necessary to know the open string (tree level) (N+2)-point amplitude of massless bosons, at least expanded at that order in α'. In this work we clarify that the previous claim is indeed valid for the bosonic open string, but for the supersymmetric one the situation is much more better than that: there are constraints in the kinematical bosonic terms of the amplitude (probably due to Spacetime Supersymmetry) such that a much lower open superstring n-point amplitude is needed to find all the α' N order terms. In this 'revisited' S-matrix approach we have checked that, at least up to α' 4 order, using these kinematical constraints and only the known open superstring 4-point amplitude, it is possible to determine all the bosonic terms of the low energy effective lagrangian. The sort of results that we obtain seem to agree completely with the ones achieved by the method of BPS configurations, proposed about ten years ago. By means of the KLT relations, our results can be mapped to the NS-NS sector of the low energy effective lagrangian of the type II string theories implying that there one can also find kinematical constraints in the N-point amplitudes and that important informations can be inferred, at least up to α' 4 order, by only using the (tree level) 4-point amplitude. © SISSA 2012.