Ab initio computation of the broadening of water rotational lines by molecular hydrogen

Theoretical cross sections for the pressure broadening by hydrogen of rotational transitions of water are compared to the latest available measurements in the temperature range 65-220 K. A high accuracy interaction potential is employed in a full close coupling calculation. A good agreement with experiment is observed above ~80 K while the sharp drop observed experimentally at lower temperatures is not predicted by our calculations. Possible explanations for this discrepancy include the failure of the impact approximation and the possible role of ortho-to-para conversion of H2.Comment: 11 pages, 3 figures, accepted for publicatio

CII in the Interstellar Medium: Excitation by H2 Revisited

C$^+$ is a critical constituent of many regions of the interstellar medium, as it can be a major reservoir of carbon and, under a wide range of conditions, the dominant gas coolant. Emission from its 158$\mu$m fine structure line is used to trace the structure of photon dominated regions in the Milky Way and is often employed as a measure of the star formation rate in external galaxies. Under most conditions, the emission from the single [CII] line is proportional to the collisional excitation rate coefficient. We here used improved calculations of the deexcitation rate of [CII] by collisions with H$_2$ to calculate more accurate expressions for interstellar C$^+$ fine structure emission, its critical density, and its cooling rate. The collision rates in the new quantum calculation are $\sim$ 25% larger than those previously available, and narrow the difference between rates for excitation by atomic and molecular hydrogen. This results in [CII] excitation being quasi-independent of the molecular fraction and thus dependent only on the total hydrogen particle density. A convenient expression for the cooling rate at temperatures between 20 K and 400 K, assuming an LTE H$_2$ ortho to para ration is $\Lambda ({\rm LTE~OPR}) = \left(11.5 + 4.0\,e^{-100\,\mathrm K/T^{\rm kin}}\right)\;e^{-91.25\,\mathrm K/T^{\rm kin}}\,n ({\rm C}^{+})\,n({\rm H}_2)\times 10^{-24}\;{\rm ergs}~{\rm cm}^{-3}~{\rm s}^{-1}$. The present work should allow more accurate and convenient analysis of the [\CII] line emission and its cooling

Collisional excitation of HC3N by para- and ortho-H2

New calculations for rotational excitation of cyanoacetylene by collisions with hydrogen molecules are performed to include the lowest 38 rotational levels of HC3N and kinetic temperatures to 300 K. Calculations are based on the interaction potential of Wernli et al. A&A, 464, 1147 (2007) whose accuracy is checked against spectroscopic measurements of the HC3N-H2 complex. The quantum coupled-channel approach is employed and complemented by quasi-classical trajectory calculations. Rate coefficients for ortho-H2 are provided for the first time. Hyperfine resolved rate coefficients are also deduced. Collisional propensity rules are discussed and comparisons between quantum and classical rate coefficients are presented. This collisional data should prove useful in interpreting HC3N observations in the cold and warm ISM, as well as in protoplanetary disks.Comment: 8 pages, 2 tables, 4 figures, accepted for publication in MNRA

Effect of Gain-Dependent Phase Shift on Fiber Laser Synchronization

Recent experiments have demonstrated synchronization of fiber laser arrays at low and moderate pump levels. It has been suggested that a key dynamical process leading to synchronized behavior is the differential phase shift induced by the gain media. We explore theoretically the role of this effect in generating inphase dynamics. We find that its presence can substantially enhance the degree of inphase stability to an extent that could be practically important. At the same time, our analysis shows that a gain-dependent phase shift is not a necessary ingredient in the dynamical selection of the inphase state, thus, leading us to reconsider the essential mechanism behind inphase selection in fiber laser arrays

A quantum and semiclassical study of dynamical resonances in the C + NO-->CN + O reaction

Accurate quantum mechanical reactive scattering calculations were performed for the collinear C+NO-->CN+O reaction using a polynomial-modified London Eyring Polanyi Sato (PQLEPS) potential energy surface (PES), which has a 4.26 eV deep well in the strong interaction region, and a reference LEPS PES, which has no well in that region. The reaction probabilities obtained for both PESs show signatures for resonances. These resonances were characterized by calculating the eigenvalues and eigenvectors of the collision lifetime matrix as a function of energy. Many resonances were found for scattering on both PESs, indicating that the potential well in the PQLEPS PES does not play the sole role in producing resonances in this relatively heavy atom system and that Feshbach processes occur for both PESs. However, the well in the PQLEPS PES is responsible for the differences in the energies, lifetimes, and compositions of the corresponding resonance states. These resonances are also interpreted in terms of simple periodic orbits supported by both PESs (using the WKB formalism), to further illustrate the role played by that potential well on the dynamics of this reaction. The existence of the resonances is associated with the dynamics of the long-lived CNO complex, which is much different than that of systems having an activation barrier. Although these results were obtained for a collinear model of the reaction, its collinearly-dominated nature suggests that related resonant behavior may occur in the real world

El rescate de las comunidades en el marco de la Globalización

La prevalencia, e incluso la agudización, en años recientes de problemas de distinta naturaleza (ambientales, sociales, económicos), particularmente en América Latina, ha conducido a diversos sectores de estos paises a cuestionar la globalización como modelo para su desarrollo. En este artículo exponemos y analizamos, en términos generales, las concepciones, características e implicaciones de la globalización, desde dos versiones antagónicas acerca del fenómeno: la primera de ellas desde la concepción que sobre este proceso han construído sus gestores y partidarios y la segunda desde la versión elaborada por sus oponentes. Al respecto, planteamos algunas similitudes existentes entre la primera versión con el paradigma dominante en la ciencia y entre la segunda versión con paradigmas emergentes. Así, en la primera versión la globalización se presenta como la única realidad posible, universal, irrefutable e irreversible, en tanto que en la segunda, se formulan distintas construcciones con relación a la globalización, que la significan como procesos cultural e historicamente constituídos y por tanto cambiantes. Esta segunda versión es la que nos sirve como base para analizar el impacto de la globalización en comunidades en situación de desventaja económica en nuestro continente y a la vez para plantear las potencialidades de éstas, fortalecidas a través de las contribuciones de la psicología social comunitaria, para resistir los efectos desfavorables que sobre ellas tiene la globalización.The prevalence and increase, specially in recent years, of diverse problems (social, economic environmental) particularly in Latin America have led various sectors to question globalization as a convenient model for the development of these countries. In this article we present and analyse, in general terms, some notions, characteristics and implications of globalization, from two antagonistic versions: The first of them refers to the notion of globalization from the point of view of its creators and adepts, while the second one is based on the version ellaborated by its oponents. In this regard, we present some similarities between the first version with the dominant paradigm in science and between the second one with emergent paradigms. Thus, in the first version globalization is understood as the unique, universal, undeniable and irreversible reality, whereas in the second one various constructions regarding globalization, which signify this phenomenon as culturally and historically constructed and hence dynamic, are formulated. This second version serves us as base for analysing the impact of globalization on economically deprived communities in our continent and simultaneously for illustrating the potentialities of these communities, empowered through the contributions of community social psychology, for resisting unfavourable effects of globalization upon them