Multi-site H-bridge breathers in a DNA--shaped double strand

We investigate the formation process of nonlinear vibrational modes representing broad H-bridge multi--site breathers in a DNA--shaped double strand. Within a network model of the double helix we take individual motions of the bases within the base pair plane into account. The resulting H-bridge deformations may be asymmetric with respect to the helix axis. Furthermore the covalent bonds may be deformed distinctly in the two backbone strands. Unlike other authors that add different extra terms we limit the interaction to the hydrogen bonds within each base pair and the covalent bonds along each strand. In this way we intend to make apparent the effect of the characteristic helicoidal structure of DNA. We study the energy exchange processes related with the relaxation dynamics from a non-equilibrium conformation. It is demonstrated that the twist-opening relaxation dynamics of a radially distorted double helix attains an equilibrium regime characterized by a multi-site H-bridge breather.Comment: 27 pages and 10 figure

Grecia y los eslavos en el "Chronicon" de San Isidoro de Sevilla

Saint Isidore of Seville in his Chronicon affirms that at the beginning of the 7th century «the Slavs took Greece from the Romans», a testimony of incomparable value to study the phenomenon of the Slavonic penetration in the Balkans and the Peloponnese, but normally underestimated. In this study we try to return to the Chronicon its real value in the matter

Reducing sample variance: halo biasing, non-linearity and stochasticity

Comparing clustering of differently biased tracers of the dark matter distribution offers the opportunity to reduce the cosmic variance error in the measurement of certain cosmological parameters. We develop a formalism that includes bias non-linearities and stochasticity. Our formalism is general enough that can be used to optimise survey design and tracers selection and optimally split (or combine) tracers to minimise the error on the cosmologically interesting quantities. Our approach generalises the one presented by McDonald & Seljak (2009) of circumventing sample variance in the measurement of $f\equiv d \ln D/d\ln a$. We analyse how the bias, the noise, the non-linearity and stochasticity affect the measurements of $Df$ and explore in which signal-to-noise regime it is significantly advantageous to split a galaxy sample in two differently-biased tracers. We use N-body simulations to find realistic values for the parameters describing the bias properties of dark matter haloes of different masses and their number density. We find that, even if dark matter haloes could be used as tracers and selected in an idealised way, for realistic haloes, the sample variance limit can be reduced only by up to a factor $\sigma_{2tr}/\sigma_{1tr}\simeq 0.6$. This would still correspond to the gain from a three times larger survey volume if the two tracers were not to be split. Before any practical application one should bear in mind that these findings apply to dark matter haloes as tracers, while realistic surveys would select galaxies: the galaxy-host halo relation is likely to introduce extra stochasticity, which may reduce the gain further.Comment: 21 pages, 13 figures. Published version in MNRA

Una comparación de algoritmos basados en trayectoria granular para el problema de localización y ruteo con flota heterogénea (LRPH)

Indexación: Scopus.We consider the Location-Routing Problem with Heterogeneous Fleet (LRPH) in which the goal is to determine the depots to be opened, the customers to be assigned to each open depot, and the corresponding routes fulfilling the demand of the customers and by considering a heterogeneous fleet. We propose a comparison of granular approaches of Simulated Annealing (GSA), of Variable Neighborhood Search (GVNS) and of a probabilistic Tabu Search (pGTS) for the LRPH. Thus, the proposed approaches consider a subset of the search space in which non-favorable movements are discarded regarding a granularity factor. The proposed algorithms are experimentally compared for the solution of the LRPH, by taking into account the CPU time and the quality of the solutions obtained on the instances adapted from the literature. The computational results show that algorithm GSA is able to obtain high quality solutions within short CPU times, improving the results obtained by the other proposed approaches.https://revistas.unal.edu.co/index.php/dyna/article/view/55533/5896

Desafíos educativos, tecnología y productividad

El propósito de este artículo es presentar la visión y experiencias del Ministerio de Educación de El Salvador en relación al desarrollo educativo del país y, en especial, en el campo de la tecnología y la productividad. En forma muy resumida se presentarán: por un lado, los esfuerzos realizados para proporcionar a nuestros jóvenes y adultos una educación de calidad y equidad; por otro, las reformas y políticas educativas utilizadas para potenciar la educación técnica y tecnológica en nuestros centros de estudio

Promoción de la cultura democrática a través de la educación

Con este artículo se pretende intercambiar ideas y reflexiones sobre un tema de tanta centralidad para esta época, como es la educación y su decisiva contribución con la gobernabilidad democrática. El diagnóstico de la situación de nuestros países y regiones, de nuestros avances y logros en el campo de la promoción de la Cultura Democrática, de nuestras limitaciones y desafíos, deben aportar y estimular nuestra capacidad de propuesta y de acción para lograr la estabilidad democrática, y así alcanzar mejores niveles de convivencia y bienestar social

Stationary and moving breathers in a simplified model of curved alpha--helix proteins

The existence, stability and movability of breathers in a model for alpha-helix proteins is studied. This model basically consists a chain of dipole moments parallel to it. The existence of localized linear modes brings about that the system has a characteristic frequency, which depends on the curvature of the chain. Hard breathers are stable, while soft ones experiment subharmonic instabilities that preserve, however the localization. Moving breathers can travel across the bending point for small curvature and are reflected when it is increased. No trapping of breathers takes place.Comment: 19 pages, 11 figure