5,668 research outputs found
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 . We analyse how the bias, the noise,
the non-linearity and stochasticity affect the measurements of 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 .
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
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