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

Order-to-disorder transition in ring-shaped colloidal stains

A colloidal dispersion droplet evaporating from a surface, such as a drying coffee drop, leaves a distinct ring-shaped stain. Although this mechanism is frequently used for particle self-assembly, the conditions for crystallization have remained unclear. Our experiments with monodisperse colloidal particles reveal a structural transition in the stain, from ordered crystals to disordered packings. We show that this sharp transition originates from a temporal singularity of the flow velocity inside the evaporating droplet at the end of its life. When the deposition speed is low, particles have time to arrange by Brownian motion, while at the end, high-speed particles are jammed into a disordered phase.Comment: accepted for PR

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

Network design: Taxi Planning

The effect of managing aircraft movements on the airport’s ground is an important tool that can alleviate the delays of flights, specially in peak hours or congested situations. Although some strategic design decisions regarding aeronautical and safety aspects have a main impact on the airport’s topology, there exists a number of other additional factors that must be evaluated according to the on ground operations, i.e. previous to the taking-off or after landing. Among these factors one can consider capacities at waiting points and directions of some corridors. These factors are related to the demand situation of a given period and influence the aircraft’s routing on the ground or short term Taxi Planning problem (or TP-S). While the TP-S problem studies the aircraft routing and scheduling on the airport’s ground under a dynamic point of view, this paper presents a Taxi Planning network design model (or TPND), attending to these additional factors of the airport’s topology and the conflicting movements of the aircraft on them with the same modelling approach used in the TP-S problem. The TPND model is formulated as a binary multicommodity network flow problem with additional side constraints under a multiobjective approach. The side constraints included are the classical limitations due to capacity and also as a distinctive approach, constraints that restrict the interference of aircraft in order to decrease the intervention of human controllers during the operations or increase their safety margins. The multiobjective approach adopted for the TPND model balances conflicting objectives: airport’s throughput, travel times, safety of operations and costs. In the paper computational results are included on two test airports solving the TPND model by “Branch and Bound” showing the effect of the conflicting objectives in the design decisions

Bovedillas fabricadas con hormigones livianos con la incorporación de residuos de construcción y demolición en sus mezclas

In Argentina, small vaults were introduced by the Italians immigrants during the 19th Century to be used in roofs and floors for housing and public buildings. These vaults were built with bricks put on edge or in sharp ends, giving them the shape of small vaults which rested on iron rafters to cover the expanse of the room. At present, in Argentina´s market we can find a variety of products, such as roof bricks made of different materials like ceramic, concrete and EPS7. These bricks are straight in their lower side and they need to be covered with a ceiling afterwards. The bricks or blocks are supported with thin concrete pre-tense beams; the system is completed with a compression layer of reinforced concrete in-situ. In the construction areas, there is a big amount of arid waste in construction and demolition of buildings that exceed in quantity the circuit reuse. Also, there is discarded material from the packaging of EPS, both wastes are problems because of their volume and, the last one is an environmental contamination agent by drain obstruction. They do not have yet a formal circuit or rooted of reduction or commercialization that could be managed either by the Urban Collectors Cooperatives or by companies. This research work, investigates the applications of concrete mixtures with the incorporations of recycled EPS and crushed rubble, which have been researched and developed at our Center in different small vaults designs in order to develop products that can compete economically with their equivalent in the national market. Thus, optimizing their characteristics in weight, vault’s visible side endings, thermal insulation and safety at work, emulating the image of the traditional brick vaults and recovering memory constructive. In this way, an efficient energetic constructive system is investigated and promoted, by developing an innovative product in technology and quality that represents an environmental improvement, which aims to reduce consumption of natural resources, trying to reduce carbon footprint and the possibility of creating green employment.En Argentina, las bovedillas fueron introducidas por los inmigrantes italianos a mediados del siglo XlX para la construcción de techos y entrepisos de viviendas y edificios públicos. Eran realizadas con ladrillos colocados de canto o de punta, dándole la forma de pequeñas bóvedas, apoyadas sobre vigas de hierro, para cubrir las luces del local. En la actualidad, encontramos en el mercado argentino productos similares ladrillos de techo realizados en diferentes materiales cerámicos, hormigón y EPS8. Dichos ladrillos o bloques son rectos en su cara inferior y necesitan una terminación de cielorraso luego de ser colocados. Son utilizados con viguetas de hormigón pretensadas donde se apoyan las piezas, el sistema se completa con una capa de compresión de hormigón armado in situ. Se cuenta por otra parte, con una cantidad de residuos de áridos de construcción y demolición de obra que exceden en cantidad al circuito de su re uso, como también materiales de descarte proveniente de embalajes de EPS, ambos significan un problema por su volumen y estos últimos son agentes de contaminación ambiental por obstrucción de sumideros, dado que no tienen aún un circuito formal ni arraigado de reducción ni de comercialización por parte de las Cooperativas de Recolectores Urbanos o empresarial. En este trabajo, se investigan las aplicaciones de mezclas de hormigones con incorporación de EPS reciclado y cascotes triturados, ya investigadas y desarrolladas en nuestro Centro, en diferentes diseños de bovedillas con el objetivo de desarrollar productos que puedan competir económicamente con sus equivalentes del mercado nacional, optimizando las características de los mismos, en cuanto a peso, terminaciones en su cara vista, aislación térmica y seguridad para trabajo en obra, emulando la imagen de las bóvedas con ladrillos tradicionales citadas y recuperando la memoria constructiva. De esta manera se investiga y promueve la aplicación de un sistema constructivo energéticamente eficiente, desarrollando un producto innovador en lo tecnológico y de calidad, que represente una mejora en lo ambiental, minimizando el consumo de los recursos naturales, transformando residuos en recursos con la meta de reducir la huella de carbono y con posibilidad de crear empleos verdes

Failure of surface color cues under natural changes in lighting

Color allows us to effortlessly discriminate and identify surfaces and objects by their reflected light. Although the reflected spectrum changes with the illumination spectrum, cone photoreceptor signals can be transformed to give useful cues for surface color. But what happens when both the spectrum and the geometry of the illumination change, as with lighting from the sun and sky? Is it possible, as a matter of principle, to obtain reliable cues by processing cone signals alone? This question was addressed here by estimating the information provided by cone signals from time-lapse hyperspectral radiance images of five outdoor scenes under natural lighting. The scenes contained mixtures of herbaceous vegetation, woodland, barren land, rock, and rural and urban buildings. For each scene, mutual information between cone signals was estimated at increasing time intervals. These estimates have an operational interpretation given by Shannon\u27s channel-coding theorem. It sets a theoretical upper limit on the number of points that can be reliably identified across time by transforming cone signals alone. For all five scenes, the number of identifiable points declined markedly with increasing interval, although not always monotonically. This decline represents an irretrievable loss in information. The implication is that processing cone signals alone cannot give reliable cues for surface color under natural changes in lighting. More complicated spatial interactions between cone signals must also be involved