Entropy and Renormalization in Chaotic Visibility Graphs

2016

Random Boolean networks response to external periodic signals

2002

Random Boolean networks have been proposed as discrete models of genetic networks. Depending on the values of their control parameters, these networks fall by themselves in order or disorder phases. These networks are autonomous systems: no external inputs are considered. Nevertheless, in the real world the genetic networks are in5uenced by external signals. Many biological rhythms have 24-h periods related to sunlight, coupled with molecular clocks. In this work we study the response of Random Boolean Networks to analytical and non-analytical external periodic signals. The relationship between external and internal parameters for the determination of the dynamical behaviour of this network…

A K s -band-selected catalogue of objects in the ALHAMBRA survey

2016

The original ALHAMBRA catalogue contained over 400 000 galaxies selected using a synthetic F814W image, to the magnitude limit AB(F814W) ≈ 24.5. Given the photometric redshift depth of the ALHAMBRA multiband data (〈 z〉 = 0.86) and the approximately I-band selection, there is a noticeable bias against red objects at moderate redshift.We avoid this bias by creating a new catalogue selected in the Ks band. This newly obtained catalogue is certainly shallower in terms of apparent magnitude, but deeper in terms of redshift, with a significant population of red objects at z > 1. We select objects using the Ks band images, which reach an approximate AB magnitude limit Ks ≈ 22. We generate masks an…

On the thermodynamic origin of metabolic scaling

2018

The origin and shape of metabolic scaling has been controversial since Kleiber found that basal metabolic rate of animals seemed to vary as a power law of their body mass with exponent 3/4, instead of 2/3, as a surface-to-volume argument predicts. The universality of exponent 3/4 -claimed in terms of the fractal properties of the nutrient network- has recently been challenged according to empirical evidence that observed a wealth of robust exponents deviating from 3/4. Here we present a conceptually simple thermodynamic framework, where the dependence of metabolic rate with body mass emerges from a trade-off between the energy dissipated as heat and the energy efficiently used by the organi…

Searching for a Common Language

2010

Perhaps you remember Steven Spielberg’s movie released in 1977, Close Encounters of the Third Kind. The memorable end of this movie shows how humans might communicate with extraterrestrials through the interchange of music, with the famous melody “D E C C G” that we all hummed.

The EM imaging reconstruction method in γ-ray astronomy

1998

Abstract The simpler imaging reconstruction methods used for γ-ray coded mask telescopes are based on correlation methods, very fast and simple-to-use but with limitations in the reconstructed image. To improve these results, other reconstruction methods have been developed, such as the maximum entropy methods or the Iterative Removal Of Sources (IROS). However, such kind of methods are slower and can be impracticable for very complex telescopes. In this paper we present an alternative image reconstruction method, based on an iterative maximum likelihood algorithm called the EM algorithm, easy to implement and that can be successfully used for not very complex coded mask systems, as is the …

Where to Look

2010

SETI scientists are convinced that, of all possible types of radiation, any signal coming to us from another galactic civilization will have the form of electromagnetic waves; therefore, the search centers exclusively on these types of radiation. Why electromagnetic waves?

Feigenbaum graphs: a complex network perspective of chaos

2011

The recently formulated theory of horizontal visibility graphs transforms time series into graphs and allows the possibility of studying dynamical systems through the characterization of their associated networks. This method leads to a natural graph-theoretical description of nonlinear systems with qualities in the spirit of symbolic dynamics. We support our claim via the case study of the period-doubling and band-splitting attractor cascades that characterize unimodal maps. We provide a universal analytical description of this classic scenario in terms of the horizontal visibility graphs associated with the dynamics within the attractors, that we call Feigenbaum graphs, independent of map…

A Place for Life

2010

The belief in the existence of extraterrestrial civilizations starts from the so-called principle of mediocrity. This principle postulates that Earth is a normal planet that rotates around a normal star, which in turn is located in a normal galaxy. That is to say, there is nothing so special in our world as to make it unique. This is a logical conclusion, toward which we are guided by the successive “Copernican turns” that science has suffered throughout its long history, and which has ­removed us from the central position we once believed to occupy in the universe.

Different World Views

2010

When we study communication systems in other animal species, we are led to the conclusion that extraterrestrial intelligent beings are likely to have systems of communication similar to the human one in at least some aspects. That is to say, communication is accomplished by means of the combination of certain information elements playing a role analogous to words, or that the system is a symbolic language (or even both things simultaneously). But in communication, it is also very important how information is transmitted (pictorially, by means of ideograms, letters, etc.), which is going to be strongly determined by the species’specific perception of the world.

Author Correction: On the thermodynamic origin of metabolic scaling

2018

The origin and shape of metabolic scaling has been controversial since Kleiber found that basal metabolic rate of animals seemed to vary as a power law of their body mass with exponent 3/4, instead of 2/3, as a surface-to-volume argument predicts. The universality of exponent 3/4 -claimed in terms of the fractal properties of the nutrient network- has recently been challenged according to empirical evidence that observed a wealth of robust exponents deviating from 3/4. Here we present a conceptually simple thermodynamic framework, where the dependence of metabolic rate with body mass emerges from a trade-off between the energy dissipated as heat and the energy efficiently used by the organi…

The Miracle of Life

2010

In the previous chapter, we have seen that it was quite easy for life to appear in our world. But how did it arise? What processes occurred for life to appear so quickly? Are these processes common to other worlds?

NGC1600 - Cluster or Field Elliptical?

2008

A study of the galaxy distribution in the field of the elliptical galaxy NGC1600 has been undertaken. Although this galaxy is often classified as a member of a loose group, all the neighbouring galaxies are much fainter and could be taken as satellites of NGC1600. The number density profile of galaxies in the field of this galaxy shows a decline with radius, with evidence of a background at approximately 1.3 Mpc. The density and number density profile are consistent with that found for other isolated early-type galaxies. NGC1600 appears as an extended source in X-rays, and the center of the X-ray emission seems not to coincide with the center of the galaxy. The velocity distribution of neig…

Monte Carlo study of an imager for low-energy γ-ray astronomy: Optimization of the design and evaluation of the scientific performances

1997

Abstract In this paper we present the phase A studies which were carried out for the optimization of the design and evaluation of the scientific performances of the Imager, which is one of the two main instruments under development for the INTEGRAL mission, selected by ESA as the next scientific mission of medium size (M2). These studies were done by Monte Carlo simulation, using the CERN GEANT-3 package. Both the whole geometry and materials defining the Imager were considered in the simulations.

Poe: cor científic. Els antecedents de la ciència-ficció

2014

Al hablar sobre los orígenes de la ciencia ficción y la literatura de anticipación, inmediatamente pensamos en los nombres de Herbert G. Wells o Jules Verne, prolíficos autores de finales del XIX y fuente de inspiración de posteriores generaciones. Pocos incluyen a Edgar Allan Poe, autor de principios del mismo siglo y fuente de inspiración de los ya mencionados. Y es que si Verne y Wells fueron los padres de la ciencia ficción, sin duda Poe fue el abuelo.

From time series to complex networks: the visibility graph

2008

In this work we present a simple and fast computational method, the visibility algorithm , that converts a time series into a graph. The constructed graph inherits several properties of the series in its structure. Thereby, periodic series convert into regular graphs, and random series do so into random graphs. Moreover, fractal series convert into scale-free networks, enhancing the fact that power law degree distributions are related to fractality, something highly discussed recently. Some remarkable examples and analytical tools are outlined to test the method's reliability. Many different measures, recently developed in the complex network theory, could by means of this new approach cha…

Horizontal visibility graphs: exact results for random time series

2009

The visibility algorithm has been recently introduced as a mapping between time series and complex networks. This procedure allows us to apply methods of complex network theory for characterizing time series. In this work we present the horizontal visibility algorithm, a geometrically simpler and analytically solvable version of our former algorithm, focusing on the mapping of random series (series of independent identically distributed random variables). After presenting some properties of the algorithm, we present exact results on the topological properties of graphs associated with random series, namely, the degree distribution, the clustering coefficient, and the mean path length. We sh…

Is Anybody Out There?

2010

Are others actually out there? If so, why don’t we know anything about them yet? Although this may seem a trivial question, it is not an easy one to answer at all.

Low Energy Gamma Ray Imager (LEGRI)

1995

The Low Energy Gamma Ray Imager (LEGRI) will be one of the three instruments carried by the first MINISAT mission. LEGRI aims to demonstrate the technological feasibility of a new generation of low energy gamma-ray telescopes with imaging, medium resolution spectroscopy and high continuum sensitivity in the 20-200 keV spectral region, based on HgI2 solid state detector technology.

Walking on exoplanets: Is Star Wars right?

2016

As the number of detected extrasolar planets increases, exoplanet databases become a valuable resource, confirming some details about planetary formation, but also challenging our theories with new unexpected properties.

The Search Starts

2010

The previous chapter has shown us that life on Earth arose surprisingly fast and easy, as soon as the conditions were right for liquid water to be sustained on the surface. We saw that there is evidence of the presence of this valuable substance in at least two other bodies in the Solar System, and these are encouraging indications that life in the Solar System might not be limited to Earth. Also, we saw that planetary systems are not rarities of nature but seem to abound across the universe, and that life is much more resistant than was once believed, which extends the limits of what can be considered a habitable world. All these facts, despite our own ignorance about many things, make num…

Diving into exoplanets: Are water seas the most common?

2019

One of the basic tenets of exobiology is the need for a liquid substratum in which life can arise, evolve, and develop. The most common version of this idea involves the necessity of water to act as such a substratum, both because that is the case on Earth and because it seems to be the most viable liquid for chemical reactions that lead to life. Other liquid media that could harbor life, however, have occasionally been put forth. In this work, we investigate the relative probability of finding superficial seas on rocky worlds that could be composed of nine different, potentially abundant, liquids, including water. We study the phase space size of habitable zones defined for those substance…

The 2017 May 20 stellar occultation by the elongated centaur (95626) 2002 GZ32

2021

Full list of authors: Santos-Sanz, P.; Ortiz, J. L.; Sicardy, B.; Benedetti-Rossi, G.; Morales, N.; Fernández-Valenzuela, E.; Duffard, R.; Iglesias-Marzoa, R.; Lamadrid, J. L.; Maícas, N.; Pérez, L.; Gazeas, K.; Guirado, J. C.; Peris, V.; Ballesteros, F. J.; Organero, F.; Ana-Hernández, L.; Fonseca, F.; Alvarez-Candal, A.; Jiménez-Teja, Y. Vara-Lubiano, M.; Braga-Ribas, F.; Camargo, J. I. B.; Desmars, J.; Assafin, M.; Vieira-Martins, R.; Alikakos, J.; Boutet, M.; Bretton, M.; Carbognani, A.; Charmandaris, V.; Ciabattari, F.; Delincak, P.; Fuambuena Leiva, A.; González, H.; Haymes, T.; Hellmich, S.; Horbowicz, J.; Jennings, M.; Kattentidt, B.; Kiss, Cs; Komžík, R.; Lecacheux, J.; Marciniak, …

Life in the Solar System?

2010

Europa, the smallest of the four moons of Jupiter discovered by Galileo­ Galilei, has attracted much speculation on whether it might be inhabited ever since it was observed by the Voyager probes. This is mostly due to the fact that water, or better said, water-ice, is the most evident feature of that world, with ice covering this interesting satellite completely, turning it into a smooth white ball.

Variances as order parameter and complexity measure for random Boolean networks

2005

Several order parameters have been considered to predict and characterize the transition between ordered and disordered phases in random Boolean networks, such as the Hamming distance between replicas or the stable core, which have been successfully used. In this work, we propose a natural and clear new order parameter: the temporal variance. We compute its value analytically and compare it with the results of numerical experiments. Finally, we propose a complexity measure based on the compromise between temporal and spatial variances. This new order parameter and its related complexity measure can be easily applied to other complex systems.

New insights into black bodies

2012

Planck's law describes the radiation of black bodies. The study of its properties is of special interest, as black bodies are a good description for the behavior of many phenomena. In this work a new mathematical study of Planck's law is performed and new properties of this old acquaintance are obtained. As a result, the exact form for the locus in a color-color diagrams has been deduced, and an analytical formula to determine with precision the black body temperature of an object from any pair of measurements has been developed. Thus, using two images of the same field obtained with different filters, one can compute a fast estimation of black body temperatures for every pixel in the image…

Order-disorder phase transition in random-walk networks

2004

In this paper we study in detail the behavior of random-walk networks (RWN's). These networks are a generalization of the well-known random Boolean networks (RBN's), a classical approach to the study of the genome. RWN's are also discrete networks, but their response is defined by small variations in the state of each gene, thus being a more realistic representation of the genome and a natural bridge between discrete and continuous models. RWN's show a clear transition between order and disorder. Here we explicitly deduce the formula of the critical line for the annealed model and compute numerically the transition points for quenched and annealed models. We show that RBN's and the annealed…

Legri Operations. Detectors and Detector Stability

2001

Two years after launch (04.21.97), LEGRI is operating on Minisat-01 in a LEO orbit. The LEGRI detector plane is formed by two type of gamma-ray solid state detectors: HgI2 and CdZnTe. Detectors are embedded in a box containing the FEE and DFE electronics. This box provides an effective detector passive shielding. Detector plane is multiplexed by a Coded Aperture System located at 54 cm and a Ta Collimator with a FCFOV of 22° and 2° angular resolution. The aim of this paper is to summarize the detector behaviour in three different time scales: before launch, during the in-orbit check-out period (IOC), and after two years of routine operation in space. Main results can be summarized as follow…

How Do We Know If There’s a Message?

2010

As we have seen, radio waves can be excellent candidates for interplanetary communication, due to the fact that our galaxy is transparent to them. The problem lies in properly identifying the origin – artificial or natural – of an arriving signal. When we tune a radio receiver and we turn the antenna toward the cosmos, we gather hundreds of different signals. Even some of the natural signals are quite suggestive, and one can be tempted to consider them emissions from other civilizations.

KIC 8462852: Will the Trojans return in 2021?

2017

KIC 8462852 stood out among more than 100,000 stars in the Kepler catalogue because of the strange features of its light curve: a wide, asymmetric dimming taking up to 15 per cent of the light at D793 and a period of multiple, narrow dimmings happening approximately 700 days later. Several models have been proposed to account for this abnormal behaviour, most of which require either unlikely causes or a finely-tuned timing. We aim at offering a relatively natural solution, invoking only phenomena that have been previously observed, although perhaps in larger or more massive versions. We model the system using a large, ringed body whose transit produces the first dimming and a swarm of Troja…

Background in low Earth orbits measured by LEGRI telescope – short and long term variability

1999

Abstract In this paper we present the first Low Energy Gamma Ray Imager (LEGRI) background measurements which were carried out in the earlier nominal operation activities of LEGRI Instrument on board MINISAT-01, after initial spacecraft and instrument check-up procedures. Short term (daily) and expected long term background variability is presented. A background model is also discussed in order to be used for celestial γ-ray emitters observations.

Analytical properties of horizontal visibility graphs in the Feigenbaum scenario

2012

Time series are proficiently converted into graphs via the horizontal visibility (HV) algorithm, which prompts interest in its capability for capturing the nature of different classes of series in a network context. We have recently shown [1] that dynamical systems can be studied from a novel perspective via the use of this method. Specifically, the period-doubling and band-splitting attractor cascades that characterize unimodal maps transform into families of graphs that turn out to be independent of map nonlinearity or other particulars. Here we provide an in depth description of the HV treatment of the Feigenbaum scenario, together with analytical derivations that relate to the degree di…

Sensitivity and Efficiency of the INTEGRAL Imager

1995

A detailed simulation program of the INTEGRAL Imager has been written and implemented using the GEANT-3 Monte Carlo code. The expected detection efficiency and continuum sensitivity have been evaluated. The results obtained for the CsI configuration of the Imager are compared with those obtained with the new configuration which foresees a top plane made of CdTe solid state detector elements.

The miniJPAS survey: a preview of the Universe in 56 colours

2021

Full list of authors: Bonoli, S.; Marín-Franch, A.; Varela, J.; Vázquez Ramió, H.; Abramo, L. R.; Cenarro, A. J.; Dupke, R. A.; Vílchez, J. M.; Cristóbal-Hornillos, D.; González Delgado, R. M.; Hernández-Monteagudo, C.; López-Sanjuan, C.; Muniesa, D. J.; Civera, T.; Ederoclite, A.; Hernán-Caballero, A.; Marra, V.; Baqui, P. O.; Cortesi, A.; Cypriano, E. S.; Daflon, S.; de Amorim, A. L.; Díaz-García, L. A.; Diego, J. M.; Martínez-Solaeche, G.; Pérez, E.; Placco, V. M.; Prada, F.; Queiroz, C.; Alcaniz, J.; Alvarez-Candal, A.; Cepa, J.; Maroto, A. L.; Roig, F.; Siffert, B. B.; Taylor, K.; Benitez, N.; Moles, M.; Sodré, L.; Carneiro, S.; Mendes de Oliveira, C.; Abdalla, E.; Angulo, R. E.; Apari…

Random walk networks

2004

Abstract Random Boolean networks are among the best-known systems used to model genetic networks. They show an on–off dynamics and it is easy to obtain analytical results with them. Unfortunately very few genes are strictly on–off switched. On the other hand, continuous methods are in principle more suitable to capture the real behavior of the genome, but have difficulties when trying to obtain analytical results. In this work, we introduce a new model of random discrete network: random walk networks, where the state of each gene is changed by small discrete variations, being thus a natural bridge between discrete and continuous models.

El lenguaje científico, la divulgación de la ciencia y el riesgo de las pseudociencias

2012

El lenguaje de la ciencia, al igual que los lenguajes técnicos, se caracteriza por su especificidad. En él palabras de uso común 'englobadas en el grupo comunidad científica del resto de la sociedad. No debe pues sorprendernos que el lenguaje científico especializado sea, en no pocas ocasiones, utilizado por algunos científicos 'aquéllos que por el hecho de ser científicos se consideran parte de una élite intelectual' como una suerte de muralla comunicativa, que los mantiene a una distancia 'prudencial' de los profanos y los diferencia del resto de los ciudadanos. Afortunadamente estos científicos son en la actualidad una minoría, ya que la mayoría entiende que la ciencia debe, ante todo, e…

Desarrollo de técnicas de obtención de imágenes en astronomía ? usando sistemas de mascara codificada

1996

Incongruencias o descuidos científicos. ¿Un recurso literario en la ciencia ficción o en la literatura fantástica?

2009

On the nature of a shell of young stars in the outskirts of the Small Magellanic Cloud

2019

Understanding the evolutionary history of the Magellanic Clouds requires an in-depth exploration and characterization of the stellar content in their outer regions, which ultimately are key to tracing the epochs and nature of past interactions. We present new deep images of a shell-like over-density of stars in the outskirts of the Small Magellanic Cloud (SMC). The shell, also detected in photographic plates dating back to the fifties, is located at ~1.9 degr from the center of the SMC in the north-east direction.The structure and stellar content of this feature were studied with multi-band, optical data from the Survey of the MAgellanic Stellar History (SMASH) carried out with the Dark Ene…

Development of imaging techniques in gamma-ray astronomy using coded mask systems : application to the telescope LEGRI = Desarrollo de técnicas de ob…

1996

En el rango de energías de la radiación gamma no es posible usar lentes o espejos para formar imágenes; por tanto es necesario usar otros sistemas. Una solución al problema son los telescopios de mascara codificada que consisten en un plano detector y un patrón de elementos transparentes y opacos antepuesto a el. Lo que detectamos es la sombra que producen las diferentes fuentes gamma del patrón de la mascara en el plano detector. A partir de ello, y conocido el patrón que produce las sombras (la mascara), reconstruimos el campo de fuentes. En este trabajo, y aplicado al telescopio LEGRI, se han estudiado cuatro algoritmos de reconstrucción de las fuentes (correlación balanceada de muestreo…