Chaotic Diffusion in the Gliese-876 Planetary System

Chaotic diffusion is supposed to be responsible for orbital instabilities in planetary systems after the dissipation of the protoplanetary disk, and a natural consequence of irregular motion. In this paper we show that resonant multi-planetary systems, despite being highly chaotic, not necessarily exhibit significant diffusion in phase space, and may still survive virtually unchanged over timescales comparable to their age.Using the GJ-876 system as an example, we analyze the chaotic diffusion of the outermost (and less massive) planet. We construct a set of stability maps in the surrounding regions of the Laplace resonance. We numerically integrate ensembles of close initial conditions, compute Poincar\'e maps and estimate the chaotic diffusion present in this system. Our results show that, the Laplace resonance contains two different regions: an inner domain characterized by low chaoticity and slow diffusion, and an outer one displaying larger values of dynamical indicators. In the outer resonant domain, the stochastic borders of the Laplace resonance seem to prevent the complete destruction of the system. We characterize the diffusion for small ensembles along the parameters of the outermost planet. Finally, we perform a stability analysis of the inherent chaotic, albeit stable Laplace resonance, by linking the behavior of the resonant variables of the configurations to the different sub-structures inside the three-body resonance.Comment: 13 pages, 7 figures, 2 tables. Accepted for publication in MNRA

The resolved structure of the extragalactic supernova remnant SNR 4449-1

We present very long baseline interferometry (VLBI) observations of the milliarcsecond-scale radio structure of the supernova remnant SNR 4449$-$1 in the galaxy NGC 4449. This young and superluminous remnant was observed at 1.6 GHz ($\lambda = 18$\,cm) with the European VLBI Network. The observations confirm earlier identifications of this object with a supernova remnant (SNR) while revealing a somewhat different morphology compared with the structure reported by Bietenholz et al. from VLBI observations at 1.4 GHz. This difference is discussed here in the context of structural sensitivity of both observations. The 1.6 GHz image yields accurate estimates of the size (0.0422 arcsec $\times$ 0.0285 arcsec and 0.8 $\times$ 0.5 pc) and age ($\sim$55 yr) of SNR 4449$-$1. With a total flux of 6.1 $\pm$ 0.6 mJy measured in the VLBI image, the historical lightcurve of the source can be well represented by a power-law decay with a power index of $-$1.19 $\pm$ 0.07. The SNR exhibits a decline rate of the radio emission of 2.2$$ $\pm$ 0.1$$ yr$^{-1}$ and a radio luminosity of 1.74 $\times$ 10$^{35}$ erg s$^{-1}$.Comment: 7 pages, 6 figures, MNRAS preprint, arXiv:1309.401

Las guerras de Cuba: Violencia y campos de concentración (1868-1898)

Andreas Stucki, Las guerras de Cuba: Violencia y campos de concentración (1868-1898), Madrid, La Esfera de los Libros, 2017, 413 pp

S5 0836+710: An FRII jet disrupted by the growth of a helical instability?

The remarkable stability of extragalactic jets is surprising, given the reasonable possibility of the growth of instabilities. In addition, much work in the literature has invoked this possibility in order to explain observed jet structures and obtain information from these structures. For example, it was recently shown that the observed helical structures in the jet in S5 0836+710 could be associated with helical pressure waves generated by Kelvin-Helmholtz instability. Our aim is to resolve the arc-second structure of the jet in the quasar S5 0836+710 and confirm the lack of a hot-spot (reverse jet-shock) found by present observing arrays, as this lack implies a loss of jet collimation before interaction with the intergalactic medium. In this work, we use an observation performed in 2008 using EVN and MERLIN. The combined data reduction has provided a complete image of the object at arc-second scales. The lack of a hot-spot in the arc-second radio structure is taken as evidence that the jet losses its collimation between the VLBI region and the region of interaction with the ambient medium. This result, together with the previous identification of the helical structures in the jet with helical pressure waves that grow in amplitude with distance, allow us to conclude that the jet is probably disrupted by the growth of Kelvin-Helmholtz instability. This observational evidence confirms that the physical parameters of jets can be extracted using the assumption that instability is present in jets and can be the reason for many observed structures. Interestingly, the observed jet is classified as a FRII object in terms of its luminosity, but its large-scale morphology does not correspond to this classification. The implications of this fact are discussed.Comment: Accepted for publication in Astronomy & Astrophysic

Quantum Thermal Machine as a Thermometer

We propose the use of a quantum thermal machine for low-temperature thermometry. A hot thermal reservoir coupled to the machine allows for simultaneously cooling the sample while determining its temperature without knowing the model-dependent coupling constants. In its most simple form, the proposed scheme works for all thermal machines which perform at Otto efficiency and can reach Carnot efficiency. We consider a circuit QED implementation which allows for precise thermometry down to $\sim$15 mK with realistic parameters. Based on the quantum Fisher information, this is close to the optimal achievable performance. This implementation demonstrates that our proposal is particularly promising in systems where thermalization between different components of an experimental setup cannot be guaranteed.Comment: Main text: 5 pages, 4 figures; Supplement: 5 page

Robust design optimization using Kriging models: Application to the robust design optimization of truss structures

El problema de diseño óptimo robusto de estructuras es una tarea computacionalmente costosa como consecuencia del acoplamiento de los procesos de cuantificación de incertidumbre y de optimización. Para hacer frente a este problema, en este artículo se propone una metodología, basada en modelos Kriging, para resolver de forma eficiente el problema de cuantificación de incertidumbre en el proceso de optimización. El modelo Kriging aproxima, de forma simultánea, la respuesta estructural en el dominio de diseño y en el dominio estocástico, permitiendo desacoplar los procesos de cuantificación de incertidumbre y de optimización. La metodología propuesta incluye un criterio de actualización de los modelos Kriging basado en la estimación del error en la predicción, que mejora la aproximación en las regiones cercanas al frente de Pareto. Se han resuelto 3 problemas para mostrar la aplicabilidad y la precisión de la metodología propuesta. Los resultados muestran que la metodología es adecuada para resolver el problema de diseño óptimo robusto con una precisión razonable y un número de evaluaciones del modelo de simulación muy inferior al que requieren los métodos convencionales.Conventional methods addressing the robust design optimization problem of structures usually require high computational requirements due to the nesting of uncertainty quantification within the optimization process. In order to address such a problem, this work proposes a methodology, based on Kriging models, to efficiently assess the uncertainty quantification in the optimization process. The Kriging model approximates the structural performance both in the design domain and in the stochastic domain, which allows to decouple the uncertainty quantification process and the optimization process. In addition, an infill criterion based on the variance of the Kriging prediction is included to update the Kriging model towards the global Pareto front. Three numerical examples show the applicability and the accuracy of the proposed methodology. The results show that the proposed method is appropriate to solve the robust design optimization problem with reasonable accuracy and a considerably lower number of function calls than required by conventional methods.Peer Reviewe

Strand bond performance in prestressed concrete accounting for bondslip

This paper presents the results of an experimental research program addressing the bond behavior of prestressing strands in pretensioned prestressed concrete members after anchorage failure has occurred. A test methodology based on measuring the prestressing strand force and strand end slip at the specimens free end was employed. Transmission- and anchorage-length tests were performed on several series of prestressed specimens with different embedment lengths using twelve concrete mixes. Average bond stresses along the transmission length and the anchorage length were obtained for specimens with release strengths ranging from 24 MPa to 55 MPa. For the anchorage analysis, a parameter was developed that includes strand slip to be used in determining anchorage length. Based on the test results, an analysis to experimentally substantiate the Stress Waves Theory of Janney has been proposed. Additionally, the potential bond performance of prestressing strands after anchorage failure at the end regions has been suggested.The content of the present paper is based on tests which were conducted in the Institute of Concrete Science and Technology (ICITECH), at Universitat Politecnica of Valencia (Spain), in collaboration with the companies PREVALESA and ISOCRON. Funding for this experimental research work was provided by the Spanish Ministry of Education and Science/Science and Innovation and ERDF (Project BIA2006-05521 and Project BIA2009-12722). The authors wish to thank the above companies as well as the concrete structures laboratory technicians at the Universitat Politecnica of Valencia for their cooperation. Finally, the authors also wish to pay their respects to C.A. Arbelaez.Martí Vargas, JR.; Serna Ros, P.; Hale, WM. (2013). Strand bond performance in prestressed concrete accounting for bondslip. Engineering Structures. 51:236-244. doi:10.1016/j.engstruct.2013.01.023S2362445

Growth of graph states in quantum networks

We propose a scheme to distribute graph states over quantum networks in the presence of noise in the channels and in the operations. The protocol can be implemented efficiently for large graph sates of arbitrary (complex) topology. We benchmark our scheme with two protocols where each connected component is prepared in a node belonging to the component and subsequently distributed via quantum repeaters to the remaining connected nodes. We show that the fidelity of the generated graphs can be written as the partition function of a classical Ising-type Hamiltonian. We give exact expressions of the fidelity of the linear cluster and results for its decay rate in random graphs with arbitrary (uncorrelated) degree distributions.Comment: 16 pages, 7 figure

Identification of the optical and near-infrared counterpart of GRS 1758-258

Context. Understood to be a microquasar in the Galactic center region, GRS 1758-258 has not yet been unambiguously identified to have an optical/near-infrared counterpart, mainly because of the high absorption and the historic lack of suitable astrometric stars, which led to the use of secondary astrometric solutions. Although it is considered with 1E 1740.7-2942 as the prototypical microquasar in the Galactic center region, the Galactic origin of both sources has not yet been confirmed. Aims. We attempt to improve previous astrometry to identify a candidate counterpart to GRS 1758-258. We present observations with the Gran Telescopio de Canarias (GTC), in which we try to detect any powerful emission lines that would infer an extragalactic origin of this source. Methods. We use modern star catalogues to reanalyze archival images of the GRS 1758-258 field in the optical and near-infrared wavelengths, and compute a new astrometric solution. We also reanalyzed archival radio data of GRS 1758-258 to determine a new and more accurate radio position. Results. Our improved astrometric solution for the GRS 1758-258 field represents a significant advancement on previous works and allows us to identify a single optical/near-infrared source, which we propose as the counterpart of GRS 1758-258. The GTC spectrum of this source is however of low signal-to-noise ratio and does not rule out a Galactic origin. Hence, new spectral observations are required to confirm or discard a Galactic nature.Comment: 4 pages, 3 figures, accepted by Astronomy and Astrophysic

Electric field effects on magnetotransport properties of multiferroic Py/YMnO3/Pt heterostructures

We report on the exchange bias between antiferromagnetic and ferroelectric hexagonal YMnO3 epitaxial thin films sandwiched between a metallic electrode (Pt) and a soft ferromagnetic layer (Py). Anisotropic magnetoresistance measurements are performed to monitor the presence of an exchange bias field. When the heteroestructure is biased by an electric field, it turns out that the exchange bias field is suppressed. We discuss the dependence of the observed effect on the amplitude and polarity of the electric field. Particular attention is devoted to the role of current leakage across the ferroelectric layer.Comment: Accepted for publication in Philosophical Magazine Letters (Special issue on multiferroics