Formation of asymmetric arms in barred galaxies

ABSTRACTWe establish a dynamical mechanism to explain the origin of the asymmetry between the arms observed in some barred disc galaxies, where one of the two arms emanating from the bar ends is very well defined, while the second one displays a ragged structure, extending between its ridge and the bar. To this purpose, we study the invariant manifolds associated with the Lyapunov periodic orbits around the unstable equilibrium points at the ends of the bar. Matter from the galaxy centre is transported along these manifolds to the periphery, forming this way the spiral arms that emanate from the bar ends. If the mass distribution in the galaxy centre is not homogeneous, because of an asymmetric bar with one side stronger than the other, or because of a non-centred bulge, the dynamics about the two unstable Lagrange points at the ends of the bar will not be symmetric as well. One of their invariant manifolds becomes more extended than the other, enclosing a smaller section and the escaping orbits on it are fewer and dispersed in a wider region. The result is a weaker arm and more ragged than the one at the other end of the bar

The influence of solvents and salts on the properties of high-voltage cathode materials

This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution license.-- et al.Lithium - ion batteries play an increasingly important role in the battery industry and they have become the dominant source of energy in the recent years, especially for portable electronic devices due to their high gravimetric energy density. This article examines the influence of mixtures of solvents with different combinations of lithium salts on the stability of two types of high-voltage cathode materials: LiNi0.5Mn1.5O4 and LiCr0.1Ni0.4Mn1.5O4 produced by a solid phase reaction. These materials were combined with several different electrolytes, cycled at various loads and higher temperature. Various combinations of solvents ethylene carbonate (EC), dimethyl carbonate (DMC) and Tetrahydrothiophene 1.1-dioxide (Sulfolane) were used for these measurements. Salts LiPF6, LiNO3 and LiTFSI were used. The influence of solvents and salts on the properties of high-voltage cathode materials was tested by cycling at different current loads and by cycling at high temperature. It was found out, by LSV analysis, that the addition of Sulfolane increases the stability of electrolyte. The addition of chromium to the cathode material LiNi0.5Mn1.5O4 causes increasing of capacity and stability at high temperature. The combination of the cathode material LiCr0.1Ni0.4Mn1.5O4 with the electrolyte 1.5 M LiPF6 EC:DMC:Sulfolane 1:2:1 w/w/w leads to increased stability in comparison with other electrolytes.This research work has been carried out in the Centre for Research and Utilization of Renewable Energy (CVVOZE). Authors gratefully acknowledge financial support from the Ministry of Education, Youth and Sports of the Czech Republic under NPU I programme (project No. LO1210).Peer Reviewe

A Novel Approach to Multimedia Ontology Engineering for Automated Reasoning over Audiovisual LOD Datasets

Multimedia reasoning, which is suitable for, among others, multimedia content analysis and high-level video scene interpretation, relies on the formal and comprehensive conceptualization of the represented knowledge domain. However, most multimedia ontologies are not exhaustive in terms of role definitions, and do not incorporate complex role inclusions and role interdependencies. In fact, most multimedia ontologies do not have a role box at all, and implement only a basic subset of the available logical constructors. Consequently, their application in multimedia reasoning is limited. To address the above issues, VidOnt, the very first multimedia ontology with SROIQ(D) expressivity and a DL-safe ruleset has been introduced for next-generation multimedia reasoning. In contrast to the common practice, the formal grounding has been set in one of the most expressive description logics, and the ontology validated with industry-leading reasoners, namely HermiT and FaCT++. This paper also presents best practices for developing multimedia ontologies, based on my ontology engineering approach

Generalized Berreman's model of the elastic surface free energy of a nematic liquid crystal on a sawtoothed substrate

In this paper we present a generalization of Berreman's model for the elastic contribution to the surface free-energy density of a nematic liquid crystal in presence of a sawtooth substrate which favours homeotropic anchoring, as a function of the wavenumber of the surface structure $q$, the tilt angle $\alpha$ and the surface anchoring strength $w$. In addition to the previously reported non-analytic contribution proportional to $q\ln q$, due to the nucleation of disclination lines at the wedge bottoms and apexes of the substrate, the next-to-leading contribution is proportional to $q$ for a given substrate roughness, in agreement with Berreman's predictions. We characterise this term, finding that it has two contributions: the deviations of the nematic director field with respect to the corresponding to the isolated disclination lines, and their associated core free energies. Comparison with the results obtained from the Landau-de Gennes model shows that our model is quite accurate in the limit $wL>1$, when strong anchoring conditions are effectively achieved.Comment: 13 pages, 9 figures; revised version submitted to Phys. Rev.

A new structural modification of stannite

[EN]: The crystal structure of the phase a-SnCu2FeS4, has been examined by EDX and electron and X-ray difraction techniques. This compound crystallizes in the tetragonal space group P4 (No. 81) with a=c= 541.4 (4) pm, Z=1, and it is a derivative structure of the basic sphalerite structure. The refinement of the structure converged to the final agreement index R(F)=0.060.[ES]: La estructura cristalina de la fase a-SnCu2FeS4 ha sido analizada por técnicas de difracción de rayos-X, electrones y Energía Dispersiva de Rayos-X. Este compuesto cristaliza en el sistema tetragonal, grupo espacial P4 (No. 81) with a=c=541,4(4) pm, Z=1 y puede ser descrita como una estructura derivada de la esfalerita. El refinamiento final de la estructura convergió a R(F)=0,060.This work was supported by FONDECYT contract 1960372 and the Programa de Intercambio Científico CONICYT (Chile) and CSIC (Spain), grant 96022.Peer Reviewe

Tourism, Competitiveness and Economic Growth: A New Analytical Model

This study reviews the theories relating to competitiveness and the indicators used for its measurement on the one hand and the studies that relate tourism and growth on the other, with the purpose of establishing the links that exist between both concepts. This enables a model to be defined in which some factors that affect tourism competitiveness combine with capital and work to determine economic growth. The provision of inherited tourism resources, together with the provision of productive resources, and the links between them are the determining elements of the capacity of an economy to produce and therefore to grow

Publicaciones médicas: ¿ciencia o negocio?

En los últimos años ha aumentado enormemente el número de revistas científicas, de tal manera que hoy día es imposible leer ni siquiera el 1% de lo que se publica sobre nuestra especialidad o sobre los campos que nos interesen. La proliferación de revistas científicas en general y en el campo de la Medicina en especial puede ser debido a muchas razones. Entre ellas destacan, en nuestra opinión, la aparición de Internet y el cambio de la razón de ser de las publicaciones científicas. Comentaremos en esta revisión las razones que han llevado a este hecho.Sociedad Canaria de Osteoporosis (2016)

Crystal structure and magnetism of Co(HPO3)⋅H2O: A novel layered compound of Co(II)

Under the terms of the Creative Commons Attribution (CC BY) license to their work.-- et al.The crystal structure and magnetic properties of Co(HPO3)⋅H2O have been determined. The solid crystallizes in space group P c a21, a=8.984(2) Å, b=7.918(2) Å, c=10.139(8) Å, V=721.2 Å3. Z=4 d calc =2.89 g/cm3. The structure consists of layers only connected by hydrogen bonds. These layers can be viewed as formed by zigzag chains of edge‐sharing Co(II)O6 octahedra interconnected by a three atom bridge (O‐P‐O) and a single oxygen bridge. ac magnetic susceptibility measurements show a sharp peak at T c =(10.8±0.1) K, and are consistent with a transition from one‐ to two‐dimensional magnetic order, in agreement with the structure. An analysis of the χT/C vs ε=(1−T c /T) data in the critical region, for T>T c , using a double‐logarithmic plot, yields a critical exponent γ=1.75 for 0.01<ε<0.1, which correspond to a two‐dimensional Ising model.The financial support of the Spanish Commission Interministerial de Cienda yTecnologia (C.I.C.Y.T. No. BP086-0187) is acknowledged. M. D. M., P. A. and F. S. thank the Spanish Ministerio de Educacion y Ciencia for predoctoral fellowships and P. G. R. for a postdoctoral fellowship.Peer Reviewe