On the solvability of the Yakubovich linear-quadratic infinite horizon minimization problem

The Yakubovich Frequency Theorem, in its periodic version and in its general nonautonomous extension, establishes conditions which are equivalent to the global solvability of a minimization problem of infinite horizon type, given by the integral in the positive half-line of a quadratic functional subject to a control system. It also provides the unique minimizing pair \lq\lq solution, control\rq\rq~and the value of the minimum. In this paper we establish less restrictive conditions under which the problem is partially solvable, characterize the set of initial data for which the minimum exists, and obtain its value as well a minimizing pair. The occurrence of exponential dichotomy and the null character of the rotation number for a nonautonomous linear Hamiltonian system defined from the minimization problem are fundamental in the analysis.Ministerio de Economía y Competitividad / FEDER, MTM2015-66330-PMinisterio de Ciencia, Innovación y Universidades, RTI2018-096523-B-I00European Commission, H2020-MSCA-ITN-2014INDAM -- GNAMPA Project 201

Li–Yorke chaos in nonautonomous Hopf bifurcation patterns - I

We analyze the characteristics of the global attractor of a type of dissipative nonautonomous dynamical systems in terms of the Sacker and Sell spectrum of its linear part. The model gives rise to a pattern of nonautonomous Hopf bifurcation which can be understood as a generalization of the classical autonomous one. We pay special attention to the dynamics at the bifurcation point, showing the possibility of occurrence of Li-Yorke chaos in the corresponding attractor and hence of a high degree of unpredictability.MINECO/FEDER, MTM2015-66330-PEuropean Commission, H2020-MSCA-ITN-201

Non-Atkinson perturbations of nonautonomous linear Hamiltonian systems: exponential dichotomy and nonoscillation

Producción CientíficaWe analyze the presence of exponential dichotomy (ED) and of global existence of Weyl functions $M^\pm$ for one-parametric families of finite-dimensional nonautonomous linear Hamiltonian systems defined along the orbits of a compact metric space, which are perturbed from an initial one in a direction which does not satisfy the classical Atkinson condition: either they do not have ED for any value of the parameter; or they have it for at least all the nonreal values, in which case the Weyl functions exist and are Herglotz. When the parameter varies in the real line, and if the unperturbed family satisfies the properties of exponential dichotomy and global existence of $M^+$, then these two properties persist in a neighborhood of 0 which agrees either with the whole real line or with an open negative half-line; and in this last case, the ED fails at the right end value. The properties of ED and of global existence of $M^+$ are fundamental to guarantee the solvability of classical minimization problems given by linear-quadratic control processes.MINECO/FEDER, MTM2015-66330-PEuropean Commission, H2020-MSCA-ITN-201

Peer Victimization in Overweight Adolescents and Its Effect on Their Self-Esteem and Peer Difficulties

This study has three objectives: to examine whether adolescents who perceive themselves as overweight differ from others in terms of offline victimization at school, cybervictimization, self-esteem, and difficulties relating to peers; to examine the possible effects of offline and cybervictimization on self-esteem and difficulties relating to peers; and to examine the possible moderating role of perceiving oneself as overweight on those effects. Previously validated questionnaires were applied to a sample of 3145 adolescents in Asturias (Spain). Descriptive, inferential, correlational, and structural equation analyses were performed. Adolescents who perceived themselves as overweight reported being victims of both offline victimization and most forms of cybervictimization to a greater extent than those who did not perceive themselves as overweight. They also reported lower self-esteem and more peer difficulties (shyness or social anxiety). In both groups of adolescents, victimization and cybervictimization were correlated with each other, both types of victimization had direct, negative effects on self-esteem, and self-esteem in turn had a direct, negative effect on peer difficulties. Furthermore, offline victimization had a direct, positive effect on peer difficulties. Perceiving oneself as overweight moderated the effect of self-esteem on peer difficulties. In adolescents perceiving themselves as overweight, low self-esteem was a stronger risk factor of peer difficulties than in the rest of the adolescents. With high overall self-esteem there were no significant differences in peer difficulties between the adolescents perceiving themselves as overweight and the rest of the adolescents

Una nueva especie de Rullierinereis y nuevos registros de Nereididae procedentes de fondos sublitorales arenosos en los alrededores de Lanzaronte (Islas Canarias)

Rullierinereis ancornunezi n. sp., collected from sandy and maërl bottoms from 19-55 m depth around Lanzarote island, is described. The new taxon is characterized by having a reduced or absent upper notopodial ligule in biramous parapodia of chaetigers 3-9 and in the middle region from chaetiger 26 onwards, and also by the shape of the homogomph notopodial falciger blade, which is short and serrated. A comparison with morphologically similar species is made. Other nereidid species collected were: Nereis lamellosa Ehlers, 1864, Nereis rava Ehlers, 1864, Neanthes caudata (Delle Chiaje, 1827) and Neanthes rubicunda (Ehlers, 1864). A map of the distribution of these species is presented.Rullierinereis ancornunezi n. sp., colectado en fondos arenosos y de maërl a 19-55 m de profundidad en la isla de Lanzarote, es descrito. El nuevo táxon se caracteriza por tener reducida la lígula superior notopodial de los parápodos birrámeos desde los setígeros 3-9 y en la región media, y por la forma de la seda falcígera homogonfa notopodial, ya que la hoja es corta y espinulada. Se realiza una comparación con especies morfológicamente similares. Otras especies de nereídidos encontradas fueron: Nereis lamellosa Ehlers, 1864, Nereis rava Ehlers, 1864, Neanthes caudata (Delle Chiaje, 1827) and Neanthes rubicunda (Ehlers, 1864). Se presenta un mapa de la distribución de estas especies en la isla de Lanzarote. &nbsp

Una semblanza de las primeras mujeres afroamericanas doctoras en matemáticas

Se presentan las biografías de cinco mujeres matemáticas nacidas entre finales del siglo XIX y primeros del siglo pasado, caracterizadas por haber sido las primeras mujeres afroamericanas doctoras en Matemáticas, tras superar con grandes esfuerzos las enormes dificultades de género impuestas por la sociedad en la que vivían. Se pretende con ello reconocer el trabajo de estas mujeres y ponerlas como ejemplos de superación y lucha de la mujer por conseguir unos objetivos similares a los del varón

Check-list of interstitial polychaetes from intertidal and shallow subtidal soft bottoms of Tenerife, Canary Islands

A check-list of polychaete species from two stations on the south coast of Tenerife (Los Abrigos and Los Cristianos) at two different tidal levels, intertidal and shallow subtidal (3 m depth) is presented. A total of 47 species were collected, the hesionid Microphthalmus pseudoaberrans Campoy & Viéitez, 1982 and the spionids Rhynchospio glutaea (Ehlers, 1897) and Spio filicornis (O.F. Müller, 1776) being the most abundant. With 18 species the family Syllidae is the most diverse, followed by the Spionidae and Paraonidae with 6 and 5 species, respectively. The interstitial polychaetes found are represented by both meiofaunalsized and small-sized macrofaunal species

Three new records of Desmodorids (Nematoda, Desmodoridae) from sandy seabeds of the Canary islands

In an ecological study of meiofaunal assemblages in two locations (Los Abrigos and Los Cristianos) of Tenerife (Canary Islands, NE Atlantic Ocean), several desmodorid species were found throughout the study period. Three species belonging to the family Desmodoridae were collected in intertidal and shallow subtidal sandy seabeds. These species were Desmodorella aff. tenuispiculum Allgen, 1928, Metachromadora sp. and Spirinia parasitifera Bastian, 1865. Descriptions, figures and tables with meristic data are presented. Moreover, differences between canarian and specimens from other geographical regions were discussed.Durante la realización de un estudio ecológico de las comunidades meiofaunales en dos localidades de muestreo (Los Abrigos y Los Cristianos) de la isla de Tenerife (Islas Canarias, Océano Atántico), varios ejemplares de desmodóridos fueron recolectados. Tres especies pertenecientes a la familia Desmodoridae fueron encontradas en fondos arenosos intermareales y submareales someros. Estas tres especies fueron: Desmodorella aff. tenuispiculum Allgen, 1928, Metachromadora sp. y Spirinia parasitifera Bastian, 1865. Se presentan descripciones, figuras y tablas con datos merísticos de estas especies. Además, se detallan las diferencias encontradas entre los ejemplares canarios y los procedentes de otras áreas geográficas