Nonlinear interfaces: intrinsically nonparaxial regimes and effects

The behaviour of optical solitons at planar nonlinear boundaries is a problem rich in intrinsically nonparaxial regimes that cannot be fully addressed by theories based on the nonlinear Schrödinger equation. For instance, large propagation angles are typically involved in external refraction at interfaces. Using a recently proposed generalized Snell's law for Helmholtz solitons, we analyse two such effects: nonlinear external refraction and total internal reflection at interfaces where internal and external refraction, respectively, would be found in the absence of nonlinearity. The solutions obtained from the full numerical integration of the nonlinear Helmholtz equation show excellent agreement with the theoretical predictions

Leaf beetles are ant-nest beetles: the curious life of the juvenile stages of case-bearers (Coleoptera, Chrysomelidae, Cryptocephalinae)

Although some species of Cryptocephalinae (Coleoptera: Chrysomelidae) have been documented with ants (Hymenoptera: Formicidae) for almost 200 years, information on this association is fragmentary. This contribution synthesizes extant literature and analysizes the data for biological patterns. Myrmecophily is more common in the tribe Clytrini than in Cryptocephalini, but not documented for Fulcidacini or the closely-related Lamprosomatinae. Myrmecophilous cryptocephalines (34 species in 14 genera) primarily live among formicine and myrmecines ants as hosts. These two ant lineages are putative sister-groups, with their root-node dated to between 77–90 mya. In the New World tropics, the relatively recent radiation of ants from moist forests to more xeric ecosystems might have propelled the association of cryptocephalines and ant nests. Literature records suggest that the defensive behavioral profile or chemical profile (or both) of these ants has been exploited by cryptocephalines. Another pattern appears to be that specialized natural enemies, especially parasitoid Hymenoptera, exploit cryptocephaline beetles inside the ant nests. With the extant data at hand, based on the minimum age of a fossil larva dated to 45 mya, we can infer that the origin of cryptocephaline myrmecophily could have arisen within the Upper Cretaceous or later. It remains unknown how many times myrmecophily has appeared, or how old is the behavior. This uncertainty is compounded by incongruent hypotheses about the origins of Chrysomelidae and angiosperm-associated lineages of cryptocephalines. Living with ants offers multiple advantages that might have aided the colonization of xeric environments by some cryptocephaline species.Fil: Agrain, Federico Alejandro. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Investigaciones de las Zonas Áridas. Provincia de Mendoza. Instituto Argentino de Investigaciones de las Zonas Áridas. Universidad Nacional de Cuyo. Instituto Argentino de Investigaciones de las Zonas Áridas; ArgentinaFil: Buffington, Matthew L.. National Museum of Natural History; Estados UnidosFil: Chaboo, Caroline S.. University of Kansas; Estados UnidosFil: Chamorro, Maria L.. National Museum of Natural History; Estados UnidosFil: Schöller, Matthias. Humboldt-Universität zu Berlin; Alemani

Comparing Online English Language Learning and Face-to-Face English Language Learning at El Bosque University in Colombia

Although there is significant research surrounding online foreign language education, there are still questions on whether the outcomes are comparable to those obtained in the traditional face-to-face classroom. This study examined four classes, two online and two face-to-face, where students took the second course of a 6-level program of English as a Second Language at El Bosque University in Colombia. The International Test of English Proficiency (iTEP) was administered to students before classes started in order to establish a baseline, and then again after the courses finished. This test evaluates English language proficiency per skill: speaking, listening, reading, writing and also presents an overall proficiency score and level. Variables such as socioeconomic strata, students’ age, instructors, previous experience with online courses, course completion, student satisfaction and attendance and time on course were also examined. Because not all online students completed all content of the course within the timeframe given, special attention was given to this variable. Results indicate that when comparing the scores of only the online students who completed all the content of the course with those of their face-to-face counterparts, there are no statistically significant differences in the outcomes of any of the four skills nor there is a difference in the overall scores; however this brings up the issue of time investment as it seems to vary based upon instructional method. A qualitative component was used to support the findings in this study. This component included instructors’ interviews, an end-of-course qualitative survey and class observations

Helmholtz bright and boundary solitons

We report, for the first time, exact analytical boundary solitons of a generalized cubic-quintic Non-Linear Helmholtz (NLH) equation. These solutions have a linked-plateau topology that is distinct from conventional dark soliton solutions; their amplitude and intensity distributions are spatially delocalized and connect regions of finite and zero wave-field disturbances (suggesting also the classification as 'edge solitons'). Extensive numerical simulations compare the stability properties of recently-reported Helmholtz bright solitons, for this type of polynomial non-linearity, to those of the new boundary solitons. The latter are found to possess a remarkable stability characteristic, exhibiting robustness against perturbations that would otherwise lead to the destabilizing of their bright-soliton counterpart

On bisectors in quaternionic hyperbolic space

In this paper, we study a problem related to geometry of bisectors in quaternionic hyperbolic geometry. We develop some of the basic theory of bisectors in quaternionic hyperbolic space $H^n_Q$. In particular, we show that quaternionic bisectors enjoy various decompositions by totally geodesic submanifolds of $H^n_Q$. In contrast to complex hyperbolic geometry, where bisectors admit only two types of decomposition (described by Mostow and Goldman), we show that in the quaternionic case geometry of bisectors is more rich. We describe an infinite family of different decompositions of bisectors in $H^n_Q$ by totally geodesic submanifolds of $H^n_Q$ isometric to complex hyperbolic space $H^n_C$.Comment: 16 page

Wave envelopes with second-order spatiotemporal dispersion : I. Bright Kerr solitons and cnoidal waves

We propose a simple scalar model for describing pulse phenomena beyond the conventional slowly-varying envelope approximation. The generic governing equation has a cubic nonlinearity and we focus here mainly on contexts involving anomalous group-velocity dispersion. Pulse propagation turns out to be a problem firmly rooted in frames-of-reference considerations. The transformation properties of the new model and its space-time structure are explored in detail. Two distinct representations of exact analytical solitons and their associated conservation laws (in both integral and algebraic forms) are presented, and a range of new predictions is made. We also report cnoidal waves of the governing nonlinear equation. Crucially, conventional pulse theory is shown to emerge as a limit of the more general formulation. Extensive simulations examine the role of the new solitons as robust attractors

Evaluación del Rendimiento, Composición y Actividad Antioxidante de Aceite de Semillas de Mora (Rubus glaucus) Extraído con CO2 Supercrítico

En este trabajo se estudió el efecto de los parámetros de extracción del aceite de semillas de mora (Rubus glaucus), utilizando CO2 supercrítico como solvente. Se evaluaron diferentes condiciones de presión y temperatura, que permitieron analizar el rendimiento, la composición y la actividad antioxidante del producto extraído. La identificación de los componentes del aceite se realizó a través de cromatografía de gases y la actividad antioxidante se determinó aplicando el método de ABTS. El rendimiento más alto fue 14.5%, obtenido bajo las mejores condiciones de trabajo: 350 bar de presión y 60°C de temperatura. El aceite proveniente de semillas de R. glaucus se caracteriza por contener un 96% de ácidos grasos insaturados, de los cuales el ácido linoléico es el más abundante (61.6%) y por la presencia de sustancias como β-sitosterol, 24-metil-cicloartanol, α-tocoferol, γ-tocoferol, δ-tocoferol, además de una capacidad antioxidante equivalente al trolox de 604 µmol/100 g aceite

El fútbol dentro del campo y fuera de él : desafíos en la transición a la élite

Una de las transiciones que ha recibido menos atención en la literatura científica es la transición de junior al deporte profesional, en concreto al fútbol de élite. Basados en el modelo de desarrollo deportivo de Wylleman y Lavallee (2004), el objetivo de este estudio es explorar de forma retrospectiva los desafíos que tuvieron que afrontar futbolistas junior al realizar la transición a la élite del fútbol. Además, se analizan las especificidades de los desafíos en función del género al realizar dicha transición. Se entrevistaron 8 chicos y 8 chicas sobre sus experiencias en la transición a la élite del fútbol. Los resultados se distribuyen en dos apartados principales: desafíos asociados al fútbol dentro del campo y desafíos asociados al fútbol fuera del campo (e.g., estructura, concepción social). El análisis de contenido muestra que los desafíos a los que tienen que hacer frente los futbolistas dentro del campo se asocian a los niveles deportivo y psicológico. Los desafíos fuera del campo además de asociarse con estos dos niveles, se asocian también a los niveles psicosocial y académico/laboral. Las diferencias respecto a los desafíos que se encuentran chicos y chicas se asocian únicamente a la categoría fútbol fuera del campo. Se discute la relevancia de afrontar con éxito estos desafíos y su importancia para una correcta adaptación a la élite del fútbol.One of the transitions that has received little attention in scientific literature is the transition from junior to professional sport, specifically in football. Based on the development model of Wylleman and Lavallee (2004), the aim of this study is to explore, retrospectively, the challenges that junior football players experienced in making the transition into elite football. In addition, this study analyses specific challenges of this transition according to gender. 8 males and 8 females were interviewed about their experience in the transition to elite football. The results are divided into two main sections: challenges associated with football on the field and challenges associated with football off the field (e.g., structure, social concept). The analysis shows the effect the challenges that football players must cope with on the field produces on the athletes and their psychological levels. Off the field challenges are also produced at those levels and, in addition, at psychosocial and academic/work-related levels. The relevance of facing these challenges successfully and their importance for proper adaptation to elite football is discussed.Uma das transições que tem recebido menos atenção na literatura científica é a transição de júnior para o desporto profissional, em concreto para o futebol de elite. Baseado no modelo de desenvolvimento desportivo de Wylleman e Lavallee (2004), o objectivo deste estudo foi explorar de forma retrospectiva os desafios que enfrentaram os futebolistas juniores ao realizar a transição para a elite do futebol. Adicionalmente, foram analisadas as especificidades dos desafios em função do género. Foram entrevistados 8 rapazes e 8 raparigas acerca das suas experiências na transição para a elite do futebol. Os resultados são distribuídos em duas secções principais: desafios associados ao futebol dentro de campo e desafios associados ao futebol fora do campo (e.g., estrutura, concepção social). A análise de conteúdo revela que os desafios que os futebolistas têm que enfrentar dentro de campo se associam aos níveis desportivo e psicológico. Os desafios fora do campo, para além de se associarem a estes dois níveis, também se associam aos níveis psicossocial e académico/laboral. As diferenças referentes aos desafios que se verificam nos rapazes e raparigas associam-se unicamente à categoria futebol fora do campo. É discutida a relevância de enfrentar com êxito estes desafios e a sua importância para uma correcta adaptação ao futebol de elite