Cyclic homogeneous Riemannian manifolds

In spin geometry, traceless cyclic homogeneous Riemannian manifolds equipped with a homogeneous spin structure can be viewed as the simplest manifolds after Riemannian symmetric spin spaces. In this paper, we give some characterizations and properties of cyclic and traceless cyclic homogeneous Riemannian manifolds and we obtain the classification of simply-connected cyclic homogeneous Riemannian manifolds of dimension less than or equal to four. We also present a wide list of examples of non-compact irreducible Riemannian $3$-symmetric spaces admitting cyclic metrics and give the expression of these metrics

Homogeneous spin Riemannian manifolds with the simplest Dirac operator

We show the existence of nonsymmetric homogeneous spin Riemannian manifolds whose Dirac operator is like that on a Riemannian symmetric spin space. Such manifolds are exactly the homogeneous spin Riemannian manifolds $(M,g)$ which are traceless cyclic with respect to some quotient expression $M=G/K$ and reductive decomposition $\mathfrak{g} = \mathfrak{k} \oplus \mathfrak{m}$. Using transversally symmetric fibrations of noncompact type, we give a list of them

Cryptic diversity and deep divergence in an upper Amazonian leaflitter frog, Eleutherodactylus ockendeni

Supplementary files available: Additional file 1: Specimen information. Museum catalogue numbers (QCAZ) for E. ockendeni and two outgroup species, GenBank accession numbers for cyt b and/or 16S fragment, and locality of origin for each individual used in the study.- Additional file 2: TN-corrected p-distance among cyt b haplotypes. TN-corrected p-distances among cyt b haplotypes of E. ockendeni, grouped by clade.[Background] The forests of the upper Amazon basin harbour some of the world's highest anuran species richness, but to date we have only the sparsest understanding of the distribution of genetic diversity within and among species in this region. To quantify region-wide genealogical patterns and to test for the presence of deep intraspecific divergences that have been documented in some other neotropical anurans, we developed a molecular phylogeny of the wide-spread terrestrial leaflitter frog Eleutherodactylus ockendeni (Leptodactylidae) from 13 localities throughout its range in Ecuador using data from two mitochondrial genes (16S and cyt b; 1246 base pairs). We examined the relation between divergence of mtDNA and the nuclear genome, as sampled by five speciesspecific microsatellite loci, to evaluate indirectly whether lineages are reproductively isolated where they co-occur. Our extensive phylogeographic survey thus assesses the spatial distribution of E. ockendeni genetic diversity across eastern Ecuador.[Results] We identified three distinct and well-supported clades within the Ecuadorean range of E. ockendeni: an uplands clade spanning north to south, a northeastern and central lowlands clade, and a central and southeastern clade, which is basal. Clades are separated by 12% to 15% net corrected p-distance for cytochrome b, with comparatively low sequence divergence within clades. Clades marginally overlap in some geographic areas (e.g., Napo River basin) but are reproductively isolated, evidenced by diagnostic differences in microsatellite PCR amplification profiles or DNA repeat number and coalescent analyses (in MDIV) best modelled without migration. Using Bayesian (BEAST) and net phylogenetic estimates, the Southeastern Clade diverged from the Upland/ Lowland clades in the mid-Miocene or late Oligocene. Lowland and Upland clades speciated more recently, in the early or late Miocene.[Conclusion] Our findings uncover previously unsuspected cryptic species diversity within the common leaflitter frog E. ockendeni, with at least three different species in Ecuador. While these clades are clearly geographically circumscribed, they do not coincide with any existing landscape barriers. Divergences are ancient, from the Miocene, before the most dramatic mountain building in the Ecuadorean Andes. Therefore, this diversity is not a product of Pleistocene refuges. Our research coupled with other studies suggests that species richness in the upper Amazon is drastically underestimated by current inventories based on morphospecies.Peer reviewe

Relación entre la fuerza horizontal ejercida contra los tacos, previa a una salida de velocidad, sobre el tiempo de movimiento y la velocidad

En el presente estudio se relaciona la fuerza horizontal ejercida contra los tacos durante el tiempo comprendido entre la señal de listos y el disparo de salida (preperíodo) con el tiempo de movimiento (TM) y la velocidad horizontal en el instante del despegue del pie adelantado de los tacos (vX(CG)) así como establecer su posible influencia sobre la posición adoptada durante el preperíodo y la existencia de un contramovimiento de los músculos relacionados con la extensión de la rodilla y la flexión plantar del pié. Se han analizado 48 salidas de velocidad, utilizando para ello una plataforma de fuerza a 400 Hz, fotogrametría bidimensional de alta velocidad (tecnología de vídeo a 250 Hz,) y un generador de señales aleatorio que controlaba la secuencia que debían de tener las indicaciones de listos y el disparo de salida, todos estos sistemas sincronizados temporalmente. Los resultados ponen de manifiesto que cuando se incrementa la tensión inicial tiende a incrementarse la velocidad de salida del CG (vX(CG)), aunque no parece tener efecto sobre el tiempo de movimiento (TM), confirmándose también la existencia de un contramovimiento en los músculos relacionados con la flexión plantar del pié más retrasado, mientras que en el tobillo más adelantado y en las dos rodillas no parece existir.Peer Reviewe

Nivel de estrés académico en estudiantes de enfermería durante la pandemia de COVID-19

Introduction. The COVID-19 pandemic has had a negative impact on the emotional health of the population, with different and inappropriate responses depending on the affected group. The research aimed to estimate the level of academic stress in nursing students from the National Autonomous University of Chota, Peru, during the COVID-19 pandemic. Methods. Observational, cross-sectional study, carried out in 122 nursing students from I to X cycle, they responded to the SISCO SV Academic Stress Inventory. Results. The level of academic stress in the stressors dimension was severe in women (64.4%) and men (77.2%), in the symptom dimension it was severe in women (42.5%) and mild in men (48.6 %) and in the dimension of coping strategies, it was severe in women (62.1%) and men (60.0%). The most frequent stressors were: task and work overload (66.4%), limited time for work (64.8%), level of demand from teachers (58.2%), exams or practices (58.2%) , teacher evaluation forms (54.1%), type of jobs requested (54.1%) and highly theoretical teachers (53.3%); the most frequent symptom was headaches (45.1%); the most used coping strategies were: listening to music or watching television (54.9%), surfing the internet (53.3%), assertive ability (51.6%), concentrating on solving the situation (49.2%) and entrust themselves to God (48.4%). The level of global academic stress was severe in women (51.7%) and men (48.6%). Conclusion. Nursing students of both sexes presented a level of severe academic stress in the dimensions and in the global assessment.Introducción. La pandemia de COVID-19 ha calado negativamente en la salud emocional de la población, con respuestas diferentes e inapropiadas según el grupo afectado. La investigación tuvo como objetivo estimar el nivel de estrés académico en estudiantes de enfermería de la Universidad Nacional Autónoma de Chota, Perú, durante la pandemia de COVID-19. Métodos. Estudio observacional, transversal, realizado en 122 estudiantes de enfermería de I a X ciclo, respondieron al Inventario de Estrés Académico SISCO SV. Resultados. El nivel de estrés académico en la dimensión estresores fue severo en mujeres (64,4%) y varones (77,2%), en la dimensión síntomas fue severo en mujeres (42,5%) y leve en varones (48,6%) y en la dimensión estrategias de afrontamiento fue severo en mujeres (62,1%) y varones (60,0%). Los estresores más frecuentes fueron: sobrecarga de tareas y trabajos (66,4%), tiempo limitado para trabajos (64,8%), nivel de exigencia de profesores (58,2%), exámenes o prácticas (58,2%), formas de evaluación de profesores (54,1%), tipo de trabajos solicitados (54,1%) y profesores muy teóricos (53,3%); el síntoma más frecuente fue los dolores de cabeza (45,1%); las estrategias de afrontamiento más utilizadas fueron: escuchar música o ver televisión (54,9%), navegar en internet (53,3%), habilidad asertiva (51,6%), concentrarse en resolver la situación (49,2%) y encomendarse a Dios (48,4%). El nivel de estrés académico global fue severo en mujeres (51,7%) y varones (48,6%). Conclusión. Los estudiantes de enfermería de ambos sexos presentaron un nivel de estrés académico severo en las dimensiones y en la valoración global

Spatial Evolution of Resonant Harmonic Mode Triads in a Blasius Boundary Layer

Blasius boundary layer evolution is studied by means of bicoherence calculations. The layer is acoustically excited at the T-S frequency to provide a controlled transition. Measurements are made using a smooth surface as well as various roughness patterns

Continental phylogeography of an ecologically and morphologically diverse Neotropical songbird, Zonotrichia capensis

[Background]: The Neotropics are exceptionally diverse, containing roughly one third of all extant bird species on Earth. This remarkable species richness is thought to be a consequence of processes associated with both Andean orogenesis throughout the Tertiary, and climatic fluctuations during the Quaternary. Phylogeographic studies allow insights into how such events might have influenced evolutionary trajectories of species and ultimately contribute to a better understanding of speciation. Studies on continentally distributed species are of particular interest because different populations of such taxa may show genetic signatures of events that impacted the continent-wide biota. Here we evaluate the genealogical history of one of the world's most broadly-distributed and polytypic passerines, the rufous-collared sparrow (Zonotrichia capensis). [Results]: We obtained control region DNA sequences from 92 Zonotrichia capensis individuals sampled across the species' range (Central and South America). Six additional molecular markers, both nuclear and mitochondrial, were sequenced for a subset of individuals with divergent control region haplotypes. Median-joining network analysis, and Bayesian and maximum parsimony phylogenetic analyses all recovered three lineages: one spanning Middle America, the Dominican Republic, and north-western South America; one encompassing the Dominican Republic, Roraima (Venezuela) and La Paz (Bolivia) south to Tierra del Fuego, Argentina; and a third, including eastern Argentina and Brazil. Phylogenetic analyses suggest that the Middle American/north-western South American clade is sister to the remaining two. Bayesian and maximum likelihood coalescent simulations used to study lineage demographic history, diversification times, migration rates and population expansion together suggested that diversification of the three lineages occurred rapidly during the Pleistocene, with negligible gene flow, leaving genetic signatures of population expansions. [Conclusions]: The Pleistocene history of the rufous-collared sparrow involved extensive range expansion from a probable Central American origin. Its remarkable morphological and behavioral diversity probably represents recent responses to local conditions overlying deeper patterns of lineage diversity, which are themselves produced by isolation and the history of colonization of South America.Funding was provided by NSERC Discovery grants to Lougheed and Handford, by CONICET, ANPCyT and IDRC, and by a National Geographic Society Research Grant to Chris Moyes.Peer Reviewe