The unbounded dead-end depth propertie is not a group invariant

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Reduction, Linearization and stability of relative equilibria for mechanical systems on riemannian manifolds

Consider a Riemannian manifold equipped with an infinitesimal isometry. For this setup, a unified treatment is provided, solely in the language of Riemannian geometry, of techniques in reduction, linearization, and stability of relative equilibria. In particular, for mechanical control systems, an explicit characterization is given for the manner in which reduction by an infinitesimal isometry, and linearization along a controlled trajectory "commute." As part of the development, relationships are derived between the Jacobi equation of geodesic variation and concepts from reduction theory, such as the curvature of the mechanical connection and the effective potential. As an application of our techniques, fiber and base stability of relative equilibria are studied. The paper also serves as a tutorial of Riemannian geometric methods applicable in the intersection of mechanics and control theory.

Prototypical Arthropod Gene Content and Genome Organisation in the Centipede Strigamia maritima

Myriapods (e.g., centipedes and millipedes) display a simple homonomous body plan relative to other arthropods. All members of the class are terrestrial, but they attained terrestriality independently of insects. Myriapoda is the only arthropod class not represented by a sequenced genome. We present an analysis of the genome of the centipede Strigamia maritima. It retains a compact genome that has undergone less gene loss and shuffling than previously sequenced arthropods, and many orthologues of genes conserved from the bilaterian ancestor that have been lost in insects. Our analysis locates many genes in conserved macro-synteny contexts, and many small-scale examples of gene clustering. We describe several examples where S. maritima shows different solutions from insects to similar problems. The insect olfactory receptor gene family is absent from S. maritima, and olfaction in air is likely effected by expansion of other receptor gene families. For some genes S. maritima has evolved paralogues to generate coding sequence diversity, where insects use alternate splicing. This is most striking for the Dscam gene, which in Drosophila generates more than 100,000 alternate splice forms, but in S. maritima is encoded by over 100 paralogues. We see an intriguing linkage between the absence of any known photosensory proteins in a blind organism and the additional absence of canonical circadian clock genes. The phylogenetic position of myriapods allows us to identify where in arthropod phylogeny several particular molecular mechanisms and traits emerged. For example, we conclude that juvenile hormone signalling evolved with the emergence of the exoskeleton in the arthropods and that RR-1 containing cuticle proteins evolved in the lineage leading to Mandibulata. We also identify when various gene expansions and losses occurred. The genome of S. maritima offers us a unique glimpse into the ancestral arthropod genome, while also displaying many adaptations to its specific life history.

Amor y Melancolía en "El demonio de la depresión", de Andrew Solomon

Les taxes de prevalença de la depressió dins la població no deixen d’augmentar, però la causa per la qual una persona desenvolupa el trastorn, tot i les múltiples hipòtesis existents, encara segueix sent desconeguda. Els serveis sanitaris s’esforcen per intentar reduir la simptomatologia observable, per aconseguir, el més 6 aviat possible, que la persona recuperi la seva vida social i laboral. Però, què és el que realment hi ha darrere d'aquesta malaltia? Quin és el principal problema amb el que s’ha d’enfrontar la ment depressiva? . Una de les qüestions més reconegudes i manifestades per la majoria dels pacients melancòlics, és la impossibilitat que se sent davant l'amor. No es pot estimar, ni a un mateix ni tampoc als altres. Es fa obvi així, la existència d’una correlació entre la capacitat d'estimar i sentir-se estimat, i la depressió. És aquest vincle i la importància del mateix, el que es pretén estudiar i presentar en el següent treball. Per a això, s'ha realitzat una anàlisi de l'obra d'Andrew Solomon, El dimoni de la depressió, on es recull detalladament què és el que succeeix en la capacitat que té la persona d’estimar i sentir-se estimat durant aquesta malaltia, corroborant-lo i ampliant-lo, posteriorment, amb diferents referències literàries sobre la patologia esmentada. Finalment s'ha procedit, a través d'Erich Fromm i el seu llibre L'art d'estimar, a l'estudi o conceptualització de l'amor i la jerarquia que ocupa aquest durant la vida de qualsevol persona, per exposar així, les conseqüències de la manca d'aquest sentiment i la necessitat del mateix per poder conservar una ment sana.

De Andrew Carnegie a OverDrive, Amazon y ¿algo más? Biblioteca pública y préstamo de libros digitales en Estados Unidos

Ressenya de: 2012 survey of ebook usage in U.S. public libraries: third annual survey. LJ/SLJ Library Research Syndicate (LRS). [New York, N.Y.]: Library Journal, 2012. 108 p. Disponible en línia a: digitalshift.com/research/ebook-usage-reports/public/> [Consulta: 27 feb. 2013].