The Flavor of Cosmology

We discuss the cosmology of models in which the standard model Yukawa couplings depend on scalar field(s), often referred to as flavons. We find that thermal corrections of the flavon potential tend to decrease the Yukawa couplings, providing an important input to model-building. Working in the specific framework of Froggatt-Nielsen models, we compute the abundance of flavons in the early universe generated both via freeze-in and from coherent oscillations induced by thermal corrections to their potential, and discuss constraints on flavon models from cosmology. We find that cosmology places important constraints on theories containing flavons even for regions of parameter space inaccessible to collider searches.Comment: 26 pages, 5 figures, 5 appendice

Direct-Coupling Analysis of nucleotide coevolution facilitates RNA secondary and tertiary structure prediction

Despite the biological importance of non-coding RNA, their structural characterization remains challenging. Making use of the rapidly growing sequence databases, we analyze nucleotide coevolution across homologous sequences via Direct-Coupling Analysis to detect nucleotide-nucleotide contacts. For a representative set of riboswitches, we show that the results of Direct-Coupling Analysis in combination with a generalized Nussinov algorithm systematically improve the results of RNA secondary structure prediction beyond traditional covariance approaches based on mutual information. Even more importantly, we show that the results of Direct-Coupling Analysis are enriched in tertiary structure contacts. By integrating these predictions into molecular modeling tools, systematically improved tertiary structure predictions can be obtained, as compared to using secondary structure information alone.Comment: 22 pages, 8 figures, supplemental information available on the publisher's webpage (http://nar.oxfordjournals.org/content/early/2015/09/29/nar.gkv932.abstract

Coping with the extremes : comparative osteology of the tepui-associated toad Oreophrynella and its bearing on the evolution of osteological novelties in the genus

The only study of the osteology of the toad genus Oreophrynella dates back to 1971 and was based on a single species. Here, we use high-resolution X-ray microcomputed tomography to analyse the osteology of all nine described Oreophrynella species, which are compared with representatives of other bufonid lineages. Oreophrynella is unique among bufonids in having opposable digits. Osteological synapomorphies confirmed for the genus are as follows: presence of parietal fontanelles and exposed frontoparietal fontanelle, absence of quadratojugal, five presacral vertebrae, distally enlarged terminal phalanges and urostyle greatly expanded into flanges. Ancestral character reconstruction indicates that arboreal habits in some Oreophrynella species are likely to have evolved after the evolution of opposable digits. Opposable digits, in combination with an extension of the interdigital integument and the relative length/orientation of the digits, are likely to be adaptations to facilitate life on rocky tepui summits and an exaptation to arboreality. Cranial simplification in Oreophrynella, in the form of cranial fontanelles and absence of the quadratojugal, is possibly driven by a reduction of developmental costs, increase in flexibility and reduction of body weight. Cranial simplification combined with the shortening of the vertebral column and the shift towards a partly firmisternal girdle might be adaptations to the peculiar tumbling behaviour displayed by Oreophrynella

On the distribution and conservation of two “Lost World” tepui summit endemic frogs, Stefania ginesi Rivero, 1968 and S. satelles Señaris, Ayarzagüena, and Gorzula, 1997

International audienceIt has been suggested that the inability to migrate in response to climate change is a key threat to tepui summit biota. Tepui summit organisms might thus seriously be threatened by global warming, and there is an urgent need to accurately evaluate their taxonomic status and distributions. We investigated phylogenetic relationships among several populations of Stefania ginesi and S. satelles, two endemic species reported from some isolated tepui summits, and we examined their IUCN conservation status. Molecular phylogenetic analysis and preliminary morphological assessment indicate that both species are actually restricted to single tepui summits and that five candidate species are involved under these names. We advocate upgrading the conservation status of S. ginesi from Least Concern to Endangered, and that of S. satelles from Near Threatened to Endangered

Surge Margin Optimization of Centrifugal Compressors Using a New Objective Function Based on Local Flow Parameters

Nowadays, 3D-CFD design optimization of centrifugal compressors in terms of surge margin is one major unresolved issue. On that account, this paper introduces a new kind of objective function. The objective function is based on local flow parameters present at the design point of the centrifugal compressor. A centrifugal compressor with vaned diffuser is considered to demonstrate the performance of this approach. By means of a variation of the beta angle distribution of impeller and diffuser blade, 73 design variations are generated and several local flow parameters are evaluated. Finally, the most promising flow parameter is transferred into an objective function and an optimization is carried out. It is shown that the new approach deliver similar results as a comparable optimization with a classic objective function using two operating points for surge margin estimation, but with less computational effort since no second operating point near surge needs to be considered

Evolution in the South American ‘Lost World’: insights from multilocus phylogeography of stefanias (Anura, Hemiphractidae, Stefania )

International audienceAimTo investigate the influence of tepuian geomorphology on species diversification in the Pantepui biogeographical region based on the phylogenetic relationships and divergence times of tepui‐endemic clades of stefania frogs (Stefania, Hemiphractidae).LocationThe ‘tepuis’ and uplands/lowlands of the Pantepui biogeographical region of northern South America, one of the least accessible and least studied areas in the world.MethodsTwo mitochondrial and two nuclear DNA sequences from 60 individuals of Stefania from 24 localities in Pantepui were employed to infer phylogenetic affinities and estimate divergence times within the genus using both concatenation and species tree analyses. Ancestral areas were inferred using multiple models in a common likelihood framework.ResultsPhylogenetic analyses revealed high diversity in the genus Stefania with 10 candidate species in the Eastern Pantepui District. Four strongly supported clades are recovered in the area, one being exclusively composed of microendemics on isolated tepui summits. Biogeographical analyses suggest episodes of fragmentation of widespread tepuian ancestors from the onset of diversification of the genus, estimated in the Oligocene (c. 26 Ma), therefore suggesting a neglected vicariant model of Pantepui evolution, the Plateau Theory.Main conclusionsAlthough our results suggest that vicariance played an important role in the diversification of Stefania, speciation in Pantepui followed an intricate pattern implying multiple nonexclusive processes. Vicariance and dispersal likely influenced diversification patterns of the Pantepui fauna, possibly according to the following sequence: (1) Cenozoic vicariance; (2) reorganization of species diversity due to periods of climatic instability; (3) recent invasions (Pleistocene) of widespread upland taxa