149 research outputs found

    A PHYLOGENETIC PERSPECTIVE OF THE AVIAN TROPHIC DIVERSIFICATION: INTEGRATING PALAEONTOLOGICAL AND NEONTOLOGICAL INFORMATION

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    From their origin in the Middle Jurassic until the present, birds have undergone one of the most important evolutionary radiations among vertebrates, with the development of great species-level diversity and the occupation of a broad spectrum of ecological niches. Since dietary shifts involve a series of morphophysiological adjustments and reflect the use of the resources, diet represents a key ecological and evolutionary parameter to understand the history of bird clades. This study combines neontological and paleontological dietary information in a phylogenetic context, aiming the understanding the role of feeding habits in bird evolution and their potential relationship with past ecological and evolutionary events. Our findings point towards an omnivorous ancestral diet for the avian clade, which is consistent with dietary information, dental structure and life style of the first birds, such as Archaeopteryx. Our results also show dietary shifts in avian evolutionary history. Faunivores predominate in the avian history, while herbivorous lineages underwent adaptive radiations possibly related to transformation of ecosystems and their plant assemblages worldwide such as the development of the angiosperms during the Cretaceous or the development of grassy environments in the Oligocene. Faunivorous and herbivorous clades arose basically through diversification within lineages, while omnivores evolved due to transitions into the strategy. The capacity to specialize and generate new trophic niches allowed faunivores and herbivores to diversify more than omnivores. Nevertheless, despite this relatively low diversification, the omnivorous strategy appears to be key to the primary processes of bird radiation and fundamental in the evolutionary success of birds.Peer reviewe

    Chaotic motion of space charge wavefronts in semiconductors under time-independent voltage bias

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    A standard drift-diffusion model of space charge wave propagation in semiconductors has been studied numerically and analytically under dc voltage bias. For sufficiently long samples, appropriate contact resistivity and applied voltage - such that the sample is biased in a regime of negative differential resistance - we find chaos in the propagation of nonlinear fronts (charge monopoles of alternating sign) of electric field. The chaos is always low-dimensional, but has a complex spatial structure; this behavior can be interpreted using a finite dimensional asymptotic model in which the front (charge monopole) positions and the electrical current are the only dynamical variables.Comment: 12 pages, 8 figure

    Caracteristicas reologicas de pastas de cal.

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    Este trabajo presenta las características reológicas de pastas de cal, especificando la influencia de su origen en la obtención de valores de trabajabilidad. El estudio se realiza sobre pastas de cal hidratada, de diferentes edades de maduración y sobre pastas procedentes de cal en polvo. En la práctica artesanal del uso de estos tipos de pasta de cal en obra, la diferencia de trabajabilidad es conocida, lo que comporta distintos rendimientos en la ejecución del revestimiento. En este estudio se presentan los primeros resultados obtenidos en cuanto a: tamaño de grano (granulometría láser); estructura cristalina (difracción de rayos X y microscopía electrónica); trabajabilidad (viscosidad plástica, índice de flujo, índice de trabajabilidad) dependiendo de la cantidad de agua añadida y de la capacidad de retención de ésta en cada pasta.Postprint (published version

    Phylogenetic biome conservatism as a key concept for an integrative understanding of evolutionary history: Galliformes and Falconiformes as study cases

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    Biomes are climatically and biotically distinctive macroecological units that formed over geological time scales. Their features consolidate them as ‘evolutionary scenarios’, with their own diversification dynamics. Under the concept of phylogenetic niche conservatism, we assessed, for the first time, the evolution of biome occupation in birds. We aimed to analyse patterns of adaptation to different climatic regimes and the determinant factors for colonization of emerging biomes by clades from different ancestral biomes. In this work, we reconstructed the biome occupation history of two clades of birds (Galliformes and Falconiformes) under an integrative perspective through a comprehensive review of ecological, phylogenetic, palaeontological and biogeographical evidence. Our findings for both groups are consistent with a scenario of phylogenetic biome conservatism and highlight the importance of changes in climate during the Miocene in the adaptation and evolution of climatic niches. In particular, our results indicate high biome conservatism associated with biomes situated in some of the extremes of the global climate gradient (evergreen tropical rainforest, steppe and tundra) for both bird taxa. Finally, the historical dynamics of tropical seasonal biomes, such as tropical deciduous woodlands and savannas, appear to have played a preponderant role during the diversification processes of these bird lineages.Depto. de Geodinámica, Estratigrafía y PaleontologíaFac. de Ciencias GeológicasTRUEMinisterio de Ciencia e Innovación (MICINN)Universidad Complutense de MadridColombian administrative Department for Science and InnovationDirección General de Investigaciones of Universidad Santiago de CaliTalent Attraction Program of the Madrid GovernmentUniversidad Complutense de Madridpu

    Acoustic evaluation of modular greenery noise barriers

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    Green noise barriers have become an alternative means of reducing urban traffic noise. In this paper, the acoustic performance of a modular greenery noise barrier is evaluated. In situ measurements of noise reflection were performed using an experimental prototype to estimate the sound absorption coefficients. These coefficients were found to have values of approximately 0.7, higher than those previously found in laboratory measurements for a similar system with a lower vegetation density. The obtained values were input into software for predicting environmental noise to analyse the expected performance of such barriers, particularly in the case of a pair of parallel barriers. A comparison with the results for reflective barriers indicates a significant improvement in sound attenuation of up to 4 dBA. The values are similar and even superior to results reported by other authors regarding the effectiveness of absorptive treatments applied to parallel barriers, and furthermore, the proposed barriers offer an aesthetic element for environmental integration.Peer ReviewedPostprint (published version

    Relación entre Medidas Zoométricas en Vacas Holstein-Friesian y Dimensiones de Cubículos en Granjas Lecheras

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    Body measurements in Portuguese Holstein-Friesian breed and its association with the dimensions of the cubicles were investigated. During a period of 5 months, body measurements and cubicles size data from 55 commercial Portuguese dairy herds were collected including in total 1054 individual cows. Data were analyzed using the general linear model and principal components. The most relevant body measurements were: height at withers (141.1±4.72 cm), height at rump (144.2±4.47 cm), length of trunk (170.8±8.31 cm), width of biiliac (55.9±4.17 cm) and perimeter of the thorax (206.8±10.43 cm). In general, the first class of parity showed significant different measures (P<0.001) associated with the development of animals. Head to head cubicle length and cubicle width were 223.0±11.0 cm and 113.0±5.0 cm respectively; whereas in cubicle against wall length was 227.0±18.0 cm and width 111.0±7.0 cm. The highest correlations were found for body measures between the different heights and between the height at chest and perimeter of the thorax. The analysis showed no relation between body measurements and dimensions of the cubicles. Principal component analysis of the different body measurements and cubicles dimensions expressed 51.4% of the total variability, in which the first factor represented 40.2% and the second factor 11.1%.info:eu-repo/semantics/publishedVersio

    MEMPHIS: a smartphone app using psychological approaches for women with chronic pelvic pain presenting to gynaecology clinics: a randomised feasibility trial.

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    OBJECTIVES: To evaluate the feasibility of a randomised trial of a modified, pre-existing, mindfulness meditation smartphone app for women with chronic pelvic pain. DESIGN: Three arm randomised feasibility trial. SETTING: Women were recruited at two gynaecology clinics in the UK. Interventions were delivered via smartphone or computer at a location of participants choosing. PARTICIPANTS: Women were eligible for the study if they were over 18, had been experiencing organic or non-organic chronic pelvic pain for 6 months or more, and had access to a computer or smartphone. 90 women were randomised. INTERVENTIONS: Daily mindfulness meditation delivered by smartphone app, an active control app which delivered muscle relaxation techniques, and usual care without app. Interventions were delivered over 60 days. PRIMARY AND SECONDARY OUTCOME MEASURES: Outcomes included length of recruitment, follow-up rates, adherence to the app interventions, and clinical outcomes measured at baseline, two, three and 6 months. RESULTS: The target sample size was recruited in 145 days. Adherence to the app interventions was extremely low (mean app use 1.8 days mindfulness meditation group, 7.0 days active control). Fifty-seven (63%) women completed 6-month follow-up, and 75 (83%) women completed at least one postrandomisation follow-up. The 95% CIs for clinical outcomes were consistent with no benefit from the mindfulness meditation app; for example, mean differences in pain acceptance scores at 60 days (higher scores are better) were -2.3 (mindfulness meditation vs usual care, 95% CI: -6.6 to 2.0) and -4.0 (mindfulness meditation vs active control, 95% CI: -8.1 to 0.1). CONCLUSIONS: Despite high recruitment and adequate follow-up rates, demonstrating feasibility, the extremely low adherence suggests a definitive randomised trial of the mindfulness meditation app used in this study is not warranted. Future research should focus on improving patient engagement. TRIAL REGISTRATION NUMBERS: NCT02721108; ISRCTN10925965; Results

    Chaos in resonant-tunneling superlattices

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    Spatio-temporal chaos is predicted to occur in n-doped semiconductor superlattices with sequential resonant tunneling as their main charge transport mechanism. Under dc voltage bias, undamped time-dependent oscillations of the current (due to the motion and recycling of electric field domain walls) have been observed in recent experiments. Chaos is the result of forcing this natural oscillation by means of an appropriate external microwave signal.Comment: 3 pages, LaTex, RevTex, 3 uuencoded figures (1.2M) are available upon request from [email protected], to appear in Phys.Rev.
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