113 research outputs found

    La Familia Atoposauridae: una aproximación a la historia de los cocodrilos enanos

    Get PDF

    The Stokes-Einstein Relation at Moderate Schmidt Number

    Full text link
    The Stokes-Einstein relation for the self-diffusion coefficient of a spherical particle suspended in an incompressible fluid is an asymptotic result in the limit of large Schmidt number, that is, when momentum diffuses much faster than the particle. When the Schmidt number is moderate, which happens in most particle methods for hydrodynamics, deviations from the Stokes-Einstein prediction are expected. We study these corrections computationally using a recently-developed minimally-resolved method for coupling particles to an incompressible fluctuating fluid in both two and three dimensions. We find that for moderate Schmidt numbers the diffusion coefficient is reduced relative to the Stokes-Einstein prediction by an amount inversely proportional to the Schmidt number in both two and three dimensions. We find, however, that the Einstein formula is obeyed at all Schmidt numbers, consistent with linear response theory. The numerical data is in good agreement with an approximate self-consistent theory, which can be used to estimate finite-Schmidt number corrections in a variety of methods. Our results indicate that the corrections to the Stokes-Einstein formula come primarily from the fact that the particle itself diffuses together with the momentum. Our study separates effects coming from corrections to no-slip hydrodynamics from those of finite separation of time scales, allowing for a better understanding of widely observed deviations from the Stokes-Einstein prediction in particle methods such as molecular dynamics.Comment: Submitte

    Fluctuating hydrodynamic modelling of fluids at the nanoscale

    Get PDF
    A good representation of mesoscopic fluids is required to combine with molecular simulations at larger length and time scales (De Fabritiis {\it et. al}, Phys. Rev. Lett. 97, 134501 (2006)). However, accurate computational models of the hydrodynamics of nanoscale molecular assemblies are lacking, at least in part because of the stochastic character of the underlying fluctuating hydrodynamic equations. Here we derive a finite volume discretization of the compressible isothermal fluctuating hydrodynamic equations over a regular grid in the Eulerian reference system. We apply it to fluids such as argon at arbitrary densities and water under ambient conditions. To that end, molecular dynamics simulations are used to derive the required fluid properties. The equilibrium state of the model is shown to be thermodynamically consistent and correctly reproduces linear hydrodynamics including relaxation of sound and shear modes. We also consider non-equilibrium states involving diffusion and convection in cavities with no-slip boundary conditions

    Arcosaurios (Crocodilia, Dinosauria) del Cretácico superior de la Conca de Tremp (Lleida, España)

    Get PDF
    The study of a great part of the material found during the excavation work carried out by a team of the «Institut de Paleontología de Sabadell» and other paleontologists of the universities of Madrid and Bellaterra, in the basin of Tremp (Maastrichtiense) in 1984 and 1985 has made possible the recognition of: 1.º A large sized Crocodilian, attributable to an adult animal of the Alligatoridae family, comparable to Crocodilus affluvelensis. 2.° Dinosaur remains atributed to three difIerent families: Atlantosauridae (represented by a large sized Sauropod, probably Hypselosaurus); Iguanodontidae (afI. Rhabdodon, medium sized Omithopod); and Hadrosauridae (Ortbomerus, small sized). 3.° Dinosaur's footprints, not very well preserved, medium and large sized, attributable to biped Omithopod. The fauna remains were always found unconnected, scattered all over large areas and with no signs of depredation. The sort of materials found reveal a certain transport which caused a selective action over the remains. Later, the efIects of the orogenic processes suffered by this area in the Tertiary period would combine with this transport.El estudio de gran parte del material hallado en los trabajos de excavación realizados por un equipo del «Institut de Paleontología de Sabadell» y otros paleontólogos de las Universidades de Madrid y Bellaterra, en la cuenca de Tremp (Maastrichtiense), durante los años 1984 y 1985, ha permitido reconocer: 1.º Un crocodílido de gran talla, atribuible a un animal adulto de la familia Alligatoridae, comparable a Crocodilus affluvelensis. 2.° Restos de dinosaurios que se han atribuido a tres familias: Atlantosauridae (representada por un saurópodo de gran talla, probablemente Hypselosaurus); Iguanodontidae (afI. Rhabdodon, ornitópodo de talla media), y Hadrosauridae (Ortbomerus, de talla pequeña). 3.° Icnitas de dinosaurios, bastante mal conservadas, de tamaño medio y grande, atribuibles a omitópodos bípedos. Los restos faunísticos han sido hallados siempre inconexos, esparcidos en extensas superficies y sin señales de depredación. El tipo de material hallado indica, en principio, un cierto transporte, el cual ejerció una acción selectiva sobre los restos. Posteriormente, a este transporte se unirían los efectos de los procesos orogénicos que afectaron la zona durante el Terciario

    Predicting the size and morphology of nanoparticle clusters driven by biomolecular recognition

    Full text link
    Nanoparticle aggregation is a driving principle of innovative materials and biosensing methodologies, improving transduction capabilities displayed by optical, electrical or magnetic measurements. This aggregation can be driven by the biomolecular recognition between target biomolecules (analytes) and receptors bound onto nanoparticle surface. Despite theoretical advances on modelling the entropic interaction in similar systems, predictions of the fractal morphologies of the nanoclusters of bioconjugated nanoparticles are lacking. The morphology of resulting nanoclusters is sensitive to the location, size, flexibility, average number of receptors per particle f̄, and the analyte-particle concentration ratio. Here we considered bioconjugated iron oxide nanoparticles (IONPs) where bonds are mediated by a divalent protein that binds two receptors attached onto different IONPs. We developed a protocol combining analytical expressions for receptors and linker distributions, and Brownian dynamics simulations for bond formation, and validated it against experiments. As more bonds become available (e.g., by adding analytes), the aggregation deviates from the ideal Bethe's lattice scenario due to multivalence, loop formation, and steric hindrance. Generalizing Bethe's lattice theory with a (not-integer) effective functionality feff leads to analytical expressions for the cluster size distributions in excellent agreement with simulations. At high analyte concentration steric impediment imposes an accessible limit value facc to feff, which is bounded by facc < feff < f̄. A transition to gel phase, is correctly captured by the derived theory. Our findings offer new insights into quantifying analyte amounts by assessing nanocluster size, and predicting nanoassembly morphologies accurately is a first step towards understanding variations of physical properties in clusters formed after biomolecular recognitionThis work has been partially funded by the Spanish Research Agencies (PID2020-117080RB-C51, PDC2021-121441-C21, PCI2019- 103600,CEX2020-001039-S, PID2019-111649RB-I00 PID2020- 117080RB-C53, MDM-2017-0720, RED2018-102626-T) and Comunidad de Madrid (NANOMAGCOST, S2018/NMT-4321). European COST Actions CA17115 (MyWave), and CA17140 (Nano2Clinic) are also acknowledged. ESD thanks Comunidad de Madrid for financial support (PEJ-2017-AI/BMD-7517). Authors thank Dr Patricia Pedraz for carefull acquisition of AFM image

    Dinosaurios del Cretácico inferior de Galve (Teruel, España)

    Get PDF
    The aim of this paper is to complete the study of the Dinosaur fauna of the syncline of Galve (Teruel, Spain). Most of the outcrops are Early Barremian in age. Nevertheless, the outcrop called Las Zabacheras could be Hauterivian and El Pelejón Hauterivian-Early Barremian in age. Theropod Dinosaurs are poorly represented. Three vertebral centra are described. They are identified as Theropoda indet. The several outcrops of Galve have yielded four forms of Sauropods. Three of them (cf. Astrodon sp., Camarasauridae indet., form A, Camarasauridae indet., form B) have been identified based on isolated teeth. The Sauropod from Las Zabacheras (Lapparent, 1960; Sanz, 1982) has been proposed as a new taxon, Aragosaurus ischiaticus n. gen. et n. sp. The material which the new taxon is based on are the bones studied by Lapparent (Museo de la Diputación de Teruel) and new ones: caudal vertebrae, chevrones, seapula, ilium, femur and autopodial material. After a research on evolutive polarity of some traits within the Sauropoda, the apomorphic character-states which define the new taxon are as follows: First caudal vertebrae with a great transversal development of the neuroapophysis (club-like), seapular blade terminally expansioned, with an intermediate development (for example between Cetiosaurs and Brachiosaurus or Rebbachisaurus). Great dorso-ventral development (acromio-glenoideus) of the anterior seapular zone (ratio miminal width of the seapular blade/maximal acromio-glenoideus height of 0.27). lliac process of ischium well developed. Pubic process of ischium with great dorso-ventral development (ratio antero-posterior length of this process/lenght of ischiadic contact with pubis, 0.63). Ischiadic process of ischium with a conspicuous final expansion. Lenght ratio humerus/femur 0.82. Lateral bulge just distal to the femoral greater trochanter. Medial condyle of femur relatively developed (ratio maximal antero-posterior diameter of medial condyle/maximal transversal distal femoral width of 0.77). The Aragosaurus taxonomic status is proposed within the family Camarasauridae (sensu Steel, 1970). The Ornithopoda described in this paper mainly belong to the family Hypsilophodontidae, except an isolated tooth identified as Ornithopoda indet. A proximal fragment of a left femur is identified as cf. Valdosaurus sp. Hypsilopbodon foxii has been identified based on a left femur and an ilium.El objetivo principal del presente trabajo ha sido completar el estudio de la fauna de dinosaurios del sinclinal de Galve, de edad mayoritariamente barremiense inferior, aunque el yacimiento de Las Zabacheras puede tener una edad Hauteriviense y el Pelejón Hauteriviense-Barremiense inferior. Los Terópodos están pobremente representados, describiéndose tres centros vertebrales que son identificados como Theropoda indet. Cuatro formas diferentes de Saurópodos han sido identificadas en los diferentes yacimientos de Galve. Tres de ellas (cf. Astrodon sp.; Camarasauridae indet., forma A; Camarasauridae indet., forma B) tan sólo mediante piezas dentarias aisladas. El Saurópodo de Las Zabacheras (Lapparent, 1960; Sanz, 1982) ha sido propuesto como un nuevo taxon, Aragosaurus ischiaticus n. gen. et n. sp. Dicho material consta de diversos restos apendiculares y pélvicos estudiados por Lapparent y depositados en el Museo de la Diputación de Teruel y nuevos elementos consistentes en diversas vértebras caudales, chevrones, escápula, isquion, fémur y restos autopodiales. Las apomorfias más relevantes que definen al nuevo taxon son su relación estilopodial (longitud húmero/fémur) de 0,82, el gran desarrollo relativo dorso-ventral del contorno de contacto con el pubis del proceso pubiano del isquion y la aparición de neuroapáfisis «mazudas» en las primeras vértebras caudales. El enclave taxonómico de Aragosaurus se propone dentro de la familia Camarasauridae (sensu Steel, 1970). Los Ornitópodos descritos en este trabajo pertenecen a la familia Hypsilophodontidae, excepto una pieza dentaria aislada identificada como Ornithopoda indet. Un fragmento proximal de un fémur izquierdo es identificado como cf. Valdosaurus sp. La especie Hypsilophodon foxii ha sido identificada en base a un fémur izquierdo y un íleon

    A New Crocodylian from the Late Maastrichtian of Spain: Implications for the Initial Radiation of Crocodyloids

    Get PDF
    The earliest crocodylians are known primarily from the Late Cretaceous of North America and Europe. The representatives of Gavialoidea and Alligatoroidea are known in the Late Cretaceous of both continents, yet the biogeographic origins of Crocodyloidea are poorly understood. Up to now, only one representative of this clade has been known from the Late Cretaceous, the basal crocodyloid Prodiplocynodon from the Maastrichtian of North America.The fossil studied is a skull collected from sandstones in the lower part of the Tremp Formation, in Chron C30n, dated at -67.6 to 65.5 Ma (late Maastrichtian), in Arén (Huesca, Spain). It is located in a continuous section that contains the K/P boundary, in which the dinosaur faunas closest to the K/P boundary in Europe have been described, including Arenysaurus ardevoli and Blasisaurus canudoi. Phylogenetic analysis places the new taxon, Arenysuchus gascabadiolorum, at the base of Crocodyloidea.The new taxon is the oldest crocodyloid representative in Eurasia. Crocodyloidea had previously only been known from the Palaeogene onwards in this part of Laurasia. Phylogenetically, Arenysuchus gascabadiolorum is situated at the base of the first radiation of crocodyloids that occurred in the late Maastrichtian, shedding light on this part of the cladogram. The presence of basal crocodyloids at the end of the Cretaceous both in North America and Europe provides new evidence of the faunal exchange via the Thulean Land Bridge during the Maastrichtian

    Does ohmic heating influence the flow field in thin-layer electrodeposition?

    Get PDF
    In thin-layer electrodeposition the dissipated electrical energy leads to a substantial heating of the ion solution. We measured the resulting temperature field by means of an infrared camera. The properties of the temperature field correspond closely with the development of the concentration field. In particular we find, that the thermal gradients at the electrodes act like a weak additional driving force to the convection rolls driven by concentration gradients.Comment: minor changes: correct estimation of concentration at the anode, added Journal-re
    • …
    corecore