294 research outputs found
Realistic modelling of irregular slabs under extreme loading
This paper presents a new triangular flat shell element for reinforced concrete slabs of complex planar configuration subjected to extreme loading. The element is developed within a co-rotational framework, and it incorporates the effects of geometric as well as material non-linearities. To improve the approximation of the solution, additional hierarchic parameters are introduced within the local system of the element. The element formulation allows for composite action between different layers under the assumption of perfect bond between the slab concrete material, the reinforcement layers and the steel deck for composite slabs. To account for floor slabs of irregular geometric configurations, due allowance is made for uniaxial reinforcement to be oriented arbitrarily within the slab plane. The paper briefly describes the element formulation followed by several numerical verification examples. The applicability of the element to modelling concrete slabs is demonstrated using several validation studies against existing experimental results. The versatility of the element is further exemplified with a realistic large-scale floor slab model subjected to extreme loading scenarios. It is shown that the developed element provides a good balance between accuracy and efficiency in the modelling of irregular floor slabs subject to extreme loading conditions
Adsorption in non interconnected pores open at one or at both ends: A reconsideration of the origin of the hysteresis phenomenon
We report on an experimental study of adsorption isotherme of nitrogen onto
porous silicon with non interconnected pores open at one or at both ends in
order to check for the first time the old (1938) but always current idea based
on Cohan's description which suggests that the adsorption of gaz should occur
reversibly in the first case and irreversibly in the second one. Hysteresis
loops, the shape of which is usually associated to interconnections in porous
media, are observed whether the pores are open at one or at both ends in
contradiction with Cohan's model.Comment: 5 pages, 4 EPS figure
Advanced calibration of a 3D masonry arch bridge model using non-destructive testing and numerical optimisation
Historical masonry arch bridges constitute the backbone of many existing transportation networks in different countries in Europe and worldwide. They represent valuable cultural heritage assets and play an essential social and economic role. Since construction, old masonry bridges have accumulated structural damage from traffic and environmental actions. Furthermore, depending on their geometrical and mechanical characteristics, they may be particularly vulnerable to extreme events like earthquakes. Thus, accurate structural assessment under different loading conditions is critical for the conservation of these structures. Realistic assessment requires suitable numerical models to represent the characteristic 3D behaviour. The complexity of this task is further compounded by the practical difficulty in obtaining essential information on the internal bridge structure and the masonry mechanical parameters, which are vital to achieve accurate response predictions against service and extreme actions. This paper presents an advanced calibration procedure for a refined macroscale bridge model, allowing for the anisotropic nature of the masonry material. The proposed calibration approach is applied to an actual multi-span masonry viaduct, where sonic, ultrasonic, and ground penetrating radar tests are conducted to investigate the internal structure of the viaduct and determine the elastic properties of the masonry materials. In addition, the dynamic characteristics of the bridge are evaluated through in-situ measurements under environmental vibrations and used for model validation. The results from a standard simplified model calibration and an enhanced calibration are compared considering the vibration modes of the bridge. Simplified calibration is carried out using the results from in-situ tests, while a statistic inference procedure and numerical optimisation are adopted in the refined calibration to achieve improved accuracy. Although the paper focuses on a specific case study, the adopted methodology can be easily applied to studying other masonry bridges and cultural heritage masonry structures
Adsorption-Induced Deformation in Nanopores: Unexpected Results Obtained by Molecular Simulations
International audienceThe adsorption of a fluid in a nanoporous material induces deformations of the solid. The saturating regime, where the solid is filled with liquid, generally exhibits a linear relationship between the liquid pressure and the solid strain. This provides an experimental way to measure the elastic moduli of the solid walls. For large pores, the strain is determined by the pressure of the liquid saturating the pores and the mechanical properties of the porous solid. What happens at the nanometric scale, where liquid/matrix interfacial effects dominate? We have performed molecular simulations of a simple Lennard-Jones fluid confined between deformable nanoplatelets. The simulations provide the deformation of the nanopore as a function of the liquid pressure, in a way similar to what is done experimentally. The results show unexpected interface effects, which could be relevant to experimental data analysis
Possible Effects of Noncommutative Geometry on Weak CP Violation and Unitarity Triangles
Possible effects of noncommutative geometry on weak CP violation and
unitarity triangles are discussed by taking account of a simple version of the
momentum-dependent quark mixing matrix in the noncommutative standard model. In
particular, we calculate nine rephasing invariants of CP violation and
illustrate the noncommutative CP-violating effect in a couple of charged
D-meson decays. We also show how inner angles of the deformed unitarity
triangles are related to CP-violating asymmetries in some typical B_d and B_s
transitions into CP eigenstates. B-meson factories are expected to help probe
or constrain noncommutative geometry at low energies in the near future.Comment: RexTev 16 pages. Modifications made. References added. Accepted for
publication in Phys. Rev.
A Hydrophobic Gate in an Ion Channel: The Closed State of the Nicotinic Acetylcholine Receptor
The nicotinic acetylcholine receptor (nAChR) is the prototypic member of the
`Cys-loop' superfamily of ligand-gated ion channels which mediate synaptic
neurotransmission, and whose other members include receptors for glycine,
gamma-aminobutyric acid, and serotonin. Cryo-electron microscopy has yielded a
three dimensional structure of the nAChR in its closed state. However, the
exact nature and location of the channel gate remains uncertain. Although the
transmembrane pore is constricted close to its center, it is not completely
occluded. Rather, the pore has a central hydrophobic zone of radius about 3 A.
Model calculations suggest that such a constriction may form a hydrophobic
gate, preventing movement of ions through a channel. We present a detailed and
quantitative simulation study of the hydrophobic gating model of the nicotinic
receptor, in order to fully evaluate this hypothesis. We demonstrate that the
hydrophobic constriction of the nAChR pore indeed forms a closed gate.
Potential of mean force (PMF) calculations reveal that the constriction
presents a barrier of height ca. 10 kT to the permeation of sodium ions,
placing an upper bound on the closed channel conductance of 0.3 pS. Thus, a 3 A
radius hydrophobic pore can form a functional barrier to the permeation of a 1
A radius Na+ ion. Using a united atom force field for the protein instead of an
all atom one retains the qualitative features but results in differing
conductances, showing that the PMF is sensitive to the detailed molecular
interactions.Comment: Accepted by Physical Biology; includes a supplement and a
supplementary mpeg movie can be found at
http://sbcb.bioch.ox.ac.uk/oliver/download/Movies/watergate.mp
GPML: an XML-based standard for the interchange of genetic programming trees
We propose a Genetic Programming Markup Language (GPML), an XML based standard for the interchange of genetic programming trees, and outline the benefits such a format would bring in allowing the deployment of trained genetic
programming (GP) models in applications as well as the subsidiary benefit of allowing GP researchers to directly share trained trees. We present a formal definition of this standard and describe details of an implementation. In addition, we present a case study where GPML is used to implement a model predictive controller for the control of a building heating plant
Increasing contextual information by merging existing archaeological data with the state of the art laser scanning in the prehistoric funerary deposit of Pastora Cave, Eastern Spain
In this paper we present a virtual reconstruction of prehistoric funerary practices in Pastora Cave,a collective burial site in Eastern Spain that dates from the Late Neolithic, Chalcolithic and Bronze Age. Modern data of the cave was captured by 3D laser scanning techniques and added to recorded archaeological data and 3D graphic information. The combination of these data sets allowed us to create a hypothetical reconstruction to analyze the material excavated in the 1940s and 50s in greater spatial context. A 3D model of the current cave was created in order to serve as a basis for modeling the relative stratigraphic information available. We present the methodology employed and the results and implications of the analysis for Pastora Cave with particular emphasis on the spatial and chronological data
Conocer para valorar y respetar : El arroyo del Azul desde la perspectiva ambiental
En las actividades desarrolladas se introducen conceptos, mensajes enfáticos sobre la importancia de las prácticas conservacionistas y los problemas relacionados con la alteraciĂłn del hábitat, cambio de uso del suelo, contaminaciĂłn por agroquĂmicos, paisaje previo a la conquista, acerca de los pueblos originarios, el proceso de agriculturaciĂłn y otros temas que en base al interĂ©s de docentes y alumnos se abordaban con mayor o menor grado de profundidad. Todo ello con la intenciĂłn de conocer el contexto regional y una manera sencilla de entender diversos procesos ecolĂłgicos que ocurren en la cuenca del arroyo del Azul. Las actividades de aulataller, se basan en que el conocimiento de diferentes aspectos vinculados al Arroyo del Azul, puede generar mayor conciencia por el cuidado del medio ambiente en la comunidad educativa, futuros habitantes; la identificaciĂłn y reconocimiento de diferentes componentes relevantes de la fauna, flora, aspectos histĂłricos, culturales, hidrográficos, podrĂa actuar como disparador de otras acciones propias de la educaciĂłn ambiental. El objetivo es brindar diferentes aspectos ambientales del Arroyo del Azul, como el inicio o incentivo de la responsabilidad en lo ambiental y la alfabetizaciĂłn ecolĂłgica. Los alumnos universitarios participantes, futuros docentes, adquieren experiencia en el mismo escenario de trabajo.Facultad de Humanidades y Ciencias de la EducaciĂł
Twenty Thousand-Year-Old Huts at a Hunter-Gatherer Settlement in Eastern Jordan
Ten thousand years before Neolithic farmers settled in permanent villages, hunter-gatherer groups of the Epipalaeolithic period (c. 22–11,600 cal BP) inhabited much of southwest Asia. The latest Epipalaeolithic phase (Natufian) is well-known for the appearance of stone-built houses, complex site organization, a sedentary lifestyle and social complexity—precursors for a Neolithic way of life. In contrast, pre-Natufian sites are much less well known and generally considered as campsites for small groups of seasonally-mobile hunter-gatherers. Work at the Early and Middle Epipalaeolithic aggregation site of Kharaneh IV in eastern Jordan highlights that some of these earlier sites were large aggregation base camps not unlike those of the Natufian and contributes to ongoing debates on their duration of occupation. Here we discuss the excavation of two 20,000-year-old hut structures at Kharaneh IV that pre-date the renowned stone houses of the Natufian. Exceptionally dense and extensive occupational deposits exhibit repeated habitation over prolonged periods, and contain structural remains associated with exotic and potentially symbolic caches of objects (shell, red ochre, and burnt horn cores) that indicate substantial settlement of the site pre-dating the Natufian and outside of the Natufian homeland as currently understood
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