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

Parametric nonlinear modelling of 3D masonry arch bridges

Detailed modelling of masonry arch bridges and viaducts presents unique computational challenges. Not only do such structures exhibit complex nonlinear behaviour, but they are also difficult to describe within a consistent computational framework for high-fidelity simulations, due to the range of interactive components with varying geometric characteristics. This paper presents a novel parametric model design tool for the generation of detailed 3D FE meshes of realistic masonry arch bridges and viaducts. This tool has been developed according to a modular description as an add-on component within the Rhino – Grasshopper environment. It allows for modular complex bridge assemblages with independent definition of the key viaduct parts, including arch barrels, spandrel walls, piers as well as multi-layered fill. Moreover, new parts can be seamlessly introduced into the framework due to its modular nature. Notably, as all components are geometrically addressable, it is possible to further enhance the model generation tool by adding non-standard routines to create more complex geometry than that allowed by the current parametric definition. Importantly, the developed strategy enables variable fidelity model generation, where different segments of an analysed viaduct can be represented by meso‑ and/or macro-scale masonry descriptions at different levels of detail. This approach further enables the consideration of initial damage in the brick/blockwork, which is a very common feature of many existing masonry bridges and viaducts

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

Aspectos preliminares de la calidad del agua del arroyo Tapalqué en la ciudad de Olavarría, provincia de Buenos Aires

In Tapalqué stream, different recreational and farming activities are developed, and on its way through Olavarría city, it receipts rainwater and sewage residues previously treated. The aim of this study is to evaluate the quality of the resource, through the determination of conventional physicochemical and bacteriological parameters, heavy metals and organochloride derivatives. Four sampling stations were monitored each 45 days (2009-2010), before and after the city, after the treatment plant and downstream near Sierra Chica town. The water was classified as oligohaline and sodium bicarbonated. Hypoxia is common at stations 3 and 4. Metals as Pb, Cd and Hg were not detected. Arsenic exceeded the allowed limits for some applications, decreasing its concentration downstream. Organochlorides substances were detected in two points, in one of them Aldrin and in the other Heptachlor and/or its derivates with values above the permitted limits. An important increase in the number of total and fecal coliform organisms in downstream stations was detected.Instituto de Limnología "Raúl A. Ringuelet

Aspectos preliminares de la calidad del agua del arroyo Tapalqué en la ciudad de Olavarría, provincia de Buenos Aires

In Tapalqué stream, different recreational and farming activities are developed, and on its way through Olavarría city, it receipts rainwater and sewage residues previously treated. The aim of this study is to evaluate the quality of the resource, through the determination of conventional physicochemical and bacteriological parameters, heavy metals and organochloride derivatives. Four sampling stations were monitored each 45 days (2009-2010), before and after the city, after the treatment plant and downstream near Sierra Chica town. The water was classified as oligohaline and sodium bicarbonated. Hypoxia is common at stations 3 and 4. Metals as Pb, Cd and Hg were not detected. Arsenic exceeded the allowed limits for some applications, decreasing its concentration downstream. Organochlorides substances were detected in two points, in one of them Aldrin and in the other Heptachlor and/or its derivates with values above the permitted limits. An important increase in the number of total and fecal coliform organisms in downstream stations was detected.Instituto de Limnología "Raúl A. Ringuelet

Aspectos preliminares de la calidad del agua del arroyo Tapalqué en la ciudad de Olavarría, provincia de Buenos Aires

In Tapalqué stream, different recreational and farming activities are developed, and on its way through Olavarría city, it receipts rainwater and sewage residues previously treated. The aim of this study is to evaluate the quality of the resource, through the determination of conventional physicochemical and bacteriological parameters, heavy metals and organochloride derivatives. Four sampling stations were monitored each 45 days (2009-2010), before and after the city, after the treatment plant and downstream near Sierra Chica town. The water was classified as oligohaline and sodium bicarbonated. Hypoxia is common at stations 3 and 4. Metals as Pb, Cd and Hg were not detected. Arsenic exceeded the allowed limits for some applications, decreasing its concentration downstream. Organochlorides substances were detected in two points, in one of them Aldrin and in the other Heptachlor and/or its derivates with values above the permitted limits. An important increase in the number of total and fecal coliform organisms in downstream stations was detected.Instituto de Limnología "Raúl A. Ringuelet

Direct observation of homogeneous cavitation in nanopores

We report on the evaporation of hexane from porous alumina and silicon membranes. These membranes contain billions of independent nanopores tailored to an ink-bottle shape, where a cavity several tens of nanometers in diameter is separated from the bulk vapor by a constriction. For alumina membranes with narrow enough constrictions, we demonstrate that cavity evaporation proceeds by cavitation. Measurements of the pressure dependence of the cavitation rate follow the predictions of the bulk, homogeneous, classical nucleation theory, definitively establishing the relevance of homogeneous cavitation as an evaporation mechanism in mesoporous materials. Our results imply that porous alumina membranes are a promising new system to study liquids in a deeply metastable state.Comment: 14 pages , 4 figures. Source files also contain Supplemental Material (Doebele_HomogeneousCavitationMembranes_SM.pdf

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.

Biometric variables predict stone tool functional performance more effectively than tool‐form attributes: a case study in handaxe loading capabilities

Both the form of a stone tool and the anatomy of the individual using it have potential to influence its cutting performance. To date, however, the selective pressures acting on stone‐tool form and hominin biometric/biomechanical attributes have been investigated in isolation and their relative influence on performance have never been compared directly. This paper examines the influence of both tool‐form attributes and biometric variation on the functional performance of Acheulean handaxes. Specifically, it investigates the impact of 13 tool attributes and eight biometric traits on the working forces applied through the edge of 457 replica tools. The relative contribution of tool‐form and biometric attributes to handaxe loading levels were examined statistically. Results identify that both tool‐form attributes and biometric traits are significantly related to loading; however, tool–user biometric variation has a substantially greater impact relative to tool‐form attributes. This difference was demonstrated by up to a factor of 10. These results bear directly on the co‐evolutionary relationships of stone tools and hominin anatomy, and the comparative strength of selective pressure acting on each. They also underline why handaxe forms may have been free to vary in form across time and space without necessarily incurring critical impacts on their functional capabilities

The activation mechanism of α1β2γ2S and α3β3γ2S GABAA receptors

The α1β2γ2 and α3β3γ2 are two isoforms of γ-aminobutyric acid type A (GABAA) receptor that are widely distributed in the brain. Both are found at synapses, for example in the thalamus, where they mediate distinctly different inhibitory postsynaptic current profiles, particularly with respect to decay time. The two isoforms were expressed in HEK293 cells, and single-channel activity was recorded from outside-out patches. The kinetic characteristics of both isoforms were investigated by analyzing single-channel currents over a wide range of GABA concentrations. α1β2γ2 channels exhibited briefer active periods than α3β3γ2 channels over the entire range of agonist concentrations and had lower intraburst open probabilities at subsaturating concentrations. Activation mechanisms were constructed by fitting postulated schemes to data recorded at saturating and subsaturating GABA concentrations simultaneously. Reaction mechanisms were ranked according to log-likelihood values and how accurately they simulated ensemble currents. The highest ranked mechanism for both channels consisted of two sequential binding steps, followed by three conducting and three nonconducting configurations. The equilibrium dissociation constant for GABA at α3β3γ2 channels was ∼2.6 µM compared with ∼19 µM for α1β2γ2 channels, suggesting that GABA binds to the α3β3γ2 channels with higher affinity. A notable feature of the mechanism was that two consecutive doubly liganded shut states preceded all three open configurations. The lifetime of the third shut state was briefer for the α3β3γ2 channels. The longer active periods, higher affinity, and preference for conducting states are consistent with the slower decay of inhibitory currents at synapses that contain α3β3γ2 channels. The reaction mechanism we describe here may also be appropriate for the analysis of other types of GABAA receptors and provides a framework for rational investigation of the kinetic effects of a variety of therapeutic agents that activate or modulate GABAA receptors and hence influence synaptic and extrasynaptic inhibition in the central nervous system