174 research outputs found

    Afinidades y disparidades entre disciplinas ecológicas y la economía

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    La teoría general de sistemas desarrolla modelos formales sensibles a ciertas mutaciones cualitativas sólo perceptibles en los sistemas abiertos. Definidos como conjunto de elementos que se relacionan entre sí y con el medio, estos sistemas demandan un tratamiento interdisciplinar del conocimiento. El extenso ámbito multidisciplinar de las ciencias ecológicas1 reconoce los sistemas abiertos como campos empíricos de observación. La toma en consideración de las interrelaciones de cada componente de un sistema, y del conjunto, con su entorno ha resultado determinante en el reconocimiento. Este planteamiento metodológico sustentado en los sistemas abiertos añade, respecto al convencional basado en los sistemas cerrados, un grado de complejidad mayor.Peer reviewe

    Glycopeptide resistance in enterococci

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    The selective pressure resulting from the extensive use of antibiotics over the last 50 years has led to the emergence of bacterial resistance and to the dissemination of resistance genes among pathogenic microorganisms. Consequently, we are now at serious risk of suffering intractable, life-threatening infections. The progressive emergence and rapid dissemination of resistance to glycopeptides, the last resort for treating nosocomial infections with enterococci resistant to usual antibiotics, constitute one of the most dramatic examples of such resistance. Enterococci are normal human commensals, but are also a frequent cause of nosocomial urinary tract infections and nosocomial bacteremia. Enterococcus faecalis causes 80 to 90% of human enterococcal infections, while Enterococcus faecium accounts for most of the remainder. During the last decade, our understanding of the genetics and biochemical basis of resistance to glycopeptides has increased greatly. Furthermore, the application of molecular methods for the diagnosis of glycopeptide-resistant enterococci has provided new insights into the epidemiology of enterococcal infections

    Verification approaches for the 3D static LES simulations of the stonecutters bridge deck

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    [Abstract:] In computational fluid dynamics (CFD) simulations, verification is the process of identifying both the spatial and the temporal discretisations providing relatively insensitive model results. The underlying goal of this task is to identify the mesh with a lower number of elements and the longer time step size compatible with the purposes of the study. In this manner, the computational burden associated with CFD methods may be decreased without compromising the accuracy of the numerical results. In general, this process is accomplished by studying three meshes with increasing discretisation levels (coarse, medium and fine), expecting that the medium one would provide satisfactory results. Once the satisfactory spatial discretisation level is selected, the different time step sizes are studied, taking into account that a Courant number (Co) of 1 is usually considered the maximum allowable value for numerical stability when adopting a LES (Large Eddy Simulation) approach. In this study, a detailed verification study considering two different approaches, providing the uncertainty level of several parameters of interest depending on the spatial and temporal discretisation is reported. The first of them consists in the curve fitting of linear or quadratic curves to selected model outputs; meanwhile the second approach relies on the Richardson extrapolation principle. These two different approaches are applied in the frame of the 3D LES numerical simulations of the Stonecutters bare deck geometry. In the study the focus is put on the sensitivity of the integral parameters, that is the force coefficients and Strouhal number, with the spatial and temporal discretisations.Ministerio de Ciencia e Innovación; PID2019-110786GB-I00Xunta de Galicia; ED431C2017/7

    Study of a static and vertically free-to-oscillate 4:1 rectangular cylinder by means of 2D URANS simulations

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    [Abstract:] Flexible structures, such as cable-supported bridges, are prone to suffer from vortex-induced vibrations (VIV) under wind flow, as their span lengths are steadily growing in the last decades. VIV is a phenomenon that takes place at reduced wind speeds. The movements of the structure at VIV are self-limited and their frequency corresponds with the natural frequency of the structure (lock in). Therefore, VIV affects the structure’s serviceability and can cause fatigue related damage. Hence, the need for identifying and avoiding this phenomenon at the early design stages is a key issue in long-span bridges design. In the present study a rectangular cylinder of width to depth ratio 4:1, which is a common simplification of a bridge deck cross section, is analysed for the static case as well as undergoing free vibration in the vertical direction under wind flow. These analyses have been carried out by 2D URANS CFD simulations, adopting two different turbulence models: the k − ω SST, which is based upon the Boussinesq eddy-viscosity approximation, and the Reynolds Stress Model, which directly calculates the components of the specific Reynolds stresses. For the static case the force coefficients, Strouhal number and the pressure coefficient distributions were calculated and compared with the available experimental data. In the case of the free-to-oscillate 4:1 rectangular cylinder, the oscillation amplitudes are compared with wind tunnel data reported in the literature. In addition, the frequencies and phase-lags between the time-dependent lift coefficient and the vertical oscillations are studied.Ministerio de Economía y Competitividad; BIA2016-76656-RMinisterio de Economía y Competitividad; BES-2014-068418Ministerio de Economía y Competitividad; BIA2013-41965-PXunta de Galicia; ED431C 2017/7

    Efficient Validation Strategies in Environmental Analytical Chemistry: A Focus on Organic Micropollutants in Water Samples

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    This article critically reviews analytical method validation and quality control applied to the environmental chemistry field. The review focuses on the determination of organic micropollutants (OMPs), specifically emerging contaminants and pesticides, in the aquatic environment. The analytical technique considered is (gas and liquid) chromatography coupled to mass spectrometry (MS), including high-resolution MS for wide-scope screening purposes. An analysis of current research practices outlined in the literature has been performed, and key issues and analytical challenges are identified and critically discussed. It is worth emphasizing the lack of specific guidelines applied to environmental analytical chemistry and the minimal regulation of OMPs in waters, which greatly affect method development and performance, requirements for method validation, and the subsequent application to samples. Finally, a proposal is made for method validation and data reporting, which can be understood as starting points for further discussion with specialists in environmental analytical chemistry.D.F.-S. acknowledges the Ministerio de Universidades in Spain for his Margarita Salas postdoctoral grant (Ref. MGS/2021/15). The authors from University Jaume I acknowledge financial support from Generalitat Valenciana (Research Group of Excellence Prometeo 2019/040) and Ministerio de Ciencia e Innovación (Ref. PID2021-127451OB-I00). J.B.Q. acknowledges funding provided by Xunta de Galicia (Ref. ED431C 2021/06), the Spanish Agencia Estatal de Investigación – MCIN/AEI/10.13039/501100011033 (Ref. PID2020-117686RB-C32).S

    Square Cylinder Under Different Turbulent Intensity Conditions by Means of Small-Scale Turbulence

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    [Abstract] The phenomenon of turbulence is present in almost every type of flow in practical applications. Depending on its level of intensity and length scale, it can modify both the aerodynamic and aeroelastic performance of a body under flow action. In wind tunnel tests, the desired turbulence level is achieved by placing obstacles, spires, grids and extra roughness generators upwind the tested model. On the other hand, when trying to reproduce turbulence effects by means of a computational fluid dynamics (CFD) approach, two options have usually been considered: synthetic turbulence generation and the reproduction of velocity and pressure fluctuations recorded from previous simulations or wind tunnel tests. Another option, whose feasibility in CFD applications is addressed in this work by means of a 2D URANS (unsteady Reynolds averaged Navier–Stokes) consists of placing a rod upstream of the studied body, near the stagnation line. This approach is based on the generation of small scale turbulence upstream of the studied body, so that the turbulent wake generated by an upwind rod impinges on the body located downwind. In the present study, by means of 2D URANS simulations, the smooth flow over a circular cylinder (the upwind rod) is studied focusing on its wake turbulence characteristics. Furthermore, the aerodynamic performance of a square cylinder, first under smooth flow, and later immersed in the turbulent wake of the upstream rod, are analysed. A substantial effort has been devoted in the verification studies of the numerical models. It has been found that the adopted numerical approach is able to reproduce the turbulent characteristics of the rod wake and assess the impact of the turbulent flow on a square cylinder, providing a promising agreement with experimental data.Xunta de Galicia; ED431C2017/7

    Aerodynamic performance of twin-box decks: a parametric study on gap width effects based on validated 2D URANS simulations

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    [Abstract:] 2D URANS simulations are conducted aiming to study the aerodynamic performance under smooth flow of twin-box decks depending on the gap distance between girders. The Stonecutters Bridge is taken as the reference geometry. In this parametric study, 14 gap to depth ratios in the range 0 ≤ G/D ≤ 9.70 are investigated, and for each geometry, 11 angles of attack in the range −10 ◦ ≤ α ≤ 10 ◦ are considered. Specific goals of this research have been: identification of the fundamental flow features, study of mean and fluctuating pressure coefficients distributions, identification of the vortex shedding mechanisms and general aerodynamic characterisation based on force coefficients. The numerical results provided herein are validated with wind tunnel data previously reported in the literature, finding a good agreement. A critical gap to depth ratio at G/D = 2.35, in terms of aerodynamic response, was identified, which is consistent with the value reported in the literature for a different bridge based on wind tunnel tests. The obtained set of data provide a general picture of the expected aerodynamic performance of a twin-box deck depending on the gap distance and could be of great value at the early design stage of long-span cable-supported bridges.Ministerio de Economía y Competitividad; BIA2016-76656-RMinisterio de Economía y Competitividad; BES-2014-068418Ministerio de Economía y Competitividad; BIA2013-41965-PXunta de Galicia; ED431C 2017/7

    A simplified CFD approach for bluff-body aerodynamics under small scale free stream turbulent flow

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    [Abstract:] The study of free stream turbulence (FST) effects on bluff bodies by means of computational approaches has been addressed so far mainly applying scale resolving methods adopting a three-dimensional domain, which is cumbersome and complex. The development of an alternative more affordable approach capable of providing reliable data, at least qualitatively, about the impact of FST in aerodynamic responses of interest would be very beneficial for the penetration of CFD techniques in industrial applications. In this work, a 2D URANS approach is adopted to numerically replicate the well-known rod-induced small scale turbulent flow in wind tunnel testing. A square cylinder is selected as canonical application case to study the effects caused by ambient turbulence (0.7%), and 3.3% and 6.8% FST levels. The numerical results for the force coefficients, base pressure coefficient, mean and fluctuating pressure coefficient distributions, time-averaged flow structures, mean streamwise velocity and Reynolds stresses distributions are reported along with experimental data in the literature for exhaustive validation. The agreement between the proposed CFD approach and the wind tunnel data is remarkable as not only qualitative agreement has been reached, but in many cases consistency between numerical and experimental data has been obtained. The proposed approach, once its feasibility and accuracy has been satisfactorily assessed, may be applied for affordably study FST-dependent aerodynamics problems of interest in wind engineering.Grant TED 2021-132243 B–I00 funded by the Ministry for Science and Innovation of Spain MCIN/AE/10.13039/501100011033 and by European Union NextGenerationEU/PRTR, and PID 2019-110786 GB-I00 funded by MCIN/AE/10.13039/501100011033, along with grants ED431C 2017/72 and ED431C 2021/33 funded by the Galician regional government. The computations have been carried out in the computer cluster Breogan and in the Galician Supercomputation Technology Centre (CESGA).Xunta de Galicia; ED431C 2017/72Xunta de Galicia; ED431C 2021/3

    Semi-automated setup of CFD simulations of rectangular cylinders and streamlined box decks

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    [Abstract:] A piece of software that acts as a Graphical User Interface (GUI) for the setup of computational fluid dynamics (CFD) models that are solved by means of the open source code OpenFOAM, is presented. The software is extensively described, with emphasis in the generation of block structured meshes using hexahedral elements. This computer program has been developed aiming at being applied in wind engineering problems of interest in civil engineering, such as the computation of force coefficients, flutter derivatives and vortex-induced vibrations. It has been devised to deal efficiently with rectangular cylinders and streamlined box decks. This software demands limited intervention from the user, and its core routines can be embedded in automated design processes such as parametric or optimal design problems in wind engineering. Two application examples have been considered: static and forced oscillation simulations of both, a side ratio 2:1 rectangular cylinder and a streamlined box deck. It has been found that this software is an efficient tool for the setup of URANS simulations in OpenFOAM, while the numerical results obtained for the studied aerodynamic and aeroelastic phe- nomena show good agreement with wind tunnel data, and their level of accuracy is equivalent to other CFD-based simulations.This work has been funded by the Galician Government (including FEDER funding) with reference GRC2013-056 and by the Spanish Ministry of Economy and Competitiveness (MINECO) with reference BIA2013-41965-P.Xunta de Galicia; GRC2013-05

    Numerical simulations of the aerodynamic response of 2D circular segments by means of URANS

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    [Abstract:] In the wind engineering field, the so-called D-section (semi-circular cylinder) has attracted some attention from researchers, since it is a galloping prone geometry. In fact, a modest number of references where this type of cross-section has been studied in the wind tunnel can be found, such as Novak and Tanaka (1974) or Weaver and Veljkovic (2005). However, to the authors’ knowledge, references in the literature concerning the CFD-based simulation of the aerodynamic response of circular segments are particularly scarce. In this work a 2D Unsteady Reynolds-Averaged Navier–Stokes (URANS) approach has been adopted with the purpose of computing force coefficients and Strouhal numbers of static circular segments at the subcritical regime considering corner angles of 90, 80, 70, 60, 50 and 40. Since the motivation of this work is to study circular segments as a simplified bridge deck geometry, the reference flow direction is parallel to the rectilinear side. It has been found that this kind of cross-section is particularly challenging since it presents massive flow separation on the rectilinear side, as well as the inherent difficulties in modeling the aerodynamic response on curved surfaces at high Reynolds numbers. For certain geometrical configurations low-Reynolds-number and curvature corrections in the k − ω Shear-Stress Transport (SST) turbulence model had to be introduced, as well as considering transition from laminar to turbulent flow, in order to obtain results similar to the experimental data.Ministerio de Economía y Competitividad; BIA2013-41965-
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