Fluxes and (co-)variances of reacting scalars in the convective boundary layer

The effects of chemistry on the transport and the mixing of reacting scalars in the convective atmospheric boundary layer (CBL) are investigated. To do this, we use large-eddy simulation (LES) to calculate explicitly the different terms of the flux and (co)variance budget equations and to analyse in particular the role of the chemical term with respect to the thermodynamical terms. We examine a set of chemical cases that are representative of various turbulent reacting flows. The chemical scheme involves two reacting scalars undergoing a second-order reaction. In addition, we study a chemical cycle, based on a first- and a second-order reaction, to study the behaviour of chemical systems in equilibrium in turbulent flows. From the budget analysis, we found that the chemical terms become more relevant when the chemical timescale is similar to the turbulent timescale. In order to detemine the importance of the chemical terms, we compared these terms to the dynamical terms of the budget equations. For the flux of reactants, the chemical term becomes the dominant sink in the bulk of the CBL. As a result, flux profiles of reacting scalars have non-linear shapes. For the covariance, which accounts for the segregation of species in the CBL, the chemical term can act as a sink or source term. Consequently, reacting scalar covariance profiles deviate considerably from the inert scalar profile. When the chemistry is in equilibrium, the chemical term becomes negligible and therefore the flux and (co-)variance profiles are similar to those of inert scalrs. On the basis of the previous budget results, we develop a parameterisation that represents the segregation of reacting species in large-scale models under convective conditions. The parameterisation is applied to an atmospheric chemical mechanism that accounts for ozone formation and depletion in the CBL. We found a good agreement between the parameterisation and the LES results

Emission scenarios for air quality management and applications at local and regional scales including the effects of the future European emission regulation (2015) for the upper Rhine valley

International audienceAir quality modeling associated with emission scenarios has become an important tool for air quality management. The set-up of realistic emission scenarios requires accurate emission inventories including the whole methodology used to calculate the emissions. This means a good description of the source characteristics including a detailed composition of the emitted fluxes. Two main approaches are used. The so-called bottom-up approach that relies on the modification of the characteristics of the sources and the top-down approach whose goal is generally to reach standard pollutant concentration levels. This paper is aimed at providing a general methodology for the elaboration of such emission scenarios and giving examples of applications at local and regional scales for air quality management. The first example concerns the impact of the installation of the urban tramway in place of the road traffic in the old centre of Strasbourg. The second example deals with the use of oxygenated and reformulated car fuels on local (Strasbourg urban area) and regional (upper Rhine valley) scales. Finally, we analyze in detail the impacts of the incoming European emission regulation for 2015 on the air quality of the upper Rhine valley

Modeling the impact of sub-grid scale emission variability on upper-air concentration

International audienceThe long standing issue of sub-grid emission heterogeneity and its influence to upper air concentration is addressed here and a subgrid model proposed. The founding concept of the approach is the assumption that average emission act as source terms of average concentration, emission fluctuations are source for the concentration variance. The model is based on the derivation of the sub-grid contribution of emission and the use of the concentration variance equation to transport it in the atmospheric boundary layer. The model has been implemented in an existing mesoscale model and the results compared with Large-Eddy Simulation data for ad-hoc simulation devised to test specifically the parametrization. The results show an excellent agreement of the models. For the first time a time evolving error bar reproducing the sub-grid scale heterogeneity of the emissions and the way in which it affects the concentration has been shown. The concentration variance is presented as an extra attribute to better define the mean concentrations in a Reynolds-average model. The model has applications from meso to global scale and that go beyond air quality

Un análisis cualitativo sobre la política de vivienda en España. La opinión de los expertos

In Spain the information about the housing park and market is clearly insufficient. In consequence the analysis about the housing problem and the own policies applied to solved it has important weakness. It has turned to the opinion of experts in analysis and management to advance in the knowledge and it has been synthesized by application of the Delphi method. By means of it, it has been consulted the characteristics of housing policies and phenomenon of the unoccupied housing. From them some reflections have been done about the nature of problems and policies applied and some proposals to improve the situation.La información sobre el parque y el mercado de vivienda en España es claramente insuficiente y, en consecuencia, el análisis sobre el problema de la vivienda y las políticas que se aplican para remediarlo poseen importantes inconsistencias. Para avanzar en el conocimiento, se ha recurrido a la opinión de expertos en análisis y gestión de políticas, que se ha sintetizado mediante la aplicación de una metodología basada en el método Delphi, en la que se ha consultado sobre las características de las políticas de vivienda y sobre el fenómeno de la vivienda desocupada respectivamente. A partir de ellas se formulan una serie de reflexiones sobre las inconsistencias en el planteamiento de las políticas que se vienen aplicando, así como algunas propuestas para mejorar la situación.L’information sur le parc et le marché de logement est clairement insuffisante en Espagne. Par conséquent, l’analyse sur le problème du logement et les politiques qui sont appliquées pour remédier lui souffrent d’importantes inconsistances. Pour avancer dans la connaissance on a recouru à l’opinion d’experts en analyse et gestion de politiques. On a été synthétisée selon la méthode Delphi. Ils ont été consultés sur les caractéristiques des politiques de logement et sur le phénomène du logement vacant respectivement. À partir d’elles on formule une série de réflexions sur la nature et la caractérisation des problèmes et des politiques qui sont appliquées ainsi que quelques propositions pour améliorer la situation

Drag-reduction strategies in wall-bounded turbulent flows using deep reinforcement learning

In this work we compare different drag-reduction strategies that compute their actuation based on the fluctuations at a given wall-normal location in turbulent open channel flow. In order to perform this study, we implement and describe in detail the reinforcement-learning interface to a computationally-efficient, parallelized, high-fidelity solver for fluid-flow simulations. We consider opposition control (Choi, Moin, and Kim, Journal of Fluid Mechanics 262, 1994) and the policies learnt using deep reinforcement learning (DRL) based on the state of the flow at two inner-scaled locations ($y^+ = 10$ and $y^+ = 15$). By using deep deterministic policy gradient (DDPG) algorithm, we are able to discover control strategies that outperform existing control methods. This represents a first step in the exploration of the capability of DRL algorithm to discover effective drag-reduction policies using information from different locations in the flow.Comment: 6 pages, 5 figure

The transformative potential of machine learning for experiments in fluid mechanics

The field of machine learning has rapidly advanced the state of the art in many fields of science and engineering, including experimental fluid dynamics, which is one of the original big-data disciplines. This perspective will highlight several aspects of experimental fluid mechanics that stand to benefit from progress advances in machine learning, including: 1) augmenting the fidelity and quality of measurement techniques, 2) improving experimental design and surrogate digital-twin models and 3) enabling real-time estimation and control. In each case, we discuss recent success stories and ongoing challenges, along with caveats and limitations, and outline the potential for new avenues of ML-augmented and ML-enabled experimental fluid mechanics

Inhibition of LpxC Increases the Activity of Iron Chelators and Gallium Nitrate in Multidrug-Resistant Acinetobacter baumannii

Infections caused by multidrug-resistant Acinetobacter baumannii would benefit from the development of novel treatment approaches. Compounds that interfere with bacterial iron metabolism, such as iron chelators and gallium nitrate, have previously been shown to have antimicrobial activity against A. baumannii. In this study, we characterize the effect of LpxC inhibitors on the antimicrobial activity of previously characterized iron chelators, 2,2'-bipyridyl (BIP) and deferiprone (DFP), and gallium nitrate (Ga(NO3)3) against A. baumannii reference strains and multidrug-resistant clinical isolates. The LpxC inhibitor LpxC-2 was synergistic with BIP for 30% of strains tested (FICI values: 0.38-1.02), whereas inhibition with LpxC-4 was synergistic with BIP for 60% of strains tested (FICI values: 0.09-0.75). In time-kill assays, combinations of BIP with both LpxC inhibitors demonstrated synergistic activity, with a more than 3 log10 reduction in bacterial counts compared to BIP alone. LpxC-2 was synergistic with Ga(NO3)3 for 50% of strains tested (FICI values: 0.27-1.0), whereas LpxC-4 was synergistic with Ga(NO3)3 for all strains tested (FICI values: 0.08-≤0.50). In time-kill assays, combinations of Ga(NO3)3 with LpxC-2 and LpxC-4 decreased the growth of both strains compared to each compound separately; however, only the combination with LpxC-4 met the defined criteria for synergy. These results identify a novel synergy between two antimicrobial classes against A. baumannii strains.This research was supported by grants MPY 380/18 from the Instituto de Salud Carlos III (ISCIII) awarded to M.J.M. V.V. is supported by the Río Hortega Program from the Instituto de Salud Carlos III. The APC was funded by MPY 380/18 from the Instituto de Salud Carlos III (ISCIII) awarded to M.J.M.S

Two-dimensional compact-finite-difference schemes for solving the bi-Laplacian operator with homogeneous wall-normal derivatives

[EN] In fluid mechanics, the bi-Laplacian operator with Neumann homogeneous boundary conditions emerges when transforming the Navier-Stokes equations to the vorticity-velocity formulation. In the case of problems with a periodic direction, the problem can be transformed into multiple, independent, two-dimensional fourth-order elliptic problems. An efficient method to solve these two-dimensional bi-Laplacian operators with Neumann homogeneus boundary conditions was designed and validated using 2D compact finite difference schemes. The solution is formulated as a linear combination of auxiliary solutions, as many as the number of points on the boundary, a method that was prohibitive some years ago due to the large memory requirements to store all these auxiliary functions. The validation has been made for different field configurations, grid sizes, and stencils of the numerical scheme, showing its potential to tackle high gradient fields as those that can be found in turbulent flows.This work was supported by RTI2018-102256-B-I00 of MINECO/FEDER and the ALBATROSS project (National Plan for Scientific and Technical Research and Innovation 2017-2020, No. PID2019-104978RB-I00).Amo-Navarro, J.; Vinuesa, R.; Conejero, JA.; Hoyas, S. (2021). Two-dimensional compact-finite-difference schemes for solving the bi-Laplacian operator with homogeneous wall-normal derivatives. Mathematics. 9(19):1-13. https://doi.org/10.3390/math9192508S11391

El fenómeno de las viviendas desocupadas

Trabajo realizado mediante encargo del Ministerio de Vivienda a través de la Fundación General de la Universidad Autónoma de Madri