Multiple Scattering Formulation of Two Dimensional Acoustic and Electromagnetic Metamaterials

This work presents a multiple scattering formulation of two dimensional acoustic metamaterials. It is shown that in the low frequency limit multiple scattering allows us to define frequency-dependent effective acoustic parameters for arrays of both ordered and disordered cylinders. This formulation can lead to both positive and negative acoustic parameters, where the acoustic parameters are the scalar bulk modulus and the tensorial mass density and, therefore, anisotropic wave propagation is allowed with both positive or negative refraction index. It is also shown that the surface fields on the scatterer are the main responsible of the anomalous behavior of the effective medium, therefore complex scatterers can be used to engineer the frequency response of the effective medium, and some examples of application to different scatterers are given. Finally, the theory is extended to electromagnetic wave propagation, where Mie resonances are found to be the responsible of the metamaterial behavior. As an application, it is shown that it is possible to obtain metamaterials with negative permeability and permittivity tensors by arrays of all-dielectric cylinders and that anisotropic cylinders can tune the frequency response of these resonances

Sound focusing by gradient index sonic lenses

Gradient index sonic lenses based on two-dimensional sonic crystals are here designed, fabricated and characterized. The index-gradient is achieved in these type of flat lenses by a gradual modification of the sonic crystal filling fraction along the direction perpendicular to the lens axis. The focusing performance is well described by an analytical model based on ray theory as well as by numerical simulations based on the multiple-scattering theory.Comment: 4 pages, 4 figure

"Legati municipales": "lex Irnitana" caps. 44-47

En este trabajo trato de dar una nueva visión de los cognitores en la lex Irnitana frente a la doctrina mayoritaria que los conceptúa como garantes juntamente con el deudor principal de los créditos que tiene el municipium contra los particulares y empresas que contratan con el municipio. Mi tesis es que los cognitores actúan como una especie de auditores de los bienes de los deudores municipales en el sentido que deben dar un informe sobre la fiabilidad y solvencia de los deudores, respondiendo en todo caso por la falsedad o cráter colusiorio de sus informes; por tanto no son garantes de la deuda en sentido estricto.In these paper and against the traditional thesis that explain the cognitores in the lex Irnitana in the samen line of those who contracta with the municipium and their praedes. I think that cognitores non assume neither personal nor real sureties with mancipes and praedes, but they have a function of public accounting for certificate the veracity and consistency of the sureties offered by the debtors, but cognitores are not praedes in strict sense

The release of phosphorus from heavily fertilized soils to dilute electrolytes: effect of soil properties

Soils heavily fertilized with P can contribute to the enrichment of P in surface runoff and can accelerate the eutrophication of streams and lakes. To describe this enrichment, information is needed on the capacity and rate of P release was characterized from soils. in Thus, 12 we carried out laboratory studies in which the release of P to a dilute electrolyte (0.002 M CaCl 2) widely different, heavily fertilized European soils. We studied: a) long-term P release under ’static’ conditions (in soil suspensions allowed to settle and left undisturbed for long periods); and b) short-term P release under ’turbulent’ conditions (rapidly stirred suspensions). The relationships between the amount of P released under static conditions and the solution/soil ratio (W) and time differed widely among soils. These differences were the probable result of differences in the content of the relatively soluble metal phosphates (capable of buffering P solution in the 10-6105M concentration range) and in the P adsorption capacity of the soils. The ratio between P released at 340 d for W = 10 000 and P exchanged isotopically at 1 d was generally > 2 in soils rich in soluble phosphates and with a high degree of surface saturation with P, while it was < 1 in soils with low surface saturation with P (acid soils with high P adsorption capacity). In soils rich in organic matter, the amounts of dissolved organic P and molybdate-reactive P released were comparable. Under turbulent conditions, the amount of P released after 2 h of soil-electrolyte contact ranged between 7 and 27 % of the P released at 340 d under static conditions. This stresses the importance that surface runoff and initial stream transport have in loading surface waters with P. The release of P under turbulent conditions was slower in acid sandy soils, where poorly crystalline Fe and Al oxides were the most important P adsorbents.Sols surfertilisés : libération de phosphore dans des électrolytes dilués. Les eaux de ruissellement prove- nant de sols surfertilisés peuvent conduire à l’eutrophisation des rivières et des lacs. Il est alors nécessaire de disposer de méthodes permettant de prévoir les vitesses de libération des phosphates à partir des particules de terre. Des études ont été entreprises au laboratoire avec douze sols européens surfertilisés mais de caractéristiques physico-chimiques très différentiées. La mise en solution du phosphore a été étudiée dans des solutions de CaCl 20,002 M en faisant varier le rapport solution-sol, W, de 10 à 10 000. Ces études ont été conduites dans deux directions: a) libération sur le long terme (340 j) et en conditions statiques; b) libération sur le court terme (2 h) et en conditions turbulentes. La quantité de P passée en solution en conditions statiques croît avec W et le temps de contact entre le sol et les solutions. La libération de P est fonction du contenu de phosphates solubles et de la capacité de rétention du P par les sols. Les quantités de P passées en solution pour W = 10 000 et durant 340 j sont élevées pour les sols pour lesquels la quantité de phosphore soluble et le degré de saturation sont élevés; elles sont faibles lorsque le degré de saturation du sol par les phosphates est peu élevé. Cette dernière situation est celle des sols acides à teneur élevée en matière organique; de plus, dans ces sols une fraction significative du phosphore passant en solution est sous forme organique. Dans les conditions turbulentes, les quantités de phosphore transférées dans la phase liquide en 2 h varient de 7 % à 27 % des quantités transférées à 340 j en conditions statiques. En conséquence la participation du phosphore durant la phase de transfert en surface vers les cours d’eau peut contribuer significativement à l’augmentation de la concentration du phosphore dans les eaux. La mise en solution du phosphore dans les conditions turbulentes semble plus lente dans les sols dont la rétention des phosphates serait contrôlée par des oxydes métalliques mal cristallisés

Assessment and improvement of the wave generation accuracy using a wave separation method

Free-wave contamination is a non-desirable but frequent characteristic in many wave tank experiments. Higherorder wave generation is not widely implemented yet, whereas the effectiveness of active wave absorption systems is frequency-dependent, and usually unknown. The resulting free-wave contamination usually remains unnoticed, but may have important consequences especially at low frequencies. We present a Generation– Separation–Compensation (GSC) procedure to identify, quantify and attenuate the free-wave contamination. The resulting wave field behaves as expected from a higher-order wave generation with no re-reflections at the wave paddle. The attenuation ratio of the unwanted energy content is relatively high (between 60% to 90%). The GSC procedure uses the general framework for wave separation proposed by Padilla and Alsina (2020) with an array of in-line probes. The application of this technique over experimental data is presented with excellent results. The robustness of the qualitative analysis is guaranteed for experimental settings fulfilling a minimum distance between the first and the last probe and a maximum spacing between probes. The stability of the quantitative analysis is guaranteed when ¿ , number of probes forming the array, is above five, and ¿¿¿¿¿/¿, ratio between the spacing of the probes forming the array and the wavelength, is within the recommended range 0.1–0.45.Peer ReviewedPostprint (published version

A general framework for wave separation in the frequency domain

A general framework for wave separation in the frequency domain is presented and evaluated with successful results using theoretical examples of nonlinear waves. This framework consists of a qualitative and a quantitative analysis. The qualitative analysis is a novel approach that provides useful information about the existing wave trains within a wave field. This information includes an estimation of the number of wave trains, their direction of propagation (seaward or shoreward), their nature (free or bound) and their relative importance. The quantitative analysis consists in a revisited wave separation method applicable to separate free and bound wave trains travelling seaward and shoreward for both high and low frequencies propagating over uneven bathymetries. This versatility represents an improvement compared to existing methods. The presented separation method is low-sensitive to noise and its robustness is tested for a range of wave separation settings. The potential application of the separation method to random waves is discussed.Peer ReviewedPostprint (author's final draft

LOCATE: prediction of plastic hotspots in coastal regions using numerical simulations in a coupled system

Los mecanismos de transporte de basura marina flotante en zonas costeras no se conocen bien, y su seguimiento con modelos numéricos es complejo debido a la geometría, procesos hidrodinámicos y la influencia de los procesos costeros, con estos últimos siendo especialmente complicados de incorporar. La herramienta LOCATE fue desarrollada para simular el movimiento y la acumulación de partículas de plástico en zonas costeras, usando mallas anidadas de diferentes resoluciones y escalas espaciales (2,5 km, 350 m y 70 m) para tener en cuenta los procesos costeros. La herramienta LOCATE acopla datos hidrodinámicos eulerianos con un modelo lagrangiano, requiriendo configuración y optimización para un funcionamiento adecuado. El modelo ha sido aplicado a la costa de Barcelona donde la geometría de costa y procesos costeros pueden actuar como acumuladores de basura y las concentraciones encontradas son comparables a otras zonas altamente contaminadas.Transport mechanisms of floating marine litter (FML) in coastal zones are poorly understood. Tracking FML dispersion with numerical models is complex due to the geometry, hydrodynamic processes and the influence of coastal processes, the latter being especially challenging to incorporate. The LOCATE tool was developed to simulate the motion and accumulation of plastic particles in coastal areas, using nested grids of varying spatial scales and resolutions (2.5 km, 350 m and 70 m) to account for coastal processes. LOCATE couples Eulerian hydrodynamic data with a Lagrangian particle solver, thus requiring configuration and optimization. As proof of concept, the model has been applied to the Barcelona coastline where the coastal geometry and processes can behave as marine litter traps and concentrations are comparable to some other heavily polluted areas

Long wave generation induced by differences in the wave-group structure

The propagation of bichromatic wave groups with differences in the wave-group structure and its influence in long-wave generation are investigated. The wave-group structure is controlled by the number of wave groups (Ng) within a repetition period. Consequently, an important energy content is measured at lower frequencies than the group frequency fg, in particular, at the repetition frequency fr. The cross-shore evolution of the energy at fr is partly explained by nonlinear energy transfers from the primary frequencies and partly by a breakpoint forcing. When Ng increases, the energy transfer to fr during wave group shoaling reduces. When Ng=3, the amplitude of fr suddenly grows at the breakpoint displaying a node-antinode pattern within the surf zone. In this case, the observed dominance of the breakpoint forcing over the energy transfers is justified by the combination of steep-slope regime and steep-wave conditions. The resultant cross-shore structure is in agreement with the Symonds et al. (1982, https://doi.org/10.1029/JC087iC01p00492) mechanism. A new methodology is proposed to identify the amplitude and phase cross-shore evolution of the radiated and reflected components. Due to energy dissipation of short waves and long waves at fg, the swash zone motion can be dominated by wave motions occurring at fr.Peer ReviewedPostprint (published version