Simple trace criterion for classification of multilayers

The action of any lossless multilayer is described by a transfer matrix that can be factorized in terms of three basic matrices. We introduce a simple trace criterion that classifies multilayers in three classes with properties closely related with one (and only one) of these three basic matrices.Comment: To be published in Optics Letter

Asteroid belt multiple flyby options for M-Class Missions

Addressing many of the fundamental questions in modern planetary science, as well as in ESA’s cosmic vision, requires a comprehensive knowledge of our Solar System’s asteroid belt. This paper investigates potential opportunities for medium-class asteroid belt survey missions in the timeframe of 2029-2030. The study has been developed in support to CASTAway Asteroid Spectroscopic Survey mission proposal, which is to be submitted to the latest ESA’s medium size mission call. CASTAway envisages the launch of a small telescope with relatively straightforward (i.e. high TRL) remote sensing instrumentation to observe asteroids at a long-range (i.e. point source), but also at a short-range, resolving them at ~10 m resolution. This paper presents a challenging multi-objective optimization problem and discusses the feasibility of such a mission concept. A baseline trajectory is presented that meets both ESA’s medium size mission constraints and the science requirements. The trajectory loops through the asteroid belt during 7 years, visiting 10 objects of a wide range of characteristics, providing sufficient survey time to obtain compositional information for 10,000s of objects and the serendipitous discovery of also 10,000s of 10-m class asteroids. The methodology developed has enabled the exploration of the entire design space for a conservative Soyuz-launch performance, and has found a total of 200 different tour opportunities of the asteroid belt; all compliant with ESA’s 5th call for medium size missions

Impacts of fuel consumption taxes on mobility patterns and CO2 emissions using a system dynamic approach

Current transport behaviour leads to increasing congestion of the infrastructure, growing dependence on fossil fuels, increasing energy demand, and growing CO2 emissions. Policies based principally on increasing system speed and in particular car speeds will lead to greater urban sprawl with increases in average trip lengths. Time saved by speed increases are traded for more distance. This trend is not sustainable in the longer term. Transport policies based just on time savings for citizens may not be the basis for our city planning strategy. The same happens with transport cost. With underpriced transport, the market undervalues land use location, which again may lead city to sprawl and could induce greater trip lengths. In this study, the efficiency of a fuel consumption or CO2 tax policy is analysed as a policy to internalise externalities of transport in a fair travel cost. Based on system dynamics theory, an integrated land use and transport model is proposed in order to assess the effects and impacts of such policy in the short, medium and long term. Different scenarios related to clean vehicles are incorporated. This model is applied to three cities Madrid, Vienna and Leeds and compares their results

The Dependence of Prestellar Core Mass Distributions on the Structure of the Parental Cloud

The mass distribution of prestellar cores is obtained for clouds with arbitrary internal mass distributions using a selection criterion based on the thermal and turbulent Jeans mass and applied hierarchically from small to large scales. We have checked this methodology comparing our results for a lognormal density PDF with the theoretical CMF derived by Hennebelle and Chabrier, namely a power-law at large scales and a log-normal cutoff at low scales, but our method can be applied to any mass distributions representing a star-forming cloud. This methodology enables us to connect the parental cloud structure with the mass distribution of the cores and their spatial distribution, providing an efficient tool for investigating the physical properties of the molecular clouds that give rise to the prestellar core distributions observed. Simulated fBm clouds with the Hurst exponent close to the value H=1/3 give the best agreement with the theoretical CMF derived by Hennebelle and Chabrier and Chabrier's system IMF. Likewise, the spatial distribution of the cores derived from our methodology show a surface density of companions compatible with those observed in Trapezium and Ophiucus star-forming regions. This method also allows us to analyze the properties of the mass distribution of cores for different realizations. We found that the variations in the number of cores formed in different realizations of fBm clouds (with the same Hurst exponent) are much larger than the expected root N statistical fluctuations, increasing with H.Comment: 27 pages including 6 figures and 2 tables. Accepted for publication in The Astrophysical Journa

A geometrical setting for the classification of multilayers

We elaborate on the consequences of the factorization of the transfer matrix of any lossless multilayer in terms of three basic matrices of simple interpretation. By considering the bilinear transformation that this transfer matrix induces in the complex plane, we introduce the concept of multilayer transfer function and study its properties in the unit disk. In this geometrical setting, our factorization translates into three actions that can be viewed as the basic pieces for understanding the multilayer behavior. Additionally, we introduce a simple trace criterion that allows us to classify multilayers in three types with properties closely related to one (and only one) of these three basic matrices. We apply this approach to analyze some practical examples that are representative of these types of matrices.Comment: 8 pages, 5 figures. To be published in J. Opt. Soc. Am.

Cogeneració amb piles de combustible: aplicació a edificis de la UPC

Les piles de combustible són dispositius electroquímics que transformen directament l’energia d’un combustible químic en energia elèctrica i calor. Entre els seus avantatges destaquen una eficiència energètica molt elevada, una menor emissió de gasos contaminants i la possibilitat de treballar en un rang de potències de mW a MW, cosa que les fa molt versàtils i amb un ampli espectre d’aplicació, des d’aplicacions estacionàries en edificis, fins a aplicacions en automoció i dispositius electrònics. A l’assignatura “Tecnologia Energètica” de l’ensenyament d’Enginyeria Industrial a l’Escola Tècnica Superior d’Enginyers Industrials de Barcelona (ETSEIB) els alumnes fan un treball aplicat (en grups de 3-4 persones) sobre algun dels aspectes tractats a l’assignatura, on s’inclouen les piles de combustible. Aquesta contribució al “II Congrés UPC Sostenible 2015” és el resultat d’un d’aquests treballs, on s’estudia l’aplicació d’una pila de combustible comercial d’àcid fosfòric (PAFC) alimentada amb gas natural i d’un acumulador de calor per a satisfer totalment el servei elèctric i sanitari al gimnàs de l’ETSEIB, en concepte de calefacció i aigua calenta sanitària. El treball inclou l’estudi de la instal•lació i consums de gas natural i electricitat del gimnàs, l’estudi i disseny del sistema de cogeneració amb la pila de combustible, la identificació de l’emplaçament adient i una aproximació a l’estudi de la viabilitat econòmica del projecte. El resultat de l’estudi és que amb una única pila de combustible PAFC de 200 kW es poden satisfer les demandes d’energia tèrmica per a la calefacció i l’obtenció d’aigua calenta sanitària del gimnàs i, a banda, també es pot cobrir part de l’energia elèctrica consumida per tot l’edifici de l’ETSEIB. L’estalvi energètic que suposa l’ús de la pila de combustible és considerable i la diversificació de vectors energètics a l’edifici és interessant per a garantir-ne el funcionament. Existeix un lloc idoni per a l’emplaçament de la pila de combustible i l’acumulador a on, a més de reunir-se les condicions tècniques que requereix la nova instal•lació, hi ha l’espai necessari per a la seva ubicació. En l’aspecte econòmic, tot i l’elevat cost d’inversió necessari per a dur a terme la instal•lació global, el període de retorn és d’uns catorze anys. Finalment, una instal•lació d’aquest tipus a la UPC representaria un exemple amb un gran impacte social cap a la sostenibilitat i eficiència energètica en edificis fent ús de les piles de combustible.Peer Reviewe

A Three-Dimensional Dynamic Supramolecular "Sticky Fingers" Organic Framework.

Engineering high-recognition host-guest materials is a burgeoning area in basic and applied research. The challenge of exploring novel porous materials with advanced functionalities prompted us to develop dynamic crystalline structures promoted by soft interactions. The first example of a pure molecular dynamic crystalline framework is demonstrated, which is held together by means of weak "sticky fingers" van der Waals interactions. The presented organic-fullerene-based material exhibits a non-porous dynamic crystalline structure capable of undergoing single-crystal-to-single-crystal reactions. Exposure to hydrazine vapors induces structural and chemical changes that manifest as toposelective hydrogenation of alternating rings on the surface of the [60]fullerene. Control experiments confirm that the same reaction does not occur when performed in solution. Easy-to-detect changes in the macroscopic properties of the sample suggest utility as molecular sensors or energy-storage materials

Buoyant microplastics in freshwater sediments – How do they get there?

The accumulation of microplastics (MPs) in the sediments of a stormwater treatment pond was studied to gain knowledge on how these facilities protect the natural environment against this emerging pollutant. Thirteen sediment samples were analyzed for MPs down to 10 μm, mapping the pattern of accumulation in the pond. The average abundance in terms of MP-number and mass was 11.8 μg kg−1 and 44,383 item kg−1, respectively. They were rather unevenly distributed, with concentrations varying up to two orders of magnitude within the pond, showing that a trustworthy quantification of MPs retained by such units must rely on many and well-distributed subsamples. Buoyant MPs made up 95.4 % of the MP-mass and 83.5 % of the MP-number and in most of the sampled locations, polypropylene dominated the polymer fingerprint, followed by polyethylene. No spatial pattern in the distribution of MPs in the pond was identified. Instead, the MP content correlated to the organic matter and silt content, indicating that the processes leading to deposition could be similar. A computational fluid dynamics model was set up and used to simulate the transport mechanisms governing the conveyance of MPs in the pond from water to sediments. The results showed that the combination of advection and dispersion were likely the driving mechanism for buoyant (and non-buoyant) MPs to get in contact with the sediment bed and spread over the pond. Once in contact with the sediments, the MPs would have some probability of being permanently incorporated and hereby preventing them from entering the downstream aquatic environment.</p

Are research methods shaping our understanding of microplastic pollution? A literature review on the seawater and sediment bodies of the Mediterranean Sea

Altres ajuts: Acord transformatiu CRUE-CSICUnidad de excelencia María de Maeztu CEX2019-000940-MThe lack of standardization on the definition and methods in microplastic (MP) research has limited the overall interpretation and intercomparison of published data. This has presented different solutions to assess the presence of these pollutants in the natural environment, bringing the science forward. Microplastics have been reported worldwide across different biological levels and environmental compartments. In the Mediterranean Sea, numerous research efforts have been dedicated to defining the MP pollution levels. The reported MP concentrations are comparable to those found in the convergence zone of ocean gyres, pointing to this basin as one of the world's greatest plastic accumulation areas. However, to what extent are the data produced limited by the methods? Here, we present the results of a systematic review of MP research methods and occurrence targeting the seawater and sediment bodies of the Mediterranean Sea. Based on this dataset, we 1) assess the discrepancies and similarities in the methods, 2) analyze how these differences affect the reported concentrations, and 3) identify the limitations of the data produced for the Mediterranean Sea. Moreover, we reaffirm the pressing need of developing a common reporting terminology, and call for international collaboration between Mediterranean countries, especially with North African countries, to provide a complete picture of the MP pollution status in this basin

Los turistas en el centro histórico de Salamanca: tránsito, percepción y (des)conocimiento

Salamanca se ha convertido en un destino relevante del turismo de interior en España gracias a la política de programación de acontecimientos culturales que se inició en 1993 con la exposición Las Edades del Hombre. Pero los turistas concentran sus itinerarios y visitas en el eje que une la Plaza Mayor con las catedrales y la Universidad a través de la Rúa Mayor. Su percepción de la riqueza patrimonial de la ciudad es, por tanto, muy limitada, como demuestran los resultados del trabajo de campo y de un cuestionario aplicado a los turistas. Este artículo propone medidas para extender la red de recorridos turísticos y enriquecer la experiencia de los turistas que visitan Salamanca