Hybrid choice model for propensity to travel and tour complexity

During the last years cities around the world have invested important quantities of money in measures for reducing congestion and car-trips. Investments which are nothing but potential solutions for the well-known urban sprawl phenomenon, also called the “development trap” that leads to further congestion and a higher proportion of our time spent in slow moving cars. Over the path of this searching for solutions, the complex relationship between urban environment and travel behaviour has been studied in a number of cases. The main question on discussion is, how to encourage multi-stop tours? Thus, the objective of this paper is to verify whether unobserved factors influence tour complexity. For this purpose, we use a data-base from a survey conducted in 2006-2007 in Madrid, a suitable case study for analyzing urban sprawl due to new urban developments and substantial changes in mobility patterns in the last years. A total of 943 individuals were interviewed from 3 selected neighbourhoods (CBD, urban and suburban). We study the effect of unobserved factors on trip frequency. This paper present the estimation of an hybrid model where the latent variable is called propensity to travel and the discrete choice model is composed by 5 alternatives of tour type. The results show that characteristics of the neighbourhoods in Madrid are important to explain trip frequency. The influence of land use variables on trip generation is clear and in particular the presence of commercial retails. Through estimation of elasticities and forecasting we determine to what extent land-use policy measures modify travel demand. Comparing aggregate elasticities with percentage variations, it can be seen that percentage variations could lead to inconsistent results. The result shows that hybrid models better explain travel behavior than traditional discrete choice models

El complejo Turbidíctico del Carbonífero del Priorato (Tarragona)

Se caracterizan las facies de una sucesion de 2.250 m de potencia de sedimentos carboniferos turbiditicos de la parte central del Priorato (zona de las vilellas-Poboleda). En los materiales paleozoicos de este area se distinguen tres unidades Iitoestratigráficas carboniferas que integran el Complejo Turbidítico del Prioraro y que yacen discordantes sobre los materiales del Devónico medio-superior (unidad 1). Los materiales de la unidad inferior (unidad 2) se depositaron en un ambiente de talud - apron y constan fundamentalmente de areniscas que intercalan niveles deslizados de liditas, calizas y areniscas. Los depdsitos de las unidades 3 y 4 rnuestran diversas asociaciones de facies tipicas de ambientes de abanico submarino profundo. La unidad 3 muestra facies de llanura de cuenca y depositos arenosos de un canal intercalado. La unidad 4 esta constituida por tres megasecuencias negativas que corresponden a otros tantos episodios de progradacion de un sistema de lóbulo de abanico submarino. Se discuten las relaciones entre las asociaciones de facies de las tres unidades litoestratigraficas del complejo turbiditico y su asimilacidn a unidades deposicionales dentro de modelos de  sedimentaoidn submarina

Fresnel coefficients as hyperbolic rotations

We describe the action of a plane interface between two semi-infinite media in terms of a transfer matrix. We find a remarkably simple factorization of this matrix, which enables us to express the Fresnel coefficients as a hyperbolic rotation.Comment: 6 pages, 3 figure

The influence of the reducing conditions on the final microstructure and performance of nickel-yttria stabilized zirconia cermets

Ni-YSZ (yttria stabilized zirconia) cermets are the most widespread composite materials to be used as SOFC fuel electrodes. These materials are generally fabricated by the reduction of NiO to Ni in a NiO-YSZ composite, where the reducing conditions have a great effect in the final microstructure of the electrode. In the present work, several reducing conditions were explored in order to find the most suitable microstructure for anode-supported microtubular solid oxide fuel cells (SOFCs). Samples were firstly reduced in either pure or diluted H (dry or humidified), at temperatures ranging from 400 to 800 °C while their DC conductivity was monitored. The highest conductivity value was measured for the sample reduced in pure humidified hydrogen at 800 °C. However, this sample experienced conductivity degradation in comparison with samples reduced under dry conditions. For the studied temperature range, nucleation of nano-porous nickel particles is firstly formed during reduction. However, from our experiments it was concluded that those nanoparticles are not stable with time, at least at temperatures between 600 °C and 800 °C. Electrochemical characterization of complete microtubular cells under real wet conditions was also performed under current load, confirming that the microstructure of the Ni-YSZ cermet is still evolving during operation.Authors would like to thank the project MAT2015-68078-R, financed by the Spanish Government (Ministerio de Economía y Competitividad) and the Feder program of the European Union.Peer Reviewe

Highly stable microtubular cells for portable solid oxide fuel cell applications

In this work, extruded support tubes based on Nickel Oxide-YSZ (yttria stabilized-zirconia) were manufactured by Powder Extrusion Moulding (PEM). An YSZ layer is then deposited by dip coating as the electrolyte and subsequently, standard La0.8Sr0.2MnO3-δ (LSM)/YSZ composites were deposited by dip coating as oxygen electrodes. Microstructure of the anode support was optimized in order to achieve the maximum fuel utilization and as a consequence, a high performance of the cells. Experiments as a function of the fuel composition showed power densities above 500 mWcm−2 at 800 °C at 0.7 V, with high fuel utilization (∼75%). Long-term durability studies were also performed for a period above 1000 hours. The experiment was conducted at 800 °C using pure humidified hydrogen at a fixed voltage of 0.8 V. It was observed that the current density of the cell is significantly evolving during the initial period of about 100 hours, as a consequence of reconditioning of nickel particles at the anode support. Once the system is stabilized, no degradation was observed up to 1000 hours under operating conditions, obtaining current densities in the range of 400 mAcm−2 at 0.8 V and 800 °C.The project MAT2015-68078-R, financed by the Spanish Government (Ministerio de Economía y Competitividad) and the Feder program of the European Union, is also acknowledged.Peer Reviewe

The influence of reduction conditions on a Ni-YSZ SOFC anode microstructure and evolution

Ni-YSZ cermets are the most widespread material used as SOFC anodes. These materials are generally fabricated through the reduction of a NiO-YSZ composite, but the reduction conditions have a great effect in the final microstructure of the electrode. In the present work several conditions were explored to reduce microtubular anode supports produced via extrusion in order to find a suitable microstructure for SOFC anodes. Samples were reduced in pure and diluted H2, either dry or humidified at temperatures ranging from 400 to 800°C while their DC conductivity was being monitored. The highest value of peak conductivity was measured in the sample reduced in humidified pure hydrogen at 800°C, but it experienced more severe conductivity degradation that other samples. The best value for the duration of the test was obtained for the sample reduced in dry diluted hydrogen at 800°C.Authors would like to thank the project MAT2012-30763, financed by the Spanish Government (Ministerio de Economía y Competitividad) and the Feder program of the European Union.Peer Reviewe

Sintering and redispersion of Pt/γ-Al2O3 catalysts: a kinetic model

The sintering and redispersion kinetics of a Pt/Al2O3 naphtha reforming catalyst have been studied. The effect of the operating conditions, temperature, and oxygen and HCl concentration on the sintering and redispersion rates have been investigated. It was found that the rate of sintering depends on temperature and oxygen partial pressure. The rate of redispersion depends both on oxygen and HCl concentrations. A new kinetic model to study the sintering and redispersion phenomena has been developed. The model considers the evolution of the metallic dispersion as a reversible process and includes the effect of the operating conditions on the dispersion variation rate.Fil: Monzón, A.. Universidad de Zaragoza; EspañaFil: Garetto, Teresita Francisca. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Investigaciones en Catálisis y Petroquímica "Ing. José Miguel Parera". Universidad Nacional del Litoral. Instituto de Investigaciones en Catálisis y Petroquímica "Ing. José Miguel Parera"; ArgentinaFil: Borgna, Armando. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Investigaciones en Catálisis y Petroquímica "Ing. José Miguel Parera". Universidad Nacional del Litoral. Instituto de Investigaciones en Catálisis y Petroquímica "Ing. José Miguel Parera"; Argentin

Constructing Fresnel reflection coefficients by ruler and compass

A simple and intuitive geometical method to analyze Fresnel formulas is presented. It applies to transparent media and is valid for perpendicular and parallel polarizations. The approach gives a graphical characterization particularly simple of the critical and Brewster angles. It also provides an interpretation of the relation between the reflection coefficients for both basic polarizations as a symmetry in the plane

In-situ preparation of a highly accessible Pt/CNF catalytic layer on metallic microchannel reactors. Application to the SELOX reaction

A general method to prepare a catalytic coating on the surface of stainless steel microreactors has been developed. The catalytic support consists of a layer of randomly oriented, highly accessible carbon nanofibers (CNFs), directly grown on the surface of the channels by chemical vapor deposition (CVD) of ethanol. These CNFs are functionalized to acquire a positive charge before a solution containing metallic nanoparticles (Pt) is flown through the channels. The nanoparticles adhere to the surface of the CNFs thanks to electrostatic interactions. This process is carried out in-situ and the method can be easily adapted to larger scale production. These catalyst-coated microchannel reactors have been tested in the selective oxidation (SELOX) of CO in the presence of H2. The results were compared to those obtained in a conventional fixed bed reactor packed with Pt/CNTs. The microreactor clearly outperformed the fixed bed reactor at the same space velocity (WSHV = 2220 l/h gPt),), achieving total CO conversion at temperatures 50ºC lower