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Salas-Molina F.,Hilaturas Ferre S.A. | Rodriguez-Aguilar J.A.,Campus UAB | Pla-Santamaria D.,University of Mondragon
Operational Research | Year: 2017

The optimum portfolio selection for an investor with particular preferences was proven to lie on the normalized efficient frontier between two bounds defined by the Ballestero (J Oper Res Soc 49:998–1000, 1998) bounding theorem. A deeper understanding is possible if the decision-maker is provided with visual and quantitative techniques. Here, we derive useful insights as a way to support investor’s decision-making through: (1) a new theorem to assess balance of solutions; (2) a procedure and a new plot to deal with discrete efficient frontiers and uncertain risk preferences; and (3) two quality metrics useful to predict long-run performance of investors. © 2017 Springer-Verlag Berlin Heidelberg

Calaza C.,Campus UAB | Fonseca L.,Campus UAB | Salleras M.,Campus UAB | Donmez I.,Campus UAB
Journal of Electronic Materials | Year: 2015

This work reports on an improved design intended to enhance the thermal isolation between the hot and cold parts of a silicon-based thermoelectric microgenerator. Micromachining techniques and silicon on insulator substrates are used to obtain a suspended silicon platform surrounded by a bulk silicon rim, in which arrays of bottom-up silicon nanowires are integrated later on to join both parts with a thermoelectric active material. In previous designs the platform was linked to the rim by means of bulk silicon bridges, used as mechanical support and holder for the electrical connections. Such supports severely reduce platform thermal isolation and penalise the functional area due to the need of longer supports. A new technological route is planned to obtain low thermal conductance supports, making use of a particular geometrical design and a wet bulk micromachining process to selectively remove silicon shaping a thin dielectric membrane. Thermal conductance measurements have been performed to analyse the influence of the different design parameters of the suspended platform (support type, bridge/membrane length, separation between platform and silicon rim,) on overall thermal isolation. A thermal conductance reduction from 1.82 mW/K to 1.03 mW/K, has been obtained on tested devices by changing the support type, even though its length has been halved. © 2015 The Author(s)

Del-Rosario-Calaf G.,Catalonia Institute for Energy Research IREC | Sumper A.,Catalonia Institute for Energy Research IREC | Sumper A.,Polytechnic University of Catalonia | Granados X.,Campus UAB | And 3 more authors.
Physics Procedia | Year: 2012

Electric power utilities usually use conventional grid simulators to perform simulations for grid design, operation and maintenance studies. Connection of superconducting devices, such as HTS cables, to real grids addresses the need for including specially-designed models in such studies. A 1G HTS cable user-written model suitable for dynamic simulations is developed and it is applied in a sample test grid to analyze its dynamic behavior under fault conditions. © 2011 Published by Elsevier B.V. Selection and/or peer-review under responsibility of the Guest Editors.

Herrero E.,Campus UAB | Ribas I.,Campus UAB | Jordi C.,University of Barcelona
Experimental Astronomy | Year: 2014

Stellar activity patterns are responsible for jitter effects that are observed at different timescales and amplitudes in the measurements currently obtained from photometric, spectroscopic and astrometric time series observations. These effects are usually considered just noise, and the lack of a characterization and correction strategy represents one of the main limitations for exoplanet sciences. Precise simulations of the stellar photosphere based on the most recent available models for main sequence stars can provide synthetic time series data. These may help to investigate the relation between activity jitters and stellar parameters when considering different active region patterns. Moreover, jitters can be analysed at different wavelength scales in order to design strategies to remove or minimize them from the passbands defined for specific instruments or space missions. In this work we present a model for a spotted rotating photosphere built from the contribution of a fine grid of surface elements, including all significant effects affecting the flux intensities and the wavelength of spectral features. The resulting time series data generated with this simulator are used in order to design strategies to minimize the effects of activity jitter from EChO infrared observations. An approach is presented to remove activity signals from the full infrared light curve by using the simultaneously obtained data in the visible range. Then, a similar strategy is used to correct data focused ontransit observations, and a methodology to remove the effects of non-occulted spots from transit depth measurements is presented. These procedures provide a correction of the transit data to a few times 10-5 for significantly active stars, which is within EChO noise standards. © 2014 Springer Science+Business Media Dordrecht.

Godignon P.,Campus UAB | Martin I.,Campus UAB | Gabriel G.,Campus UAB | Gomez R.,Campus UAB | And 2 more authors.
Materials Science Forum | Year: 2010

Silicon Carbide is mainly used for power semiconductor devices fabrication. However, SiC material also offers attractive properties for other types of applications, such as high temperature sensors and biomedical devices. Micro-electrodes arrays are one of the leading biosensor applications. Semi-insulating SiC can be used to implement these devices, offering higher performances than Silicon. In addition, it can be combined with Carbon Nanotubes growth technology to improve the devices sensing performances. Other biosensors were SiC could be used are microfluidic based devices. However, improvement of SiCOI starting material is necessary to fulfill the typical requirements of such applications. © (2010) Trans Tech Publications.

Alonso A.,Autonomous University of Barcelona | Vigues N.,Facultat de Ciencies | Rodriguez-Rodriguez R.,International University of Catalonia | Borrise X.,CSIC - National Center of Microelectronics | And 4 more authors.
Nanotechnology | Year: 2016

This paper presents the study of the dynamics of the formation of polymer-assisted highly-orientated polycrystalline cubic structures (CS) by a fractal-mediated mechanism. This mechanism involves the formation of seed Ag@Co nanoparticles by InterMatrix Synthesis and subsequent overgrowth after incubation at a low temperature in chloride and phosphate solutions. These ions promote the dissolution and recrystallization in an ordered configuration of pre-synthetized nanoparticles initially embedded in negatively-charged polymeric matrices. During recrystallization, silver ions aggregate in AgCl@Co fractal-like structures, then evolve into regular polycrystalline solid nanostructures (e.g. CS) in a single crystallization step on specific regions of the ion exchange resin (IER) which maintain the integrity of polycrystalline nanocubes. Here, we study the essential role of the IER in the formation of these CS for the maintenance of their integrity and stability. Thus, this synthesis protocol may be easily expanded to the composition of other nanoparticles providing an interesting, cheap and simple alternative for cubic structure formation and isolation. © 2016 IOP Publishing Ltd.

Sabater-Mir J.,Campus UAB | Cuadros J.,Campus UAB | Garcia P.,Campus UAB
CEUR Workshop Proceedings | Year: 2013

In this paper we propose the use of a cognitive architecture as a mechanism to improve the level of personalization in a recommen- dation process. The main idea is to use the cognitive architecture as an advisor that lies between the user and a set of specialized recommenders. The cognitive architecture should know about the strengths and weak- nesses of the recommenders, when they can be used and their degree of reliability given the amount of information available, among other things. With this information and the detailed knowledge about the user needs, it should be able to provide much more reliable and trustful recommenda- Tions by combining the strengths of each recommender given the specific context. The exibility of a cognitive architecture in this place of the recommendation process will allow also to consider a much more sophis- Ticated interaction with the user by allowing for example argumentation processes between the user and the system.

Camara N.,Campus UAB | Caboni A.,Campus UAB | Huntzinger J.-R.,Montpellier University | Tiberj A.,Montpellier University | And 3 more authors.
Materials Science Forum | Year: 2010

Epitaxial graphene growth is significantly different depending on the polarity of the 6H-SiC surface: Si- or C-face. On the Si-face, a uniform coverage of few layers on the whole sample can be obtained, but with electrical properties disturbed by the presence of a Carbon-rich buffer layer at the interface. On the contrary, on the C-face, we demonstrated that almost free-standing very large monolayers of graphene can be obtained by covering the sample with a graphitic cap during the growth. © (2010) Trans Tech Publications.

Mazin D.,Campus UAB
Frascati Physics Series | Year: 2013

Ground-based gamma-ray astronomy has had a major breakthrough with the impressive results obtained using systems of imaging atmospheric Cherenkov telescopes. Ground-based gamma-ray astronomy has a huge potential in astrophysics, particle physics and cosmology. CTA is an international initiative to build the next generation instrument, with a factor of 5-10 improvement in sensitivity in the 100 GeV to 10TeV range and the extension to energies well below 100 GeV and above 100TeV. CTA will consist of two arrays (one in the Northern hemisphere and one in the Southern hemisphere) for full sky coverage and will be operated as an open observatory. This paper briefly reports on the status and presents the major design concepts of CTA. © Società Italiana di Fisica.

Elizalde E.,Campus UAB
Nuovo Cimento della Societa Italiana di Fisica C | Year: 2013

The role of the Riemann zeta function as a regularization tool is briefly review and a general scheme for the physically relevant quadratic and linear cases is discussed. The use and importance of the Chowla-Selberg series formula, together with its non-trivial extensions, to deal with situations where the spectrum is known explicitly is stressed. The derivation of such formulas is shown to rely on other fundamental expressions of mathematics, as the Poisson summation formula and Jacobi's theta function identity. Their uses in the zeta regularization of infinite quantities in quantum field theory is sketched. The second part of the paper addresses operator zeta functions, regularized traces and residues, and the multiplicative anomaly or defect of the determinant, together with potential applications. © Società Italiana di Fisica.

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