Facultat de Fisica

Barcelona, Spain

Facultat de Fisica

Barcelona, Spain
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Zribi M.,CNRS Center for the Study of the Biosphere from Space | Parde M.,LATMOS | Boutin J.,LOCEAN | Fanise P.,LATMOS | And 14 more authors.
Progress in Electromagnetics Research Symposium | Year: 2011

The CAROLS "Cooperative Airborne Radiometer for Ocean and Land Studies" L band radiometer was designed and built as a copy of the EMIRAD II radiometer constructed by the Technical University of Denmark team. It is a fully polarimetric and direct sampling corre- lation radiometer. CAROLS is installed on board a dedicated French ATR42 research aircraft, in conjunction with other airborne instruments. Following initial laboratory qualifications and other scientific campaigns, SMOS CAL/VAL campaigns involving 22 flights were carried out over South West France, the Valencia site and the Bay of Biscay (Atlantic Ocean) in spring 2010, in coordination with in situ field campaigns.

Ancilotto F.,University of Padua | Ancilotto F.,CNR Institute of Materials | Barranco M.,Facultat de Fisica | Barranco M.,University of Barcelona | And 3 more authors.
Journal of Low Temperature Physics | Year: 2016

We have developed a density functional (DF) which reproduces by constructing either the metastable liquid or the solid equation of state of bulk para-hydrogen, as derived from quantum Monte Carlo zero temperature calculations. As an application, we have used it to study the structure and energetics of small para-hydrogen clusters made of up to (Formula presented.) molecules. We compare our results for liquid clusters with diffusion Monte Carlo (DMC) calculations and find a fair agreement between them. In particular, the transition found within DMC between hollow-core structures for small N values and center-filled structures at higher N values is reproduced. The present DF approach yields results for (pH(Formula presented.))(Formula presented.) clusters indicating that for small N values a liquid-like character of the clusters prevails, while solid-like clusters are instead energetically favored for (Formula presented.). © 2016 Springer Science+Business Media New York

Campanelli M.,CNR Institute of atmospheric Sciences and Climate | Nakajima T.,University of Tokyo | Khatri P.,Chiba University | Takamura T.,Chiba University | And 4 more authors.
Atmospheric Measurement Techniques | Year: 2014

Sun-sky radiometers are instruments created for aerosol study, but they can measure in the water vapour absorption band allowing the estimation of columnar water vapour in clear sky simultaneously with aerosol characteristics, with high temporal resolution. A new methodology is presented for estimating calibration parameters (i.e. characteristic parameters of the atmospheric transmittance and solar calibration constant) directly from the sun-sky radiometer measurements. The methodology is based on the hypothesis that characteristic parameters of the atmospheric transmittance are dependent on vertical profiles of pressure, temperature and moisture occurring at each site of measurement. To obtain the parameters from the proposed methodology some seasonal independent measurements of columnar water vapour taken over a large range of solar zenith angle simultaneously with the sun-sky radiometer measurements, are needed. In this work high time resolution columnar water vapour measurements by GPS were used as independent data set, but also the case when such measurements are not available was considered by developing the surface humidity method (SHM). This methodology makes it possible to retrieve the needed independent data set of columnar water vapour using the standard surface meteorological observations (temperature, pressure and relative humidity) more readily available. The time pattern of columnar water vapour from sun-sky radiometer retrieved using both the methodologies was compared with simultaneous measurements from microwave radiometer, radiosondings and GPS. Water vapour from sun-sky radiometer, obtained using GPS independent measurements, was characterized by an error varying from 1% up to 5%, whereas water vapour from SHM showed an error from 1% up to 11%, depending on the local columnar water occurring at the site during the year. These errors were estimated by comparing water vapour series from sun-sky radiometer against measurements taken by GPS at a nearby station. The accordance between retrievals from sun-sky radiometer and simultaneous measurements from the other instruments was found always within the error both in the case of SHM and of the GPS independent data set. Water vapour obtained using characteristic parameters of the atmospheric transmittance dependent on water vapour was also compared against GPS retrievals, showing a clear improvement with respect to the case when these parameters are kept fixed. © Author(s) 2014.

Fernandez-Martinez A.,Facultat de Fisica | Fernandez-Martinez A.,University of Barcelona | Garcia-Santiago A.,Facultat de Fisica | Garcia-Santiago A.,University of Barcelona | And 4 more authors.
Journal of Magnetism and Magnetic Materials | Year: 2014

The magnetic properties of two nanogranular 0.25 0.75 3 manganites with different average grain sizes have been studied. Besides the well-known exchange bias effect and the appearance of ferromagnetic clusters in the grains of both samples, the results show the occurrence of an antiferromagnetic transition and spin-glass properties. Both samples are described as core-shell magnetic systems, whose main difference is found in the interface between the outer ferromagnetic and the inner antiferromagnetic phases of the grains. © 2014 Elsevier B.V.

Kusmierz L.,Jagiellonian University | Rubi J.M.,Facultat de Fisica | Gudowska-Nowak E.,Jagiellonian University
Journal of Statistical Mechanics: Theory and Experiment | Year: 2014

We analyze energetics of a non-Gaussian process described by a stochastic differential equation of the Langevin type. The process represents a paradigmatic model of a nonequilibrium system subject to thermal fluctuations and additional external noise, with both sources of perturbations considered as additive and statistically independent forcings. We define thermodynamic quantities for trajectories of the process and analyze contributions to mechanical work and heat. As a working example we consider a particle subjected to a drag force and two statistically independent Lévy white noises with stability indices α = 2 and α = 1. The fluctuations of dissipated energy (heat) and distribution of work performed by the force acting on the system are addressed by examining contributions of Cauchy fluctuations (α = 1) to either bath or external force acting on the system. © 2014 IOP Publishing Ltd and SISSA Medialab srl.

Reguera D.,Facultat de Fisica
AIP Conference Proceedings | Year: 2013

Phase transitions such as condensation or crystallization are important and omnipresent phenomena in nature. The mechanism triggering most of them is the formation of a rare embryo or nucleus of the new phase by random fluctuations. This initiating mechanism is known as nucleation and its understanding and control is of utmost interest in a wide range of scientific and technological disciplines. However, despite significant advances and intense investigations for more than a century, nucleation remains one of the few unpredictable classical phenomena, where discrepancies between theory and experiments commonly span orders of magnitude. In this contribution, we will summarize our recent efforts to test rigorously the validity and accuracy of CNT using computer simulations. We will critically review the several assumptions and misconceptions regarding CNT and discuss which of them have been solved and how far theory is from reaching the ultimate goal of providing accurate predictions for one of the most crucial processes in atmospheric and condensed matter science. © 2013 AIP Publishing LLC.

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