Articles de revista
http://hdl.handle.net/2117/7020
20150829T23:38:25Z

Subharmonic excitation in amplitude modulation atomic force microscopy in the presence of adsorbed water layers
http://hdl.handle.net/2117/27854
Subharmonic excitation in amplitude modulation atomic force microscopy in the presence of adsorbed water layers
Santos Hernández, Sergio; Barcons Xixons, Víctor; Verdaguer, Albert; Chiesa, Matteo
In ambient conditions, nanometric water layers form on hydrophilicsurfaces covering them and significantly changing their properties and characteristics. Here we report the excitation of subharmonics in amplitude modulation atomic force microscopy induced by intermittent water contacts. Our simulations show that there are several regimes of operation depending on whether there is perturbation of water layers. Single period orbitals, where subharmonics are never induced, follow only when the tip is either in permanent contact with the water layers or in pure noncontact where the water layers are never perturbed. When the water layers are perturbed subharmonic excitation increases with decreasing oscillation amplitude. We derive an analytical expression which establishes whether water perturbations compromise harmonic motion and show that the predictions are in agreement with numerical simulations. Empirical validation of our interpretation is provided by the observation of a range of values for apparent height of water layers when subharmonic excitation is predicted.
20111202T00:00:00Z

Superregenerative reception of narrowband FSK modulations
http://hdl.handle.net/2117/27802
Superregenerative reception of narrowband FSK modulations
Palà Schönwälder, Pere; Bonet Dalmau, Jordi; López Riera, Alexis; Moncunill Geniz, Francesc Xavier; Águila López, Francisco del; Giralt Mas, Ma. Rosa
In this paper we investigate the possibilities of narrowband FSK detection using a superregenerative (SR) receiver. Previous SR FM demodulation techniques rely on detecting the amplitude variations caused by the different frequencies involved in FSK modulation. However, this requires relatively high frequency deviations because the frequency response of SR receivers is not very selective. In this paper we take a different approach, exploiting the distinct phase trajectories of FSK modulations resulting from the transmitted data. The wellknown fact that the SR oscillator response preserves the phase information of the received signal is successfully exploited to allow the detection of several FSK modulations. These include the special case of MSK, opening the way to applying the SR principle to several communication standards, such as IEEE 802.15.4. The key ideas for symbol synchronization are also presented. Experimental results on a 10 kbit/s proofofconcept MSK receiver, achieving a sensitivity better than 114 dBm in the HF band, validate the proposed approach.
20150301T00:00:00Z

PEM fuel cell fault diagnosis via a hybrid methodology based on fuzzy and pattern recognition techniques
http://hdl.handle.net/2117/24153
PEM fuel cell fault diagnosis via a hybrid methodology based on fuzzy and pattern recognition techniques
Escobet Canal, Antoni; Nebot Castells, M. Àngela; Múgica Álvarez, Francisco
In this work, a fault diagnosis methodology termed VisualBlockFuzzy Inductive Reasoning, i.e. VisualBlockFIR, based on fuzzy and pattern recognition approaches is presented and applied to PEM fuel cell power systems. The innovation of this methodology is based on the hybridization of an artificial intelligence methodology that combines fuzzy approaches with well known pattern recognition techniques. To illustrate the potentiality of VisualBlockFIR, a nonlinear fuel cell simulator that has been proposed in the literature is employed. This simulator includes a set of five fault scenarios with some of the most frequent faults in fuel cell systems. The fault detection and identification results obtained for these scenarios are presented in this paper. It is remarkable that the proposed methodology compares favorably to the modelbased methodology based on computing residuals while detecting and identifying all the proposed faults much more rapidly. Moreover, the robustness of the hybrid fault diagnosis methodology is also studied, showing good behavior even with a level of noise of 20 dB.
© IFAC 2014. This work is posted here by permission of IFAC for your personal use. Not for distribution. The original version was published in ifacpapersonline.net
20140801T00:00:00Z

Optimal control of a water distribution network in a supervisory control system
http://hdl.handle.net/2117/24932
Optimal control of a water distribution network in a supervisory control system
Cembrano Gennari, Gabriela; Wells, G; Quevedo Casín, Joseba Jokin; Pérez Magrané, Ramon; Argelaguet Isanta, María Rosa
This paper deals with the use of optimal control techniques in water distribution networks. An optimal control tool, developed in
the context of a European research project is described and the application to the city of Sintra (Portugal) is presented.
20000501T00:00:00Z

Decomposition of geometric constraint graphs based on computing fundamental circuits. Correctness and complexity
http://hdl.handle.net/2117/24627
Decomposition of geometric constraint graphs based on computing fundamental circuits. Correctness and complexity
Joan Arinyo, Robert; Tarres Puertas, Marta Isabel; Vila Marta, Sebastià
In geometric constraint solving, Decomposition Recombination solvers (DRsolvers) refer to a general solving approach where the problem is divided into a set of subproblems, each subproblem is recursively divided until reaching basic problems which are solved by a dedicated equational solver. Then the solution to the starting problem is computed by merging the solutions to the subproblems.; Triangle or treedecomposition is one of the most widely used approaches in the decomposition step in DRsolvers. It may be seen as decomposing a graph into three subgraphs such that subgraphs pairwise share one graph vertex. Shared vertices are called hinges. Then a merging step places the geometry in each subproblem with respect to the other two.; In this work we report on a new algorithm to decompose biconnected geometric constraint graphs by searching for hinges in fundamental circuits of a specific planar embedding of the constraint graph. We prove that the algorithm is correct. (C) 2014 Elsevier Ltd. All rights reserved.
20140701T00:00:00Z

Forward backward asymmetries of lepton pairs in events with a large transverse momentum jet at hadron colliders
http://hdl.handle.net/2117/24587
Forward backward asymmetries of lepton pairs in events with a large transverse momentum jet at hadron colliders
Águila López, Francisco del; Ametller Congost, Lluís; Talavera Sánchez, Pedro
We discuss forwardbackward charge asymmetries for leptonpair production in association with a largetransversemomentum jet at hadron colliders. The lepton charge asymmetry relative to the jet direction AjFB gives a new determination of the effective weak mixing angle sin2lept
eff M2 Z with a statistical precision after cuts of 10 3 (8 10 3) at LHC (Tevatron). This is to be compared with the current uncertainty at LEP and SLD from the asymmetries alone, 2 10 4. The identification of b jets
also allows for the measurement of the bottomquark–Z asymmetry AbFB at hadron colliders, the resulting statistical precision for sin2lept eff M2
Z being 9 10 4 (2 10 2 at Tevatron), also lower than the reported precision at e+ e colliders, 3 10 4.
20021001T00:00:00Z

A low inband radiation superregenerative oscillator
http://hdl.handle.net/2117/24580
A low inband radiation superregenerative oscillator
Palà Schönwälder, Pere; Bonet Dalmau, Jordi; Moncunill Geniz, Francesc Xavier; Águila López, Francisco del; Giralt Mas, Ma. Rosa
This brief describes a superregenerative (SR) voltagecontrolled oscillator as a building block for SR receivers where most of the oscillator spectrum components are outside the reception frequency band. This allows overcoming one of the main drawbacks of SR receivers, i.e., the potential interference to nearby receivers operating at the same frequency due to oscillator reradiation. We perform a qualitative analysis of the solution of the circuit equations, describe the most relevant parameters for design, and provide some numerical simulation results. Experimental results on a proofofconcept implementation validating the described principle and a discussion of the observed behavior are provided.
20130527T00:00:00Z

Phase contrast and operation regimes in multifrequency atomic force microscopy
http://hdl.handle.net/2117/23181
Phase contrast and operation regimes in multifrequency atomic force microscopy
Santos Hernández, Sergio
In amplitude modulation atomic force microscopy the attractive and the repulsive force regimes induce phase shifts above and below 90°, respectively. In the more recent multifrequency approach, however, multiple operation regimes have been reported and the theory should be revisited. Here, a theory of phase contrast in multifrequency atomic force microscopy is developed and discussed in terms of energy transfer between modes, energy dissipation and the kinetic energy and energy transfer associated with externally driven harmonics. The single frequency virial that controls the phase shift might undergo transitions in sign while the average force (modal virial) remains positive (negative). © 2014 AIP Publishing LLC.
20140407T00:00:00Z

Unlocking higher harmonics in atomic force microscopy with gentle interactions
http://hdl.handle.net/2117/22859
Unlocking higher harmonics in atomic force microscopy with gentle interactions
Santos Hernández, Sergio; Barcons Xixons, Víctor; Font Teixidó, Josep; Verdaguer Prats, Albert
In dynamic atomic force microscopy, nanoscale properties are encoded in the higher harmonics. Nevertheless, when gentle interactions and minimal invasiveness are required, these harmonics are typically undetectable. Here, we propose to externally drive an arbitrary number of exact higher harmonics above the noise level. In this way, multiple contrast channels that are sensitive to compositional variations are made accessible. Numerical integration of the equation of motion shows that the external introduction of exact harmonic frequencies does not compromise the fundamental frequency. Thermal fluctuations are also considered within the detection bandwidth of interest and discussed in terms of higherharmonic phase contrast in the presence and absence of an external excitation of higher harmonics. Higher harmonic phase shifts further provide the means to directly decouple the true topography from that induced by compositional heterogeneity.
20140311T00:00:00Z

A superregenerative QPSK receiver
http://hdl.handle.net/2117/22014
A superregenerative QPSK receiver
Palà Schönwälder, Pere; Bonet Dalmau, Jordi; Moncunill Geniz, Francesc Xavier; Águila López, Francisco del; Giralt Mas, Ma. Rosa
In this paper we present a description and experimental verification of a superregenerative receiver (SR) for QPSK signals. Exploiting the fact that a conventional SR generates pulses which preserve the input phase information, we take $N$ 1bit samples of each generated pulse. A suitable choice of the sampling frequency gives as a result a bit vector containing a subsampled version of each PSK pulse. Extremely simple digital processing of the vectors from two consecutive pulses allows symbol decision, together with information on signal quality and frequency displacements. Although presented for the QPSK case, the principle may be applied to the MPSK case with obvious changes. Experimental results on a 20 kbit/s proofof concept receiver in the 27 MHz band, achieving a sensitivity of103 dBm, with an FPGAbased implementation of the digital part, validate the proposed approach.
20140101T00:00:00Z