DSpace Collection:
http://hdl.handle.net/2117/7020
20141123T11:24:49Z

PEM fuel cell fault diagnosis via a hybrid methodology based on fuzzy and pattern recognition techniques
http://hdl.handle.net/2117/24153
Title: PEM fuel cell fault diagnosis via a hybrid methodology based on fuzzy and pattern recognition techniques
Authors: Escobet Canal, Antoni; Nebot Castells, M. Àngela; Múgica Álvarez, Francisco
Abstract: 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.
Description: © 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
20141224T14:59:34Z

Decomposition of geometric constraint graphs based on computing fundamental circuits. Correctness and complexity
http://hdl.handle.net/2117/24627
Title: Decomposition of geometric constraint graphs based on computing fundamental circuits. Correctness and complexity
Authors: Joan Arinyo, Robert; Tarres Puertas, Marta Isabel; Vila Marta, Sebastià
Abstract: 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.
20141110T10:06:18Z

Forward backward asymmetries of lepton pairs in events with a large transverse momentum jet at hadron colliders
http://hdl.handle.net/2117/24587
Title: Forward backward asymmetries of lepton pairs in events with a large transverse momentum jet at hadron colliders
Authors: Águila López, Francisco del; Ametller Congost, Lluís; Talavera Sánchez, Pedro
Abstract: 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.
20141106T19:13:03Z

A low inband radiation superregenerative oscillator
http://hdl.handle.net/2117/24580
Title: A low inband radiation superregenerative oscillator
Authors: Palà Schönwälder, Pere; Bonet Dalmau, Jordi; Moncunill Geniz, Francesc Xavier; Águila López, Francisco del; Giralt Mas, Ma. Rosa
Abstract: 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.
20141106T18:06:44Z

Phase contrast and operation regimes in multifrequency atomic force microscopy
http://hdl.handle.net/2117/23181
Title: Phase contrast and operation regimes in multifrequency atomic force microscopy
Authors: Santos Hernández, Sergio
Abstract: 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.
20140606T15:03:25Z

Unlocking higher harmonics in atomic force microscopy with gentle interactions
http://hdl.handle.net/2117/22859
Title: Unlocking higher harmonics in atomic force microscopy with gentle interactions
Authors: Santos Hernández, Sergio; Barcons Xixons, Víctor; Font Teixidó, Josep; Verdaguer Prats, Albert
Abstract: 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.
20140506T14:12:40Z

A superregenerative QPSK receiver
http://hdl.handle.net/2117/22014
Title: A superregenerative QPSK receiver
Authors: Palà Schönwälder, Pere; Bonet Dalmau, Jordi; Moncunill Geniz, Francesc Xavier; Águila López, Francisco del; Giralt Mas, Ma. Rosa
Abstract: 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.
20140312T16:09:55Z

Enhanced sensitivity and contrast with bimodal atomic force microscopy with small and ultrasmall amplitudes in ambient conditions
http://hdl.handle.net/2117/21802
Title: Enhanced sensitivity and contrast with bimodal atomic force microscopy with small and ultrasmall amplitudes in ambient conditions
Authors: Santos Hernández, Sergio
Abstract: Here, we introduce bimodal atomic force microscopy operated with subnm and ultrasmall, i.e., subangstrom, first and second mode amplitudes in ambient conditions. We show how the tip can be made to oscillate in the proximity of the surface and in perpetual contact with the adsorbed water layers while the second mode amplitude and phase provide enhanced contrast and sensitivity.
Nonlinear and nonmonotonic behavior of the experimental observables is discussed theoretically with a view to high resolution, enhanced contrast, and minimally invasive mapping. Fractions of meV of energy dissipation are shown to provide contrast above the noise level.
20140227T18:55:59Z

Improved switching strategy for selective harmonic elimination in DCAC signal generation via pulsewidth modulation
http://hdl.handle.net/2117/20457
Title: Improved switching strategy for selective harmonic elimination in DCAC signal generation via pulsewidth modulation
Authors: Palacios Quiñonero, Francisco; Vicente Rodrigo, Jesús; Molina Hernández, M. Antonia; Karimi, Hamid Reza
Abstract: We present an advanced design methodology for pulsewidthmodulated (PWM) DCAC signal generation. Using design methods
based on the Walsh transform, AC sinusoidal signals can be approximated by suitable PWM signals. For different AC amplitudes,
the switching instants of the PWM signals can be efficiently computed by using appropriate systems of explicit linear equations.
However, the equation systems provided by conventional implementations of this approach are typically only valid for a restricted
interval of AC amplitudes and, in general, a supervised implementation of several equation systems is necessary to cover the full AC
amplitude range. Additionally, obtaining suitable equation systems for designs with a large number of switching instants requires
solving a complex optimization problem. In defining the constitutive pulses of a PWM signal, a suitable partition of the time interval
is used as a reference system. In the new methodology, pulses are chosen to be symmetric with respect to the partition points,
and the switching times are specified by means of switching ratios with respect to the endpoint subintervals. This approach leads
to particularly simple Walsh series representations, introduces a remarkable computational simplification, and achieves excellent
results in reducing the harmonic distortion.
20131024T16:38:30Z

Stability, resolution, and ultralow wear amplitude modulation atomic force microscopy of DNA: small amplitude small setpoint imaging
http://hdl.handle.net/2117/20287
Title: Stability, resolution, and ultralow wear amplitude modulation atomic force microscopy of DNA: small amplitude small setpoint imaging
Authors: Santos Hernández, Sergio; Barcons Xixons, Víctor; Christenson, Hugo K.; Billingsley, Daniel J.; Bonass, William A.; Font Teixidó, Josep; Thomson, Neil H.
Abstract: A way to operate fundamental mode amplitude
modulation atomic force microscopy is
introduced which optimizes stability and resolution for a given tip size and shows negligible tip
wear over extended time periods (
24 h). In small amplitude smal
l setpoint (SASS) imaging,
the cantilever oscillates with subnanometer am
plitudes in the proximity of the sample, without
the requirement of using large drive forces, a
s the dynamics smoothly lead the tip to the surface
through the water layer. SASS is demonstrat
ed on single molecules of doublestranded DNA in
ambient conditions where sharp silicon tips (R
2–5 nm) can resolve the righthanded double
helix
20131003T17:28:18Z

Optimization of oxygen transfer through venturibased systems applied to the biological sweetening of biogas
http://hdl.handle.net/2117/16824
Title: Optimization of oxygen transfer through venturibased systems applied to the biological sweetening of biogas
Authors: Rodriguez, Ginesta; Dorado Castaño, Antonio David; Bonsfills Pedrós, Anna; Sanahuja Moliner, Ricard; Gabriel, David; Gamisans Noguera, Javier
20121031T11:49:52Z

Investigation of nanoscale interactions by means of subharmonic excitation
http://hdl.handle.net/2117/16728
Title: Investigation of nanoscale interactions by means of subharmonic excitation
Authors: Santos Hernández, Sergio; Phillips, M.A.; Verdaguer, Albert; Font Teixidó, Josep; Chiesa, Matteo; Gadelrab,, K.; Stefancich, M.; Armstrong, P.; Li, G.; Souier, T.; Thomson, Neil H.; Barcons Xixons, Víctor
Abstract: Multifrequency atomic force microscopy holds promise as a method to provide qualitative and quantitative information about samples with high spatial resolution. Here, we provide experimental evidence of the excitation of subharmonics in ambient conditions in the regions where capillary interactions are predicted to be the mechanism of excitation. We also
experimentally decouple a second mechanism for subharmonic excitation that is highly
independent of environmental conditions such as relative humidity. This implies that material properties could be mapped. Subharmonic excitation could lead to experimental determination of surface water affinity in the nanoscale whenever water interactions are the mechanism of excitation.
20121016T10:01:28Z

Quantification of dissipation and deformation in ambient atomic force microscopy
http://hdl.handle.net/2117/16725
Title: Quantification of dissipation and deformation in ambient atomic force microscopy
Authors: Santos Hernández, Sergio; Gadelrab,, K.; Barcons Xixons, Víctor; Stefancich, M.; Chiesa, Matteo
Abstract: A formalism to extract and quantify unknown quantities such as
sample deformation, the viscosity of the sample and surface energy hysteresis
in amplitude modulation atomic force microscopy is presented. Recovering
the unknowns only requires the cantilever to be accurately calibrated and the
dissipative processes occurring during sample deformation to be well modeled.
The theory is validated by comparison with numerical simulations and shown
to be able to provide, in principle, values of sample deformation with picometer
resolution.
20121016T08:18:07Z

Spatial horizons in amplitude and frequency modulation atomic force microscopy
http://hdl.handle.net/2117/15767
Title: Spatial horizons in amplitude and frequency modulation atomic force microscopy
Authors: Font Teixidó, Josep; Santos Hernández, Sergio; Barcons Xixons, Víctor; Thomson, Neil H.; Verdaguer, Albert; Chiesa, Matteo
Abstract: In dynamic atomic force microscopy (AFM) the cantilever is vibrated and its dynamics
are monitored to probe the sample with nanoscale and atomic resolution. Amplitude and
frequency modulation (AM and FM) atomic force microscopy have established
themselves as the most powerful, robust and reliable techniques in the field.
Nevertheless, it is still debatable whether one or the other technique is preferred in a
given medium or experiment. Here, we quantitatively establish the limitations in
resolution of one and the other technique by introducing the concept of space horizon
SH and quantifying it. The SH is the limiting space boundary beyond which collective
atomic interactions do not affect the detection parameters of a given feedback system.
We show that while an FM feedback can resolve an atom where an AM feedback might
fail, relative contrast is in fact equivalent for both feedback systems. That is, if the AM
feedback could detect sufficiently small amplitude shifts and there was no noise, single
atom imaging would be equivalent in AM and FM.
20120427T15:40:55Z

A highresolution UWB IR superregenerative receiver front end with an SRD quench shaper
http://hdl.handle.net/2117/15691
Title: A highresolution UWB IR superregenerative receiver front end with an SRD quench shaper
Authors: Moncunill Geniz, Francesc Xavier; Bonet Dalmau, Jordi; Palà Schönwälder, Pere; Águila López, Francisco del; Giralt Mas, Ma. Rosa
Abstract: We present a simple receiver front end that makes use of the baseband superregeneration principle to detect ultrawideband (UWB) impulse radio signals. The UWB antenna is directly connected to the core circuit consisting of a resistorcapacitor (RC) network coupled to a negative resistance that varies under the control of an external quench generator. Due to a steprecoverydiode quench shaper, 50ps timedomain sensitivity windows are generated that filter the received pulses and reject noise and interference. The circuit achieves high gain, exhibits automatic gain control, and directly demodulates binary phase modulations.
20120330T15:01:17Z