Articles de revista
http://hdl.handle.net/2117/7020
20160212T07:56:43Z

Establishing nanoscale heterogeneity with nanoscale force measurements
http://hdl.handle.net/2117/78535
Establishing nanoscale heterogeneity with nanoscale force measurements
Chang, YunHsiang, YunHsiang; Olukan, Tuza; Lai, ChiaYun; Santos, Sergio; Lin, TzeYu; Apostoleris, Harry; Font Teixidó, Josep; Barcons Xixons, Víctor; Chiesa, Matteo
Establishing the presence or absence of nanoscale compositional heterogeneity with nanoscale resolution is becoming instrumental for the development of many fields of science. Force versus distance measurements and parameters directly or indirectly derived from these profiles can be potentially employed for this purpose with sophisticated instruments such as the atomic force microscope (AFM). On the other hand, standards are necessary to reproducibly and conclusively support hypothesis from experimental data and these standards are still emerging. Here, we define a set of standards for providing data originating from atomic force measurements to be employed to compare between sample properties, parameters, or, more generally, compositional heterogeneity. We show that reporting the mean and standard deviation only might lead to inconsistent conclusions. The fundamental principle behind our investigation deals with the very definition of reproducibility and repeatability in terms of accuracy and precision, and we establish general criteria to ensure that these hold without the need of restricting assumptions.
20151029T19:05:50Z
Chang, YunHsiang, YunHsiang
Olukan, Tuza
Lai, ChiaYun
Santos, Sergio
Lin, TzeYu
Apostoleris, Harry
Font Teixidó, Josep
Barcons Xixons, Víctor
Chiesa, Matteo
Establishing the presence or absence of nanoscale compositional heterogeneity with nanoscale resolution is becoming instrumental for the development of many fields of science. Force versus distance measurements and parameters directly or indirectly derived from these profiles can be potentially employed for this purpose with sophisticated instruments such as the atomic force microscope (AFM). On the other hand, standards are necessary to reproducibly and conclusively support hypothesis from experimental data and these standards are still emerging. Here, we define a set of standards for providing data originating from atomic force measurements to be employed to compare between sample properties, parameters, or, more generally, compositional heterogeneity. We show that reporting the mean and standard deviation only might lead to inconsistent conclusions. The fundamental principle behind our investigation deals with the very definition of reproducibility and repeatability in terms of accuracy and precision, and we establish general criteria to ensure that these hold without the need of restricting assumptions.

Periodicity in bimodal atomic force microscopy
http://hdl.handle.net/2117/76907
Periodicity in bimodal atomic force microscopy
Lai, ChiaYun; Barcons Xixons, Víctor; Santos, Sergio; Chiesa, Matteo
Periodicity is fundamental for quantification and the application of conservation principles of many important systems. Here, we discuss periodicity in the context of bimodal atomic force microscopy (AFM). The relationship between the excited frequencies is shown to affect and control both experimental observables and the main expressions quantified via these observables, i.e., virial and energy transfer expressions, which form the basis of the bimodal AFM theory. The presence of a fundamental frequency further simplifies the theory and leads to close form solutions. Predictions are verified via numerical integration of the equation of motion and experimentally on a mica surface.
20150917T14:41:26Z
Lai, ChiaYun
Barcons Xixons, Víctor
Santos, Sergio
Chiesa, Matteo
Periodicity is fundamental for quantification and the application of conservation principles of many important systems. Here, we discuss periodicity in the context of bimodal atomic force microscopy (AFM). The relationship between the excited frequencies is shown to affect and control both experimental observables and the main expressions quantified via these observables, i.e., virial and energy transfer expressions, which form the basis of the bimodal AFM theory. The presence of a fundamental frequency further simplifies the theory and leads to close form solutions. Predictions are verified via numerical integration of the equation of motion and experimentally on a mica surface.

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.
20150508T16:01:38Z
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.

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.
20150506T17:58:45Z
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.

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
20141224T14:59:34Z
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.

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.
20141204T19:16:12Z
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.

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.
20141110T10:06:18Z
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.

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.
20141106T19:13:03Z
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.

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.
20141106T18:06:44Z
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.

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.
20140606T15:03:25Z
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.