Departaments de Matemàtica Aplicada
http://hdl.handle.net/2117/3917
2015-09-02T13:39:54ZSecure and efficient anonymization of distributed confidential databases
http://hdl.handle.net/2117/76549
Secure and efficient anonymization of distributed confidential databases
Herranz Sotoca, Javier; Nin Guerrero, Jordi
Let us consider the following situation: t entities (e.g., hospitals) hold different databases containing different records for the same type of confidential (e.g., medical) data. They want to deliver a protected version of this data to third parties (e.g., pharmaceutical researchers), preserving in some way both the utility and the privacy of the original data. This can be done by applying a statistical disclosure control (SDC) method. One possibility is that each entity protects its own database individually, but this strategy provides less utility and privacy than a collective strategy where the entities cooperate, by means of a distributed protocol, to produce a global protected dataset. In this paper, we investigate the problem of distributed protocols for SDC protection methods. We propose a simple, efficient and secure distributed protocol for the specific SDC method of rank shuffling. We run some experiments to evaluate the quality of this protocol and to compare the individual and collective strategies for solving the problem of protecting a distributed database. With respect to other distributed versions of SDC methods, the new protocol provides either more security or more efficiency, as we discuss through the paper.
2014-01-01T00:00:00ZFault diagnosis and fault-tolerant control of wind turbines via a discrete time controller with a disturbance compensator
http://hdl.handle.net/2117/76425
Fault diagnosis and fault-tolerant control of wind turbines via a discrete time controller with a disturbance compensator
Vidal Seguí, Yolanda; Tutivén Gálvez, Christian; Rodellar Benedé, José; Acho Zuppa, Leonardo
This paper develops a fault diagnosis (FD) and fault-tolerant control (FTC) of pitch actuators in wind turbines. This is accomplished by combining a disturbance compensator with a controller, both of which are formulated in the discrete time domain. The disturbance compensator has a dual purpose: to estimate the actuator fault (which is used by the FD algorithm) and to design the discrete time controller to obtain a FTC. That is, the pitch actuator faults are estimated, and then, the pitch control laws are appropriately modified to achieve an FTC with a comparable behavior to the fault-free case. The performance of the FD and FTC schemes is tested in simulations with the aero-elastic code FAST.
2015-05-12T00:00:00ZAAR-based decomposition algorithm for non-linear convex optimisation
http://hdl.handle.net/2117/76414
AAR-based decomposition algorithm for non-linear convex optimisation
Rabiei, Syednima; Muñoz Romero, José
n this paper we present a method for decomposing a class of convex nonlinear programmes which are frequently encountered in engineering plastic analysis. These problems have second-order conic memberships constraints and a single complicating variable in the objective function. The method is based on finding the distance between the feasible sets of the decomposed problems, and updating the global optimal value according to the value of this distance. The latter is found by exploiting the method of averaged alternating reflections, which is here adapted to the optimisation problem at hand. The method is specially suited for non-linear problems and as our numerical results show, its convergence is independent of the number of variables of each sub-domain. We have tested the method with an illustrative example and with problems that have more than 10,000 variables.
2015-01-01T00:00:00ZStructural damage detection using principal component analysis and damage indices
http://hdl.handle.net/2117/76413
Structural damage detection using principal component analysis and damage indices
Tibaduiza Burgos, Diego Alexander; Mujica Delgado, Luis Eduardo; Rodellar Benedé, José; Güemes Gordo, Alfredo
One of the most important tasks in structural health monitoring corresponds to damage detection. In this task, the existence
of damage should be determined. In the literature, several potentially useful techniques for damage detection can
be found, and their applicability to a particular situation depends on the size of the critical damages that are admissible in
the structure. Almost all of these techniques follow the same general procedure: the structure is excited using actuators,
and the dynamical response is sensed at different locations throughout the structure. Any damage will change this vibrational
response. The state of the structure is diagnosed by means of the processing of these data. Several studies have
shown that the detection of changes in a structure depends on the distance from the damage to the actuator as well as
the configuration of the sensor network. In this article, the authors considered the advantage of using an active piezoelectric
system, where the lead zirconate titanate transducers are used as actuator and sensors in different actuation
phases. In each actuation phase of the diagnosis procedure, one lead zirconate titanate transducer is used as actuator (a
known electrical signal is applied), and the others are used as sensors (collecting the wave propagated through the structure
at different points). An initial baseline model for undamaged structure is built applying principal component analysis
to the data collected by several experiments and after the current structure (damaged or not) is subjected to the same
experiments, and the collected data are projected into the principal component analysis models. Two of these projections
and four damage indices (T2-statistic, Q-statistic, combined index, and I2 index) by each actuation phase are used to
determine the presence of damages and to distinguish between them. These indices are calculated based on the analysis
of the residual data matrix to represent the variability of the data projected within the residual subspace and the new
space of the principal components. To validate the approach, data from two aeronautical structures—an aircraft skin
panel and an aircraft turbine blade—are used.
2015-01-08T00:00:00ZMeasuring the relevance of factors in the occurrence of events
http://hdl.handle.net/2117/76392
Measuring the relevance of factors in the occurrence of events
Fragnelli, Vito; Freixas Bosch, Josep; Pons Vallès, Montserrat; Sanmiquel Pera, Lluís
A new way to compare the relevance of the different factors intervening in the occurrences of an event is presented and developed in this paper. The idea behind the method comes from cooperative game theory but the focus is slightly different because factors are not necessarily rational decision-makers and because the only data available are obtained by repetition of the event. The concept of relevance measure for a factor in a set of data is introduced, some significant examples are given and the main properties of relevance measures are defined and studied. One of these measures, the fair measure, is proved to have interesting properties which characterize it. Two real world situations, one about traffic accidents and the other one about mining accidents, both of them with real data, are used to show the use of relevance measures to compare factors in each one of these events.
2014-05-09T00:00:00ZA discrete-time chaotic oscillator based on the logistic map: A secure communication scheme and a simple experiment using Arduino
http://hdl.handle.net/2117/76390
A discrete-time chaotic oscillator based on the logistic map: A secure communication scheme and a simple experiment using Arduino
Acho Zuppa, Leonardo
This paper presents a modified discrete-time chaotic system obtained from the standard logistic map model. Then, a secure communication system is given and numerical experiments are carry out using the conceived discrete-time chaotic oscillator. Moreover, an experiment of our chaotic model is realized using the Arduino-UNO board.
2015-03-29T00:00:00ZSuccess and decisiveness on proper symmetric games
http://hdl.handle.net/2117/76379
Success and decisiveness on proper symmetric games
Freixas Bosch, Josep; Pons Vallès, Montserrat
This paper provides a complete study for the possible rankings of success and decisiveness
for individuals in symmetric voting systems, assuming anonymous and independent
probability distributions. It is proved that for any pair of symmetric voting
systems it is always possible to rank success and decisiveness in opposite order whenever
the common probability of voting for “acceptance” is big enough. On the contrary, for
probability values lower than one–half it is not possible to reverse the ranking of these
two measures.
2013-11-20T00:00:00ZDesigualtats matricials lineals amb valors complexos
http://hdl.handle.net/2117/76376
Desigualtats matricials lineals amb valors complexos
Rubió Massegú, Josep; Palacios Quiñonero, Francisco; Rossell Garriga, Josep Maria
Sovint ens trobem davant de desigualtats matricials lineals (LMIs) on les matrius involucrades prenen valors complexos. Es ben conegut que tota LMI complexa es pot reduir a una LMI real. En aquest treball establim les propietats que permeten fer el procés de reducció de LMI complexa a LMI real de manera el més simplicada possible.
2015-07-12T00:00:00ZPrácticas complementarias al curso de Matemáticas II al tema de las derivadas parciales: Procesamiento digital de imágenes
http://hdl.handle.net/2117/76336
Prácticas complementarias al curso de Matemáticas II al tema de las derivadas parciales: Procesamiento digital de imágenes
Acho Zuppa, Leonardo
Documento docente sobre algunas aplicaciones de las derivadas parciales al procesamiento digital de imágenes.
Documento docente sobre algunas aplicaciones de las derivadas parciales al procesamiento digital de imágenes.
2015-04-08T00:00:00ZControl difuso para el seguimiento de guiñada del AUV Cormorán
http://hdl.handle.net/2117/76334
Control difuso para el seguimiento de guiñada del AUV Cormorán
González Agudelo, Julián; Gomáriz Castro, Spartacus; Batlle Arnau, Carles
2015-03-31T00:00:00Z