Articles de revista
http://hdl.handle.net/2117/3918
Mon, 30 May 2016 03:22:34 GMT2016-05-30T03:22:34ZRecovering the conductances on grids: A theoretical justification
http://hdl.handle.net/2117/87425
Recovering the conductances on grids: A theoretical justification
Arauz Lombardia, Cristina; Carmona Mejías, Ángeles; Encinas Bachiller, Andrés Marcos; Mitjana Riera, Margarida
In this work, we present an overview of the work developed by the
authors in the context of inverse problems on nite networks. This study performs
an extension of the pioneer studies by E.B. Curtis and J.A. Morrow, and
sets the theoretical basis for solving inverse problems on networks. We present
just a glance of what we call overdetermined partial boundary value problems,
in which any data are not prescribed on a part of the boundary, whereas in
another part of the boundary both the values of the function and of its normal
derivative are given. The resolvent kernels associated with these problems are
described and they are the fundamental tool to perform an algorithm for the
recovery of the conductance of a 3{dimensional grid. We strongly believe that
the columns of the partial overdetermined Poisson kernel are the discrete counterpart
of the so{called CGO solutions (complex geometrical optic solutions)
that, in their turn, are the key to solve inverse continuous problems on planar
domains. Finally, we display the steps needed to recover the conductances in
a 3{dimensional grid.
Fri, 27 May 2016 10:33:35 GMThttp://hdl.handle.net/2117/874252016-05-27T10:33:35ZArauz Lombardia, CristinaCarmona Mejías, ÁngelesEncinas Bachiller, Andrés MarcosMitjana Riera, MargaridaIn this work, we present an overview of the work developed by the
authors in the context of inverse problems on nite networks. This study performs
an extension of the pioneer studies by E.B. Curtis and J.A. Morrow, and
sets the theoretical basis for solving inverse problems on networks. We present
just a glance of what we call overdetermined partial boundary value problems,
in which any data are not prescribed on a part of the boundary, whereas in
another part of the boundary both the values of the function and of its normal
derivative are given. The resolvent kernels associated with these problems are
described and they are the fundamental tool to perform an algorithm for the
recovery of the conductance of a 3{dimensional grid. We strongly believe that
the columns of the partial overdetermined Poisson kernel are the discrete counterpart
of the so{called CGO solutions (complex geometrical optic solutions)
that, in their turn, are the key to solve inverse continuous problems on planar
domains. Finally, we display the steps needed to recover the conductances in
a 3{dimensional grid.Detection of structural changes through principal component analysis and multivariate statistical inference
http://hdl.handle.net/2117/87419
Detection of structural changes through principal component analysis and multivariate statistical inference
Pozo Montero, Francesc; Arruga Cantalapiedra, Ignacio; Mujica Delgado, Luis Eduardo; Ruiz Ordóñez, Magda; Podivilova, Elena
This article introduces a new methodology for the detection of structural changes using a statistical data-driven modeling approach by means of a distributed piezoelectric active sensor network at different actuation phases. The three main features that characterize the proposed methodology are (a) the nature of the data used in the test since vectors of principal component analysis projections are used instead of the entire measured response of the structure or the coefficients of an AutoRegressive model, (b) the number of data used since the test is based on two random samples instead of some characteristic indicators, and (c) the samples come from a multidimensional variable and therefore a test for the plausibility of a value for a normal population mean vector is performed. The framework of multivariate statistical inference is used with the objective of the classification of structures in healthy or damaged. The novel scheme for damage detection presented in this article —based on multivariate inference over the principal component analysis projections of the raw data—is applied, validated, and tested on a small aluminum plate. The results show that the presented methodology is able to accurately detect damages, that is, for each actuation phase, a unique and reliable damage detection indicator is obtained no matter the number of sensors and/or actuators. It is worth noting that a major contribution of this article is that there exists an entire range of significance levels where the multivariate statistical inference is able to offer a correct decision although all of the univariate tests make a wrong decision.
Fri, 27 May 2016 08:44:29 GMThttp://hdl.handle.net/2117/874192016-05-27T08:44:29ZPozo Montero, FrancescArruga Cantalapiedra, IgnacioMujica Delgado, Luis EduardoRuiz Ordóñez, MagdaPodivilova, ElenaThis article introduces a new methodology for the detection of structural changes using a statistical data-driven modeling approach by means of a distributed piezoelectric active sensor network at different actuation phases. The three main features that characterize the proposed methodology are (a) the nature of the data used in the test since vectors of principal component analysis projections are used instead of the entire measured response of the structure or the coefficients of an AutoRegressive model, (b) the number of data used since the test is based on two random samples instead of some characteristic indicators, and (c) the samples come from a multidimensional variable and therefore a test for the plausibility of a value for a normal population mean vector is performed. The framework of multivariate statistical inference is used with the objective of the classification of structures in healthy or damaged. The novel scheme for damage detection presented in this article —based on multivariate inference over the principal component analysis projections of the raw data—is applied, validated, and tested on a small aluminum plate. The results show that the presented methodology is able to accurately detect damages, that is, for each actuation phase, a unique and reliable damage detection indicator is obtained no matter the number of sensors and/or actuators. It is worth noting that a major contribution of this article is that there exists an entire range of significance levels where the multivariate statistical inference is able to offer a correct decision although all of the univariate tests make a wrong decision.On the one-phase reduction of the Stefan problem with a variable phase change temperature
http://hdl.handle.net/2117/87232
On the one-phase reduction of the Stefan problem with a variable phase change temperature
Myers, Timothy; Font, F
The one-phase reduction of the Stefan problem, where the phase change temperature is a variable, is analysed. It is shown that problems encountered in previous analyses may be traced back to an incorrectly formulated Stefan condition. Energy conserving reductions for Cartesian, cylindrically and spherically symmetric problems are presented and compared with solutions to the two-phase problem.
Fri, 20 May 2016 16:56:59 GMThttp://hdl.handle.net/2117/872322016-05-20T16:56:59ZMyers, TimothyFont, FThe one-phase reduction of the Stefan problem, where the phase change temperature is a variable, is analysed. It is shown that problems encountered in previous analyses may be traced back to an incorrectly formulated Stefan condition. Energy conserving reductions for Cartesian, cylindrically and spherically symmetric problems are presented and compared with solutions to the two-phase problem.Boundary layer analysis and heat transfer of a nanofluid
http://hdl.handle.net/2117/87173
Boundary layer analysis and heat transfer of a nanofluid
MacDevette, M.M.; Myers, Timothy; Wetton, B.
A theoretical model for nanofluid flow, including Brownian motion and thermophoresis, is developed and analysed. Standard boundary layer theory is used to evaluate the heat transfer coefficient near a flat surface. The model is almost identical to previous models for nanofluid flow which have predicted an increase in the heat transfer with increasing particle concentration. In contrast our work shows a marked decrease indicating that under the assumptions of the model (and similar ones) nanofluids do not enhance heat transfer. It is proposed that the discrepancy between our results and previous ones is due to a loose definition of the heat transfer coefficient and various ad hoc assumptions.
Wed, 18 May 2016 17:53:49 GMThttp://hdl.handle.net/2117/871732016-05-18T17:53:49ZMacDevette, M.M.Myers, TimothyWetton, B.A theoretical model for nanofluid flow, including Brownian motion and thermophoresis, is developed and analysed. Standard boundary layer theory is used to evaluate the heat transfer coefficient near a flat surface. The model is almost identical to previous models for nanofluid flow which have predicted an increase in the heat transfer with increasing particle concentration. In contrast our work shows a marked decrease indicating that under the assumptions of the model (and similar ones) nanofluids do not enhance heat transfer. It is proposed that the discrepancy between our results and previous ones is due to a loose definition of the heat transfer coefficient and various ad hoc assumptions.Enumerating simplicial decompositions of surfaces with boundaries
http://hdl.handle.net/2117/87102
Enumerating simplicial decompositions of surfaces with boundaries
Bernardi, Olivier; Rué Perna, Juan José
It is well-known that the triangulations of the disc with n + 2 vertices on its boundary are counted by the nth Catalan number C(n) = 1 n+1 (2n n ) . This paper deals with the generalisation of this problem to any compact surface S with boundaries. We obtain the asymptotic number of simplicial decompositions of the surface S with n vertices on its boundary. More generally, we determine the asymptotic number of dissections of S when the faces are d-gons with d belonging to a set of admissible degrees ¿ ¿ {3, 4, 5, . . .}. We also give the limit laws for certain parameters of such dissections
Tue, 17 May 2016 11:54:09 GMThttp://hdl.handle.net/2117/871022016-05-17T11:54:09ZBernardi, OlivierRué Perna, Juan JoséIt is well-known that the triangulations of the disc with n + 2 vertices on its boundary are counted by the nth Catalan number C(n) = 1 n+1 (2n n ) . This paper deals with the generalisation of this problem to any compact surface S with boundaries. We obtain the asymptotic number of simplicial decompositions of the surface S with n vertices on its boundary. More generally, we determine the asymptotic number of dissections of S when the faces are d-gons with d belonging to a set of admissible degrees ¿ ¿ {3, 4, 5, . . .}. We also give the limit laws for certain parameters of such dissectionsOn polynomial representation functions for multivariate linear forms
http://hdl.handle.net/2117/87101
On polynomial representation functions for multivariate linear forms
Rué Perna, Juan José
Given an infinite sequence of positive integers A, we prove that for every nonnegative integer k the number of solutions of the equation n = a1 +· · ·+ak, a1, . . . , ak ¿ A, is not constant for n large enough. This result is a corollary of our main theorem, which partially answers a question of S´ark¨ozy and S´os on representation functions for multivariate linear
forms. Additionally, we obtain an Erd¿os-Fuchs type result for a wide variety of representation functions.
Tue, 17 May 2016 11:46:52 GMThttp://hdl.handle.net/2117/871012016-05-17T11:46:52ZRué Perna, Juan JoséGiven an infinite sequence of positive integers A, we prove that for every nonnegative integer k the number of solutions of the equation n = a1 +· · ·+ak, a1, . . . , ak ¿ A, is not constant for n large enough. This result is a corollary of our main theorem, which partially answers a question of S´ark¨ozy and S´os on representation functions for multivariate linear
forms. Additionally, we obtain an Erd¿os-Fuchs type result for a wide variety of representation functions.Borane polyhedra as building blocks for unknown but potentially isolatable new molecules: extensions based on computations of the known B18H22 isomers
http://hdl.handle.net/2117/87093
Borane polyhedra as building blocks for unknown but potentially isolatable new molecules: extensions based on computations of the known B18H22 isomers
Oliva, Josep M.; Rué Perna, Juan José; Hnyk, Drahomír; Kennedy, John D.; Rosenfeld, Vladimir
Known borane polyhedral cluster characteristics can be used for predicting new architectural constructs. We propose additional structures derived from B18H22 : three positional isomers different from the well-known anti-B18H22 and syn-B18H22 boranes. We have also derived two new cyclic structures based on the condensation of borane pentagonal pyramids and bipyramids. Borane polyhedral concatenation of molecules is also considered from a mathematical point of view.
Tue, 17 May 2016 09:55:33 GMThttp://hdl.handle.net/2117/870932016-05-17T09:55:33ZOliva, Josep M.Rué Perna, Juan JoséHnyk, DrahomírKennedy, John D.Rosenfeld, VladimirKnown borane polyhedral cluster characteristics can be used for predicting new architectural constructs. We propose additional structures derived from B18H22 : three positional isomers different from the well-known anti-B18H22 and syn-B18H22 boranes. We have also derived two new cyclic structures based on the condensation of borane pentagonal pyramids and bipyramids. Borane polyhedral concatenation of molecules is also considered from a mathematical point of view.Juan Navarro Loidi , Don Pedro Giannini o las matemáticas de los artilleros del siglo xviii , Segovia: Biblioteca de Ciencia y Artillería.
http://hdl.handle.net/2117/87090
Juan Navarro Loidi , Don Pedro Giannini o las matemáticas de los artilleros del siglo xviii , Segovia: Biblioteca de Ciencia y Artillería.
Massa Esteve, Maria Rosa
Tue, 17 May 2016 09:22:16 GMThttp://hdl.handle.net/2117/870902016-05-17T09:22:16ZMassa Esteve, Maria RosaExtending Brickell-Davenport theorem to non-perfect secret sharing schemes
http://hdl.handle.net/2117/86923
Extending Brickell-Davenport theorem to non-perfect secret sharing schemes
Farràs Ventura, Oriol; Padró Laimon, Carles
One important result in secret sharing is the Brickell-Davenport Theorem: every ideal perfect secret sharing scheme de nes a matroid that is uniquely determined by the access structure. Even though a few attempts have been made, there is no satisfactory de nition of ideal secret sharing scheme for the general case, in which non-perfect schemes are considered as well. Without providing another unsatisfactory de nition of ideal non-perfect secret sharing scheme, we present a generalization of the Brickell-Davenport Theorem to the general case. After analyzing that result under a new point of view and identifying its combinatorial nature, we present a characterization of the (not necessarily perfect) secret sharing schemes that are associated to matroids. Some optimality properties of such schemes are discussed.
Wed, 11 May 2016 10:34:11 GMThttp://hdl.handle.net/2117/869232016-05-11T10:34:11ZFarràs Ventura, OriolPadró Laimon, CarlesOne important result in secret sharing is the Brickell-Davenport Theorem: every ideal perfect secret sharing scheme de nes a matroid that is uniquely determined by the access structure. Even though a few attempts have been made, there is no satisfactory de nition of ideal secret sharing scheme for the general case, in which non-perfect schemes are considered as well. Without providing another unsatisfactory de nition of ideal non-perfect secret sharing scheme, we present a generalization of the Brickell-Davenport Theorem to the general case. After analyzing that result under a new point of view and identifying its combinatorial nature, we present a characterization of the (not necessarily perfect) secret sharing schemes that are associated to matroids. Some optimality properties of such schemes are discussed.On secret sharing with nonlinear product reconstruction
http://hdl.handle.net/2117/86921
On secret sharing with nonlinear product reconstruction
Cascudo, Ignacio; Cramer, Ronald; Mirandola, Diego; Padró Laimon, Carles; Xing, Chaoping
Multiplicative linear secret sharing is a fundamental notion in the area of secure multi- party computation (MPC) and, since recently, in the area of two-party cryptography as well. In a nutshell, this notion guarantees that \the product of two secrets is obtained as a linear function of the vector consisting of the coordinate-wise product of two respective share-vectors
Wed, 11 May 2016 10:22:41 GMThttp://hdl.handle.net/2117/869212016-05-11T10:22:41ZCascudo, IgnacioCramer, RonaldMirandola, DiegoPadró Laimon, CarlesXing, ChaopingMultiplicative linear secret sharing is a fundamental notion in the area of secure multi- party computation (MPC) and, since recently, in the area of two-party cryptography as well. In a nutshell, this notion guarantees that \the product of two secrets is obtained as a linear function of the vector consisting of the coordinate-wise product of two respective share-vectors