Articles de revista
http://hdl.handle.net/2117/3918
20170628T10:49:24Z

Gevrey estimates for one dimensional parabolic invariant manifolds of nonhyperbolic fixed points
http://hdl.handle.net/2117/105920
Gevrey estimates for one dimensional parabolic invariant manifolds of nonhyperbolic fixed points
Baldomá Barraca, Inmaculada; Fontich, Ernest; Martín, Pau
We study the Gevrey character of a natural parameterization of one dimensional invariant manifolds associated to a parabolic direction of fixed points of analytic maps, that is, a direction associated with an eigenvalue equal to 1. We show that, under general hypotheses, these invariant manifolds are Gevrey with type related to some explicit constants. We provide examples of the optimality of our results as well as some applications to celestial mechanics, namely, the Sitnikov problem and the restricted planar three body problem.
20170628T10:25:44Z
Baldomá Barraca, Inmaculada
Fontich, Ernest
Martín, Pau
We study the Gevrey character of a natural parameterization of one dimensional invariant manifolds associated to a parabolic direction of fixed points of analytic maps, that is, a direction associated with an eigenvalue equal to 1. We show that, under general hypotheses, these invariant manifolds are Gevrey with type related to some explicit constants. We provide examples of the optimality of our results as well as some applications to celestial mechanics, namely, the Sitnikov problem and the restricted planar three body problem.

Poincare series of multiplier ideals in twodimensional local rings with rational singularities
http://hdl.handle.net/2117/105918
Poincare series of multiplier ideals in twodimensional local rings with rational singularities
Alberich Carramiñana, Maria; Álvarez Montaner, Josep; Dachs Cadefau, Ferran; González Alonso, Víctor
We study the multiplicity of the jumping numbers of an mmprimary ideal a in a twodimensional local ring with a rational singularity. The formula we provide for the multiplicities leads to a very simple and efficient method to detect whether a given rational number is a jumping number. We also give an explicit description of the Poincare series of multiplier ideals associated to a proving, in particular, that it is a rational function.
20170628T09:20:53Z
Alberich Carramiñana, Maria
Álvarez Montaner, Josep
Dachs Cadefau, Ferran
González Alonso, Víctor
We study the multiplicity of the jumping numbers of an mmprimary ideal a in a twodimensional local ring with a rational singularity. The formula we provide for the multiplicities leads to a very simple and efficient method to detect whether a given rational number is a jumping number. We also give an explicit description of the Poincare series of multiplier ideals associated to a proving, in particular, that it is a rational function.

Cyclicunion operation to obtain latin squares
http://hdl.handle.net/2117/105914
Cyclicunion operation to obtain latin squares
García Planas, María Isabel; Roca Borrego, Didac
With the power that has taken the information technologies, one has developed the study and research about cryptography, and cryptanalysis, in which Latin squares are ideal candidates for being used in cryptographic systems because the Cayley tables of the finite groups are Latin squares. This fact has awakened a new interest in the study of Latin squares by applying them to the study of code theory and error correcting codes. They also play a significant role in the statistical theory of experimental design.
In this work, we develop an algorithm for the generation of Latin squares based on the cyclicunion operation defined for effect
20170628T07:41:07Z
García Planas, María Isabel
Roca Borrego, Didac
With the power that has taken the information technologies, one has developed the study and research about cryptography, and cryptanalysis, in which Latin squares are ideal candidates for being used in cryptographic systems because the Cayley tables of the finite groups are Latin squares. This fact has awakened a new interest in the study of Latin squares by applying them to the study of code theory and error correcting codes. They also play a significant role in the statistical theory of experimental design.
In this work, we develop an algorithm for the generation of Latin squares based on the cyclicunion operation defined for effect

Signcryption schemes with threshold unsigncryption, and applications
http://hdl.handle.net/2117/105873
Signcryption schemes with threshold unsigncryption, and applications
Herranz Sotoca, Javier; Ruiz, Alexandre; Sáez Moreno, Germán
The goal of a signcryption scheme is to achieve the same functionalities as encryption and signature together, but in a more efficient way than encrypting and signing separately. To increase security and reliability in some applications, the unsigncryption phase can be distributed among a group of users, through a (t, n)threshold process. In this work we consider this task of threshold unsigncryption, which has received very few attention from the cryptographic literature up to now (maybe surprisingly, due to its potential applications). First we describe in detail the security requirements that a scheme for such a task should satisfy: existential unforgeability and indistinguishability, under insider chosen message/ciphertext attacks, in a multiuser setting. Then we show that generic constructions of signcryption schemes (by combining encryption and signature schemes) do not offer this level of security in the scenario of threshold unsigncryption. For this reason, we propose two new protocols for threshold unsigncryption, which we prove to be secure, one in the random oracle model and one in the standard model. The two proposed schemes enjoy an additional property that can be very useful. Namely, the unsigncryption protocol can be divided in two phases: a first one where the authenticity of the ciphertext is verified, maybe by a single party; and a second one where the ciphertext is decrypted by a subset of t receivers, without using the identity of the sender. As a consequence, the schemes can be used in applications requiring some level of anonymity, such as electronic auctions.
The final publication is available at link.springer.com
20170626T15:08:46Z
Herranz Sotoca, Javier
Ruiz, Alexandre
Sáez Moreno, Germán
The goal of a signcryption scheme is to achieve the same functionalities as encryption and signature together, but in a more efficient way than encrypting and signing separately. To increase security and reliability in some applications, the unsigncryption phase can be distributed among a group of users, through a (t, n)threshold process. In this work we consider this task of threshold unsigncryption, which has received very few attention from the cryptographic literature up to now (maybe surprisingly, due to its potential applications). First we describe in detail the security requirements that a scheme for such a task should satisfy: existential unforgeability and indistinguishability, under insider chosen message/ciphertext attacks, in a multiuser setting. Then we show that generic constructions of signcryption schemes (by combining encryption and signature schemes) do not offer this level of security in the scenario of threshold unsigncryption. For this reason, we propose two new protocols for threshold unsigncryption, which we prove to be secure, one in the random oracle model and one in the standard model. The two proposed schemes enjoy an additional property that can be very useful. Namely, the unsigncryption protocol can be divided in two phases: a first one where the authenticity of the ciphertext is verified, maybe by a single party; and a second one where the ciphertext is decrypted by a subset of t receivers, without using the identity of the sender. As a consequence, the schemes can be used in applications requiring some level of anonymity, such as electronic auctions.

Energy conservation in the onephase supercooled Stefan problem
http://hdl.handle.net/2117/105609
Energy conservation in the onephase supercooled Stefan problem
Myers, Timothy; Mitchell, Sarah Louise; Font Clos, Francesc
A onephase reduction of the onedimensional twophase supercooled Stefan problem is developed. The standard reduction, employed by countless authors, does not conserve energy and a recent energy conserving form is valid in the limit of small ratio of solid to liquid conductivity. The present model assumes this ratio to be large and conserves energy for physically realistic parameter values. Results for three onephase formulations are compared to the twophase model for parameter values appropriate to supercooled salol (similar values apply to copper and gold) and water. The present model shows excellent agreement with the full twophase model.
© <year>. This manuscript version is made available under the CCBYNCND 4.0 license http://creativecommons.org/licenses/byncnd/4.0/
20170619T12:18:00Z
Myers, Timothy
Mitchell, Sarah Louise
Font Clos, Francesc
A onephase reduction of the onedimensional twophase supercooled Stefan problem is developed. The standard reduction, employed by countless authors, does not conserve energy and a recent energy conserving form is valid in the limit of small ratio of solid to liquid conductivity. The present model assumes this ratio to be large and conserves energy for physically realistic parameter values. Results for three onephase formulations are compared to the twophase model for parameter values appropriate to supercooled salol (similar values apply to copper and gold) and water. The present model shows excellent agreement with the full twophase model.

A mathematical model for the motion of an inflight soccer ball
http://hdl.handle.net/2117/105606
A mathematical model for the motion of an inflight soccer ball
Myers, Timothy; Mitchell, Sarah Louise
In this paper, an analytical and numerical study of the threedimensional equations describing the motion through the air of a spinning ball is presented. The initial analysis involves constant drag coefficients, but is later extended to involve drag varying with the spin ratio. Excellent agreement is demonstrated between numerical, analytical and experimental results. The analytical solution shows explicitly how the ball’s motion depends on parameters such as ball roughness, velocity and atmospheric conditions. The importance of applying threedimensional models, rather than twodimensional approximations, is demonstrated.
The final publication is available at link.springer.com
20170619T12:03:06Z
Myers, Timothy
Mitchell, Sarah Louise
In this paper, an analytical and numerical study of the threedimensional equations describing the motion through the air of a spinning ball is presented. The initial analysis involves constant drag coefficients, but is later extended to involve drag varying with the spin ratio. Excellent agreement is demonstrated between numerical, analytical and experimental results. The analytical solution shows explicitly how the ball’s motion depends on parameters such as ball roughness, velocity and atmospheric conditions. The importance of applying threedimensional models, rather than twodimensional approximations, is demonstrated.

Numerical exploration of the limit ring problem
http://hdl.handle.net/2117/105460
Numerical exploration of the limit ring problem
Barrabés Vera, Esther; Cors Iglesias, Josep Maria; Hall, G.R.
The aim of this work is to provide an insight of an idealized model of a planetary ring. The model is a limit case of the planar circular restricted 1 + n body problem, where an infinitesimal particle moves under the gravitational influence of a large central body and n smaller bodies located on the vertices of a regular ngon. When considering n tending to infinity, a model depending on one parameter is obtained. We study the main important structures of the problem depending on this parameter (equilibria, Hill’s regions, linear stability, …). We use Poincaré maps, for different values of the parameter, in order to predict the width of the ring and the richness of the dynamics that occur is discussed. This work is a continuation of the work presented in Barrabés by (SIAM J Appl Dyn Syst 9:634–658, 2010).
The final publication is available at Springer via http://dx.doi.org/10.1007/s1234601200820
20170615T14:42:33Z
Barrabés Vera, Esther
Cors Iglesias, Josep Maria
Hall, G.R.
The aim of this work is to provide an insight of an idealized model of a planetary ring. The model is a limit case of the planar circular restricted 1 + n body problem, where an infinitesimal particle moves under the gravitational influence of a large central body and n smaller bodies located on the vertices of a regular ngon. When considering n tending to infinity, a model depending on one parameter is obtained. We study the main important structures of the problem depending on this parameter (equilibria, Hill’s regions, linear stability, …). We use Poincaré maps, for different values of the parameter, in order to predict the width of the ring and the richness of the dynamics that occur is discussed. This work is a continuation of the work presented in Barrabés by (SIAM J Appl Dyn Syst 9:634–658, 2010).

Separability by semivalues modified for games with coalition structure
http://hdl.handle.net/2117/105390
Separability by semivalues modified for games with coalition structure
Amer Ramon, Rafael; Giménez Pradales, José Miguel
Two games are inseparable by semivalues if both games obtain the same allocation whatever semivalue is considered. The problem of separability by semivalues reduces to separability from the null game. For four or more players, the vector subspace of games inseparable from the null game by semivalues contains games different to zerogame. Now, for five or more players, the consideration of a priori coalition blocks in the player set allows us to reduce in a significant way the dimension of the vector subspace of games inseparable from the null game. For these subspaces we provide basis formed by games of a particular type.
The original publication is available at www.rairoro.org
20170613T15:21:57Z
Amer Ramon, Rafael
Giménez Pradales, José Miguel
Two games are inseparable by semivalues if both games obtain the same allocation whatever semivalue is considered. The problem of separability by semivalues reduces to separability from the null game. For four or more players, the vector subspace of games inseparable from the null game by semivalues contains games different to zerogame. Now, for five or more players, the consideration of a priori coalition blocks in the player set allows us to reduce in a significant way the dimension of the vector subspace of games inseparable from the null game. For these subspaces we provide basis formed by games of a particular type.

Use of wiris quizzes in an online calculus course
http://hdl.handle.net/2117/105260
Use of wiris quizzes in an online calculus course
Calm, Remei; Masià, Ramon; Olivé, Carme; Parés Mariné, Núria; Pozo Montero, Francesc; Ripoll, Jordi; Sancho Vinuesa, Teresa
Calculus courses often present a large number of difficulties to undergraduate students of scientific studies, especially in engineering degrees. These difficulties are sometimes related to teaching and assessment strategies. In this paper, a teaching innovation experience is presented within the framework of the Universitat Oberta de Catalunya. This teaching experience is focused on a continuous assessment through a systematic use of the socalled WIRIS quizzes. Academic outcomes are very positive from both quantitative and qualitative viewpoints.
20170609T06:29:14Z
Calm, Remei
Masià, Ramon
Olivé, Carme
Parés Mariné, Núria
Pozo Montero, Francesc
Ripoll, Jordi
Sancho Vinuesa, Teresa
Calculus courses often present a large number of difficulties to undergraduate students of scientific studies, especially in engineering degrees. These difficulties are sometimes related to teaching and assessment strategies. In this paper, a teaching innovation experience is presented within the framework of the Universitat Oberta de Catalunya. This teaching experience is focused on a continuous assessment through a systematic use of the socalled WIRIS quizzes. Academic outcomes are very positive from both quantitative and qualitative viewpoints.

Wind turbine synchronous reset pitch control
http://hdl.handle.net/2117/105205
Wind turbine synchronous reset pitch control
Vidal Seguí, Yolanda; Acho Zuppa, Leonardo; Cifre Font, Ignasi; Garcia Manzanera, Àlex; Pozo Montero, Francesc; Rodellar Benedé, José
Reset controllers are commonly used to smooth the transient response of systems. We use this technique to improve a standard baseline pitch controller for offshore wind turbines (WTs). The introduction of this strategy enhances the overall performance of the WT. In particular, the foreaft and sidetoside accelerations of the WT tower are significantly reduced, whilst a steadier power output is obtained, in comparison to the standard baseline pitch controller. Furthermore, our designed pitch control’s main advantage, with respect to the baseline, is its ease of implementation and reduced complexity as it does not require a gainscheduling technique, nor pitch position measurement (thus, it is insensitive to pitch sensor faults). The proposed approach has been simulated on the NREL 5MW prototype offshore turbine model, mounted on a jacket support. The simulations are carried out using the aerohydroservoelastic simulator FAST, and key observations are thoroughly discussed.
20170607T10:51:30Z
Vidal Seguí, Yolanda
Acho Zuppa, Leonardo
Cifre Font, Ignasi
Garcia Manzanera, Àlex
Pozo Montero, Francesc
Rodellar Benedé, José
Reset controllers are commonly used to smooth the transient response of systems. We use this technique to improve a standard baseline pitch controller for offshore wind turbines (WTs). The introduction of this strategy enhances the overall performance of the WT. In particular, the foreaft and sidetoside accelerations of the WT tower are significantly reduced, whilst a steadier power output is obtained, in comparison to the standard baseline pitch controller. Furthermore, our designed pitch control’s main advantage, with respect to the baseline, is its ease of implementation and reduced complexity as it does not require a gainscheduling technique, nor pitch position measurement (thus, it is insensitive to pitch sensor faults). The proposed approach has been simulated on the NREL 5MW prototype offshore turbine model, mounted on a jacket support. The simulations are carried out using the aerohydroservoelastic simulator FAST, and key observations are thoroughly discussed.