Articles de revista
http://hdl.handle.net/2117/3918
Sat, 21 Apr 2018 09:54:48 GMT2018-04-21T09:54:48ZExtending small arcs to large arcs
http://hdl.handle.net/2117/116509
Extending small arcs to large arcs
Ball, Simeon Michael
An arc is a set of vectors of the k-dimensional vector space over the finite field with q elements Fq , in which every subset of size k is a basis of the space, i.e. every k-subset is a set of linearly independent vectors. Given an arc G in a space of odd characteristic, we prove that there is an upper bound on the largest arc containing G. The bound is not an explicit bound but is obtained by computing properties of a matrix constructed from G. In some cases we can also determine the largest arc containing G, or at least determine the hyperplanes which contain exactly k-2 vectors of the large arc. The theorems contained in this article may provide new tools in the computational classification and construction of large arcs.
This is a post-peer-review, pre-copyedit version of an article published in European Journal of Mathematics. The final authenticated version is available online at: https://doi.org/10.1007/s40879-017-0193-x
Fri, 20 Apr 2018 10:47:24 GMThttp://hdl.handle.net/2117/1165092018-04-20T10:47:24ZBall, Simeon MichaelAn arc is a set of vectors of the k-dimensional vector space over the finite field with q elements Fq , in which every subset of size k is a basis of the space, i.e. every k-subset is a set of linearly independent vectors. Given an arc G in a space of odd characteristic, we prove that there is an upper bound on the largest arc containing G. The bound is not an explicit bound but is obtained by computing properties of a matrix constructed from G. In some cases we can also determine the largest arc containing G, or at least determine the hyperplanes which contain exactly k-2 vectors of the large arc. The theorems contained in this article may provide new tools in the computational classification and construction of large arcs.Sliding joints in 3D beams: conserving algorithms using the master-slave approach
http://hdl.handle.net/2117/116508
Sliding joints in 3D beams: conserving algorithms using the master-slave approach
Muñoz Romero, José; Jelenic, Gordan
This paper proposes two time-integration algorithms for motion of geometrically
exact 3D beams under sliding contact conditions. The algorithms are derived using the socalled
master–slave approach, in which constraint equations and the related time-integration
of a system of differential and algebraic equations are eliminated by design. Specifically, we
study conservation of energy and momenta when the sliding conditions on beams are imposed
and discuss their algorithmic viability. Situations where the contact jumps to adjacent finite
elements are analysed in detail and the results are tested on two representative numerical
examples. It is concluded that an algorithmic preservation of kinematic constraint conditions
is of utmost importance.
Fri, 20 Apr 2018 10:11:10 GMThttp://hdl.handle.net/2117/1165082018-04-20T10:11:10ZMuñoz Romero, JoséJelenic, GordanThis paper proposes two time-integration algorithms for motion of geometrically
exact 3D beams under sliding contact conditions. The algorithms are derived using the socalled
master–slave approach, in which constraint equations and the related time-integration
of a system of differential and algebraic equations are eliminated by design. Specifically, we
study conservation of energy and momenta when the sliding conditions on beams are imposed
and discuss their algorithmic viability. Situations where the contact jumps to adjacent finite
elements are analysed in detail and the results are tested on two representative numerical
examples. It is concluded that an algorithmic preservation of kinematic constraint conditions
is of utmost importance.How to deal with the modelling of epidemics? Some ideas and examples to be implemented in the classroom!
http://hdl.handle.net/2117/116507
How to deal with the modelling of epidemics? Some ideas and examples to be implemented in the classroom!
Ginovart Gisbert, Marta
The general objective of this work is to deal with different approaches for the representation of an epidemic considering the state of the individuals in the population, Susceptible, Infected or Recovered (SIR), which generate models that students can explore with the computer using the contents acquired in mathematics subjects. Specifically, the purposes of the tasks designed focus on the identification and analyses of the variables and parameters involved in an epidemic through three modelling methodologies: i) Simple systems of ordinary differential equations reflecting the SIR representation; ii) Systems of difference equations and matrix representations by means of discretization of the time variable in the SIR formulation; and iii) Computational simulations from the use of the agent-based model “Virus” already implemented in the NetLogo platform. Exploration and comparison of the dynamics of Ebola and AIDS epidemics show the students the potential of modelling in this context and allow them to link with real applications. The assessment given by students of this activity was positive showing their interest in the topic
Fri, 20 Apr 2018 10:01:07 GMThttp://hdl.handle.net/2117/1165072018-04-20T10:01:07ZGinovart Gisbert, MartaThe general objective of this work is to deal with different approaches for the representation of an epidemic considering the state of the individuals in the population, Susceptible, Infected or Recovered (SIR), which generate models that students can explore with the computer using the contents acquired in mathematics subjects. Specifically, the purposes of the tasks designed focus on the identification and analyses of the variables and parameters involved in an epidemic through three modelling methodologies: i) Simple systems of ordinary differential equations reflecting the SIR representation; ii) Systems of difference equations and matrix representations by means of discretization of the time variable in the SIR formulation; and iii) Computational simulations from the use of the agent-based model “Virus” already implemented in the NetLogo platform. Exploration and comparison of the dynamics of Ebola and AIDS epidemics show the students the potential of modelling in this context and allow them to link with real applications. The assessment given by students of this activity was positive showing their interest in the topicAdaptive-smith predictor for controlling an automotive electronic throttle over network
http://hdl.handle.net/2117/116499
Adaptive-smith predictor for controlling an automotive electronic throttle over network
Caruntu, Constantin; Vargas, Alessandro; Acho Zuppa, Leonardo; Pujol Vázquez, Gisela
The paper presents a control strategy for an automotive electronic throttle,
a device used to regulate the power produced by spark-ignition engines. Controlling
the electronic throttle body is a difficult task because the throttle accounts strong
nonlinearities. The difficulty increases when the control works through communication
networks subject to random delay. In this paper, we revisit the Smith-predictor
control, and show how to adapt it for controlling the electronic throttle body over a
delay-driven network. Experiments were carried out in a laboratory, and the corresponding
data indicate the benefits of our approach for applications.
Fri, 20 Apr 2018 08:50:32 GMThttp://hdl.handle.net/2117/1164992018-04-20T08:50:32ZCaruntu, ConstantinVargas, AlessandroAcho Zuppa, LeonardoPujol Vázquez, GiselaThe paper presents a control strategy for an automotive electronic throttle,
a device used to regulate the power produced by spark-ignition engines. Controlling
the electronic throttle body is a difficult task because the throttle accounts strong
nonlinearities. The difficulty increases when the control works through communication
networks subject to random delay. In this paper, we revisit the Smith-predictor
control, and show how to adapt it for controlling the electronic throttle body over a
delay-driven network. Experiments were carried out in a laboratory, and the corresponding
data indicate the benefits of our approach for applications.Feasibility of precise navigation in high and low latitude regions under scintillation conditions
http://hdl.handle.net/2117/116484
Feasibility of precise navigation in high and low latitude regions under scintillation conditions
Juan Zornoza, José Miguel; Sanz Subirana, Jaume; González Casado, Guillermo; Rovira Garcia, Adrià; Camps Carmona, Adriano José; Riba Sagarra, Jaume; Barbosa, José; Blanch Llosa, Estefania; Altadill, David; Orús Pérez, Raul
Scintillation is one of the most challenging problems in Global Navigation Satellite Systems (GNSS) navigation. This phenomenon appears when the radio signal passes through ionospheric irregularities. These irregularities represent rapid changes on the refraction index and, depending on their size, they can produce also diffractive effects affecting the signal amplitude and, eventually producing cycle slips. In this work, we show that the scintillation effects on the GNSS signal are quite different in low and high latitudes.
For low latitude receivers, the main effects, from the point of view of precise navigation, are the increase of the carrier phase noise (measured by s¿) and the fade on the signal intensity (measured by S4) that can produce cycle slips in the GNSS signal. With several examples, we show that the detection of these cycle slips is the most challenging problem for precise navigation, in such a way that, if these cycle slips are detected, precise navigation can be achieved in these regions under scintillation conditions.
For high-latitude receivers the situation differs. In this region the size of the irregularities is typically larger than the Fresnel length, so the main effects are related with the fast change on the refractive index associated to the fast movement of the irregularities (which can reach velocities up to several km/s). Consequently, the main effect on the GNSS signals is a fast fluctuation of the carrier phase (large s¿), but with a moderate fade in the amplitude (moderate S4). Therefore, as shown through several examples, fluctuations at high-latitude usually do not produce cycle slips, being the effect quite limited on the ionosphere-free combination and, in general, precise navigation can be achieved also during strong scintillation conditions.
Thu, 19 Apr 2018 13:58:46 GMThttp://hdl.handle.net/2117/1164842018-04-19T13:58:46ZJuan Zornoza, José MiguelSanz Subirana, JaumeGonzález Casado, GuillermoRovira Garcia, AdriàCamps Carmona, Adriano JoséRiba Sagarra, JaumeBarbosa, JoséBlanch Llosa, EstefaniaAltadill, DavidOrús Pérez, RaulScintillation is one of the most challenging problems in Global Navigation Satellite Systems (GNSS) navigation. This phenomenon appears when the radio signal passes through ionospheric irregularities. These irregularities represent rapid changes on the refraction index and, depending on their size, they can produce also diffractive effects affecting the signal amplitude and, eventually producing cycle slips. In this work, we show that the scintillation effects on the GNSS signal are quite different in low and high latitudes.
For low latitude receivers, the main effects, from the point of view of precise navigation, are the increase of the carrier phase noise (measured by s¿) and the fade on the signal intensity (measured by S4) that can produce cycle slips in the GNSS signal. With several examples, we show that the detection of these cycle slips is the most challenging problem for precise navigation, in such a way that, if these cycle slips are detected, precise navigation can be achieved in these regions under scintillation conditions.
For high-latitude receivers the situation differs. In this region the size of the irregularities is typically larger than the Fresnel length, so the main effects are related with the fast change on the refractive index associated to the fast movement of the irregularities (which can reach velocities up to several km/s). Consequently, the main effect on the GNSS signals is a fast fluctuation of the carrier phase (large s¿), but with a moderate fade in the amplitude (moderate S4). Therefore, as shown through several examples, fluctuations at high-latitude usually do not produce cycle slips, being the effect quite limited on the ionosphere-free combination and, in general, precise navigation can be achieved also during strong scintillation conditions.Classification of b^m-Nambu structures of top degree
http://hdl.handle.net/2117/116466
Classification of b^m-Nambu structures of top degree
Miranda Galcerán, Eva; Planas Bahí, Arnau
We obtain sufficient conditions for the existence and uniqueness of a positive compact almost automorphic solution to a logistic equation with discrete and continuous delay. Moreover, we provide a counterexample to some results in literature which deal with the uniqueness of almost periodic solutions to logistic type equations.
Thu, 19 Apr 2018 11:41:15 GMThttp://hdl.handle.net/2117/1164662018-04-19T11:41:15ZMiranda Galcerán, EvaPlanas Bahí, ArnauWe obtain sufficient conditions for the existence and uniqueness of a positive compact almost automorphic solution to a logistic equation with discrete and continuous delay. Moreover, we provide a counterexample to some results in literature which deal with the uniqueness of almost periodic solutions to logistic type equations.Memorial to Javier Cilleruelo: A Problem list
http://hdl.handle.net/2117/116463
Memorial to Javier Cilleruelo: A Problem list
Candela, Pablo; Rué Perna, Juan José; Serra Albó, Oriol
This is a list of problems in combinatorial number theory gathered on the occasion of the meeting The Music of Numbers to honor the memory of the late Javier Cilleruelo (1961-2016).
Thu, 19 Apr 2018 10:38:05 GMThttp://hdl.handle.net/2117/1164632018-04-19T10:38:05ZCandela, PabloRué Perna, Juan JoséSerra Albó, OriolThis is a list of problems in combinatorial number theory gathered on the occasion of the meeting The Music of Numbers to honor the memory of the late Javier Cilleruelo (1961-2016).The diameter of cyclic Kautz digraphs
http://hdl.handle.net/2117/116461
The diameter of cyclic Kautz digraphs
Böhmová, Katerina; Dalfó Simó, Cristina; Huemer, Clemens
We present a new kind of digraphs, called cyclic Kautz digraphs CK(d, `), which are subdigraphs of the well-known Kautz digraphs K(d, `). The latter have the smallest diameter among all digraphs with their number of vertices and degree. Cyclic Kautz digraphs CK(d, `) have vertices labeled by all possible sequences a1 . . . a` of length `, such that each character ai is chosen from an alphabet containing d + 1 distinct symbols, where the consecutive characters in the sequence are different (as in Kautz digraphs), and now also requiring that a1 , a` . Their arcs are between vertices a1a2 . . . a` and a2 . . . aà`+1, with a1 , a` and a2 , a`+1. We give the diameter of CK(d, `) for all the values of d and `, and also its number of vertices and arcs
Thu, 19 Apr 2018 10:00:39 GMThttp://hdl.handle.net/2117/1164612018-04-19T10:00:39ZBöhmová, KaterinaDalfó Simó, CristinaHuemer, ClemensWe present a new kind of digraphs, called cyclic Kautz digraphs CK(d, `), which are subdigraphs of the well-known Kautz digraphs K(d, `). The latter have the smallest diameter among all digraphs with their number of vertices and degree. Cyclic Kautz digraphs CK(d, `) have vertices labeled by all possible sequences a1 . . . a` of length `, such that each character ai is chosen from an alphabet containing d + 1 distinct symbols, where the consecutive characters in the sequence are different (as in Kautz digraphs), and now also requiring that a1 , a` . Their arcs are between vertices a1a2 . . . a` and a2 . . . aà`+1, with a1 , a` and a2 , a`+1. We give the diameter of CK(d, `) for all the values of d and `, and also its number of vertices and arcsHybrid cell-centred/vertex model for multicellular systems with equilibrium-preserving remodelling
http://hdl.handle.net/2117/116439
Hybrid cell-centred/vertex model for multicellular systems with equilibrium-preserving remodelling
Mosaffa, Payman; Rodríguez Ferran, Antonio; Muñoz Romero, José
We present a hybrid vertex/cell-centred model for mechanically simulating planar cellular monolayers undergoing cell reorganisation. Cell centres are represented by a triangular nodal network, while the cell boundaries are formed by an associated vertex network. The two networks are coupled through a kinematic constraint which we allow to relax progressively. Special attention is paid to the change of cell-cell connectivity due to cell reorganisation or remodelling events. We handle these situations by using a variable resting length and applying an Equilibrium-Preserving Mapping (EPM) on the new connectivity, which computes a new set of resting lengths that preserve nodal and vertex equilibrium. We illustrate the properties of the model by simulating monolayers subjected to imposed extension and during a wound healing process. The evolution of forces and the EPM are analysed during the remodelling events. As a by-product, the proposed technique enables to recover fully vertex or fully cell-centred models in a seamless manner by modifying a numerical parameter of the model. This article is protected by copyright. All rights reserved.
This is the peer reviewed version of the following article:
Mosafa, P., Rodriguez-Ferran, A., Muñoz, J.J. Hybrid cell-centred/vertex model for multicellular systems with equilibrium-preserving remodelling. "International journal for numerical methods in biomedical engineering - Online", Març 2018, vol. 34, núm. 3, p. 1-24, which has been published in final form at http://onlinelibrary.wiley.com/doi/10.1002/cnm.2928/pdf. This article may be used for non-commercial purposes in accordance
with Wiley Terms and Conditions for Self-Archiving
Wed, 18 Apr 2018 11:56:23 GMThttp://hdl.handle.net/2117/1164392018-04-18T11:56:23ZMosaffa, PaymanRodríguez Ferran, AntonioMuñoz Romero, JoséWe present a hybrid vertex/cell-centred model for mechanically simulating planar cellular monolayers undergoing cell reorganisation. Cell centres are represented by a triangular nodal network, while the cell boundaries are formed by an associated vertex network. The two networks are coupled through a kinematic constraint which we allow to relax progressively. Special attention is paid to the change of cell-cell connectivity due to cell reorganisation or remodelling events. We handle these situations by using a variable resting length and applying an Equilibrium-Preserving Mapping (EPM) on the new connectivity, which computes a new set of resting lengths that preserve nodal and vertex equilibrium. We illustrate the properties of the model by simulating monolayers subjected to imposed extension and during a wound healing process. The evolution of forces and the EPM are analysed during the remodelling events. As a by-product, the proposed technique enables to recover fully vertex or fully cell-centred models in a seamless manner by modifying a numerical parameter of the model. This article is protected by copyright. All rights reserved.Constancy regions of mixed multiplier ideals in two-dimensional local rings with rational singularities
http://hdl.handle.net/2117/116413
Constancy regions of mixed multiplier ideals in two-dimensional local rings with rational singularities
Alberich Carramiñana, Maria; Alvarez Montaner, Josep; Dachs Cadefau, Ferran
The aim of this paper is to study mixed multiplier ideals associated with a tuple of ideals in a two-dimensional local ring with a rational singularity. We are interested in the partition of the real positive orthant given by the regions where the mixed multiplier ideals are constant. In particular we reveal which information encoded in a mixed multiplier ideal determines its corresponding jumping wall and we provide an algorithm to compute all the constancy regions, and their corresponding mixed multiplier ideals, in any desired range.
Wed, 18 Apr 2018 07:39:28 GMThttp://hdl.handle.net/2117/1164132018-04-18T07:39:28ZAlberich Carramiñana, MariaAlvarez Montaner, JosepDachs Cadefau, FerranThe aim of this paper is to study mixed multiplier ideals associated with a tuple of ideals in a two-dimensional local ring with a rational singularity. We are interested in the partition of the real positive orthant given by the regions where the mixed multiplier ideals are constant. In particular we reveal which information encoded in a mixed multiplier ideal determines its corresponding jumping wall and we provide an algorithm to compute all the constancy regions, and their corresponding mixed multiplier ideals, in any desired range.