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Publication Open Access Optimization and design of wireless systems for the implementation of context aware scenarios in railway passenger vehicles(IEEE, 2017) Azpilicueta Fernández de las Heras, Leyre; Astrain Escola, José Javier; López Iturri, Peio; Granda, Fausto; Vargas Rosales, César; Villadangos Alonso, Jesús; Perallos Ruiz, Asier; Bahillo, Alfonso; Falcone Lanas, Francisco; Ingeniería Matemática e Informática; Matematika eta Informatika Ingeniaritza; Ingeniería Eléctrica y Electrónica; Ingeniaritza Elektrikoa eta ElektronikoaIn this paper, intra-wagon wireless communication performance is analyzed, in order to account for inherent scenario complexity in the deployment phase of wireless systems toward the implementation of a context-aware environment. A real commercial passenger wagon has been simulated by means of an in-house-developed 3-D ray launching code, accounting for embedded wagon elements as well as variable user densities within the passenger wagon. Onboard measurements of a designed and deployed wireless sensor network are obtained, showing good agreement with wireless channel estimations for two different frequencies of operation. Energy consumption behavior and user density impact have also been analyzed and estimated as a function of network topology and the operational mode. These results can aid in wireless transceivers deployment configurations, in order to minimize power consumption, optimize interference levels, and increase overall service performance.Publication Open Access Implementation of wireless sensor network architecture for interactive shopping carts to enable context-aware commercial areas(IEEE, 2016) López Iturri, Peio; Azpilicueta Fernández de las Heras, Leyre; Astrain Escola, José Javier; Aguirre Gallego, Erik; Salinero, Eduardo; Villadangos Alonso, Jesús; Falcone Lanas, Francisco; Ingeniería Eléctrica y Electrónica; Ingeniaritza Elektrikoa eta Elektronikoa; Ingeniería Matemática e Informática; Matematika eta Informatika Ingeniaritza; Institute of Smart Cities - ISCAn interactive shopping cart to enable context aware environments within large commercial areas is presented. A wireless sensor network was designed, with specific nodes embedded within the shopping carts and infrastructure nodes in the shopping area. Due to the complexity of wireless propagation, given the large amount of obstacles and the inclusion of users, an in house deterministic method based on 3D Ray Launching was employed, providing results in terms of adequate transceiver deployment to minimize interference, energy consumption and maximize data throughput. The proposed system was tested in a real commercial scenario, with the implementation of an ad-hoc monitor shopping application, exhibiting successful detection rates in order of 99%. The proposed systems provides an interactive shopping experience for users as well as for commercial managers.Publication Open Access Basketball player on-body biophysical and environmental parameter monitoring based on wireless sensor network integration(IEEE, 2021) Picallo Guembe, Imanol; López Iturri, Peio; Astrain Escola, José Javier; Aguirre Gallego, Erik; Azpilicueta Fernández de las Heras, Leyre; Celaya Echarri, Mikel; Villadangos Alonso, Jesús; Falcone Lanas, Francisco; Matematika eta Informatika Ingeniaritza; Ingeniaritza Elektrikoa, Elektronikoaren eta Telekomunikazio Ingeniaritzaren; Institute of Smart Cities - ISC; Ingeniería Matemática e Informática; Ingeniería Eléctrica, Electrónica y de ComunicaciónSport activities have benefited in recent years from the progressive adoption of different technological assets in order to improve individual as well as group training, collect different statistics or enhance the spectator experiences. The progressive adoption of Internet of Things paradigms can also be considered within the scope of sport activities, providing high levels of user interactivity as well as enabling cloud-based data storage and processing. In this work, a system for monitoring biophysical, kinematic and environmental parameters within the development of basketball training is presented. A set of on-body nodes with multiple sensors and wireless body area network capabilities have been designed, implemented and tested under real training conditions during a match. Wireless channel analysis results have been obtained with the aid of in house implemented deterministic 3D ray launching algorithm, providing accurate coverage/capacity estimations in relation with human body consideration in the field as well as in the stadium. Measurement results give relevant information in relation with individual player characteristics as well as with team characteristics, providing a flexible tool to improve training development of basketball.Publication Open Access Radio wave propagation and WSN deployment in complex utility tunnel environments(MDPI, 2020) Celaya Echarri, Mikel; Azpilicueta Fernández de las Heras, Leyre; López Iturri, Peio; Picallo Guembe, Imanol; Aguirre Gallego, Erik; Astrain Escola, José Javier; Villadangos Alonso, Jesús; Falcone Lanas, Francisco; Ingeniaritza Elektrikoa, Elektronikoaren eta Telekomunikazio Ingeniaritzaren; Matematika eta Informatika Ingeniaritza; Institute of Smart Cities - ISC; Ingeniería Eléctrica, Electrónica y de Comunicación; Ingeniería Matemática e InformáticaThe significant growth of wireless communications systems in the last years has led to the adoption of a wide range of applications not only for the general public but, also, including utilities and administrative authorities. In this context, the notable expansion of new services for smart cities requires, in some specific cases, the construction of underground tunnels in order to enable the maintenance and operation works of utilities, as well as to reduce the visual impact within the city center. One of the main challenges is that, inherently, underground service tunnels lack coverage from exterior wireless communication systems, which can be potentially dangerous for maintenance personnel working within the tunnels. Accordingly, wireless coverage should be deployed within the underground installation in order to guarantee real-time connectivity for safety maintenance, remote surveillance or monitoring operations. In this work, wireless channel characterization for complex urban tunnel environments was analyzed based on the assessment of LoRaWAN and ZigBee technologies operating at 868 MHz. For that purpose, a real urban utility tunnel was modeled and simulated by means of an in-house three-dimensional ray-launching (3D-RL) code. The utility tunnel scenario is a complex and singular environment in terms of radio wave propagation due to the limited dimensions and metallic elements within it, such as service trays, user pathways or handrails, which were considered in the simulations. The simulated 3D-RL algorithm was calibrated and verified with experimental measurements, after which, the simulation and measurement results showed good agreement. Besides, a complete wireless sensor network (WSN) deployment within the tunnels was presented, providing remote cloud data access applications and services, allowing infrastructure security and safety work conditions. The obtained results provided an adequate radio planning approach for the deployment of wireless systems in complex urban utility scenarios, with optimal coverage and enhanced quality of service.Publication Open Access Decoupling mixed finite elements on hierarchical triangular grids for parabolic problems(Elsevier, 2018) Arrarás Ventura, Andrés; Portero Egea, Laura; Ingeniería Matemática e Informática; Matematika eta Informatika IngeniaritzaIn this paper, we propose a numerical method for the solution of time-dependent flow problems in mixed form. Such problems can be efficiently approximated on hierarchical grids, obtained from an unstructured coarse triangulation by using a regular refinement process inside each of the initial coarse elements. If these elements are considered as subdomains, we can formulate a non-overlapping domain decomposition method based on the lowest-order Raviart–Thomas elements, properly enhanced with Lagrange multipliers on the boundaries of each subdomain (excluding the Dirichlet edges). A suitable choice of mixed finite element spaces and quadrature rules yields a cell-centered scheme for the pressures with a local 10-point stencil. The resulting system of differential-algebraic equations is integrated in time by the Crank–Nicolson method, which is known to be a stiffly accurate scheme. As a result, we obtain independent subdomain linear systems that can be solved in parallel. The behavior of the algorithm is illustrated on a variety of numerical experiments.Publication Open Access Optimal monotonicity-preserving perturbations of a given Runge–Kutta method(Springer, 2018) Higueras Sanz, Inmaculada; Ketcheson, David I.; Kocsis, Tihamér A.; Ingeniería Matemática e Informática; Matematika eta Informatika IngeniaritzaPerturbed Runge–Kutta methods (also referred to as downwind Runge–Kutta methods) can guarantee monotonicity preservation under larger step sizes relative to their traditional Runge–Kutta counterparts. In this paper we study the question of how to optimally perturb a given method in order to increase the radius of absolute monotonicity (a.m.). We prove that for methods with zero radius of a.m., it is always possible to give a perturbation with positive radius. We first study methods for linear problems and then methods for nonlinear problems. In each case, we prove upper bounds on the radius of a.m., and provide algorithms to compute optimal perturbations. We also provide optimal perturbations for many known methods.Publication Open Access Convergent and asymptotic expansions of solutions of differential equations with a large parameter: Olver cases II and III(Rocky Mountain Mathematics Consortium, 2015) Ferreira González, Chelo; López García, José Luis; Pérez Sinusía, Ester; Ingeniería Matemática e Informática; Matematika eta Informatika IngeniaritzaThis paper continues the investigation initiated in [Lopez, 2013]. We consider the asymptotic method designed by F. Olver [Olver, 1974] for linear differential equations of the second order containing a large (asymptotic) parameter . We consider here the second and third cases studied by Olver: differential equations with a turning point (second case) or a singular point (third case). It is well-known that his method gives the Poincar´e-type asymptotic expansion of two independent solutions of the equation in inverse powers of . In this paper we add initial conditions to the differential equation and consider the corresponding initial value problem. By using the Green function of an auxiliary problem, we transform the initial value problem into a Volterra integral equation of the second kind. Then, using a fixed point theorem, we construct a sequence of functions that converges to the unique solution of the problem. This sequence has also the property of being an asymptotic expansion for large (not of Poincar´e-type) of the solution of the problem. Moreover, we showPublication Open Access Representations of hypergeometric functions for arbitrary parameter values and their use(2017) Karp, D. B.; López García, José Luis; Ingeniería Matemática e Informática; Matematika eta Informatika IngeniaritzaIntegral representations of hypergeometric functions proved to be a very useful tool for studying their properties. The purpose of this paper is twofold. First, we extend the known representations to arbitrary values of the parameters and show that the extended representations can be interpreted as examples of regularizations of integrals containing Meijer's G function. Second, we give new applications of both, known and extended representations. These include: inverse factorial series expansion for the Gauss type function, new information about zeros of the Bessel and Kummer type functions, connection with radial positive de nite functions and generalizations of Luke's inequalities for the Kummer and Gauss type functions.Publication Open Access Asymptotic behaviour of the Urbanik semigroup(Elsevier, 2015) Berg, Christian; López García, José Luis; Ingeniería Matemática e Informática; Matematika eta Informatika IngeniaritzaWe revisit the product convolution semigroup of probability densities ec(t); c > 0 on the positive half-line with moments (n!)c and determine the asymptotic behaviour of ec for large and small t > 0. This shows that (n!)c is indeterminate as Stieltjes moment sequence if and only if c > 2. When c is a natural number ec is a Meijer-G function. From the results about ec we obtain the asymptotic behaviour at 1 of the convolution roots of the Gumbel distribution.Publication Open Access New series expansions of the 3F2 function(2015) López García, José Luis; Pagola Martínez, Pedro Jesús; Pérez Sinusía, Ester; Ingeniería Matemática e Informática; Matematika eta Informatika IngeniaritzaWe can use the power series definition of 3F2(a1, a2, a3; b1, b2; z) to compute this function for z in the unit disk only. In this paper we obtain new expansions of this function that are convergent in larger domains. Some of these expansions involve the polynomial 3F2(a1,−n, a3; b1, b2; z) evaluated at certain points z. Other expansions involve the Gauss hypergeometric function 2F1. The domain of convergence is sometimes a disk, other times a half-plane, other times the region |z|2 < 4|1 − z|. The accuracy of the approximation given by these expansions is illustrated with numerical experiments.Publication Open Access From start to finish: teenagers on the autism spectrum developing their own collaborative game(Emerald, 2017) Bossavit, Benoît; Parsons, Sarah; Ingeniería Matemática e Informática; Matematika eta Informatika IngeniaritzaPurpose: The purpose of this paper is to investigate how teenagers on the autism spectrum respond to their involvement in the creation of a collaborative game, meeting the curriculum requirements in programming at secondary level in England. Design/methodology/approach: Two autistic teenagers were involved in participatory design processes to elaborate and develop together a collaborative game of their choice using the visual programming software, Kodu Game Lab. Findings: With the support of adults (teachers and the researcher), the participants were able to demonstrate and strengthen their participation, problem-solving and programming skills. The participants expressed their preferences through their attitudes towards the tasks. They created a game where the players did not need to initiate any interaction between each other to complete a level. Furthermore, the students naturally decided to work separately and interacted more with the adults than with each other. This is a small case study and so cannot be generalised. However, it can serve as starting point for further studies that involve students with autism in the development of interactive games. Practical implications: It has been shown that disengaged students can develop various skills through their involvement in software programming. Originality/value: Overall, this paper presents the involvement of teenagers on the autism spectrum in the initial design and development of a collaborative game with an approach that shaped, and was shaped by, the students’ interests. Although collaboration was emphasised in the intended learning outcomes for the game, as well as through the design process, this proved difficult to achieve in practice suggesting that students with autism may require stronger scaffolding to engage in collaborative learning.Publication Open Access Modified Douglas splitting methods for reaction–diffusion equations(Springer, 2017) Arrarás Ventura, Andrés; Hout, K. J. in ’t; Hundsdorfer, W.; Portero Egea, Laura; Ingeniería Matemática e Informática; Matematika eta Informatika IngeniaritzaWe present modifications of the second-order Douglas stabilizing corrections method, which is a splitting method based on the implicit trapezoidal rule. Inclusion of an explicit term in a forward Euler way is straightforward, but this will lower the order of convergence. In the modifications considered here, explicit terms are included in a second-order fashion. For these modified methods, results on linear stability and convergence are derived. Stability holds for important classes of reaction–diffusion equations, and for such problems the modified Douglas methods are seen to be often more efficient than related methods from the literature.Publication Open Access Orthogonal basis for the optical transfer function(Optical Society of America, 2016) Ferreira González, Chelo; López García, José Luis; Navarro, Rafael; Pérez Sinusía, Ester; Ingeniería Matemática e Informática; Matematika eta Informatika IngeniaritzaWe propose systems of orthogonal functions qn to represent optical transfer functions (OTF) characterized by including the diffraction-limited OTF as the first basis function q0 OTF perfect. To this end, we apply a powerful and rigorous theoretical framework based on applying the appropriate change of variables to well-known orthogonal systems. Here we depart from Legendre polynomials for the particular case of rotationally symmetric OTF and from spherical harmonics for the general case. Numerical experiments with different examples show that the number of terms necessary to obtain an accurate linear expansion of the OTF mainly depends on the image quality. In the rotationally symmetric case we obtained a reasonable accuracy with approximately 10 basis functions, but in general, for cases of poor image quality, the number of basis functions may increase and hence affect the efficiency of the method. Other potential applications, such as new image quality metrics are also discussed.Publication Open Access Orthogonal basis with a conicoid first mode for shape specification of optical surfaces: reply(Optical Society of America, 2016) Ferreira González, Chelo; López García, José Luis; Navarro, Rafael; Pérez Sinusía, Ester; Ingeniería Matemática e Informática; Matematika eta Informatika IngeniaritzaWe present some comments to the paper 'Orthogonal basis with a conicoid first mode for shape specification of optical surfaces: comment'.Publication Open Access Avoiding the order reduction when solving second-order in time PDEs with Fractional Step Runge–Kutta–Nyström methods(Elsevier, 2016) Moreta, M. Jesús; Bujanda Cirauqui, Blanca; Jorge Ulecia, Juan Carlos; Ingeniería Matemática e Informática; Matematika eta Informatika IngeniaritzaWe study some of the main features of Fractional Step Runge–Kutta–Nyström methods when they are used to integrate Initial–Boundary Value Problems of second order in time, in combination with a suitable spatial discretization. We focus our attention on the order reduction phenomenon, which appears if classical boundary conditions are taken at the internal stages. This drawback is specially hard when time dependent boundary conditions are considered. In this paper we present an efficient technique, very simple and computationally cheap, which allows us to avoid the order reduction; such technique consists in modifying the boundary conditions for the internal stages of the method.Publication Open Access Scalability approaches for causal multicast: a survey(Springer, 2016) Juan Marín, Rubén de; Decker, Hendrik; Armendáriz Íñigo, José Enrique; Bernabéu Aubán, José M.; Muñoz Escoí, Francesc D.; Ingeniería Matemática e Informática; Matematika eta Informatika IngeniaritzaMany distributed services need to be scalable: internet search, electronic commerce, e-government... In order to achieve scalability those applications rely on replicated components. Because of the dynamics of growth and volatility of customer markets, applications need to be hosted by adaptive systems. In particular, the scalability of the reliable multicast mechanisms used for supporting the consistency of replicas is of crucial importance. Reliable multicast may propagate updates in a predefined order (e.g., FIFO, total or causal). Since total order needs more communication rounds than causal order, the latter appears to be the preferable candidate for achieving multicast scalability, although the consistency guarantees based on causal order are weaker than those of total order. This paper provides a historical survey of different scalability approaches for reliable causal multicast protocols.Publication Open Access A fully discrete Calderón calculus for the two-dimensional elastic wave equation(Elsevier, 2015) Domínguez Baguena, Víctor; Sánchez Vizuet, Tonatiuh; Sayas, Francisco Javier; Ingeniería Matemática e Informática; Matematika eta Informatika IngeniaritzaIn this paper we present a full discretization of the layer potentials and boundary integral operators for the elastic wave equation on a parametrizable smooth closed curve in the plane. The method can be understood as a non-conforming Petrov–Galerkin discretization, with a very precise choice of testing functions by symmetrically combining elements on two staggered grids, and using a look-around quadrature formula. Unlike in the acoustic counterpart of this work, the kernel of the elastic double layer operator includes a periodic Hilbert transform that requires a particular choice of the mixing parameters. We give mathematical justification of this fact. Finally, we test the method on some frequency domain and time domain problems, and demonstrate its applicability on smooth open arcs.Publication Open Access Improved accuracy for time-splitting methods for the numerical solution of parabolic equations(Elsevier, 2015) Arrarás Ventura, Andrés; Portero Egea, Laura; Ingeniería Matemática e Informática; Matematika eta Informatika IngeniaritzaIn this work, we study time-splitting strategies for the numerical approximation of evolutionary reaction–diffusion problems. In particular, we formulate a family of domain decomposition splitting methods that overcomes some typical limitations of classical alternating direction implicit (ADI) schemes. The splitting error associated with such methods is observed to be O(t2) in the time step. In order to decrease the size of this splitting error to O(t3), we add a correction term to the right-hand side of the original formulation. This procedure is based on the improved initialization technique proposed by Douglas and Kim in the framework of ADI methods. The resulting non-iterative schemes reduce the global system to a collection of uncoupled subdomain problems that can be solved in parallel. Computational results comparing the newly derived algorithms with the Crank–Nicolson scheme and certain ADI methods are presented.Publication Open Access Eventual consistency: origin and support(Slovak Academy of Sciences, Institute of Informatics, 2018) Muñoz Escoí, Francesc D.; García Escrivá, José Ramón; Sendra Roig, Juan Salvador; Bernabéu Aubán, José M.; González de Mendívil Moreno, José Ramón; Ingeniería Matemática e Informática; Matematika eta Informatika IngeniaritzaEventual consistency is demanded nowadays in geo-replicated services that need to be highly scalable and available. According to the CAP constraints, when network partitions may arise, a distributed service should choose between being strongly consistent or being highly available. Since scalable services should be available, a relaxed consistency (while the network is partitioned) is the preferred choice. Eventual consistency is not a common data-centric consistency model, but only a state convergence condition to be added to a relaxed consistency model. There are still several aspects of eventual consistency that have not been analysed in depth in previous works: 1. which are the oldest replication proposals providing eventual consistency, 2. which replica consistency models provide the best basis for building eventually consistent services, 3. which mechanisms should be considered for implementing an eventually consistent service, and 4. which are the best combinations of those mechanisms for achieving different concrete goals. This paper provides some notes on these important topics.Publication Open Access Order barrier for low-storage DIRK methods with positive weights(Springer, 2018) Higueras Sanz, Inmaculada; Roldán Marrodán, Teodoro; Ingeniería Matemática e Informática; Matematika eta Informatika IngeniaritzaIn this paper we study an order barrier for low-storage diagonally implicit Runge-Kutta (DIRK) methods with positive weights. The Butcher matrix for these schemes, that can be implemented with only two memory registers in the van der Houwen implementation, has a special structure that restricts the number of free parameters of the method. We prove that third order low-storage DIRK methods must contain negative weights, obtaining the order barrier p ≤ 2 for these schemes. This result extends the well known one for symplectic DIRK methods, which are a particular case of low-storage DIRK methods. Some other properties of second order low-storage DIRK methods are given.