Recursos de colección

Archivo Digital UPM (109.492 recursos)

This is an institutional repository providing access to the research output of the institution. Primarily contains thesis.

Materia = Matemáticas

Mostrando recursos 1 - 20 de 1.252

  1. Stability of steady states of the Cauchy problem for the exponential reaction-diffusion equation

    Tello del Castillo, José Ignacio
    Abstract We consider the Cauchy problem ut = u + eu, x ∈ RN , t ∈ (0, T ), u(x, 0) = u0, x ∈ RN , where u0 ∈ C(RN ) and T > 0. We first study the radial steady states of the equation and the number of intersections distinguishing four different cases: N = 1, N = 2, 3 N 9 and N 10, writing explicitly every steady state for N = 1 and N = 2. Then we study the large time behavior of solutions of the parabolic problem.

  2. Regularity of solutions to a lubrication problem with discontinuous separation data

    Tello del Castillo, José Ignacio
    Abstract We study the regularity ofthe solution to the Reynolds equation for incompressible and compressible fluids when the gap between the lubricated surfaces, “h(x; y)”, presents a discontinuity in a two-dimensional bounded domain. As in the one-dimensional problem studied by Rayleigh, the solution P does not belong to C1 (�) but we obtain that |∇P| is bounded, i.e. P ∈ W 1;∞(�).

  3. Mathematical analysis of a simple model for the growth of necrotic tumors in presence of inhibitors

    Tello del Castillo, José Ignacio; Díaz Díaz, Jesús Ildefonso
    We study a mathematical model for the growth of tumors with two free boundaries : the inner boundary delaying the necrotic zone and the outer boundary delaying the tumor.We consider the presence of inhibitors and establish the existence and uniqueness of the solution for the model under suitable conditions on the inhibitors interaction and the tumor growth.

  4. Mathematical analysis and stability of a chemotaxis model with logistic term.

    Tello del Castillo, José Ignacio
    In this paper we study a non-linear system of dierential equations arising in chemotaxis. The system consists of a PDE that describes the evolution of a population and an ODE which models the concentration of a chemical substance. We study the number of steady states under suitable assumptions, the existence of one global solution to the evolution problem in terms of weak solutions and the stability of the steady states.

  5. On a nonlocal nonlinear ODE arising in magnetic recording.

    Tello del Castillo, José Ignacio
    Abstract In this paper we study the uniqueness of the solution for a nonlinear ODE with nonlocal terms. We consider a limit case of a one-dimensional equation arising in magnetic recording. The equation models the tape deflection where the magnetic head profile, with trenches to control the tape position, is a known function.

  6. A note on some inverse problems arising in lubrication theory

    Tello del Castillo, José Ignacio; Díaz Díaz, Jesús Ildefonso
    Abstract. It is well-known that the pressure of a lubricating fluid filling the gap between two solid surfaces satisfies the Reynolds equation involving the distance function, h, between both planes, as a crucial coefficient. Nevertheless, in most of the applications the function h is not known a priori. Here we consider the simple case in which the surfaces are two parallel planes and assume prescribed the total force applied upon one of the surfaces. We give some sufficient conditions on the total force in order to solve this inverse problem. We show that in the incompressible case, such a condition is also...

  7. Stability of solutions of chemotaxis equations in reinforced random walks

    Tello del Castillo, José Ignacio; Friedman, Avner
    Abstract In this paper we consider a nonlinear system of differential equations consisting of one parabolic equation and one ordinary differential equation. The system arises in chemotaxis, a process whereby living organisms respond to chemical substance by moving toward higher, or lower, concentrations of the chemical substance, or by aggregating or dispersing. We prove that stationary solutions of the system are asymptotically stable.

  8. Head media interaction in magnetic recording

    Tello del Castillo, José Ignacio; Friedman, Avner
    The tape-head interaction in magnetic recording is modeled by a coupled system of a second-order differential equation for the pressure and a fourth-order differential equation for the tape deflection. There is also the constraint that the spacing between the head and the tape remains positive. In this paper, we study the stationary one-dimensional case and establish the existence of a smooth solution.

  9. Optimización del diseño geométrico de glorietas mediante algoritmos genéticos

    Rubio Martín, Juan Luis
    Las glorietas son un tipo de nudo que canaliza los flujos procedentes de tres o más accesos por medio de una calzada anular. De la experiencia acumulada en países de todo el mundo se deduce que en muchos casos este tipo de nudo ofrece numerosas ventajas respecto a las intersecciones convencionales. Por este motivo, se ha extendido su aplicación como solución alternativa a las intersecciones urbanas e interurbanas convencionales. La definición del trazado en planta de una glorieta es un proceso iterativo en el cual se deben establecer las características de un número importante de elementos geométricos para posteriormente comprobar...

  10. Cumulative measure of correlation for multipartite quantum states

    García López De Lacalle, Jesús; Fonseca de Oliveira, André Luiz; Buksman Hollander, Efrain
    The present article proposes a measure of correlation for multiqubit mixed states. The measure is de?ned recursively, accumulating the correlation of the subspaces, making it simple to calculate without the use of regression. Unlike usual measures, the proposed measure is continuous additive and re?ects the dimensionality of the state space, allowing to compare states with di?erent dimensions. Examples show that the measure can signal critical points (CPs) in the analysis of Quantum Phase Transitions (QPTs) in Heisenberg models.

  11. Stata web services: Toward Stata-based healthcare informatics applications integrated in a service-oriented architecture (SOA)

    Zlotnik Enaliev, Alexander; Escobar, Modesto; Gallardo, Ascensión; Montero Martínez, Juan Manuel
    Stata has many functions that can be used in decision support systems, forecasting systems, and, generally, applications that use analytical or modeling functionalities. A web interface with an HTML/JS graphical user interface or an XML-based web service are convenient approaches for exposing Stata-based programs on public and private computer networks. However, using Stata through a web interface or integrating it into a corporate software environment such as a service-oriented architecture can be challenging. Usually, Stata-based programs need to be translated (reimplemented) in a different programming language to be used through the aforementioned interfaces. These reimplementations can be problematic, time consuming,...

  12. Uniform families of minimal rational curves on Fano manifolds

    OcchettA, Gianluca; Solá Conde, Luis; Watanabe, KiwamU
    It is a well known fact that families of minimal rational curves on rational homogeneous manifolds of Picard number one are uniform, in the sense that the tangent bundle to the manifold has the same splitting type on each curve of the family. In this note we prove that certain?stronger?uniformity conditions on a family of minimal rational curves on a Fano manifold of Picard number one allow to prove that the manifold is homogeneous.

  13. How to resist synchronization attacks

    Pisarchik, Alexander N.; Jiménez Rodríguez, Maricela; Jaimes-Reátegui, Rider
    Conventional synchronization-based chaotic communication is vulnerable to synchronization attacks enable to recuperate system parameters. However, it is possible to make these attacks inefficient. The simple way to resist synchronization attacks is to change a parameter of the master system faster than the time needed for the system to synchronize. To verify this idea we construct a hybrid communication system composed of two chaotic Rössler oscillators and the chaotic logistic map. The latter is used for fast variation of the most sensitive system parameter when the Rössler oscillators synchronize. The algorithm is robust to noise in the communication channel.

  14. Wind turbine fatigue loads statistical estimation from standard signals

    Pérez Campuzano, Darío
    Fatigue loads represent a critical element in several aeronautical applications and Wind Turbines (WTs) are not an exception. Their evolution over the machine service life usually determines its life span, hence their behavior knowledge can cause a relevant economic impact on the Cost of Energy (CoE). Nevertheless, their measurements are frequently difficult or expensive and estimations arising from other known signals can be carried out instead. This thesis aims to design a load estimation model using standard signal as inputs by means of statistical and machine learning procedures. It includes an input selection stage and the models layout arrangement and assessment,...

  15. Hyperconnectivity is a fundamental response to neurological disruption

    Hillary, Frank G.; Román, Cristina A.; Venkatesan, Umesh; Rajtmajer, Sarah; Bajo Breton, Ricardo; Castellanos, Nazareth
    In the cognitive and clinical neurosciences, the past decade has been marked by dramatic growth in a literature examining brain "connectivity" using noninvasive methods. We offer a critical review of the blood oxygen level dependent functional MRI (BOLD fMRI) literature examining neural connectivity changes in neurological disorders with focus on brain injury and dementia. The goal is to demonstrate that there are identifiable shifts in local and large-scale network connectivity that can be predicted by the degree of pathology. We anticipate that the most common network response to neurological insult is hyperconnectivity but that this response depends upon demand and...

  16. An efficient implementation of the synchronization likelihood algorithm for functional connectivity

    Rosales García, Francisco Javier; García Dopico, Antonio; Bajo Breton, Ricardo; Nevado, Angel
    Measures of functional connectivity are commonly employed in neuroimaging research. Among the most popular measures is the Synchronization Likelihood which provides a non-linear estimate of the statistical dependencies between the activity time courses of different brain areas. One aspect which has limited a wider use of this algorithm is the fact that it is very computationally and memory demanding. In the present work we propose new implementations and parallelizations of the Synchronization Likelihood algorithm with significantly better performance both in time and in memory use. As a result both the amount of required computational time is reduced by 3 orders...

  17. Synchronization of intermittent behavior in ensembles of multistable dynamical systems

    Sevilla Escoboza, Ricardo; Martín Buldú, Javier; Pisarchik, Alexander N.; Boccaletti, Stefano; Gutierrez, Ricardo
    We propose a methodology to analyze synchronization in an ensemble of diffusively coupled multistable systems. First, we study how two bidirectionally coupled multistable oscillators synchronize and demonstrate the high complexity of the basins of attraction of coexisting synchronous states. Then, we propose the use of the master stability function (MSF) for multistable systems to describe synchronizability, even during intermittent behavior, of a network of multistable oscillators, regardless of both the number of coupled oscillators and the interaction structure. In particular, we show that a network of multistable elements is synchronizable for a given range of topology spectra and coupling strengths,...

  18. Selective monostability in multi-stable systems

    Sevilla Escoboza, Ricardo; Pisarchik, Alexander N.; Jaimes-Reátegui, Rider; Huerta Cuellar, Guillermo
    We propose a robust method that allows a periodic or a chaotic multi-stable system to be transformed to a monostable system at an orbit with dominant frequency of any of the coexisting attractors. Our approach implies the selection of a particular attractor by periodic external modulation with frequency close to the dominant frequency in the power spectrum of a desired orbit and simultaneous annihilation of all other coexisting states by positive feedback, both applied to one of the system parameters. The method does not require any preliminary knowledge of the system dynamics and the phase space structure. The efficiency of...

  19. Functional brain networks: great expectations, hard times and the big leap forward

    Papo, David; Zanin, Massimiliano; Pineda Pardo, José Ángel; Boccaletti, Stefano; Martín Buldú, Javier
    Many physical and biological systems can be studied using complex network theory, a new statistical physics understanding of graph theory. The recent application of complex network theory to the study of functional brain networks has generated great enthusiasm as it allows addressing hitherto non-standard issues in the field, such as efficiency of brain functioning or vulnerability to damage. However, in spite of its high degree of generality, the theory was originally designed to describe systems profoundly different from the brain. We discuss some important caveats in the wholesale application of existing tools and concepts to a field they were not...

  20. New insights into the suitability of the third dimension for visualizing multivariate/multidimensional data: a study based on loss of quality quantification

    Gracia Berna, Antonio; González Tortosa, Santiago; Robles Forcada, Victor; Menasalvas Ruiz, Ernestina; Von Landesberger, Tatiana
    Most visualization techniques have traditionally used two-dimensional, instead of three-dimensional representations to visualize multidimensional and multivariate data. In this article, a way to demonstrate the underlying superiority of three-dimensional, with respect to two-dimensional, representation is proposed. Specifically, it is based on the inevitable quality degradation produced when reducing the data dimensionality. The problem is tackled from two different approaches: a visual and an analytical approach. First, a set of statistical tests (point classification, distance perception, and outlier identification) using the two-dimensional and three-dimensional visualization are carried out on a group of 40 users. The results indicate that there is an...

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