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61.
Ruben Sevilla Sonia Fernández-Méndez Antonio Huerta 《Archives of Computational Methods in Engineering》2011,18(4):441-484
The development of NURBS-Enhanced Finite Element Method (NEFEM) is revisited. This technique allows a seamless integration
of the CAD boundary representation of the domain and the finite element method (FEM). The importance of the geometrical model
in finite element simulations is addressed and the benefits and potential of NEFEM are discussed and compared with respect
to other curved finite element techniques. 相似文献
62.
63.
Antonio Fernández Anta José Luis López-Presa M. Araceli Lorenzo Pilar Manzano Juan Martinez-Romo Alberto Mozo Christopher Thraves 《Theory of Computing Systems》2011,48(1):1-22
In this paper we generalize the Continuous Adversarial Queuing Theory (CAQT) model (Blesa et al. in MFCS, Lecture Notes in
Computer Science, vol. 3618, pp. 144–155, 2005) by considering the possibility that the router clocks in the network are not synchronized. We name the new model Non Synchronized
CAQT (NSCAQT). Clearly, this new extension to the model only affects those scheduling policies that use some form of timing.
In a first approach we consider the case in which although not synchronized, all clocks run at the same speed, maintaining
constant differences. In this case we show that all universally stable policies in CAQT that use the injection time and the
remaining path to schedule packets remain universally stable. These policies include, for instance, Shortest in System (SIS)
and Longest in System (LIS). Then, we study the case in which clock differences can vary over time, but the maximum difference
is bounded. In this model we show the universal stability of two families of policies related to SIS and LIS respectively
(the priority of a packet in these policies depends on the arrival time and a function of the path traversed). The bounds
we obtain in this case depend on the maximum difference between clocks. This is a necessary requirement, since we also show
that LIS is not universally stable in systems without bounded clock difference. We then present a new policy that we call
Longest in Queues (LIQ), which gives priority to the packet that has been waiting the longest in edge queues. This policy
is universally stable and, if clocks maintain constant differences, the bounds we prove do not depend on them. To finish,
we provide with simulation results that compare the behavior of some of these policies in a network with stochastic injection
of packets. 相似文献
64.
65.
Fredrik Larsson Pedro Díez Antonio Huerta 《Computer Methods in Applied Mechanics and Engineering》2010,199(37-40):2383-2402
In this contribution, we present an a posteriori error estimator for the incompressible Stokes problem valid for a conventional mixed FE formulation. Due to the saddle-point property of the problem, conventional error estimators developed for pure minimization problems cannot be utilized straight-forwardly. The new estimator is built up by two key ingredients. At first, a computed error approximation, exactly fulfilling the continuity equation for the error, is obtained via local Dirichlet problems. Secondly, we adopt the approach of solving local equilibrated flux-free problems in order to bound the remaining, incompressible, error. In this manner, guaranteed upper and lower bounds, of the velocity “energy norm” of the error as well as goal-oriented (linear) output functionals, with respect to a reference (overkill) mesh are obtained. In particular, it should be noted that this approach requires no computation of hybrid fluxes. Furthermore, the estimator is applicable to mixed FE formulations using continuous pressure approximations, such as the Mini and Taylor–Hood class of elements. In conclusion, a few simple numerical examples are presented, illustrating the accuracy of the error bounds. 相似文献
66.
We describe a solution to the SAT problem via non-confluent P systems with active membranes, without using membrane division rules. Furthermore, we provide an algorithm for simulating such devices on a nondeterministic Turing machine with a polynomial slowdown. Together, these results prove that the complexity class of problems solvable non-confluently and in polynomial time by this kind of P system is exactly the class . 相似文献
67.
An obnoxious facility is to be located inside a polygonal region of the plane, maximizing the sum of the k smallest weighted Euclidean distances to n given points, each protected by some polygonal forbidden region. For the unweighted case and k fixed an O(n2logn) time algorithm is presented. For the weighted case a thorough study of the relevant structure of the multiplicatively weighted order-k-Voronoi diagram leads to the design of an O(kn3+n3logn) time algorithm for finding an optimal solution to the anti-t-centrum problem for every t=1,…,k, simultaneously. 相似文献
68.
Luis de-Marcos José Ramón Hilera Roberto Barchino Lourdes Jiménez José Javier Martínez José Antonio Gutiérrez José María Gutiérrez Salvador Otón 《Computers & Education》2010
Mobile learning is considered an evolution of e-learning that embraces the ubiquitous nature of current computational systems in order to improve teaching and learning. Within this context it is possible to develop mobile applications oriented to learning, but it is also important to assess to what extent such applications actually work. In this paper we present a new tool designed to reinforce students’ knowledge by means of self-assessment. Improvement in student achievement was evaluated and an attitudinal survey was also carried out to measure student attitudes towards this new tool. Three different experimental groups were selected for this research, with students aged from 14 to 21 years old, including high-school and university students. Results show that this kind of tool improves student achievement, especially amongst younger learners, with a relatively low impact on current teaching activities and methodology. 相似文献
69.
Jose M. Álvarez Theo Gevers Antonio M. López 《International Journal of Computer Vision》2010,90(1):45-61
Color is a powerful visual cue in many computer vision applications such as image segmentation and object recognition. However,
most of the existing color models depend on the imaging conditions that negatively affect the performance of the task at hand.
Often, a reflection model (e.g., Lambertian or dichromatic reflectance) is used to derive color invariant models. However,
this approach may be too restricted to model real-world scenes in which different reflectance mechanisms can hold simultaneously. 相似文献
70.
Carlos Ariño Emilio Pérez Antonio Sala 《Engineering Applications of Artificial Intelligence》2010,23(8):1420-1427
This paper presents a novel control design technique in order to obtain a guaranteed cost fuzzy controller subject to constraints on the input channel. This guaranteed cost control law is obtained via multi-parametric quadratic programming. The result is a piecewise fuzzy control law where the state partition is defined by fuzzy inequalities. The parameters of the Lyapunov function can be obtained previously using Linear Matrix Inequalities optimization. 相似文献