A public key cryptosystem based on block upper triangular matrices

We propose a public key cryptosystem based on block upper triangular matrices. This system is a variant of the Discrete Logarithm Problem with elements in a finite group, capable of increasing the difficulty of the problem while maintaining the key size. We also propose a key exchange protocol that guarantees that both parties share a secret element of this group and a digital signature scheme that provides data authenticity and integrity.

Quantitative stability of linear infinite inequality systems under block perturbations with applications to convex systems

The original motivation for this paper was to provide an efficient quantitative analysis of convex infinite (or semi-infinite) inequality systems whose decision variables run over general infinite-dimensional (resp. finite-dimensional) Banach spaces and that are indexed by an arbitrary fixed set J. Parameter perturbations on the right-hand side of the inequalities are required to be merely bounded, and thus the natural parameter space is l ∞(J). Our basic strategy consists of linearizing the parameterized convex system via splitting convex inequalities into linear ones by using the Fenchel–Legendre conjugate. This approach yields that arbitrary bounded right-hand side perturbations of the convex system turn on constant-by-blocks perturbations in the linearized system. Based on advanced variational analysis, we derive a precise formula for computing the exact Lipschitzian bound of the feasible solution map of block-perturbed linear systems, which involves only the system’s data, and then show that this exact bound agrees with the coderivative norm of the aforementioned mapping. In this way we extend to the convex setting the results of Cánovas et al. (SIAM J. Optim. 20, 1504–1526, 2009) developed for arbitrary perturbations with no block structure in the linear framework under the boundedness assumption on the system’s coefficients. The latter boundedness assumption is removed in this paper when the decision space is reflexive. The last section provides the aimed application to the convex case.

ICT in higher education: an experience with e-books

The present paper seeks to explain the diverse advantages of virtual books and also the main barriers that make it difficult their implementation in the classroom. A brief review of the literature on ICT, e-learning, distance education and e-books will be complemented with a case study about the preparation, development and implementation of an e-book. The paper could be helpful both for systems analysts and for teachers when they are developing and implementing e-books.

E.books: ventajas e implementación

Los e.books, o libros electrónicos, dan respuesta a muchas de las necesidades planteadas en la educación superior del siglo XXI. Suponen restar cierto protagonismo a los libros impresos, que sólo permiten el aprendizaje a través de la lectura y la comprensión, y que son generalmente estáticos y poco interactivos. Por el contrario los libros-plataforma multimedia 2.0 tienen indudables ventajas sobre los convencionales: se pueden acceder desde diversos soportes (ordenador, tablet, smartphone…), son accesibles y utilizables en cualquier momento y en cualquier lugar sin necesidad de trasportarlos físicamente, suponen un ahorro de costes, ya que el coste del libro-plataforma virtual es de un 70 a un 80% más barato que el impreso, contienen útiles archivos que se pueden ver o descargar, contienen enlaces (hipervínculos) a webs externas para ampliar la información, etc. Mediante este trabajo pretendemos explicar las diversas ventajas de los libros virtuales, pero también proponer diversas pautas que puedan ser útiles para su implementación en el aula. Para ello además de una revisión de la literatura sobre el tema se explicará la experiencia que hemos tenido en la elaboración, desarrollo e implementación de un e.book.

Comparison of Lattice-Fluid Binary Parameters For Mixtures and Block Copolymers

The aim of this report is to discuss the method of determination of lattice-fluid binary interaction parameters by comparing well characterized immiscible blends and block copolymers of poly(methyl methacrylate) (PMMA) and poly(ϵ−caprolactone) (PCL). Experimental pressure-volume-temperature (PVT) data in the liquid state were correlated with the Sanchez—Lacombe (SL) equation of state with the scaling parameters for mixtures and copolymers obtained through combination rules of the characteristic parameters for the pure homopolymers. The lattice-fluid binary parameters for energy and volume were higher than those of block copolymers implying that the copolymers were more compatible due to the chemical links between the blocks. Therefore, a common parameter cannot account for both homopolymer blend and block copolymer phase behaviors based on current theory. As we were able to adjust all data of the mixtures with a single set of lattice-binary parameters and all data of the block copolymers with another single set we can conclude that both parameters did not depend on the composition for this system. This characteristic, plus the fact that the additivity law of specific volumes can be suitably applied for this system, allowed us to model the behavior of the immiscible blend with the SL equation of state. In addition, a discussion on the relationship between lattice-fluid binary parameters and the Flory–Huggins interaction parameter obtained from Leibler's theory is presented.