Search results for "matemàtica"
showing 10 items of 147 documents
Static output-feedback control for vehicle suspensions: a single-step linear matrix inequality approach
2013
In this paper, a new strategy to design static output-feedback controllers for a class of vehicle suspension systems is presented. A theoretical background on recent advances in output-feedback control is first provided, which makes possible an effective synthesis of static output-feedback controllers by solving a single linear matrix inequality optimization problem. Next, a simplified model of a quarter-car suspension system is proposed, taking the ride comfort, suspension stroke, road holding ability, and control effort as the main performance criteria in the vehicle suspension design. The new approach is then used to design a static output-feedbackH∞controller that only uses the suspensi…
Z-permutable subgroups of finite groups
2016
Let Z be a complete set of Sylow subgroups of a finite group G, that is, a set composed of a Sylow p-subgroup of G for each p dividing the order of G. A subgroup H of G is called Z-permutable if H permutes with all members of Z. The main goal of this paper is to study the embedding of the Z-permutable subgroups and the influence of Z-permutability on the group structure.
La observación de aula como herramienta de desarrollo profesional: el caso del OCDE Global Teaching InSights
2023
Se presenta el proyecto Global Teaching InSights Video Study, de la Organización para la Cooperación y el Desarrollo Económicos [OCDE], cuyo objetivo es potenciar la grabación y el análisis de sesiones de clases como herramienta de desarrollo profesional y de formación de docentes de matemáticas. Se describe el trabajo llevado a cabo por los autores coordinando grupos de trabajo que se encargaron de diseñar un estudio de caso basado en un vídeo de una clase real. La difusión pública de los vídeos producidos permite, además, abordar el diseño de investigaciones centradas en observación guiada de la práctica de la enseñanza de las matemáticas.
Las matemáticas del cubo de Rubik
2013
[ES] En este artículo mostramos cómo podemos utilizar el cubo de Rubik para presentar algunos conceptos básicos de la teoría de grupos y cómo podemos usar esta para resolver el cubo de Rubik.
Podria Descartes embarcar en la nau de Neurath?
1999
En aquest article Josep Lluís Blasco reflexiona sobre els suggeriments epistemològics de Descartes, des de la perspectiva de la teoria del coneixement del segle XX, i es pregunta fins a quin punt es pot considerar que Descartes inaugurà l’epistemologia moderna i quina és la vigència del seu legat. Enceta la seua anàlisi amb la metàfora de la nau d’Otto Neurath, segons la qual el coneixement científic no té uns fonaments sòlids perquè és un constructe teòric que s’ha de revisar de manera contínua, i afegeix la modificació que en fa Quine en situar a la mateixa nau la filosofia i la ciència. Blasco examina si Descartes podria embarcar en dita nau, i conclou que la resposta no és tan senzilla …
Scaling and data collapse for the mean exit time of asset prices
2005
We study theoretical and empirical aspects of the mean exit time of financial time series. The theoretical modeling is done within the framework of continuous time random walk. We empirically verify that the mean exit time follows a quadratic scaling law and it has associated a pre-factor which is specific to the analyzed stock. We perform a series of statistical tests to determine which kind of correlation are responsible for this specificity. The main contribution is associated with the autocorrelation property of stock returns. We introduce and solve analytically both a two-state and a three-state Markov chain models. The analytical results obtained with the two-state Markov chain model …
On the equivalence between the Scheduled Relaxation Jacobi method and Richardson's non-stationary method
2017
The Scheduled Relaxation Jacobi (SRJ) method is an extension of the classical Jacobi iterative method to solve linear systems of equations ($Au=b$) associated with elliptic problems. It inherits its robustness and accelerates its convergence rate computing a set of $P$ relaxation factors that result from a minimization problem. In a typical SRJ scheme, the former set of factors is employed in cycles of $M$ consecutive iterations until a prescribed tolerance is reached. We present the analytic form for the optimal set of relaxation factors for the case in which all of them are different, and find that the resulting algorithm is equivalent to a non-stationary generalized Richardson's method. …
Radial conformal motions in Minkowski space–time
1999
A study of radial conformal Killing fields (RCKF) in Minkowski space-time is carried out, which leads to their classification into three disjointed classes. Their integral curves are straight or hyperbolic lines admitting orthogonal surfaces of constant curvature, whose sign is related to the causal character of the field. Otherwise, the kinematic properties of the timelike RCKF are given and their applications in kinematic cosmology is discussed.
A kinematic method to obtain conformal factors
2000
Radial conformal motions are considered in conformally flat space-times and their properties are used to obtain conformal factors. The geodesic case leads directly to the conformal factor of Robertson-Walker universes. General cases admitting homogeneous expansion or orthogonal hypersurfaces of constant curvature are analyzed separately. When the two conditions above are considered together a subfamily of the Stephani perfect fluid solutions, with acceleration Fermi-Walker propagated along the flow of the fluid, follows. The corresponding conformal factors are calculated and contrasted with those associated with Robertson-Walker space-times.
Monads in double categories
2010
We extend the basic concepts of Street's formal theory of monads from the setting of 2-categories to that of double categories. In particular, we introduce the double category Mnd(C) of monads in a double category C and define what it means for a double category to admit the construction of free monads. Our main theorem shows that, under some mild conditions, a double category that is a framed bicategory admits the construction of free monads if its horizontal 2-category does. We apply this result to obtain double adjunctions which extend the adjunction between graphs and categories and the adjunction between polynomial endofunctors and polynomial monads.