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Prieto J.L.,Technical University of Madrid | Munoz M.,CSIC - Institute of Applied Physics | Martinez E.,University of Salamanca
Physical Review B - Condensed Matter and Materials Physics | Year: 2011

The process of injection of a magnetic domain wall (DW) by means of a 25-100 ns current pulse flowing through an adjacent conductive track has been studied in detail. We find that the probability of creating a DW through this method is 100% for a wide range of amplitudes of the current pulse and of the external magnetic field, including zero external magnetic field. Micromagnetic simulations show that the DW is created in the first nanosecond of the pulse, and its movement is strongly influenced by the induced Oersted field, which can reach considerable values, especially in the perpendicular-to-plane direction. The edge roughness and temperature play also a crucial role in determining the type of DW that travels through the wire. Experimentally we show that a map of the probability of injection of a DW by a current pulse can be a very powerful method to check the structural quality of the nanostripe, which has very important practical consequences for research in this area. © 2011 American Physical Society.

Fuster-Sabater A.,CSIC - Institute of Applied Physics
Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics) | Year: 2011

In this paper, a procedure of decomposition of nonlinearly filtered sequences in primary characteristic sequences has been introduced. Such a procedure allows one to analyze structural properties of the filtered sequences e.g. period and linear complexity, which are essential features for their possible application in cryptography. As a consequence of the previous decomposition, a simple constructive method that enlarges the number of known filtered sequences with guaranteed cryptographic parameters has been developed. The procedure here introduced does not impose any constraint on the characteristics of the nonlinear filter. © 2011 Springer-Verlag.

Akerman J.,Technical University of Madrid | Munoz M.,CSIC - Institute of Applied Physics | Maicas M.,Technical University of Madrid | Prieto J.L.,Technical University of Madrid
Physical Review B - Condensed Matter and Materials Physics | Year: 2010

This study explores experimentally the stochastic nature of the domain wall depinning in permalloy nanowires using notches of various shapes and depths. The presence of the domain wall in the notch is detected through its anisotropic magnetoresistance (AMR), which is measured with high precision in order to detect even small changes in the domain wall profile. These measurements showed that variations in the depinning field are related with changes, sometimes very small, in the AMR profile, which indicates that small changes in the pinned domain wall profile can affect largely the depinning process. As these small changes are many times unpredictable and uncontrollable, the stochastic nature of the depinning could have negative consequences for practical applications based on permalloy nanowires. © 2010 The American Physical Society.

Fuster-Sabater A.,CSIC - Institute of Applied Physics | Caballero-Gil P.,University of La Laguna
Applied Soft Computing Journal | Year: 2011

In this paper, a method of obtaining cryptographic sequences based on discrete time chaotic dynamical systems is presented. The importance of the proposal is due to that such cryptographic sequences are also output sequences of a nonlinear keystream generator known as generalized self-shrinking generator, which is still considered secure for symmetric cryptography. It is remarkable that the linearity of the proposed chaotic model based on additive one-dimensional cellular automata might be used to launch a cryptanalysis against such nonlinear generators. © 2010 Elsevier B.V. All rights reserved.

Masque J.M.,CSIC - Institute of Applied Physics | Maria M.E.R.,Technical University of Madrid
Advances in Theoretical and Mathematical Physics | Year: 2012

Let M → N (resp. C → N) be the fibre bundle of pseudo-Riemannian metrics of a given signature (resp. the bundle of linear connections) on an orientable connected manifold N. A geometrically defined class of firstorder Ehresmann connections on the product fibre bundle M × N C is determined such that, for every connection γ belonging to this class and every DiffN-invariant Lagrangian density Λ on J1(M × N C), the corresponding covariant Hamiltonian Λγ is also DiffN-invariant. The case of DiffN-invariant second-order Lagrangian densities on J2M is also studied and the results obtained are then applied to Palatini and Einstein-Hilbert Lagrangians. © 2012 International Press.

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