Chaotic systems with a null conditional Lyapunov exponent under nonlinear driving.

Control of a chaotic system by homogeneous nonlinear driving, when a conditional Lyapunov exponent is zero, may give rise to special and interesting synchronizationlike behaviors in which the response evolves in perfect correlation with the drive. Among them, there are the amplification of the drive attractor and the shift of it to a different region of phase space. In this paper, these synchronizationlike behaviors are discussed, and demonstrated by computer simulation of the Lorentz model [E. N. Lorenz, J. Atmos. Sci. 20 130 (1963)] and the double scroll [T. Matsumoto, L. O. Chua, and M. Komuro, IEEE Trans. CAS CAS-32, 798 (1985)].

Amazon.es : incògnites i expectatives. Amb Enric Faura i Pep Torn

Debat a l'Internauta, el primer programa de ràdio del país sobre la xarxa, una col·laboració entre la UOC i Vilaweb. Fa menys d'una setmana que es va confirmar la notícia: la plataforma de comerç electrònic més potent de la xarxa, Amazon, va obrir dimecres de la setmana passada la filial ibèrica. Amazon és actualment el portal de venda en línia més important i divers, amb un catàleg de milions de llibres impresos i electrònics, a més d'un gavadal de productes com ara compactes, DVD, jocs, aparells d'electrònica de consum i, fins i tot, roba, alimentació i mobiliari. De moment, Amazon.es ha aterrat a casa nostra amb una oferta de productes físics, entre els quals hi ha cinquanta mil llibres impresos en català, però obre tantes oportunitats com interrogants. Com afectarà les llibreries convencionals? Tindran mercat ara plataformes de llibre digital més modestes? Estimularà el negoci del llibre electrònic? Facilitarà l'autoedició de llibres? Farà créixer el nombre de lectors en català? En parlem amb Enric Faura, de la plataforma Edi.cat, i amb l'expert Pep Torn, director de l'àrea de Biblioteca i Recursos Documentals de la UOC.

Catalogación y valoración de las webquests desde el área de educación física y el tratamiento de temáticas transversales

Gears of the current millennium have been activated by the hit entry into the information society that has generated a whole range of social and educational changes, it is difficult to stay out of their influence, such as: the dizzying presence of new technologies (NNTT) and the entrenchment of a crisis of values. Physical education has been affected by this avalanche of developments that have sparked the birth of original teaching and learning tools that can be applied in the classroom. In this sense, WebQuests have been configured as a unifying and educational activities that allow addressing the treatment of specific thematic area that we are dealing with the work of certain cross¿cutting. But how do you know what product we have before us, what is its effectiveness? What criteria will allow us to classify it as a fit and capable of being applied in our particular educational context? To clarify these and other issues that any teacher could arise before the election of a multimedia educational materials, our particular object of study has a double claim on the one hand, developing two tools: the card catalog and the heading of Valuation of WebQuests and secondly, to apply these tools in order to find out / determine the degree of quality of a sample of WebQuests. In this article sets forth, in summary form, the various stages of what our research has gone since the establishment of a synthesized theoretical basis, via the definition of the basic guidelines for the design of the exhibition and research results and ending with The list of the ideas and proposals arising from thework.

A Secure Mobile-based Authentication System

Financial information is extremely sensitive. Hence, electronic banking must provide a robust system to authenticate its customers and let them access their data remotely. On the other hand, such system must be usable, affordable, and portable.We propose a challengeresponse based one-time password (OTP) scheme that uses symmetriccryptography in combination with a hardware security module. The proposed protocol safeguards passwords from keyloggers and phishing attacks.Besides, this solution provides convenient mobility for users who want to bank online anytime and anywhere, not just from their owntrusted computers.

Comments on "On the relationship between fractal dimension and the performance of multi-resonant dipole antennas using Koch curves"

Comentaris referits a l'article següent: K. J. Vinoy, J. K. Abraham, and V. K. Varadan, “On the relationshipbetween fractal dimension and the performance of multi-resonant dipoleantennas using Koch curves,” IEEE Transactions on Antennas and Propagation, 2003, vol. 51, p. 2296–2303.

On the thermal noise introduced by a resistor in a circuit

Comentari sobre l'article publicat anteriorment pels mateixos autors: Vargas, M; Pallás, R; The seemingly paradoxical noise behaviour some active circuits. IEEE Transactions on Instrumentation and Measurement. 1994, vol. 43, núm. 5, p. 764-767

Comments on "On resistor-induced thermal noise in linear circuits"

Correspondència referida a l'article de R. Giannetti, publicat ibid. vol.49 p.87-88

Linear and nonlinear terrain deformation maps from a reduced set of interferometric SAR images

In this paper, an advanced technique for the generation of deformation maps using synthetic aperture radar (SAR) data is presented. The algorithm estimates the linear and nonlinear components of the displacement, the error of the digital elevation model (DEM) used to cancel the topographic terms, and the atmospheric artifacts from a reduced set of low spatial resolution interferograms. The pixel candidates are selected from those presenting a good coherence level in the whole set of interferograms and the resulting nonuniform mesh tessellated with the Delauney triangulation to establish connections among them. The linear component of movement and DEM error are estimated adjusting a linear model to the data only on the connections. Later on, this information, once unwrapped to retrieve the absolute values, is used to calculate the nonlinear component of movement and atmospheric artifacts with alternate filtering techniques in both the temporal and spatial domains. The method presents high flexibility with respect to the required number of images and the baselines length. However, better results are obtained with large datasets of short baseline interferograms. The technique has been tested with European Remote Sensing SAR data from an area of Catalonia (Spain) and validated with on-field precise leveling measurements.

Sea state effect on the sea surface emissivity at L-band

In May 1999, the European Space Agency (ESA) selected the Earth Explorer Opportunity Soil Moisture and Ocean Salinity (SMOS) mission to obtain global and frequent soil moisture and ocean salinity maps. SMOS' single payload is the Microwave Imaging Radiometer by Aperture Synthesis (MIRAS), an L-band two-dimensional aperture synthesis radiometer with multiangular observation capabilities. At L-band, the brightness temperature sensitivity to the sea surface salinity (SSS) is low, approximately 0.5 K/psu at 20/spl deg/C, decreasing to 0.25 K/psu at 0/spl deg/C, comparable to that to the wind speed /spl sim/0.2 K/(m/s) at nadir. However, at a given time, the sea state does not depend only on local winds, but on the local wind history and the presence of waves traveling from far distances. The Wind and Salinity Experiment (WISE) 2000 and 2001 campaigns were sponsored by ESA to determine the impact of oceanographic and atmospheric variables on the L-band brightness temperature at vertical and horizontal polarizations. This paper presents the results of the analysis of three nonstationary sea state conditions: growing and decreasing sea, and the presence of swell. Measured sea surface spectra are compared with the theoretical ones, computed using the instantaneous wind speed. Differences can be minimized using an "effective wind speed" that makes the theoretical spectrum best match the measured one. The impact on the predicted brightness temperatures is then assessed using the small slope approximation/small perturbation method (SSA/SPM).