Breaking a chaos-based secure communication scheme designed by an improved modulation method

Recently Bu and Wang [Chaos, Solitons & Fractals 19 (2004) 919] proposed a simple modulation method aiming to improve the security of chaos-based secure communications against return-map-based attacks. Soon this modulation method was independently cryptanalyzed by Chee et al. [Chaos, Solitons & Fractals 21 (2004) 1129], Wu et al. [Chaos, Solitons & Fractals 22 (2004) 367], and \'{A}lvarez et al. [Chaos, Solitons & Fractals, accepted (2004), arXiv:nlin.CD/0406065] via different attacks. As an enhancement to the Bu-Wang method, an improving scheme was suggested by Wu et al. by removing the relationship between the modulating function and the zero-points. The present paper points out that the improved scheme proposed by Wu et al. is still insecure against a new attack. Compared with the existing attacks, the proposed attack is more powerful and can also break the original Bu-Wang scheme. Furthermore, it is pointed out that the security of the modulation-based schemes is not so satisfactory from a pure cryptographical point of view. The synchronization performance of this class of modulation-based schemes is also discussed.Comment: elsart.cls, 18 pages, 9 figure

Misalignment & Co.: (Pseudo-)scalar and vector dark matter with curvature couplings

Motivated by their potential role as dark matter, we study the cosmological evolution of light scalar and vector fields non-minimally coupled to gravity. Our focus is on a situation where the dominant contribution to the energy density arises from the misalignment mechanism. In addition, we also discuss the possibility that dark matter is generated in a stochastic scenario or from inflationary fluctuations. Even small deviations in the non-minimal couplings from the standard scenarios lead to significant qualitative and quantitative changes. This is due to the curvature-coupling driven superhorizon evolution of the homogeneous field and the non-zero momentum modes during inflation. Both the relic density yield and the large-scale density fluctuations are affected. For the misalignment mechanism, this results in a weakening of the isocurvature constraints and opens up new viable regions of parameter space.Comment: 25 pages, 8 figures. References updated and discussion of vector longitudinal modes expande

Aspectos de lo fantástico en la narrativa de Gonzalo Torrente Ballester

Conferencias y Comunicaciones del primer Congreso Internacional de literatura fantástica y ciencia ficción, celebrado del 6 al 9 de mayo de 2008 en la Universidad Carlos III de Madri

Tratamiento de efluentes contaminados con priones. Diseño de un reactor químico

The control and elimination of prionic infective agents that may be present in the effluents, turns out to be a complicated mechanism inside a High Containment bological Facility. There are two ways to carry out this neutralization: Installation of thermal systems to ensure achieve a minimum temperature of 134 ° C sterilization plateau for a residence time of 18 minutes, and the use of chemical reactors based on the addition of sodium hypochlorite so the mixture maintained 2% of free chlorine during the reaction period. This study presents the design phases, elements and benefits, of a chemical reactor that allows the treatment of prion effluents in order to serve as a model to biocontainment facilities with areas of animal experimentation, who want to develop their work with prions.El control e inactivación de priones que pueden estar presentes en los efluentes, resulta ser un mecanismo complicado dentro de una Instalación de Alta Contención Biológica. Existen dos alternativas para llevar a cabo esta inactivación: la Instalación de sistemas de tratamiento térmico de efluentes que garanticen alcanzar una temperatura mínima de 134ºC en meseta de esterilización durante un tiempo de residencia de 18 minutos, y el uso de reactores químicos basados en la adición de hipoclorito sódico de forma que la mezcla mantenga un 2% de cloro libre durante el periodo de reacción. El presente estudio, expone el diseño con sus fases, elementos y sus ventajas, de un reactor químico que permita el tratamiento de efluentes priónicos con el fin de que sirva de modelo a instalaciones biocontenidas que dispongan de áreas de experimentación animal y que pretendan desarrollar sus trabajos con priones

Quantum state transfer in disordered spin chains: How much engineering is reasonable?

The transmission of quantum states through spin chains is an important element in the implementation of quantum information technologies. Speed and fidelity of transfer are the main objectives which have to be achieved by the devices even in the presence of imperfections which are unavoidable in any manufacturing process. To reach these goals, several kinds of spin chains have been suggested, which differ in the degree of fine-tuning, or engineering, of the system parameters. In this work we present a systematic study of two important classes of such chains. In one class only the spin couplings at the ends of the chain have to be adjusted to a value different from the bulk coupling constant, while in the other class every coupling has to have a specific value. We demonstrate that configurations from the two different classes may perform similarly when subjected to the same kind of disorder in spite of the large difference in the engineering effort necessary to prepare the system. We identify the system features responsible for these similarities and we perform a detailed study of the transfer fidelity as a function of chain length and disorder strength, yielding empirical scaling laws for the fidelity which are similar for all kinds of chain and all disorder models. These results are helpful in identifying the optimal spin chain for a given quantum information transfer task. In particular, they help in judging whether it is worthwhile to engineer all couplings in the chain as compared to adjusting only the boundary couplings.Comment: 20 pages, 13 figures. Revised version, title changed, accepted by Quantum Information & Computatio