Analytical calculation of the Peierls-Nabarro pinning barrier for one-dimensional parametric double-well models

Lattice effects on the kink families of two models for one-dimensional nonlinear Klein-Gordon systems with double-well on-site potentials are considered. The analytical expression of the generalized Peierls-Nabarro pinning potential is obtained and confronted with numerical simulations.Comment: RevTex, 10 pages, 4 figure

Elemental iron (Fe0) for better drinking water in rural areas of developing countries

Many of the reasons behind the anthropogenic contamination problems in rural environments of developing countries lie in changes in the traditional way of life and the ignorance on the toxic potential of introduced manufactured products. A generalization trend exists within the international community suggesting that water in developing countries is of poor quality. However, the water quality is rarely analytically determined. Existing potabilization solutions may be prohibitively expensive for the rural populations. Therefore, efficient and affordable technologies are still needed to ameliorate the water quality. In the recent two decades,elemental iron has shown the capacity to remove all possible contaminants (including viruses) from the groundwater. This paper presents a concept to scale down the conventional iron barrier technology to meet the requirements of small communities and households in rural environments worldwide.researc

Formules scientifiques pour l’optimisation de la réponse acoustique du tambour d’appel africain

Le tambour d’appel africain (TAA) est le véhicule sonore de l’existence africaine. Il est associé à de nombreuses expressions traditionnelles et cultuelles. Le processus de fabrication présente quelques inconvénients : durée longue, difficulté à fabriquer des tambours acoustiquement identiques, pauvreté tonale et portée acoustique limitée. Dans le but d’apporter quelques solutions aux inconvénients susmentionnés, nous établissons les équations dynamiques du fonctionnement du TAA grâce aux lois de la mécanique et de l’acoustique. Les fréquences propres de vibration des lèvres et de la cavité sont obtenues. Deux formules scientifiques qui permettent d’optimiser la réponse acoustique des TAAs sont établies. Elles peuvent servir comme normes de fabrication afin d’obtenir des puissances sonores maximales et de gérer convenablement les intervalles musicaux. Les résultats théoriques sont validés par des mesures expérimentales et des tests dans des ateliers de fabrication.Mots clés: Tambour d’appel africain, fréquences propres, formules scientifiques, optimisation de la fabricationEnglish AbstractThe African calling drum is a sound instrument associated to various traditional and cultural expressions in Africa. Its fabrication process presents some limits: long duration, difficulty in fabricating acoustically identical drums, tonal poverty and limited sound range. In order to find some solutions to these limits, dynamical equations describing the functioning of the African calling drum are derived using mechanical and acoustical laws. The natural frequencies of vibration of the drum shells and drum cavity are obtained. They are used to obtain formula for the fabrication of drums with maximal sound powers and convenient management of the musical intervals. The theoretical results are validated by the experiment and tests in some fabrication sites.Keywords: African calling drum, natural frequencies, scientific formula, optimization of the fabricatio

Kinks in the discrete sine-Gordon model with Kac-Baker long-range interactions

We study effects of Kac-Baker long-range dispersive interaction (LRI) between particles on kink properties in the discrete sine-Gordon model. We show that the kink width increases indefinitely as the range of LRI grows only in the case of strong interparticle coupling. On the contrary, the kink becomes intrinsically localized if the coupling is under some critical value. Correspondingly, the Peierls-Nabarro barrier vanishes as the range of LRI increases for supercritical values of the coupling but remains finite for subcritical values. We demonstrate that LRI essentially transforms the internal dynamics of the kinks, specifically creating their internal localized and quasilocalized modes. We also show that moving kinks radiate plane waves due to break of the Lorentz invariance by LRI.Comment: 11 pages (LaTeX) and 14 figures (Postscript); submitted to Phys. Rev.

Chaos In New Polynomial Discrete Logistic Maps With Fractional Derivative And Applications For Text Encryption

In this paper, we propose new polynomial discrete logistic equations based on the classical logistic map, which exhibit chaotic behavior as control parameters vary. We also explore versions with fractional derivatives. Using the chaotic sequence generated by these equations, we develop an encryption scheme for text. The scheme relies on initial conditions, control parameters, and a transformation of text characters into values between 0 and 1, followed by a transformation to discrete chaotic values for transmissio