Simón Bolívar University

About: Simón Bolívar University is a education organization based out in Caracas, Venezuela. It is known for research contribution in the topics: Population & Crystallization. The organization has 5912 authors who have published 8294 publications receiving 126152 citations.

Mass media and heterogeneous bounds of confidence in continuous opinion dynamics

Abstract: This work focuses on the effects of an external mass media on continuous opinion dynamics with heterogeneous bounds of confidence. We modified the original Deffuant et al. and Hegselmann and Krause models to incorporate both, an external mass media and a heterogeneous distribution of confidence levels. We analysed two cases, one where only two bounds of confidence are taken into account, and other where each individual of the system has her/his own characteristic level of confidence. We found that, in the absence of mass media, diversity of bounds of confidence can improve the capacity of the systems to reach consensus. We show that the persuasion capacity of the external message is optimal for intermediate levels of heterogeneity. Our simulations also show the existence, for certain parameter values, of a counter-intuitive effect in which the persuasion capacity of the mass media decreases if the mass media intensity is too large. We discuss similarities and differences between the two heterogeneous versions of these continuous opinion dynamic models under the influence of mass media.

Effects of filler treatments on the mechanical and morphological behavior of PP+wood flour and PP+sisal fiber

Abstract: Composites were prepared from waste wood flour, sisal fiber and polypropylene (PP) The surface of the filler was modified to enhance the chemical affinity between hydrophilic cellulosic and hydrophobic polymer The treatments studied were: a) The addition of a coupling agent; b) chemical treatment with NaOH; and c) the addition of functionalized polypropylene (Polybond 3150 and 3200) After treatment, mixtures of PP with 40% and 20% of the filler, wood flour and sisal fiber respectively, were extruded and injection molded In the case of wood flour, a mixture of two particle sizes (mesh 20 and 40, 50% each) was used, and in the case of sisal, 10 mm long fibers were selected Results showed that, regardless of the treatment to which the filler was previously submitted, Young’s modulus was always higher for mixtures prepared with wood flour, with values varying between 2839 and 3150 MPa Whereas for mixtures with sisal fiber, the modulus’ values varied between 1704 and 2220 MPa Values of breaking strength, elongation at break and impact strength for PP mixtures with treated sisal fiber were always higher than those for mixtures of PP with wood flour Based on these results, we can conclude that sisal fiber is an organic filler which, due to its mechanical and morphological characteristics, has a reinforcing effect higher than that of wood flour

Sensorless speed measurement of AC machines using analytic wavelet transform

Abstract: A new method for the sensorless speed estimation of AC machines, using the analytic wavelet transform of the stator current signal, is proposed for a direct torque control drive. A comparison with results obtained using the short-time Fourier transform is included. The proposed method can be implemented in real time on a digital signal processor. The time-frequency resolution obtained and the computation time required by the proposed algorithm are improved in comparison to existing techniques, and the method can be applied over the entire speed range.

Computation of Cable Impedances Based on Subdivision of Conductors

Abstract: The frequency-dependent resistances and inductances of cables can either be found from analyt ical formulas, or with numerical methods based on finite elements or subdivision of conductors. While analytical formulas are limited to coaxial configurations, numerical methods can be used for non-concentric configurations as well. This paper discusses the method of subdivision into subconductors of circular, square or elemental shape, and compares the results for the case of a coaxial cable, where exact solutions are available from analytical formulas. The inclusion of ground return impedances is discussed next. The method is then applied to the calculation of impedances of pipe-type cables with magnetic pipe material, and of internal impedances of stranded conductors in the power line carrier frequency range.