Computational material design for acoustic cloaking

A topology optimization technique based on the topological derivative and the level set function is utilized to design/synthesize the microstructure of a pentamode material for an acoustic cloaking device. The technique provides a microstructure consisting of a honeycomb lattice composed of needle‐like and joint members. The resulting metamaterial shows a highly anisotropic elastic response with effective properties displaying a ratio between bulk and shear moduli of almost three orders of magnitude. Furthermore, in accordance with previous works in the literature, it can be asserted that this kind of microstructure can be realistically fabricated. The adoption of a topology optimization technique as a tool for the inverse design of metamaterials with applications to acoustic cloaking problems is one contribution of this paper. However, the most important achievement refers to the analysis and discussion revealing the key role of the external shape of the prescribed domain where the optimization problem is posed. The efficiency of the designed microstructure is measured by comparing the scattering wave fields generated by acoustic plane waves impinging on bare and cloaked bodies. Copyright © 2017 The Authors. International Journal for Numerical Methods in Engineering Published by John Wiley & Sons Ltd.     

Modeling of a linear motor feed drive including pre-rolling friction and aperiodic cogging and ripple

This work addresses the systematic modeling of a linear feed drive based on a linear synchronous motor, a helpful step in control design for precise machine tools using linear motors. The model considers the electrical dynamics, ripple, cogging effects, and friction. For ripple and cogging, periodic and aperiodic behaviors are analyzed, and simple models are proposed to reflect the observed behavior. Friction is represented by the generalized Maxwell-slip model Al-Bender (IEEE Trans Autom Control 50:1883–1887, 2005), and the particular manner in which pre-rolling parameters and Stribeck curve were determined for the current system is shown here for completeness. Finally, the model shows a good performance both in simulation and feedforward control.     

Topology verification for isosurface extraction

The broad goals of verifiable visualization rely on correct algorithmic implementations. We extend a framework for verification of isosurfacing implementations to check topological properties. Specifically, we use stratified Morse theory and digital topology to design algorithms which verify topological invariants. Our extended framework reveals unexpected behavior and coding mistakes in popular publicly available isosurface codes.     

Discovering the campus together: A mobile and computer-based learning experience

One of the most relevant difficulties faced by first-year undergraduate students is to settle into the educational environment of universities. This paper presents a case study that proposes a computer-assisted collaborative experience designed to help students in their transition from high school to university. This is done by facilitating their first contact with the campus and its services, the university community, methodologies and activities. The experience combines individual and collaborative activities, conducted in and out of the classroom, structured following the Jigsaw Collaborative Learning Flow Pattern. A specific environment including portable technologies with network and computer applications has been developed to support and facilitate the orchestration of a flow of learning activities into a single integrated learning setting. The result is a Computer Supported Collaborative Blended Learning scenario that has been evaluated with first-year university students of the degrees of Software and Audiovisual Engineering within the subject Introduction to Information and Communications Technologies. The findings reveal that the scenario improves significantly students’ interest in their studies and their understanding about the campus and services provided. The environment is also an innovative approach to successfully support the heterogeneous activities conducted by both teachers and students during the scenario. This paper introduces the goals and context of the case study, describes how the technology was employed to conduct the learning scenario, the evaluation methods and the main results of the experience.     

Influence of electrode array parameters used in electrotherapy on tumor growth kinetics: A mathematical simulation

Evaluation of the distance between the electrodes, voltage applied to them, and number of electrodes in tumor growth kinetics is very useful for effective tumor destruction when electrotherapy is used. However, a study of this type has not yet been proposed. The aim of this paper is to simulate the influence of such parameters and the point–point electrode configuration on the tumor growth kinetics through a Modified Gompertz Equation. The results show a good agreement between the simulations performed in this study and the experimental results reported by our group and other authors. A critical distance between electrodes and a threshold ratio between the applied electric field and that distributed in the tumor are revealed, for which higher electrotherapy antitumor effectiveness is reached. In conclusion, electrotherapy antitumor effectiveness not only depends on the distance between the electrodes, voltage applied to them, and number of electrodes, but also on the ratio between the applied electric field and that distributed in the tumor. In addition, the results of these simulations may be used to help physicians choose the most appropriate treatment for patients with malignant solid tumors, as we have implemented in a current clinical trial.     

Mineralization of Ibuprofen and Humic Acid through Catalytic Ozonation

Advanced oxidation methods are used to remove traces of pharmaceuticals from aquatic environments. The application of a catalyst improves the total organic carbon removal during ozonation of pharmaceuticals in water. The aim of this study was to use MnO₂-CuO/ γ-Al₂O₃ catalyst for ozonation of ibuprofen (5 mgL^?1) and evaluate the effect of the presence of humic acid in the removal process. The presence of the catalyst increased the mineralization percentage of ibuprofen from 27% for noncatalytic ozonation to 55% in the presence of catalyst. The presence of humic acid increased noncatalytic mineralization by 10%. The reusability and stability of the catalyst, and its ability to adsorb reaction by-products were demonstrated.     

Experimental assessment of slant‐path rain attenuation variability in the Ka‐band

This study is based on the results of a slant‐path Ka‐band propagation experiment carried out in Madrid, Spain, regarding rain attenuation, which is the main propagation impairment in this frequency band. The experimental and statistical results correspond to seven complete years of measurements, a period large enough to accomplish a comprehensive analysis in order to characterize the variability of rain rate and attenuation. It is shown that year‐to‐year variability is significant in temperate climates as Madrid's. The aforementioned significance is also apparent with regards to seasonal, monthly, worst‐month and hourly variability concerning rain attenuation, which are also discussed and related when possible to the variability of the rain phenomena, either represented by the total amounts of rainfall in the different periods or by rain rate statistics. Copyright © 2015 John Wiley & Sons, Ltd.     

Control study on mixing enhancement in boundary layers of membrane systems

This paper proposes an activation scheme for improving the mixing in the boundary layer of pressure-driven membrane systems such as reverse osmosis and ultrafiltration. Through the application of an external electric field, a flow of ions in the vicinity of the membrane surface is generated, creating an electro-osmotic flow that should reduce the extent of concentration polarization. An optimal control problem is formulated and solved to determine the waveform of the control action required to produce an electric field that can effectively increase mixing in the vicinity of the membrane surface with improved energy efficiency. This paper uses a mixing index in terms of a measure of spatial gradients of the perturbation velocities, which describes the mixing caused by both length stretching and vortices. The efficacy of the proposed control is validated by Computational Fluid Dynamics (CFD) simulations.     

Learning from Imbalanced Data Sets with Weighted Cross-Entropy Function

Neural Processing Letters - This paper presents a novel approach to deal with the imbalanced data set problem in neural networks by incorporating prior probabilities into a cost-sensitive...