A 2D ultrasonic array design incorporating hexagonal-shaped elements for NDE applications

Contemporary 2D Ultrasonic arrays suffer from low SNR and limited steering capabilities. Yet, there is a great desire in the industry to increase the operational frequency, in order to enhance their volumetric imaging resolution. State-of-the art arrays use an orthogonal matrix of rectangular elements as this is a natural step forward from the conventional 1D array structure. The objective of this work is to evaluate properties of triangular, rather than rectangular ceramic pillars in a 1-3 connectivity piezoelectric composite for application in a hexagonal-element 2D array. A 3MHz prototype device exploiting new hexagonal substructure have been manufactured. Measured mechanical cross-coupling level is -21.9dB between neighbouring hexagonal elements, providing validation of simulation result. Corroboration between measured and FE modelled device behaviour is demonstrated

A theoretical analysis of a piezoelectric ultrasound device with an active matching layer

This paper investigates the use of magnetically active materials in the matching layer of a piezoelectric transducer. This then allows the performance of the device to be dynamically altered by applying an external field. The effect that this new matching layer has on the performance of a typical device is theoretically investigated here. It transpires that the additional flexibility of an active matching layer can be used to maintain the efficiency of the device as the external load is varied

PREVENTION OF DNA SUGAR, HUMAN PERIPHERAL LYMPHOCYTES AND ERYTHROCYTES DAMAGES FROM FREE RADICAL INDUCED OXIDATION BY NATURAL ANTIOXIDANTS

Objective: The present study focused on the identification of particular extract which shows signification protection of DNA sugar against excessive oxidation. Methods: The different extracts (water, alcohol, alcohol: water, and hexane) of Agathi seeds (Sesbania grandiflora Linn) were evaluated using various antioxidant and other relevant assays like DNA sugar protection and antioxidant activities. Results: The alcohol: water (1:1) extract of S. grandiflora Linn seeds showed the highest antioxidant and free radical scavenging activity. It inhibited membrane lipid peroxidation by 55% at 50 μg/ml, scavenged approximately 69% of hydroxyl and 1,1-diphenyl-2-picrylhydrazayl radicals at 2–3 fold lower concentrations compared to the other extracts. In addition, the alcohol: water extract inhibited ferrous sulfate: ascorbate-induced sugar oxidation of DNA and also showed non-toxic nature against lymphocytes. Conclusion: These results establish the antioxidant potential of the extract, which could be used as natural antioxidant source

Combined mutation differential evolution to solve systems of nonlinear equations

This paper presents a differential evolution heuristic to compute a solution of a system of nonlinear equations through the global optimization of an appropriate merit function. Three different mutation strategies are combined to generate mutant points. Preliminary numerical results show the effectiveness of the presented heuristic.Fundação para a Ciência e a Tecnologia (FCT

Solving systems of nonlinear equations by harmony search

In this paper, we aim to analyze the performance of some variants of the harmony search (HS) metaheuristic when solving systems of nonlinear equations through the global optimization of an appropriate merit function. The HS metaheuristic draws its inspiration from an artistic process, the improvisation process of musicians seeking a wonderful harmony. A new differential best HS algorithm, based on an improvisation operator that mimics the best harmony and uses a differential variation, is proposed. Computational experiments involving a well-known set of small-dimensional problems are presented.Fundação para a Ciência e a Tecnologia (FCT

Solving nonlinear equations by a tabu search strategy

Solving systems of nonlinear equations is a problem of particular importance since they emerge through the mathematical modeling of real problems that arise naturally in many branches of engineering and in the physical sciences. The problem can be naturally reformulated as a global optimization problem. In this paper, we show that a metaheuristic, called Directed Tabu Search (DTS) [16], is able to converge to the solutions of a set of problems for which the fsolve function of MATLAB® failed to converge. We also show the effect of the dimension of the problem in the performance of the DTS.Fundação para a Ciência e a Tecnologia (FCT

Nonmonotone hybrid tabu search for Inequalities and equalities: an experimental study

The main goal of this paper is to analyze the behavior of nonmonotone hybrid tabu search approaches when solving systems of nonlinear inequalities and equalities through the global optimization of an appropriate merit function. The algorithm combines global and local searches and uses a nonmonotone reduction of the merit function to choose the local search. Relaxing the condition aims to call the local search more often and reduces the overall computational effort. Two variants of a perturbed pattern search method are implemented as local search. An experimental study involving a variety of problems available in the literature is presented.Fundação para a Ciência e a Tecnologia (FCT

Solving systems of inequalities and equalities by a nonmonotone hybrid tabu search method

Series : AIP Conference Proceedings, Vol. 1479This paper presents a derivative-free nonmonotone hybrid tabu search to compute a solution of overdetermined systems of inequalities and equalities through the global optimization of an appropriate merit function. The proposed algorithm combines global and local searches aiming to reduce computational effort. Preliminary numerical results show the effectiveness of the combined heuristic.Fundação para a Ciência e a Tecnologia (FCT

Combining global tabu search with local search for solving systems of equalities and inequalities

This papers aims at providing a combined strategy for solving systems of equalities and inequalities. The combined strategy uses two types of steps: a global search step and a local search step. The global step relies on a tabu search heuristic and the local step uses a deterministic search known as Hooke and Jeeves. The choice of step, at each iteration, is based on the level of reduction of the l2-norm of the error function observed in the equivalent system of equations, compared with the previous iterationFundação para a Ciência e a Tecnologia (FCT

On metaheuristics for solving the parameter estimation problem in dynamic systems: A comparative study

This paper presents an experimental study that aims to compare the practical performance of well-known metaheuristics for solving the parameter estimation problem in a dynamic systems context. The metaheuristics produce good quality approximations to the global solution of a finite small-dimensional nonlinear programming problem that emerges from the application of the sequential numerical direct method to the parameter estimation problem. Using statistical hypotheses testing, significant differences in the performance of the metaheuristics, in terms of the average objective function values and average CPU time, are determined. Furthermore, the best obtained solutions are graphically compared in relative terms by means of the performance profiles. The numerical comparisons with other results in the literature show that the tested metaheuristics are effective in achieving good quality solutions with a reduced computational effort.The authors would like to acknowledge the financial support of CIDEM, R&D Unit, funded by the Portuguese Foundation for the Development of Science and Technology (FCT), Ministry of Science, Technology and Higher Education, under the Project UID/EMS/0615/2016, and of COMPETE: POCI-01-0145-FEDER-007043 and FCT within the Projects UID/CEC/00319/2013 and UID/MAT/00013/2013.info:eu-repo/semantics/publishedVersio