Particle Swarm Algorithms to solve engineering problems: a comparison of performance

In many disciplines, the use of evolutionary algorithms to perform optimizations is limited because of the extensive number of objective evaluations required. In fact, in real-world problems, each objective evaluation is frequently obtained by time-expensive numerical calculations. On the other hand, gradient-based algorithms are able to identify optima with a reduced number of objective evaluations, but they have limited exploration capabilities of the search domain and some restrictions when dealing with noncontinuous functions. In this paper, two PSO-based algorithms are compared to evaluate their pros and cons with respect to the effort required to find acceptable solutions. The algorithms implement two different methodologies to solve widely used engineering benchmark problems. Comparison is made both in terms of fixed iterations tests to judge the solution quality reached and fixed threshold to evaluate how quickly each algorithm reaches near-optimal solutions. The results indicate that one PSO algorithm achieves better solutions than the other one in fixed iterations tests, and the latter achieves acceptable results in less-function evaluations with respect to the first PSO in the case of fixed threshold tests.Fil: Tomassetti, Giordano. Centro Ricerche Frascati; ItaliaFil: Cagnina, Leticia Cecilia. Universidad Nacional de San Luis. Facultad de Ciencias Físico Matemáticas y Naturales. Departamento de Informática. Laboratorio Investigación y Desarrollo en Inteligencia Computacional; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico San Luis; Argentin

Pareto-Optimization of HTS CICC for High-Current Applications in Self-Field

The ENEA superconductivity laboratory developed a novel design for Cable-in-Conduit Conductors (CICCs) comprised of stacks of 2nd-generation REBCO coated conductors. In its original version, the cable was made up of 150 HTS tapes distributed in five slots, twisted along an aluminum core. In this work, taking advantage of a 2D finite element model, able to estimate the cable's current distribution in the cross-section, a multiobjective optimization procedure was implemented. The aim of optimization was to simultaneously maximize both engineering current density and total current flowing inside the tapes when operating in self-field, by varying the cross-section layout. Since the optimization process involved both integer and real geometrical variables, the choice of an evolutionary search algorithm was strictly necessary. The use of an evolutionary algorithm in the frame of a multiple objective optimization made it an obliged choice to numerically approach the problem using a nonstandard fast-converging optimization algorithm. By means of this algorithm, the Pareto frontiers for the different configurations were calculated, providing a powerful tool for the designer to achieve the desired preliminary operating conditions in terms of engineering current density and/or total current, depending on the specific application field, that is, power transmission cable and bus bar systems

A Comparison of Performance

In many disciplines, the use of evolutionary algorithms to perform optimizations is limited because of the extensive number of objective evaluations required. In fact, in real-world problems, each objective evaluation is frequently obtained by time-expensive numerical calculations. On the other hand, gradient-based algorithms are able to identify optima with a reduced number of objective evaluations, but they have limited exploration capabilities of the search domain and some restrictions when dealing with noncontinuous functions. In this paper, two PSO-based algorithms are compared to evaluate their pros and cons with respect to the effort required to find acceptable solutions. The algorithms implement two different methodologies to solve widely used engineering benchmark problems. Comparison is made both in terms of fixed iterations tests to judge the solution quality reached and fixed threshold to evaluate how quickly each algorithm reaches near-optimal solutions. The results indicate that one PSO algorithm achieves better solutions than the other one in fixed iterations tests, and the latter achieves acceptable results in lessfunction evaluations with respect to the first PSO in the case of fixed threshold tests

Electrothermal analysis of a twisted stacked YBCO cable-in-conduit conductor

A YBCO cable-in-conduit conductor (CICC) for high field magnet applications as well as for energy transmission is under development at the ENEA Frascati Superconductivity Lab- oratory. The cable is designed to carry up to 20 kA at 5 K and 12 T and is composed of five stacks of 30 YBCO tapes each, arranged in a twisted stacked configuration inside an aluminum stabilizer and an external jacket. The cooling is provided by forced convection of supercritical helium that flows in a central channel and in cavities manufactured between the superconducting stacks and the aluminum core. A first dummy prototype of the cable has been produced by TRATOS Cavi S.p.A., Italy, in order to assess the feasibility of the manufacturing process. This paper presents a 3-D coupled electric and thermal model of the cable, developed at the University of Bologna in a COMSOL Multiphysics environment. The model adopts a homogenization procedure to describe the tape stacks in a finite-element method approach with considerable saving on the number of degrees of freedom. The model is applied to the computation of the cable current sharing temperature and to the investigation of quench due to a distributed disturbance

OPTICAL SPECTROMETER FOR MEASURING THE RATIO OF ATOMIC HYDROGEN AND MOLECULAR HYDROGEN IN AN ABS

At the test bench in Ferrara, we constructed an optical spectrometer that measures the relative population of the atomic and molecular hydrogen in the discharge tube of our atomic beam source (ABS). The spectrometer consists of a rotating grating, achromatic lenses, slits, and a sensitive photo-detector connected to a computer. Due to the rotation of the grating, the optical spectrum is scanned over the detector, and the intensities of hydrogen spectral lines are recorded. The intensity ratio of recorded hydrogen atomic lines to hydrogen molecular lines gives qualitative information about the degree of dissociation. With the device’s high sensitivity and spectral resolution, it will be possible to monitor vacuum conditions and gas impurities in the ABS discharge tube

Comparison of two mechanical disaggregation methods of fresh lung tissues for extraction of high-quality RNA

Gene expression studies are widely used in medical, biological, and pharmaceutical research. Obtaining high-quality RNA from tissues is a prerequisite for high-quality data that should accurately represent gene expression levels in-vivo. The main source of technical bias, which could affect the results from transcriptomic studies, is variation in RNA quality. In this regard, tissue preparation is critical: different disruption techniques can affect RNA quality, influencing further applications. Mechanical disaggregation is a common, inexpensive, and simple method to obtain a high cell yield, demonstrated to efficiently disrupt the extracellular matrix and release single cells. However, its efficacy is operator-dependent, leading to poorly reproducible results. A fast, reproducible, and standardized technique could undoubtedly overcome this problem, avoiding wasting time and resources. In this study, our goal was to evaluate the impact of two mechanical tissue disruption techniques on the purity and quality of RNA extracted from fresh lung biopsies. The samples were processed in parallel using manual mechanical disaggregation or an automated mechanical device. The results showed that samples processed with the automated device had a higher integrity compared to those processed manually with a median Fragmentation Index of 0.86 and 0.71 respectively. This difference is statistically significant (p = 0.0084). Overall, our results indicated that the use of automatic mechanical disaggregation could undoubtedly help to overcome the technical biases related to fresh tissues processing.</p

Applications des plasmas produits par le laser à excimères HERCULES-L : du recuit du silicium à la lithographie par rayons X

Un laser à excimères de grand volume, HERCULES-L, a été développé dans le cadre d'un programme européen pour des applications industrielles concernant le traitement de surface du silicium et la génération de plasmas par laser. Les performances de ce laser sont particulièrement adaptées pour le traitement de grandes surfaces et pour la création de photons EUV (hv ~ 100 eV) par plasma assisté par laser