Enhancing the performance of hybrid genetic algorithms by differential improvement

A differential improvement modification to Hybrid Genetic Algorithms is proposed. The general idea is to perform more extensive improvement algorithms on higher quality solutions. Our proposed Differential Improvement (DI) approach is of rather general character. It can be implemented in many different ways. The paradigm remains invariant and can be easily applied to a wider class of optimization problems. Moreover, the DI framework can also be used within other Hybrid metaheuristics like Hybrid Scatter Search algorithms, Particle Swarm Optimization, or Bee Colony Optimization techniques.     

Laser-induced transformation of a-C:H thin films

In this work, we report the laser irradiation effects on the properties of various types of amorphous hydrogenated carbon (a-C:H) films. The influence of the initial carbon film (hydrogen concentration, sp³/sp² ratio, and sp² clustering) is studied. The results show that a loss of hydrogen and an increase of the sp² phase are the main processes in the laser power range between 1.8 and 5 MW/cm². Only these processes are stronger for “more polymer-like” and “graphite-like” films than for “more diamond-like” films.     

The role of hydrogen in a-C:H films deposited from hexane or acetylene using direct ion beam deposition method

The present work provides results of amorphous hydrogenated carbon (a-C:H) films deposited by direct ion beam deposition method. Hexane (C₆H₁₄+H_delivery) or acetylene (C₂H₂) precursors and their mixture with hydrogen (H₂) were used. The films were characterized by Raman spectroscopy (RS), ellipsometry, and electrical resistance measurements. RS indicates increase in sp³/sp² bonding ratio and disorder in graphite clusters, upon increasing of hydrogen content (from 0% to 50% for acetylene precursor) in the deposition gas mixture. The opposite trend is observed when the hydrogen concentration exceeded 50% (for acetylene) or additional hydrogen was added (for hexane). The data of electrical resistance measurements support the correlations defined by RS.     

Deposition and structure characterization of carbon films prepared at atmospheric pressure by plasma jet

Amorphous carbon films were deposited on stainless steel substrates by plasma jet chemical vapor deposition (PJCVD). The carbon coatings have been prepared at atmospheric pressure in an argon/acetylene mixture. The Ar/C₂H₂ gas volume ratio varied from 100:1 to 200:1, while the distance between the plasma torch nozzle exit and the samples was 0.005–0.02 m. Scanning electron microscope analysis demonstrated that the surface roughness and growth rate of the coatings increase with the decrease of the Ar/C₂H₂ ratio. The ERDA results showed that the hydrogen concentration rises from 5 at.% to 27 at.% with the increase of the distance from 0.005 to 0.02 m. The increase of the Ar/C₂H₂ ratio from 100:1 to 200:1 slightly increases the hydrogen and oxygen concentration in the films. The Raman spectroscopy results indicated that the sp³ C–C carbon sites are replaced by sp³ CH_2–3 bonds with the increase of the deposition distance. The microhardness of the carbon films deposited at 0.005 m was in range of 7.1–9.3 GPa.     

Multifunctional iron and iron oxide nanoparticles in silica

Iron and iron oxide nanoparticles in silica layers deposited by sol–gel techniques on Si wafers were formed and studied. It was shown that multifunctional nanoparticles of different iron oxides possessing various physical properties can be fabricated by means of post-growth annealing of (SiO₂:Fe)/SiO₂/Si samples in various atmospheres. The hematite, maghemite, and iron nanoparticles were found to be dominant upon annealing the samples in air, argon, and hydrogen atmosphere, respectively. The physical properties of produced hybrid structures were studied by Raman and FT-IR spectroscopy, spectroscopic ellipsometry, AFM, and magnetic measurements. The sol–gel technique with subsequent annealing procedure is demonstrated to be an effective method for the formation of multifunctional hybrid structures composed of iron or iron oxide nanoparticles in silica matrix.     

The influence of nanosecond pulse laser irradiation on the properties of a-C:H films

Plasma-deposited amorphous hydrogenated carbon (a-C:H) films are determined both by the carbon sp³/sp² bonding ratio and the hydrogen content. As the energy of the bonds C-H (C-C) is considerably smaller than that of CC or CC bonds, so the hydrogen concentration and the physical properties of a-C:H films can be varied by laser irradiation. The properties of produced films were investigated by Rutherford backscattering (RBS) and elastic recoil detection (ERD) spectroscopy, null-ellipsometry, and Raman spectroscopy (RS). It was found that films with higher hydrogen concentration are more sensitive to nanosecond pulse laser irradiation.     

Hydrogen influence on the structure and properties of amorphous hydrogenated carbon films deposited by direct ion beam

The present work provides results for amorphous hydrogenated carbon (a-C:H) films grown by direct ion beam deposition method. Acetylene and its mixtures with hydrogen were used. The films were characterized by Rutherford backscattering spectrometry, elastic recoil detection, Raman spectroscopy, ellipsometry, infrared spectroscopy, and microhardness measurements. These techniques indicated that an admixture of hydrogen yields a lower deposition rate, a higher content of total and bounded hydrogen in the a-C:H films, and a lower film density. The optical and mechanical properties depend on both, hydrogen concentrations in the gas phase and in the films, and show a strong diamond-like component, which reaches maximum at 34 at.% of hydrogen. Further hydrogen dilution enhanced only sp² clustering and possible reduced a number of both sp³ and C-C sp³ bonds. We suppose that these effects (in the high hydrogen concentration range) are not only related to the ion irradiation difference between the light hydrogen and the much heavier carbon but also to the diffusion in the a-C:H films.     

Multicriteria Evaluation of Building Foundation Alternatives

In real conditions, decision makers usually deal with multiple objectives and should make a decision in a state of certainty or uncertainty. The selection of the best constructions for a building from a number of alternatives is of great importance for owners, contractors, and stakeholders. Dozens of multicriteria/multi‐attribute decision‐making (MCDM/MADM) models developed for evaluating the performance of the available alternatives can be used for selecting the most suitable alternative from a given finite set of options based on a set of attributes. A guide to systematic selection among the available alternatives of building structures is the integrated methodology, thoroughly analyzed in the article. The article presents a MCDM model for selecting the type of foundation for a single‐storey dwelling house based on the WASPAS‐G (Weighted Aggregated Sum Product Assessment) method and Analytic Hierarchy Process (AHP) approach. The aggregate criteria weights are determined by using the AHP and experts’ judgement methods.     

An implementation of the iterated tabu search algorithm for the quadratic assignment problem

In this paper, we describe an implementation of the iterated tabu search (ITS) algorithm for the quadratic assignment problem (QAP), which is one of the well-known problems in combinatorial optimization. The medium- and large-scale QAPs are not, to this date, practically solvable to optimality, therefore heuristic algorithms are widely used. In the proposed ITS approach, intensification and diversification mechanisms are combined in a proper way. The goal of intensification is to search for good solutions in the neighbourhood of a given solution, while diversification is responsible for escaping from local optima and moving towards new regions of the search space. In particular, the following enhancements were implemented: new formula for fast evaluation of the objective function and efficient data structure; extended intensification mechanisms (including randomized tabu criterion, combination of tabu search and local search, dynamic tabu list maintaining); enhanced diversification strategy using periodic tabu tenure and special mutation procedure. The ITS algorithm is tested on the different instances taken from the QAP library QAPLIB. The results from the experiments demonstrate promising efficiency of the proposed algorithm, especially for the random QAP instances.