Armantas Ostreika

Maximally diverse grouping: an iterated tabu search approach

The maximally diverse grouping problem (MDGP) consists of finding a partition of a set of elements into a given number of mutually disjoint groups, while respecting the requirements of group size constraints and diversity. In this paper, we propose an iterated tabu search (ITS) algorithm for solving this problem. We report computational results on three sets of benchmark MDGP instances of size up to 960 elements and provide comparisons of ITS to five state-of-the-art heuristic methods from the literature. The results demonstrate the superiority of the ITS algorithm over alternative approaches. The source code of the algorithm is available for free download via the internet.

Brand communication in social media: The use of image colours in popular posts

Recent scientific and theoretical studies defining brand communication in social media emphasize the significance consumer engagement in brand-related content. Popularity of brand messages and the reach of target audiences depends on consumer engagement in social media. Therefore, many business companies are seeking to increase an impact on consumers using social media analysis and consumer engagement technics. Usually, consumer actions such as likes, comments and shares in social media channels are used to estimate the popularity of brand posts. One of the factors, which has not widely analyzed before, is the impact of colors for popularity of visual brand-related posts. In this paper, we analyze the effect of colors for popularity of brand-related posts in social media. We analyze our own dataset of images collected from 35 most popular brand Facebook groups. Our results show that black, gray and brown colors were more often used in images of more popular brand-related posts.

An Ontology Oriented Approach for E-Learning Objects Design and Improvement

A Semantic Web is one of the most emerging research areas nowadays. Ontology is a formal specification of the particular domain that describes a set of objects and properties that the objects might have. The development of learning objects for integrated learning environments based on Semantic Web services (SWS) are still at a very early stage. The SWS technology allows teachers to design and personalize learning objects (LO) presented for the necessary content. The aim of this paper is to outline the state-of-the-art research along those lines and to suggest a realistic way towards the educational Semantic Web. With regard to the aim we first propose a LO design (or redesign) model on service-based interoperability framework, in order to open up, share and reuse educational systems’ content and knowledge components. The research will focus on LO design and redesign by proposing ontology-driven possibilities that reflect the modularization in the educational information systems. Some brief examples of implementation on the Virtual Campus platform of the Politehnica University Timisoara are also given.

An Iterated Tabu Search Approach for the Clique Partitioning Problem

Given an edge-weighted undirected graph with weights specifying dissimilarities between pairs of objects, represented by the vertices of the graph, the clique partitioning problem (CPP) is to partition the vertex set of the graph into mutually disjoint subsets such that the sum of the edge weights over all cliques induced by the subsets is as small as possible. We develop an iterated tabu search (ITS) algorithm for solving this problem. The proposed algorithm incorporates tabu search, local search, and solution perturbation procedures. We report computational results on CPP instances of size up to 2000 vertices. Performance comparisons of ITS against state-of-the-art methods from the literature demonstrate the competitiveness of our approach.

Block Matching Based Obstacle Avoidance for Unmanned Aerial Vehicle

Unmanned aerial vehicles (UAVs) are becoming very popular now. They have a variety of applications: search and rescue missions, crop inspection, 3D mapping, surveillance and military applications. However, many of the lower-end UAV do not have obstacle avoidance systems installed, which can lead to broken equipment or people may get injured. In this paper, we describe the design of low-cost UAV with computer vision based obstacle avoidance system. We used Block Match (BM) and Semi Global Block Match (SGBM) algorithms for detection of obstacles in stereo images. We constructed custom UAV platform, and demonstrated the effectiveness of UAV with an obstacle avoidance system in real-world field testing conditions.

Dot-Matrix Hologram Rendering Algorithm and its Validation through Direct Laser Interference Patterning

The fight against forgery of valuable items demands efficient and reasonably priced solutions. A security tag featuring holographic elements for anti-counterfeiting is one of them. However, the content and colours of a diffraction image that would be seen by an observer are often counterintuitive in the design stage. Here, we propose an original algorithm based on the conical diffraction formalism, which can be used to describe the variations of a diffraction image with respect to all aspects of observation. We validate the output of the algorithm by comparing it to test holograms, which we have produced by employing direct laser interference patterning (DLIP) in electrochemically grown nickel foil. We have employed a motorized femtosecond laser system to micro-machine arrays of 65 µm × 65 µm sized diffraction gratings with a defined orientation and pitch on the order of 1 µm. Based on completed diffraction efficiency measurements, we determined optimal ablation parameters, i.e. 57.4 mJ/cm2 fluence per pulse and 1100 pulses/pixel. Furthermore, we show how accurate the proposed algorithm is through measured diffraction spectra as well as captured diffraction images of test holograms produced using the obtained parameters. Finally, we showcase anti-counterfeiting tag prototypes with complex holographic effects, i.e. colour reconstruction, animation effects, and image multiplexing. The proposed algorithm can severely shorten the time between design and production of a holographic tag, especially when realizing it via a competitive origination technology—DLIP.

Multi-scale finite element modeling of 3D printed structures subjected to mechanical loads

Purpose The purpose of this paper is to investigate the influence of geometrical microstructure of items obtained by applying a three-dimensional (3D) printing technology on their mechanical strength. Design/methodology/approach Three-dimensional printed items (3DPI) are composite structures of complex internal constitution. The buildup of the finite element (FE) computational models of 3DPI is based on a multi-scale approach. At the micro-scale, the FE models of representative volume elements corresponding to different additive layer heights and different thicknesses of extruded fibers are investigated to obtain the equivalent non-linear nominal stress–strain curves. The obtained results are used for the creation of macro-scale FE models, which enable to simulate the overall structural response of 3D printed samples subjected to tensile and bending loads. Findings The validation of the models was performed by comparing the computed results against the experimental ones, where satisfactory agreement has been demonstrated within a marked range of thicknesses of additive layers. Certain inadequacies between computed against experimental results were observed in cases of thinnest and thickest additive layers. The principle explanation of the reasons of inadequacies takes into account the poorer quality of mutual adhesion in case of very thin extruded fibers and too-early solidification effect. Originality/value Flexural and tensile experiments are simulated by FE models that are created with consideration to microstructure of 3D printed samples.

A simple centerline extraction approach for 2D polygons

T his paper describes a new two task approach for extracting the centerline from simple 2D polygons. An algorithm of the first task, which generates a set of points for future centerline, is presented. The idea of the algorithm is to use the polygon hatching by parallel lines and creating paths from its middle points in different polygon rotations. The centerline is derived from the intersection points between these paths. The algorithm was developed for printed circuit board insulation process and its execution time for a few hundred polygons is less than one second. The algorithm is easy to understand and implement. DOI: http://dx.doi.org/10.5755/j01.itc.45.3.12964