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Robust clustering of languages across Wikipedia growth
Kristina Ban, Matjaž Perc, Zoran Levnajić, 2017, original scientific article

Abstract: Wikipedia is the largest existing knowledge repository that is growing on a genuine crowdsourcing support. While the English Wikipedia is the most extensive and the most researched one with over 5 million articles, comparatively little is known about the behaviour and growth of the remaining 283 smaller Wikipedias, the smallest of which, Afar, has only one article. Here, we use a subset of these data, consisting of 14 962 different articles, each of which exists in 26 different languages, from Arabic to Ukrainian. We study the growth of Wikipedias in these languages over a time span of 15 years. We show that, while an average article follows a random path from one language to another, there exist six well-defined clusters of Wikipedias that share common growth patterns. The make-up of these clusters is remarkably robust against the method used for their determination, as we verify via four different clustering methods. Interestingly, the identified Wikipedia clusters have little correlation with language families and groups. Rather, the growth of Wikipedia across different languages is governed by different factors, ranging from similarities in culture to information literacy.
Keywords: Wikipedia, language, growth dynamics, data analysis, clustering
Published: 13.11.2017; Views: 13; Downloads: 0
.pdf Full text (1004,06 KB)

Second-order free-riding on antisocial punishment restores the effectiveness of prosocial punishment
Attila Szolnoki, Matjaž Perc, 2017, original scientific article

Abstract: Economic experiments have shown that punishment can increase public goods game contributions over time. However, the effectiveness of punishment is challenged by second-order free-riding and antisocial punishment. The latter implies that noncooperators punish cooperators, while the former implies unwillingness to shoulder the cost of punishment. Here, we extend the theory of cooperation in the spatial public goods game by considering four competing strategies, which are traditional cooperators and defectors, as well as cooperators who punish defectors and defectors who punish cooperators. We show that if the synergistic effects are high enough to sustain cooperation based on network reciprocity alone, antisocial punishment does not deter public cooperation. Conversely, if synergistic effects are low and punishment is actively needed to sustain cooperation, antisocial punishment does is viable, but only if the cost-to-fine ratio is low. If the costs are relatively high, cooperation again dominates as a result of spatial pattern formation. Counterintuitively, defectors who do not punish cooperators, and are thus effectively second-order free-riding on antisocial punishment, form an active layer around punishing cooperators, which protects them against defectors that punish cooperators. A stable three-strategy phase that is sustained by the spontaneous emergence of cyclic dominance is also possible via the same route. The microscopic mechanism behind the reported evolutionary outcomes can be explained by the comparison of invasion rates that determine the stability of subsystem solutions. Our results reveal an unlikely evolutionary escape from adverse effects of antisocial punishment, and they provide a rationale for why second-order free-riding is not always an impediment to the evolutionary stability of punishment.
Keywords: complex systems, interdisciplinary physics, punishment, cooperation
Published: 13.11.2017; Views: 13; Downloads: 0
.pdf Full text (1,15 MB)

Strong edge geodetic problem in networks
Paul Manuel, Sandi Klavžar, Antony Xavier, Andrew Arokiaraj, Elizabeth Thomas, 2017, original scientific article

Abstract: Geodesic covering problems form a widely researched topic in graph theory. One such problem is geodetic problem introduced by Harary et al. Here we introduce a variation of the geodetic problem and call it strong edge geodetic problem. We illustrate how this problem is evolved from social transport networks. It is shown that the strong edge geodetic problem is NP-complete. We derive lower and upper bounds for the strong edge geodetic number and demonstrate that these bounds are sharp. We produce exact solutions for trees, block graphs, silicate networks and glued binary trees without randomization.
Keywords: geodetic problem, strong edge geodetic problem, computational complexity, transport networks
Published: 03.11.2017; Views: 17; Downloads: 0
.pdf Full text (657,86 KB)

Mitigating the conflict between pitfall-trap sampling and conservation of terrestrial subterranean communities in caves
Peter Kozel, Tanja Pipan, Nina Šajna, Slavko Polak, Tone Novak, 2017, original scientific article

Abstract: Subterranean habitats are known for their rich endemic fauna and high vulnerability to disturbance. Many methods and techniques are used to sample the biodiversity of terrestrial invertebrate fauna in caves, among which pitfall trapping remains one of the most frequently used and effective ones. However, this method has turned out to be harmful to subterranean communities if applied inappropriately. Traditionally, pitfall traps have been placed in caves solely on the ground. Here we present an optimized technique of pitfall trapping to achieve a balance between sampling completeness and minimal disturbance of the fauna in the cave. Monthly we placed traps for two days in two parallel sets, a ground trap and an upper one−just below the ceiling−along the cave. In the upper set, about 10% additional species were recorded compared to the ground set. Greater species diversity in the cave was the consequence of both the increased sampling effort and the amplified heterogeneity of sampled microhabitats. In caves sampled by traditional pitfall trapping, overlooked species may be a consequence of methodological biases, leading to lower biodiversity estimates. In our research, incidence-based estimations mostly surpassed abundance-based ones and predicted 95% coverage of the species richness within about two years of sampling. The sampling used contributes at the same time to both the more effective and less invasive inventory of the subterranean fauna. Thus, it may serve as an optional sampling to achieve optimal balance between required data for biodiversity and ecological studies, and nature conservation goals.
Keywords: biodiversity estimators, microhabitats, sampling effort, sampling techniques, biological inventories
Published: 30.10.2017; Views: 19; Downloads: 0
.pdf Full text (2,53 MB)

Relation between plant species diversity and landscape variables in Central-European dry grassland fragments and their successional derivates
Igor Paušič, Danijel Ivajnšič, Mitja Kaligarič, Nataša Pipenbaher, 2017, original scientific article

Abstract: A systematic field survey of an area of 843 ha in the traditional Central-European agricultural landscape of Goričko Nature Park in Slovenia revealed 80 fragments of dry semi-natural grasslands. Vascular plant species diversity was studied in relation to landscape variables and to threat (Slovenian red-listed species). Our results show that fragment size does not affect plant species diversity. In addition, fragment shape index is not related to Alpha diversity. Higher Alpha diversity was observed for abandoned grassland fragments. The lowest Alpha diversity was perceived on more mesic fragments, where habitat specialists are much scarcer. It was confirmed that the highest diversity of specialists are in the driest fragments, both still mowed and abandoned. With an increase in the number of distinctly different bordering habitat types, the total number of species per fragment generally does not increase, except in the case of those fragments that are already in different succession stages. Abandoned and typical dry grasslands are associated with a higher number of bordering habitats. Typical dry grassland fragments and abandoned ones, which probably derived mostly from drier (less productive) grasslands, are found on lower altitude and have a lower shape index. Habitat specialists Sedum sexangulare, Polygala vulgaris and Spiranthes spiralis have higher frequency in fragments with a lower shape index. This means that these oligotrophic specialists occur in smaller fragments. But Orchis morio has higher frequencies of occurrence on polygons with a higher shape index, which confirms the observation that this species occurs in larger and more irregular fragments, as well as close to houses and fields and along the roads.
Keywords: habitat specialists, traditional agricultural landscape, semi-natural dry grasslands, Goričko Nature Park, NE Slovenia
Published: 24.10.2017; Views: 28; Downloads: 2
.pdf Full text (1,03 MB)

Kako učitelji kemije udejanjajo svoje potrebe profesionalnega razvoja v sistemu nadaljnjega izobraževanja in usposabljanja
Darinka Sikošek, Branka Čagran, 2016, original scientific article

Abstract: Osnovni namen nadaljnjega izobraževanja in usposabljanja kot oblike vseživljenjskega učenja je zagotavljanje profesionalnega razvoja in strokovne ter osebnostne rasti različnih poklicnih profilov, tudi učiteljev. Prav vrsta in kakovost programov, namenjenih nadaljnjemu izobraževanju in usposabljanju strokovnih delavcev v vzgoji in izobraževanju, posebej učiteljem kemije, predstavlja osrednjo temo pričujočega prispevka. Izhajajoč iz rezultatov opravljene empirične raziskave, ki smo jo izvedli na vzorcu učiteljev kemije v slovenskih osnovnih in srednjih šolah, ugotavljamo, da je želja po razvoju kompetenc poglavitno gibalo (lat. nervus rerum) njihove udeležbe v programih iz Kataloga programov nadaljnjega izobraževanja in usposabljanja, glavno oviro pa predstavlja neustrezen čas izvedbe programov (glede pedagoških obveznosti učiteljev). Seveda se učitelji najpogosteje udeležujejo posodobljenih programov, kakor tudi programov izven Kataloga.
Keywords: izobraževanje učiteljev, profesionalni razvoj, strokovna usposobljenost, kemija
Published: 21.09.2017; Views: 27; Downloads: 2
.pdf Full text (172,17 KB)

Link prediction on Twitter
Sanda Martinčić-Ipšić, Edvin Močibob, Matjaž Perc, 2017, original scientific article

Abstract: With over 300 million active users, Twitter is among the largest online news and social networking services in existence today. Open access to information on Twitter makes it a valuable source of data for research on social interactions, sentiment analysis, content diffusion, link prediction, and the dynamics behind human collective behaviour in general. Here we use Twitter data to construct co-occurrence language networks based on hashtags and based on all the words in tweets, and we use these networks to study link prediction by means of different methods and evaluation metrics. In addition to using five known methods, we propose two effective weighted similarity measures, and we compare the obtained outcomes in dependence on the selected semantic context of topics on Twitter. We find that hashtag networks yield to a large degree equal results as all-word networks, thus supporting the claim that hashtags alone robustly capture the semantic context of tweets, and as such are useful and suitable for studying the content and categorization. We also introduce ranking diagrams as an efficient tool for the comparison of the performance of different link prediction algorithms across multiple datasets. Our research indicates that successful link prediction algorithms work well in correctly foretelling highly probable links even if the information about a network structure is incomplete, and they do so even if the semantic context is rationalized to hashtags.
Keywords: link prediction, data mining, Twitter, network analysis
Published: 15.09.2017; Views: 141; Downloads: 5
.pdf Full text (6,98 MB)

Two new zinc(II) acetates with 3- and 4-aminopyridine
Brina Dojer, Andrej Pevec, Ferdinand Belaj, Matjaž Kristl, 2015, original scientific article

Abstract: The synthesis and characterization of two new zinc(II) coordination compounds with 3- and 4-aminopyridine are reported. They were obtained after adding a water solution of $Zn(CH_3COO)_2$ · $2H_2O$ or dissolving solid $Zn(CH_3COO)_2$ · $2H_2O$ in methanol solutions of 3- and 4-aminopyridine. The products were characterized structurally by single-crystal X-ray diffraction analysis. Colourless crystals of the compound synthesized by the reaction of $Zn(CH_3COO)_2$ · $2H_2O$ and 3-aminopyridine (3-apy), are built of trinuclear complex molecules with the formula $[Zn_3(O_2CCH_3)_6(3- apy)_2(H_2O)_2]$(1). The molecules consists of two terminal $Zn$ atoms, coordinated tetrahedrally, and one central $Zn$ atom, coordinated octahedrally. Colourless crystals, obtained by the reaction of $Zn(CH_3COO)_2$ · $2H_2O$ with 4-aminopyridine (4-apy), consist of a mononuclear complex $[Zn(O_2CCH_3)_2(4-apy)_2]$(2). Hydrogen-bonding interactions in the crystal structures of both complexes are reported.
Keywords: zinc(II) acetate dihydrate, aminopyridine, x-ray crystal structure, hydrogen bonds
Published: 30.08.2017; Views: 51; Downloads: 2
.pdf Full text (1,06 MB)

Omega polynomial revisited
Mircea V. Diudea, Sandi Klavžar, 2010, original scientific article

Abstract: Omega polynomial was proposed by Diudea (Omega Polynomial, Carpath. J. Math., 2006, 22, 43-47) to count the opposite topologically parallel edges in graphs, particularly to describe the polyhedral nanostructures. In this paper, the main definitions are re-analyzed and clear relations with other three related polynomials are established. These relations are supported by close formulas and appropriate examples.
Keywords: mathematics, chemical graph theory, counting polynomials, Ommega polynomial, Theta polynomial, Pi polynomial, PI index, Sadhana polynomial, Cluj-Ilmenau index, CI index
Published: 24.08.2017; Views: 57; Downloads: 3
.pdf Full text (263,85 KB)

Roman domination number of the Cartesian products of paths and cycles
Polona Pavlič, Janez Žerovnik, 2012, original scientific article

Abstract: Roman domination is a historically inspired variety of general domination such that every vertex is labeled with labels from $\{0,1,2\}$. Roman domination number is the smallest of the sums of labels fulfilling condition that every vertex, labeled 0, has a neighbor, labeled 2. Using algebraic approach we give ▫$O(C)$▫ time algorithm for computing Roman domination number of special classes of polygraphs (rota- and fasciagraphs). By implementing the algorithm we give formulas for Roman domination number of the Cartesian products of paths and cycles ▫$P_n \Box P_k$▫, ▫$P_n \Box C_k$▫ for ▫$k \leq 8$▫ and ▫$n \in {\mathbb N}$▫ and for ▫$C_n \Box P_k$▫ and ▫$C_n \Box C_k$▫ for ▫$k \leq 5$▫, ▫$n \in {\mathbb N}$▫. We also give a list of Roman graphs among investigated families.
Keywords: graph theory, Roman domination number, Cartesian product, polygraphs, path algebra
Published: 23.08.2017; Views: 53; Downloads: 0
.pdf Full text (719,06 KB)

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