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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: 60; Downloads: 0
.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: 24; Downloads: 0
.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: 37; Downloads: 0
.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: 28; Downloads: 0
.pdf Full text (719,06 KB)

Cross-linked porous poly(acrylic acid-co-acrylamide) from high internal phase emulsions: preparation and functionalisation
Janja Majer, Peter Krajnc, 2009, original scientific article

Abstract: By using emulsions with high volume fractions of internal phase as polymerisation media porous copolymers of acrylic acid and acrylamide, cross-linked by methylenebisacrylamide, were prepared. The ratio of acrylic acid to acrylamide were varied (molar ratios 70:30, 50:50, 30:70) in order to yield polymers with various loading of acidic functional groups. Porous polymers with an open-cellular architecture were obtained with void diameters between 2.8 μm and 3.9 μm and with interconnecting pores approx. 0.3 μm in diameter. The chemical composition of the polymers influenced the conversion degrees during the process of functionalisation of acidic groups to acid chloride, being the highest in the case of polymer with the lowest content of acrilyc acid.
Keywords: porous monoliths, copolymers, polyacrylic acid, polyacrylamide, plyHIPE, high internal phase emulsion
Published: 17.08.2017; Views: 53; Downloads: 0
.pdf Full text (218,85 KB)

The number of moves of the largest disc in shortest paths on Hanoi graphs
Simon Aumann, Katharina Götz, Andreas Hinz, Ciril Petr, 2014, original scientific article

Abstract: In contrast to the widespread interest in the Frame-Stewart conjecture (FSC) about the optimal number of moves in the classical Tower of Hanoi task with more than three pegs, this is the first study of the question of investigating shortest paths in Hanoi graphs ▫$H_p^n$▫ in a more general setting. Here ▫$p$▫ stands for the number of pegs and ▫$n$▫ for the number of discs in the Tower of Hanoi interpretation of these graphs. The analysis depends crucially on the number of largest disc moves (LDMs). The patterns of these LDMs will be coded as binary strings of length ▫$p-1$▫ assigned to each pair of starting and goal states individually. This will be approached both analytically and numerically. The main theoretical achievement is the existence, at least for all ▫$n \geqslant p(p-2)$▫, of optimal paths where ▫$p-1$▫ LDMs are necessary. Numerical results, obtained by an algorithm based on a modified breadth-first search making use of symmetries of the graphs, lead to a couple of conjectures about some cases not covered by our ascertained results. These, in turn, may shed some light on the notoriously open FSC.
Keywords: graph theory, Tower of Hanoi, Hanoi graphs, shortest paths, symmetries, breadth-first search
Published: 14.08.2017; Views: 55; Downloads: 2
.pdf Full text (376,70 KB)

Link prediction in multiplex online social networks
Mahdi Jalili, Yasin Orouskhani, Milad Asgari, Nazanin Alipourfard, Matjaž Perc, 2017, original scientific article

Abstract: Online social networks play a major role in modern societies, and they have shaped the way social relationships evolve. Link prediction in social networks has many potential applications such as recommending new items to users, friendship suggestion and discovering spurious connections. Many real social networks evolve the connections in multiple layers (e.g. multiple social networking platforms). In this article, we study the link prediction problem in multiplex networks. As an example, we consider a multiplex network of Twitter (as a microblogging service) and Foursquare (as a location-based social network). We consider social networks of the same users in these two platforms and develop a meta-path-based algorithm for predicting the links. The connectivity information of the two layers is used to predict the links in Foursquare network. Three classical classifiers (naive Bayes, support vector machines (SVM) and K-nearest neighbour) are used for the classification task. Although the networks are not highly correlated in the layers, our experiments show that including the cross-layer information significantly improves the prediction performance. The SVM classifier results in the best performance with an average accuracy of 89%.
Keywords: social networks, complex networks, signed networks, link prediction, machine learning
Published: 08.08.2017; Views: 56; Downloads: 1
.pdf Full text (940,17 KB)

Morphological evolution of the skull in closely related bandicoot rats
Boris Kryštufek, Franc Janžekovič, Rainer Hutterer, Tina Klenovšek, 2016, original scientific article

Abstract: We addressed the effects of phylogeny, ecology, and allometry on shape variation in ventral cranium, mandible and maxillary tooth-row in all five extant bandicoot rats. These rats are classified into two genera (Bandicota and Nesokia) and occupy different ecological niches along fossorial to aquatic gradient. The analysed structures are controlled by different gene loci, have diverse developmental patterns and different functional roles what induced us to hypothesize that they respond differently to the interplay between phylogenetic constrains and selective pressures. This was indeed the case in our results. Ventral cranial shape contained an apparent phylogenetic signal at various levels of taxonomic hierarchy of bandicoot rats and therefore accurately replicated the taxonomic hierarchy within the group. Molar crowns, which are less rich in anatomical complexity than the ventral cranium, provided a taxonomic grouping that was less straightforward in comparison with the skull. The phylogenetic signal was diluted in the mandible, probably by adaptive trends for the ecological niche. Unsurprisingly, an ecological gradient from a fossorial to aquatic ecotype explained 19.1% of mandibular shape variation. The major differences between ecotypes were on mandibular landmarks associated with insertion of major muscles that move the mandible during chisel-tooth drilling in fossorial B. bengalensis and N. indica. Among the three structures, the mandible was also the most affected by allometry, with size accounting for 14.0% of shape variability. Nesokia and Bandicota are by far the youngest murine taxa still attributed to a generic level. Small genetic differences however sharply contrast with unique shape features, evident in craniodental structures of these rats. This is particularly relevant for the endangered N. bunnii which is only known from a small range and peripheral isolate in Iraq. Morphological uniqueness emphasizes its ‘value’ in conservation policies more accurately than genetic metrics, making it more “visible” in a bunch of pest rats.
Keywords: fossorial ecotype, mandible, molars, phenotypic plasticity, phylogenetic structuring
Published: 07.08.2017; Views: 26; Downloads: 1
.pdf Full text (7,18 MB)

Computation of focus quantities of three-dimensional polynomial systems
Valery Romanovski, Douglas Shafer, 2014, original scientific article

Abstract: Fix a collection of polynomial vector fields on $R^3$ with a singularity at the origin, for every one of which the linear part at the origin has two pure imaginary and one non-zero eigenvalue. Some such systems admit a local analytic first integral, which then defines a local center manifold of the system.Conditions for existence of a first integral are given by the vanishing certain polynomial or rational functions in the coefficients of the system called focus quantities. In this paper we prove that the focus quantities have a structure analogous to that in the two-dimensional case and use it to formulate an efficient algorithm for computing them.
Keywords: integrability, focus quantities, center conditions
Published: 07.08.2017; Views: 40; Downloads: 0
.pdf Full text (486,16 KB)

New data on distribution of the European pond turtle Emys orbicularis (Linnaeus, 1758) in the Podravje region (NE Slovenia)
Marijan Govedič, Milan Vogrin, Dejan Bordjan, Dominik Bombek, Damijan Denac, Tatjana Gregorc, Franc Janžekovič, Nino Kirbiš, Melita Vamberger, 2016, short scientific article

Abstract: Ten new observations of the European pond turtle Emys orbicularis (Linnaeus, 1758) in the Podravje region are presented. One observation is fairly old, while the others have been made in the last six years. Most of the data are just random observations and do not give a complete overview of the species distribution in the Podravje region. New data suggest that the European pond turtle is more abundant in the Drava River basin than previously known. Distribution and population size of the species in the Drava River basin still remain to be investigated in detail and not only at the Natura 2000 Drava site, especially in the areas of potential habitats prior to planning any new activities.
Keywords: European pond turtle, Emys orbicularis, Drava river, Podravje, Slovenia
Published: 07.08.2017; Views: 33; Downloads: 1
.pdf Full text (363,19 KB)

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