1. Wiener numbers of pericondensed benzenoid hydrocarbonsSandi Klavžar, Ivan Gutman, Amal Rajapakse, 1997, izvirni znanstveni članek Opis: Using a recently developed technique for the calculation of the Wiener number (W) of benzenoid systems, we determine explicit expressions for W for several homologous series of pericondensed benzenoid hydrocarbons. An elementary proof for the correctness of the used method is also included.
Ključne besede: mathematics, chemical graph theory, distance in graphs, Wiener number, benzenoids
Objavljeno v DKUM: 05.07.2017; Ogledov: 1455; Prenosov: 171
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2. Corroborating a modification of the Wiener indexIvan Gutman, Janez Žerovnik, 2002, drugi znanstveni članki Opis: In a recent work [Chem. Phys. Lett. 333 (2001) 319-321] Nikolić, Trinajstić, and Randie put forward a novel modification ▫$^m$▫W of the Wiener index. We now show that ▫$^m$▫W possesses the basic properties required by a topological index to be acceptable as a measure of the extent of branching of the carbon-atom skeleton of the respective molecule (and therefore to be a structure-descriptor, potentially applicable in QSPR and QSAR studies). In particular, if ▫$T_n$▫ is any n-vertex tree, different from the n-vertex path ▫$P_n$▫ and the n-vertex star ▫$S_n$▫, then mw(Pn) < mW(Tn) < mW(Sn). We also show how the concept of the modified Wiener index can be extended to weighted molecular graphs.
Ključne besede: graph theory, distance, molecular graphs, modified Wiener index, weigted modified Wiener index, branching, chemical graph theory
Objavljeno v DKUM: 05.07.2017; Ogledov: 1146; Prenosov: 87
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3. A class of modified Wiener indicesIvan Gutman, Damir Vukičević, Janez Žerovnik, 2004, izvirni znanstveni članek Opis: The Wiener index of a tree T obeys the relation W(T) = Σen1(e) • n2(e) where n1(e) and n2(e) are the number of vertices on the two sides of the edge e, and where the summation goes over all edges of T. Recently Nikolić, Trinajstić and Randić put forward a novel modification mW of the Wiener index, defined as mW(T) = Σe[n1(e) • n2(e)]–1. We now extend their definition as mWλ(T) = Σe[n1(e) • n2(e)]λ, and show that some of the main properties of both W and mW are, in fact, properties of mWλ, valid for all values of the parameter λ≠0. In particular, if Tn is any n-vertex tree, different from the n-vertex path Pn and the n-vertex star Sn, then for any positive λ, mWλ(Pn) > mWλ(Tn) > mWλ(Sn), whereas for any negative λ, mWλ(Pn) < mWλ(Tn) < mWλ(Sn). Thus mWλ provides a novel class of structure-descriptors, suitable for modeling branching-dependent properties of organic compounds, applicable in QSPR and QSAR studies. We also demonstrate that if trees are ordered with regard to mWλ then, in the general case, this ordering is different for different λ.
Ključne besede: graph theory, chemical graph theory, modified Wiener index, Nikolić-Trinajstić-Randić index, branching
Objavljeno v DKUM: 05.07.2017; Ogledov: 1196; Prenosov: 100
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4. A theorem on Wiener-type invariants for isometric subgraphs of hypercubesSandi Klavžar, Ivan Gutman, 2006, izvirni znanstveni članek Opis: Let ▫$d(G,k)$▫ be the number of pairs of vertices of a graph ▫$G$▫ that are at distance ▫$k$▫, ▫$lambda$▫ a real (or complex) number, and ▫$W_lambda(G) = sum_{k ge 1}d(G,k)k^lambda$▫. It is proved that for a partial cube ▫$G$▫, ▫$W_{lambda + 1}(G) = |mathcal{F}| W_lambda(G) - sum_{mathnormal{F} in mathcal{F}} W_lambda(G setminus F)$▫ where ▫$mathcal{F}$▫ is the partition of ▫$E(G)$▫ induced by the Djokovic-Winkler relation ▫$Theta$▫. This result extends a previously known result for trees and implies several relations for distance-based topological indices.
Ključne besede: mathematics, graph theory, graph distance, hypercube, partial cube, Wiener number, hyper-Wiener indeks
Objavljeno v DKUM: 10.07.2015; Ogledov: 1388; Prenosov: 127
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5. On the role of hypercubes in the resonance graphs of benzenoid graphsKhaled Salem, Sandi Klavžar, Ivan Gutman, 2006, drugi znanstveni članki Opis: The resonance graph ▫$R(B)$▫ of a benzenoid graph ▫$B$▫ has the perfect matchings of ▫$B$▫ as vertices, two perfect matchings being adjacent if their symmetric difference forms the edge set of a hexagon of ▫$B$▫. A family ▫$mathscr{P}$▫ of pair-wise disjoint hexagons of a benzenoid graph ▫$B$▫ is resonant in ▫$B$▫ if ▫$B -- mathscr{P}$▫ contains at least one perfect matching, or if ▫$B -- mathscr{P}$▫ is empty. It is proven that there exists a surjective map ▫$f$▫ from the set of hypercubes of ▫$R(B)$▫ onto the resonant sets of B such that a ▫$k$▫-dimensional hypercube is mapped into a resonant set of cardinality ▫$k$▫.
Ključne besede: matematika, teorija grafov, benzenoidni graf, popolno prirejanje, resonančni graf, hiperkocka, mathematics, graph theory, benzenoid graph, perfect matching, resonance graph, hypercube
Objavljeno v DKUM: 10.07.2015; Ogledov: 1589; Prenosov: 79
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