1. Graphs with total mutual-visibility number zero and total mutual-visibility in Cartesian productsJing Tian, Sandi Klavžar, 2024, original scientific article Abstract: If $G$ is a graph and $X\subseteq V(G)$, then $X$ is a total mutual-visibility set if every pair of vertices $x$ and $y$ of $G$ admits a shortest $x,y$-path $P$ with $V(P) \cap X \subseteq \{x,y\}$. The cardinality of a largest total mutual-visibility set of $G$ is the total mutual-visibility number $\mu_{\rm t}(G)$ of $G$. Graphs with $\mu_{\rm t}(G) = 0$ are characterized as the graphs in which no vertex is the central vertex of a convex $P_3$. The total mutual-visibility number of Cartesian products is bounded and several exact results proved. For instance, $\mu_{\rm t}(K_n\,\square\, K_m) = \max\{n,m\}$ and $\mu_{\rm t}(T\,\square\, H) = \mu_{\rm t}(T)\mu_{\rm t}(H)$, where $T$ is a tree and $H$ an arbitrary graph. It is also demonstrated that $\mu_{\rm t}(G\,\square\, H)$ can be arbitrary larger than $\mu_{\rm t}(G)\mu_{\rm t}(H)$.
Keywords: mutual-visibility set, total mutual-visibility set, bypass vertex, Cartesian product of graphs, trees
Published in DiRROS: 26.08.2024; Views: 19; Downloads: 9
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2. Persistent homology with selective Rips complexes detects geodesic circlesŽiga Virk, 2024, original scientific article Abstract: This paper introduces a method to detect each geometrically significant loop that is a geodesic circle (an isometric embedding of $S^1$) and a bottleneck loop (meaning that each of its perturbations increases the length) in a geodesic space using persistent homology. Under fairly mild conditions, we show that such a loop either terminates a 1- dimensional homology class or gives rise to a 2-dimensional homology class in persistent homology. The main tool in this detection technique are selective Rips complexes, new custom made complexes that function as an appropriate combinatorial lens for persistent homology to detect the above mentioned loops. The main argument is based on a new concept of a local winding number, which turns out to be an invariant of certain homology classes.
Keywords: simple closed geodesic, Rips complex, persistent homology, local winding number
Published in DiRROS: 26.08.2024; Views: 17; Downloads: 8
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3. Complexity of 2-rainbow total domination problemTadeja Kraner Šumenjak, Aleksandra Tepeh, 2024, original scientific article Abstract: In this paper,we extend the findings of recent studies on $k$-rainbow total domination by placing our focus on its computational complexity aspects. We show that the problem of determining whether a graph has a $2$-rainbow total dominating function of a given weight is NP-complete. This complexity result holds even when restricted to planar graphs. Along the way tight bounds for the $k$-rainbow total domination number of rooted product graphs are established. In addition, we obtain the closed formula for the $k$-rainbow total domination number of the corona product $G ∗ H$, provided that $H$ has enough vertices.
Keywords: domination, rainbow domination, rooted product, NP-complete
Published in DiRROS: 26.08.2024; Views: 14; Downloads: 4
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4. The remedy for a world without transcendence : Georges Bataille on sacrifice and the theology of transgressionLuka Trebežnik, 2024, original scientific article Abstract: Georges Bataille is undoubtedly a key reference for all relevant contemporary thoughts about sacrifice. This article attempts to follow his impulses and intuitions, which are often misunderstood because they are highly personal, provocative, and suggestive. The problem of sacrifice is approached in three concentric circles. The first presents a view from a distance, from the cosmic standpoint of “base materialism” and “general economy.” The second takes a closer look at the sacrificial site and deals with Bataille’s fascination with Aztec sacrificial culture. The concluding third part looks at sacrifice from the point of the altar, the place of communication and communal consumption of death, as a site of the emergence of the sacred and of community. In this way, the article seeks to highlight Bataille’s transgressive thinking as a worthwhile contribution to post-metaphysical theology.
Keywords: sacrifice, transgression, violence, sacred, communication, Aztecs, Bataille
Published in DiRROS: 26.08.2024; Views: 16; Downloads: 7
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5. Analysis of eigenvalue condition numbers for a class of randomized numerical methods for singular matrix pencilsDaniel Kressner, Bor Plestenjak, 2024, original scientific article Abstract: The numerical solution of the generalized eigenvalue problem for a singular matrix pencil is challenging due to the discontinuity of its eigenvalues. Classically, such problems are addressed by first extracting the regular part through the staircase form and then applying a standard solver, such as the QZ algorithm, to that regular part. Recently, several novel approaches have been proposed to transform the singular pencil into a regular pencil by relatively simple randomized modifications. In this work, we analyze three such methods by Hochstenbach, Mehl, and Plestenjak that modify, project, or augment the pencil using random matrices. All three methods rely on the normal rank and do not alter the finite eigenvalues of the original pencil. We show that the eigenvalue condition numbers of the transformed pencils are unlikely to be much larger than the ▫$\delta$▫-weak eigenvalue condition numbers, introduced by Lotz and Noferini, of the original pencil. This not only indicates favorable numerical stability but also reconfirms that these condition numbers are a reliable criterion for detecting simple finite eigenvalues. We also provide evidence that, from a numerical stability perspective, the use of complex instead of real random matrices is preferable even for real singular matrix pencils and real eigenvalues. As a side result, we provide sharp left tail bounds for a product of two independent random variables distributed with the generalized beta distribution of the first kind or Kumaraswamy distribution.
Keywords: singular pencil, singular generalized eigenvalue problem, eigenvalue condition number, randomized numerical method, random matrices
Published in DiRROS: 26.08.2024; Views: 12; Downloads: 6
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6. Pairs of fixed points for a class of operators on Hilbert spacesAbdelhak Mokhtari, Kamel Saoudi, Dušan Repovš, 2024, original scientific article Abstract: In this paper, existence of pairs of solutions is obtained for compact potential operators on Hilbert spaces. An application to a second-order boundary value problem is also given as an illustration of our results.
Keywords: Hilbert spaces, potential operators, genus, fixed point theorem, boundary value problem
Published in DiRROS: 26.08.2024; Views: 3; Downloads: 6
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7. Preliminarno istraživanje utjecaja orijentacije vlakana u mikroarmiranim mortovimaJulien Michels, Matija Gams, 2016, original scientific article Abstract: U radu se obrađuje utjecaj čeličnih vlakana u mikroarmiranim mortovima. Uzorci morta u svježem stanju, s nasumično raspoređenim vlaknima su smješteni u spiralnu zavojnicu i izloženi elektromagnetskom polju u cilju postizanja usmjerenosti vlakana. Lokacija i orijentacija vlakana je određena rengenskom snimkom. Provedena su ispitivanja čvrstoće na savijanje uz kontrolu progiba ISC sustavom (engl. Digital Image Correlation System - ICS). S obzirom na orijentaciju vlakana, rezultati su pokazali poboljšanu disipaciju energije i veću energiju pri lomu kod uzoraka s usmjerenim vlaknima.
Published in DiRROS: 23.08.2024; Views: 91; Downloads: 61
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8. Environmental life cycle assessment of railway bridge materials using UHPFRCKarmen Fifer Bizjak, Aljoša Šajna, Katja Slanc, Friderik Knez, 2016, original scientific article Abstract: The railway infrastructure is a very important component of the world’s total transportation network. Investment in its construction and maintenance is significant on a global scale. Previously published life cycle assessment (LCA) studies performed on road and rail systems very seldom included infrastructures in detail, mainly choosing to focus on vehicle manufacturing and fuel consumption. This article presents results from an environmental study for railway steel bridge materials for the demonstration case of the Buna Bridge in Croatia. The goal of these analyses was to compare two different types of remediation works for railway bridges with different materials and construction types. In the first part, the environmental impact of the classical concrete bridge construction was calculated, whereas in the second one, an alternative new solution, namely, the strengthening of the old steel bridge with ultra-high-performance fibre-reinforced concrete (UHPFRC) deck, was studied. The results of the LCA show that the new solution with UHPFRC deck gives much better environmental performance. Up to now, results of LCA of railway open lines, railway bridges and tunnels have been published, but detailed analyses of the new solution with UHPFRC deck above the old bridge have not previously been performed.
Keywords: railway, materials, ife cycle assessment, bridge, environmental
Published in DiRROS: 23.08.2024; Views: 88; Downloads: 130
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9. Seismic behavior of strengthened URM masonry - an overview of research at ZAGPetra Triller, Miha Tomaževič, Marjana Lutman, Matija Gams, 2017, published scientific conference contribution Abstract: Four experimental campaigns performed at ZAG over almost a decade and dealing with strengthening of masonry using FRPs are briefly presented. The campaigns show in-situ tests on strengthened walls in an actual building, the cyclic shear laboratory tests where different materials and FRP layouts were explored, use of innovative flexible materials instead of mortar or epoxy, and finally the test of a full scale building model where all aspects of strengthening a building using FRPs are investigated.
Keywords: FRP, seismic strengthening, in-situ tests, laboratory tests, full scale tests
Published in DiRROS: 22.08.2024; Views: 106; Downloads: 53
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10. Modelling of deformable polymer to be used for joints between infill masonry walls and R. C. framesMatija Gams, Arkadiusz Kwiecień, Jože Korelc, Theodoros Rousakis, Alberto Viskovic, 2017, published scientific conference contribution Abstract: In the paper an idea to use a deformable polymer material for the joint between R.C. frames and masonry infills is presented. As an early step of testing the idea, experimental tests of the polymer in monotonic uniaxial tension at different load rates are performed and analyzed. The load rates range from very fast (8.3 mm/s) to very slow (0.00083 mm/s). The material exhibits a very strong strain rate effect and viscous behavior. In the second part of the paper a numerical model is developed and implemented into a finite element to simulate the results of the tests. The model is based on a new family of strain measures, called the Darjani-Naghdabadi strain measures and a classical viscosity formulation. Almost perfect model predictions up to collapse at 50-150% elongation are obtained by using calibration based on minimization of error.
Keywords: masonry infills, deformable polymer joint, viscosity, modelling
Published in DiRROS: 19.08.2024; Views: 144; Downloads: 55
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