61. Analysis of eigenvalue condition numbers for a class of randomized numerical methods for singular matrix pencilsDaniel Kressner, Bor Plestenjak, 2024, izvirni znanstveni članek Povzetek: 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.
Ključne besede: singular pencil, singular generalized eigenvalue problem, eigenvalue condition number, randomized numerical method, random matrices
Objavljeno v DiRROS: 26.08.2024; Ogledov: 73; Prenosov: 39
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62. Pairs of fixed points for a class of operators on Hilbert spacesAbdelhak Mokhtari, Kamel Saoudi, Dušan Repovš, 2024, izvirni znanstveni članek Povzetek: 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.
Ključne besede: Hilbert spaces, potential operators, genus, fixed point theorem, boundary value problem
Objavljeno v DiRROS: 26.08.2024; Ogledov: 82; Prenosov: 39
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63. Preliminarno istraživanje utjecaja orijentacije vlakana u mikroarmiranim mortovimaJulien Michels, Matija Gams, 2016, izvirni znanstveni članek Povzetek: 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.
Objavljeno v DiRROS: 23.08.2024; Ogledov: 140; Prenosov: 99
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64. Environmental life cycle assessment of railway bridge materials using UHPFRCKarmen Fifer Bizjak, Aljoša Šajna, Katja Slanc, Friderik Knez, 2016, izvirni znanstveni članek Povzetek: 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.
Ključne besede: railway, materials, ife cycle assessment, bridge, environmental
Objavljeno v DiRROS: 23.08.2024; Ogledov: 144; Prenosov: 169
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65. Seismic behavior of strengthened URM masonry - an overview of research at ZAGPetra Triller, Miha Tomaževič, Marjana Lutman, Matija Gams, 2017, objavljeni znanstveni prispevek na konferenci Povzetek: 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.
Ključne besede: FRP, seismic strengthening, in-situ tests, laboratory tests, full scale tests
Objavljeno v DiRROS: 22.08.2024; Ogledov: 149; Prenosov: 77
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66. 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, objavljeni znanstveni prispevek na konferenci Povzetek: 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.
Ključne besede: masonry infills, deformable polymer joint, viscosity, modelling
Objavljeno v DiRROS: 19.08.2024; Ogledov: 166; Prenosov: 72
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67. Optimizing process parameters of clay-based ceramics with addition of construction and demolition wasteBiljana Angjusheva, Vilma Ducman, Monika Fidancevska, Vojo Jovanov, 2021, izvirni znanstveni članek Povzetek: Construction and demolition waste produced in the Republic of North Macedonia remains a major economic and environmental problem because all construction and demolition waste ends up in local dumps or is disposed of in a landfill. The objective of this study was to investigate the influence of the process parameters on the physical and mechanical properties of clay-based ceramics with partial replacement of clay with construction and demolition waste. Determination of the chemical composition of the waste demolition brick using X-ray fluorescence showed that it consisted of different oxides such as SiO2, Al2O3, Fe2O3 and CaO and minor contents of alkaline and earth alkaline oxides. Production of these ceramics was conducted through the consolidation of clay and waste demolition brick with the evaluation of the main process parameters such as sintering temperature [ST], the content of waste demolition brick [WDB] and isothermal period at the final temperature [IP]. The final model equations for density and bending strength dependence of the main process parameters were obtained and presented. The microstructure of the ceramics determined by SEM shows that the waste material is homogeneously dispersed in the clay matrix.
Ključne besede: CDW, clay, ceramics, properties
Objavljeno v DiRROS: 19.08.2024; Ogledov: 159; Prenosov: 91
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68. Krožni in nizko-ogljični gradbeni proizvodiJanez Turk, Tajda Potrč Obrecht, Katja Malovrh Rebec, Patricija Ostruh, 2023, elaborat, predštudija, študija Ključne besede: smernica, sekundarni proizvodi, ponovna uporaba, reciklaža, LCA
Objavljeno v DiRROS: 19.08.2024; Ogledov: 159; Prenosov: 554
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69. Vpliv dodatka nanofibrilirane celuloze na mehanske lastnosti poli(3-hidroksibutirata)Vesna Žepič Bogataj, Erika Švara Fabjan, Ida Poljanšek, Primož Oven, 2017, izvirni znanstveni članek Povzetek: Namen prispevka temelji na inovativnem postopku izdelave nanokompozitov na osnovi poli(3-hidroksibutirata) (PHB) in nanofibrilirane celuloze (NFC). Raziskovalno delo obravnava pripravo koncentratnih mešanic PHB-prahu in NFC v vodni raztopini za tehnologijo ekstruzijskega mešanja. Ekstrudat koncentrirane mešanice PHB/NFC je bil nato uporabljen kot dodatek h granulirani obliki PHB pri pripravi brizganih vzorcev z različnimi utežnimi deleži NFC. V prispevku so podane določene omejitve pri predelavi tovrstnih materialov in predlagane uporabne rešitve za njihovo optimiziranje. Morfološke lastnosti nanokompozitnih komponent smo raziskali z elektronsko mikroskopijo (FE-SEM), mehanske lastnosti pa z nateznim preizkusom. Morfološka preiskava koncentratnih mešanic je razkrila prepleteno sestavo celuloznih nanofibril in polimernih kroglic, pri čemer se posamezne fibrile prepletajo v obliki širših pramenov in ustvarjajo videz zamrežene strukture znotraj polimerne komponente. Mikroskopski posnetki nanokompozitnih mešanic in izboljšane mehanske lastnosti izhodnih materialov potrjujejo,da je adhezivni stik med matrično in ojačitveno komponento dosežen, porazdelitev celuloznih nanofibril po polimerni osnovi pahomogena. Nanokompoziti z visokimi utežnimi deleži NFC (10 % utežnega deleža) dosegajo pomembno večje vrednosti modula elastičnosti (Et = 1720 MPa) in raztezka pri pretrgu (b = 3,1 %) ter prenesejo višje pretržne napetosti ( M = 26 MPa) v primerjavi z referenčnim polimernim vzorcem (Et = 1340 MPa;b = 2,4 %; M = 20 MPa). Rezultati študije dokazujejo, da je ob pravilni predpripravi polimernih mešanic in optimizaciji tehnologije ekstruzijske predelave, mogoče izdelati trdne in žilave materiale, pri čemer delež ojačitvene faze narekuje stopnjo izboljšave končnih lastnosti biopolimerne osnove.
Ključne besede: nanofibrilirana celuloza, poli(3-hidroksibutirat), morfologija, mehanske lastnosti, ekstruzija, tehnologija brizganja
Objavljeno v DiRROS: 14.08.2024; Ogledov: 213; Prenosov: 112
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70. Comparison of the mineralogy and microstructure of EAF stainless steel slags with reference to the cooling treatmentMojca Loncnar, Ana Mladenovič, Marija Zupančič, Peter Bukovec, 2017, izvirni znanstveni članek Povzetek: TIn the present study the differences in the mineralogical composition and microstructure of various types of EAF stainless steel (EAF S) slag with regard to the cooling treatment, the operation practice in an EAF (electric arc furnace) and environmental ageing reactions were evaluated. It was shown that the mineralogy of the investigated EAF S slags varied from one slag to another, depending on the quality of the produced stainless steel. The production process of the treated steel also has a strong influence on the mineralogy of the slags. The conditions during water cooling treatment were not sufficient to prevent the crystallization of primary mineral phases, which occurs predominantly in air-cooled EAF S slags, probably due to the high basicity of the investigated slags. However, the water cooling treatment of hot slag leads to the absence of γ-CaSiO 4 and the formation of secondary mineral phases predominantly calcite, portlandite, ettringite, calcium aluminate hydrate and calcium silicate hydrate. It has been shown that during the environmental ageing test (down-flow column test) secondary mineral phases were formed, which were the same as those formed during the water cooling treatment.
Ključne besede: electric arc furnace stainless steel slag, cooling path, microstructure, mineralogy
Objavljeno v DiRROS: 14.08.2024; Ogledov: 197; Prenosov: 125
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