1. Maximum independent sets in direct products of cycles or trees with arbitrary graphsTjaša Paj, Simon Špacapan, 2015, izvirni znanstveni članek Opis: The direct product of graphs ▫$G = (V(G),E(G))$▫ and ▫$H = (V(H),E(H))$▫ is the graph, denoted as ▫$G \times H$▫, with vertex set ▫$V(G \times H) = V(G )\times V(H)$▫, where vertices ▫$(x_1,y_1)$▫ and ▫$(x_2,y_2)$▫ are adjacent in ▫$G \times H$▫ if ▫$x_1x_2 \in E(G)$▫ and ▫$y_1y_2 \in E(H)$▫. Let ▫$n$▫ be odd and ▫$m$▫ even. We prove that every maximum independent set in ▫$P_n \times G$▫, respectively ▫$C_m \times G$▫, is of the form ▫$(A \times C) \cup (B \times D)$▫, where ▫$C$▫ and ▫$D$▫ are nonadjacent in ▫$G$▫, and ▫$A \cup B$▫ is the bipartition of ▫$P_n$▫ respectively ▫$C_m$▫. We also give a characterization of maximum independent subsets of ▫$P_n \times G$▫ for every even ▫$n$▫ and discuss the structure of maximum independent sets in ▫$T \times G$▫ where ▫$T$▫ is a tree. Ključne besede: direct product, independent set Objavljeno: 07.04.2017; Ogledov: 90; Prenosov: 0 Polno besedilo (173,48 KB) |
2. Factors influencing the yielding constraint by cracked welded componentsDražan Kozak, Jelena Vojvodič-Tuma, Nenad Gubeljak, Damir Semenski, 2005, izvirni znanstveni članek Opis: The effect of strength mismatch for welded joints performed with different geometries on the yielding constraint has been investigated in the context of single-edged fracture-toughness specimens subjected to bending SE(B) using the finite-element method. The crack was located in the centre of the weld. Two geometri cal parameters have been identified as being the most important: the crack-Iength ratio a/W and the sIenderness of the welded joint (W-a)/H. They were systematically varied as follows: a/W = 0.1; 0.2; 0.3; 0.4; 0.5 and W = 2H, 4H, 8H, 16H, 24H. Basic equations and plane-strain finite-element solutions for the overmatched SE(B) specimen with all configuration combinations are given. The results are in good agreement with those in literature. This paper aims to establish yield-Ioad solutions for the same weldment configurations, but with materials dissimilarity present within the weld. This situation is usually encountered during repair welding. For this purpose, a practical combination of filler materials, with the same portion of overmatched part with M = 1.19 and undermatched part with M = 0.86, has been selected. Plane-strain solutions for the heterogeneous weld with the cracklocated in the overmatched half were obtained. The influence of the yielding-constraint key parameters has al so been evaluated. Yield-Ioad results for the specimens performed with different weld widths have the greatest scattering for the a/W = 0.5. The transition from the overmatched to the undermatched solution with increasing H is evident. On the other hand, the behaviour of the specimen with a shallow crack is dictated by the overmatch region ahead of the crack tip and depends very little on the weld slenderness. An approximated 3-D area of the yield-Ioad solutions depending ona/W and (W-a)lH has been proposed. Furthermore, the stress triaxility parameter h has been calculated using 2-D and 3-D finite-element analysis, and given as a field in the spec imen to get an insight into yielding-constraint regions. It was found that the 3-D yield-Ioad solutions are very close to the plane-strain solutions. Also, the effect of a/W on the yielding constraint is more significant than the effect of Mand (W-a)/H. Ključne besede: welded structures, welded joints, fracture mechanics, cracks, SE(B) specimens, yielding load, yielding constraint parameters Objavljeno: 06.04.2017; Ogledov: 83; Prenosov: 2 Polno besedilo (793,79 KB) |
3. Low temperature impact toughness of the main gas pipeline steel after long-term degradationP. O. Maruščak, Irina Danyliuk, R.T. Biščak, Tomaž Vuherer, 2014, izvirni znanstveni članek Opis: The correlation of microstructure, temperature and Charpy V-notch impact properties of a steel 17G1S pipeline steel was investigated in this study. Within the concept of physical mesomechanics, the dynamic failure of specimens is represented as a successive process of the loss of shear stability, which takes place at different structural/scale levels of the material. Characteristic stages are analyzed for various modes of failure, moreover, typical levels of loading and oscillation periods, etc. are determined. Relations between low temperature derived through this test, microstructures and Charpy (V-notch) toughness test results are also discussed in this paper. Ključne besede: impact toughness, fracture, damage, gas pipeline, steel, degradation Objavljeno: 03.04.2017; Ogledov: 31; Prenosov: 0 Polno besedilo (699,32 KB) |
4. Chemical modification and characterization of poly(ethylene terephthalate) surfaces for collagen immobilizationMioara Drobota, Zdenka Peršin, Lidija Fras, Tamilselvan Mohan, Karin Stana-Kleinschek, Aleš Doliška, Matej Bračič, Volker Ribitsch, Valeria Harabagiu, Sergiu Coseri, 2013, izvirni znanstveni članek Opis: The functionalization of poly(ethylene terephthalate) (PET) surface films by reactions with multifunctional amines such as triethylenetetramine (TETA), and tetraethylenepentamine (TEPA) was investigated. For the functionalization of PET films surface we used a new way of treatment, a 'sandwich model'. Physical-chemical properties of functionalized PET films were analysed. Qualitative and quantitative determination of the introduced amine groups were examined by means of Fourier Transform Infrared Attenuated Total Reflexion(FTIR - ATR), X-ray photoelectron spectroscopy (XPS), and potentiometric titration. Gained wetting properties were determined by using contact angle measurements and thoroughly analysed by acid-base approach. In addition, surface topography was investigated by atomic force microscopy (AFM). The amount of the introduced amino groups after TETA incorporation has been found to be two times higher as compared to TEPA. Wetting properties were significantly improved after aminolysis. Surface free energy was higher for PET - TETA treated film than that observed for PET - TEPA treated which is in accordance with titration results. The collagen immobilization onto PET treated films was evidenced by using AFM and subsequently by using XPS. Ključne besede: PET, aminolysis, AFM, collagen immobilization Objavljeno: 03.04.2017; Ogledov: 18; Prenosov: 1 Polno besedilo (2,48 MB) |
5. Weak k-reconstruction of Cartesian productsWilfried Imrich, Blaž Zmazek, Janez Žerovnik, 2003, izvirni znanstveni članek Opis: By Ulam's conjecture every finite graph ▫$G$▫ can be reconstructed from its deck of vertex deleted subgraphs. The conjecture is still open, but many special cases have been settled. In particular, one can reconstruct Cartesian products. We consider the case of ▫$k$▫-vertex deleted subgraphs of Cartesian products and prove that one can decide whether a graph ▫$H$▫ is a ▫$k$▫-vertex deleted subgraph of a Cartesian product ▫$G$▫ with at least ▫$k+1$▫ prime factors on at least ▫$k+1$▫ vertices each, and that ▫$H$▫ uniquely determines ▫$G$▫. This extends previous works of the authors and Sims. This paper also contains a counterexample to a conjecture of MacAvaney. Ključne besede: mathematics, graph theory, reconstruction problem, Cartesian product, composite graphs Objavljeno: 31.03.2017; Ogledov: 48; Prenosov: 0 Polno besedilo (197,33 KB) |
6. On acyclic colorings of direct productsSimon Špacapan, Aleksandra Tepeh, 2008, izvirni znanstveni članek Opis: A coloring of a graph ▫$G$▫ is an acyclic coloring if the union of any two color classes induces a forest. It is proved that the acyclic chromatic number of direct product of two trees ▫$T_1$▫ and ▫$T_2$▫ equals ▫$\min\{ \Delta(T_1) + 1, \Delta(T_2) + 1\}$▫. We also prove that the acyclic chromatic number of direct product of two complete graphs ▫$K_m$▫ and ▫$K_n$▫ is ▫$mn-m-2$▫, where ▫$m \ge n \ge 4$▫. Several bounds for the acyclic chromatic number of direct products are given and in connection to this some questions are raised. Ključne besede: mathematics, graph theory, coloring, acyclic coloring, distance-two coloring, direct product Objavljeno: 31.03.2017; Ogledov: 19; Prenosov: 0 Polno besedilo (142,13 KB) |
7. A new method for determining extra time by considering ergonomic loads in the garment and metal working industriesVekoslav Verhovnik, Andrej Polajnar, 1993, izvirni znanstveni članek Opis: The changing labour conditions in the garment and metal-working industries have led to the necessity of determining new extra times to establish the time standard. In this paper, a method of measuring stress and strain imposed upon the operator in new working conditions by determining the additional production coefficient is presented. The method gives criteria and grades to assess stress at the workplace. Physical stress (dynamic and static), thermal and visual stress, discomfort caused by noise, aerosols, gases and vapours, and the stress due to monotony are assessed. The stresses are expressed by ecological, physiological and psychological indexes. The indexes are pondered. Ponderation includes the factor of the magnitude and the time of exposure to stress. Ponderation is expressed by the number of points, the total being an adequate presentation of the stresses. Stress and strain decrease the working performance of the operator. Therefore they must be included in the standard to compensate for the operator's lower working efficiency due to physical and psychological strain at the workplace, Short breaks and stops allowed during work enable the operator to perform work tasks without getting excessively tired. The necessary correction of the production time is made by applying the ergonomic coefficient Ker. Ključne besede: job analysis, production planning, stress assessment, time study, working conditions, working environment Objavljeno: 30.03.2017; Ogledov: 30; Prenosov: 1 Polno besedilo (7,13 MB) |
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10. The influence of surface coatings on the tooth tip deflection of polymer gearsBoštjan Trobentar, Srečko Glodež, Jože Flašker, Boštjan Zafošnik, 2016, izvirni znanstveni članek Opis: When designing gear drives made of polymer, the tooth tip deflection is a crucial parameter in respect to the proper gear drive operation. Excessive tooth tip deflection can lead to serious disturbances of gear meshing and consequently to increased noise and wear of the teeth flanks. In such cases the tooth tip deflection can be reduced through the use of stiff surface coatings on the tooth flanks. In this paper the influence of different coating materials and thicknesses on the tooth tip deflection of polymer gears is analysed using comprehensive finite element computational analysis. The numerical results obtained are then used to define an approximate equation for the calculation of gear tooth tip deflection for the coating material used and the thickness of the surface coating layer. The results show that the tooth tip deflection decreases with large values of the coating material Young’s modulus and with the coating layer thickness. Ključne besede: polymer gears, surface coatings, tooth deflection, numerical analysis Objavljeno: 27.03.2017; Ogledov: 16; Prenosov: 0 Polno besedilo (578,86 KB) |