1. Optimal scan time for evaluation of parathyroid adenoma with [18F]-fluorocholine PET/CTSebastijan Rep, Luka Ležaič, Tomaž Kocjan, Marija Pfeifer, Mojca Jensterle Sever, Urban Simončič, Petra Tomše, Marko Hočevar, 2015, original scientific article Keywords: lesions representing enlarged parathyroid tissue, triple-phase, standardized uptake value, retention index, lesion contrast, rak (medicina), obščitnični adenomi, diagnostika Published in DiRROS: 22.04.2024; Views: 15; Downloads: 6 Full text (850,44 KB) This document has many files! More... |
2. Thermal characterisation of the cooling phase of post-flashover compartment firesAndrea Lucherini, Balša Jovanović, Jose L. Torero, Ruben Van Coile, Bart Merci, 2024, original scientific article Abstract: The main characteristics of the cooling phase of post-flashover compartment fires are studied using a simplified first-principles heat transfer approach to establish key limitations of more traditional methodologies (e.g., Eurocode). To this purpose, the boundary conditions during cooling are analysed. To illustrate the importance of a first-principles approach, a detailed review of the literature is presented followed by the presentation of a simplified numerical model. The model is constructed to calculate first-order thermal conditions during the cooling phase. The model is not intended to provide a precise calculation method but rather baseline estimates that incorporate all key thermal inputs and outputs. First, the thermal boundary conditions in the heating phase are approximated with a single (gas) temperature and the Eurocode parametric fire curves, to provide a consistent initial condition for the cooling phase and to be able to compare the traditional approach to the first- principles approach. After fuel burnout, the compartment gases become optically thin and temperatures decay to ambient values, while the compartment solid elements slowly cool down. For simplicity, convective cooling of the compartment linings is estimated using a constant convective heat transfer coefficient and all linings surfaces are assumed to have the same temperature (no net radiative heat exchange). All structural elements are assumed to be thermally thick. While these simplifications introduce quantitative errors, they enable an analytical solution for transient heat conduction in a semi-infinite solid that captures all key heat transfer processes. Comparisons between the results obtained using both approaches highlight how, even when considering the same fire energy input, the thermal boundary conditions according to the Eurocode parametric fire curves lead to an increase energy accumulated in the solid after fuel burnout and a delay in the onset of cooling. This is not physically correct, and it may lead to misrepresentation of the impact of post-flashover fires on structural behaviour. Keywords: cooling phase, fire decay, fire dynamics, compartment fires, structural fire engineering, fire safety Published in DiRROS: 15.04.2024; Views: 89; Downloads: 45 Full text (6,40 MB) This document has many files! More... |
3. Beta–gamma phase-amplitude coupling as a non-invasive biomarker for Parkinson’s diseas : insights from Electroencephalography studiesTisa Hodnik, Stiven Roytman, Nicolaas I. Bohnen, Uroš Marušič, 2024, review article Abstract: Phase-amplitude coupling (PAC) describes the interaction of two separate frequencies in which the lower frequency phase acts as a carrier frequency of the higher frequency amplitude. It is a means of carrying integrated streams of information between micro- and macroscale systems in the brain, allowing for coordinated activity of separate brain regions. A beta–gamma PAC increase over the sensorimotor cortex has been observed consistently in people with Parkinson’s disease (PD). Its cause is attributed to neural entrainment in the basal ganglia, caused by pathological degeneration characteristic of PD. Disruptions in this phenomenon in PD patients have been observed in the resting state as well as during movement recordings and have reliably distinguished patients from healthy participants. The changes can be detected non-invasively with the electroencephalogram (EEG). They correspond to the severity of the motor symptoms and the medication status of people with PD. Furthermore, a medication-induced decrease in PAC in PD correlates with the alleviation of motor symptoms measured by assessment scales. A beta–gamma PAC increase has, therefore, been explored as a possible means of quantifying motor pathology in PD. The application of this parameter to closed-loop deep brain stimulation could serve as a self-adaptation measure of such treatment, responding to fluctuations of motor symptom severity in PD. Furthermore, phase-dependent stimulation provides a new precise method for modulating PAC increases in the cortex. This review offers a comprehensive synthesis of the current EEG-based evidence on PAC fluctuations in PD, explores the potential practical utility of this biomarker, and provides recommendations for future research. Keywords: neurodegenerative diseases, Parkinson’s disease, electroencephalography, phase-amplitude coupling Published in DiRROS: 21.03.2024; Views: 101; Downloads: 49 Full text (604,09 KB) This document has many files! More... |
4. Application of a meshless space-time adaptive approach to phase-field modelling of polycrystalline solidificationTadej Dobravec, Boštjan Mavrič, Božidar Šarler, 2023, published scientific conference contribution Abstract: We have developed a 2-D numerical meshless adaptive approach for phase-field modelling of dendritic solidification. The quadtree-based approach decomposes the computational domain into quadtree sub-domains of different sizes. The algorithm generates uniformly-distributed computational nodes in each quadtree sub-domain. We apply the meshless radial basis function generated finite difference method and the forward Euler scheme to discretise governing equations in each computational node. The fixed ratio between the characteristic size and the node spacing of a quadtree sub-domain ensures space adaptivity. The adaptive time-stepping accelerates the calculations further. In the framework of previous research studies, we used the approach to solve quantitative phase-field models for single dendrite growth in pure melts and dilute binary alloys. In the present study, we upgrade the solution procedure for the modelling growth of multiple differently oriented dendrites. Along with the space-time adaptive approach, we apply non-linear preconditioning of the phase-field equation to increase computational efficiency. We investigate a novel numerical approach's accuracy and computational efficiency by simulating the equiaxed dendrite growth from a dilute binary alloy. Keywords: dendritic growth, phase-field method, meshless methods, polycrystalline solidification Published in DiRROS: 21.03.2024; Views: 97; Downloads: 54 Full text (2,77 MB) This document has many files! More... |
5. On the Schrödinger-Poisson system with $(p,q)$-LaplacianYueqiang Song, Yuanyuan Huo, Dušan Repovš, 2023, original scientific article Abstract: We study a class of Schrödinger-Poisson systems with $(p,q)$-Laplacian. Using fixed point theory, we obtain a new existence result for nontrivial solutions. The main novelty of the paper is the combination of a double phase operator and the nonlocal term. Our results generalize some known results. Keywords: double phase operator, Schrödinger-Poisson systems, (p, q)–Laplacian, fixed point theory Published in DiRROS: 14.03.2024; Views: 88; Downloads: 39 Full text (686,98 KB) This document has many files! More... |
6. Formulation of the method of fundamental solutions for two-phase Stokes flowZlatko Rek, Božidar Šarler, 2024, original scientific article Abstract: The method of fundamental solutions with a subdomain technique is used for the solution of the free boundary problem associated with a two-phase Stokes flow in a 2D geometry. The solution procedure is based on the collocation of the boundary conditions with the Stokeslets. It is formulated for the flow of unmixing fluids in contact, where the velocity, pressure field, and position of the free boundary between the fluids must be determined. The standard formulation of the method of fundamental solutions is, for the first time, upgraded for the case with mixed velocity and pressure boundary conditions and verified on a T-splitter single-phase flow with unsymmetric pressure boundary conditions. The standard control volume method is used for the reference solution. The accurate evaluation of the velocity derivatives, which are required to calculate the balance of forces at the free boundary between the fluids, is achieved in a closed form in contrast to previous numerical attempts. An algorithm for iteratively calculating the position of the free boundary that involves displacement, smoothing and repositioning of the nodes is elaborated. The procedure is verified for a concurrent flow of two fluids in a channel. The velocity and velocity derivatives show fast convergence to the analytical solution. The developed boundary meshless method is easy to code, accurate and computationally efficient since only collocation at the fixed and free boundaries is needed. Keywords: Stokes equations, two-phase flow, free boundary problems, method of fundamental solutions, subdomain technique Published in DiRROS: 28.02.2024; Views: 101; Downloads: 58 Full text (3,40 MB) This document has many files! More... |
7. Grain size distribution of DP 600 steel using single-pass asymmetrical wedge testUrška Klančnik, Peter Fajfar, Jan Foder, Heinz Palkowski, Jaka Burja, Grega Klančnik, 2023, original scientific article Keywords: wedge test, hot-rolling, grain size distribution, dual-phase steel Published in DiRROS: 07.02.2024; Views: 169; Downloads: 70 Full text (4,64 MB) This document has many files! More... |
8. Study on dissolution of Ba-containing inoculant in ductile cast iron melt and nucleation of graphiteMarica Tonkovič-Prijanovič, Primož Mrvar, Jaka Burja, Črtomir Donik, Mitja Petrič, 2023, original scientific article Keywords: inoculant, inoculant dissolving, reaction zone, phase composition, graphite nucleation, ductile cast iron, barium inoculant Published in DiRROS: 07.02.2024; Views: 132; Downloads: 62 Full text (17,37 MB) This document has many files! More... |
9. A coupled domain–boundary type meshless method for phase-field modelling of dendritic solidification with the fluid flowTadej Dobravec, Boštjan Mavrič, Rizwan Zahoor, Božidar Šarler, 2023, original scientific article Abstract: Purpose - This study aims to simulate the dendritic growth in Stokes flow by iteratively coupling a domain and boundary type meshless method. Design/methodology/approach - A preconditioned phase-field model for dendritic solidification of a pure supercooled melt is solved by the strong-form space-time adaptive approach based on dynamic quadtree domain decomposition. The domain-type space discretisation relies on monomial augmented polyharmonic splines interpolation. The forward Euler scheme is used for time evolution. The boundary-type meshless method solves the Stokes flow around the dendrite based on the collocation of the moving and fixed flow boundaries with the regularised Stokes flow fundamental solution. Both approaches are iteratively coupled at the moving solid–liquid interface. The solution procedure ensures computationally efficient and accurate calculations. The novel approach is numerically implemented for a 2D case. Findings - The solution procedure reflects the advantages of both meshless methods. Domain one is not sensitive to the dendrite orientation and boundary one reduces the dimensionality of the flow field solution. The procedure results agree well with the reference results obtained by the classical numerical methods. Directions for selecting the appropriate free parameters which yield the highest accuracy and computational efficiency are presented. Originality/value - A combination of boundary- and domain-type meshless methods is used to simulate dendritic solidification with the influence of fluid flow efficiently. Keywords: dendritic solidification, Stokes flow, phase-field method, space-time adaptivity, meshless methods, RBF-FD, modified method of regularised sources Published in DiRROS: 07.02.2024; Views: 144; Downloads: 62 Full text (1,07 MB) This document has many files! More... |
10. Austenite reversion suppression with deep cryogenic treatment : a novel pathway towards 3rd generation advanced high-strength steelsPatricia Jovičević Klug, Matic Klug Jovičević, Lars Thormählen, Jeffrey McCord, Michael Rohwerder, Matjaž Godec, Bojan Podgornik, 2023, original scientific article Keywords: Martensitic stainless steel, deep cryogenic treatment, microstructure, mechanical properties, microstructural transformations, phase transformation Published in DiRROS: 02.02.2024; Views: 149; Downloads: 81 Full text (13,70 MB) This document has many files! More... |