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A conceptual model for a circular city : a case study of Maribor, Slovenia
Kristijan Brglez, Matjaž Perc, Rebeka Kovačič Lukman, 2024, izvirni znanstveni članek

Opis: Cities play a crucial role in achieving sustainable development. Decision-makers require assistance in developing city transformation plans amidst the emergence of various city models. A content analysis using concept mapping was conducted to examine smart, circular, and green city models. The analysis, supported by Leximancer, revealed that city models are evolving by adopting benefcial solutions from competitors, refecting a strong focus on sustainable development. Additionally, twentyfour research areas essential for implementing a circular city were identifed and validated. Furthermore, a conceptual model for a circular city was developed, incorporating the Defne-Measure-Analyse-Improve-Control tool and a problem-solving system. Testing the model on Maribor highlighted challenges in monitoring the transition towards circularity. The study validates the established model but emphasises the need for further research and case studies to verify its practicality. This scientifc research enhances the understanding of city models and their evolution towards sustainability, providing valuable insights for decision-makers and urban planners.
Ključne besede: city models, conceptual model, content analysis, problem-solving structure
Objavljeno v DKUM: 29.03.2024; Ogledov: 45; Prenosov: 2
.pdf Celotno besedilo (2,08 MB)
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Cationised fibre-based cellulose multi-layer membranes for sterile and high-flow bacteria retention and inactivation
Vanja Kokol, Monika Kos, Vera Vivod, Nina Gunde-Cimerman, 2023, izvirni znanstveni članek

Opis: Low-cost, readily available, or even disposable membranes in water purification or downstream biopharma processes are becoming attractive alternatives to expensive polymeric columns or filters. In this article, the potential of microfiltration membranes prepared from differently orientated viscose fibre slivers, infused with ultrafine quaternised (qCNF) and amino-hydrophobised (aCNF) cellulose nanofibrils, were investigated for capturing and deactivating the bacteria from water during vacuum filtration. The morphology and capturing mechanism of the single- and multi-layer structured membranes were evaluated using microscopic imaging and colloidal particles. They were assessed for antibacterial efficacy and the retention of selected bacterial species (Escherichia coli, Staphylococcus aureus, Micrococcus luteus), differing in the cell envelope structure, hydrodynamic biovolume (shape and size) and their clustering. The aCNF increased biocidal efficacy significantly when compared to qCNF-integrated membrane, although the latter retained bacteria equally effectively by a thicker multi-layer structured membrane. The retention of bacterial cells occurred through electrostatic and hydrophobic interactions, as well as via interfibrous pore diffusion, depending on their physicochemical properties. For all bacterial strains, the highest retention (up to 100% or log 6 reduction) at >50 L/h∗bar∗m2 flow rate was achieved with a 4-layer gradient-structured membrane containing different aCNF content, thereby matching the performance of industrial polymeric filters used for removing bacteria.
Ključne besede: fibrous membrane, cationised cellulose nanofibrils, amino-hydrophobised cellulose nanofibrils, antibacterial activity, multi-layer structure, flux, bacteria retention
Objavljeno v DKUM: 28.03.2024; Ogledov: 48; Prenosov: 0
.pdf Celotno besedilo (3,99 MB)
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Introducing auxetic behavior to syntactic foams
Nejc Novak, Miha Kolar, Nima Movahedi, Matej Vesenjak, Zoran Ren, Thomas Fiedler, 2020, izvirni znanstveni članek

Opis: This paper proposes an innovative multi-material approach for introducing auxetic behaviour to syntactic foams (SFs). By carefully designing the size, shape, and orientation of the SFs, auxetic deformation behaviour was induced. Re-entrant hexagon-shaped SF elements were fabricated using expanded perlite (EP) particles and a plaster of Paris slurry first. Then, an auxetic pattern of these SF elements was arranged within a stainless-steel casting box. The empty spaces between the SF elements were filled with molten aluminium alloy (A356) using the counter-gravity infiltration casting technique. The cast auxetic composite had a bulk density of 1.52 g/cm3. The cast composite was then compressed under quasi-static loading to characterise its deformation behaviour and to determine the mechanical properties, especially the Poisson’s ratio. The cast composite deformation was auxetic with a Poisson’s ratio of −1.04. Finite Element (FE) simulations were conducted to understand the deformation mechanism better and provide means for further optimisation of the geometry.
Ključne besede: auxetic cellular structure, syntactic foams, experimental tests, mechanical properties, Poisson’s ratio
Objavljeno v DKUM: 28.03.2024; Ogledov: 46; Prenosov: 3
.pdf Celotno besedilo (8,46 MB)
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Cotton woven fabrics as protective polymer materials against solar radiation in the range of 210–1200 nm
Polona Dobnik-Dubrovski, Darinka Fakin, Alenka Ojstršek, 2023, izvirni znanstveni članek

Opis: The proposed paper describes the influence of woven fabric constructional parameters (type of weave, relative fabric density) and colouration (obtained by eco-friendly dyeing) on the solar transmittance of cotton woven fabrics in the range of 210-1200 nm. The cotton woven fabrics in their raw state were prepared according to Kienbaum's setting theory, at three levels of relative fabric density and three levels of the weave factor, and then exposed to the dyeing process with natural dyestuffs (beetroot, walnut leaves). After ultraviolet/visible/near-infrared (UV/VIS/IRA) solar transmittance and reflection in the range of 210-1200 nm were recorded, the influence of the fabric construction and colouration were analysed. The guidelines for fabric constructor were proposed. The results show that the walnut-coloured satin samples at the third level of relative fabric density provide the best solar protection in the whole solar spectrum. All the tested eco-friendly dyed fabrics offer good solar protection, while only raw satin fabric at the third level of relative fabric density can be classified as solar protective material with even better protection in IRA region than some coloured samples.
Ključne besede: fabric engineering, solar protection, woven fabric structure, natural dyeing of polymer material, testing
Objavljeno v DKUM: 15.02.2024; Ogledov: 135; Prenosov: 2
.pdf Celotno besedilo (1,93 MB)
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Dynamic characterisation of novel three-dimensional axisymmetric chiral auxetic structure
Anja Mauko, Yunus Emre Yilmaz, Nejc Novak, Tomáš Doktor, Matej Vesenjak, Zoran Ren, 2024, izvirni znanstveni članek

Opis: The study presents an extensive mechanical and computational characterisation of novel cellular metamaterial with axisymmetric chiral structure (ACS) at different strain rates. The Direct Impact Hopkinson Bar (DIHB) testing device was used for impact testing up to 21 m/s striker speed, which was insufficient to reach the shock deformation regime. Thus, using computational simulations to estimate the structure behaviour at high strain rates was necessary. Experimental and computational results showed that all ACS structures exhibit a nominal stress–strain relationship typical for cellular materials. As the loading conditions shifted to a dynamic regime, the micro–inertia effect became increasingly pronounced, leading to a corresponding rise in structure stiffness. The Poisson's ratio in all ACS increases gradually, making them superior to traditional cellular materials, which experience a sudden increase in Poisson's ratio during loading. Additionally, the study found that the structures exhibited a rise in the auxetic effect with an increase in strain rate, highlighting the benefits of axisymmetric structures in high-loading regimes. Overall, the obtained results provide valuable insights into the mechanical properties of ACS under different loading regimes and will contribute to further design improvements and the fabrication of novel ACS metamaterials.
Ključne besede: axisymmetric chiral structure, auxetic, chiral unit cell, impact testing, dynamic characterisation, finite element simulations
Objavljeno v DKUM: 15.02.2024; Ogledov: 128; Prenosov: 12
.pdf Celotno besedilo (7,73 MB)
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The multivariable Zhang-Zhang polynomial of phenylenes
Niko Tratnik, 2023, izvirni znanstveni članek

Opis: The Zhang-Zhang polynomial of a benzenoid system is a well-known counting polynomial that was introduced in 1996. It was designed to enumerate Clar covers, which are spanning subgraphs with only hexagons and edges as connected components. In 2018, the generalized Zhang-Zhang polynomial of two variables was defined such that it also takes into account 10-cycles of a benzenoid system. The aim of this paper is to introduce and study a new variation of the Zhang-Zhang polynomial for phenylenes, which are important molecular graphs composed of 6-membered and 4-membered rings. In our case, Clar covers can contain 4-cycles, 6-cycles, 8-cycles, and edges. Since this new polynomial has three variables, we call it the multivariable Zhang-Zhang (MZZ) polynomial. In the main part of the paper, some recursive formulas for calculating the MZZ polynomial from subgraphs of a given phenylene are developed and an algorithm for phenylene chains is deduced. Interestingly, computing the MZZ polynomial of a phenylene chain requires some techniques that are different to those used to calculate the (generalized) Zhang-Zhang polynomial of benzenoid chains. Finally, we prove a result that enables us to find the MZZ polynomial of a phenylene with branched hexagons.
Ključne besede: Zhang-Zhang polynomial, phenylene, Clar cover, Kekulé structure
Objavljeno v DKUM: 09.02.2024; Ogledov: 121; Prenosov: 6
.pdf Celotno besedilo (719,26 KB)
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Naive prediction of protein backbone phi and psi dihedral angles using deep learning
Matic Broz, Marko Jukič, Urban Bren, 2023, izvirni znanstveni članek

Opis: Protein structure prediction represents a significant challenge in the field of bioinformatics, with the prediction of protein structures using backbone dihedral angles recently achieving significant progress due to the rise of deep neural network research. However, there is a trend in protein structure prediction research to employ increasingly complex neural networks and contributions from multiple models. This study, on the other hand, explores how a single model transparently behaves using sequence data only and what can be expected from the predicted angles. To this end, the current paper presents data acquisition, deep learning model definition, and training toward the final protein backbone angle prediction. The method applies a simple fully connected neural network (FCNN) model that takes only the primary structure of the protein with a sliding window of size 21 as input to predict protein backbone φ and ψ dihedral angles. Despite its simplicity, the model shows surprising accuracy for the φ angle prediction and somewhat lower accuracy for the ψ angle prediction. Moreover, this study demonstrates that protein secondary structure prediction is also possible with simple neural networks that take in only the protein amino-acid residue sequence, but more complex models are required for higher accuracies.
Ključne besede: protein structure prediction, backbone dihedral angles, deep neural network, fully connected neural network, FCNN, protein secondary structure prediction
Objavljeno v DKUM: 01.12.2023; Ogledov: 177; Prenosov: 21
.pdf Celotno besedilo (3,60 MB)
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Computer modelling of the residual limb for the development of prosthetic sockets and liners with the cellular structure : doctoral disertation
Vasja Plesec, 2023, doktorska disertacija

Opis: The production of lower limb prostheses continues to rely primarily on manual methods, which are outdated and characterized by labour-intensive processes, lengthy time requirements, high costs, and a heavy reliance on the expertise of prosthetists. Achieving a satisfactory fit between the residual limb and socket remains a challenge, often leading to discomfort, pain, and potential wearer tissue damage. However, advancements in computer technology and numerical simulation offer an opportunity to predict stresses and strains experienced by the residual limb during prosthesis usage. This, in turn, aids in the development process by enhancing the design of the prosthetic socket and liner through virtual environments. In this dissertation we developed a generic numerical transtibial model to bridge the gap between clinical practice and numerical simulations. Biomechanically validated, this model generates outcomes applicable to a broader amputee population, facilitating comparative analysis of socket and liner designs and materials under different loading conditions. Furthermore, the dissertation explores the utilization of a 3D-printed socket manufactured through the cost-effective fused filament fabrication process, using polylactic acid filament, aiming to reduce the costs and establish a streamlined production process. The 3D-printed socket was evaluated within the virtual environment using the developed transtibial model. The numerical findings indicate that the 3D-printed socket can effectively withstand the loads encountered during the stages of prosthesis donning, single-leg stance, heel strike, and push-off, thereby presenting a viable alternative to the prevalent composite socket. Additionally, a cellular structure composed of a flexible thermoplastic elastomeric material is proposed as a prosthetic liner to enhance comfort by reducing contact pressure while maintaining the required stability. Numerical results indicate that by manipulating cellular parameters such as unit cell type and relative density of the structure, a customized response can be achieved. This customized response effectively reduces contact pressure for a given scenario without increasing displacement, thereby improving comfort while maintaining stability.
Ključne besede: lower-limb prosthesis, generic numerical transtibial model, 3D-printed socket, cellular structure liner, finite element method
Objavljeno v DKUM: 14.11.2023; Ogledov: 467; Prenosov: 23
.pdf Celotno besedilo (3,64 MB)

Quantum chaos in the extended Dicke model
Qian Wang, 2022, izvirni znanstveni članek

Opis: We systematically study the chaotic signatures in a quantum many-body system consisting of an ensemble of interacting two-level atoms coupled to a single-mode bosonic field, the so-called extended Dicke model. The presence of the atom–atom interaction also leads us to explore how the atomic interaction affects the chaotic characters of the model. By analyzing the energy spectral statistics and the structure of eigenstates, we reveal the quantum signatures of chaos in the model and discuss the effect of the atomic interaction. We also investigate the dependence of the boundary of chaos extracted from both eigenvalue-based and eigenstate-based indicators on the atomic interaction. We show that the impact of the atomic interaction on the spectral statistics is stronger than on the structure of eigenstates. Qualitatively, the integrablity-to-chaos transition found in the Dicke model is amplified when the interatomic interaction in the extended Dicke model is switched on.
Ključne besede: quantum chaos, extended Dicke model, spectral statistics, eigenstate structure
Objavljeno v DKUM: 13.10.2023; Ogledov: 208; Prenosov: 17
.pdf Celotno besedilo (3,46 MB)
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