1. Ellipsoidal soft micro-particles suspended in dilute viscous flowJana Wedel, Matjaž Hriberšek, Jure Ravnik, Paul Steinmann, 2025, izvirni znanstveni članek Opis: Soft particles in viscous flows are prevalent both in nature and in various industrial applications. Notable examples include biological cells such as blood cells and bacteria as well as hydrogels and vesicles. To model these intriguing particles, we present an extension of our recent, efficient, and versatile pseudo-rigid body approach, originally developed for initially spherical soft particles suspended in arbitrary macroscale viscous flows. The novel extension allows modeling the barycenter and shape dynamics of soft initially non-spherical, i.e. ellipsoidal particles by introducing a novel shape and orientation tensor. We consider soft, micrometer-sized, ellipsoidal particles deforming affinely. To this end, we combine affine deformations (as inherent to a pseudo-rigid body) and the Jeffery-Roscoe model to analytically determine the traction exerted on a soft ellipsoidal particle suspended locally in a creeping flow at the particle scale. Without loss of generality, we assume nonlinear hyperelastic material behavior for the particles considered. The novel extension of our recent numerical approach for soft particles demonstrates that the deformation and motion of the particles can be accurately reproduced also for ellipsoidal particles and captures results from the literature, however, at drastically reduced computational costs. Furthermore, we identify both the tumbling and trembling dynamic regime for soft ellipsoidal particles suspended in simple shear flow again capturing results from the literature. Our extended approach is first validated using experimental and numerical studies from the literature for quasi-rigid as well as soft particles, followed by a comparison of the effects of particle deformability for some well-known fluid flow cases, such as laminar pipe flow, lid-driven cavity flow, and a simplified bifurcation. We find that taking particle deformability into account leads to notable deviations in the particle trajectory compared to rigid particles, with increased deviations for higher initial particle aspect ratio. Furthermore, we demonstrate that our approach can track a statistically relevant number of soft particles in complex flow situations. Ključne besede: soft particles, Lagrangian particle tracking, pseudo-rigid bodies, point-particle method Objavljeno v DKUM: 19.05.2025; Ogledov: 0; Prenosov: 2
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2. A novel pseudo-rigid body approach to the non-linear dynamics of soft micro-particles in dilute viscous flowJana Wedel, Matjaž Hriberšek, Jure Ravnik, Paul Steinmann, 2024, izvirni znanstveni članek Opis: We propose a novel, demonstrably effective, utmost versatile and computationally highly efficient
pseudo-rigid body approach for tracking the barycenter and shape dynamics of soft, i.e. nonlinearly deformable micro-particles dilutely suspended in viscous flow. Pseudo-rigid bodies are
characterized by affine deformation and thus represent a first-order extension to the kinematics
of rigid bodies. Soft particles in viscous flow are ubiquitous in nature and sciences, prominent
examples, among others, are cells, vesicles or bacteria. Typically, soft particles deform severely
due to the mechanical loads exerted by the fluid flow. Since the shape dynamics of a soft particle -
a terminology that shall here also include its orientation dynamics - also affects its barycenter
dynamics, the resulting particle trajectory as a consequence is markedly altered as compared to
a rigid particle. Here, we consider soft micro-particles of initially spherical shape that affinely
deform into an ellipsoidal shape. These kinematic conditions are commensurate with i) the affine
deformation assumption inherent to a pseudo-rigid body and ii) the celebrated Jeffery-Roscoe
model for the traction exerted on an ellipsoidal particle due to creeping flow conditions around
the particle. Without loss of generality, we here focus on non-linear hyperelastic particles for the
sake of demonstration. Our novel numerical approach proves to accurately capture the particular
deformation pattern of soft particles in viscous flow, such as for example tank-treading, thereby
being completely general regarding the flow conditions at the macro-scale and, as an option, the
constitutive behavior of the particle. Moreover, our computational method is highly efficient and
allows straightforward integration into established Lagrangian tracking algorithms as employed
for the point-particle approach to track rigid particles in dilute viscous flow. Ključne besede: soft particles, pseudo-rigid bodies, Barycenter and shape dynamics, Lagrangian particle tracking Objavljeno v DKUM: 19.09.2024; Ogledov: 0; Prenosov: 19
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3. Interplay between particle trapping and heterogeneity in anomalous diffusionHaroldo V. Ribeiro, Angel A. Tateishi, Ervin K. Lenzi, Richard L. Magin, Matjaž Perc, 2023, izvirni znanstveni članek Opis: Heterogeneous media diffusion is often described using position-dependent diffusion coefficients and estimated indirectly through mean squared displacement in experiments. This approach may overlook other mechanisms and their interaction with position-dependent diffusion, potentially leading to erroneous conclusions. Here, we introduce a hybrid diffusion model that merges a position-dependent diffusion coefficient with the trapping mechanism of the comb model. We derive exact solutions for position distributions and mean squared displacements, validated through simulations of Langevin equations. Our model shows that the trapping mechanism attenuates the impact of media heterogeneity. Superdiffusion occurs when the position-dependent coefficient increases superlinearly, while subdiffusion occurs for sublinear and inverse power-law relations. This nontrivial interplay between heterogeneity and state-independent mechanisms also leads to anomalous yet Brownian, and non-Brownian yet Gaussian regimes. These findings emphasize the need for cautious interpretations of experiments and highlight the limitations of relying solely on mean squared displacements or position distributions for diffusion characterization. Ključne besede: particle trapping, heterogeneity, diffusion, statistical physics Objavljeno v DKUM: 11.09.2024; Ogledov: 38; Prenosov: 4
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4. New Approach for Fertiliser Size Assessment Using Contactless ScanningAndrius Laucka, Darius Andriukaitis, Algimantas Valinevicius, Mindaugas Zilys, Dangirutis Navikas, Leonas Balasevicius, Audrius Merfeldas, Roman Sotner, Jan Jerabek, Zhixiong Li, Jožef Ritonja, 2023, izvirni znanstveni članek Ključne besede: camera, particle, measurement, silhuette, volume, position Objavljeno v DKUM: 22.05.2024; Ogledov: 157; Prenosov: 22
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5. A novel particle–particle and particle–wall collision model for superellipsoidal particlesJana Wedel, Mitja Štrakl, Matjaž Hriberšek, Paul Steinmann, Jure Ravnik, 2023, izvirni znanstveni članek Ključne besede: multiphase flow, Lagrangian particle tracking, superellipsoid, collision, friction Objavljeno v DKUM: 28.03.2024; Ogledov: 171; Prenosov: 9
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6. Coefficient of tangential restitution for non-spherical particlesJana Wedel, Matjaž Hriberšek, Paul Steinmann, Jure Ravnik, 2024, izvirni znanstveni članek Opis: In various industrial and naturally occurring multiphase flows, whether dilute or dense, particle interaction plays a crucial role. In most cases, the particles are non-spherical, which poses a computational challenge in terms of particle motion and particle interaction, i.e. both particle–particle and particle–wall collisions. In this study, we present a novel frictional particle collision model to be used in general fluid flows. The model is derived for superellipsoidal particle shapes and thus allows consideration of frictional collisions of a wide variety of particle geometries. In this context, we derive an expression for the tangential coefficient of restitution applicable to arbitrarily shaped particles. Furthermore, we present the performance of the novel model by applying it to demonstrative examples ranging from two- to multi-particle systems. Ključne besede: non-spherical particles, particle collision, tangential restitution coefficient, superellipsoids Objavljeno v DKUM: 26.02.2024; Ogledov: 293; Prenosov: 49
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7. Green Processing of Neat Poly(lactic acid) Using Carbon Dioxide under Elevated Pressure for Preparation of Advanced Materials : A Review (2012–2022)Stoja L. Milovanović, Ivana Lukic, Gabrijela Horvat, Zoran Novak, Sulamith Frerich, Marcus Petermann, Carlos A. García-González, 2023, pregledni znanstveni članek Opis: This review provides a concise overview of up-to-date developments in the processing of neat poly(lactic acid) (PLA), improvement in its properties, and preparation of advanced materials using a green medium (CO2 under elevated pressure). Pressurized CO2 in the dense and supercritical state is a superior alternative medium to organic solvents, as it is easily available, fully recyclable, has easily tunable properties, and can be completely removed from the final material without post-processing steps. This review summarizes the state of the art on PLA drying, impregnation, foaming, and particle generation by the employment of dense and supercritical CO2 for the development of new materials. An analysis of the effect of processing methods on the final material properties was focused on neat PLA and PLA with an addition of natural bioactive components. It was demonstrated that CO2-assisted processes enable the control of PLA properties, reduce operating times, and require less energy compared to conventional ones. The described environmentally friendly processing techniques and the versatility of PLA were employed for the preparation of foams, aerogels, scaffolds, microparticles, and nanoparticles, as well as bioactive materials. These PLA-based materials can find application in tissue engineering, drug delivery, active food packaging, compostable packaging, wastewater treatment, or thermal insulation, among others. Ključne besede: aerogels, drying, foaming, impregnation, particle generation, PLA Objavljeno v DKUM: 06.02.2024; Ogledov: 395; Prenosov: 31
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9. Measurement of two-particle correlations of hadrons in ▫$e^+ e^-$▫ collisions at BelleY.-C. Chen, Marko Bračko, Samo Korpar, Peter Križan, Tomaž Podobnik, Marko Starič, Luka Šantelj, 2022, izvirni znanstveni članek Opis: The measurement of two-particle angular correlation functions in high-multiplicity e+e− collisions at √s=10.52 GeV is reported. In this study, the 89.5 fb−1 of hadronic e+e− annihilation data collected by the Belle detector at KEKB are used. Two-particle angular correlation functions are measured in the full relative azimuthal angle (Δϕ) and three units of pseudorapidity (Δη), defined by either the electron beam axis or the event-shape thrust axis, and are studied as a function of charged-particle multiplicity. The measurement in the thrust axis analysis, with mostly outgoing quark pairs determining the reference axis, is sensitive to the region of additional soft gluon emissions. No significant anisotropic collective behavior is observed with either coordinate analyses. Near-side jet correlations appear to be absent in the thrust axis analysis. The measurements are compared to predictions from various event generators and are expected to provide new constraints to the phenomenological models in the low-energy regime. Ključne besede: Particle & resonance production, Quark & gluon jets, Quark-gluon plasma Objavljeno v DKUM: 24.08.2023; Ogledov: 396; Prenosov: 9
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10. Measurement of the branching fraction and ▫$CP$▫ asymmetry for ▫$B \to \bar{D}^0 \pi$▫ decaysT. Bloomfield, Jyoti Prakash Biswal, Marko Bračko, Samo Korpar, Peter Križan, Rok Pestotnik, Tomaž Podobnik, Marko Starič, Luka Šantelj, 2022, izvirni znanstveni članek Opis: We measure the branching fractions and CP asymmetries for the decays B⁰ → D¯ 0π⁰ and B⁺ → D¯ 0π⁺, using a data sample of 772 × 10⁶ BB¯ pairs collected at the ϒ(4S) resonance with the Belle detector at the KEKB e⁺e− collider. The branching fractions obtained and direct CP asym-metries are B(B⁰ → D¯ 0π⁰)=[2.70 0.06(stat) 0.10(syst)]×10−⁴, B(B⁺ → D¯ 0π⁺)=[4.53 0.02(stat) 0.15(syst)]×10−³, ACP(B⁰ → D¯ 0π⁰)= [+0.42 2.05(stat) 1.22(syst)]%, and ACP(B⁺ → D¯ 0π⁺) = [+0.19 0.36(stat) 0.57(syst)]%. The measurements of B are the most precise to date and are in good agreement with previous results, as is the measurement of ACP(B⁺ → D¯ 0π⁺). The measurement of ACP for B⁰ → D¯ 0π⁰ is the first for this mode, and the value is consistent with Standard Model expectations. Ključne besede: branching fraction, hadronic decays, particle decays, mesons, CP violation, precision measurements Objavljeno v DKUM: 17.08.2023; Ogledov: 364; Prenosov: 39
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