Search the repository

A+ | A- | | SLO | ENG

Abstract: This study investigates heat and mass transfer during energetic melt-coolant interactions, focusing on film boiling around a hot melt particle in subcooled convective flow. The considered conditions, free-flow velocities of a few m/s, melt particle temperatures of several thousand K, particle diameters of several tens of a μm, and liquid subcooling of several tens of a K, align with TREPAM experiments (CEA, France). A two-phase computational fluid dynamics framework, based on the Volume of Fluid method, is used. An improved phase-change model is implemented, combining Chen’s explicit formulation of the phase-change intensity factor with the robustness of the conventional Lee model. The approach reduces sensitivity to empirical parameters and enhances phase-change localisation. Additional constraints on the intensity factor ensure numerical stability under extreme thermal conditions relevant to vapour energetic melt-coolant interactions. Simulations of TREPAM experiments demonstrate improved heat flux predictions and enhanced flow dynamics capture. Analysis of the simulated velocity fields reveal secondary flows in the vapour wake, impacting heat and mass transfer and emphasizing the need to resolve vapor-phase flow conditions. To fully validate proposed modifications to phase-change model further numerical and experimental investigation is required, focusing on vapour film morphology and localized heat transfer intensity.
Keywords: film boiling, extreme thermal conditions, phase-change modelling, computational fluid dynamics, two-phase flow
Published in DiRROS: 16.09.2025; Views: 270; Downloads: 130
Full text (4,40 MB)
This document has many files! More...

Keywords: varstvo gozdov, morfološke analize
Published in DiRROS: 16.09.2025; Views: 222; Downloads: 0
This document has many files! More...

Abstract: The demand for rapid, field-deployable detection of hazardous substances has intensified the search for plasmonic sensors with both high sensitivity and fabrication simplicity. Conventional approaches to plasmonic substrates, however, often rely on lithographic precision or complex chemistries limiting scalability and reproducibility. Here, a facile, one-step synthesis of vertically aligned 2D nanosheets composed of intergrown Cu2O/CuO crystallites is presented, fabricated via oxygen plasma discharge on copper substrates. Decorated with a discontinuous Ag nanoparticle layer, the substrates serve as high-performance plasmonic metasurface exhibiting nanomolar sensitivity of explosive molecules, with detection limits as low as 4–5 nm for tetryl and 2–3 nm for HMX under 488 nm excitation. Importantly, the SERS (Surface enhanced Raman scattering) activity expands into a broad spectral range (488, 535, 633 nm), enabled by the formation of plasmonic “hotspots” network within nanoparticle gaps, crevices, that cumulatively boost SERS signal. A pronounced red-shift in the symmetric NO2 stretching mode of tetryl is further demonstrated, attributed to LUMO-mediated charge transfer from the Ag Fermi level—highlighting the need for laser- and substrate-sensitive interpretation of vibrational data. Together, these findings advance the rational design of low-cost, reproducible SERS substrates for trace chemical detection, with potential for integration into autonomous sensing platforms.
Keywords: plasmonic sensors, surface enhanced Raman scattering
Published in DiRROS: 16.09.2025; Views: 388; Downloads: 146
Full text (5,41 MB)
This document has many files! More...

Published in DiRROS: 15.09.2025; Views: 323; Downloads: 74
Full text (4,56 MB)

Abstract: The recent discovery of ferroelectric nematic liquid crystalline phases marks a major breakthrough in soft matter research. An intermediate phase, often observed between the nonpolar and the ferroelectric nematic phase, shows a distinct antiferroelectric response to electric fields. However, its structure and formation mechanisms remain debated, with flexoelectric and electrostatics effects proposed as competing mechanisms. By controlling the magnitude of electrostatic forces through ion addition in two representative ferroelectric nematic materials, it is shown that the primary mechanism for the emergence of antiferroelectric order is the flexoelectric coupling between electric polarization and splay deformation of the nematic director. The addition of ions significantly expands the temperature range over which the antiferroelectric phase is observed, with this range increasing with increasing ion concentration. Polarizing optical microscopy studies and second harmonic generation (SHG) microscopy reveal the splayed structure modulated in 2D, while SHG interferometry confirms its antiferroelectric character. The model previously used to describe pretransitional behavior is extended by incorporating the electrostatic contribution of ions. The model shows qualitative agreement with the experiments, accurately reproducing the phase diagram and temperature-dependent evolution of the modulation period of the observed structure.
Keywords: ferroelectric nematic liquids, flexoelectricity, antiferroelectric order
Published in DiRROS: 15.09.2025; Views: 315; Downloads: 138
Full text (32,84 MB)
This document has many files! More...