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11 - 20 / 2000
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Sedem desetletij metasekvoje (Metasequoia glyptostroboides Hu et Cheng) v Sloveniji
Iza Petek, Gregor Božič, Dušan Jurc, Kristjan Jarni, Robert Brus, 2024, review article

Abstract: Metasekvoja (Metasequoia glyptostroboides Hu et Cheng) je ena najpozneje odkritih drevesnih vrst na Zemlji in hkrati zelo stara vrsta, ki se morfološko skozi milijone let skoraj ni spremenila. Odkrita je bila šele sredi 20. stoletja na Kitajskem, le nekaj let za tem, ko so znanstveniki odkrili njene fosilne ostanke in predvidevali, da gre za izumrlo vrsto. Po odkritju se je o metasekvoji veliko govorilo in pisalo, sadili so jo po vsem svetu z namenom preučevanja, saj je bilo odkritje živih osebkov senzacija za ves botanični svet. Danes se je v luči podnebnih sprememb in ob iskanju novih možnosti za večjo odpornost gozda metasekvoja kot potencialno uporabna vrsta zopet znašla pod drobnogledom. Njeno močno užlebljeno deblo in obstojnost odmrlih vej lahko predstavljajo težavo pri obdelavi njenega proti glivam sicer zelo odpornega lesa, hkrati pa zaradi edinstvenega videza deluje izredno estetsko predvsem v urbanem okolju. Kot gospodarsko vrsto jo uporabljajo ponekod na Kitajskem, v Evropi jo sadijo predvsem v testnih nasadih in v urbanem okolju. V preglednem prispevku je po sedmih desetletjih prisotnosti metasekvoje v Sloveniji podrobneje predstavljena zgodovina njenega odkrivanja, dosedanja uporaba in ocenjen je njen prihodnji potencial.
Keywords: Slovenija, Metasequoia glyptostroboides, zgodovina, odkritje, lastnosti, drevesne vrste
Published in DiRROS: 22.12.2024; Views: 170; Downloads: 28
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Unveiling the potential of ▫$(CoFeNiMnCr)_3O_4$▫ high-entropy oxide synthesized from CoFeNiMnCr high-entropy alloy for efficient oxygen-evolution reaction
Barbara Ljubec Božiček, Jitka Hreščak, Monika Kušter, Janez Kovač, Iztok Naglič, Boštjan Markoli, Barbara Šetina, Martin Šala, Sandra Drev, Živa Marinko, Miran Čeh, Belisa Alcantara Marinho, 2024, original scientific article

Abstract: Electrochemical water-splitting is a promising green technology for the production of hydrogen. One of the bottlenecks, however, is the oxygen evolution half-reaction (OER), which could be overcome with the development of a suitable electrocatalyst. Recently, non-noble metal, high-entropy oxides (HEO) have been investigated as potential OER electrocatalysts, but complex synthesis approaches that usually produce the material in powder form limit their wider utilization. Here, an innovative synthesis strategy of formulating a nanostructured (CoFeNiMnCr)3O4 HEO thin film on a CoFeNiMnCr high entropy alloy (HEA) using facile electrochemical and thermal treatment methods is presented. The CoFeNiMnCr HEA serves as exceptional support to be electrochemically treated in an ethylene glycol electrolyte with ammonium fluoride to form a rough and microporous structure with nanopits. The electrochemically treated CoFeNiMnCr HEA surface is more prone to oxidation during a low-temperature thermal treatment, leading to the growth of a spinel (CoFeNiMnCr)3O4 HEO thin film. The (CoFeNiMnCr)3O4 HEO exhibits a superior overpotential of 341 mV at 10 mA cm−2 and a Tafel slope of 50 mV dec−1 along with remarkable long-term stability in alkaline media. The excellent catalytic activity and stability for the OER can serve as a promising platform for the practical utilization of (CoFeNiMnCr)3O4 HEO.
Keywords: electrochemical water-spliting, electrocatalysts
Published in DiRROS: 20.12.2024; Views: 86; Downloads: 32
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Influence of surface preparation of aluminum alloy AW-5754 and stainless steel X5CRNI18-10 on the properties of bonded joints
Nataša Zdravković, Damjan Klobčar, Dragan Milčić, Matevž Zupančič, Borut Žužek, Miodrag Milčić, Aleksija Ðurić, 2024, original scientific article

Abstract: Adhesive bonding has proven to be a reliable method of joining materials, and the development of new adhesives has made it possible to use bonding in a variety of applications. This article addresses the challenges of bonding metals such as the aluminum alloy EN AW-5754 and the stainless steel X5CrNi18-10. In this study, the effects of laser cleaning and texturing on the surface properties and strength of two bonded joints were investigated and compared with mechanical preparation (hand sanding with Scotch-Brite and P180 sandpaper). The bonded joints were tested with three different epoxy adhesives. During the tests, the adhesion properties of the bonded surface were determined by measuring the contact angle and assessing the wettability, the surface roughness parameters for the different surface preparations, and the mechanical properties (tensile lap-shear strength). Based on the strength test results, it was found that bonded joints made of stainless steel had 16% to 40% higher strength than aluminum alloys when using the same adhesive and surface preparation. Laser cleaning resulted in maximum shear strength of the aluminum alloy bond, while the most suitable surface preparation for both materials was preparation with P180 sandpaper for all adhesives.
Keywords: adhesive bonding, surface preparation, aluminum alloy AW-5754, stainless steel X5CrNi18-10, epoxy adhesives
Published in DiRROS: 20.12.2024; Views: 77; Downloads: 36
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18.
On the thermal stability of multilayer optics for use with high X-ray intensities
Margarita Zakharova, Zlatko Rek, Božidar Šarler, Saša Bajt, 2024, original scientific article

Abstract: High-intensity X-ray free electron laser (XFEL) beams require optics made of materials with minimal radiation absorption, high diffraction efficiency, and high radiation hardness. Multilayer Laue lenses (MLLs) are diffraction-based X-ray optics that can focus XFEL beams, as already demonstrated with tungsten carbide/silicon carbide (WC/SiC)-based MLLs. However, high atomic number materials such as tungsten strongly absorb X-rays, resulting in high heat loads. Numerical simulations predict much lower heat loads in MLLs consisting of low atomic number Z materials, although such MLLs have narrower rocking curve widths. In this paper, we first screen various multilayer candidates and then focus on Mo2C/SiC multilayer due to its high diffraction efficiency. According to numerical simulations, the maximum temperature in this multilayer should remain below 300°C if the MLL made out of this multilayer is exposed to an XFEL beam of 17.5 keV photon energy, 1 mJ energy per pulse and 10 kHz pulse repetition rate. To understand the thermal stability of the Mo2C/SiC multilayer, we performed a study on the multilayers of three different periods (1.5, 5, and 12 nm) and different Mo2C to SiC ratios. We monitored their periods, crystallinity, and stress as a function of annealing temperature for two different heating rates. The results presented in this paper indicate that Mo2C/SiC-based MLLs are viable for focusing XFEL beams without being damaged under these conditions.
Keywords: x-ray optics, multilayer Laue lens, thermal stability, numerical simulation
Published in DiRROS: 20.12.2024; Views: 72; Downloads: 33
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19.
Simulation of temperature field in steel billets during reheating in pusher-type furnace by meshless method
Qingguo Liu, Umut Hanoglu, Zlatko Rek, Božidar Šarler, 2024, original scientific article

Abstract: Using a meshless method, a simulation of steel billets in a pusher-type reheating furnace is carried out for the first time. The simulation represents an affordable way to replace the measurements. The heat transfer from the billets with convection and radiation is considered. Inside each of the billets, the heat diffusion equation is solved on a two-dimensional central slice of the billet. The diffusion equation is solved in a strong form by the Local Radial Basis Function Collocation Method (LRBFCM) with explicit time-stepping. The ray tracing procedure solves the radiation, where the view factors are computed with the Monte Carlo method. The changing number of billets in the furnace at the start and the end of the loading and unloading of the furnace is considered. A sensitivity study on billets' temperature evolution is performed as a function of a different number of rays used in the Monte Carlo method, different stopping times of the billets in the furnace, and different spacing between the billets. The temperature field simulation is also essential for automatically optimizing the furnace’s productivity, energy consumption, and the billet’s quality. For the first time, the LRBFCM is successfully demonstrated for solving such a complex industrial problem.
Keywords: pusher-type reheating furnace, steel, temperature field, radiation, convection, diffusion, strong form meshless method, radial basis functions
Published in DiRROS: 20.12.2024; Views: 66; Downloads: 34
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