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Loss of oxygen atoms on well-oxidized cobalt by heterogeneous surface recombination
Domen Paul, Miran Mozetič, Rok Zaplotnik, Jernej Ekar, Alenka Vesel, Gregor Primc, Denis Đonlagić, 2023, izvirni znanstveni članek

Opis: Calorimetry is a commonly used method in plasma characterization, but the accuracy of the method is tied to the accuracy of the recombination coefficient, which in turn depends on a number of surface effects. Surface effects also govern the kinetics in advanced methods such as atomic layer oxidation of inorganic materials and functionalization of organic materials. The flux of the reactive oxygen atoms for the controlled oxidation of such materials depends on the recombination coefficient of materials placed into the reaction chamber, which in turn depends on the surface morphology, temperature, and pressure in the processing chamber. The recombination coefficient of a well-oxidized cobalt surface was studied systematically in a range of temperatures from 300 to 800 K and pressures from 40 to 200 Pa. The coefficient increased monotonously with decreasing pressure and increasing temperature. The lowest value was about 0.05, and the highest was about 0.30. These values were measured for cobalt foils previously oxidized with oxygen plasma at the temperature of 1300 K. The oxidation caused a rich morphology with an average roughness as deduced from atomic force images of 0.9 µm. The results were compared with literature data, and the discrepancy between results reported by different authors was explained by taking into account the peculiarities of their experimental conditions.
Ključne besede: heterogeneous surface recombination, recombination coefficient, cobalt, cobalt oxide, temperature dependence, pressure dependence, plasma, oxygen
Objavljeno v DKUM: 26.03.2024; Ogledov: 119; Prenosov: 7
.pdf Celotno besedilo (3,59 MB)
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Cavitation erosion modelling : comparison of different driving pressure approaches
Luka Kevorkijan, Marko Pezdevšek, Ignacijo Biluš, Gorazd Hren, 2023, izvirni znanstveni članek

Opis: In this paper we compared different driving pressure approaches to calculate the cavitation potential energy from a source, which is transferred to a surface. The first approach used the reference pressure, the second approach used the pressure calculated at each timestep with no averaging, the third approach used the averaged pressure values from all timesteps included in one shedding cycle, and the last approach used pressure values from the steady state simulations results. The results show that for all formulations the averaged pressure values and steady state pressure values give similar results in terms of mean potential power distribution on the hydrofoil surface as in absolute values. The reference pressure approach gave similar results for the derivative and divergence formulation while for the source term the mean potential power distribution on the hydrofoil surface differs and the maximums were near the leading edge. The approach where we used no pressure averaging gave adequate results in terms of mean potential power distribution but differs from other approaches in absolute values which were considerably lower for all potential power formulations.
Ključne besede: cavitation, erosion potentional, driving pressure, numerical simulations
Objavljeno v DKUM: 21.02.2024; Ogledov: 247; Prenosov: 9
.pdf Celotno besedilo (796,29 KB)
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Development of an experimental Dead-End microfiltration layout and process repeatability analysis
Gorazd Bombek, Luka Kevorkijan, Grega Hrovat, Drago Kuzman, Aleks Kapun, Jure Ravnik, Matjaž Hriberšek, Aleš Hribernik, 2024, izvirni znanstveni članek

Opis: Microfiltration is an important process in the pharmaceutical industry. Filter selection and validation is a time-consuming and expensive process. Quality by design approach is important for product safety. The article covers the instrumentalization and process control of a laboratory-scale dead-end microfiltration layout. The layout is a downscale model of the actual production line, and the goal is filter validation and analysis of process parameters, which may influence filter operation. Filter size, fluid pressure, valve plunger speed, and timing issues were considered. The focus is on the identification of the most influential process parameters and their influence on the repeatability of pressure oscillations caused by valve opening. The goal was to find the worst-case scenario regarding pressure oscillations and, consequently, filter energy intake. The layout was designed as compact as possible to reduce pressure losses between the filter and valve. Valve-induced pressure oscillations proved to be prevailing over the water hammer effect. Several filters in sizes between 3.5 cm2 and 6900 cm2 were tested, and some recommendations were suggested for the reduction of energy intake of the filter and to improve the repeatability of the process.
Ključne besede: filtration, pressure oscillations, repeatability, processes, parameters
Objavljeno v DKUM: 01.02.2024; Ogledov: 272; Prenosov: 14
.pdf Celotno besedilo (5,64 MB)
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Microwave Synthesis of Poly(Acrylic) Acid-Coated Magnetic Nanoparticles as Draw Solutes in Forward Osmosis
Sabina Vohl, Irena Ban, Mihael Drofenik, Hermina Bukšek, Sašo Gyergyek, Irena Petrinić, Claus Hélix-Nielsen, Janja Stergar, 2023, izvirni znanstveni članek

Opis: Polyacrylic acid (PAA)-coated magnetic nanoparticles (MNP@PAA) were synthesized and evaluated as draw solutes in the forward osmosis (FO) process. MNP@PAA were synthesized by microwave irradiation and chemical co-precipitation from aqueous solutions of Fe2+ and Fe3+ salts. The results showed that the synthesized MNPs have spherical shapes of maghemite Fe2O3 and superparamagnetic properties, which allow draw solution (DS) recovery using an external magnetic field. Synthesized MNP, coated with PAA, yielded an osmotic pressure of ~12.8 bar at a 0.7% concentration, resulting in an initial water flux of 8.1 LMH. The MNP@PAA particles were captured by an external magnetic field, rinsed in ethanol, and re-concentrated as DS in repetitive FO experiments with deionized water as a feed solution (FS). The osmotic pressure of the re-concentrated DS was 4.1 bar at a 0.35% concentration, resulting in an initial water flux of 2.1 LMH. Taken together, the results show the feasibility of using MNP@PAA particles as draw solutes.
Ključne besede: magnetic nanoparticles, microwave synthesis, polyacrilic acid, osmotic pressure, draw solution, forward osmosis
Objavljeno v DKUM: 05.12.2023; Ogledov: 288; Prenosov: 14
.pdf Celotno besedilo (3,00 MB)
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P-x,y equilibrium data of the binary systems of 2-propanol, 1-butanol and 2-butanol with carbon dioxide at 313.15 K and 333.15 K
Dragana Borjan, Maša Knez Marevci, Željko Knez, 2022, izvirni znanstveni članek

Opis: The ability to predict the behaviour of high-pressure mixtures of carbon dioxide and alcohol is important for industrial purposes. The equilibrium composition of three binary carbon dioxide-alcohol systems was measured at temperatures of 313.15 K and 333.15 K and at pressures of up to 100 bar for carbon dioxide-2-propanol, up to 160 bar for carbon dioxide-1-butanol and up to 150 bar for carbon dioxide-2-butanol. Different equilibrium compositions of carbon dioxide in alcohols were observed despite their similar molecular weight (M2-propanol = 60.100 g mol−1, M1-butanol = 74.121 g mol−1 and M2-butanol = 74.122 g mol−1) and place in the functional hydroxyl group (first or second carbon molecule). It is assumed that the differences in the phase equilibria are due to different vapor pressures, polarities and solute-solute interactions.
Ključne besede: high-pressure phase equilibrium, carbon dioxide, 2-propanol, 1-butanol, 2-butanol
Objavljeno v DKUM: 17.08.2023; Ogledov: 328; Prenosov: 21
.pdf Celotno besedilo (1,82 MB)
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Time pressure, work-related spousal support seeking, and relationship satisfaction : spillover and crossover effects among dual-earner couples
Sara Tement, Katarina Katja Mihelič, Bettina Kubicek, 2023, izvirni znanstveni članek

Opis: The present study examined how time pressure at work is transmitted to the home domain and how it affects individuals’ (spillover) as well as their partners’ relationship satisfaction (crossover). We examined the role of work-related spousal support seeking and proposed that it serves as a mediator of the spillover as well as the crossover process. We further explored whether the proposed spillover-crossover process is gender-contingent. Using a sample of 308 dual-earner couples, we found support for a positive link between time pressure at work and spousal support seeking. As hypothesized, spousal support seeking served also as a crossover mechanism. However, distinct spillover and crossover processes were found for men and women. These findings not only point to a new spillover and crossover mechanism but also highlight gender-specific patterns in the role of support seeking. As this coping strategy is feasible when job stressors are high, it should be considered a part of stress management trainings and organizational practices.
Ključne besede: spillover, crossover, time pressure, dual-earner couples, work-related spousal support, relationship satisfaction, gender differences
Objavljeno v DKUM: 13.07.2023; Ogledov: 357; Prenosov: 40
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Interleukin response in patients treated with abbreviated laparotomy for severe intraabdominal sepsis
Tomaž Jagrič, Maksimiljan Gorenjak, Evgenija Homšak, Bojan Krebs, 2022, izvirni znanstveni članek

Ključne besede: intraabdominal sepsis, surgery, negative wound pressure therapy, interleukin-6, interleukin-10
Objavljeno v DKUM: 16.02.2023; Ogledov: 452; Prenosov: 32
.pdf Celotno besedilo (179,64 KB)
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Konstruiranje motoriziranega sistema za pozicioniranje hitrih kamer : diplomsko delo
Nejc Dvoršek, 2020, diplomsko delo

Opis: V diplomskem delu je opisana nadgradnja Split Hopkinson Pressure Bar (SHPB) preizkuševališča z motoriziranim sistemom za pozicioniranje dveh hitrih kamer. Kameri dodata raziskavi karakteristik materialov nov vir podatkov in način analiziranja le teh. Kameri se delita na horizontalno in vertikalno. Vsaka kamera bo imela svoj motoriziran sistem, ki bo zmožen krmilja po vseh treh koordinatah v prostoru. Sistem za horizontalno kamero je že bil razvit na Czech Technical University v Pragi in ga je potrebno prilagoditi za SHPB v Mariboru. Vertikalni del je potrebno na novo skonstruirati. Oba motorizirana sistema bosta za nosilne dele uporabljala lahke aluminijast profile. Za krmilje pa bodo uporabljena kroglična vretena in okrogla vodila skupaj s pripadajočimi krogličnimi maticami in linearnimi krogličnimi ležaji. Horizontalni in vertikalni motoriziran sistem bo možno upravljati posamezno ali skupaj kot celoto.
Ključne besede: Split Hopkinson Pressure Bar, hitra kamera, krmilje, konstruiranje, linearno vodilo, kroglično vreteno
Objavljeno v DKUM: 24.09.2020; Ogledov: 918; Prenosov: 72
.pdf Celotno besedilo (5,92 MB)

Modificiranje zeolitov za izboljšanje selektivnosti pri separaciji plinov : diplomsko delo univerzitetnega študijskega programa I. stopnje
Mitja Čuš, 2019, diplomsko delo

Opis: Diplomsko delo je potekalo v sodelovanju s podjetjem Silkem d.o.o v njihovem raziskovalnem laboratoriju. Delo zajema modificiranje zeolitov z namenom, da izboljšamo separacijo plinov, natančneje kisika in dušika iz atmosferskega zraka. Namen diplomskega dela je ugotoviti in laboratorijsko preveriti kateri zeoliti so primerni za molekularna sita za namene adsorpcije pod povišanim tlakom in pod podtlakom. Zeolit Na13X smo modificirali z ionsko izmenjavo s CaCl2 in s tem dobili zeolit Ca13X. Molekularna sita so temeljnega pomena pri separaciji zraka s procesom adsorpcije pod povišanim tlakom (PSA-pressure swing adsorption) in adsropcije pod podtlakom (VPSA-vacuum pressure swing adsorption). PSA in VPSA sta procesa pridobivanja oziroma bogatenja kisika, ki sta energetsko manj potratna kot pridobivanje kisika z uveljavljenimi metodami kot je to utekočinjanje zraka (ohlajevanje zraka), med seboj pa se razlikujeta po obratovalnem tlaku. Zeolitna molekularna sita se uporabljajo za proizvodnjo medicinskega kisika v kisikovih generatorjih. Raziskovali smo kako vplivajo struktura zeolita, obratovalni tlak, višina kolone in zadrževalni čas na učinkovitost adsorpcije. Velja, da je separacija zraka učinkovitejša z večjo aktivno površino zeolita, separacijski učinek pa višji z višjim obratovalnim tlakom. Višja kot je kolona, daljši je zadrževalni čas, z večanje višine pa je tudi večja količina polnila, kar pomeni večjo aktivno površino in s tem boljšo adsorpcijo. Modifikacija zeolita Na13X je potekala tako, da smo omenjen zeolit dodali v raztopino CaCl2 in šaržo intenzivno mešali 48 ur. Šaržo smo nato prefiltrirali in posušili. Ca13X smo granulirali v laboratoriju z Eirichovim granulatorju. Zeolitu Ca13X smo dodali deionizirano vodo in vezivo atapulgit ter granulirali do velikosti, primerne za nasutje. Pred uporabo zeolita smo granule kalcinirali pri 500 °C, saj s kalcininacijo dosežemo aktivacijo zeolita in izparevanje vlage ter drugih adsorbiranih snovi. Z aktiviranimi zeoliti smo napolnili kolono in merili koncentracijo kisika na izhodu s kisikovim merilcem. Ugotovili smo, da je ionsko izmenjan kalcijev zeolit Ca13X bolj primeren za molekularno sito pri separaciji plinov iz zraka. Visoke koncentracije kisika doseže tudi zeolit 5A, vendar je za procesa PSA in VPSA bolj primeren kalcijev zeolit Ca13X.
Ključne besede: ionska izmenjava, zeolit 13X, kalcijev zeolit 13X, adsorpcija, Pressure swing adsorption, Vacuum pressure swing adsorption, separacija zraka.
Objavljeno v DKUM: 10.10.2019; Ogledov: 1527; Prenosov: 173
.pdf Celotno besedilo (1,24 MB)

Dušica Mirković, 2019, doktorska disertacija

Opis: The aim of this doctoral research was to develop and optimize parenteral nanoemulsions as well as the total parenteral nutrition (TPN) admixture containing a nanoemulsion obtained in the course of the optimization process (hereinafter referred to as optimal nanoemulsion), and to examine their physicochemical and biological quality as well. In addition, the quality of the prepared nanoemulsions was compared with the quality of the industrial nanoemulsion (Lipofundin® MCT/LCT 20%), and, in the end, the TPN admixture initially prepared was also compared with the admixture into which the industrial emulsion was incorporated. Parenteral nanoemulsions that were considered in this dissertation were prepared by the high-pressure homogenization method. This method is the most widely applied method for the production of nanoemulsions due to the shortest length of homogenization time, the best-obtained homogeneity of the product and the smallest droplet diameter. For the nanoemulsion formulation, preparation and optimization purposes, by using, firstly, the concept of the computer-generated fractional design, and, after that, the full experimental design, the assessment of both direct effects of different formulation and process parameters (the oil phase type, the emulsifier type and concentration, a number of homogenization cycles and the pressure under which homogenization was carried out) as well as the effects of their interactions on the characteristics of prepared nanoemulsions was performed. Monitoring the nanoemulsion physical and chemical stability parameters was carried out immediately after their preparation, and then after 10, 30 and 60 days. It included the visual inspection, the measurement of the droplet diameter (the mean and volume droplet diameter), the polydispersity index, the ζ-potential, the pH value, the electrical conductivity, and the peroxide number. After the preparation and after 60 days, the biological evaluation (the sterility test and the endotoxic test) of the prepared nanoemulsions was carried out. As far as the characterization of the TPN admixture is concerned, it included practically the same parameters. The dynamics of monitoring the characteristics of the TPN admixture was determined on the basis of practical needs of hospitalized patients (0h, 24h and 72h). The scope and comprehensiveness of this issue indicated the need to divide the doctoral dissertation into three basic stages. The first stage was preliminary. Using the 24-1 fractional factorial design, nanoemulsions for the parenteral nutrition were prepared. They contained either a combination of soybean and fish oil, or a combination of medium chain triglycerides and fish oil. In addition, the type and the amount of an emulsifier used, a number of high-pressure homogenization cycles, and the homogenization pressure, were also varied. The measurement of the above-mentioned parameters for the industrial nanoemulsion was parallely carried out (Lipofundin® MCT/LCT 20%). The objective of this part of the research was to identify critical numerical factors having the most significant effect on the characteristics that define the prepared parenteral nanoemulsions. Parameters that were singled out as the result of this stage of the research (the emulsifier concentration and a number of homogenization cycles) were used as independent variables in the second stage of the research.
Ključne besede: nanoemulsions, total parenteral nutrition admixtures, high pressure homogenization, design of experiments, optimization, analysis of variance, artificial neural networks
Objavljeno v DKUM: 07.06.2019; Ogledov: 11853; Prenosov: 17
.pdf Celotno besedilo (2,82 MB)

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