The study of aerosol dispersion in indoor environments is essential to understanding and mitigating airborne virus transmission, such as SARS-CoV-2. Computational Fluid Dynamics (CFD) has emerged as a valuable tool for investigating aerosol dispersion, providing an alternative to costly experimental methods. In this study, we investigated the performance of four (4) Reynolds-averaged Navier-Stokes (RANS) turbulence models in predicting aerosol dispersion from a human body coughing in a small, ventilated indoor environment. We compared the Standard, RNG, Realizable k-ϵ models and the SST k- ω model using the same boundary conditions. We initially observed that the horizontal distance of the coughed aerosols after 10.2s dispersion time was substantially shorter with the standard k-ϵ turbulence compared to the other three turbulence models compared to the SST k-ω model, the RNG, and realizable k-ϵ models exhibit a high degree of similarity in their dispersion patterns. Specifically, we observed that the aerosols dispersed horizontally faster with the RNG and Realizable k-ϵ models. In conclusion, when compared to qualitative data from the literature, our observations exclude the standard k-ϵ turbulence. However, to select the most appropriate turbulence model for capturing the cough flow and aerosol dispersion dynamics, further detailed validation against both quantitative and qualitative data is needed.

The paper considers the possibility of improving the technical characteristics of gas surge arresters for the co-ordination of insulation at low voltage, medium voltage and high voltage levels. The idea for improving the characteristics of a gas surge arrester is based on the application of the radioactive source 241Am in the area of the surge arrester cathode. Intensive ionization with alpha particles significantly increases the number of free electrons in the space between electrodes, which shortens the time of their transition to initial electrons. This changes the Paschen curve of the gas surge arrester, narrows and flattens its impulse characteristic and reduces the stochasticity of the response of the gas surge arrester. All this results in a significant improvement in the characteristics of the gas surge arrester at all voltage levels. This improvement is particularly noticeable in the case of low voltage surge arresters. The paper is basically theoretical-experimental research. The experiments were performed under well-controlled laboratory conditions. The combined measurement uncertainty of all measurements was acceptable.

Šerijatska vjenčanja kršćana iz različitih su se razloga prakticirana gotovo kroz cijelo razdoblje osmanske vladavine. Za kršćanske parove koji bi svoju vezu ozakonili pred kadijom vrijedila su ista pravila kao i za muslimane, što je u odnosu na strogoću crkvenih propisa imalo svoje prednosti. Tako su se kršćani mogli vjenčati s bližim srodnikom ili pripadnikom druge Crkve, razvesti se, a u slučaju rastave ili muževe smrti udovica je, barem neko vrijeme, bila osigurana iznosom vjenčanog dara koji se dogovarao prije vjenčanja.

In this paper the influence of different process parameters on surface roughness responses in plasma jet cutting process was investigated. Experimentations were conducted on shipbuilding aluminium 5083 sheet thickness 8 mm. Experimental work was performed according to Taguchi L27 orthogonal array by varying four parameters such as gas pressure, cutting speed, arc current and cutting height. Due to complexity of manufacturing process and aim to cover wide experimental space few constraints regarding cutting area were defined. Surface roughness parameters Ra and Rz were analysed as cut quality responses. In order to define mathematical model that will be able to describe effects of process parameters on surface roughness artificial intelligence (AI) fuzzy logic (FL) technique was applied. After functional relations between input parameters and surface roughness responses were defined prediction accuracy of developed fuzzy logic model was checked by comparison between experimental and predicted data. Mean absolute percentage error (MAPE) as well as coefficient of determination (R2) were used as validation measures. Finally, optimal process conditions that lead to minimal surface roughness were defined by creating response surface plots.

The removal of copper ions from aqueous solutions using bean shells as an adsorbent is presented in this paper. The influence of the solution solution pH on the biosorption capacity was investigated. The biosorption capacity increased with the increase in the solution pH. The pseudo-second order kinetic model showed the best agreement with the analyzed experimental data, indicating that chemisorption could be a possible way of binding the copper ions to the surface of the bean shells. The Langmuir isotherm model best fitted the analyzed isotherm data. The SEM-EDS analysis was performed before and after the biosorption process. The change in the morphology of the sample after the biosorption process was evident, whereby K, Mg, Si, and Ca were possibly exchanged with copper ions. Response Surface Methodology (RSM) based on the Box-Behnken design (BBD) was used to optimize the biosorption process, with the selected factors: the solution pH, initial copper ions concentration, and contact time. The optimum biosorption conditions were determined to be: pH = 3-4, initial copper ions concentration 100 mg dm-3, and contact time 10-30 minutes.