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U ovom radu predloženo je i primijenjeno šest novih matematičkih modela temeljenih na poluempirijskom proračunu za karakterizaciju procesa sušenja u pećnici kompozita cementne žbuke ojačane celuloznim vlaknima (CMCRCF). Pokusi sušenja provedeni su pri četiri razine temperature sušenja u pećnici (70, 85, 105 i 120 °C) s četiri različita udjela celuloznih vlakana (0, 5, 10 i 20 %). Dobiveni rezultati uspoređeni su s onima dobivenim regresijskom analizom šest najčešće primjenjivanih matematičkih modela sušenja (Newton, Page, Page modified1, Page modified2, Handerson Pabis i Logarithmic) uz šest predloženih modela. Regresijska točnost procesa sušenja procijenjena je koeficijentom determinacije (R2), srednjom kvadratnom pogreškom (MSE), korijenom srednje kvadratne pogreške (RMSE) i srednjom apsolutnom pogreškom (MAE). Primijenjeni su i dodatni kriteriji da bi se osigurala veća valjanost odabranih modela. Dobivene vrijednosti pokazuju dobro slaganje predloženog modela MR9 s eksperimentalnim vrijednostima, što znači da predloženi model može jasno interpretirati eksperimentalne podatke o sušenju i predvidjeti suho stanje CMCRCF-a. In this paper, six novel mathematical models based on semi-empirical calculus are proposed and applied to characterise the oven-drying process of cement mortar composites reinforced with cellulosic fibres (CMCRCFs). The drying experiments were carried out on four levels of oven-drying temperatures (70, 85, 105, and 120 °C), with four different cellulosic fibres content (0, 5, 10, and 20 %). Obtained results were compared to those derived by regression analysis of six most typically used mathematical drying models (Newton, Page, Page modified1, Page modified2, Handerson Pabis, and Logarithmic) in addition to six proposed models. The regression accuracy of the drying process was evaluated by the coefficient of determination (R2), low mean square error (MSE), low root mean squared error (RMSE), and mean absolute error (MAE). Additional criteria were used to ensure more validity of the selected models. The obtained values indicate a highly accurate fit of the proposed model MR9, meaning that the proposed model can clearly interpret the experimental drying data and predict the dry state of CMCRCFs.

The present study aimed to evaluate the potential of mesoporous silica MCM-41 and Al-MCM-41 (molar ratio Si/Al = 20) for the removal of Rhodamine 6G (Rh6G) from aqueous solution. The adsorbents were characterised by XRD, FTIR, SEM-EDX, BET, and UV-Raman. Obtained results related to XRD analysis indicated that the MCM-41 structure remained intact after the incorporation of Al species. Kinetic adsorption study showed that the higher removal (88.75 %, 26.62 mg g–1) of Rh6G dye was achieved by Al-MCM-41 at 60 min. FTIR analysis showed that hydrogen bonding played the dominant role in the Rh6G removal mechanism, while the pH results showed that electrostatic interaction was also a key factor. This study shows that the prepared mesoporous materials are inexpensive and efficient adsorbents for the removal of cationic dyes. Cilj ovog istraživanja bio je procijeniti potencijal mezoporoznih silikata MCM-41 i Al-MCM-41 (molarni omjer Si/Al = 20) za uklanjanje rodamina 6G (Rh6G) iz vodene otopine. Za karakterizaciju adsorbensa primijenjeni su XRD, FTIR, SEM-EDX, BET i UV-Raman. Rezultati XRD analize pokazali su da je struktura MCM-41 nakon ugradnje iona Al ostala netaknuta. Kinetička analiza adsorpcije pokazala je da je u 60. minuti veće uklanjanje Rh6G bojila postignuto uporabom Al-MCM-41 (88,75 %, 26,62 mg g–1). FTIR analiza pokazala je da vodikova veza ima dominantnu ulogu u mehanizmu uklanjanja Rh6G, dok su rezultati pH pokazali da je elektrostatička interakcija također ključni čimbenik. Ovo istraživanje pokazalo je da su pripremljeni mezoporozni materijali jeftini, ali učinkoviti adsorbensi za uklanjanje kationskih boja.

Ash is a by-product of wood biomass combustion that must be removed daily from stoves or fireplaces. Therefore, operators or owners are exposed to the potential impact of ash. The goal of this study was to determine whether heavy metal present in wood pellet ash posed a health concern to stove operators/owners. The risk assessment procedure was carried out in several steps, including exposure evaluation, toxicity evaluation, and risk categorisation. The hazard coefficient (HQ) and non-carcinogenic hazard index (HI) were calculated for Cd, Cr, Cu, Ni, Pb, and Zn. HQ had the highest value for the ingestion pathway (3.62 ∙ 10–6), and the value for non-carcinogenic HI was 3.70 ∙ 10–6. The value HI < 1 suggests that there is no risk to operator health related to heavy metals in analysed wood pellets ash. The carcinogenic risk (CR) was calculated for Ni, Pb, Cr, and Cd, and the values were within the permitted limits. The risk assessment based on HI and CR indicators proved that there was no significant health concern regarding exposure to the analysed ashes. Pepeo je nusproizvod izgaranja drvne biomase koji se svakodnevno mora uklanjati iz peći ili kamina. Stoga su operateri ili vlasnici izloženi potencijalnom utjecaju pepela. Ovo istraživanje ima cilj procijeniti zdravstveni rizik izloženosti operatera/vlasnika pepelu drvenih peleta zbog sadržaja teških metala. Postupak procjene rizika proveden je u nekoliko koraka uključujući procjenu izloženosti, procjenu toksičnosti i kategorizaciju rizika. Izračunati su koeficijent opasnosti (HQ) i indeks nekarcinogene opasnosti (HI) za Cd, Cr, Cu, Ni, Pb i Zn. HQ je imao najveću vrijednost za izloženost putem gutanja (3.62 ∙ 10–6), a vrijednost za nekarcinogeni HI bila je 3.70 ∙ 10–6. Vrijednost HI < 1 ukazuje na to da sadržaj teških metala u analiziranom pepelu ne predstavlja rizik za zdravlje operatera. Karcinogeni rizik (CR) izračunat je za Ni, Pb, Cr i Cd, a vrijednosti su bile unutar dopuštenih granica. Rizik procijenjen primjenom HI i CR pokazatelja potvrdio je da ne postoji značajna opasnost za zdravlje osoba koje dolaze u kontakt s analiziranim pepelom.

The aim in this work was to investigate the change in microstructure, phase transformation temperatures, and thermal properties due to the quenching of the investigated Cu-Al-Mn and Cu-Al-Mn-Ti alloys in ribbon form. This paper presents the results of microstructure analysis and thermal properties of Cu-Al-Mn and Cu-Al-Mn-Ti shape memory alloys produced in ribbon form by melt spinning technique. The microstructural analysis was carried out before and after quenching. After casting of the investigated alloys, annealing at 900 °C for 30 min was performed, followed by water quenching. The microstructural analysis was carried out by optical and scanning electron microscopy equipped with an energy dispersive spectrometer and by X-ray diffractometer. Thermodynamic calculation of a ternary Cu-Al-Mn system in equilibrium condition was performed using Thermo-Calc 5 software. Phase transformation temperatures were determined by differential scanning calorimetry and electrical resistance measuring. The results of microstructural analysis show the presence of martensite microstructures before and after quenching in the Cu-Al-Mn alloy, while in the Cu-Al-Mn-Ti alloy martensite microstructure exists only after quenching. Phase transformation temperatures decreased after quenching and titanium addition. Cilj rada bio je istražiti promjene u mikrostrukturi, temperaturama transformacije i toplinskim svojstvima nastale uslijed kaljenja Cu-Al-Mn i Cu-Al-Mn-Ti legura u obliku trake. U radu su prikazani rezultati mikrostrukturne analize i toplinskih svojstava Cu-Al-Mn i Cu-Al-Mn-Ti legura s prisjetljivosti oblika proizvedenih u obliku trake postupkom melt spinning. Mikrostrukturna analiza je provedena prije i nakon kaljenja. Nakon lijevanja istraživane legure su žarene pri 900 °C u trajanju 30 minuta, nakon čega je slijedilo kaljenje u vodi. Mikrostrukturna analiza je provedena optičkim i pretražnim elektronskim mikroskopom opremljenim energetsko disperzijskim spektroskopom te rendgenom. Termodinamički proračun ternarnog Cu-Al-Mn sustava proveden je u ravnotežnim uvjetima pomoću Thermo-Calc 5 programskog paketa. Temperature fazne transformacije određene su diferencijalnom pretražnom kalorimetrijom i mjerenjem električnog otpora. Rezultati mikrostrukturne analize pokazuju prisutnost martenzitne mikrostrukture prije i nakon kaljenja Cu-Al-Mn legure, dok u Cu-Al-Mn-Ti leguri martenzitna mikrostruktura postoji samo nakon kaljenja. Temperature faznih transformacija smanjuju se nakon kaljenja i dodatka titana.

For major thermal engines used in industrial sectors, the use of chillers has been growing steadily over the previous decades. Indeed, this is linked strongly to their large energy performance despite their investment costs, which are still high, in particular for low powers. Performance coefficients for absorption chillers are relatively low, and their profitability depends on the costs of the main equipment and more particularly on the price of the absorber. Several studies focusing on the development of mass contactors are underway with the principal objective of further improving their performance of mass and energy transfer. Relating to the mass and heat transfer, it is specified that the contact between the phases in circulation is ensured by different types of contactors. The transfer performance is correlated with the heat and mass transfer coefficient on the one hand, and the specific exchange area, i.e., the exchange area per unit volume of the contactor on the other hand. These contactors are distinguished by their mode of contact between phases (bubbling, spraying, falling film, etc.). While the exchange coefficient depends on the hydrodynamics regime in the contactor (flow regime and physicochemical properties of phases), the specific exchange area is dictated by its operating mode. Any limitation of its use for a specific application (physicochemical phenomena, such as crystallisation, deposited dust, etc.) requires research and development of better devices more adapted. Moreover, the most used contactors in chemical engineering are plate columns, packed columns, falling film columns, spray columns, etc. In order to intensify exchanges, a new absorber of the pulverised type is to be explored in relation with the physicochemical properties of the phases, and of their hydrodynamic flow conditions in the sprayed column. Therefore, an experimental study of the influence of operating variables (nozzle diameter, fluids flow rate, their concentrations, size of droplets, etc.) on the overall coefficient of mass transfer in gaseous phase in the absorber of the absorber chiller was conducted. After having fixed the pressure in the absorber, the first part of the study allowed developing new correlations linking the experimental results of the KG ∙ a to all operating variables (L, C, dd, etc.). The second part was devoted to the simulation of the absorption chiller functioning by introducing the concept of energy and exergy yields based on the mass transfer correlations. Posljednjih desetljeća vidljiv je stalan porast upotrebe rashladnih uređaja kod glavnih toplinskih motora koji se upotrebljavaju u industrijskim sektorima. Koeficijenti učinka apsorpcijskih rashladnih uređaja relativno su niski, a njihova isplativost ovisi o troškovima glavne opreme, točnije o cijeni apsorbera. U tijeku je nekoliko studija razvoja kontaktora masa usmjerenih na poboljšanje prijenosa tvari i energije u kontaktorima. Vezano uz prijenos tvari i topline, specificirano je da se kontakt između cirkulirajućih faza ostvaruje različitim tipovima kontaktora. Učinak prijenosa koreliran je s koeficijentom prijenosa tvari i topline s jedne strane te specifičnom površinom izmjene, tj. površinom izmjene po jedinici volumena kontaktora, s druge strane. Kontaktori se razlikuju po načinu kontakta faza (mjehurići, raspršenje, padajući film, itd.). Dok koeficijent izmjene ovisi o hidrodinamičkom režimu u kontaktoru (režim protoka i fizikalno-kemijska svojstva faza), specifična površina izmjene ovisi o njegovu načinu rada. Ograničenje njegove uporabe na neku određenu primjenu (fizikalno-kemijske pojave poput kristalizacije) zahtijeva istraživanje i razvoj uređaja koji bi više bili prilagođeni spomenutoj primjeni. Štoviše, najčešće upotrebljavani kontaktori u kemijskom inženjerstvu su kolone s pliticama, kolone s punilima, kolone s padajućim filmovima, kolone za raspršivanje, itd. S ciljem povećanja izmjena, istražit će se novi praškasti apsorber i to s obzirom na fizikalno-kemijska svojstva faza i njihove hidrodinamičke uvjete strujanja u koloni za raspršivanje. Stoga je provedeno istraživanje utjecaja radnih varijabli (promjera mlaznice, protoka fluida, koncentracije fluida, veličine kapljica, itd.) na ukupni koeficijent prijenosa tvari u plinovitoj fazi u apsorberu rashladnog uređaja. Nakon fiksiranja tlaka u apsorberu, prvi dio istraživanja omogućio je razvoj novih korelacija koje povezuju eksperimentalne KG ∙ a rezultate sa svim radnim varijablama (L, C, dd, itd.). Drugi dio bio je posvećen simulaciji rada apsorpcijskog rashladnog uređaja uvođenjem koncepta energetskih i eksergijskih prinosa temeljenih na izrazima za prijenos tvari.

Microbial bile salt hydrolases (BSHs) catalyse the hydrolysis of glycine and taurine-linked bile salts in the small intestine of humans. Achieving the effects of structural changes in BSH molecules on biocatalytic efficiency (kcat/Km) and activation energy (Ea) is necessary to determine biocatalytic performances of the enzymes. Amino acids responsible for biocatalytic activity or substrate specificity in BSH molecules were modified to determine the effects of structural changes on kcat/Km values and Ea values of the bioconversion reactions. Purified wild type positive control enzyme (pCON2) and mutant recombinant target enzymes (F18L and Y24L) reacted with six conjugated pure bile salt substrates at working temperature and pH conditions. The results of the hydrolysis conversion analysis conducted at various pH conditions were used to estimate kcat/Km, and the assays conducted at various temperature conditions were used to approximate Ea of the biocatalytic reactions. The quantified kcat/Km value was found remarkably highest with mutant recombinant enzymes (Y24L), while the efficiency value with wild type (pCON2) was determined as lowest, indicating that the structural modifications in BSH molecules showed higher values. The alterations with the mutant-type enzymes F18L and Y24L resulted in decreasing kcat/Km and increasing Ea estimations of the hydrolysis conversion reactions. Mikrobne hidrolaze žučnih soli (BSH) kataliziraju hidrolizu soli glicina i taurina u tankom crijevu ljudi. Aminokiseline odgovorne za biokatalitičku aktivnost ili specifičnost supstrata u BSH molekulama modificirane su da bi se odredio utjecaj strukturnih promjena BSH molekula na biokatalitičku učinkovitost (kcat/Km) i energiju aktivacije (Ea) reakcija biokonverzije. Pročišćen prirodni enzim pCON2, upotrijebljen kao kontrola, a mutantni enzimi (F18L i Y24L) reagirali su sa šest čistih supstrata konjugiranih žučnih soli pri radnim uvjetima pH i temperature. Eksperimenti provedeni pri različitim pH vrijednostima primijenjeni su u procjeni kcat/Km vrijednosti biokatalitičkih reakcija, dok su eksperimenti provedeni pri različitim temperaturama primijenjeni u aproksimaciji njihovih Ea vrijednosti. Iznos kcat/Km bio je najveći kod mutantnih enzima (Y24L), a najniži kod kontrole (pCON2), što ukazuje da su strukturne modifikacije u BSH molekulama povezane s većom učinkovitosti. Preinake kod mutantnih enzima F18L i Y24L rezultirale su smanjenjem vrijednosti kcat/Km te povećanjem procijenjene Ea vrijednosti reakcija hidrolize.

This study is a contribution for radiation dose calculations of a hypothetical accident of a 1 MW research reactor Triga Mark II using HotSpot code. A postulated accidental release of noble gases and halogens were considered. The total effective dose (TED) was estimated for 1 day and 50 years after release. The total damage of fuel element cladding with a maximum radioactivity was considered. The obtained results show minimal TED values at the beginning of the release and at a shorter distance from the source. The maximum calculation results are acceptable and below the recommended public dose limit. Ovo istraživanje doprinos je izračunima doze zračenja hipotetske nesreće istraživačkog reaktora Triga Mark II od 1 MW primjenom HotSpot koda. Razmatrano je slučajno oslobađanje plemenitih plinova i halogena. Određena je vrijednost ukupne učinkovite doze nakon 1 dana i nakon 50 godina. Razmatrano je ukupno oštećenje obloge dijela s maksimalnom radioaktivnošću. Dobiveni rezultati pokazuju minimalne vrijednosti ukupne učinkovite doze na početku ispuštanja i na manjoj udaljenosti od izvora. Maksimalni rezultati izračuna su prihvatljivi i ispod preporučenog doznog ograničenja.

The purpose of this study was to assess the antioxidant activity of the fresh extracts of Croatian and Greek watermelon seeds. Samples were prepared using two extraction methods: Soxhlet and maceration. Ethanol was used as a solvent in the Soxhlet, and methanol in the maceration method. The mass fractions of the extracts obtained by maceration were lower compared to those obtained by the Soxhlet method. The antioxidant capacity of fresh watermelon-seed extracts was determined by DPPH (2,2-diphenyl-1-picrylhydrazyl radical) method. The antioxidant capacity of the extracts was also expressed via IC50 (half maximal inhibitory concentration). Based on the obtained IC50 values (1.41 to 2.60 mg ml−1), all tested extracts showed antiradical activity but antioxidant capacity was better in extracts obtained by the maceration method. The reason for this may be the use of methanol as a solvent, which was to be expected, since methanol is a more polar solvent than ethanol. The neutralisation capacity of DPPH radicals of analysed extracts was compared to the neutralisation capacity of ascorbic acid as standard. The concentrations of tested extracts required to neutralize 50 % of DPPH radicals were significantly higher than the required concentration of ascorbic acid (0.25 mg ml–1). This work is licensed under a Creative Commons Attribution 4.0 International License. Svrha ovog istraživanja bila je procijeniti antioksidativno djelovanje ekstrakata svježih sjemenki lubenice uzgojenih u Hrvatskoj i Grčkoj. Ekstrakti su pripremljeni dvjema metodama: Soxhletovom metodom i maceracijom. Etanol je upotrijebljen kao otapalo u Soxhletovoj metodi, a metanol u maceraciji. Maseni udjeli ekstrakta dobiveni maceracijom niži su od onih dobivenih Soxhletovom metodom. Antioksidacijski kapacitet ekstrakta svježih sjemenki lubenice određen je metodom DPPH (2,2-difenil-1-pikrilhidrazilni radikal). Antioksidacijski kapacitet ekstrakata također je izražen s IC50 (polovica maksimalne inhibitorne koncentracije). Na temelju dobivenih vrijednosti IC50 (1,41 do 2,60 mg ml−1), svi ispitani ekstrakti pokazali su antiradikalno djelovanje, ali je antioksidacijski kapacitet bio bolji u ekstraktima dobivenim metodom maceracije. Razlog tome može biti upotreba metanola kao otapala, što se moglo očekivati budući da je metanol polarnije otapalo od etanola. Kapacitet neutraliziranja DPPH radikala analiziranih ekstrakata uspoređen je sa standardom za neutraliziranje askorbinske kiseline. Koncentracije svih ispitnih ekstrakata potrebne za neutraliziranje 50 % radikala DPPH bile su znatno veće od potrebne koncentracije askorbinske kiseline (0,25 mg ml–1). Ovo djelo je dano na korištenje pod licencom Creative Commons Imenovanje 4.0 međunarodna.

Decarbonisation means reducing or ideally eliminating the greenhouse gas emissions by evaluating all processes in a system from a “low-carbon” perspective. This review describes the current state of the fertiliser industry, and the options and recommendations for its decarbonisation. Decarbonisation of the fertiliser industry can be achieved with the developing technologies in terms of raw materials, energy usage, and operating conditions in the fertiliser production processes. Low-carbon fertilisers can be realised with the improvements that can be made in the life cycle of the fertiliser, from the derivation of the raw materials to the formation of the final products. Today, many decarbonisation studies with new technologies that can be created in ammonia production, which is the most energy-intensive process in the fertiliser industry, are at the research stage. This paper reviews the use of hydrogen source in ammonia production and achieving biomass gasification or electrolysis with low carbon footprints, reducing greenhouse gas emissions in nitric acid production, integrating carbon capture and storage technologies into the fertiliser processes, and increasing the efficiency of low-carbon agricultural practices. This work is licensed under a Creative Commons Attribution 4.0 International License. Dekarbonizacija podrazumijeva smanjenje ili, u idealnom slučaju, potpunu eliminaciju emisija stakleničkih plinova kroz procjenu svih uključenih procesa iz niskougljične perspektive. Ovaj pregledni rad opisuje trenutno stanje u industriji gnojiva, te daje mogućnosti i preporuke za njenu dekarbonizaciju. Dekarbonizacija industrije gnojiva može se postići razvojem tehnologija bilo da se radi o proizvodnji sirovina, korištenju energije ili radnim uvjetima procesa proizvodnje. Niskougljična gnojiva mogu se realizirati kroz poboljšanja tijekom procesa proizvodnje, od dobivanja sirovina do nastanka konačnih proizvoda. Danas se provode istraživanja dekarbonizacije vezana uz nove tehnologije koje se mogu primijeniti kod proizvodnje amonijaka kao energetski najintenzivnijeg procesa u industrijskoj proizvodnji gnojiva. Ovaj rad dotiče se izvora vodika u proizvodnji amonijaka te postizanja plinifikacije ili elektrolize biomase s niskim ugljičnim otiskom, smanjenja emisija stakleničkih plinova u proizvodnji dušične kiseline, integriranja tehnologija hvatanja i skladištenja ugljika u procese proizvodnje gnojiva te povećanje učinkovitosti niskougljičnih praksi u poljoprivredi. Ovo djelo je dano na korištenje pod licencom Creative Commons Imenovanje 4.0 međunarodna.