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INOVATIVNI PRISTUP OPTIMIZACIJI KRUGA MLJEVENJA U POSTROJENJU ZA PROIZVODNJU MIKRONIZIRANOGA PRAHA
No full textThis research was conducted to investigate and optimize the comminution circuit of the Arak Company in which bentonite micronized powder is produced. The criterion for evaluating was the optimal performance of grinding systems and the efficiency of the devices, and simultaneous optimization was considered in feed and product sizes, capacity, and energy. In addition to the Bond formula, Morrell and Austin relations, as an innovative approach, have also been employed to study the different parameters such as rotation speed and mill filling percent. In this unit, the main grinding operation is performed by a tube ball mill that is located in a closed circuit with two air separators. The size of the final product is finer than 75 microns, and 48 kilowatt-hours of energy are consumed to produce one ton of bentonite. About 59% of the total plant energy consumption was related to the grinding circuit of tube mill. The size of the tube mill feed was 3500 microns (d80), the percentage of charge and accumulation were 21 and 14% respectively, the average diameter of the steel balls was 60 mm and the relative rotation speed of the mill was 79%. The results showed that the efficiency of the grinding circuit is poor, and it was merely about 30%. By increasing the percentage of charge of the tube mill from 21 to 70%, increasing the size of the mill feed by 7000 microns, using balls with diameter ofIstraživanje je provedeno s ciljem analize i optimizacije kruga mljevenja u proizvodnome postrojenju tvrtke Arak, specijaliziranome za proizvodnju mikroniziranoga bentonitnog praha. Kriteriji vrednovanja obuhvaćali su optimalne performanse sustava mljevenja, energetsku učinkovitost opreme te istodobnu optimizaciju ulazne i izlazne granulacije, kapaciteta i specifične potrošnje energije. Uz Bondovu formulu u analizi su kao inovativan pristup primijenjene i Morrellove te Austinove jednadžbe s naglaskom na utjecaj radnih parametara poput brzine vrtnje i stupnja ispunjenosti mlina. Glavna operacija usitnjavanja u predmetnome postrojenju odvija se u cilindričnome mlinu s kuglama, koji je konfiguriran u zatvorenome krugu s dvama zračnim separatorima. Konačni proizvod dostiže finoću manju od 75 µm, uz specifičnu potrošnju energije od 48 kWh po toni bentonita. Analiza je pokazala da se približno 59 % ukupne potrošnje energije postrojenja odnosi na krug mljevenja mlina s kuglama. Ulazna veličina čestica (d₈₀) iznosila je 3500 µm, stupanj popunjenosti i akumulacije materijala bili su 21 % i 14 %, prosječni promjer kugli iznosio je 60 mm, a relativna brzina vrtnje mlina 79 %. Rezultati su uputili na nisku učinkovitost kruga mljevenja, tek oko 30 %. Provedene simulacije i prijedlozi optimizacije pokazuju da bi se povećanjem stupnja popunjenosti mlina s kuglama od 21 % na 70 %, povećanjem ulazne granulacije na 7000 µm, uporabom kugli promjera manjega od 40 mm te smanjenjem relativne brzine vrtnje na 60 % mogla ostvariti povećana učinkovitost kruga mljevenja i do 50 %. Dodatno je utvrđeno kako se približno 16 % krupnih čestica u proizvodu javlja u obliku aglomerata, pri čemu njihovo smanjenje ima izravan utjecaj na smanjenje specifične potrošnje energije i povećanje ukupne učinkovitosti procesa mljevenja
Marine Coolant Fluids’ Effect on the Mechanical Properties of Glass Fiber-Reinforced Composites
Get PDFThis study examines the effect of coolant and antifreeze solutions such as distilled water, ethylene glycol-based antifreeze with organic acid technology (OAT), and ethylene glycol-based antifreeze with inorganic inhibitors and glycerol (IAT/HOAT) on the tensile strength of glass fiber-reinforced polyester (GFRP-P) and vinyl ester (GFRP-VE) composites. Standardized specimens were produced and immersed in these solutions for three months at room temperature. Following exposure, tensile tests were conducted using the universal testing machine, supported by microscopic analysis to evaluate surface damage and internal structural changes such as composite layer delamination. The tensile test results show the highest decrease in tensile strength for GFRP-P specimens immersed in HOAT antifreeze (16.3%), whereas GFRP-VE specimens exhibit only a minimal reduction (3.4%). This difference is attributed to the higher chemical aggressiveness and alkalinity of the HOAT antifreeze. Furthermore, the decrease in the tensile strength of GFR-P exposed to OAT antifreeze is 6.1%, whereas GFRP-VE demonstrates a significantly smaller reduction of 1%, which can be attributed to the less aggressive chemical composition of the OAT formulation compared to HOAT. In contrast, the influence of distilled water on GFRP-P specimens is manifested as a tensile strength decrease of 12.7%, whereas GFRP-VE specimens show a reduction of 11%, attributed to the fluid’s density and the rate of hydrolytic degradation. These results contribute to a deeper understanding of the effects of various coolant media on the performance of GFRP in marine cooling systems, highlighting GFRP-VE as a more suitable matrix for prolonged exposure to coolant environments
Rational and consistent use of drug-coated balloons in a single percutaneous coronary intervention center in Croatia: five-year experience
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PLA Degrading Enzymes from Metagenomic Databases
No full textIn this study, we report the discovery and characterization of novel polylactic acid (PLA)-degrading enzymes sourced from the MGnify metagenomic database. Six candidate enzymes were initially identified, with subsequent efforts focused on two metagenomic enzymes that exhibited better activity and stability compared to the others. A biochemical characterization combined with N-terminal modifications was performed to assess the impact of N-terminal length and composition on enzyme activity and solubility. Our results underscore the significant potential of metagenomic resources for uncovering new biocatalysts, while also highlighting the critical role of protein engineering in addressing limitations such as low solubility, poor thermostability, and suboptimal expression in heterologous hosts. This work advances the development of efficient biocatalysts for the sustainable degradation and recycling of PLA
Concurrent subacute myocardial infarction and bilateral pneumonia presenting as acute heart failure: a case report
No full textThe role of telemedicine in prehospital emergency management of ST-elevation myocardial infarction
No full textLathyrus palustris – a newly discovered species in Slovenia
No full textA conspicuous wetland species, Lathyrus palustris L. with Holarctic distribution has been discovered as new for the flora of Slovenia, although the wetland flora and vegetation of the country is relatively well studied. We recorded the species in the area of the intermittent Lake Cerknica, growing in different herbaceous wetland plant communities. The ecology fits the data from the surrounding regions. Our finding fills an important gap in the distribution area between Southeastern and Central Europe, where the species’ rarity has resulted in it being declared endangered and accordingly protected
Mukokela crvuljka u pacijentice s ulceroznim kolitisom – prikaz slučaja
No full textAim: We present the rare case of a patient who was incidentally diagnosed with mucocele of the vermiform appendix by radiologic examination due to symptoms of ulcerative colitis (UC) and point out the importance of making this diagnosis before surgery. Case report: A 66-year-old woman was admitted for bloody diarrhea, nausea, diffuse abdominal pain and fever. Ultrasonography revealed an anechoic tubular lesion with dorsal enhancement in the right lower quadrant of the abdomen. Computed tomography showed a cystically dilated appendix with low-density intraluminal contents, without wall thickening or inflammatory changes in the surrounding area. Colonoscopy with biopsy revealed acute UC. After the symptoms had subsided, an appendectomy was performed with very careful manipulation to avoid leakage of fluid into the abdominal cavity. Histopathology revealed a dilated appendix filled with abundant mucus and lined with mucinous epithelium without mitosis or atypia, suggesting a simple mucocele. Conclusion: Appendiceal mucocele is a morphologic term for an enlarged, mucus-filled appendix, regardless of the underlying pathology, which may be non-neoplastic or neoplastic. It is a very rare disease and often goes unrecognized. The concomitant occurrence of appendiceal mucocele and UC is particularly rare and there is still no reliable evidence of a causal connection between the two. Resection is recommended for all mucoceles as there is a possibility of malignancy. Preoperative diagnosis is important to prevent spontaneous or iatrogenic rupture. If diagnostic imaging techniques reveal a cystic lesion in the right lower quadrant of the abdomen, an appendicocele should be considered in the differential diagnosis.Cilj: Prikazati rijedak slučaj pacijentice kojoj je dijagnosticirana mukokela crvuljka slučajno, radiološkim pregledima učinjenim zbog simptoma ulceroznog kolitisa, te ukazati na važnost postavljanja ove dijagnoze prije operacije. Prikaz slučaja: Pacijentica u dobi od 66 godina zaprimljena je zbog proljevastih stolica s nešto krvi i sluzi, mučnine, difuzne boli u trbuhu i povišene tjelesne temperature. Ultrazvučnim pregledom nađena je anehogena tubularna lezija s dorzalnim pojačanjem u donjem desnom kvadrantu abdomena. Kompjutorizirana tomografija pokazala je cistično dilatiran crvuljak s intraluminalnim sadržajem niskog denziteta, bez zadebljanja stijenke ili okolnih upalnih promjena. Kolonoskopijom s biopsijom dokazan je akutni ulcerozni kolitis. Nakon smirivanja simptoma ulceroznog kolitisa učinjena je apendektomija uz vrlo pažljivu manipulaciju i korištenje nepropusne vrećice da se izbjegne izlijevanje tekućeg sadržaja u peritonealnu šupljinu. Histopatološki radilo se o dilatiranom crvuljku ispunjenom obilnom sluzi, obloženom mucinoznim epitelom bez mitoza ili atipija, te je postavljena dijagnoza jednostavne mukokele. Zaključak: Mukokela crvuljka morfološki je termin za dilatirani crvuljak ispunjen sluzi, neovisno o patologiji u pozadini koja može biti neneoplastične ili neoplastične prirode. To je vrlo rijetka bolest i često ostaje neprepoznata. Osobito je rijetka istodobna pojava mukokele crvuljka i ulceroznog kolitisa i još uvijek nema pouzdanih dokaza o uzročnoj povezanosti između njih. Kod svih mukokela preporučuje se resekcija zbog mogućnosti maligniteta. Predoperacijska dijagnoza važna je zbog sprječavanja spontane ili jatrogene rupture. Kad se slikovnim dijagnostičkim metodama otkrije cistična lezija u desnom donjem kvadrantu abdomena, u diferencijalnoj dijagnozi treba razmotriti mukokelu crvuljka