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High-temperature coatings
No full textU ovom radu opisana je visokotemperaturna korozija te je dan uvid u zaštitu od korozije korištenjem visokotemperaturnih premaza te je opisano zaštitno djelovanje premaza te vrste veziva u premazu. Visokotemperaturni premazi imaju ključnu ulogu u zaštiti površina izloženih ekstremnim temperaturama, koroziji i drugim okolišnim utjecajima. Ovakvi premazi bi trebali izdržati dugotrajno izlaganje visokim radnim temperaturama bez pojave oštećenja, održavaju barijerni integritet kako bi se spriječio kontakt podloge s vlagom i ostalim korozivnim tvarima, sadrže postojane pigmente koji nisu osjetljivi na toplinu i prianjaju na podlogu bez ljuštenja. Visokotemperaturni premazi sastoje se od organskih ili anorganskih materijala, a obično su izrađeni od silikonskih smola i pigmenata koji ostaju stabilni čak i kod izlaganja ekstremnoj toplini. U eksperimentalnom dijelu rada ispitane su četiri vrste visokotemperaturnih premaza u slanoj i vlažnoj komori te su uzorci izloženi visokim temperaturama kako bi se vidjelo njihovo ponašanje pri visokim temperaturama. Također je provedeno mjerenje otpora premaza pomoću elektrokemijske impedancijske spektroskopije.This paper describes high-temperature corrosion and provides insight into corrosion protection using high-temperature coatings. The protective action of coatings and the binding agent's role in the coating are explained. High-temperature coatings play a crucial role in safeguarding surfaces exposed to extreme temperatures, corrosion, and other
environmental influences. These coatings should withstand prolonged exposure to high operating temperatures without damage, maintain barrier integrity to prevent substrate contact with moisture and other corrosive substances, and contain stable pigments resistant to heat while adhering to the substrate without peeling. High-temperature coatings consist of organic or inorganic materials, typically made from silicone resins and heat-stable pigments. In the experimental part of the study, four types of high-temperature coatings were tested in a salt spray and humidity chamber, and samples were exposed to high temperatures to observe their behavior under these conditions. Additionally, the resistance of the coatings was measured using electrochemical impedance spectroscopy
Determinaton of transmission gear ratio of Formula Student race car adjusted to acceleration test
No full textU sklopu ovog rada, zadatak je bio provesti proračun za odabir prijenosnog omjera za Formula student bolid te validacija istog putem simulacija u računalnom alatu AVL VSM. Proračun je baziran na 2D modelu koncentrirane mase i modelu bicikla. Potrebni parametri su geometrija bolida, parametri aerodinamičkog paketa, momentna karakteristika elektromotora te model gume. Ograničenje samog proračuna je jednostavan model vozila u kojem nisu promatrana prigušenja tijekom ubrzanja. Iz tog razloga su provedene simulacije različitih prijenosnih omjera pomoću VSM-a u kojem je bilo potrebno definirati model vozila, staza procedure Acceleration i model vozača. U samom radu je detaljno opisan tijek proračuna, svi korišteni parametri te je opisan postupak simuliranja Formula student procedure Acceleration. Konačni rezultati su komentirani te je odabran prijenosni omjer 12.As part of this work, the task was to carry out calculations for the selection of the transmission ratio for the Formula student car and its validation through simulation in the computer tool AVL VSM. The calculation is based on a 2D concentrated mass model and a bicycle model. The required parameters are the geometry of the car, the parameters of the aerodynamic package, the torque characteristic of the electric motor and the tire model. The limitation of the calculation itself is a simple vehicle model in which damping during acceleration was not observed. For this reason, simulations of different transmission ratios were carried out using VSM, in which it was necessary to define the vehicle model, the path of the Acceleration procedure and the driver model. The paper itself describes the calculation process in detail, all the parameters used, and describes the procedure for simulating the Formula student procedure Acceleration. The final results were commented and a transmission ratio of 12 was chosen
Testing of weld joints according to standard HRN EN ISO 14555
No full textU teorijskom dijelu rada opisani su postupci zavarivanja svornjaka s detaljnim uvidom u
postupak elektrolučnog zavarivanja svornjaka s odmakom luka uz primjenu keramičkog prstena
ili zaštitnog plina (postupak 783). Također, detaljno su opisane metode ispitivanja zavarenih
spojeva svornjaka prema zahtjevima norme HRN EN ISO 14555 ovisno o razini kvalitete,
promjeru svornjaka i radnoj temperaturi.
U eksperimentalnom dijelu rada prvotno su postupkom 783 zavarena dva tipa uzoraka
svornjaka koja se sastoje od 12 zavarenih svornjaka promjera Ø22 mm i 12 zavarenih svornjaka
promjera Ø19 mm, te su zatim na njima provedena ispitivanja definirana prema normi HRN
EN ISO 14555 što uključuje vizualni pregled, test savijanja, makroanalizu i test vlačne čvrstoće.
Kriteriji prihvatljivosti dobivenih rezultata ispitivanja definirani su prema normi HRN EN ISO
3834-2, te se daje analiza rezultata i procjena razine kvalitete zavarenih spojeva. Na kraju je
određena prikladnost provedenih ispitivanja za primjenu ovih dvaju tipova zavarenih svornjaka
u radnim uvjetima i za različite načine opterećenja.The teoretical part of this thesis covers stud welding processes with detailed insight in stud arc
welding using ceramic ferrule or shielding gas (process 783). Investigation methods of those
welding joints according to HRN EN ISO 14555 standard in terms of quality levels, stud
diameter and ambient temperature are also described in detail.
In experimental part, two types of samples were welded using process 783. Samples were
consisted of 12 welded studs of diameter Ø22 mm and 12 welded studs of diameter Ø19 mm.
Therefore, they were investigated with visual examination, bend test, macro examination and
tensile test according to HRN EN ISO 14555 standard. Furthermore, acceptance criteria was
defined and analysis of results was carried out as well as evaluation of quality levels of welding
joints according to HRN EN ISO 3834-2 standard. Finally, suitability of experiments done was
defined for use in working ambient for both types of welded studs as well as their use with
different types of stress
Triaenophorosis in Northern Pike (Esox lucius) from the Mrežnica River
No full textOko 1500 vrsta trakavica parazitira u ribama i neke mogu uzrokovati značajne bolesti.
Među njima treba izdvojiti trakavice roda Triaenophorus i to vrste T. nodulosus i T. crassus,
koje uzrokuju trienoforozu štuke. U crijevu konačnog domaćina, tj. ribi iz porodice Esocidae,
ove odrasle trakavice uzrokuju erozije i ulceracije sluznice praćene staničnom infiltracijom i
fibrozom. Budući da je štuka (E. lucius i E. masquinongy) jedini konačni domaćin trakavice i
da protiv trienoforoze u Republici Hrvatskoj nema registriranog lijeka, smanjenje populacije
štuke u otvorenim vodama, smanjit će učestalost i intenzitet bolesti. U diplomskom radu,
histološkom pretragom crijeva štuke invadirane odraslim trakavicama T. nodulosus, istražena
je patogenost parazita za konačnog domaćina. Materijal za istraživanje porijeklom je iz rijeke
Mrežnice i prikupljen je tijekom 2021. godine u sklopu provedbe projekta Hrvatske zaklade za
znanost („Biomolekule koje vežu metale i zdravstveni poremećaji kod slatkovodnih
organizama izloženih industrijskom otpadu“; šifra projekta IP-2019-04-2636, voditeljica
projekta dr. sc. Zrinka Dragun, Institut Ruđer Bošković).About 1500 tapeworms (Cestoda) parasitise fish, and some of them may cause
important diseases. Among them are cestodes of the genus Triaenophorus, specifically T.
nodulosus and T. crassus, which cause triaenophorosis in pikes (Esox sp.). In northern pike (E.
lucius), their definitive host, these adult tapeworms cause intestinal ulceration with cellular
infiltration and fibrosis. Since in Croatia the northern pike is the only definitive host and there
are no legally approved anthelmintics, the only strategy to control triaenophorosis in natural
waters is to reduce the population of northern pike. In the present study, the pathogenic effect
of adult T. nodulosus was assessed by histological examination. The material (infected fish)
was collected in 2021 at the Mrežnica River. The study was carried out as part of the Croatian
Science Foundation-supported project Metal-binding biomolecules and health disturbances of
freshwater organisms exposed to industrial wastes (IP-2019-04-2636)
Application of metal-plastic composites in the railway industry
No full textCilj diplomskog rada je ustanoviti vrijednost smične čvrstoće ljepljenog spoja polimera i metala u ovisnosti o temperaturi. Sklop ljepljenog spoja čini sendvič konstrukcija koja se sastoji od dvije metalne ploče između kojih se nalazi PET (poli (etilen – tereftalat)) ispuna. Ispitivanje se provodilo pri različitim temperaturama te se vidi da se s porastom temperature, smična čvrstoća snižava. Isto tako, ispitivanje se provodilo s različitim debljinama ispune te je zaključak da debljina ispune ne utječe na smičnu čvrstoću. U radu je prikazano kako ispitna tijela s dobrom pripremom površine imaju višestruko bolju čvrstoću spoja od ispitnih tijela s lošom pripremom površine i kao takva su ne upotrebljiva u eksploatacijskim uvjetima, odnosno važno je odrediti na koji način pripremiti površinu tih materijala za postizanje dobrog ljepljenog spoja.The aim of the thesis is to determine the shear strength value of the adhesive bond between polymer and metal depending on the temperature. The adhesive joint assembly consists of a sandwich structure comprising two metal plates with a PET (poly(ethylene - terephthalate)) core. Testing was conducted at various temperatures, revealing that the shear strength decreases with increasing temperature. Similarly, tests were conducted with different core thicknesses, concluding that core thickness does not affect shear strength. The thesis demonstrates that test specimens with well-prepared surfaces exhibit significantly higher joint strength compared to those with poorly prepared surfaces, rendering them unsuitable for operational conditions. Therefore, it is crucial to determine the appropriate surface preparation methods for these materials to achieve a good adhesive bond
Determination of potassium and sodium in dietary supplements therapies for inflammatory bowel diseases by atomic absorption spectrometry
No full textDodaci prehrani u širokoj su primjeni i važni su za održavanje zdravlja kod ljudi. Budući da više od
60 % bolesnika koristi dodatke prehrani u ublažavanju simptoma upalnih bolesti crijeva, cilj ovog
rada bio je procijeniti kvalitetu dodataka prehrani s obzirom na sadržaj kalija i natrija. Sadržaj
navedenih makroelemenat u dodacima prehrani koji sadrže biljne vrste: indijski tamjanovac,
kurkumu, justiciju i crni papar određen je primjenom plamene tehnike atomske apsorpcijske
spektrometrije nakon provedene mikrovalne digestije. Rezultati istraživanja pokazali su dominantnu
zastupljenost kalija i značajno manji sadržaj natrija te širok raspon oba makroelementa u
analiziranim dodacima prehrani. Rezultati su pokazali manji sadržaja kalija u suhim ekstraktima
nego u usitnjenim biljnim drogama. Dodaci prehrani za liječenje upalnih bolesti crijeva mogu se
smatrati dobrim izvorom minerala, a pozitivan omjer Na/K primjenu i kod drugih bolesnika.Dietary supplements are widely used and are important for maintaining people's health. Since more
than 60% of patients use dietary supplements to alleviate the symptoms of inflammatory bowel
diseases, this work aimed to evaluate the quality of dietary supplements with regard to potassium
and sodium content. The content of the mentioned macroelements in dietary supplements containing
botanical species, Indian frankincense, turmeric, black paper, and justice was determined using the
flame technique of atomic absorption spectrometry after microwave digestion. The obtained results
showed a dominant presence of potassium, a significantly lower sodium content, and a wide range
of macroelements in the analyzed dietary supplements. The results showed a lower potassium
content in dry extracts than in crushed herbal drugs. Dietary supplement therapies for inflammatory
bowel diseases can be considered a good source of minerals, and a positive Na/K ratio can also be
used in other patient
Phytochemical composition and antioxidant activity of fruit of Ribes uva-crispa L. (Grossulariaceae)
No full textOvim diplomskim radom analiziran je fitokemijski sastav te je ispitano antioksidacijsko djelovanje plodova vrste Ribes uva-crispa L. Identifikacija flavonoida (rutina, kvercitrina i izokvercitrina) i fenolnih kiselina (klorogenske kiseline) provedena je primjenom tankoslojne kromatografije. U vodenom i metanolnom ekstraktu plodova R. uva-crispa L. utvrđena je prisutnost rutina i izokvercitrina te klorogenske kiseline. Kvantifikacija fenolnih kiselina (izraženih kao klorogenska kiselina) i ukupnih polifenola (izraženih kao galna kiselina) provedena je spektrofotometrijskim metodama.
Sadržaj fenolnih kiselina, izražen kao klorogenska kiselina iznosio je 0,45 %, dok je udio ukupnih polifenola, izražen kao galna kiselina iznosio 2,5 %. Antioksidacijsko djelovanje ekstrakta ispitano je dvjema spektrofotometrijskim metodama: određivanjem sposobnosti hvatanja DPPH slobodnog radikala (IC50: 331,56 ± 15,90 μg/mL,) te određivanjem sposobnosti hvatanja NO radikala (IC50: 332,22 ± 11,22 μg/mL).
Ovaj rad potvrdio je fitoterapijski potencijal vrste Ribes uva-crispa L.In this master's thesis the phytochemical composition and antioxidant activity of the fruits of Ribes uva-crispa L. were analyzed. The identification of flavonoids (rutin, quercitrin and isoquercitrin) and phenolic acids (chlorogenic acid) was conducted using thin-layer chromatography. The presence of rutin, isoquercitrin and chlorogenic acid was determined in the water and methanol extracts of R. uva-crispa L. fruits. The quantification of phenolic acids (expressed as chlorogenic acid) and total polyphenols (expressed as gallic acid) was performed using spectrophotometric methods. The content of phenolic acids, expressed as chlorogenic acid was 0,45 %, while the amount of total polyphenols, expressed as gallic acid was 2,5 %. The antioxidant activity of extracts was defined using two spectrophotometric methods: the determination of the DPPH free radical scavenging ability (IC50: 331,56 ± 15,90 μg/mL) and the determination of the NO radical scavenging ability (IC50: 332,22 ± 11,22 μg/mL).
This study confirmed the phytotherapeutic potential of Ribes uva-crispa L
DEVELOPMENT OF BOTANICAL CONCEPTS THROUGH ELEMENTARY AND SECONDARY EDUCATION
No full textOvim je istraživanjem analizirana usvojenost koncepata botanike kroz osnovnoškolsko i srednjoškolsko obrazovanje te međuodnosi sa stavovima i interesima učenika, studenata i nastavnika za botaniku. Istraživanje je diskontinuirano provođeno tijekom 15 godina, prije i poslije stupanja na snagu novog kurikuluma Prirode i Biologije te prije i poslije online nastave. Pismene provjere provedene su u tiskanom obliku ili online, a anketno istraživanje online. Utvrđeno je da je usvojenost botaničkih koncepata mala, a zbog neprimjerenih nastavnih programa dolazi do stvaranja brojnih miskoncepcija, od kojih neke nastaju i tijekom edukacije studenata nastavničkih profila. Interesi i stavovi učenika najveći su za procese u biljnom organizmu, a učitelja i nastavnika za ekologiju biljaka. Međutim, interesi i stavovi učenika ne mogu se povezati s usvojenošću koncepata botanike, kao ni uspješnost učenika s interesima nastavnika, koji smatraju važnim znanje o biljkama, ali dosadnom školsku botaniku. Na temelju ovog istraživanja identificirane su miskoncepcije i predložen potencijalni novi kurikulum botanike.This research analysed the acquisition of botany concepts through primary and secondary education and the interrelationships with the attitudes and interests of students and teachers in botany. The research was carried out discontinuously over 15 years, before and after the ratification of the new Nature and Biology curriculum and before and after online classes. Written tests were conducted in printed form or online, and polls only online. It has been established that the acquisition of botanical concepts is low, and due to inappropriate teaching programs, numerous misconceptions are created, some of which arise during the education of future teachers. Students' interests and attitudes are greatest for processes in the plant organism, and teachers for plant ecology. However, students' interests and attitudes cannot be linked to the acquisition of botany concepts, nor can students' success with the interests of teachers, who consider plant knowledge important but school botany boring. Based on this research, misconceptions were identified and a potential new botany curriculum was proposed
Effect of exposure to α-cypermethrin on markes of oxidative stress in pregnant female rats
No full textPiretroidi su skupina insekticida koja ima široku primjenu u agronomiji, veterini i kućanstvu. Utvrđeno je kako piretroidi mogu djelovati kao hormonski otrovi, a posredni mehanizam između izloženosti hormonskim otrovima i njihovim učincima na ljudsko zdravlje može biti oksidacijski stres, karakteriziran poremećajem ravnoteže prooksidansa i antioksidansa. Najpoznatiji sintetski piretorid je α-cipermetrin koji se zbog svoje lipofilne prirode nakuplja u masnom tkivu, jetri i mozgu te može ući u posteljicu. Cilj ovog istraživanja bio je odrediti utjecaj izloženosti α-cipermetrinu na indukciju oksidacijskog stresa mjerenjem određenih markera u tkivima ženki štakora izloženih navedenom pesticidu u dozama 1, 10 i 19 mg kg−1 dan−1 za vrijeme gestacije. U krvi, mozgu i posteljicama ženki štakora određivani su koncentracija malondialdehida tekućinskom kromatografijom visoke djelotvornosti, a količina reaktivnih kisikovih spojeva i reduciranog glutationa te katalitička aktivnost enzima katalaze, superoksid dismutaze i glutation peroksidaze spektrofotometrijski. Poremećaj oksidacijsko- antioksidacijske ravnoteže uočen je u svim analiziranim tkivima i to ponajviše nakon izloženosti α-cipermetrinu u dozi od 1 mg kg-1. Indukcija oksidacijskog stresa u mozgu gravidnih štakorica ukazuje na moguća fiziološka oštećenja majke, a u posteljici da postoji mogućnost i za poremećaj funkcije endokrinog sustava.Pyrethroids are a group of insecticides that are widely used in agronomy, veterinary medicine and household. It has been recognized that pyrethroids can act as endocrine disruptors, and the intermediate mechanism of exposure and effect on human health can be oxidative stress, characterized by a disturbance in the balance of prooxidants and antioxidants. The well known synthetic pyrethroid is α-cypermethrin, which due to its lipophilic nature accumulates in fatty tissue, liver and brain, but there is also the possibility of its passage through the placenta. The aim of this research is to determine the impact of exposure to α-cypermethrin on the induction of oxidative stress by measuring respective markers in the tissues of female rats exposed to the pesticide in doses of 1, 10 and 19 mg kg-1 day-1 during gestation. We analyzed the concentration of malondialdehyde by high-performance liquid chromatography, and the amount of reactive oxygen species, reduced glutathione, and the catalytic activity of the enzymes catalase, superoxide dismutase and glutathione peroxidase by spectrophotometry in the blood, brain and placentas of female rats. Disturbance of the oxidation-antioxidant balance was observed in all analyzed tissues, mostly after exposure to α-cypermethrin at a dose of 1 mg kg-1. The induction of oxidative stress in the brain of pregnant rats indicates possible physiological damage to the mother, and in the placenta, potential for disruption of the function of the endocrine system
Analysis of CAD activities in a multi-user CAD environment
No full textUpotreba CAD (eng. Computer Aided Design) alata važna je u kasnijim fazama razvoja proizvoda. Korištenjem CAD alata, razvojni tim kreira digitalni model proizvoda. Tradicionalni CAD alati omogućuju asinkroni rad na digitalnim modelima čime je otežana kolaboracija između članova tima. Razvojem računarstva u oblaku omogućeni je razvoj višekorisničkih CAD alata. Jedan od vodećih višekorisničkih CAD alata smještenih u oblaku (eng. Cloud-based software) je Onshape® tvrtke PTC koja omogućuje sinkroni rad više članova tima na istom modelu. Onshape® omogućuje kontinuirano praćenje aktivnosti članova razvojnog tima prilikom CAD modeliranja. Za potrebe rada korišteni su podaci o CAD aktivnostima studentske udruge koja se bavi izradom raketa. U praćenom razdoblju postoje zapisi o 18453947 aktivnosti proizašlih od strane 491 korisnika (članova tima). Na samom početku rada provedeno je istraživanje postojeće literature vezanu za analizu CAD aktivnosti što je uvelike pomoglo definiranju pristupa samoj analizi podataka. Analiza aktivnosti podijeljena je u tri dijela. U sklopu prvog dijela generirane su grupe korisnika i Onshape dokumenata s obzirom na broj zabilježenih aktivnosti, te je provedena analiza aktivnosti za svaku generiranu grupu. U drugom dijelu analize, za potrebe klasteriranja dokumenata i korisnika, korišteni su K-Means i GMM algoritam. Pomoću oba algoritma provedeno je klasteriranje podataka o aktivnostima te su navedeni rezultati analize. Struktura CAD aktivnosti grupa dokumenata i korisnika ovisi o pristupu grupiranja istih. Generirani klasteri pomoću dva različita algoritma daju drugačije rezultate ističući pojedine klastere (s obzirom na strukturu CAD aktivnosti) od ostalih klastera U sklopu trećeg dijela analize odrađeni je pregled kolaboracije unutar tima. Korisnici (Članovi tima) Analiziranjem dinamike promjena mreže kolaboracije utvrđeno je postojanje podtimova koji rade zajedno, ali ti podtimovi variraju na mjesečnoj bazi.The usage of CAD (Computer-Aided Design) tools is important in the later stages of product development. With CAD tools, the design team can create digital models of the product. Traditional CAD (single-user CAD) tools enable work from one PC and one user at a time on a single CAD model. This restriction makes collaboration more difficult.
The development of cloud computing has enabled the creation of multi-user CAD tools. One of the leading multi-user CAD tools is Onshape, a PTC company product that allows more than one user to work on a CAD model simultaneously. Onshape also enables tracking of user activity using the Audit Trail module.
For this master’s thesis, a dataset of CAD activity from a student association involved in rocket design is used. During the tracking period, 18,453,947 CAD activity were recorded from 491 users. At the beginning of this work, a survey of the existing literature related to the analysis of CAD activities was conducted, which greatly helped define the approach to data analysis.
The analysis of CAD activity is divided into three parts. The first part involves grouping users and Onshape documents based on the number of recorded timestamps. Each created group is analyzed separately. In the second part, GMM (Gaussian Mixture Model) and K-Means clustering algorithms are used to generate clusters of documents and users. Clustering of data for CAD activity is performed using each algorithm, and the results are compared. Each approach to data grouping provides different insights into the structure of CAD activity. The use of different clustering algorithms results in the creation of some clusters that differ in their approach to CAD activity.
The last part is the analysis of user collaboration. After analyzing the dynamics of the collaboration network, the existence of sub-teams was established, but only on a monthly basis