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Null-translation surfaces with constant curvatures in Lorentz-Minkowski 3-space
No full textTranslation surface is a surface formed by two curves moving along each other. In this paper we analyze this kind of surfaces in Lorentz-Minkowski 3-space R31 , which is the smooth manifold R3 endowed by a flat Lorentzian pseudometric. Translation surfaces in R31 can be classified with respect to the causal character of their generating curves (spacelike, timelike or null (lightlike)). We are specially interested in translation surfaces generated by at least one null curve, which we refer to as null-translation surfaces. In the present paper we determine all nulltranslation surfaces of constant mean curvature and prove that the only null-translation surfaces of constant Gaussian curvature are cylindrical surfaces
Determination of nitrate migration and distribution through eutric cambisols in an area without anthropogenic sources of nitrate (Velika Gorica well field, Croatia)
No full textNatural potential sources of nitrate contamination involve decaying of organic matter, bacterial production, atmospheric deposition, and soil N. The study presents the first results of nitrate distribution and migration through soil horizons of the Eutric Cambisols, one of the most common soils developed in the area of the Zagreb aquifer and situated in an area without potential anthropogenic sources of nitrate (first sanitary protection zone of the Velika Gorica well field). A total of 16 parameters of soil water and 16 parameters of soil were used to conduct statistical techniques and analyse associated factors within the soil zone. The results indicate that in the deepest soil horizon, nitrogen is present mostly as nitrate due to nitrification under aerobic conditions which promote stability and the potential for nitrate transport. It was found that nitrate concentrations are the result of soil N nitrification, caused by a NO3−/Cl− molar ratio higher than 1 and the absence of precipitation isotopic signature. The results also show that within the coarse-grained Eutric Cambisols N primarily migrates to deeper parts of unsaturated zone in the form of nitrate and nitrite
Impact of the COVID-19 crisis on the mining sector in Croatia
No full textMining as a human activity shares the fate of humanity in all global situations that affect the planet. These are, to a lesser extent, positive effects such as the opening of the world market, the industrial revolution, etc., and, to a greater extent, negative effects such as various conflicts or pandemics that have a global character. The COVID-19 pandemic has had an unprecedented impact on all sectors of human society, justifying a scientific interest in assessing its impact at global and local levels. Recently, the World Health Organization declared the end of the pandemic, after which the Croatian government did the same. This also marks the end of the research period for the preparation of this paper. The paper is about the study of the impact of the pandemic on the Croatian mining sector in Croatia. In addition to statistical data on production and the number of employees in the mining sector, the results of a survey of economic entities and conclusions about the management of companies in crisis situations were processed
Utjecaj praha kore mandarine na filtracijska svojstva i temperaturnu stabilnost isplaka na bazi vode
No full textThe growing energy demand in the world, as well as the current geopolitical situation, require countries to additional investments in the exploration and production of hydrocarbons from their own sources. This means that companies must develop new fields which have remained undeveloped until now mostly because extremely harsh environment where they are located (deep sea, high temperature, high pressure, heavy oils, etc.). The development of these new fields requires the development and adoption of new technology, among other things, and the development of a temperature-stable drilling fluid system able to fulfil all tasks according to the new technical challenges. Except for the technological challenges, there are also growing concerns related to the influence of the drilling operation on the environment. All of the above encourage the industry to develop new, inexpensive, and environmentally friendly additives which will be able to satisfy all technical and technological requirements and challenges of modern drilling. In the last few years, there has been a growing trend of laboratory research that includes different types of biodegradable waste as a potential additive that can achieve useful properties in mud. In this paper, the influence of mandarin peel powder on the filtration properties of mud after the aging process at elevated temperatures is examined. This eco-friendly additive was added to water-based muds in concentrations of 1% and 2% by volume of water. Laboratory research have shown stable filtration properties of the water-based mud containing mandarin peel powder even after exposing the mud to temperatures higher than 130 °C.Sve veća potražnja za energijom u svijetu, kao i trenutna geopolitička situacija, zahtijevaju od zemalja dodatna ulaganja u istraživanje i proizvodnju ugljikovodika iz vlastitih izvora. To znači da tvrtke moraju razviti nova polja koja su do sada ostala nerazrađena uglavnom zbog izuzetno zahtjevnih uvjeta u podzemlju gdje se ona nalaze (duboko more, visoka temperatura, visoki tlak, teška nafta, itd.). Razvoj ovih novih polja zahtijeva razvoj i usvajanje novih tehnologija, između ostalog, i razvoj temperaturno stabilnog bušotinskih fluida koji mogu ispuniti sve zadatke sukladno tehničkim izazovima koji se pred njih stavljaju. Osim tehnoloških izazova, raste i zabrinutost vezana uz utjecaj bušaćih operacija na okoliš. Sve navedeno potiče industriju na razvoj novih, cjenovno povoljnijih i ekološki prihvatljivih aditiva koji će moći zadovoljiti sve tehničko-tehnološke zahtjeve i izazove suvremenog bušenja. Posljednjih nekoliko godina sve je veći trend laboratorijskih istraživanja koja uključuju različite vrste biorazgradivog otpada kao potencijalnih aditiva kojima se u isplaci mogu postići korisna svojstva. U ovom radu ispituje se utjecaj praha kore mandarine na filtracijska svojstva isplake nakon procesa starenja pri povišenim temperaturama. Ovaj ekološki prihvatljivi aditiva dodavan je u isplake na bazi vode u koncentracijama od 1% i 2% na volumen vode. Ispitivanja su pokazala stabilna filtracijska svojstva isplake na bazi vode koja sadrži prah kore mandarine i nakon izlaganja isplake temperaturama višim od 130 °C
Nuclear and radiological data available in the International Atomic Energy Agency (IAEA) databases
No full textHaving access to relevant data is essential for ensuring the quality and outreach of research work. In the context of the nuclear field, access to information and data facilitates competence building, long-term professional development, research, and information dissemination. Potential users of nuclear information resources come from different domains: scientists, experts, students, and the public. One of the main roles of the International Atomic Energy Agency (IAEA) is to ensure and promote peaceful uses of atomic energy worldwide. Through their activities, the IAEA strongly encourages the exchange of scientific and technical information. This paper presents an overview of different nuclear and radiological data available in several International Atomic Energy Agency databases. All data is available free of charge for educational and informational use. A summary of information is given for each database presented on the content, access options, copyright, acknowledgement, and dissemination of the available information. A concise summary of this various data might help in capacity building, as well as encourage research and information sharing between different stakeholders in the field
Improved conceptual design of LILW repository
No full textGiven the forthcoming need for the construction of a repository for low and intermediate radioactive level waste in the Republic of Croatia, this paper proposes a repository design which is, from a geotechnical point of view, simple, practical and safe, and significantly improved considering current conceptual designs. Existing low and intermediate radioactive level waste repositories are mostly vault-type, near-surface constructions with some kind of covering (top) system of protective layers. However, most of these repositories do not have a bottom protective system, apart from concrete flooring (base). The reasons for such designs include the presumed longevity of the waste packages (containers), which are mostly reinforced concrete and/or steel containers. Considering that the concrete is a material which will, under certain conditions, deteriorate (e.g. dissolution of the cement matrix), and so potentially release radionuclides to the environment, it is essential to design the repository in such a manner that all forms of early release of radionuclides are prevented. The improved conceptual design of low and intermediate radioactive level waste repository presented in this paper is intended to provide an improved containment of radionuclides from waste and ensure the long term safety of the repository. This paper is the first in a series which will cover the basic design of the repository, systems of protective layers and preliminary slope stability analyses
Kartiranje sinriftne ispune i tektonska kontrola distribucije kolektorskih stijena: primjer iz Dravskog bazena, Panonski bazenski sistem
No full textThe Drava Basin in the SW Pannonian Basin System was originally formed by passive rifting with accompanying sedimentary infill. Although this has been the subject of much previous exploration, an account of tectonic control has been lacking. Based on cores, wireline logging and seismic data, the tectonostratigraphic interpretation and control on depositional systems of the syn-rift infill in the eastern part of the Drava Basin were studied. Reservoir characteristics are investigated based on available petrophysical data from wells and on analogue data from similar settings
Systems for extraction of acid gases from gas produced in oil and gas fields in Croatia : master's thesis
No full textPrirodni plin je energent s velikim potencijalom povećanja primjene u budućnosti. Opisuje se kao tranzicijski energent zbog manje štetnog utjecaja na okoliš u odnosu na ostala fosilna goriva (ugljen i nafta). Razvoj procesa obrade prirodnog plina omogućio je eksploataciju rezervi prirodnog plina u čijem su sastavu u manjoj ili većoj koncentraciji prisutni kiseli plinovi (ugljikov dioksid i sumporovodik). U radu je dat pregled procesa obrade prirodnog plina s naglaskom na procesima izdvajanja kiselih plinova. Opisani su tehnologije i postrojenja izdvajanja kiselih plinova u Hrvatskoj, kao i rezultati najnovijih istraživanja tzv. hibridnih otapala.Natural gas is an energy source with a great potential that could be more used in the future. It is called a transitional energy source because it has less harmful effects on the environment compared to other fossil fuels (coal and petroleum). The development of the natural gas processing has allowed the exploitation of natural gas reserves containing acid gases (carbon dioxide and hydrogen sulphide) in smaller or larger concentrations. The thesis provides an overview of the natural gas processing process, focusing on acid gas separation processes. It also describes plants and technologies for acid gas recovery in Croatia and the results of recent hybrid solvent research
Well construction optimization by eliminating intermediate casing string : master's thesis
No full textIzrada bušotina uključuje složeni niz poslova s ciljem dosezanja ležišta ugljikovodika ili geotermalne vode. Kako bi bušotina bila kvalitetno i sigurno izrađena te omogućila buduću eksploataciju ležišta, potrebno ju je pravilno konstruirati. Naftne kompanije posljednjih desetljeća pokušavaju optimizirati uobičajene prakse pri projektiranju bušotina te tako uštediti financijska sredstva. Jedan od dijelova projektiranja konstrukcije jest i projektiranje zacjevljenja bušotine, odnosno pravilni odabir promjera i dubina ugradnje zaštitnih cijevi određenih mehaničkih karakteristika kako bi odolijevale promjenjivim uvjetima tijekom cijelog radnog vijeka bušotine. Trošak nabave zaštitnih cijevi te njihova ugradnja i cementiranje predstavlja veliki dio troškova izrade bušotine. Stoga, projektantski je izazov dizajnirati takvo zacjevljenje koje će izdržati sva naprezanja uz što manji trošak. U radu je obrađen teoretski pristup pri konstruiranju zacjevljenja i mogući uzroci odstupanja završne konstrukcije bušotine od projektiranih vrijednosti. U sklopu toga, izrađene su i uspoređene dvije konstrukcije bušotine X na istražnom polju Y, s različitim brojem nizova zaštitnih cijevi. Za potrebe projektiranja konstrukcije bušotine korišten je softverski paket Landmark, modul StressCheckTM.Drilling wells involves a complex series of operations with the goal of reaching hydrocarbon or geothermal water reservoirs. In order for the well to be properly and safely made and to enable the future exploitation of the reservoir, it must be correctly constructed. In recent decades, oil companies have been trying to optimize the usual practice when constructing wells and thus save financial resources. One part of well construction is the casing design, that is, the correct selection of the diameter and installation depth of casing strings with certain mechanical characteristics in order to withstand changing conditions during the entire life of the well. The cost of procuring casings and their installation and cementing represents a large part of the well construction costs. Therefore, the challenge is to design such casing strings that will withstand all stresses with the least possible cost. The thesis deals with the theoretical approach of casing design and the possible causes of the deviation of the final construction of the well from the designed values. As a part of this, two constructions of well X on the exploratory field Y, with different number of casing strings, were made and compared. Landmark software, the StressCheckTM module, was used for the well construction purposes
Testing the presence of radon in building materials : master's thesis
No full textU ovom radu ispitana je prisutnost odnosno koncentracija radona i torona kao rezultat ekshalacije iz građevinskih materijala. Brojni građevinski materijali sadrže elemente u tragovima čijim radioaktivnim raspadom nastaju nove nestabilne jezgre tzv. kćerke. Krajnji produkt raspada radona su teški metali te energija ionizacije koji predstavljaju opasnost za živu tvar. Mjerenja su izvođena u laboratoriju za spektroskopiju na RGN fakultetu na 5 uzoraka različitih građevinskih materijala. Izmjerene vrijednosti ravnotežne koncentracije za uzorke granita i cementa nekoliko su puta veće od prosječne procijenjene vrijednosti koncentracije za građevinski materijal. Usporedba rezultata dobivenih tijekom ovog ispitivanja s rezultatima iz objedinjene baze mjerenja ekshalacije radona iz građevinskog materijala ukazuje na velike razlike u dobivenim vrijednostima. Prisutnost i povišene vrijednosti koncentracije radona u uzorcima građevinskog materijala izmjerene prilikom ovog ispitivanja potvrđuju potrebu za praćenjem vrijednosti radona u građevinskom materijalu iskazanu u drugim znanstvenim radovima na istu temu.In this thesis, the presence and the concentration of radon and thoron as a result of exhalation from building materials was examined. Numerous building materials contain trace elements whose radioactive decay creates new unstable nuclei, the so-called daughters. The final products of radon decay are heavy metals and ionization energy, which pose a danger to living beings. The measurements were performed at the RGN Faculty in the spectroscopy laboratory on 5 samples of different building materials. The measured equilibrium concentration values for the granite and cement samples are several times higher than the average estimated concentration value for the construction material. A comparison of the results obtained during this test with the results from the unified database of measurements of radon exhalation from building materials indicates large differences in the obtained values. The presence and elevated values of radon concentration in construction material samples measured during this test confirm the need to monitor the radon value in construction material stated in other scientific works on the same topic