The decline of educational hypergamy in the former Yugoslav republics

U radu se istražuju promene obrazovnog sastava bračnih partnera u bivšim jugoslovenskim republikama, posebno opadanje učešća brakova u kojima su muškarci obrazovaniji od žena (hipergamni brakovi). U osnovi ovih promena jeste razvoj tercijarnog obrazovanja i nastanak polne asimetrije visokoobrazovanih lica, usled kojih je u prve dve decenije XX veka došlo do porasta učešća bračnih zajednica u kojima su žene obrazovanije. Analiza se pretežno temelji na podacima Demografske (vitalne) statistike, a period koji je obuhvaćen istraživanjem odnosi se na poslednjih pedeset godina. Koristeći se specifičnim pokazateljima (F i H indeksom) i korelacionom analizom, dobijeni su rezultati koji su pokazali da obrazovna hipergamija opada u svim istraživanim zemljama, kao i da je opadanje hipergamije povezano sa prevagom žena među visokoobrazovanim licima. Rezultati daju nove uvide u tumačenje izbora partnera posredstvom socioekonomskih karakteristika, ali i ukazuju na ključnu ulogu koju u procesu selekcije ima obrazovna kompozicija stanovništva.This paper examines marital market preferences and opportunities, given the gender asymmetry of education and the limited supply of equally educated partners (especially in the higher education segment), and explores selection patterns resulting from new composite changes for at-risk populations entering into a marriage. Specifically, we are researching mixed marriages by education and changes in the patterns of that selection in the former Yugoslav republics. The assessment of the impact of changes in educational characteristics by gender on patterns of marital pairing and the reduction of the level of educational hypergamy was performed by analysing the movement of F-index and H-index values from 1970 to 2020 and their correlation coefficient. The results showed that educational hypergamy is declining in all countries and that the decline in hypergamy is positively associated with the predominance of women among highly educated individuals

The change in educational assortative mating in Serbia and Slovenia, 1970–2020

This paper explores marital matching patterns from the perspective of the partners' educational attainment, focusing on the link between gender asymmetry in education and educational hypergamy. In order to assess to what extent the tendency for women to marry men of higher educational status is related to the educational gender gap in Serbia and Slovenia, we calculate an index for women's educational advantage, and an index for the prevalence of educational hypergamy. Our results confirm the following: the growth of education is associated with an increase in female educational advantage; the relationship between female educational advantage and educational hypergamy is strongly negative; and there are no significant differences in assortative mating patterns between Serbia and Slovenia

Nadzorna ovlašćenja poslodavaca u savremenim uslovima rada - analiza slučaja i mogući vidovi rešavanja radnih sporova

U radu se razmatraju i analiziraju nadzorna ovlašćenja poslodavaca u savremenim uslovima radne organizacije. Sprovođenje nadzora integrisano je u svakodnevni život i rad ljudi, protoke kapitala i razvoj karijere. Informatizacija radne sfere doprinela je značajnim promenama u odnosu poslodavca i zaposlenog. Stoga je predmet istraživanja fokusiran na prostorne, vremenske i etičke dimenzije poslodavčevih ovlašćenja, usled prihvatanja savremenih informacionih i komunikacionih tehnologija u proces rada. Zapravo, osnovni cilj istraživanja jeste prespitivanje i određivanje poslodavčevih nadzornih ovlašćenja. U poslednjem delu rada, ukazuje se na moguće vidove rešavanja sporova u kontekstu prekoračenja poslodavčevčevih ovlašćenja, s posebnim osvrtom na domaću sudsku praksu

Probability of failure of thermal power plant boiler tubing system due to corrosion

Korozija predstavlja nepovratni proces degradacije materijala. Zbog nepovoljanog uticaja koji ima na radne osobine materijal, posebno materijala cevnog sistema kotla, ona predstavlja predstavlja neizostavni deo rada termoenergetskih postrojenja i glavni uzrok mnogih otkaza. Pored uobičajenih metoda za procenu preostalog radnog veka korisno je primeniti i metode za procenu pouzdanosti kotlovskih cevi termoenergetskih postrojenja koje su oštećene korozijom. Korelacijom rezultata koji se dobijaju primenom ove dve različite metode moguće je dobiti bolja saznanja o trenutnom stanju materijala cevi uz istovremeno izvođenje tačnije procene njihovog ponašanja tokom dalje eksploatacije. Stoga je u ovom radu na primeru cevi ulazne zone paketa naknadnog pregrejača prikazan integralni pristup procene preostalog radnog veka i pouzdanosti. Razmatranja ove vrste su veoma značajna za pristupe u održavanju koji su zasnovani na riziku.Corrosion is irreversible process of material degradation. Due to detrimental effects exerted on the operating material characteristics, especially in the boiler tube system, it is of one the most important issues in the operation of thermal plants and is considered to be the root cause of many outages. Besides common remaining life assessment methods, it is useful to apply a method of reliability evaluation of the thermal power plant boiler tubes with corrosion damages. Correlation of results obtained by these two methods makes possible to obtain a better knowledge of current tubes material state as well as a more accurate assessment of their behavior during future exploitation. Therefore, an integrated approach of remaining life assessment and reliability evaluation, on the first stage reheater tubes system example, is presented in this paper. Considerations of this kind are very important for the risk-based maintenance programs

Probability of failure of thermal power plant boiler tubing system due to corrosion

Korozija predstavlja nepovratni proces degradacije materijala. Zbog nepovoljanog uticaja koji ima na radne osobine materijal, posebno materijala cevnog sistema kotla, ona predstavlja predstavlja neizostavni deo rada termoenergetskih postrojenja i glavni uzrok mnogih otkaza. Pored uobičajenih metoda za procenu preostalog radnog veka korisno je primeniti i metode za procenu pouzdanosti kotlovskih cevi termoenergetskih postrojenja koje su oštećene korozijom. Korelacijom rezultata koji se dobijaju primenom ove dve različite metode moguće je dobiti bolja saznanja o trenutnom stanju materijala cevi uz istovremeno izvođenje tačnije procene njihovog ponašanja tokom dalje eksploatacije. Stoga je u ovom radu na primeru cevi ulazne zone paketa naknadnog pregrejača prikazan integralni pristup procene preostalog radnog veka i pouzdanosti. Razmatranja ove vrste su veoma značajna za pristupe u održavanju koji su zasnovani na riziku.Corrosion is irreversible process of material degradation. Due to detrimental effects exerted on the operating material characteristics, especially in the boiler tube system, it is of one the most important issues in the operation of thermal plants and is considered to be the root cause of many outages. Besides common remaining life assessment methods, it is useful to apply a method of reliability evaluation of the thermal power plant boiler tubes with corrosion damages. Correlation of results obtained by these two methods makes possible to obtain a better knowledge of current tubes material state as well as a more accurate assessment of their behavior during future exploitation. Therefore, an integrated approach of remaining life assessment and reliability evaluation, on the first stage reheater tubes system example, is presented in this paper. Considerations of this kind are very important for the risk-based maintenance programs

Hydrogen embrittlement of low carbon structural steel

Hydrogen embrittlement (HE) of steels is extremely interesting topic in many industrial applications, while a predictive physical model still does not exist. A number of studies carried out in the world are unambiguous confirmation of that statement. Bearing in mind multiple effects of hydrogen in certain metals, the specific mechanism of hydrogen embrittlement is manifested, depending on the experimental conditions. In this paper structural, low carbon steel, for pressure purposes, grade 20- St.20 (GOST 1050-88) was investigated. Numerous tested samples were cut out from the boiler tubes of fossil fuel power plant, damaged due to high temperature hydrogen attack and HE during service, as a result of the development of hydrogen-induced corrosion process. Samples were prepared for the chemical composition analysis, hardness measurement, impact strength testing (on instrumented Charpy machine) and microstructural characterization by optical and scanning electron microscopy - SEM/EDX. Based on multi-scale special approach, applied in experimental investigations, the results, presented in this paper, indicate the simultaneous action of the hydrogen-enhanced decohesion (HEDE) and hydrogen enhanced localized plasticity (HELP) mechanisms of HE, depending on the local concentration of hydrogen in investigated steel. These results are consistent with some models proposed in literature, about a possible simultaneous action of the HELP and HEDE mechanisms in metallic materials

Life estimation of first stage high pressure gas turbine blades

Posle pojave prevremenih lomova koji su se javili kod lopatica prvog stepena turbine visokog pritiska određenog tipa turboreaktora u jednoj lokalnoj avio kompaniji, usledila su istraživanja u cilju određivanja njihovog sigurnog (pouzdanog) radnog veka. Lopatice prvog stepena turbine visokog pritiska su tokom rada izložene simultanom delovanju pritiska gasa iz komore za sagorevanje, centrifugalne sile u slučaju rotorskih lopatica, velikim temperaturnim promenama, kao i agresivnoj radnoj sredini. Kombinacija svih navedenih činilaca izaziva vrlo kompleksno naponsko stanje lopatica kao i mogućnost pojave višestrukih mehanizama oštećivanja: zamora izazvanog fluktuacijama u mehaničkom naponu, termo-mehaničkog zamora usled temperaturnih promena i korozije naponski opterećenih delova. Da bi se odredio radni vek u navedenim uslovima, neophodno je proceniti napone kojima su lopatice izložene uzimajući u obzir nekoliko promenljivih koje se u radu tretiraju deterministički. Razmatran je prenos toplote između sagorelih gasova i metala lopatica turbine. Izračunat je ukupni napon na dve vrste lopatica imajući u vidu termičke efekte i mehaničko opterećenje. Naponski ciklus je zatim izračunat za različite faze rada turboreaktora uz varijacije termičkih i mehaničkih osobina. Procena sigurnog radnog veka je izvršena primenom dva pristupa: inicijalnog modela i pristupa sa tolerancijom oštećenja uzimajući u obzir mehanički rast oštećenja i rast korozionog pita. Proračun je primenjen i na statorske i na rotorske lopatice turbine visokog pritiska turboreaktora koje su izrađene od čelika NI 738. Nađeno je da su ovo komponente visokog rizika, tako da je procenjen i rizik sa aspekta potencijalnih posledica od loma. Dobijeni rezultati su razmatrani u cilju rešavanja problema i donošenja sigurne odluke sa aspekta procedure održavanja ali i konstrukcijskog rešenja.Based on very early occurring ruptures found in the first stage high pressure turbine blades of a turbo reactor in a local aviation company, this study has the aim to determine their safe life. The first stage blades are subjected to simultaneous action of gas pressure coming from the combustion chamber, centrifugal forces in the case of the rotor blades and to important temperatures transients, which progress in a very aggressive environment due to hot gases. These combined parameters cause a high state of stress involving several complex mechanisms of damage, such as: fatigue caused by mechanical stress fluctuations, thermo-mechanical fatigue caused by temperature variations and corrosion caused on the stressed elements. Life cycle determination asks for stress evaluation of blades regarding several variables which are approached deterministically in the study. Heat exchange between combustion gases and metal blades is considered. The total stress on two kinds of blades is calculated by the addition of the thermal effect and the mechanical loading. The stress cycle is then calculated for different steps of the engine function during the operation by considering the variation of the thermal and the mechanical properties of the system. Safe life determination is done by two different approaches: the safe life approach by the initiation model and the damage tolerance approach considering the defect growth mechanics and considering the pitting corrosion effect. The calculation is applied for stator and rotor blades of an aero engine high pressure turbine made of NI 738. Since these parts are high risk components from the point of view of potential failure consequences, the risk is assessed as well. The results obtained are studied to determine the solution to the problem, and to propose a safe decision to be taken about the design or maintenance procedures.

Hydrogen embrittlement of low carbon structural steel

Hydrogen embrittlement (HE) of steels is extremely interesting topic in many industrial applications, while a predictive physical model still does not exist. A number of studies carried out in the world are unambiguous confirmation of that statement. Bearing in mind multiple effects of hydrogen in certain metals, the specific mechanism of hydrogen embrittlement is manifested, depending on the experimental conditions. In this paper structural, low carbon steel, for pressure purposes, grade 20- St.20 (GOST 1050-88) was investigated. Numerous tested samples were cut out from the boiler tubes of fossil fuel power plant, damaged due to high temperature hydrogen attack and HE during service, as a result of the development of hydrogen-induced corrosion process. Samples were prepared for the chemical composition analysis, hardness measurement, impact strength testing (on instrumented Charpy machine) and microstructural characterization by optical and scanning electron microscopy - SEM/EDX. Based on multi-scale special approach, applied in experimental investigations, the results, presented in this paper, indicate the simultaneous action of the hydrogen-enhanced decohesion (HEDE) and hydrogen enhanced localized plasticity (HELP) mechanisms of HE, depending on the local concentration of hydrogen in investigated steel. These results are consistent with some models proposed in literature, about a possible simultaneous action of the HELP and HEDE mechanisms in metallic materials

Pandemija virusa COVID-19 kao ograničavajući faktor demografskog razvoja lokalnih samouprava u Srbiji

U prostornom planiranju stanovništvo je prepoznato kao specifičan resurs koji se mora kontinuirano pratiti, naročito u kriznim periodima, kada dolazi do određenih strukturnih promena u društvu. Plmer takvih promena jesu demografski trendovi nastali kao direktna posledica pandemije virusa COVID-19. Pandemije najintezivnije utiču na demografski razvoj preko povišenog nivoa mortaliteta u populaciji, stoga je u fokusu ovog rada uticaj virusa COVID-19 na smrtnost stanovništva na regionalnom i lokalnom nivou u Srbiji. U postupku istraživanja biće izdvojeni klasteri regiona i opština u Srbiji koji se međusobno diferenciraju prema nivou smrtnosti uzrokovanog ovim virusom. Rezultati su pokazali da su od kovida bile najugroženije opštine sa starim stanovništvom, ali je opšti zaključak da razlika u nivou smrtnosti od virusu najvećim delom zavisi od učestalosti kontakata u populaciji, koji su u radu apstrahovani preko udela višegeneracijskih domaćinstava. Konstatovano je da pandemija, s obzirom na kontinuitet procesa starenja u većini lokalnih samouprava Srbije, utiče na dalju eroziju demografskih resursa mnogih regiona Srbije. Istraživanja kojima su u fokusu negativni uticaji pandemije na demografski razvitak značajna su zarad kreiranja adekvatnih populacionih mera na lokalnom nivou, ali i kao preduslov za njihovu reviziju u skladu sa recentnim demografskim trendovima

Life estimation of first stage high pressure gas turbine blades

Posle pojave prevremenih lomova koji su se javili kod lopatica prvog stepena turbine visokog pritiska određenog tipa turboreaktora u jednoj lokalnoj avio kompaniji, usledila su istraživanja u cilju određivanja njihovog sigurnog (pouzdanog) radnog veka. Lopatice prvog stepena turbine visokog pritiska su tokom rada izložene simultanom delovanju pritiska gasa iz komore za sagorevanje, centrifugalne sile u slučaju rotorskih lopatica, velikim temperaturnim promenama, kao i agresivnoj radnoj sredini. Kombinacija svih navedenih činilaca izaziva vrlo kompleksno naponsko stanje lopatica kao i mogućnost pojave višestrukih mehanizama oštećivanja: zamora izazvanog fluktuacijama u mehaničkom naponu, termo-mehaničkog zamora usled temperaturnih promena i korozije naponski opterećenih delova. Da bi se odredio radni vek u navedenim uslovima, neophodno je proceniti napone kojima su lopatice izložene uzimajući u obzir nekoliko promenljivih koje se u radu tretiraju deterministički. Razmatran je prenos toplote između sagorelih gasova i metala lopatica turbine. Izračunat je ukupni napon na dve vrste lopatica imajući u vidu termičke efekte i mehaničko opterećenje. Naponski ciklus je zatim izračunat za različite faze rada turboreaktora uz varijacije termičkih i mehaničkih osobina. Procena sigurnog radnog veka je izvršena primenom dva pristupa: inicijalnog modela i pristupa sa tolerancijom oštećenja uzimajući u obzir mehanički rast oštećenja i rast korozionog pita. Proračun je primenjen i na statorske i na rotorske lopatice turbine visokog pritiska turboreaktora koje su izrađene od čelika NI 738. Nađeno je da su ovo komponente visokog rizika, tako da je procenjen i rizik sa aspekta potencijalnih posledica od loma. Dobijeni rezultati su razmatrani u cilju rešavanja problema i donošenja sigurne odluke sa aspekta procedure održavanja ali i konstrukcijskog rešenja.Based on very early occurring ruptures found in the first stage high pressure turbine blades of a turbo reactor in a local aviation company, this study has the aim to determine their safe life. The first stage blades are subjected to simultaneous action of gas pressure coming from the combustion chamber, centrifugal forces in the case of the rotor blades and to important temperatures transients, which progress in a very aggressive environment due to hot gases. These combined parameters cause a high state of stress involving several complex mechanisms of damage, such as: fatigue caused by mechanical stress fluctuations, thermo-mechanical fatigue caused by temperature variations and corrosion caused on the stressed elements. Life cycle determination asks for stress evaluation of blades regarding several variables which are approached deterministically in the study. Heat exchange between combustion gases and metal blades is considered. The total stress on two kinds of blades is calculated by the addition of the thermal effect and the mechanical loading. The stress cycle is then calculated for different steps of the engine function during the operation by considering the variation of the thermal and the mechanical properties of the system. Safe life determination is done by two different approaches: the safe life approach by the initiation model and the damage tolerance approach considering the defect growth mechanics and considering the pitting corrosion effect. The calculation is applied for stator and rotor blades of an aero engine high pressure turbine made of NI 738. Since these parts are high risk components from the point of view of potential failure consequences, the risk is assessed as well. The results obtained are studied to determine the solution to the problem, and to propose a safe decision to be taken about the design or maintenance procedures.