Wormholes in viable f(R)f(R) modified theories of gravity and Weak Energy Condition

In this work wormholes in viable $f(R)$ gravity models are analysed. We are interested in exact solutions for stress-energy tensor components depending on different shape and redshift functions. Several solutions of gravitational equations for different $f(R)$ models are examined. Found solutions imply no need for exotic material, while this need is implied in the standard general theory of relativity. Simple expression for WEC violation near the throat is derived and analysed. High curvature regime is also discussed, as well as the question of the highest possible values of Ricci scalar for which WEC is not violated near the throat, and corresponding functions are calculated for the several models. The approach here differs from the one that has been common since no additional assumptions to simplify the equations are made, and functions in $f(R)$ models are not taken to be arbitrary functions, but rather a feature of the theory that has to be evaluated on the basis of consistency with observations for the Solar System and cosmological evolution.Comment: 8 pages, 10 figures, accepted by the European Physical Journal

Creation of wormholes during the cosmological bounce

In this work we demonstrate that wormholes can in principle be naturally created during the cosmological bounce without the need for the exotic matter or any kind of additional modifications of the gravitational sector, apart from the one enabling the cosmological bounce. This result is general and does not depend on the details of the modifications of gravitational equations needed to support the bounce. To study the possible existence of wormholes around the cosmological bounce we introduce general modifications of Einstein's field equations need to support the bouncing solutions. In this regime we show that it is possible to construct a cosmological wormhole solution supported by matter, radiation and vacuum energy, satisfying the Weak Energy Condition (WEC), which asymptotically approaches the Friedmann-Lema\^{i}tre-Robertson-Walker (FLRW) metric. However, at a specific cosmological time, which depends on the parameters of the bouncing cosmological model, the WEC describing the matter needed to support such wormholes is spontaneously violated. This means that such wormholes could potentially exist in large numbers during some period around the bounce, significantly changing the causal structure of space-time, and then vanish afterwards.Comment: 17 pages, 3 figure

Synthesizing a new type of mullite lining

Various possibilities for developing new mullite-based refractory linings that can be applied in a casting process were investigated and are presented in this paper. An optimization of the refractory-lining composition design with the controlled rheological properties was achieved by applying different lining components and altering the lining-production procedure. Mullite was used as a high-temperature filler. A mullite sample was tested with the following methods: X-ray diffraction analysis, differential thermal analysis and scanning-electron microscopy. The particle shape and particle size were analyzed with the program package for an image analysis called OZARIA 2.5. It was proved that an application of this type of lining has a positive effect on the surface quality, structural and mechanical properties of the castings of Fe-C alloys obtained by casting into sand molds, according to the method of expandable patterns (the EPC casting process)

POJAVNOST SUICIDALNOSTI U BOLESNIKA HOSPITALIZIRANIH NA KLINICI ZA PSIHIJATRIJU SKB MOSTAR U PERIODU 2004.-2013.

UVOD: I pored evidentnog napretka medicine i psihijatrije posljednjih desetljeća se registrira porast suicidalnosti psihijatrijskih bolesnika. Osobe koje se poradi nekog oblika suicidalnog ponašanja hospitaliziraju u psihijatrijskim ustanovama predstavljaju populaciju s posebice visokim rizikom od naknadnog suicida. CILJ: Istražiti pojavnost suicidalnosti i epidemiološke karakteristike suicidalnih bolesnika hospitaliziranih na Klinici za psihijatriju Sveučilišne kliničke bolnice (SKB) Mostar. METODE: Proveli smo retrospektivno istraživanje u kojemu smo analizirali podatke iz povijesti bolesti 189 bolesnika koji su hospitalizirani na Klinici za psihijatriju SKB Mostar u razdoblju od 2004. do 2013. REZULTATI: Bolesnici koji su pokušali suicid češće su bili ženskog spola (59,2 %), nezaposleni (47,6 %), srednjeg stupnja obrazovanja (52,4 %), oženjeni (45,5 %), bez djece (37,6 %) te su učestalije dolazili iz gradskih sredina (75,7 %). Nije nađeno razlika u učestalosti pokušaja suicida između muškaraca i žena s obzirom na kalendarske karakteristike. Žene su statistički značajno učestalije imale dijagnoze iz skupine afektivnih i poremećaja ličnosti, dok su muškarci statistički značajno učestalije bolovali od poremećaja iz shizofrenog kruga (p=0,003). Najučestalija metoda pokušaja suicida je bila trovanje (54,0 %), a promatrano po spolu značajno učestalije u žena (p<0,001). Muškarci su značajno učestalije pokušavali suicid tjelesnim ozljeđivanjem (p<0,001), te zloupotrebljavali alkoholna pića (p=0,001) i psihoaktivne tvari (p=0,003) u odnosu na žene. ZAKLJUČAK: Pokušaji suicida su bili učestaliji u osoba ženskog spola. Žene su statistički značajno učestalije imale dijagnoze iz skupine afektivnih i poremećaja ličnosti, dok su muškarci statistički značajno učestalije bolovali od poremećaja iz shizofrenog kruga. Žene su statistički značajno učestalije pokušavale suicid trovanjem, a muškarci tjelesnim ozljeđivanjem

The Unification of Laws in the Kingdom of Serbs, Croats and Slovenes / Yugoslavia

Rad predstavlja poseban pogled na jugoslovensku Kraljevinu, iz ugla stvaranja i primene prava. Odmah po proglašenju Kraljevine Srba, Hrvata i Slovenaca (1. decembra 1918) izjednačenje zakona postavljeno je kao jedna od vrhovnih političkih vrednosti i glavni zadatak Vlade. Do donošenja Ustava (28. juna 1921), proces izjednačenja zakona tekao je putem donošenja uredbi “zakonskog značaja” (vladavina uredbi). Vidovdanskim ustavom predviđena su dva načina izjednačavanja zakona: legalizacijom ranijih uredbi i donošenjem zakona po predlogu Vlade od Zakonodavnog odbora (“malog parlamenta”) po skraćenom postupku. Ovaj zakonodavni postupak, sa kojim je Vlada ostala odlučujući zakonodavni činilac, nije poslužio cilju. Glavni zakoni (Krivični zakonik i zakonici o krivičnom i parničnom postupku) doneti su tek pod režimom diktature (1929). Građanski zakonik nije donet do kraja trajanja Kraljevine Jugoslavije, pa se građani “nisu osećali kao članovi jedne zajednice”. Isto je bilo u sferi izvršnog prava do 1938, a u pogledu okućja (zemljoradničkog minimuma) i kasnije. Izjednačenje zakona odvijalo se u senci sukoba srbijanskih i prečanskih pravnika (pravnika iz krajeva bivše Austro-Ugarske). Izjednačeni zakoni su doneti uglavnom suprotno gledištima srbijanskih pravnika. Kraljevina SHS je od zemlje sa šest pravnih područja postala zemlja u kojoj je jedan deo njenih građana (građani bivše Kraljevine Srbije) doveden u situaciju da živi pod “nasiljem” nametnutog prava. Žrtvovanje parlamentarizma od strane Srbijanaca, zarad izjednačenja zakona, okrenulo se protiv njih samih.This article provides a special look into the Yugoslav Kingdom from the standpoint of the creation and enforcement of law. Soon after the proclamation of the single Kingdom of Serbs, Croats and Slovenes (1 December 1918), the unification of laws became one of the supreme political values and a priority task of the government. Until the adoption of the Constitution of 1921, the unification of laws took place by way of enactment of decrees of ‘legal importance’ (‘government of decrees’). According to the Constitution of 1921, there were two ways in which the unification of laws could be carried out: by legalizing former decrees and by passing laws by the legislative committee (“little parliament”) in a summary procedure. But the goal was not achieved that way. The principal laws (the criminal code and the codes of criminal and civil procedure, respectively) were passed under the regime of the dictatorship (1929). The Civil Code was not passed until the fall of the Kingdom of Yugoslavia, so the citizens ‘did not feel as the members of the same community’ in that regard. The same was true in the field of executive law until 1938, and later concerning the homestead (farmer’s minimum). The unification of laws took place in the shadow of the conflict between Serbian lawyers and lawyers from the former Austria-Hungary. Unified laws were passed mainly regardless of the disagreement of Serbian lawyers. Many of institutes of law of former Kingdom of Serbia (limitation in the use of witnesses, limitation of the peasant\u27s benchmark ability, execution of the death penalty by a firing squad) were repealed by new Yugoslav laws. The Kingdom of SCS turned from being a country that consisted of six legal systems to a country in which a part of her citizens (citizens of the former Kingdom of Serbia) were forced to suffer the “violence” of the imposed laws. Serbians had sacrificed parliamentarism for the purpose of unifying laws, which eventually came at a great cost. The unification of laws indicated that Croats and Slovenes leaned towards a real union or that they did not want any kind of community with Serbians

Survey of satisfaction of individual user of banking services in developed countries and possibilities of improvement in Serbia

Savremeni načini poslovanja tržišta, kao i novi zahtevi korisnika, nameću bankama obavezu da prilagode tradicionalno bankarstvo novim zahtevima klijenata. Postojanje velikog broja banaka, odnosno konkurencije na tržištu, primoravaju banke da korisnicima pružaju veći broj usluga i to po pristupačnim cenama. Poznato je da banke u prošlosti nisu imale potrebu za ispitivanjem potreba i želja korisnika, ali u novije vreme situacija se promenila, pa banke sada osluškuju potrebe korisnika i na taj način postaju pristupačnije. Pored elektronskog bankarstva koje je doživelo ekspanziju poslednjih desetak godina, zahvaljujući kojem se obavlja veliki broj usluga, čak i putem mobilnih telefona, korisnicima je omogućeno da obave veliki broj finansijskih usluga – od provere stanja na računu, plaćanja računa, pa do podnošenja zahteva za neki kreditni proizvod. Zahvaljujući informacionim tehnologijama, banke su unapredile i modernizovale svoje poslovanje. Zahtevi korisnika stalno se menjaju i prilagođavaju promenama, te se očekuje da usluga koja se pruža bude modernija i da manje košta. Bankarske usluge su značajne i za društveno-ekonomsko poslovanje. Merenje satisfakcije korisnika u bankarskom sektoru je značajno jer pruža odgovore na mnoga pitanja i podstiče razvoj i rast bankarstva. Kvalitet usluge je važan na svim uslužnim nivoima. U literaturi postoje mnoga istraživanja u vezi sa merenjem zadovoljstva korisnika. U ovoj doktorskoj tezi koristi se Servqual model za merenje očekivanja i percepcije korisnika bankarskih usluga koje će biti predmet istraživanja. U okviru ove doktorske teze izvršeno je empirijsko istraživanje individualnih korisnika bankarskih usluga u Republici Srbiji, Crnoj Gori, BiH i Republici Srpskoj, Hrvatskoj, Sloveniji i Slovačkoj. Takođe, dat je prikaz stanja kvaliteta bankarskih usluga u Nemačkoj, Francuskoj i Češkoj na osnovu sekundarnih izvora podataka. Istraživanje se sastoji od dva nivoa. Prvi nivo jeste istraživanje koje zapravo otkriva šta korisnici očekuju od banke i kako doživljavaju bankarsku uslugu. Drugi nivo je motivaciono istraživanje, a logički se nadovezuje na rezultate iz prvog nivoa. To je dubinsko istraživanje sa ciljem da se utvrdi u kom pravcu banke mogu usvojiti preporuku za svoje poslovanje

Treba li državi dozvoliti cenzurisanje umjetničkih djela?

Nagrađeni radovi

Modeling the radio-evolution of supernova remnants by using hydrodynamic simulations and non-linear diffusive shock acceleration

Eksplozije supernovih (SN) obogacuju Univerzum razlicitim teskim elementima. Ovi elementi su gradivni blokovi sveta oko nas i nas samih. Ostaci supernovih (OSN) su izvanredni astronomski objekti koji su takode od velikog naucnog znacaja, jer pruzaju uvid u mehanizme eksplozija supernovih i predstavljaju vazne izvore galakti ckih kosmickih zraka. Radio-posmatranja su medu najstarijim sredstvima za proucavanje ovih objekata. Radio-sjaj i spektar, posebno mladih OSN, predstavljaju rezultat aktivnog ubrzavanja elektrona na udarnim talasima. U ovoj doktorskoj disertaciji, analizira se radio-evolucija OSN primenom trodimenzionalnih hidrodinami ckih simulacija i nelinearnog difuznog ubrzavanja cestica. Hidrodinamicke simulacije, razvijane i prilagodavane u ovoj disertaciji, omogucavaju nam eksplicitno racunanje modikacije udarnih talasa od strane kosmickih zraka. Takode, ukljucujemo konzistentan numericki tretman pojacanja magnetnog polja usled rezonantnih i nerezonantnih nestabilnosti izazvanih kosmickim zracenjem. Modelovali smo radio-evoluciju najmladeg poznatog Galaktickog OSN G1.9+0.3 i zakljucili da je rastuca radio-emisija cesta pojava kod jako mladih OSN. Nas model nam je omogucio da izvedemo vazne zakljucke o sadasnjem i predvidanja o buducem ponasanju radio-emisije ovog OSN. Takode smo primenom simulacija razvili i opsti model radio-evolucije OSN, za sirok spektar relevantnih zickih parametara, kao sto su gustina okolne sredine, energija eksplozije supernove, ekasnost ubrzavanja i pojacanja magnetnog polja. Pouzdanost nasih radio-evolutivnih traka potvrdena je na posmatrackom uzorku, koji se sastoji od Galaktickih i vangalaktickih OSN...Supernova (SN) explosions disperse the dierent heavy elements across the Universe. These elements are the building blocks which make up the world around and inside us. Supernova remnants (SNRs) are extraordinary astronomical objects that are also of high scientic interest, because they provide insights into aforementioned supernova explosion mechanisms, and because they are important sources of Galactic cosmic rays (CRs). Radio observations are among the oldest means to study these objects. The radio luminosity and spectra of SNRs, especially young ones, requires active acceleration of electrons by the SNR shocks. In this doctoral dissertation, radio evolution of SNRs is investigated by using three-dimensional hydrodynamic modelling and non-linear diusive shock acceleration of CRs in SNRs. Hydrodynamic simulations, developed and adopted in this dissertation, allow us to explicitly account for the shock modication by CRs. We also include consistent numerical treatment of magnetic eld amplication (MFA) due to CR resonant and non-resonant streaming instabilities. We modelled the peculiar nature of radio evolution of the youngest known Galactic SNR G1.9+0.3 and concluded that increasing radio emission is a common occurrence among very young SNRs. Our model enabled us to make important conclusions about the present and predictions about the future properties of radio emission from this SNR. We also developed more general model of the radio evolution of SNRs, by performing simulations for wide range of the relevant physical parameters, such as the ambient density, the supernova explosion energy, the acceleration eciency and the MFA eciency..