Browsing Astronomy and Geoscience by Issue Date
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Komarčić, Lazar (Belgrade , 1902)[more][less]
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Mišković, Vojislav (Belgrade , 1939)[more][less]
URI: http://hdl.handle.net/123456789/465 Files in this item: 1
VojislavMiskovi ... eLUniversiteDeBelgrade.pdf ( 2.547Mb ) -
Brkić, Zaharije (Belgrade , 1958)[more][less]
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Teleki, Đorđe (Belgrade , 1964)[more][less]
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Lazović, Jovan (Belgrade , 1964)[more][less]
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Kubičela, Aleksandar (Belgrade , 1973)[more][less]
URI: http://hdl.handle.net/123456789/120 Files in this item: 1
phdAleksandarKubicela.pdf ( 30.99Mb ) -
Angelov, Trajče (Belgrade , 1980)[more][less]
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Šegan, Stevo (Belgrade , 1987)[more][less]
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Dačić, Miodrag (, 1998)[more][less]
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Jovanović, Predrag (Belgrade , 2005)[more][less]
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Damljanović, Goran (Faculty of Mathematics, University of Belgrade , 2007)[more][less]
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Pavlović, Rade (Faculty of Mathematics, University of Belgrade , 2008)[more][less]
Abstract: We investigate the ful¯llment of conditions for application of Nekhoroshev theorem to real dynamical system, such as the motion of asteroids under the perturbation by major planets. We have in particular analyzed the regions of the phase space where asteroid families of Koronis and Veritas are located. The results obtained for a number of selected family members indicate that in these regions even stricter conditions (convexity, quasi-convexity and 3- jet), than the condition of steepness required by the theorem, are fullled. Consequently, the theorem of Nekhoroshev can be applied to members of Koronis family and to the members of Veritas family with regular motion. URI: http://hdl.handle.net/123456789/717 Files in this item: 1
phdRadePavlovic.pdf ( 3.135Mb ) -
Ilić, Dragana (Belgrade , 2008)[more][less]
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Arbutina, Bojan (Faculty of Mathematics, University of Belgrade , 2009)[more][less]
Abstract: The main research topic of this dissertation are extreme mass ratio contact close binary systems, q 0.1, of W Ursae Majoris (W UMa) type. These close binaries (CBs) represent an interesting class of objects in which ”normal”, approximately one solar mass main-sequence star is in contact with a significantly less massive companion, M2 ∼ 0.1 M . Earlier theoretical investigations of these systems found that there is a minimum mass ratio qmin = M2/M1 ≈ 0.085 − 0.095 (obtained for n = 3 polytrope - fully radiative primary) above which these CBs are stable and could be observed. If the mass ratio is lower than qmin, or, equivalently, if orbital angular momentum is only about three times larger than the spin angular momentum of a massive primary, a tidal instability develops (Darwin’s instability) forcing eventually the stars to merge into a single, rapidly rotating object (such as FK Com-type stars or blue stragglers). However, there appear to be some W UMa-type CBs with empirically obtained values for the mass ratio below the theoretical limit for stability. The aim of this dissertation is to try to resolve the discrepancy between theory and observations by considering rotating polytropes. By including in theory the effects of higher central condensation due to rotation we were able to reduce qmin to the new theoretical value qmin = 0.070 − 0.074, for the overcontact degree f = 0 − 1, which is more consistent with the observed population. Other candidate systems for stellar mergers such as AM CVn-type stars have also been discussed in the dissertation. URI: http://hdl.handle.net/123456789/716 Files in this item: 1
phdBojanArbutina.pdf ( 6.326Mb ) -
Valjarević, Aleksandar (Niš , 2012)[more][less]
Abstract: The territory of Kosovo and Metohia has alwaus represented the hidrology interesting area of study, in which they compared the parameters of water drainage and their physical properties. Generalization is one of the methods for these porposes and may be used and the results can be applied to various forms of digital maps. URI: http://hdl.handle.net/123456789/3118 Files in this item: 1
ValjarevicAleksandarDD.pdf ( 39.32Mb ) -
Stalevski, T. Marko (Belgrade, Gent , 2012)[more][less]
URI: http://hdl.handle.net/123456789/2487 Files in this item: 1
Marko_Stalevski_doktorska_disertacija.pdf ( 6.024Mb ) -
Todorović, Nataša (Beograd , 2012)[more][less]
Abstract: Nehoroševljeva teorema (1977) igra veoma značajnu ulogu u razumevanju prirode hamiltonijanskih sistema. Pored činjenice da daje prikaz celokupne dinamike faznog prostora, ova teorema obezbeđuje i stabilnost kvazi-integrabilnih sistema u smislu da se vremena stabilnosti dejstava eksponencijalno produžavaju smanjenjem parametra poremećaja. Jedan od uslova teoreme je da integrabilna aproksimacija hamiltonijanske funkcije zadovoljava takozvani uslov strmosti. Pretpostavka izneta u dokazu teoreme je da pored parametra poremećaja, i strmost utiče na stabilizaciju sistema. Cilj doktorske teze bio je da se ova pretpostavka proveri numeričkim putem, kao i da se ilustruje uticaj strmosti na dinamiku sistema. Korišćen je model četvorodimenzione kvazi-integrabilne strme simplektičke mape, na kojoj se intenzitet strmosti lako podešava pomoću odgovarajućeg parametra. Oslanjajući se na tzv. Brzi indikator Ljapunova (Fast Lyapunov Indicator- FLI), numeričku metodu za detekciju haosa, prikazana je rezonantna struktura modela i merena je difuzija Arnoldovog tipa na odabranoj rezonanci. U prvom delu eksperimenta su za fiksirane vrednosti parametra strmosti merene promene difuzije u odnosu na smanjenje poremećaja, i potvrđeno je da se vrednost eksponenata fitovane funkcije povećava (sistem se stabilizuje) što je sistem strmiji. Otkriveno je i da eksponencijalna funkcija u strmoj nekonveksnoj oblasti u izvesnom smislu osciluje, što je rezultat koji još uvek nema svoju teorijsku interpretaciju. Takođe, primećeno je da se sa povećanjem strmosti, hiperboličke tačke zajedno sa svojom okolinom izmeštaju sa rezonantne krive. I konačno, u eksperimentu u kojem je meren direktan uticaj strmosti na brzinu difuzije, potvrđena je pretpostavka iz dokaza Nehoroševljeve teoreme, o postojanju kritične vrednosti parametra strmosti. Za vrednosti koje su manje od kritične, strmost nema uticaj na brzinu difuzije, dok je za vrednosti koje su veće od kritične, ovaj uticaj eksponencijalan. Štaviše, vrednost eksponenta ove funkcije u izvesnom smislu ima opšti karakter to jest ne zavisi od ostalih parametara sistema. Detaljnije analitičko objašnjenje ovog rezulata, svakako je jedan od budućih zadataka u interpretaciji Nehoroševljeve teoreme. URI: http://hdl.handle.net/123456789/3569 Files in this item: 1
Ntodorovic_Doktorat_1R.pdf ( 2.955Mb ) -
Onić, Dušan (Beograd , 2013)[more][less]
Abstract: The evolution of supernova remnants is linked to the propagation of a collisionless shock wave, formed during the initial expansion of high-velocity supernova ejecta through the interstellar environment. Theoretical studies of shock waves are very important for the analysis of supernova remnants, as well as processes in the interstellar medium in general. In this doctoral dissertation, some theoretical results based on the magnetohydrodynamical theory of shock waves are presented, with special emphasis on ideal radiative magnetohydrodynamics for the optically thick case. Particularly, solutions for the case when jump in adiabatic index and/or ratio of gas to total pressure is allowed, are discussed. The main hypothesis of this dissertation is that thermal bremsstrahlung radiation at radio continuum frequencies can provide a signi cant contribution in the case of several Galactic supernova remnants. This hypothesis can give a natural explanation for nearly concave up radio continuum spectra of several Galactic supernova remnants that are expanding in the environment with higher than average density. In this context, it is important to identify the existence of the possible indicators of ensemble of thermal electrons at su ciently low temperatures and su ciently high densities so that the thermal bremsstrahlung radiation linked to a particular remnant could be observed at radio continuum frequencies (vicinity, interaction or expansion through the molecular cloud, presence of the cooled thermal X-ray electrons during the post Sedov-Taylor phases, detection of low-frequency turnovers associated with thermal absorption linked to the remnant, detection in H , identi cation of radio recombination lines linked to the remnant, etc). The signi cant presence of thermal component could theoretically explain radiospectral indices less than 0.5 measured for several evolutionary older supernova remnants, (mainly of mixed-morphology class) that expand in the high density region. Actually, these smaller radio-spectral indices, under the assumption of simple power law, would represent a natural manifestation of a signi cant fraction of thermal emission at radio continuum frequencies. However, present knowledge of the radio continuum spectra of Galactic supernova remnants is still not determined precisely enough for any de nite conclusions to be made about the inherent thermal radio-emission from supernova remnants. A thorough analysis is only possible in the case of three Galactic supernova remnants (3C396, IC443, 3C391) for which the thermal contribution is determined despite high associated uncertainties. New observations in the near future will lay the groundwork for making rmer conclusions about the existence of the so-called radio thermally active supernova remnants. This dissertation highlights the importance of observations of supernova remnants in X and -rays, and multiwavelength analysis is general. Besides, it suggests a possible detection of -rays from supernova remnant 3C434.1 based on the observations made by Fermi. URI: http://hdl.handle.net/123456789/3051 Files in this item: 1
Onic_Dusan_disertacija.pdf ( 10.67Mb ) -
Milisavljević, R. Slaviša (Belgrade , 2013)[more][less]
Abstract: The problem of the minimal mutual distances for two confocal elliptical orbits (local minima), in the literature known as the proximity calculation for minor planets and recognised recently as Minimal Orbit Intersection Distance – MOID, occupies a very important place in astronomical studies, not only because of the prediction of possible collisions of asteroids and other celestial bodies, but also because of the fact that by analysing the behaviour of asteroids during their encounters it is possible to determine their masses, changes of orbital elements and other important characteristics. Dealing with this problem in this thesis the author has analysed the distance function for two elliptical confocal orbits of minor planets combining analytical and numerical methods for proximity calculation. A survey of all relevant results in this field from the middle of the XIX century till our days indicates that the problem has been transformed from looking for a solution of two transcendental equations by applying various methods and approximations of long duration towards efficient and rapid solutions of vector equations of the system which describes the problem. In the thesis a simple and efficient analytic-numerical method has been developed, presented and applied. It finds out all the minima and maxima in the distance function and, indirectly, makes it possible to determine also the inflection points. The method is essentially based on Simovljevic’s (1974) graphical interpretation and on transcendental equations developed by Lazovic (1993). The present method has been examined on almost three million pairs of real elliptical asteroid orbits and its possibilities and the computation results have been compared to the algebraic solutions given by Gronchi (2005). The case of a pair of confocal orbits with four proximities found by Gronchi (2002), who applied the method of random samples and carried out numerous simulations with different values of orbital elements, gave the motivation to try here to find out such a pair among the real pairs of asteroid orbits. Thanks to the efficacy of the method developed in the thesis two such pairs have been found and their parameters are presented. In addition to the one meantioned above a further analysis of distance function through simulations including more than 20 million different pairs of asteroid orbits has resulted in several additional interesting solutions of the distance function. The results are given in the form of tables and plots showing the diversity of solutions for the distance function. URI: http://hdl.handle.net/123456789/2490 Files in this item: 1
phdSlavisaMilisavljevic.pdf ( 3.815Mb ) -
Jovanović, Bora (Beograd , 2014)[more][less]
Abstract: Одређивање разлике динамичког и светског времена и предвиђање промена у брзини Земљине ротације Апстракт Проблем прецизног предвиђања Земљине просторне оријентације је у директној вези са познавањем будућих вредности параметара Земљине ротациеј, помоћу којих се врше трансформације између небеског и терестричког система. Ти параметри су зависни од мноштва астрономских и геофизичких узрока, за чије збирно дејство још увек не постоје одговарајући теоријски модели, који би могли довољно прецизно да описују промене Земљине оријентације. Зато се предикције параметара Земљине ротације мање ослањају на геофизичке теорије, а више на математичка моделирања, која су заснована на разним нумеричким методама. Овај рад је имао за циљ да докаже да је искључиво математичким приступом(без коришћења геофизичких модела и корекција) могуће постићи унапређења у предвиђањима неравномерности скале светског времена UT1. Познато је да тај параметар има најбржу и највећу промену, јер у потпуности пресликава Земљину ротацију са свим њеним неравномерностима. Због чега његове предикције имају најмању тачност. У раду је коришћена оригинална нумеричка метода за извођење апроксимативних функција у облику суме хармоника и експоненцијала(HE). На основу реалних података рађене су предикције за 10 дана, 30 дана и 500 дана у непрекидном периоду од годину и по дана. Додатно, приказани су и, до сада остварени, резултати једне дуговремене предикције која је истим начином урађена раније. Сопствени резултати су упоређивани са одговарајућим резултатима других аутора, који су користили разне друге методе предикције, током реализације међународног пројекта “Earth Orientation Parameters Prediction Comparison Campaign”(EOPPCC). Показало се да HE метод даје сличне резултате као и друге методе када се ради о 10- дневним и 30-дневним предикцијама, али у случају 500 дневних предикција дао је убедљиво најбољи резултат. Да је овај метод заиста погодан за предикције на дужим временским интервалима, приказују и до сада (8 година) остварени резултати једне 10- годишње предикције. Може се закључити да је предикцију величине ΔТ, која се публикује у астрономским годишњацима, могуће знатно унапредити, коришћењем HE метода. Кључне речи: Време, светско време, терестричко време, референтни системи Научна област: Астрономија Ужа научна област: Земљина ротација УДК: 521.933:519:65(043.3) URI: http://hdl.handle.net/123456789/3508 Files in this item: 1
jovanovic_bora.pdf ( 11.69Mb )
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