Browsing Mathematics by Title

Janković, Slobodan (Beograd , 1979)[more][less]

Marković, Marijan (Belgrade , 2013)[more][less]
Abstract: This work consists of three chapters. The first one contains some well known facts about Hardy classes of harmonic, analytic, and logarithmically subharmonic functions in the unit disk, as well as their applications. Then we briefly talk about the harmonic and minimal surfaces, the classical isoperimetric inequality, and the more recent results related to this inequality. One of the most elegant way to establish the isoperimetric inequality is via Carleman’s inequality for analytic functions in disks. In the second chapter we present the results from our recent work [29] for harmonic mappings of a disc onto a Jordan surface. In this chapter we establish the versions of classical theorems of Carath´eodory and Smirnov for mappings of the previous type. At the end of the head we apply these results to prove the isoperimetric inequality for Jordan harmonic surfaces bounded by rectifiable curves. In the third chapter, according to the author paper [35], we prove an inequality of the isoperimetric type, similar to Carleman’s, for functions of several variables. The first version of this inequality is for analytic functions in a Reinhardt domain. The second one concerns the functions that belong to Hardy spaces in polydiscs. URI: http://hdl.handle.net/123456789/2586 Files in this item: 1
Markovic_Marijan.pdf ( 709.3Kb ) 
Kovačević, Ilija (Belgrade)[more][less]

Gilezan, Koriolan (Belgrade)[more][less]

Jovanović, Boško (Belgrade)[more][less]

Hoxha, Isak (Priština)[more][less]

Mihajlović, Bojana (Beograd , 2016)[more][less]
Abstract: The subject of this dissertation belongs to scientific field of spectral graph theory, a young branch of mathematical combinatorics, i.e. graph theory, which finds important applications in many areas, such as chemistry, physics, computer science, telecommunications, sociology, etc., and various fields of mathematics. Spectral graph theory connects basic properties and the structure of a graph with characteristics of the spectra of its matrices (adjacency matrix, Laplacian matrix, etc.). In this dissertation we only work with the adjacency matrix. The second largest eigenvalue of the adjacency matrix of a graph (or, simply, second largest eigenvalue of a graph), as well as its distance from the largest eigenvalue, are very important especially in applications of spectral graph theory in computer science. The property of a graph that one of its eigenvalues does not exceed some given value is a hereditary one; therefore, many of the investigations of this kind have been directed at finding the maximal allowed graphs, or minimal forbidden graphs for that property. In this dissertation we determine some classes of graphs whose second largest eigenvalue does not exceed some given value, and, for that purpose, we develop some very useful tools. In methodological sense, investigations in this dissertation represent a combined approach consisting of application of the algebraic apparatus and methods of spectral graph theory and combinatorial reasoning, whilst at some stages the expert system newGRAPH has been used. The dissertation consists of eight chapters, each of which is divided into subchapters. In the beginning, some important previous work is shown, and afterwards we present some original elements of the algebraic and combinatorial apparatus that speed up and simplify the further work. We define some mappings between certain families of graphs, some of which preserve the sign of the expression 2 2 , and, using them, we describe and systematize some (already known) results in a new way. Further on we completely determine all maximal reflexive tricyclic cacti which are not RSdecidable and whose cycles do not form a bundle, from the classes 1 R and 3 R , and we give some partial results about the class 2 R , using previously induced mappings (until now only the graphs from the remaining class 4 R have been completely determined [40], [46]). Next, we completely describe all minimal forbidden graphs in the class of bicyclic graphs with a bridge, and all minimal forbidden graphs in the class 3 R  the approach that so far has never been used with reflexive graphs. Then we determine the maximal number of the cycles for RSundecidable reflexive cacti whose cycles do form a bundle, and, therefore, generally for RSundecidable reflexive cacti and we describe three classes of maximal reflexive RSundecidable reflexive cacti that contain a bundle. Further on, some of the previous results are generalized: the generalized RStheorem is stated and proved (socalled GRStheorem) for any r , r 0 ; previously induced mappings are generalized, their properties are proved and various examples of classes of graphs with the property 2 r (for r 0 ) are given. Based on this, we describe all GRSundecidable maximal graphs for the property 2 2 in the class of unicyclic and multicyclic graphs, and also all RSundecidable maximal θgraphs for this property as well as all GRSundecidable maximal trees with the property 2 5 1 2 . Furthermore, we investigate the limit 3 (as in [28]) and we describe all trees with the diameter 3 and the diameter larger than 8, with the property 2 3 , as well as all GRSundecidable multicyclic cacti with the same property. Finally, we introduce and apply socalled σmodifications of Smith trees. We describe seven σmodifications and corresponding extensions, and we notice the appearance in (already known) results in the class of multicyclic reflexive cacti with 4 cycles. Applying some extensions to certain families of tricyclic cacti, we obtained the results in the class of multicyclic reflexive cacti with 4 cycles, using a different approach [48]. Finally, in the conclusion, we suggest some possible directions of further investigations. URI: http://hdl.handle.net/123456789/4445 Files in this item: 1
Mihailovic_Bojana.pdf ( 6.960Mb ) 
Acketa, Dragan (Novi Sad , 1984)[more][less]

Vučemilović, Ante (Belgrade)[more][less]

Cerović, Blagoje (Novi Sad , 1982)[more][less]

Crvenković, Siniša (Novi Sad , 1981)[more][less]

Crvenković, Siniša (Novi Sad , 1981)[more][less]
Abstract: Teorija semigrupa razvija se kao samostalna °blast savremene algebre, Predmet izu6avanja teorije semigrupa su razne kiase semigrupa tj. semigrupe koje zadovoljavaju dati uslov. U ovom radu razmatramo semigrupe iz nekih podklasa kiase regularnih semigrupa. Pojam regularnosti, koji je uveo J. von Neumann [31] za prstene, su Thierrin i BarHep preneli u teoriju semigrupa 6to se pokazalo zna6ajnim za razvoj teorije semigrupa umAte. Ovde se posebno ispituje jedna podklasa kiase kompletno regularnih semigrupa tzv. klasa (m,n)*antiinverznih semigrupa. Ova klasa obuhvata klasu antiinverznih semigrupa ill Pojam bazisne kiase, neke klase semigrupa, uveo je E.C. JThnHH [25]. U radu odredjujemo bazisne kiase za razne kiase semigrupa. Zna6ajnu klasu semigrupa 6ine polumr0e. P.M. Cohn [9] i C. Pe6aHe su 1965. godine pokazali da je svaka algebra podalgebra neke semigrupe. U Glavi IV opisujemo klasu algebri koje su podalgebre polumrea. U Glavi I su navedeni elementarni pojmovi o semigrupama, grupama, algebrama, idealima, kongruencijama, itd. Dati Virtual Library of Faculty of Mathematics  University of Belgrade elibrary.matf.bg.ac.rs ii su dokazi nekih teorema koje se koriste u radu. Ovaj materijal uzet je iz [7] i [22]. Takodje, dat je dokaz G. upone za teoremu CohnPe6aHe. U Glavi II ispituju se (m,n)*antiinverzne semigrupe. Materijal ove glave preuzet je iz [ 61, [11] i [12]. U ta6ki 2. date su neke dekompozicije (m,n)*antiinverznih semigrupa. Teorema 2.3. glavni je rezultat ove glave. Greenove relacije razmatraju se u ta6ki 3. Dobija se niz karakterizaci  ja semigrupa iz klase m,n . Na kraju Glave II navedena su tvrdjenja Eiji dokazi su izostavljeni jer su sli6ni dokazima teorema u [ 21. U Glavi III ispituju se bazisne klase raznih klasa semigrupa. Dat je algoritam kojim odredjujemo bazisnu klasu bilo koje klase (m,n)*antiinverznih semigrupa. Primeri bazisnih klasa za razne semigrupe dati su u ta6ki 2. Materim, n jal za take 1. i 2. uzet je iz [121. U ta6ki 3. razmatraju se QS* (OS ) semigrupe tj. semigrupe nje sve prave podsemi  m,n m,n grupe pripadaju klasi m,n (Sm,n ). Teoremom 3.1. data je karakterizacija semigrupa klase QS*m,n (QS m,n ). Problem egzistencije bazisne klase semigrupa ije sve prave podsemigrupe zadovoljavaju uslov oblika (Vx)(By)4)(x,y) re§en je u ta6ki 4. Na kraju 4. data je nekoliko primera. Materijal iz ta6aka 3. i 4. ovde je prvi put izloen. U Glavi IV opisane su podalgebre polumr0a. Potreban i dovoljan uslov da neka algebra bude podalgebra polumree dat je u taCki 1. Lema 1.3. je kljufta lema u dokazu teoreme 1.1. Virtual Library of Faculty of Mathematics  University of Belgrade elibrary.matf.bg.ac.rs iii Dokaz ove leme izvodi se koristedi pojam transformacije U tadki 2. navedeni su neki specijalni sludajevi koji su neposredna posledica teoreme 1.1. Materijal za ovu glavu uzet je iz [18]. Literatura koja je korigdena u ovom radu navedena je na kraju i 6ine je 44 bibliografske jedinice. Dr Stojan Bogdanovid svojim idejama i savetima pornogao mi je pri izradi ovog rada zbog 6eqa mu dugujem trajnu zahvalnost. Akademik profesor (op( 11 HynoHa velikodugno je pristao na saradnju sa autorom ovog rada. Zahvaljujem se profesoru 6to je prihvatio moju saradnju i omogudio mi da rezultato zajedni6kocr rada izlo2im u Glavi IV. Profesor Svetozar Milid prihvatio se da bude mentor pri izradi ove disertacije. Imam prijatnu du2nost da se zahvalim profesoru Milidu za nesebi6nu pa2nju koju posvedije mom radu. URI: http://hdl.handle.net/123456789/4094 Files in this item: 1
Neke_klase_semigrupa.PDF ( 10.42Mb ) 
Koledin, Tamara (Beograd , 2013)[more][less]
Abstract: Spectral graph theory is a branch of mathematics that emerged more than sixty years ago, and since then has been continuously developing. Its importance is re ected in many interesting and remarkable applications, esspecially in chemistry, physics, computer sciences and other. Other areas of mathematics, like linear algebra and matrix theory have an important role in spectral graph theory. There are many di erent matrix representations of a given graph. The ones that have been studied the most are the adjacency matrix and the Laplace matrix, but also the Seidel matrix and the socalled signless Laplace matrix. Basically, the spectral graph theory establishes the connection between some structrural properties of a graph and the algebraic properties of its matrix, and considers structural properties that can be described using the properties of the eigenvalues of its matrix. Systematized former results from this vast eld of algebraic graph theory can be found in the following monographs: [20], [21], [23] i [58]. This thesis contains original results obtained in several sub elds of the spectral graph theory. Those results are presented within three chapters. Each chapter is divided into sections, and some sections into subsections. At the beginning of each chapter (in an appropriate sections), we formulate the problem considered within it, and present the existing results related to this problem, that are necessary for further considerations. All other sections contain only original results. Those results can also be found in the following papers: [3], [4], [47], [48], [49], [50], [51] and [52]. In the rst chapter we consider the second largest eigenvalue of a regular graph. There are many results concerning graphs whose second largest eigenvalue is upper bounded by some (relatively small) constant. The second largest eigenvalue plays an important role in determining the structure of regular graphs. There is a known characterization of regular graphs with only one positive eigenvalue (see [20]), and regular graphs with the property 2 ≤ 1 have also been considered (see [64]). Within this thesis we extend the results given in [64], and we also present some general results concerning the relations between some structural and spectral properties of regular trianglefree graphs. Connected regular graphs with small number of distinct eigenvalues have been extensively studied, since they usually have an interesting (combinatorial) struc ture. Van Dam and Spence considered the problem of determining the structure of connected regular graphs with exactly four distinct eigenvalues, and they achieved important results presented in papers [27] and [32]. All connected regular bipar tite graphs with exactly four distinct eigenvalues are characterized as the incidence graphs of balanced incomplete block designs (see monograph [20]). There are also results concerning regular bipartite graphs with exactly ve distinct eigenvalues (see [33]). In this thesis, in the second chapter, we consider regular bipartite graphs with three distinct nonnegative eigenvalues, and also quadranglefree regular bipartite graphs. Besides some general results similar to those given in the rst chapter, but this time for bipartite graphs, we also present results concerning the relations between regular bipartite graphs and certain kinds of block designs. In the third chapter we consider the socalled nested graphs and their signless Laplace matrix. Nested graphs play an important role in the research concerning graphs with maximal index, in terms of the adjacency matrix and in terms of the signless Laplace matrix. It is a known fact that a graph with maximal index, or maximal Qindex, of given order and size, must be nested graph (see [7] and [22]). Here we consider bipartite nested graphs (the socalled double nested graphs). We also present results concerning double nested graphs that are similar to the existing results concerning their nonbipartite counterparts. There are no many results con cerning the second largest eigenvalue of the signless Laplace matrix of a graph (see, for example, [6] or [25]). That is why we consider the relations between the structure of nested graphs and the second largest eigenvalue (but also some URI: http://hdl.handle.net/123456789/3049 Files in this item: 1
Koledin_Tamara.pdf ( 7.477Mb ) 
Zolić, Arif (Belgrade)[more][less]

Protić, Ljubomir (Belgrade)[more][less]

Kočinac, Ljubiša (Belgrade , 1983)[more][less]

Pap, Endre (Novi Sad)[more][less]

Perović, Aleksandar (Belgrade)[more][less]
Abstract: The interpretation method is a characteristic common for all results from this thesis. The thesis consists of five chapters and two appendices. A brief overview of the contents of the thesis and the obtained results are presented in Chapter 1. Logical background and the wellknown notions the basic notions, definitions and properties from forcing are given in the appendices of the thesis. An elementary proof of equivalence between Cohen forcing and forcing with propositional Lindenbaum algebras is presented in Chapter 2. Dense embedding and the interpretation method are used in that proof. A complete axiomatization of the notion of qualitative probability is presented in Chapter 3. Probabilistic logic LPP_2 LPP_2^FR(n) and LPP^S are extended with the qualitative probability operator π. Several formal techniques as infinite rules, elimination of quantifiers and interpretation method (implicitly), are used to prove the extended completeness theorem and decidability for these logics. In Chapter 4 of the thesis a complete axiomatization of the logic with polynomial weight formulas is presented and the extended completeness theorem is proved. Applications of the interpretation method are given. By using that method the compactness theorem for the nonarchimedean valued probabilistic logics is proved in Chapter 5. URI: http://hdl.handle.net/123456789/100 Files in this item: 1
phdAleksandarPerovic.pdf ( 700.0Kb ) 
Laban, Miloš (Belgrade , 1980)[more][less]

Janković, Svetlana (Belgrade)[more][less]