Auflistung Doctoral Dissertations nach Titel
-
Stančić, Olivera (Beograd , 2018)[more][less]
Zusammenfassung: Hub Location Problems (HLP) represent an important class of optimiza- tion problems due to their numerous applications in many areas of real life. They often arise from practical situations that require routing of the flow from origin node (supplier) to the destination node (customer) under given conditions, such that the value of considered objective function is optimal. Hubs are special objects (nodes in the network) that represent centres for consolidation and flow collection between two selected locations - suppliers and customers. As transportation costs (per unit of flow) along the links that connect hub nodes are lower compared to other links in the network, directing the flow to hubs may lead to significant reductions of transportation cost in the network. The subject of this doctoral dissertation is one class of hub location problems, denoted as Hub Maximal Covering Problems (HMCPs) in the literature. The goal of HMCPs is to determine optimal locations for establishing certain number of hubs in order to maximize the total flow between all the covered origin-destination pairs, under the assumption of binary or partial covering. Three variants of the hub maximal covering problem are considered: uncapacitated single allocation p -hub maximal covering problem (USApHMCP), uncapacitated multiple allocation p -hub maximal covering problem (UMApHMCP) and uncapacitated r -allocation p -hub maximal covering problem (UrApHMCP). Note that the UrApHMCP has not been studied in the literature so far. All three considered problems are proven to be NP- hard. In case of USApHMCP, for the given set of hubs, the obtained sub-problem of optimal allocation of non-hub nodes by established hubs is also NP-hard. In this dissertation, new mathematical models for USApHMCP with binary and partial covering are proposed. The main advantage of the newly proposed models, in respect to existing ones from the literature, is the fact that small modifications of the new models enable their transformation to new models for p -hub maximal covering problems with different allocation schemes. More precisely, new models for UMApHMCP and UrApHMCP can be obtained from the newly proposed mod- els for USApHMCP in both coverage cases. All proposed models for USApHMCP and UMApHMCP are compared with the existing ones from the literature in the terms of efficiency within the framework of exact CPLEX 12.6 solver. Several hub data sets from the literature are used in numerical experiments when comparing the formulations. The obtained experimental results indicate that new models for UMApHMCP with both binary and partial coverage show the best performance in terms of solutions’ quality and execution times. For UrApHMCP and both coverage criteria, three mathematical models are proposed, and compared in terms of effi- ciency using the exact CPLEX 12.6 solver. It turns out that the exact solver finds optimal or feasible solutions only for small-size problem instances. Having in mind the complexity of all three problems under consideration and the results obtained by CPLEX 12.6 solver, the conclusion is that, in practice, exact methods can not provide solutions for large problem dimensions. For this reason, it was necessary to implement adequate heuristic or metaheuristic methods, in order to obtain high-quality solutions in short execution times, even in the case of large problem dimensions. Up to now, only simple but insufficiently effective heuris- tic methods for solving USApHMCP and UMApHMCP with binary coverage have been proposed in the literature, while the HMCP variants with partial coverage have not been previosly solved by using metaheuristic methods. As UrApHMCP with binary and partial coverage has not been previously considered in the litera- ture, no solution methods suggested for this problem existed up to now. Inspired by previous successful applications of variable neighborhood search method (VNS) to other hub location problems from the literature, this metaheuristic approach is applied to the considered HMCP problems. In this dissertation, several variants of VNS metaheuristic are designed and implemented: General Variable Neighborhood Search (GVNS) for USApHMCP, Basic Variable Neighborhood Search (BVNS) for UMApHMCP and a variant of General Variable Neighborhood Search (GVNS-R) for UrApHMCP. In the case of UrApHMCP, two additional metaheuristic meth- ods are proposed: Greedy Randomized Adaptive Search Procedure with Variable Neighborhood Descent (GRASP-VND) and Genetic Algorithm (GA). Constructive components of all proposed metaheuristics are adapted to the characteristics of the considered problems. Experimental study was conducted on the existing hub data sets from the lit- erature, which include instances with up to 1000 nodes in the network. The ob- tained results show that the proposed metaheuristics for the considered problems reach all known optimal solutions previously obtained by CPLEX 12.6 solver or establish new best-known solutions in significantly shorter CPU time compared to CPLEX 12.6. The proposed GVNS and BVNS metaheuristics quickly reach all known optimal solutions on small-size problem instances when solving USApHMCP and UMApHMCP, respectively. In the case of large-size problem instances, which have not been previously used for testing purposes for these problems, the proposed GVNS and BVNS return their best solutions in short execution times. The results obtained by the proposed GVNS-R and GRASP-VND for UrApHMCP on large-size problem instances indicate their effectiveness in both coverage cases. The proposed GA method showed to be successful only for UrApHMCP in binary covering, on instances up to 200 nodes. The variants of hub maximal covering problems considered in this dissertation are important from both theoretical and practical points of view. The new mathe- matical models proposed in this dissertation for the considered variants of HMCP, represent a scientific contribution to the theory of hub location problems, mathemat- ical modeling and optimization. Designed and implemented metaheuristic methods for solving the studied variants of HMCP are the scientific contribution to the field of optimization methods for solving location problems, as well as the development of software. The considered variants of HMCP have numerous applications in the optimization of telecommunication and transport systems, air passenger and goods transport, emergency services, postal and other delivery systems, so that the results obtained in this doctoral dissertation can be applied in practice, partially or com- pletely. URI: http://hdl.handle.net/123456789/4750 Dateien zu dieser Ressource: 1
StancicOliveradisertacija.pdf ( 1.688Mb ) -
Stojanović, Stevan (Belgrade , 1969)[more][less]
URI: http://hdl.handle.net/123456789/19 Dateien zu dieser Ressource: 1
phdStevanStojanovic.pdf ( 2.232Mb ) -
Berisha, Muharrem (Pristina , 1979)[more][less]
URI: http://hdl.handle.net/123456789/352 Dateien zu dieser Ressource: 1
phdMuharemBerisa.pdf ( 1.272Mb ) -
Mateljević, Miodrag (Belgrade)[more][less]
URI: http://hdl.handle.net/123456789/346 Dateien zu dieser Ressource: 1
phdMiodragMateljevic.pdf ( 2.438Mb ) -
Melentijević, Petar (Beograd , 2018)[more][less]
Zusammenfassung: In this thesis we study sharp estimates of gradients and operator norm estimates in harmonic function theory. First, we obtain Schwarz-type inequalities for holomorphic mappings from the unit ball B n to the unit ball B m , and then analoguous inequalities for holomorphic functions on the disk D without zeros and pluriharmonic functions from the unit ball B n to ( − 1 , 1) . These extend results from [ 32 ] and [ 18 ]. Also, we give a new proof of the fact that positive harmonic function in the upper-half plane is a contraction with resprect to hyperbolic metrics on both H and R + ([ 47 ]). Besides that, in the second chapter, we construct the examples to show that the analoguous does not hold for the higher-dimensional upper-half spaces. All mentioned results are from the authors’ paper [55]. In the third chapter we intend to calculate the exact seminorm of the weighted Berezin transform considered as an operator from L ∞ ( B n ) to the ”smooth” Bloch space ([57]). The fourth chapter contains results concerning Bergman projection. We solve the problem posed by Kalaj and Marković in [ 28 ] on determining the exact seminorm of the Bergman projections from L ∞ ( B n ) to the B ( B n ) . The crucial obstacle is the fact that B ( B n ) is equipped with M− invariant gradient seminorm. Also, we provide the sharp gradient estimates of the Bergman projection of an L p function in the unit ball B n , as well as its consequences on Cauchy projection and certain gradient estimates for the functions from the Hardy and Bergman spaces.We obtain the exact values of the Bloch’s seminorms and norms for the Cauchy projection on L ∞ ( S n ) . These results are based on the papers [56] and [58]. The last chapter contains the proof of the one part of Hollenbeck-Verbitsky conjecture from [ 26 ]. Exactly, we find the exact norms of ( | P + | s + | P − | s ) 1 s for 0 < s ≤ 2 on L p ( T ) , where P + is the Riesz projection and P − = I − P + . Also we give the appropriate dual estimates and prove that they are sharp. The paper [ 45 ] is motivated by the results from [25] and [33]. URI: http://hdl.handle.net/123456789/4749 Dateien zu dieser Ressource: 1
doktorat_Petar_merged.pdf ( 1.507Mb ) -
Popović, Biljana (Belgrade)[more][less]
URI: http://hdl.handle.net/123456789/26 Dateien zu dieser Ressource: 1
phdBiljanaPopovic.pdf ( 1.628Mb ) -
Stanimirović, Predrag (Niš)[more][less]
URI: http://hdl.handle.net/123456789/190 Dateien zu dieser Ressource: 1
phdPredragStanimirovic.pdf ( 5.471Mb ) -
Oskanjan, Vasilije (Belgrade)[more][less]
URI: http://hdl.handle.net/123456789/131 Dateien zu dieser Ressource: 1
phdVasilijeOskanjan.pdf ( 41.32Mb ) -
Dotlić, Milan (Beograd , 2015)[more][less]
Zusammenfassung: The thesis considers numerical methods for the computation of subsurface flow and transport of mass and energy in an anisotropic piecewise continuous medium. This kind of problems arises in hidrology, petroleum engineering, ecology and other fields. Subsurface flow in a saturated medium is described by a linear partial differential equation, while in an unsaturated medium it is described by the Richards nonlinear partial differential equation. Transport of mass and energy is described by advectiondiffusion equations. The thesis considers several finite volume methods for the discretization of diffusive and advective terms. An interpolation method for discretization of diffusion through discontinuous media is presented. This method is applicable to several nonlinear finite volume schemes. The presence of a well in the reservoir determines the subsurface flow to a large extent. Standard numerical methods produce a completely wrong flux and an inaccurate hydraulic head distribution in the well viscinity. Two methods for the well flux correction are introduced in this thesis. One of these methods gives second-order accuracy for the hydraulic head and first-order accuracy for the flux. Explicit and implicit time discretizations are presented. Preservation of the maximum and minimum principles in all considered schemes is analyzed. All considered schemes are tested using numerical examples that confirm teoretical results. URI: http://hdl.handle.net/123456789/4236 Dateien zu dieser Ressource: 1
phdDotlic_Milan.pdf ( 5.137Mb ) -
Milosavljević, Dragan (Belgrade , 1986)[more][less]
URI: http://hdl.handle.net/123456789/238 Dateien zu dieser Ressource: 1
phdDraganMilosavljevic.PDF ( 6.718Mb ) -
Georgijević, Dušan (Belgrade)[more][less]
URI: http://hdl.handle.net/123456789/327 Dateien zu dieser Ressource: 1
phdDusanGeorgijevic.pdf ( 2.373Mb ) -
Miličić, Pavle (Belgrade)[more][less]
URI: http://hdl.handle.net/123456789/112 Dateien zu dieser Ressource: 1
phdPavleMilicic.pdf ( 49.82Mb ) -
Trifunović, Miodrag (Novi Sad)[more][less]
URI: http://hdl.handle.net/123456789/313 Dateien zu dieser Ressource: 1
phdMiodragTrifunovic.pdf ( 55.19Mb ) -
Vuković, Veljko (Pristina , 1984)[more][less]
URI: http://hdl.handle.net/123456789/173 Dateien zu dieser Ressource: 1
phdVeljkoVukovic.pdf ( 4.933Mb ) -
Mostafa, Attila (Beograd , 2015)[more][less]
Zusammenfassung: First of all I would like to express my praises and sincere thanks to almighty Allah, start with no end and end will never start, for his divine assistance and guidance, which gave me the ability to succeed. I Thank you Allah, for life, health, and the energy that you have given me to reach my professional goals. Iwould like to gratefully and sincerely thank my supervisor Prof PhD Miodrag Mateljevi´c as well as dr Miljan Kneževi´c for their guidance, understanding, patience, and most importantly, their friendship during my graduate studies at my faculty. Their mentorship was paramount in providing a well-rounded experience consistent my career goals. My sincere appreciation, thanks and gratitude to all the academic staff members of Faculty of Mathematics, University of Belgrade. I would to thank Libyan Embassy in Belgrade to provide material and moral support. URI: http://hdl.handle.net/123456789/4339 Dateien zu dieser Ressource: 1
Attia Mostafa_thesis.pdf ( 3.337Mb ) -
Louka, Hana Almoner (Beograd , 2016)[more][less]
Zusammenfassung: This thesis has been written under the supervision of my mentor dr. Vladimir Bo zin at the University of Belgrade in the academic year 2016. The topic of this thesis is quantum information theory, with special attention to quantum contract signing protocols. The thesis is divided into four chapters. Chapter 1 gives introduction to Quantum mechanics and necessary mathematical background. Chapter 2 is about quantum information theory. Quantum algorithms, including Schor's and Grover's, are described. Chapter 3 deals with classical contract signing, and cryptography. Also discussed is the RSA algorithm and BB84 quantum key distribution. Chapter 4 describes quantum signing protocol, and proves, among other things, asymptotic behavior for probability of cheating. URI: http://hdl.handle.net/123456789/4342 Dateien zu dieser Ressource: 1
hana-thesis2-1.pdf ( 711.2Kb ) -
Grbić, Milana (Beograd , 2020)[more][less]
Zusammenfassung: In this dissertation some actual problems of bioinformatics and computational biology are explored,together with the methods for solving them. The following problems are considered: partitioning ofsparse biological networks intok-plexsubnetworks, prediction of the role of metabolites in metabolicreactions, partitioning of biological networks into highly connectedcomponents and the problem ofidentification of significant groups of proteins by adding new edges to the weighted protein interacti-ons network. The aforementioned problems have theoretical importance in areas of machine learningand optimization, and practical application in biological research. Inaddition to solving the afore-mentioned problems from the computational aspect, the dissertation explores further application ofthe obtained results in the fields of biology and biochemistry, as well as the integration of resultswithin existing bioinformatics tools.The problem of predicting the role of metabolites in metabolic reactions is solved by a predictivemachine learning method based on the conditional random fields, whilefor the remaining threeproblems the algorithams based on variable neighbourhood search are developed. For solving theproblem of identification of significant groups of proteins by adding new edges to the weighted proteininteractions network, the variable neighbourhood search is only the first phase of the proposedsolution, while in the second and the third phase of the proposed method, the integration withadditional biological information and bioinformatics tools are performed.The proposed computational methods of partitioning and groupingin biological networks confirmexisting findings in a new manner and lead to new discoveries about biological elements and theconnections between them. By solving these problems and by interpreting the obtained resultsin this dissertation, a scientific contribution was made to the scientific field of computer science,particularly to the scientific disciplines of bioinformatics and computational biology. URI: http://hdl.handle.net/123456789/5088 Dateien zu dieser Ressource: 1
grbic_Milana_disertacija.pdf ( 8.740Mb ) -
Davidović, Tatjana (Belgrade , 2006)[more][less]
-
Radović, Viktor (Beograd , 2017)[more][less]
Zusammenfassung: The main goal of this dissertation is improvement of an approach for identi- cation of the members of asteroid families, based on the hierarchical clustering method. An additional step is introduced in order to reduce a so-called chaining e ect. The introduced algorithm consists of four main steps. In the rst step, the hierarchical clustering method is applied to the initial catalogue of proper elements in order to obtain a preliminary list of family members. In the second step, using available physical properties, and based upon the de ned criteria, the interlopers are identi ed. In the third step, objects identi ed as interlopers in the second step, are excluded from the initial catalogue of proper orbital elements, producing a modi ed catalogue. Finally, in the fourth step, the HCM analysis is performed again, but this time using the modi ed catalogue of proper elements. It is shown that in this way a number of potential interlopers among family members is signi cantly reduced. Moreover, an on-line based portal (Asteroids Families Portal; AFP) to apply this procedure is developed, and is freely available to all interested researchers. The second goal of the dissertation is to determine the limitations of the backward integration method, used for estimation of ages of young asteroid families. This aim is achieved through numerical simulations of the evolution of a ctitious family. By determining instants of secular angles i $ clustering, a linear relationship is found between the depth of a clustering and the age of a family. According to the obtained results, the backward integration method could be successfully applied to families not older than 18 Myrs. URI: http://hdl.handle.net/123456789/4504 Dateien zu dieser Ressource: 1
Radovic_teza.pdf ( 22.32Mb ) -
Jovanović, Jasmina (Beograd , 2022)[more][less]
Zusammenfassung: The analysis of biological sequence similarity between different species is significant in identifying functional, structural or evolutionary relationships among the species. Biological sequence similarity and analysis of newly discovered nucleotide and amino acid sequences are demanding tasks in bioinformatics. As biological data is growing exponentially, new and innovative algorithms are needed to be constantly developed to get faster and more effective data processing. The challenge in sequence similarity analysis algorithms is that sequence does not always have obvious features and the dimension of sequence features may be very high for applying regular feature selection methods on sequences. It is important to have a simple and effective algorithm for determining biological sequence relationships. This thesis proposes two new methods for sequence transformation in feature vectors that takes into consideration statistically significant repetitive parts of analyzed sequences, as well as includes different approaches for determination of nucleotide sequence similarity and sequence classification for predicting taxonomy groups of biological sequence data. The first method is based on information theory and fact that both position and frequency of repeated sequences are not expected to occur with the identical presence in a random sequence of the same length. The second method includes building signatures of biological sequences and profiles of taxonomic classes based on repetitive parts of sequences and distances between these repeats. Proposed methods have been validated on multiple data sets and compared with results obtained using different well known and accepted methods in this field like BLAST, Clustal Omega and methods based on k-mers. Resulted precision for proposed methods is close to values provided for existing methods for the majority of tested data-sets, and time performance depends strictly to used infrastructure and sequence type. Methods provide results that are comparable with other commonly used methods focused on resolving the same problem, taking into consideration statistically significant repetitive parts of sequences with different characteristics. URI: http://hdl.handle.net/123456789/5440 Dateien zu dieser Ressource: 1
JasminaJovanovic.pdf ( 3.984Mb )