Sharif Digital Repository

Deployment of demands, increase in users and new services highlight the necessity of effective frequency allocation i.e. dynamic allocation instead of fixed allocation. Cognitive radio is a proper solution for dynamic frequency allocation. Cognitive radio can scan the spectrum and use the idle bands for transmitting and receiving data. The main part of this radio which is responsible for the most pivotal task is spectrum sensing. Recently, varied methods have been proposed to sense the spectrum. The scope of this research is on designing a very high-speed spectrum sensing system. In this thesis, in order to meet the required scan rate, a tunable complex filter with 40MHz pass-band has... 

Network methods have had profound influence in many domains and fields in the past decade. Community structure is a very important property of complex networks, but the precise definition of a community remains an unresolved problem and Community detection in complex networks has recently attracted wide attention in several research areas such as social networks, communication networks, and biological systems. Complex network studies grow by the scientific community, thanks to the increasing accessibility of real-world network data. The emphasis of use analysis on the network algorithms and community structure is one of the most important problems in the field of complex network. Many... 

The bis-cyclometalated platinum(II) complexes [Pt(ptpy)2], 3, and [Pt(fppy)2], 4, in which, ptpy = 2-(p-tolyl)pyridine and fppy = 2-(2,4-difluorophenyl)pyridine have been prepared. The reaction of 3 with one equiv [Au(PPh3)]+ (prepared from the reaction between AuCl(PPh3) and AgOTf) gave the heterobinuclear complex [Pt(ptpy)2Au(PPh3)].OTf, 5, by formation of a Pt→Au dative bond. The structure of all complexes were characterized using multinuclear NMR spectroscopy in solution phase and the structures of 4 and 5 determined using X-ray crystallography in solid state. The structure of heterobinuclear complex 5 shows an unusual Pt-Au bond that supported by Au-Cipso bond. The absorption and... 

The reaction of AuCl(SMe2) with two equiv of 2-vinylpyridine(2-Vpy) and one equiv of AgOTf gave the gold(I) complex [Au(2-Vpy)2], 1. Also the cationic gold(I) complex [Au(1,8-Naph)2][NTf2], 2, in which NTf2 is Bis(trifluoromethanesulfonyl)imide, has been prepared from the reaction of AuCl(SMe2), two equiv 1,8-naphthyridine and one equiv Ag(NTf2). The partial replacement of the NTf2 counter ion by PF6 using the reaction of 2 with one equiv TlPF6 leads to formation of the gold(I) complex [Au(1,8-Naphthyridine)2]〖"[NTf2]" 〗_("1" ⁄"3" ) 〖"[PF6]" 〗_("2" ⁄"3" ), 3. The solid state structure of 3 was determined using X-ray crystallography and its optical properties have been studied at room... 

Elliptic curve cryptography (ECC) has received attention because it can achieve a security level similar to other asymmetric methods while using a key with smaller length. Although ECC is more efficient compared to other asymmetric methods, fast computation of ECC is always desirable. In this thesis,a fixed-base comb point multiplication method has been modified to perform regular point multiplication. Additionally, two low-complexity and lowlatency architectures for the modified point multiplication algorithm has been proposed. In order to achieve these architectures, a low-latency pipelined digit-level field multiplier for all national institute of standards and technology (NIST)... 

Nowadays, the world is based on the interaction between individuals, groups and different systems. The actual networks that have a complex structure and behavior are called complex networks. Complex networks are one of the new knowledge that studies the connections. The complex systems represented as graph, with non-trivial topological features—features that do not occur in simple networks.With the vast development of computer networks, complex networks appear in different categories such as social networks, citation networks, collaboration networks and communication networks. Data mining is the process of exploring hidden knowledge in data bases and it has applications in complex networks.... 

In analyzing the structural organization of many real-world networks, identifying important nodes has been a fundamental problem. The network centrality concept deals with the assessment of the relative importance of network nodes based on specific criteria. Central nodes can play significant roles on the spread of influence and idea in social networks, the user activity in mobile phone networks, the contagion process in biological networks, and the bottlenecks in communication networks. High computational cost and the requirement of full knowledge about the network topology are the most significant obstacles for applying the general concept of network centrality to large real-world social... 

This Thesis identifies the pattern of technological learning in developing complex products systems (CoPS). The experiences of Iran in missile development in the defense industry has been studied to explain the learning process in attaining indigenous technological capability. The case study of TOW missile development including international technology transfers has been explored to investigate the technological learning patterns. The role of policy initiatives had excessive importance through technological learning in the case study  

In neural systems of living organism, moreover than differences in anatomic structure of cells, there is also differences in physiological functions of analogous cells.Specification and categorization of neurons based on physiological functions is one of objectives of neuroscience. Study of cognitive behaviors and systematic study of neural system, modeling and practical applications in neural prosthesis design are some of applications of categorizing neural cells. Neural signals can be studied by Spike rate of a single neuron activity or Local Field Potential (LFP) of a finite number of neurons. In previous studies neurons of first visual cortex are divided into two groups of simple and... 

Pipelines are main means of gas and oil transfer, and thus, leak detection in them for prevention or control of contingencies is highly important. Examination of acoustic waves resulted from diverse vibrational characteristics of damaged points has led to possibility of invention of varied industrial tools for non-destructive test. This research’s objective is examining acoustic and vibrational signals propagated by leakage point as a tool for locating leakage’s place and accuracy assessment of them in leak detection. For leak detection of the devised experimental system, a new method has been employed to calculate time delay; this method, which is called Residual Complexity, is based on... 

Computational complexity of graph problems is an important branch in the-oretical computer science. We introduce to some of ideas for computing the complexity of graph problems with some kind and beautiful examples. Next, we show hardness and inapproximability of some problems. Representation number of graphs has been introduce by Pavel Erdos by Number theory. We prove n1−ϵ inapproximability of that. Lucky number η has been studied by Grytczuk et.al . We show for planar and 3-colorable graphs, it is NP-Complete whether η = 2. Note that since a conjecture, for those graphs, 2 ≤ η ≤ 3. Also for each k ≥ 2, we show NP-completeness of η ≤ k for the graphs. Proper orientation number −→ is a... 

Stochastic Algebraic Topology studies stochastic or less known spaces that depend on many random variables from the perspective of algebra. Examples of such spaces included random graphs of Erdos and Renyi and random simplicial spaces of higher dimension . In this thesis , we study algebraic aspects of these spaces such as homotopy groups and homology groups from probabilistic point of view , when the number of vertices of these spaces tend to infinity . The study of these spaces have a lot of applications, since the data for a given space can be incomplete . They are also used in big system structures. We have given a collection of new results in stochastic algebraic topology of two... 

In this study, a series of polyoxometalates nanoclusters is synthesized and their catalytic properties have been investigated in oxidation and coupling reactions. In the first and second sections, {Mo36} nanoclusters are primarily prepared. Then, the mesoporous silica, as a solid surface with a regular chanals and cavities through electrostatic interactions between polyoxo anions and amine functional groups with positive charge, is used to stabilize the nanocluster as well as the final structure of SBA-15-NH3 +•{Mo36}- formed. As a green and environmentally friendly substrate, natural zeolite is used to stabilize the nanoclusters and the {Mo36}@zeolite obtained. Both heterogeneous catalysts... 

In the contest of conversion of water to hydrogen and oxygen there is a need for catalysts which will effectively support the oxidation of water. In nature, photosystem II relies on manganese for the oxidation of water. The water oxidizing complex (WOC) contains a cluster of four manganese atoms. In the past few years, there has been a tremendous surge in research on the synthesis of various manganese compounds aimed at simulating WOC of PS II. In this project, several manganese oxides as heterogeneous catalysts in water oxidation have been synthesized and characterized by FT-IR, X-ray diffraction, TGA, XPS, SEM and BET. Some of these oxides are able to oxidize water in the presence of... 

In this thesis, we have tried to study one of the most well known collective behavior phenomena known as the Wisdom of the crowd, from the perspective of statistical physics. In recent decades with the appearance of Social Networks and mass media, collective social phenomena have become a critical topic in the life of every human being. In the Wisdom of crowd phenomenon, the overall process is to ask the crowd’s opinion regarding a special topic and after aggregating the predicted values, the aggregated quantity is declared as the wisdom of the crowd. It has been observed that in some polls and elections, the result of the wisdom of crowd outperforms every individual of the group and in some... 

Local scour around bridge piers is one of the main causes of bridge failures Application of existing equations to complex flow patterns is problematic and often leads to questionable results in the field applications. A lack of understanding of the complex flow field and erosion mechanisms seems to be at least partly responsible for this state. Despite the rapid expansion of the literature on the flow around cylindrical piers, there are still challenges for flow field comprehension and estimating design scour depths around complex bridge piers. Due to geotechnical and economical reasons, bridge designs often leads to a complex foundation. Laboratory studies of local scour around complex... 

Peppermint oil is one of the most often used food ingredients and it is volatile. Many common procedures such as microencapsulation have been used for protecting volatile food ingredients. For this research, L-menthol was chosen as the core material to be encapsulated. L-menthol is responsible for the minty flavor and cooling sensation of food and pharmaceutical products. The encapsulation of L-menthol was prepared by complex coacervation, using gum Arabic and gelatin as wall material and tannic acid as cross-linking agent. The effect of various processing parameters, including wall material, core material, tannic acid and tween¬80 concentrations, on particle size and efficiency was... 

The complexation between folic acid and the complexes of Cu(L)2 (L = Glycine, Alanine, Valine) were investigated using UV.Vis spectroscopy. The values of the equilibrium constant K and molar absorption coefficient Ɛ of the complexes were estimated in the aquation environment at various temperatures. The temperature dependence of the K can be used for the determination of the thermodynamic reaction quantities (∆G, ∆H, ∆S) for linear regression fits to the Van’t Hoff equation. The kinetic studies reveals that the stoichiometry of reaction were 1:1 for these systems. All reaction were endothermic and the values of the ∆H are positive. In all cases entropy increased and the values of the ∆S... 

Studying of synthetic models which have many similarities to Oxygen Evolving Complex (OEC) in Photosystem II (PS II) can play a very significant role in gaining an insight to mechanism of oxidation of water in PS II. The aim of this study is to investigate the mechanistic and kinetic aspects of oxidation of dopamine as an important neurotransmitter in body by tri and tetranuclear oxo-bridge manganese clusters which have been reported in the past to get some information about the influence of protonation and deprotonation of oxo-bridges and water molecules bonded to these clusters on properties of them in redox reactions.In aqueous media, the trinuclear complex... 

A social network represents a set of entities and their relationships. Telecommunication networks, online social networks, and paper citation networks are some examples of networks in real world. Nowadays, analysis of social networks is an interesting research area with important applications. Particularly, managers of the social networks and the decision makers often require intelligent decision support for futures study in these social systems. The demanded decision support systems make it possible to define the desired social problem and to analyze the ”what-if scenarios.“ Computer simulation is an appropriate approach toward such decision support systems. In this approach, the desired...