Sharif Digital Repository

In this study, a three dimensional molybdenum oxide based coordination polymer of{(M¬o2O6)(4,4'–bpy)}n was synthesized by solvothermal process. Excellent properties of the fabricated metal–organic framework such as crystallinity, porosity, sufficient thermal stability and possession of different interactions encouraged us to employ it as a novel extraction phase in sample preparation. Extraction efficiency of the MOF–based sorbent was evaluated in needle trap extraction of some chlorobenzenes as volatile aromatic organic compounds in conjugation with gas chromatography–mass spectrometry. To achieve maximum efficiency and sensitivity, influential parameters including desorption time and... 

Periodic mesoporous organosilicas (PMOs) are a new class of porous materials with high surface area, ordered structures, and uniform pore sizes. There is a high structural diversity in these materials due to the possibility of choosing different building blocks, functionalization and chemical modification of organic groups. Considering the stated advantages, the synthesis and application of different classes of adsorbents based on periodic mesopore organosilica compounds are the main goals of this thesis. In this regard, in the first research, an attempt was made to use organosilica precursors based on the tyrosine amino acid in the preparation of PMO and then its adsorption capacity towards... 

Fabrication and characterization of different surface charged cellulose electrospun scaffolds including cellulose acetate, cellulose, carboxymethyl cellulose and quaternary ammonium cationic cellulose for biomedical applications have been reported in this research. We describe preparation of cellulosic nanofibers through the electrospinning following deacetylation cellulose acetate. Moreover, surface modification of electrospun cellulose nanofibers is carried out to obtain carboxymethyl cellulose and quaternized cellulose nanofibers, respectively. At last, the structural, morphological, mechanical, swelling, wettability and the cell culture properties of the scaffolds were analyzed and... 

Reducing the size of transistors has dramatically increased the impacts of NBTI, HCI, and EM phenomena in comparison with decade ago. These phenomena are able to have influence on properties of different parts of a chip to make it changed gradually; including threshold voltage of a transistor and electrical conductivity of interconnections. These changes are known as the aging of a transistors that diminish the performance and reliability of a chip. A common reason that plays a significant role in all these phenomena is temperature. The temperature becomes more important when the power density increases per unit area due to decreased size of transistors, which is a trend in multi-core... 

Deposition of solid particles present in the process air on the walls of furnaces is one of the challenges in industries. This phenomenon has various causes. For example, in a furnace, the temperature of particles increases as they pass in front of the furnace burners, and due to the softening of the particles, their chances of deposition increase when they collide with the walls. Over time, with the growth of deposited particle layers on the combustion chamber walls, the performance of the combustion system gradually becomes impaired. present research aims to design air jets intersecting with the process air path, with the purpose of reducing the temperature of particles prone to deposition... 

In many papers, GDP is used as a measure of economic growth, which is shown to possess a nonlinear structure. The study focuses on the nonlinear Granger causality between liquidity, government spending, oil revenues and economic growth by markov-switching vector autoregressive and markov- switching Granger causality approach for the period of 1369-1397 for Iran. The empirical results from MSAI(2)-VAR(4) suggest that Oil revenues and government spending have a significant impact on economic growth in both regimes. Also, markov- switching Granger causality results are quite different from the traditional Granger causality results, that suggests the nonlinear Granger causality has more... 

The use of microelectrode arrays in neural networks has offered a wonderful opportunity for evaluating numerous properties and interactions with excitable tissues such as the brain and spinal cord in the laboratory. In neural network applications, microelectrode arrays can be utilized to analyze nerve impulses or interact with neurons. They are either used to record neural data or to stimulate spinal cord nerves. Previous research has revealed that stimulating the spinal epidural region can help restore after spinal cord injuries (SCIs), which is the key to using them in the rehabilitation of living beings, including humans. According to the international campaign for the treatment of SCI... 

In this study, at first the V2O5 spent catalysts were characterized. The aim was to identifying whether these catalyst may be regenerated. Then, for feasibility study of them, three methods were applied: washing, diffusion and milling the spent catalysts for their subsequent reproduction. A variety of techniques such as XRD, XRF, AAS, TPR and TPO were applied in order to identify factors contributing in vanadium pentoxide catalysts deactivation. The results showed that approximately all of pollutants caused their performance deterioration, while they still have some active phases. Then, the polluted catalysts were washed (their yield increased from 43% to 72.2%). In the underside of the... 

The control and management of social networks’ potentials has been an important research subject for many organizations and researchers in recent years. Social network of an organization includes all the people that at least once have established a social relationship with the organization directly or indirectly. This relationship can be formal or informal, spontaneous or controlled, and deep or shallow. But in any case, the stronger the communication between people’s social relationships (as members of that social network) become and the more increases in the number of members of that social network, the easier path to success the organization could achieve. Hence, the critical success... 

The microstructures of stainless steels consist of an austenitic matrix with almost continuous network of primery carbides.This class of steel had replaced the traditional super alloys with a reduction in costs and has similar properties under conditions of creep, which is one of the principal degradation mechanisms leading to failure in service at elevated temperaturs , therefore, their mechanical properties such as tensile strength and creep resistance are particularly important in hot deformation. Recently the effects of temperature and aging time on static strain aging in worked stainless steel have been investigated. In this study the deformation behavior of HP-series austenitic... 

Design of optimal controllers for nonlinear systems and even for linear systems is one of the most important parts of the control science. In optimal controller design, our aim is to maximize or minimize some kind of cost function associated with that particular problem. Such cost functions are usually combining the overall control effort, system’s energy, or some other important specifications of the system. Explicit solution for linear quadratic controllers exists under some mild conditions such as stabilizability of the system. The solution is in the form of a full state-feedback law. But in practical problems, we may not have access to all of the system state variables. The problem can... 

A control strategy for islanded (autonomous) operation of a microgrid consisting of two Distributed Generation (DG) units is proposed in this thesis. The DG units are connected together in a radial configuration. Each DG unit utilizes a voltage-sourced converter (VSC) to interface to its dedicated load. The DG units and the loads are to operate in the islanded mode of operation. To provide autonomous operation for the microgrid, voltage and frequency of the loads should be regulated. The proposed control strategy utilizes (i) an internal oscillator for frequency control in an open loop manner and (ii) a decentralized servomechanism controller to regulate the load voltage. The microgrid is...