Sharif Digital Repository

A liquid crystal is a state of matter composed of highly anisotropic building blocks. When liquid crystals are exposed to surfaces with given shapes and anchoring conditions, the orientation of their molecules gets spatially disordered and topological defects may form in the system. The interplay between liquid crystals and the geometry and topology of the colloidal particles has motivated extensive recent studies.In this thesis, we present the numerical modeling results for two faceted colloidal particles in a thermotropic nematic liquid crystal. To obtain the equilibrium nematic field with a finiteelement method, we numerically minimize the free energy of the system that based on the... 

Topological defects are interesting phenomena which can be observed in ordered phases such as oriented active fluids or nematic liquid crys¬ tals. Topological defects are determined by the overall structure of the director field in an active fluid in nematic phase and by exerting force to the units of the active particles they can interact or cause motion in the environment. Studying them as particles with dynamical equations, instead of studying the director field of the nematic environment, would provide us the power to study the characteristics of their motion. The equations of motion for multi¬defect systems have been previously stud¬ ied and in this work we focus on the chaotic... 

Among the various materials, silicon anodes have the highest lithium absorption in lithium-ion batteries. But this high lithium absorption capacity can cause 300 percent volume expansion and large stresses. Experimental observations show that charge and discharge cycles may cause plastic deformation in some parts of the electrode particle. On the other hand, there is a possibility of a ratcheting phenomenon due to changing in elastic properties of the electrode material during the charging and discharging processes. However, this phenomenon has not been reported for silicon spherical electrode particles yet.This study aims to model the elastic-plastic behavior of silicon spherical electrode... 

Dental implants should be biocompatible. This ability cause bone growth beside implant and increases stability of implant. Manufactoring method and materials used in implants are main parameters affectig biocompatibility of implants. Fabrication of functionally graded structures is a novel method to increase biocompatibility. Stress shielding is one of the main causes of failures in current dental implants. This phenomenon takes place due to different young modulus of dental implants and host bone. Pouros structures remedial this problem and implant’s young modulus comes closer to host bone. The aim of this project is to study feasibily of fabrication of functionally graded titanium dental... 

The main objective of all managers of the economic organizations, manufacturing and industrial companies and service providers is to take steps toward improvement and effective use of different resources like workforce, capital, materials, energy and information. To attain the desired productivity, managers have to observe requirements such as establishment of a working organizational structure, effective implementation methods, safe equipment and tools, balanced working atmosphere and qualified human force as the most important factor. Therefore productivity culture should be publicized throughout the organization, and human force should be considered as the main component of this process.... 

The current study deals with application of a surfactant-like Brønsted acidic ionic liquid (IL) 1-dodecyl-3-methylimidazolium hydrogensulfate (catalys 1) for Mannich reaction at room temperature. The reaction has been efficiently proceeds in water as solvent without using any harmful and expensive organic additives. Our observation has been shown that the reaction is selective for cyclohexanone and no product was observed by using cyclopentanone at room temperature. Density functional theory (DFT) calculations were performed to provide evidence about the nature of reactivity of the cyclohexanone/cyclopentanone. The activity of the catalyst 2 (1-dodecyl-2,3-dimethylimidazolium... 

Magnesium and its alloys have gained a lot of interest recently in the field of biodegradable implants, particularly in the field of orthopedics, mainly due to their excellent compatibility, low density and similarity of their mechanical properties with the human bone. However, the main weakness of magnesium for such applications is that it corrodes faster than the time required for complete healing of the tissue. Different properties of Mg can be improved by making composites. In this research, 1% and 2% of MgO microparticles were added to the Mg-1Zn-0.2Ag alloy. These composites were made by the stir casting technique, and after that, the samples' microstructure, mechanical... 

High-quality online services demand reliable and fast packet delivery at the network layer. However, clear evidence documents the existence of compromised routers in the ISP and enterprise networks, threatening network availability and reliability. A compromised router can stealthily drop, modify, inject, or delay packets in the forwarding path to launch Denial-of-Service, surveillance, man-in-the-middle attacks, etc. So researches tried to create intrusion detection methods to identify adversarial routers and switches. To this end, data-plane fault localization (FL) aims to identify faulty links and is an effective means of achieving high network availability. FL protocols use... 

Briefly in this thesis, these subjects have been investigated: In recent years, water is used as a solvent instead of an organic solvents have become more and more important due to cheap and environmental consideration. In this context, preparation of quinoxaline, pyrrole, new 1,4-dihydropyridine and reduction of imine to amine with 1,4-dihydropyridine derivatives as the reducing agents with the use of one-pot multicomponent reaction have been reported. The existence of several hydrogen bonding groups (NH) in the new dihydropyridines they acts as biologically active compounds in the forthcoming years. In continuation, oxidation of thiols to disulfides in the presence of NBS and NCS and... 

This thesis contains four chapters. In first chapter the role of water in organic reactions as a ecofriendly solvent, computational chemistry and dynamic nuclear magnetic resonance were studied. In the second chapter synthesis of new 4-hydroxy pyrrole derivatives in water were reported. For the synthesis of these compounds arylglyoxal derivatives, 1,3-dicarbonyl compounds and ammonium acetate were used. The reaction conditions are very mild. The third chapter contains the synthesis of new (4 or 5)-Aryl-2-aryloeil-(1H)-imidazole compounds in aqueous media. We also investigated the tauto-isomerisation of isomeric imidazoles during this reaction using DNMR technique. In forth chapter a... 

In recent decades, nano-structured materials have been allocated specific position for wide use in various fields. The nano-diamonds has attracted the attention of many researchers. The inherent characteristics of a diamond like spherical structure of nanoparticles and carbon atoms which have used their full capacity in the chemical bonds,also the same surface as the radiography particles which have empty orbital, provides an ability to perform a variety of surface modification on the particle . This article introduces the nanocomposites based on polymer, constituents specification and discuss properties of nanocomposites after mixing components together. Lots of studies was on... 

In this thesis, heterogenous catalysts based on magnetic nanoparticles were synthesized. In these catalysts, magnetic nanoparticles were coated with defferent fuctional groups to produce a catalyst with magnetic properties which is easily separated from the reaction medium. The structure of synthesized catalyst was characterized using techniques such as transmission electron microscopy (TEM), scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FTIR), and CHNS elemental analysis. Easy preparation, low cost, biodegradability and high thermal stability are advantages of these catalysts. At the end, the catalytic properties of resulted catalysts were investigated in many... 

This thesis contains two parts .In the first part a catalyst such as AlCl3/Al20 has been demonstrated to catalyze Michael addition reaction of amines to a,�- unsaturated compounds with high yields , short reaction time and under solvent-free condition.The Michael addition to a,�- unsaturated compounds produces quantitively the mono addition products.The next part is about olefins epoxidation . Alkene epoxidation is a useful reaction in organic synthesis. Epoxides play an important role in industrial intermediates for the production of fine chemicals as well as pharmaceuticals .The hydrogen peroxide has been used as an oxidant because it is considered as an economical and appropriate reagent... 

The method of nonlinear time history analysis is well known as one of the most accurate techniques in seismic analysis of structures. However, this method needs much effort in terms of required data and computational cost. Within the time constrains of design consulting firms, more simple analysis tools are also desirable. One of the simple methods which have been gaining ground, as an alternative to time history analysis, is nonlinear static pushover analysis. In this method, the capacity curve of the structure with respect to the roof displacement is established. In nonlinear static pushover analysis, disproportionate increases in the roof displacement and even outright reversals the... 

Enanthioselective synthesis of biological molecules are so important in synthetic chemistry, and because of their biological activities, β-amino carbonyl compounds have earned so much attention in this area of chemistry. Mannich reaction is a classical method for synthesis of these molecules. The Mannich reaction is a three-component reaction between an enolizable CH-acidic carbonyl compound, an amine, and an aldehyde producing β-amino carbonyl compounds. But acidic or basic difficult circumstances, long reaction time, low yield and enantioselectivity, are the drawbacks of classical methods. In this project, we used titania-based solid acid as an enantioselective catalyst to overcome these... 

Nowadays, pile usage in construction of deep foundations has increased significantly, instead of shallow foundation in areas that shallow foundations doesn’t provide enough bearing capacity and measuring the velocity and acceleration due to pile driving is very important. Because, all responses of building and individuals located near the pile driving site influenced by these three parameters: pile vertical displacement, peak particle acceleration (PPA) and peak particle velocity (PPV). One can estimates these important parameters by numerical analysis of pile driving process in different distances and depths to determining the effect of pile driving. Compared values obtained from numerical... 

Cardiovascular diseases are the leading cause of death globally so early diagnosis of them is important. Many researchers focused on this field. First signs of cardiac diseases appear in the electrocardiogram signal. This signal represents the electrical activity of the heart so it’s primarily used for the detection and classification of cardiac arrhythmias. Permanent monitoring of this signal is not possible for specialists so we should do this by means of Artificial Intelligence. In this thesis, we use recurrent neural networks to classify electrocardiogram’s arrhythmias. This deep learning method, use two sources of data to learn from. The first part of data is global for everyone and the... 

Confining nematic liquid crystal between two curved boundary conditions while the nematic molecules have a degenerate planar anchoring leads to complex and beautiful textures of molecular disparagement(defect) in the bulk and on the surfaces. Such the liquid crystal shells are made with double-emulsion techniques in microfluidic devices have provided applications for micro-scale colloidal linkers.In this work, we have numerically minimized the elastic energy in one-constant approximation in present of Fournier’s degenerate surface potential with finite element method. The nematic shell is confined between two spherical surfaces that we have studied the final energies and their related...