Sharif Digital Repository

During the last decade, thanks to a combination of exploding computational power and improved physical insight into material behavior, continuum and atomistic simulations improved greatly. Both classes of methods are now used to solve problems, which are more complicated than ever with greater accuracy than ever before. Nevertheless, there still exist problems for which neither method alone is sufficient. In general, atomistic simulations cannot be used for such length scales due to the restrictions on the number of atoms that can be simulated, along with the time scales, which they can be simulated for. In contrast, continuum simulations tend to fail at the atomic scale, for example due to... 

Because of mistakes in the design and calculation, incoherence between construction and design, structural changes, changes in loads and also damages caused by the passage of the time, concrete structures need to be improved and strengthened. Polymeric sheets reinforced by fibers (FRP), according to their appropriate characteristic, are more efficient for strengthening concrete structures. Most studies on confined columns refers to confined RC columns with FRP and less mentioned about prestressed columns. In this study, the behavior of prestressed columns is analyzed by modeling a case of prestressed column in a nonlinear analysis software. Samples of confined concrete columns with CFRP and... 

Carbon dioxide is one of the most significant greenhouse gases in biocycle. This gas makes the equilibrium temperature by absorbing IR radiations on the earth. It is the reason that prevent the earth from freezing. Increasing CO2 emissions in atmosphere, makes problems such as global warming. According to the Kyoto Protocol, all the countries attended to this protocol, must decrease greenhouse gases emissions. Although H2 fuel is one of the best alternative fuel against fossil fuels, the most important industrial process (steam-methane reforming) produce CO2 as by-product. Thus, gas separation has a prominent role in industrial processes such as CO2 capture and H2 purification.Today, gas... 

In this study, a thermo-mechanical model was utilized to investigate the welding residual stresses as well as thermal responses in dissimilar joint of carbon steel to stainless steel. A thermo-elastic-plastic analysis was first developed to assess temperature and deformation fields during and after welding operation. The employed model was capable of considering the effects of various factors such as, dilution, welding parameters and welding sequence on the developed residual stress as well as temperature distribution. In the next stage, the achieved predicted results together with EBSD data were used to correlate micro and macro residual plastic strains in the HAZ of the stainless steel... 

Thermodynamic modeling is a useful method for predicting of asphaltene precipitation due to various reasons, such as CO2 injection, mixing of different oils in oil storage and pressure changes. However, the application of solid model and thermodynamic micellization model, for prediction of asphaltene precipitation under gas injection condition, hasnot been improved. In this work, two computer codes which are based on two different asphaltene precipitation thermodynamic models, 1-Thermodynamic Micellization Model and 2- Solid Model, have been developed, and, used for predicting of asphaltene precipitation data reported in the literature as well as the experimental data obtained from high... 

The flexural behavior of reinforced concrete beams through application of FRP is studied, considering FRP-concrete bonding. Moreover, the nonlinear behavior of concrete (generation of crack and crush) is taken into consideration. Different parameters such as the number of layers of CFRP sheets, the effect of tensile reinforcing bars, the effect of using glass fibers, and modeling resin layer between the concrete and FRP are investigated. The results are compared with the existing experimental tests and those obtained from analytical method, ACI 440.2R-08 and ISIS Canada. The results show that by adding CFRP sheet to the control beam, the stiffness and flexural strength of the beam improves... 

Carbonate matrix acidizing using hydrochloric acid which causes CO2 generation is one of the most popular well stimulation techniques in recent decades. Lots of the wormhole propagation models developed for laboratory scale, assumes that the cores are fully saturated with aqueous solution and no CO2 gas is produced. Final purpose of this research is to develop a geochemical model describing equilibrium composition of a 3 phase system of acidic solution-gas-rock accurately in common pressure and temperature conditions of carbonate matrix acidizing to obtain main inputs of acid reactive flow in porous media from it. In this regard, concept of the “extent of the reaction” is defined and after... 

Excessive usage of fossil fuels and emissions of GreenHouse Gases (GHG) have led to many environmental problems such as climate change. The carbon dioxide emission accounts for 82% of GHG emissions and has the highest retention time in the atmosphere. The study on carbon dioxide is an important issue recently. The carbon dioxide emission from the energy and industrial sectors are 30% and 21%, respectively. It is possible to capture carbon dioxide from the flue gas may be utilized as material and fuel. Developing the utilization of carbon dioxide to replace storage is a solution for implementing carbon capture. The carbon planning model, is based on the selection of technology that is... 

The main aim of this project is to develop a model for risk assessment of energy service companies (ESCO) using energy efficiency and emission trading markets. For this purpose, structure of the market has been developed and then by explaining the interactions between ESCO and other members of the market, ESCO's cash flows have been determineded. In the next stage, probability distribution of the cash flows have been extracted and risk assessment have been performed. The differences in energy prices coming from subsidies is the foundation of this market. In this market, ESCO will sell the saved energy rights which has been achieved in the low price level sector to the other sector with high... 

In 2002 Baskaran and Jafari published an article that was about a spin-1 collective mode. Similarity between carbon nanotubes and graphene was a motivation for working on this project, in order to find another spin mode by considering random phase approximation as a simple way of finding collective motion of a physical systems. Moreover rolling graphene sheet induce diffrent physical properties as a result of chiral axis . In this project we focus only on achiral nanotubes and at last find two collective modes in this structures  

Classical theory of elasticity, which is founded upon results of mechanical experiments on the large scale materials, has reasonable results in predicting mechanical properties. The basic idea in this theory is that stress at a point of the material is only a function of the local strain and it is independent of the nonlocal strains. Therefore, the size of the material does not play any role in analyzing mechanical behavior of materials using this theory. However, results from experiments and atomic simulations have shown that in nano scale materials, such as carbon nanotubes (CNTs) and their composites, mechanical properties are strongly dependent on the size parameters of these materials.... 

Metal foams are considered as a group of new materials and are applied widely in various areas due to their particular properties such as low density, high strength-to-weight ratio and appropriate mechanical, thermal, physical, electrical and magnetic properties. The aim of the present study is acquiring the technical knowledge of Zinc foam production by melting route and also optimizing the effective parameters on the foam stability. For this reason, 4 Zinc foams were produced at different times and temperatures. The amount of Calcium as the melt fluidity reducing agent and Titanium hydride and Zinc carbonate as the blowing agent were the same in all the specimens. The effect of heat... 

This study investigates the effect of adding hydroxyapatite nanoparticles and multi-walled carbon nanotubes in pure and modified form on the flexural properties and hardness of denture base Polymethyl Methacrylate. Polymethyl Methacrylate (PMMA) is still the most common denture base material. In fact, the mechanical properties of this resin have played a significant role in expanding its use in dentistry. But in the long-term use of resins, defects such as low resistance to crack growth, low flexural strength and brittleness can be seen. In fact, flexural fatigue occurs as a result of repeated flexural stresses, and it can be described as the main reason for crack growth and propagation in... 

Thermodynamic properties of supercritical carbon dioxide change near the critical point. High cycle efficiency is realized by having the main compressor to operate near the critical point of CO_2 to benefit from reduced compression work. In addition the high efficiency, compactness, nontoxicity, cheap working fluid and possibility of using dry cooling instead of wet cooling, s-CO_2 has many application such as nuclear, fossil fuel, renewable sources like solar thermal and waste heat. With regards to sCO_2 thermodynamic properties, suitable equation of state with high accuracy has been determined, and then is used in the design modeling. Recompression Brayton cycle with steady state flow is... 

well known metal-free nanostructure carbon-based catalyst, mesoporous graphitic carbon nitride, with diverse morphologies were synthesized by using ethylendiamine/carbontetrachloride as a precursor, SBA-15 and SBA-15 nanorod as hard templates. We have investigated morphology effect on the catalytic performance. The catalysts were characterized by means of low angle and wide angle XRD, BET, FT-IR, CHNOS, FE-SEM analysis. Because of high surface area, pore volume and high nitrogen content, which acts as lewis basic site, for the first time, carbon nitride is chosen for selective catalytic oxidation of hydrogen sulfide to sulfure. Reaction was taken place in a fixed-bed reactor and at... 

Ferrite spinels are very valuable as heterogeneous catalysts and have the ability to separate. In this dissertation, ferrite nanoparticles were synthesized by co-precipitation method and used in carbon-phosphorus and phosphorus-sulfur bond formation reactions. The structure of these compounds was investigated by different techniques. The ferromagnetic CuFe2O4 ferrite catalyst was expanded in the C-P bond formation reaction, resulting in a convenient and efficient method. Phosphorylation of alkenes was performed using a model reactant, dialkyl phosphite as a source of phosphorous compounds, and beta-ketophosphosphonates were synthesized. Beta-ketophosphonates are important intermediates for... 

Emission of aromatic and aliphatic compounds to atmosphere is a major environmental concern for many urban societies. Catalytic oxidation of volatile organic compounds (VOCs) is an efficient and low operating cost technology for reduction of air pollution.
First, dispersed copper oxide nano-catalysts supported on almond shell-based activated carbon were prepared for catalytic oxidation of toluene in air. The Response Surface Methodology (RSM) was used to express the catalyst removal efficiency in terms of catalyst metal loading and calcination temperature. Calcination temperature had a significant effect on the catalyst activity only at high metal loadings (upper 8% wt.). Two different... 

Nowadays, increased pollutants in the air threat the society health condition and Volatile Organic Compounds (VOCs) are the most hazardous ones among them. In the present study, catalytic oxidation as a prominent of the VOCs removal method from air, have attracted attentions due to high removal efficiency and suitable kinetic reaction. Because of its common industrial applications, toluene is intended to be eliminated through a low cost carbon supported catalyst which is synthesised in the laboratory. Construction method, carbonaceous support type, catalyst metal and its load, calcination temperature and time are among influencing design characteristics. A combination of Impregnation and... 

Miniaturization of electronic devices with portable, flexible and wearable characteristics created a great demand for high-performance microscale energy storage devices with lightweight and flexible properties. Among the energy storage devices, wire-shaped micro-supercapacitors have recently received tremendous attention due to their small size, lightweght, and high flexibility. In the first part, the porous dendritic Ni-Cu film was prepared on Cu wire substrate (CW) for fabrication of high- performance wire-type micro-supercapacitors (micro-SCs). The porous structure with dendritic morphology provides a high surface area, short ion diffusion pathway and low contact resistance between... 

One of the remarkable subject in advanced electrochemistry is, design and architecting new advanced materials with new electrochemical capabilities. One of the notable capabilities is electrocatalysis. Extensive researches are carrying out into the design and preparation of electrocatalyst materials to take advantage of these materials in fabrication of electrochemical sensors and storage/conversion devices. In this field nonoporous materials attracted a lot of attentions due to their unique features. In order to make use of the nanoporous materials as the electrocatalysts, these materials must be fabricated into continuous supported thin films on the electrode surface, which is the...