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    How particle shape affects the flow through granular materials

    , Article Physical Review E - Statistical, Nonlinear, and Soft Matter Physics ; Volume 85, Issue 3 , 2012 ; 15393755 (ISSN) Nemati Hayati, A ; Ahmadi, M. M ; Mohammadi, S
    2012
    Abstract
    Flow through the pores of granular materials has many instances in practice. Therefore, it is interesting to realize how some parameters, such as the shape of the particles affect the passing flow. Following the recent mathematical theory proposed by the authors, this paper deals with the issue of how tortuosity and permeability are influenced by the particle shape. Comparison of the results with the experimental data reveals the competency of the theory in predicting the impact of particle geometry  

    The Role of Oil Price Shocks in Bussiness Cycles of an Oil-Exporting Country: Facts from Iran with a General Equillibrium Approach

    , M.Sc. Thesis Sharif University of Technology Hayati, Mojtaba (Author) ; Madanizadeh, Ali (Supervisor)
    Abstract
    In this research, we develop a Real Business Cycle model for Iran, as Small Open Economy. In this model, which is designed to measure the role of oil price shocks in Iran’s business cycles, the positive oil price shocks, as well as increasing the revenue of exporting oil, raises the price of oil-based tradable goods. Additionally, it causes the fiscal policy variables (taxes and government expenditures) to change. Also the productivity of this economy is fluctuated by oil price fluctuations. The model is estimated via Impulse Response Function Matching method using a SVAR model as the auxiliary model. The results from the theoretical model show that near 50 percent of non-oil GDP cycles and... 

    Unsupported advance length in tunnels constructed using New Austrian Tunnelling Method and ground surface settlement

    , Article International Journal for Numerical and Analytical Methods in Geomechanics ; Volume 37, Issue 14 , 2013 , Pages 2170-2185 ; 03639061 (ISSN) Nemati Hayati, A ; Ahmadi, M. M ; Hajjar, M ; Kashighandi, A ; Sharif University of Technology
    2013
    Abstract
    Tunnels constructed using New Austrian Tunnelling Method (NATM) are always based on certain round (unsupported) advance lengths, after which, the temporary lining is placed. The settlement of the ground surface resulting from such construction is of high significance in design and practice. The existing data in this respect, however, is scarce. It is the aim of this paper to propose a semi-analytical procedure based on three-dimensional finite element analyses to predict the maximum surface settlement of the ground in NATM tunnels under different combinations of tunnel diameter, overburden depth, round length and soil and lining properties. The comparison of the results with three case... 

    Theoretical and Numerical Analysis of Shock Waves Propagation in Porous Medium

    , Ph.D. Dissertation Sharif University of Technology Nemati Hayati, Ali (Author) ; Ahmadi, Mohammad Mehdi (Supervisor) ; Mohammadi, Soheil ($item.subfieldsMap.e)
    Abstract
    Particulate porous mateials have always been of interest in terms of reducing shock waves effects in different protective applications. Therefore, the physics governing the flow in porous media is especially significant for which different models have been presented by the researchers. The complexities of these media have caused many existing models to be unable to properly predict the behavior of granular media under shock loadings. On the other hand, the complexity of the equations makes the numerical solution of them cumbersome and costly in a way that many researchers do not solve the whole coupled equations and reduce their number. In addition, current high-resolution TVD solutions of... 

    Synthesis of Magnesium Aluminate Spinel Nanoparticles Using Chemical Method and Investigation of the Effect of Zirconia on Spinel Composites Properties

    , M.Sc. Thesis Sharif University of Technology Maddahi, Vahid (Author) ; Nemati, Ali (Supervisor)
    Abstract
    In this research, a powder containing magnesium-aluminate spinel particles is prepared based on co-precipitation method and 5% , 10%, 15% and 20% zirconia-contained composites are produced as second phase from the synthesized powder. The raw materials used in the synthesis comprise hexa-hydrated magnesium nitrate, nona-hydrated aluminum nitrate, ammonium bicarbonate, 28% ammonium solution and distilled water. The properties of the powder is then investigated using STA, XRD and SEM tests. Also, XRD and SEM analyses as well as triple point flexural strength and Vickers hardness tests are carried out in order to investigate the effect of adding zirconia to the powders. The variations of the... 

    The Effects of Composition on Hardness and Toughness of ZrO2-Based Ceramics

    , M.Sc. Thesis Sharif University of Technology Farooghi, Mohammad (Author) ; Nemati, Ali (Supervisor)
    Abstract
    The purpose of this thesis is the construction of hard and tough Zirconia bodies from economical raw materials using minimum sintering time and temperature.
    Stabilizers cause tetragonal particles to be remained in cubic phase. Most additives are Ca, Ce, Mg and Y ions the whole of which are rare earth elements and make solid solutions with Zirconia.
    In this project different percents of CaO, MgO, CeO2, and Y2O3 were mixed with ZrO2 and they were sintered after granulation, cold pressing and Cold Isostatic Pressing. Using jar milling and fast milling, the particle size of purchased ZrO2 was reduced to 0.7 um. The whole needed additives were purchased with particle size below 300 nm.... 

    Optical Properties of Gel Cast and Sintered Alumina Ceramics

    , M.Sc. Thesis Sharif University of Technology Ghorbani, Mohammad (Author) ; Nemati, Ali (Supervisor)
    Abstract
    In this process transparent polycrystalline alumina ceramic was provided by submicron alumina gel casting and spark plasma sintering. The monomer system in this process including met acrylamide and methylene bis acrylamide was chosen as a monomer and cross linker. These two agents comprise 5%wt of the precursor with the ratio of 3 to 1 respectively. With the optimization of Dolapix CE64 as a dispersant and providing the suspension with 76%wt, a greenware with the density of 56.3% wt was obtained. Differential thermal analysis of green body showed that the existing monomers are removed by the time the body reaches 550°C. In order to access high real in-line transmittance, the microstructure... 

    Preparation and Characterization of a Lithium Ion Conducting Electrolyte

    , M.Sc. Thesis Sharif University of Technology Toofan, Samin (Author) ; Nemati, Ali (Supervisor)
    Abstract
    In recent years lithium-air batteries captured worldwide attention because of their high energy density. Solid state electrolytes is one of the main components of lithium-air batteries. Lithium almunium titanium phosphate(LATP) is a nasicon type ion conduction which may be of great potential as solid electrolyte. The object of this thesis was the preparation of LATP solid electrolyte which can be used in a lithium-air battery. To reach this goal LATP powder was synthesized using a solution-based method and an appropriate crystallization temperature was selected based on obtained results of X-ray diffraction analysis. In the next step solid electrolytes was prepared under different pressing... 

    The Effect of Nano-TiO2 and CaF2 Additives on Formulation and Properties of SiO2-Li2O Glass-Ceramics

    , M.Sc. Thesis Sharif University of Technology Gol, Saba (Author) ; Nemati, Ali (Supervisor)
    Abstract
    The goal of the present study is to analyze the effect of CaF2 and nano-TiO2 as additives on formulation and properties of common dental glass-ceramics. To achieve the goal, a glass system based on SiO2-Al2O3-Li2O-K2O-P2O5-ZnO-ZrO2 was considered to produce glass-ceramic samples and the additives, nano-TiO2 and CaF2, with the 0.5, 1, and 1.5 %Wt was added to the system. After the melting process, the glass samples poured in the water and ferrite was produced. In the next step, the ferrite was milled and pressed. In the heat treatment step, the samples were treated in the temperature range of 650-850°C in order to gain lithium disilicate glass-ceramics. In the last step, the chemical... 

    A Comparison of the Effects of Additives Alumina Nanoparticles and Microparticles on Microstructure and Properties of Magnesia-Doloma Refractory

    , M.Sc. Thesis Sharif University of Technology Shahraki, Aziz (Author) ; Nemati, Ali (Supervisor)
    Abstract
    Magnesia-Doloma refractories has advantages such as stability in alkaline environments, clean steel production, resistance to acid slag, good cement kiln coating flexibility, low production cost. It also has some weaknesses such as low resistance to thermal shock and quick hydration. In the present study using Birjand Mines Magnesite powders and Dolomites from Zefreh, Esfahan, Magnesia-Doloma clinkers were pressed under the pressure 90 MP and prepared at 1650⁰C in furnace under air atmosphere. The effect of adding 0, 2, 4, 6, and 8% of the Microparticles and Nanoparticles of α-Alumina on microstructure, physical properties, hydration resistance and Thermal shock resistance was studied. Phase... 

    An Investigation on Photocatalytic Behavior of Heavily Doped Titania

    , M.Sc. Thesis Sharif University of Technology Hoseinian, Farideh (Author) ; Nemati, Ali (Supervisor)
    Abstract
    TiO2 has been considered the most promising photocatalyst for the degradation of pollutants in air or water; however, it shows poor absorption of visible light and requires ultraviolet (UV) light for activation. We have successfully synthesized a visible-light-active carbon and nitrogen and yttrium tridoped TiO2 catalyst. In this study, Nanocrystalline photocatalysts of TiO2 doped with yttrium, codoped with carbon and nitrogen and tridoped with carbon and nitrogen and yttrium were prepared by the sol–gel method and investigated by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), diffuse reflectance spectroscopy ( DRS), Scanning electron microscopy (SEM/EDS) and... 

    Electrical and Optical Properties of Doped (Ba, Sr)TiO3 Layers Prepared Via Sol-gel Method

    , M.Sc. Thesis Sharif University of Technology Emadi, Fahimeh (Author) ; Nemati, Ali (Supervisor)
    Abstract
    The main purpose of this research was simultaneous doping of carbon and nickel in the structure of barium strontium titanate, in order to investigate its dielectric and optical properties. Powders and films of BST, was synthesized by the sol-gel method in six different compositions: without any dopant, 0.04mol nickel dopant, 0.04mol nickel dopant accompanied by different amounts of carbon (0.01, 0.02, 0.03 and 0.04 mol). Suspensions were dip coated on alumina and quartz substrates. Structural features and chemical bonds, were studied through thermal analysis, XRD, FT-IR, FESEM and AFM. For electrical and optical properties, LCR-meter and UV-Vis were used. XRD and FESEM proved that nickel... 

    Formulation and Properties of Scaffolds based on Hydroxyapatite Composites Containing Titanium Dioxide and Magnesium Oxide

    , M.Sc. Thesis Sharif University of Technology Arab, Mehdi (Author) ; Nemati, Ali (Supervisor)
    Abstract
    This study investigates the effect of titanium dioxide and magnesium oxide additives on hydroxyapatite synthesized by sol-gel and composite with the predominant phase of hydroxyapatite by in situ method to improve mechanical properties. Scaffold samples were synthesized with nanometer-sized hydroxyapatite and composite powder particles by gel casting and sintered at 1200 ° C. Then, to evaluate the synthesized powders, simultaneous thermal analysis (STA), X-ray diffraction test, FTIR test, FESEM, EDS, and MAP analysis were used. Also, to evaluate the mechanical properties of the scaffolds, a compressive test was used, and to evaluate the scaffolds' density, the Archimedes method was used.... 

    Synthesis and Microstructure of Multi Valent Heavily Doped TiO2 Ceramics

    , M.Sc. Thesis Sharif University of Technology Motahari, Majid (Author) ; Nemati, Ali (Supervisor)
    Abstract
    In this project, the nanostructured titanium oxide with heaily doping of oxides of cerium and tin was synthesized using the sol-gel process and its properties were studied. To synthesize TiO2, titanium tetraisopropoxide precursor was used. Cerium nitrate and aqueous tin chloride precursors were utilized for cerium and tin synthesis. Then, they were mixed with Titania precursor causing a severe doping. After that, a gel was produced and it was aged and eventually, it was dried and calcined. XRD and SEM were used to determine the phase and particle size SEM and XRD results showed that doping had great impact on TiO2 crystals. The approximate size of nanoparticles was calculated using... 

    Studying the Effect of Carbon Nanotubes Addition on the Mechanical and Hydration Properties and Microstructure of Magnesia Doloma Refractories

    , M.Sc. Thesis Sharif University of Technology Mohammadi, Hooman (Author) ; Nemati, Ali (Supervisor)
    Abstract
    Magnesia-doloma refractories are alkaline products made by combining sintered or fused dolomite and magnesite. These refractories contain 50-80 wt% magnesium and a higher percentage of magnesium oxide, provides desirable properties such as improved refractoriness and resistance to air moisture absorption. Magnesia-doloma refractories have significant weaknesses, including rapid hydration due to the presence of CaO and MgO phases. These refractories are also primarily used with carbon additives in the industry, where increasing the carbon weight percentage in these refractories weakens their strength and some of mechanical properties. In the present study, the effect of adding carbon... 

    The Effect of Nano Mullite, Spinel as an Additive on Aluminum Based Composite

    , M.Sc. Thesis Sharif University of Technology Dargi, Hassan (Author) ; Nemati, Ali (Supervisor)
    Abstract
    In this research, the additive effect of mullite and spinel nanoparticles on aluminum-based composites has been investigated in order to improve mechanical properties. Composite samples with synthesized mullite powder particles and spinel with the sizes of 80 nm and 200 microns respectively with values of (1.5, 3, 4.5) percent and spinel particles with values of (3, 6, 9) percent as phase The reinforcement, whose particles are preheated to 200°C and inside the aluminum foils, due to better wetting time with the background, was added to the background phase by the vortex casting method, and the temperature was cast at 750°C. . Then, in order to check the prepared powders and the... 

    Investigation of graphite oxidation kinetics in MgO-C composite via artificial neural network approach

    , Article Computational Materials Science ; Volume 39, Issue 4 , 2007 , Pages 723-728 ; 09270256 (ISSN) Ali Nemati, Z ; Moetakef, P ; Sharif University of Technology
    2007
    Abstract
    In this study an artificial neural network (ANN) model was developed to predict the oxidation behavior of magnesia graphite composites. After mechanism evaluation in different conditions, the kinetic parameters such as effective diffusion coefficient and diffusion activation energy of oxidation were calculated from ANN predicted results at different graphite content. The obtained mechanism and kinetic parameters were compared with experimental data. First of all, the reliability of the model was checked with different available data. It was found that the model results were in good agreement with experimental data prediction. The results showed that the main mechanism of oxidation was pore... 

    Effects of Ce-Co Substitution on Magnetic and Dielectric Properties of Barium Hexaferrite Nanoparticles Synthetized by Sol-Gel Auto-Combustion Route

    , M.Sc. Thesis Sharif University of Technology Lellahgani, Zahra (Author) ; Nemati, Ali (Supervisor)
    Abstract
    In this study, the substituted barium hexaferrite nanoparticles with general formula Ba1-xCexFe12-xCoxO19 (x = 0, 0.1, 0.2 and 0.3) were prepared by the sol-gel auto combustion method. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FE-SEM), Mossbauer spectroscopy (MS), vibrating sample magnetometer (VSM) and performing network analyzer (PNA) were employed to investigation of structural, magnetic, dielectric and microwave properties of barium hexaferrite nanoparticles. Moreover, differential scanning calorimetry (DSC) were performed to observe the formation mechanism of barium hexaferrite. DSC studies showed that barium... 

    Synthesis of Fe3O4@ SiO2 Core-shell Magnetic Nanoparticles with Porous SiO2 Shell Extracted from Rice Husk Ash

    , M.Sc. Thesis Sharif University of Technology Aharipour, Nazli (Author) ; Nemati, Ali (Supervisor)
    Abstract
    Magnetic nanoparticles, especially magnetic nanoparticles with silicate coatings, have attracted the attention of many researchers; Mainly because the silica shell can be functionalized with different molecules and functional groups and used in biological applications as targeted drug carriers. This study aimed to synthesize Fe3O4 core-shell nanoparticles with continuous and porous SiO2 shells on the surface of Fe3O4 particles. So that the coating is done evenly and with a strong connection. The procedure was as follows: core nanoparticle individual nanoparticles were made by the single-step method. To extract silica from rice husk, rice husk was subjected to heat treatment to obtain rice... 

    Photocatalytic activity of TiO2-capped ZnO nanoparticles [electronic resource]

    , Article Journal of Materials Science: Materials in Electronics ; 2011 , Vol. 23, Issue 2, P.361-369 Lak, A. (Aidin) ; Simchi, A. (Abdolreza) ; Nemati, Ziarat Ali ; Sharif University of Technology
    Abstract
    Using a combined hydrothermal and sol–gel route, TiO2-capped ZnO nanoparticles with an average size of 60 nm were prepared. The titania shell was amorphous with a thickness of ~10 nm. Formation of Zn2TiO4 phase at higher calcination temperature was noticed. Effects of Ti/Zn molar ratio and coating time on the thickness of TiO2 shell and the photoactivity of the particles for decolorization of Methylene Blue (MB) under UV lamp irradiation (3 mW/cm2) were investigated. The nanoparticles were characterized by X-ray diffraction, transmission electron microscopy, fourier-transform infrared spectrometry (FTIR), diffuse reflectance spectroscopy (DLS), and atomic absorption spectroscopy. Analysis of...