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Explicit approximate solution for finding the natural frequency of the motion of pendulum by using the HAM
, Article Applied Mathematical Sciences ; Volume 3, Issue 21-24 , 2009 , Pages 1023-1030 ; 1312885X (ISSN) ; Doosthoseini, A ; Doosthoseini, E ; Abachi, T ; Sharif University of Technology
2009
Abstract
In this work, we use a powerful analytical method called homotopy analysis method (HAM) to derive the frequency of a nonlinear oscillating system. Unlike the perturbation method, the HAM does not require the addition of a small physically parameter to the differential equation. It is applicable to strongly and weakly nonlinear problems. Moreover, the HAM involves an auxiliary parameter, h, which renders the convergence parameter of series solutions Controllable, and increases the convergence, and increases the convergence significantly. This article depicts that the HAM is an efficient and powerful method for solving oscillating systems
A fuzzy expert system for prescribing atorvastatin optimum dose
, Article Koomesh ; Volume 13, Issue 1 , 2011 , Pages 43-50 ; 16087046 (ISSN) ; Hassanpour Ezatti, M ; Navidi, H ; Abachi, T ; Sharif University of Technology
2011
Abstract
Introduction: Today, Fuzzy expert systems have helped physicians in cases of uncertainty in medical decision making for prescribing drugs. Narrowing of coronary heart and reduction in heart blood flow are important causes of coronary heart disease (CHD). Control of blood lipid level is a routine treatment in CHD patients. But damage to liver is a common side effect of lipid lowering drug medication. Measurement of plasma Alanine aminotransferase level is considered as a marker of liver damage. The aim of this study was to determination of optimal dose of atorvastatin using Fuzzy expert system. Materials and Methods: in this study, Fuzzy expert system based on drug dose determination was...
Effect of VC and (Ta, Nb)C on wear of WC-10Co based cemented carbides
, Article Tribology - Materials, Surfaces and Interfaces ; Volume 3, Issue 1 , 2009 , Pages 31-36 ; 17515831 (ISSN) ; Ganji, Y ; Sharif University of Technology
2009
Abstract
WC-Co cemented carbides, including small angular tungsten carbides particles, are used extensively to improve wear resistance. Some additives can affect mechanical and wear properties of these materials. In this study, the effect of VC and (Ta, Nb)C content on wear of WC- 10Co were considered. The tests were performed at normal load of 230 N and sliding distance of 800 m up to 3200 m. Wear tests were carried out using dry sand/rubber wheel apparatus. Wear rate, standard and modified wear coefficients were calculated. The microstructures of prepared specimens were examined by optical microscopy. The morphological analysis of the worn surfaces was made by SEM. The results show that VC content...
Production of Copper-Graphene Nanocomposites Via Molecular Level Mixing, Evaluation of the Effect of Some Processing Parameters on Micro-Structure and Physical-Mechanical Properties
, M.Sc. Thesis Sharif University of Technology ; Abachi, Parvin (Supervisor)
Abstract
This research aimed at production of Cu-rGO via the combination of Molecular-Level-Mixing (MLM) method and powder metallurgy route (PM). First, Cu-GO composite powder was produced via MLM method. Subsequently, the resultant powder was mixed with electrolytic copper powder.Synthesis process included adjustment of the solution containing copper sulfate and 2Na.EDTA using NaOH solution. In the next step, GO suspension was added to the aforementioned solution. Finally, reduction of copper powder and formation of nanocomposite powder completed via the addition of Sodium Borohydrate. Nanocomposite powder was washed and dried in vacuum oven in 70˚C. GO reduction process took place using a tube...
Comparison of experimental and analytical fracture toughness values of SiCP/QE22 Mg-alloy composites
, Article Materials and Design ; Volume 27, Issue 6 , 2006 , Pages 520-525 ; 02641275 (ISSN) ; Purazrang, K ; Sharif University of Technology
2006
Abstract
In the present work, the fracture toughness data generated on the QE22 magnesium alloy as the matrix alloy and SiC particles reinforced composites using the short rod standard specimens. The short rod specimens of 18 mm diameter were prepared from the extruded rods in the extrusion direction. The fracture toughness values are primarily evaluated experimentally and then analytically by using mathematical methods. The suitability of these methods to predict this property was also discussed. Results showed that the incorporation of the SiC particles with three different shapes (i.e. sharp, blocky and round) decreases in general the fracture toughness of the QE22 Mg-alloy. This effect is...
An Intelligent Spectrum Management Framework in Cognitive Radio Networks
, M.Sc. Thesis Sharif University of Technology ; Hemmatyar, Afshin (Supervisor)
Abstract
Cognitive radio is a tool for optimal use of radio spectrum, not used by the primary users all the time. Two main features of a cognitive radio are cognitive capability and reconfigurability. An intelligent cognitive radio uses its cognition ability to identify the environmental parameters and makes future decisions based on this information. Then the reconfigurability is used to set the sending parameters to the calculated values in the cognition phase. Cogition phase consists of major steps; spectrum sensing, decision, mobility and handoff. Throughout this thesis we first propose a cooperative sensing scheme using algorithmic techniques based on sensors’ spatial information through...
Dry sliding wear behavior of SiCP/QE22 magnesium alloy matrix composites
, Article Materials Science and Engineering A ; Volume 435-436 , 2006 , Pages 653-657 ; 09215093 (ISSN) ; Masoudi, A ; Purazrang, K ; Sharif University of Technology
2006
Abstract
In present work, an attempt has been made to investigate the wear behavior of particle reinforced composites based on one of the proper magnesium alloys. The SiCP/QE22 composites and QE22 unreinforced specimens were produced via the powder metallurgy route. The volume fractions of SiC particles with three different shapes, i.e. sharp, blocky and round, were selected in the range of 10-25 vol.%. The dry sliding tests were conducted on unreinforced matrix and SiCP/QE22 composites using pin-on-disk apparatus, according to ASTM G99-95a standard. The applied loads were selected as 3, 5 and 20 N. The tests were carried out under sliding speeds of 0.5 and 1.2 m/s. In all tests, the sliding...
Effect of rotational speed and probe profile on microstructure and hardness of AZ31/Al2O3 nanocomposites fabricated by friction stir processing
, Article Materials and Design ; Volume 32, Issue 4 , 2011 , Pages 2034-2041 ; 02641275 (ISSN) ; Kokabi, A. H ; Abachi, P ; Sharif University of Technology
2011
Abstract
Friction stir processing (FSP) was used to fabricate AZ31/Al2O3 nanocomposites for surface applications. The effects of probe profile, rotational speed and the number of FSP passes on nanoparticle distribution and matrix microstructure were studied. The grain refinement of matrix and improved distribution of nanoparticles were obtained after each FSP pass. By increasing the rotational speed, as a result of greater heat input, grain size of the base alloy increased and simultaneously more shattering effect of rotation, cause a better nanoparticle distribution. The average grain size of matrix of the composites was in the range of 1-5μm and the microhardness of them was 85-92Hv
The effect of Cobalt Replacement by Nickel on Microstructure, Physical and Mechanical Properties of WC-Co Hardmetals
, M.Sc. Thesis Sharif University of Technology ; Pourazerang, Kazem (Supervisor) ; Abachi, Parvin (Supervisor)
Abstract
WC-Co hardmetals that are produced through powder metallurgy rout are vastely used as wear resistant parts. In these materials hard particles of wolfram carbide are embodied in a cobalt binder. Because of their high hardness and adequate toughness, hardmetals have found wide range of applications in cutting tool industry. During the last decades a number of researches have been carried out to improve their mechanical and wear properties by different binders and carbide particle sizes. Because of high hardness, Tungsten carbide has a good wear resistant. It has very low thermal expansion coefficient and high wetting ability with molten metals. Unlike high hardness, it has limited toughness....
Preparation of Cu-TiC Nanocomposite and Investigation of Microstructure, physical and Mechanical Properties
, M.Sc. Thesis Sharif University of Technology ; Pourazarang, Kazem (Supervisor) ; Abachi, Parvin (Co-Advisor)
Abstract
In this study, Cu-TiC nanocomposites were produced by high energy ball milling of elemental powders and in situ formation of TiC in the copper base. Cu and 5,10,20 and 40 wt% Ti powder blend were milled for 60 h, then graphite powders were added and milling was continued for 10 h again and Finally Cu-TiC composite powders with 10.68, 20.16, 36.24 and 60.25 vol% of reinforcements (6.18, 12.2, 23.82 and 45.47 wt%) were produced. The effect of time on the solution of titanium in the copper was studied by X-Ray diffraction analysis (XRD). crystallite size and lattice strain of copper were determined 12nm and 1.04% subsequently for Cu-40wt%TiC after 60 h milling. to ensure the formation of...
production of Nickel- Aluminide Nanocomposite Reinforced with Al2O3 Nanoparticles Via Mechanical Alloying Route and Field Activated Sintering Technique
, M.Sc. Thesis Sharif University of Technology ; Abachi, Parvin (Supervisor) ; Pourazarang, Kazem (Supervisor)
Abstract
Nickel aluminides are intermetalics with complex structures that have high metlting points. However, brittlement at room temperature and low high_temperature strength (above 700 ̊C) can be mentioned as their short comings. Nowadays, many efforts have been proceeded to produce theirs composites, so that one can benefit from ceramics and intermettalics properties simultaneously. In this project, the main was aim to produce NiAl matrix nanocomposite reinforced with Alumina Al2O3. The composite is processed using milling and mechanical alloying. This is a good way to produce intermetallics and their composites with high melting points without any need to supply high temperature during...
Modeling the Effect of Pressure on the Shrinkages Distribution
, M.Sc. Thesis Sharif University of Technology ; Davami, Parviz (Supervisor) ; Abachi, Parvin (Supervisor)
Abstract
Due to the shrinkage defects, casting parts is sometimes unusable; as a result, researchers is tackling porosity removal problem, so that they would be able to cast parts in a way that have the least porosity. Nowadays, simulation is used to predict the location of the porosity. The design and the elimination of defects, which leads to additional costs, can reduce the overall costs in the projects.
In this thesis, we focus on shrinkage defects. The main cause of porosity is the drop of pressure. As a matter of fact, the thermal agitation of the molecules is weaker than the strong intermolecular forces that would pull the molecules; therefore, the molten metals’ density will be increased...
In this thesis, we focus on shrinkage defects. The main cause of porosity is the drop of pressure. As a matter of fact, the thermal agitation of the molecules is weaker than the strong intermolecular forces that would pull the molecules; therefore, the molten metals’ density will be increased...
Producing Cu-TiB2 Nano Composite Using Powder Metallurgy Route and Study on its Mechanical and Physical Behavior
, M.Sc. Thesis Sharif University of Technology ; Pourazrang, Kazem (Supervisor) ; Abachi, Parvin (Supervisor)
Abstract
In applications such as high duty sliding contacts and other electrical components requiring good electrical- and thermal-conductivity, proper mechanical wear resistance in combination with arc erosion resistance are required.The Cu/TiB2 nano-composite seems to be a good candidate for such cases. At present work TiB2 nano-particles has been selected as reinforcement, due to its valuable properties, i.e., high melting point (2850 - 2900 °C), low linear CTE (8.10 µmm-1 °C-1), thermal conductivity (60.0 - 120 W/m-K) as well as low specific electrical resistivity (10 - 30 μΩ.cm) and high hardness (25-35 GPa HV). Additionally, there are limited articles which have focused on evaluation of...
Production and Investigation of Microstructure and Some Physical and Mechanical Properties of Copper Matrix Composites Reinforced with Micro-nano Yttria Stabilized Zirconium Oxide (YSZ) Particles
, M.Sc. Thesis Sharif University of Technology ; Purazarang, Kazem (Supervisor) ; Abachi, Parvin (Supervisor)
Abstract
In this study, the ultrafine-nanometric yttria stabilized zirconia (YSZ) particles were used for reinforcing of copper metal powder. To producing of bulk nanocomposite specimens, the copper powder and the proper volume percent of reinforcement powders (i.e. 2, 3 and 5) were mixed using Turbula mixer for one hour. Before the mixing of two metallic powders and ceramic nanoparticles, for separation of agglomerated zirconium oxide nanoparticles that witch leads to producing of nanocomposite specimens with satisfactorily distributed secondary phase, the ultrasonic devise with enough quantity of ethanol as neutral liquid have been used for 15 minutes. The powders mixture have been placed under...
Preparation of Cu-MoSi2 Nanocomposite by Mechanical Alloying and Investigation of Properties
, M.Sc. Thesis Sharif University of Technology ; Pourazarang, Kazem (Supervisor) ; Abachi, Parvin (Supervisor)
Abstract
In this study, to synthesize molybdenum disilicide nano powder, mixed powder of Mo and Si were ball milled for 15, 30, 45 and 55 hours. By the results of the analyses, milled powders for time intervals of 55 hours were heat treated to release the stresses. This process was carried out in an argon vacuum tube furnace at 1000˚C for 1 hour. XRD analysis was carried for sample. Finally, MoSi2 powder with 86.62 nm crystallite size was used as reinforcement. Cu-MoSi2 composite powder with 2, 3, 5wt% were produced. Cu-MoSi2 with 2wt% reinforcement was milled for 60 hours. Powder composite was compacted by Spark Plasma Sintering . Microstructure of composite was investigated by scanning electron...
Production of Zirconium based Amorphous Alloy by Mechanical Alloying and Sintering Al-based Composite with Amorphous Particles
, M.Sc. Thesis Sharif University of Technology ; Pourazarang, Kazem (Supervisor) ; Abachi, Parvin (Supervisor)
Abstract
Production of copper-zirconium amorphous alloys by mechanical alloying and the process of changing crystal structure to amorphous, was examined. The amount of progress of amorphization has been checked by x-ray analysis after different hours of milling. By increasing the percentage of zirconium in this type of alloy, the process of amorphization has been improved. But There is a limiting factor which is due to the tendency of zirconium to produce oxide and nitride phase. Also, the effect of excessive elements on crystal structure changing has been checked. Hence, adding elements like nickel or aluminum has a different effect on the process of amorphization. adding aluminum to the system...
Synthesis and Characterization of a Composite of ZIF-8 and TiO2 NPs as a Photocatalyst Material for Water Treatment
, M.Sc. Thesis Sharif University of Technology ; Dolati, Abolghasem (Supervisor) ; Abachi, Parvin (Supervisor)
Abstract
During the past few years, hexavalent chromium (Cr(VI)) is of environmental concern due to its high toxicity and mobility. Therefore, removing it from industrial wastewater is of chief significance. In this research, efficient photocatalyst materials (xµLTiO2NPs@ZIF-8) for the reduction of Cr(VI) from water resources were firstly synthesized. This composite was prepared by an in situ method with zeolitic imidazolate framework-8 as the matrix. TiO2 and ZIF-8 were selected for their excellent stability in aqueous media, high photoactivity, non-toxicity, and high surface area. The structure of the as-synthesized materials was characterized by X-ray powder diffraction (XRD), scanning electron...
Fabrication and Characterization of Electrochemical Properties of Porous Ni and Ni/rGO Nanocomposite by Electrochemical Deposition for Pseudocapacitor Application
, M.Sc. Thesis Sharif University of Technology ; Abachi, Parvin (Supervisor) ; Dolati, Abolghasem (Supervisor)
Abstract
Fabrication of porous hybrid coatings, specially in combination with carbon compounds, can improve the electrochemical behavior of the coating. In this study, graphene oxide (GO) was first synthesized by tour method. After examining different methods to create a porous coating, the electrochemical coating method for simultaneous deposition of GO and nickel on the copper substrate was selected. CTAB was used to form nanometer porosity in the coating structure. In order to investigate the effect of GO on the properties of the deposited coating, two porous coatings of nickel (Ni) and nickel reduced-graphene oxide (Ni-rGO) were investigated by different analyzes. These analyzes include FESEM...
Fabrication and Characterization of Polylactic Acid-Mg Composites by 3d Printing Method for Biomedical Applications
, M.Sc. Thesis Sharif University of Technology ; Alizadeh, Reza (Supervisor) ; Abachi, Parvin (Supervisor)
Abstract
Polylactic acid (PLA) is considered as a great option to be employed as 3D porous scaffold in tissue engineering applications owing to its excellent biocompatibility and processability. However, relatively weak mechanical properties, low degradation rate and inappropriate biodegradability limit its extensive usage. In order to overcome the mentioned challenges, micrometric magnesium (Mg) particles were incorporated into the PLA matrix by the fused deposition modeling (FDM) technique. The effects of various Mg contents (i.e., 2, 4, 6, 8 and 10 wt%) on the mechanical, thermal, structural, wettability, rheological, biodegradability characteristics and cellular behavior of the 3D porous PLA-Mg...
The Fabrication of Copper base Chromium Oxide Reinforced Nanocomposite and Investigation of its Mechanical and Physical Properties
, M.Sc. Thesis Sharif University of Technology ; Pourazarang, Kazem (Supervisor) ; Abachi, Parvin (Supervisor)
Abstract
It is well known that Cu/Al2O3 nanocomposites have high potential for use in structural, electrical applications which enhanced mechanical characteristics are required. In the present work, in order to improve the in-situ oxidation kinetic of solute element, chromium was used instead of aluminum. At the initial stage, elemental Cu and Cr powders were mechanically alloyed for 60h under argon atmosphere. It was followed by mechanically milling of Cu-Cr pre-alloyed and Cu2O powders. The nanocomposite specimens, containing different amounts of Cr2O3, depending on the Cr content in the range of 1-3 wt. %, were produced by in-situ oxidation of Cu-Cr pre-alloyed powders. To prevent oxidation of...