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A novel 3-dimentional ultra high precision positioning platform for micro machining cutting tools
, Article 3rd International Conference on Control, Automation and Robotics, ICCAR 2017, 22 April 2017 through 24 April 2017 ; 2017 , Pages 284-288 ; 9781509060870 (ISBN) ; Yadegari, A ; Rashidi, D ; Sharif University of Technology
Institute of Electrical and Electronics Engineers Inc
2017
Abstract
Ultra-high precision machining is proposed by externally actuating the work piece in linear motions in the X-Y plane and linear motion in the Z-axis. To solve the problems in the machining process such as nonlinearity and low repeatability positioning accuracy of machining tools in a larger scale, a novel platform for cutting tools in micro machining based on electrostatic linear micromotors and piezoelectric stack actuator system is presented. © 2017 IEEE
Shear behavior of ultra-high performance concrete
, Article Construction and Building Materials ; Volume 183 , 2018 , Pages 554-564 ; 09500618 (ISSN) ; Joghataie, A ; Mirmiran, A ; Sharif University of Technology
Elsevier Ltd
2018
Abstract
The application of ultra-high performance concrete (UHPC) as an alternative to conventional/normal concrete (NC) has grown rapidly in recent years. However, there is limited knowledge on its shear behavior, which is essential for developing design guidelines for structural applications. A detailed parametric study was conducted on 38 beam specimens, half of which were made of UHPC and the other half made of NC. To ensure applicability of findings, two types of UHPC mixes were used, a proprietary and a generic mix. Eighteen of the beams were prepared and tested in Tabriz, Iran, while the other 20 were made and tested in Miami, FL. Test parameters included type of concrete (UHPC and NC), shear...
Ultra-high voltage SnO2 based varistors prepared at low temperature by two-step sintering
, Article Journal of Alloys and Compounds ; Volume 805 , 2019 , Pages 794-801 ; 09258388 (ISSN) ; Delshad Chermahini, M ; Alipour, S ; Mahmoudi, P ; Safaee, I ; Abdollahi, M ; Sharif University of Technology
Elsevier Ltd
2019
Abstract
In this research, full density, single phase microstructure (in the XRD and SEM detection limits), and fine-grained SnO2 varistors with an average grain size of 0.65 μm was acquired at low temperature by the two-step sintering technique. The sintering temperature was successfully decreased from 1300 °C in the normal sintering to 1150 °C and 1100 °C of respectively the first and the second stage in the two-step sintering. The mechanism of grain growth suppression of the two-step sintered samples was discussed and it was suggested that in addition to triple point junction, solute drag and/or nano-secondary phases contribute to cease the grain growth. These SnO2 varistors exhibited ultra-high...
Determining shear capacity of ultra-high performance concrete beams by experiments and comparison with codes
, Article Scientia Iranica ; Volume 26, Issue 1A , 2019 , Pages 273-282 ; 10263098 (ISSN) ; Joghataie, A ; Sharif University of Technology
Sharif University of Technology
2019
Abstract
In this research, 19 specimens of ultra-high performance fiber-reinforced concrete rectangular beams were made and their shear resistance was determined experimentally. The results were compared with estimations by ACI 318, RILEM TC 162-TDF, Australian guideline, and Iranian national building regulations. To compare the code estimations, the ratio of experimental shear strength to predicted shear strength was calculated for each code. This ratio is in fact a measure of safety factor on the one hand and a measure of precision of the estimation on the other hand. Based on the results of both studies, the authors concluded that the Australian guideline, with the amount of 2.5, provided the...
Determining shear capacity of ultra-high performance concrete beams by experiments and comparison with codes
, Article Scientia Iranica ; Volume 26, Issue 1A , 2019 , Pages 273-282 ; 10263098 (ISSN) ; Joghataie, A ; Sharif University of Technology
Sharif University of Technology
2019
Abstract
In this research, 19 specimens of ultra-high performance fiber-reinforced concrete rectangular beams were made and their shear resistance was determined experimentally. The results were compared with estimations by ACI 318, RILEM TC 162-TDF, Australian guideline, and Iranian national building regulations. To compare the code estimations, the ratio of experimental shear strength to predicted shear strength was calculated for each code. This ratio is in fact a measure of safety factor on the one hand and a measure of precision of the estimation on the other hand. Based on the results of both studies, the authors concluded that the Australian guideline, with the amount of 2.5, provided the...
Preparation and Investigation the Properties of UHMWPE/Graphene Nanocomposites Via in Situ Polymerization Using Ziegler Natta Catalyst
, Ph.D. Dissertation Sharif University of Technology ; Ramezani Saadat Abadi, Ahmad (Supervisor)
Abstract
The main object of the presented thesis is manufacturing ultra high molecular weight polyethylene(UHMWPE)/Graphene nanocomposites by insitu polymerization using Ziegler Natta catalysts. In this study, three types of Ziegler Natta Catalysts such as Magnesium ethoxide supported, single-supported and bi-supported have been studied. Experimental conditions are optimized (from point of productivity and molecular weight) by Design expert software with response surface methodology (Box-Behnken design). Effect of process parameters like temperature, pressure and [Al]/[Ti] molar ratio on productivity and Molecular weight are investigated. Also, the effect of hydrogen presence and type of cocatalyst...
Preparation and Investigation of Ziegler-natta Catalyst with Nano MoS2 Support in UHMWPE Synthesis
, M.Sc. Thesis Sharif University of Technology ; Ramazani Saadat Abad, Ahmad (Supervisor)
Abstract
Ultra high molecular weight polyethylene has attracted the attention of numerous researchers and industries. This polymer due to its strong properties can be used in advanced military industries, medical engineering and cases in which high strength and high abrasion resistance is required. Present study aims to fabricate UHMWPE/Molybdenum disulfide composites, using in-situ polymerization. Before carrying out the polymerization process, nanoparticles of molybdenum disulfide underwent various processes such as oxidation, pickling, ultrasonic and thermal shock, in order to increase the interlayer distance and creating functional groups on the surface, then various analyzes, such as XRD, FESEM,...
Investigation of Sintering Mechanism and Phase Evolution in Ternary System of TaC-HfC-ZrC
, Ph.D. Dissertation Sharif University of Technology ; Faghihi Sani, Mohammad Ali (Supervisor) ; Golestani-fard, Farhad (Supervisor)
Abstract
Ultra-high temperature ceramics (UHTCs) are a class of materials that have melting points above 3000°C and include borides, carbides and nitrides of some transition metals such as ZrB2, ZrC, HfB2, HfC, HfN, TaC. These compounds are of particular interest because of the unique property combination such as high electrical and thermal conductivity, chemical inertness against molten metals or non basic slags, and good thermal shock resistance. Sintering of these compounds is very difficult due to their high melting point and utilization of sintering aids or new consolidation routes is necessary to achieve high density sintered bodies. In this research, phase evolution and kinetics of diffusion...
Experimental Investigation of Biodiesel Production from Oils by Transesterification Method Catalyzed by Nano-heterogeneous Catalysts
, M.Sc. Thesis Sharif University of Technology ;
Abstract
Today polyolefin definitely is one of the most applicable polymers in the world. One of these polymers is ultra-high molecular weight polyethylene. Being applicable in a number of high-tech industries such as military service, battery separators, and other areas, expands the usage of these polymers. Electrospinning is one of the molding methods in order to synthesize fiber polymers. Using this method, a great deal of polymer fibers have been prepared. It is worth noting that the device used for olefins should have temperature control and temperature increase ability. The electrospinning device with the temperature control has not been built in the country; therefore, this device has been...
Spark plasma sintering of TaC-HfC UHTC via disilicides sintering aids
, Article Journal of the European Ceramic Society ; Volume 33, Issue 8 , 2013 , Pages 1479-1484 ; 09552219 (ISSN) ; Faghihi-Sani, M. A ; Golestani Fard, F ; Mandal, H ; Sharif University of Technology
2013
Abstract
Ta0.8Hf0.2C ceramic has the highest melting point among the known materials (4000°C). Spark plasma sintering is a new route for consolidation of materials, specially ultra high temperature ceramics (UHTCs), which are difficult to be sintered at temperatures lower than 2000°C.The purpose of this study is to consolidate Ta0.8Hf0.2C by spark plasma sintering at low temperature using MoSi2 and TaSi2 as sintering aid. In this regard, effect of different amounts of sintering aids and carbides ratio on densification behavior and mechanical properties of Ta1-xHfxC were investigated.Fully consolidation of Ta0.8Hf0.2C was achieved in presence of 12vol.% sintering aid after sintering at 1650°C for 5min...
Design and Implementation of a Fault Detecting Algorithm for a High Voltage Underground Cable Using UHF Wireless Measuring Method
, M.Sc. Thesis Sharif University of Technology ; Vakilian, Mehdi (Supervisor)
Abstract
One of the common problems in using high voltage network is the occurrence of partial electrical discharge in high voltage equipment such as cables. This problem may not be serious at first, but over time it can cause wear, corrosion, or reduction of equipment life, and eventually, if not prevented in a timely manner, can cause electrical sparks, larger problems, and possibly equipment and network become irreparable. On the one hand, due to very clear reasons, we need the voltage level to be high, and on the other hand, due to the application of high voltage level and the need to optimally design the insulation system to reduce their dimensions and construction costs, there will be the...
High performance Dyneema® fiber laminate for impact resistance/macro structural composites
, Article Journal of Thermoplastic Composite Materials ; Volume 25, Issue 4 , 2012 , Pages 403-414 ; 08927057 (ISSN) ; Yazdanirad, M ; Mirhabibi, A ; Sharif University of Technology
2012
Abstract
UHMWPE composite materials are increasingly used in armors design due to their high strength-to-weight ratios and energy absorption capacities. In this study the effect of production parameters upon the terminal ballistic properties of UHMWPE composite were examined under different conditionings. The composite armor plate laminates were produced by hot pressing with three different pressing times from 10-30 minutes and the laminates conditioned at +115, +125, and +135°C. The molding temperature of SK66 fiber composite has the main direct effect on the ballistic absorption energy, so the relation of molding temperature with the adhesive bonding force between layers, the thickness of the...
Design of Digital Backend of the RFID Reader and Design of Baseband Signal Conditioning Circuits and Simulating RFID System
, M.Sc. Thesis Sharif University of Technology ; Sharif Bakhtiar, Mehrdad (Supervisor)
Abstract
In this Thesis, first, UHF RFID Class1 Generation 2 was studied accurately and Required Signaling, Timing and Circuit Parameters for Design Readers in this Band, was Extracted from Standard. an important algorithm for Tags inventory, that Protocol leaves the way of implementation to designer, was introduced and simulated. Also a effective method was presented that detect bit streams received by readers in low SNR. Some parts of Baseband Signal conditioning circuits, including filter and variable gain amplifier, wad designed in 0.18 um CMOS Technology. In Second part, communication protocol between server and readers was introduced with some Scenarios that make communication easier and make...
Studying the Effect of Zirconia & GNP on Mechanical, Tribological & Biological Properties of UHMWPE-HAp Nanocomposites used in Total Hip Joint Replacement
, M.Sc. Thesis Sharif University of Technology ; Bagheri, Reza (Supervisor) ; Faghihi Sani, Mohammad Ali (Supervisor)
Abstract
Medical engineering advances in total joint replacements and society’s rising demand for long lasting materials, have proven it essential to manufacture materials that are more similar to the original tissue in the fields of mechanical, tribological and biological properties. Ultra High Molecular Weight Polyethylene(UHMWPE), is a polymer widely used in arthroplasty applications due to its biocompatibility, chemical stability and proper mechanical properties. In this study, UHMWPE-HAp nanocomposites reinforced with Zirconia and Graphene were manufactured aiming to reach a structure that is more compatible with bone tissue and also to improve overall properties. First, using ultrasonication...
Detection, Characterization and Analysis of Partial Discharge Signals Frequency Spectrum Related to Different Oil Transformer Faults using UHF Antenna
, M.Sc. Thesis Sharif University of Technology ; Vakilian, Mehdi (Supervisor)
Abstract
One of the electromagnetic methods for partial discharge detection is known as UHF detection. In this method the electromagnetic radiations from PD sources over a wide frequency band of UHF are detected and the related spectrums over the UHF frequency band are captured for diagnostic. The absence of noise in UHF band (300 MHz- 3GHz) is the most important advantage of this method if compared with other electrical PD detection methods. To capture electromagnetic signals and radiations generated by PD sources, application of an electromagnetic sensor, named antenna, is necessary. Therefore one of the goals in this thesis is to select, design, and build a suitable antenna for PD detection....
Radio Receiver Design for Cognitive Radio in The UHF Band
, M.Sc. Thesis Sharif University of Technology ; Fotowat Ahmady, Ali (Supervisor)
Abstract
With the ever-increasing communication need for propagating signals in authorized empty bands, the goal of this thesis is based on finding these unused bands and using them,which called Cognitive Radio. In this project, design and implementation of radio frequency building blocks of a receiver in the UHF band (400 to 800 MHz) is performed. In this project, however, the radio frequency building blocks include low noise amplifier, high-frequency quadrature mixers, high-frequency oscillators, tunable low-pass filter,band select filter,phase-locked loop and synthesizer, all of which are introduced, examined and implemented. Moreover, a new method which mitigates the speed limitation is verified....
Topology and vulnerability of the Iranian power grid
, Article Physica A: Statistical Mechanics and its Applications ; Vol. 406, issue , July , 2014 , p. 24-33 ; ISSN: 03784371 ; Jalili, M ; Alipour, Z ; Sharif University of Technology
Abstract
In this paper we investigated the structural properties of the ultra high voltage power transmission network of Iran. We modeled the power grid as a network with 105 nodes and 142 connection links. We found that the Iranian power grid displays a relatively moderate clustering coefficient-much larger than that of corresponding random networks-and small characteristics path length comparable to that of corresponding random networks; i.e. the power grid is a small-world network with exponential degree distribution. Global efficiency was considered as an indicator of grid's performance and the influence of random and intentional nodal failures on the efficiency was investigated. We also studied...
Fine-grained SnO2 varistors prepared by microwave sintering for ultra-high voltage applications
, Article Materials Letters ; Volume 230 , 2018 , Pages 9-11 ; 0167577X (ISSN) ; Mahmoudi, P ; Abdollahi, M ; Ebadzadeh, T ; Sharif University of Technology
Elsevier B.V
2018
Abstract
In this research, fine-grained SnO2-based varistors with a simple microstructure and the mean grain size of 0.8 µm were obtained by the microwave sintering method. The breakdown electric field measured for these varistors was 12 kV/cm that is 3 times higher than the conventional-sintered varistors. The high nonlinear coefficient (60) and low leakage current density (9 µA/cm2) were achieved in fine-grained SnO2 varistors. The fine-grained SnO2 varistors appropriately clamped pulse current surges and the calculated value of the clamping voltage ratio of these varistors was 2. The excellent electrical properties and protective effect of fine-grained SnO2 varistors showed that these varistors...
Effects of HfB2 addition on pressureless sintering behavior and microstructure of ZrB2-SiC composites
, Article International Journal of Refractory Metals and Hard Materials ; Volume 94 , 2021 ; 02634368 (ISSN) ; Bavand Vandchali, M ; Mashhadi, M ; Nemati, A ; Sharif University of Technology
Elsevier Ltd
2021
Abstract
In this study the effects of HfB2 addition were investigated on the sintering behavior, densification and microstructure of ZrB2-SiC in the presence of B4C and MoSi2 as a sintering catalyst. 5, 10, 15 and 20 wt% of HfB2 was substituted with ZrB2 in ultra-high temperature ceramic composites of ZrB2-SiC. Additionally, the effect of using nano-scale against common micron size SiC was compared. All compositions were sintered for 1 h in 2100 °C and 2150 °C. Relative and bulk density and open porosity percentage of samples were calculated by Archimedes method. Dimensional changes of pellets and their weight reduction after pyrolysis and sintering proved that increasing of HfB2 leads to increasing...
Investigation of EGRET gamma-ray sources by an extensive air shower experiment
, Article 29th International Cosmic Ray Conference, ICRC 2005, Pune, 3 August 2005 through 10 August 2005 ; Volume 6 , 2005 , Pages 29-32 ; Samimi, J ; Bahmanabadi, M ; Sharif University of Technology
Tata Institute of Fundamental Research
2005
Abstract
Ultra-high-energy ( E ≥ TeV) Extensive Air Showers (EASs) have been monitored for a period of five years (1997-2003 ), using a small array of scintillator detectors in Tehran, Iran. The data have been analyzed to take in to account of the dependence of source counts on zenith angle. During a calendar year different sources come in the field of view of the detector at varying zenith angles. Because of varying thickness of the overlaying atmosphere, the shower count rate is extremely dependent on zenith angle which have been carefully analyzed over time. High energy gamma-ray sources from the EGRET third catalogue where observed and the data were analyzed using an excess method. Upper limits...