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ahmadi-dastjerdi--ali
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A low-power high-speed comparator for analog to digital converters
, Article 2016 IEEE International Symposium on Circuits and Systems, ISCAS 2016, 22 May 2016 through 25 May 2016 ; Volume 2016-July , 2016 , Pages 2010-2013 ; 02714310 (ISSN); 9781479953400 (ISBN) ; Baraani Dastjerdi, M ; Fotowat Ahmadi, A ; Sharif University of Technology
Institute of Electrical and Electronics Engineers Inc
2016
Abstract
A low-power high-speed two-stage dynamic comparator is presented. In this circuit, PMOS transistors are used at the input of the first and second stages of the comparator. At the evaluation phase, the second stage is activated after the first stage with a predetermined delay to achieve a controllable pre-amplifier gain. Also, the first stage is turned off after the delay to reduce overall power consumption. Simulation results in 0.18 μτη CMOS technology, prove that the proposed circuit reduces the power consumption by a factor of two and reduces comparison time as large as 210ps in the same budget of offset voltage compared to the conventional circuit. Moreover, the offset voltage and power...
Optimization of process parameters for reducing warpage in selected laser sintering of polymer parts
, Article Additive Manufacturing ; Volume 18 , 2017 , Pages 285-294 ; 22148604 (ISSN) ; Movahhedy, M. R ; Akbari, J ; Sharif University of Technology
2017
Abstract
Selective Laser Sintering (SLS) is a rapidly growing additive manufacturing process, because it has the capacity to build parts from a variety of materials. However, the dimensional accuracy of the fabricated parts in this process is dependent on the ability to control phenomena such as warpage and shrinkage. This research presents an optimization algorithm to find the best processing parameters for minimizing warpage. The finite element method was used to simulate the sintering of a layer of polymer powder, and the warpage of the layer was calculated. The numerical model was verified through comparison with experimental results. A back-propagation neural network was used to formulate the...
Multisystem Global Navigation Satellite System Receiver
, M.Sc. Thesis Sharif University of Technology ; Fotowat Ahmady, Ali (Supervisor)
Abstract
Nowdays, Navigation sattelite systems are playing critial role in human life. In many equipments such as cell phone, transmitters , transportation systems ,etc. Accurate and reliable navigation is needed.
GPS was the first navigation sattelite system but today rival nations have delevoped or are developing parallel systems. These systems are Glonass operated by Russisa, Galileo by Europe and Beidou By china. GPS can not suffice human needs alone so the proposed solution is to exploit all above mentioned altenative systems. In this case, we can achieve higher accuracy, lower navigation time and more reliable navigation.
In this thesis the receiver is designed to receive all above...
GPS was the first navigation sattelite system but today rival nations have delevoped or are developing parallel systems. These systems are Glonass operated by Russisa, Galileo by Europe and Beidou By china. GPS can not suffice human needs alone so the proposed solution is to exploit all above mentioned altenative systems. In this case, we can achieve higher accuracy, lower navigation time and more reliable navigation.
In this thesis the receiver is designed to receive all above...
Reducing part Warpage by Optimizing Process Parameters in Selective Laser Sintering
, M.Sc. Thesis Sharif University of Technology ; Movahhedy, Mohammad Reza (Supervisor) ; Akbari, Javad (Supervisor)
Abstract
One of the newest methods of rapid prototyping is SLS . In this day, SLS is more common in compare others methods, because it uses little time and man does not nearly interfere in the producing stages of part which is made by SLS method. Also, sophisticated parts, which cannot be built by other methods, can be produced by SLS method. One of the disadvantages of SLS method is low dimensions accuracy of parts produced in this way. This problem has two major reasons: Shrinkage and Warpage. These two phenomena are created because of ununiformed temperature distribution. Others features which have effect on dimensions accuracy are residual stress, porosity and removing space of between powder...
Technological Capabilities and Knowledge Network Evolution in the Path of Innovation: a Case Study of Knowledge-based Firms
, M.Sc. Thesis Sharif University of Technology ; Maleki, Ali (Supervisor) ; Miremadi, Iman (Co-Supervisor)
Abstract
This Thesis aim to study the evolution of knowledge network in the path of innovation capability accumulation in knowledge-based firms, active in Iran's innovation system as a sanctioned economy. The research, by an in-depth case study and at the micro level, examines the accumulation of capabilities and the evolution of the knowledge networks for two knowledge-based firms active in the manufacture of linear accelerators and cargo-scanners as high-tech products. The results show that 1) the accumulation of capabilities from low levels to advance is based on product diversity and the knowledge inputs, which was first through "using, doing and interacting" has changed to "science, technology...
Mobile(SMS) Advertising Value Chain, With a Focus on Factors Affecting Subscribers Acceptance of SMS Advertising in Iran
, M.Sc. Thesis Sharif University of Technology ; Kermanshah, Ali (Supervisor)
Abstract
Mobile technology has become Ubiquitous and common in all over the world from the first years of 21st century. Mobile has been used as a strong media in marketing and specifically in advertising due to it’s unique features and various functions. Currently (2008) mobile media is not used very aggressively in Iran. Considering the quick expansions of mobile networks in Iran and growth of subscribers, it is anticipated that Mobile will affect many businesses and consumer market very soon in Iran. This study is the first academic research in the country on Mobile advertising via SMS. The purpose of this thesis is to provide the better understanding of the Mobile advertising via SMS in high...
Analysis of Effect of Parametric Oscillation in Phase Noise Degradation in Frequency Multipliers
, Ph.D. Dissertation Sharif University of Technology ; Banai, Ali (Supervisor)
Abstract
Variation of the input driving power can cause in some varactor and BJT frequency multipliers parametric instability. If parametric oscillations are present in the circuit, output phase noise of the multiplier degrades remarkably in some specific driving levels. Phase noise of the varactor and BJT multiplier is calculated by the conversion matrix method using generalized nodal analysis. By the conversion method the phase noise degradation can be predicted precisely. In the calculation of phase noise the effect of the noise sources that are modulated by the large signal drive and the conversion of components of the internal noise sources of the device to the output spectrum due to circuit...
Design and Implementation of Novel Devices in Ka Band Using Ridge Gap Waveguide Technology
, Ph.D. Dissertation Sharif University of Technology ; Banai, Ali (Supervisor)
Abstract
Ridge gap waveguide is a new technology with low loss and high power handling capability in millimeter wave(mm-wave) frequencies. In this technology there is no need for electrical connection between the constitutive parts and using dielectric material as a substrate. This thesis focuses on the capabilities of this technology in realization of devices used in communication systems at the mm-wave frequency. Novel devices based on this technology have been designed, fabricated and tested. The main goal of the thesis is realization of the whole RF front end of a communication system in Ka band based on this technology. So at first step, a ridge gap waveguide transmission line is evaluated and a...
Performance Enhancement in Cache Networks
, Ph.D. Dissertation Sharif University of Technology ; Movaghar, Ali (Supervisor)
Abstract
Cache networks play a key role in today’s Internet. Inspired by the successful deployment of caching in content delivery networks (CDNs), pervasive caching now is a fundamental concept in storage-assisted future Internet architectures, e.g., information-centric networks (ICN), and 5G. However, despite the clear and increasing economic advantages of caching for the network operators, it does not take place efficiently due to various problems. The emergence of in-network caching has created new challenges for modeling and performance evaluation of networks. In addition, content providers (CPs), who alone have the detailed demand data required for optimal content placement, have no natural...
Design and Implementation of Tunable Microwave Gain Equalizer
,
M.Sc. Thesis
Sharif University of Technology
;
Banai, Ali
(Supervisor)
Abstract
Modern broadband microwave and millimeter-wave systems often struggle with excessive pass band ripple and negative gain slopes due to the loss of transmission lines such as coaxial cables, or ripples in the gain characteristic of broadband amplifiers. The common solution for this problem is using a gain equalizer to compensate for the intrinsic pass band variation with some extra loss in the band of interest in return.Designed equalizers often have a constant slope in their bandwidth. However, having ripples in pass band or in other words slope changing in some parts of the band is one of the issues that designers should deal with. In this thesis, after reviewing the previous works on the...
Design and Simulation of ELoran Receiver
, M.Sc. Thesis Sharif University of Technology ; Fotowat Ahmadi, Ali (Supervisor)
Abstract
In recent years, eLoran system has been introduced as backup to global navigation systems like GPS, because of their vulnerability. eLoran is a low frequency (100 kHz) system. Its long wavelength allows indoor positioning.
Main eLoran advantages rather than Loran-C are: better accuracy (near 10m), using 9th pulse positioning modulation (PPM) as loran data channel (LDC) and all-in-view receivers
In this thesis, eLoran pulses are simulated in GRI. Also, a new analoge-digital circuit for faster pulse detection is developed.
Also, it is proved that an oscillator with same frequency and phase as enterance signal, responses faster than a band pass filter and envelope detector. So, a...
Main eLoran advantages rather than Loran-C are: better accuracy (near 10m), using 9th pulse positioning modulation (PPM) as loran data channel (LDC) and all-in-view receivers
In this thesis, eLoran pulses are simulated in GRI. Also, a new analoge-digital circuit for faster pulse detection is developed.
Also, it is proved that an oscillator with same frequency and phase as enterance signal, responses faster than a band pass filter and envelope detector. So, a...
TDC & MMD Design for Bluetooth Low Energy Standard Transmitter
, M.Sc. Thesis Sharif University of Technology ; Fotowwat Ahmadi, Ali (Supervisor)
Abstract
IoE devices are going to integrate with our environment. It has been predicted that there would be more than 6 connected devices per each person by 2020. Currently what obstruct this technology from continuing its evolusion path, is its dependence on Ultra Low-Power devices, and for this reason there is a huge concenteration on Radio-Frequency standards which can make devices more power efficient. Within these standards, Bluetooth Low Energy (BLE) attracted designers consentration for its similarities with conventional Bluetooth and its dominance in cellphones and other portable devices.In this project, we have attempted to design a trasmitter for BLE standard based on an All Digital Phase...
Development of Fragility Curves of Confined Masonry Buildings
, M.Sc. Thesis Sharif University of Technology ; Bakhshi, Ali (Supervisor)
Abstract
Masonry buildings are one of the most vulnerable structures against earthquakes, and therefore their seismic response should be evaluated in order to mitigate casualties in the future. Although there are numerous experimental and analytical studies on these buildings, few have aimed on Confined Masonry (CM) buildings to simulate and predict their seismic performance. To estimate damage, assess vulnerability and choose the best retrofitting method, fragility curves can be utilized as a powerful tool. In this paper, the hysteretic behavior of two typical CM walls with and without opening is calibrated in both In-plane (IP) and Out-of-Plane (OOP) loading directions making use of OPENSEES...
High Efficiency, Low Distortion Boundary Conduction Mode Boost PFCs for Different Power Ranges
, Ph.D. Dissertation Sharif University of Technology ; Fotowat-Ahmadi, Ali (Supervisor)
Abstract
In this thesis, new boundary conduction mode boost PFCs are proposed and implemented for different power levels according to the characteristics and requirements of each power level. For medium power applications, we have proposed a new zero voltage switching PFC based on a synchronous boost converter which is controllable with conventional boundary conduction mode PFC control ICs without requiring any additional timing adjustment control circuits other than a special high side driver that consists of only low voltage components. Based on mathematical calculations, we have proposed two sipmle circuit solutions to reduce the high level of line current zero crossing distortion in the proposed...
Numerical Modeling of Deep Geothermal Energy Reservoirs
, M.Sc. Thesis Sharif University of Technology ; Pak, Ali (Supervisor)
Abstract
Geothermal energy is one of the most important sources of energy that is increasingly becoming more popular all over the world. In this study, the performance of deep geothermal energy as a form of geothermal energy was evaluated using a numerical modeling approach. To do so, first, the thermo-hydraulic behavior of geothermal reservoirs was studied to help achieve the most efficient arrangement for production and injection wells. The results show that to optimize production and injection wells, there are two factors to consider. Firstly, the distance between production and injection wells must be high. Secondly, the production wells must be uniformly distributed throughout the reservoir so...
A Low-power Low-noise Multi-Channel Biopotential Measurement IC with Motion Artifact Suppression Capability
, M.Sc. Thesis Sharif University of Technology ; Fotowat-Ahmadi, Ali (Supervisor)
Abstract
Long-term Multi-Channel Bio-Signal monitoring in a comfort way is demanding for emerging applications in everyday life. Typically, in multi-channel amplification, one amplifier per channel is employed. However, the bio-signal amplification requires lower bandwidth in comparison with the available speed of CMOS amplifiers. Therefore, it is sensible to develop a practical circuit trading the excess CMOS bandwidth with power consumption. The proposed circuit, which has three inputs, performs amplification through three stages; First, the inputs are applied to a 3 to 1 time-domain multiplexer. Second, a Current Feedback Instrumentation Amplifier (CFIA) is utilized. Finally, the amplified signal...
Finite Element Model Updating Using API User Interface
, M.Sc. Thesis Sharif University of Technology ; Bakhshi, Ali (Supervisor)
Abstract
Damage in civil infrastructure is an unavoidable phenomenon. Therefore, using structural health monitoring methods is of great importance. In this thesis, the location and severity of damage in a structure are simultaneously determined using the solution of sensitivity equations of the frequency response function and its principal components. The derived sensitivity equations are quasi-linear and do not require higher-order derivatives of the principal components of the frequency response function in their formulation. Using these sensitivity equations, error minimization through the least squares method, and the finite element model updating method along with the API user interface, the...
Reuse of Abandoned Oil Wells Using a Geothermal-Based Hybrid ORC Unit/Thermoelectric Generator: Energy,Exergy, Thermo-economic Analyses and Multi-criteria Optimisation
, M.Sc. Thesis Sharif University of Technology ; Moosavi, Ali (Supervisor) ; Sadr Hosseini, Hani (Co-Supervisor)
Abstract
In this thesis, three novel geothermal-based ORC systems are proposed to enhance efficiency and to recover the waste heat recovery. The proposed systems are modeled based on basic ORC system (concept 1), ORC system with internal heat exchanger (concept 2), and regenerative ORC system (concept 3). Accordingly, two thermoelectric generators are introduced into the systems to exploit the waste heat of the system. For this purpose, the condenser is replaced by a TEG unit, while the other TEG unit is employed to recover the waste heat of the reinjected geothermal fluid. A comprehensive numerical investigation is conducted to compare the proposed systems from thermodynamic and thermo-economic...
Trade in Intermediate Goods and The Welfare Gain from International Trade
, M.Sc. Thesis Sharif University of Technology ; Madanizadeh, Ali (Supervisor)
Abstract
In this thesis, I introduce a general equilibrium model of international trade that takes into account the industry linkages between intermediate goods and consumption goods producers to quantitatively measure the countries’ welfare gains and losses from different trade policies on intermediate and consumption goods. My model extends the inter-industry trade model of Ricardo (1817), intra-industry model of Krugman (1980), and firm heterogeneous model of Melitz (2003). Reduction of tariffs affect welfare of countries through direct effects on income, cost of export, and cost of input bundles of production (labor and intermediate goods), and indirectly through changes in term of trades, and...
Trust-based Probabilistic Key Management in MANETs
, M.Sc. Thesis Sharif University of Technology ; Movaghar Rahimabadi, Ali (Supervisor)
Abstract
Self-organized public key management scheme in mobile ad hoc networks (MANETs) is an inevitable solution to achieve different security services. The aim of such schemes is to find an efficient protocol which makes the node able to obtain the authenticated public key of another node. Public key transmission and verification is achieved using certificate chain or message authentication code, thus it needs other nodes cooperation. It is also notable that in heterogeneous MANETs which include malicious nodes, this method suffers from low throughput and spoofing attack. In this thesis, a novel certificateless, on-demand self-organized public key management scheme is proposed which is based on the...