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    A 5.3ps 8b Time to digital converter using a new gain-reconfigurable time amplifier

    , Article IEEE Transactions on Circuits and Systems II: Express Briefs ; 2018 ; 15497747 (ISSN) Molaei, H ; Hajsadeghi, K. H ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2018
    Abstract
    Time amplifiers (TA) are the key building blocks of the two-step time-to-digital converters. High resolution TAs suffer from inaccuracy the gain due to employing meta-stability behavior of the SR latches. In the proposed method, two offset NAND gates are placed in parallel with the NAND gates of the conventional SR latch to get a linear re-configurable gain. Gain of the TA is controlled only by the driving strength of the NAND gates. To confirm the effectiveness of the proposed method, an 8-bit two step time to digital converter (TDC) was designed and laid-out in 0.18 μ m CMOS technology. Using a supply voltage of 1.2V, the proposed TDC consumes 1.1mW at 30MS/s throughput. IEEE  

    Transient and steady-state analysis of heat, mass, and momentum transfer in developing and fully-developed regions of homogeneous tubular reactors with non-Newtonian fluid flow

    , Article Energy Conversion and Management ; Volume 65 , 2013 , Pages 308-321 ; 01968904 (ISSN) Abbaszadeh Molaei, E ; Hashemi Amrei, S. M. H ; Molaei Dehkordi, A ; Haghi, M ; Sharif University of Technology
    2013
    Abstract
    In this article, the problem of simultaneous heat, mass, and momentum transfer in the developing region of tubular reactors with homogeneous chemical reaction and laminar power-law fluid flow under unsteady-state conditions has been solved. In this regard, the general governing equations were solved using finite-difference method and analyzed carefully. Moreover, the influences of various parameters and dimensionless numbers such as power-law index, heat of reaction, reaction order, and Damköhler number value on the numerical results were investigated. In addition, the numerical results obtained for the fully-developed velocity distribution of Newtonian fluid flow and Sherwood number value... 

    Numerical investigation of gas bubble behavior in tapered fluidized beds

    , Article Particuology ; Volume 38 , June , 2018 , Pages 152-164 ; 16742001 (ISSN) Khodabandehlou, R ; Askaripour, H ; Molaei Dehkordi, A ; Sharif University of Technology
    Elsevier B.V  2018
    Abstract
    In this article, the behavior of gas bubbles in tapered fluidized beds is investigated with the use of a two-fluid model incorporating kinetic theory of granular flow. The effects of various parameters such as apex angle, particle size, and particle density on the size distribution and the rise velocity of gas bubbles were examined. In addition, the simulation results for the bubble fraction and axial velocity of gas bubbles were compared with experimental data reported in the literature and good agreement was observed. As the apex angle was increased, the fraction of gas bubbles with large sizes increased and the fraction of bubbles with small sizes decreased. As the particle size... 

    Numerical investigation of gas bubble behavior in tapered fluidized beds

    , Article Particuology ; 2017 ; 16742001 (ISSN) Khodabandehlou, R ; Askaripour, H ; Molaei Dehkordi, A ; Sharif University of Technology
    2017
    Abstract
    In this article, the behavior of gas bubbles in tapered fluidized beds is investigated with the use of a two-fluid model incorporating kinetic theory of granular flow. The effects of various parameters such as apex angle, particle size, and particle density on the size distribution and the rise velocity of gas bubbles were examined. In addition, the simulation results for the bubble fraction and axial velocity of gas bubbles were compared with experimental data reported in the literature and good agreement was observed. As the apex angle was increased, the fraction of gas bubbles with large sizes increased and the fraction of bubbles with small sizes decreased. As the particle size... 

    Markov model of drive-motor systems for reliability calculation

    , Article International Symposium on Industrial Electronics 2006, ISIE 2006, Montreal, QC, 9 July 2006 through 13 July 2006 ; Volume 3 , 2006 , Pages 2286-2291 ; 1424404975 (ISBN); 9781424404971 (ISBN) Molaei, M ; Oraee, H ; Fotuhi Firuzabad, M ; Sharif University of Technology
    2006
    Abstract
    Due to considerable use of electric drives in industrial applications, reliability assessment of drive-motor systems both in design and operating phases is of considerable importance. Reliability assessment of drive-motor systems is presented in this paper. Using the basic component of a drivemotor system, a suitable reliability block diagram is first developed. The system availability and reliability is then determined using developed block diagram. The impacts on system reliability of various parameters such as failure rate and repair rate of system components are investigated. The proposed technique is then applied to a practical drive-motor system and the results are presented. © 2006... 

    Tuning the wetting properties of SiO2-based nanofluids to create durable surfaces with special wettability for self-cleaning, anti-fouling, and oil-water separation

    , Article Industrial and Engineering Chemistry Research ; Volume 61, Issue 23 , 2022 , Pages 8005-8019 ; 08885885 (ISSN) Esmaeilzadeh, P ; Ghazanfari, M. H ; Molaei Dehkordi, A ; Sharif University of Technology
    American Chemical Society  2022
    Abstract
    Surfaces with special wettability have aroused lots of attention due to their broad applications in many fields. In this work, we systematically report selective and various fabrications of nanofluids based on readily available materials such as SiO2 nanoparticles and polydimethylsiloxane to create superhydrophobic, superoleophobic, superhydrophilic/superoleophobic, and underwater superoleophobic coatings. The efficiency of prepared coatings is investigated on mineral rock plates as porous substrates via the straightforward and cost-effective solution-immersion technique. The static water contact angle of 170°, effortless bouncing of water droplets, and self-cleaning property with a near... 

    Numerical Study of Bubble Behavior in Two-and Three-Dimensional Gas-Solid Fluidized Beds

    , M.Sc. Thesis Sharif University of Technology Abbaszadeh Molaei, Esmaeil (Author) ; Molaei Dehkordi, Asghar (Supervisor)
    Abstract
    Because of the importance of gas-solid fluidized beds in chemical industrial plants, many experimental and modeling efforts have been conducted the prediction of their behaviors up to now. Gas bubbles have a pivotal role in the hydrodynamics of bubbling gas-solid fluidized beds; so, fundamental understanding of the bubbling behavior of fluidized beds is required to describe bubble-related phenomena such as solids mixing and segregation, reaction conversion, heat and mass transfer, erosion of heat-transfer tubes and particle entrainment. In this work, the effects of different parameters such as bed aspect ratio, bed width, superficial gas velocity, and particle size distribution on the... 

    Particle swarm optimization with an enhanced learning strategy and crossover operator

    , Article Knowledge-Based Systems ; Volume 215 , 2021 ; 09507051 (ISSN) Molaei, S ; Moazen, H ; Najjar Ghabel, S ; Farzinvash, L ; Sharif University of Technology
    Elsevier B.V  2021
    Abstract
    Particle Swarm Optimization (PSO) is a well-known swarm intelligence (SI) algorithm employed for solving various optimization problems. This algorithm suffers from premature convergence to local optima. Accordingly, a number of PSO variants have been proposed in the literature. These algorithms exploited different schemes to improve performance. In this paper, we propose a new variant of PSO with an enhanced Learning strategy and Crossover operator (PSOLC). This algorithm applies three strategies, comprising altering the exemplar particles, updating the PSO parameters, and integrating PSO with Genetic Algorithm (GA). In the proposed learning strategy, each particle is guided by the best... 

    Novel type of two-impinging-jets reactor for solid-liquid enzyme reactions

    , Article AIChE Journal ; Volume 52, Issue 2 , 2006 , Pages 692-704 ; 00011541 (ISSN) Molaei Dehkordi, A ; Sharif University of Technology
    2006
    Abstract
    The isomerization of D-glucose to D-fructose using the immobilized glucose isomerase, as a typical model system of solid-liquid enzyme reactions has been carried out in a novel type of two-impinging-jets reactor (TIJR), which is characterized by a rotating inner cylinder in a stationary one. Because of the impinging process, turbulence, and complex trajectory of the solid particles within the reactor, the fractional conversion of glucose obtained in the TIJR increased dramatically compared to that obtained by conventional reaction systems. A compartment model was considered to describe the pattern of flow [residence time distribution (RTD) of solid particles] within the TIJR. Considering... 

    Biorecovery of heavy metals from oil waste water by adapted Thiobacillus Ferrooxidans

    , M.Sc. Thesis Sharif University of Technology Molaei, Sima (Author) ; Yaghmaei, Soheila (Supervisor)
    Abstract
    Acidophilic microorganisms such as Thiobacillus ferrooxidans have the capability to carry out process of biorecovery of heavy metals. Its principle is the microbial production of the sulphuric acid and simultaneous recovery of metals. Acidithiobacillus ferrooxidans derives the energy for their metabolism from ferrous iron oxidation process which can be affected by the presence of heavy metals in the medium. In this study the ability of Acidithiobacillus ferrooxidans, on the biorecovery of heavy metals in shake flask has been investigated The adaptation of the Acidithiobacillus ferrooxidans to a kind of heavy metal such as Nickel, Cobalt, Vanadium, Molybdenum, Tungsten and the mixture of the... 

    A low power high resolution time to digital converter for ADPLL application

    , Article 59th IEEE International Midwest Symposium on Circuits and Systems, MWSCAS 2016, 16 October 2016 through 19 October 2016 ; 2017 ; 15483746 (ISSN); 9781509009169 (ISBN) Molaei, H ; Hajsadeghi, K ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2017
    Abstract
    A new nonlinear Time to Digital Converter (TDC) based on time difference amplification is the proposed. A new gain compensation method is presented to expand the DR of conventional × 2 Time Amplifiers (TAs). Instead of conventional gain compensation approach based on changing strength of current sources, the proposed technique uses current difference which results more stable gain over wider DR. In order to avoid two different paths of the stages, a sign bit detection part is the proposed at the front of the TDC to allow using one path of stages for both positive and negative input time differences. As a result, the most advantages of the proposed TDC are its high resolution, wide DR, and... 

    A low-power comparator-reduced flash ADC using dynamic comparators

    , Article 24th IEEE International Conference on Electronics, Circuits and Systems, ICECS 2017, 5 December 2017 through 8 December 2017 ; Volume 2018-January , 2018 , Pages 5-8 ; 9781538619117 (ISBN) Molaei, H ; Hajsadeghi, K ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2018
    Abstract
    This paper presents a new low-power reduced comparator flash ADC. The proposed ADC uses dynamic comparators to perform a high-speed low-power conversion. In order to reduce offset and kick-back noise effect of conventional dynamic comparators, a new comparator with a higher pre-amplifier gain along with the mathematical analysis is presented. The proposed 4bit ADC is simulated in 0.18um with 1.8-υ supply voltage. SNDR and SFDR of the ADC are 23dB and 26.5dB, respectively. The ADC consumes only 0.95mw at the sampling rate of 400MS/s. © 2017 IEEE  

    A 5.3-ps, 8-b time to digital converter using a new gain-reconfigurable time amplifier

    , Article IEEE Transactions on Circuits and Systems II: Express Briefs ; Volume 66, Issue 3 , 2019 , Pages 352-356 ; 15497747 (ISSN) Molaei, H ; Hajsadeghi, K ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2019
    Abstract
    Time amplifiers (TAs) are the key building blocks of the two-step time-to-digital converters. High resolution TAs suffer from inaccuracy the gain due to employing meta-stability behavior of the SR latches. In the proposed method, two offset NAND gates are placed in parallel with the NAND gates of the conventional SR latch to get a linear re-configurable gain. Gain of the TA is controlled only by the driving strength of the NAND gates. To confirm the effectiveness of the proposed method, an 8-bit two step time to digital converter (TDC) was designed and laid-out in 0.18- μm CMOS technology. Using a supply voltage of 1.2 V, the proposed TDC consumes 1.1 mW at 30 MS/s throughput. © 2004-2012... 

    Wireless interfacing to cortical neural recording implants using 4-FSK modulation scheme

    , Article IEEE International Conference on Electronics, Circuits, and Systems, 6 December 2015 through 9 December 2015 ; Volume 2016 March , 2016 , Pages 221-224 ; 9781509002467 (ISBN) Eslampanah Sendi, M. S ; Judy, M ; Molaei, H ; Sodagar, A. M ; Sharifkhani, M ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2016
    Abstract
    This paper used a 4-level frequency shift keying (4-FSK) modulation scheme to enhance the density of wireless data transfer from implantable biomedical microsystems to the outside world. Modeling and simulation of the wireless channel for 4-FSK modulation in the case of a neural recording implant has been done. To realize the 4-FSK scheme, the modulator and demodulator circuits are proposed, designed and simulated in a 0.18-μm CMOS process, and in the 174-216 MHz frequency band at a data rate of 13.5 Mbps. Operated using a 1.8 V supply voltage, the modulator circuit consumes a power of 7.8 μW  

    Reactive Crystallization in an Impinging Jets Reactor

    , M.Sc. Thesis Sharif University of Technology Raoufi, Farzan (Author) ; Molaei Dehkordi, Asghar (Supervisor)
    Abstract
    Reactive crystallization or precipitation is an important industrial process. Many chemicals and biochemicals such as catalysts and pigments are produced by precipitation. Because of the advantages of impinging jets in chemical engineering processes, the main aim of this research was to investigate the application of this method in precipitation and to study the effects of different operating and design parameters on the product’s quality and properties. Two chemical models of barium sulfate and copper oxalate were used as main products. Each of these chemicals was produced by a liquid-liquid reaction of two aqueous solutions, which were fed to an impinging-jets reactor. Effects of... 

    Solid-Liquid Heterogeneous Catalytic Reactions in a New Two-Impinging-Jets Reactor

    , M.Sc. Thesis Sharif University of Technology Ghasemi, Mohammad (Author) ; Molaei Dehkordi, Asghar (Supervisor)
    Abstract
    In this work the transesterification reaction of waste cooking oil in the present of solid catalyst as a type of solid-liquid catalytic reaction, has been studied. For this purpose, two types of alkali solid catalysts were synthesized. CaO-ZrO2 and KOH/γ-Al2O3 catalysts were prepared by co-precipitation and impregnation method, respectively. These catalysts were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), X-ray fluorescence (XRF), BET surface area, and temperature programmed desorption of CO2 (TPD-CO2). The obtained results for the CaO-ZrO2 catalysts indicate that with increasing Ca/Zr atomic ratio, the activity of catalysts increases, but the stability... 

    A 12 Bit Delta-Sigma Modulator For Wireless Applications

    , M.Sc. Thesis Sharif University of Technology Molaei, Hassan (Author) ; Hajsadeghi, Khosrow (Supervisor)
    Abstract
    Analog to digital converters are one of the most important component of Bluetooth and GSM receivers. The pipeline and Successive Approximation Register (SAR) ADCs are mainly used in these receivers. However, the pipeline ADCs consume lots of power and SAR ADCs suffer the resolution in advanced technologies. On the other hand, the Delta-Sigma ADCs are capable of achieving high resolution with a low power. So in this thesis, the various kinds and different implementations of Delta-Sigma Modulators are introduced. The system level design and the conversion between Discrete-Time Modulators and Continuous-Time Modulators are explained. The non-ideality effects such as limited gain and bandwidth... 

    Adsorption of xylene isomers on Na-BETA zeolite: Equilibrium in batch adsorber

    , Article Microporous and Mesoporous Materials ; Volume 172 , 2013 , Pages 136-140 ; 13871811 (ISSN) Molaei Dehkordi, A ; Khademi, M ; Sharif University of Technology
    2013
    Abstract
    In this article, adsorption of p-xylene, m-xylene, o-xylene, and ethylbenzene on Na-BETA type zeolite in liquid phase at 15, 25, and 35 °C has been studied and the single adsorption isotherms have been obtained and reported. The Langmuir isotherm model was used to describe the experimental adsorption isotherm data. It was found that p-xylene is more strongly adsorbed component followed by ethylbenzene, m-xylene and o-xylene. This means that this adsorbent is selective for p-xylene. Using Langmuir isotherm model, the saturation adsorption capacities of the adsorbent were obtained as follows 143 mg/g for p-xylene, 105 mg/g for ethylbenzene, 83 mg/g for m-xylene, and 68 mg/g for o-xylene at 25... 

    Transesterification of waste cooking oil to biodiesel using Ca and Zr mixed oxides as heterogeneous base catalysts

    , Article Fuel Processing Technology ; Volume 97 , 2012 , Pages 45-51 ; 03783820 (ISSN) Molaei Dehkordi, A ; Ghasemi, M ; Sharif University of Technology
    2012
    Abstract
    Heterogeneous solid catalysts comprising CaO and ZrO 2 mixed oxides with various Ca-to-Zr molar ratios were synthesized by means of coprecipitation method. These synthesized mixed oxide catalysts were used for the transesterification of waste cooking oil (WCO) as feedstock with methanol to produce biodiesel fuel (BDF) at 65 °C and 1 atm. The influences of Ca-to-Zr molar ratio, catalyst loading, methanol-to-oil molar ratio, and the reaction time on the BDF yield were carefully investigated. In addition, the stability of prepared solid catalysts was studied. These catalysts were characterized by using techniques of X-ray diffraction, X-ray florescence, X-ray photoelectron spectroscopy, surface... 

    The effect of dynamic strain aging on subsequent mechanical properties of dual-phase steels

    , Article Journal of Materials Engineering and Performance ; Volume 19, Issue 4 , June , 2010 , Pages 607-610 ; 10599495 (ISSN) Molaei, M. J ; Ekrami, A ; Sharif University of Technology
    2010
    Abstract
    Dual-phase (DP) steels with different martensite contents were produced by subjecting a low carbon steel to various heat treatment cycles. In order to investigate the effect of dynamic strain aging (DSA) on mechanical properties, tensile specimens were deformed 3% at 300 °C. Room temperature tensile tests of specimens which deformed at 300 °C showed that both yield and ultimate tensile strengths increased, while total elongation decreased. The fatigue limit increased after pre-strain in the DSA temperature range. The effects of martensite volume fraction on mechanical properties were discussed