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Gel-sol synthesis and aging effect on highly crystalline anatase nanopowder
, Article Bulletin of Materials Science ; Volume 34, Issue 6 , October , 2011 , Pages 1189-1195 ; 02504707 (ISSN) ; Askari, M ; Sadrnezhaad, S. K ; Sharif University of Technology
2011
Abstract
Highly crystalline TiO 2 anatase nanoparticles were synthesized via gel-sol method by using titanium isopropoxide and triethanolamine. The products were characterized by X-ray diffraction, transmission electron microscopy, thermogravimetric/differential thermal analysis and nitrogen gas absorption methods. The particle size ranged from 7 to 24 nm having specific surface area of 64 to 220 m 2/g. Selective Ti(OH) 4 gel specifications and hydrothermal test conditions resulted in thermodynamically- stable phase-formation. Aging at 130°C for 4 h resulted in particle size of 7 nm; while at 130 and 160°C for 12 h resulted in 12 and 21 nm, respectively
An investigation on tensile properties of coiled carbon nanotubes using molecular dynamics simulation
, Article Diamond and Related Materials ; Volume 74 , 2017 , Pages 154-163 ; 09259635 (ISSN) ; Karimi Taheri, K ; Karimi Taheri, A ; Sharif University of Technology
Elsevier Ltd
2017
Abstract
A coiled carbon nanotube (CCNT) can be formed from the distortion of parent toroidal carbon nanotube with a uniform pitch length and a uniform spring rise angle. In this research molecular dynamics simulation was carried out to assess the tensile properties of three CCNT having indexes of (3,3), (4,4), and (5,5). The results indicated that Stone-Wales defects are necessary for thermodynamic stability of the CCNTs. The stress-strain curves showed that the yield stress, yield strain, and failure strain are decreased with increase in temperature. The force-displacement curves revealed that the spring constant of these materials is highly depended on the tube diameter and rising angle, while it...
Study on Nucleation and Growth of Titanium Dioxide Nano Particles via Gel-Sol Method
, M.Sc. Thesis Sharif University of Technology ; Askari, Masoud (Supervisor)
Abstract
Nanotechnology is an efficient method suitable for fabrication and production of minimal single dimensional nanometric structures. Such materials and systems can be logically designed that lead to new and optimized biological, chemical and physical properties and characteristics due to their size. Nucleation and growth –appearance of a new phase out of an old phase – is a ubiquitous phenomenon in nature. Fundamental understanding of nanoparticles nucleation and growth mechanism allows more control on form, size and composition and allows tuning of the above said properties easily with use of different reactive conditions as a result of this ability . Nanoparticles of titania are one of...
Solvent Extraction of Leaching Solution Containing Rare Earth Elements from Apatite Concentrate
, M.Sc. Thesis Sharif University of Technology ; Yoozbashizadeh, Hossein (Supervisor)
Abstract
In this research, Chadormalou apatite concentrate was dissolved by 40% nitric acid and a solid to liquid ratio of 0.4 at 70 ° C for 2 hours, and its rare earth elements were dissolved. Recovery percents for Cerum, Neodymium and Lanthanum were 62.4, 48.7 and 49.6, respectively. In the solvent extraction step, the effect of HQ concentration as extractant, pH, temperature and phase ratio on the concentration of the adsorbed elements in organic phase, extraction percentage, distribution ratio and separation factor of rare earths were investigated. Organic solutions containing HQ in the kerosene alone pricipitated after contacting with PLS solutions. In order to prevent HQ pricipitation in the...
Optimizing structural and mechanical properties of coiled carbon nanotubes with nsga-ii and reactive molecular dynamics simulation
, Article Journal of Physical Chemistry C ; Volume 125, Issue 11 , 2021 , Pages 6237-6248 ; 19327447 (ISSN) ; Rangriz, F ; Karimi Taheri, A ; Abdi Jalebi, M ; Sharif University of Technology
American Chemical Society
2021
Abstract
Coiled carbon nanotubes (CCNTs) have increasingly become a vital factor in the new generation of nanodevices and energy-absorbing materials due to their outstanding properties. Here, the multiobjective optimization of CCNTs is applied to assess their mechanical properties. The best trade-off between conflicting mechanical properties (e.g., yield stress and yield strain) is demonstrated and the optimization of the geometry enables us to find the astonishing CCNTs with a stretchability of 400%. These structures have been recognized for the first time in the field. We derived several highly accurate analytical equations for the yield stress and yield strain by the implementation of...
Computer Simulation of Coiled Carbon Nanotubes Deformation By Molecular Dynamics Approach
, M.Sc. Thesis Sharif University of Technology ; Karimi Taheri, Ali (Supervisor)
Abstract
A Coiled Carbon Nanotube (CCNT) can be geometrically viewed as a graphene sheet whose rolled and twisted to form a helically coiled nanotube. It is the strongest material ever measured with strengthexceeding more than hundred times of steel.The strength of a CCNT iscritically influenced by temperature, tube diameter, strain rate and pitch angle. In this study,a Molecular Dynamics (MD) simulationis performed to understand the effect of temperature, strain rate, tube diameter and pitch angle on the mechanical properties of CCNTs. Results indicate thatexisting the stone-wales defects is necessaryfor thermodynamic stability of CCNTs.According to the stress-strain curves it was observed thatyield...
Connectivity analysis of one-dimensional ad hoc networks with arbitrary spatial distribution for variable and fixed number of nodes
, Article IEEE Transactions on Mobile Computing ; Volume 11, Issue 10 , 2012 , Pages 1425-1435 ; 15361233 (ISSN) ; Ashtiani, F ; Sharif University of Technology
2012
Abstract
In this paper, we propose an analytical approach to compute the probability of connectivity for one-dimensional ad hoc networks. The proposed analysis gives the exact probability of connectivity for an arbitrary distribution of nodes, provided that nodes are independently and identically distributed. We conduct separate analyses for two cases; in the first case, the number of nodes varies by time under a stationary distribution and in the second case, there is a fixed (known) number of nodes in the network. Using the approaches presented in this work, we are able to derive closed-form formulas for the probability of connectivity for some spatial distributions, while for more complicated...
A new mechanism for wall climbing operation based on 4-bar linkage
, Article 8th Biennial ASME Conference on Engineering Systems Design and Analysis, ESDA2006, Torino, 4 July 2006 through 7 July 2006 ; Volume 2006 , 2006 ; 0791837793 (ISBN); 9780791837795 (ISBN) ; Sayyaadi, H ; Sharif University of Technology
2006
Abstract
Wall walking robots are designed for different purposes, rescue operations, wall inspections and jobs such as painting and cleaning and fire fighting for tall buildings. These are some cases that these types of robots are extensively used. This paper describes a design of a new serial mechanism for wall climbing job. In deed we are seeking to define a minimum degree of freedom mechanism to be applied in a robot moving vertically on a surface. This mechanism has 5 links, but at any point it works with its 4 links, actually in each cycle of motion the linkage will be interchanged. Copyright © 2006 by ASME
Peak to mean envelope power ratio of oversampled OFDM signals: An analytical approach
, Article International Conference on Communications (ICC2001), Helsinki, 11 June 2000 through 14 June 2000 ; Volume 5 , 2001 , Pages 1476-1480 ; 05361486 (ISSN) ; Khalaj, B. H ; Sharif University of Technology
2001
Abstract
Orthogonal frequency division multiplexing (OFDM) has a large peak to mean envelope power ratio (PMEPR), which can result in significant signal distortion in presence of nonlinear amplifiers. In this paper, we will show that peak of the continuous envelope of OFDM signal can be bounded by maximum of corresponding oversampled sequence. This fact is then used as the corner stone of our study in two parts. In the first part, statistical analysis is used to find probability upper bound for complementary cumulative distribution function of PMEPR. It is also proven that for large number of subcarriers, only one redundant bit is necessary to limit PMEPR within %10 of its maximum value. In the...
A control-theoretic energy management for fault-tolerant hard real-time systems
, Article Proceedings - IEEE International Conference on Computer Design: VLSI in Computers and Processors, 3 October 2010 through 6 October 2010 ; 2010 , Pages 173-178 ; 10636404 (ISSN) ; 9781424489350 (ISBN) ; Hosseingholi, M ; Ejlali, A ; Sharif University of Technology
2010
Abstract
Recently, the tradeoff between low energy consumption and high fault-tolerance has attracted a lot of attention as a key issue in the design of real-time embedded systems. Dynamic Voltage Scaling (DVS) is known as one of the most effective low energy techniques for real-time systems. It has been observed that the use of control-theoretic methods can improve the effectiveness of DVS-enabled systems. In this paper, we have investigated reducing the energy consumption of fault-tolerant hard real-time systems using feedback control theory. Our proposed feedback-based DVS method makes the system capable of selecting the proper frequency and voltage settings in order to reduce the energy...
NF analysis of LNA with Lossy passive network at the input
, Article 41st International Conference on Telecommunications and Signal Processing, TSP 2018, 4 July 2018 through 6 July 2018 ; 2018 ; 9781538646953 (ISBN) ; Rabbani, R ; Sharif Bakhtiar, M ; Sharif University of Technology
Institute of Electrical and Electronics Engineers Inc
2018
Abstract
It is widely accepted that the presence of a lossy network, such as a SAW filter or balun, at the input of LNA increases NF of the overall circuit by an amount equal to the insertion loss of the lossy network. In this work it is shown that this idea is not exactly true and it considerably underestimates the overall NF. To verify this claim, Z-model of the lossy network is added before the LNA and the overall noise figure is recalculated for some commonly used LNA topologies. It is shown that in common gate LNA and common source LNA with resistive feedback the accepted equation underestimates the overall NF by 1.3 dB for an insertion loss of 2 dB. In common source with resistive matching and...
Wide-range single-ended CMOS track-and-hold circuit
, Article IEICE Electronics Express ; Volume 4, Issue 12 , 2007 , Pages 400-405 ; 13492543 (ISSN) ; Sedighi, B ; Sharif Bakhtiar, M ; Sharif University of Technology
2007
Abstract
This paper investigates the performance of a MOS track-and-hold circuit as the front end of a wide input range and high-speed single-sided ADC. In order to reduce charge injection and clock feedthrough errors, a new technique for employing a dummy transistor in the bootstrapped switch of the track and hold circuit is introduced. Performance of the proposed circuit for the two cases of constant and non-linear hold capacitor is studied. It is also shown that how and when dummy switch and bulk switching method can improve the accuracy of theT/H. © IEICE 2007
A divide-by-3 frequency divider for I/Q generation in a multi-band frequency synthesizer
, Article APCCAS 2008 - 2008 IEEE Asia Pacific Conference on Circuits and Systems, Macao, 30 November 2008 through 3 December 2008 ; 2008 , Pages 1383-1386 ; 9781424423422 (ISBN) ; Atarodi, M ; Sharif Bakhtiar, M ; Sharif University of Technology
2008
Abstract
A divide-by-3 frequency divider for Inphase and Quadrature (I/Q) LO signal generation in a multi-band frequency synthesizer is presented. Using divisor numbers other than powers of 2 (2n) for quadrature signal generation, reduces the required frequency range of the VCO in multi-band frequency synthesizers. The divide-by-3 circuit is designed in a 0.18um CMOS technology. © 2008 IEEE
Performance comparison of switched-capacitor and switched-current pipeline ADCs
, Article 2007 IEEE International Symposium on Circuits and Systems, ISCAS 2007, New Orleans, LA, 27 May 2007 through 30 May 2007 ; 2007 , Pages 2252-2255 ; 02714310 (ISSN) ; Sedighi, B ; Sharif Bakhtiar, M ; Sharif University of Technology
Institute of Electrical and Electronics Engineers Inc
2007
Abstract
In this paper a theoretical comparison between the performance of switched-capacitor (SC) and switched-current (SI) pipeline analog-to-digital converters (ADCs) is presented. Power dissipation and die area of SC and SI implementations are compared based on linearity and noise constraints. It is shown that if nonlinearity errors of the class AB SI ADCs are removed by calibration, their performance prevails that of the SC ADCs. Also it is shown that class AB SI ADCs occupy less die area than SC ADCs for a given resolution. © 2007 IEEE
A low voltage, high speed, high resolution class AB switched current sample and hold
, Article ISCAS 2006: 2006 IEEE International Symposium on Circuits and Systems, Kos, 21 May 2006 through 24 May 2006 ; 2006 , Pages 1039-1042 ; 02714310 (ISSN); 0780393902 (ISBN); 9780780393905 (ISBN) ; Jahanian, A ; Sharif Bakhtiar, M ; Sharif University of Technology
2006
Abstract
A high speed, high resolution switched-current sample and hold (SI S/H) based on a new class AB transconductance stage is presented. Simulations performed on the SI S/H in standard 0.18um CMOS technology with 1.5v supply voltage indicate low power dissipation, high sampling speed and high SNR. © 2006 IEEE
A new architecture for analog sampled-data neural filters
, Article IEEE International Symposium on Circuits and Systems 2005, ISCAS 2005, Kobe, 23 May 2005 through 26 May 2005 ; 2005 , Pages 2494-2497 ; 02714310 (ISSN) ; Analui, B ; Sharif Bakhtiar, M ; Sharif University of Technology
2005
Abstract
A new architecture for analog sampled-data filters is presented. This architecture is based on implementing the difference equation of the filter using a neural network. It results in lower sensitivity of filter coefficients to hardware nonidealities. Different tradeoffs in the hardware implementation of the filter are discussed. A design example is also presented. © 2005 IEEE
A stochastic approach for valuing customers in banking industry: A case study
, Article Industrial Engineering and Management Systems ; Volume 19, Issue 4 , 2021 , Pages 744-757 ; 15987248 (ISSN) ; Mehraeen, M ; Pooya, A ; Sharif, H ; Sharif University of Technology
Korean Institute of Industrial Engineers
2021
Abstract
This study provides a stochastic dynamic programming model with a Markov chain that explicitly focuses on the customer as well as a new model for valuing the customers in the banking industry. The proposed framework calculates individual customer’s lifetime value dynamically. The study follows a stochastic dynamic programming model that is based on the Markov chain. The deduced findings are illustrated with supplementary context from an outstanding case study. The findings underline the importance of the stochastic model for calculating customer lifetime value based on customer behavior. The presented framework provides a beneficial way for future research and valuable insight for allocating...
New results on the peak power of OFDM signals based on oversampling
, Article IEEE International Conference on Communications ; Volume 2 , 2002 , Pages 866-871 ; 05361486 (ISSN) ; Gharavi Alkhansari, M ; Khalaj, B. H ; Sharif University of Technology
2002
Abstract
In this paper, we introduce a new bound for the peak of the continuous envelope of an OFDM signal based on the maximum of its corresponding oversampled sequence, that is considerably tighter than the recent results presented in [4]. The proposed bound is then used as the basis of our study in two parts. In the first part, we find an upper bound for the regrowth of the peak of the digitally clipped oversampled sequence after discrete to continuous conversion. We also show that for oversampling rates greater than π/√2, the peak regrowth percentage depends only on oversampling rate, regardless of the number of subcarriers. In the second part, we propose new and tight relative error bounds for...
On the peak-to-average power of OFDM signals based on oversampling
, Article IEEE Transactions on Communications ; Volume 51, Issue 1 , 2003 , Pages 72-78 ; 00906778 (ISSN) ; Gharavi Alkhansari, M ; Hossein Khalaj, B ; Sharif University of Technology
2003
Abstract
Orthogonal frequency-division multiplexing (OFDM) introduces large amplitude variations in time, which can result in significant signal distortion in the presence of nonlinear amplifiers. In this paper, we introduce a new bound for the peak of the continuous envelope of an OFDM signal, based on the maximum of its corresponding oversampled sequence, that is shown to be very tight as the oversampling rate increases. The bound is then used to derive a closed-form probability upper bound for complementary cumulative distribution function of the peak-to-mean envelope power ratio of uncoded OFDM signals for sufficiently large numbers of subcarriers. As another application of the bound for...
A new architecture for rail-to-rail input constant-gm CMOS operational transconductance amplifiers
, Article Proceedings of the 2003 International Symposium on Low Power Electronics and Design, (ISLPED'03), Seoul, 25 August 2003 through 27 August 2003 ; 2003 , Pages 353-358 ; 15334678 (ISSN) ; Lotfi, R ; Sharif Bakhtiar, M ; Sharif University of Technology
2003
Abstract
A new architecture for constant-gm rail-to-rail(R-R) input stages is presented that has less than 5% deviation in gm over the entire range of the input common-mode voltage. Furthermore, a new structure for folded cascode amplifier based on the use of a floating current source is presented. Employing these techniques a low-power operational transconductance amplifier(OTA) with 100MHz unity-gain bandwidth, 106dB gain, 60° phase margin, 2.65V swing, and 6.4nVA/√Hz input-referred noise with R-R input common-mode range is realized in a 0.8μm CMOS technology. This amplifier dissipates 10mW from a 3V power supply