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    Simultaneous preconcentration and speciation of iron(II) and iron(III) in water samples by 2-mercaptobenzimidazole-silica gel sorbent and flow injection analysis system

    , Article Analytica Chimica Acta ; Volume 424, Issue 2 , 2000 , Pages 233-242 ; 00032670 (ISSN) Bagheri, H ; Gholami, A ; Najafi, A ; Sharif University of Technology
    2000
    Abstract
    2-Mercaptobenzimidazole, loaded on silica gel (MBI-SG) was used for preconcentration and speciation of iron(II) and iron(III) in water samples. The speciation is based upon selective retention of iron(III) on MBI-SG sorbent and quantitatively passing iron(II) ions. This type of sorbent was not only capable of separating theses two ions but also could concentrate them. The adsorbed iron(III) on MBI-SG was desorbed from the column by an SCN- solution and transferred to the detection device. The effluent, then, was treated with hydrogen peroxide to oxidize iron(II) into iron(III) and subsequently was pumped through the MBI-SG column. A home-made flow injection system was coupled with a UV-VIS... 

    Exact boundary controllability of vibrating non-classical Euler-Bernoulli micro-scale beams

    , Article Journal of Mathematical Analysis and Applications ; Vol. 418, issue. 2 , 2014 , pp. 985-997 ; ISSN: 0022247X Vatankhah, R ; Najafi, A ; Salarieh, H ; Alasty, A ; Sharif University of Technology
    Abstract
    This study investigates the exact controllability problem for a vibrating non-classical Euler-Bernoulli micro-beam whose governing partial differential equation (PDE) of motion is derived based on the non-classical continuum mechanics. In this paper, it is proved that via boundary controls, it is possible to obtain exact controllability which consists of driving the vibrating system to rest in finite time. This control objective is achieved based on the PDE model of the system which causes that spillover instabilities do not occur  

    Boundary stabilization of non-classical micro-scale beams

    , Article Applied Mathematical Modelling ; Volume 37, Issue 20-21 , 2013 , Pages 8709-8724 ; 0307904X (ISSN) Vatankhah, R ; Najafi, A ; Salarieh, H ; Alasty, A ; Sharif University of Technology
    2013
    Abstract
    In this paper, the problem of boundary stabilization of a vibrating non-classical micro-scale Euler-Bernoulli beam is considered. In non-classical micro-beams, the governing Partial Differential Equation (PDE) of motion is obtained based on the non-classical continuum mechanics which introduces material length scale parameters. In this research, linear boundary control laws are constructed to stabilize the free vibration of non-classical micro-beams which its governing PDE is derived based on the modified strain gradient theory as one of the most inclusive non-classical continuum theories. Well-posedness and asymptotic stabilization of the closed loop system are investigated for both cases... 

    Fuzzy project scheduling with discounted cash flows

    , Article Economic Computation and Economic Cybernetics Studies and Research ; Volume 5 , 2012 ; 0424267X (ISSN) Shavandi, H ; Najafi, A. A ; Moslehirad, A ; Sharif University of Technology
    Abstract
    Project scheduling to maximize the net present value of the cash flows has been a topic of recent research. These researches assume that the duration of activities is known either with certitude or at least with some probability. However, in many applications the structure of the duration of activities is imprecise. In this paper, the project scheduling problem with discounted cash flows under fuzzy environment is considered. The duration of activities are assumed triangular fuzzy numbers. The derived mathematical model is a multi-objective non-linear programming model and for solving it the Taylor expansion is used to transform the objective function to a linear form. To interpret the fuzzy... 

    Bi-objective resource constrained project scheduling problem with makespan and net present value criteria: Two meta-heuristic algorithms

    , Article International Journal of Advanced Manufacturing Technology ; Volume 69, Issue 1-4 , 2013 , Pages 617-626 ; 02683768 (ISSN) Khalili, S ; Najafi, A. A ; Niaki, S.T. A ; Sharif University of Technology
    2013
    Abstract
    Traditionally, the model of a resource-constrained project-scheduling problem (RCPSP) contains a single objective function of either minimizing project makespan or maximizing project net present value (NPV). In order to be more realistic, in this paper, two multi-objective meta-heuristic algorithms of multi-population and two-phase sub-population genetic algorithms are proposed to find Pareto front solutions that minimize the project makespan and maximize the project NPV of a RCPSP, simultaneously. Based on standard test problems constructed by the RanGen project generator, a comprehensive computational experiment is performed, where response surface methodology is employed to tune the... 

    Sum capacity bounds and design of errorless codes for binary asynchronous CDMA systems

    , Article 2012 19th International Conference on Telecommunications, ICT 2012, 23 April 2012 through 25 April 2012, Jounieh ; 2012 ; 9781467307475 (ISBN) Dashmiz, S ; Mansouri, S. M ; Najafi, A ; Marvasti, F ; Sharif University of Technology
    IEEE  2012
    Abstract
    In this paper, some codes are designed for a binary chip-asynchronous CDMA system which guarantee errorless communication in the absence of noise. These codes also show good performance for noisy channels. In addition, lower and upper bounds for the sum channel capacity are derived for finite and asymptotic cases with the assumption of both noiseless and noisy channels. The results are derived assuming that user delays are known at the receiver end. The performance of proposed codes in the noisy case is also compared to both Gold sequences and a similar class of binary sequences with constrained amount of correlation  

    Statistical design of genetic algorithms for combinatorial optimization problems

    , Article Mathematical Problems in Engineering ; Volume 2011 , 2011 ; 1024123X (ISSN) Shahsavar, M ; Najafi, A. A ; Niaki, S. T. A ; Sharif University of Technology
    2011
    Abstract
    Many genetic algorithms (GA) have been applied to solve different NP-complete combinatorial optimization problems so far. The striking point of using GA refers to selecting a combination of appropriate patterns in crossover, mutation, and and so forth and fine tuning of some parameters such as crossover probability, mutation probability, and and so forth. One way to design a robust GA is to select an optimal pattern and then to search for its parameter values using a tuning procedure. This paper addresses a methodology to both optimal pattern selection and the tuning phases by taking advantage of design of experiments and response surface methodology. To show the performances of the proposed... 

    The simultaneous determination of archie's parameters by application of modified genetic algorithm and hdp methods: A comparison with current methods via two case studies

    , Article Petroleum Science and Technology ; Volume 30, Issue 1 , Mar , 2011 , Pages 54-63 ; 10916466 (ISSN) Godarzi, A. A ; Najafi, I ; Najafi, A ; Ghazanfari, M. H ; Sharif University of Technology
    2011
    Abstract
    Although different procedures have been proposed to calculate the parameters of Archie's (1942) equation, most of them suffer from lack of accuracy because these are not solved simultaneously In this article, by applying two novel methods, a modified genetic algorithm (MGA) and homogeneous distribution of parameters (HDP), the above-mentioned unknown parameters were determined simultaneously. Furthermore, for two case studies using two data sets from Permian Glerito and Permian Clearfork reservoirs, a comparison is made between other methods (e.g., traditional graphical method and SmnaM; Frailey et al., 2001) and the proposed methods that demonstrated the greater accuracy of the two newly... 

    Three self-adaptive multi-objective evolutionary algorithms for a triple-objective project scheduling problem

    , Article Computers and Industrial Engineering ; Volume 87 , September , 2015 , Pages 4-15 ; 03608352 (ISSN) Shahsavar, A ; Najafi, A. A ; Niaki, S. T. A ; Sharif University of Technology
    Elsevier Ltd  2015
    Abstract
    Finding a Pareto-optimal frontier is widely favorable among researchers to model existing conflict objectives in an optimization problem. Project scheduling is a well-known problem in which investigating a combination of goals eventuate in a more real situation. Although there are many different types of objectives based on the situation on hand, three basic objectives are the most common in the literature of the project scheduling problem. These objectives are: (i) the minimization of the makespan, (ii) the minimization of the total cost associated with the resources, and (iii) the minimization of the variability in resources usage. In this paper, three genetic-based algorithms are proposed... 

    An efficient genetic algorithm to maximize net present value of project payments under inflation and bonus-penalty policy in resource investment problem

    , Article Advances in Engineering Software ; Volume 41, Issue 7-8 , July–August , 2010 , Pages 1023-1030 ; 09659978 (ISSN) Shahsavar, M ; Akhavan Niaki, S. T ; Najafi, A. A ; Sharif University of Technology
    2010
    Abstract
    In order to develop a more realistic resource-constrained project-scheduling model that is applicable to real-world projects, in this paper, the resource investment problem with discounted cash flows and generalized precedence relations is investigated under inflation factor such that a bonus-penalty structure at the deadline of the project is imposed to force the project not to be finished beyond the deadline. The goal is to find activity schedules and resource requirement levels that maximize the net present value of the project cash flows. The problem is first mathematically modeled. Then, a genetic algorithm (GA) is designed using a new three-stage process that utilizes design of... 

    Economic production quantity model with scrapped items and limited production capacity

    , Article Scientia Iranica ; Volume 17, Issue 1 E , 2010 , Pages 58-69 ; 10263098 (ISSN) Taleizadeh, A ; Najafi, A. A ; Akhavan Niaki, S.T ; Sharif University of Technology
    2010
    Abstract
    In this paper, an Economic Production Quantity (EPQ) model is studied, in which the production defective-rate follows either a uniform or a normal probability distribution. Shortages are allowed and take a backorder state, and the existence of only one machine causes a limited production capacity for the common cycle length of all products. The aim of this research is to determine the optimal production quantity of each product, such that the expected total cost including holding, shortage, production, setup and defective items cost is minimized. The mathematical model of the problem is derived, for which the objective function is proved to be convex. Then, a derivative approach is utilized... 

    Multiproduct single-machine production system with stochastic scrapped production rate, partial backordering and service level constraint

    , Article Journal of Computational and Applied Mathematics ; Volume 233, Issue 8 , 2010 , Pages 1834-1849 ; 03770427 (ISSN) Taleizadeh, A. A ; Akhavan Niaki, S. T ; Najafi, A. A ; Sharif University of Technology
    Abstract
    In this paper, a multiproduct single-machine production system under economic production quantity (EPQ) model is studied in which the existence of only one machine causes a limited production capacity for the common cycle length of all products, the production defective rates are random variables, shortages are allowed and take a combination of backorder and lost sale, and there is a service rate constraint for the company. The aim of this research is to determine the optimal production quantity, the allowable shortage level, and the period length of each product such that the expected total cost, including holding, shortage, production, setup and defective items costs, is minimized. The... 

    A two-part self-adaptive technique in genetic algorithms for project scheduling problems

    , Article Journal of Modern Project Management ; Volume 4, Issue 2 , 2016 , Pages 64-73 ; 23173963 (ISSN) Shahsavar, A ; Akhavan Niaki, S. T ; Najafi, A. A ; Sharif University of Technology
    Editora Mundos Sociais  2016
    Abstract
    The present paper introduces a novel two-part self-adaptive technique in designing the genetic algorithm for project scheduling problems. One part of the algorithm includes a self-adaptive mechanism for genetic operators like crossover and mutation. The second part contains another self-adaptive mechanism for genetic parameters such as crossover probability. The parts come in turn repeatedly within a loop feeding each other with the information regarding the performance of operators or parameters. The capability of the method is tested and confirmed in comparison to metaheuristic and exact algorithms based on well-known benchmarks  

    Project scheduling and equipment planning with random breakdowns

    , Article RAIRO - Operations Research ; Volume 51, Issue 4 , 2017 , Pages 1189-1209 ; 03990559 (ISSN) Shafikhani, A ; Najafi, A. A ; Akhavan Niaki, S. T ; Sharif University of Technology
    Abstract
    Most of the research works conducted on Project Scheduling Problem (PSP) especially Resource Constrain Project Scheduling Problem (RCPSP) either ignore equipment planning or schedule the activities first, and then plan for the required equipment. Moreover, little works that consider simultaneous PSP and Equipment Planning (EP) are based on the assumption that the equipment is continuously available. However, in reality, equipment is subject to either random breakdowns or deterministic maintenance programs that make it not being available all the time. In this paper, the PSP and EP problems are simultaneously considered in closer to reality situations in which the equipment is not always... 

    Open-shop production scheduling with reverse flows

    , Article Computers and Industrial Engineering ; Volume 153 , 2021 ; 03608352 (ISSN) Aghighi, S ; Akhavan Niaki, S. T ; Mehdizadeh, E ; Najafi, A. A ; Sharif University of Technology
    Elsevier Ltd  2021
    Abstract
    The purpose of this paper is to present a mixed-integer linear programming model for the scheduling problem in an open-shop manufacturing system involving reverse flows, where two job flows (direct and reverse) in two opposite directions are processed on the same machines. The aim is to minimize the maximum completion time of all jobs on all machines (i.e., the makespan). A numerical example is presented and solved using the GAMS software (version 25.1.2) to validate the proposed mathematical model. As this problem is NP-hard, a vibration damping-based optimization (VDO) algorithm is proposed to solve large-scale problems in reasonable execution times. Besides, the Taguchi experimental... 

    Open-shop production scheduling with reverse flows

    , Article Computers and Industrial Engineering ; Volume 153 , 2021 ; 03608352 (ISSN) Aghighi, S ; Akhavan Niaki, S. T ; Mehdizadeh, E ; Najafi, A. A ; Sharif University of Technology
    Elsevier Ltd  2021
    Abstract
    The purpose of this paper is to present a mixed-integer linear programming model for the scheduling problem in an open-shop manufacturing system involving reverse flows, where two job flows (direct and reverse) in two opposite directions are processed on the same machines. The aim is to minimize the maximum completion time of all jobs on all machines (i.e., the makespan). A numerical example is presented and solved using the GAMS software (version 25.1.2) to validate the proposed mathematical model. As this problem is NP-hard, a vibration damping-based optimization (VDO) algorithm is proposed to solve large-scale problems in reasonable execution times. Besides, the Taguchi experimental... 

    Modeling and qualitative experiments on swirling bubbly flows: Single bubble with rossby number of order 1

    , Article Journal of Fluids Engineering, Transactions of the ASME ; Volume 125, Issue 2 , 2003 , Pages 239-246 ; 00982202 (ISSN) Magaud, F ; Najafi, A. F ; Angilella, J. R ; Souhar, M ; Sharif University of Technology
    2003
    Abstract
    The behavior of an isolated bubble in a single-phase swirling flow is investigated theoretically and experimentally. The Rossby number is such that the liquid flow can be approximated by a solid-body rotation superposed to a uniform axial velocity. The equations of the motion of the bubble are solved analytically and numerically, by assuming that the bubble is small and does not modify the water flow. Two kinds of bubbles have been considered: clean bubbles and bubbles with a contaminated interface. In the latter case the bubble is treated as a solid sphere. In both cases a critical angular velocity ωc for the rotating device is found. When ω<ωc the trajectory of the bubble is a conical... 

    Use of a novel initiator for synthesis of amino-end functionalized polystyrene (NH 2-PS) by atom transfer radical polymerization

    , Article Journal of Polymer Research ; Volume 19, Issue 1 , January , 2012 ; 10229760 (ISSN) Pourjavadi, A ; Seidi, F ; Jahromi, P. E ; Salimi, H ; Roshan, S ; Najafi, A ; Bruns, N ; Sharif University of Technology
    2012
    Abstract
    Here we report a versatile new method for endfunctionalizing polystyrene. In order to produce polystyrene with an amino end group, 2-(3-bromo-3- phenylpropyl) isoindoline-1,3-dione was synthesized and used as a novel initiator for ATRP. After ATRP polymerization, tri-n-butyltin hydride ((n-Bu) 3SnH) reductively replace existing halogens on polymer chains by hydrogen. Finally, the phthaloyl groups on polymer backbone were cleaved by treatment with hydrazine yielding amino terminated polystyrene. A polymer with M n≈10,350 and M w/M n01.17 was obtained. Therefore, this method allows the preparation of amino end functionalized polystyrene of narrow polydispersity with complete degree of... 

    Leaching of a zinc ore and concentrate using the Geocoat™ technology

    , Article Minerals Engineering ; Volume 24, Issue 1 , 2011 , Pages 64-69 ; 08926875 (ISSN) Soleimani, M ; Petersen, J ; Roostaazad, R ; Hosseini, S ; Mohammad Mousavi, S ; Najafi, A ; Vasiri, A. K ; Sharif University of Technology
    Abstract
    In this study, the Geocoat™ technology was used for the extraction of zinc from a mineral concentrate obtained from the Kooshk mine (Yazd, Iran) by a culture dominated by the mesophilic bacterium Acidithiobacillus ferrooxidans in a packed column bioreactor. A low grade sphalerite ore was used as support for the concentrate coating. During the 100 days of leaching pH, Fe3+, Fetotal, microbial population density and zinc extraction were measured. The final zinc extraction from concentrate and low grade support was 97% and 78%, respectively, and it was found that leaching from the support does not proceed significantly before leaching from the coating is completed  

    Solving MEC model of haplotype reconstruction using information fusion, single greedy and parallel clustering approaches

    , Article 6th IEEE/ACS International Conference on Computer Systems and Applications, AICCSA 2008, Doha, 31 March 2008 through 4 April 2008 ; 2008 , Pages 15-19 ; 9781424419685 (ISBN) Asgarian, E ; Moeinzadeh, M. H ; Sharifian-R, S ; Najafi-A, A ; Ramezani, A ; Habibi, J ; Mohammadzadeh, J ; Sharif University of Technology
    2008
    Abstract
    Haplotype information has become increasingly important in analyzing fine-scale molecular genetics data, Due to the mutated form in human genome; SNPs (Single Nucleotide Polymorphism) are responsible for some genetic diseases. As a consequence, obtaining all SNPs from human populations is one of the primary goals of studies in human genomics. In this paper, a data fusion method based on multiple parallel classifiers for reconstruction of haplotypes from a given sample Single Nucleotide Polymorphism (SNP) is proposed. First, we design a single greedy algorithm for solving haplotype reconstructions. [2] is used as an efficient approach to be combined with first classification method. The...