Search for: trade-offs
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    Time-cost-quality trade-off in project scheduling with linguistic variables

    , Article World Applied Sciences Journal ; Volume 18, Issue 3 , 2012 , Pages 404-413 ; 18184952 (ISSN) Shahsavari Pour, N ; Modarres, M ; Tavakkoli Moghaddam, R ; Sharif University of Technology
    Time, cost and quality are among the crucial aspects of each project. In recent years, the demands of project stakeholders regarding reductions in the total cost and time of a project along with achieving the acceptable quality of the project have risen significantly. This leads researchers to developing models that incorporate the quality factor to previously existing time cost trade-off models.We develop a model for discrete time-cost-quality trade-off problem. For each activity, an execution mode can be selected from a number of possible ones. The time and cost of each mode are assumed to be crisp but the quality of each mode is a linguistic variable. Therefore, in this paper, fuzzy logic... 

    The discrete time-cost-quality trade-off problem using a novel hybrid genetic algorithm

    , Article Applied Mathematical Sciences ; Volume 4, Issue 41-44 , 2010 , Pages 2081-2094 ; 1312885X (ISSN) Shahsavari Pour, N ; Modarres, M ; Aryanejad, M. B ; Tavakoli Moghadam, R ; Sharif University of Technology
    Time, cost and quality are among the major objectives of any project. In recent years, the demands of project stakeholders regarding reductions in the total cost and time of a project along with achieving the desirable quality of the project have risen significantly. This leads researchers to developing models that incorporate the quality factor to previously existing time-cost trade-off models. This study presents a model for the discrete time-cost-quality trade-off problem. In this model there are a number of execution modes to select for each activity, and the best execution mode (t, c, q) of the activities should be determined to optimize total cost and time objectives, subjected to... 

    A multi-objective invasive weeds optimization algorithm for solving multi-skill multi-mode resource constrained project scheduling problem

    , Article Computers and Chemical Engineering ; Volume 88 , 2016 , Pages 157-169 ; 00981354 (ISSN) Maghsoudlou, H ; Afshar Nadjafi, B ; Akhavan Niaki, S. T ; Sharif University of Technology
    Elsevier Ltd  2016
    A new multi-skill multi-mode resource constrained project scheduling problem with three objectives is studied in this paper. The objectives are: (1) minimizing project's makespan, (2) minimizing total cost of allocating workers to skills, and (3) maximizing total quality of processing activities. A meta-heuristic algorithm called multi-objective invasive weeds optimization algorithm (MOIWO) with a new chromosome structure guaranteeing feasibility of solutions is developed to solve the proposed problem. Two other meta-heuristic algorithms called non-dominated sorting genetic algorithm (NSGA-II) and multi-objective particle swarm optimization algorithm (MOPSO) are used to validate the... 

    Return code schemes for electronic voting systems

    , Article 2nd International Joint Conference on Electronic Voting, E-Vote-ID 2017, 24 October 2017 through 27 October 2017 ; Volume 10615 LNCS , 2017 , Pages 198-209 ; 03029743 (ISSN); 9783319686868 (ISBN) Khazaei, S ; Wikström, D ; Sharif University of Technology
    Springer Verlag  2017
    We describe several return code schemes for secure vote submission in electronic voting systems. We consider a unified treatment where a return code is generated as a multiparty computation of a secure MAC tag applied on an encrypted message submitted by a voter. Our proposals enjoy a great level of flexibility with respect to various usability, security, and performance tradeoffs. © 2017, Springer International Publishing AG  

    Rainbow table TMTO attack optimization considering online sequential search time

    , Article 2014 International Congress on Technology, Communication and Knowledge, ICTCK 2014, 26 November 2014 through 27 November 2014 ; 2015 ; 9781479980215 (ISBN) Hadi, M ; Jahromi, M. M ; Rezaiy, H. R ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2015
    In this paper, we propose an optimized parameter selection procedure for rainbow table Time Memory Trade-Off (TMTO) attack with sequential online search. Unlike previous works that mainly deal with minimizing required memory in the rainbow table TMTO attack we simultaneously focus on the required memory and online search time. Our parameter selection technique is optimized regarding the minimization of the required memory subject to a certain success probability and a maximum online search time. Obtained results are two compact mathematical expressions for determining rainbow table TMTO attack parameters, number and length of chains. The application of our optimized parameter selection... 

    A time-cost trade-off model by incorporating fuzzy earned value management: A statistical based approach

    , Article Journal of Intelligent and Fuzzy Systems ; Volume 28, Issue 4 , 2015 , Pages 1909-1919 ; 10641246 (ISSN) Salari, M ; Bagherpour, M ; Reihani, M. H ; Sharif University of Technology
    IOS Press  2015
    Time-cost trade-off problems (TCT) are well-known in project management contents. This approach normally applied for scheduling of a project especially where the project should be completed under pre-determined deadline. This paper aims to extend time-cost trade-off (TCT) problems in order to provide a well-organized mechanism for both scheduling and rescheduling processes of a project. The proposed mechanism includes project scheduling which concerns with the TCT problem, monitoring of project performance during execution phase using earned value management (EVM), and also predicting project future performance through statistical modeling. Once the predicted values of project performance... 

    Solving the discrete time/resource trade-off problem in project scheduling with genetic algorithms

    , Article Applied Mathematics and Computation ; Volume 191, Issue 2 , 2007 , Pages 451-456 ; 00963003 (ISSN) Ranjbar, M. R ; Kianfar, F ; Sharif University of Technology
    In this paper, we develop a metaheuristic procedure for solving the discrete time/resource trade-off problem in the field of project scheduling. In this problem, a project contains activities interrelated by finish-start-type precedence constraints with a time lag of zero, which require a single constrained renewable resource. Each activity has a specified work content and can be performed in different modes, i.e. with different durations and resource requirements; as long as the required work content is met. The objective is to schedule each activity in one of its modes in order to minimize the project makespan. To tackle this problem, we use a genetic algorithm in which a new method based... 

    Optimal reserve capacity allocation with consideration of customer reliability requirements

    , Article Energy ; Volume 35, Issue 9 , 2010 , Pages 3883-3890 ; 03605442 (ISSN) Najafi, M ; Ehsan, M ; Fotuhi Firuzabad, M ; Akhavein, A ; Afshar, K ; Sharif University of Technology
    An algorithm for determining optimal reserve capacity in a power market is presented in this paper. Optimization process in the proposed algorithm is based on the cost-benefit trade off. Market clearance is executed with consideration of uncertainties of power system components in an aggregated environment. It is assumed that both generating units and interruptible loads participate in the reserve market. In addition, customers' reliability requirements are considered as constraints for decision making process of ISO. The rendered method considers random outages of generating units and transmission lines and determined outage of interruptible loads and employs Monte Carlo Simulation (MCS)... 

    The Study of Firm Specific Determinants of Capital Structure: Evidence form Iranian Frims Listed on Tehran Stock Exchange

    , M.Sc. Thesis Sharif University of Technology Saeedi, Hesamoddin (Author) ; Zamani, Shiva (Supervisor)
    Since the seminal work of Modigliani and Miller, the basic question of whether a unique combination of debt and equity capital maximizes the firm value, and if so, what factors could influence a firm’s optimal capital structure have been the subject of frequent debate in the capital structure literature. Empirical work in this area has lagged behind the theoretical research, perhaps because the relevant firm attributes are expressed in terms of fairly abstract concepts that are not directly observable and furthermore capital structure decision-making is even more complicated when it is examined in an international context, particularly in developing countries where markets are characterized... 

    An Empirical Investigation of the link between Quantity and Quality in the Fertility Choice

    , M.Sc. Thesis Sharif University of Technology Fareghbal Khameneh, Mohammad Amin (Author) ; Vesal, Mohammad (Supervisor) ; Rahmati, Mohammad Hossein (Co-Advisor)
    Weexaminetherelationshipbetweenfamilysizeandchildreneducationaloutcomes. Using a 2 percent sample of Iran Populaion Census 2011, we construct a sample of school age children. Estimation using unrestricted OLS with controls shows an inverse-U relationship between family size and educational outcomes; children educational performance improves significantly as their number increases form 1 to 2, but for families with 3 or more children, increasing the number of childern deteriorates educational outcomes  

    Study of Energy and Compression-Ratio Tradeoff in Portable Sequencers

    , M.Sc. Thesis Sharif University of Technology Sojoodi, Hossein (Author) ; Goudarzi, Maziar (Supervisor)
    Recently, portable genome sequencing devices have been introduced to the market, which have also made it possible to provide these services in remote locations or outside the laboratory. The amount of raw data from the readings of a sequencer for the entire genome of a human or plant can be in the hundreds of gigabytes, making it difficult and expensive to maintain and transfer to the center for such sequencing. Fortunately, these readings have a lot of redundancy, and many new algorithms have been proposed to compress them based on the intrinsic properties of this data. Sequencing devices were mainly used in the laboratory environment, which naturally had virtually unlimited access to urban... 

    Channel simulation via interactive communications

    , Article IEEE International Symposium on Information Theory - Proceedings ; 2012 , Pages 3053-3057 ; 9781467325790 (ISBN) Yassaee, M. H ; Gohari, A ; Aref, M. R ; Sharif University of Technology
    IEEE  2012
    In this paper, we study the problem of channel simulation via interactive communication, known as the coordination capacity, in a two-terminal network. We assume that two terminals observe i.i.d. copies of two random variables and would like to generate i.i.d. copies of two other random variables jointly distributed with the observed random variables. The terminals are provided with two-way communication links, and shared common randomness, all at limited rates. Two special cases of this problem are the interactive function computation studied by Ma and Ishwar, and the tradeoff curve between one-way communication and shared randomness studied by Cuff. The latter work had inspired Gohari and... 

    On quota violations of OPEC members

    , Article Energy Economics ; Volume 68 , 2017 , Pages 410-422 ; 01409883 (ISSN) Ghoddusi, H ; Nili, M ; Rastad, M ; Sharif University of Technology
    Over the last decades quota violations have become a norm for OPEC countries. However, the academic literature on OPEC focuses more on its production behavior than on analyzing the quota allocation process or characterizing quota violation patterns. This paper offers a theoretical model with empirical evidence to explain OPEC members’ incentives for abiding or violating quotas. We first offer a cartel model with a quota allocation rule and an endogenous capacity choice. The model highlights the trade-off between building spare capacity to bargain for a higher legitimate quota versus risking quota violation punishment. Using the quarterly data from 1995 to 2007, we empirically support the... 

    Playing games with bounded entropy

    , Article IEEE International Symposium on Information Theory - Proceedings, 25 June 2017 through 30 June 2017 ; 2017 , Pages 1460-1464 ; 21578095 (ISSN) ; 9781509040964 (ISBN) Valizadeh, M ; Gohari, A ; Sharif University of Technology
    We study a two-player zero-sum game in which one of the players is restricted to mixed strategies with limited randomness. More precisely, we consider the maximum payoff that the maximizer (Alice) can secure with limited randomness h. This problem finds an operational interpretation in the context of repeated games with non-ideal sources of randomness. The computational aspects of this problem has not received much attention in the game theory literature. We begin by observing the equivalence of this problem with entropy minimization problems in other scientific contexts. Next, we provide two explicit lower bounds on the entropy-payoff tradeoff curve. To do this, we provide and utilize new... 

    Fundamental limit for gain and resolution in analog optical edge detection

    , Article Optics Express ; Volume 28, Issue 2 , 2020 , Pages 898-911 Karimi, P ; Khavasi, A ; Mousavi Khaleghi , S. S ; Sharif University of Technology
    OSA - The Optical Society  2020
    In this paper, the relation between gain and resolution of an ideal analog optical differentiator in two different cases and their fundamental limits are investigated. Based on this relation, a figure of merit for comparison of the designed differentiators in recent papers is proposed. The differentiators are optimized using this figure of merit, and they are compared with each other to determine the best one. Also, a new differentiator is presented based on the dielectric slab waveguide in which the trade-off between its gain and resolution is easily controllable, and its best operating point is determined. © 2020 Optical Society of America under the terms of the OSA Open Access Publishing... 

    Optimum transmission delay for function computation in NFV-based networks: the role of network coding and redundant computing

    , Article IEEE Journal on Selected Areas in Communications ; 2018 ; 07338716 (ISSN) Tahmasebi, B ; Maddah Ali, M. A ; Parsaeefard, S ; Hossein Khalaj, B ; Sharif University of Technology
    In this paper, we study the problem of delay minimization in NFV-based networks. In such systems, the ultimate goal of any request is to compute a sequence of functions in the network, where each function can be computed at only a specific subset of network nodes. In conventional approaches, for each function, we choose one node from the corresponding subset of the nodes to compute that function. In contrast, in this work, we allow each function to be computed in more than one node, redundantly in parallel, to respond to a given request. We argue that such redundancy in computation not only improves the reliability of the network, but would also, perhaps surprisingly, reduce the overall... 

    Improvement of Communication Cost and Waiting Time Trade off in Content Delivery Networks

    , M.Sc. Thesis Sharif University of Technology Ghasemi Rahni, Hamid (Author) ; Jafari Siavoshani, Mahdi (Supervisor)
    By increasing the use of Internet and sharing information in this platform, servers are equipped with more robust hardware and a wider bandwidth network. But the growth of data and services is such that a server, no matter how powerful, does not have the ability to respond all users! Several servers are used to solve this problem. Data centers, content delivery networks, and so on are emerged depending on types of service. One of the important issues in these systems is how to distribute loads between servers in a proportional manner. In this thesis, we first examine the relationship between cost and response time on user requests. Cost can be considered as a communication cost or financial... 

    Project Portfolio Selection Under Uncertainty by Fuzzy and Robust Optimization Methods

    , M.Sc. Thesis Sharif University of Technology Ajam, Meraj (Author) ; Kianfar, Farhad (Supervisor)
    In this thesis, project portfolio selection under uncertainty conditions is considered. Firstly, the problem is modeled with mathematical programming and also this problem has two objective functions that contain maximizing profitability and minimizing surplus resources. Each project has resource costs and contract prices. In addition, uncertainties for these parameters should be considered. Secondly, another innovation in this research is considering Cost/Time trade-off for duration and cost. To satisfy this subject, each project has different scenarios with various duration and usage of resources. Since the project has two objective functions, ε-constraint method is applied to optimizing... 

    An Augmented Weighted Tchebycheff Approach for Solving a Multi-Objective Model for Supplier Selection and Oorder Allocation under Volume Discount
    (Case study: Supplier selection and order allocation in a drilling company)

    , M.Sc. Thesis Sharif University of Technology Chitgar, Sahar (Author) ; Mahdavi-Amiri, Nezam (Supervisor)
    In order to achieve a compromised solution for a multi-objective problem, we make use of the Tchebycheff norm to minimize the distance from the current estimate of the objectives from the ideal point. Solutions obtained from the Tchebycheff approach are weakly efficient for multi-objective problems. For a better solution, the augmented weighted Tchebycheff norm has been proposed. Here, we use the satisficing tradeoff algorithm to solve the augmented weighted Tchebycheff problems. Since the supplier selection problem is usually a multi objective problem, we use the augmented weighted Tchebycheff method for obtaining its solutions. Numerical results are presented illustrating the performance... 

    A Solution to Exploration/Exploitation Trade-off in Recommender Systems

    , M.Sc. Thesis Sharif University of Technology Feyzabadi Sani, Mohammad Javad (Author) ; Rabiee, Hamid Reza (Supervisor) ; Hosseini, Abbas (Supervisor)
    The growing use of the Internet has led to the creation of new businesses around it. Traditional businesses have to use the Internet in order to maintain their competitive conditions. One of the most important strategies for developing sales on the Internet is the proper use of recommendation systems.With the advent of businesses in cyberspace, the way has been paved for the use of recommendation systems in this space.Recommendation systems should exploit their knowledge about users’ preferences and explore their new preferences simultaneously. Establish a balance between exploring users’ new interests and exploiting known interests is key to build a good recommendation system. Existing data...