Search for: hierarchical-structures
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    Robust optimal control for large-scale systems with state delay

    , Article Transactions of the Institute of Measurement and Control ; Vol. 36, Issue. 4 , June , 2014 , pp. 551-558 ; ISSN: 01423312 Rahmani, M ; Sadati, N ; Sharif University of Technology
    Optimal control of large-scale uncertain dynamic systems with time delays in states is considered in this paper. For this purpose, a two-level strategy is proposed to decompose the large-scale system into several interconnected subsystems at the first level. Then optimal control inputs are obtained by minimization of convex performance indices in presence of uncertainties, in the form of states and interactions feedback. The solution is achieved by bounded data uncertainty problems, where the uncertainties are only needed to be bounded and it is not required to satisfy the so-called 'matching conditions'. At the second level, a simple substitution-type interaction prediction method is used... 

    A bio-inspired modular hierarchical structure to plan the sit-to-stand transfer under varying environmental conditions

    , Article Neurocomputing ; Volume 118 , 2013 , Pages 311-321 ; 09252312 (ISSN) Sadeghi, M ; Emadi Andani, M ; Parnianpour, M ; Fattah, A ; Sharif University of Technology
    Human motion planning studies are of considerable importance in producing human-like trajectories for various industrial or clinical applications (e.g. assistive robots). In this case, the capability of Central Nervous System (CNS) in generating a large repertoire of actions can be inspirational to develop more efficient motion planning approaches. Here, inspired by structural and functional modularity in the CNS, a novel modular and hierarchical model is developed to plan the sit-to-stand (STS) transfer under varying environmental conditions. In this model, the planning process is distributed among several functionally simple modules. The cooperation of modules enables the model to plan the... 

    Two-level optimal load-frequency control for multi-area power systems

    , Article International Journal of Electrical Power and Energy Systems ; Volume 53, Issue 1 , December , 2013 , Pages 540-547 ; 01420615 (ISSN) Rahmani, M ; Sadati, N ; Sharif University of Technology
    In large-scale power systems, classical centralized control approaches may fail due to geographically distribution of information and decentralized controllers result in sub-optimal solution for load-frequency control (LFC) problems. In this paper, a two-level structure is presented to obtain optimal solution for LFC problems and also reduce the computational complexity of centralized controllers. In this approach, an interconnected multi-area power system is decomposed into several sub-systems (areas) at the first-level. Then an optimization problem in each area is solved separately, with respect to its local information and interaction signals coming from other areas. At the second-level,... 

    Mining distributed frequent itemsets using a gossip based protocol

    , Article Proceedings - IEEE 9th International Conference on Ubiquitous Intelligence and Computing and IEEE 9th International Conference on Autonomic and Trusted Computing, UIC-ATC 2012 ; 2012 , Pages 780-785 Bagheri, M ; Mirian Hosseinabadi, S. H ; Mashayekhi, H ; Habibi, J ; Sharif University of Technology
    Recently, there has been a growing attention in frequent itemset mining in distributed systems. In this paper, we present an algorithm to extract frequent itemsets from large distributed datasets. Our algorithm uses gossip as the communication mechanism and does not rely on any central node. In gossip based communication, nodes repeatedly select other random nodes in the system, and exchange information with them. Our algorithm proceeds in rounds and provides all nodes with the required support counts of itemsets, such that each node is able to extract the global frequent itemsets. For local iteration and generation of candidate itemsets, a trie data structure is used, which facilitates the... 

    A mixture of modular structures to describe human motor planning level: A new perspective based on motor decomposition

    , Article 2011 18th Iranian Conference of Biomedical Engineering, ICBME 2011 ; 2011 , Pages 199-204 ; 9781467310055 (ISBN) Sadeghi, M ; Andani, M. E ; Fattah, A ; Parnianpour, M ; Sharif University of Technology
    A modular hierarchical structure is developed to describe human movement planning level. The modular feature of the proposed model enables it to generalize planning a task. The movements are planned based on decomposing a task into its corresponding subtasks (motion phases). There is a module responsible for one condition. The final plan is constructed using soft computing of the plans proposed by different modules. Each module estimates the kinematics of the joints at the end of each subtask; we call them kinematic estimator modules (KEMs). A timing module estimates the duration of motion and a gating module determines the responsibility of each KEM under different conditions. To evaluate... 

    Development of a new analytical tool to design hierarchical truss beams for natural frequency

    , Article Journal of Mechanical Science and Technology ; Volume 25, Issue 10 , October , 2011 , Pages 2495-2503 ; 1738494X (ISSN) Fazli, N ; Malaek, S. M. B ; Abedian, A ; Teimouri, H ; Sharif University of Technology
    A set of recursive equations are introduced for optimum design of a wide range of hierarchical truss beams to satisfy a minimum required natural frequency. The design equations are based on a general analytical solution, which are derived based on a critical dimensional analysis. A practical example is examined in both 2D and 3D spaces, which promises substantial mass reduction, as much as 99%, when using high order hierarchical truss beams. The results are verified by numerical evaluation of three case studies. The approach looks also very promising to design nanostructures when it comes to the problems associated with vibration  

    Two-level robust optimal control of large-scale nonlinear systems

    , Article IEEE Systems Journal ; Volume 9, Issue 1 , 2015 , Pages 242-251 ; 19328184 (ISSN) Sadati, N ; Rahmani, M ; Saif, M ; Sharif University of Technology
    Finding an optimal control strategy for a nonlinear uncertain system is a challenging problem in the area of nonlinear controller design. In this paper, a two-level control algorithm is developed for robust optimal control of large-scale nonlinear systems. For this purpose, using a decomposition/coordination framework, the large-scale nonlinear system is first decomposed into several smaller subsystems, at the first level, where a closed-form solution as a feedback of states and interactions is obtained to optimize each subsystem. At the second level, a substitution-type prediction method, as a coordination strategy, is used to compensate the nonlinear terms of the system and to predict the... 

    Towards a knowledge based approach to style driven architecture design

    , Article Procedia Computer Science, 5 March 2015 through 6 March 2015 ; Volume 62 , 2015 , Pages 236-244 ; 18770509 (ISSN) Moaven, S ; Habibi, J ; Alidoosti, R ; Parvizi Mosaed, A ; Bahrami, M ; Sharif University of Technology
    Nowadays, knowledge is the key to success in all software engineering processes. This valuable knowledge, obtained through analysis, design, development, and maintenance processes of the system, should be saved and reused in designing and developing current and similar systems. Using pre-existing knowledge is a practical approach which reduces design complexity, improves software architecture design and manages software quality. In this paper, we describe an approach to create architecture design knowledge using a hierarchical structure of architectural styles based on quality attributes. Knowledge is most importance asset of our approach that reuses similar domains, correlates architectures... 

    Designing a collaborative digital library to improve educational systems accompanied by a perspective from Iranian scholar attitudes

    , Article International Conference on Enterprise Information Systems and Web Technologies 2010, EISWT 2010, 12 July 2010 through 14 July 2010 ; 2010 , Pages 132-140 ; 9781617820656 (ISBN) Badashian, A. S ; Firouz Abadi, A. D ; Khalkhali, I ; Shafiei, M. S ; Vojdanijahromi, R ; Sharif University of Technology
    In this article, a universal collaborative and competitive approach is introduced for deployment of digital collections in an ideal Digital Library for future's educational system. A hierarchical structure is proposed to be used for browsing and searching within mass of digital contents provided for union of curriculums worldwide. The collaborative and open-source aspects of the system guarantee the growth of the Digital Library. On the other hand, the competitive and reviewing aspects guarantee the accuracy of the novel library contents. Two experiments confirm the need for such a universal Digital Library worldwide to enhance learning capabilities, increase accessibility, avoid redundancy... 

    FTS: An efficient tree structure based tool for searching in large data sets

    , Article ICIME 2010 - 2010 2nd IEEE International Conference on Information Management and Engineering, 16 April 2010 through 18 April 2010 ; Volume 2 , April , 2010 , Pages 294-298 ; 9781424452644 (ISBN) Saejdi Badashian, A ; Najafpour, M ; Mahdavi, M ; Ashurzad Delcheh, M ; Khalkhali, I ; Sharif University of Technology
    This paper addresses the issue of finding and accessing desired items when a large amount of data items are concerned, by proposing some concepts based on Tree Search Structure -a hierarchical structure for information retrieval. The proposed concepts are applicable to several environments such as File Managers on PCs, help tree views, site maps, taxonomies, and cell phones. A software tool, FTS (File Tree Search), that is developed to utilize the proposed concepts is also presented  

    Micromechanics and constitutive modeling of connective soft tissues

    , Article Journal of the Mechanical Behavior of Biomedical Materials ; Volume 60 , 2016 , Pages 157-176 ; 17516161 (ISSN) Fallah, A ; Ahmadian, M. T ; Firozbakhsh, K ; Aghdam, M. M ; Sharif University of Technology
    Elsevier Ltd 
    In this paper, a micromechanical model for connective soft tissues based on the available histological evidences is developed. The proposed model constituents i.e. collagen fibers and ground matrix are considered as hyperelastic materials. The matrix material is assumed to be isotropic Neo-Hookean while the collagen fibers are considered to be transversely isotropic hyperelastic. In order to take into account the effects of tissue structure in lower scales on the macroscopic behavior of tissue, a strain energy density function (SEDF) is developed for collagen fibers based on tissue hierarchical structure. Macroscopic response and properties of tissue are obtained using the numerical... 

    A road map for knowledge management systems design using axiomatic design approach

    , Article MATEC Web of Conferences, 13 September 2017 through 15 September 2017 ; Volume 127 , 2017 ; 2261236X (ISSN) Houshmand, M ; Amani, M ; Slatineanu, L ; Sharif University of Technology
    Successful design and implementation of knowledge management systems have been the main concern of many researchers. It has been reported that more than 50% of knowledge management systems have failed, therefore, it is required to seek for a new and comprehensive scientific approach to design and implement it. In the design and implementation of a knowledge management system, it is required to know 'what we want to achieve' and 'how and by what processes we will achieve it'. A literature review conducted and axiomatic design theory selected for this purpose. For the first time, this paper develops a conceptual design of knowledge management systems by means of a hierarchical structure,... 

    State of the art review on design and manufacture of hybrid biomedical materials: Hip and knee prostheses

    , Article Proceedings of the Institution of Mechanical Engineers, Part H: Journal of Engineering in Medicine ; Volume 231, Issue 9 , 2017 , Pages 785-813 ; 09544119 (ISSN) Bahraminasab, M ; Farahmand, F ; Sharif University of Technology
    The trend in biomaterials development has now headed for tailoring the properties and making hybrid materials to achieve the optimal performance metrics in a product. Modern manufacturing processes along with advanced computational techniques enable systematical fabrication of new biomaterials by design strategy. Functionally graded materials as a recent group of hybrid materials have found numerous applications in biomedical area, particularly for making orthopedic prostheses. This article, therefore, seeks to address the following research questions: (RQ1) What is the desired structure of orthopedic hybrid materials? (RQ2) What is the contribution of the literature in the development of... 

    Enforcing access control policies over data stored on untrusted server

    , Article 2017 14th International ISC (Iranian Society of Cryptology) Conference on Information Security and Cryptology, ISCISC 2017, 6 September 2017 through 7 September 2017 ; 2018 , Pages 54-57 ; 9781538665602 (ISBN) Soltani, N ; Jalili, R ; Sharif University of Technology
    One of the security issues in data outsourcing scenario is the enforcement of data owner's access control policies. This includes some challenges; namely, the number of keys required to access authorized resources, efficient policy updating, write access control enforcement, user and data owner overhead, and preserving confidentiality of data and policies. Most of the existing solutions address only some of the challenges, while they impose high overhead on both the data owner and users. Though, policy management in the Role-Based Access Control (RBAC) model is easier and more efficient due to the existence of role hierarchical structure and role inheritance; most of the existing solutions... 

    Swing up and arm trajectory tracking of the furuta pendulum with sliding mode control

    , Article 5th RSI International Conference on Robotics and Mechatronics, IcRoM 2017, 25 October 2017 through 27 October 2017 ; 2018 , Pages 346-351 ; 9781538657034 (ISBN) Karamin Manesh, M. J ; Nikzad Goltapeh, A ; Sharif University of Technology
    In this paper, the swing-up problem of the Furuta pendulum has been solved by introducing a new combined method based on the frequency response, and the sliding mode method. Furthermore, a trajectory tracking controller has been introduced and applied to the Furuta pendulum; which the pendulum remained regulated at the upward position, while the arm tracks a desired time-varying trajectory. The hierarchical sliding mode control (HSMC) approach has been employed to achieve the mentioned goals. The Furuta system is made up of two subsystems. Based on this physical structure, the hierarchical structure of the sliding surfaces is designed as follows: first, the sliding surface of each subsystem... 

    A graph-theoretic approach toward autonomous skill acquisition in reinforcement learning

    , Article Evolving Systems ; Volume 9, Issue 3 , 2018 , Pages 227-244 ; 18686478 (ISSN) Kazemitabar, S. J ; Taghizadeh, N ; Beigy, H ; Sharif University of Technology
    Springer Verlag  2018
    Hierarchical reinforcement learning facilitates learning in large and complex domains by exploiting subtasks and creating hierarchical structures using these subtasks. Subtasks are usually defined through finding subgoals of the problem. Providing mechanisms for autonomous subgoal discovery and skill acquisition is a challenging issue in reinforcement learning. Among the proposed algorithms, a few of them are successful both in performance and also efficiency in terms of the running time of the algorithm. In this paper, we study four methods for subgoal discovery which are based on graph partitioning. The idea behind the methods proposed in this paper is that if we partition the transition... 

    A lightweight hierarchical authentication scheme for internet of things

    , Article Journal of Ambient Intelligence and Humanized Computing ; 2018 , Pages 1-13 ; 18685137 (ISSN) Akbarzadeh, A ; Bayat, M ; Zahednejad, B ; Payandeh, A ; Aref, M. R ; Sharif University of Technology
    Springer Verlag  2018
    The Internet of Things (IoT) technology enables numerous things with different processing power and storage capacity to communicate and share data with each other. Considering the constrained devices of the IoT network in terms of processing and storage, designing a lightweight authentication scheme is quite important. So in this paper, we propose a lightweight authentication scheme based on Chebyshev Chaotic Maps. In the proposed scheme we apply a hierarchical structure to define different access controls for various entities. We then provide a formal analysis via the BAN logic to show the security of our scheme. Moreover, we compare our proposed scheme with previous ones in terms of... 

    Automatic discovery of subgoals in reinforcement learning using strongly connected components

    , Article 15th International Conference on Neuro-Information Processing, ICONIP 2008, Auckland, 25 November 2008 through 28 November 2008 ; Volume 5506 LNCS, Issue PART 1 , 2009 , Pages 829-834 ; 03029743 (ISSN); 3642024890 (ISBN); 9783642024894 (ISBN) Kazemitabar, J ; Beigy, H ; Asia Pacific Neural Network Assembly (APNNA); International Neural Network Society (INNS); IEEE Computational Intelligence Society; Japanese Neural Network Society (JNNS); European Neural Network Society (ENNS) ; Sharif University of Technology
    The hierarchical structure of real-world problems has resulted in a focus on hierarchical frameworks in the reinforcement learning paradigm. Preparing mechanisms for automatic discovery of macro-actions has mainly concentrated on subgoal discovery methods. Among the proposed algorithms, those based on graph partitioning have achieved precise results. However, few methods have been shown to be successful both in performance and also efficiency in terms of time complexity of the algorithm. In this paper, we present a SCC-based subgoal discovery algorithm; a graph theoretic approach for automatic detection of subgoals in linear time. Meanwhile a parameter tuning method is proposed to find the... 

    Autonomous unmanned helicopter landing system design for safe touchdown on 6DOF moving platform

    , Article 5th International Conference on Autonomic and Autonomous Systems, ICAS 2009, Valencia, 20 April 2009 through 25 April 2009 ; 2009 , Pages 245-250 ; 9780769535845 (ISBN) Esmailifar, S. M ; Saghafi, F ; Sharif University of Technology
    In this research, an adaptive control system is designed for a safe touchdown of an unmanned helicopter during its landing phase on a 6DOF moving platform. In this paper the landing phase is divided into the approach and touchdown stages. In the first stage, the helicopter tries to attenuate the initial position and direction errors and in the next stage, the platform's attitude is tracked for a safe touchdown. The hierarchical structure of the proposed control system includes supervisory and tracking levels. The supervisory level recognizes the landing stage and the tracking level controls and compensates the errors based on SDRE (State Dependent Riccati Equation) method. The robustness and... 

    Three-dimensional bioprinting of functional skeletal muscle tissue using gelatin methacryloyl-alginate bioinks

    , Article Micromachines ; Volume 10, Issue 10 , 2019 ; 2072666X (ISSN) Seyedmahmoud, R ; Çelebi Saltik, B ; Barros, N ; Nasiri, R ; Banton, E ; Shamloo, A ; Ashammakhi, N ; Dokmeci, M. R ; Ahadian, S ; Sharif University of Technology
    MDPI AG  2019
    Skeletal muscle tissue engineering aims to fabricate tissue constructs to replace or restore diseased or injured skeletal muscle tissues in the body. Several biomaterials and microscale technologies have been used in muscle tissue engineering. However, it is still challenging to mimic the function and structure of the native muscle tissues. Three-dimensional (3D) bioprinting is a powerful tool to mimic the hierarchical structure of native tissues. Here, 3D bioprinting was used to fabricate tissue constructs using gelatin methacryloyl (GelMA)-alginate bioinks. Mechanical and rheological properties of GelMA-alginate hydrogels were characterized. C2C12 myoblasts at the density 8 × 106 cells/mL...