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    Deformation and stability of surface states in Dirac semimetals

    , Article Physical Review B ; Volume 97, Issue 16 , April , 2018 , Article number 165129 ; 24699950 (ISSN) Kargarian, M ; Lu, Y. M ; Randeria, M ; Sharif University of technology
    American Physical Society  2018
    The unusual surface states of topological semimetals have attracted a lot of attention. Recently, we showed [Proc. Natl. Acad. Sci. USA 113, 8648 (2016)PNASA60027-842410.1073/pnas.1524787113] that for a Dirac semimetal (DSM) arising from band inversion, such as Na3Bi and Cd3As2, the expected double Fermi arcs on the surface are not topologically protected. Quite generally, the arcs deform into states similar to those on the surface of a strong topological insulator. Here we address two questions related to deformation and stability of surface states in DSMs. First, we discuss why certain perturbations, no matter how large, are unable to destroy the double Fermi arcs. We show that this is... 

    Full characterization of a spin liquid phase: From topological entropy to robustness and braid statistics

    , Article Journal of Physics A: Mathematical and Theoretical ; Volume 50, Issue 14 , 2017 ; 17518113 (ISSN) Jahromi, S. S ; Langari, A ; Sharif University of Technology
    Institute of Physics Publishing  2017
    We use the topological entanglement entropy (TEE) as an efficient tool to fully characterize the Abelian phase of a Z2 ×Z2 spin liquid emerging as the ground state of topological color code (TCC), which is a class of stabilizer states on the honeycomb lattice. We provide the fusion rules of the quasiparticle (QP) excitations of the model by introducing single- or two-body operators on physical spins for each fusion process which justify the corresponding fusion outcome. Besides this, we extract the TEE from Renyi entanglement entropy (EE) of the TCC, analytically and numerically by finite size exact diagonalization on the disk shape regions with contractible boundaries. We obtain that the EE... 

    XMulator: A listener-based integrated simulation platform for interconnection networks

    , Article 1st Asia International Conference on Modelling and Simulation - Asia Modelling Symposium 2007, AMS 2007, 27 March 2007 through 30 March 2007 ; 2007 , Pages 128-132 ; 0769528457 (ISBN); 9780769528458 (ISBN) Nayebi, A ; Meraji, S ; Shamaei, A ; Sarbazi Azad, H ; Al Dabass D ; Zobel R ; Abraham A ; Turner S ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2007
    Simulation is perhaps the most cost-effective tool to evaluate the operation of a system under design. A flexible, easy to extend, fully object-oriented, and multilayered simulator for interconnection networks can be a very useful tool for multicomputer designers and researchers. It is so desirable to attach newly designed components to the existing models and to exploit detailed results. This paper presents XMulator, an object-oriented listener-based simulation environment for evaluating multicomputer interconnection networks. The simulator involves a toolbox of various network topologies, routing algorithms, switching techniques, and flexible router models. This work introduces a... 

    On topological polynomials of weighted graphs

    , Article Studia Universitatis Babes-Bolyai Chemia ; Issue 4 , December , 2012 , Pages 65-71 ; 12247154 (ISSN) Ghorbani, M ; Hosseinzadeh, M. A ; Diudea, M. V ; Sharif University of Technology
    Two edges e and f of a plane graph G are in relation opposite, e op f, if they are opposite edges of an inner face of G. Relation op enables the partition the edge set of G into opposite edge strips ops. On this ground, Diudea defined Omega and Theta polynomial while Ashrafi et al. defined the Sadhana polynomial. In this paper a weighted version of these polynomials was introduced and several relations between them are demonstrated. Some molecular weights are suggested in view of using the derived topological indices in correlational studies  

    A note of Zagreb indices of nanostar dendrimers

    , Article Optoelectronics and Advanced Materials, Rapid Communications ; Volume 4, Issue 11 , April , 2010 , Pages 1877-1880 ; 18426573 (ISSN) Ghorbani, M ; Hosseinzadeh, M. A ; Sharif University of Technology
    The Zagreb indices have been introduced more than thirty years ago by Gutman and Trinajstić. In this paper we introduce a new version of Zagreb indices and then we compute them for an infinite family of nanostar dendrimers  

    On wiener index of special case of link of fullerenes

    , Article Optoelectronics and Advanced Materials, Rapid Communications ; Volume 4, Issue 4 , 2010 , Pages 538-539 ; 18426573 (ISSN) Ghorbani, M ; Hosseinzadeh, M. A ; Sharif University of Technology
    Let ∑ be the class of finite graphs. A topological index is a function Top from ∑ into real numbers with this property that Top(G) = Top(H), if G and H are isomorphic. is defined as half sum of the distances between all the pairs of vertices in a molecular graph. The goal of this paper is to further the study of Wiener index of special case of a chain of fullerenes  

    Topology specialization for networks-on-chip in the dark silicon era

    , Article Advances in Computers ; Volume 110 , 2018 , Pages 217-258 ; 00652458 (ISSN); 9780128153581 (ISBN) Modarressi, M ; Sarbazi Azad, H ; Sharif University of Technology
    Academic Press Inc  2018
    Following Moore's law, the number of transistors on chip has grown exponentially for decades. This growing transistor count, coupled with recent architecture and compiler advances, has resulted in an unprecedented exponential performance increase of computers. With the end of Dennard scaling, however, the power required to operate all transistors at the full performance level simultaneously grows across the technology generations. Consequently, chips will keep an increasing fraction of transistors power gated or dark to remain within the power envelope. The power-gated part of the chip, known as dark silicon, is expected to comprise a significant portion of the die real estate in new... 

    Quantum 2-body hamiltonian for topological color codes

    , Article Fortschritte der Physik ; Volume 57, Issue 11-12 , 2009 , Pages 1103-1110 ; 00158208 (ISSN) Bombin, H ; Kargarian, M ; Martin Delgado, M. A ; Sharif University of Technology
    We introduce a two-body quantum Hamiltonian model with spins1/2 located on the vertices of a 2D spatial lattice. The model exhibits an exact topological degeneracy in all coupling regimes. This is a remarkable non-perturbative effect. The model has a Z2 ×Z2 gauge group symmetry and string-net integrals of motion. There exists a gapped phase in which the low-energy sector reproduces an effective topological color code model. High energy excitations fall into three families of anyonic fermions that turn out to be strongly interacting. All these, and more, are new features not present in honeycomb lattice models like Kitaev model. © 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim  

    Effects of Spin- Orbit Coupling on the Phase Diagram of Doped Mott Insulator

    , M.Sc. Thesis Sharif University of Technology Kheirkhah, Majid (Author) ; Vaezi, Abolhassan (Supervisor) ; Ejtehadi, Mohammad Reza (Supervisor)
    In the past few years, topological insulators (TIs), topological superconductors and their experimental observation have been in the center of condensed maer physicists’ aention. Kane and Mele proposed the simplest and the first model exhibiting TI phase for non-interacting electrons on the two dimensional honeycomb laice. On the other hand, in the Hubbard model for nonzero doping and near the half filling, the high temperature superconductivity is predicted theoretically. In this thesis, we fist investigate the interacting topological insulators by adding the Hubbard interaction to the Kane-Mele model. en, in the strong correlation limit we find an effective spin model -the so called... 

    Investigation of a Transition from Topologically Ordered Phase to Ferromagnetic Phase

    , M.Sc. Thesis Sharif University of Technology Zarkeshian, Parisa (Author) ; Karimipour, Vahid (Supervisor) ; Memarzadeh Esfahani, Laleh (Supervisor)
    Topologically ordered phases are of great interest in the field of quantum information and quantum computation in order that their degenerate ground states provide a suitable space for coding and processing the quantum information. Such space is resistant to local errors intrinsically. A natural question to ask is to what degree these topological phases are resilient against perturbations and how the transition from topological order to another kind of order occurs.In this thesis, at first we introduce the concept of topological order. We explain the Kitaev model, which is the first introduced topological model on lattice, and study the common properties between topologically ordered systems... 

    A novel high-performance and low-power mesh-based NoC

    , Article IPDPS 2008 - 22nd IEEE International Parallel and Distributed Processing Symposium, Miami, FL, 14 April 2008 through 18 April 2008 ; 2008 ; 9781424416943 (ISBN) Sabbaghi Nadooshan, R ; Modarressi, M ; Sarbazi Azad, H ; Sharif University of Technology
    In this paper, a 2D shuffle-exchange based mesh topology, or 2D SEM (Shuffle-exchange Mesh) for short, is presented for network-on-chips. The proposed two-dimensional topology applies the conventional well-known shuffle-exchange structure in each row and each column of the network. Compared to an equal sized mesh which is the most common topology in on-chip networks, the proposed shuffle-exchange based mesh network has smaller diameter but for an equal cost. Simulation results show that the 2D SEM effectively reduces the power consumption and improves performance metrics of the on-chip networks with regard to the conventional mesh topology. ©2008 IEEE  

    Automatic optimal feeder design in steel casting process

    , Article Computer Methods in Applied Mechanics and Engineering ; Volume 197, Issue 9-12 , 2008 , Pages 921-932 ; 00457825 (ISSN) Tavakoli, R ; Davami, P ; Sharif University of Technology
    A method for automatic optimal feeder design in steel casting processes is presented. The initial design is the casting part (without feeders) which is placed in a suitable mold box. Design of each feeder contains the following steps: determination of the feeder-neck connection point on the casting surface, initial feeder design, feeder shape optimization and feeder topology optimization. Completing designing the first feeder, the method attends to designing the next one, if it is required, and the same procedure will be repeated. In the presented method, feeders are designed in a descending order of their sizes. The feasibility of the presented method is supported with an illustrative... 

    Optimal feeder design in sand casting process by growth method

    , Article International Journal of Cast Metals Research ; Volume 20, Issue 5 , 2007 , Pages 288-296 ; 13640461 (ISSN) Tavakoli, R ; Davami, P ; Sharif University of Technology
    The computer aided optimal feeder design in the sand casting process is considered. The design problem is formulated as an additive evolutionary topology optimisation problem. The initial design of the presented method is a casting part which is placed in a suitable environmental mould box. The method is composed of three stages: determination of the feeder neck connection point, construction of the feeder neck and the feeder growth. During the growth stage, the feeder topology is improved gradually until satisfying some predefined criteria. The technological constraints and user contribution can be easily incorporated in the presented method. The success of the proposed method is supported... 

    Performance evaluation of fully adaptive routing under different workloads and constant node buffer size

    , Article 11th International Conference on Parallel and Distributed Systems Workshops, ICPADS 2005, Fukuoka, 20 July 2005 through 22 July 2005 ; Volume 2 , 2005 , Pages 510-514 ; 15219097 (ISSN); 0769522815 (ISBN) Rezazad, M ; Sarbazi Azad, H ; Ma J ; Yang L. T ; Sharif University of Technology
    In this paper, the performance of some popular direct interconnection networks, namely the mesh, torus and hypercube, are studied with adaptive wormhole routing for different traffic patterns. We investigate the effect of the number of virtual channels and depth of their buffers on the performance of such strictly orthogonal topologies under uniform, hot-spot and matrix-transpose traffic patterns for generated messages, while the total buffer size associated to each physical channel is kept constant. In addition we analyze the effect of escape channel buffer length on the performance of a fully adaptive routing algorithm. It is shown that the optimal number of virtual channels and buffer... 

    Flocking algorithms in networks with directed switching velocity interaction topologies

    , Article Asian Journal of Control ; Vol. 16, issue. 4 , July , 2014 , p. 1141-1154 Atrianfar, H ; Haeri, M ; Sharif University of Technology
    This paper studies flocking algorithms for multi-agent systems with directed switching velocity interaction topologies. It is assumed that the position information of each agent is available for agents within its neighborhood region of radius r, however, they communicate the velocity information between each other through unidirectional links modeled by a particular class of directed topologies. A new energy function is defined to analyze the global stability and a sufficient condition is derived for asymptotic flocking in the face of switching topologies. The proposed control strategy guarantees the achievement of desired formations, while avoiding collisions among agents. It also ensures... 

    A novel consensus protocol using facility location algorithms

    , Article Proceedings of the IEEE International Conference on Control Applications, 8 July 2009 through 10 July 2009, Saint Petersburg ; 2009 , Pages 914-919 ; 9781424446025 (ISBN) Doostmohammadian, M. R ; Sayyaadi, H ; Moarref, M ; Sharif University of Technology
    This paper introduces a new consensus protocol whose features are different from known consensus protocols available in the literature. The relation between discrete coverage algorithms over a convex polygon for solving a facility location problem (n-median problem) along with some notions in agreement over acyclic digraphs have been used to establish a novel constrained consensus protocol. Its convergence for the special case of acyclic digraphs with switching topology is presented. Extension of the results for other graph topologies and communication links are left for future works. © 2009 IEEE  

    Some topological properties of star graphs: The surface area and volume

    , Article Discrete Mathematics ; Volume 309, Issue 3 , 2009 , Pages 560-569 ; 0012365X (ISSN) Imani, N ; Sarbazi Azad, H ; Akl, S. G ; Sharif University of Technology
    The star graph, as an interesting network topology, has been extensively studied in the past. In this paper, we address some of the combinatorial properties of the star graph. In particular, we consider the problem of calculating the surface area and volume of the star graph, and thus answering an open problem previously posed in the literature. The surface area of a sphere with radius i in a graph is the number of nodes in the graph whose distance from a given node is exactly i. The volume of a sphere with radius i in a graph is the number of nodes within distance i from the given node. In this paper, we derive explicit expressions to calculate the surface area and volume in the star graph.... 

    Topological phase diagram of the disordered 2XY model in presence of generalized Dzyaloshinskii-Moriya interaction

    , Article Journal of Physics Condensed Matter ; Volume 32, Issue 1 , 2020 Habibi, A ; Ghadimi, R ; Jafari, S. A ; Sharif University of Technology
    Institute of Physics Publishing  2020
    The topological index of a system determines its edge physics. However, in situations such as strong disorder where due to level repulsion the spectral gap closes, the topological indices are not well-defined. In this paper, we show that the localization length of zero modes determined by the transfer matrix method reveals much more information than the topological index. The localization length can provide not only information about the topological index of the Hamiltonian itself, but it can also provide information about the topological indices of the 'relative' Hamiltonians. As a case study, we study a generalized XY model (2XY model) further augmented by a generalized... 

    Quench dynamics in one-dimensional optomechanical arrays

    , Article Physical Review A ; Volume 101, Issue 2 , 2020 Raeisi, S ; Marquardt, F ; Sharif University of Technology
    American Physical Society  2020
    Nonequilibrium dynamics induced by rapid changes of external parameters is relevant for a wide range of scenarios across many domains of physics. For waves in spatially periodic systems, quenches will alter the band structure and generate new excitations. In the case of topological band structures, defect modes at boundaries can be generated or destroyed when quenching through a topological phase transition. Here, we show that optomechanical arrays are a promising platform for studying such dynamics, as their band structure can be tuned temporally by a control laser. We study the creation of nonequilibrium optical and mechanical excitations in one-dimensional arrays, including a bosonic... 

    The 2D DBM: an attractive alternative to the simple 2D mesh topology for On-Chip networks

    , Article 26th IEEE International Conference on Computer Design 2008, ICCD, Lake Tahoe, CA, 12 October 2008 through 15 October 2008 ; 2008 , Pages 486-490 ; 9781424426584 (ISBN) Sabbaghi Nadooshan, R ; Modarressi, M ; Sarbazi Azad, H ; Sharif University of Technology
    During the recent years, 2D mesh network-onchip has attracted much attention due to its suitability for VLSI implementation. The 2-dimensional de Bruijn topology for network-on-chip is introduced in this paper as an attractive alternative to the popular simple 2D mesh NoC. Its cost is equal to that of the simple 2D mesh but it has a logarithmic diameter. We compare the proposed network and the popular mesh network in terms of power consumption and network performance. Compared to the equal sized simple mesh NoC, the proposed de Bruijn-based network has better performance while consuming less energy. © 2008 IEEE