Search for: crystal-lattices
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    Finite element model of SWCNT under hydrostatic pressure

    , Article AIP Conference Proceedings, 10 April 2007 through 12 April 2007, Sharjah ; Volume 929 , 2007 , Pages 82-88 ; 0094243X (ISSN) ; 0735404399 (ISBN); 9780735404397 (ISBN) Sakhaee Pour, A ; Ahmadian, M. T ; Sharif University of Technology
    A finite element technique is used to mimic radial deformation of single-walled carbon nanotubes under hydrostatic pressure. The elastic deformation of nanotubes is modeled via elastic beams. Properties of the beam element are evaluated by considering characteristics of the covalent bonds between the carbon atoms in a hexagonal lattice. Applying the beam model in a three dimensional space, the elastic properties of the nanotube in the transverse direction are evaluated. The effects of diameter and wall thickness on the radial and circumferential elastic moduli of zigzag and armchair nanotubes are considered. Results are in good agreement with molecular structural mechanics data in the... 

    Entanglement of bosonic modes in symmetric graphs

    , Article Physical Review A - Atomic, Molecular, and Optical Physics ; Volume 72, Issue 3 , 2005 ; 10502947 (ISSN) Asoudeh, M ; Karimipour, V ; Sharif University of Technology
    The ground and thermal states of a quadratic Hamiltonian representing the interaction of bosonic modes or particles are always Gaussian states. We investigate the entanglement properties of these states for the case where the interactions are represented by harmonic forces acting along the edges of symmetric graphs-i.e., one-, two-, and three-dimensional rectangular lattices, mean-field clusters, and platonic solids. We determine the entanglement of formation (EOF) as a function of the interaction strength, calculate the maximum EOF in each case, and compare these values with the bounds found previously for quadratic Hamiltonians. © 2005 The American Physical Society  

    General reaction-diffusion processes with separable equations for correlation functions

    , Article Physical Review E - Statistical Physics, Plasmas, Fluids, and Related Interdisciplinary Topics ; Volume 66, Issue 4 , 2002 , Pages 9- ; 1063651X (ISSN) Karimipour, V ; Sharif University of Technology
    We consider general multispecies models of reaction diffusion processes and obtain a set of constraints on the rates which give rise to closed systems of equations for correlation functions. Our results are valid in any dimension and on any type of lattice. We also show that under these conditions the evolution equations for two point functions at different times are also closed. As an example we introduce a class of two species models that may be useful for the description of voting processes or the spreading of epidemics. © 2002 The American Physical Society  

    Modal analysis of metallic nanocantilevers with FCC lattice using atomic approximation method

    , Article 2006 ASME International Mechanical Engineering Congress and Exposition, IMECE2006, Chicago, IL, 5 November 2006 through 10 November 2006 ; 2006 ; 1096665X (ISSN); 0791837904 (ISBN); 9780791837900 (ISBN) Amiri, F ; Pishkenari, H. N ; Mahboobi, S. H ; Meghdari, A ; Sharif University of Technology
    American Society of Mechanical Engineers (ASME)  2006
    In this research, we will use an accelerator for MD simulations, called Atomic Approximation Method, which leads to more efficient simulations without harming the physical properties in simulations. The main idea of this method is to define a virtual material with lower number of atoms, which has the same physical properties as the original material. To demonstrate the validity of the proposed technique the modal analysis results are compared with the ones of the conventional molecular dynamics method. It is shown that this method accelerates conventional MD simulations significantly. Copyright © 2006 by ASME  

    Photonic crystal devices analysis based on perturbation theory

    , Article Photonic Crystal Materials and Devices IV, San Jose, CA, 23 January 2006 through 26 January 2006 ; Volume 6128 , 2006 ; 0277786X (ISSN); 0819461709 (ISBN); 9780819461704 (ISBN) Chamanzar, M ; Khorasani, S ; Atabaki, A ; SPIE ; Sharif University of Technology
    A novel approach for photonic crystals devices analysis, based on perturbation theory is reported. In this method the photonic crystal device is considered as the superposition of a parent lattice and a perturbing one. Then the solution is investigated in terms of the eigensolutions of the parent lattice. This way, one can easily obtain analytic expressions within the first order perturbation, describing the effects of different parameters on the eigensolutions of the structure. The perturbation theory employed in this work is typical of what is conventionally used in quantum mechanics literature. The proposed method is explicit, works fast, and does not involve complicated numerical... 

    Precision photonic band structure calculation of Abrikosov periodic lattice in type-II superconductors

    , Article Physica C: Superconductivity and its Applications ; Volume 460-462 II, Issue SPEC. ISS , 2007 , Pages 1222-1223 ; 09214534 (ISSN) Kokabi, A ; Zandi, H ; Khorasani, S ; Fardmanesh, M ; Sharif University of Technology
    We have performed a numerical solution for band structure of an Abrikosov vortex lattice in type-II superconductors forming a periodic array in two dimensions for applications of incorporating the photonic crystals concept into superconducting materials with possibilities for optical electronics. The implemented numerical method is based on the extensive numerical solution of the Ginzburg-Landau equation for calculating the parameters of the two-fluid model and obtaining the band structure from the permittivity, which depends on the above parameters and the frequency. This is while the characteristics of such crystals highly vary with an externally applied static normal magnetic field,... 

    Photonic band structure of abrikosov lattices in superconductors

    , Article Photonic Crystal Materials and Devices VI, San Jose, CA, 22 January 2007 through 25 January 2007 ; Volume 6480 , 2007 ; 0277786X (ISSN) Zandi, H ; Kokabi, A ; Jafarpour, A. A ; Khorasani, S ; Fardmanesh, M ; Adibi, A ; Sharif University of Technology
    We have performed a numerical solution for band structure of an Abrikosov vortex lattice in type-11 superconductors forming a periodic array in two dimensions for applications of incorporating the photonic crystals concept into superconducting materials with possibilities for optical electronics. The implemented numerical method is based on the extensive numerical solution of the Ginzburg-Landau equation for calculating the parameters of the two-fluid model and obtaining the band structure from the permittivity, which depends on the above parameters and the frequency. This is while the characteristics of such crystals highly vary with an externally applied static normal magnetic field,... 

    On a theorem of Ihara

    , Article Scientia Iranica ; Volume 12, Issue 1 , 2005 , Pages 1-9 ; 10263098 (ISSN) Rastegar, A ; Sharif University of Technology
    Sharif University of Technology  2005
    Let p be a prime number and let n be a positive integer prime to p. By an Ihara-result, one means the existence of an injection with torsion-free cokernel, from a full lattice, in the space of p-old modular forms, into a full lattice, in the space of all modular forms of level np. In this paper, Ihara-results are proven for genus two Siegel modular forms, Siegel-Jacobi forms and Hilbert modular forms. Ihara did the genus one case of elliptic modular forms [1]. A geometric formulation is proposed for the notion of p-old Siegel modular forms of genus two, using clarifying comments by R. Schmidt [2] and, then, following suggestions in an earlier paper [3] on how to prove Ihara results. The main... 

    The radiated fields of the fundamental mode of photonic crystal fibers

    , Article Optics Express ; Volume 13, Issue 11 , 2005 , Pages 3999-4004 ; 10944087 (ISSN) Dabirian, A ; Akbari, M ; Mortensen, N. A ; Sharif University of Technology
    Optical Society of American (OSA)  2005
    The six-fold rotational symmetry of photonic crystal fibers has important manifestations in the radiated fields in terms of i) a focusing phenomena at a finite distance from the end-facet and ii) the formation of low-intensity satellite peaks in the asymptotic far field. For our study, we employ a surface equivalence principle which allows us to rigorously calculate radiated fields starting from fully-vectorial simulations of the near field. Our simulations show that the focusing is maximal at a characteristic distance from the end-facet. For large-mode area fibers the typical distance is of the order 10 x A with A being the pitch of the triangular air-hole lattice of the photonic crystal... 

    Algorithmic proof for the completeness of the two-dimensional Ising model

    , Article Physical Review A - Atomic, Molecular, and Optical Physics ; Volume 86, Issue 5 , 2012 ; 10502947 (ISSN) Karimipour, V ; Zarei, M. H ; Sharif University of Technology
    We show that the two-dimensional (12D) Ising model is complete, in the sense that the partition function of any lattice model on any graph is equal to the partition function of the 2D Ising model with complex coupling. The latter model has all its spin-spin coupling equal to iπ4 and all parameters of the original model are contained in the local magnetic fields of the Ising model. This result has already been derived by using techniques from quantum information theory and by exploiting the universality of cluster states. Here we do not use the quantum formalism and hence make the completeness result accessible to a wide audience. Furthermore, our method has the advantage of being algorithmic... 

    Transmission line model for extraction of transmission characteristics in photonic crystal waveguides with stubs: Optical filter design

    , Article Optics Letters ; Volume 37, Issue 8 , 2012 , Pages 1322-1324 ; 01469592 (ISSN) Khavasi, A ; Miri, M ; Rezaei, M ; Mehrany, K ; Rashidian, B ; Sharif University of Technology
    A simple and efficient transmission line model is proposed here to study how the transmission characteristics of photonic crystal waveguides are tailored by introduction of stubs patterned in the photonic crystal lattice. It is shown that band-pass and band-stop optical filters can be easily designed and optimized when stubs of appropriate length are brought in. Since the lengths of the designed stubs are not necessarily integer multiples of the photonic crystal lattice constant, a geometric shift in a portion of the photonic crystal structure is shown to be essential. The proposed model is verified by using a rigorous numerical method. An excellent agreement is observed between the... 

    Phase diagram of the frustrated J 1-J 2 transverse field Ising model on the square lattice

    , Article Journal of Physics: Conference Series ; Volume 969, Issue 1 , 19 April , 2018 ; 17426588 (ISSN) Sadrzadeh, M ; Langari, A ; Sharif University of Technology
    Institute of Physics Publishing  2018
    We study the zero-Temperature phase diagram of transverse field Ising model on the J 1-J 2 square lattice. In zero magnetic field, the model has a classical Néel phase for J 2/J 1 < 0.5 and an antiferromagnetic collinear phase for J 2/J 1 > 0.5. We incorporate harmonic fluctuations by using linear spin wave theory (LSWT) with single spin flip excitations above a magnetic order background and obtain the phase diagram of the model in this approximation. We find that harmonic quantum fluctuations of LSWT fail to lift the large degeneracy at J 2/J 1 = 0.5 and exhibit some inconsistent regions on the phase diagram. However, we show that anharmonic fluctuations of cluster operator approach (COA)... 

    Computational modeling of the interaction of two edge cracks, and two edge cracks interacting with a nanovoid, via an atomistic finite element method

    , Article Computational Materials Science ; Volume 42, Issue 2 , 2008 , Pages 186-193 ; 09270256 (ISSN) Adelzadeh, M ; Shodja, H. M ; Rafii Tabar, H ; Sharif University of Technology
    The competition and interaction of two edge cracks within the triangular lattice of an fcc material are addressed. We have also examined the effect of presence of a nanovoid in the vicinity of one of the crack-tips, on the competition of the cracks. An atomic scale finite element method (AFEM) [B. Liu, Y. Huang, H. Jiang, S. Qu, K.C. Hwang, The atomic-scale finite element method, Comput. Methods Appl. Mech. Eng. 193 (2004) 1849-1864], based on the Morse interatomic potential, is employed to explore the events in the (1 1 1) plane. Particular attention is given to the phenomenon of brittle-to-ductile transition (BDT) that occurs during crack propagation. © 2007 Elsevier B.V. All rights... 

    Artificial neural network modeling of mechanical alloying process for synthesizing of metal matrix nanocomposite powders

    , Article Materials Science and Engineering A ; Volume 466, Issue 1-2 , 2007 , Pages 274-283 ; 09215093 (ISSN) Dashtbayazi, M. R ; Shokuhfar, A ; Simchi, A ; Sharif University of Technology
    An artificial neural network model was developed for modeling of the effects of mechanical alloying parameters including milling time, milling speed and ball to powder weight ratio on the characteristics of Al-8 vol%SiC nanocomposite powders. The crystallite size and lattice strain of the aluminum matrix were considered for modeling. This nanostructured nanocomposite powder was synthesized by utilizing planetary high energy ball mill and the required data for training were collected from the experimental results. The characteristics of the particles were determined by X-ray diffraction, scanning and transmission electron microscopy. Two types of neural network architecture, i.e. multi-layer... 

    Synthesis of SBR/PMMA core/shell latices: the role of initiator and surfactant on particle morphology and instability performance

    , Article Journal of Applied Polymer Science ; Volume 105, Issue 3 , 2007 , Pages 1412-1419 ; 00218995 (ISSN) Moghbeli, M. R ; Mohammadi, N ; Bagheri, R ; Sharif University of Technology
    Poly(butadiene-stat-styrene)/poly(methylmetacrylate), SBR/PMMA, structural latices were synthesized by using equal moles of different kinds of surfactants: anionic, nonionic, and anionic/nonionic mixture in a two-stage emulsion polymerization. The results indicate that the application of anionic surfactants for the first stage, accompanying sodium persulfate initiator, KPS, for both stages led to core/shell and raspberry morphologies depended upon the hydrophilic lipophilic balance (HLB) of the surfactant. On the other hand, a core/shell structure was observed for structural latices which were synthesized via application of nonionic or anionic/non-ionic mixed surfactants along with... 

    Relationship between lattice relaxation and electron delocalization in diamond vacancies

    , Article Proceedings of the 23rd International Conference on Defects in Semiconductors, 24 July 2005 through 29 July 2005 ; Volume 376-377, Issue 1 , 2006 , Pages 324-326 ; 09214526 (ISSN) Heidari Saani, M ; Esfarjani, K ; Hashemi, H ; Vesaghi, M. A ; Basiri, A. R ; Sharif University of Technology
    Single electron wavefunction of a vacancy in diamond lattice has been calculated in different symmetric configurations of the nearest neighbor (NN) atoms. We used ab initio density functional theory (DFT) and unrestricted Hartree-Fock (UHF) cluster methods. The variation of electron or spin localization on NN atoms have been investigated with respect to the lattice relaxation in the ground state of the neutral and negatively charged vacancy. Calculated variations are not symmetric with respect to the sign of the lattice relaxation. We obtain about 90% localization for electronic charge and spin density for the neutral and negatively charged vacancy, respectively. This is in good agreement... 

    Monte Carlo simulation of a lattice model for the dynamics of randomly branching double-folded ring polymers

    , Article Physical Review E ; Volume 104, Issue 1 , 2021 ; 24700045 (ISSN) Ghobadpour, E ; Kolb, M ; Ejtehadi, M. R ; Everaers, R ; Sharif University of Technology
    American Physical Society  2021
    Supercoiled DNA, crumpled interphase chromosomes, and topologically constrained ring polymers often adopt treelike, double-folded, randomly branching configurations. Here we study an elastic lattice model for tightly double-folded ring polymers, which allows for the spontaneous creation and deletion of side branches coupled to a diffusive mass transport, which is local both in space and on the connectivity graph of the tree. We use Monte Carlo simulations to study systems falling into three different universality classes: ideal double-folded rings without excluded volume interactions, self-avoiding double-folded rings, and double-folded rings in the melt state. The observed static properties... 

    Thermal Hall and Nernst responses in ultrathin magnetic films of pyrochlore lattice

    , Article Journal of Physics Condensed Matter ; Volume 33, Issue 26 , 2021 ; 09538984 (ISSN) Sheikhi, B ; Kargarian, M ; Langari, A ; Sharif University of Technology
    IOP Publishing Ltd  2021
    The ultrathin films of pyrochlore lattice along [111] direction provide a fertile ground for exploring topological states in oxide materials, where the electron correlations are strong and magnetically ordered states are favored. As a result of strong interactions, most of states are magnetic insulators with strong Dzyaloshinskii–Moriya and anisotropic spin interactions. We considered three types of heterostructures, a bilayer of triangular-kagome (TK), and two trilayers of triangular-kagome-triangular (TKT) and kagome-triangular-kagome (KTK) thin films. The ground states are magnetically ordered with the low-energy excitations, the magnons, characterized by nontrivial topology. While for TK... 

    Studies on the properties and structure of electron-beam crosslinked low-density polyethylene/poly[ethylene-co-(vinyl acetate)] blends

    , Article Polymer International ; Volume 54, Issue 4 , 2005 , Pages 686-691 ; 09598103 (ISSN) Dadbin, S ; Frounchi, M ; Sabet, M ; Sharif University of Technology
    Blends of low-density polyethylene (LDPE) and poly[ethylene-co-(vinyl acetate)] (PEVA), crosslinked by electron-beam (EB) radiation, formed separate crystalline lattices with a homogeneous amorphous phase. The crystallinity of the EB-exposed samples slightly decreased, as verified by a slight reduction in the densities and melting heats and temperatures of the samples. The results obtained from both gel content and hot set tests showed that the degree of crosslinking in the amorphous regions was dependent on the dose and blend composition. The molecular weights between the crosslinks, measured from creep data, showed that an increasing PEVA content resulted in tighter network structures,... 

    A combined first principles and analytical determination of the modulus of cohesion, surface energy, and the additional constants in the second strain gradient elasticity

    , Article International Journal of Solids and Structures ; Volume 50, Issue 24 , 2013 , Pages 3967-3974 ; 00207683 (ISSN) Ojaghnezhad, F ; Shodja, H. M ; Sharif University of Technology
    Mindlin's (1965) second strain gradient theory due to its competency in capturing the effects of edges, corners, and surfaces is of particular interest. Formulation in this framework, in addition to the usual Lamé constants, requires the knowledge of sixteen additional materials constants. To date, there are no successful experimental techniques for measuring these material parameters which reflect the discrete nature of matter. The present work gives an accurate remedy for the atomistic calculations of these parameters by utilizing the first principles density functional theory (DFT) for the calculations of the atomic force constants combined with an analytical formulation. It will be shown...