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    Formalism of overlaps of valence bond states with any number of triplon

    , Article Iranian Journal of Physics Research ; Volume 11, Issue 3 , 2011 ; 16826957 (ISSN) Ghorbani, E ; Jafari, S. A ; Shabazi, F ; Sharif University of Technology
    Resonating valence bond (RVB) states are suitable candidates for ground state of the Heisenberg model on various two dimensional lattices. When a singlet valence bond is broken to produce a triplet state, the resulting excitation is called a triplon. In this paper, we obtain formulas for the overlap and also matrix elements of si sjoperator between states with arbitrary number of triplons. Our results are valid for any 2D lattice  

    Bipolar transistor based on graphane

    , Article Journal of Physics: Conference Series, 5 July 2010 through 10 July 2010 ; Volume 248 , 2010 ; 17426588 (ISSN) Gharekhanlou, B ; Tousaki, S. B ; Khorasani, S ; Sharif University of Technology
    Graphane is a semiconductor with an energy gap, obtained from hydrogenation of the two-dimensional grapheme sheet. Together with the two-dimensional geometry, unique transport features of graphene, and possibility of doping graphane, p and n regions can be defined so that p-n junctions become feasible with small reverse currents. Our recent analysis has shown that an ideal I-V characteristic for this type of junctions may be expected. Here, we predict the behavior of bipolar juncrion transistors based on graphane. Profiles of carriers and intrinsic parameters of the graphane transistor are calculated and discussed  

    Fourier modal method formulation for fast analysis of two-dimensional periodic arrays of graphene

    , Article Journal of the Optical Society of America B: Optical Physics ; Vol. 31, issue. 5 , 2014 , pp. 987-993 ; ISSN: 07403224 Nekuee, S. A. H ; Khavasi, A ; Akbari, M ; Sharif University of Technology
    Recently, an approximate boundary condition [Opt. Lett. 38, 3009 (2013)] was proposed for fast analysis of onedimensional periodic arrays of graphene ribbons by using the Fourier modal method (FMM). Correct factorization rules are applicable to this approximate boundary condition where graphene is modeled as surface conductivity. We extend this approach to obtain the optical properties of two-dimensional periodic arrays of graphene. In this work, optical absorption of graphene squares in a checkerboard pattern and graphene nanodisks in a hexagonal lattice are calculated by the proposed formalism. The achieved results are compared with the conventional FMM, in which graphene is modeled as a... 

    Two-dimensional clustering of nanoparticles on the surface of cellulose fibers

    , Article Journal of Physical Chemistry C ; Volume 113, Issue 28 , 2009 , Pages 12022-12027 ; 19327447 (ISSN) Khajeh Aminian, M ; Taghavinia, N ; Irajizad, A ; Mahdavi, M ; Ye, J ; Chavoshi, M ; Vashaei, Z ; Sharif University of Technology
    Density of surface charges of cellulose fibers and -potential of TiO2 nanoparticles in the solution were measured and controlled by pH. The adsorption and clustering of TiO2 nanoparticles on the surface of cellulose fibers were studied using scanning electron microscopy (SEM) and a scale in different situations of repulsion and attraction between the particles and surface. The experiments show formation of two-dimensional clusters of nanoparticles on the surface. Weight measurement of the adsorbed particles and clusters via the adsorption time results in that there are three stages containing nucleation, two-dimensional growth and saturation for clustering of nanoparticles on the surface.... 

    Generation and recombination in two-dimensional bipolar transistors

    , Article Applied Physics A: Materials Science and Processing ; Vol. 115, issue. 3 , 2014 , pp. 737-740 ; ISSN: 00304018 Gharekhanlou, B ; Khorasani, S ; Sharif University of Technology
    We study the effects of recombination and generation process on the operation of bipolar junction transistor based on two-dimensional materials, and in particular, graphone. Here, we use Shockley-Read-Hall model to study these process. First, we investigate the current-voltage characteristics of a graphone p-n junction considering generation and recombination process. Then, we calculate the estimated changes in current gain, cutoff frequency, and output characteristics of a graphone bipolar junction transistor designed in a recent study  

    Extended two-dimensional PCA for efficient face representation and recognition

    , Article 2008 IEEE 4th International Conference on Intelligent Computer Communication and Processing, ICCP 2008, Cluj-Napoca, 28 August 2008 through 30 August 2008 ; October , 2008 , Pages 295-298 ; 9781424426737 (ISBN) Safayani, M ; Manzuri Shalmani, M. T ; Khademi, M ; Sharif University of Technology
    In this paper a novel method called Extended Two-Dimensional PCA (E2DPCA) is proposed which is an extension to the original 2DPCA. We state that the covariance matrix of 2DPCA is equivalent to the average of the main diagonal of the covariance matrix of PCA. This implies that 2DPCA eliminates some covariance information that can be useful for recognition. E2DPCA instead of just using the main diagonal considers a radius of r diagonals around it and expands the averaging so as to include the covariance information within those diagonals. The parameter r unifies PCA and 2DPCA. r=1 produces the covariance of 2DPCA, r=n that of PCA. Hence, by controlling r it is possible to control the... 

    N-way partial least squares with variable importance in projection combined to GC × GC-TOFMS as a reliable tool for toxicity identification of fresh and weathered crude oils

    , Article Analytical and Bioanalytical Chemistry ; Volume 407, Issue 1 , 2014 , pp 285-295 ; ISSN: 16182650 Mostafapour, S ; Parastar, H ; Sharif University of Technology
    In this study, N-way partial least squares (NPLS) is proposed to correlate comprehensive two-dimensional gas chromatography-time of flight mass spectrometry (GC × GC-TOFMS) data of different aromatic oil fractions (fresh and weathered) to their toxicity values. Before NPLS modeling, since drift and wander of baseline interfere with information of sought analytes in GC × GC-TOFMS data, a novel method called two-dimensional asymmetric least squares is thus developed for comprehensive correction of the baseline contributions in both chromatographic dimensions. The algorithm is termed comprehensive because it functions to correct the entire chromatogram in both dimensions and it preserves the... 

    Synthesis, characterizations and catalytic studies of a new two-dimensional metal-organic framework based on Co-carboxylate secondary building units

    , Article Journal of Solid State Chemistry ; Volume 223, March , 2014 , Pages 32-37 ; ISSN: 00224596 Bagherzadeh, M ; Ashouri, F ; Dakovic, M ; Sharif University of Technology
    A metal-organic framework [Co3(BDC)3(DMF)2(H2O)2] was synthesized and structurally characterized. X-ray single crystal analysis revealed that the framework contains a 2D polymeric chain through coordination of 1,4-benzenedicarboxylic acid linker ligand to cobalt centers. The polymer crystallize in monoclinic P21 /n space group with a=13.989(3) Å, b=9.6728(17) Å, c=16.707(3) Å, and Z=2. The polymer features a framework based on the perfect octahedral Co-O6 secondary building units. The catalytic activities of [Co3(BDC)3(DMF)2(H2O)2]n for olefins oxidation was conducted. The heterogeneous catalyst could be facilely separated from the reaction mixture, and reused three times without significant... 

    Synthesis, structural characterization and application of a 2D coordination polymer of Mn-terephthalate as a heterogeneous catalyst for olefin oxidation

    , Article Polyhedron ; Volume 69 , 17 February , 2014 , Pages 167-173 ; ISSN: 02775387 Bagherzadeh, M ; Ashouri, F ; Crossed D Signakovic, M ; Sharif University of Technology
    A metal-organic coordination polymer of [Mn3(1,4- benzenedicarboxylate)3(DMF)4] ([Mn3(BDC) 3(DMF)4]n) was synthesized and characterized by IR spectra, elemental analysis (CHN), thermal gravimetric analysis (TGA) and single crystal X-ray diffraction analysis. The structure of [Mn 3(BDC)3(DMF)4]n is a 2D-periodic framework based on Mn(II)-terephthalate secondary building units (SBUs). The catalytic oxidation of various olefins was effectively carried out with [Mn 3(BDC)3(DMF)4]n. Moreover, the influence of key reaction parameters, including the solvents, reaction temperatures and nature of oxidant were studied. The optimized conditions were achieved by TBHP as the efficient oxidant in... 

    A review of 2D-based counter electrodes applied in solar-assisted devices

    , Article Coordination Chemistry Reviews ; Volume 324 , 2016 , Pages 54-81 ; 00108545 (ISSN) Irani, R ; Naseri, N ; Beke, S ; Sharif University of Technology
    Elsevier  2016
    The alarming energy and environmental crisis of our modern era necessitates scientists to propose alternatives to replace the scarce and harmful fossil fuels. The Sun, as a free, and abundant clean energy resource, presents a motivation for researchers to convert the sunlight to electrical power and store the H2 as an energy carrier by developing solar cells as well as water splitting devices, respectively. One of the fundamental parts of a solar energy convertor (solar cell/photoelectrochemical device), where the reduction reaction occurs, is the counter electrode (CE); the CE is commonly based on rare Pt. It is critical to substitute costly CEs with efficient, low-cost replacements, which... 

    Dynamic renormalization group analysis of propagation of elastic waves in two-dimensional heterogeneous media

    , Article Physical Review B - Condensed Matter and Materials Physics ; Volume 77, Issue 1 , 2008 ; 10980121 (ISSN) Sepehrinia, R ; Bahraminasab, A ; Sahimi, M ; Rahimi Tabar, M. R ; Sharif University of Technology
    We study localization of elastic waves in two-dimensional heterogeneous solids with randomly distributed Lamé coefficients, as well as those with long-range correlations with a power-law correlation function. The Matin-Siggia-Rose method is used, and the one-loop renormalization group (RG) equations for the coupling constants are derived in the limit of long wavelengths. The various phases of the coupling constants space, which depend on the value ρ, the exponent that characterizes the power-law correlation function, are determined and described. Qualitatively different behaviors emerge for ρ<1 and ρ>1. The Gaussian fixed point (FP) is stable (unstable) for ρ<1 (ρ>1). For ρ<1, there is a... 

    Optimizing allocation of two dimensional irregular shapes using an agent based approach

    , Article Wec 05: Fourth World Enformatika Conference, Istanbul, 24 June 2005 through 26 June 2005 ; Volume 6 , 2005 , Pages 241-244 ; 9759845857 (ISBN) Halavati, R ; Shouraki, S. B ; Noroozian, M ; Zadeh, S. H ; Ardil C ; Sharif University of Technology
    Packing problems arise in a wide variety of application areas. The basic problem is that of determining an efficient arrangement of different objects in a region without any overlap and with minimal wasted gap between shapes. This paper presents a novel population based approach for optimizing arrangement of irregular shapes. In this approach, each shape is coded as an agent and the agents' reproductions and grouping policies results in arrangements of the objects in positions with least wasted area between them. The approach is implemented in an application for cutting sheets and test results on several problems from literature are presented. COPYRIGHT © ENFORMATIKA  

    A technique for detection of interfacial waves forming a two-dimensional pattern

    , Article Fluid Dynamics Research ; Vol. 46, issue. 1 , 2014 ; ISSN: 01695983 Safaie, A ; Fazeli M ; Jamali, M ; Sharif University of Technology
    In this paper, we consider resonant interaction between a surface wave and sub-harmonic interfacial waves forming a two-dimensional pattern at the interface between two fluid layers. The resulting interfacial pattern changes both in time and space. An image processing technique is proposed to extract information about the evolution of the component interfacial waves in a wave flume. The technique proved to give accurate and consistent results when applied to different stages of the interaction. The experimental measurements were used to verify the theoretical predictions. The method can be used for detection of some other wave motions  

    Circuit model in design of THz transparent electrodes based on two-dimensional arrays of metallic square holes

    , Article IEEE Transactions on Terahertz Science and Technology ; Vol. 4, issue. 3 , April , 2014 , p. 383-390 Shirmanesh, G. K ; Yarmoghaddam, E ; Khavasi, A ; Mehrany, K ; Sharif University of Technology
    In this paper, we propose a circuit model for two-dimensional arrays of metallic square holes located on a homogeneous substrate, in order to propose a new scheme containing this type of metamaterials to obtain transparent electrodes with simultaneous terahertz transparency and low electrical resistance. The results of the introduced circuit model, which is a fully analytical model with explicit expressions, are in almost complete agreement with the full-wave simulations. Thanks to this analytical model, we can employ standard binomial matching transformer in order to minimize the reflected power from the structure at a desired frequency. Furthermore, taking advantage of this model, we... 

    Kitaev-Ising model and the transition between topological and ferromagnetic order

    , Article Physical Review A - Atomic, Molecular, and Optical Physics ; Volume 87, Issue 3 , March , 2013 ; 10502947 (ISSN) Karimipour, V ; Memarzadeh, L ; Zarkeshian, P ; Sharif University of Technology
    We study the Kitaev-Ising model, where ferromagnetic Ising interactions are added to the Kitaev model on a lattice. This model has two phases which are characterized by topological and ferromagnetic order. Transitions between these two kinds of order are then studied on a quasi-one-dimensional system, on a ladder, and on a two-dimensional periodic lattice, a torus. By exactly mapping the quasi-one-dimensional case to an anisotropic XY chain we show that the transition occurs at zero λ, where λ is the strength of the ferromagnetic coupling. In the two-dimensional case the model is mapped to a two-dimensional Ising model in transverse field, where it shows a transition at a finite value of λ.... 

    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... 

    Circuit model for mode extraction in lossy/lossless photonic crystal waveguides

    , Article Journal of the Optical Society of America B: Optical Physics ; Volume 29, Issue 1 , 2012 , Pages 170-177 ; 07403224 (ISSN) Habibi, N ; Khavasi, A ; Miri, M ; Mehrany, K ; Sharif University of Technology
    An approximate circuit model is proposed for mode extraction in two-dimensional photonic crystal waveguides. The dispersion equation governing the complex propagation constant of the photonic crystal waveguide is then related to the resonance condition in the proposed circuit model. In this fashion, a scalar complex transcendental equation is given for mode extraction. To avoid searching for the complex roots of the derived scalar dispersion equation, however, the real and imaginary parts of the sought-after propagation constant are extracted by using the physical resonance condition and its corresponding quality factor in the here-proposed circuit model, respectively. All the necessary... 

    Two-dimensional warranty cost analysis for second-hand products

    , Article Communications in Statistics - Theory and Methods ; Volume 40, Issue 4 , 2011 , Pages 684-701 ; 03610926 (ISSN) Shafiee, M ; Chukova, S ; Saidi-Mehrabad, M ; Niaki, S. T. A ; Sharif University of Technology
    In spite of the recent steady increase of the volume of the second-hand markets, often customers remain in doubt regarding the quality and durability of the secondhand products. Aiming to reduce and share this uncertainty, dealers offer warranty on their products. Offering warranty for second-hand products is a relatively new marketing strategy employed by dealers of used electronic equipment, furniture, automobiles, etc. Usually, for used products, the dealer's expected warranty cost is a function of product reliability, past age and usage, servicing strategy and conditions and terms of the warranty policy/contract. Sometimes the offered policy is limited by two parameters, typically the... 

    Stiffer double-stranded DNA in two-dimensional confinement due to bending anisotropy

    , Article Physical Review E - Statistical, Nonlinear, and Soft Matter Physics ; Volume 94, Issue 6 , 2016 ; 15393755 (ISSN) Salari, H ; Eslami Mossallam, B ; Ranjbar, H. F ; Ejtehadi, M. R ; Sharif University of Technology
    American Physical Society  2016
    Using analytical approach and Monte Carlo (MC) simulations, we study the elastic behavior of the intrinsically twisted elastic ribbons with bending anisotropy, such as double-stranded DNA (dsDNA), in two-dimensional (2D) confinement. We show that, due to the bending anisotropy, the persistence length of dsDNA in 2D conformations is always greater than three-dimensional (3D) conformations. This result is in consistence with the measured values for DNA persistence length in 2D and 3D in equal biological conditions. We also show that in two dimensions, an anisotropic, intrinsically twisted polymer exhibits an implicit twist-bend coupling, which leads to the transient curvature increasing with a... 

    Two dimensional optimal linear detector for slowly fluctuating target

    , Article IET International Radar Conference 2009, Guilin, 20 April 2009 through 22 April 2009 ; Issue 551 CP , 2009 ; 9781849190107 (ISBN) Rafie, A. H ; Norouzi, Y ; Taban, M. R ; Sharif University of Technology
    In this paper, we propose a two dimensional optimal linear detector (2-D OLD) for slowly fluctuating target in Gaussian interference. We assume that the samples of received signal in the range and in the successive pulsation times are collected in a two dimensional array. In conventional detectors, each column of this matrix (the Samples of the same pulsation time) is detected separately and the binary results may be integrated for successive pulsation times in order to improve the detection performance. In fact, by applying binary integration, we ignore the considerable correlation among 2-D data in the azimuth direction. In the proposed 2-D OLD detector, this correlation is considered,...