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    Theoretical investigation of the hydrogen abstraction reaction of the OH radical with CH2FCH2F (HFC-152): A dual-level direct dynamics study

    , Article Journal of Physical Chemistry A ; Volume 111, Issue 33 , 2007 , Pages 8095-8103 ; 10895639 (ISSN) Taghikhani, M ; Parsafar, G. A ; Sharif University of Technology
    The hydrogen abstraction reaction of the OH radical with CH 2FCH22F (HFC-152) is studied theoretically over the 150-3000 K temperature range. In this study, the two most recently developed hybrid density functional theories, namely, BBlK and MPWBlK, are applied, and their efficiency in reaction dynamics calculation is discussed. The BBlK/6-31+G(d,p) method gives the best result for the potential energy surface (PES) calculations, including barrier heights, reaction path information (the first and second derivatives of PES), geometry of transition state structures, and even weak hydrogen bond orientations. The rate constants were obtained by the dual-level direct dynamics with the... 

    First Principles Studies of Mechanical, Physical, and Electronic Properties of a-Si - also, Diffusion of a Self-interstitial Atom in an Ultra-thin fcc Film Via Lattice Statics

    , Ph.D. Dissertation Sharif University of Technology Tabatabaei, Maryam (Author) ; Mohammadi Shodja, Hossein (Supervisor)
    By employing first principles density functional theory-based (DFT) molecular dynamics (MD), the influences of dangling and floating bonds as well as distorted tetrahedral bonds are studied on the mechanical, physical, and electronic properties of amorphous Si (a-Si). For further examination of the effects of these geometrical defects, two distinct amorphous samples, namely as-quenched and annealed are generated and examined. To verify the validity of the representative cells, the obtained radial distribution function, pair correlation function, and cohesive energy are compared with those corresponding results presented in the literature. Moreover, the surface energy is calculated at final... 

    Efficient photo-dissociation of CH4 and H2CO molecules with optimized ultra-short laser pulses

    , Article AIP Advances ; Volume 5, Issue 11 , 2015 ; 21583226 (ISSN) Rasti, S ; Irani, E ; Sadighi Bonabi, R ; Sharif University of Technology
    American Institute of Physics Inc  2015
    The fragmentation dynamics of CH4 and H2CO molecules have been studied with ultra-short pulses at laser intensityof up to 1015Wcm-2. Three dimensional molecular dynamics calculations for finding the optimized laser pulses are presented based on time-dependent density functional theory and quantum optimal control theory. A comparison of the results for orientation dependence in the ionization process shows that the electron distribution for CH4 is more isotropic than H2CO molecule. Total conversion yields of up to 70% at an orientation angle of 30o for CH4 and 65% at 900 for H2CO are achieved which lead to enhancement of dissociation probability  

    Reduction of oscillations via fractional order pre-filtering

    , Article Signal Processing ; Volume 107 , February , 2015 , Pages 407-414 ; 01651684 (ISSN) Tavazoei, M. S ; Sharif University of Technology
    Elsevier  2015
    In this paper, an effective way is proposed for reduction of oscillations in the response of dynamical systems. In this regard, it is analytically shown that the undesirable oscillations in the response of dynamical systems can be reduced using a simple input shaping fractional order filter. The effectiveness of the proposed fractional calculus based technique is numerically verified in reduction of oscillations in a mass-spring-damper system, a low-pass Chebyshev filter, and a PI-controlled two-mass drive system  

    Neutron noise simulation using ACNEM in the hexagonal geometry

    , Article Annals of Nuclear Energy ; Volume 113 , 2018 , Pages 246-255 ; 03064549 (ISSN) Hosseini, A ; Vosoughi, N ; Vosoughi, J ; Sharif University of Technology
    Elsevier Ltd  2018
    In the present study, the development of a neutron noise simulator, DYN-ACNEM, using the Average Current Nodal Expansion Method (ACNEM) in 2-G, 2-D hexagonal geometries is reported. In first stage, the static neutron calculation is performed. The neutron/adjoint flux distribution and corresponding eigen-values are calculated using the algorithm developed based on power iteration method by considering the coarse meshes. The results of the static calculation are validated against the well-known IAEA-2D benchmark problem. In the second stage, the dynamic calculation is performed in the frequency domain in which the dimension of the variable space of the noise equations is lower than the time... 

    Neutron noise simulation by GFEM and unstructured triangle elements

    , Article Nuclear Engineering and Design ; Volume 253 , 2012 , Pages 238-258 ; 00295493 (ISSN) Hosseini, S. A ; Vosoughi, N ; Sharif University of Technology
    In the present study, the neutron noise, i.e. The stationary fluctuation of the neutron flux around its mean value, is calculated in 2-group forward and adjoint diffusion theory for both hexagonal and rectangular reactor cores. To this end, the static neutron calculation is performed at the first stage. The spatial discretization of equations is based on linear approximation of Galerkin Finite Element Method (GFEM) using unstructured triangle elements. Using power iteration method, forward and adjoint fluxes with the corresponding eigenvalues are obtained. The results are then benchmarked against the valid results for BIBLIS-2D and IAEA-2D benchmark problems and DONJON computer code. The... 

    Development of a 2-D 2-group neutron noise simulator for hexagonal geometries

    , Article Annals of Nuclear Energy ; Volume 37, Issue 8 , 2010 , Pages 1089-1100 ; 03064549 (ISSN) Malmir, H ; Vosoughi, N ; Zahedinejad, E ; Sharif University of Technology
    In this paper, the development of a neutron noise simulator for hexagonal-structured reactor cores using both the forward and the adjoint methods is reported. The spatial discretisation of both 2-D 2-group static and dynamic equations is based on a developed box-scheme finite difference method for hexagonal mesh boxes. Using the power iteration method for the static calculations, the 2-group neutron flux and its adjoint with the corresponding eigenvalues are obtained by the developed static simulator. The results are then benchmarked against the well-known CITATION computer code. The dynamic calculations are performed in the frequency domain which leads to discarding of the time... 

    Weakly nonlocal micromorphic elasticity for diamond structures vis-à-vis lattice dynamics

    , Article Mechanics of Materials ; Volume 147 , 2020 Shodja, H. M ; Moosavian, H ; Sharif University of Technology
    Elsevier B.V  2020
    In this work, after formulating the weakly nonlocal micromorphic equations of motion for non-Bravais crystals with general anisotropy, specialization to diamond structures is made. A critical dilemma is the determination of the elastic moduli tensor appearing in the equations of motion. From the equivalency of these equations with the pertinent equations obtained in the context of lattice dynamics, the expressions of the components of the elastic moduli tensors in terms of the atomic force constants are derived analytically. Subsequently, the atomic force constants are calculated via ab initio density functional perturbation theory (DFPT) with high precision. As a benchmark for the accuracy...