Search for: calculation
0.009 seconds
Total 377 records

    Dft study on gas-phase interaction between histidine and alkali metal ions (li+, na+, k+); and influence of these ions on histidine acidity

    , Article Journal of Theoretical and Computational Chemistry ; Volume 8, Issue 3 , 2009 , Pages 475-490 ; 02196336 (ISSN) Tavasoli, E ; Fattahi, A. R ; Sharif University of Technology
    The gas-phase metal affinities of histidine Li+, Na+ and K+ ions have been determined theoretically employing the hybrid B3LYP exchangecorrelation functional and using 6-311++G** basis sets. All computations indicate that the metal ion affinity decreases on going from Li+ to Na+ and K+ for the considered amino acid. Different types of M+ coordinations on several histidine conformers/tautomers were considered in detail. The optimized structures indicate that Li+ and Na+ prefer a tri-dentate coordination, bonding with a nitrogen atom of imidazole ring (N τ), NH2, and an oxygen atom of a carbonyl, while in the K+-histidine lowest-energy conformer, the cation appears to be bi-coordinated to both... 

    Mixed branes at angle in compact spacetime

    , Article Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics ; Volume 475, Issue 1-2 , 2000 , Pages 39-45 ; 03702693 (ISSN) Arfaei, H ; Kamani, D ; Sharif University of Technology
    In this article the interaction of branes at angles with respect to each other with non-zero internal gauge fields are calculated by construction of the boundary states in spacetime in which some of its directions are compact on tori. The interaction depends on both angle and fields. (C) 2000 Elsevier Science B.V  

    Ab initio calculations of characteristic lengths of crystalline materials in first strain gradient elasticity

    , Article Mechanics of Materials ; Volume 61 , 2013 , Pages 73-78 ; 01676636 (ISSN) Shodja, H. M ; Zaheri, A ; Tehranchi, A ; Sharif University of Technology
    Incorporation of the first gradient of strain, in addition to the strain itself, into the strain energy density of an elastic solid leads to Mindlin's first strain gradient theory, which is useful for examination of size effect as well as other mechanical phenomena at the nano-scale. For isotropic elastic solids, the first strain gradient theory, in addition to the two independent Lamé constants, gives rise to five new material constants which in turn reduce to two material parameters, ℓ1 and ℓ2 with dimension of length. The evaluation of these parameters, however, has posed serious challenges, both experimentally and theoretically. In this work ab initio method is used to compute the... 

    An experimental and theoretical study on the structure and photoactivity of XFe2O4 (X = Mn, Fe, Ni, Co, and Zn) structures1

    , Article Russian Journal of Physical Chemistry A ; Volume, 88, Issue 13 , December , 2014 , pp. 2451-2461 ; 1531-863X Padervand, M ; Vossoughi, M ; Yousefi, H ; Salari, H ; Gholami, M. R. (Mohammad Reza) ; Sharif University of Technology
    XFe2O4 magnetic nanoparticles (X = Mn, Fe, Co, Ni, and Zn) were prepared by using two methods: coprecipitation and hydrothermal. The synthesized nanoparticles were compared according to the separation in an external magnetic field and finally, the hydrothermal method was specified as a better synthesis method. The magnetic nanoparticles were characterized by physico-chemical analysis methods such as Vibrating Sample Magnetometer (VSM), X-ray diffraction (XRD), Fourier Transform Infrared spectroscopy (FTIR), nitrogen adsorption-adsorption isotherm and Transmission Electron Microscopy (TEM). Magnetic properties of synthesized nanoparticles were studied by ab-initio theoretical methods to... 

    Tandem dinucleophilic cyclization of cyclohexane-1,3-diones with pyridinium salts

    , Article Beilstein Journal of Organic Chemistry ; Volume 9 , 2013 , Pages 1119-1126 ; 18605397 (ISSN) Kiamehr, M ; Moghaddam, F. M ; Mkrtchyan, S ; Semeniuchenko, V ; Supe, L ; Villinger, A ; Langer, P ; Laroshenko, V. O ; Sharif University of Technology
    The cyclization of cyclohexane-1,3-diones with various substituted pyridinium salts afforded functionalized 8-oxa-10-aza-tricyclo[ 2,7]trideca-2(7),11-dienes. The reaction proceeds by regioselective attack of the central carbon atom of the 1,3-dicar-bonyl unit to 4-position of the pyridinium salt and subsequent cyclization by base-assisted proton migration and nucleophilic addition of the oxygen atom to the 2-position, as was elucidated by DFT computations. Fairly extensive screening of bases and additives revealed that the presence of potassium cations is essential for formation of the product  

    Cycloplatinated(II) complexes containing bridging bis(diphenylphosphino)acetylene: Photophysical study

    , Article Journal of Luminescence ; Volume 179 , 2016 , Pages 222-229 ; 00222313 (ISSN) Jamshidi, M ; Nabavizadeh, S. M ; Sepehrpour, H ; Niroomand Hosseini, F ; Kia, R ; Rashidi, M ; Sharif University of Technology
    Elsevier  2016
    Reaction of the known cycloplatinated (II) complexes [PtAr(C^N)(SMe2)], in which Ar=p–MeC6H4 or p–MeOC6H4 and C^N= 2-phenylpyridinate (ppy) or benzo[h]quinolinate (bhq), with 0.5 equivalent of the bidentate phosphine ligand 1,1′–bis(diphenylphosphino)acetylene, dppac, in acetone at room temperature gave the symmetrical binuclear cycloplatinated(II) complexes [Pt2Ar2(C^N)2(μ–dppac)], 1–4, in which dppac acts as a bridging bidentate ligand. All the complexes were fully characterized using multinuclear (1H, 31P and 195Pt) NMR spectroscopy and the complex [Pt2(p–MeC6H4)2(ppy)2(μ–dppac)], 1, was further identified by single crystal X-ray structure determination. Additional information about the... 

    Chrysin/β-cyclodextrin supramolecular system: a quantum mechanical investigation

    , Article Journal of the Iranian Chemical Society ; Volume 15, Issue 10 , 2018 , Pages 2401-2410 ; 1735207X (ISSN) Ghiasi, M ; Gerayeli, N ; Tafazzoli, M ; Sharif University of Technology
    Chrysin is a bioflavonoid which possesses a wide range of important biological activities. In present study, we used a quantum mechanical approach to shed light on the antioxidant ability and antioxidant mechanism of chrysin to scavenge hydroxyl radical (˙OH) in solution phase. The analysis of the theoretical bond dissociation enthalpy (BDE) values and spin density of the radicals to determine the delocalization possibilities at B3LYP/6-311++G** level clearly shows the importance of the A-ring and the 7-OH group in antioxidant reactivity. In the next step, the inclusion of chrysin with β-CD has been investigated extensively using theoretical methods. Density functional theory (M05-2X)... 

    A rare type of Rhenium(I) diimine complexes with unsupported coordinated phosphine oxide ligands: Synthesis, Structural Characterization, Photophysical and theoretical study

    , Article European Journal of Inorganic Chemistry ; Volume 2019, Issue 39-40 , 2019 , Pages 4350-4357 ; 14341948 (ISSN) Nayeri, S ; Jamali, S ; Pavlovskiy, V. V ; Porsev, V. V ; Evarestov, R. A ; Kisel, K. S ; Koshevoy, I. O ; Shakirova, J. R ; Tunik, S. P ; Sharif University of Technology
    Wiley-VCH Verlag  2019
    This paper presents synthesis and photophysical investigation of a very rare type of the ReI diimine complexes, [Re(diimine)(CO)3(OPR3)]+, R = Ph, Cy; diimine – phenanthroline and neocuproine, containing monodentate (unsupported) phosphine oxide ligands. The obtained compounds have been structurally characterized in solid phase by using XRD crystallography, which revealed unusual distortions in the pseudo octahedral rhenium environment, which may be ascribed to intramolecular interligand (phosphine oxide – diimine) interaction rather than to crystal packing effect. Optimization of the ground state structure of these molecules with the DFT method also confirmed intramolecular origin of the... 

    Conformational study of a strained tolanophane by dynamic 1H NMR spectroscopy and computational methods

    , Article Monatshefte fur Chemie ; Volume 139, Issue 10 , 2008 , Pages 1185-1189 ; 00269247 (ISSN) Darabi, H. R ; Azimzadeh Arani, M ; Tafazzoli, M ; Ghiasi, M ; Sharif University of Technology
    The existence of a short C-H⋯π (alkyl-alkyne) interaction in the structure of a strained and relatively rigid tolanophane is expected to hinder the rotation about the C-C sp3 single bond. Variable-temperature NMR experiments (performed in three solvents, CDCl3, THF-d8, and acetone-d6) and ab initio density functional calculations were carried out to investigate its dynamic nature. An energy barrier of 48.6 kJ/mol is determined at coalescence (210 K) with acetone-d6 which is in good agreement with calculation result (54 kJ/mol). © 2008 Springer-Verlag  

    Accurate determination of interlaminar stresses in general cross-ply laminates

    , Article Mechanics of Advanced Materials and Structures ; Volume 11, Issue 1 , 2004 , Pages 67-92 ; 15376494 (ISSN) Tahani, M ; Nosier, A ; Sharif University of Technology
    Reddy's layerwise theory is used to investigate analytically the interlaminar stresses near the free edges of general (unsymmetric and symmetric) cross-ply composite laminates with various boundary conditions subjected to mechanical and hygrothermal loadings. Laminates with finite dimensions are considered and full three-dimensional stresses in the interior and the boundary-layer regions are calculated. The results obtained from this theory are compared with those available in the literature. It is found that the theory can predict very accurately the stresses in the interior region and near the free edges of both finite and long laminates  

    Mechanics and morphology of single-walled carbon nanotubes: From graphene to the elastica

    , Article Philosophical Magazine ; Volume 93, Issue 17 , 2013 , Pages 2057-2088 ; 14786435 (ISSN) Delfani, M. R ; Shodja, H. M ; Ojaghnezhad, F ; Sharif University of Technology
    The elastica is referred to the shape of the curve into which the centreline of a flexible lamina is bent. Hence, single-walled carbon nanotubes (SWCNTs) are treated as the elastica obtained from bending of graphene. The corresponding large deformation accompanies both the material and geometrical non-linearities. The morphology of the free-standing SWCNTs such as the natural angle of twist, bond lengths, tube radius and wall thickness are determined. Moreover, it is shown that the induced self-equilibriated strain field has a remarkable impact on the mechanical behaviour of the nanotube. Utilization of an appropriate non-linear continuum constitutive relation for graphene leads to exact... 

    A simultaneous method for phase identification and equilibrium calculations in reactive mixtures

    , Article Chemical Engineering Research and Design ; Volume 89, Issue 10 , 2011 , Pages 1901-1908 ; 02638762 (ISSN) Avami, A ; Saboohi, Y ; Sharif University of Technology
    Phase identification is an important aspect of flash calculations which can affect the phase and chemical equilibria. A new simultaneous approach for reactive mixtures, based on τ-method which relies on modification equation for mole fraction summation, is introduced in this paper. In the proposed methodology, phase identification and solution of governing equations can be performed simultaneously and effectively. In addition, prior knowledge of the number of phases in advance is not required. Present methodology has been verified with the help of case studies and results are discussed in the present paper. The results indicate that the present method gives us information about presence of... 

    A simple and fast method for comparison of corrosion inhibition powers between pairs of pyridine derivative molecules

    , Article Corrosion ; Volume 61, Issue 8 , 2005 , Pages 778-783 ; 00109312 (ISSN) Lashgari, M ; Arshadi, M. R ; Parsafar, Gh. A ; Sharif University of Technology
    National Assoc. of Corrosion Engineers International  2005
    Ab initio quantum chemical calculations at the density functional theory (DFT) level were performed on eight pyridine derivative molecules as corrosion inhibitors for iron in an acidic solution. In this regard, the geometry of the molecules were optimized using the B3LYP/6-31G method first, and then interactions of these optimized structures with the iron atom were explored using the B3LYP/LANL1MB method. Two modes of adsorption were considered, i.e., planar adsorption (P) via the pyridine ring and vertical adsorption (V) through a nitrogen atom. The interaction energy was minimized through the variation of the inhibitor molecule-iron atom distance. These minimum energy values, along with... 

    Job Scheduling in a Single Machine with Ability to Run Jobs in Parallel

    , M.Sc. Thesis Sharif University of Technology Mashayekh, Khadijeh (Author) ; Abam, Mohammad Ali (Supervisor)
    This thesis introduces and investigates a new kind of scheduling model, in which the total amount of computational resources to be allocated at each moment by the processor is constrained and upper bounded by a constant. The time for a task to be executed is also dependent on the computational resources, dedicated to it by the processor, assuming that the multiplication of the execution time by the dedicated computational resources is a constant for each job. We investigate various objective functions, such as minimizing the number of tardy jobs, minimizing maximum latency and etc, under varying constraints. The investigated objective functions are: a) Minimize number of tardy jobs b)... 

    Simulation of Kick Control Process During Drilling with Assumption of Two-phase Flow

    , M.Sc. Thesis Sharif University of Technology Jahanpeima, Yaser (Author) ; Jamshidi, Saeed (Supervisor)
    During the drilling of oil and gas wells, the probability of a kick resulting in blow out is high. In the event of a kick, well should be controlled immediately and prevented blowing out. Common methods include: driller method, wait and weight method and concurrent method. In this project, simulation of well control process is done for common well control methods, for water based muds and oil based muds. Movement of different fluids, their combination and removal of fluid from the well are simulated and the results are listed. The flash calculations are done for oil based mud and dissolution of kick fluid in the oil based mud is considered. After simulating and calculating necessary... 

    A joint experimental and theoretical study of kinetic and mechanism of rearrangement of allyl p-tolyl ether

    , Article Journal of Molecular Structure: THEOCHEM ; Volume 893, Issues 1–3 , January , 2009 , Pages 73–76 Irani, M. (Mehdi) ; Haqgu, M. (Mohammad) ; Talebi, A ; Gholami, M. R. (Mohammad Reza) ; Sharif University of Technology
    A joint theoretical and experimental study of the kinetic and mechanism of the rearrangement of allyl p-tolyl ether was performed in order to study the kinetic and mechanism of the reaction. Experimental studies were performed in gas phase over a temperature range of 493.15–533.15 K. The experimental Arrhenius parameters of this reaction were measured to be Ea = 36.08 kcal mol−1, ΔS# = −7.88 cal mol−1 K−1, and Log A = 11.74, experimentally. Using GC for the mixture of the reaction with and without cyclohexene demonstrated that the reaction is clean without any radical intermediates. The experimental results show that the studied reaction is unimolecular and proceeds through a concerted... 

    Mapping dispersion fluctuations along optical fibers using brillouin probing and a fast analytic calculation

    , Article CLEO: Science and Innovations, CLEO_SI 2013, San Jose, CA ; 2013 ; 9781557529725 (ISBN) Alishahi, F ; Vedadi, A ; Denisov, A ; Soto, M. A ; Mehrany, K ; Brès, C. S ; Thévenaz, L ; Sharif University of Technology
    We propose a new system which can generate digital holograms using natural color information. The proposed system can generate about 10 digital holographic video frames per a second using about 6K light sources  

    A generalized set of correlations for plus fraction characterization

    , Article Petroleum Science ; Volume 9, Issue 3 , August , 2012 , Pages 370-378 ; 16725107 (ISSN) Jamialahmadi, M ; Zangeneh, H ; Hosseini, S. S ; Sharif University of Technology
    Springer  2012
    The importance of accurate determination of the critical properties of plus fractions in prediction of phase behaviour of hydrocarbon mixtures by equations of state is well known in the petroleum industry. It has been stated in various papers (Elsharkawy, 2001) that using the plus fraction as a single group in equation of state calculations reduces the accuracy of the results. However in this work it has been shown that using the proper values of critical temperature and pressure for the plus fraction group can estimate the properties of hydrocarbon mixtures, and they are accurate enough to be used in reservoir engineering and enhanced oil recovery calculations. In this paper, a new method... 

    Methane molecule over the defected and rippled graphene sheet

    , Article Solid State Communications ; Volume 152, Issue 15 , August , 2012 , Pages 1493-1496 ; 00381098 (ISSN) Shayeganfar, F ; Neek Amal, M ; Sharif University of Technology
    Elsevier  2012
    Adsorption of a methane molecule (CH 4) onto a defected and rippled graphene sheet is studied using ab initio and molecular mechanics calculations. The optimal adsorption position and orientation of this molecule on the graphene surface (motivated by the recent realization of graphene sensors to detect individual gas molecules) is determined and the adsorption energies are calculated. In light of the density of states, we used the SIESTA code. It is found that (i) classical force field yields adsorption energy comparable with experimental result and ab initio calculation; (ii) the periodic nature of the van der Waals potential energy stored between methane and perfect sheet is altered due to... 

    Tunable bandgap opening in the proposed structure of silicon-doped graphene

    , Article Micro and Nano Letters ; Volume 6, Issue 8 , 2011 , Pages 582-585 ; 17500443 (ISSN) Azadeh, M. S. S ; Kokabi, A ; Hosseini, M ; Fardmanesh, M ; Sharif University of Technology
    A specific structure of doped graphene with substituted silicon impurity is introduced and ab initio density-functional approach is applied for the energy band structure calculation of the proposed structure. Using the band structure calculation for different silicon sites in the host graphene, the effect of silicon concentration and unit cell geometry on the bandgap of the proposed structure is also investigated. Chemically, silicon-doped graphene results in an energy gap as large as 2eV according to density-functional theory calculations. As the authors will show, in contrast to previous bandgap engineering methods, such structure has significant advantages including wide gap tuning...