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    Conversion of Methane into Heaviour Hydrocarbures using Nanosecond Lasers

    , Ph.D. Dissertation Sharif University of Technology Navid Khoshgonab, Hamze Ali (Author) ; Sadighi Bonabi, Rasoul (Supervisor)
    Abstract
    In this thesis the conversion of methane into higher hydrocarbures using pulsed nanosecond lasers has been studied. The lasers of 532 nm of second harmonic of Nd: YAG, 355 nm of 3rd harmonic of Nd: YAG and 248 nm of KrF have been used in this project. Acetylene, ethylen and ethane have been detected using gas chromatography detection system, which showed acetylene as a dominant product. For each wavelength the amount of the laser energy and the fraction of secondary products have been measured. Also the dependence of amount of produced components on chamber pressure has been studied for 355 nm laser. During the irradiation time of methane no considerable changes in temperature and pressure... 

    Thermodynamic Modeling of Hydrogen Hydrate Formation with and without Help Molecules

    , M.Sc. Thesis Sharif University of Technology Ghorbanzadeh, Maryam (Author) ; Taghikhani, Vahid (Supervisor) ; Ghotbi, Siroos (Supervisor)
    Abstract
    In this study equilibrium condition of pure hydrogen hydrates is determined with Lee-Holder model. Two hydrogen molecules and four hydrogen molecules encaged in the small and large cavities respectively. Langmuir constant of hydrogen is calculated with the Exp-6 potential. Lee et al. reported parameter of this model by integrating ab initio calculation with classical statistical thermodynamics. This model reasonably predicts dissociation pressures of hydrogen hydrates.Calculated reference parameters are used in modeling of binary hydrogen hydrates. Lattice distortion model is used for modeling of binary hydrogen hydrates with tetrahydrofuran (THF) as a promoter. Cavity radius and parameters... 

    Modeling of Natural Gas Components Hydrate Formation by Using Neural Network

    , M.Sc. Thesis Sharif University of Technology Ameri, Azadeh (Author) ; Ghotbi, Siroos (Supervisor) ; Taghikhani, Vahid (Supervisor)
    Abstract
    In this study two approaches were applied to predict the hydrate dissociation pressure of natural gas in the presence of aqueous water. One approach applied van der Waals and Platteeuw solid solution theory & PR EOS the other applied a feed forward multi layers artificial neural network (ANN) with 19 input variables (temperature, existence of hydrocarbon liquid and ice phase, gas phase composition, inhibitor composition in aqueous phase), and one hidden layer with 17 neurons. In comparison of both methods it was concluded that, in temperature above 12℃ , ANN is more accurate than thermodynamic model, but in lower temperature thermodynamic model is comparable with ANN. The trained network... 

    Interaction of Femtosecond Lasers with Molecule

    , M.Sc. Thesis Sharif University of Technology Dehghani Tafti, Zeinab (Author) ; Sadighi Bonabi, Rasul (Supervisor)
    Abstract
    Using field assisted dissociation model and with a classic view the dissociation probability is calculated when it a molecule is exposed with a Ti:sapphire laser with wavenumber of 800nm and the energy of . using gradient optimization method we find a tailored two rectangular laser pulse for controlling the dissociation of C-H bond of . Using classical method reduced the complicacy of solving schrodinger equation. In our optimization method in contrast with the usual controlling method experimental data is not needed and this reduced the controlling costs.

     

    , M.Sc. Thesis Sharif University of Technology Eiravani, Hossaen (Author) ; Fattahi, Alireza (Supervisor)
    Abstract
    It is believed that intramolecular hydrogen bonding and also conjugation can affect the acidity power of organic molecules. But simultaneous effects of intramolecular hydrogen bonding and conjugation have not investigated systematically yet. In this project, we choose Ascorbic acid as a basic structure. Then we have changed its structure conveniently, and have explored the roles of hydrogen bonding and conjugation on the acidity of this molecule by using B3LYP functional with the 6-311++G(d,p) basis set. After that we similarly investigate these effects on the acidity of three different systems, including enols, enamines and alcohols. In this project we probe the effect of different hydrogen... 

    Survying the Process of Photodissociation of Methane with Using the Femto Second Lasers

    , M.Sc. Thesis Sharif University of Technology Irani, Elnaz (Author) ; Sadighi Bonabi, Rasoul (Supervisor)
    Abstract
    In this project , the dissociation of methane in the presence of Ti:Sapphire laser with parameters of 1014wcm-2, 800nm wave lengths and 100fs pulse width have been investigated theoretically, by using the Gaussian03 package –computational chemistry program that is capable of predicting many properties of atomic and molecular systems. It is based upon the fundamental laws of quantum mechanism. By considering some limitations in approximate techniques and incapability of advancing them, numerical calculation of solving the time dependent Schrödinger equation in order to improve the results and find more quantum dynamic information is applied. Therefore at first, by Gaussian03 package some of... 

    Molecular Dynamics Study in the Interaction of Intense Femtosecond Laser Pulse with Methane Molecule

    , Ph.D. Dissertation Sharif University of Technology Irani, Elnaz (Author) ; Sadighi-Bonabi, Rasul (Supervisor) ; Anvari, Abbas (Co-Advisor) ; Asgari, Reza (Co-Advisor)
    Abstract
    In this project, the ionization and dissociation of methane molecule by intense femto-second lasers has been studied. Dissociation probability is calculated for interacting CH4 molecule under Ti: Sapphire laser pulse with pulse durations of 10- 40fs in intensities at the range of 1014-1016 Wcm-2. Calculations are carried out with time-dependent density functional theory using Gaussian03 and Octopus packages as powerful computational chemical physics programs. Due to importance of the dependence of interaction dynamics to laser parameters, the effect of these parameters including different intensities, polarization, various pulse durations and pulse envelopes are investigated. The optimal... 

    Extraordinary swelling behavior of poly (AMPS) organogelin solvent/DMSO binary mixed media

    , Article Journal of Applied Polymer Science ; Volume 117, Issue 2 , July , 2010 , Pages 1127-1136 ; 00218995 (ISSN) Zohuriaan Mehr, M. J ; Kabiri, K ; Kheirabadi, M ; Sharif University of Technology
    2010
    Abstract
    The present article deals with super-swelling behavior of crosslinked homopolymer of 2-acrylamido-2-methylpropane sulfonic acid, poly(AMPS), in binary mixtures of dimethyl sulfoxide (DMSO) and various polar solvents including water, mono-, and polyhydric alcohols, and amide solvents such as N-methyl pyrrolidone. Extraordinary phase transition sequences including a new unusual swelling phenomenon, referred to as "overentrant" swelling, was observed for this polymeric organogel in the solvent/DMSO mixtures. The swelling behaviors were preliminarily explained based on the major interactions involved in the solvation process and dielectric constant of the swelling media. It was established that... 

    Dissociation of C-H molecular bond of methane by pulse shaped ultra-intense laser field

    , Article Chemical Physics Letters ; Volume 560 , 2013 , Pages 60-65 ; 00092614 (ISSN) Zare, S ; Irani, E ; Navid, H. A ; Dehghani, Z ; Anvari, A ; Sadighi Bonabi, R ; Sharif University of Technology
    2013
    Abstract
    The effects of laser field and laser pulse width on the dissociation probability of C-H bond of CH4 have been investigated. Calculation of time dependent Schrödinger equation by grid spectral method is carried out and it is produced optimistic results in comparison to the earlier Quasi-classical calculations. The results show that there is an excellent match with experimental data. In this work, a number of results in the emerging field of laser with intensity of I = 8 × 1013 W cm-2 and pulse duration of 100 fs are presented. The present modulated field leads to more than 20% improvement in the dissociation probability  

    Mechanisms and kinetics of Thiotepa and tepa hydrolysis: DFT study

    , Article Journal of Molecular Modeling ; Volume 18, Issue 8 , 2012 , Pages 3563-3576 ; 16102940 (ISSN) Torabifard, H ; Fattahi, A ; Sharif University of Technology
    Springer  2012
    Abstract
    N,N′,N″-triethylenethiophosphoramide (Thiotepa) and its oxo analogue (Tepa) as the major metabolite are trifunctional alkylating agents with a broad spectrum of antitumor activity. In vivo and vitro studies show alkylation of DNA by Thiotepa and Tepa can follow two pathways, but it remains unclear which pathway represents the precise mechanism of action. In pathway 1, these agents are capable of forming cross-links with DNA molecules via two different mechanisms. In the first mechanism, the ring opening reaction is initiated by protonating the aziridine, which then becomes the primary target of nucleophilic attack by the N7-Guanine. The second one is a direct nucleophilic ring opening of... 

    Electrostatically defying cation-cation clusters: Can likes attract in a low-polarity environment?

    , Article Journal of Physical Chemistry A ; Volume 117, Issue 38 , 2013 , Pages 9252-9258 ; 10895639 (ISSN) Shokri, A ; Ramezani, M ; Fattahi, A ; Kass, S. R ; Sharif University of Technology
    2013
    Abstract
    Like-charge ion pairing is commonly observed in protein structures and plays a significant role in biochemical processes. Density functional calculations combined with the conductor-like polarizable continuum model were employed to study the formation possibilities of doubly charged noncovalently linked complexes of a series of model compounds and amino acids in the gas phase and in solution. Hydrogen bond interactions were found to offset the Coulombic repulsion such that cation-cation clusters are minima on the potential energy surfaces and neither counterions nor solvent molecules are needed to hold them together. In the gas phase the dissociation energies are exothermic, and the... 

    Recent results of edge plasma parameters measurements in IR-T1 tokamak by probe

    , Article Journal of Fusion Energy ; Volume 29, Issue 3 , June , 2010 , Pages 271-274 ; 01640313 (ISSN) Shariatzadeh, R ; Emami, M ; Ghoranneviss, M ; Abaspour Tehrani Fard, A ; Sharif University of Technology
    2010
    Abstract
    Langmuir probes (LP) are the most common diagnostics for the local measurement of very important plasma parameters such as plasma density, electron temperature, plasma potential and the electron energy distribution function (EEDF). In this paper the applicability of the first derivative Langmuir probe method in processing the electron part of the current-voltage (I-V) characteristics in IR-T1 Tokamak is reported. The EEDF at different radial positions in the edge region and Scrape off Layer (SOL) are derived and the values of the plasma potential, electron temperature and electron density are estimated. Results comparison between the first derivative method and Stangeby method shows a... 

    Optimization of two tailored rectangular femtosecond laser pulses in methane dissociation

    , Article Proceedings of SPIE - The International Society for Optical Engineering, 12 April 2010 through 16 April 2010 ; Volume 7721 , April , 2010 ; 0277786X (ISSN) ; 9780819481948 (ISBN) Sadighi Bonabi, R ; Dehghani, Z ; Irani, E ; The Society of Photo-Optical Instrumentation Engineers (SPIE); Brussels Photonics Team (B-PHOT); Brussels-Capital Region; Fonds Wetenschappelijk Onderzoek (FWO); International Commission for Optics (ICO) ; Sharif University of Technology
    2010
    Abstract
    Based on the quantum mechanics principles and classically calculated dressed potential surfaces by using field assisted dissociation model the dissociation probability for CH4 + molecule exposed with a 100 femtosecond 8 Jcm-2 Ti:sapphire laser pulses is calculated. Using the gradient optimization method two tailored rectangular laser pulses for controlling the dissociation of C-H bond of CH4 + molecule along laser pulse direction is found. In the proposed optimization method, the complicacy of solving Schrodinger wave equation is reduced by using classical method and in contrast to the usual controlling and pulse shaping methods of chemical reactions, the experimental data is not needed and... 

    Potential and energy of the monoenergetic electrons in an alternative ellipsoid bubble model

    , Article Physical Review A - Atomic, Molecular, and Optical Physics ; Volume 81, Issue 2 , 2010 ; 10502947 (ISSN) Sadighi Bonabi, R ; Rahmatallahpur, S ; Sharif University of Technology
    Abstract
    The electron acceleration in the bubble regime is considered during the intense laser-plasma interaction. The presented ellipsoid cavity model is more consistent than the previous spherical model, and it explains the monoenergetic electron trajectory more accurately. At the relativistic region, the maximum energy of electrons in the ellipsoid model is about 24% more than the spherical model, and this is confirmed by PIC and the measured experimental results reported here. The electron energy spectrum is also calculated, and it is found that the energy distribution ratio of electrons ΔE/E for the ellipsoid model in the here reported condition is about 11% which is less than the one third that... 

    Hydrogen storage in decorated multiwalled carbon nanotubes by Ca, Co, Fe, Ni, and Pd nanoparticles under ambient conditions

    , Article Journal of Physical Chemistry C ; Volume 115, Issue 14 , 2011 , Pages 6994-7001 ; 19327447 (ISSN) Reyhani, A ; Mortazavi, S. Z ; Mirershadi, S ; Moshfegh, A. Z ; Parvin, P ; Golikand, A. N ; Sharif University of Technology
    Abstract
    We report a study on hydrogen storage in Ca, Co, Fe, Ni, and Pd decorated multiwalled carbon nanotubes (MWCNTs) by using two techniques: volumetric and electrochemical. The results showed that hydrogen molecules are adsorbed on the defect sites and transported to the spaces between adjacent carbon via diffusion through both defect sites and opened tips into the layers. Hydrogen storage capacity can be improved in the decorated MWCNT by Co, Fe, Ni, and Ca metals in two approaches: (i) H2 adsorption via Kubas interaction and (ii) dissociation of H2 molecules on the metal particles. The results reveal that Pd are more effective catalyst for hydrogen storage process. It was found that... 

    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
    Abstract
    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  

    Optimal control of dissociation of nitrogen molecule with intense ultra-short laser pulse shaping

    , Article Journal of Molecular Structure ; Volume 1083 , March , 2015 , Pages 121-126 ; 00222860 (ISSN) Rasti, S ; Irani, E ; Sadighi Bonabi, R ; Sharif University of Technology
    Elsevier  2015
    Abstract
    (GraphPresented) The quantum optimal control theory in conjunction with time dependent density functional theory is used to optimize the laser pulse shape for dissociation of nitrogen molecule. For several initial peak intensities and frequency ranges, the optimum shapes are produced and compared to determine the most efficient pulse. Ehrenfest molecular dynamics model is also used to test the dissociation process. The corresponding snapshots of density and time dependent electron localization function are presented. It is noticed that when the frequency ranges of laser pulses are doubled, it leads to 60% faster dissociation of N2 molecule  

    The effect of ultraviolet lasers on conversion of methane into higher hydrocarbons

    , Article Laser and Particle Beams ; Volume 31, Issue 3 , 2013 , Pages 481-486 ; 02630346 (ISSN) Navid, H. A ; Irani, E ; Sadighi Bonabi, R ; Sharif University of Technology
    2013
    Abstract
    Conversion of CH4 molecule into higher hydrocarbons using two different wavelengths of 248 nm KrF laser and 355 nm of third harmonic of Nd:YAG laser is studied experimentally and theoretically. The stable products are analyzed and the effect of pressure on conversion of methane is measured. The detected reaction products are C2H2, C2H4, and C2H6. The conversion efficiency of 33.5% for 355 nm in comparison to 2.2% conversion for 248 nm for C2H2 is achieved. The potential of laser parameters as an important variable in controlling of final products is investigated  

    Possibility of methane conversion into heavier hydrocarbons using nanosecond lasers

    , Article Spectrochimica Acta - Part A: Molecular and Biomolecular Spectroscopy ; Volume 156 , 2016 , Pages 118-122 ; 13861425 (ISSN) Navid, H. A ; Irani, E ; Sadighi Bonabi, R ; Sharif University of Technology
    Elsevier  2016
    Abstract
    Effect of nanosecond lasers on the methane dissociation is experimentally studied by using three different laser wavelengths at 248 nm, 355 nm and 532 nm. C2H2 generation is measured as a major reaction product in experiments and the energy consumptions in production of this component are measured as 5.8 MJ/mol, 3.1 MJ/mol and 69.0 MJ/mol, for 355 nm, 532 nm and 248 nm wavelengths, respectively. The mechanism of conversion and production of new stable hydrocarbons is also theoretically investigated. It is found that in theoretical calculations, the ion-molecule reactions should be included and this leads to a unique approach in proper explanation of the experimental measurements  

    Benchmarking of Monte Carlo model of Siemens Oncor® linear accelerator for 18MV photon beam: determination of initial electron beam parameters

    , Article Journal of X-Ray Science and Technology ; Volume 27, Issue 6 , 2 January , 2020 , Pages 1047-1070 Najafzadeh, M ; Hoseini Ghafarokhi, M ; Bolagh, R. S. M ; Haghparast, M ; Zarifi, S ; Nickfarjam, A ; Farhood, B ; Chow, J. C. L ; Sharif University of Technology
    IOS Press  2020
    Abstract
    OBJECTIVE: This study aims to benchmark a Monte Carlo (MC) model of the 18 MV photon beam produced by the Siemens Oncor® linac using the BEAMnrc and DOSXYZnrc codes. METHODS: By matching the percentage depth doses and beam profiles calculated by MC simulations with measurements, the initial electron beam parameters including electron energy, full width at half maximum (spatial FWHM), and mean angular spread were derived for the 10×10 cm2 and 20×20 cm2 field sizes. The MC model of the 18 MV photon beam was then validated against the measurements for different field sizes (5×5, 30×30 and 40×40 cm2) by gamma index analysis. RESULTS: The optimum values for electron energy, spatial FWHM and mean...