Search for: theoretical-investigations
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    Theoretical investigation of the capture effect in intensity-modulation direct-detection microwave photonic links

    , Article Applied Optics ; Volume 52, Issue 28 , 2013 , Pages 7011-7021 ; 1559128X (ISSN) Hosseini, S. E ; Banai, A ; Sharif University of Technology
    Optical Society of American (OSA)  2013
    We introduce the capture effect concept in microwave photonic links (MWPLs) for the first time to our knowledge. The capture effect or the small-signal suppression is the change in the amplitude ratio of the two signals between input and output of the intensity-modulation direct-detection (IMDD) MWPLs. An analytical explanation of the performance of external IMDD MWPLs due to the effects of nonlinearity combined with sum of several input sinusoidal signals is given.We have investigated the suppression of a weaker signal in these links. General analytic expression for the small-signal suppression is derived using a nonlinear analytical approach. We show that the small-signal suppression is... 

    Theoretical investigation of Li2MnSiO4 as a cathode material for Li-ion batteries: A DFT study

    , Article Journal of Materials Chemistry A ; Volume 1, Issue 8 , 2013 , Pages 2847-2855 ; 20507488 (ISSN) Kalantarian, M. M ; Asgari, S ; Mustarelli, P ; Sharif University of Technology
    Transition metal lithium orthosilicates are of interest as cathode materials for lithium batteries. Density functional theory (DFT) calculations were performed to evaluate the structural and electrochemical properties of the different polymorphs of Li2MnSiO4. Our computational studies predict superior properties for the Pmn21 polymorph even after extraction of two Li per formula unit. We state that the shortcomings observed for Li2MnSiO4 as a cathode are caused by two mechanisms. Switching of the magnetic state occurs during the first cycles. The subsequent transition, under delithiated conditions, from the Pmn21 or Pmnb polymorphs to the electrochemically weakest P21/n polymorph is the... 

    Theoretical investigation of electromagnetically induced phase grating in RF-driven cascade-Type atomic systems

    , Article Applied Optics ; Volume 54, Issue 11 , 2015 , Pages 3484-3490 ; 1559128X (ISSN) Sadighi Bonabi, R ; Naseri, T ; Sharif University of Technology
    A new scheme for investigating electromagnetically induced grating in four-level cascade-Type of 87Rb cold atoms is presented. The novel result indicates that the diffraction efficiency of phase grating is dramatically enhanced due to the presence of an RF-driven field and a diffraction efficiency up to 34% can be obtained. Furthermore, it is found that the frequency detuning of the applied laser fields with the corresponding atomic transition and the interaction length can improve the efficiency of the phase grating in the present atomic model. This work has potential applications in all-optical communication processes  

    A novel phenolic ionic liquid for 1.5 molar CO2 capture: Combined experimental and DFT studies

    , Article RSC Advances ; Volume 5, Issue 71 , Jun , 2015 , Pages 58005-58009 ; 20462069 (ISSN) Vafaeezadeh, M ; Aboudi, J ; Mahmoodi Hashemi, M ; Sharif University of Technology
    Royal Society of Chemistry  2015
    A phenolic-based ionic liquid (IL), 1-(2-hydroxyethyl)-2,3-dimethylimidazolium phenoxide has been introduced for 1.5 molar carbon dioxide (CO2) absorption at ambient conditions without using special methodologies or precautions. The structure of the IL was characterized by various methods such as FT-IR, 1H NMR, 13C NMR, elemental analysis (EA) and thermogravimetric analysis (TGA). The ability of this IL for CO2 uptake reaches to its maximum value after 2 h. The IL has been reused fr several times with constant efficiency. Density functional theory (DFT) calculations at the B3LYP/6-311++G∗∗ level of calculation have been carried out to gain more structural knowledge... 

    Experimental and theoretical investigation of cubic stabilization of instability of an interface in surface wave motion

    , Article Physics of Fluids ; Volume 32, Issue 2 , 26 February , 2020 Jamali, M ; Behzadi, S ; Safaie, A ; Fazeli, M ; Sharif University of Technology
    American Institute of Physics Inc  2020
    Motivated by recent laboratory and field observations, this paper reports the first quantitative measurements of the stabilization phase of interfacial instability in a two-layer fluid in surface wave motion. The instability results from the formation of a resonant triad between the surface wave and noise-level sub-harmonic interfacial waves. To exclude the effects of interfacial mixing on the interaction, the experiments were carried out with immiscible fluids. Carrying out a resonant interaction analysis to the third order of nonlinearity using a Lagrangian formulation, we also show for the first time that the three-wave resonance is inherently accompanied by a harmonic four-wave resonant... 

    Theoretical modeling of generation of hat-top intensity profile from Gaussian beam by means of a two-stage beam shaper

    , Article Optics Communications ; Volume 294 , 2013 , Pages 182-187 ; 00304018 (ISSN) Haghighatzadeh, A ; Golnabi, H ; Sharif University of Technology
    Both theoretical and experimental results of an optical beam shaping system are investigated in this report. The described system is a two-stage beam shaping device including a fiber-bundle and a prism-duct. A source light is used to illuminate the fiber-bundle and the image of output beam is captured by a CCD camera. The fiber-bundle output beam shape shows a linear arrangement of circular spots lights, which are placed in a rectangular cross section of about 21.37 mm×2.44 mm. In another study, the photograph picture of the prism output beam is taken by a digital camera. The prism output beam cross section is a square shape with a dimension of about 4×4 mm2. According to the experimental... 

    Hydrogen-passivated graphene antidot structures for thermoelectric applications

    , Article 2011 12th Int. Conf. on Thermal, Mechanical and Multi-Physics Simulation and Experiments in Microelectronics and Microsystems,EuroSimE 2011 ; 18 April 2011 through 20 April , 2011 ; 9781457701078 (ISBN) Karamitaheri, H ; Pourfath, M ; Faez, R ; Kosina, H ; Sharif University of Technology
    In this work, we present a theoretical investigation of the thermal conductivity of hydrogen-passivated graphene antidot lattices. Using a fourth nearest-neighbor force constant method, we evaluate the phonon dispersion of hydrogen-passivated graphene antidot lattices with circular, hexagonal, rectangular and triangular shapes. Ballistic transport models are used to evaluate the thermal conductivity. The calculations indicate that the thermal conductivity of hydrogen-passivated graphene antidot lattices can be one fourth of that of a pristine graphene sheet. This reduction is stronger for right-triangular and iso-triangular antidots among others, all with the same area, due to longer... 

    Study of beam divergence of a fiber-bundle prism-coupled waveguide using ray tracing

    , Article Optik ; Volume 126, Issue 4 , 2015 , Pages 394-399 ; 00304026 (ISSN) Haghighatzadeh, A ; Golnabi, H ; Sharif University of Technology
    Urban und Fischer Verlag Jena  2015
    Experimental and theoretical results of a two-stage beam shaping system based on a flexible plastic fiber-bundle and a prism duct are described in this study. An imaging technique is used to investigate the divergence effect on the output beam images and intensity profiles. Photograph pictures of the output beam at different axial distances are taken by a digital camera and the image data is converted into a response curve and presented in this study. According to the experimental results, the propagation in the free space transforms a square beam with a hat-top intensity distribution into a rectangular beam with a conical intensity distribution. For theoretical investigations, using VOB... 

    Formation of a catalytically active intermediate for oxidation in H2O2/ionic liquid system: experimental and theoretical investigations

    , Article Research on Chemical Intermediates ; Volume 43, Issue 4 , 2017 , Pages 2615-2625 ; 09226168 (ISSN) Alinezhad, H ; Vafaeezadeh, M ; Mahmoodi Hashemi, M ; Sharif University of Technology
    Springer Netherlands  2017
    Abstract: A metal-free method for activation of hydrogen peroxide (H2O2) is introduced using piperidinium trifluoroacetate (PPHTFA) ionic liquid as catalyst. The catalyst has been used for selective oxidation of thioanisole to its corresponding sulfoxide at room temperature. It was found that the selectivities were reduced by increasing the reaction temperature. In this work, no organic solvents or metallic salts were used for activation of H2O2. Mechanistic studies suggested that the reaction proceeds via in situ formation of trifluoro hydroperoxy species as an active catalytic intermediate. Formation of the catalytic intermediate was screened by NMR, IR and Mass Spectroscopy analysis.... 

    Performance evaluation of a novel compact humidification-dehumidification desalination system coupled with a heat pump for design and off-design conditions

    , Article Energy Conversion and Management ; Volume 194 , 2019 , Pages 160-172 ; 01968904 (ISSN) Faegh, M ; Shafii, M. B ; Sharif University of Technology
    Elsevier Ltd  2019
    In this study, the theoretical investigation of a novel heat pump assisted humidification-dehumidification desalination system has been carried out. The conventional dehumidifier of the humidification-dehumidification system was removed and the evaporator of the heat pump was utilized for direct dehumidification of air. Besides, the heat pump condenser was used as the saline water heater of the humidification-dehumidification cycle. First, the sizes of the components were calculated at design conditions for fixed input operational conditions namely the ambient air temperature, relative humidity, and inlet saline water temperature. However, the input operating conditions vary at off-design... 

    Pressure induced structural, electronic, optical and thermal properties of CsYbBr3, a theoretical investigation

    , Article Journal of Materials Research and Technology ; Volume 10 , 2021 , Pages 687-696 ; 22387854 (ISSN) Saeed, M ; Ali, M. A ; Murad, S ; Ullah, R ; Alshahrani, T ; Laref, A ; Murtaza, G ; Sharif University of Technology
    Elsevier Editora Ltda  2021
    This article presents the variation of structural, electronic, thermal and optical properties of a halide perovskite CsYbBr3with increasing pressure, employing density functional theory. The pressure effect was determined in range of 0-15 GPa. In which stability of CsYbBr3remains valid, as, verified from negative values of enthalpy of formation and phonon dispersion curves. A significant change was observed in lattice constant, bond lengths, bulk modulus and its pressure derivative, volume and ground state energy, with increasing pressure. The calculated electronic properties presented CsYbBr3as a semiconductor with direct band gap of 3.61 eV. However, pressure rise shift the Yb-d states... 

    Theoretical investigation of the effect of hydrogen bonding on the stereoselectivity of the Diels-Alder reaction

    , Article New Journal of Chemistry ; Volume 45, Issue 36 , 2021 , Pages 16760-16772 ; 11440546 (ISSN) Taherinia, D ; Mahmoodi, M. M ; Fattahi, A ; Sharif University of Technology
    Royal Society of Chemistry  2021
    In this article, we report the computational examination of the impact of hydrogen bonding (HB) on the stereoselectivity of a series of Diels-Alder (DA) reactions. Four different types of diene/dienophile couples were studied including (a) cyclopenta-2,4-dien-1-ol and heteroatom-substituted cyclopentenes, (b) substituted cyclopentadienes andN-protonated 2,5-dihydro-1H-pyrrole, (c) furan andN-protonated 5-azabicyclo[2.1.1]hex-2-ene, and (d)N-protonated cyclopenta-2,4-dien-1-amine and α,β-unsaturated carbonyl compounds. These systems were designed such that the HB can only exist in theexoreaction pathway. The optimized structures of the transition states (TSs) and products, along with the... 

    Glucose interaction with Au, Ag, and Cu clusters: Theoretical investigation

    , Article International Journal of Quantum Chemistry ; Volume 113, Issue 8 , 2013 , Pages 1062-1070 ; 00207608 (ISSN) Jamshidi, Z ; Farhangian, H ; Tehrani, Z. A ; Sharif University of Technology
    Interactions of α-D-glucose with gold, silver, and copper metal clusters are studied theoretically at the density functional theory (CAM-B3LYP) and MP2 levels of theory, using trimer clusters as simple catalytic models for metal particles as well as investigating the effect of cluster charge by studying the interactions of cationic and anionic gold clusters with glucose. The bonding between α-D-glucose and metal clusters occurs by two major bonding factors; the anchoring of M atoms (M = Cu, Ag, and Au) to the O atoms, and the unconventional M.H-O hydrogen bond. Depending on the charge of metal clusters, each of these bonds contributes significantly to the complexation. Binding energy... 

    Laser induced surface processing with gold nanoparticle arrays embedded in a transparent matrix

    , Article Nano ; Volume 8, Issue 1 , January , 2013 ; 17932920 (ISSN) Askari, A. A ; Bahrampour, A. R ; Sharif University of Technology
    Gold nanoparticles are widely used as high efficient photon-thermal energy converters in a broad range of applications. This paper presents a theoretical investigation on using the optothermal properties of gold nanoparticle arrays to generate nanoscale molten and rubbery regions on the surface of an amorphous polymeric film. Nanoparticles are assumed to be embedded in a transparent silica layer and illuminated with a 7.5 ns pulsed laser at 532 nm. Simulation results are presented for systems with single gold nanoparticles, dimers and chains. Both electromagnetic and thermal interaction between nanoparticles are found to be important factors in determining the result of surface processing.... 

    Interactions of coinage metal clusters with histidine and their effects on histidine acidity; Theoretical investigation

    , Article Organic and Biomolecular Chemistry ; Volume 10, Issue 47 , Oct , 2012 , Pages 9373-9382 ; 14770520 (ISSN) Javan, M. J ; Jamshidi, Z ; Tehrani, Z. A ; Fattahi, A ; Sharif University of Technology
    Understanding the nature of interaction between metal nanoparticles and biomolecules such as amino acids is important in the development and design of biosensors. In this paper, binding of M3 clusters (M = Au, Ag and Cu) with neutral and anionic forms of histidine amino acid was studied using density functional theory (DFT-B3LYP). It was found that the interaction of histidine with M3 clusters is governed by two major bonding factors: (a) the anchoring N-M and O-M bonds and (b) the nonconventional N-H⋯M and O-H⋯M hydrogen bonds. The nature of these chemical bonds has been investigated based on quantum theory of atoms in molecules (QTAIM) and natural bond orbital (NBO) analyses. In the next... 

    Copper, gold, and silver decorated magnetic core–polymeric shell nanostructures for destruction of pathogenic bacteria

    , Article Russian Journal of Physical Chemistry A ; Volume 91, Issue 5 , 2017 , Pages 936-945 ; 00360244 (ISSN) Padervand, M ; Kiani Karanji, A ; Elahifard, M. R ; Sharif University of Technology
    Maik Nauka-Interperiodica Publishing  2017
    Fe3O4 magnetic nanoparticles (MNPs) were prepared by co-precipitation method. The nanoparticles were silica coated using TEOS, and then modified by the polymeric layers of polypropylene glycol (PPG) and polyethylene glycol (PEG). Finally, the core-shell samples were decorated with Ag, Au, and Cu nanoparticles. The products were characterized by vibrating sample magnetometry (VSM), TGA, SEM, XRD, and FTIR methods. The antibacterial activity of the prepared samples was evaluated in inactivation of E. coli and S. aureus microorganisms, representing the Gram-negative and Gram-positive species, respectively. The effect of solid dosage, bacteria concentration and type of polymeric modifier on the... 

    Experimental and theoretical investigations on spray characteristics of bio-ethanol blends using a direct injection system

    , Article Scientia Iranica ; Volume 24, Issue 1 , 2017 , Pages 237-248 ; 10263098 (ISSN) Ghahremani, A. R ; Jafari, M ; Ahari, M ; Saidi, M. H ; Hajinezhad, A ; Mozafari, A. A ; Sharif University of Technology
    Sharif University of Technology  2017
    In the present work, the spray characteristics of bio-ethanol and its blends have been experimentally and theoretically investigated. To have a comprehensive study, the effects of ambient condition and injection pressure on the spray of different blends have been considered. Macroscopic and microscopic characteristics of spray such as tip penetration length, cone angle, projected area, volume, Sauter Mean Diameter (SMD), and Ohnesorge number are investigated precisely. Besides, air entrainment and atomization analyses have been carried out to improve mixture formation process. Using curve fitting and least squares method, theoretical correlations have been suggested in such a way to predict... 

    On the sensitivity of the nanostructural parameters on youngg"s modulus of PLSNs in fully intercalated structures

    , Article Journal of Composite Materials ; Volume 43, Issue 24 , 2009 , Pages 2921-2941 ; 00219983 (ISSN) Zehtab Yazdi, A ; Bagheri, R ; Kazeminezhad, M ; Sharif University of Technology
    Polymer-layered silicate nanocomposites have been observed to demonstrate enhanced mechanical properties particularly at low weight fractions of silicate. Experimental and theoretical investigations reveal that numerous structural parameters strongly influence the modulus of such nanocomposites. A multiscale micromechanical model is developed which considers a wide range of different affecting parameters including the particle aspect ratio, the number of silicate layers per stack, the d-spacing ratio between the layers, the penetration of polymer chains along silicate sheets, the intercalation feature, and the particle volume fraction. The developed model illustrates the accuracy and... 

    The theoretical investigation of the proposed optical fiber torsion sensor based on computer-generated-hologram (CGH)

    , Article Optics Communications ; Volume 463 , 2020 Esmailzadeh Noghani, F ; Tofighi, S ; Bahrampour, A. R ; Sharif University of Technology
    Elsevier B.V  2020
    Optical fiber torsion sensors have significant importance for structural health monitoring. In this paper, an optical fiber torsion sensor based on computer-generated-hologram (CGH) is proposed and investigated theoretically. In the proposed structure a dual mode fiber (DMF) is used as a sensing element. An acoustic source can be employed to induce a fiber grating. The acoustic induced fiber grating (AIFG) causes the fundamental LP01 mode of DMF couples to LP11 o and LP11 e fiber modes. In the presence of torsion in DMF, the profiles of LP01, LP11 o and LP11 e modes rotate relative to the absence of fiber torsion. At the end of DMF a suitable CGH can be employed to resolve spatially the... 

    Experimental and theoretical investigation of centrifugal compressor performance characteristics

    , Article Proceedings of the ASME Turbo Expo, 9 June 2008 through 13 June 2008, Berlin ; Volume 6, Issue PART B , 2008 ; 9780791843161 (ISBN) Motavalli, M ; Hajilouy Benisi, A ; Nili Ahmadabadi, M ; International Gas Turbine Institute ; Sharif University of Technology
    Prediction of compressor performance is a basic step in design of this turbomachine, while designer can optimize plan by considering various conditions and calculating machine performance. Flow field in centrifugal compressor is threedimensional and intricate. Since 2-D and 3-D methods are very costly, consequently the mean line method usually is used for predicting compressor performance. The energy loss coefficients are used for this method. Because of the intricacy in flow and analysis of losses, most energy loss coefficients are attained by experimental procedures, however just some of them are determined according to theory and nature of the flow field. The purpose of this work is...