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    Effect of treatment time and temperature on microstructure and corrosion behavior of Zn-Ni electrophosphate coating

    , Article Journal of Alloys and Compounds ; Volume 688 , 2016 , Pages 596-604 ; 09258388 (ISSN) BaratiDar Darband, G ; Afshar, A ; Rabani, M ; Sharif University of Technology
    Elsevier Ltd  2016
    In this study, the effect of phosphating time and temperature on microstructure and corrosion behavior of Zn-Ni electrophosphate coating with a galvanized steel as a substrate, were investigated. SEM and X-ray diffraction methods were used for investigation the microstructure and phase analysis, respectively. And immersion test, potentiodynamic polarization test, and Electrochemical Impedance Spectroscopy tests were used for the study of corrosion behavior. The results of this study indicated that the best coating morphology is obtained in the range between 20 and 30 min and 40–50° C. Moreover, results of corrosion studies showed that the corrosion mechanism is under diffusion control due to... 

    Tunable polarization converter based on one-dimensional graphene metasurfaces

    , Article Journal of the Optical Society of America B: Optical Physics ; Volume 35, Issue 10 , 2018 , Pages 2574-2581 ; 07403224 (ISSN) Tavakol, M. R ; Rahmani, B ; Khavasi, A ; Sharif University of Technology
    OSA - The Optical Society  2018
    We introduce a new metasurface structure for controlling the polarization of light by leveraging a wellharmonized combination of graphene and dielectric. The proposed metasurface is composed of an array of rectangular pillars laterally sandwiched by ribbons of graphene. Being able to dynamically change the polarization state of the reflected wave, the proposed structure is employed to realize a switchable polarization converter, which is able to act as a reflector (co-polarizer)/right-hand circular (RHC) quarter-wave plate or RHC/cross/ left-hand circular (LHC) polarizer based on its design configuration. The reflected amplitude in all states of functionality is remarkably high. It is also... 

    Tailoring the graphene polarity through the facile and one-step electrochemical exfoliation in low concentration of exfoliation agents

    , Article FlatChem ; Volume 22 , July , 2020 Goodarzi, M ; Pircheraghi, G ; Khonakdar, H. A ; Sharif University of Technology
    Elsevier B.V  2020
    Graphene nanoplatelets with different oxidation degrees, from low polar few-layer graphene (FLG) to high polar graphene oxide (GO) in the same current and concentration of the oxidizing agent in low concentrated electrolytes ((NH4)2SO4, Sodium Do-decyl Sulfate (SDS), and HNO3) are prepared through a one-step and cost-effective electrochemical synthesis route to find the effect of electrolyte on the surface polarity of powders. In order to use a wide variety of electrolytes, basic, neutral, and acidic electrolytes in a concentration as low as 0.2 M are used. Exfoliated graphene nanoplatelets without any further process are obtained to simplify and accelerate the synthesis process. Several... 

    A time modulated array with polarization diversity capability

    , Article IEEE Access ; Volume 9 , 2021 , Pages 53735-53744 ; 21693536 (ISSN) Mazaheri, M. H ; Fakharzadeh, M ; Akbari, M ; Safavi Naeini, S ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2021
    The Time Modulated Array (TMA) provides multiple radiation beams at different frequencies, by turning the radiating elements on and off. In this paper, we propose to add polarization diversity to a wireless communication link by leveraging the capabilities of the TMA. The proposed architecture switches between two orthogonal polarizations, instead of turning the antenna off, providing polarization diversity for the receivers. We show that the beams of each polarization at the sidebandsare exactly the same. However, the switching sequence should be optimized for the fundamental frequency to provide the same radiation level at each sideband. Two different switching sequences are proposed,... 

    Accurate liquid-volume calculations for pure polar compounds using a volume-translated Peng-Robinson equation of state

    , Article Scientia Iranica ; Volume 6, Issue 5 , 2000 , Pages 115-124 ; 10263098 (ISSN) Ghotbi, C ; Behzadi, B ; Feyzi, F ; Sharif University of Technology
    Sharif University of Technology  2000
    In this paper, the accuracy of Peng-Robinson equation of state for vapor-liquid equilibrium calculations has been studied for pure polar compounds and is compared with some other equations of state. This equation has then been modified using the volume-translation technique to improve saturated liquid-volume predictions in low to intermediate temperature and pressure ranges. Two different generalized forms of the translation parameter have been proposed in terms of critical compressibility factor and the reduced dipole moment multiplied by the acentric factor. The proposed generalized equations demonstrate more accurate results compared with the original Peng-Robinson and other selected... 

    Quality improvement of millimeter-wave imaging systems using optimized dual polarized arrays

    , Article IEEE Transactions on Antennas and Propagation ; Volume 69, Issue 10 , 2021 , Pages 6848-6856 ; 0018926X (ISSN) Rezaei, M ; Zamani, H ; Fakharzadeh, M ; Memarian, M ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2021
    In this article, we propose a software-hardware system to improve the quality of image recovery in millimeter-wave (MMW) imaging systems, which aims to benefit from copolarization and cross-polarization scatterings from the target. The proposed dual-polarized antenna array structures consist of two orthogonal subarrays with the same phase center, where each subarray is comprised of 2 imes 1 or 4 imes 1 rectangular edge fed patches and the optimized ground defects. These compact structures, which support radiation of two orthogonal linear polarizations, are designed on a single-layer board using crossover technique. The dual-polarized scattering from the target is captured by the orthogonal... 

    Analysis of degree of polarization as a control signal in PMD compensation systems aided by polarization scrambling

    , Article Journal of Lightwave Technology ; Volume 26, Issue 16 , 15 August , 2008 , Pages 2865-2872 ; 07338724 (ISSN) Safari, M ; Shishegar, A. A ; Sharif University of Technology
    The performance of degree of polarization (DOP) is investigated as a control signal in polarization-mode dispersion (PMD) compensation systems aided by polarization scrambling. The relation between the input and output polarization states of a signal propagating through a polarization scrambler and a PMD-induced optical fiber is described by a 3 × 3 Stokes transfer matrix. The average DOP of the output signal over a period of polarization scrambling is derived as an alternative to the conventional DOP-based control signal, i.e., minimum DOP. In the presence of first- and all-order PMDs, the performance of the average and minimum DOPs in monitoring of differential group delay (DGD) for... 

    Crosstalk elimination in the detection of dual-beam optical tweezers by spatial filtering

    , Article Review of Scientific Instruments ; Volume 85, Issue 5 , May , 2014 ; ISSN: 00346748 Ott, D ; Reihani, S. N. S ; Oddershede, L. B ; Sharif University of Technology
    In dual-beam optical tweezers, the accuracy of position and force measurements is often compromised by crosstalk between the two detected signals, this crosstalk leading to systematic and significant errors on the measured forces and distances. This is true both for dual-beam optical traps where the splitting of the two traps is done by polarization optics and for dual optical traps constructed by other methods, e.g., holographic tweezers. If the two traps are orthogonally polarized, most often crosstalk is minimized by inserting polarization optics in front of the detector; however, this method is not perfect because of the de-polarization of the trapping beam introduced by the required... 

    Behavior of plasmonic nanoparticle array in near- and far-field coupling regimes for transverse electric and transverse magnetic polarizations

    , Article Journal of the Optical Society of America B: Optical Physics ; Volume 30, Issue 8 , 2013 , Pages 2286-2291 ; 07403224 (ISSN) Shahmansouri, A ; Rashidian, B ; Sharif University of Technology
    Optical Society of American (OSA)  2013
    We have previously reported the results of plasmonic behavior of an Au nanodisk array in the far-field coupling regime under oblique illumination with transverse electric polarization. In this paper, those results are studied in more detail. Here, results for transverse magnetic polarization are also presented and discussed. In addition to the far-field coupling regime, the results for the near-field coupling regime are also reported. Effects of different parameters, such as substrate thickness and array periodicity on the shape of plasmon spectra are discussed. It will be shown that in the far-field coupling regime, the diffractive grating orders can have a major role in the behavior of the... 

    Ultra-Sharp Transmission Resonances in Periodic Arrays of Graphene Ribbons in TE Polarization

    , Article Journal of Lightwave Technology ; Volume 34, Issue 3 , 2016 , Pages 1020-1024 ; 07338724 (ISSN) Khavasi, A ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc 
    When illuminated by TM polarized waves, periodic arrays of graphene ribbons are known to exhibit plasmonic resonances due to their dual inductive-capacitive nature. It is demonstrated here that even in TE polarization, resonances can be observed in these structure. These resonances, which are of nonplasmonic origin, are explained by means of a circuit model. It is shown that, for a certain frequency range, arrays of graphene ribbons have both capacitive and inductive properties, which lead to an ultra-sharp inductor-capacitor resonance. The banw idth of this resonance can be as narrow as ∼0.0002 nm at a wavelength of 630 nm. The resonance can also be viewed as the grating excitation of a TE... 

    Broadband, polarization-insensitive, and wide-angle optical absorber based on fractal plasmonics

    , Article IEEE Photonics Technology Letters ; Volume PP, Issue 99 , 2016 ; 10411135 (ISSN) Eshaghian Dorche, A ; Abdollahramezani, S ; Chizari, A ; Khavasi, A ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2016
    In this paper, a plasmonic absorber consisting of a metal-dielectric-metal stack with a top layer of Sierpinski nanocarpet is theoretically investigated. Such a compact absorber depicts broadband angle-independent behavior over a wide optical wavelength range (400 700 nm) and a broad range of incidence angles (0 80). Including several feature sizes, such a fractal-like structure shows average simulated extinction response of 0:85 for either transverse electric or magnetic polarization states under normal incidence. Underlying mechanisms of absorbance due to excited surface plasmon modes as well as electric/magnetic dipole resonances are well revealed by investigating electric field, magnetic... 

    Second Harmonic Generation (SHG) measurement affected by electric field

    , Article Scientia Iranica ; Volume 14, Issue 3 , 2007 , Pages 236-239 ; 10263098 (ISSN) Amjadi, A ; Rajai, P ; Latifi, H ; Sharif University of Technology
    Sharif University of Technology  2007
    A type II (eoe: extraordinary-ordinary-extraordinary) phase matching condition in a 2nd Harmonic Generation of Nd-YAG laser under a high electric field in a uniaxial KDP crystal has been measured. Type II phase matching takes place when the two mixing waves are of orthogonal polarizations (extraordinary-ordinary) and the 2nd harmonic radiation corresponds to an extraordinary wave. By applying an electric field along the X(Y) axes of the crystal, a new phase-matching angle was measured under the influence of different electric fields. The deflection angle of the SHG beam was measured as a function of the applied voltage. An optical collector will focus the 1st harmonic and a fraction of its... 

    Statistical anisotropies in gravitational waves in solid inflation

    , Article Journal of Cosmology and Astroparticle Physics ; Vol. 2014,Issue. 9 , 2014 ; ISSN: 14054179 Akhshik, M ; Emami, R ; Firouzjahi, H ; Wang, Y ; Sharif University of Technology
    Solid inflation can support a long period of anisotropic inflation. We calculate the statistical anisotropies in the scalar and tensor power spectra and their cross-correlation in anisotropic solid inflation. The tensor-scalar cross-correlation can either be positive or negative, which impacts the statistical anisotropies of the TT and TB spectra in CMB map more significantly compared with the tensor self-correlation. The tensor power spectrum contains potentially comparable contributions from quadrupole and octopole angular patterns, which is different from the power spectra of scalar, the cross-correlation or the scalar bispectrum, where the quadrupole type statistical anisotropy dominates... 

    Investigation of a quasi-3D plasmonic nanostructure for TE and TM polarizations

    , Article Journal of the Optical Society of America B: Optical Physics ; Vol. 31, issue. 11 , 2014 , p. 2838-2844 Shahmansouri, A ; Rashidian, B ; Sharif University of Technology
    Quasi-3D plasmonic nanostructures consisting of a metallic film perforated as an array of nanoholes, separated by a gap from a nanodisk array, are theoretically investigated under plane wave illumination with transverse electric and transverse magnetic polarizations. The results are compared with the results of a simple nanodisk array. A full discussion involving the couplings between plasmon resonance in nanodisks, surface plasmon polaritons on the interfaces of metallic film, and different diffractive grating orders that contribute in the couplings will be presented. The large difference between the plasmon behavior of the nanodisk array alone and nanodisk array in the presence of nanohole... 

    Sulfide stress corrosion cracking and hydrogen induced cracking of A216-WCC wellhead flow control valve body

    , Article Case Studies in Engineering Failure Analysis ; Volume 1, Issue 3 , 2013 , Pages 223-234 ; 22132902 (ISSN) Ziaei, S. M. R ; Kokabi, A. H ; Nasr Esfehani, M ; Sharif University of Technology
    The wellhead flow control valve bodies which are the focal point of this failure case study were installed in some of the upstream facilities of Khangiran's sour gas wells. These valve bodies have been operating satisfactorily for 3 years in wet H2S environment before some pits and cracks were detected in all of them during the periodical technical inspections. One failed valve body was investigated by chemical and microstructural analytical techniques to find out the failure cause and provide preventive measures. The valve body alloy was A216-WCC cast carbon steel. During investigation many cracks were observed on the inner surface of the valve body grown from the surface pits. The results... 

    Preparation of mesh-reinforced cellulose acetate forward osmosis membrane with very low surface roughness

    , Article Korean Journal of Chemical Engineering ; Volume 34, Issue 12 , 2017 , Pages 3170-3177 ; 02561115 (ISSN) Mirkhalili, S. M ; Mousavi, S. A ; Ramazani Saadat Abadi, A ; Sadeghi, M ; Sharif University of Technology
    Mesh-reinforced cellulose acetate (CA)-based membranes were prepared for forward osmosis (FO) by immersion precipitation. Casting compositions such as CA percent and 1, 4-dioxane/acetone ratio and also preparation conditions such as evaporation time, coagulation bath and annealing temperatures were tested for membranes’ performance. The results were compared with commercially CTA membranes. The best membrane (17.9% polymer and 1, 4-dioxane/acetone ratio of 1.89) showed water flux of 9.3 L/m2h (LMH) and RSF of 0.536 mol NaCl/m2h. Moreover, the membrane structure was reinforced by a polyester mesh, which created micro pores in the back of the membrane. This caused higher water flux and RSF... 

    Analysis of wideband circularly polarized ferrite-loaded antenna based on unidirectional resonant modes

    , Article IEEE Transactions on Magnetics ; Volume 53, Issue 9 , 2017 ; 00189464 (ISSN) Mashhadi, M ; Rejaei, B ; Komjani, N ; Ghalibafan, J ; Sharif University of Technology
    We propose a wideband circularly polarized antenna that consists of a metallic patch and some parasitically coupled elements mounted on a grounded dielectric-ferrite substrate. The metallic patch is fed by a proximity-coupled feed line placed between the ferrite and the dielectric layers. The parasitically coupled elements are included to improve the impedance bandwidth of antenna and are excited through the metallic patch. The antenna utilizes the resonant modes of the structure, which rotate only in the clockwise or counter-clockwise direction. A semi-Analytical solution based on the magnetic wall approximation shows that the resonance frequencies of the clock-and counter-clockwise... 

    A dual circularly reconfigurable polarization patch antenna for fifth generation mobile communication systems

    , Article Progress In Electromagnetics Research C ; Volume 105 , 2020 , Pages 73-84 Mallat, N. K ; Nouri, M ; Aghdam, S. A ; Zia, M. T ; Harb, B ; Jafarieh, A ; Sharif University of Technology
    Electromagnetics Academy  2020
    In this paper, a reconfigurable patch antenna with Circular Polarization (CP) diversity with theoretical discussion and verification is proposed for fifth generation (5G) of mobile communication systems. The proposed antenna contains two PIN diodes, which are correctly placed on the ground plane to obtain polarization diversity. By switching between two ON/OFF modes in the PIN diodes, the proposed antenna can support either the RHCP mode or the LHCP mode. An antenna with the well-matched impedance bandwidths (S11 ≤ −10 dB) of 2.5 GHz (27 ∼ 29.5 GHz) and 3 GHz (36 ∼ 39 GHz) and the dual-band 3-dB axial ratios of 6% (27.3–29 GHz) and 8.4% (35–38.2 GHz) operates in both the RHCP and LHCP modes.... 

    Investigation of human skin collagen distribution in response to polarized laser by ellipsometry

    , Article Proceedings of the 6th IASTED International Conference on Biomedical Engineering, BioMED 2008, 13 February 2008 through 15 February 2008, Innsbruck ; 2008 , Pages 307-312 ; 9780889867215 (ISBN) Fattahi, H ; Tahvildari, R ; Amjadi, A ; Nejhad, M. B ; Sharif University of Technology
    The important role of collagen fibers in LILT has been observed. However there is still unclear information about light characteristics, such as coherence and polarization. Collagens behavior in response to different polarization is presented in this study. We investigate the distribution and structure of collagen bundles in full-thickness human skin in response to laser with different polarization by ellipsometry technique. For this study, we chose skin from the back part of a white man. The light source is HeNe laser. Samples are irradiated by three different polarizations. Sample S is irradiated using the electric field vector of the polarized laser radiation aligned in parallel with the... 

    Polarization insensitive gratings in slab structure

    , Article Iranian Journal of Electrical and Computer Engineering ; Volume 3, Issue 1 , 2004 , Pages 39-46 ; 16820053 (ISSN) Mehrany, K ; Rashidian, B ; Sharif University of Technology
    Diffraction of electromagnetic waves by a media containing periodic changes of characteristics is widely used in many optical devices and processing methods. Usually diffractive structures contain periodic changes of relative electric permittivity. In this article, we have analyzed electromagnetic wave interaction with a media containing periodic changes of both relative electric permittivity, and relative magnetic permeability. Most of this work is based on using transfer matrix approach and rigorous coupled wave method for analysis of both TE and TM polarizations. Our analytical formulation proves the possibility of polarization insensitivity in diffractive behavior of these structures...