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Total 29 records

    Graphene nanopores in broadband wide-angle optical cavity resonance absorbers

    , Article Surfaces and Interfaces ; Volume 30 , 2022 ; 24680230 (ISSN) Bidmeshkipour, S ; Akhavan, O ; Sharif University of Technology
    Elsevier B.V  2022
    Abstract
    A cavity resonator containing graphene nanopores (GNPs), along with a metallic layer (Ag, as a reflector) and a dielectric layer (SiO2, as a spacer), has been proposed for broadband wide-angle absorption of light. The GNP/SiO2/Ag multilayers showed high significant increase in the absorption efficiency (with respect to the G/SiO2/Ag multilayer) in a broad spectral range (from ultra-violet (UV) and visible range to near-infrared (NIR)), due to the cavity resonance and absorptions induced by the oxygen-containing functional groups formed around the nanopores of graphene. The dependences of the cavity resonance absorption on the quality of the GNP layer, dimension of the cavity and the incident... 

    Phase-shifterless phase-noise measurement of microwave oscillators using high-Q cavity frequency discriminator

    , Article 81st ARFTG Microwave Measurement Conference: Metrology for High Speed Circuits and Systems ; 2013 ; 9781467349826 (ISBN) Gheidi, H ; Banai, A ; Sharif University of Technology
    2013
    Abstract
    This paper presents application of high-Q cavity resonator in phase-shifter less technique. A mathematical analysis is presented to show the dependency of the measured phase noise in terms of loaded quality factor and resonance frequency of the high-Q cavity resonator. Experimental measurements resulted from different methods for a synthesized oscillator at 9.976 GHz show great validity and accuracy of the proposed technique. This technique needs no tuning for the phase-shifter and can introduce better sensitivity compared to the setup that uses a delay-line as a frequency discriminator element due to much lower insertion loss particularly at high carrier frequencies. The sensitivity of -113... 

    Design, Analysis and Synthesis of Dual-Mode Waveguide Filter in Q Band

    , M.Sc. Thesis Sharif University of Technology Jahanbakht, Mohammad Hosein (Author) ; Banai, Ali (Supervisor)
    Abstract
    Today in the most microwave and millimeterwave systems, one or more filters are used due to interference and noise phenomena. Microwave filters are manufactured in different environments such as waveguide, microstrip and SIW. For military and satellite applications that high power handling and low loss are in preference, the only appropriate environment is the waveguide. Other priority which is more important in satellite application is the low weight and small size of the product; Because of that, the idea of dual-mode waveguide filter was proposed in the early 70 decade. These kind of filters are able to produce two poles in one cavity resonator, which can decrease weight and size of the... 

    Raman random laser in one-dimensional system

    , Article Journal of the Optical Society of America B: Optical Physics ; Vol. 31, Issue. 6 , 2014 , Pages 1308-1315 ; ISSN: 07403224 Bahrampour, A ; Shojaie, E ; Sani, M ; Sharif University of Technology
    Abstract
    The probability of occurrence of random cavities' resonance frequency in the Stokes bandwidth of the Raman active medium can cause Raman laser oscillation in the random structures. Due to the small bandwidth of Raman line shape, the probability of the simultaneous appearance of random cavity resonance frequencies in the cascade Stokes line shapes is small. As a result, the cascade Raman laser oscillation effects on the saturation behavior are negligible. The nonlinear transmission matrix method is employed to determine the statistical behavior of a Raman random laser. Our results showed that the statistical behavior depends on the position of the Stokes line shape relative to the center of... 

    Design and Implementation of a Low Phase Noise Oscillator using Oversized Cavity Resonator

    , M.Sc. Thesis Sharif University of Technology Hassannejad, Hamid Reza (Author) ; Banai, Ali (Supervisor)
    Abstract
    The aim of doing this project is design and fabrication of a X band low phase noise oscillator Using oversized cavity resonator and transposed gain amplifier.One of the most important factors in reducing oscillators phase noise is the quality factor of its resonator and by increasing the quality factor, we can reduce the phase noise. So by doing this , in this project we want to increase the quality factor of the resonator part of the oscillator and design an oscillator in the X frequency band ( approximately 8 GHz ) .As we know the Q factor for waveguide cavity resonator is increased when we use them in the higher order modes and there is a great improvement in Q factor T when we use them... 

    Analysis of chaotic behavior in an optical microresonator

    , Article Optics Communications ; Vol. 332, issue , 2014 , pp. 31-35 ; ISSN: 00304018 Vahedi, M ; Bahrampour, A. R ; Safari, H. R ; Sharif University of Technology
    Abstract
    In this paper, for the first time, chaotic behavior of a classical moving-mirror Fabry-Perot cavity is obtained by finding numerical solution of a system of delay differential equations (previously obtained by a phenomenological approach (T. Carmon, M. C. Cross, K. J. Vahala, Phys. Rev. Lett. 98 (2007) 167203)). Fourier transform of the electromagnetic power for different values of pump power is calculated. By increasing the power, a period-doubling route to chaos is observed. Since the quality factor of the cavity has an important role in the chaotic behavior, variation of Lyapunov exponent and threshold power for the onset of chaos versus quality factor are investigated. A near linear... 

    A New cavity resonance assisted by anisotropic metasurfaces

    , Article IEEE Transactions on Microwave Theory and Techniques ; Volume 66, Issue 7 , 2018 , Pages 3224-3233 ; 00189480 (ISSN) Li, X ; Memarian, M ; Itoh, T ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2018
    Abstract
    A new resonance phenomenon is demonstrated in waveguide cavities, which simultaneously uses two orthogonal modes (polarizations). This resonance is formed by bouncing waves with similar handedness, between two simple anisotropic metasurfaces having a relative rotation angle. The rotated anisotropic metasurfaces can cross couple the waves from one polarization to the other at the cavity end. The field profile of the resonant mode does not exhibit nodes and antinodes, thus the resonant frequency is not solely determined by the cavity length, unlike common resonators. The resonance condition is theoretically demonstrated from both field and transmission line perspectives, and is validated by... 

    Orthogonal-mode dual-band rectangular waveguide filters

    , Article 27th Iranian Conference on Electrical Engineering, ICEE 2019, 30 April 2019 through 2 May 2019 ; 2019 , Pages 1534-1537 ; 9781728115085 (ISBN) Golzar, M.H ; Memarian, M ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2019
    Abstract
    In this paper, we present a design method of dual-band waveguide rectangular cavity filters, with a series in-line topology. The coupling matrix is based on asynchronously tuned designs, where two sets of resonances exist for the two bands. Thus the filter is inherently different than the typical dual-band designs in the literature, as existing designs utilize resonators at the same frequency. The design at Ku band validates the underlying idea and concept, and the theory of the detuned coupling matrix. This rectangular waveguide implementation can provide noticeable miniaturization in applications with high-power requirements  

    Investigation of the effect of adding nano-encapsulated phase change material to water in natural convection inside a rectangular cavity

    , Article Journal of Energy Storage ; Volume 40 , 2021 ; 2352152X (ISSN) Golab, E ; Goudarzi, S ; Kazemi Varnamkhasti, H ; Amigh, H ; Ghaemi, F ; Baleanu, D ; Karimipour, A ; Sharif University of Technology
    Elsevier Ltd  2021
    Abstract
    The present simulation aims to investigate adding NEPCM nanoparticles to water in the natural convection inside a cavity by using FVM method and SIMPLE algorithm. Nano-encapsulated phase change material (NEPCM) consists of a shell and core with phase change property. The NEPCM particles in base fluid have the ability to transfer heat by absorbing and dissipating heat in the liquid-solid phase change state. In this study, the energy wall phenomenon due to the phase change of NEPCM core has appeared that the whose energy transfer strength is proportional to the latent heat of NEPCM core and the thickness of the energy wall. Moreover, the relationship between the energy wall and the heat... 

    Design and Implementation of phase Locked Loop Using Low phase Noise Oscillator with Oversized Cavity Resonator

    , M.Sc. Thesis Sharif University of Technology Aghakasiri, Ali (Author) ; Banai, Ali (Supervisor)
    Abstract
    Phase noise is one of the most important parameters in communication systems especially in receivers. Implementation of low phase noise oscillators has always been important.One of the most important parameters in reducing the phase noise of the oscillator is the quality factor of the cavity used in its structure. As a result, increasing the quality factor of the cavity can reduce the oscillation phase noise. Cylindrical waveguides in higher order modes have a higher quality factor than the main modes of excitement. As a result, this property can be used to increase the quality factor of the cavity and reduce the phase noise of the oscillator. This will increase the size of the cavity. The... 

    A theoretical multi-reflection method for analysis of optomechanical behavior of the Fabry-Perot cavity with moving boundary condition

    , Article Optics Communications ; Volume 284, Issue 19 , 2011 , Pages 4789-4794 ; 00304018 (ISSN) Bahrampour, A. R ; Vahedi, M ; Abdi, M ; Ghobadi, R ; Golshani, M ; Tofighi, S ; Parvin, B ; Sharif University of Technology
    Abstract
    The opto-mechanical coupling and the generation of Stokes and anti-Stokes frequencies in the in-band and intra-band regimes of operation of the Fabry-Perot cavity with a moving mirror on the basis of multi-reflection method (MRM) are described by a unique theory. The frequency characteristic function of the Fabry-Perot filter is modified. By increasing the amplitude of mirror oscillation the Fabry-Perot bandwidth increases and normal mode splitting occurred. The conversion efficiencies of the Stokes and anti-Stokes frequencies versus the mechanical amplitude of oscillation have an optimum value. Also, the delay function corresponding to the radiation pressure is obtained  

    How photocatalytic activity of the MAO-grown TiO2 nano/micro-porous films is influenced by growth parameters?

    , Article Applied Surface Science ; Volume 256, Issue 13 , 2010 , Pages 4253-4259 ; 01694332 (ISSN) Bayati, M. R ; Golestani Fard, F ; Moshfegh, A. Z ; Sharif University of Technology
    2010
    Abstract
    Pure titania porous layers consisted of anatase and rutile phases, chemically and structurally suitable for catalytic applications, were grown via micro-arc oxidation (MAO). The effect of applied voltage, process time, and electrolyte concentration on surface structure, chemical composition, and especially photocatalytic activity of the layers was investigated. SEM and AFM studies revealed that pore size and surface roughness of the layers increased with the applied voltage, and the electrolyte concentration. Moreover, the photocatalytic performance of the layers synthesized at medium applied voltages was significantly higher than that of the layers produced at other voltages. About 90% of... 

    Photo-degradation of methelyne blue over V2O5- TiO2 nano-porous layers synthesized by micro arc oxidation

    , Article Catalysis Letters ; Volume 134, Issue 1-2 , 2010 , Pages 162-168 ; 1011372X (ISSN) Bayati, M. R ; Golestani Fard, F ; Zaker Moshfegh, A ; Sharif University of Technology
    Abstract
    V2O5-TiO2 porous layers were synthesized via micro-arc oxidation for the first time. The effect of the applied voltage on morphology, composition, and photo-activity of the layers was investigated. The layers, which consisted of anatase, rutile, and vanadium pentoxide phases, revealed an enhanced photo-activity. About 93% of methylene blue solution was degraded on the synthesized layers after 120 min UV-irradiation with a reaction rate constant of k = 0.0228 min-1. The band gap energies of the vanadia-titania and pure titania layers were calculated as 2.56 and 3.39 eV, respectively  

    Stability, size and optical properties of colloidal silver nanoparticles prepared by electrical arc discharge in water

    , Article EPJ Applied Physics ; Volume 48, Issue 1 , 2009 , Pages 10601p1-10601p7 ; 12860042 (ISSN) Ashkarran, A. A ; Iraji Zad, A ; Ahadian, M. M ; Hormozi Nezhad, M. R ; Sharif University of Technology
    2009
    Abstract
    We have fabricated and characterised colloidal silver nanoparticles by the electrical arc discharge method in DI water. Size and optical properties of the silver nanoparticles were studied versus different arc currents. Optical absorption indicates a plasmonic peak at 392 nm for 10 A which increases to 398 nm for 20 A arc current. This reveals that by raising the arc current the size of the nanoparticles increases. Optical absorption of silver nanoparticles after 3 weeks shows precipitation of them in a water medium. The effect of different surfactant and stabilizer concentrations such as cethyl trimethylammonium bromide (CTAB), polyvinyl pyrrolidone (PVP), sodium citrate, sodium dodecyl... 

    Fuzzy control of an electric arc furnace off-gas process

    , Article 2008 ASME International Mechanical Engineering Congress and Exposition, IMECE 2008, Boston, MA, 31 October 2008 through 6 November 2008 ; Volume 10, Issue PART A , 2009 , Pages 471-477 ; 9780791848715 (ISBN) Hasannia, A ; Esteki, H ; Sharif University of Technology
    2009
    Abstract
    Electric arc furnaces are used to make steel from scrap iron in steel industry. Nowadays, the aim of more researches in this area is to increase yield of furnace and it's compatibility with environment. One of the methods to achieve these purposes is to control the off-gas system as relative pressure in furnace would be kept negative. Because the combustion gases inside the furnace must not leak into the plant environment. However for preventing of loss of energy, the amount of this negative number must be small. In this paper, new intelligent control method named fuzzy emotional control, applied to off- gas system to control the relative pressure in the furnace and its result is compared to... 

    Phase-field simulation of weld solidification microstructure in an Al-Cu alloy

    , Article Modelling and Simulation in Materials Science and Engineering ; Volume 16, Issue 6 , 11 August , 2008 ; 09650393 (ISSN) Farzadi, A ; Do Quang, M ; Serajzadeh, S ; Kokabi, A. H ; Amberg, G ; Sharif University of Technology
    2008
    Abstract
    Since the mechanical properties and the integrity of the weld metal depend on the solidification behaviour and the resulting microstructural characteristics, understanding weld pool solidification is of importance to engineers and scientists. Thermal and fluid flow conditions affect the weld pool geometry and solidification parameters. During solidification of the weld pool, a columnar grain structure develops in the weld metal. Prediction of the formation of the microstructure during welding may be an important and supporting factor for technology optimization. Nowadays, increasing computing power allows direct simulations of the dendritic and cell morphology of columnar grains in the... 

    A simulink study of electric arc furnace power quality improvement by using statcom

    , Article 2008 IEEE International Conference on Industrial Technology, IEEE ICIT 2008, Chengdu, 21 April 2008 through 24 April 2008 ; 2008 ; 9781424417063 (ISBN) Tavakkoli, A ; Ehsan, M ; Batahiee, S. M. T ; Marzband, M ; Sharif University of Technology
    2008
    Abstract
    The nonlinear and time varying nature of electric arc furnaces (EAFs) create flicker, harmonics, and voltage/current unbalances. Nowadays to improve the performance of EAFs and the power quality problems of electrical systems around them high speed compensators like STATCOM are needed. This paper uses a time domain model for electric arc furnaces and a new model of STATCOM respectively for creating and improving mentioned power quality problems. In this paper, first we investigate and simulate electric arc furnace and STATCOM using SIMULINK/PSB. Second, we simulate a network including them completely. The proposed models take into account arcing conditions and associated effects improvement... 

    Prediction of grain growth behavior in haz during gas tungsten arc welding of 304 stainless steel

    , Article Journal of Materials Engineering and Performance ; Volume 18, Issue 9 , 2009 , Pages 1193-1200 ; 10599495 (ISSN) Jamshidi Aval, H ; Serajzadeh, S ; Kokabi, A. H ; Sharif University of Technology
    2009 
    Abstract
    In this study, the thermal cycles and the grain structure in the weld heat-affected zone (HAZ) are predicted. At the first stage, a combined heat transfer and fluid flow model is employed to assess the temperature fields during and after welding of 304 stainless steel and then, the evolution of grain structure is conducted using the predicted temperature distribution and an analytical model of grain growth. The grain sizes of the CGHAZ (coarse grain heat affected zone) achieved from the model are basically in agreement with those obtained from experimental measurement under different heat inputs in the range of 0.33-1.07 MJ/m. Both the experimental data and the calculated results show that... 

    Three dimensional analysis of an AC electric arc furnace

    , Article IECON Proceedings (Industrial Electronics Conference), 3 November 2009 through 5 November 2009 ; 2009 , Pages 3697-3702 Kiyoumarsi, A ; Nazari, A ; Ataei, M ; Khademhosseini Beheshti, H ; Karimi, H ; Sharif University of Technology
    Abstract
    AC electric arc furnaces (EAFs) highly reduce power quality of the network by generating disturbances such as flicker and harmonics. These disturbances are due to the nonlinear electromagnetic and thermal field behaviors of the AC arcs. Analysis of these nonlinear behaviors is required for improving power quality in the network. This paper presents a three-dimensional finite element modeling of the electromagnetic fields in an AC three-phase electric arc furnace. The model includes the electrodes, arcs and molten bath. Current density, voltage and magnetic field intensity in the arcs, molten bath and electrodes are predicted as a result of applying the three-phase AC voltages to the EAF.... 

    Studies of Iranian heavy oils pertinent to reservoir conditions for their auto-ignition to initiate fire flooding

    , Article Chemical Engineering Communications ; Volume 196, Issue 5 , 2009 , Pages 643-657 ; 00986445 (ISSN) Price, D ; Razzaghi, S ; Kharrat, R ; Rashtchian, D ; Vossoughi, S ; Sharif University of Technology
    2009
    Abstract
    In this work, the potential for the auto-ignition of Iranian heavy oil during in situ combustion (ISC) process conditions was studied. Kinetic studies were carried out using thermal analysis techniques. Effects of oxygen partial pressure, reservoir pressure, and clay on the auto-ignition condition were investigated. Based on the experimental results obtained, a kinetic equation was derived for each of the different oil samples in the presence of different sands. The effect of partial pressure of oxygen in the injected air showed that at atmospheric pressure, low temperature combustion (LTC) was initiated at 275°C. Also, enriching the injected air by oxygen lowers the initial LTC temperature...