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    Beam manipulation by hybrid plasmonic-dielectric metasurfaces

    , Article Plasmonics ; 2019 ; 15571955 (ISSN) Arik, K ; Hemmatyar, O ; Kavehvash, Z ; Sharif University of Technology
    Springer  2019
    A hybrid plasmonic-dielectric metasurface is proposed in order to manipulate beam propagation in desired manners. The metasurface is composed of patterned hybrid graphene-silicon nano-disks deposited on a low-index substrate, namely silica. It is shown that the proposed hybrid metasurface simultaneously benefits from the advantages of graphene-based metasurfaces and dielectric ones. Specially, we show that the proposed hybrid metasurface not only provides reconfigurability, just like previously proposed graphene-based metasurfaces, but also similar to dielectric metasurfaces, is of low loss and CMOS-compatible. Such exceptional features give the metasurface exceptional potentials to realize... 

    Beam manipulation by hybrid plasmonic-dielectric metasurfaces

    , Article Plasmonics ; Volume 15, Issue 3 , 2020 , Pages 639-645 Arik, K ; Hemmatyar, O ; Kavehvash, Z ; Sharif University of Technology
    Springer  2020
    A hybrid plasmonic-dielectric metasurface is proposed in order to manipulate beam propagation in desired manners. The metasurface is composed of patterned hybrid graphene-silicon nano-disks deposited on a low-index substrate, namely silica. It is shown that the proposed hybrid metasurface simultaneously benefits from the advantages of graphene-based metasurfaces and dielectric ones. Specially, we show that the proposed hybrid metasurface not only provides reconfigurability, just like previously proposed graphene-based metasurfaces, but also similar to dielectric metasurfaces, is of low loss and CMOS-compatible. Such exceptional features give the metasurface exceptional potentials to realize... 

    Self-focusing up to the incident laser wavelength by an appropriate density ramp

    , Article Laser and Particle Beams ; Volume 29, Issue 4 , 2011 , Pages 453-458 ; 02630346 (ISSN) Sadighi Bonabi, R ; Moshkelgosha, M ; Sharif University of Technology
    This work is devoted to improving relativistic self-focusing of intense laser beam in underdense unmagnetized plasma. New density profiles are introduced to achieve beam width parameter up to the wavelength of the propagating laser. By investigating variations of the beam width parameter in presence of different density profiles it is found that the beam width parameter is considerably decreased for the introduced density ramp comparing with uniform density and earlier introduced density ramp profiles. By using this new density profile high intensity laser pulses are guided over several Rayleigh lengths with extremely small beam width parameter  

    Differential effects of fonf and fonfs on learning english lax vowels in an efl context

    , Article Journal of Asia TEFL ; Volume 16, Issue 2 , 2019 , Pages 499-515 ; 17383102 (ISSN) Tabandeh, F ; Moinzadeh, A ; Barati, H ; Sharif University of Technology
    Asian Association of Teachers of English as a Foreign Language  2019
    This study investigated the differential effects of focus-on-form (FonF: explicit instruction followed by focused tasks) and focus-on-forms (FonFS: explicit instruction followed by controlled exercises) on learning English lax vowels (i.e., /ɪ/, /ʊ/, /ʌ/) by Persian English as a foreign language (EFL) learners. To this end, 48 learners took a voluntary 6-hour course: the experimental group (n = 17) received FonF, the comparison group (n = 16) received FonFS, and the control group (n = 15) engaged in theme-based discussions with no focus on the target vowels. Learners’ pronunciations were elicited in controlled read-aloud and spontaneous picture description tasks and acoustically measured for... 

    A novel approach to generating extended depth of focus beams using a phase mask

    , Article Frontiers in Optics, FiO 2006, Rochester, NY, 10 October 2006 through 10 October 2006 ; 2006 ; 21622701 (ISSN); 1557528187 (ISBN); 9781557528186 (ISBN) Massoumian, F ; Shamsi, D ; Bazargan, H ; Sharif University of Technology
    Optical Society of America (OSA)  2006
    We present a novel method in which a phase mask is used to modulate a beam in order to produce a large extension in the focal depth at the focus of a lens. © 2005 Optical Society of America  

    Plasma density ramp for relativistic self-focusing of an intense laser: Comment

    , Article Journal of the Optical Society of America B: Optical Physics ; Volume 27, Issue 9 , 2010 , Pages 1731-1734 ; 07403224 (ISSN) Sadighi Bonabi, R ; Yazdani, E ; Habibi, M ; Lotfi, E ; Sharif University of Technology
    Optical Society of American (OSA)  2010
    Gupta et al. [J. Opt. Soc. Am. B. 24, No. 5 (2007)] have introduced a localized upward plasma density ramp to overcome the defocusing of a laser beam. We report that there are fundamental mistakes in their work. First, the density profile formula that they have introduced is dimensionally incorrect. Second, the calculated dielectric constant is wrong as well, which renders their main spot size equation and the quantitative results unacceptable, and it seriously falters the results of the self-focusing. We correctly derived a new equation of the spot size, and the computational curves are also presented  

    A method for focused crawling using combination of link structure and content similarity

    , Article 2006 IEEE/WIC/ACM International Conference on Web Intelligence, WI'06, Hong Kong, 18 December 2006 through 22 December 2006 ; 2006 , Pages 753-756 ; 0769527477 (ISBN); 9780769527475 (ISBN) Jamali, M ; Sayyadi, H ; Hariri, B. B ; Abolhassani, H ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2006
    The rapid growth of the world-wide web poses unprecedented scaling challenges for general-purpose crawlers and search engines. A focused crawler aims at selectively seek out pages that are relevant to a pre-defined set of topics. Besides specifying topics by some keywords, it is customary also to use some exemplary documents to compute the similarity of a given web document to the topic. In this paper we Introduce a new hybride focused crawler, which uses link structure of documents as well as similarity of pages to the topic to crawl the web © 2006 HEE  

    Numerical and experimental evaluation of high-intensity focused ultrasound-induced lesions in liver tissue ex vivo

    , Article Journal of ultrasound in medicine : official journal of the American Institute of Ultrasound in Medicine ; Volume 37, Issue 6 , 2018 , Pages 1481-1491 ; 15509613 (ISSN) Haddadi, S ; Ahmadian, M. T ; Sharif University of Technology
    OBJECTIVES: Recent advances in the field of acoustics and piezoelectric and ultrasound transducers have led to new approaches to the diagnosis and treatment of certain diseases. One method of treatment with ultrasonic waves is high-intensity focused ultrasound (HIFU) treatment, which is a thermal therapeutic method used to treat malignant tumors. Although a variety of treatment-planning strategies using ultrasonic waves have been investigated, little clinical success has been achieved. Computational modeling is a powerful tool for predicting device performance. METHODS: The heating induced by a concave transducer with operating powers of 85 and 135 W was studied, and the experimental results... 

    Improving the relativistic self-focusing of intense laser beam in plasma using density transition

    , Article Physics of Plasmas ; Volume 16, Issue 8 , 2009 ; 1070664X (ISSN) Sadighi Bonabi, R ; Habibi, M ; Yazdani, E ; Sharif University of Technology
    The propagation of a Gaussian beam in underdense plasma with upward increasing density ramp is analyzed. In this work are shown that the spot size oscillations of laser beam increases and its amplitude shrinks with proper plasma density ramp. This causes the laser beam to become more focused and penetrations deep into the plasma by reduction of diffraction effect. The related focusing parameters are optimized to get the best possible focusing at the relativistic threshold intensity of Nd-glass laser and the effect of the laser intensity in the self-focusing parameters is also investigated. The analytical calculations are presented and showed more reliable results in comparison to the... 

    Production of Electron and Flat Ion Blocks by Using Ultra Intense Laser, Particularly in the Ultraviolet Range

    , Ph.D. Dissertation Sharif University of Technology Zare, Somayye (Author) ; Anvari, Abbas (Supervisor) ; Sadighi Bonabi, Rasoul (Supervisor)
    In the present work, interaction of high power and ultra short laser pulse with plasma in both under relativistic and relativistic regimes is investigated. The accelerated ions and electron are studied. The effect of pulse laser shapes on generating of the optimum wakefield is studied to find the maximum generated wakefield amplitude. It is found that similar to the wakefield amplitude generated by single pulse, the wakefield amplitude produced by dual trailing depends on the pulse shape and their permutation. Furthermore, the interaction of sub-picosecond UV laser in sub-relativistic intensities with deuterium is investigated. At high plasma temperatures, based on the quantum correction in... 

    Form-Focused Vocabulary Instruction: A Comparative Analysis of the Effect of Translation, Definition, Etymology, and Imageable Expressions on Retention of Idioms

    , M.Sc. Thesis Sharif University of Technology Sedaghatkar, Mozhgan (Author) ; Jahangard, Ali (Supervisor)
    Currently, in the light of researches that have supported the necessity for pedagogical interventions to push L2 learners towards higher levels of proficiency, form-focused instruction (FFI) approach has gained critical importance in L2. FFI comprises both traditional approaches to teaching forms and more communicative approaches based on giving attention to form that are primarily meaning-focused. Considering FOF, the present study focused on idioms learning in L2 classrooms.Idiom is the inseparable part of teaching English as a foreign language and has an influential role in improving the communicative competence. However, it is not appropriately catered for in many English classes in... 

    Self-Focusing of Laser Beam in Relativistic Quantum Plasma

    , M.Sc. Thesis Sharif University of Technology Rezaee, Sajad (Author) ; Sadighi Bonabi, Rasoul (Supervisor)
    The phenomenon of relativistic self-focusing in nuclear fusion and laser-plasma interactions is very important. Under the influence of this phenomenon, the laser beam can move in plasma a few Rayleigh lengths and the interaction efficiency is improved. The relativistic self-focusing in inhomogeneous, homogeneous, collisional and collisionless plasmas has been studied in various conditions of plasma and laser in classical physics. In this thesis the propagation of a laser pulse at the X-ray wavelength range and its relativistic self-focusing in quantum plasma is investigated by numerical simulations. Initially, the interaction with a collisionless ramped density profile plasma target is... 

    Design & Prototyping of a Reflective Optical Hybrid Incremental-Absolute Encoder Based on Compact Disc Technology

    , M.Sc. Thesis Sharif University of Technology Sadri, Sobhan (Author) ; Vossoughi, Gholamreza (Supervisor)
    The reflective optical rotary encoders are used greatly in automation systems for speed and position measurements. Their approach of reading code as pulses which results in position and speed information is very similar to what a CD-ROM driver performs to read the saved data as pits and lands on the compact disc data layer. Moreover, the micron size of pits and lands in compact disc promise a high-resolution, and low cost rotary encoder based on CD-ROM technology. In this thesis, two concepts of length coding and hybrid incremental-absolute coded discs are proposed. To verify the implementation of these concepts, the rotary encoder set based on CD-ROM technology is designed and tested. It... 

    Analysis of twisted laser beam focusing and defocusing in plasma

    , Article Physica Scripta ; Volume 88, Issue 3 , August , 2013 ; 00318949 (ISSN) Khamedi, M ; Bahrampour, A. R ; Sharif University of Technology
    Using the source dependent expansion method and paraxial approximation, the evolution of the beam spot size (BSS) in laser plasma interaction is investigated. Considering a collisionless mechanism, the self-focusing of a Laguerre-Gaussian (LG) light beam in a plasma medium is studied and the evolution of the BSS is solved analytically for the non-saturating nonlinearity state, and numerically for the saturating state. The self-focusing of a doughnut beam depends on the initial BSS, in which if the initial BSS gets bigger, the beam in the medium will be focused faster. We show that if the nonlinear effect of the plasma medium is saturated, the LG beam profile can remain stable and the BSS... 

    Studying soft X-Rays emitted by SUT-PF using a cylindrical bent crystal spectrometer

    , Article Journal of Fusion Energy ; Volume 35, Issue 2 , 2016 , Pages 346-351 ; 01640313 (ISSN) Etaati, G. R ; Hosseinzadeh, A ; Nazmabadi, M ; Sharif University of Technology
    Plasma focus is a copious source of electrons, ions, neutrons, and X-rays. SUT-PF is a 7 kJ Mather type plasma focus device. In order to study soft X-rays emitted by this device a bent crystal spectrometer has been designed and constructed based on Johann method. Before recording spectral lines, using a photodiode detector and a pinhole camera, optimum parameters for maximum emission of soft X-rays have been studied and registered. Results show that ionized Argon atomic lines mostly have wavelengths between 3 and 4 Å. Among them 1s2–1s2p transition with a wavelength of 3.943 Å represents the most intense line  

    Inertial microfluidics: a method for fast prediction of focusing pattern of particles in the cross section of the channel

    , Article Analytica Chimica Acta ; Volume 1083 , 2019 , Pages 137-149 ; 00032670 (ISSN) Mashhadian, A ; Shamloo, A ; Sharif University of Technology
    Elsevier B.V  2019
    Inertial microfluidics is utilized as a powerful passive method for particle and cell manipulation, which uses the hydrodynamic forces of the fluid in the channel to focus particles in specific equilibrium positions in the cross section of the channel. To achieve high performance manipulation, knowledge of focusing pattern of particles in the cross section of channel is essential. In this paper, we propose a method to address this important issue. To this end, firstly inertial microfluidics is analyzed in rectangular cross section channels. The results indicate that fluid flow velocity and channel's cross-sectional profiles have great impacts on the forces exerted on particles. Next, these... 

    Computational inertial microfluidics: a review

    , Article Lab on a Chip ; Volume 20, Issue 6 , 2020 , Pages 1023-1048 Razavi Bazaz, S ; Mashhadian, A ; Ehsani, A ; Saha, S. C ; Krüger, T ; Ebrahimi Warkiani, M ; Sharif University of Technology
    Royal Society of Chemistry  2020
    Since the discovery of inertial focusing in 1961, numerous theories have been put forward to explain the migration of particles in inertial flows, but a complete understanding is still lacking. Recently, computational approaches have been utilized to obtain better insights into the underlying physics. In particular, fundamental aspects of particle focusing inside straight and curved microchannels have been explored in detail to determine the dependence of focusing behavior on particle size, channel shape, and flow Reynolds number. In this review, we differentiate between the models developed for inertial particle motion on the basis of whether they are semi-analytical, Navier-Stokes-based,... 

    Three-dimensional finite-difference time-domain analysis of nonlinear self-focusing in air

    , Article 2008 International Symposium on Telecommunications, IST 2008, Tehran, 27 August 2008 through 28 August 2008 ; October , 2008 , Pages 163-168 ; 9781424427512 (ISBN) Rastegarfar, H ; Shishegar, A. A ; Sharif University of Technology
    Through using a three-dimensional finitedifference time-domain (3D-FDTD) scheme, we analyze nonlinear self-focusing in air as a Kerr medium. For sufficiently intense laser beams, the gaseous medium can behave as a strong positive lens which tends to focus the beam. Our simulations' major focus is on the propagation characteristics of an intense continuous-wave laser beam. Necessary relations have been introduced into the conventional FDTD formulation to account for the nonlinear behavior of air. The results clearly indicate that sufficient amounts of optical intensity may lead to self-focusing immediately in front of the laser aperture. ©2008 IEEE  

    Analysis and Modeling "Time-of-Flight Particle Sizer" with CFD

    , M.Sc. Thesis Sharif University of Technology Bodaghkhani, Armin (Author) ; Saeedi, Mohammad Saeed (Supervisor) ; Sani, Mahdi (Supervisor)
    In this study different models of an aerodynamic particle sizer and aerodynamic focusing lens were introduced and governing equations for an aerodynamic focusing lens for flow fields and particle motions were discussed. An aerodynamic focusing lens was simulated for analyzing particle motions and flow fields. Two kinds of models are considered; One was Ahmadi`s model and the other one was Wang`s model and both models are axisymmetric. The results show that for small particles (sub 30 nanometers), Brownian motions were highly effective on transmission efficiency and producing particle beams. The two models are compared and the results show that Ahmadi`s model produce narrower particle beams... 

    CTC Cluster Separation on Microfluidics Chip

    , M.Sc. Thesis Sharif University of Technology Rostami, Peyman (Author) ; Firouzabadi, Bahar (Supervisor) ; Saidi, Mohammad Said (Supervisor)
    According to statistics in 2012, around 14 million people worldwide have cancer, and 8 million have died that year, according to estimates, this number will increase to 21 millions new cancer case and 13 million mortality in 2030. Despite years of research on cancer, many questions about the mechanism of the spread of cancer in the body remain unanswered so far. The proposed models identify that the cells isolated from the primary tumor and transmit them to the circulatory system in the form of circulating tumor cells (CTCs) or in the form of clusters as responsible for the incidence of cancer. This process is called metastasis. Recent studies have reported the high potential of metastasis...