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    Polyethylene quality control in an industrial scale fluidized bed reactor

    , Article Indian Journal of Chemical Technology ; Volume 25, Issue 1 , January , 2018 , Pages 21-30 ; 0971457X (ISSN) Vahidi, O ; Shahrokhi, M ; Sharif University of Technology
    National Institute of Science Communication and Information Resources (NISCAIR)  2018
    Polymer quality control in an industrial scale polyethylene fluidized bed reactor has been addressed. Since online measurements of polymer properties (melt index and density) are not available, they must be controlled indirectly via other available measurements. In the present paper, two algebraic equations correlating polyethylene melt index and density with the measureable concentrations of chemical components are obtained. Having the desired polyethylene properties and using these correlations, desired concentrations of chemical components are calculated and used via corresponding control loops. By using the infrequently available polyethylene property measurements, the correlation... 

    Control of Elements Ratio in Alloy Deposition System

    , M.Sc. Thesis Sharif University of Technology Kishani Farahani, Esmat (Author) ; Rashidian, Bijan (Supervisor)
    Nowadays, thin film alloy deposition has much importance. These alloys are used for various opto-electronic device applications such as liquid crystal displays, flat panel displays, plasma displays, solar cells and computer memories. Exact control of elements ratio in alloy is one of the important issues in deposition of thin film alloys. In alloy deposition with electron beam gun method from its elements, uniformity improvement of each layer is a way to maintain elements ratio in different parts of sample. This uniformity has much importance especially in optical coatings such as high quality antireflection coatings, highly selective filters and low loss reflectance coatings. In this... 

    Design of fractional order proportional-integral-derivative controller based on moment matching and characteristic ratio assignment method

    , Article Proceedings of the Institution of Mechanical Engineers. Part I: Journal of Systems and Control Engineering ; Volume 225, Issue 8 , December , 2011 , Pages 1040-1053 ; 09596518 (ISSN) Tabatabaei, M ; Haeri, M ; Sharif University of Technology
    This paper presents a new analytical method to design fractional-order proportional- integral-derivative (PID) controllers. The control parameters are calculated so that the closedloop system approximates a desired transfer function with transient response requirements. This function is determined based on the characteristic ratio assignment method. The control parameters are calculated by matching the first three moments of the closed-loop transfer function with the corresponding values of the desired system. Furthermore, to ensure closed-loop stability the proposed method is improved by using the shifted moments around the crossover frequency. Illustrative examples are given to show the... 

    Parametric stability of symmetrically laminated composite super-elliptical plates

    , Article Journal of Composite Materials ; Volume 50, Issue 28 , 2016 , Pages 3935-3951 ; 00219983 (ISSN) Ghaheri, A ; Nosier, A ; Keshmiri, A ; Sharif University of Technology
    SAGE Publications Ltd 
    Static and parametric stability of thin symmetrically laminated composite super-elliptical plates resting on Winkler-type foundation and subjected to uniform in-plane harmonic loads, under clamped, simply supported and free boundary conditions, are investigated based on the classical laminated plate theory. The governing equations are obtained from a variational approach and then the classical Ritz method is used to reduce the problem into a set of coupled Mathieu-Hill equations. Hsu's technique is utilized to determine the dynamic instability regions of principal and combination resonance frequencies. Extensive numerical data are provided to examine the effects of plate aspect ratio,... 

    Cardiac contraction motion compensation in gated myocardial perfusion SPECT: a comparative study

    , Article Physica Medica ; Volume 49 , 2018 , Pages 77-82 ; 11201797 (ISSN) Salehi, N ; Rahmim, A ; Fatemizadeh, E ; Akbarzadeh, A ; Farahani, M. H ; Farzanefar, S ; Ay, M. R ; Sharif University of Technology
    Associazione Italiana di Fisica Medica  2018
    Introduction: Cardiac contraction significantly degrades quality and quantitative accuracy of gated myocardial perfusion SPECT (MPS) images. In this study, we aimed to explore different techniques in motion-compensated temporal processing of MPS images and their impact on image quality and quantitative accuracy. Material and method: 50 patients without known heart condition underwent gated MPS. 3D motion compensation methods using Motion Freezing by Cedars Sinai (MF), Log-domain Diffeomorphic Demons (LDD) and Free-Form Deformation (FFD) were applied to warp all image phases to fit the end-diastolic (ED) phase. Afterwards, myocardial wall thickness, myocardial to blood pool contrast, and... 

    Fabrication, modeling and optimization of lyophilized advanced platelet rich fibrin in combination with collagen-chitosan as a guided bone regeneration membrane

    , Article International Journal of Biological Macromolecules ; Volume 125 , 2019 , Pages 383-391 ; 01418130 (ISSN) Ansarizadeh, M ; Mashayekhan, S ; Saadatmand, M ; Sharif University of Technology
    Elsevier B.V  2019
    In this study, lyophilized advanced platelet rich fibrin (A-PRF) was used in combination with collagen-chitosan membrane for the first time to combine advantages of both collagen and A-PRF membranes. Response surface methodology (RSM) was used to design the experimental condition and to correlate the effects of parameters, including chitosan/collagen (chit/col) weight ratio and A-PRF concentration on Young's modulus, mesenchymal stem cell (MSCs) viability and degradation rate of the membranes. Results showed that Young's modulus of the membranes was intensified by increasing chit/col weight ratio and decreasing A-PRF concentration from 3 to 8 MPa. Cell viability of MSCs was improved by both...