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    A biomechanical model to analyze normal, degenerated, and fused cervical spines using Iar's concept

    , Article Iranian Journal of Science and Technology, Transaction B: Engineering ; Volume 28, Issue 4 B , 2004 , Pages 423-433 ; 03601307 (ISSN) Meghdari, A ; Bahrami, A. H ; Sharif University of Technology
    During voluntary flexion/extension of the head-neck system, the cervical spine undergoes a stepwise motion from upper to lower regions with a specific pattern. The motion of each vertebra is composed of a translation and rotation with respect to lower vertebrae, which may be considered as an absolute rotation about an axis called instantaneous axis of rotation (IAR). The location of this axis is different between normal and degenerated spines. A biomechanical computer model of the head and cervical vertebrae, including eight separate rigid links and nine spinal muscles as actuating elements was developed to evaluate and compare inter-segmental force-moments and muscle forces in normal,... 

    Oil-soluble drag-reducing polymers [electronic resource]

    , Article Journal of polymer materials ; December 1994, Volume 11, Number 4; Page(s) 239 To 247 Zohurian Mehr, M. J. (Mohammad Jalal) ; Pourjavadi, A ; Nadali, M ; Sharif University of Technology
    This article reviews the oil-soluble polymeric drag-reducing agents (DRAs) with an outlook to their large-scale application in petroleum industry. A general discussion on mechanism of the DR phenomenon and mechanical degradation of the drag reducers in turbulent flow is offered with an emphasis on the molecular parameters. Furthermore, low charge density associating polymers, as a new class of oil-soluble flow improvers, are described  

    Null controllability of degenerate/singular parabolic equations

    , Article Journal of Dynamical and Control Systems ; Volume 18, Issue 4 , 2012 , Pages 573-602 ; 10792724 (ISSN) Fotouhi, M ; Salimi, L ; Sharif University of Technology
    Springer  2012
    The purpose of this paper is to provide a full analysis of the null controllability problem for the one dimensional degenerate/singular parabolic equation ut - (a(x)ux)x - λ/x βu = 0, (t,x) ∈ (0, T) × (0,1), where the diffusion coefficient a(·) is degenerate at x = 0. Also the boundary conditions are considered to be Dirichlet or Neumann type related to the degeneracy rate of a(·). Under some conditions on the function a(·) and parameters β, λ, we prove global Carleman estimates. The proof is based on an improved Hardy-type inequality  

    Controllability results for a class of one dimensional degenerate/singular parabolic equations

    , Article Communications on Pure and Applied Analysis ; Volume 12, Issue 3 , 2013 , Pages 1415-1430 ; 15340392 (ISSN) Fotouhi, M ; Salimi, L ; Sharif University of Technology
    We study the null controllability properties of some degenerate/singular parabolic equations in a bounded interval of ℝ. For this reason we derive a new Carleman estimate whose proof is based on Hardy inequalities  

    Biomechanical effects of lumbar fusion surgery on adjacent segments using musculoskeletal models of the intact, degenerated and fused spine

    , Article Scientific Reports ; Volume 11, Issue 1 , 2021 ; 20452322 (ISSN) Ebrahimkhani, M ; Arjmand, N ; Shirazi Adl, A ; Sharif University of Technology
    Nature Research  2021
    Adjacent segment disorders are prevalent in patients following a spinal fusion surgery. Postoperative alterations in the adjacent segment biomechanics play a role in the etiology of these conditions. While experimental approaches fail to directly quantify spinal loads, previous modeling studies have numerous shortcomings when simulating the complex structures of the spine and the pre/postoperative mechanobiology of the patient. The biomechanical effects of the L4–L5 fusion surgery on muscle forces and adjacent segment kinetics (compression, shear, and moment) were investigated using a validated musculoskeletal model. The model was driven by in vivo kinematics for both preoperative (intact or... 

    Topological Defects in Confined Nematics by Planar Anchoring

    , M.Sc. Thesis Sharif University of Technology Seyed Nejad, Reza (Author) ; Ejtehadi, Mohammad Reza (Supervisor) ; Mozaffari, Mohammad Reza (Supervisor)
    Confining nematic liquid crystal between two curved boundary conditions while the nematic molecules have a degenerate planar anchoring leads to complex and beautiful textures of molecular disparagement(defect) in the bulk and on the surfaces. Such the liquid crystal shells are made with double-emulsion techniques in microfluidic devices have provided applications for micro-scale colloidal linkers.In this work, we have numerically minimized the elastic energy in one-constant approximation in present of Fournier’s degenerate surface potential with finite element method. The nematic shell is confined between two spherical surfaces that we have studied the final energies and their related... 

    , M.Sc. Thesis Sharif University of Technology Zargarzadeh, Mehrzad (Author) ; Maddah Hosseini, Hamid Reza (Supervisor)
    Age-related macular degeneration (AMD) is the most common cause of vision loss in those aged over 50. There are two main types of AMD, Wet and Dry form. Wet AMD is more severe though more treatable. There are three conventional treatments for AMD including laser therapy, surgery and intravitreal injection of anti-VEGF into the eye. Delivery of drugs to the posterior segment of the eye is still challenging and several implants and devices are currently under investigation for their ability to stimulate the retina, producing visual percepts. The application of intravitreal bevacizumab (Avastin) has expanded tremendously from the time of its introduction into ophthalmic care since 3 years ago.... 

    Control of Heat Equations

    , Ph.D. Dissertation Sharif University of Technology Salimi, Leila (Author) ; Fotouhi Firouzabad, Morteza (Supervisor)
    The controllability problem may be formulated roughly as follows. Consider an evolution system (either described in terms of partial or ordinary differential equations) on which we are allowed to act by means of a suitable choice of the control (the right-hand side of the system, the boundary conditions, etc.). Given a time interval 0 < t < T, and initial and final states, the goal is to determine whether there exists a control driving the given initial data to the given final ones in time T. Now, consider the simplest parabolic equation, namely heat equation and suppose that one could act by appropraite controls on this system. The null controllability problem which is one of the very... 

    Design and Construction of High-voltage Linear Regulator with Minimal Losses for Power Supply of Microwave Tube Cathode

    , M.Sc. Thesis Sharif University of Technology Osanloo, Mohsen (Author) ; Kaboli, Shahriyar (Supervisor)
    Microwave tubes are widely used in the telecommunications transmitters. high voltage power supplies are used to feed them. According to the specifications that arises for microwave tubes, To take advantage of these tubes need to maintain and stabilize voltage in a certain amount to be felt. If the tube supply voltage changes, the desired output parameters such as RF output power quality will change. To stabilize the voltage is within acceptable limits provided in different ways. One common method is the use of switching regulators due to the high efficiency compared to linear regulators considered. But it also will bring problems. Some of these problems can be pointed to electromagnetic... 

    NF analysis of LNA with Lossy passive network at the input

    , Article 41st International Conference on Telecommunications and Signal Processing, TSP 2018, 4 July 2018 through 6 July 2018 ; 2018 ; 9781538646953 (ISBN) Rasekh, A ; Rabbani, R ; Sharif Bakhtiar, M ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2018
    It is widely accepted that the presence of a lossy network, such as a SAW filter or balun, at the input of LNA increases NF of the overall circuit by an amount equal to the insertion loss of the lossy network. In this work it is shown that this idea is not exactly true and it considerably underestimates the overall NF. To verify this claim, Z-model of the lossy network is added before the LNA and the overall noise figure is recalculated for some commonly used LNA topologies. It is shown that in common gate LNA and common source LNA with resistive feedback the accepted equation underestimates the overall NF by 1.3 dB for an insertion loss of 2 dB. In common source with resistive matching and... 

    A regenerative approach towards recovering the mechanical properties of degenerated intervertebral discs: Genipin and platelet-rich plasma therapies

    , Article Proceedings of the Institution of Mechanical Engineers, Part H: Journal of Engineering in Medicine ; Volume 231, Issue 2 , 2017 , Pages 127-137 ; 09544119 (ISSN) Nikkhoo, M ; Wang, J. L ; Abdollahi, M ; Hsu, Y. C ; Parnianpour, M ; Khalaf, K ; Sharif University of Technology
    SAGE Publications Ltd  2017
    Degenerative disc disease, associated with discrete structural changes in the peripheral annulus and vertebral endplate, is one of the most common pathological triggers of acute and chronic low back pain, significantly depreciating an individual's quality of life and instigating huge socioeconomic costs. Novel emerging therapeutic techniques are hence of great interest to both research and clinical communities alike. Exogenous crosslinking, such as Genipin, and platelet-rich plasma therapies have been recently demonstrated encouraging results for the repair and regeneration of degenerated discs, but there remains a knowledge gap regarding the quantitative degree of effectiveness and... 

    Design of a UWB Reconfigurable LNA with Variable Gain

    , M.Sc. Thesis Sharif University of Technology Sepidband, Paria (Author) ; Atarodi, Mojtaba (Supervisor) ; Fotowat Ahmady, Ali (Supervisor)
    In recent years, lots of efforts has been done to implement Ultra-Wideband (UWB) Low Noise Amplifiers (LNAs), and Reconfigurable Low Noise Amplifiers, to achieve low Noise Figure (NF) and power dissipation, and high gain and linearity. In this thesis an Ultra-Wideband CMOS Low Noise Amplifier is presented. Due to really low power consumption and extremely high data rates, the UWB standard is popular in the consumer market. The LNA is the outer most part of an UWB transceiver, which provides enough gain to the signal with the least possible noise and distortion. 0.18u CMOS technology has been chosen for the design of the LNA at the transistor level. Two different bandwidths in a single LNA... 

    Synthesis of Magnetite (Fe3O4)-Avastin Nanocomposite as a Potential Drug for AMD Treatment

    , M.Sc. Thesis Sharif University of Technology Zargarzadeh, Mehrzad (Author) ; Maddah Hosseini, Hamid Reza (Supervisor) ; Delavary, Hamid (Co-Advisor)
    Age-related macular degeneration (AMD) is the most common cause of vision loss in those aged over 50. There are two main types of AMD, Wet and Dry form. Wet AMD is more severe though more treatable. There are three conventional treatments for AMD including laser therapy, surgery and intravitreal injection of anti-VEGF into the eye. Delivery of drugs to the posterior segment of the eye is still challenging and several implants and devices are currently under investigation for their ability to stimulate the retina, producing visual percepts. The application of intravitreal bevacizumab (Avastin) has expanded tremendously from the time of its introduction into ophthalmic care since 3 years ago.... 

    A Fully Differential Highly Linear Low Power Ultra Wideband LNA

    , M.Sc. Thesis Sharif University of Technology Ghasemi, Reza (Author) ; Haj Sadeghi, Khosro (Supervisor)
    This work uses a hierarchical approach for designing the integrated UWB LNA in MOSFET technology. It first offers a brief treatment of the two important types of noise: the thermal noise of channel and the gate-induced noise, in MOSFET. Then the CS and CS-CG configurations for narrow-band LNAs are considered and the requirements for the wide-band operation in UWB are specified. Noise cancelling technique is also introduced, while five wideband prototype designs, with the noise-cancelling technique used in two designs, are re-examined and tested by simulation. Some proposed methods are then applied to these designs for better performance and obtaining practical insight. The final main... 

    A stabilized piezolaminated nine-nodded shell element formulation for analyzing smart structures behaviors

    , Article Mechanics of Advanced Materials and Structures ; Volume 23, Issue 2 , 2016 , Pages 187-194 ; 15376494 (ISSN) Hosseini Kordkheili, S. A ; Salmani, H ; Afshari, S. S. G ; Sharif University of Technology
    Taylor and Francis Inc  2016
    An explicit hybrid stabilization method is utilized together with a reduced order integration scheme to stabilize spurious zero energy modes from the sub-integrated degenerated shell element. This stabilization is achieved after employing appropriate contravariant higher order stress modes. The relevant finite element formulation of the piezolaminated nine-nodded shell element is then derived to analyze smart structures behaviors. To show the capabilities of the presented formulation, it has been implemented in a finite element code. The developed code is used to analyze some typical problems. The results are compared with those obtained from other schemes in the literature and experiments  

    A highly-linear dual-gain CMOS low-noise amplifier for X-band

    , Article IEEE Transactions on Circuits and Systems II: Express Briefs ; 2017 ; 15497747 (ISSN) Meghdadi, M ; Piri, M ; Medi, A ; Sharif University of Technology
    A highly linear X-band low-noise amplifier (LNA) is proposed and implemented in a standard 0.18-μm CMOS technology. The LNA features both high and low-gain operation modes. In its normal high-gain mode, the LNA shows a small-signal gain of 13.6 dB with an IIP3 of +9.5 dBm and a noise figure of 4.7 dB. The two-stage amplifier draws 90 mA from the 3.3V power supply to achieve +14.8 dBm output P1dB (+2.2 dBm input P1dB). In the low-gain mode, the gain is reduced by about 10 dB to further enhance the linearity and to accommodate very large blockers. Accordingly, the input P1dB is enhanced to +13.7 dBm while the noise figure is increased by 8.1 dB. A technique is also introduced to maintain the... 

    A low-power temperature-compensated CMOS peaking current reference in subthreshold region

    , Article Proceedings - IEEE International Symposium on Circuits and Systems, 28 May 2017 through 31 May 2017 ; 2017 ; 02714310 (ISSN) ; 9781467368520 (ISBN) Eslampanah, M. S ; Kananian, S ; Zendehrouh, E ; Sharifkhani, M ; Sodagar, A. M ; Shabany, M ; Sharif University of Technology
    In this paper, a new method to achieve very small current reference levels on integrated circuits with immunity to temperature variations using peaking current source with MOSFETs operating in subthreshold region is proposed. By adding a source degeneration resistor to the conventional peaking current source architecture, a zero temperature coefficient current can be generated. The proposed low-power circuit operating in the weak inversion region is designed, simulated, and fabricated in a 0.18-μm standard CMOS process. Measurement results verify the circuit operation with about 5% variation over the span of -40° C to +100° C (industrial temperature grade). The supplied current is designed... 

    A meta-model analysis of a finite element simulation for defining poroelastic properties of intervertebral discs

    , Article Proceedings of the Institution of Mechanical Engineers, Part H: Journal of Engineering in Medicine ; Volume 227, Issue 6 , 2013 , Pages 672-682 ; 09544119 (ISSN) Nikkhoo, M ; Hsu, Y. C ; Haghpanahi, M ; Parnianpour, M ; Wang, J. L ; Sharif University of Technology
    Finite element analysis is an effective tool to evaluate the material properties of living tissue. For an interactive optimization procedure, the finite element analysis usually needs many simulations to reach a reasonable solution. The metamodel analysis of finite element simulation can be used to reduce the computation of a structure with complex geometry or a material with composite constitutive equations. The intervertebral disc is a complex, heterogeneous, and hydrated porous structure. A poroelastic finite element model can be used to observe the fluid transferring, pressure deviation, and other properties within the disc. Defining reasonable poroelastic material properties of the... 

    Smart liposomal drug delivery for treatment of oxidative stress model in human embryonic stem cell-derived retinal pigment epithelial cells

    , Article International Journal of Pharmaceutics ; Volume 548, Issue 1 , 2018 , Pages 62-72 ; 03785173 (ISSN) Behroozi, F ; Abdkhodaie, M. J ; Sadeghi Abandansari, H ; Satarian, L ; Kazemi Ashtiani, M ; Jaafari, M. R ; Baharvand, H ; Sharif University of Technology
    Oxidative stress has been implicated in the progression of age-related macular degeneration (AMD). Treatment with antioxidants seems to delay progression of AMD. In this study, we suggested an antioxidant delivery system based on redox-sensitive liposome composed of phospholipids and a diselenide centered alkyl chain. Dynamic light scattering assessment indicated that the liposomes had an average size of 140 nm with a polydispersity index below 0.2. The percentage of encapsulation efficiency of the liposomes was calculated by high-performance liquid chromatography. The carriers were loaded with N-acetyl cysteine as a model antioxidant drug. We demonstrated responsiveness of the nanocarrier... 

    Biomechanical response of intact, degenerated and repaired intervertebral discs under impact loading – Ex-vivo and In-Silico investigation

    , Article Journal of Biomechanics ; Volume 70 , March , 2018 , Pages 26-32 ; 00219290 (ISSN) Nikkhoo, M ; Wang, J. L ; Parnianpour, M ; El-Rich, M ; Khalaf, K ; Sharif University of Technology
    Elsevier Ltd  2018
    Understanding the effect of impact loading on the mechanical response of the intervertebral disc (IVD) is valuable for investigating injury mechanisms and devising effective therapeutic modalities. This study used 24 porcine thoracic motion segments to characterize the mechanical response of intact (N = 8), degenerated (Trypsin-denatured, N = 8), and repaired (Genepin-treated, N = 8) IVDs subject to impact loading. A meta-model analysis of poroelastic finite element simulations was used in combination with ex-vivo creep and impact tests to extract the material properties. Forward analyses using updated specimen-specific FE models were performed to evaluate the effect of impact duration. The...