Search for: higher-frequencies
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    A modal coupling procedure to improve residual modal effects based on experimentally generated data

    , Article Journal of Sound and Vibration ; Volume 331, Issue 1 , 2012 , Pages 66-80 ; 0022460X (ISSN) Hosseini Kordkheili, S. A ; Momeni Massouleh, S. H ; Kokabi, M. J ; Bahai, H ; Sharif University of Technology
    In this paper a modal coupling procedure is developed to improve residual modal effects based on experimentally generated data. While showing that CraigChangs proposed approximation function for higher frequency modes does not compare well with the exact function, a new procedure is developed in order to re-express the dynamic residuals. For this purpose, all frequency dependent terms of the Maclaurin series in CraigChangs proposed method are replaced by a general compatible function, which includes the neglected higher order terms. However, this function no longer appears in final equation of motion. Results from case studies for the discrete, continuous and experimental models are... 

    Permutation approach, high frequency trading and variety of micro patterns in financial time series

    , Article Physica A: Statistical Mechanics and its Applications ; Vol. 413, issue , 2014 , pp. 25-30 ; ISSN: 03784371 Aghamohammadi, C ; Ebrahimian, M ; Tahmooresi H ; Sharif University of Technology
    Permutation approach is suggested as a method to investigate financial time series in micro scales. The method is used to see how high frequency trading in recent years has affected the micro patterns which may be seen in financial time series. Tick to tick exchange rates are considered as examples. It is seen that variety of patterns evolve through time; and that the scale over which the target markets have no dominant patterns, have decreased steadily over time with the emergence of higher frequency trading  

    Laser diode modulation under large signal conditions

    , Article 2013 21st Iranian Conference on Electrical Engineering ; May , 2013 , Page(s): 1 - 5 ; 9781467356343 (ISBN) Ahmadian, A ; Sharif University of Technology
    Large signal behavior of the Laser Diode is analyzed with the aim of finding a qualitative relationship between modulation amplitude and the change in the shape of its transfer function. It is found that, at quasi-static conditions, increasing the amplitude of the modulating signal smoothes out the original piecewise-linear transfer function of the diode. It further shifts the now smoothed knee point to lower DC currents. As the frequency increases, however, these effects become less and less pronounced. In addition, the transfer function becomes rather wavy due to the failure of current density to reach the saturation level necessary for adequate stimulated emission. At even higher... 

    Ultrasonic ion pumps in bio-battery's electrolyte

    , Article Advanced Materials Research, 7 January 2012 through 8 January 2012 ; Volume 463-464 , January , 2012 , Pages 909-913 ; 10226680 (ISSN) ; 9783037853634 (ISBN) Amjadi, A ; Ebrahimi, A ; Sherafati, A ; Khalilgharibi, N ; Zand, M. K ; Dibazar, M. S. S ; Sobhani, S. O ; Sharif University of Technology
    Bio-batteries are environmental friendly electricity generation devices that utilize energy from biological sources, like glucose[1] [2]. It consists of an anode with digesting enzymes and a cathode comprising oxygen-reducing enzymes. Immobilizing enzymes is a considerable issue in these kinds of devices. In this article, we propose two new methods for immobilizing and shifting particles likewise enzymes used in bio-batteries towards the anode or cathode end. Our experiments illustrate how tiny particles could be trapped in the nodes of the ultrasonic standing waves and by two methods of displacing the nodes, we can transfer the particles towards a desired location. First method is based on... 

    Vibration analysis of Setar for extracting the frequency response function (FRF)

    , Article ASME International Mechanical Engineering Congress and Exposition, Proceedings, 13 November 2009 through 19 November 2009 ; Volume 15 , 2010 , Pages 485-490 ; 9780791843888 (ISBN) Mansour, H ; Arzanpour, S ; Alghassi, H ; Behzad, M ; Sharif University of Technology
    Extraction of the frequency response of a musical instrument is the first step to analyze its vibration characteristic. This research introduces the results of several experiments implemented on Setar, a Persian long-necked lute. Setar has a wooden, reflective sound-box which is highly coupled with its surrounding air. High level of damping in addition to the composite properties in Setar, consequences dissimilar frequency domain vibration patterns. At lower frequencies, the response exhibits very distinct modal behavior, while in higher frequencies an overall effect of close modes is demonstrated. In this paper different approaches are utilized to handle both frequency regimes; and their... 

    Nonlinear dynamic modeling of smart composite with piezoelectric nitinol and MMC

    , Article Proceedings of the ASME Conference on Smart Materials, Adaptive Structures and Intelligent Systems 2009, SMASIS2009, 21 September 2009 through 23 September 2009, Oxnard, CA ; Volume 2 , 2009 , Pages 141-148 ; 9780791848975 (ISBN) Amini, A ; Mehdigholi, H ; Elahinia, M ; Sharif University of Technology
    In this paper, one smart composite involving nitinol, piezoelectric and MMC is modeled. This simulation covers all criteria in these advanced materials and theoretically solves the five-order equation. Furthermore, numerical sample is investigated and results have been explored. The results represent the relationship between natural frequency of the structure, temperature, the lateral deflection and martensite ratio of shape memory alloy. The results show nonlinearity response in dynamic motion in lower natural frequency and linear behavior in higher frequency. In this simulation, numerical approximation has been avoided. Copyright © 2009 by ASME  

    Reflected shock tube experiments on aeroacoustic signature of hot jets

    , Article Journal of Mechanical Science and Technology ; Volume 31, Issue 8 , 2017 , Pages 3811-3820 ; 1738494X (ISSN) Jahromi, I. B ; Ebrahimi, M ; Ghorbanian, K ; Sharif University of Technology
    We used a reflected shock tube to investigate the acoustic signature of a hot jet at the far-field. Experiments were performed at Mach = 1.4 and a total temperature of Tt = 950 Kelvin. Far-field acoustic signatures of the hot jet at six polar angles θ = 15˚ to θ = 90˚ from the jet axis) were measured and imaged by the means of continuous wavelet transform in scalograms. The results were compared with experiments from a steady test facility at similar test conditions. Further, the primary characteristics of noise events in jet far-field were compared with analytical models considering wavepacket as the main source of jet noise. The results indicate that higher frequency events at θ = 90˚... 

    Design of a wideband terahertz absorber composed of graphene patches

    , Article IET Optoelectronics ; Volume 13, Issue 5 , 2019 , Pages 235-239 ; 17518768 (ISSN) Karimi, P ; Maddahali, M ; Bakhtafrouz, A ; Shahabadi, M ; Sharif University of Technology
    Institution of Engineering and Technology  2019
    Here, the design of a wideband absorber operating at terahertz frequencies is presented. The design is based on an analytical circuit model of graphene arrays of rectangular patches obtained from the presented circuit model of graphene arrays of disks. A recently proposed method is generalised for the design of wideband absorbers at higher frequencies The bandwidth is increased by correct tuning of the input impedance for a structure composed of two layers of graphene arrays and a metal-backed dielectric layer. Using two-layer graphene arrays, the authors decrease the slope of the imaginary part of the input impedance to increase the bandwidth. The designed absorber works at a frequency of... 

    An n-path enhanced-q tunable filter with reduced harmonic fold back effects

    , Article IEEE Transactions on Circuits and Systems I: Regular Papers ; Volume 60, Issue 11 , 2013 , Pages 2867-2877 ; 15498328 (ISSN) Mohammadpour, A ; Behmanesh, B ; Atarodi, S. M ; Sharif University of Technology
    A high-Q, tunable, bandpass filtered amplifier structure is proposed which is based on a novel Q enhancement technique in N-path filters. Using Fourier series analysis, frequency response of an N-path filter as well as the aliasing effects which are present in it are derived. Frequency translation of unwanted contents at higher frequencies to the center frequency of the bandpass filter is called harmonic fold back (HFB). It is shown that using an additional N-path filter with the same clock frequency but different clock phases can reduce the HFB. The required conditions for fold back elimination are derived fromFourier series expansion analysis. In order to achieve HFB reduction as well as... 

    Discriminating early stage AD patients from healthy controls using synchronization analysis of EEG

    , Article 2011 6th International Conference on Digital Information Management, ICDIM 2011 ; 2011 , Pages 282-287 ; 9781457715389 (ISBN) Jalili, M ; Sharif University of Technology
    In this paper we study how the meso-scale and micro-scale electroencephalography (EEG) synchronization measures can be used for discriminating patients suffering from Alzheimer's disease (AD) from normal control subjects. To this end, two synchronization measures, namely power spectral density and multivariate phase synchronization, are considered and the topography of the changes in patients vs. Controls is shown. The AD patients showed increased power spectral density in the frontal area in theta band and widespread decrease in the higher frequency bands. It was also characterized with decreased multivariate phase synchronization in the left fronto-temporal and medial regions, which was... 

    Sub-threshold charge recovery circuits

    , Article Proceedings - IEEE International Conference on Computer Design: VLSI in Computers and Processors, 3 October 2010 through 6 October 2010, Amsterdam ; 2010 , Pages 138-144 ; 10636404 (ISSN) ; 9781424489350 (ISBN) Khatir, M ; Mohammadi, H. G ; Ejlali, A ; IEEE; IEEE Circuits and Systems Society; IEEE Computer Society; HiPEAC Compilation Architecture ; Sharif University of Technology
    Embedded systems account for wide range of applications. However, the design of such systems is faced with a diverse spectrum of criteria. The energy consumption, performance, and demanding security concerns are some of the most significant challenges in designing of such systems. With these challenges, the design process can be managed more easily if a flexible logic circuit with the ability of satisfying the abovementioned concerns is taken into account. To achieve such a logic circuit, in this paper we have combined the sub-threshold operation and charge recovery techniques. Using our technique, lower power consumption, ability of operating at higher frequencies, and more security (to... 

    Effects of structural configuration on vibration control of smart laminated beams under random excitations

    , Article Journal of Mechanical Science and Technology ; Volume 24, Issue 5 , 2010 , Pages 1119-1125 ; 1738494X (ISSN) Zabihollah, A ; Sharif University of Technology
    The influence of structural configuration on vibration responses of smart laminated beams under random loading is studied. The effect of laminate configurations and locations of sensors/actuators in the smart system is also investigated. The layer-wise approximation for displacement and electric potential is utilized to construct the finite element model. The closed-loop control response is determined through an optimal control algorithm based on the Linear Quadratic Regulator (LQR). The correlation coefficient between the input random force and the applied actuating voltage for various configurations is also computed. It is revealed that for softer configurations, the correlation... 

    HAZ softening behavior of strain-hardened Al-6.7Mg alloy welded by GMAW and pulsed GMAW processes

    , Article International Journal of Advanced Manufacturing Technology ; Volume 92, Issue 5-8 , 2017 , Pages 2255-2265 ; 02683768 (ISSN) Hadadzadeh, A ; Mahmoudi Ghaznavi, M ; Kokabi, A. H ; Sharif University of Technology
    Gas metal arc welding (GMAW) process was used to weld plates of strain-hardened Al-6.7Mg alloy. It was observed that HAZ softening issue occurred extensively for the current material using the GMAW process. So, as a solution, pulsed current was employed and the plates were welded by pulsed GMAW (PGMAW) process. The effects of peak current (93, 120, 140, and 160 A) and pulse frequency (0.5, 2.0, and 5.0 Hz) on the strength of the weldments were investigated. For high peak currents (160 A), catastrophic defects were formed in the weld metal. It was observed that for the lowest pulse frequency (0.5 Hz), increasing the peak current increased the weld strength. The peak current did not change the... 

    Investigation of bias current and modulation frequency dependences of detectivity of YBCO TES and the effects of coating of Cu-C composite absorber layer

    , Article IEEE Transactions on Applied Superconductivity ; Volume 19, Issue 4 , 2009 , Pages 3688-3693 ; 10518223 (ISSN) Moftakharzadeh, A ; Kokabi, A ; Bozbey, A ; Ghodselahi, T ; Vesaghi, M. A ; Khorasani, S ; Banzet, M ; Schubert, J ; Fardmanesh, M ; Sharif University of Technology
    Bolometric response and noise characteristics of YBCO superconductor transition edge IR detectors with relatively sharp transition and its resulting detectivity are investigated both theoretically and experimentally. The magnitude of response of a fabricated device was obtained for different bias currents and modulation frequencies. Using the measured and calculated bolometric response and noise characteristics, we found and analyzed the device detectivity versus frequency for different bias currents. The detectivity versus chopping frequency of the device did not decrease following the response strongly, due to the decrease of the noise at higher frequencies up to 1 kHz, resulting in... 

    Electrodynamics of tilted dirac and weyl materials: a unique platform for unusual surface plasmon polaritons

    , Article Physical Review B ; Volume 100, Issue 20 , 2019 ; 24699950 (ISSN) Jalali Mola, Z ; Jafari, A ; Sharif University of Technology
    American Physical Society  2019
    The electrodynamics of Weyl semimetals is an extension of Maxwell's theory where in addition to field strength tensor Fμν, an axion field enters the theory which is parametrized by a four-vector bμ=(b0,b). In tilted Weyl materials (TWMs) an additional set of parameters ζ=(ζx,ζy,ζz) enters the theory that can be encoded into the metric of the spacetime felt by electrons in TWMs. This allows an extension of Maxwell's electrodynamics that describes electric and magnetic fields in TWMs, and tilted Dirac materials (TDMs) that correspond to bμ=0. The tilt parameter ζ appearing as an off-diagonal metric matrix element, mixing time and space components, which mingles E and B fields, whereby the... 

    Dirac leaky wave antennas

    , Article 5th International Conference on Millimeter-Wave and Terahertz Technologies, MMWaTT 2018, 18 December 2018 through 20 December 2018 ; Volume 2018-December , 2019 , Pages 1-5 ; 21570965 (ISSN); 9781538677179 (ISBN) Rezaee, S ; Memarian, M ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2019
    Dirac leaky-wave antennas (DLWAs) are derived from photonic crystals exhibiting Dirac cone dispersion around their Γ-point. DLWAs provide high directive beams and continuous frequency beam scanning, non-fluctuating leakage constant and real non-zero Bloch impedance at and around broadside, due to the closed and linear Dirac dispersion relation around broadside. These features, along with their inherent compatibility for higher frequency designs (larger unit cells compared to metamaterials), make DLWAs an ideal candidate for the upper microwave, mm-wave and terahertz frequencies, and for applications such as radar, 5G, spectroscopy, etc. In this review, we cover the recent developments on...