Search for: fourier-analysis
Total 26 records
M.Sc. Thesis Sharif University of Technology ; Seyed Reihani, Morteza
Surface tension is the most important interfacial parameter of a liquid. This quantity plays a key role in many processes such as extraction, distillation, absorption and chemical reactions. Various methods are proposed for measuring this quantity among which, the laser based methods are the most accurate ones. Unlike most of the mechanical methods, laser based methods remotely measure the surface tension. The aim of the current thesis is to measure the surface tension using laser beam, more specifically using homodyne detection system. This method implemented in both reflected and transmitted modes. In each of the mentioned methods, first the laser beam was incident to the liquid-air...
Article Optics Letters ; Volume 33, Issue 2 , 2008 , Pages 159-161 ; 01469592 (ISSN) ; Mehrany, K ; Jazayeri, A. H ; Sharif University of Technology
Li's Fourier factorization rule [J. Opt. Soc. Am. A 13, 1870 (1996)] was recently shown to be problematic to apply to highly conducting metallic gratings. We provide further information about the applicability of different differential methods and are concerned with the relation of observed numerical artifacts, the total number of retained space harmonics, the presence of both positive and negative permittivity inside the groove region, and the validity of Li's inverse rule. Two different cases corresponding to lossless and low-loss binary metallic gratings are considered, and it is shown that an increase in the number of retained space harmonics can relieve the presence of numerical...
Article International Journal of Mechanical Sciences ; Volume 53, Issue 9 , 2011 , Pages 777-785 ; 00207403 (ISSN) ; Kargarnovin, M. H ; Sharif University of Technology
The present paper addresses an analytical method to determine the overall behavior of piezocomposite materials containing body centered cubic (BCC) distribution of arbitrary oriented ellipsoidal heterogeneities. This approach is based on the extension of the electromechanical equivalent inclusion method (EMEIM) to interacting multi-inhomogeneities. In this treatment the short and long range interactions of the piezoelectric particles are appropriately incorporated through the homogenizing eigenstrainelectric field. The periodicity of the microstructure of the medium suggests representing the eigenfields in terms of Fourier series, accounting for the matrixparticle, interparticle and...
Article Signal Processing ; Volume 88, Issue 8 , August , 2008 , Pages 2114-2121 ; 01651684 (ISSN) ; Farsi, A ; Ghaed, M. H ; Karimi Ghartemani, M ; Sharif University of Technology
This paper studies the subject of adaptive noise cancelation using the Kalman filtering technique to achieve high precision and fast convergence. It is shown that the Kalman filter can successfully be designed to detect and extract periodic noises which may be constituted of different sinusoidal components with possibly unknown and/or time-varying frequencies. This highlights the feature of Kalman filter in synthesizing periodic noises in the time-domain which is not possible using Fourier-based methods such as DFT. Usefulness of the method is discussed in the context of two examples: active cancelation of periodic noises from audio waveforms and filtering of electrocardiogram measurements....
The application of numerical Laplace inversion methods for type curve development in well testing: A comparative study, Article Petroleum Science and Technology ; Volume 29, Issue 7 , 2011 , Pages 695-707 ; 10916466 (ISSN) ; Dejam, M ; Ghazanfari, M. H ; Sharif University of Technology
In this work the Fourier series and Zakian and Schapery methods are considered to numerically solve the Laplace transform of a pressure distribution equation for radial flow and to generate the type curves for three different boundary conditions. The results show that the Schapery method leads to approximate solutions for small values of dimensionless time. For large values, however, this method is almost accurate and hence is recommended because it is fast to apply compared to other algorithms. It has been found that the accuracy of the Schapery method for early time prediction can be improved to almost a perfect match with analytical results through multiplying the Schapery relation by a...
Assessment of the resonance frequency of cantilever carbon nanocones using molecular dynamics simulation, Article Applied Physics Letters ; Volume 100, Issue 17 , 2012 ; 00036951 (ISSN) ; Amini, H ; Hosseinian, A. R ; Sharif University of Technology
The resonance frequencies of cantilever carbon nanocones (CNCs) up to 4 nm in height are determined using molecular dynamics simulation based on adaptive intermolecular reactive empirical bond order potential. The frequency content of the free vibrations of CNCs under a lateral initial excitation at the tip is analyzed using fast Fourier transformation, and the resonance frequencies are obtained. The results are reported for various samples to investigate the dependency of the resonance frequency to the geometrical parameters and temperature of CNCs
Article Scientia Iranica ; Volume 18, Issue 4 A , 2011 , Pages 861-866 ; 10263098 (ISSN) ; Mofid, M ; Alanjari, P ; Sharif University of Technology
This study pertains to the free vibration problem of beams on an elastic foundation of the Winkler type, which is distributed over a particular length of the beam. Closed form solutions are developed by solving the governing differential equations of beams. Moreover, an innovative mathematical approach is proposed to find the precise analytical solution of the free vibration of beams with mixed boundary conditions. Results are discussed in detail through verification studies. Ultimately, it was concluded that the proposed mathematical method could successfully obtain the exact solution to the free vibration problem of beams on partial elastic foundations under mixed boundary conditions
Article Signal Processing ; Volume 91, Issue 2 , February , 2010 , Pages 191-202 ; 01651684 (ISSN) ; Haeri, M ; Sharif University of Technology
This paper deals with estimation of fractional order and pole locator in fractional order systems. The estimation is based on Bode diagram of the system that is obtained using input and output measurements. Here the magnitude diagram is approximated with number of straight lines depending on the level of complexity and in consequence a very good estimation of fractional order and acceptable approximations of pole locators are determined. Relying on the proposed method, complexity of fractional order system identification which is mostly due to the estimation of fractional order is substantially resolved. Some example simulation results are provided to explain the work and show its...
Article Signal Processing ; Volume 88, Issue 10 , 2008 , Pages 2417-2424 ; 01651684 (ISSN) ; Izadnia, S ; Vahedi, M ; Sharif University of Technology
In this paper, we have developed an efficient method for obtaining an orthonormal wavelet that is matched to a given signal. The error between the wavelet and the given signal is minimized subject to the constraints of the amplitude and phase of the band-limited wavelet spectrum. To consider the constraints of the minimization problem, the Lagrange multipliers technique is applied. Variational method reduced the optimal matching problem to the solution of a set of functional equations for the amplitude and phase of the wavelet spectrum. Continuous functional equations were written in terms of Fourier coefficients of the phase of the transfer function of the quadrature low pass filter at the...
Article IEEE Transactions on Signal Processing ; Volume 55, Issue 1 , 2007 , Pages 85-93 ; 1053587X (ISSN) ; Karimi Ghartemani, M ; Bakhshai, A ; Sharif University of Technology
Noise reduction and signal decomposition are among important and practical issues in time-domain signal analysis. This paper presents an adaptive notch filter (ANF) to achieve both these objectives. For noise reduction purpose, the proposed adaptive filter successfully extracts a single sinusoid of a possibly time-varying nature from a noise-corrupted signal. The paper proceeds with introducing a chain of filters which is capable of estimating the fundamental frequency of a signal composed of harmonically related sinusoids, and of decomposing it into its constituent components. The order of differential equations governing this algorithm is 2n + 1, where n is the number of constituent...
Article Circuits, Systems, and Signal Processing ; Vol. 34, Issue. 2 , 2014 , pp. 483-512 ; ISSN: 1531-5878 ; Ahmadi, A ; Makki, S. V. A. - D ; Soleimani, H ; Bavandpour, M ; Sharif University of Technology
This paper presents a digital hardware implementation of a frequency adaptive Hopf oscillator along with investigation on systematic behavior when they are coupled in a population. The mathematical models of the oscillator are introduced and compared in sense of dynamical behavior by using system-level simulations based on which a piecewise-linear model is developed. It is shown that the model is capable to be implemented digitally with high efficiency. Behavior of the oscillators in different network structures to be used for dynamic Fourier analysis is studied and a structure with more precise operation which is also more efficient for FPGA-based implementation is implemented. Conceptual...
Article Optics Letters ; Volume 38, Issue 16 , 2013 , Pages 3009-3012 ; 01469592 (ISSN) ; Sharif University of Technology
Li's Fourier factorization rules [J. Opt. Soc. Am. A 13, 1870 (1996)] should be applied to achieve a fast convergence rate in the analysis of diffraction gratings with the Fourier modal method. I show, however, that Li's inverse rule cannot be applied for periodic patterns of graphene when the conventional boundary condition is used. I derive an approximate boundary condition in which a nonzero but sufficiently small height is assumed for the boundary. The proposed boundary condition enables us to apply the inverse rule, leading to a significantly improved convergence rate. A periodic array of graphene ribbons is in fact a special type of finite-conductivity strip grating, and thus the...
Article Acta Mechanica ; Volume 220, Issue 1-4 , 2011 , Pages 15-32 ; 00015970 (ISSN) ; Nosier, A ; Sharif University of Technology
Boundary-layer effects in lengthy cross-ply laminated circular cylindrical shell panels under uniform axial extension are investigated by two analytical solutions. First, Reddy's layerwise theory with state-space approach is utilized to determine the local interlaminar stresses. In this method, the general displacement field is discretized through the shell thickness by a linear shape function. When the shell panel is subjected to an axial force, the axial strain is estimated by an equivalent single-layer theory. Second, the stress-function approach along with Fourier series expansion is applied to develop a novel elasticity solution. The elasticity solution, which is based on simply-support...
Factors affecting the gravity drainage mechanism from a single matrix block in naturally fractured reservoirs, Article Special Topics and Reviews in Porous Media ; Volume 2, Issue 2 , 2011 , Pages 115-124 ; 21514798 (ISSN) ; Ghazanfari, M. H ; Mashayekhizadeh, V ; Kamyab, M ; Sharif University of Technology
Despite numerous experimental and numerical studies, fundamental understanding of how the matrix block height, the density difference between petroleum and gas, and matrix capillary pressure could affect the oil recovery from a single matrix block in naturally fractured reservoirs remains a topic of debate in the literature. In this work a one-dimensional gravity drainage model developed by Firoozabadi and Ishimoto (1994) is considered and numerically solved. The Fourier series method is applied for a numerical Laplace inversion of the dimensionless mathematical model; this type of inversion method has rarely been used in petroleum applications. The obtained results revealed that by...
Development of chitosan/bacterial cellulose composite films containing nanodiamonds as a potential flexible platform for wound dressing, Article Materials ; Volume 8, Issue 9 , 2015 , Pages 6401-6418 ; 19961944 (ISSN) ; Mahmoudi, N ; Morales Cid, G ; Tamjid, E ; Navas Martos, F. J ; Soriano Cuadrado, B ; Paniza, J. M. L ; Simchi, A ; Sharif University of Technology
MDPI AG 2015
Chitosan/bacterial cellulose composite films containing diamond nanoparticles (NDs) with potential application as wound dressing are introduced. Microstructural studies show that NDs are uniformly dispersed in the matrix, although slight agglomeration at concentrations above 2 wt % is seen. Fourier transform infrared spectroscopy reveals formation of hydrogen bonds between NDs and the polymer matrix. X-ray diffraction analysis indicates reduced crystallinity of the polymer matrix in the presence of NDs. Approximately 3.5-fold increase in the elastic modulus of the composite film is obtained by the addition of 2 wt % NDs. The results of colorimetric analysis show that the composite films are...
A brief comparison of adaptive noise cancellation, wavelet and cycle-by-cycle fourier series analysis for reduction of motional artifacts from PPG signals, Article IFMBE Proceedings, 30 April 2010 through 2 May 2010 ; Volume 32 IFMBE , April , 2010 , Pages 243-246 ; 16800737 (ISSN) ; 9783642149979 (ISBN) ; Moein, A ; Sharif University of Technology
The accuracy of Photoplethysmographic signals is often not adequate due to motional artifacts induced in the recording site. Over recent decades there has been a widespread effort to reduce these artifacts and different methods are used for this aim. Nevertheless there are still some contradictory results reported by different methods about their effectiveness in artifact reduction. In this paper, we aim to compare three of established methods for PPG noise reduction on a unique dataset. Among different reported methods, we have chosen Adaptive Noise Cancellation (ANC), Discrete Wavelet Transform (DWT) and a newly developed method Cycle-by-cycle Fourier Series Analysis (CFSA) for denoising....
Article Scientia Iranica ; Volume 17, Issue 5 A , SEPTEMBER-OCTOBER , 2010 , Pages 387-395 ; 10263098 (ISSN) ; Vafai, A ; Mofid, M ; Sharif University of Technology
In this paper, the steady-state stresses in a homogeneous isotropic half-space under a moving wheel-type load with constant subsonic speed, prescribed on a finite patch on the boundary, are investigated. Navier's equations of motion in 2D case were modified via Stokes-Helmholtz resolution to a system of partial differential equations. A double Fourier-Laplace transformation procedure was employed to solve the system of partial differential equations in a new moving reference system, regarding the boundary conditions. The effects of force transmission from the contact patch to the half-space have been considered in the boundary conditions. Utilizing a property of Laplace transformation leads...
Improved fourier analysis of periodically patterned graphene sheets embedded in multilayered structures and its application to the design of a broadband tunable wide-angle polarizer, Article IEEE Journal of Quantum Electronics ; Volume 53, Issue 3 , 2017 ; 00189197 (ISSN) ; Borji, A ; Zeidaabadi Nezhad, A ; Shahabadi, M ; Sharif University of Technology
Numerical modeling of periodically patterned graphene sheets (PPGS) embedded in planar multilayered media using Fourier-based methods suffers from very slow convergence because of the fact that the conductivity is zero in unfilled areas of the patterned surface and, thus, the so-called Li's inverse rule is not applicable. In this paper, a simple and efficient approach is proposed to overcome this problem such that the exact boundary condition can be applied and the surface current density on PPGS can be obtained accurately. Here, the PPGS is modeled as a conductive surface and only its conductivity representation by the Fourier series is modified. The proposed method can be used easily for...
Article Iranian Journal of Science and Technology, Transaction B: Engineering ; Volume 33, Issue 5 , 2009 , Pages 425-439 ; 10286284 (ISSN) ; Nobari, A ; Sabzehparvar, M ; Moghaddam, M. M ; Haddadpour, H ; Sharif University of Technology
Flight dynamics of the guided vehicle is modelled by the aid of linear and angular equations of motions using Lagrange's approach in this paper. Governing equations of the control system and the elastic behavior of the vehicle are added to the equations of dynamic states. Flexibility effect is modelled using the normal modes, generalized coordinates and forces. For validation of modified FORTRAN simulation code, the stability of specific vehicles is determined and compared with the same results in the literature. Using this code and by solving the governing equations for the desired flight vehicle, the aeroservoelasticity is analyzed and then the results are compared with the rigid cases and...
Article Macromolecular Symposia ; Volume 274, Issue 1 , 2008 , Pages 49-54 ; 10221360 (ISSN) ; Pourjavadi, A ; Noei Aghaei, M. A ; Sharif University of Technology
Graft copolymerization of methyl methacrylate (MMA) was carried out on bagasse fibers in an aqueous medium using eerie ammonium nitrate (CAN) as initiator under a neutral atmosphere. In order to obtain the optimum condition for graft copolymerization, the effects of initiator concentration, temperature, time of reaction, and monomer concentration were studied. The maximum grafting percent was found to be 122%. The bagasse grafted poly(methyl methacrylate) was characterized by FTIR and its thermal behavior was characterized by TGA. Copyright © 2008 WILEY-VCH Verlag GmbH & Co. KGaA