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approximation-theory
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Total 107 records
An effective image based surface roughness estimation approach using neural network
, Article 2006 World Automation Congress, WAC'06, Budapest, 24 June 2006 through 26 June 2006 ; 2006 ; 1889335339 (ISBN); 9781889335339 (ISBN) ; Milani Fard, A ; Goodarzvand Chegini, A ; Sharif University of Technology
IEEE Computer Society
2006
Abstract
The accurate measurement of surface roughness is essential in ensuring the desired quality of machined parts. The most common method of measuring the surface roughness of machined parts is using a surface profile-meter with a contact stylus, which can provide direct measurements of surface profiles. This method has its own disadvantageous such as workpiece surface damage due to mechanical contact between the stylus and the surface, In this paper we proposed a eontactless method using image processing and artificial neural network as a pattern classifier. Having trained the network for any specific workpiece with 10 sample patterns, the system would learn how to approximate the actual surface...
Photonic crystal devices analysis based on perturbation theory
, Article Photonic Crystal Materials and Devices IV, San Jose, CA, 23 January 2006 through 26 January 2006 ; Volume 6128 , 2006 ; 0277786X (ISSN); 0819461709 (ISBN); 9780819461704 (ISBN) ; Khorasani, S ; Atabaki, A ; SPIE ; Sharif University of Technology
2006
Abstract
A novel approach for photonic crystals devices analysis, based on perturbation theory is reported. In this method the photonic crystal device is considered as the superposition of a parent lattice and a perturbing one. Then the solution is investigated in terms of the eigensolutions of the parent lattice. This way, one can easily obtain analytic expressions within the first order perturbation, describing the effects of different parameters on the eigensolutions of the structure. The perturbation theory employed in this work is typical of what is conventionally used in quantum mechanics literature. The proposed method is explicit, works fast, and does not involve complicated numerical...
Surface modeling of complicated geometries with incomplete erroneous data points- An extension to B-spline approach
, Article 2005 27th Annual International Conference of the Engineering in Medicine and Biology Society, IEEE-EMBS 2005, Shanghai, 1 September 2005 through 4 September 2005 ; Volume 7 VOLS , 2005 , Pages 1634-1637 ; 05891019 (ISSN); 0780387406 (ISBN); 9780780387409 (ISBN) ; Farahmand, F ; Meghdari, A ; Sharif University of Technology
2005
Abstract
Based on the analogy between the B-spline curve modeling and the force-deflection behavior of a beam subjected to lateral point loads, an extension to the B-spline surface modeling method was introduced. The proposed method has strong extrapolating capability and can develop accurate surface models over an incomplete net of data points without affecting the original data. Extrapolation of the incomplete part of the data net Is conducted simultaneously with interpolation of the existing part, with no need to recalculation. Approximation or data smoothing is a natural extension of the method, however, the smoothing intensity can be controlled continuously without reducing the number of spline...
Efficient polynomial root finding using SIMD extensions
, Article 11th International Conference on Parallel and Distributed Systems Workshops, ICPADS 2005, Fukuoka, 20 July 2005 through 22 July 2005 ; Volume 2 , 2005 , Pages 529-533 ; 15219097 (ISSN); 0769522815 (ISBN) ; Ahmadi, H ; Sarbazi Azad, H ; Ma J ; Yang L. T ; Sharif University of Technology
2005
Abstract
In this paper, the parallel implementations of different iterative polynomial root finding methods on a processor with SIMD processing capability are reported. These methods are based on the construction of a sequence of approximations that converge to the set of roots. We have chosen four widely used methods namely Newton's, Durand-Kerner's, Aberth-Ehrlich's, and QD and implemented them using the SIMD instruction set of the Pentium processor with C++ and assembly language. Experiments show that a speedup of 3 or higher can be achieved, depending on the order of polynomial, required accuracy, and the method employed. © 2005 IEEE
Thermal entanglement of spins in the Heisenberg model at low temperatures
, Article Physical Review A - Atomic, Molecular, and Optical Physics ; Volume 70, Issue 5 A , 2004 , Pages 052307-1-052307-5 ; 10502947 (ISSN) ; Karimipour, V ; Sharif University of Technology
2004
Abstract
The entanglement between two spins in the ferromagnetic Heisenberg chain at low temperatures was calculated. It was shown that if a magnetic field is applied to a ferromagnetic Heisenberg chain, then pairwise entanglement develops between spins at arbitrary given states. It was also shown that the entanglement profile is a Gaussian with a characteristic length depending on the temperature and the coupling between spins only when the ground state and the one-particle states are populated. The magnetic field was shown to affect only the amplitude of the profile and not its characteristic length
High pressure effects in YBCO and YSCO
, Article Physica Status Solidi C: Conferences ; Volume 1, Issue 7 , 2004 , Pages 1859-1862 ; 16101634 (ISSN) ; Mossalla, B ; Akhavan, M ; Sharif University of Technology
2004
Abstract
Electronic structure calculations for two isofamilies, YBa 2Cu3O7 (YBCO) and YSr2Cu 3O7 (YSCO) high Tc cuprates, have been done for ambient and high pressures (-15 GPa
Mathematical modeling and statistical analysis of second harmonic generation effects with thin and thick crystal in ultrahigh speed optically amplified digital lightwave communication system [electronic resource]
, Article IEEE Journal of Lightwave Technology ; 2009 Vol. 27, No. 16, PP. 3438-3452 ; Salehi, J.A ; Sharif University Of Technology
Abstract
In this paper, we present an in depth analysis and discussions on the behavior and performance of using either thin or thick second harmonic generation (SHG) crystals prior to photodetector in ultrahigh-speed optically amplified digital lightwave communication systems. Our study begins by considering a conventional low-speed optically amplified lightwave receiver and study its performance in ultrahigh-speed regime and show its substantially degraded behavior, indicating the need to use advance optical nonlinear elements such as SHG prior to photodetection. In studying SHG effects, we begin by discussing the mathematical models of thin and thick SHG crystals in the context of statistical...
On the characteristics and design of yielding elements used in steel-braced framed structures
, Article Structural Design of Tall and Special Buildings ; Volume 22, Issue 2 , 2013 , Pages 179-191 ; 15417794 (ISSN) ; Mofid, M ; Sharif University of Technology
2013
Abstract
In this paper, the behavior of a concentric braced frame structure equipped with yielding elements (YE), based on energy concepts, has been investigated extensively. When a severe earthquake occurs, energy will get absorbed through structural elements, which causes destruction. In order to reduce structural damage, input energy should be dissipated. YE will act as a fuse and absorb a great deal of earthquake input energy. Two one-story steel frames with different bay-to-height ratios (B/H < 1 and B/H > 1) are investigated. YE is located in the braces intersection. First, through studying the elastic behavior of the frame, the best location, angle and shape of YE is proposed. Subsequently, a...
Model reference adaptive control in fractional order systems using discrete-time approximation methods
, Article Communications in Nonlinear Science and Numerical Simulation ; Volume 25, Issue 1-3 , August , 2015 , Pages 27-40 ; 10075704 (ISSN) ; Nojoumian, M. A ; Salarieh, H ; Meghdari, A ; Sharif University of Technology
Elsevier
2015
Abstract
In this paper, model reference control of a fractional order system has been discussed. In order to control the fractional order plant, discrete-time approximation methods have been applied. Plant and reference model are discretized by Grünwald-Letnikov definition of the fractional order derivative using "Short Memory Principle". Unknown parameters of the fractional order system are appeared in the discrete time approximate model as combinations of parameters of the main system. The discrete time MRAC via RLS identification is modified to estimate the parameters and control the fractional order plant. Numerical results show the effectiveness of the proposed method of model reference adaptive...
Electrical equivalent circuit of multi-mode flexible beams with piezoelectric elements
, Article Journal of Intelligent Material Systems and Structures ; Volume 19, Issue 5 , 2008 , Pages 621-627 ; 1045389X (ISSN) ; Meghdari, A ; Sharif University of Technology
2008
Abstract
Surface mounted piezoelectric sensors and actuators on elastic structures are often connected to electrical networks. The coupled equations of motion of the elastic structure with piezoelectric elements are already well known. However, due to complex behavior of some electrical elements in the electrical network, it is not an easy task to obtain the integrated equations of the whole system. A good remedy for this problem is to take advantage of an equivalent electrical circuit (EEC) representation of the mechanical part, leading the entire system to be represented as an electrical circuit. In this study, the authors propose a new method for constructing the EEC. This method is based upon the...
Generalized nonlinear 3D Euler-Bernoulli beam theory
, Article Iranian Journal of Science and Technology, Transaction B: Engineering ; Volume 32, Issue 1 , 2008 , Pages 1-12 ; 10286284 (ISSN) ; Khorsandijou, S. M ; Sharif University of Technology
2008
Abstract
The issue of the new elastic terms discovered in the nonlinear dynamic model of an enhanced nonlinear 3D Euler-Bernoulli beam is discussed. While the elastic orientation is negligible, the nonlinear dynamic model governing tension-compression, torsion and two spatial bendings is presented. Considering this model, some new elastic terms can be identified in the variation of elastic potential energy in each bending motion equation, and in each transverse shear force. Due to the new terms, each term of a bending equation and a transverse shear force, finds a counterpart in the other bending equation and transverse shear force, but the equations remain asymmetric. The new terms have arisen,...
Scheduling to minimize gaps and power consumption
, Article SPAA'07: 19th Annual Symposium on Parallelism in Algorithms and Architectures, San Diego, CA, 9 June 2007 through 11 June 2007 ; 2007 , Pages 46-54 ; 159593667X (ISBN); 9781595936677 (ISBN) ; Ghodsi, M ; Hajiaghayi, M. T ; Sayedi Roshkhar, A. S ; Zadimoghaddam, M ; Sharif University of Technology
2007
Abstract
This paper considers scheduling tasks while minimizing the power consumption of one or more processors, each of which can go to sleep at a fixed cost α. There are two natural versions of this problem, both considered extensively in recent work: minimize the total power consumption (including computation time), or minimize the number of "gaps" in execution. For both versions in a multiprocessor system, we develop a polynomial-time algorithm based on sophisticated dynamic programming. In a generalization of the power-saving problem, where each task can execute in any of a specified set of time intervals, we develop a (1 + 23 α)-approximation, and show that dependence on α is necessary....
Fuzzy wavelet modeling using data clustering
, Article 1st IEEE Symposium on Computational Intelligence and Data Mining, CIDM 2007, Honolulu, HI, 1 April 2007 through 5 April 2007 ; 2007 , Pages 114-119 ; 1424407052 (ISBN); 9781424407057 (ISBN) ; Marami, B ; Sharif University of Technology
2007
Abstract
In this paper, a novel approach for tuning the parameters of fuzzy wavelet systems which are used for modeling of nonlinear and complex systems is proposed. In fuzzy inference system, each fuzzy rule is analogous to a wavelet basis function multiplied by a coefficient. Using clustering techniques, the center of these basis functions are located in the detected center of clusters. In this way, not only the approximation accuracy is increased, but also the number of unknown parameters is decreased. The feasibility of the proposed method is shown by modeling two highly nonlinear functions. The comparison of the results using the proposed approach, with the previous schemes, shows the...
Numerical investigation of steady density currents flowing down an incline using v2̄ - F turbulence model
, Article Journal of Fluids Engineering, Transactions of the ASME ; Volume 129, Issue 9 , 2007 , Pages 1172-1178 ; 00982202 (ISSN) ; Firoozabadi, B ; Farhanieh, B ; Sharif University of Technology
2007
Abstract
The governing equations of two-dimensional steady density currents are solved numerically using a finite volume method. The v2̄-f turbulence model, based on standard k - s model, is used for the turbulence closure. In this method, all Reynolds stress equations are replaced with both a transport equation for v2̄ and an elliptic relaxation equation for f, a parameter closely related to the pressure strain redistribution term. The Simple-C procedure is used for pressure-velocity coupling. In addition, Boussinesq's approximation is used to obtain the momentum equation. The computed height of the progressive density current is compared to the measured data in the literature, resulting in good...
The linear stability of a developing thermal front in a porous medium: the effect of local thermal non-equilibrium
, Article International Journal of Heat and Mass Transfer ; Volume 50, Issue 15-16 , 2007 , Pages 3090-3099 ; 00179310 (ISSN) ; Noghrehabadi, A. R ; Rees, D. A. S ; Sharif University of Technology
2007
Abstract
In this paper we analyze the stability of the developing thermal boundary layer which is induced by a step-change in the temperature of the lower horizontal boundary of a uniformly cold semi-infinite porous medium. Particular attention is paid to the influence of local thermal non-equilibrium between the fluid and solid phases and how this alters the stability criterion compared with corresponding criterion when the phases are in local thermal equilibrium. A full linear stability analysis is developed without approximation, and this yields a parabolic system of equations for the evolving disturbances. Criteria for the onset of convection are derived as a function of the three available...
Unconditionally stable fully explicit finite difference solution of solidification problems
, Article Metallurgical and Materials Transactions B: Process Metallurgy and Materials Processing Science ; Volume 38, Issue 1 , 2007 , Pages 121-142 ; 10735615 (ISSN) ; Davami, P ; Sharif University of Technology
2007
Abstract
An unconditionally stable fully explicit finite difference method for solution of conduction dominated phase-change problems is presented. This method is based on an asymmetric stable finite difference scheme for approximation of diffusion terms and application of the temperature recovery method as a phase-change modeling method. The computational cost of the presented method is the same as the explicit method per time-step, while it is free from time-step limitation due to stability criteria. It robustly handles isothermal and nonisothermal phase-change problems and is very efficient when the global temperature field is desirable (not accurate front position). The robustness, stability,...
Coupling of the electronic band structure with Ag phonon modes in Y123 and Y124 systems
, Article 4th International Conference on Magnetic and Superconducting Materials, MSM'05, Agadir, 5 September 2006 through 8 September 2006 ; Volume 3, Issue 9 , 2006 , Pages 3140-3143 ; 18626351 (ISSN) ; Mossalla, B ; Akhavan, M ; Sharif University of Technology
2006
Abstract
Ab initio frozen-phonon calculations have been performed for k = 0 A g Raman modes of two superconducting systems Y123 and Y124. We have used the local density approximation pseudopotential method in our calculations by VASP code. Results have been compared with other computational and experimental data for similar systems. Then we present changes of electronic band structure with the change of ionic positions in each Ag mode for both systems. © 2006 WILEY-VCH Verlag GmbH & Co. KGaA
Phonon frequency calculations of GdBCO and PrBCO
, Article 4th International Conference on Magnetic and Superconducting Materials, MSM'05, Agadir, 5 September 2006 through 8 September 2006 ; Volume 3, Issue 9 , 2006 , Pages 3162-3165 ; 18626351 (ISSN) ; Khasroabadi, H ; Akhavan, M ; Sharif University of Technology
2006
Abstract
Ab initio frozen-phonon calculations have been performed for k = 0 A g Raman modes of superconducting GdBa2Cu3O 7 and insulating PrBa2Cu3O7. We have used the generalized gradient approximation full-potential linear augmented plane-wave method in our calculations by Wien2k code. Results have been compared with other computational and experimental data for similar systems. © 2006 WILEY-VCH Verlag GmbH & Co. KGaA
An approximation algorithm for d1-optimal motion of a rod robot with fixed rotations
, Article International Journal of Computer Mathematics ; Volume 83, Issue 3 , 2006 , Pages 357-370 ; 00207160 (ISSN) ; Ghodsi, M ; Sharif University of Technology
2006
Abstract
Given a translating and rotating rod robot in a plane in the presence of polygonal obstacles with the initial and final placements of the rod known, the d1-optimal motion planning problem is defined as finding a collision-free motion of the rod such that the orbit length of a fixed but arbitrary point F on the rod is minimized. In this paper we study a special case of this problem in which the rod can translate freely, but can only rotate by some pre-specified given angles around F. We first characterize the d1-optimal motion of the robot under the given conditions and then present a (1 + ε)-approximation algorithm for finding the optimal path. The running time of the algorithm is bounded by...
Modification of the GV-MSA model in obtaining the activity and osmotic coefficients of aqueous electrolyte solutions
, Article Fluid Phase Equilibria ; Volume 240, Issue 2 , 2006 , Pages 167-172 ; 03783812 (ISSN) ; Taghikhani, V ; Ghotbi, C ; Sharif University of Technology
2006
Abstract
In this work a modified form of the Ghotbi-Vera Mean Spherical Approximation model (MGV-MSA) has been used to correlate the mean ionic activity coefficients (MIAC) for a number of symmetric and asymmetric aqueous electrolyte solutions at 25 °C. In the proposed model the hard sphere as well as the electrostatic contributions to the MIAC and the osmotic coefficient of the previously GV-MSA model has been modified. The results of the proposed model for the MIAC of the electrolyte solutions studied in this work are used to directly calculate the values of the osmotic coefficients without introducing any new adjustable parameter. In the MGV-MSA model the cation diameter as well as the relative...