Search for: transformers
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    On linear transformations preserving at least one eigenvalue

    , Article Proceedings of the American Mathematical Society ; Volume 132, Issue 6 , 2004 , Pages 1621-1625 ; 00029939 (ISSN) Akbari, S ; Aryapoor, M ; Sharif University of Technology
    Let F be an algebraically closed field and T: Mn(F) → Mn(F) be a linear transformation. In this paper we show that if T preserves at least one eigenvalue of each matrix, then T preserves all eigenvalues of each matrix. Moreover, for any infinite field F (not necessarily algebraically closed) we prove that if T: Mn(F) → M n(F) is a linear transformation and for any A ∈ Mn(F) with at least an eigenvalue in F, A and T(A) have at least one common eigenvalue in F, then T preserves the characteristic polynomial  

    Tunable delay line based on Fourier-transformation and linear phase modulation with high time-bandwidth product

    , Article Photonische Netze - 13. ITG-Fachtagung 2020 ; 2020 , Pages 229-231 Mokhtari, A ; Preubler, S ; Jamshidi, K ; Akbari, M ; Schneider, T ; Sharif University of Technology
    VDE Verlag GmbH  2020
    We recruit basic properties of Fourier transformation to realize an electrically tunable delay line and increase the delay by creating a loop in the structure. The proposed method has been experimentally tested and verified for up to 5 roundtrips. The relative delay/advancement was increased up to 5 times compared to the original setup while preserving the original setup's advantages. © VDE VERLAG GMBH  

    Temporal resolution enhancement of video sequences using transform domain

    , Article Proceedings of the 2008 International Conference on Image Processing, Computer Vision, and Pattern Recognition, IPCV 2008, 14 July 2008 through 17 July 2008, Las Vegas, NV ; 2008 , Pages 185-190 ; 1601320787 (ISBN); 9781601320780 (ISBN) Atrianfar, H ; Atrianfar, M ; Atrianfar, H ; Sharif University of Technology
    Temporal interpolation has been recently proposed as a solution for increasing temporal resolution or even for predicting missing or corrupted frames within a video sequence . In this paper new technique on temporal interpolation are presented, by mainly exploiting properties of the very popular and highly efficient transforms such as Discrete Cosine Transform and Discrete Wavelet Transform . Novelty of the approach is that resolution enhancement is done by adding the new coefficients in transform domain . In addition we further give a method for computing PSNR of the frames . Finally simulation on a number of video sequences is presented in order to compare the performance of this two... 

    Optimizing the operation of current differential protection by power differential relay for three phase transformer

    , Article 2006 IEEE GCC Conference, GCC 2006, Manama, 20 March 2006 through 22 March 2006 ; 2006 ; 9780780395909 (ISBN) Bahmani, B ; Esmi Jahromi, M ; Ranjbar, A. M ; Sharif University of Technology
    To avoid the needless trip by magnetizing inrush current, the second harmonic component is commonly used for blocking differential relay in power transformers. However, the main problems of the current comparison method are in the very high inrush currents and relatively small fault currents regarding winding short circuits. Also The second harmonic component in fault current is increased in long lines which may blocks the relay operation. This paper describes a method to discriminate internal fault from inrush current and faults with a high second harmonic component by the sum of active power flowing into the transformer from each terminal. The average power is almost negligible for... 

    Fuzzy wavelet and contourlet based contrast enhancement

    , Article 28th Annual International Conference of the IEEE Engineering in Medicine and Biology Society, EMBS'06, New York, NY, 30 August 2006 through 3 September 2006 ; 2006 , Pages 6635-6638 ; 05891019 (ISSN); 1424400325 (ISBN); 9781424400324 (ISBN) Nezhadarya, E ; Shamsollahi, M. B ; Sayadi, O ; Sharif University of Technology
    This paper presents a fuzzy approach for contrast enhancement, based on two multi-scale transforms, namely wavelet and contourlet transforms. Separability and nondirectionality of conventional 2D wavelet transform, makes it unsuitable for sparsely representation of curve or line shaped image objects. On the other hand, the contourlet transform is a good alternative for this purpose. In this paper, coefficient enhancement, both in wavelet and contourlet spaces, is carried out by making use of simple fuzzy rules. These rules make the enhancement procedure more understandable and flexible. With this method, the knowledge and experience of the expert from the distribution of the coefficients can... 

    A two dimensional wavelet packet approach for ECG compression

    , Article 6th International Symposium on Signal Processing and Its Applications, ISSPA 2001, Kuala Lumpur, 13 August 2001 through 16 August 2001 ; Volume 1 , 2001 , Pages 226-229 ; 0780367030 (ISBN); 9780780367036 (ISBN) Moghaddam, A. R. A ; Nayebi, K ; Sharif University of Technology
    IEEE Computer Society  2001
    An improved compression algorithm for ECG signals is presented using temporal alignment of beats and 2-D wavelet packet transform (WPT). This 2-D transform based approach utilizes the fact that the electrocardiogram (ECG) signals generally show two types of correlation, namely correlation between subsequent samples within each ECG cycle (intrabeat) and correlation between subsequent cycles (interbeat). One simple compression algorithm in the 2-D WPT domain, which is applied to some records in the MIT-BIH arrhythmia database shows lower percent root mean square difference (PRD) than 1-D wavelet based compression methods for the same compression ratio (CR). © 2001 IEEE  

    Microstructural characterization of HIP consolidated NiTi–nano Al2O3 composites [electronic resource]

    , Article Journal of Alloys and Compounds ; 5 September 2014, Volume 606, Pages 21–26 Farvizi, M ; Ebadzadeh, T ; Vaezi, M. R ; Yoon, E. Y ; Kim, Y. J ; Kim, H. S ; Simchi, A. (Abdolreza) ; Sharif University of Technology
    The microstructure and phase transformational behavior of NiTi-based composites reinforced with 6 wt.% of α-alumina nanoparticles have been investigated. Two kinds of starting materials, elemental Ni–Ti and prealloyed austenitic NiTi, were used to prepare the composites. The samples were consolidated using a hot isostatic pressing method. The X-ray diffraction results showed that while unreinforced NiTi mainly contained B2 phase at room temperature, martensitic B19′ phase appeared in the microstructure after addition of the α-alumina nanoparticles. The differential scanning calorimetry measurements indicated that the martensitic transformation temperatures were elevated in the composite... 

    Modeling the correlation between heat treatment, chemical composition and bainite fraction of pipeline steels by means of artificial neural networks

    , Article Neural Network World ; Volume 23, Issue 4 , 2013 , Pages 351-367 ; 12100552 (ISSN) Khalaj, G ; Pouraliakbar, H ; Mamaghani, K. R ; Khalaj, M. J ; Sharif University of Technology
    In the present study, bainite fraction results of continuous cooling of high strength low alloy steels have been modeled by artificial neural networks. The artificial neural network models were constructed by 16 input parameters including chemical compositions (C, Mn, Nb, Mo, Ti, N, Cu, P, S, Si, Al, V), Nb in solution, austenitizing temperature, initial austenite grain size and cooling rate over the temperature range of the occurrence of phase transformations. The value for the output layer was the bainite fraction. According to the input parameters in feed-forward back-propagation algorithm, the constructed networks were trained, validated and tested. To make a decision on the completion... 

    Two novel chaos-based algorithms for image and video watermarking

    , Article Iranian Journal of Electrical and Electronic Engineering ; Volume 8, Issue 2 , 2012 , Pages 97-107 ; 17352827 (ISSN) Mohammadi, S ; Talebi, S ; Hakimi, A ; Sharif University of Technology
    IJEEE  2012
    In this paper we introduce two innovative image and video watermarking algorithms. The paper's main emphasis is on the use of chaotic maps to boost the algorithms' security and resistance against attacks. By encrypting the watermark information in a one dimensional chaotic map, we make the extraction of watermark for potential attackers very hard. In another approach, we select embedding positions by a two dimensional chaotic map which enables us to satisfactorily distribute watermark information throughout the host signal. This prevents concentration of watermark data in a corner of the host signal which effectively saves it from being a target for attacks that include cropping of the... 

    Designing and implementing basic sciences ontology based on concepts and relationships of relevant thesauri

    , Article Iranian Journal of Information Processing Management ; Volume 30, Issue 3 , Nov , 2015 , Pages 677-696 ; 22518223 (ISSN) Hosseini Beheshti, M. S ; Ejei, F ; Sharif University of Technology
    Iranian Research Institute for Scientific Information and Documentation  2015
    Currently, the main portion of knowledge is stored in electronic texts and documents and for transferring that knowledge effectively, we must use proper methods to gather and retrieve relevant information. Ontologies provide means to produce structured documents and use intelligent search instead of keyword search. Ontology defines the common words and concepts used to describe and represent an area of knowledge. However, developing ontologies is a time consuming and labor work. So, many ontology developers try to facilitate and speed up this process by reusing other resources. In fact, thesaurus contains semantic information and hierarchical structure that make it an appropriate resource... 

    Analysis of partial discharge by eavelet-hilbert transform

    , Article European Transactions on Electrical Power ; Volume 19, Issue 8 , 2009 , Pages 1140-1152 ; 1430144X (ISSN) Sarikhani, A ; Reihani, E ; Nabizadeh, N ; Hooshmand, A ; Davodi, M ; Sharif University of Technology
    Time-frequency and time-scale transforms are one of the powerful mathematical methods for feature extraction of non-stationary signals such as partial discharge (PD) signals. Modified Fourier-based transforms and Wavelet transforms are well known among them. PD signals can be analyzed by these influential methods but normally with some serious limitations and inadequacies. This paper proposes a new approach based on Wavelet-Hilbert transform for the analysis of electrical PD signals. The mathematical model of a Wavelet-Hilbert transform is described. Contemplating of natural behavior of PD, that is, stochastic and non-stationary an artificial multi-source of PD is simulated in a Detail model... 

    Influence of electrostatic shielding of disc winding on increasing the series capacitance in transformer

    , Article 2007 IEEE Lausanne POWERTECH, Lausanne, 1 July 2007 through 5 July 2007 ; 2007 , Pages 1780-1784 ; 9781424421909 (ISBN) Bagheri, M ; Vakilian, M ; Hekmati, A ; Heidarzadeh, R ; Sharif University of Technology
    Strike of a lightning stroke to the high voltage terminal of a power transformer results in an impulse stress on its windings. The magnitude of the series capacitance of the windings has an important effect on the impulse voltage distribution and the stresses along the windings. Increasing the series capacitances of the windings, the impulse voltage distribution becomes more linear and the stress on the winding is reduced. So interleaved windings rather than disc windings are used in power transformer windings to increase the series capacitances. In this paper, the electrostatic shielding, used in disc windings to increase the windings series capacitance, and for linearization of its impulse... 

    Guest editor's comments on special issue on nonuniform sampling

    , Article Sampling Theory in Signal and Image Processing ; Volume 7, Issue 2 , 1 May , 2008 , Pages 109-112 ; 15306429 (ISSN) Marvasti, F ; Sharif University of Technology

    A catalyzed method to remove polychlorinated biphenyls from contaminated transformer oil

    , Article Environmental Science and Pollution Research ; 2021 ; 09441344 (ISSN) Maghami, A ; Gholipour Zanjani, N ; Khorasheh, F ; Arjmand, M ; Sharif University of Technology
    Springer Science and Business Media Deutschland GmbH  2021
    The disposal of polychlorinated biphenyls (PCBs) as persistent organic pollutants from the environment has been normally performed by isolation from soil or water because of their biological activity and toxic potential. In the present investigation, catalytic hydrodehalogenation was used to detoxify PCBs-contaminated transformer oil. All reactions were directed on an oil containing 11.09 wt% of PCBs utilizing palladium supported on multi-walled carbon nanotubes (Pd/MWCNTs). The amount of hexa-chlorine homologues reduced considerably from 5.07% to less than 800 ppm utilizing HDC at the atmosphere of argon. Moreover, the amounts of long half-lives and bioaccumulative congener of PCB 153... 

    Modelling of metal flow during hot forging with regard to microstructural aspects

    , Article International Journal of Machine Tools and Manufacture ; Volume 44, Issue 14 , 2004 , Pages 1537-1545 ; 08906955 (ISSN) Serajzadeh, S ; Mirbagheri, S. M. H ; Taheri, A. K ; Zebarjad, S. M ; Sharif University of Technology
    A mathematical model has been proposed for evaluation of velocity and temperature fields in hot forging operations for axisymmetric parts. The model can be applied to determine forging load, strain rate, strain and temperature distributions. In addition, the effects of temperature and strain rate on metal flow have been considered through simultaneous modelling of dynamic phase transformation within the deforming metal. Hot forging experiments have been carried out under different working conditions and the results have been compared with the predictions. A good agreement between the simulated and experimental results was found. © 2004 Elsevier Ltd. All rights reserved  

    Modelling of temperature history and phase transformations during cooling of steel

    , Article Journal of Materials Processing Technology ; Volume 146, Issue 3 , 2004 , Pages 311-317 ; 09240136 (ISSN) Serajzadeh, S ; Sharif University of Technology
    A mathematical model based on the finite element method and additivity rule has been developed to predict temperature history and microstructural changes during cooling of steel. The utilized model considers the effects of various factors including initial austenite grain size and its role on the kinetics of pearlite and ferrite transformations, amount of residual strain within the cooling material, heat of transformation and variation of thermo-physical properties of the steel during cooling. The model can be employed as a guideline to design new cooling programs for achieving the desired microstructure and mechanical properties. To verify the results of the modelling, time-temperature... 

    Prediction of ferrite grain size and tensile properties of a low carbon steel

    , Article Materials Science and Technology ; Volume 20, Issue 1 , 2004 , Pages 106-110 ; 02670836 (ISSN) Kazeminezhad, M ; Karimi Taheri, A ; Sharif University of Technology
    Maney Publishing  2004
    A relationship between ferrite grain size, cooling rate from austenitising temperature, austenitising time, and austenitising temperature is developed to predict the ferrite grain size of a low carbon steel. The coefficients of that relationship are determined experimentally. A Hall-Petch relationship is used to predict the yield stress and fracture stress from the predicted ferrite grain size. Considering the experimental results, maximum errors of 12-5% and 6·5% were found in the prediction of ferrite grain size and strengths, respectively  

    On dynamic assignment of impatient customers to parallel queues

    , Article 2003 International Conference on Dependable Systems and Networks, San Francisco, CA, 22 June 2003 through 25 June 2003 ; 2003 , Pages 751-759 Movaghar, A ; Sharif University of Technology
    Consider a number of parallel queues, each having unlimited capacity and multiple identical exponential servers. The service discipline in each queue is first-come-first-served (FCFS). Customers arrive according to a state-dependent Poisson process with an arrival rate which is a function of the total number of customers in the system. Upon arrival, a customer joins a queue according to a state-dependent stationary policy, where the state of the system is taken to be the number of customers in each queue. No jockeying among queues is allowed. Each arriving customer has a generally distributed deadline until the beginning of its service, after which it must depart the system immediately. An... 

    A memory efficient algorithm for multi-dimensional wavelet transform based on lifting

    , Article 2003 IEEE International Conference on Accoustics, Speech, and Signal Processing, Hong Kong, 6 April 2003 through 10 April 2003 ; Volume 6 , 2003 , Pages 401-404 ; 15206149 (ISSN) Taghavi, Z ; Kasaei, S ; Sharif University of Technology
    Conventional implementation of multi-dimensional wavelet transform (e.g. 3-D wavelet) requires whether a high amount of "in access" memory or a continual access to slow memory of a processor which makes it infeasible for most applications. In this paper, we proposed a novel algorithm for computation of an n-D discrete wavelet transform (DWT) based on lifting scheme. In addition to benefits of lifting scheme (which causes a major reduction in computational complexity and performs the total computations in time domain), our real-time approach computes the coefficients for all kinds of 1st and 2 nd generation wavelets with short delay and optimized utilization of the slow and fast memories of a... 

    The effect of carbon on the restoration phenomena during hot deformation of carbon steels

    , Article Zeitschrift fuer Metallkunde/Materials Research and Advanced Techniques ; Volume 94, Issue 8 , 2003 , Pages 916-921 ; 00443093 (ISSN) Serajzadeh, S ; Karimi Taheri, A ; Zebarjad, S. M ; Sharif University of Technology
    Carl Hanser Verlag  2003
    A study has been made to determine the influence of the carbon content on the kinetics of dynamic and static recrystallization during and after hot deformation of carbon steels. For this purpose, single- and double-hit hot compression experiments at various strain rates and temperatures together with the Avrami-type kinetics equation and Bergstrom approach have been utilized to investigate recrystallization behavior. The results show that the apparent activation energy of hot deformation decreases with increasing carbon content and this phenomenon results in a faster dynamic recrystallization at high temperatures and/or low strain rates. Also, increasing carbon content leads to a higher rate...