نتایج جستجو برای: frequency response analysis

تعداد نتایج: 3949673  

پایان نامه :وزارت علوم، تحقیقات و فناوری - دانشگاه صنعتی خواجه نصیرالدین طوسی - دانشکده مهندسی برق و کامپیوتر 1391

power transformers are important equipments in power systems. thus there is a large number of researches devoted of power transformers. however, there is still a demand for future investigations, especially in the field of diagnosis of transformer failures. in order to fulfill the demand, the first part reports a study case in which four main types of failures on the active part are investigate...

پایان نامه :وزارت علوم، تحقیقات و فناوری - دانشگاه رازی - پژوهشکده ادبیات 1389

the present study reports an analysis of response articles in four different disciplines in the social sciences, i.e., linguistics, english for specific purposes (esp), accounting, and psychology. the study has three phases: micro analysis, macro analysis, and e-mail interview. the results of the micro analysis indicate that a three-level linguistic pattern is used by the writers in order to cr...

Journal: :iranian journal of electrical and electronic engineering 0
منیری moniri فرشاد farshad

power transformers are key components in electrical power supplies and their failure could cause severe consequences on continuity of service and also generates substantial costs. identifying problems at an early stage, before catastrophic failure occurs, is a great benefit for reliable operation of power transformers. frequency response analysis (fra) is a new, well-known and powerful diagnost...

Journal: :international journal of nanoscience and nanotechnology 2015
e. maani miandoab f. tajaddodianfar h. nejat pishkenari h. m. ouakad

many of nonlinear systems in the field of engineering such as nano-resonator and atomic force microscope can be modeled based on duffing equation. analytical frequency response of this system helps us analyze different interesting nonlinear behaviors appearing in its response due to its rich dynamics. in this paper, the general form of duffing equation with cubic nonlinearity as well as paramet...

Journal: :international journal of smart electrical engineering 2014
v. behjat mojtaba mahvi ebrahim rahimpour

the frequency response analysis (fra) test has been recognized as one of the sensitive tools available for detecting electrical and mechanical faults inside power transformers. however, there is still no universally systematic interpretation technique for these tests. many research efforts have employed different statistical criteria in order to aid the interpretative capability of the fra, but...

Journal: :modeling and simulation in electrical and electronics engineering 2015
mehdi bagheri toan phung

frequency response analysis (fra) is popular technique which has been used since the last decade as a diagnostic method for transformers. however, accurate interpretation of fra measurements is still challenging. recent studies reveal that apart from winding deformation, fra data can also be influenced by moisture variation in transformer paper insulation. hence, a specific transformer’s model ...

پایان نامه :وزارت علوم، تحقیقات و فناوری - دانشگاه ارومیه 1377

the methods which are used to analyze microstrip antennas, are divited into three categories: empirical methods, semi-empirical methods and full-wave analysis. empirical and semi-empirical methods are generally based on some fundamental simplifying assumptions about quality of surface current distribution and substrate thickness. thses simplificatioms cause low accuracy in field evaluation. ful...

پایان نامه :وزارت علوم، تحقیقات و فناوری - دانشگاه علامه طباطبایی - دانشکده ادبیات و زبانهای خارجی 1388

the present study was an attempt to conduct a contrastive analysis between general english (ge) and english for specific purposes (esp) texts in terms of cohesion and cohesive devices. to this end, thirty texts from different esp and ge textbooks were randomly selected. then they were analyzed manually to find the frequency of cohesive devices. cohesive devices include reference, substitution, ...

Journal: :iranian journal of radiation research 0
a. mirzajani medical physics group, tehran university of medical sciences, tehran, iran n. riyahi-alam medical physics group, tehran university of medical sciences, tehran, iran m.a. oghabian medical physics group, tehran university of medical sciences, tehran, iran k. firuznia radiology group, tehran university of medical sciences, tehran, iran h. saberi neurosurgery group, tehran university of medical sciences, tehran

abstract  background: the brain response to temporal frequencies (tf) has been already reported, but with no study reported for different tf with respect to various spatial frequencies (sf).  materials and methods: fmri was performed by 1.5t ge-system in 14 volunteers during checkerboard, with tfs of 4, 6, 8 and 10hz in low and high sfs of 0.5 and 8cpd.  results: average percentage bold signal ...

پایان نامه :وزارت علوم، تحقیقات و فناوری - دانشگاه صنعتی اصفهان - دانشکده فیزیک 1390

in this thesis, barium ferrite nano particles were prepared by sol-gel method. their structural and magnetic properties of samples have been investigated using thermo gravimetric analysis (tg-dta), x-ray powder diffractometer (xrd), fourier transform infrared (ftir), scanning electron microscopy (sem), field emission scanning electron microscopy (fesem), ac susceptometer, vibrating sample magne...

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