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Jafar Rasi,Behzad Mozaffari Tazehkand,Javad Musevi Niya 한국전자통신연구원 2015 ETRI Journal Vol.37 No.1
In this paper, a selective coefficient updating (SCU) approach at each branch of the per-tone equalization (PTEQ) structure has been applied for insufficient cyclic prefix (CP) length. Because of the high number of adaptive filters and their complex adaption process in the PTEQ structure, SCU has been proposed. Using this method leads to a reduction in the computational complexity, while the performance remains almost unchanged. Moreover, the use of set-membership filtering with variable step size is proposed for a sufficient CP case to increase convergence speed and decrease the average number of calculations. Simulation results show that despite the aforementioned algorithms having similar performance in comparison with conventional algorithms, they are able to reduce the number of calculations necessary. In addition, compensation of both the channel effect and the transmitter/receiver in-phase/quadrature-phase imbalances are achievable by these algorithms.
Experimental and Numerical Study of a Tube in Tube Force Limiting Device
Jafar Ghalejoughi,Mohammad Reza Sheidaii,Saeed Tariverdilo 한국강구조학회 2020 International Journal of Steel Structures Vol.20 No.4
The buckling and sudden capacity loss of the compression member can be prevented using a proposed tube in tube force limiting device (TTFLD). In this way, the brittle post-buckling behavior of the compression member can be converted into an elasto-plastic behavior. The TTFLD consists of two tubes with unequal diameter, one of which is placed into the other tube. The outer tube operates as a casing for the inner compression tube and the fl exural stiff ness of the outer tube restrains the buckling of the inner tube. The present study has experimentally investigated and evaluated a number of experimental specimens. Next, numerical analysis of these specimens has been done using fi nite element software. Further, the behavior of the tube in tube force limiting device have been investigated under important parameters such as the gap between the inner and outer tubes (gap), the inner tube or main member slenderness ratio (λ), and the ratio of outer tube length to inner tube length ( L 2∕L 1) , by extending the numerical studies to further examples. Using this TTFLD is an eff ective, simple and economical method to prevent the buckling of compression member and can lead to a favorable increase in the bearing and deformability capacity of the compression members with diff erent values of slenderness ratio. The compressive strength of the member will increase signifi cantly, if the gap size is less than about 43% of the inner tube’s gyration radius, and the length ratio is greater than about 55%.
Jafar Siahbalaee,Sadegh Vaez-Zadeh,Farzad Tahami 전력전자학회 2009 JOURNAL OF POWER ELECTRONICS Vol.9 No.6
The main objective of this a paper is to improve the efficiency of permanent magnet synchronous motors (PMSMs) by using an improved direct torque control (DTC) strategy. The basic idea behind the proposed strategy is to predict the impact of a small change in the stator flux amplitude at each sampling period to decrease electrical loss before the change is applied. Accordingly, at every sampling time, a voltage vector is predicted and applied to the machine to fulfill the flux change. The motor drive simulations confirm a significant improvement in efficiency as well as a very fast and smooth response under the proposed strategy.
A Power-Efficient CMOS Adaptive Biasing Operational Transconductance Amplifier
Jafar Torfifard,Abu Khari Bin A’ain 한국전자통신연구원 2013 ETRI Journal Vol.35 No.2
This paper presents a two-stage power-efficient class-AB operational transconductance amplifier (OTA) based on an adaptive biasing circuit suited to low-power dissipation and low-voltage operation. The OTA shows significant improvements in driving capability and power dissipation owing to the novel adaptive biasing circuit. The OTA dissipates only 0.4 μW from a supply voltage of ±0.6 V and exhibits excellent high driving, which results in a slew rate improvement of more than 250 times that of the conventional class-AB amplifier. The design is fabricated using 0.18-μm CMOS technology.
Jafar Soltani,Jamshid Sojdei 전력전자학회 1998 ICPE(ISPE)논문집 Vol.- No.-
This paper describes the dynamical performance of a four - quadrant criculation current mode control of dc motor drive, using the controlled flywleeling technique, a four - quadrant closed - loop control drive with an inner current control loop and a speed fuzzy PI regulator is designed.<br/> The obtained comouter simulation results of a dc motor drive below and and above the base speed are demonstrated. These result showthat compare to a conventional dual - converter - fed dc motor drive with simultaneous control, the overal system performance has been improved and also, agood stabilty and robstness has been achieved.