• The Transactions of the Korean Institute of Electrical Engineers D
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• v.54 no.1
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• pp.26-32
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• 2005

Rotor position information is essential in the operation of the switched reluctance motor(SRM) drive for generation the phase current switching signals. When an incremental encoder is used as a rotor position sensor, the initial rotor position can not be detected. Some sensorless rotor position estimation methods also have the same problem. In these systems, to initially align the rotor, the forced alignment method has a delay and reverse rotation before the motor can start. Therefore it can not be acceptable for unidirectional drive systems. So the forced alignment method is not desirable in all drive systems and the research on the SRM drives should be directed to a system without rotor alignment. In this paper, a new detection method of initial rotor position using the rate of change of current is suggested. Firstly, di/dt versus θ/sub R/ reference table, which is the relation between the rate of change of current and rotor position, is generated and then the squared Euclidean distance method is used to estimate the rotor position based on the table. The simulated and experimental results are presented demonstrating the feasibility and accuracy of this method.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.42 no.5 s.335
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• pp.13-22
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• 2005

IEEE 802.11a is a standard for the high-speed wireless local area network (WLAN), supporting from 6 up to 54 Mbps in a 5 GHz band. We propose a channel equalization algerian and a sampling clock recovery algorithm by utilizing the Viterbi decoder output of the IEEE 802.11a WLAN standard. The proposed channel equalizer adaptively compensates channel variations. The proposed system uses re-encoded Viterbi decoder outputs as reference symbols for the adaptation of the channel equalizer. It also extracts sampling phase information with the Viterbi decoder outputs for fine adjustment of the sampling clock. The proposed sampling clock recovery and equalizer are more robust to noise and frequency selective fading environments than conventional systems using only four pilot samples.

• Korean Journal of Optics and Photonics
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• v.10 no.1
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• pp.47-52
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• 1999

This study describes a simple and effective experimental determination of pump-power dependence of refractive indices and dispersions of erbium-doped fibers (EDFs) of various doping concentrations. Systermatical analysis on light-induced change of the refractive indices and dispersion for a signal wavelength range of 1510 nm-1560 nm with a pump of 980 nm wavelength has been made by measuring the pump-induced phase changes of the signal beam in Mach-Zehnder type interferometer, which has an optically pumped EDF and a reference EDF in each of the two arms, respectively. The measured pump-induced refractive indices match well with the theoritically predicted ones. The results show that pump-induced refractivity and dispersion changes of the EDF increase with the increasing pump power and $Er^{3+}$-doping concentration as expected from theory.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.15 no.5
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• pp.81-89
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• 2001

Power system stabilizer act efficiently to damp the electromechanical oscillations in interconnected power systems. This paper presents an algorithm for the optimal parameter selection of a power system stabilizer in two-area power systems with a series HVDC link. This method is one of the classical techniques by allocating properly pole-zero positions to fit as closely as desired the ideal phase lead between the voltage reference and the generator electrical power and by changing the gain to produce a necessary damping torque over the matched frequency range. The small signal stability and transient stability studies using the PSS parameters obtained from this method show that a natural oscillation frequency of the study case system is adequately damped. The simulation used in the paper was performed by the Power System Toolbox software program based on MATLAB.

• Journal of ILASS-Korea
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• v.1 no.1
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• pp.63-75
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• 1996

The purpose of this study is to investigate the break-up characteristics by taking advantage of a two-phase coaxial nozzle. Air and water are utilized as working fluids and the mass ratio air/water has been controlled to characterize the atomization, diffusion and development of mixing process. By way of a photographic technique, conventional developing structures and diffusion angles have been analyzed systematically with variations of mass ratios. The turbulent flow components of the atomized particles were measured by a two channel LDV system and the data were treated by an on-lined measurement equipment. According to the photographic results the spreading angles decreased because the axial inertia moment was relatively higher than the lateral one with respect to the increase of mass ratio. It is found the jet flow diffuses linearly in a certain limit region while the atomizing characteristics, in terms of the distributions of particle diameters did not show particular differences. It may be expected that these fundamental results can be used as reference data in studying the atomization, breakup and diffusions.

• Carbon letters
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• v.26
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• pp.43-50
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• 2018

In this research, a novel and efficient quinoline thioacetamide functionalized magnetic graphene oxide composite ($GO@Fe_3O_4@QTA$) was synthesized and utilized for dispersive magnetic solid phase preconcentration of Cd(II) and Ni(II) ions in urine and various food samples. A number of diverse methods were employed for characterization of the new nanosorbent. The design of experiments approach and response surface methodology were applied to monitor and find the parameters that affect the extraction performance. After sorption and elution steps, the concentrations of target analytes were measured by employing FAAS. The highest extraction performance was achieved under the following experimental conditions: pH, 5.8; sorption time, 6.0 min; $GO@Fe_3O_4@QTA$ amount, 17 mg; 2.4 mL $1.1mol\;L^{-l}$ $HNO_3$ solution as the eluent and elution time, 13.0 min. The detection limit is 0.02 and $0.2ng\;mL^{-1}$ for Cd(II), and Ni(II) ions, respectively. The accuracy of the new method was investigated by analyzing two certified reference materials (sea food mix, Seronorm LOT NO 2525 urine powder). The interfering study revealed that there are no interferences from commonly occurring ions on the extractability of target ions. Finally, the new method was satisfactorily employed for rapid extraction and determination of target ions in urine and various food samples.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.7 no.11
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• pp.2657-2675
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• 2013

A novel neighbor selection-based fingerprinting algorithm using matrix correlation (MC) for Wi-Fi localization is presented in this paper. Compared with classic fingerprinting algorithms that usually employ a single received signal strength (RSS) sample, the presented algorithm uses multiple on-line RSS samples in the form of a matrix and measures correlations between the on-line RSS matrix and RSS matrices in the radio-map. The algorithm makes efficient use of on-line RSS information and considers RSS variations of reference points (RPs) for localization, so it offers more accurate localization results than classic neighbor selection-based algorithms. Based on the MC algorithm, an error estimation method using artificial neural network is also presented to fuse available information that includes RSS samples and localization results computed by the MC algorithm and model the nonlinear relationship between the available information and localization errors. In the on-line phase, localization errors are estimated and then used to correct the localization results to reduce negative influences caused by a static radio-map and RP distribution. Experimental results demonstrate that the MC algorithm outperforms the other neighbor selection-based algorithms and the error estimation method can reduce the mean of localization errors by nearly half.

• Proceedings of the KSRS Conference
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• 2005.10a
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• pp.178-181
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• 2005

The positioning accuracy of the Global Positioning System (GPS) has been improved considerably during the past two decades. The main error sources such as ionospheric refraction, orbital uncertainty, antenna phase center variation, signal multipath, and tropospheric delay have been reduced substantially, if not eliminated. In this study, the GPS data collected by the GPS receivers that were established as continuously operating reference stations by International GNSS Service (IGS), Ministry of the Interior (MOl), Central Weather Bureau (CWB), and Industrial Technology Research Institute (ITRI) Of Taiwan are utilized to investigate the impact of atmospheric water vapor on GPS positioning determination. The surface meteorological measurements that were concurrently acquired by instruments co-located with the GPS receivers include temperature, pressure and humidity data. To obtain the influence of the GPS height on the proposed impact study. A hydrodynamic ocean tide model (GOTOO.2 model) and solid earth tide were used to improve the GPS height. The surface meteorological data (pressure, temperature and humidity) were introduced to the data processing with 24 troposphere parameters. The results from the studies associated with different GPS height were compared for the cases with and without a priori knowledge of surface meteorological measurements. The finding based on the measurements in 2003 is that the surface meteorological measurements have an impact on the GPS height. The associated daily maximum of the differences is 1.07 cm for the KDNM station. The impact is reduced due to smoothing when the average of the GPS height for the whole year is considered.

• Nuclear Engineering and Technology
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• v.28 no.5
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• pp.440-451
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• 1996

With emphasis on safety, this study addresses for better design condition for the cooling system in a wet-type interim spent fuel storage facility, using a probabilistic safety assessment method. To incorporate the design renovation into the design phase, a simple approach is proposed. By taking the cooling system of a reference design, a fault tree analysis was performed to identify the weak point of the considered system, and then basic factors for design renovation were defined. A total of 21 design alternatives were selected through the combination of the basic factors. Finally, the optimum design alternative for the cooling system is derived by means of the cost and effect analysis based on the estimated cost, system reliability and assumed probabilistic safety criteria. With the assumption that the failure frequency of at-reactor spent fuel cooling system compiles with probabilistic safety criteria for the interim spent fuel cooling system, it was shown that the optimum alternative should have l00% cooling loop redundancy with one pump per cooling loop and a cleanup system installed separately from the main loop. Furthermore, it also should be classified into safety system. The result of this study can be used as a useful basis to identify factors of safety concern and to establish design requirements in the future. The method also can be applied for other nuclear facilities.

• Transactions on Electrical and Electronic Materials
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• v.15 no.6
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• pp.309-314
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• 2014

This work proposes an integrated high frequency divider with an inductive peaking technique implemented in a current mode logic (CML) frequency divider. The proposed divider is composed with a master-slave flip-flop, and the master-slave flip-flop acts as a latch and read circuits which have the differential pair and cross-coupled n-MOSFETs. The cascode bias is applied in an inductive peaking circuit as a current source and the cascode bias is used for its high current driving capability and stable frequency response. The proposed divider is designed with $0.18-{\mu}m$ CMOS process, and the simulation used to evaluate the divider is performed with phase-locked loop (PLL) circuit as a feedback circuit. A divide-by-two operation is properly performed at a high frequency of 20 GHz. In the output frequency spectrum of the PLL, a peak frequency of 2 GHz is obtained witha divide-by-eight circuit at an input frequency of 250 MHz. The reference spur is obtained at -64 dBc and the power consumption is 13 mW.