• Polymer(Korea)
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• v.27 no.4
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• pp.323-329
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• 2003

Stretchable Polypyrrole films using functionalized doping agent, di(2-ethylhexyl) sulfosuccinate sodium salt (NaDEHS), were synthesized by chemical and electrochemical method. Chemically and electrochemically Prepared Polypyrrole films were stretch-oriented (L/L$\_$0/＝ 1.0 ∼ 2.5) by zone drawing method and the electrical conductivities were measured. As the draw ratio was increased, the electrical conductivities were increased. This result was confirmed by the increase in crystallinity through the increase in draw ratio. The temperature dependence of electrical conductivity showed that 3D-variable range hopping model (L/L$\_$0/ ＝ 1.0∼2.0) and ID-VRH model (L/L$\_$0/ ＝ 2.5) gave the best fit to the data for stretched Ppy-DEHS films.

• Journal of Korea Multimedia Society
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• v.12 no.5
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• pp.728-736
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• 2009

We propose a method using the genetic algorithm to solve the maximum set cover problem. It is needed for scheduling the power of sensor nodes in extending the lifetime of the wireless sensor network with variable sensing range. The existing Greedy Heuristic method calculates the power scheduling of sensor nodes repeatedly in the process of operation, and so the communication traffic of sensor nodes is increased. The proposed method reduces the amount of communication traffic of sensor nodes, and so the energies of nodes are saved, and the lifetime of network can be extended. The effectiveness of this method was verified through computer simulation, and considering the energy losses of communication operations about 10% in the network lifetime is improved.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.30 no.11C
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• pp.1091-1097
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• 2005

In this paper, we propose fast motion estimation algorithm. Local statistics of a motion vector is highly correlated to motion vectors of its neighboring blocks. According to the property, block-based motion search range is adaptively determined in order to reduce unnecessary search points. Based on the determined search range, motion vector is obtained by variable step search motion estimation. Experimental results show that comparing to Full search motion estimation, the motion searching points of proposed algorithm is reduced as much as $98\%$. Moreover, PSNR and Bit Rate are almost same to Full search method.

• Proceedings of the KSME Conference
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• 2003.04a
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• pp.213-219
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• 2003

Acoustic emission behavior during fatigue crack growth test was investigated under various loading condition. To describe the acoustic emission activity, counts rate (d/dn) was related with SIFR (stress intensity factor range, K). Results indicated that SIFR could be divided into two parts according to its relationship with counts rate. For $K<25_{MPa\sqrt{m}}$, counts rate was increased as the SIFR increased. However, for values greater than $25_{MPa\sqrt{m}}$ , decreasing behavior was shown. This behavior of counts rate corresponding SIFR was keeping the same trend regardless of load range or crack length. Acoustic emission response to the single overload was sudden drop and slow recovery in counts rate like crack growth retardation. Under variable loading condition, counts rate of each loading block was same as that of constant amplitude loading. Overall experimental data was somewhat scattered since sensitive characteristics of acoustic emission method. However, these empirical relations indicated that counts rate was uniquely correlate with single parameter, SIFR.

• Journal of the Society of Naval Architects of Korea
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• v.51 no.3
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• pp.193-202
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• 2014

This paper presents a new method of sampling the climatic data for infrared signature analysis. Historical hourly data from a stationary marine buoy of KMA(Korean Meteorological Administration) are used to select a small number of sample points (N=100) to adequately cover the range of statistics(PDF, CDF) displayed by the original data set (S=56,670). The method uses a coarse bin to subdivide the variable space ($3^5$=243 bins) to make sample points cover the original data range, and a single-point ranking system to select individual points so that uniform coverage (1/N = 0.01) is obtained for each variable. The principal component analysis is used to calculate a joint probability of the coupled climatic variables. The selected sample data show good agreement to the original data set in statistical distribution and they will be used for statistical analysis of infrared signature and susceptibility of naval ships.

• Journal of IKEEE
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• v.22 no.3
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• pp.780-785
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• 2018

In this work, We investigated the frequency-dependent capacitance tunability of a metal-ferroelectric-metal variable capacitor fabricated using ALD $HfO_2$ ferroelectric material. The capacitance of the MFM capacitor could be tuned as a function of the bias voltage, up to the microwave frequency range. We observed a capacitance tuning range of ~3 % up to 2.5 GHz, proving the feasibility of the use of ALD $HfO_2$ in the microwave frequency band.

• KIEE International Transaction on Electrical Machinery and Energy Conversion Systems
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• v.2B no.3
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• pp.81-89
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• 2002

The sensorless AC motor drive is a popular topic of study due to the cost and reliability of speed and position sensors. Most sensorless algorithms are based on the mathematical modeling of motors including electrical variables such as phase current and voltage. Therefore, the accuracy of such variables largely affects the performance of the sensorless AC motor drive. However, the output voltage of the SVPWM-VSI, which is widely used in sensorless AC motor drives, has considerable errors. In particular, the SVPWM-VSI is error-prone in the low speed range because the constant DC link voltage causes poor resolution in a low output voltage command and the output voltage is distorted due to dead time and voltage drop. This paper investigates a novel high-performance strategy for overcoming these problems in a sensorless ac motor drive. In this paper, a variation of the DC link voltage and a direct compensation for dead time and voltage drop are proposed. The variable DC link voltage leads to an improved resolution of the inverter output voltage, especially in the motor's low speed range. The direct compensation for dead time and voltage drop directly calculates the duration of the switching voltage vector without the modification of the reference voltage and needs no additional circuits. In addition, the proposed strategy reduces a current ripple, which deteriorates the accuracy of a monitored current and causes torque ripple and additional loss. Simulation and experimentation have been performed to verify the proposed strategy.

• Journal of computational fluids engineering
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• v.16 no.3
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• pp.75-81
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• 2011

The turbo blowers having large power capacity are generally composed of the variable inlet guide vane, the impeller and the variable diffuser. In the present study, the effect of the stagger angles on the aerodynamic performances has been investigated by CFD methods. The design specifications of the reference model having 400kW power were given as 7.43kg/s of mass flow rate, 1.66 of pressure ratio with 12000rpm of impeller rotating speed. As the first simulation parameter, the diffuser vane angle was varied in the range of ${\pm}$20 degree from the initial-design point. The inlet guide vane angles, as the second one, was changed in the range of ${\pm}$40 degree from the initial-design point. The commercial Navier-Stokes solver, ANSYS-CFX, was applied to solve the three-dimensional unsteady flow fields inside the turbo blower. Through the numerical results, the desirable setting angles were proposed to fit the best performance to the variation of the operating conditions.

• Korean Journal of Occupational Health Nursing
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• v.25 no.4
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• pp.340-351
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• 2016

Purpose: The purpose of this study was to identify depression and its influencing factor of nurses among comprehensive nursing care service ward. Methods: The research was cross-sectional descriptive study. The subjects of the study were 173 nurses of comprehensive nursing care service ward in Gyeonggi-do. Data collection was done using self-reported structured questionnaires asking about job stress, emotional labor, job burnout, somatic symptoms, turnover intention, depression and general characteristics from May 16 to June 3, 2016. Data were analyzed with SPSS/WIN 19.0 program. Results: Mean scores of job stress were 159.15(range 43~215), emotional labor 30.90(range: 9~45), job burnout 59.45 (range: 0~132), somatic symptoms 24.03 (range: 12~60), turnover intention 5.61 (range 0~18) and depression 19.25 (range: 0~60) and reported as depression in 63.6%. Somatic symptoms (${\beta}=.26$, p<.001), job burnout (${\beta}=.37$, p<.001) had significant associations with depression and the most important variable was job burnout. Conclusion: It is necessary to apply the developed program to reduce job burnout in hospitals and to prevent and/or control depression. And also, it needs to improve working conditions and increase the nursing staff to reduce somatic symptoms for nurses among comprehensive nursing care service ward.

• Journal of Korea Water Resources Association
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• v.37 no.3
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• pp.173-184
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• 2004

The objective of this study is to examine the usefulness of climate model simulations (GCM) in Korea water resource management. The methods are based on probabilistic measures of the effectiveness of GCM simulations of an indicator variable for discriminating high versus low regional observations of a target variable. The formulation uses the significance probability of the Kolmogorov-Smirnov test for detecting differences between two variables. AMIP-II(Atmospheric Model Intercomparison Project-II) type GCM simulation done by ECMWF(European Centre for Medium-Range Weather Forecasts) was used for indicator variable and observed mean average precipitation(MAP) values on 7 major river basins were used as target variable. Monte Carlo simulation is used to establish the significance of the estimator values. The results show that GCM simulations done by ECMWF are skillful in discriminating the high from the low of the observed MAP for wet season in all seven basins of Korea, but not enough for dry season.