• Korean Journal of Social Welfare
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• v.65 no.3
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• pp.107-130
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• 2013

This study conducted a meta-analysis on the studies related with job satisfaction of social workers. For data analysis, journals, theses, and dissertations published between 1990 and 2013 were reviewed systematically. Through this process, this study calculated average effect size of each variable and explored moderator variables. The study results were as follows. First, this study significantly identified 27 variables related with job satisfaction of social workers. Second, the results indicated that large effect size variables included empowerment, organizational climates, supervision, relationship with boss, leadership, social support, work environment, reward system factor, self-esteem, work autonomy. Third, moderator analyses were conducted utilizing characteristics of organization. Moderate effects were identified in the following variables including role conflict, specialization, recognition, promotion, relationship with peer, supervision. Finally, the implications of the study findings were discussed.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.17 no.12 s.115
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• pp.1143-1149
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• 2006

The microstrip square open loop resonator has been employed to reduce the phase noise in VCO. The microstrip square open loop resonator has the large coupling coefficient value, which makes a high Q value, and has reduced the phase noise of VCO. To increase the tuning range of VCO, varactor diode has been connected at the tunable negative resistance in VCO. The output power and harmonic characteristics of VCO has been obtained 4.83 dBm and -28.83 dBc, respectively. The phase noise of VCO has been $-112.33{\sim}-116.16dBc/Hz$ @ 100 kHz in the tuning range, $5.735{\sim}5.845GHz$.

• Proceedings of the KWS Conference
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• 2009.11a
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• pp.14-14
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• 2009

자동차 차체와 같은 박판을 접합하기 위해서 인버터 DC 저항 점 용접공정은 매우 널리 사용되어지고 있다. 이는 교류 용접에 비해 적은 전류로 용접이 가능하고, 더 넓은 적정 용접 영역을 가지며, 보다 적은 전극마모를 가지는 인버터 DC 저항 점용접의 특성에 기인한다. 아울러 최근에는 파워 소자와 같은 인버터 구성에 필요한 구성 요소의 가격이 낮아져, 전반적으로 용접기의 가격이 하락하였고, 구성 장치에 대한 신뢰성이 증가하였으며, 기존보다 전력의 사용량이 감소하여 인버터 DC 저항점 용접공정의 사용이 더욱 증가하고 있는 상황이다. 또한 차량의 경량화에 대한 요구가 증가함에 따라 고 장력 강판의 적용이 확대되고 있다. 이러한 재료의 우수한 용접을 위해 인버터 DC 저항 점 용접시스템의 개발이 더욱 활발하게 이루어지고 있다. 하지만 인버터 DC 저항 점용접 시스템을 구성하더라도 모재의 특성이 전류 파형에 영향을 주게 되어, 정 전류 제어가 적용되지 못하면 전류 파형이 불안정해지게 되고 원하는 전류가 발생되지 않게 되어 스패터가 발생하거나, 용접 품질에 영향을 줄 수 있게 된다. 본 연구에서는 인버터 DC 저항 점용접 시스템을 구성하고, 정 전류의 제어를 위한 퍼지 제어 알고리즘을 개발하여 적용하였다. 퍼지제어기의 환산 계수를 최적화하기 위해서 유전 알고리즘을 적용하였으며, 실험에는 고장력강을 대상으로 정 전류 용접 공정을 수행하였다.

• Journal of Korean Society of Steel Construction
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• v.16 no.5 s.72
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• pp.683-694
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• 2004

Advanced analysis and optimal design of semi-rigid space steel frames were presented. The advanced analysis can predict the combined nonlinear effects of connection, geometry, and material on the behavior and strength of semi-rigid frames. The Kishi-Chen power model was used to describe the nonlinear behavior of semi-rigid connections. Geometric nonlinearity was determined using stability functions. Material nonlinearity was determined using the Column Research Council (CRC) tangent modulus and the parabolic function. The direct search method proposed by Choi and Kim was used as optimization technique. One by one, the member with the largest unit value evaluated using the LRFD interaction equation were placed adjacent to a larger member selected from the database. The objective function was assumed to be the weight of steel frame, while the constraint functions were load-carrying capacities, deflections, inter-story drifts, and the ductility requirements. The member sizes determined using the proposed method were compared to those derived from the conventional LRFD method.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.32 no.4
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• pp.242-251
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• 2020

In this study, the extraction efficiency and reflection coefficient by a two-dimensional OWC (Oscillating Water Column) WEC (wave energy converter) installed in front of a seawall was investigated for regular/irregular waves. The matched eigenfunction expansion method (MEEM) based on the linear potential theory was applied as an analytical tool. The diffraction problem by the incident wave in the open-chamber and the radiation problem by the oscillating pressure in the closed-chamber were solved to obtain the volume fluxes at the internal free-surface. Applying the volume fluxes into the continuity equation for the airflow in a chamber, we got the oscillating air pressure. The maximum extracted power and corresponding reflection coefficient were determined at the optimal turbine coefficient that maximizes the extracted power. OWC device designed for a high extracted efficiency simultaneously contributes to reduce reflected waves.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.13 no.5
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• pp.203-208
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• 2013

In this paper, we proposed a performance improvement method of the double talk detector which can operate before the echo canceller converges. Microphone input signal is filtered by the linear prediction filter and this filtered signal is used for detection. The coefficients of the linear prediction filter are given by the far-end talker signal. During single talk, filtered signal has low power since the characteristics of the echo signal is similar with those of the far-end talker signal. But, during double talk, the filtered signal does not have low power because the signal of different characteristics is included in the microphone signal. Double talk is detected by this difference. Simulations using real speech signals verified that the proposed method outperformed the conventional methods.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37 no.6A
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• pp.450-457
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• 2012

For orthogonal frequency-division multiplexing (OFDM) systems, we propose a blind channel estimation scheme based on non-redundant precoding. In the proposed scheme, a modified covariance matrix is first obtained by dividing the covariance matrix of the received signal vector by the precoding matrix element-by-element. Then, the channel vector is estimated as an eigenvector corresponding to the largest eigenvalue of the modified covariance matrix. The eigenvector can be obtained by power method with low computational complexity instead of the complicated eigenvalue decomposition. We analytically derive a mean square error (MSE) of the proposed channel estimation scheme and show that the analysis result coincides well with the simulation result. Also, simulation results show that the proposed scheme has better MSE and bit error rate (BER) performance than conventional channel estimation schemes.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.11
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• pp.1749-1755
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• 2010

The performance of power window system was decided by driving characteristics of the window regulator part and reaction by the glass run. The performance of power window system usually has been predicted by experimental methods. In this paper, an analytical method using the explicit code was suggested to overcome the limit of the experimental methods. The friction coefficient of glass run was obtained by the friction test at various conditions and the Mooney-Rivlin model was used. Also, a mechanism of window regulator consisted of the fast belt system and the slip ring elements. And, we conducted the analysis considering characteristic of a motor and obtained the lifting speed of automotive glass with high reliability

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2006.05a
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• pp.361-364
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• 2006

The numerical methods of finding the optimal position of optical phase conjugator (OPC) and the optimal fiber dispersions are proposed, which are able to effectively compensate overall channels in $8\times40$ Gbps WDM system with non zero - dispersion shifted fiber (NZ-DSF) as an optical fiber. And BER characteristics in the system with two induced optimal parameters are compared with those in the system with the currently used mid-span spectral inversion (MSSI) in order to confirm the availability of the proposed methods. It is confirmed that the applying two induced optimal parameters into WDM system contribute to reduce power penalty to 4 times than that of WDM system with the conventional MSSI.

• Journal of Korean Society of Steel Construction
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• v.15 no.6 s.67
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• pp.661-672
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• 2003

The advanced analysis and optimal design of semi-rigid frame were presented. Advanced analysis can predict the combined nonlinear effects of connection, geometry, and material on the behavior and strength of semi-rigid frames. The Kishi-Chen power model was used to describe the nonlinear behavior of semi-rigid connections. Geometric nonlinearity was determined using stability functions. On the other hand, material nonlinearity was determined using the Column Research Council (CRC) tangent modulus and parabolic function. The direct search method proposed by Choi and Kim was used as optimization technique. The member with the largest unit value evaluated using the LRFD interaction equation was replaced one by one with an adjacent larger member selected from the database. The objective function was assumed as the weight of steel frame, with the constraint functions accounting for load-carrying capacities, deflections. inter-story drifts, and ductility requirement. Member sizes determined by the proposed method were compared with those derived using the conventional LRFD method.