• 한국통신학회논문지
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• 제32권9C호
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• pp.867-880
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• 2007

본 논문에서는 임의의 배율로 디지털 영상을 확대와 축소하는 개선된 cubic convolution 보간법을 제안한다. 제안하는 공간해상도조정 방법은 압축된 HD 비트스트림이나 SD 비트 스트림을 transcoding시키는 과정에서 다양한 형식의 해상도를 조정하기위해 사용된다. Transcoder등 다양한 응용분야에서 영상의 화질은 유지하면서 크기를 조정하는 것은 매우 중요한 기술이다. 해상도조정은 원본 디지털 데이터를 연속함수로 변환하는 단계와 새로운 샘플링간격에 맞게 재표본화하는 단계, 이렇게 두 단계로 구분된다. 우리는 원본영상과 해상도조정 된 영상사이의 관계를 고려하여 보간 필터의 kernel 개선에 초점을 맞췄다. 본 논문에서는 MPEG 표준에서 고려하는 다양한 영상포맷들간 해상도를 변환시키기 위한 기술을 제안한다. 이 방법은 기존의 방법과 비교하였을 때, 정보 손실을 최소화하여 고화질의 해상도 변환 기능을 가능하게 한다.

• 한국전자통신학회논문지
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• 제15권1호
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• pp.107-114
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• 2020

본 논문에서는 하둡 플랫폼에서 비용 효율적 빅데이터 분석을 수행하기 위한 클러스터 규모의 설정 방안을 연구한다. 의료기관의 경우 진료기록의 병원 외부 저장이 가능해짐에 따라 클라우드 기반 빅데이터 분석 요구가 증가하고 있다. 본 논문에서는 대중적으로 많이 사용되고 있는 클라우드 서비스인 아마존 EMR 프레임워크를 분석하고, 비용 효율적으로 하둡을 운용하기 위해 클러스터의 규모를 산정하기 위한 모델을 제시한다. 그리고, 다양한 조건에서의 실험을 통해 맵리듀스의 실행에 영향을 미치는 요인을 분석한다. 이를 통해 비용 대비 처리시간이 가장 효율적인 클러스터를 설정함으로써 빅데이터 분석시 효율성을 증대시킬 수 있다.

• 천문학회보
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• 제39권2호
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• pp.74.2-74.2
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• 2014

Magnetohydrodynamics(MHD) dynamo depends on many factors such as viscosity ${\gamma}$, magnetic diffusivity ${\eta}$, magnetic Reynolds number $Re_M$, external driving source, or magnetic Prandtl number $Pr_M$. $Pr_M$, the ratio of ${\gamma}$ to ${\eta}$ (for example, galaxy ${\sim}10^{14}$), plays an important role in small scale dynamo. With the high PrM, conductivity effect becomes very important in small scale regime between the viscous scale ($k_{\gamma}{\sim}Re^{3/4}k_fk_f$:forcing scale) and resistivity scale ($k_{\eta}{\sim}PrM^{1/2}k_{\gamma}$). Since ${\eta}$ is very small, the balance of local energy transport due to the advection term and nonlocal energy transfer decides the magnetic energy spectra. Beyond the viscous scale, the stretched magnetic field (magnetic tension in Lorentz force) transfers the magnetic energy, which is originally from the kinetic energy, back to the kinetic eddies leading to the extension of the viscous scale. This repeated process eventually decides the energy spectrum of the coupled momentum and magnetic induction equation. However, the evolving profile does not follow Kolmogorov's -3/5 law. The spectra of EV (${\sim}k^{-4}$) and EM (${\sim}k^0$ or $k^{-1}$) in high $Pr_M$ have been reported, but our recent simulation results show a little different scaling law ($E_V{\sim}k^{-3}-k^{-4}$, $EM{\sim}k^{-1/2}-k^{-1}$). We show the results and explain the reason.

• Journal of Power Electronics
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• 제10권3호
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• pp.313-319
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• 2010

This paper proposes a new compensation algorithm for the current measurement errors in a DFIG (Doubly Fed Induction Generator). Generally, current measurement path with current sensors and analog devices has non-ideal factors like offset and scaling errors. As a result, the dq-axis currents of the synchronous reference frame have one and two times ripple components of the slip frequency. In this paper, the main concept of the proposed algorithm is implemented by integrating the 3-phase rotor currents into the stationary reference frame to compensate for the measured current ripples in a DFIG. The proposed algorithm has several beneficial features: easy implementation, less computation time, and robustness with regard to variations in the electrical parameters. The effectiveness of the proposed algorithm is verified by several experiments.

• 제어로봇시스템학회논문지
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• 제8권3호
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• pp.193-198
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• 2002

In this paper, we Propose a PD+I fuzzy controller using an error-accumulating applying factor. In fuzzy control, analytical study was done formerly, in which fuzzy control can be classified by PD type and PI type, and also the study for getting merits of both types was done, too. But the mixed type has a complex structure and many parameters. The proposed fuzzy controller is 2-input 2-out-put and PD type fuzzy control is used as a basic structure. And the proposed controller annihilates a steady-state error and improves transient responses because of using the error-accumulating applying factor which is determined in the real time along the current state of controlled process. Futhermore it is easy to tune the system because of decreasing the number of scaling factors and the I type controller with resetting resolves the integral wind-up problem. Finally we apply the proposed scheme to various plants and show the performance betterment.

• Korea-Australia Rheology Journal
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• 제20권1호
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• pp.27-34
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• 2008

Clay suspensions in liquid polymers exhibit a time-dependent behaviour that includes viscoelastic as well as thixotropic features. Because of the presence of interacting clay platelets, particulate networks can develop, which are broken down during flow and rebuild upon cessation of the flow. Here, the use of thixotropic techniques in probing flow-induced structures in nanocomposites is explored with data on a hectorite-poly(isobutylene) model system. By means of fast stress jump measurements the hydrodynamic contributions to the steady state stresses are determined as well as those caused by the stretching of the clay floes. Flow reversal measurements do not provide a clear indication of flow-induced anisotropy in the present case. The recovery of the clay microstructure upon cessation of flow is followed by means of overshoot and dynamic measurements. The development of a particulate network is detected by the appearance and growth of a low frequency plateau of the storage moduli. The modulus-frequency curves after various rest times collapse onto universal master curves, regardless of the pre-shear history or temperature. The scaling factors for this master curve are the crossover parameters. The crossover moduli are nearly a linear function of the crossover frequency, the relation being identical for recovery after shearing at different shear rates. This function depends, however, on temperature.

• 공업화학
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• 제18권4호
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• pp.366-370
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• 2007

신제품을 개발할 때 인간의 감성 즉 시각, 청각, 후각, 미각, 촉각에 대한 소비자의 반응에 대한 정보는 대단히 중요하다. 이제까지 촉각에 대한 연구는 다른 감성에 비하여 상대적으로 취약하였던 바, 본 연구에서는 각기 다른 표면 조도를 갖는 플라스틱 시료들에 대하여 체계적인 연구를 시도하였다. 37쌍의 긍정적과 부정적 형용사로 감성적 반응을 조사하여 통계적으로 분석하고 표면 조도와 인간 감성과의 관계를 분석하였다. 일반적으로 사용되는 평균선호도가 아닌 최선빈도를 사용하여 요인분석, 다변량척도분석, 군집분석들을 수행하였다.

• International Journal of Railway
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• 제4권4호
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• pp.109-115
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• 2011

An analysis and design method for reducing aerodynamic noise in high-speed trains based on biomimetics of noiseless flight of owl is proposed. Five factors related to the morphology of the flight feather have been selected, and the candidate optimal shape of the flight feather is determined. The turbulent flow field analysis demonstrates that the optimal shape leads to diminished vortex formation by causing separation of the flow as well as allowing the fluid to climb up along the surface of the flight feather. To determine the effect of scaling of the owl's flight feather on the noise reduction, a two-fold and a four-fold scaled up model of the feather are constructed, and the numerical simulations are carried out to obtain the aerodynamic noise levels for each scale. Original model is found to reduce the noise level by 10 dBA, while two-fold increase in length dimensions reduces the noise by 12 dBA. Validation of numerical solution using wind tunnel experimental measurements is presented as well.

• 한국안전학회지
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• 제23권5호
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• pp.111-118
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• 2008

In usual safety signs are final means to transmit hazard information so that the importance of them cannot be emphasized too much. Nevertheless, in Korea, few people are interested in functions of safety signs so that evaluation of safety signs are seldom committed. This research was conducted to evaluate and compare perceptional characteristics of safety signs, especially "Fall" signs, by Semantic Differential Method and Multi-dimensional Scaling Method, with undergraduate students as well as industrial workers. According to research results on several signs evaluated high through suggested procedure, action inducibility was different for students majoring in different sciences, but it had common elements in the sense of 'openness' or 'arrangements'. Besides, perceptional images on safety signs were mainly recognized with bases of 'arrangement' for student group and 'simplicity' for industrial workers, respectively, and their maps corresponded well with each other by partial rotating so that students and workers seemed to recognize safety signs with similar factors though their name might be different. However, since perceptional characteristics including image map, comprehensibility, and action inducibility were similar for student group whereas those were not for worker group, it was concluded that the test for action inducibility would be absolutely necessary for safety signs for workers' group.

• Journal of Welding and Joining
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• 제28권5호
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• pp.99-105
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• 2010

Inverter DC resistance spot welding process has been very widely used for joining such as automotive body sheet metal. Because the lobe area of DC welding is larger than AC welding and DC welding has low electrode wear. So the use of Inverter DC resistance spot welding process has been further increased. And the application of high tensile steel is growing for light weight vehicle. To improve the weldability of high strength steel, the development of Inverter DC resistance spot welding system is more conducted. However, Inverter DC resistance spot welding system has a few problems. Current waveform is unstable and the expulsion has been occurred by characteristics of steel. In this study, inverter DC resistance spot welding system was made. And Fuzzy control algorithm was applied for constant current. The genetic algorithm was applied to optimize the fuzzy scaling factors, in order to optimize the fuzzy control.