• Proceedings of the Korean Vacuum Society Conference
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• 2012.08a
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• pp.351-352
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• 2012

UV LED에서 p-GaN층의 높은 일함수와 자체 면저항이 크기 때문에 current spreading layer인 ITO (indium tin oxide) 투명전극이 사용되고 있다. 따라서 높은 UV 파장대 투과율과 낮은 면 저항이 매우 중요하다. 본 연구에서, RF magnetron sputter를 사용하여 ITO 투명전극을 glass(boro33)에 120 nm 두께로 증착하였다. 그 후 RTA (rapid thermal annealing)을 이용해 120초 동안 $600^{\circ}C$에서 Air, $N_2$ (15 sccm), vacuum 환경에서 열처리를 하여 UV-Vis-NIR spectrophotometer를 사용해 ITO 박막의 투과율을 측정하고, Hall measurement system을 이용하여 전기적 특성을 측정하였다. Fig. 1과 같이 열처리 환경에 따라 ITO 박막의 투과율이 변하고 또한 Table 1과 같이 전기적 특성도 변함을 알 수 있었다. Air 환경에서의 열처리는 reference 샘플과 비교 했을 때 400 nm 이하의 파장에서 투과율이 증가하였지만 400 nm 이상의 파장에서는 투과율이 낮아짐을 볼 수 있고, 면 저항 (Ohm/sq)은 오히려 reference (as deposited) 샘플과 비교하여 24 Ohm/sq 증가하는 것을 알 수 있었다. 반면에 $N_2$, vacuum 환경에서 열처리는 reference (as deposited) 샘플 보다 380 nm 파장대에서 16% 정도 높은 투과율을 보였고, 면저항 역시 2배 이상 낮아졌다. 둘 다 비슷한 투과율과 면저항을 나타내었지만 vacuum 환경이 좀 더 우수한 광학적 특성을 나타내었고 반면에 $N_2$ 환경은 좀 더 낮은 면저항을 나타내었다. ITO 박막을 증착한 후 vacuum 환경에서 열처리를 통하여 제작된 UV-LED (중심 파장 380 nm)가 Fig. 2와 같이 입력 전류 450 mA에서 광출력이 46% 정도 향상 되었고 안정된 I-V 특성 보였다.

• Korean Journal of Remote Sensing
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• v.15 no.3
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• pp.195-208
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• 1999

In the classification of satellite images, the representative of training of classes is very important factor that affects the classification accuracy. Hence, in order to improve the classification accuracy, it is required to optimize pre-classification stage which determines classification parameters rather than to develop classifiers alone. In this study, the normality of training are calculated at the preclassification stage using SPOT XS and LANDSAT TM. A correlation coefficient of multivariate Q-Q plot with 5% significance level and a variance of initial training are considered as an object function of genetic algorithm in the training normalization process. As a result of normalization of training using the genetic algorithm, it was proved that, for the study area, the mean and variance of each class shifted to the population, and the result showed the possibility of prediction of the distribution of each class.

• Journal of the Korea Society for Simulation
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• v.32 no.3
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• pp.67-74
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• 2023

A semiconductor fabrication facility(FAB) is one of the most capital-intensive and large-scale manufacturing systems which operate under complex and uncertain constraints through hundreds of fabrication steps. To improve fab performance with intuitive scheduling, practitioners have used weighted-sum scheduling. Since the determination of weights in the scheduling significantly affects fab performance, they often rely on simulation-based decision making for obtaining optimal weights. However, a large-scale and high-fidelity simulation generally is time-intensive to evaluate with an exhaustive search. In this study, we investigated three sampling methods (i.e., Optimal latin hypercube sampling(OLHS), Genetic algorithm(GA), and Decision tree based sequential search(DSS)) for the optimization. Our simulation experiments demonstrate that: (1) three methods outperform greedy heuristics in performance metrics; (2) GA and DSS can be promising tools to accelerate the decision-making process.

• Journal of the Korean Institute of Intelligent Systems
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• v.22 no.1
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• pp.94-99
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• 2012

This paper discusses a decentralized sampled-data control problem for large-scale nonlinear systems. The system is represented in Takagi-Sugeno's form. Next, we design a decentralized analog controller based on the overlapping decomposition technique. The final step is to apply the intelligent digital redesign scheme for converting the analog controller into the sampled-data one. Design condition is represented in terms of linear matrix inequalities. A simulation result is provided for the effectiveness of the proposed design method.

• Journal of KIISE:Databases
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• v.41 no.4
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• pp.256-261
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• 2014

The problem of top-${\kappa}$ set similarity joins finds the top-${\kappa}$ pairs of records ranked by their similarities between two sets of input records. We propose an efficient algorithm to return top-${\kappa}$ similarity join pairs using a sampling technique. From a sample of the input records, we construct a histogram of set similarity joins, and then compute an estimated similarity threshold in the histogram for top-${\kappa}$ join pairs within the error bound of 95% confidence level based on statistical inference. Finally, the estimated threshold is applied to the traditional similarity join algorithm which uses the min-heap structure to get top-${\kappa}$ similarity joins. The experimental results show the good performance of the proposed algorithm on large real datasets.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.15 no.5
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• pp.1111-1118
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• 2011

Several data from equipments on shipboard have been used for the safe navigation of ships. Due to the varieties of data, however, there may be difficulties to manage those data separately. Therefore, it can be effective to develop database for the integrated management of ship data. However, the database may become full soon because huge amount of data are saved continuously. To cope with this problem, this paper proposes multistage database which can always keep the database under full by means of sampling mechanism. To verify the functionality of the methodology, a prototype system has been implemented and tested.

• Proceedings of the IEEK Conference
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• 2000.09a
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• pp.131-135
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• 2000

본 논문에서는 고성능 고정 소수점 DSP (Digital Signal Processor) 코어인 Vincent6 코어 [1]를 이용하여 ITU-T C.728 음성 부호화기를 실시간으로 구현하였다 G.728 은 16 kb/s전송률의 ITU-T표준 음성 부호화기이며, 입력신호는 8 kHz로 샘플링되며 샘플 당 16 bit 로 양자화된 PCM 신호이다. G.728 은 LD-CELP(Low Delay Code Excited Linear Prediction)라고도 하며, 알고리 듬 delay는 0.625ms 이다. Vincent6 DSP core 는 VLIW (Very-Long Instruction Word) 특성을 가지므로 다중 명령 (multiple instruction)을 수행할 수 있다 이를 위해서 G.728 annex G를 이용하여 고정 소숫점 연산으로 코드를 작성한 후, 이를 vincent6 어셈블리 코드로 구현하였다. 최종적으로 구현된 코드는 ITU-T 의 test vector 에 대 해 bit exact 한 결과를 보이며 34 MCPS (Million Cycles Per Second)의 계산량을 가지며 사용 메모리크기는 데이터 메모리가 약 9KByte, 프로그램 메모리가 약 57 KByte 이다.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.26 no.1
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• pp.88-93
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• 2015

To estimate RCS(Radar Cross Section) at arbitrary incident angles for large objects, an interpolation method is required based on the pre-calculated RCS database at finite discrete sampling points. It is numerically difficult to compute the RCS by a large object at all required sampling points, since the computation time may be very long for one sampling point and many sampling points are required to satisfy the exact sampling condition. Therefore, it may be required to accurately estimate the RCS at any incident angles based on a database whose size is as small as possible. In this paper, the accuracy of two interpolation methods base on the sinc-and VSH(Vector Spherical Harmonics) functions are numerically compared.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.43 no.12 s.354
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• pp.61-67
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• 2006

This paper proposes the algorithm for tracking of the residual phase errors incurred by carrier frequency offset and sampling frequency offset in the orthogonal frequency division multiplexing (OFDM) systems which are suitable for high data rate wireless communications. In the OFDM systems the subcarriers which are orthogonal to each other are modulated by digital data and transmitted simultaneously. The carrier frequency offset causes degradation of signal to noise ratio(SNR) performance and interference between the adjacent subcarriers. The errors in the sampling timing caused by the sampling frequency difference between the transmitter and the receiver sides also cause a major performance degradation in the OFDM systems. The residual error tracking and compensation mechanism is essential in the OFDM system since the carrier and the sampling frequency offset cause the loss of orthogonality resulting in the system performance loss. This paper proposes the scheme where the channel gain and the payload data information are reflected in the residual error tracking process which results in the reduction of the estimation error and the tracking performance improvements under the frequency selective fading wireless channels.

• Journal of the Korea Computer Graphics Society
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• v.23 no.1
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• pp.25-32
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• 2017

This paper proposes a novel acceleration method for particle based large scale fluid simulation. Traditional particle-based fluid simulation has been implemented by interacting with physical quantities of neighbor particles through the Smoothed Particle Hydrodynamics(SPH) technique[1]. SPH method has the characteristic that there is no visible change compared to the computation amount in a part where the particle movement is small, such as a calm surface or inter-fluid. This becomes more prominent as the number of particles increases. Previous work has attempted to reduce the amount of spare computation by adaptively dividing each part of the fluid. In this paper, we propose a technique to calculate the motion of the entire particles by using the physical quantities of the near sampled particles by sampling the particles inside the fluid at regular intervals and using them as reference points of the fluid motion. We propose a technique to adaptively generate a triangle map based on the position of the sampled particles in order to efficiently search for nearby particles, and we have been able to interpolate the physical quantities of particles using the barycentric coordinate system. The proposed acceleration technique does not perform any additional correction for two classes of fluid particles. Our technique shows a large improvement in speed as the number of particles increases. The proposed technique also does not interfere with the fine movement of the fluid surface particles.