• Korean Journal of Optics and Photonics
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• v.4 no.4
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• pp.420-427
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• 1993

Dielectric thin film mirrors are embedded in multimode and single-mode fibers by a fusion splicing technique. The fibers with $45{\circ}$ angled embedded mirrors serve as ultra-compact directional couplers with low excess optical loss of 0.2 dB for multimode and 0.5 dB for single mode at 1.3 ${\mu}m$ and excellent mechanical properties. The reflectance is wavelength dependent and strongly polarization depencient. Far-field scans of the reflected output power measured with a white-light source show a pattern which is almost circularly symmetric with aspect ratio of 1.09 at 5% of the peak power. The splitting ratio in a multimode coupler measured with a diode laser source is much less dependent on input coupling conditions than in conventional fused biconical-taper couplers, indicating that these couplers are less susceptible to modal noise occuring in optical fiber communication systems. Spectral properties of multilayer internal mirrors normal to the fiber axis have been investigated experimentally, and a matrix analysis has been used to explain the results.

• Proceedings of the Materials Research Society of Korea Conference
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• 1994.11a
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• pp.86-86
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• 1994

박막 EL소자의 투명전극으로 제작된 ITO막의 전기적, 광학적 특성을 조사하였다. Plama CVD방법으로 제작된 ITO막은 증착시 산소결핍으로 인한 비 다량결합(non-stochiometry) 에 의해 In이 석출되어 흑화현상이 일어나 전기전도도와 광투과율을 향상을 위해 산소분위기에서 30$0^{\circ}C$로 4분간 열처리를 행하였다. 한편 ITO막의 비저항 $\rho$와 광투과율 T를 Van der pauw법과 단색 분광계로 각각 측정하였다. 그 결과 상온에서 10-15$\Omega$/$\square$의 면저항과 400-1000nm의 파장영역에서 85-95%의 광투과율을 가져 박막 EL소자의 투명전극 조건을 만족하였다. 열처리에 대학 ITO막의 구조적 특성을 알아보기 위해 X-선회절장치(JEOL.JDX-8030)로 조사하였다. Fig.1은 X-선 회절 패턴을 나타낸다. 열처리후 ITO막은 상대적으로 최대 강도(peak intensity) 가 증가함으로써 열처리에 의해 결정성 향상이되었음을 알수 있다. Fig.2는 파장에 따른 ITO막의 광투과도를 나타낸다.

• Proceedings of the KIEE Conference
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• 2009.07a
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• pp.1358_1359
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• 2009

가스 절연 개폐장치(Gas Insulated Switchgear : GIS)의 고체 스페이서에 경사기능성 재료(Functionally Graded Material : FGM)를 적용할 때, 전계의 완화를 예상할 수 있다. 특히, 균일 유전율 분포를 가지는 스페이서에서 양극 근처에 집중된 높은 전계가 FGM 스페이서를 사용할 때, 스페이서와 $SF_6$ 가스의 접촉부로 옮겨지며, 그 크기가 완화됨을 확인할 수 있었다[1]. 본 연구에서는 상용 고체 스페이서의 양극 부근에서의 전계 집중을 감소시키기 위해 전극 형상의 최적화를 수행하였다. 최적화 기법으로는 완전계승계획법(Full Factorial Design : FFD)과 결합된 반응표면법(Response Surface Method : RSM)을 이용하였으며, 균일 유전율 스페이서에서 양극 형상을 최적화하였다. 또한 타원형 유전율 분포를 가지는 FGM 스페이서를 이용함으로써, 상용 GIS 모델에 비해 최대 전계가 크게 완화될 수 있음을 확인하였으며, 상용 GIS의 외함부의 크기를 줄여 실제 소형화 가능 여부를 확인하였다.

• Korean Journal of Optics and Photonics
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• v.14 no.5
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• pp.521-529
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• 2003

For complex-coupled (CC) DFB lasers, we found that there might be little correlation between the single mode yields at threshold and above threshold. At threshold, the single mode yield considering f number of in-phase (IP) CC DFB lasers is the same as that of anti-phase (AP) CC DFB lasers. However, the single mode yield as a function of injection current above threshold of IP CC DFB lasers is much different from that of AP CC DFB lasers. In the case of IP CC DFB lasers, the single mode yield increases as the coupling coefficient ratio (CR) increases, while, in the case of AP CC DFB lasers, the single mode yield decreases rapidly regardless of CR as the injection current increases. In the case of AR-HR combinations, the effect of AR ref1ectivity on the single mode yield increases as the coupling strength decreases. As the coupling strength decreases, the CR at which the increase rate of the single mode yield starts to decrease, increases, and the maximum single mode yield increases. Single mode yields of AR-HR and AR-AR combinations are larger than those of AR-CL and CL-CL combinations.

• Korean Journal of Optics and Photonics
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• v.5 no.2
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• pp.286-290
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• 1994

Lasing characteristics of an Er-doped fiber laser have been investigated at various conditions of resonator reflectivities and pump powers. Variation of the laser wavelength with various mirror reflectivities has been compared with the theoretical analysis based on absorption, gain spectra, and resonator parameters. The maximum slope efficiency of 38% was obtained with the resonator's mirror reflectivities of 100% and 4% on both sides, and the threshold powers were varied from 7.8 mW to 5.6 mW, and lasing wavelengths were varied $1.532\mum to 1.563\mum and 1.558 \mum to 1.570 \mum$ for 6 and 15.8 mlong Er-doped fiber, respectively, as the resonator reflectivities were changed from 0.0016 to 0.9.to 0.9.

• Journal of KIISE:Software and Applications
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• v.29 no.3
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• pp.192-201
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• 2002

Automated text classification is considered as an important method to manage and process a huge amount of documents in digital forms that are widespread and continuously increasing. Recently, text classification has been addressed with machine learning technologies such as k-nearest neighbor, decision tree, support vector machine and neural networks. However, only few investigations in text classification are studied on real problems but on well-organized text corpus, and do not show their usefulness. This paper proposes and analyzes text classification methods for a real application, email document classification task. First, we propose a combining method of multiple neural networks that improves the performance through the combinations with maximum and neural networks. Second, we present another strategy of combining multiple machine learning classifiers. Voting, Borda count and neural networks improve the overall classification performance. Experimental results show the usefulness of the proposed methods for a real application domain, yielding more than 90% precision rates.

• The Journal of the Acoustical Society of Korea
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• v.21 no.4
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• pp.407-414
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• 2002

In this paper, we present a method that automatically generates concatenate morpheme based language models to improve the performance of Korean large vocabulary continuous speech recognition. The focus was brought into improvement against recognition errors of monosyllable morphemes that occupy 54% of the training text corpus and more frequently mis-recognized. Knowledge-based method using POS patterns has disadvantages such as the difficulty in making rules and producing many low frequency concatenate morphemes. Proposed method automatically selects morpheme-pairs from training text data based on measures such as frequency, mutual information, and unigram log likelihood. Experiment was performed using 7M-morpheme text corpus and 20K-morpheme lexicon. The frequency measure with constraint on the number of morphemes used for concatenation produces the best result of reducing monosyllables from 54% to 30%, bigram perplexity from 117.9 to 97.3. and MER from 21.3% to 17.6%.

• Applied Chemistry for Engineering
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• v.23 no.2
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• pp.210-216
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• 2012

For the recycling of rapid-cooled steel slag, various specimens were prepared with the various replacement ratios of the rapid-cooled steel slag and the addition ratios of polymer binders. The physical properties of these specimens were then investigated by absorption test, compressive strength test, flexural strength test and hot water resistance test, and the pore and the micro-structure analysis was performed using scanning electron microscope. Results showed that the flexural strength increased with the increase of rapid-cooled steel slag and polymer binder, but the compressive strength showed a maximum strength at a certain proportion. By the hot water resistance test, compressive strength and flexural strength decreased remarkably and the total pore volume increased but the pore diameter decreased. SEM observation of the structure before the hot water resistance test revealed a very compact infusion of structure but the decomposition or thermal degradation appeared in polymer binders when observed after the hot water resistance test.

• Journal of the Korean Institute of Telematics and Electronics
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• v.2 no.1
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• pp.10-13
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• 1965

본논문은 단종된 전송선과 개방된 전송선 및 2개의 결합저항기로 구성된 초광대역전송선형 FM변별기의 동적인 해석(dynamic analysis)을 취급하였다. 변별기의 출력파형의 Harmonic Distortion과 입력신호의 최대허용주파수변위와의 제관계를 Fourier transfrom으로 상세하게 해석하였다. 결합저항계수r(Fig 1 참조)는 변별기의 감도와 입력신호의 전주파수변위에 걸쳐 입력 Impedance가 일정하다는 견지에서 일로 놓아야 된다는 것이 판명되었다. 이론상으로는 100%의 주파수변위를 가진 FM신호라도 본변별기로 불과 2.6% Harmonic distortion으로 검파할 수 있으며 또한 검파시에 변별기의 입력 Impedance는 전종선의 특성 Impedance Z0로 일정하게 유지된다. 이론적인 결과를 뒷받침하기 위하여 실험결과를 첨부하였다. 본실험에서는 변별기의 특성곡선이 중심주파수 85.5Mc를 중심으로 40%의 주파수변위에 대하여 Linear하며, 또한 이때의 변별기의 입력 Impedance의 변화율은 이상치 Z0의 ±14% 이내이다.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2009.11a
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• pp.35-38
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• 2009

본 논문에서는 신호 공간 다이버시티 (Signal Space Diversity) 기법이 적용된 시스템에서 최대비 합성 (Maximal Ratio Combining) 수신시 성능 이득에 대해서 분석하였다. 먼저 심볼 오류율(Symbol Error Rate)을 수학적으로 유도하였다. 유도된 공식으로부터 상한(Upper Bound) 분석을 통해 공간 신호 다이버시티 기법이 결합될 경우 기존 대비 2배, 즉 '$2{\times}$수신안테나수' 만큼의 다이버시티 이득을 가짐을 증명하였다. 그리고 모의실험 결과와 유도된 공식 결과 값이 서로 일치함을 보여 정확성을 입증하였으며, 유도된 공식을 기반으로 신호 대 잡음비(SNR; Signal-to-Noise Ratio), 수신 안테나 개수 등 주어진 시스템 변수에 따른 최적 회전 각도를 정확히 도출할 수 있음을 보였다.