• Korean Journal of Materials Research
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• v.8 no.3
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• pp.245-251
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• 1998

Bi-doped n-type PbTe thermoeletric materials were fabricated by mechanical alloying and hot pressing. The intering characteristics and thermoelectric properties of the hot- pressed PbTe were characterized and compared with the properties of the specimens prepared by meltingigrinding method. The hot-pressed PbTe specimens fabricated by mechanical alloying exhibited more negative Seebeck coefficient, higher electrical resistivity and lower thermal conductivity. compared to ones prepared by meltingigrinding. The maximum figure-of-merit increased and the temperature for the maximum figure-of-merit shifted to lower temperature for the specimens fabricated by mechanical alloying. When hot pressed at $650^{\circ}C$, 0.3 wt% Bi-doped PbTe fabricated by mechanical alloying and meltingjgrinding exhibited maximum figure-of-merits of $1.33\times10^{-3}/K$ at $200^{\circ}C$ and $1.07\times10^{-3}/K$ at $400^{\circ}C$ respectively.

• The Korean Journal of Applied Statistics
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• v.33 no.3
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• pp.257-267
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• 2020

We introduce multivariate exponential smoothing models based on a vector innovations structural time series framework. The models enable us to exploit potential inter-series dependencies to improve the fit and forecasts of multivariate (vector) time series. Models are applied to forecast the exchange rates of the UK pound (UKP) and US dollar (USD) against the Korean won (KRW) observed on monthly basis; subseqently, we compare their performance with alternative models. We observe that the multivariate exponential smoothing models are superior to alternatives.

• 한국전기화학회:학술대회논문집
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• 2002.10a
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• pp.18-18
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• 2002

• Proceedings of the Korean Institute of Industrial Safety Conference
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• 2005.10a
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• pp.352-356
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• 2005

• Journal of the Korean Vacuum Society
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• v.21 no.4
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• pp.219-224
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• 2012

We study for long-term performance of amorphous silicon solar cells under light exposure. The performance is predicted with a kinetic model in which the carrier lifetimes are determined by the defect density. In particular, the kinetic model is described by the stretched-exponential relaxation of defects to reach equilibrium. In this report, we simulate the light-induced degradation of the amorphous silicon solar cells with the kinetic model and AMPS-1D computer program. And data measured for outdoor performances of various solar cells are compared with the simulated results. This study focuses on examining the light-induced degradation for the following amorphous silicon pin solar cells: thickness${\approx}$300 nm, built-in potential${\approx}$1.05 V, defect density (at t=0)${\approx}5{\times}10^{15}cm^{-3}$, short-circuit current density (at t=0)${\approx}15.8mA/cm^2$, fill factor (at t=0)${\approx}0.691$, open-circuit voltage (at t=0)${\approx}0.865V$, conversion efficiency (at t=0)${\approx}9.50%$.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.21 no.11
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• pp.2191-2198
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• 2017

The PME(precision measurement equipment) used in the measurement to check the performance of the equipment in military weapon system is periodically calibrated to maintain measurement reliability during the life cycle. Previous studies suggest that reliability models are determined by considering sample size and characteristics of equipment. However, it may not be fit well to apply a single model assuming the same characteristic distribution for the maintenance date of many kinds of PMEs. This paper proposes that the most suitable calibration interval for maintenance data is selected through the F-test and the performance index evaluation among the calibration intervals estimated from the measurement reliability models assuming the characteristic of the bath-tub curve during the life cycle of various PMEs. The research results show that the reliabilities of various types of equipment are maintained during calibration intervals.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.19 no.6
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• pp.1064-1074
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• 1994

In this paper, an optimum TCM(trellis coded modulation)combined with CPM(continuous phase modulation) signal is investigated, and the performances are evaluated on the two-ray fading channel, which is one of the well-known frequency-selected because of their relatively good power and spectrum efficiency, and the modulation index is varied from 0.1 to 0.6. The performance is evaluated for each modulation index. The constraint length of the encoder, which is comprised in TCM, is chosen to be 2 and 3. From the performance evaluations, when the constraint length is 3 and modulation index 0.5, a power gain if the optimum TCM over the scheme without coding is observed to be 2.0dB for 1REC and 2.1dB for 3RC, respectively, on the fading channel. Thus, a significant improvement on the line quality is expected when the optimum TCM presented in this paper is employed in digital mobile radio applications.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.450.2-450.2
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• 2014

열전재료는 열-전기가 상호 가역적으로 변하는 재료로서, 최근 에너지 변환소재 분야에서 각광받고 있다. 열전재료의 특성 효율은 무차원 열전 성능지수(dimensionless figure of merit, $ZT={\alpha}2{\sigma}T/{\kappa}$)로 나타낼 수 있다. 여기서 ${\alpha}$는 제벡계수(Seebeck coefficient), ${\sigma}$는 전기전도도(electrical conductivity), ${\kappa}$는 열전도도(thermal conductivity), T는 Kelvin 온도를 나타낸다. 500 K에서 800 K까지의 중온 영역에서 우수한 열전특성을 보이는 $Mg_2X$ (X=Si, Ge, Sn)와 이들의 고용체는 성분원소가 독성이 없고, 매장량이 많아 친환경 열전 재료로 각광받고 있다. $Mg_2X$ 고용체 중 $Mg_2Si_{1-x}Ge_x$는 기존 $Mn_2Si$, $Mg_2Ge$, $Mg_2Sn$계 보다 더 우수한 열전 성능지수를 보인다. 다양한 제조 방법들이 시도되고 있으나, 조성설계 및 구조, 성능 조절의 어려움이 있고, Mg의 산화와 휘발 및 Mg, Si, Ge의 융점 차이가 크고 중력 편석과 반응하지 않은 원소들로 인해 제조가 상당히 어렵다. Sb가 도핑된 $Mg_2Si_{0.5}Ge_{0.5}Sb_y$ (y=0, 0.005, 0.01, 0.02, 0.03) 고용체를 고상반응으로 합성하고 진공열간 압축성형을 통해 성공적으로 제조하였다. 고용 상을 확인하기 위하여 X선 회절분석을 실시하였고, 고용체 형성과 도핑에 따른 전기적 특성변화를 평가하기 위해 Hall 효과를 측정하여 전자 이동특성을 분석하였고, 323~823 K까지 전기전도도, 제벡계수, 열전도도의 측정을 통해 열전 성능지수를 평가하였다.

• Journal of the Korean Institute of Intelligent Systems
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• v.23 no.4
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• pp.304-309
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• 2013

This paper proposes a intelligent approach on range decision of figure of merit. Unknown range of the underwater target and the non-fixed signal excess make the uncertainty for the tracking process. Using the input data of signal excess related to the range, we establish the rule of the fuzzy set and the original data acquired by sonar can be transformed to the fuzzified data set. To reduce the error arisen from the unexpected data, we use the new data transformed in fuzzy set. The piecewise relations of the min value, max one, and the mean one are calculated. The three values are used for the expected range of the underwater target. By analysing the fluctuation of the data, we can expect the target's position and the characteristics of the maneuvering. The examples are presented to show the performance and the effectiveness of the proposed method.

• Journal of Korea Water Resources Association
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• v.49 no.10
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• pp.877-885
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• 2016

In this study, the Standard Precipitation Index(SPI), meteorological drought index, was used to evaluate the temporal and spatial assessment of drought forecasting results for all cross Korea. For the drought forecasting, the Multi Layer Perceptron-Artificial Neural Network (MLP-ANN) was selected and the drought forecasting was performed according to different forecasting lead time for SPI (3) and SPI (6). The precipitation data observed in 59 gaging stations of Korea Meteorological Adminstration (KMA) from 1976~2015. For the performance evaluation of the drought forecasting, the binary classification confusion matrix, such as evaluating the status of drought occurrence based on threshold, was constituted. Then Receiver Operating Characteristics (ROC) score and F score according to conditional probability are computed. As a result of ROC analysis on forecasting performance, drought forecasting performance, of applying the MLP-ANN model, shows satisfactory forecasting results. Consequently, two-month and five-month leading forecasts were possible for SPI (3) and SPI (6), respectively.