• 환경영향평가
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• 제14권5호
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• pp.317-335
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• 2005

This paper is primarily intended to propose a new concept of "aggregate control of road density" which is defined as the area-wide road surface per watershed area. An empirical study for experimental sites was conducted to confirm how a standard GIS technology can be used to assist in estimating the road density in terms of total volume threshold control. Guidelines for a replicable methodology are presented to provide a strong theoretical basis for the standardization of factors involved in the estimation of the road space threshold; the meaningful classification of road types, delination of watershed boundary, interpretation for distribution trends of road density etc. A variety of visual maps using overlay analysis can be generated over large areas quickly and easily to show the fact that some degree of road space already exists in the experimental sites. They could be used as an evidence to limit further construction of road network in comparison with other tributary watershed. It is anticipated that this research output could be used as a valuable reference to confirm the potential of introducing the new concept of "site specific road density" to support more scientific and objective decision-making in the process of road construction project.

• 한국광학회:학술대회논문집
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• 한국광학회 2000년도 제11회 정기총회 및 00년 동계학술발표회 논문집
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• pp.276.1-277
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• 2000

Absorptive bistable laser diode was analyzed by using traveling wave model in conjunction with the finite-difference method. Carrier and photon density distributions were calculated and the output characteristics were obtained. The results for both the steady-state and transient (switching) cases were compared with those of the rate equation approach.

• 한국생산제조학회지
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• 제22권4호
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• pp.643-651
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• 2013

This study applied a laser cleaning method (dry cleaning) that is used for cleaning semiconductor elements to dental implant cleaning. The lasers used in this study were pulsed fiber lasers with wavelengths of 1,064 and 532 nm. The peak output, energy per pulse, energy density per pulse, time of pulse experiment, and number of pulse experiments served as process variables for this study, and the variables were changed for each experiment. As a result, a laser with a wavelength of 532 nm showed much higher cleaning efficiency than its 1,064 nm counterpart. As the wavelength range decreased, the quantized energy increased and the reflection rate of the titanium used for the implant decreased; consequently, the energy absorption rate increased. Therefore, it is proposed that the energy density by wavelength has a greater influence on cleaning than does the output size.

• 한국전기전자재료학회논문지
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• 제18권10호
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• pp.945-949
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• 2005

We have grown GaN layers with in-situ SiN mask by metal organic chemical vapor deposition (MOCVD) and study the physical properties of the GaN layer. We have also fabricate PN junction light emitting diode (LED) to investigate the effect of the SiN mask on its optical property By inserting a SiN mask, (102) the full width at half maximum (FWHM) decreased from 480 arcsec to 409 arcsec and threading dislocation (TD) density decreased from $3.21{\times}10^9\;cm^{-2}$ to $9.7{\times}10^8\;cm^{-2}$. The output power of the LED with a SiN mask increased from 198 mcd to 392 mcd at 20 mA. We have thus shown that the SiN mask improved significantly the physical and optical properties of the GaN layer.

• 전자공학회논문지A
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• 제31A권10호
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• pp.79-86
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• 1994

Gain-guided broad-area single quantum well separate confinement heterostructure diode lasers have been fabricated from structures grown by metal organic vapor phase epitaxy. The active layer of the epi-structure is InGaAs emitting 962-965nm and the guiding layer GaAs. The channel width is fixed to 150${\mu}$m and the cavity length varys within the range of 300~800${\mu}$m. For uncoated LD's, the output power of 0.7W has been obtaained at a pulsed current level of 2A, which results about 60% external quantum efficiency. The threshold current density is 200A/cm$^{2}$ for the cavity lengths of 800.mu.m LD's. The stain effect upon the transparent current density has been observed. The internal quantum efficiency is expected to be 88% and the internal loss to be 18$cm^{-1}$. The beam divergence has been measured to be 7$^{\circ}$to lateral and 40$^{\circ}$to transverse direction. finally, 1.2W continuous-wave output power has been obtained at a current level of 2A for AR/HR coated LD's die-bonded on Cu heat-sink and cooled by TEC.

• Structural Monitoring and Maintenance
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• 제4권1호
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• pp.1-15
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• 2017

Installation of sensors networks for continuous in-service monitoring of structures and their efficiency conditions is a current research trend of paramount interest. On-line monitoring systems could be strategically useful for road infrastructures, which are expected to perform efficiently and be self-diagnostic, also in emergency scenarios. This work researches damage detection in composite concrete-steel structures that are typical for highway overpasses and bridges. The techniques herein proposed assume that typical damage in the deck occurs in form of delamination and cracking, and that it affects the peak power spectral density of dynamic curvature. The investigation is performed by combining results of measurements collected by long-gauge fiber optic strain sensors installed on monitored structure and a statistic approach. A finite element model has been also prepared and validated for deepening peculiar aspects of the investigation and the availability of the method. The proposed method for real time applications is able to detect a documented unusual behavior (e.g., damage or deterioration) through long-gauge fiber optic strain sensors measurements and a probabilistic study of the dynamic curvature power spectral density.

• 방송공학회논문지
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• 제15권5호
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• pp.665-671
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• 2010

본 논문에서는 DVB-T2 (digital video broadcasting for terrestrial - 2nd generation) 시스템을 위한 터보 등화기를 제안 하고 그 성능을 분석하였다. 터보 등화기는 MAP (maximum a posteriori) 검파기와 LDPC (low density parity check) 복호기로 구성 되었다. LS(least square) 채널 추정 기반 SISO (soft-input-soft-output) MAP 등화기는 LDPC 복호기에 외래 확률 값을 준다. 터보 등화기의 성능을 반복 횟수에 따라 컴퓨터 실험을 통하여 분석하였다.

• 전력전자학회논문지
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• 제22권4호
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• pp.345-352
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• 2017

In this paper, a non-dissipative snubber for reducing the switching losses in the step down converter is proposed. The conventional step down converter, e.g., buck converter, suffers from serious switching losses and consequentially heat generation because of its hard switching. Thus, it is unsuitable for high switching frequency operation. Reduction of the reactive components' size, such as an output inductor and capacitor, is difficult. The proposed snubber can slow down the increasing current slopes and switch voltage at turn-on and turn-off transients, thereby significantly reducing the switching loses. Additionally, the slowly increasing current during switch turn-on transition, can effectively solve the output rectifier diode reverse recovery problem. Therefore, the proposed non-dissipative snubber not only leads to the efficiency of converter operation at high switching frequency but also reduces the reactive components size in proportion to the switching frequency. To confirm the validity of the proposed circuit, theoretical analysis and experimental results from a 150 W, 1 MHz prototype are presented.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2002년도 추계학술대회 논문집 전기기기 및 에너지변환시스템부문
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• pp.64-66
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• 2002

Recently. switched reluctance motor is noticed because it is simple in structure and mechanically strong. SRM has great competitive power, and the study is developed about improving the characteristics of SRM. The current density of winding becomes larger in designing SRM that has the characteristics of the low voltage and high current. Hence the current density of SRM of a vehicle is high. And in order that we drive SRM in variable speed and protect the switching device. the current of SRM is limited by chopping. So it is impossible to obtain object value of output characteristics by limited current. In this paper, the author design the shape of SRM from Miller's output equation, and verify the design of SRM by using FEM. The waveform of chopping current is predicted by simulation and concur with experimental result. And the torque is improved by applying overlap current.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제14권10호
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• pp.4214-4230
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• 2020

This paper introduces a pilot allocation scheme for massive MIMO systems based on deep convolutional neural network (CNN) learning. This work is an extension of a prior work on the basic deep learning framework of the pilot assignment problem, the application of which to a high-user density nature is difficult owing to the factorial increase in both input features and output layers. To solve this problem, by adopting the advantages of CNN in learning image data, we design input features that represent users' locations in all the cells as image data with a two-dimensional fixed-size matrix. Furthermore, using a sorting mechanism for applying proper rule, we construct output layers with a linear space complexity according to the number of users. We also develop a theoretical framework for the network capacity model of the massive MIMO systems and apply it to the training process. Finally, we implement the proposed deep CNN-based pilot assignment scheme using a commercial vanilla CNN, which takes into account shift invariant characteristics. Through extensive simulation, we demonstrate that the proposed work realizes about a 98% theoretical upper-bound performance and an elapsed time of 0.842 ms with low complexity in the case of a high-user-density condition.