• 환경영향평가
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• 제20권5호
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• pp.765-777
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• 2011

According to the total pollution load management system, exact prediction and analysis of water quality and discharge has been required in order to allocate the amount of pollution load to each local government. In this study, QUAL2E model was used for comparison with other water quality models and improve the inadequate to forecast future water quality. And Various calibration and verification methods were applied to deal with existing uncertainties of parameter during modeling water quality. For user convenience, A GUI(Graphical User Interface) system named "QL2-XP" model is developed by object-oriented language for the user convenience and practical usage. Suggested GUI system consist of hydraulic analysis, water quality analysis, optimized model calibration processes, and postprocessing the simulation results. Therefore this model will be effectively utilized to manage practical and efficient water quality.

• 대한원격탐사학회:학술대회논문집
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• 대한원격탐사학회 2008년도 춘계학술대회 논문집
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• pp.158-163
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• 2008

In inverse synthetic aperture radar (ISAR) imaging, An ISAR autofocusing algorithm is essential to obtain well-focused ISAR images. Traditional methods have relied on the approximation that the phase error due to target motion is a function of the cross-range dimension only. However, in the stepped-frequency radar system, it tends to become a two-dimensional function of both down-range and cross-range, especially when target's movement is very fast and the pulse repetition frequency (PRF) is low. In order to remove the phase error along down-range, this paper proposes a method called SAEM (subarray averaging and entropy minimization) [1] that uses a subarray averaging concept in conjunction with the entropy cost function in order to find target motion parameters, and a novel 2-D optimization technique with the inherent properties of the proposed entropy-based cost function. A well-focused ISAR image can be obtained from the combination of the proposed method and a traditional autofocus algorithm that removes the phase error along the cross-range dimension. The effectiveness of this method is illustrated and analyzed with simulated targets comprised of point scatters.

• 한국통신학회논문지
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• 제21권8호
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• pp.2003-2012
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• 1996

The 16- and 32-state Trellis-coded M-ary 4-dimensional (4-D) orthogonal modulation scheme with a frequency-reuse technique have been investigated. Here, 5 coded bits form a rate 4/5 convolutional encoder provide 32 possible symbols. Then the signals are mapped by a M-ary 4-D orthogonal modulator, where each signal has equal energy and is PSK modulated. In the M-ary 4-D modulator, we have employed the vectors which is derived by the optimization technique of signal waveforms in a 4-D sphere. This technique is usedin maximizing the minimum Euclidean distance between a set of signal poits on a multidimensional sphere. By combinig trellis coding with M-ary 4-D modulation and proper set-partitioning, we have obtained a considerable impeovement in the free minimum distance of the system over an AWGN channel. The 16-state scheme obtains coding gains up to 5.5 dB over the uncoded two-independent QPSK scheme and 2.5 dB over the two-independent 2-D TCM scheme. And, the 32-state scheme obtains coding gains up to 6.4 dB over the uncoded two-independent QPSK schemeand 3.4 dB over the two-independent 2-D TCM scheme.

• 대한기계학회논문집
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• 제17권6호
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• pp.1330-1341
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• 1993

본 연구에서는 회전대우(revolute joint)들로 이루어진 1자유도 평면기구들의 특성을 파악하고 그래이프이론(graph theory)을 이용하여 기구의 형태를 행렬로 표시 하여 체이터베이스에 저장하였다. 또한 기구의 특성중의 하나인 작업조건(function specification)에 따른 무오차점(precision point)의 최대 개수를 알아내는 프로그램 을 개발하여 이로써 얻은 정보를 또 다른 데이타베이스에 저장하였다. 이와같이 구축 된 데이터베이스들로부터 설계자의 요구에 적합한 기구를 선택하여 형태합성 문제를 해결하였다.

• 한국정밀공학회지
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• 제27권2호
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• pp.13-19
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• 2010

Due to the rapid spread of mobile handheld devices, industrial demands for micro-scale holes with a diameter of even smaller than $10{\mu}m$ in sapphire/silicon wafers have been increasing. Holes in sapphire wafers are for heat dissipation from LEDs; and those in silicon wafers for interlayer communication in three-dimensional integrated circuit (IC). We have developed a sapphire wafer driller equipped with a 532nm laser in which a cooling chuck is employed to minimize local heat accumulation in wafer. Through the optimization of process parameters (pulse energy, repetition rate, number of pulses), quality holes with a diameter of $30{\mu}m$ and a depth of $100{\mu}m$ can be drilled at a rate of 30holes/sec. We also have developed a silicon wafer driller equipped with a 355nm laser. It is able to drill quality through-holes of $15{\mu}m$ in diameter and $150{\mu}m$ in depth at a rate of 100holes/sec.

• Geomechanics and Engineering
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• 제23권1호
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• pp.1-13
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• 2020

To give a solution for seismic stability of tunnel faces subjected to earthquake ground shakings, the pseudo-dynamic approach is originally introduced to analyze tunnel face stability in this study. In the light of the upper-bound theorem of limit analysis, an advanced three-dimensional mechanism combined with pseudo-dynamic approach is proposed. Based on this mechanism, the required support pressure on tunnel face can be obtained by equaling external work rates to the internal energy dissipation and implementing an optimization searching procedure related to time. Both time and space feature of seismic waves are properly accounted for in the proposed mechanism. For this reason, the proposed mechanism can better represent the actual influence of seismic motion and has a remarkable advantage in evaluating the effects of vertical seismic acceleration, soil amplification factor, seismic wave period and initial phase difference on tunnel face stability. Furthermore, the pseudo-dynamic approach is compared with the pseudo-static approach. The difference between them is illustrated from a new but understandable perspective. The comparison demonstrates that the pseudo-static approach is a conservative method but still could provide precise enough results as the pseudo-dynamic approach if the value of seismic wavelengths is large or the height of soil structures is small.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2012년도 제42회 동계 정기 학술대회 초록집
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• pp.331-331
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• 2012

With the NAND Flash scaling down, it becomes more and more difficult to follow Moore's law to continue the scaling due to physical limitations. Recently, three-dimensional (3D) flash memories have introduced as an ideal solution for ultra-high-density data storage. In 3D flash memory, as the process reason, we need to use poly-Si TFTs instead of conventional transistors. So, after combining charge trap flash (CTF) structure and poly-Si TFTs, the emerging device SONOS-TFTs has also suffered from some reliability problem such as hot carrier degradation, charge-trapping-induced parasitic capacitance and resistance which both create interface traps. Charge pumping method is a useful tool to investigate the degradation phenomenon related to interface trap creation. However, the curves for charge pumping current in SONOS TFTs were far from ideal, which previously due to the fabrication process or some unknown traps. It needs an optimization and the important geometrical effect should be eliminated. In spite of its importance, it is still not deeply studied. In our work, base-level sweep model was applied in SONOS TFTs, and the nonideal charge pumping current was optimized by adjusting the gate pulse transition time. As a result, after the optimizing, an improved charge pumping current curve is obtained.

• 한국레이저가공학회지
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• 제18권3호
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• pp.1-5
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• 2015

A 3D printer based on laser powder deposition (LPD), also known as DED (direct energy deposition), has been developed for fabricating metal parts. The printer uses a ytterbium fiber laser (1070nm, 1kW) and is equipped with an Ar purge chamber, a three-dimensional translation stage and a powder feeding system composed of a powder chamber and delivery nozzles. To demonstrate the performance of the printer, a tapered cylinder of 320mm in height has been fabricated successfully using Ti-6Al-4V powders. The process parameters including the laser output power, the scan speed, and the powder feeding rate have been optimized. A 3D printed test specimen shows mechanical properties (yield strength, ultimate tensile strength, and elongation) exceeding the criteria to employed in a variety of Ti alloy applications.

• 한국자동차공학회논문집
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• 제16권6호
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• pp.26-32
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• 2008

This research presents a simulation for the fuel economy of parallel diesel hybrid vehicle. Diesel engines compared to gasoline engines have the advantages of higher fuel economy and lower $CO_2$ emission. One of the most ways to meet future fuel economy and emissions regulation is to combine diesel engine technology with a hybrid electric vehicle. The simulation of HEV is growing need for rapid analysis of the many configurations and component options. WAVE, a one-dimensional engine analysis tool, was used to a 2.7L diesel engine. ADVISOR, designed for rapid analysis of the performance and fuel economy of vehicle models, was used to conventional and hybrid electric vehicle by the use of output file from WAVE as the input engine data file for ADVISOR. A parallel diesel HEV is at least $19.7{\sim}36%$ higher fuel economy and improved acceleration ability compared to a conventional diesel vehicle. The energy loss of the parallel diesel HEV is $23{\sim}38%$ less than the conventional vehicle using regeneration.

• Korean Journal of Geomatics
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• 제1권1호
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• pp.95-101
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• 2001

In a route plan, the route selection is a complicated problem to consider the spatial distribution and influence through overall related data and objective analysis on the social, economic and technical condition. The developed system in this study was compared and estimated by deciding a practical section for its validity and efficiency. Using Geographic Information System (GIS), the various information required for route selections in database was constructed, the characteristics of subject area by executing three-dimensional terrain analysis was grasped effectively, and the control point through buffering, overlay and location operation was extracted. An optimum route was selected by calculating the sum of alternatives to the sub-criteria weight, and from this result, there is a difference between real route and proposed route according to the prioritization of decision criteria based on the importance. This research could be constructed and applied geospatial information to the reasonable route plan and an optimum route selection efficiently using GIS. Therefore, the applications are presented by applying Analytic Hierarchy Process (AHP) to the decision-making of information needed in route selection.