• 한국정보통신학회논문지
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• 제20권1호
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• pp.117-122
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• 2016

본 논문에서는 차량 추돌 방지 단거리 레이더용 24-GHz CMOS 고주파 전력 증폭기 (RF power amplifier)를 제안한다. 이러한 회로는 클래스-A 모드 증폭기로서 단간 (inter-stages) 공액 정합 (conjugate matching) 회로를 가진 공통-소스 단으로 구성되어 있다. 제안한 회로는 TSMC $0.13-{\mu}m$ 혼성신호/고주파 CMOS 공정 ($f_T/f_{MAX}=120/140GHz$)으로 설계하였다. 2볼트 전원전압에서 동작하며, 저전압 전원에서도 높은 전력 이득, 낮은 삽입 손실 및 낮은 음지수를 가지도록 설계되어 있다. 전체 칩 면적을 줄이기 위해 넓은 면적을 차지하는 실제 인덕터 대신 전송선(transmission line)을 이용하였다. 설계한 CMOS 고주파 전력 증폭기는 최근 발표된 연구결과에 비해 $0.1mm^2$의 가장 작은 칩 크기, 40mW의 가장 적은 소비전력, 26.5dB의 가장 높은 전력이득, 19.2dBm의 가장 높은 포화 출력 전력 및 17.2%의 가장 높은 최대 전력부가 효율 특성을 보였다.

• Journal of Biosystems Engineering
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• 제43권2호
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• pp.119-127
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• 2018

Purpose: Fermented feedstuffs have been found to improve productivity, reduce manure odor, and increase immunity. However, because there is not a commercialized pelletizing system for fermented total mixed ration (TMR) for pig feeding in Korea, a pelletizing system using TMR fermented feed was developed. Methods: The particle size, density, and volumetric density of the TMR feeds used in the test were measured. The pellet durability index (PDI, %) value of the pelletized TMR feed based on its moisture content, and the amount of pellet production based on the rotation speed of the compression roller were measured. Results: The test materials, TMR1 and TMR2, were approximately compressed to 387 kg/m3 with 18.2% (w.b.) and 544 kg/m3 with 22.2% (w.b.), respectively. Throughout this pellet molding test, the moisture content from 15 to 20% (w.b.) of mixture feedstuffs, including fermented forage, could be used for pellet molding. Based on the results, a small-scale pellet molding system of fermented TMR was designed and manufactured for pig farms. As rotation speed increased, the throughput increased, whereas the moisture content decreased by approximately 2% (w.b.) because of pellet molding. The best yield of pellets with 94.2% PDI was of 536 kg/h at 135 rpm rotation speed. Conclusions: Although the throughput of the prototype increased as the rotation speed increased, it was difficult to operate because of the greater noise and the lower PDI (%) at the higher rotation speed of the pellet molding rotor. It was found that the best production of pellets using the prototype was 536 kg/h having a PDI of 94.2% or more at a rotation speed of 135 rpm.

• 대한의용생체공학회:의공학회지
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• 제31권2호
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• pp.94-98
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• 2010

In magnetic resonance electrical impedance tomography (MREIT), a current-injection MR imaging method is adopted to produce a cross-sectional image of an electrical conductivity distribution in addition to MR images. The purpose of this study was to test the feasibility of MREIT for differentiating the canine lung parenchyma without and with pneumonia. Three normal healthy beagles and two mixed breed dogs with pneumonia were used. After attaching electrodes around the chest, we placed the dog inside our MR scanner. We injected as much as 30 mA current in a form of short pulses into the chest region. Reconstructed conductivity images of normal canine lungs exhibit a peculiar pattern of a relatively coarse salt and pepper noise. On the contrary, conductivity images of pneumonic canine lungs show significantly enhanced contrast of the lesions while the corresponding MR images show a little bit of contrast in the middle and caudal lung parenchyma due to the accumulation of pleural fluid. This preliminary study indicates that MREIT imaging of the chest may deliver unique new diagnostic information.

• Wind and Structures
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• 제26권5호
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• pp.267-277
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• 2018

Numerical simulations are performed of a long flexible cylinder undergoing vortex-induced vibration at a Reynolds number of 500. The cylinder is pinned at both ends, having an aspect ratio of 100 (cylinder length to cylinder diameter) and a mass ratio of 4.2 (structural mass to displaced fluid mass). Temporal and spatial information on the cross-flow (CF) and in-line (IL) vibrations is extracted. High modal vibrations up to the $6^{th}$ in the CF direction and the $11^{th}$ in the IL direction are observed. Both the CF and IL vibrations feature a multi-mode mixed pattern. Mode competition is observed. The $2^{nd}$ mode with a low frequency dominates the IL vibration and its existence is attributed to a wave group propagating back and forth along the span. Distributions of fluid force coefficients are correlated to those of the CF and IL vibrations along the span. Histograms of the x'-y motion phase difference are evaluated from the total simulation time and a complete vibration cycle representing the standing or travelling wave pattern. Correlations between the phase difference and the vibrations are discussed. Vortex structures behind the cylinder show an interwoven near-wake pattern when the standing wave pattern dominates, but an oblique near-wake pattern when the travelling wave pattern prevails.

• Journal of Forest and Environmental Science
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• 제30권1호
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• pp.152-160
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• 2014

The purpose of this study is to investigate and analyze the physical characteristics and tranquility of the valleys located in Gangwon region. For this study we analyzed the field survey data 135 valleys using GIS. The elements for measurement of tranquility were divided into visual elements including terrain, objects, forest, water and auditory elements including noise. These elements were divided further into positive and negative factors. The weight of each element and item was calculated by applying the AHP method. The results of this study are as follows. The length of the valley ranged from 126 m to 17 km, and the elevation ranged from 40 m to 1,800 m. Type of mixed forest was common in the valleys. The depth of the water was over 20 cm in 83% of the total area and most of the water was in good condition in visual quality. Regarding the positive factors of tranquility, the weighted scores of the objects, waterfall sounds and visual transparence of the water were of relatively high value. Relatively high values were also shown in closed and curved topography in the landform, forest type and natural forests. In the negative factors, the weights of the objects and forest elements had high values. Within the facility groups, facility of the river produced a considerable negative. After applying the index of tranquility, the natural physical attributes affected the tranquility value, more than the manmade structures to a much greater degree.

• 한국자기학회:학술대회 개요집
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• 한국자기학회 2003년도 하계학술연구발표회 및 한.일 공동심포지엄
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• pp.220-221
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• 2003

Equiatomic FePt and CoPt alloy thin films have received considerable attention as possible magnetic and magneto-optic recording because of their high magnetic anisotropy energy and high coercivity. The high coercivity in these thin films is due to the presence of finely dispersed ordered FePt phase mixed with disordered FePt phase. However, a high temperature treatment, either substrate heating during deposition or post annealing, is needed to obtain the ordered L1$\_$0/ phase with high value of magneto crystalline anisotropy. Recent microstructural studies on these films suggest that the average grain size ranges from 10-50 nm and the grains are magnetically coupled between each other. On the other hand, the ultrahigh-density magnetic recording media with low media noise imposes the need of a material, which consists of magnetically isolated grains with size below 10 nm. The magnetic grain isolation can be controlled by the amount of additional non-magnetic element in the system which determines the interparticle separation and therefore the interparticle interactions. Recently, much research work has been done on various non-magnetic matrices. Preliminary studies showed that the samples prepared in B$_2$O$_3$ and Carbon matrices have shown strong perpendicular anisotropy and fine grain size down to 4nm, which suggest these nanocomposite films are very promising and may lead to the realization of a magnetic medium capable of recording densities beyond 1 Tb/in$^2$. So, in this work, the effect of Carbon doping on the magnetic properties of FePt nanoparticles were investigated.

• 전자공학회논문지B
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• 제33B권1호
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• pp.144-152
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• 1996

대규모 병렬처리가 가능하고 칩당 뉴론 집적도가 높은 펄스형 디지털 다계층 신경망 구조를 제안하였다. 제안된 신경망에서는 대수적인 신경망연산이 의사-랜덤 펄스 시퀀스(pseudo-random pulse sequences)와 단순 디지털 논리 게이트를 이용하여 확률적 프로세스로 대치되었다. 확률적 프로세스의 결과로 나타나는 신경망 연산의 통계적 모델을 제시하였으며 이를 바탕으로 랜덤잡음의 영향과 연산의 정확도를 분석하였다. 이진인식 문제를 적용하여 제안된 신경망의 성능을 평가하고 제시한 통계적 분석결과의 정당성을 검증하였다. Gate 레벨과 register transfer 레벨로 기술된 신경망의 VHDL 모델의 시뮬레이션 결과는 개발된 통계적모델로 예측된 인식추정치와 실제 인식률이 거의 일치함을 보였으며, 또한 숫자인식률에 있어서도 일반 Back-Propagation 신경망의 인식률과 거의 차이가 없음을 보였다.

• 전기학회논문지
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• 제62권12호
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• pp.1744-1749
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• 2013

Acoustic feedback is perceived as whistling or howling, which is a major complaint of hearing-aids users. Acoustic feedback cancellation is important in hearing-aids because acoustic feedback degrades performance of the hearing aid device by reducing maximum insertion gain. Adaptive systems for estimate acoustic feedback path and feedback suppression algorithms have been proposed in order to solve this problem. A typical feedback cancellation algorithm is LMS(least mean squares) because of its computational efficiency. However it has problem of convergence performance in high correlated input signal. In this paper, we propose a new variable step-size normalized LMS(least mean squares) algorithm using VAD(voice activity detection) to overcome the limitation of the LMS algorithm. The VAD algorithm is GSAP(global speech absence probability) and the feedback cancellation algorithm is normalized LMS. The proposed algorithm applies different step-size between voice and non-voice using VAD, for high stability, fast convergence speed and low misalignment when correlated inputs, such as speech. The result of simulation with white noise mixed speech signal, the proposed algorithm shows high performance then traditional algorithm in terms of stability, convergence speed and misalignment.

• Structural Monitoring and Maintenance
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• 제1권1호
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• pp.131-157
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• 2014

Special track systems used to divert a train to other directions or other tracks are generally called 'railway turnout'. A traditional turnout system consists of steel rails, switches, crossings, steel plates, fasteners, screw spikes, timber bearers, ballast and formation. The wheel rail contact over the crossing transfer zone has a dip-like shape and can often cause detrimental impact loads on the railway track and its components. The large impact also emits disturbing noises (either impact or ground-borne noise) to railway neighbors. In a brown-field railway track where an existing aged infrastructure requires renewal or maintenance, some physical constraints and construction complexities may dominate the choice of track forms or certain components. With the difficulty to seek for high-quality timbers with dimensional stability, a methodology to replace aged timber bearers in harsh dynamic environments is to adopt an alternative material that could mimic responses and characteristics of timber in both static and dynamic loading conditions. A critical review has suggested an application of an alternative material called fibre-reinforced foamed urethane (FFU). The full-scale capacity design makes use of its comparable engineering characteristics to timber, high-impact attenuation, high damping property, and a longer service life. A field trial to investigate in-situ behaviours of a turnout grillage system using an alternative material, 'fibre-reinforced foamed urethane (FFU)' bearers, has been carried out at a complex turnout junction under heavy mixed traffics at Hornsby, New South Wales, Australia. The turnout junction was renewed using the FFU bearers altogether with new special track components. Influences of the FFU bearers on track geometry (recorded by track inspection vehicle 'AK Car'), track settlement (based on survey data), track dynamics, and acoustic characteristics have been measured. Operational train pass-by measurements have been analysed to evaluate the effectiveness of the replacement methodology. Comparative studies show that the use of FFU bearers generates higher rail and sleeper accelerations but the damping capacity of the FFU help suppress vibration transferring onto other track components. The survey data analysis suggests a small vertical settlement and negligible lateral movement of the turnout system. The static and dynamic behaviours of FFU bearers appear to equate that of natural timber but its service life is superior.

• Journal of Communications and Networks
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• 제11권5호
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• pp.433-444
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• 2009

The bi-directional relay channel is the natural extension of a three-terminal relay channel where node a transmits to node b with the help of a relay r to allow for two-way communication between nodes a and b. That is, in a bi-directional relay channel, a and b wish to exchange independent messages over a shared channel with the help of a relay r. The rates at which this communication may reliably take place depend on the assumptions made on the relay processing abilities. We overview information theoretic limits of the bi-directional relay channel under a variety of conditions, before focusing on half-duplex nodes in which communication takes place in a number of temporal phases (resulting in protocols), and nodes may forward messages in four manners. The relay-forwarding considered are: Amplify and forward (AF), decode and forward (DF), compress and forward (CF), and mixed forward. The last scheme is a combination of CF in one direction and DF in the other. We derive inner and outer bounds to the capacity region of the bi-directional relay channel for three temporal protocols under these four relaying schemes. The first protocol is a two phase protocol where a and b simultaneously transmit during the first phase and the relay r alone transmits during the second. The second protocol considers sequential transmissions from a and b followed by a transmission from the relay while the third protocol is a hybrid of the first two protocols and has four phases. We provide a comprehensive treatment of protocols in Gaussian noise, obtaining their respective achievable rate regions, outer bounds, and their relative performance under different SNR and relay geometries.