• 한국분말재료학회지
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• 제20권3호
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• pp.174-179
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• 2013

The study on the fabrication of iron powder from forging scales using hydrogen gas has been conducted on the effect of hydrogen partial pressure, temperature, and reactive time. The mechanism for the reduction of iron oxides was proposed with various steps, and it was found that reduction pattern might be different depending on temperature. The iron content in the scale and reduction ratio of oxygen were both increased with increasing reactive time at 0.1atm of hydrogen partial pressure. On the other hand, for over 30 minutes at 0.5 atm of hydrogen partial pressure, the values were found to be almost same. In the long run, iron metallic powder was obtained with over 90% of iron content and an average size of its powder was observed to be about $100{\mu}m$.

• 한국가시화정보학회지
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• 제16권3호
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• pp.26-34
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• 2018

In the present study, an experimental assessment has been made of the drag reducing efficiency of the outer-layer vertical blades, which were first devised by Hutchins(1). A detailed flow field measurements have been performed using 2-D time resolved PIV with a view to enabling the identification of drag reduction mechanism. In addition, an experimental investigation has been made of the applicability of outer-layer vertical blades to real ship model. The arrays of outer-layer vertical blades have been installed onto the flat side and flat bottom of a 300k KVLCC model. A series of towing tank test has been carried out to investigate resistance (CTM) reduction efficiency with various geometric parameters and installed places of blades. The installation of vertical blades led to the CTM reduction of 1.44~3.17% near the service speed.

• 대한전자공학회논문지TC
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• 제46권6호
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• pp.86-93
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• 2009

본 논문에서는 다중 사용자 다중 입출력 시스템을 위해 격자 감소 기법 기반 전부호화(preceding) 기법에 대해 연구하였다. 송신 단에서 완벽한 채널 상태 정보(CSI : Channel state information)를 이용할 수 있을 때, 벡터 분산 기법(VP : vector perturbation)은 큰 채널 전송 용량(sum capacity)을 얻을 수 있으면서 간단한 수신기로 구현될 수 있다. 그러나 VP 기법의 부호화는 비결정적 난해(NP-hard : nondeterministic polynomial time-hard) 문제이다. 이에 반해 격자 감소 기법 기반의 VP 기법은 부호화 복잡도를 크게 줄일 수 있다. 본 논문에서는 기본 및 이중 베이시스의 동시 감소를 통한 Seysen 격자 감소 기반 VP 기법(VP-SLR : vector perturbation with Seysen's lattice reduction)을 제안한다. 모의실험 결과는 LLL 기반 VP기법(VP-LLL : vector perturbation with Lenstra-Lenstra-Lovasz lattice reduction)에 비해 제안된 VP-SLR 기법이 더 낮은 비트 오류율(BER : bit error rate)과 더 큰 전송 용량을 가짐을 보여준다.

• 청정기술
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• 제21권2호
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• pp.96-101
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• 2015

수소를 환원제로 사용한 산화철의 유동 환원에서, 환원율에 대한 다양한 공정 변수를 통해 산화철의 하나인 적철광의 환원 거동을 면밀히 관찰하였다. 본 연구를 위해 특별히 설계된 실험실 규모의 유동층 장치에서 목적으로 하는 환원 특성에 대한 가스 속도, 환원 시간 및 온도의 최적 값을 평가 하였다. 최적의 환원율을 나타낸 온도는 750 ℃, 환원 시간은 30분이며 이들을 다음의 시험을 위한 시작점으로 매개 변수 값을 설정 하였다. 가장 높은 관심을 갖는 변수들 중 하나는 가스의 소비 원단 위로, 이는 최적의 조건에서 산화철 1톤을 기준하여 90% 이상의 환원율을 달성하기 위해 요구되는 가스의 양을 말한다. 이 매개 변수는 실험실 수준 장치의 스케일 엎에 있어서 중요한 인자이며, 본 연구를 통해 1,500 Nm³/ton-ore가 산화철이 가장 높은 환원율을 갖기 위한 최적의 가스 소비 원단위 임을 확인하였다.

• Archives of Plastic Surgery
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• 제34권4호
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• pp.461-465
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• 2007

Purpose: Nasal bone fracture may be the most common fracture among facial trauma. However, diagnosis and treatment tend to be overlooked while the reduction and maintenance of fragments remain complicated. Thus, the results are plagued with high rate of nasal deformity which leads cosmetic and functional discomfort. We took advantage of the fact that the nasal bone is one of the thinnest facial bone while at the same time being located close to the skin and utilized ultrasound in performing reduction of nasal bone. Methods:This method was performed on 25 patients with nasal bone fracture. The CL 15-7 linear array transducer (10-15MHz) ultrasound which provides a total of 7 views (3 axial views and 4 transverse views) of the elevator under the bony fragments was enough for the surgeon to accurately perform the reduction. Results: In our class, an accurate and precise reduction has been made possible by real time images before, during, and after the procedure with the help of ultrasound while reducing the exposure to radiation. Conclusion: Compared to previous methods, satisfaction of patients has increased in the nasal tip, minimal fracture of the side wall and secondary reduction cases. Therefore, the incorporation of ultrasound in the closed reduction of nasal bone may prove to be a useful method.

• 한국자동차공학회논문집
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• 제7권7호
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• pp.221-228
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• 1999

A full-time four wheel drive vehicle is driven literally full time by the front and the rear wheels. Front and rear drive shafts are rotated rapidly in the extremely torsional state, which can cause various vibration and noise problems. The purpose of this study is to reduce the vibration and the noise of the full -time four wheel drive vehicle. In this paper, both the causes and the methods for reduction of torsional vibration are suggested. For this study, the characteristics of the torsional vibration are analyzed by free and forced torsional vibration simulation. And this paper described the influence upon the torsional vibration with emphasis shafting system. The validity of simulation models is checked by the field test. The forced vibration simulation with the variations of shaft design factors are performed by the checked models. According to the simulation , the resonance region shifts and the torque fluctuation varies in the system,. Finally, the methods and the effects for the torsional vibration reduction in driveline are proposed.

• 전력전자학회논문지
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• 제20권3호
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• pp.201-208
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• 2015

The effects of dead-time and offset error, which cause output current distortion in single-phase grid-connected inverters are investigated this paper. Offset error is typically generated by measuring phase current, including the voltage unbalance of analog devices and non-ideal characteristics in current measurement paths. Dead-time inevitably occurs during generation of the gate signal for controlling power semiconductor switches. Hence, the performance of the grid-connected inverter is significantly degraded because of the current ripples. The current and voltage, including ripple components on the synchronous reference frame and stationary reference frame, are analyzed in detail. An algorithm, which has the proportional resonant controller, is also proposed to reduce current ripple components in the synchronous PI current regulator. As a result, computational complexity of the proposed algorithm is greatly simplified, and the magnitude of the current ripples is significantly decreased. The simulation and experimental results are presented to verify the usefulness of the proposed current ripple reduction algorithm.

• Bulletin of the Korean Chemical Society
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• 제28권9호
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• pp.1523-1530
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• 2007

The first reduction peak of the cyclic voltammogram (CV) for sulfur reduction in dimethyl sulfoxide has been studied using time resolved Fourier transform electrochemical impedance spectroscopic (FTEIS) analysis of small potential step chronoamperometric currents. The FTEIS analysis results reveal that the impedance signals obtained during short potential steps can be resolved into electron transfer reactions of two different time constants in a high frequency region. The FTEIS method provides snap shots of impedance profiles during an earlier phase of the reaction, leading to time resolved EIS measurements. Our results obtained by the FTEIS analysis are consistent with a series of electron transfer and chemical equilibrium steps of a complex reaction, making up an ECE (electrochemical-chemical-electrochemical) mechanism postulated from the results of computer simulation.

• 대한공간정보학회지
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• 제24권2호
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• pp.37-46
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• 2016

The difference between definition time of GPS (Global Positioning System) position data and actual display time of car positions on a map could reduce the accuracy of car positions displayed in PND (Portable Navigation Device)-type CNS (Car Navigation System). Due to the time difference, the position of the car displayed on the map is not its current position, so an improved method to fix these problems is required. It is expected that a method that uses predicted future positionsto compensate for the delay caused by processing and display of the received GPS signals could mitigate these problems. Therefore, in this study an analysis was conducted to correct late processing problems of map positions by mapmatching using a Kalman filter with only GPS position data and a RRF (Road Reduction Filter) technique in a light-weight CNS. The effects on routing services are examined by analyzing differences that are decomposed into along and across the road elements relative to the direction of advancing car. The results indicate that it is possible to improve the positional accuracy in the along-the-road direction of a light-weight CNS device that uses only GPS position data, by applying a Kalman filter and RRF.

• 한국세라믹학회지
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• 제43권9호
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• pp.582-587
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• 2006

Decomposition behavior of $ferro-Si_3N_4$was investigated with varying temperature and holding time in mud components for high temperature refractory applications. Porosities gradually increased with increasing temperature and holding time due to the carbothermal reduction of $Si_3N_4\;and\;SiO_2$. Silicon monoxide (SiO) as a intermediate resulted from evaporation of $Si_3N_4\;and\;SiO_2$ reacted with C sources to generate needle-like ${\beta}-SiC$ and Fe in $Si_3N_4$ acted as a catalyst in order to enhance growth of SiC grain with the preferred orientation. SiC generation yield increased with increasing holding time, all of the $Si_3N_4\;and\;SiO_2$ affected on SiC formation up to 2h. However, SiC generation was only dependent on residual $SiO_2$ over 2h, because the carbothermal reduction reaction of $Si_3N_4$ was no longer possible at that time.