• Membrane and Water Treatment
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• 제13권4호
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• pp.201-208
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• 2022

Emulsion Liquid Membrane (ELM) is a prominent technique for the separation of heavy metal ions from wastewater due to the fast extraction and is a single-stage operation of stripping-extraction. The selection of the components (Surfactant and Carrier) of ELM is a very significant step for its preparation. In the ELM technique, the primary water- in-oil (W/O) emulsion is emulsified in water to produce water-in-oil-in-water (W/O/W) emulsion. The water in oil emulsion was prepared by mixing the membrane phase and internal phase. To prepare the membrane phase, the extractant D2EHPA (di-2-ethylhexylphosphoric acid) was used as a mobile carrier, Span-80 as a surfactant, and Paraffin as a diluent. Moreover, the internal (receiving) phase was prepared by dissolving sulphuric acid in water. Di-(2- ethylhexyl) phosphoric acid such as surfactant concentration, carrier concentration, sulphuric acid concentration in the receiving (internal) phase, agitation time (emulsion phase and feed phase), the volume ratio of the membrane phase to the receiving phase, the volume ratio of the external feed phase to the primary water-in-oil emulsion and pH of feed were studied on the percentage extraction of metal ions at 20℃. The results show that it is possible to remove 78% for As(V), 98% for Cd(II), and 99% for Pb(II). Emulsion Liquid Membrane (ELM) is a well-known technique for separating heavy metal ions from wastewater due to the fast extraction and is a single-stage operation of stripping-extraction. The selection of ELM components (Surfactant and Carrier) is a very significant step in its preparation. In the ELM technique, the primary water-in-oil (W/O) emulsion is emulsified to produce water-in-oil-in-water (W/O/W) emulsion. The water in the oil emulsion was prepared by mixing the membrane and internal phases. The extractant D2EHPA (di-2-ethylhexylphosphoric acid) was used as a mobile carrier, Span-80 as a surfactant, and Paraffin as a diluent. Moreover, the internal (receiving) phase was prepared by dissolving sulphuric acid in water. Di-(2-ethylhexyl) phosphoric acid such as surfactant concentration, carrier concentration, sulphuric acid concentration in the receiving (internal) phase, agitation time (emulsion phase and feed phase), the volume ratio of the membrane phase to the receiving phase, the volume ratio of the external feed phase to the primary water-in-oil emulsion and pH of feed were studied on the percentage extraction of metal ions at 20℃. The results show that it is possible to remove 78% for As(V), 98% for Cd(II), and 99% for Pb(II).

• 한국결정학회지
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• 제7권1호
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• pp.73-80
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• 1996

단일 온도대역 수평 Bridgman(1-T HB)법에 의해 2인치 직경의 GaAs 단결정을 성장시키기 위하여 그 장치를 설계·제작하였고, undoped, Si-doped 및 Zn-doped 단결정을 성장하였다. 단결정성의 측면에서 성장횟수별 비로 0.73의 단결정성을 보였고, 격자결함 밀도(etch pit density)는 n-type의 경우 평균 5,000/cm2, p-type의 경우 10,000/cm2, 그리고 undoped의 경우 20,000/cm2 정도를 보였다. 한편 undoped GaAs 단결정의 경우, Hall 측정에 의한 carrier 농도가 ∼1×1016/cm3인 것으로 나타나 기존의 이중 온도대역(2-T : double temperature zone) 또는 삼중 온도대역(3-T : three temperature zone) 수평 Bridgman 방식에 비하여 Si 유입량이 절반 수준인 것으로 측정되었다. 따라서 1-T HB 방식에 의하여 2-T나 3-T HB 방법보다 나은 수율을 갖고 더 순도가 높은 GaAs 단결정을 성장시킬 수 있었다.

• 한국산업정보학회논문지
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• 제25권2호
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• pp.29-37
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• 2020

본 논문에서는 중계기를 활용하여 직교 블록 부호화된 SSB (Single side band) SFBC (Space frequency block code) SC (Single carrier)-FDMA (Frequency division multiple access) 시스템을 제안하고, 수신국과 중계기 간의 SNR (Signal-to-noise power ratio)값을 기준으로 SSB SFBC SC-FDMA 시스템 성능을 측정한다. 잘 알려진 바와 같이. 중계기의 복원된 전송 신호를 이용하여 블록 부호를 생성한 후 수신국으로 재전송함으로써 중계기 기반 전송 시스템의 수신 성능을 향상시킬 수 있다. 본 논문에서는 SSB 시스템의 켤레 복소수 대칭 특성을 이용하여 블록 부호를 구현하도록 제안함으로써 시스템 계산 복잡도는 크게 증가시키지 않으면서 중계기 기반의 SSB SC-FDMA 전송 시스템의 성능을 향상시킬 수 있다. 본 논문에서 제안한 다중 중계기 기반의 SSB SFBC SC-FDMA 전송 시스템의 SNR 성능이 단일 중계기를 활용한 SSB SC-FDMA 전송 시스템보다 10^-2 SER(Symbol error rate) 수준에서 4 dB 이상 향상되는 것을 시뮬레이션을 통해 확인할 수 있다.

• 한국산학기술학회논문지
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• 제20권7호
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• pp.423-429
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• 2019

최근에 초고속 광대역 무선통신 전송 시스템의 수신 성능 개선을 위한 다양한 기술들이 제안되고 있다. 본 논문에서는 주파수 공간 블록 부호화된 단일 측대 파형 SC (Single Carrier) FDMA (Frequency Division Multiple Access) 전송 시스템을 제안한다. 본 논문에서 제안된 주파수 공간 블록 부호화된 단일 측대 파형 SC FDMA 전송 시스템에서는 PAM (Pulse Amplitude Modulation) 신호의 DFT (Discrete Fourier Transform) 확산에 따라 생성되는 켤레 복소수 대칭을 활용하여 주파수 공간 블록 부호를 구현한다. 이를 통해 시스템 계산 복잡도를 크게 증가시키지 않으면서 단일 측대 파형 SC FDMA 전송 시스템의 성능 개선을 위한 송신 다이버시티 이득을 획득할 수 있다. 본 논문에서 제안된 주파수 공간 블록 부호화 단일 측대 파형 SC FDMA 시스템의 신호 대 잡음 비 성능이 단일 안테나 기반의 단일 측대 파형 SC FDMA 시스템보다 $10^{-2}$ 심볼 오류율 수준에서 약 4 dB 이상 개선되는 것을 실험을 통해 확인할 수 있다.

• 대한기계학회논문집
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• 제15권1호
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• pp.252-261
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• 1991

본 연구에서는 2상 횡분류의 평균 유동특성을 비교적 정확히 예측할 수 있는 방법을 제시하는데 있다. 이를 위하여 2상 기체 분류속에 유입되는 자유흐름의 질량 유입을 Keffer와 Baines의 유입함수를 이용하기로 하며, 입자와 기체분류사이의 궤적 이탈을 고려하기로 한다. 이런 모델을 이용하여 2상 횡분류의 분출초기의 입자와 기 체분류의 속도비(particle to gas velocity ratio at the jet exit)가 유동에 미치는 영향을 알아보고자 한다.

• Journal of electromagnetic engineering and science
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• 제9권1호
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• pp.17-24
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• 2009

In recent years, OFDMA(orthogonal frequency division multiple access) and SC-FDMA(Single Carrier Frequency Division Multiple Access) have been widely studied for the uplink of a mobile communication system. In this paper, PAPR(Peak-to-Average Power Ratio) and BER(Bit Error Rate) performance of the OFDMA and SC-FDMA systems are studied in relation to the uplink of a mobile communication system. Three kinds of sub-carrier allocation methods in the OFDMA system and 2 kinds of sub-carrier allocation methods in SC-FDMA system are suggested to compare and improve system performance. Simulation results show that in the OFDMA system, the first sub-band allocation method has better PAPR reduction performance than the other methods. In the SC-FDMA system, the distributed allocation method offers similar P APR, compared with the sub-band allocation method. P APR can be further reduced by adding a spectrum shaping filter with an appropriate roll of factor. Furthermore, it is found that on average, SC-FDMA can reduce the PAPR by more than 5 dB compared to OFDMA, when the total sub-carrier number is 1,024 and the sub-carrier number allocated to each user changes trom 8 to 512. Because of the frequency diversity and low PAPR characteristics, SC-FDMA system of the distributed sub-carrier allocation method can achieve better BER performance than the OFDMA system.

• 한국측량학회:학술대회논문집
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• 한국측량학회 2006년도 춘계학술발표회 논문집
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• pp.39-45
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• 2006

This paper describes an effective and fast algorithm for GPS carrier-phase ambiguity resolution (AR) which can apply for structure monitoring, and a series of simulation analyses have been carried out to demonstrate the performance of the algorithm. The results show that single-frequency AR performance is significantly improved In term of Time-To-Fix-First (TTFF) ambiguity.

• 제어로봇시스템학회논문지
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• 제10권11호
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• pp.1037-1043
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• 2004

In this paper, a new fault detection and isolation algorithm fur inertial sensor system is proposed. To identify the inertial sensor fault, single antenna GPS receiver is used as an effective redundancy source. To use GPS receiver as redundancy for the inertial sensors, the algorithm to estimate the attitude and acceleration using single antenna GPS receiver is adopted. By using Doppler shift of carrier phase signal and kinetic characteristics of aircraft, attitude information of aircraft can be obtained at the coordinated flight condition. Based on this idea, fault diagnosis algorithm for inertial sensors using single antenna GPS based attitude is proposed. For more effective FDI, decision variables considering the aircraft maneuver are proposed. The effectiveness of the proposed algorithm is verified through the numerical simulations.

• 한국광학회:학술대회논문집
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• 한국광학회 2007년도 동계학술발표회 논문집
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• pp.241-242
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• 2007

• 대한전기학회논문지
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• 제32권6호
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• pp.205-210
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• 1983

This paper presents a steady-state computer solution of the fundamental semiconductor one-dimensional transport equations, describing a single (metal-semiconductor) contact device, involving only one type of charge carrier. The computations are conveniently made by the