• 한국통신학회논문지
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• 제35권1C호
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• pp.123-129
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• 2010

본 논문에서는 안정된 다중경로환경에서 동기 (coherent) 단일 및 이중 이른-늦은 상관차 판별기로 범역위성항법시스템 민간용 신호의 부호동기를 결정했을 때 잔존하는 오차인 부호동기추적편이를 분석한다. 이를 위해 중심 주파수 1575.42MHz의 대표적인 위성항법신호대역에서 이진위상천이 및 이진천이반송파 변조된 민간용신호 및 그 처리과정을 모형화하고, 이 모형을 바탕으로 다양한 경우에 대해 각 부호동기추적편이를 비교 분석한다.

• 한국해양공학회:학술대회논문집
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• 한국해양공학회 2003년도 춘계학술대회 논문집
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• pp.109-114
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• 2003

Wireless communication systems are inevitable for efficient underwater activities. Because of the poor propagation characteristics of light and electromagnetic waves, acoustic waves are generally used for the underwater wireless communication. Although there are many kinds of information type, visual images take an essential role especially for search and identification activities. For this reason, we developed an acoustic-based underwater image transmission system under a dual use technology project supported by MOCIE (Ministry of Commerce, Industry and Energy). For the application to complicated and time-varying underwater environments all-digital transmitter and receiver systems are investigated. Array acoustic transducers are used at the receiver, which have the center frequency of 32kHz and the bandwidth of 4kHz. To improve transmission speed and quality, various algorithms and systems are used. The system design techniques will be discussed in detail including image compression/ decompression system, adaptive beam- forming, fast RLS adaptive equalizer, ${\partial}/4$ QPSK (Quadrilateral Phase Shift Keying) modulator/demodulator, and convolution coding/ Viterbi. Decoding.

• Journal of Communications and Networks
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• 제14권5호
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• pp.501-509
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• 2012

This paper proposes a joint timing synchronization, channel estimation, and data detection for the impulse radio ultra-wideband systems. The proposed timing synchronizer consists of coarse and fine timing estimation. The synchronizer discovers synchronization points in two stages and performs adaptive threshold based on the maximum pulse averaging and maximum (MAX-PA) method for more precise synchronization. Then, iterative channel estimation is performed based on the discovered synchronization points, and data are detected using the selective rake (S-RAKE) detector employing maximal ratio combining. The proposed synchronizer produces two signals-the start signal for channel estimation and the start signal for start frame delimiter (SFD) detection that detects the packet synchronization signal. With the proposed synchronization, channel estimation, and SFD detection, an S-RAKE receiver with binary pulse position modulation binary phase-shift keying modulation was constructed. In addition, an IEEE 802.15.4a channel model was used for performance comparison. The comparison results show that the constructed receiver yields high performance close to perfect synchronization.

• 한국소음진동공학회논문집
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• 제13권6호
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• pp.460-466
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• 2003

The aeroacoustic characteristics and noise reduction method of a centrifugal fan for a bagless vacuum cleaner were studied. The major noise source of vacuum cleaner is the centrifugal fan. The impeller of the fan rotates over 30000 rpm and generates very high-level piercing noise. It was found that the dominant noise source of the fan is generated from the aerodynamic interaction between the highly rotating impeller and stationary diffuser. In order to reduce the high tonal sound generated from the aerodynamic interaction between the impeller and diffuser, tapered impeller was carefully designed and tested. The trailing edge of the tapered impeller was inclined and this reduces the flow interactions between the rotating impeller and the stationary diffuser because of some phase shift. The static efficiency of the new impeller is slightly lower than the conventional one. The overall SPL is reduced about 3.6 dBA. The SPL of blade passing frequency(BPF) is reduced about 6 dBA and the $2^{nd}$ BPF is reduced about 20 dBA. The vacuum cleaner with the tapered impeller has lower noise level than that of the previous impeller and the strong tonal sound was dramatically reduced.

• 반도체디스플레이기술학회지
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• 제16권4호
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• pp.11-15
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• 2017

Red phosphors, $Sr_2Si_5N_8:Eu^{2+}$, were synthesized as a single-phase crystal structure by optimizing carbon and $Eu^{2+}$ contents in a carbothermal reduction nitridation method. With increasing $Eu^{2+}$ contents, the photoluminescence spectra were red-shifted from 600 nm peak for 1 mol% for to 700 nm for 7 mol%. It was suggested that this red shift is attributed to the energy transfer from one low-energy sited $Eu^{2+}$ (1) to other high-energy sited $Eu^{2+}$ (2). Finally, the best red sample (620 nm emission peak and 80 nm half width for 3 mole% of $Eu^{2+}$) was packaged on a Blue LED together with two additional green and yellow phosphors, the fabricated White LED showed a high color-rendering index of 90 and white color coordinates of x= 0.321 and y = 0.305.

• Journal of Advanced Marine Engineering and Technology
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• 제23권6호
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• pp.761-769
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• 1999

In this paper the effect of aging heat treatment to the Corrosion behavior for the Nimonic 80A superalloy was studied by AC Impedance methods. Tested solution was 3.5% with tempera-ture $25^{\circ}C$ Electro-chemical corrosion test were carried out for the Nimonic 80A super-alloy which solution heat treated at $1080^{\circ}C$ for 8 hours followed by aging heat treated at $650^{\circ}C,\;700^{\circ}C,\;750^{\circ}C\;800^{\circ}C$ and $850^{\circ}C$ with 16hours under vacuum environment. The obtained results were as follows; 1. Base metal and solution-treated materials were exhibited similar corrosion tendency as Ran-dle equivalent cell. The value of passive film resistance was 579 ohms for the base metal and 124,770 ohms for the solutionized metal such a difference was arose by the ${{\gamma}_^'}$ precipitate on the metal surface during heat treatment. 2. The measure value of $R_p$ for heat-treated at $650^{\circ}C,\;700^{\circ}C,\;800^{\circ}C$and $850^{\circ}C$ were 97,943, 93, 111, 26,961, 15,798 and 11,780ohm respectively. Which indicated that the passive film resistance Rp was reduced as aging temperature increased due to the growth of grain size and sensitization at the grain boundary. 3. The similar tendency was exhibited for corrosion behavior of the electro-chemical corrosion polarization method and AC impedance method and confirmed that AC impedance method was useful tool for corrosion research.

• 한국전자파학회논문지
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• 제30권1호
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• pp.23-27
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• 2019

본 논문에서는 비 침습적, 비 파괴적으로 샘플의 단층구조와 단층의 미세진동을 실시간으로 동시에 영상화하는 마이크로 바이브로 토모그라피(micro vibro tomography: MVT) 시스템 개발 및 미세진동 측정 방법을 제안한다. 제안한 방법은 광 간섭 단층촬영기술(optical coherence tomography: OCT)을 기반으로 하여, 샘플의 위상변이를 이용해 마이크로 단위의 움직임을 측정하는 알고리즘을 적용한 방법이다. 본 실험에서는 고막을 모방한 라텍스 샘플에 2~5 kHz 주파수의 음파를 인가시키고, 음파에 의한 샘플의 미세진동을 제안한 MVT 시스템을 이용하여 측정하였다. 그 결과, 고막 모방 샘플의 단층구조와 미세진동을 동시에 영상화할 수 있었고, 표면부의 미세진동을 MVT 표면 진동 이미지로 프로젝팅하여 고막 모방 샘플의 전체적인 진동 형태를 관찰할 수 있었다.

• Journal of Microbiology and Biotechnology
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• 제11권1호
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• pp.40-49
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• 2001

The present work presents a novel approach for the dynamic quantification of respiration rates on a small scale by using lysine-producing Corynebacterium glutamicum ATCC 21253. Cells sampeld from batch cultures at different times were incubated ina 12-ml scale bioreactor equipped with a membrane mass spectrometer. Under dynamic conditions, gas exchange across the gas-liquid phase, specific respiration rates, and RQ values were precisely measured. For this purpose, suitable mass balances were formulated. The transport coefficients for $O_2$ and $CO_2$, crucial for calculating the respiration activity, were determined as $k_La_{O2}=9.18h^{-1}$ and $k_La_{CO2}=5.10h^{-1}$ at 400 rpm. The application of the proposed method to batch cultures of C. glutamicum ATCC 21253 revealed the maximum specific respiration rates of $q_{O2}=8.4\;mmol\;g^{-1}h^{-1}\;and\;q_{CO2}=8.7\;mmol\;g^{-1}h^{-1}$ in the middle of the exponential growth phase after 5 h of cultivation. When the cells changed from growth to lysine production due to the depletion of the essential amino acids theonine, methionine, and leucine, $q_{O2}\;and\;q_{CO2}$ decreased significantly and RQ increased. The respiration data exhibited an excellent agreement with previous cultivations of the strain [13]. This confirms the potential of the developed approach to realistically reflect the metabolic activities of cells at their point of sampling. The short-term influence of added threonine, methionine, and leucine was highest during the shift from growth to lysine production, where $q_{O2}\;and\;q_{CO2}$ increased 50% within one minute after the pulse addition of these compounds. Non-growing, yet lysine-producing cells taken from the end of the batch cultivation revealed no metabolic stimulation with the addition of threonine, methionine, and leucine.

• 대한통합의학회지
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• 제4권3호
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• pp.109-119
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• 2016

Purpose : The purpose of this research is to find clinical effects of functional resistance training using weighted vest on gross motor and balance abilities of children with dyskinetic cerebral palsy. Methods : This study selects 3 subjects for 8~12 years old who were diagnosed with children with dyskinetic cerebral palsy. The Design is ABA design of single-subject research design. Baseline(A) and TypeII Baseline(A : 12weeks) phases were received with NDT treatment, Intervention(B : 12weeks) phase provided with 40 minute functional resistance training using weighted vest in a session twice a week. In order to analyze the measure results of gross motor function and performance, balance abilities in children dyskinetic cerebral palsy during baseline, intervention and typeII baseline phase. Result : A statistically significant differences in the total GMFM including walking/running/jumping during baseline, intervention, typeII baseline, but no significant differences in the lying/rolling, sitting, crawling/kneeling and standing. A statistically significant differences in the total GMPM including dissociated movement, coordination, weight shift, stability during baseline, intervention, typeII baseline, but no significant differences in the body alignment domains. A statistically significant differences in the length and surface area ellipse of center of pressure during baseline, intervention, typeII baseline. Conclusion : The intervention method to facilitate multi-joint and closed kinematic chain movement equipped weighted vest applied functional resistance training on children with dyskinetic cerebral palsy effectively improve on gross motor function and performance, balance abilities.

• 한국자기학회지
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• 제19권6호
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• pp.191-196
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• 2009

비대칭 거대 자기임피던스 효과를 보이는 자기장 열처리된 CoFeSiB 비정질 리본에서 자기 바이어스 현상을 MOKE 방법을 이용하여 연구하였다. 열처리 과정에서 리본의 양 표면에 형성된 경자성 결정층이 내부 연자성 비정질 상의 자화특성에 미치는 영향을 조사하기 위해 열처리 후 화학적 에칭에 의해 한쪽 및 양쪽 표면의 결정층을 깎아낸 시편들을 준비하고 각 시편에 대해 비정질 상의 자화곡선을 MOKE 방법으로 측정하였다. 열처리 과정에서 표면에 형성된 경자성층이 내부의 비정질 연자성 상에 바이어스 자기장을 작용하고 있다는 것과 바이어스 자기장의 방향이 경자성층의 자화방향에 반대 방향임을 자기이력곡선의 이동을 통해 확인하였다.