• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2001년도 춘계학술대회논문집
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• pp.465-472
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• 2001

This paper describes the characteristics of wind induced noise from high-voltage overhead transmission facilities which include transmission lines. insulator strings. and aviation beacon spheres installed on the overhead ground wires. High-voltage overhead transmission lines generate an audible wind noise due to the alternate shedding of wind-induced vortices. The frequency spectrum from the insulator strings reveals its resonance peak. This resonance sound mechanism has been supposed the self-excitation phenomenon of the resonance and the velocity fluctuation. The booming noises from the aviation beacon spheres are detected and analysed.

• Journal of applied mathematics & informatics
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• 제27권5_6호
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• pp.1257-1264
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• 2009

In this paper, we study the existence of solutions for three-point boundary value problem at resonance by using the continuation theorem of Mawhin. Some known results are improved.

• Investigative Magnetic Resonance Imaging
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• 제23권2호
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• pp.157-161
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• 2019

In this study, we report arterial spin labelling perfusion, proton MR spectroscopy and susceptibility-weighted MR findings of acute necrotizing encephalopathy in a child with rotavirus infection.

• 한국연소학회:학술대회논문집
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• 한국연소학회 2006년도 제33회 KOSCO SYMPOSIUM 논문집
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• pp.86-94
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• 2006

This paper investigates the effects of acoustic forcing on NOx emissions and mixing process in the near field region of turbulent hydrogen nonpremixed flames. The resonance frequency was selected to force the coaxial air jet acoustically, because the resonance frequency is effective to amplify the forcing amplitude and reduce NOx emissions. When the resonance frequency is acoustically excited, a streamwise vortex is formed in the mixing layer between the coaxial air jet and coflowing air. As the vortex develops downstream, it entrains both ambient air and combustion products into the coaxial air jet to mix well. In addition, the strong vortex pulls the flame surface toward the coaxial air jet, causing intense chemical reaction. Acoustic excitation also causes velocity fluctuations of coaxial air jet as well as fuel jet but, the maximum value of centerline fuel velocity fluctuation occurs at the different phases of $\Phi$=$180^{\circ}$ for nonreacting case and $\Phi$=$0^{\circ}$ for reacting case. Since acoustic excitation enhances the mixing rate of fuel and air, the line of the stoichiometric mixture fraction becomes narrow. Finally, acoustic forcing at the resonance frequency reduces the normalized flame length by 15 % and EINOx by 25 %, compared to the flame without acoustic excitation.

• Journal of Power Electronics
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• 제15권5호
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• pp.1409-1420
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• 2015

In this paper, an algorithm using two bi-quad filters to suppress the wide-band resonance for PMSM servo systems is proposed. This algorithm is based on the double bi-quad filters structure, so it is named, "double bi-quad filter." The conventional single bi-quad filter method cannot suppress unexpected mechanical terms, which may lead to oscillations on the load side. A double bi-quad filter structure, which can cancel the effects of compliant coupling and suppress wide-band resonance, is realized by inserting a virtual filter after the motor speed output. In practical implementation, the proposed control structure is composed of two bi-quad filters on both the forward and feedback paths of the speed control loop. Both of them collectively complete the wide-band resonance suppression, and the filter on the feedback path can solve the oscillation on the load side. Meanwhile, with this approach, in certain cases, the servo system can be more robust than with the single bi-quad filter method. A step by step design procedure is provided for the proposed algorithm. Finally, its advantages are verified by theoretical analysis and experimental results.

• BMB Reports
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• 제38권5호
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• pp.591-594
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• 2005

One of the small proteins from Helicobacter pylori, HP1242, was investigated by the solution nuclear magnetic resonance (NMR) spectroscopy. HP1242 is known as a 76-residue conserved hypothetical protein and its function cannot be identified based on sequence homology. Here, the results of the backbone $^1H$, $^{15}N$, and $^{13}C$ resonance assignments of the HP1242 are reported using double- and triple-resonance techniques. About 95% of all of the $^1HN$, $^{15}N$, $^{13}CO$, $^{13}C{\alpha}$, and $^{13}C{\beta}$ resonances that cover 75 non- Proline residues of the 76 residues are clarified through sequential- and specific- assignments. In addition, three helical regions were clearly identified on the basis of the resonance assignments.

• 전력전자학회논문지
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• 제21권2호
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• pp.168-174
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• 2016

In this paper, current control using PI controller in the synchronous reference frame is analyzed through the relationship among bandwidth, resonance frequency, and sampling frequency in the grid-connected inverter with LCL filter. Stability is investigated by using bode plot in frequency domain and root locus in discrete domain. The feedback variable is the grid current, which is regulated by the PI controller in the synchronous reference frame. System delay is modeled as 1.5Ts, which contains computational and PWM modulator delay. Two resonance frequencies are given at 815 Hz and 3.16 kHz from LCL filter parameters. Sufficient phase and gain margins can be obtained to guarantee stable current control, in case that resonance frequency is above one-sixth of the sampling frequency. Unstable current control is performed when resonance frequency is below one-sixth of the sampling frequency. Analysis results of stability from frequency response and discrete response is the same regardless of resonance frequency. Finally, stability of current control based on theoretical analysis is clearly verified through simulation and experiment in grid-connected inverters with LCL filter.

• 대한전자공학회논문지TC
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• 제45권8호
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• pp.41-46
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• 2008

본 논문에서는 금속 평행평판에 일반 유전체 기판인 FR4 대신 Metamaterial을 삽입할 경우에 발생할 수 있는 전자기 공진 특성과 임피던스 변화에 대하여 연구하였다. 기판을 DPS는 물론 Metamateral인 ENG, MNG, DNG 형으로 나눠, 투자율 함수를 위해 SRR 형식의 Lorentz 모델과, 유전율 함수를 위해 금속선 주기 배열 형식의 Drude 모델을 정확한 계산이 가능한 Full-wave 모드해석기법에 반영하여 평행평판이 가지는 공진모드들과 임피던스의 변화양상을 관측하였다. 관측을 통해 전자장비의 품질을 저하시키는 평행평판의 불요공진모드 억제를 위한 기판설계 가이드라인을 수립할 수 있었다.

• 한국자기공명학회논문지
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• 제10권2호
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• pp.197-202
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• 2006

[ $^{11}B$ ] nuclear magnetic resonance (NMR) measurements were performed on the single crystals of $TbB_4$ to investigate local electronic structure and 4f spin dynamics. $^{11}B$ NMR spectrum, Knight shift, spin-lattice and spin-spin relaxation rates were measured down to 4K at 8T. $^{11}B$ NMR shift and linewidth are huge and strongly temperature dependent due to the 4f moments. In addition, both are proportional to magnetic susceptibility, indicating that the hyperfine field at the boron site originates from the 4f spins of Tb. Below $T_N$, the single broad resonance peak of $^{11}B$ NMR splits into several peaks reflecting the local magnetic fields due to antiferromagnetic spin arrangements. The longitudinal and the transverse relaxation rates, $1/T_1\;and\;1/T_2$, independent of temperature above $T_N$, decreases tremendously confirming huge suppression of spin fluctuation below $T_N$.

• Investigative Magnetic Resonance Imaging
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• 제25권4호
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• pp.229-251
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• 2021

Arteriosclerosis is the leading cause of stroke, with a fatality rate surpassing that of ischemic heart disease. High-resolution vessel wall magnetic resonance imaging is generally recognized as a non-invasive and panoramic method for the evaluation of arterial plaque; however, this method requires improved signal-to-noise ratio and scanning speed. Recent advances in high-density head and neck coil arrays are characterized by broad coverage, multiple channels, and closefitting designs. This review analyzes fast magnetic resonance imaging from the perspective of accelerated algorithms for vessel wall imaging and demonstrates the need for effective algorithms for signal acquisition using advanced radiofrequency system. We summarize different phased-array structures under various experimental objectives and equipment conditions, introduce current research results, and propose prospective research studies in the future.