• Wind and Structures
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• 제13권4호
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• pp.363-374
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• 2010

Appropriate scaling methods for wind tunnel modelling of building internal pressures induced through a dominant opening were investigated. In particular, model cavity volume distortion and geometric scaling of the opening details were studied. It was found that while model volume distortion may be used to scale down buildings for wind tunnel studies on internal pressure, the implementation of the added volume must be done with care so as not to create two cavity resonance systems. Incorrect scaling of opening details was also found to generate incorrect internal pressure characteristics. Furthermore, the effective air slug or jet was found to be longer when the opening was near a floor or sidewall as evidenced by somewhat lower Helmholtz frequencies. It is also shown that tangential flow excitation of Helmholtz resonance for off-centre openings in normal flow is also possible.

• 대한의용생체공학회:학술대회논문집
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• 대한의용생체공학회 1997년도 춘계학술대회
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• pp.484-488
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• 1997

In this Paper, We use Maximum-Intensity Projection(MIP) algorithms. Maximum-Intensity Projection algorithms currently used for construction of magnetic resonance angiograms. The blood flow in a volume of interest is represented by bright intensities in the MR data volume. The flow within the vasculature shows up in the projections plane. By relating the intensities of the pixel to their location in the slice, the total number of pixels considered for the projection plane was reduced, thus saving calculation time. The algorithm was written in visual C++.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2000년도 춘계학술대회논문집
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• pp.633-638
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• 2000

This paper reports an example of flow-induced vibration in a very large plant and the whole procedure of reducing the vibration. During the operation of flue gas desurfurization unit of the thermal power plant, serious vibration occurred at all around the unit. The worst vibration was recorded on the heat exchanger surface, which weighed 180 tones, as 17.8 m/$s^2$ in vibration amplitude at 34Hz. To identify the vibration, frequency analysis on the response vibration, the expected excitation force and the system resonance was executed. This investigation revealed that the cause of the vibration was vortex shedding from the circular pipes in the heat exchanger. Vortices from the pipes excited acoustic resonance in the heat exchanger room, which, in turn, made the structure vibrate. Through inserting the baffles between the pipes, which had an effect of cutting the acoustic wave at resonance frequency, the vibration was eliminated dramatically.

• Investigative Magnetic Resonance Imaging
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• 제21권2호
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• pp.106-108
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• 2017

The perfusion change in acute symptomatic hypoglycemic encephalopathy (ASHE) is not well known. We present the perfusion-weighted imaging of a patient with ASHE. The area of diffusion-weighted imaging abnormalities and adjacent normal-appearing white matter showed increased cerebral blood volume and flow, and shortening of time-to-peak.

• Investigative Magnetic Resonance Imaging
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• 제2권1호
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• pp.83-88
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• 1998

목적 : 저자는 생체의 방추형 동맥류를 단순화 시킨 비박동성 방추형 유체 모형을 이용하여 방추형 유체의 자기공명 혈과조영술의 신호강도를 분석하고 컴퓨터를 이용한 유체의 모의 실험과 비교하여 임상적으로 방추형 동맥류의 자기공명 혈관조영술의 신호강도의 해석에 도움이 되는 자료를 얻고자 하였다. 대상 및 방법 : 증류수를 유체로 이용한 비박동성 방추형 동맥류 유체 모형에서 3D TOF MRA를 촬영하여 영상을 얻고 각 영상에서 유체의 평균 신호강도를 측정하였으며, 컴퓨터에서 동일 형태의 방추형 유체를 모의 실험하여 유속의 분포, 방향을 얻어 비교 분석하였다. 결과 : 자기공명 혈관조영술에서 방추형 유체의 유입부와 유출부의 신호강도는 균질한 신호 강도를 보였으나, 팽대부에서는 비균질한 신호강도를 보였으며, 유출부로의 이행부위에서는 중심부 저신호강도, 주변부 고신호강도의 과녁 모야으로 보였다. 방추형 유체의 평균 신호강도는 팽대부에서 서서히 감소하다가 유출부로의 이행 부위에서 급속히 감소하였다가 회복되어 유출부에서는 유입부와 같은 정도의 신호강도를 보였다. 컴퓨터를 이용한 모의실험에서 유입부와 유출부에서는 층류의 소견이었으며, 유입부 이행부위 빛 팽대부에서는 유속의 감소와 주변부로의 방향변화가 있었다. 유출부로의 이행부위에서는 유속이 급속히 회복되었고, 중심부분으로의 방향 변화가 현저하였다. 결론 : 방추형 유체는 자기공명 혈관조영술에서 유출부로의 이행부위에서 신호소실과 과녁모양을 보이며, 이는 급격한 유속증가 및 방향 변화에 따른 위상 전위 때문이다.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2006년도 제26회 춘계학술대회논문집
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• pp.337-340
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• 2006

본 논문은 초음속 제트에서 발생하는 천음속 공명현상에 대한 실험적 연구를 기술한다. 초음속 노즐이 매우 낮은 압력비에서 작동될 때, 노즐내의 확대부에서 충격파가 발생한다. 천음속 공명현상은 이러한 충격파의 불안정한 진동에 의한 강한 음파의 발생에 기인한다. 제트 유동장은 쉴리렌 광학장치를 이용하여 가시화 하였다. 제트유동의 천음속 공명현상을 조사하기 위하여, 음향측정을 수행하였다. 천음속 공명 현상의 음향특성은 스크리치 톤과 비교하였다. 본 연구에서 얻어진 결과에 의하면, 스크리치 톤의 주파수와는 달리, 천음속 톤의 주파수는 노즐 압력비가 증가할수록 증가한다.

• Investigative Magnetic Resonance Imaging
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• 제4권1호
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• pp.20-26
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• 2000

Gradient moment nulling techniques require the introduction of an additional gradient on each axis for each order of motion correction to be applied. The additional gradients introduce new constraints on the sequence design and increase the demands on the gradient system. The purpose of this paper is to demonstrate techniques for optimization of gradient echo gradient moment nulling sequences within the constraints of the gradient hardware. Flow compensated pulse sequences were designed and implemented on a clinical magnetic resonance imaging system. The design of the gradient moment nulling sequences requires the solution of a linear system of equations. A Mathematica package was developed that interactively solves the gradient moment nulling problem. The package allows the physicist to specify the desired order of motion compensation and the duration of the gradients in the sequence with different gradient envelopes. The gradient echo sequences with first, second, and third order motion compensation were implemented with minimum echo time. The sequences were optimized to take full advantage of the capabilities of the gradient hardware. The sequences were used to generate images of phantoms and human brains. The optimized sequences were found to have better motion compensation than comparable standard sequences.

• 대한화학회지
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• 제15권4호
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• pp.177-181
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• 1971

Free radicals of lysozyme produced by $Ti-H_2O_2$ system were studied in aqueous solution at room temperature using ESR with a continuous flow-mixing. The spectra, each consisting of a doublet with 5.5 G splitting and a broad resonance covering 80 G splitting are closely similar in shape to that for solid irradiated in vacuum at $77^{\circ}K$ and observed at room temperature immediately on warming. The result is assumed to indicate that the secondary protein radical components formed within 0.01 second, dead time of the mixing chamber, and initiated by hydrogen atom abstraction at ${\alpha}$-carbon atom of peptide chain in liquid solution at room temperature are identical to those resulting from the initial formation of a mixture of positive holes and negative ions by ionization processes as well as radical fragments by the rupture of chemical bonds in the solid during similar time at the same temperature. A broad resonance is observed with considerable amplitude on the high field side of the doublet, which is quite dissimilar to the spectra of irradiated solid lysozyme. This resonance was tentatively attributed to the polypeptide free radical in which unpaired electrons are localized on side chain.

• 대한기계학회논문집B
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• 제25권9호
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• pp.1272-1280
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• 2001

An experimental study has been conducted to elucidate the resonance of natural convection in a side-heated square enclosure having a mechanically oscillating bottom wall. Under consideration is the impact of the imposed oscillating frequency, amplitude and the system Rayleigh number on the fluctuation of air temperatures. The experimental results show that the magnitude of the fluctuation of air temperature is substantially augmented at a specific forcing frequency of the oscillating bottom wall. The resonant frequency is increased with the increase of the Rayleigh number and it is little affected by the amplitude of the oscillating wall. It is also found that the resonant frequency is relevant to the Brunt- V$\"{a}$iS$\"{a}$l$\"{a}$ frequency which represents the stratification degree of the system.

• Nuclear Engineering and Technology
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• 제51권4호
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• pp.1017-1023
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• 2019

The increase of the alternate current frequency results in increased rotational speed of the electrical motors and connected pumps. The consequence for the reactor coolant pumps is increased flow in primary coolant system. Increase of the current frequency can be initiated by the subsynchronous resonance phenomenon (SSR). This paper analyses the implications of the SSR and consequential increase of the frequency on the nuclear power plant safety. The Simulink $MATLAB^{(R)}$ model of the steam turbine and governor system and RELAP5 computer code of the pressurized water reactor are used in the analysis. The SSR results in fast increase of reactor coolant pumps speed and flow in the primary coolant system. The turbine trip value is reached in short time following SSR. The increase of flow of reactor coolant pumps results in increase of heat removal from reactor core. This results in positive reactivity insertion with reactor power increase of 0.5% before reactor trip is initiated by the turbine trip. The main parameters of the plant did not exceed the values of reactor trip set points. The pressure drop over reactor core is small discarding the possibility of core barrel lift.