• Proceedings of the Korea Crystallographic Association Conference
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• 2002.11a
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• pp.3-3
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• 2002

Many studies on crystal growth mechanisms of the hen egg-white lysozyme protein crystals have mainly performed by optical microscopy and atomic force microscopy (AFM). As results, two types of growth mechanisms, which are a two-dimensional nucleation mechanism and a spiral growth mechanism, were identified. However, there was no direct evidence of grown-in screw dislocations at the spiral sites. We first observed the screw dislocations in tetragonal lysozyme crystals using synchrotron X-ray topography. In addition, to confirm the characteristics of dislocations, we have observed some elastic constants in lysozyme crystals in terms of the sound velocity measurement by pulse echo methods. Tetragonal hen egg-white lysozyme crystals were grown by the concentration gradient method. The crystals were grown in test tubes, with an inner diameter of 8 ㎜ and 80 ㎜ in length, held vertically. The test tubes were kept at 23C for 2 weeks. The maximum size of crystals were 3×3×4 ㎟. The high quality crystals were examined by Laue topography with a water filter using synchrotron radiation. Figure is a X-ray topograph. Several straight screw dislocations were observed. We also determined Burgers vector to be a [110] direction. The measurement of sound velocity was performed by the digital signal processing method. the crystals were placed in stainless steel vessel, which was filled with lysozyme solution used for crystal growth. We observed the longitudinal sound velocity along the [110] direction in the tetragonal is obtained to be 1817 ㎧. Therefore, Young modulus and shear modulus were evaluated to be 2.70 Gpa and 1.02 Gpa, respectively, if we assumed Poisson ratio is 0.33. These results will be discussed at the meeting.

• The Journal of the Acoustical Society of Korea
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• v.16 no.2
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• pp.26-30
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• 1997

In this paper, the thickness measurement method of adhesive layers of multilayers using power cepstrum signal processing technique has been proposed. The peak values for reflected signal from each layer have been separated by power cepstrum technique. Therefore, thickness of adhesive layers have been measured by the intervals of peak signal. In the experiment, the adhesive layers of 0.5mm-0.75mm thickness using epoxy(2-Ton and Plastic Steel Putty(A)) between the aluminum and the brass were formed. The adhesive layer thickness which is calculated with data of reflected signal by ultrasonic pulse-echo method was within error 1.34% of the measured values.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2000.07a
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• pp.651-653
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• 2000

In this study, a distance-measurement system was proposed by using principle of the Michelson Interferometer and a fundamental research was carried out. In case of the rnichelson interferometer, relativity distance was measured by relativity-difference of two course of light. But wavelength of light source were changed in this system in order to use interference phenomenon of michelson interferometer in measuring absolutely distance. Wavelength of input signal were changed periodically and were interfered electrically. So absolute distance can be calculated by using $\Delta\lambda$ and measuring $\eta\Delta$ in electric interference. Nose by a external factor was small in this system because a absolutely distance was measured by phase difference. And a dispersion of noise was small in pulse-echo response because a error was occurred in range of phase difference of signal. Also very wide range can be measured by only single system because informations of distance were acquisited in wavelength level.

• Electrical & Electronic Materials
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• v.8 no.5
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• pp.572-579
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• 1995

Most of conventional ultrasonic transducers are constructed to generate either longitudinal or shear waves, but not both of them. We investigate the mechanism of dual mode transducers that generate both of the longitudinal and shear waves simultaneously with single PZT element. The study is aimed to find the optimally desired cut by examining the anisotropic piezoelectric properties. Theory predicts that a mixed P/S mode transducer can be constructed using a rotated Z-cut of PZT piezoelectric ceramics. We study the performance of a PZT element as a function of its rotation angle so that its efficiency is optimized to excite the two waves as much as equally strong. The results are verified by the waveform in pulse-echo computer simulation and experiments. When the transducer is subjected to impedance analysis, it shows two thickness mode resonances, each of which being a mixed P/S thickness mode. By examining wave speeds on E transmitter delay line receiver setup, it is confirmed that the transducer can transmit and detect both longitudinal and shear wave simultaneously.

• Nuclear Engineering and Technology
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• v.50 no.6
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• pp.890-898
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• 2018

Nondestructive inspection (NDI) is an integral part of structural integrity analyses of dry storage casks that house spent nuclear fuel. One significant concern for the structural integrity is stress corrosion cracking in the heat-affected zone of welds in the stainless steel canister that confines the spent fuel. In situ NDI methodology for detection of stress corrosion cracking is investigated, where the inspection uses a delivery robot because of the presence of the harsh environment and geometric constrains inside the cask protecting the canister. Shear horizontal (SH) guided waves that are sensitive to cracks oriented either perpendicular or parallel to the wave vector are used to locate welds and to detect cracks. SH waves are excited and received by electromagnetic acoustic transducers (EMATs) using noncontact ultrasonic transduction and pulse-echo mode. A laboratory-scale canister mock-up is fabricated and inspected using the proposed methodology to evaluate the ability of EMATs to excite and receive SH waves and to locate welds. The EMAT's capability to detect notches from various distances is evaluated on a plate containing 25%-through-thickness surface-breaking notches. Based on the results of the distances at which notch reflections are detectable, NDI coverage for spent nuclear fuel storage canisters is determined.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2012.05a
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• pp.562-569
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• 2012

The rubber side could be contaminated using the existing pulse echo method because the ultrasonic wave was incident on the rubber side from the interior of the steel motor case, which could lead to the critical disbond defect. To develop the test method which can be replaced the existing method, the ultrasonic wave was incident on steel face of the steel/rubber adhesive test block. Rubber resonance frequencies measured from the steel/rubber adhesive test block were in good agreement with theoretically predicted rubber resonance frequencies. This paper was described about the ultrasonic resonance method to convert the rubber resonance frequency into the rubber thickness.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2012.05a
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• pp.230-237
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• 2012

The ultrasonic resonance method was applied to detect the disbond interface and empty layer between steel and FRP of the exit cone. The ultrasonic resonance method can easily detect the disbond interface and empty layer by amplifying the ultrasonic signal, but pulse echo method is difficult to distinguish adhesive interface from disbond interface or empty layer. The resonance frequency was predicted using the pressure reflection coefficient of 3-layered medium, and measured from ultrasonic signal of the test block using Fast Fourier Transform. The ultrasonic resonance proved that the predicted resonance frequency was in good agreement with the measured resonance frequency.

• Journal of the Korean Society of Propulsion Engineers
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• v.13 no.2
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• pp.9-16
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• 2009

The object of this study is to develop new examination technique for detecting debond in adhesive interface of different kinds of materials. Ultrasonic signal was modeled by theoretically analyzing ultrasonic propagation phenomenon of the adhesive interface and debonding interface. The test method using the phase reversal of the debonding interface applied to the FRP/Rubber test block. Aluminum/Rubber test block with the flat bottom hole was manufactured to evaluate quantitatively the minimum detection ability of defects. The pulse echo reflection method and the phase reversal method were mutually compared and it was estimated that the phase reversal method could detect the debond on the basis of the theoretically predicted ultrasonic signal and ultrasonic test data.

• Proceedings of the KIEE Conference
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• 2007.04a
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• pp.58-60
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• 2007

Magnetic Resonance Imaging(MRI) has become a very widely used medical procedur e. Clo.sed and open systems are typically used with static magnetic fields at or below 2 Tesla. BWhole body SAR(specific absorbsion rate) is the value of SAR averaged over the entire body of the patient over any period of 15 minutes. Head SAR is the value of SAR averaged over the head of the patient for any period of 10 minutes. SAR is a measure of the absorption of electromagnetic energy in the body' (typically in watts per kilogram (W/kg)). The normal operating mode comprises values of head SAR not higher than 3 W/kg. The second level controlled operating mode comprises values higher than 3 W/kg. Current FDA guidance limits the SAR in the whole body. including the head to a range of 1.5 to 4.0 W/kg, depending on the patient's clinical condition. SAR, limit restrictions are incorporated in all MRI systems. and domestic' s guidance limits the SAR in a part body. including the head to 3.2w/kg and less. The purpose of this study is to evaluate on change of head SAR in using MRI pulse sequence and to check if exceed 3.2(w/kg) level in domestic a part exposure through measured head SAR. 23 patient's the average head SAR of pulse sequence is that T2WI sagittal is 0.5375. T2WI axial(FSE) is 0.4817, T1WI axial(SE) is, 0.8179. FLAIR axial is 0.4580. GRE axial is 0.0077, Diffusion is 0.0824w/kg. The head SAR exposed per patient was proved 2.3845w/kg less than the international standard. Coefficient of correlation for the relations body weight and SAR or for the relations ETL(echo train length) and SAR is 1 value. Coefficient of correlation for the relations between TR(time to repeat) and SAR is -0.602 value. so SAR increased relative to weight body and ETL. But the relations between TR and SAR is negative definite.

• Investigative Magnetic Resonance Imaging
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• v.18 no.2
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• pp.151-156
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• 2014

Purpose : Spin-echo (SE) technique is most commonly used pulse sequence for T1-weighted MR imaging. T1-weighted fluid-attenuated inversion recovery (T1FLAIR) is a relatively new pulse sequence and it provides higher tissue contrast between the gray matter (GM) and white matter (WM) of the brain than T1-weighted SE (T1SE) sequence. However, there has been controversy for the evaluation of enhancing brain tumors with T1FLAIR compared to T1SE. The purpose of this study was to compare T1FLAIR and T1SE sequences for the evaluation of enhancing intracranial tumors. Materials and Methods: Fifty-two patients with enhancing brain tumors were evaluated with contrast-enhanced (CE) T1SE and T1FLAIR imaging. Eight quantitative criteria were calculated: lesion-to-WM contrast ratio (CR) and contrast-to-noise ratio (CNR), lesion-to-GM CR and CNR, lesion-to-CSF CR and CNR, and WM-to-GM CR and CNR. For qualitative evaluation, two radiologists assessed lesion conspicuity on CE T1SE and T1FLAIR sequences with three-scale: 1, T1SE superior; 2, sequence equal; T1FLAIR superior. Results: Seventy-nine tumors (31 primaries, 48 metastases) were assessed. For quantitative measurement, the T1FLAIR lesion-to-GM, lesion-to-CSF, WM-to-GM CR and CNR values were comparable and statistically superior to those of the T1SE images (p < 0.001 in all). However, lesion-to-WM CR and CNR were similar on both two sequences without statistically significant difference (p = 0.661, 0.662, respectively). For qualitative evaluation, both radiologists assessed that T1FLAIR images were superior to T1SE images for the evaluation of lesion conspicuity. Conclusion: For the evaluation of enhancing intracranial tumors, T1FLAIR sequence was superior or comparable to T1SE sequence.