• Investigative Magnetic Resonance Imaging
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• v.6 no.2
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• pp.120-128
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• 2002

Purpose : To demonstrate that the relaxographic method provides additional information such as the distribution of relaxation times and water content which are poentially applicable to clinical medicine. Materials and Methods : First, the computer simulation was performed with the generated relaxation data to verify the accuracy and reliabilility of the relaxographic method (CONTINI). Secondly, in or der to see how well the CONTIN quantifies and resolves the two different ${T_1}$ environments, we calculated the oil to water peak area ratios and identified peak positions of ${T_1}-distribution$ curve of the phantom solutions, which consist of four centrifugal tubes (10 ml) filled with the compounds of 0, 10, 20, 30% of corn oil and distilled water, using CONTIN. Finally, inversion recovery MR images for a volunteer are acquired for each TI ranged from 40 to 1160 msec with TR/TE=2200/20 msec. From the 3 different ROIs (GM, WM, CSF), CONTIN analysis was performed to obtain the ${T_1}$-distribution curves, which gave peak positions and peak area of each ROI location. Results : The simulation result shows that the errors of peak positions were less in the higher peak (centered ${T_1}=600$ msec) than in the lower peak (centered ${T_1}=150$ msec) for all SNR but the errors of peak areas were larger in the higher peak than in the lower peak. The CONTIN analysis of the measured relaxation data of phantoms revealed two peaks between 20 and 60 msec and between 500 and 700 msec. The analysis gives the peak area ratio as oil 10%: oil 20%: oil 30% = 1:1.3:1.9, which is different from the exact ratio, 1:2:3. For human brain, in ROI 3 (CSF), only one component of -distributions was observed whereas in ROI 1(GM) and in ROI 2 (WM) we observed two components of ${T_1}-distribution$. For the WM and CSF there was great agreement between the observed ${T_1}-relaxation$ times and the reported values. Conclusion : we demonstrated that the relaxographic method provided additional information such as the distribution of relaxation times and water content, which were not available in the routine relaxometry and ${T_1}/{T_2}$ mapping techniques. In addition, these additional information provided by relaxographic analysis may have clinical importance.

• Journal of Korean Society of Transportation
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• v.2 no.1
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• pp.17-31
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• 1984

공항의 용량측정은 수요군의 흐름에서 발생하는 소비시간분석을 요구하며 공항체계 의 대부분 시설에서는 흐름의 시간변위를 연속대기례에 의한 비효율적방법으로 예측할수도 있으나 청사내의 여객동선에 대해서는 여러 시설을 활용하려는 여객의 선택선호로 인하여 확률적 접근이 바람직하다. 본 논문은 공항의 청사내에서 부대시설에 의하여 소비되는 여객 의 이완시간을 예측하는 모형을 개발하였다. 총이완시간은 여객이 각 시설을 이용하는 확률 과 이용시간의 기대치에 대한 함수로서 계산되었으며 정상적인 여객의 동선이 이들 시설에 의하여 영향을 받을 경우에만 정의되도록 하였다. 이 이완도는 연속된 청사의 기능시설에 대한 여객동선분포의 입력과 출력을 설명하는데 쓰이게 되며 나아가서는 청사전반의 용량산 정을 위한 지표를 제공한다. 모형 검증을 위한 자료는 매표대와 보안검사대 사이의 부대시 설을 중심으로 수집되었으며 자료의 특성과 모형의 심요성이 논의되었다.

• Journal of the Korean Magnetics Society
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• v.22 no.3
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• pp.73-78
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• 2012

We calculated the electron spin resonance (ESR) line-profile function. The line-width of single-walled carbon nanotube (SWNT) was studied as a function of the temperature at a frequency of 9.5 GHz in the presence of external electromagnetic radiation. The temperature dependence of the line-widths is obtained with the projection operator method (POM) proposed by Argyres and Sigel. The scattering is little affected in the low-temperature region (T < 200 K). We conclude that the calculation process presented in this method is useful for optical transitions in SWNT.

• Transactions of the Korean Society of Mechanical Engineers
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• v.13 no.4
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• pp.689-696
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• 1989

In this experimental study, relative particle size distribution was measureed at the inlet and outlet of the slit impactor using the particle sizer. The imployed measuring method of the size distribution was different from the conventional method. This measurement system has the advantage of obtaining the particle collection efficiency for various particle size easily and at once compared with other methods. The effects of jet to plate distance and Reynolds number on the characteristic impactor efficiency curves have been studied. In the results of this experiment, the increment of collection efficiency was observed as Reynolds number increases in the case of S/W = 1/2 but was very slight. The influence of S/W is more remarkable than that of Reynolds number on the particle collection efficiency.

• Investigative Magnetic Resonance Imaging
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• v.2 no.1
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• pp.73-82
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• 1998

Purpose : A precise NMR technique for measuring the rate of water exchange and cell membrane permeability across the hepatocyte membrane using liver-specific MR contrast agent is described. Materials and Methods : The rat hepatocytes isolated by perfusion of the livers were used for the NMR measurements. All experiments were performed on an IBM field cycling relaxometer operating from 0.02MHz to 60 MHz proton Larmor frequency. spin-echo pulse sequence was empolyed to measure spin-lattice relaxation time, T1. The continuous distribution analysis of water proton T1 data from rat hepatocytes containing low concentrations of the liver specific contrast agent, Gd-EOB-DTPA, modeled by a general two compartment exchange model. Results : The mean residence time of water molecule inside the hepatocyte was approximately 250 msec. The lower limit for the permeability of the hepatocyte membrane was $(1.3{\pm}0.1){\;}{\times}{\;}10^{-3}cm/sec$. The CONTIN analysis, which seeks the natural distribution of relaxation times, reveals direct evidence of the effect of diffusive exchange. the diffusive water exchange is not small in the intracellular space in the case of hepatocytes. Conclusions : Gd-EOB-DTPA, when combined with continuous distribution analysis, provides a robust method to study water exchange and membrane permeability in hepatocytes. Water exchange in hepatocyte is much slower thatn that in red blood cells. Therefore, tissue-specific contrast agent may be used as a functional agent to give physiological information such as cell membrane permeability.

• Polymer(Korea)
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• v.36 no.4
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• pp.507-512
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• 2012

Thin (~650 nm) and ultrathin (~50 nm) films of neat PMMA and PMMA containing 5 wt% of methacryl-polyhedral oligomeric silsesquioxane were prepared in this work. The effects of film thickness and POSS on glass transition temperature ($T_g$) and isothermal physical aging were investigated by means of differential scanning calorimetry (DSC). $T_g$ depression was observed as film thickness was decreased and Ma-POSS molecules were incorporated. Enthalpy relaxation (${\Delta}H_{Relax}$) due to the isothermal physical aging was reduced by ultra-thin film thickness and the addition of Ma-POSS. KWW (Kohlrausch-Williams-Watts) equation was used to fit ${\Delta}H_{Relax}$ vs. aging time data providing the fitting parameters; maximum enthalpy recovery (${\Delta}H_{\infty}$), relaxation time (${\tau}$) and non-exponentiality parameter (${\beta}$).

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.45 no.9
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• pp.8-13
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• 2008

Noise in homogeneous extrinsic semiconductor samples is calculated due to distributed diffusion noise sources. As the length of the device shrinks at a fixed bias voltage, the ac-wise short-circuit noise current shows excess noise as well as thermal noise spectra. This excess noise behaves like a full shot noise when the channel length becomes very small compared with the extrinsic Debye length. For the first time, the analytic formula of the excess noise in extrinsic semiconductors from velocity-fluctuation noise sources is given for finite frequencies. This formula shows the interplay between transit time, dielectric relaxation time, and velocity relaxation time in determining the terminal noise current as well as the carrier density fluctuation. As frequency increases, the power spectral density of the excess noise rolls off. This formula sheds light on noise in nanoscale MOSFETs where quasi-ballistic transport plays an important role in carrier transport and noise.

• Journal of radiological science and technology
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• v.38 no.3
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• pp.253-259
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• 2015

The information of contrast media concentration on target organ is very important to get reduce the side effect and high contrast imaging. We investigated alternation of signal intensity as a function of the modality of Gd-based contrast media on spin echo and ultra short time echo (UTE) of T1 effective pulse sequence at 3T MRI unit. Gadoxetic acid, which is a MRI T1 contrast medium, was used to manufacture an agarose phantom diluted in various molarities, and sterile water and agarose 2% were used as the buffer solution for the dilution. The gold standard T1 calculation was based on coronal single section imaging of the phantom mid-point with 2D Inversion recovery spine-echo pulse sequence MR imaging for testing of phantom accuracy. The 1-2mmol/L and 7mmol/L was shown the maximum signal intensity on spin echo and UTE respectively. We confirm the difference of contrast media concentration which was shown the maximum signal intensity depending on the T1 effective pulse sequence.

• Progress in Medical Physics
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• v.10 no.1
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• pp.23-32
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• 1999

Combined MRI and Relaxogram approach was introduced as a very useful tool for fat study. The phantoms simulating homogeneous mixture of fat and non-fat environments were measured with spin echo pulse sequence on a 0.15 T whole body imager. From 45 scans, the Tl values were obtained by fitting the data to continuous distribution (CONTIN) of relaxation time. This relaxogram gives broad distributions of relaxation time, which are characterized by a number of peaks with characteristic T1 values. Two distinct peaks in relaxogram were observed and identified as signals from com oil and gelatin gel. This model system can be served as simulating the distribution of fat in muscle. Also the relative ratio of two components, which is proportional to the area under the peak, is estimated and compared to nominal values. Based on the good agreement between two predictions, the values from our proposed method agreed with nominal values within $\pm$7 % error. The effects of different concentration of contrast agent and different region of interest are presented. To optimize total scan times, the minimum required data points and so further reduction in total scan times are discussed.

• Clinical and Experimental Pediatrics
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• v.48 no.7
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• pp.745-752
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• 2005

Purpose : Adolescent obesity is known to be associated with complications such as hypertension, coronary artery disease and insulin resistance. We measured the common carotid artery by ultrasound as a predictor of atherosclerosis, and investigated the relationship between carotid artery parameters and serum cytokines in obese adolescents. Methods : Twenty-nine obese adolescents(16-17 years old, obesity index>130 percent) and twentyseven normal controls were included. Obesity index and body mass index were calculated from their height and weight. Skin fold thickness was measured at the triceps, and fat mass and fat distribution by bioelectrical impedence analysis. Blood pressure was measured at resting state and serum lipid, insulin, and homocysteine levels after a 12-hour fasting period. Intimal wall thickness, systolic and diastolic diameters of the common carotid artery were measured by ultrasound, and compliance and distensibility calculated by equation. Results : Systolic and diastolic diameters of the carotid artery significantly correlated with arm circumference, body mass index, fat distribution and fat mass. The higher systolic blood pressure was, the larger systolic and diastolic diameter. The higher diastolic blood pressure was, the larger carotid intimal thickness. Insulin levels had positive correlations with systolic, diastolic diameters and serum homocysteine level with intimal thickness. Conclusion : The carotid artery diameter significantly increased with the degree of obesity and blood pressure. The carotid intimal wall thickness significantly correlated with diastolic blood pressure. Measurement of carotid artery thickness, insulin and homocysteine levels might be useful to predict the development of coronary artery disease.