• Progress in Medical Physics
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• v.21 no.1
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• pp.52-59
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• 2010

To examine among patients with vertebral compression fracture the extent to which signal-to-noise ratio (SNR) and Apparent Diffusion Coefficient (ADC) values at the lumbar vertebral compression fracture site vary on diffusion-weighted MR images according to varying b values on the 1.5T MR device. Diffusion-weighted MR images of 30 patients with compression fracture due to chronic osteoporosis who underwent vertebral MRI from Jan. 2008 to Nov. 2009 were respectively obtained using a 1.5-T MR scanner with the b values increased from 400, 600, 800, 1,000 to $1,200\;s/mm^2$. For diffusion-weighted MR images with different b values, the signal-to-noise ratio (SNR) was assessed at three sites: the site of compression fracture of the lumbar vertebral body at L1 to L5, and both the upper and lower discs of the said fracture site, while for ADC map images with different b values, the SNR and ADC were respectively assessed at those three sites. As a quantitative analysis, diffusion-weighted MR images and ADC map images with b value of $400\;s/mm^2$ (the base b values) were respectively compared with the corresponding images with each different b value. As far as qualitative analysis is concerned, for both diffusion-weighted MR and ADC map images with b value of $400\;s/mm^2$, the extent to which signal intensity values obtained at the site of compression fracture of the lumbar vertebral body at L1 to L5 vary according to the increasing b values were examined. The quantitative analysis found that for both diffusion-weighted MR and ADC map images, as the b values increased, the SNR were relatively lowered at all the three sites, compared to the base b value. Also, it was found that as the b values increased, ADC valueswere relatively lowered at all the three sites on ADC map images. On the other hand, the qualitative analysis found that as the b values increased to more than $400\;s/mm^2$, the signal intensity gradually decreased at all the sites, while at the levels of more than $1,000\;s/mm^2$, severe image noises appeared at all of the three sites. In addition, higher signal intensity was found at the site of compression fracture of the lumbar vertebral body than at the discs. Findings showed that with the b value being increased, both the signal-to-noise ratio (SNR) and Apparent Diffusion Coefficient (ADC) values gradually decreased at all the sites of the lumbar vertebral compression fracture and both the upper and lower discs of the fracture site, suggesting that there is a possibility of a wider range of applications to assessment of various vertebral pathologies by utilizing multi b values in the diffusion-weighted MRI examination.

• Tuberculosis and Respiratory Diseases
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• v.59 no.4
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• pp.374-379
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• 2005

Background : The single-breath carbon monoxide diffusion capacity (DLCO) and the per unit alveolar volume (KCO; $D_LCO/VA$) gave discordant values when there was an abnormal alveolar volume (VA). However, the clinical significance of the discordant values in patients with airflow limitation has not been examined. This study investigated the $D_LCO$ and KCO changes after improving the airflow limitation. Methods : The baseline $D_LCO$ and KCO with lung volume were measured in patients with an airflow obstruction. The effective alveolar volume was measured using the single-breath $CH_4$ dilution method. The patients divided into two groups according to the baseline values: (1) increased KCO in comparison with the $D_LCO$ (high discordance) (2) decreased or not increased KCO in comparison with the $D_LCO$ (low discordance). The diffusion capacity and lung volume were measured after treatment. Results : There was no significant difference in the baseline lung volumes including the $FEV_1$ and FVC between the two groups. The $FEV_1$ and FVC were significantly increased in the high discordance group compared with the low discordance group after treating the airflow limitation. The $D_LCO$ and alveolar volume were significant higher in the high discordance group compared with the low discordance group while the TLC was not. Conclusion : The discordance between the $D_LCO$ and KCO could be translated into an airflow reversibility in patients with an airflow limitation.

• Applied Chemistry for Engineering
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• v.10 no.6
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• pp.876-880
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• 1999

The surfactant self-diffusion coefficients of mixed micellar solutions of ionic and nonionic surfactants have been measured by the NMR pulsed field gradient spin echo(FT-PGSE) method. In addition, the line widths of $^1H$ NMR signal have been monitored. The system investgated are $C_{12}EO_5/SDS/D_2O$, $C_{12}EO_5/DTAC/D_2O$, and $C_{12}EO_8/SDS/D_2O$. In the sample series, the molar ratios of $D_2O$ to surfactant(ionic+nonionic) were kept constant while the surfactant mixing ratio was varied. For the $C_{12}EO_5$ system, the surfactant self-diffusion coefficient indicates minimum when the surfactant mixing ratio is about 20% ionic surfactant. The observed decrease in self-diffusion coefficients as nonionic surfactant was replaced by ionic surfactant is interpreted to mainly be due to an increased micelle-micelle repulsion. The increase in self-diffusion coefficients occurring at higher fraction of ionic surfactant is shown to be due to a decrease in micelle size. For the $C_{12}EO_8$ system, the effect of the surfactant mixing ratio is much weaker which can be understood by considering the molecular geometry and large headgroup area. The proton NMR line widths correlate well with the self-diffusion coefficients and broadening of the alkyl chain methylene signals is found when the self-diffusion coefficients is low.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.06a
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• pp.410-410
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• 2007

광섬유 내에 첨가되어 있는 $GeO_2$ 등의 물질을 얼 확산시켜서 만드는 열확산 코어 광섬유는 열확산 기술에 따른 광섬유의 MFD(Mode Field Diameter)를 국소적으로 확대하여 굴절률 분포를 변화시킨 광섬유로 혹의 비틀림 및 간격에 대한 허용범위가 넓어지게 하여 접속 손실을 감소시킬 수 있다. 본 연구에서는 열확산 코어 광섬유를 제조할 때 안정된 얼확산 문제를 해결하기 위한 방법으로 트윈 토치를 이용한 프레임 브러싱 기법의 안정화된 코어 확장형 광섬유 제조시스템을 제작하였다. 또한 제작된 열확산 코어 광섬유 제조시스템을 이용하여 단일모드 조건을 만족하는 다양한 종류의 열확산 코어 광섬유가 제작됨을 확인할 수 있었다.

• Journal of the Korea Concrete Institute
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• v.22 no.2
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• pp.255-262
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• 2010

The purpose of this study is to provide preliminary data on chloride diffusion of lightweight aggregate concrete containing crushed stone-powder. Accordingly, the study performed experiments using concrete aggregates of Crushed Aggregate (CG), Single-sized Lightweight Aggregate (SLG), Continuous Graded Lightweight Aggregate (CLG), and using water-binder ratio of 0.4, 0.5, 0.6, and using binder of FA and BFS. The chloride diffusion coefficient is calculated according to the NT BUILD 492. Diffusion coefficient of SLG and CLG were higher than that of CG concrete, but the difference was not significant. Also, chloride diffusion coefficient data indicated that it was highly affected by water-binder ratio, and it decreased with the decrease in waterbinder ratio. The admixture substitution of FA15% was effective in decreasing the diffusion coefficient only with water-binder ratio of 0.4 while admixture substitution of FA10+BFS20% was effective with all levels of water-binder ratio. The result of study shows lightweight aggregate concrete containing crushed stone-powder has slightly higher chloride diffusion coefficient than CG concrete, but the difference is not significant such that it can be overcome by adjusting water-binder ratio and admixture substitution. In addition, the data indicate the chloride diffusion coefficient of lightweight aggregate concrete can be estimated from the strength of lightweight aggregate.

• Journal of Digital Convergence
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• v.11 no.1
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• pp.361-368
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• 2013

The purpose of this study is to know the clinical usefulness of optimal b-values by quantitative, qualitative evaluation of DW-MRI for lesions of benignity and malignity of female pelvis. The b-values used in DWI were 600, 800, 1000, 1200, 1400($s/mm^2$). Mean SNR and CNR of myoma in b-value 800 were the highest result as $84.6{\pm}4.57$(p=0.024) and $50.13{\pm}5.47$(p=0.028), Mean SNR and CNR of cervical cancer were the highest result as $12.0{\pm}2.04$(p=0.047) and $10.6{\pm}1.24$(p=0.001), Mean ADC value in myoma and cervical cancer in b-value 800 were $1.19{\times}10^{-3}mm^2/s$(p=0.008), $0.96{\times}10^{-3}mm^2/s$(p=0.027). As a qualitative analysis, the delineation and conspicuity were the highest result as $4.02{\pm}0.18$(p=0.028), $4.39{\pm}0.25$(p=0.015) on b-value 800. DW-MRI is an important method, and the optimal b values is 800 $s/mm^2$ for differentiation between benign and malignant lesions of female pelvis.

• Proceedings of the Korea Water Resources Association Conference
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• 2007.05a
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• pp.2120-2124
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• 2007

본 연구에서는 천해역에서 수평 방향으로 방류되는 비부력 원형 난류제트에 대한 수리모형실험을 수행하여, 파랑이 제트의 확산에 미치는 영향을 검토하였다. 수리모형실험시 대상 파랑은 진폭이 작은 규칙파를 적용하였으며, 난류제트의 순간적인 유속장은 입자화상유속계(particle image velocimetry, PIV)기법을 이용하여 측정하였다. 평균유속장은 PIV기법으로 측정된 순간유속장을 위상평균하여 계산하였으며, 파의 진폭을 변화시키며 실험을 수행하였고, 파의 진폭변화에 따른 제트의 유속분포로부터 제트의 중심선과 제트단면을 추정하였다. 제트의 중심선속도는 파의 진폭이 증가함에 따라 중심선속도의 감소 시점이 빨라졌으며, 제트의 횡단면분포의 고유특성인 자기상사성(self-similarity)이 단계적으로 사라졌다. 제트 중심선의 속도와 제트 유속 단면은 제트의 확산정도를 알 수 있는 중요한 인자로서 파랑 진폭의 크기에 따른 이들 인자의 변화로부터 파랑의 분산이 난류제트의 확산현상에 미치는 영향을 알 수 있었다.

• Journal of the Korea Concrete Institute
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• v.25 no.2
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• pp.145-153
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• 2013

Recently, accelerated chloride diffusion coefficients are used for an evaluation of chloride behavior. Similar as apparent diffusion coefficients, accelerated diffusion coefficients decrease with time. In this study, decrease in diffusion coefficient with time is simulated with porosity. Utilizing DUCOM-program, porosities from 15 mix proportions are obtained and diffusion coefficients are modelled with regression analysis of porosity for 270 days. Considering non-linear binding capacity which means the relation between free and bound chloride ion, chloride behavior in high performance concrete is evaluated. Through utilizing the previous test results for concrete under chlorides for 180 days, the applicability of the proposed technique is verified. The proposed technique is evaluated to reasonably predict the chloride behavior in concrete with various w/c (water to cement) ratios and mineral admixtures (GGBFS and FA). It is also shown that decrease in chloride diffusion should be considered for chloride prediction in concrete with mineral admixture since it has very clear decrease in diffusivity with time.

• Journal of the Korean Geographical Society
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• v.34 no.4
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• pp.395-418
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• 1999

문화지리학도는 종교를 인간의 가치관과 풍속을 형성하는 가장 중요한 인자의 하나로 평가하는 바, 이는 문화지역 설정의 기준이 된다. 이 논문은 18세기 말부터 19세기 말까지 충청도 서부해안 내포지방에서의 가톨릭교 확산에 대하여 고찰한 글이다. 농민.행상.상인.선부 등 주로 평민층으로 구성된 가톨릭 공동체는 조정의 가혹한 박해에도 불구하고 가톨릭교 확산에서 중요한 역할을 감당해 왔다.

• The Korean Journal of Financial Studies
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• v.10 no.1
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• pp.1-44
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• 2004

연속시간모형은 시간의 흐름에 대응되는 자본자산의 운동의 성질과 시간의 흐름에 따라 형성되는 자본자산의 가격을 동시적으로 파악할 수 있는 것이 큰 장점이다. 연속시간 확률미분방정식을 구성하는 표류함수와 확산함수가 폐형해나 해석적 형태로 존재하지 않는 경우가 대부분이다. 여기에서 모수추정의 어려움이 발생한다. 전이 확률밀도함수의 인지 또는 발견의 어려움과 표류함수와 확산함수의 적분 불가능성은 최대가능도법의 사용을 어렵게 만든다. 여기에서 모수방법 보다는 비모수방법을 통하여 연속 확률 미분방정식을 추정하려는 성향이 존재한다. 밀도를 모르면 표본적률을 사용하여 모수를 추정할 수 있으므로 일반화 적률법이 연속시간 확률미분방정식의 모수 추정과 검정에 사용되고 있다. 전이밀도의 값을 시뮬레이션을 통하여 얻는 마코브연쇄 몬테카를로 방법, 전이밀도를 무한소 생성작용소를 통하여 얻는 방법, 비 모수방법, 여러 종류의 전개에 의하여 얻은 표류함수와 확산함수의 전이밀도에 대한 최대가능도법 등 여러 종류의 연속시간 확률미분방정식의 실증분석에서 사용되고 있다. 이 논문에서는 연속시간 확률미분방정식의 실증분석 방법들을 정리하는데 목적이 있다. 이일균(2004)은 이 논문과의 자매논문으로 시뮬레이션에 의한 확률미분방정식의 추정을 다루고 있어 시뮬레이션방법은 그 논문에 미룬다.