• Journal of Korean Neurosurgical Society
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• v.55 no.5
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• pp.267-272
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• 2014

Objective : Differentiation of demyelination in white matter from axonal damage can be determined using diffusion tensor imaging (DTI). In this study using meningioma patients an attempt was made to evaluate the relationship between preoperative weakness and the changes of diffusion parameters in the corticospinal tract (CST) using DTI. Methods : Twenty-six patients with meningioma were enrolled in this study. Eleven of them suffered from objective motor weakness and were classified as Group 1. The remaining 15 patients did not present motor weakness and were classified as Group 2. Fiber tractography and CST diffusion parameters were obtained using DTIStudio. The ratios (lesion side mean value/contralateral side mean value) of CST diffusion parameters were compared with 1.0 as a test value using a one-sample t-test. Results : In Group 1, fractional anisotropy (FA), tensor trace (TT), and radial diffusivity (RD, ${\lambda}2$ and ${\lambda}3$) of the CST were significantly different between two hemispheres, but axial diffusivity (AD, ${\lambda}1$) of the CST was not significantly different between two hemispheres. In Group 2, FA and ${\lambda}3$ of CST did not differ significantly between the hemispheres. In Group 2, TT, ${\lambda}1$, and ${\lambda}2$ of CST in the ipsilateral hemisphere were significantly higher than those of the unaffected hemisphere. However, the differences were small. Conclusion : Motor weakness was related to a low FA and high TT resulting from increased RD of the CST fibers. CST diffusion changes in patients with weakness are similar to those for demyelination.

• Journal of computational fluids engineering
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• v.17 no.3
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• pp.1-10
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• 2012

Large Eddy Simulation(LES) of turbulent mass transfer in fully developed turbulent pipe flow has been performed to study the effect of Reynolds number on the concentration fields at $Re_{\tau}=180$, 395, 590 based on friction velocity and pipe radius. Dynamic subgrid-scale models for the turbulent subgrid-scale stresses and mass fluxes were employed to close the governing equations. Fully developed turbulent pipe flows with constant mass flux imposed at the wall are studied for Sc=0.71. The mean concentration profiles and turbulent intensities obtained from the present LES are in good agreement with the previous numerical and experimental results currently available. To show the effects of Reynolds number on the turbulent mass transfer, the mean concentration profile, root-mean-square of concentration fluctuations, turbulent mass fluxes, cross-correlation coefficient, turbulent diffusivity and turbulent Schmidt number are presented.

• Journal of Biosystems Engineering
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• v.42 no.4
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• pp.314-322
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• 2017

Purpose: This study was conducted to investigate the hot air drying characteristics of squash slices depending on the drying conditions (input air velocity, input air temperature, and sample thickness). Methods: The developed drying system was equipped with a controllable air blower and electric finned heater, drying chamber, and ventilation fan. Squash (summer squash called Korean zucchini) samples were cut into slices of two different thicknesses (5 and 10 mm). These were then dried at two different input air temperatures (60 and $70^{\circ}C$) and air velocities (5 and 7 m/s). Six well-known drying models were tested to describe the experimental drying data. A non-linear regression analysis was applied to determine model constants and statistical indices such as the coefficient of determination ($R^2$), reduced chi-square (${\chi}^2$), and root mean square error (RMSE). In addition, the effective moisture diffusivity ($D_{eff}$) was estimated based on the curve of ln(MR) versus drying time. Results: The results clearly showed that drying time decreased with an increase in input air temperature. Slice thickness also affected the drying time. Air velocity had a greater influence on drying time at $70^{\circ}C$ than at $60^{\circ}C$ for both thicknesses. All drying models accurately described the drying curve of squash slices regardless of slice thickness and drying conditions; the Modified Henderson and Pabis model had the best performance with the highest R2 and the lowest RMSE values. The effective moisture diffusivity ($D_{eff}$) changes, obtained from Fick's diffusion method, were between $1.67{\times}10^{-10}$ and $7.01{\times}10^{-10}m^2/s$. The moisture diffusivity was increased with an increase in input air temperature, velocity, and thickness. Conclusions: The drying time of squash slices varied depending on input temperature, velocity, and thickness of slices. The further study is necessary to figure out optimal drying condition for squash slices with retaining its original quality.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2005.11a
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• pp.134-135
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• 2005

To improve mean-life and reliability of power cable, we have investigated volume resistivity and thermal conductivity showed by changing the content of acetylene black which is the component parts of semiconductive shield in underground power transmission cable. The sheets were primarily kneaded in their pellet form material samples for 5 minutes on rollers ranging between 70[$^{\circ}C$] and 100[$^{\circ}C$]. Then they were produced as sheets after pressing for 20 minutes at 180[$^{\circ}C$] with a pressure of 200[kg/cm]. The content of conductive acetylene black was the variable, and their contents were 20, 30 and 40[wt%], respectively. Volume resistivity of specimens was measured by volume resistivity meter after 10 minutes in the preheated oven of both $25\pm1[^{\circ}C]$ and $90\pm1[^{\circ}C]$. Thermal conductivity was measured by Nano Flash Diffusivity. The measurement temperatures of thermal conductivity using Nano Flash Diffusivity were both 25[$^{\circ}C$] and 55[$^{\circ}C$]. From these experimental results, volume resistivity was high according to an increase of the content of acetylene black. And thermal conductivity was increased to an increase of the content of acetylene black. And thermal conductivity were increased by heating rate because volume of materials was expanded according to rise in temperature.

• Environmental Engineering Research
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• v.10 no.6
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• pp.294-305
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• 2005

The effectiveness of fly ash-, quicklime-, and quicklime-fly ash-based stabilization/solidification(S/S) in chromium(Cr) contaminated soils was investigated using modified semi-dynamic leaching tests. Artificial soil samples composed of kaolinite or montmorillonite contaminated with chromium nitrate(4000 mg $Cr^{3+}\;kg^{-1}$ of solid) were prepared and then subjected to S/S treatment using quicklime, fly ash, or quick lime-fly ash. The effectiveness of the treatment was evaluated by assessing the cumulative fraction of leached $Cr^{3+}$ as well as, by computing the effective diffusivity ($D_e$) and the leachability index (LX) of the treated samples. The reduction in $Cr^{3+}$ release for the untreated samples was more pronounced in the presence of montmorillonite, which was attributed to sorption. Treatment with quicklime, fly ash, or quick lime-fly ash was significantly effective in reducing $Cr^{3+}$ release most probably due to the formation of pozzolanic reaction products and $Cr(OH)_3$ precipitation. The most effective treatment was observed in montmorillonite-sand soil samples treated with quicklime-fly ash (99.8% removal). The mean $D_e$ decreased significantly and the mean LX was greater than 9 for all treated samples, indicating that the treated soils were acceptable for "controlled utilization". The mechanism controlling $Cr^{3+}$ leaching from all treated samples during the first 5 days appeared to be diffusion.

• Proceedings of the Korean Society for Agricultural Machinery Conference
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• 2000.11b
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• pp.246-253
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• 2000

The optimal equations to predict the soil tempratures of twelve cities in the region of the southern part of the Korea such as Changhung, Cheju, Chinju, Kwangju, Masan, Miryang, Mokpo, Muan, Pusan, Sogwipo, Ulsan, Yoosu, were suggested as function of time and soil depth and the time dependent variation and soil depth dependent distribution of temperature were analyzed for the back data of the geothermal energy utilization system design and agricultural usages. The equation form is $T(x,\;t)\;=\;T_{m}\;-\;T_{so}{\cdot}Exp(-\xi){\cdot}cos{\omega}(t\;-\;t_{o}\;-\;x\;/\sqrt{2{\alpha}{\omega}}$) and it can predict the soil temperatures well with the correlation factor of 0.98 or upwards for most data. The range of mean soil temperature was $14.99~18.53^{\circ}C$ and soil surface temperature swing, 11.65~14.54 days, soil thermal diffusivity, $0.025~0.069\;m^2/day$ except Mokpo of $0.100\;m^2/day$, and phase shift, 19.66~27.81 days. During about thirty years from 1960s to 1990s, the mean soil temperature was increased by $0.04~1.25^{\circ}C$. The temperature difference depending on soil depth was not significant.

• Korean Journal of Psychosomatic Medicine
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• v.25 no.2
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• pp.153-165
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• 2017

Objectives : Recent neuroimaging studies focus on dysfunctions in connectivity between cognitive circuits and emotional circuits: anterior cingulate cortex that connects dorsolateral orbitofrontal cortex and prefrontal cortex to limbic system. Previous studies on pediatric depression using DTI have reported decreased neural connectivity in several brain regions, including the amygdala, anterior cingulate cortex, superior longitudinal fasciculus. We compared the neural connectivity of psychotropic drug naïve adolescent patients with a first onset of major depressive episode with healthy controls using DTI. Methods : Adolescent psychotropic drug naïve patients(n=26, 10 men, 16 women; age range, 13-18 years) who visited the Korea University Guro Hospital and were diagnosed with first onset major depressive disorder were registered. Healthy controls(n=27, 5 males, 22 females; age range, 12-17 years) were recruited. Psychiatric interviews, complete psychometrics including IQ and HAM-D, MRI including diffusion weighted image acquisition were conducted prior to antidepressant administration to the patients. Fractional anisotropy(FA), radial, mean, and axial diffusivity were estimated using DTI. FMRIB Software Library-Tract Based Spatial Statistics was used for statistical analysis. Results : We did not observe any significant difference in whole brain analysis. However, ROI analysis on right superior longitudinal fasciculus resulted in 3 clusters with significant decrease of FA in patients group. Conclusions : The patients with adolescent major depressive disorder showed statistically significant FA decrease in the DTI-based structure compared with healthy control. Therefore we suppose DTI can be used as a bio-marker in psychotropic drug-naïve adolescent patients with first onset major depressive disorder.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.11a
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• pp.160-161
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• 2006

To Improve the mean-life and the reliability of power cable, we have investigated thermal conductivity of XLPE insulator and semiconducting materials in l54[kV] underground power transmission cable. Specimens were made of sheet form with the nine of specimens for measurement. Thermal conductivity were measured by Nano Flash Diffusivity thermal conductivity measurement temperature ranges of XLPE insulator were from 20[$^{\circ}C$] to 90[$^{\circ}C$], and the heating rate was 1[$^{\circ}C$/mm]. In case of semiconducting materials. the measurement temperature ranges of thermal conductivity were from 20[$^{\circ}C$] to 60[$^{\circ}C$], and the heating rate was 1[$^{\circ}C$/min].

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.9
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• pp.2443-2453
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• 1994

The structure of turbulence of fully developed flow through four concentric annuli with the rough outer wall was investigated experimentally for a Reynolds number range Re=15, 000-93, 000. Turbulence intensities were measured in three(u, v, w) directions, and turbulence shear stresses in annuli of radius=0.13, 0.26, 0.4 and 0.56, respectively. Due to the square roughness element attached periodically along the axial direction, the radial velocity fluctuations show similar distribution regardless of the different .alpha.cases. However, the axial and circumferential velocity fluctuation profiles demonstrate the longitudinal turbulence structures are strongly influenced by the .alpha. values. The turbulent eddy viscosity deduced form mean velocity distributions and the measured Reynolds shear stresses are also presented and discussed.

• International Journal of Air-Conditioning and Refrigeration
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• v.9 no.2
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• pp.77-84
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• 2001

Experimental and computational studies were carried out to investigate the turbulent heat transfer enhancement of the cooling system in nuclear reactor by large scale vortex generation. The large scale vortex motion was generated by rearranging the inclination angels of mixing vanes to the coordinate direction. Axial development of mean and turbulent velocities in the subchannels were measured by the 2-color LDV system. Eddy diffusivity concept based on $\kappa{-}\varepsilon$ model was employed to calculate the turbulent heat and momentum transfers in the subchannel. The turbulences generated by split mixing vanes has small length scales so that they maintain only about $10D_H$ after the spacer grid. On the other hand, the turbulences generated by the large scale vortex motions continue longer and remain up to $25D_H$ after the spacer grid.