• Investigative Magnetic Resonance Imaging
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• v.16 no.1
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• pp.6-15
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• 2012

Purpose : The objective of this study was to develop background gradient correction method using excitation pulse profile compensation for accurate fat and $T_2{^*}$ quantification in the liver. Materials and Methods: In liver imaging using gradient echo, signal decay induced by linear background gradient is weighted by an excitation pulse profile and therefore hinders accurate quantification of $T_2{^*}$and fat. To correct this, a linear background gradient in the slice-selection direction was estimated from a $B_0$ field map and signal decays were corrected using the excitation pulse profile. Improved estimation of fat fraction and $T_2{^*}$ from the corrected data were demonstrated by phantom and in vivo experiments at 3 Tesla magnetic field. Results: After correction, in the phantom experiments, the estimated $T_2{^*}$ and fat fractions were changed close to that of a well-shimmed condition while, for in vivo experiments, the background gradients were estimated to be up to approximately 120 ${\mu}T/m$ with increased homogeneity in $T_2{^*}$ and fat fractions obtained. Conclusion: The background gradient correction method using excitation pulse profile can reduce the effect of macroscopic field inhomogeneity in signal decay and can be applied for simultaneous fat and iron quantification in 2D gradient echo liver imaging.

• Korean Journal of Veterinary Research
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• v.12 no.1
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• pp.37-50
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• 1972

Another comparison of alveolar gas pressures, in a continuously rebreathing dog lung, with pulmonary arterial (mixed venous) blood, again showed alveolar pressures to be the higher for $CO_2$ and usually $O_2$ (positive ${\Delta}Pco_2$, and ${\Delta}Po_2$). ${\Delta}Pco_2$ was almost invariably positive, it was independant of time and of plasma pH changes produced by acid or bicarbonate infusion, but proportional to blood $CO_2$ level. It was seemingly little affected by the distribution or magnitude of blood flow nor did it result from failure of $CO_2$ equilibrium within the blood, but it did rise with carbonic anhydrase inhibition. ${\Delta}Po_2$ was more variable and sometimes negative, particularly at low blood flow rates. It seemed in dependant of time, and plasma pH changes, apart from an inverse relationship with that resulting from $CO_2$ changes. It existed despite considerable potential for gas exchange, and was unaffected by inhibition of the $CO_2$ reactions.

• Journal of the Korean Association of Geographic Information Studies
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• v.17 no.1
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• pp.35-49
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• 2014

In order to understand the impacts of surface characteristics and the distance from the urban heat island center to suburban areas on the mean night time air temperature, we analyzed GIS and AWS observational data. Spatial distributions of mean night time air temperature during the summer and winter periods of 2004-2011(six years) were utilized. Results show that the temperature gradients were different by distance and direction. We found high correlation between mean night-time air temperature and artificial land cover area within 1km and 200m radii during both summer(R=0.84) and winter(R=0.78) seasons. Regression models either from 1km and 200m land surface data explained the distribution of night-time temperature equally well if the input data had sufficient resolution with detailed attribute including building area and height.

• Journal of Wetlands Research
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• v.14 no.1
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• pp.75-87
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• 2012

Hyporheic zone is a region beneath and alongside a stream, river, or lake bed, where there is mixing of shallow groundwater and surfacewater. Hyporheic exchange controls a variety of physical, biogeochemical and thermal processes, and provides unique ecotones in a aquatic ecosystem. Field and experimental observations, and modeling studies indicate that hyporheic exchange is mainly in response to pressure gradients driven by the geomorphological features of stream beds. In the reach scale of a stream, pool-riffle structures dominate the exchange patterns. Flow over a pool-riffle sequence develops recirculation zones and stagnation points, and this flow structures make irregular pressure gradient which is driving force of the hyporheic exchange. In this study, 3 D hydro-dynamic model solves the Reynolds-averaged Navier-Stokes equations for the surface water and Darcy's Law and the continuity equation for ground water. The two sets of equations are coupled via the pressure distribution along the interface. Simulation results show that recirculation zones and stagnation points in the pool-riffle structures dominantly control the upwelling and downwelling patterns. With decrease of recirculation zones, length of donwelling zone formed in front of riffles is reduced and position of maximum downwelling point moves downward. The numerical simulation could successfully predict the behavior of hyporheic exchange and contribute the field study, river management and restoration.

• Journal of the Korean Chemical Society
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• v.29 no.5
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• pp.472-477
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• 1985

The rates for the aquation of $cis-[Co(en)(NH_3)_2Cl_2]Cl in acetone-water mixtures have been measured at various pressures and temperatures by the electric conductivity method. The rate constant measured at 25$^{\circ}$C in pure water solvent is 3.47 ${\times}10^{-4}$/sec. Rate constants are increased with increasing temperature, and decreased with increasing pressure and mole fraction of acetone. Activation volumes and other activation parameters are calculated from these rate constants. The activation volumes are all positive and lie in the limited range +2.82~+$8.2cm^3$/mole. The rate constants in aqueous acetone solution are analyzed with the solvent compositions. Plots of log $k_{obs}$ vs. Grunwald-Winstein Y values show that log $k_{obs}$ varies linearly and the gradients are about 0.25. The applications of a free energy cycle relating the process initial state ${\to}$ transition state in water to that in acetone-water mixture show that the changes in solvation of the transition state have a dominant effect on the rate. From these results the aquation of this complex would be discussed in terms of dissociative mechanism ($I_d$).

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.9 no.1
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• pp.94-100
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• 1999

Mercurous chloride($Hg_2Cl_2$) crystals hold promise for many acousto-optic and opto-electronic applications, which are prepared in closed ampoules by the physical vapor transport(PVT) growth methods. The thermal boundary conditions established by imposing different temperature on sidewalls of the enclosure cause simultaneous horizontal and vertical convectie flow in the PVT processes of$Hg_2Cl_2$ . It is found that for the ratios of horizontal to vertical thermal Rayleigh numbers$Ra_H/Ra{\ge}1.5$, the convective flow structure changes from multicellular to unicellular for the base parametric state of Ra=($2.79{\times}10^4$) , Pr=0.91, Le=1.01, Pe=4.60, Ar=0.2 and$C_V =1.01$. For the $\Delta T^{*}_H$ greater than 0.3, the $$\mid$U$\mid$_{max}$is increased with increasing $\Delta$ T^{*}_H$ and decreasing the aspect ratio. For the aspect ratios ranging from 0.1 to 1.0, there is a direct and linear relationship between $$\mid$U$\mid$_{max}$ and $\sqrt{{\Delta}T^_H\;^{\ast}}$.A decrease in the aspect ratio destabilizes the convective flow and results in an increase of the magnitude of convection in the crystal growth reactor. The vertical gradient tends to destabilize the convective flow which leads to oscillations, whereas the horizontal gradient stabilizes the convection.

• Journal of Acupuncture Research
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• v.19 no.3
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• pp.64-76
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• 2002

Objective : The purpose of this study is to investigate the mechanism and effect of moxibustion objectively and to be used as the quantitative data for developing the new thermal stimulating treatment by observing the combustion characteristics of commercial moxaes. Methods : We have selected two types(large-size moxa A(LMA), large-size moxa B(LMB)) among large moxaes used widely in the clinic. We examined combustion times, temperatures, temperature gradients in each period during a combustion of moxa. Results : 1. The ascending temperature gradient measured in the central point of non-contacted surface was fastest, the average ascending temperature gradient of both moxaes was $0.0384^{\circ}C/sec$, $0.0123^{\circ}C/sec$ respectively, 3.1 times faster in LMA. The maximum ascending temperature gradient was also about 2.9 times faster in LMA. The time required for the maximum ascending temperature gradient from ignition was 254sec, 411sec respectively. 2. The minimum descending temperature gradient in the retaining period was $-0.0250^{\circ}C/sec$, $-0.0090^{\circ}C/sec$ respectively and the average descending temperature gradient was $-0.0160^{\circ}C/sec$, $-0.0037^{\circ}C/sec$ respectively on the non-contact surface. 3. On the basis of the non-contact surface($A_I$), the time at which the effective stimulus period began to occur was about 264sec, 796sec respectively after an ignition, the time at which the maximum temperature began to occur was about 373sec, 1323sec respectively after an ignition, and the maximum temperature was $0.9^{\circ}C$ higher in LMA. The maximum ascending temperature gradient was also about 4.2 times faster in LMA. Conclusion : It was thought that not only the figure of moxicombustion device, but also the form and size of moxa had influence on the combustion characteristics deciding the performance of stimulus seriously.

• The Journal of Engineering Geology
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• v.12 no.1
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• pp.35-51
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• 2002

This study aims to establish the methodology for design of an optimum water curtain system of the unlined underground oil storage cavern satisfying the requirements of hydrodynamic performance in a volcanic terrain of the south coastal area. For the optimum water curtain system in the storage facility, the general characteristics of groundwater flow system in the site are quantitatively described, i.e. distribution of hydraulic gradients, groundwater inflow rate into the storage caverns, and hydrogeologic influence area of the cavern. In this study, numerical models such as MODFLOW, FracMan/MAFIC and CONNECTFLOW are used for calculating the hydrogeological stability parameters. The design of a horizontal water curtain system requires considering the distance between water curtain and storage cavern, spacing of the water curtain boreholes, and injection pressure. From the numerical simulations at different scales, the optimum water curtain systems satisfying the containment criteria are obtained. The inflow rates into storage caverns estimated by a continuum model ranged from about 120 m$^3$/day during the operation stage to 130~140m$^3$/day during the construction stage, whereas the inflow rates by a fracture network model are 80~175m$^3$/day. The excavation works in the site will generate the excessive decline of groundwater level in a main fracture zone adjacent to the cavern. Therefore, the vertical water curtain system is necessary for sustaining the safe groundwater level in the fracture zone.

• Korean Journal of Agricultural and Forest Meteorology
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• v.11 no.1
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• pp.27-38
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• 2009

The multi-level profile system is designed to measure the vertical profile of $H_2O$ and $CO_2$ concentrations in the surface layer to estimate the storage effects within the plant canopy. It is suitable for long-term experiments and can be used also in advection studies for estimating the spatial variability and vertical gradients in concentration. It enables the user to calculate vertical fluxes of water vapor, $CO_2$ and other trace gases using the surface layer similarity theory and to infer their sources or sinks. The profile system described in this report includes the following components: sampling system, calibration and flow control system, closed path infrared gas analyzer(IRGA), vacuum pump and a datalogger. The sampling system draws air from 8 inlets into the IRGA in a sequence, so that for 80 seconds air from all levels is measured. The calibration system, controlled by the datalogger, compensates for any deviations in the calibration of the IRGA by using gas sources with known concentrations. The datalogger switches the corresponding valves, measures the linearized voltages from the IRGA, calculates the concentrations for each monitoring level, performs statistical analysis and stores the final data. All critical components are mounted in an environmental enclosure and can operate with little maintenance over long periods of time. This report, as a practical manual, is designed to provide helpful information for those who are interested in using profile system to measure evapotranspiration and net ecosystem exchanges in complex terrain.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.14 no.6
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• pp.69-77
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• 2000

In this paper, the effects of the positions of the potential and current probes on the measurements of the ground resistance and potential gradients with the fall-of-potential method are described and the testing techniques to minimize the measuring errors are proposed. The fall-of-potential method is theoretically based on the potential and current measuring principle and the measuring error is primarily caused by the position and ground resistance of the measuring probes. The ground resistance is calculated by applying the 61.8% and rule in the fall-of-potential method, and then the potential probe is located on the straight line between the grounding electrode to be measured and the current probe. However, sometimes the grounding electrode to be measured and the measuring probes in on-site test might not be arranged on the straight line with adequate distance because there are building, road block, construction and other establishments. Provided that the grounding electrode to be measured and the measuring probes ar out of position on the straight line or have inadequate distance, the measurement of the ground resistance classically falls into an error and the measured ground resistance should be corrected. Measurements were focused on the grounding electrode system made by the ground rods of 2.4m long. It was found that the suitable separation between the grounding electrode to be measured and the current probe is more than 5 times of the length of the grounding electrode to be measured.