• Korean Chemical Engineering Research
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• v.43 no.6
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• pp.704-714
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• 2005

Phase separations of Poly(4-vinylphenol)(PVPh)/Ethyl Acetate and PVPh/Butyl Acetate solutions were measured using the thermal optical analysis (TOA) method. The experimental phase separation data were correlated with liquid-liquid equilibria relations based on PC-SAFT equation of state. The phase separations of these system showed the behaviors of LCST (lower critical solution temperature)-type. The measured cloud temperatures were lowered with increasing in molecular weights of polymer(PVPh), and cloud temperatures of PVPh/Ethyl Acetate solutions shifted to lower temperature regions, compared to the PVPh/Butyl Acetate solutions. Extents of cross-association between solvent molecule and polymer in the PVPh/Ethyl Acetate solutions were measured using the FT-IR spectrum analysis method, and cross-association parameters of PC-SAFT model were estimated from experimental extents of cross-association. By using the estimated cross-association parameters between PVPh and solvent molecule, binodal and spinodal curves of liquid-liquid equilibria in PVPh/Ethyl Acetate and PVPh/Butyl Acetate solutions were calculated from PC-SAFT equation of state. The calculated binodal curves of these system were shown to be well agreeable with the experimental cloud temperature curves.

• Journal of the Korean Chemical Society
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• v.52 no.1
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• pp.84-95
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• 2008

In this study, preconceptions held by chemistry major secondary school science teachers were searched in relation to explanations of water evaporation phenomena with phase equilibrium diagrams. 25 chemistry major science teachers were selected to complete questionnaires developed in this study and 6 among of them were selected to participate in follow-up interviews. Among these, 10 participants were selected for an evaluation of the change of their preconceptions through lessons developed in this study. From the results, it was found that many teachers believed that the phase equilibrium diagram could not explain water evaporation phenomena. They also thought that there was no relation between vapor pressure and the vertical axis of the phase equilibrium diagram. However, after the lessons in earth science, they recognized that the vapor pressure curve of the phase equilibrium diagram could be explained by adopting a saturated vapor curve. Because they had known the process of application the conceptions of saturated situation, nonsaturated situation, process of equilibrium movement in saturated vapor curve. They could understand natural phenomena such as evaporation with the phase equilibrium diagram through a change in their conceptions as guided from science lessons integrating earth science and chemistry.

• Journal of the Korean Geotechnical Society
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• v.40 no.3
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• pp.41-54
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• 2024

Regular monitoring plays a crucial role in ensuring the safety of geotechnical structures. Currently, nondestructive methods are employed to monitor such structures to minimize the impact, e.g., sensor-based accelerometers, displacement meters, image-based lasers, and drone imaging. These technologies can observe surface changes; however, they frequently suffer difficulties in terms of identifying changes in internal properties. To monitor changes in internal properties, in situ geotechnical investigations can be employed. A nondestructive test that can be used for this purpose is the spectral analysis of surface wave (SASW) test using geophones. The SASW test is a nondestructive method; however, due to the time required for data interpretation and the difficulty in analyzing the data, it is challenging to use the SASW test for monitoring applications that require frequent observations. However, it is possible to apply the first-step analysis, which yields the dispersion curve, for monitoring rather than the complete SASW analysis, which yields the shear wave velocity. Thus, this paper presents a fundamental study on the phase difference that derives the dispersion curve to utilize the SASW test for monitoring. The reliability of each phase difference interval is examined to determine the boundary to the subjected monitor. The study used phase difference data obtained using a geophone from a single-layered, homogeneous ground site to evaluate reliable boundaries. The findings of this study are expected to improve the utility of monitoring by identifying the ideal boundary for phase difference data.

• Journal of Korean Neurosurgical Society
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• v.58 no.6
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• pp.539-546
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• 2015

Objective : To report the learning curve of percutaneous endoscopic lumbar discectomy (PELD) for a surgeon who had not been previously exposed to this procedure based on the period and detailed technique with a retrospective matched comparative design. Methods : Of 213 patients with lumbar disc herniation encountered during the reference period, 35 patients who were followed up for 1 year after PELD were enrolled in this study. The patients were categorized by the period and technique of operation : group A, the first 15 cases, who underwent by the 'in-and-out' technique; group B, the next 20 cases, who underwent by the 'in-and-out-and-in' technique. The operation time, failure rate, blood loss, complication rate, re-herniation rate, the Visual Analogue Scale (VAS) for back and leg were checked. The alteration of dural sac cross-sectional area (DSCSA) between the preoperative and the postoperative MRI was checked. Results : Operative time was rapidly reduced in the early phase, and then tapered to a steady state for the 35 cases receiving the PELD. After surgery, VAS scores for the back and leg were decreased significantly in both groups. Complications occurred in 2 patients in group A and 2 patients in group B. Between the two groups, there were significant differences in operative time, improvement of leg VAS, and expansion of DSCSA. Conclusion : PELD learning curve seems to be acceptable with sufficient preparation. However, because of their high tendency to delayed operation time, operation failure, and re-herniation, caution should be exercised at the early phase of the procedure.

• Journal of the Korean Ceramic Society
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• v.38 no.10
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• pp.936-941
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• 2001

The influence of the ${Al_2}{O_3}$ particle size on flaw tolerance of the $ZrO_2/{Al_2}{O_3}$ composites prepared by mixing 5.31 mol% ${Y_2}{O_3}$-4.45 mol% ${Nb_2}{O_5}$-90.31 mol% $ZrO_2$ and ${Al_2}{O_3}$ was investigated. The composites exhibited rising R-curve behavior and plateau fracture toughness of 7.9 and $8.8MPam^{1/2}$ for the additions of 20 vol% of 0.2 and $2.8{\mu}m$ ${Al_2}{O_3}$ particles, respectively. The difference in the fracture toughness resistance was attributed mainly to the grain size of tetragonal $ZrO_2$ phase in the composites, which scaled with the ${Al_2}{O_3}$ particle size.

• The Journal of the Acoustical Society of Korea
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• v.22 no.1
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• pp.61-68
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• 2003

The guided wave has been widely employed to characterize thin plates and layered media. The dispersion curves of phase and group velocities are essential for the quantitative application of guided waves. In the present work, a fully automated system for the measurement of backward radiation of LLW has been developed. The specimen moves in two dimensional plane as well as in angular rotation. The signals of backward radiation of LLW were measured from an elastic plate in which specific modes of Lamb wave were strongly generated. Phase velocity of the corresponding modes was determined from the incident angle. The generated Lamb waves propagated forward and backward with the leakage of energy into water. Backward radiated LLW was detected by the same transducer and its frequency components were analyzed to extract the related information to the dispersion curves. The dispersion curves of phase velocity were measured by varying the incident angle. Moving the specimen in the linear direction of LLW propagation, group velocity was determined by measuring the transit time shift in the ultrasonic waveform.

• Nuclear Engineering and Technology
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• v.41 no.10
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• pp.1263-1274
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• 2009

Several experimental tests to simulate a reflood phase of a cold-leg LBLOCA of the APR1400 have been performed using the ATLAS facility. This paper describes the related experimental results with respect to the thermal-hydraulic behavior in the core and the system-core interactions during the reflood phase of the cold-leg LBLOCA conditions. The present descriptions will be focused on the LB-CL-09, LB-CL-11, LB-CL-14, and LB-CL-15 tests performed using the ATLAS. The LB-CL-09 is an integral effect test with conservative boundary condition; the LB-CL-11 and -14 are integral effect tests with realistic boundary conditions, and the LB-CL-15 is a separated effect test. The objectives of these tests are to investigate the thermal-hydraulic behavior during an entire reflood phase and to provide reliable experimental data for validating the LBLOCA analysis methodology for the APR1400. The initial and boundary conditions were obtained by applying scaling ratios to the MARS simulation results for the LBLOCA scenario of the APR1400. The ECC water flow rate from the safety injection tanks and the decay heat were simulated from the start of the reflood phase. The simulated core power was controlled to be 1.2 times that of the ANS-73 decay heat curve for LB-CL-09 and 1.02 times that of the ANS-79 decay curve for LB-CL-11, -14, and -15. The simulated ECC water flow rate from the high pressure safety injection pump was 0.32 kg/s. The present experimental data showed that the cladding temperature behavior is closely related to the collapsed water level in the core and the downcomer.

• Korean Journal of Radiology
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• v.1 no.3
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• pp.142-151
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• 2000

Objective: To determine the optimal scan timing for contrast-enhanced magnetic resonance angiography and to evaluate a new timing method based on the arteriovenous circulation time. Materials and Methods: Eighty-nine contrast-enhanced magnetic resonance angiographic examinations were performed mainly in the extremities. A 1.5T scanner with a 3-D turbo-FLASH sequence was used, and during each study, two consecutive arterial phases and one venous phase were acquired. Scan delay time was calculated from the time-intensity curve by the traditional (n = 48) and/or the new (n = 41) method. This latter was based on arteriovenous circulation time rather than peak arterial enhancement time, as used in the traditional method. The numbers of first-phase images showing a properly enhanced arterial phase were compared between the two methods. Results: Mean scan delay time was 5.4 sec longer with the new method than with the traditional. Properly enhanced first-phase images were found in 65% of cases (31/48) using the traditional timing method, and 95% (39/41) using the new method. When cases in which there was mismatch between the target vessel and the time-intensity curve acquisition site are excluded, erroneous acquisition occurred in seven cases with the traditional method, but in none with the new method. Conclusion: The calculation of scan delay time on the basis of arteriovenous circulation time provides better timing for arterial phase acquisition than the traditional method.

• Journal of Advanced Marine Engineering and Technology
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• v.33 no.1
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• pp.131-137
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• 2009

In this paper, we have manufactured hole type PRAM unit cell using phase change material $Ge_2Sb_2Te_5$. The phase change material $Ge_2Sb_2Te_5$ was deposited on hole of 500 nm size using sputtering method. Reset current of PRAM unit cell was confirmed by measuring R-V characteristic curve. Reset current of manufactured hole type PRAM unit cell is 15 mA, 100 ns. And electro and thermal characteristics of hole type PRAM unit cell were analyzed by 3-D finite element analysis. From simulation temperature of PRAM unit cell was $705^{\circ}C$.

• Journal of Korean Vacuum Science & Technology
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• v.6 no.4
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• pp.153-157
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• 2002

The electronic structures of Gd$_{5}$Si$_2$Ge$_2$ compound, which has a giant magnetocaloric effect, in the monoclinic and orthorhombic phases were calculated using the tight-binding linear-muffin-tin-orbital method within the atomic-sphere approximation. The calculated total energies of the monoclinic and orthorhombic structures in the paramagnetic phase confirm that the orthorhombic structure is more stable than monoclinic structure. The density of states (DOS) at the Fermi level of the orthorhombic phase is higher than that of the monoclinic phase in the paramagnetic phase, fulfilling the Stoner criterion. The calculated charge density verified the breaking of Ge(Si)-Ge(Si) bonding in the basal plane upon the orthorhombic-monoclinic phase transition. The DOS curve fairly well reproduces the photoemission spectrum.m.