• Journal of the Korean Ceramic Society
• /
• v.42 no.1
• /
• pp.62-68
• /
• 2005

Oxidtion behavior of $Si_{3}N_{4}$ ceramics with the different porosity by the Nitrided Pressureless Sintering (NPS) were investigated in pure oxygen gas atmosphere at 1000 to $1300^{circ}C$. The thickness of formed oxide film on the surface of silicon nitride ceramics was increased with oxidation time and temperature. The oxide film thickness of 5A5Y5Si and 5A5Y10Si specimens for 100 h at 1300^{circ}C$ was about 10 $\mu$m and 20 $\mu$m, respectively. The oxidation of 5A5Y5Si and 5A5Y10Si specimens follows the parabolic behavior with an apparent activation energy of 215 kJ/mol and 104 kJ/mol, respectively. The flexural strength of 5A5Y5Si specimens after oxidation test for 500 h at 1300^{circ}C were maintained as-received value of 500 ma. On the other hand, that of 5A5Y10Si specimens were decreased about 100 MPa in as-received value.

• Tunnel and Underground Space
• /
• v.28 no.3
• /
• pp.232-246
• /
• 2018

In this study, the relationship between in situ seismic wave velocities and RMR (rock mass rating) was investigated in a test bed for the examination of the basis of rock classification (RMR) based on seismic wave velocity. The seismic wave velocity showed a monotonous increase with depth. It was also found that there was no systematic correlation between the seismic wave velocity (Vp) and other parameters (RQD, joint spacing, UCS, rock core Vp, and RMR) collected at the same depth of the same borehole. However, correlative relation was observed among RMR, RQD, and joint spacing. On the other hand, when all the data in the borehole (three holes) are examined without considering the depth, Vp still shows no correlation with RMR parameters (e.g., correlative coefficient for uniaxial compressive strength and joint spacing are 0.039 and 0.091, respectively), but Vp shows weak correlative relation with RMR and RQD (correlative coefficient for RQD and RMR are 0.193 and 0.211, respectively). Thus, it is found that it is difficult to deduce physical properties of rock mass directly from seismic wave velocities, but the seismic wave velocity can be used as a tool to approximate rock mass properties because of weaker correlation between Vp and RMR with RQD. In addition, the velocity value of for soft and moderate rocks suggested by widely used construction standards is slower than that of the observed velocity, implying that the standards need to be examined and revised.

• Journal of Environmental Impact Assessment
• /
• v.16 no.1
• /
• pp.69-77
• /
• 2007

This study has been conducted to assess blackish-water phenomena in Dam reservoir. To searching for the reason, we survey physical changes in reservoir and analyze metal and organic content in particulate materials and water. The blackish-water phenomena in lake A are occurred with turbidity increases in turnover season irregularly. It was reported on 6 Jan. 2005 weakly and the water column mixed with 35~40m depth and water temperature shows $7^{\circ}C$. The turbidity of AD and AM site increased up to 20NTU. Especially, AN site shows 27NTU, such a result makes that Dam manager conclude it to blackish-water phenomena. The results of sequential extraction analysis show that over 80% of Al, Cr and Fe is existed in residual form in sediment. On the other hand, the most part of Mn shows exchangeable and carbonates form, which have a good possibility of release to water column. Mn contents in pore waters of the sediment samples are also found to be ~4 times higher than Fe contents. The metal contents in pore water of different dam sites are in order of AN (Fe: 9.98, Mn: 40.6) > AD(8.33, 37.5) > DD(1.91, 2.55). According to the results of extracted organic materials from sediment, humic substances is occupied with over 85% in total organic carbon including 23~45% of humic acid (HA) and 0.9~8.5% of fulvic acid (FA). However, HA content in pore water is not detectable while FA contents, acid-soluble humic fractions is higher than that of sediment(10~15%). which indicating that FA is a main humic components affecting water color. The color unit per DOC of FA in pore waters of different dam sites are found to be higher in lake A than lake D. From the results, it could be suggested that blackish-water phenomena of lake A are mainly arise from higher concentration of Mn and water soluble organic fractions (e.g., FA) released from sediments as well as the strength of turnover in Dam reservoir.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.19 no.2
• /
• pp.405-412
• /
• 2018

The budget is an essential tool for the systematic management of the organizational performance and for diagnosing the status of an organization. Effective budget execution is important to hospital management due to the nonprofit nature of hospitals. On the other hand, there are few studies regarding the budgetary slack of hospitals in Korea. The purpose of this study was to investigate the effects of the university hospital budgeting system characteristics on the budgetary slack. For this purpose, the data from 118 staff of a university hospital located in Seoul were collected by self-administered surveys. Frequency analysis, correlation analysis, and multiple regression analysis were carried out using Stata Ver. 14. The main results of this study were as follows. First, information asymmetry has a positive influence on the budgetary slack. Second, budget feedback and budget motivation have a negative effect on the budgetary slack. These findings suggest that the sharing of budget-related information among hospital staff is important for efficient hospital management. In addition, it is necessary to establish ways to enhance the feedback and motivation in budgetary activities for managing the budgetary slack systematically. The major strength of this study is that it draws attention to research concerning the budgetary slack of hospitals in the absence of research on the budgetary slack. The significance of this study was to provide an empirical basis for improving the efficiency of hospital management.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.18 no.2
• /
• pp.689-696
• /
• 2017

The practical applications of ordinary high-fluidity concrete have been limited due to several drawbacks, such as high hydration heat, high amount of shrinkage, and non-economic strength development. On the other hand, due to its advantages, such as improvement of construction quality, reduction of construction cost and period, the development of high-fluidity concrete is a pressing need. This study examined the properties of high-fluidity concrete, which can be manufactured on the low binders using a viscosity agent to prevent the segregation of materials. The optimal viscosity agent was selected by an evaluation of the mechanical properties of high-fluidity concrete among six viscosity agents. The acrylic type and urethane type viscosity agents showed the best performance within the range where no material separation occurred. The mechanical properties were evaluated to examine the optimal amount of AC and UT viscosity agent added by mixing two viscosity agents according to the adding ratio and blending them together with high performance water reducing agent. When the ratio of the AC : UT viscosity agents was 5:5, it was most suited for high-fluidity concrete with low binders by increasing the workability and effect of the reducing viscosity.

• Journal of Korean Tunnelling and Underground Space Association
• /
• v.16 no.6
• /
• pp.543-552
• /
• 2014

This research covers correlation analysis between the machine data measured from EPB Shield TBM construction site and the ground condition during excavation, and figures out how the machine data are affected by the change of ground conditions through single and mixed parameter analysis. It was found that when the ground is changed from hard rock to soft rock, the ratio of the cutter torque to thrust force increases. The relationship between the ratio of the cutter torque to thrust force and the penetration rate shows that the ratio has a certain range of values for hard rock; on the other hand, it increases for soft rock. It means that we can recognize a sign of appearance of weak zone by assessing the ratio of the cutter touque to thrust force according to each penetration rate. Multiple regression analysis of the machine data showed that the cutter torque increases with the increases of the total thrust force, and it decreases with the increase of the uniaxial compressive strength of the ground.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.19 no.4
• /
• pp.69-76
• /
• 2018

This study examined the effect of the heat treatment and alloying elements (B, Ti) on the microstructures and mechanical properties of API J55 steel. The experiments were carried out using various austenization temperatures ($880^{\circ}C$, $910^{\circ}C$, $940^{\circ}C$), cooling methods (water quenching, oil quenching) and tempering temperatures (none, $550^{\circ}C$, $650^{\circ}C$) with J55 and J55+B,Ti steels. The phase diagram and CCT curve were simulated based on the chemical compositions of the J55 and J55+B,Ti steels to predict the microstructures. The results showed that the A1 and A3 temperatures decreased and, as a result, the noses of the ferrite and bainite parts of the CCT curve moved to the right. Various microstructures were formed, namely martensite, bainite, ferrite and pearlite, in accordance with the heat treatment, which had an effect on the hardness, tensile strength and toughness. Martensite was formed after water quenching, but bainite and ferrite appeared after oil quenching with the J55 specimens. On the other hand, martensite was formed, regardless of the cooling method (water quenching, oil quenching), with the J55+B,Ti specimens, because of the improvement of the hardenability caused by the addition of boron. Therefore, the J55+B,Ti specimens exhibited much higher mechanical properties than the J55 specimens, even after the tempering treatment, since the addition of Ti caused fine precipitates to be formed, which inhibited grain growth at the recrystallization temperature.

• Progress in Superconductivity
• /
• v.6 no.1
• /
• pp.79-83
• /
• 2004

We fabricated Bi-2223/Ag superconductor tape with 55 filaments and estimated the magnetic field dependence of critical current (I$_{c}$) and index n (n) up to 30 T at 4.2 K. The I$_{c}$ and n were characterized as a function of external magnetic field parallel to the tape surface on increasing and decreasing field, using a 35 T hybrid magnet. The $I_{c}$ was estimated to be 325 A, and n was 32, 22, and 26 in the electric field range of $0.1 ∼1\mu$V/cm, 1∼10 $\mu$V/cm, and 0.1∼10 $\mu$V/cm, respectively, under self-field at 4.2 K. It was observed that $I_{c}$ was dependent on magnitude of magnetic field and it decreased exponentially as the field increased; in a parallel and increasing field, It was 128 A at 30 T which is approximately 40% of critical current in self-field. In addition, the $I_{c}$ was higher on decreasing field than that on increasing one. On the other hand, n did not significantly depend on field strength up to 30 T, nor varied on whether increasing or decreasing field; n value in 0.1∼1 $\mu$V/cm was 23.0$\pm$5.2 and 27.8$\pm$8.0 on increasing and decreasing field, respectively. The n value on decreasing magnetic field was slightly higher than that on increasing field. This hysteretic behavior of n was similar to that of$ I_{c}$, which is related to the trapped flux at the grain boundary.ary.

• Maxillofacial Plastic and Reconstructive Surgery
• /
• v.32 no.4
• /
• pp.324-331
• /
• 2010

The radial forearm free flap (RFFF) has become a workhorse flap as a means of reconstructing surgical defects in the head and neck region. We have transferred 12 RFFFs with fasciocutaneous type on oral cavity defects in 12 patients after cancer resection and submucous fibrotic lesion ablation from 2005 to 2007 at Department of oral and maxillofacial surgery, Pusan National University Hospital. We reviewed retrospectively patients' charts and followed up the patients. Clinical analysis on the cases with RFFFs focusing on flap morbidity, indications and available vessels was done. The results of study are follows: 1. RFFF could be applied for all kind of defects after resection of tongue, floor of mouth, buccal mucosa, denuded bone of palate, maxilla, and mandible. 2. All free flaps could be used for primary reconstruction. The survival rate of 12 RFFFs was 92%. Partial marginal loss of the flaps was shown as 3 cases among 12 cases. Large size-vessels like superior thyroid artery, facial artery, internal jugular vein were favorable for microvascular anastomosis. 3. Parenteral nutrition instead of nasal L-tube also can be favorable for postoperative a week for better healing of the flap if the patients couldn't be tolerable with nasal tubing. 4. Donor sites with thigh skin graft were repaired with wrist band for 2 weeks. The complications included scarring, abnormal sensation on hand, and reduced grip strength in few patients, but those didn't induce major side effects. 5. Most RFFFs were well healed even if mortality rate of cancer patients was shown as 50% (5/10 persons). The mortality of patients was not correlated with morbidity of the flaps. We could identify the usefulness of RFFF for restoration of oral function, esthetics if the flap design, tissue transfer indications, and well controlled operation are proceeded.

• Korean Journal of Childcare and Education
• /
• v.10 no.5
• /
• pp.229-248
• /
• 2014

The purpose of this study is to draw guidelines on how to select traditional games that would efficiently help and develop multiple intelligences in children. Guidelines standard of section inquiries were prepared through a Delphi survey targeting twenty experts in early childhood education and traditional games. As a result, linguistic intelligence questions regarding writing, listening, speaking and vocabulary acquisition were selected. logical-mathematical intelligence questions regarding strategy, counting, patterns, hypothesis, verification, and comparing, contrasting, calculating ability were selected. Spatial intelligence questions regarding drawing, coloring, representation activities, operating and creating were selected, physical performance intelligence questions regarding global muscles, eye-hand coordination, flexibility, accommodation force, balance, agility and muscular strength were selected. Musical intelligence included questions about singing, and playing musical instruments. Interpersonal intelligence included perspective-taking, role-sharing, cooperation and discussion. For intrapersonal intelligence questions regarding personal significance-ties, planning-decision making, emotional expression and problem solving were selected. Finally, in relation to naturalist intelligence, questions regarding living organisms, inanimate objects and seasons were selected. In addition, traditional games were analyzed based on the finalized guidelines, and the results showed that each of the traditional games would not only work with one intelligence at a time but with other different intelligence as well. In the light of that, the study confirmed the validity of the guidelines on how to select traditional games that would develop multiple intelligences in children.