• Proceedings of the Korean Society of Precision Engineering Conference
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• 1995.04b
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• pp.33-38
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• 1995

In this study, unsistered, pre-sintered and sintered low purity alumina ceramics were machined with various tools to clarify the machniability, the optimum tool materials and the optimum tool materials and the optimum cutting conditions. The maon conclusions obtained were as follows. (1) Machined withalloy steel tool, the machinabilty of te pre-sintered ceramics becomes better with the decrease of pre-sintering temperature, but that of unsintered ceramics(white body) was extremely poor. (2) In the case of carbide tool K01, the tool life in machining white body was the longest, and the machinabilty of pre-sintered ceramics becomes poorer with the increase of the pre-sintering temperature. (3) In the case of ceramic tool, the 10000-1100 .deg. C pre-sintered ceramics showed te best machinability within a certain cutting speed range. So far as dry machining, the above combination and conditions showed the highest productivity. (4) When the pre-sintered ceramics were wet machined withsintered diamond tool, the tool life becomes extremelylong, and higher cutting speed can be can be used than in the case offull-sintered ceramics. The productivity of wet cutting is much higher than that ofdry cutting.

• Journal of the Korean Society for Nondestructive Testing
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• v.29 no.3
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• pp.219-223
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• 2009

This paper prescribed the structural integrity of the API 5L X65 pipeline subjected to tensile pre-strain. The effects of pre-strain on the mechanical properties of API 5L X65 pipe were substantially investigated through a variety of the experimental procedures. Axial tensile pre-strain of 1.5, 5 and 10% was applied to plate-type tensile specimens cut from the pipe body prior to mechanical testing. Tensile test revealed that yield strength and tensile strength were increased with increasing tensile pre-strain. The increasing rate of the yield strength owing to the pre-strain is greater than that of the tensile strength. However, the pre-strain up to 5% had a little effect on the decreasing of the fracture toughness. The structural integrity of the API 5L X65 pipeline subjected to large plastic deformation was evaluated through the fitness-for service code.

• International Journal of Fluid Machinery and Systems
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• v.1 no.1
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• pp.10-23
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• 2008

The development of pre-set wavelength G$\ddot{o}$rtler vortices are studied in the boundary-layer flows on concave surfaces of 1.0 and 2.0 m radius of curvature. The wavelengths of the vortices were pre-set by thin wires of 0.2 mm diameter placed 10 mm upstream and perpendicular to the concave surface leading edge. Velocity contours were obtained from velocity measurements using a single hot-wire anemometer probe. The most amplified or dominant wavelength is found to be 15 mm for free-stream velocity of 2.1 m/s and 3.0 m/s on the concave surface of R = 1 m and 2 m, respectively. The velocity contours in the cross-sectional planes at several streamwise locations show the growth and breakdown of the vortices. Three different regions can be identified based on the growth rate of the vortices. The occurrence of a secondary instability mode is also shown in the form of mushroom-like structures as a consequence of the non-linear growth of the G$\ddot{o}$rtler vortices. By pre-setting the vortex wavelength to be much larger and much smaller than the most amplified one, the splitting and merging of G$\ddot{o}$rtler vortices can be respectively observed.

• Journal of Ginseng Research
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• v.35 no.1
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• pp.45-51
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• 2011

Wild ginseng has been used as a traditional medicine for thousands of years and for increase physical strength in Korea, China and Japan. This study reports that cultivated wild ginseng (CWG) inhibits adipocyte differentiation of 3T3-L1 pre-adipocytes in a concentration-dependent manner. Inhibition of adipocyte differentiation is one possible anti-obesity strategy. CWG inhibits the expression of the adipocyte differentiation regulator peroxisome proliferators-activated receptor (PPAR)${\gamma}$ and CCAAT/enhancer-binding protein ${\alpha}$mRNA. It also inhibited the expression of PPAR${\gamma}$ and adiponectin at the protein level during the differentiation of pre-adipocytes into adipocytes. Additionally, CWG blocked the cell cycle at the sub-$G_1$ phase transition, causing cells to remain in the pre-adipocyte state. These results indicate that CWG inhibits adipocyte differentiation and adipogenesis through pre-adipocyte cell cycle arrest in cultured 3T3-L1 cells.

• Journal of Korean Home Economics Education Association
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• v.7 no.2
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• pp.35-50
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• 1995

The purpose of this study was to investigate the recognition degrees of contents in Home Economics textbook for middle school students among pre-middle school students and their parents. It is for developing better Home Economics textbook. Three objectives of this study were ; 1) To find the recognition degrees of the fact that Home Economics subject is supposed to utilize for not only girls, but boys students in middle schools in 1996 among pre-middle school students and their parents. 2) To find the degrees of necessity in each field of Home Economics subject among pre-middle school students and their parents. 3) To find the differences in recognition degrees of understandings, attitudes, and sills of Home Economics subject between pre-middle school students and their parents. Questionnaire survey method was utilized to 1,205 sixth grade students and their parents in Pusan. The results of this study as follows; 1) It was low that the recognition degrees of the fact that Home Economics subject is supposed to utilize for both girls and boys in middle school among both pre-middle school students and their parents. This result implies that it is important to important to disseminate the curriculum change in Home Economics practice to the public. 2) It was high that the recognition degree of necessity in each field of Home Economics subject among pre-middle school students and their parents. The recognition degree were different according to sociodemographic factors. That is , $\circled1$the recognition degrees of students were lower than their parents; $\circled2$ the recognition degrees of parents who have high education were higher than those who have low education ; $\circled3$ the recognition degree of an environmental field was highest. 3) There were little differences between pre-middle school students and their parents in the recognition degrees of understandings, attitudes, and skills of Home Economics subjects: The recognition degrees of girls fathers showed higher scores than boys fathers those of in understandings and skills of Home Economics subject. The recognition degrees of girls fathers showed higher scores than those of girls in attitudes of Home Economics subject.

• Communications of Mathematical Education
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• v.32 no.1
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• pp.1-22
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• 2018

The purpose of the study was to examine the effects of mentoring experience in STEAM classes on pre-service mathematics teachers' teaching competency for STEAM education. The study was conducted with 23 pre-service mathematics teachers who participated in the mentoring program affiliated with free learning semester system during one semester. To investigate the changes of pre-service mathematics teachers' teaching competencies for STEAM education and the effects of the mentoring program, pre, post questionnaires, lesson journals, and whole group discussion data were collected. According to the results, pre-service mathematics teachers' competencies for 'knowledge of STEAM education', 'subject matter knowledge', 'teaching and learning methods', and 'learning environments and circumstances' categories were improved significantly after the mentoring program. Especially, some results indicated that pre-service mathematics teachers' teaching experiences in real STEAM classrooms were very helpful for the development of understandings of STEAM education and construction of practical knowledge.

• Restorative Dentistry and Endodontics
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• v.40 no.1
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• pp.23-29
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• 2015

Objectives: The aim of this study was to evaluate the effect of pre-etching on the bond strength of silorane-based composite specific adhesive system to dentin. Materials and Methods: Thirty human molars were randomly divided into 5 groups according to the different bonding strategies. For teeth restored with silorane-based composite (Filtek Silorane, 3M ESPE), the specific self-etching adhesive system (Adhesive System P90, 3M ESPE) was used with and without pre-etching (Pre-etching/Silorane and Silorane groups). Teeth restored with methacrylate based-composite (Filtek Z250, 3M ESPE) were hybridized with the two-step self-etching system (Clearfil SE Bond, Kuraray), with and without pre-etching (Pre-etching/Methacrylate and Methacrylate groups), or three-step adhesive system (Adper Scotchbond Multi-Purpose, 3M ESPE) (Three-step/Methacrylate group) (n = 6). The restored teeth were sectioned into stick-shaped test specimens ($1.0{\times}1.0mm$), and coupled to a universal test machine (0.5 mm/min) to perform microtensile testing. Results: Pre-etching/Methacrylate group presented the highest bond strength values, with significant difference from Silorane and Three-step/Methacrylate groups (p < 0.05). However, it was not significantly different from Pre-etching/Silorane and Methacrylate groups. Conclusions: Pre-etching increased bond strength of silorane-based composite specific adhesive system to dentin.

• Korean Journal of Applied Biomechanics
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• v.31 no.2
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• pp.140-147
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• 2021

Objective: The purpose of this study is to identify the mechanism of changes in maximum voluntary torque with the magnitude and duration of pre-activation torque during voluntary isometric knee extension. Method: 11 male subjects (age: 25.91±2.43 yrs., height: 173.12±3.51 cm, weight: 76.45±7.74 kg) participated in this study. The subjects were required to produce maximal voluntary isometric torque with a particular pre-activation torque condition. The properties of pre-activation torque consisted of the combinations of 1) three levels of magnitude, e.g., 32 Nm, 64 Nm, 96 Nm, and 2) two levels of duration, e.g., 1 sec, and 3 sec; thus, a total of six conditions were given to the subjects. The force and EMG data were measured using the force transducers and wireless EMG sensor, respectively. Results: The results showed that the maximum voluntary torque increased the most with relatively large and fast (96 Nm, 1 sec) pre-activation condition. Similarly, with relatively large and fast (96 Nm, 1 sec) preactivation, it was found that the integrated EMG (iEMG) of the agonist muscles increased, while no significant changes in the co-contraction of the antagonist muscles for the knee extension. Also, the effect of pre-activation conditions on the rate of torque development was not statistically significant. Conclusion: The current findings suggest that relatively larger in magnitude and shorter in duration as the properties of pre-activation lead to a larger magnitude of maximal voluntary torque, possibly due to the increased activity of the agonist muscles during knee extension.

• Korean Journal of Medicinal Crop Science
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• v.26 no.1
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• pp.1-7
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• 2018

Background: Rehmanniae radix preparata (RRP) has been used as a traditional medicine and is one of the most important oriental herbal medicines. However, the physical characteristics of RRP are not suitable for use in industry. The present study was under-taken to determined the preparation method of RRP powder and the physicochemical characteristics of RRP powder by milling under different pre-freezing temperatures. Methods and Results: Moisture content, powder yield, particle size, bulk density, compressive stress, extraction yield, and 5-HMF content of PRR powders by milling with pre-freezing temperatures (-20, -40, -60, and $-80^{\circ}C$) were analyzed, and correlation among these factors was determined. Powder yield increased and particle size decreased in a pre-freezing temperature-dependent manner from -20 to $-60^{\circ}C$. The Hausner ratio increased from 1.186 to 1.225 with decreasing temperature from -20 to $-80^{\circ}C$, whereas compressive stress showed the opposite trend. Extraction yield and 5-HMF content were not significantly different between RRP powder. Significant correlations were observed among pre-freezing temperature and physical characteristics (e.g., yield, particle size, Hausner ratio, and compressive stress). Conclusions: These results suggest that the pre-freezing temperature is an important factor affecting the physical characteristics of PRR powder and applicable to the industrial production of RRP powder.

• Journal of Korean Academy of Nursing
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• v.33 no.8
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• pp.1153-1160
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• 2003

Purpose. 1) To identify the time taken from symptom onset to the arrival at the hospital (pre-hospital delay time) and time taken from the arrival at the hospital to the initiation of the major treatment (in-hospital delay time) 2) to examine whether rapid treatment results in lower mortality. 3) to examine whether the pre- and in-hospital delay time can independently predict in-hospital mortality. Methods. A retrospective study with 586 consecutive AMI patients was conducted. Results. Pre-hospital delay time was 5.25 (SD=10.36), and in-hospital delay time was 1.10 (SD=1.00) hours for the thrombolytic therapy and 50.24 (SD=121.18) hours for the percutaneous transluminal coronary angio-plasty (PTCA). In-hospital mortality was the highest when the patients were treated between 4 to 48 hours after symptom onset using PTCA (p=.02), and when treated between 30 minutes and one hour after hospital arrival using thrombolytics (p=.01). Using a hierarchical logistic regression model, the pre- and in-hospital delay times did not predict the in-hospital mortality. Conclusion. Pre- and in-hospital delay times need to be decreased to meet the desirable therapeutic time window. Thrombolytics should be given within 30 minutes after arrival at the hospital, and PTCA should be initiated within 4 hours after symptom onset to minimize in-hospital mortality of AMI patients.