• Polymer(Korea)
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• v.36 no.6
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• pp.693-698
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• 2012

In this study aluminum isopropyl oxide ($Al(O-i-Pr)_3$) was supported on the amine-functionalized surface of silica to synthesize high molecular weight (MW) polylactide (PLA), and it was tested for PLA polymerization behaviors. A silica was funtionalized with silane compound having amine groups, then in-situ treated with $Al(O-i-Pr)_3$. $Al(O-i-Pr)_3$ attached to amine group on silica showed activity only in the presence of MAO (methyl aluminoxane). At the polymerization temperature of $115^{\circ}C$, the conversion and the MW of PLA were increased as the amount of silane was increased. At the polymerization temperature of $130^{\circ}C$, the conversion was decreased while the MW was increased drastically and reached to MW 44000 g/mol when the amine concentration was 3.0 mmol/g. A bimodal type GPC curve was shown at the polymerization temperature of $115^{\circ}C$. As the amount of amine group increased, the peaks of GPC curve were merged. At the polymerization of $130^{\circ}C$, a unimodal GPC curve was shown. $Al(O-i-Pr)_3$ supported on amine-functionalized silica was able to produce higher MW PLA with enhanced activity compared to homogeneous $Al(O-i-Pr)_3$.

• Journal of the Korean Society of Physical Medicine
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• v.9 no.1
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• pp.45-53
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• 2014

PURPOSE: In this study, we tried to find out what kind of exercise was more effective in sleep disorder by comparing melatonin in blood after applying low intensity with high intensity exercise to sleep disordered rats induced by experiment. METHODS: We used male Sprague-Dawley rats which were 8weeks old and weighted 300g. They were supplied with water and food without any restriction. We kept the room temperature at $25^{\circ}C$ and controld the length of day and night in 12 hours blocks, respectively. We divided the rats 60 into 2 groups. To one group we applied low intensity exercise, and to the other we applied high intensity exercise for 15minutes per day over a period of 4 weeks. We extracted the blood from abdominal aorta before, after exercise, moved into EDTA tube, performed centrifugation. We decanted the serum $200{\mu}l$ from the blood into microcentrifuge tube by samples and moved into polypropylene culture tubes with micro pipette. We split enzyme solution $50{\mu}l$ into the tubes with melatonin direct kits and make them react at $37^{\circ}C$ for 2 hours. We split assay buffer $50{\mu}l$ into each tube and mixed melatonin tracer $50{\mu}l$ and melatonin antiserum $50{\mu}l$, respectively. After we made them react in room temperature, we decanted the superficial layer with a centrifuge and measured the activity for 1 minute by competitive method with ${\gamma}$-counter equipment. We draw a standard curve through logit-log graph with CPM(counts per minute) and counted the melatonin by B/B0. We conducted independent t-test to examine the homogeneous of melatonin value of before low-intensity and high-intensity exercise. We performed paired t-test to compare before and after low-intensity and high-intensity exercise, respectively. We carried out independent t-test to compare melatonin value after low-intensity and high-intensity exercise. Significance level was .05. RESULTS: The results were as follows; firstly melatonin was more increased in the group who was exposed to high intensity exercise when we compared before to after high and low intensity exercise, respectively. Secondly, high intensity exercise was more effective than low intensity exercise when we compared the two. CONCLUSION: In conclusion, secretion of melatonin which is the material of sleep improvement could be promoted by high intensity exercise. Low intensity exercise acted as a stress rather than improving sleep and had a negative effect on the secretion of melatonin because the melatonin was affected by stress.

• Proceedings of the KSRS Conference
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• 2006.03a
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• pp.341-343
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• 2006

The current spectral shape matching method (SSMM), developed by Ahn and Shanmugam (2004), relies on the assumption that the path radiance resulting from scattered photons due to air molecules and aerosols and possibly direct-reflected light from the air-sea interface is spatially homogeneous over the sub-scene of interest, enabling the retrieval of water-leaving radiances ($L_w$) from the satellite ocean color image data. This assumption remains valid for the clear atmospheric conditions, but when the distribution of aerosol loadings varies dramatically the above postulation of spatial homogeneity will be violated. In this study, we present the second version of SSMM which will take into account the horizontal variations of aerosol loading in the correction of atmospheric effects in SeaWiFS ocean color image data. The new version includes models for the correction of the effects of aerosols and Raleigh particles and a method fur computation of diffuse transmittance ($t_{os}$) as similar to SeaWiFS. We tested this method over the different optical environments and compared its effectiveness with the results of standard atmospheric correction (SAC) algorithm (Gordon and Wang, 1994) and those from in-situ observations. Findings revealed that the SAC algorithm appeared to distort the spectral shape of water-leaving radiance spectra in suspended sediments (SS) and algal bloom dominated-areas and frequently yielded underestimated or often negative values in the lower green and blue part of the electromagnetic spectrum. Retrieval of water-leaving radiances in coastal waters with very high sediments, for instance = > 8g $m^{-3}$, was not possible with the SAC algorithm. As the current SAC algorithm does not include models for the Asian aerosols, the water-leaving radiances over the aerosol-dominated areas could not be retrieved from the image and large errors often resulted from an inappropriate extrapolation of the estimated aerosol radiance from two IR bands to visible spectrum. In contrast to the above results, the new SSMM enabled accurate retrieval of water-leaving radiances in a various range of turbid waters with SS concentrations from 1 to 100 g $m^{-3}$ that closely matched with those from the in-situ observations. Regardless of the spectral band, the RMS error deviation was minimum of 0.003 and maximum of 0.46, in contrast with those of 0.26 and 0.81, respectively, for SAC algorithm. The new SSMM also remove all aerosol effects excluding areas for which the signal-to-noise ratio is much lower than the water signal.

• The Journal of Korean Academy of Prosthodontics
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• v.44 no.6
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• pp.740-750
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• 2006

Statement of problems. In an attempt to reduce screw loosening, dry lubricant coatings such as pure gold or tefron have been applied to the abutment screw. However, under repeated tightening and loosening procedures, low wear resistance and adhesion strength of coating material produced free particles on the surface of abutment screw and increased frictional resistance resulting in screw tightening problems. Purpose. The aim of this study was to compare friction coefficient, adhesion strength, vickers hardness and evaluate coating surface of titanium alloy specimens coated with TiN(titanium nitride), ZrN(zirconium nitride) and WC(tungsten carbide). Material and method. Titanium alloy(Ti-6Al-4V) discs of 12mm in diameter and 1mm in thickness divided into 4 groups. TiN, ZrN and WC was coated for the specimens of 3 groups respectively, and those of 1 group were not coated. Each group was made up of 4 specimens. In this study, sputtering method was used among the PVD(Physical Vapor Deposition) techniques available for TiN, ZrN and WC coatings. Friction coefficient, adhesion strength, vickers hardness and coating surface of 4 groups were measured. Results. 1. For all three coating conditions, friction coefficient was significantly decreased. Especially, ZrN coated surface showed the lowest value. $TiN(0.39{\pm}0.02)$, $ZrN(0.24{\pm}0.01)$, $WC(0.31{\pm}0.03)$. 2. TiN coating showed the highest adhesion strength, however ZrN coating had the lowest value. $TiN(25.3N{\pm}1.6)$, $ZrN(14.8N{\pm}0.6)$, $ WC(18.4N{\pm}0.7)$. 3. Vickers hardness of all three coatings was remarkably increased as compared with that of none coated specimen. TiN coating had the highest Vickers hardness, however WC coating showed the lowest value. $TiN(1865.2{\pm}33.8)$, $ZrN(1814.4{\pm}18.6)$, $WC(1008.5{\pm}35.9)$. 4. The ZrN or WC coated specimen showed a homogeneous and smooth surface, however the rough surface with defects was observed for TiN coating. Conclusions. When TiN, ZrN and WC coating applied to the abutment screw, frictional resistance would be reduced, as a result, the greater preload and prevention of the screw loosening could be expected.

• Journal of the Korean Wood Science and Technology
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• v.42 no.6
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• pp.666-674
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• 2014

In this study, we investigated mechanical properties of Korean softwoods after applying thermal compression. Density of compressed woods was notably increased with thermal compression. In case of 50% compression set, density of Korean pine (Pinus koraiensis), Japanese red pine (P. densiflora), and Larch (Larix kaempferi) wood was increased by 71%, 74%, and 76%, respectively, when compared to the control group. The strength of woods was increased and quality of the woods became homogeneous with an increases in the compression set. On the 50% compression set, the compressive strength, bending strength, and hardness of Korean pine wood was increased by 76%, 83%, and 55%, respectively compared to the control group. Longitudinal compressive strengths of Japanese red pine wood increased by 69%, 130%, and 76%, respectively and those of Larch wood increased by 77%, 120%, and 44%, respectively. In thermal compression wood, mechanical properties of Larch wood was the highest, while those of Korean pine wood were the lowest. However, Japanese red pine wood showed the highest in the increase rate of mechanical properties after the thermal compression.

• Journal of Science and Technology Studies
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• v.6 no.2 s.12
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• pp.77-102
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• 2006

This paper analyzes shaping of the discourse of "avoidance of S&T" throughout 2002 in Korea and main ideas on it and argues that the Korean S&T community is not homogeneous. The Korean S&T community consists of many subgroups with different interest mainly according to the institutions where they work as well as their specialties, qualifications, and tasks. The discourse of avoidance of S&T" was begun with the first notice of the rapid decrease in applications of Korean SAT for S&T majors in the middle of 2001. The decrease was interpreted as a warning sign of the avoidance of S&T among teenagers and developed into the avalanche of discussions on the causes of such rapid decrease around the end of the year. However, through 2002, the "avoidance of S&T' was developed into a general policy agenda covering most of problems in S&T, not just a teenagers' issue any more. Many scientists and engineers claimed that their own difficulties and problems be the main causes of the "avoidance of S&T". In the name of measures to overcome the avoidance, they requested the government to solve their problems and to accept their demands. Those claims varied from group to group. Some of them were shared among all scientists and engineers; some of them were criticized by other groups with different interest in it; some of them did not get any attention of other groups. Scientists and engineers seemed to have no idea on cooperative strategy to draw positive response to their requests from the government.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.5
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• pp.10-16
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• 2016

This work investigates the size and dispersion characteristics of silver nanoparticles synthesized by a liquid phase reduction method using PAA. The experimental variables were the molecular weight and doses of the PAA, reducing agent, dispersant, and organic solvent (ethanol-acetone). UV-visible spectrophotometer results confirm the formation of the silver particles, and SEM indicates size in the nanometer range. As the ultrasonication time increases, there is a tendency toward smaller agglomerates of nanoparticles. The agglomerates were dispersed into 1-5 agglomerates of particles by ultrasonication for 3 hours or more. Relatively spherical nanoparticles were produced with a completely homogeneous dispersion and size of 49.56-85.75 nm by ultrasonication using BYK-192, a dispersant containing copolymer with a pigment affinic group. The average size of the silver nanoparticles was increased to 36.82, 50.66, and 56.06 nm with increasing molecular weight of PAA. Also, the size of the nanoparticles increased with the capping of PAA on the surfaces of the nanoparticles when increasing the amount of PAA. The addition of hydrazine as a reducing agent produced relatively small particles because many nuclei were created by the reduction reaction. The ethanol-acetone solvent helped with the regular arrangement of the silver nanoparticles.

• Restorative Dentistry and Endodontics
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• v.23 no.1
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• pp.366-378
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• 1998

Thermocondensation root canal filling technique have been used to fill accessary canals or to obtain homogeneous root caral fillings. But these thermocondensation technique inevitably produce heat in the canal which can be transmitted through the dentin and cementum and consequently damage periodontal ligamental cells and osteoblasts. In this study, System $B^{TM}$(Analytic technology, WA.D.S.A.) was used to evaluate the reaction of periodontal ligament tissue to "Continous Wave condensation technique" introduced by Buchanan, and the transmitted root surface temperature was measured according to measured root thicknesses. 12 Mandibular incisors of two adult dogs were used for the experiment. 6 controls were filled by lateral condensation technique with sealer.3 specimens were apically filled by Continuous Wave technique at $200^{\circ}C$ for 5 seconds and remaining 3 specimens were additionally backfilled using System $B^{TM}$(Analytic technology, WA.D.S.A.) was used to evaluate the reaction of periodontal ligament tissue to "Continous Wave condensation technique" introduced by Buchanan, and the transmitted root surface temperature was measured according to measured root thicknesses. 12 Mandibular incisors of two adult dogs were used for the experiment. 6 controls were filled by lateral condensation technique with sealer.3 specimens were apically filled by Continuous Wave technique at $200^{\circ}C$ for 5 seconds and remaining 3 specimens were additionally backfilled using System $B^{TM}$ at $100^{\circ}C$ for 20 seconds. Six weeks later, the dogs were sacrificed and the teeth stained with Hematoxylin and Eosin for histologic examination. 6 extracted human teeth were used to measure the transmitted temperature. After cutting off the crown, the canals were prepared and divided into 3 groups with root thickness of 1.5mm, 1.0mm, 0.5mm, 2 teeth in each group. Inside each root canal, System $B^{TM}$ was heated as with the temperature for the apically condensed and the back filled group, and the transmitted heat was measured on the external surface of the root. The temperature of System $B^{TM}$ heat spreader at $200^{\circ}C$ and $100^{\circ}C$ was also measured at root temperature. It can be concluded as follows: 1. In the thin area (200-$250{\mu}m$) of the root, root resorption could be seen even with heating at $200^{\circ}C$ for 5 seconds. 2. When the spreader was heated at $200^{\circ}C$ for 5 seconds and additionally at $100^{\circ}C$ for 20 seconds for backfill, all teeth showed root resorption regardless of their root thickness. 3. The transmitted external root surface temperature was higher as the root thickness decreased and as the heating time increased. In the thermocompaction technique using System $B^{TM}$, the spreader should be heated for the minimal time and used only in the apical area. The heated spreader shouldn't inserted to the binding point of the canal and backfilling should be done with other means of minimally heated gutta percha technique.

• Journal of the Korean Institute of Landscape Architecture
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• v.49 no.6
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• pp.16-26
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• 2021

For urban parks' rational and efficient management, research on creating green spaces in living area through citizen participation is continuously being conducted. However, in existing studies, citizens are recognized as a homogeneous group, and research on the intention to participate in park management according to user characteristics has not been conducted. A few studies have attempted to show differences through conceptual variables, such as user satisfaction and attachment to parks, but studies on sociodemographic factors, such as the users' age, have not been conducted. This study was conducted to ascertain the differences in preferred parks and park management participation methods by age, targeting various parks located in ten districts of Incheon Metropolitan City. Regression analysis was performed after collecting 1,226 questionnaires, applying a population-proportional allocation in the ten districts. As a result of the study, it was found that the difference according to the age of users has the most influence on the willingness to manage the park rather than the satisfaction or other factors. Also, a chi-square analysis was conducted to find the differences in preferred urban parks and management methods by age. The results showed that the choice to manage parks was statistically higher for those in their 50s or older, and the differences in preferred park types and desired park greening methods suggested implications for park management plans by age.

• 한국노년학
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• v.29 no.4
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• pp.1327-1340
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• 2009

The purposes of the study were (1) to identify the level of successful aging of older people living in a city, (2) to identify associated factors with successful aging, and (3) to identify a risk group for successful aging using classification and regression trees (CART) analysis. One hundred eighty seven older people (>65years) participated in the cross-sectional survey. Trained interviewers collected data with a structured questionnaire on demographic information, Korean geriatric depression score, activity of daily living(ADL), instrumental activity of daily living(IADL), and Young's successful aging instrument in subject's home. A CART analysis split subjects into ten homogeneous small groups based on five determinant factors. Older people who are male, with higher education, living with family, and not receiving Medicaid showed better scores in successful aging than their counter parts. Depression was a strong primary determinant for successful aging. A risk group for successful aging of older people was identified by depression and IADL. An intervention to prevent and manage depression and to improve physical function of older people can be developed to promote successful aging of older people. It is suggested to consider an assessment of depression to develop the policies for older people welfare.