• Journal of radiological science and technology
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• v.30 no.4
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• pp.381-389
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• 2007

The purpose of this study is investigation of radiation dose in CT scan. Data were collected from various references and organizations. Doses measured by CT scanners of each medical organization were analyzed and they were calculated through the examination protocol. The results are as follows : 1. $CTDI_W$ value per 100mAs measured by Head Phantom was the highest in <4-slice MDCT scanner> of 24.20 mGy. $CTDI_W$ values were significantly different among scanner generations(p < 0.01). 2. $CTDI_W$ value per 100 mAs measured using body phantom was the highest in <4-slice MDCT scanner> of 13.58 mGy and the $CTDI_W$ values were significantly different among scanner generations(p < 0.01). 3. When contrast medium was not used, the highest scanner was <16 slice MDCT> of $818.83\;mGy{\codt}cm$ in exposure dose in brain scan(p < 0.05). When the contrast medium was used, the highest scanner was <4 slice MDCT> and its average was $1,460.77\;mGy{\cdot}cm$(p < 0.1). 4. When the contrast medium was not used, the highest scanner was <16-slice MDCT> of $521.63\;mGy{\cdot}cm$ on average in terms of the exposure dose in chest inspection(p<0.05). when the contrast medium was used, the highest scanner was found in 8 slice MDCT scanner and its average was $1,174.70\;mGy{\cdot}cm$. There was no statistically significant difference among scanners. 5. When the contrast medium was not used, the highest scanner was <16-slice MDCT> and its average was $856.27\;mGy{\cdot}cm$ in exposure dose on the abdomen-pelvis(p<0.05). when the contrast medium was used, the highest scanner was <16-slice MDCT> and its average was $1,720.64\;mGy{\cdot}cm$ on average (p < 0.05). 6. When the contrast medium was not used, the highest scanner was <8-slice MDCT> and its average was $612.07\;mGy{\cdot}cm$ in exposure dose in liver inspection(p < 0.05). when the contrast medium was used, the highest scanner was <8-slice MDCT scanner> and its average was $2,197.93\;mGy{\cdot}cm$ in exposure dose(p < 0.1). seventy six point two percent of medical facilities were in risk of radiation exposure while the number of phase was three to four times in their dose inspection of contrast medium.

• Journal of Korean Society of Environmental Engineers
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• v.33 no.6
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• pp.396-404
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• 2011

An investigation on the removals of PAH-quinone compounds, which are commonly produced from the biological and/or chemical treatments of PAH-contaminated soils, from the aqueous phase via birnessite (${\delta}-MnO_2$)-mediated oxidative transformation is described. It was demonstrated that acenaphthenequinone (APQ), p-PAH quinone can be removed via birnessite-mediated oxidative-coupling reactions, and anthraquinone (AQ) and 1,4-naphthoquinone (1,4-NPQ), o-PAH quinones were efficiently removed by birnessite-mediated cross-coupling reactions in the presence of catechol (CAT) as a reactive mediator. The removals of PAH-quinone compounds followed pseudo-first-order reactions, and the rate constant (k, $hr^{-1}$) for the removals of 1,4-NPQ under the experiment conditions (1,4-NPQ = 10 mg/L, CAT = 50 mg/L, ${\delta}-MnO_2$ = 1.0 g/L, pH 5, Reaction time = 6~96 hr) was 0.0426, which was about 4 times lower than that of APQ (0.173). With the observed pseudo-first order rate constants with respect to birnessite loadings under the same experimental conditions, the surface-normalized specific rate constant, $K_{surf}$, for 1,4-NPQ was determined to be $8.5{\times}10^{-4}L/m^2{\cdot}hr$. The analysis of the kinetic data with respect to birnessite loading indicated that the cross-coupling reactions of 1,4-NPQ consist of two different reaction steps over time and the results have also been discussed in terms of the reaction mechanisms.

• Journal of Bio-Environment Control
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• v.21 no.3
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• pp.207-212
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• 2012

The objective of the present study is to identify the physico-chemical characteristics of used plug media (UPM) and its effect on growth response of tomato and cucumber seedlings. The UPM from commercial media Mix#5 (Sungro co., Ltd.) was used in this study. This media was sterilized by sterilizer at $120^{\circ}C$ in 30 minutes at 1.5 atm. Physicochemical properties of UPM was compared with new plug media (NPM). Physical properties such as air volume, particle density, solid volume, bulk density were investigated by three phase device (DIK-1130, Japan). And chemical characteristics such as $NO_3$-N, $P_2O_5$, K, Mg, Ca, $SiO_2$, CEC, OM were investigated by soil spectrophotometer (PTIZEN 1412SA, Mecasys Co., Ltd). The result indicates that air volume and water holding capacity of UPM are lower than NPM (25%, 15%, respectively). Bulk density and soil weight are more than two times higher than NPM per unit volume. Compared to NPM, there were no significant different for pH and EC. But CEC of UPM is lower than NPM 40%. In order to compare growth response and ability absorption of inorganic elements by plants, cucumber and tomato seedlings were used and chemical characteristics after growing of mediums were determined. The result indicated that seeding quality of tomato and cucumber in UPM is less than in NPM and almost inorganic ions of UPM are lower than NPM. So it is necessary to improve physicochemical properties of UPM.

• Asia-Pacific Journal of Business Venturing and Entrepreneurship
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• v.9 no.1
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• pp.119-132
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• 2014

This study analyzed the failure prediction model of the firms listed on the KOSDAQ by considering whether there are embezzlement, malpractice and the largest shareholder changes or not. This study composed a total of 166 firms by using two-paired sampling method. For sample of failed firm, 83 manufacturing firms which delisted on KOSDAQ market for 4 years from 2009 to 2012 are selected. For sample of normal firm, 83 firms (with same item or same business as failed firm) that are listed on KOSDAQ market and perform normal business activities during the same period (from 2009 to 2012) are selected. This study selected 80 financial ratios for 5 years immediately preceding from delisting of sample firm above and conducted T-test to derive 19 of them which emerged for five consecutive years among significant variables and used forward selection to estimate logistic regression model. While the precedent studies only analyzed the data of three years immediately preceding the delisting, this study analyzes data of five years immediately preceding the delisting. This study is distinct from existing previous studies that it researches which significant financial characteristic influences the insolvency from the initial phase of insolvent firm with time lag and it also empirically analyzes the usefulness of data by building a firm's fail prediction model which considered embezzlement/malpractice and the largest shareholder changes as dummy variable(non-financial characteristics). The accuracy of classification of the prediction model with dummy variable appeared 95.2% in year T-1, 88.0% in year T-2, 81.3% in year T-3, 79.5% in year T-4, and 74.7% in year T-5. It increased as year of delisting approaches and showed generally higher the accuracy of classification than the results of existing previous studies. This study expects to reduce the damage of not only the firm but also investors, financial institutions and other stakeholders by finding the firm with high potential to fail in advance.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.08a
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• pp.174-175
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• 2012

(In, Ga) N-based III-nitride semiconductor materials have been viewed as the most promising materials for the applications of blue and green light emitting devices such as light-emitting diodes (LEDs) and laser diodes. Although the InGaN alloy can have wide range of visible wavelength by changing the In composition, it is very hard to grow high quality epilayers of In-rich InGaN because of the thermal instability as well as the large lattice and thermal mismatches. In order to avoid phase separation of InGaN, various kinds of structures of InGaN have been studied. If high-quality In-rich InGaN/GaN multiple quantum well (MQW) structures are available, it is expected to achieve highly efficient phosphor-free white LEDs. In this study, we proposed a novel InGaN double hetero-structure grown on GaN nano-pyramids to generate broad-band red-color emission with high quantum efficiency. In this work, we systematically studied the optical properties of the InGaN pyramid structures. The nano-sized hexagonal pyramid structures were grown on the n-type GaN template by metalorganic chemical vapor deposition. SiNx mask was formed on the n-type GaN template with uniformly patterned circle pattern by laser holography. GaN pyramid structures were selectively grown on the opening area of mask by lateral over-growth followed by growth of InGaN/GaN double hetero-structure. The bird's eye-view scanning electron microscope (SEM) image shows that uniform hexagonal pyramid structures are well arranged. We showed that the pyramid structures have high crystal quality and the thickness of InGaN is varied along the height of pyramids via transmission electron microscope. Because the InGaN/GaN double hetero-structure was grown on the nano-pyramid GaN and on the planar GaN, simultaneously, we investigated the comparative study of the optical properties. Photoluminescence (PL) spectra of nano-pyramid sample and planar sample measured at 10 K. Although the growth condition were exactly the same for two samples, the nano-pyramid sample have much lower energy emission centered at 615 nm, compared to 438 nm for planar sample. Moreover, nano-pyramid sample shows broad-band spectrum, which is originate from structural properties of nano-pyramid structure. To study thermal activation energy and potential fluctuation, we measured PL with changing temperature from 10 K to 300 K. We also measured PL with changing the excitation power from 48 ${\mu}W$ to 48 mW. We can discriminate the origin of the broad-band spectra from the defect-related yellow luminescence of GaN by carrying out PL excitation experiments. The nano-pyramid structure provided highly efficient broad-band red-color emission for the future applications of phosphor-free white LEDs.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.29 no.6
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• pp.327-340
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• 2017

This article reviews the papers published in the Korean Journal of Air-Conditioning and Refrigeration Engineering during 2016. It is intended to understand the status of current research in the areas of heating, cooling, ventilation, sanitation, and indoor environments of buildings and plant facilities. Conclusions are as follows. (1) The research works on the thermal and fluid engineering have been reviewed as groups of flow, heat and mass transfer, the reduction of pollutant exhaust gas, cooling and heating, the renewable energy system and the flow around buildings. CFD schemes were used more for all research areas. (2) Research works on heat transfer area have been reviewed in the categories of heat transfer characteristics, pool boiling and condensing heat transfer and industrial heat exchangers. Researches on heat transfer characteristics included the results of the long-term performance variation of the plate-type enthalpy exchange element made of paper, design optimization of an extruded-type cooling structure for reducing the weight of LED street lights, and hot plate welding of thermoplastic elastomer packing. In the area of pool boiling and condensing, the heat transfer characteristics of a finned-tube heat exchanger in a PCM (phase change material) thermal energy storage system, influence of flow boiling heat transfer on fouling phenomenon in nanofluids, and PCM at the simultaneous charging and discharging condition were studied. In the area of industrial heat exchangers, one-dimensional flow network model and porous-media model, and R245fa in a plate-shell heat exchanger were studied. (3) Various studies were published in the categories of refrigeration cycle, alternative refrigeration/energy system, system control. In the refrigeration cycle category, subjects include mobile cold storage heat exchanger, compressor reliability, indirect refrigeration system with $CO_2$ as secondary fluid, heat pump for fuel-cell vehicle, heat recovery from hybrid drier and heat exchangers with two-port and flat tubes. In the alternative refrigeration/energy system category, subjects include membrane module for dehumidification refrigeration, desiccant-assisted low-temperature drying, regenerative evaporative cooler and ejector-assisted multi-stage evaporation. In the system control category, subjects include multi-refrigeration system control, emergency cooling of data center and variable-speed compressor control. (4) In building mechanical system research fields, fifteenth studies were reported for achieving effective design of the mechanical systems, and also for maximizing the energy efficiency of buildings. The topics of the studies included energy performance, HVAC system, ventilation, renewable energies, etc. Proposed designs, performance tests using numerical methods and experiments provide useful information and key data which could be help for improving the energy efficiency of the buildings. (5) The field of architectural environment was mostly focused on indoor environment and building energy. The main researches of indoor environment were related to the analyses of indoor thermal environments controlled by portable cooler, the effects of outdoor wind pressure in airflow at high-rise buildings, window air tightness related to the filling piece shapes, stack effect in core type's office building and the development of a movable drawer-type light shelf with adjustable depth of the reflector. The subjects of building energy were worked on the energy consumption analysis in office building, the prediction of exit air temperature of horizontal geothermal heat exchanger, LS-SVM based modeling of hot water supply load for district heating system, the energy saving effect of ERV system using night purge control method and the effect of strengthened insulation level to the building heating and cooling load.

• Journal of the Korean Applied Science and Technology
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• v.33 no.3
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• pp.498-506
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• 2016

1, 2-Hexanediol galactoside (HD-gal) has been previously synthesized from 1, 2-hexanediol (HD), in which recombinant ${\beta}$-galactosidase (${\beta}$-gal) of Escherichia coli (E. coli) was used for transgalactosylation reaction. In this study, a method for HD-gal purification from the reaction mixture was particularly investigated. Using ${\beta}$-gal-containing E. coli, HD-gal was synthesized from 75 mM HD for 48 hr under 300 g/l lactose concentration. Then, HD-gal synthesis from HD was confirmed by TLC analysis, and the existence of E. coli ${\beta}$-gal during 48 hr-reaction was also confirmed by Western blotting, in which the conversion yield of HD to HD-gal reached about 94% during 48 hr. To establish an efficient method for HD-gal purification, we carried out the solvent extraction of the reaction mixture, followed by silica gel chromatography, particularly in order to remove the residual HD. Two water-immiscible solvents, such as methylene chloride and ethyl acetate, were investigated comparatively to find out appropriate solvent. Then, it was found that residual HD was almost removed when ethyl acetate extraction of water phase of reaction mixture was carried out four times. Subsequently, silica gel chromatography was carried out, and purified HD-gal could be finally obtained. The production yield for HD-gal from 75 mM HD was $8.9{\pm}0.6%$ (n=3) (mole basis) or $21.1{\pm}1.4%$ (n=3) (weight basis). For further study, using purified HD-gal, we will investigate the minimum inhibitory concentrations (MICs) of HD-gal against bacteria. In addition, cytotoxicity to human skin cells of HD-gal will be examined.

• The korean journal of orthodontics
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• v.29 no.5 s.76
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• pp.551-562
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• 1999

This study was undertaken to investigate the relation between orthodontic force magnitude and the amount of tooth movement. And more light force application for reducing root resorption Twenty-four rats were divided into three experimental groups(A, B, C) based on force magnitude and application method. Springs of 50g force were applied to A group, springs of 100g force were applied to B group and springs of 25g force were applied to C group initially, and after 4 days springs of C group were changed to springs of 50g force. Two kinds of $sentally^{(R)}$(GAC U.S.A.) closed coil spring, 50g and 100g, were used. And we made 25g springs by heat treatment process of 50g springs. Each spring was inserted between the maxillary central incisor and the maxillary left first molar. Amounts of tooth movement were measured everyday by digital caliper($Digimatic^{(R)}$, Mitutoyo, Japan) under inhalation anesthesia for 15 days. After 15 days, all rats were sacrificed and histological samples were obtained with Hematoxyline-Eosin stain and Masson's trichrome stain. Following conclusion were made; 1. Group B showed the mean cumulative tooth movement of $2.19{\pm}0.41mm$ at 15th day, which was greatest among three groups, followed by group C($2.06{\pm}0.10mm$), group A($1.90{\pm}0.49mm$) respectively. however, there was no statistically difference among three groups. 2. All groups showed general tooth movement pattern and A, B, C group finished lag phase at 9th, 8th, 7th day, but there was no statistical significance. 3. Group A,B,C showed root resorption and especially group B showed the most severe root resorption and group C showed milder root resorption than other groups. According to the above results, large initial force with the development of a flirty widespread hyalinized zone may cause severe root resorption, so initial force should be applied lightly to reduce hyalinized area and eventually root resorption and then increased force will induce efficient tooth movement.

• Journal of Korean Academy of Nursing
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• v.21 no.2
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• pp.129-149
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• 1991

Circadian rhythm is entrained in the 24-hour time interval by periodic factors in the environment, known as zeitgeber. But most rotating work schedules are outside the range of the entrainment of the pacemaker timing the human circadian sleep - wake cycle. It has been postulated that physiological and emotional disturbances occur in most human functions when the circadian rhythm is disturbed. So application of circadian principles to the design of shift schedules can aid in maintaining the temporal integrity of the circadian system and thereby minimize for the shift worker any detrimental consequences of circadian disruption. This study was a quasi-experimental study to test the effect of shift intervals for the clinical nurse on the circadian rhythm. Twenty nurses newly employed in general units of two hospitals were selected as an experimental group and twelve college nursing students as a control group. Both groups were selected according to an established criteria using a purposive sampling technique. Ten subjects were assigned to a weekly shift group and another ten to a biweekly shift group engaged in a semi -continuous shift schedule(sunday off) with a backward direction, that is, morning -evening - night shift. The control group worked a morning shift for 42 days. Oral temperature rhythm, waking tim, sleep - wake cycle, fatigue, and mental performance were measured during the experimental period. The data collection period was from April 30, 1990 to June 10, 1990. MANOVA, paired t-test, ANOVA, and Student Newman Keuls method were used for statistical analysis. The results are summarized as follows. 1. Phase delay in the acrophase of temperature rhythm was shown according to the backward rotating shift. A complete adaptation to work on the night shift was achieved between the sixth and ninth day of the night shift. 2. There was no difference in either waking time or sleep- wake cycle according to the duration of the working day for every shift group. Significant difference was found in the waking time and the sleep -wake cycle for subjects on the morning, evening, and night shift in both of the shift groups(weekly shift group : λ＝0.121, p＜0.01, λ＝0.112, p＜0.01, biweekly shift group : λ＝0.116, p＜0.01, λ＝0.084, p＜0.01). 3. There was no difference in fatigue between the first working day and the last working day for the control group and for the biweekly shift group. In the weekly shift group, physical fatigue was significantly different for the first day and the sixth day of the night shift(t＝-2.28, p＜0.05). Physical fatigue and total fatigue on the first day of the night shift showed a significant difference among the control group, the weekly shift group, and the biweekly shift group(F＝5.79, p＜0.01, F＝4.56, p＜0.05). There was a significant difference between the shift groups and the control group(p＜0.05), Physical fatigue, neurosensory fatigue and total fatigue on the last day of the night shift showed a significant difference among the control group, the weekly shift group, and the biweekly shift group(F＝12.65, p＜0.01, F＝7.77, p＜0.01, F＝9.68, p＜0.01). There was a significant difference between the shift groups and the control group(p＜0.05). 4. No difference in mental performance was seen between the first day and the last day of work in each case. An arithmatic test on the first day of the night shift revealed a significant difference among the control group, the weekly shift group, and the biweekly shift group(F＝3.79, p＜0.05). There was a significant difference between the shift groups and the control group(p＜0.05) . The digital symbol substitution test and the arithmetic test on the last day of the night shift showed a significant difference among the control group, the weekly shift group, and the biweekly shift group(F＝3.68, p＜0.05, F＝5.55, p＜0.01), and both showed a significant difference between the shift groups and the control group(p＜0.05). Accordingly, this study showed that during night duty, the waking time, sleep- wake cycle, and fatigue increased and mental performance decreased compared with morning and evening duty. It was also found that the weekly shift group had a higher fatigue score on the sixth day of night duty as compared to the -first day, but the waking time, sleep- wake cycle, and mental performance revealed no difference for the duration of the night duty or between shift groups, and complete adaptation of temperature rhythm was achieved between the sixth and ninth day of night duty. It is possible to conclude from these results that for intermediate circadian type in a healthy young woman, a biweekly shift system is more compatible with the circadian timing system than weekly shift system.

• Journal of Periodontal and Implant Science
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• v.23 no.1
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• pp.97-108
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• 1993

One of the important initial events required for periodontal regeneration is the attachment and subsequent spreading of periodontal ligament cells on the root surface. The purposes of this study is to investigate the attachment and spreading pattern of human periodontal ligament cell on the surface of glass slides. After establishment of a cell line of the primary cell culture from the periodontal ligament of 1st premolar teeth which were extracted for the purpose of orthodontic treatment, author dispersed the cells at $5{\times}10^3\;cells/ml$ into the each 35mm culture petri-dish containing 2 glass slides. To observe the morphological changes of the cells which attached to the surfaces of glasses at every designed time schedule, author used the inverted phase contrast microscope and scanning electron microscope. During the whole experiment culture condition was at $37^{\circ}C$, 100% Humidity, 5% $CO_2$ gas incubator. The following results were obtained. Periodontal ligament cells showed spherical outline and started to attach to glass surface by basal sytoplasmic extension after 10min in culture. After 30min in culture, periodontal ligament cells were attached to glass surface by well - developed filopodia which protruded from the lamellipodia. The cell surface is covered with bubble-like structures and occasional microvillus can be seen with diffculty among these structures. After 1.5hr in culture, peridontal ligament cells shhowed radially well-spread cytoplasm and the nucleus was centered on its cytoplasm. Unspread central region of the cell was covered with numerous microvilli. The change of cell attachment and spreading pattern was manifest at 6hr in culture. At this time, periodontal ligament cell showed elongated outline and an oval-shaped nucleus. After 12hr in culture, periodontal ligament cells showed more stretched fibroblast-like appearance with polarity. Two long lamellipodia can be seen around the both terminal ends of cells. After 24hr in culture, periodontal ligament cells showed spindle shapes and an oval-shaped nucleus was slanted toward one side of the cell.