• Korean Journal of Materials Research
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• v.34 no.1
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• pp.34-43
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• 2024

New piezoelectric and triboelectric materials for energy harvesting are being widely researched to reduce their processing cost and complexity and to improve their energy conversion efficiency. In this study, BaTiO₃ films of various thickness were deposited on Ni foams by R.F. magnetron sputtering to study the piezoelectric and triboelectric properties of the porous spongy structure materials. Then piezoelectric nanogenerators (PENGs) were prepared with spongy structured BaTiO₃ and PDMS composite. The output performance exhibited a positive dependence on the thickness of the BaTiO₃ film, pushing load, and poling. The PENG output voltage and current were 4.4 V and 0.453 ㎂ at an applied stress of 120 N when poled with a 300 kV/cm electric field. The electrical properties of the fabricated PENG were stable even after 5,000 cycles of durability testing. The triboelectric nanogenerators (TENGs) were fabricated using spongy structured BaTiO₃ and various polymer films as dielectrics and operated in a vertical contact separation mode. The maximum peak to peak voltage and current of the composite film-based triboelectric nanogenerator were 63.2 V and 6 ㎂, respectively. This study offers new insights into the design and fabrication of high output nanogenerators using spongy structured materials.

• Journal of Periodontal and Implant Science
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• v.54 no.2
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• pp.108-121
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• 2024

Purpose: The aim of this study was to compare changes in soft and hard tissue and the histologic composition following early implant placement in sites with alveolar ridge preservation or spontaneous healing (SH), as well as implant performance up to 1 year after crown insertion. Methods: Thirty-five patients with either intact buccal bone plates or dehiscence of up to 50% following single-tooth extraction of incisors, canines, or premolars were included in the study. They were randomly assigned to undergo one of three procedures: deproteinized bovine bone mineral with 10% collagen (DBBM-C) covered by a collagen matrix (DBBM-C/CM), DBBM-C alone, or SH. At 8 weeks, implant placement was carried out, and cone-beam computed tomography scans and impressions were obtained for profilometric analysis. Patients were followed up after the final crown insertion and again at 1 year post-procedure. Results: Within the first 8 weeks following tooth extraction, the median height of the buccal soft tissue contour changed by -2.11 mm for the DBBM-C/CM group, -1.62 mm for the DBBM-C group, and -1.93 mm for the SH group. The corresponding height of the buccal mineralized tissue changed by -0.27 mm for the DBBM-C/CM group, -2.73 mm for the DBBM-C group, and -1.48 mm for the SH group. The median contour changes between crown insertion and 1 year were -0.19 mm in the DBBM-C/CM group, -0.09 mm in the DBBM-C group, and -0.29 mm in the SH group. Conclusions: Major vertical and horizontal ridge contour changes occurred, irrespective of the treatment modality, up to 8 weeks following tooth extraction. The DBBM-C/CM preserved more mineralized tissue throughout this period, despite a substantial reduction in the overall contour. All 3 protocols led to stable tissues for up to 1 year.

• Journal of Korean Ophthalmic Optics Society
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• v.17 no.1
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• pp.47-52
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• 2012

Purpose: This study was to evaluate visual fatigue with passing of watching 3D TV in short term and with experience of watching 3DTV in long term. Methods: 98 adult subjects aged $33.5{\pm}5.5$ years (22 to 51 years; 12 females and 86 males) agreed to participate in this study. Subjects were asked to watch 52 inch LED 2D and 3D television (Shutter glasses method) at 2.7 meters for 65minutes with wearing their habitual glasses or contact lenses. For evaluating visual fatigue, subjects were verbally responded to 11 questions : eye straining, eye paining, dry eye, sore eye, watery eye, photophobia, blur vision, diplopia, eye fatigue, headache, and dizziness with scale 0 to 3 at each measurement while watching 3D and 2D TV. Results: The mean scores of visual fatigue were $2.08{\pm}2.14$, $3.19{\pm}3.02$, $3.40{\pm}3.37$, $3.53{\pm}3.07 $for after 5 minutes, 25 minutes, 45 minutes, and 65 minutes respectively for 3D TV, and $0.40{\pm}1.03$, $0.22{\pm}0.70$, $0.22{\pm}0.58$, and $0.17{\pm}0.52$ after 25, 45, and 65 minutes respectively for 2D TV. Visual fatigue for watching 3D TV was significantly higher than for watching 2D TV at all measurements sessions (paired t-test, p < 0.001). The visual fatigue significantly increased during watching 3D TV for 65 minutes (p < 0.001, RM-ANOVA). The visual fatigue during watching 3D TV was significantly increased until 25 minutes (paired t-test, p < 0.001), stable after that. For correlation between visual fatigue and 3D watching experience, the more 3D watching experiences were significantly the less visual fatigues in photophobia, blur vision, diplopic and dizzy symptoms (ANOVA, all F(1, 96) = 4.500, all p < 0.05), but there was not significantly different in the other symptoms (ANOVA, F (1, 96) = 2.123, p = 0.148). Conclusions: Visual fatigue for watching 3D TV was higher than for watching 2D TV, increase by 25 minutes. It was different by symptoms for correlation between visual fatigue and 3D watching experience.

• Journal of the Korean earth science society
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• v.24 no.8
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• pp.684-690
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• 2003

Recently Choongchung provinces in the central part of South Korea have received increasing attention because of the newly Planned administrative capital construction. In this area, a seismic network of Korea National University of Education has been installed since September 1996, and analyzed Q$_P^{-1}$ and Q$_S^{-1}$ by the extended Coda normalization method based on 60 events recorded by 2 stations of the network. To compensate for insufficient data, we combined the data from 33 events observed at 1 of the stations of the network of Korea Institute of Geology, Mining & Materials. Estimated Q$_P^{-1}$ and Q$_S^{-1}$ showed frequency dependence that decrease from (1.9${\pm}$3.0)${\times}$10$^{-3}$ and (2.4${\pm}$1.4)${\times}$10$^{-3}$ at 3.0 Hz to (5.4${\pm}$1.5)${\times}$10$^{-4}$ and (6.3${\pm}$1.1)${\times}$10$^{-4}$ at 24 Hz, respectively. Using a power law dependent on frequency, the best fit of Q$_P^{-1}$ and Q$_S^{-1}$ are 0.003f$^{-0.62}$ and 0.006f$^{-0.71}$ respectively. These values correspond to those of seismically stable regions, and are slightly less dependent on frequency than those of the southeastern part of Korea due to high Q$^{-1}$ values in high frequencies. Further observations are required in the central part of S. Korea to evaluate the difference of Q$^{-1}$ between central and southeastern parts of S. Korea.

• Journal of the korean academy of Pediatric Dentistry
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• v.37 no.1
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• pp.1-12
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• 2010

The aim of this study was to evaluate the preventive effect of commercially available anticariogenic products, specifically, the tooth cream containing Casein phosphopeptide-amorphous calcium phosphate(CPP-ACP), fluoride varnish and low-level fluoride mouthrinse on enamel erosion induced by carbonated beverage in a short period of time. Enamel specimens were treated as follows and were then kept in artificial saliva for 24 hours followed by further processing by alternately soaking them in Cola beverage and in distilled water for 1 minute each five times. Group 1: control group (no treatment) Group 2: tooth cream with CPP-ACP Group 3: fluoride varnish (1,000 ppm F) Group 4: low-level fluoride mouthrinse (227 ppm F) Group 5: fluoride varnish + tooth cream with CPP-ACP Group 6: low-level fluoride mouthrinse + tooth cream with CPP-ACP Microhardness and erosion depth were measured and the mineral loss of each specimen was evaluated by measuring the volumetric fluorescence change(${\Delta}Q$) against the stable fluorescent grid using quantitative light-induced fluorescence(QLF). The experiment lasted for 6 days repeated each day. The results were as follows: 1. The microhardness was increased as follows: Group $1{\leq}2{\leq}4$<6<$3{\fallingdotseq}5$. 2. The mean erosion depth was increased as follows: Group $5{\fallingdotseq}3$<6<$4{\fallingdotseq}2{\fallingdotseq}1$. 3. The ${\Delta}Q$ was increased as follows: Group $1{\fallingdotseq}2{\leq}4{\leq}6{\leq}3{\fallingdotseq}5$. The decrement of ${\Delta}Q$ was similar between group 1 and 2, group 4 and 6 and group 3 and 5. 4. The ${\Delta}Q$ showed positive correlation with microhardness (r=0.96, p<0.05), while it was negatively correlated to erosion depth (r=-0.96, p<0.05).

• KEPCO Journal on Electric Power and Energy
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• v.5 no.3
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• pp.209-213
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• 2019

Recently, demand for high energy density and long cycling stability of energy storage system has increased for application using with frequency regulation (F/R) in power grid. Supercapacitor have long lifetime and high charge and discharge rate, it is very adaptable to apply a frequency regulation in power grid. Supercapacitor can complement batteries to reduce the size and installation of batteries. Because their utilization in a system can potentially eliminate the need for short-term frequent replacement as required by batteries, hence, saving the resources invested in the upkeep of the whole system or extension of lifecycle of batteries in the long run of power grid. However, low energy density in supercapacitor is critical weakness to utilization for huge energy storage system of power grid. So, it is still far from being able to replace batteries and struggle in meeting the demand for a high energy density. But, today, LIC (Lithium Ion Capacitor) considered as an attractive structure to improve energy density much more than EDLC (Electric double layer capacitor) because LIC has high voltage range up to 3.8 V. But, many aspects of the electrochemical performance of LIC still need to be examined closely in order to apply for commercial use. In this study, in order to improve the capacitance of LIC related with energy density, we designed new method of pre-doping in anode electrode. The electrode in cathode were fabricated in dry room which has a relative humidity under 0.1% and constant electrode thickness over $100{\mu}m$ was manufactured for stable mechanical strength and anode doping. To minimize of contact resistance, fabricated electrode was conducted hot compression process from room temperature to $65^{\circ}C$. We designed various pre-doping method for LIC structure and analyzing the doping mechanism issues. Finally, we suggest new pre-doping method to improve the capacitance and electrochemical stability for LIC.

• Korean Journal of Remote Sensing
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• v.37 no.5_1
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• pp.989-998
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• 2021

In the utilization of optical satellite imagery, which is greatly affected by clouds, periodic composite technique is a useful method to minimize the influence of clouds. Recently, a technique for selecting the optimal pixel that is least affected by the cloud and shadow during a certain period by directly inputting cloud and cloud shadow information during period compositing has been proposed. Accurate extraction of clouds and cloud shadowsis essential in order to derive optimal composite results. Also, in the case of an surface targets where spectral information is important, such as crops, the loss of spectral information should be minimized during cloud-free compositing. In thisstudy, clouds using two spectral indicators (Haze Optimized Tranformation and MeanVis) were used to derive a detection technique with low loss ofspectral information while maintaining high detection accuracy of clouds and cloud shadowsfor cabbage fieldsin the highlands of Gangwon-do. These detection results were compared and analyzed with cloud and cloud shadow information provided by Sentinel-2A/B. As a result of analyzing data from 2019 to 2021, cloud information from Sentinel-2A/B satellites showed detection accuracy with an F1 value of 0.91, but bright artifacts were falsely detected as clouds. On the other hand, the cloud detection result obtained by applying the threshold (=0.05) to the HOT showed relatively low detection accuracy (F1=0.72), but the loss ofspectral information was minimized due to the small number of false positives. In the case of cloud shadows, only minimal shadows were detected in the Sentinel-2A/B additional layer, but when a threshold (= 0.015) was applied to MeanVis, cloud shadowsthat could be distinguished from the topographically generated shadows could be detected. By inputting spectral indicators-based cloud and shadow information,stable monthly cloud-free composited vegetation index results were obtained, and in the future, high-accuracy cloud information of Sentinel-2A/B will be input to periodic cloud-free composite for comparison.

• Journal of Korean Society of Forest Science
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• v.79 no.1
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• pp.56-70
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• 1990

Eighteen Korean white pine (P. koraiensis S. et Z.) families were tested in 3 different regions from age 5 to 9. Family and site were significant sources of variation for seedling survival and field growth, whereas the effects of family x site interaction ware relatively small as compared with the former sources of variation. Variance components estimated from the separate and combined sites indicated that the most variabilities were associated with individual trees within plot. Family ${\times}$ site interaction components as a percentage of family variance decreased sharply with age. Heritability estimates varied with testing site and tree age. Combined analyses, however, showed a moderate change in heritability with increasing tree ages, and demonstrated high and stable trends of estimates, particularly in family heritabilities of tree height ($h_F{^2}=0.789-0.798$). The gains estimated from combined analysis have expected maximum or near-maximum efficiencies at age 6 or 7. Given equal intensity of selection, mass selection showed the most efficient gains within and across the sites. However, for the differences between mass and combined selections are small, selection made on the combination of family and within-family would be more effective in improving genetic gains. Indirect selection method indicated that 5-and 6-years height were all good predictors of 9-year-old height with little loss of relative efficiency (less than 10%) as compared with direct family selection at age 9. Phenotypic and genetic correlations computed on the basis of family mean values of height and diameter have shown predominantly high, positive, and statistically significant (1% level) relationships between all tested pairs of traits, which indicates that family growth maintained statistically consistent trends with age. The best families are those that maintained a stable superiority overall sites and ages in growth performance, therefore, it can be suggested that early identification of superior families at age 9 is feasible at age 5 or 6 in Pinus koraiensis S. et Z.

• Journal of Radiation Protection and Research
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• v.25 no.4
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• pp.223-232
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• 2000

Comparative study was performed for the assessment of DNA damage and Chromosomal aberration in human lymphocyte exposed to low dose radiation using fluorescence in situ hybridization(FISH) and single cell gel electrophoresis(SCGE). Chromosomal aberrations in human lymphocytes exposed to radiation at doses of 5, 10, 30 and 50cGy were analysed with whole chromosome-specific probes by human chromosome 1, 2 and 4 according to PAINT system. FISH with chromosome-specific probe has been used to be a valid and rapid method fer detection of chromosome rearrangements induced by low dose radiation. The frequencies of stable translocation per cell equivalents were 0.0116, 0.0375, 0.040f, 0.0727 and 0.0814 for 0, 5, 10, 30 and 50cGy, respectively, and those of dicentric were 0.00, 0.0125, 0.174, 0.0291 and 0.0407 respectively. Radiation induced DNA damage in human lymphocyte in a dose-dependent manner at low doses from 5cGy to 50cGy, which were analysed by single tell gel electrophoresis(SCGE). From above results, FISH seemed to be useful for radiation biodosimetry by which the frequencies of stable aberrations in human lymphocyte can be observed more easily than by conventional method and SCGE also seemed to be sensitive method f9r detecting DNA damage by low dose radiation exposure, so that those methods will improve our technique to perform meaningful biodosimetry for radiation at low doses.

• Food Science of Animal Resources
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• v.28 no.2
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• pp.232-239
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• 2008

The objective of this study is to estimate the shelf-life of Tteokgalbi containing dietary fiber extracted from rice bran by using the predictive microbiology. This Tteokgalbi was made with 0%, 1%, 2%, and 3% dietary fiber. The number of total viable cells, anaerobic, psychrotrophic, and heat-stable bacteria and coliforms was calculated during 15 days of storage under $4{\pm}1^{\circ}C$ and the obtained data was applied to Baranyi function. The evaluation of fitness between predicted and observed data showed that these were matched in a satisfactory way. Heat-stable bacteria was detected lower than <1 log CFU/g and coliforms were not detected during the storage. The changes of total viable cells and psychrotrophic bacteria in Tteokgalbi were increased gradually, but dramatically increased after 3 days of storage. The models of total viable cells and anaerobic bacteria showed very similar growth trends and values of growth parameters each other. The estimated shelf-life of each Tteokgalbi was calculated from the predictive model of total viable cells and the estimated shelf-life was 1.7, 2.3, 2.3, and 2.4 days, respectively. The results suggested that the prediction of bacteria growth could be used to evaluate the microbiological safety and determine the shelf-life of Tteokgalbi as ready-to-eat food in the local market.