• Journal of Korean Society of Coastal and Ocean Engineers
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• v.26 no.3
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• pp.174-183
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• 2014

Seabed beneath and near coastal structures may undergo large excess pore water pressure composed of oscillatory and residual components in the case of long durations of high wave loading. This excess pore water pressure may reduce effective stress and, consequently, the seabed may liquefy. If liquefaction occurs in the seabed, the structure may sink, overturn, and eventually increase the failure potential. In this study, to evaluate the liquefaction potential on the seabed, numerical analysis was conducted using the expanded 2-dimensional numerical wave tank to account for an irregular wave field. In the condition of an irregular wave field, the dynamic wave pressure and water flow velocity acting on the seabed and the surface boundary of the composite breakwater structure were estimated. Simulation results were used as input data in a finite element computer program for elastoplastic seabed response. Simulations evaluated the time and spatial variations in excess pore water pressure, effective stress, and liquefaction potential in the seabed. Additionally, the deformation of the seabed and the displacement of the structure as a function of time were quantitatively evaluated. From the results of the analysis, the liquefaction potential at the seabed in front and rear of the composite breakwater was identified. Since the liquefied seabed particles have no resistance to force, scour potential could increase on the seabed. In addition, the strength decrease of the seabed due to the liquefaction can increase the structural motion and significantly influence the stability of the composite breakwater. Due to limitations of allowable paper length, the studied results were divided into two portions; (I) focusing on the dynamic response of structure, acceleration, deformation of seabed, and (II) focusing on the time variation in excess pore water pressure, liquefaction, effective stress path in the seabed. This paper corresponds to (II).

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.26 no.3
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• pp.160-173
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• 2014

Seabed beneath and near coastal structures may undergo large excess pore water pressure composed of oscillatory and residual components in the case of long durations of high wave loading. This excess pore water pressure may reduce effective stress and, consequently, the seabed may liquefy. If liquefaction occurs in the seabed, the structure may sink, overturn, and eventually increase the failure potential. In this study, to evaluate the liquefaction potential on the seabed, numerical analysis was conducted using the expanded 2-dimensional numerical wave tank to account for an irregular wave field. In the condition of an irregular wave field, the dynamic wave pressure and water flow velocity acting on the seabed and the surface boundary of the composite breakwater structure were estimated. Simulation results were used as input data in a finite element computer program for elastoplastic seabed response. Simulations evaluated the time and spatial variations in excess pore water pressure, effective stress, and liquefaction potential in the seabed. Additionally, the deformation of the seabed and the displacement of the structure as a function of time were quantitatively evaluated. From the results of the analysis, the liquefaction potential at the seabed in front and rear of the composite breakwater was identified. Since the liquefied seabed particles have no resistance to force, scour potential could increase on the seabed. In addition, the strength decrease of the seabed due to the liquefaction can increase the structural motion and significantly influence the stability of the composite breakwater. Due to limitations of allowable paper length, the studied results were divided into two portions; (I) focusing on the dynamic response of structure, acceleration, deformation of seabed, and (II) focusing on the time variation in excess pore water pressure, liquefaction, effective stress path in the seabed. This paper corresponds to (I).

• Journal of radiological science and technology
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• v.38 no.3
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• pp.245-252
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• 2015

To obtain the best SNR (signal to noise ratio) due to changes in CTDI (computed tomography dose index) made for the purpose of setting the optimum image obtained by reducing the dose in abdominal CT. Abdominal CT scans of 59 patients a $400-499cm^2$ (n = 12), $500-599cm^2$ (n = 21), $600-699cm^2$ (n = 17), $700-799cm^2$ (n = 9) were separated by four groups and the effective dose was used in the Excel to get the area of the patient using the ImageJ program. Patients of CTDI, DLP, SNR, the effective dose were analyzed. Abdominal CT area was increased to 13 mGy in CTDI is 7.3 mGy, DLP to 732 in $394.4mGy{\cdot}cm$, also effective dose was 5.9 mSv increase in 11mSv. SNR is 15 dB was maintained at 12.7. CTDI according to the average of the abdominal area of 8.9 mGy, the average of the DLP was $481.54mGy{\cdot}cm$, the effective dose is calculated to be 7.2 mSV. Effective dose was calculated by multiplying the load factor of DLP in the abdomen showed no statistically significant difference of (p < .05), there was a significant difference in SNR (p > . 05). To improve image quality of abdominal CT scan image in consideration of the CTDI according to the volume of the patient it should be able to reduce the radiation exposure of the patients.

• The korean journal of orthodontics
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• v.32 no.2 s.91
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• pp.107-115
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• 2002

The aim of this study was to investigate experimentally the mechanical and histological effect of drilling process on the stability of micro-implant used for the orthodontic anchorage. For this purpose, 32 micro-implants(Osas$^{(R)}$, Epoch medical, ${\phi}$1.6 mm) were inserted into maxilla, mandible and palate in two beagle dogs. 16 micro-implants(8 per dog) were inserted after drilling with pilot drilling bur (drill method group). 16 micro-implants(8 per dog) were inserted without drilling (drill-free method group). After 1 week, micro-implants were loaded by means of Ni-Ti coil spring (Ni-Ti springs-extension$^{(R)}$, Ormco) with 200-300 gm force. Following 12 weeks, the micro-implants and the surrounding bone were removed. Before sacrifice, the mobilities were tested with Periotest$^{(R)}$(Siemens). Undecalcified serial sections with the long axis were made and the histologic evaluations were done. The results of this study were as follow ; 1. The osseointegration was found in both of drill-free method group and drill method group 2. Two of drill method group and one of drill-free method group in 32 micro-implants were lost after loading. 3. The mobilities of drill-free method group were less than drill method group 4. The bone contact on surface of micro-implants in drill-free method group was more than drill method group but there was no significant difference between groups. 5. The bone density in threads of micro-implants in drill-free method group was more than drill method group and there was significant difference between groups. These results suggest that drill-free method in insertion of micro-implants is superior to drill method on the stabilities, bone remodeling and osseointegrations under early loading.

• Journal of the korean academy of Pediatric Dentistry
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• v.36 no.3
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• pp.440-447
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• 2009

This study was performed to compare the wear resistance of sealant and flowable resins for analyzing the effect of flowable resin as a sealant in preventive resin restorations. Specimens were made and Vicker's hardness number and surface roughness were measured. SEM observations of the polished and abraded surfaces were established. Kruskal-Wallis rank test and Mann-Whitney U test at the significant level of ${\alpha}$=0.05 were used. The following results were obtained: 1. The microhardness was decreased among groups in following order: Z350 (3M ESPE, U.S.A), Estelite (Tokuyama Dental, Japan) and Ultraseal (Ultradent, U.S.A). There were significant differences in all groups (p<0.0001). 2. The surface roughness was decreased among groups in following order: Ultraseal XT plus, Palfique Estelite LV and Filtek Z350 flowable. However, there is no statistically significant differences in roughness among Estellite, Z350 and Ultraseal at the significance level of ${\alpha}$=0.05, with p=0.116 3. SEM observation of the unworn and worn surfaces revealed the qualitative differences in the wear appearance among groups. The results in this study indicate that flowable resin is better than sealant in aspect of physical properties.

• The Journal of Korean Academy of Prosthodontics
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• v.48 no.2
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• pp.151-157
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• 2010

Purpose: The purposes of this study was to evaluates shear bond strength between zirconia core and veneer-ceramic in order to examine the clinical practice of colored zirconia block fabricated by infiltration method into the metal chloride solution. Material and methods: CNU block and $Everest{(R)}$ ZS blank were used. VITA In-$Ceram{(R)}$2000 YZ Coloring liquid (LL1) and 3 aqueous metal chloride solutions containing chromium and molybdenum ingredients were used. 40 zirconia specimens were prepared into cuboid shape ($5{\times}5{\times}10 mm$). All specimens were divided into 5 groups by infiltrating into the coloring liquids. After that, porcelain was build up into the shape of $5{\times}5{\times}4mm^3$, followed by sintering. The maximum loading and shear bond strength was measured. Failure patterns and failure sites were examined. Results: 1. There were no statistical differences in shear bond strength between zirconia blocks (P > .05). 2. There were no statistically significant differences in shear bond strength between non-colored and colored zirconia blocks, while shear bond strength of non-colored zirconia blocks is higher than that of colored specimen (P > .05). 3. In the comparison with shear bond strength among colored zirconia blocks, there were no statistical differences according to kinds of coloring liquid (P > .05). 4. Mixed failure patterns were mainly observed in the failure between zirconia and veneering ceramic. The veneering ceramic failure of all specimens was observed in either interface of zirconia or veneering ceramic. Conclusion: Shear bond strength between colored zirconia and veneering ceramic shows lower tendency than non-colored zirconia, but there was clinically allowable value.

• Restorative Dentistry and Endodontics
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• v.24 no.2
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• pp.408-415
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• 1999

When a zinc-oxide eugenol type sealer was placed in root canals treated previously with calcium hydroxide, acceleration of its setting and the yellowish discoloration were observed clinically. The purpose of this study was to evaluate the properties of calcium hydroxide-eugenol compound. Some physical properties of calcium hydroxide-eugenol compound were compared with a manufactured zinc-oxide eugenol based root canal sealer, Tubli-seal$^{(R)}$ in terms of water solubility, water sorption, film thickness and microleakage. Solubility and water sorption were determined by the use of the method described in American Dental Association Specification(ADAS) no. 57. Ten samples of each material were prepared into disks 20mm in diameter and 1.5mm in thickness. The samples were immersed in 50ml of distilled water at $37{\pm}1^{\circ}C$ for 7 days. The samples were then removed and placed in a desiccator. The values for solubility and water sorption were calculated using differences between the weights of same sample. Film thickness was determined by the use of the method described in ADAS no. 57 too. A small quantity of mixed cement was placed between two glass plates of which thickness was measured previously. 15Kg loading was applied and total thickness of the glass plates and the cement film was measured. The thickness difference was recorded as the material's film thickness. Microleakage was determined with a dye penetration method. Experimental materials were placed between the dentin surface of bovine tooth and the acrylic rod. These units were immersed in Pelican ink (W-Germany) for three days. Dye-penetrated dentin surfaces of bovine tooth were measured using the NIB Image 1.60 Macintosh program. The results are as follows: 1. Water solubility value of calcium hydroxide-eugenol compound (20.98${\pm}$2.94%) was statistically higher than those of Tubli-seal$^{(R)}$(2.52${\pm}$0.49%)(p<0.05). 2. Water sorption value of calcium hydroxide-eugenol compound (59.72${\pm}$17.75%) was statistically higher than those of Tubli-seal$^{(R)}$(3.15${\pm}$0.76%)(p<0.05). 3. Film thickness value of calcium hydroxide-eugenol compound (0.36${\pm}$0.03mm) was statistically higher than those of Tubli-seal$^{(R)}$(0.12${\pm}$0.1mm)(p<0.05). 4. Dye penetration value after 3 days-immersion of calcium hydroxide-eugenol compound(57.63${\pm}$25.85%) was statistically higher than those of Tubli-seal$^{(R)}$(28.05${\pm}$23.46%)(p<0.05).

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.34 no.2
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• pp.37-45
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• 2022

A simplified model using the lifetime distribution has been presented to estimate the Mean Residual Life (MRL) of rubble-mound breakwaters, which is not like a stochastic process model based on time-dependent history data to the cumulative damage progress of rubble-mound breakwaters. The parameters involved in the lifetime distribution can be easily estimated by using the upper and lower limits of lifetime and their likelihood that made a judgement by several experts taking account of the initial design lifetime, the past sequences of loads, and others. The simplified model presented in this paper has been applied to the rubble-mound breakwater with TTP armor layer. Wiener Process (WP)-based stochastic model also has been applied together with Monte-Carlo Simulation (MCS) technique to the breakwater of the same condition having time-dependent cumulative damage to TTP armor layer. From the comparison of lifetime distribution obtained from each models including Mean Time To Failure (MTTF), it has found that the lifetime distributions of rubble-mound breakwater can be very satisfactorily fitted by log-normal distribution for all types of cumulative damage progresses, such as exponential, linear, and logarithmic deterioration which are feasible in the real situations. Finally, the MRL of rubble-mound breakwaters estimated by the simplified model presented in this paper have been compared with those by WP stochastic process. It can be shown that results of the presented simplified model have been identical with those of WP stochastic process until any ages in the range of MTT F regardless of the deterioration types. However, a little of differences have been seen at the ages in the neighborhood of MTTF, specially, for the linear and logarithmic deterioration of cumulative damages. For the accurate estimation of MRL of harbor structures, it may be desirable that the stochastic processes should be used to consider properly time-dependent uncertainties of damage deterioration. Nevertheless, the simplified model presented in this paper can be useful in the building of the MRL-based preventive maintenance planning for several kinds of harbor structures, because of which is not needed time-dependent history data about the damage deterioration of structures as mentioned above.

• Journal of Wetlands Research
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• v.26 no.1
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• pp.21-31
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• 2024

Macromia daimoji Okumura, 1949 was designated as an endangered species and also categorized as Class II Endangered wildlife on the International Union for Conservation of Nature (IUCN) Red List in Korea. The spatial distribution of this species ranged within a region delimited by northern latitude from Sacheon-si(35.1°) to Yeoncheon-gun(38.0°) and eastern longitude from Yeoncheon-gun(126.8°) to Yangsan-si(128.9°). They generally prefer microhabitats such as slowly flowing littoral zones of streams, alluvial stream islands and temporarily formed puddles in the sand-based lowland streams. The objectives of this study were to analyze the similarity of benthic macroinvertebrate communities in M. daimoji habitats, to predict the current potential distribution patterns as well as the changes of distribution ranges under global climate change circumstances. Data was collected both from the Global Biodiversity Information Facility (GBIF) and by field surveys from April 2009 to September 2022. We adopted MaxEnt model to predict the current and future potential distribution for M. daimoji using downloaded 19 variables from the WorldClim database. The differences of benthic macroinvertebrate assemblages in the mainstream of Nakdonggang were smaller than those in its tributaries and the other streams, based on the surrounding environments and stream sizes. MaxEnt model presented that potential distribution displayed high inhabiting probability in Nakdonggang and its tributaries. Applying to the future scenarios by Intergovernmental Panel on Climate Change (IPCC), SSP1 scenario was predicted to expand in a wide area and SSP5 scenario in a narrow area, comparing with current potential distribution. M. daimoji is not only directly threatened by physical disturbances (e.g. river development activities) but also vulnerable to rapidly changing climate circumstances. Therefore, it is necessary to monitor the habitat environments and establish conservation strategies for preserving population of M. daimoji.

• Restorative Dentistry and Endodontics
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• v.27 no.2
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• pp.158-174
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• 2002

The aim of this study was to investigate the effect of light irradiation modes on polymerization shrinkage, degree of cure and microleakage of a composite resin. VIP$^{TM}$ (Bisco Dental Products, Schaumburg, IL, USA) and Optilux 501$^{TM}$ (Demetron/Kerr, Danbury, CT, USA) were used for curing Filtek$^{TM}$ Z-250 (3M Dental Products, St. Paul., MN, USA) composite resin using following irradiation modes: VIP$^{TM}$ (Bisco) 200mW/$\textrm{cm}^2$ (V2), 400mW/$\textrm{cm}^2$ (V4), 600mW/$\textrm{cm}^2$ (V6), Pulse-delay (200 mW/$\textrm{cm}^2$ 3 seconds, 5 minutes wait, 600mW/$\textrm{cm}^2$ 30seconds, VPD) and Optilux 501$^{TM}$ (Demetron/Kerr) C-mode (OC), R-mode (OR). Linear polymerization shrinkage of the composite specimens were measured using Linometer (R&B, Daejeon, Korea) for 90 seconds for V2, V4, V6, OC, OR groups and for up to 363 seconds for VPD group (n=10, each). Degree of conversion was measured using FTIR spectrometer (IFS 120 HR, Bruker Karlsruhe, Germany) at the bottom surface of 2 mm thick composite specimens V2, Y4, V6, OC groups were measured separately at five irradiation times (5, 10, 20, 40, 60 seconds) and OR, VPD groups were measured in the above mentioned irradiation modes (n=5 each). Microhardness was measured using Digital microhardness tester (FM7, Future-Tech Co., Tokyo, Japan) at the top and bottom surfaces of 2mm thick composite specimens after exposure to the same irradiation modes as the test of degree of conversion(n=3, each). For the microleakage test, class V cavities were prepared on the distal surface of the ninety extracted human third molars. The cavities were restored with one of the following irradiation modes : V2/60 seconds, V4/40 seconds, V6/30 seconds, VPD , OC and OR. Microleakage was assessed by dye penetration along enamel and dentin margins of cavities. Mean polymerization shrinkage, mean degree of conversion and mean microhardness values for all groups at each time were analyzed using one-way ANOVA and Duncan's multiple range test, and using chi-square test far microleakage values. The results were as follows : . Polymerization shrinkage was increased with higher light intensity in groups using VIP$^{TM}$ (Bisco) : the highest with 600mW/$\textrm{cm}^2$, followed by Pulse-delay, 400mW/$\textrm{cm}^2$ and 200mW/$\textrm{cm}^2$ groups, The degree of polymerization shrinkage was higher with Continuous mode than with Ramp mode in groups using Optilux 501$^{TM}$ (Demetron/Kerr). . Degree of conversion and microhardness values were higher with higher light intensity. The final degree of conversion was in the range of 44.7 to 54.98% and the final microhardness value in the range of 34.10 to 56.30. . Microleakage was greater in dentin margin than in enamel margin. Higher light intensity showed more microleakage in dentin margin in groups using VIP$^{TM}$ (Bisco). The microleakage was the lowest with Continuous mode in enamel margin and with Ramp mode in dentin margin when Optilux 501$^{TM}$ (Demetron/Kerr) was used.