• Restorative Dentistry and Endodontics
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• v.21 no.2
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• pp.602-618
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• 1996

The purpose of this study was to investigate the effect of acid treatment of fluoride applied dentin surface with various concentrations of phosphoric acid for various periods of time on dentin bonding. Dentin specimens prepared from freshly extracted bovine mandibular anterior teeth were divided into fluoridated and nonfluoridated groups. Specimens of nonfluoridated group were pretreated with 10% phosphoric acid for 15 seconds. Those of fluoridated groups were treated with 2% sodium fluoride or 2% stannous fluoride solution for 5 minutes and stored in $37^{\circ}C$ distilled water for 3 days, followed by phosphoric acid treatment. The concentrations of phosphoric acid were 10%, 32% or 50% and the treatment periods of time were 15, 30 or 60 seconds. All the specimens were bonded with All Bond$^{(R)}$ 2 and Bisfil$^{TM}$ composite resin. After bonded specimens were stored in $37^{\circ}C$ distilled water for 24 hours, tensile bond strengths of each specimens were measured and the pretreated dentin and the fractured dentin surfaces were examined under the scanning electron microscope. The results were as follows : The tensile bond strengths from the fluoridated groups were significantly lower than those from the nonfluoridated group when the concentrations of phosphoric acid and the treatment periods of time were equal in all the groups (p<0.05). In general, the higher the concentration of phosphoric acid and the longer the treatment period of time for acid etching on the fluoride applied dentin surface, the higher were the bond strength values. Recovery of bond strength of the dentin bonding agent was better in the NaF applied group than in the $SnF_2$ applied one. SEM findings of NaF applied and $SnF_2$ applied dentin surfaces demonstrated reaction product-covered and partially or completely obstructed dentinal tubules. SEM findings of dentin surfaces fluoridated for 5 minutes followed by etching showed wider tubular openings and more clean dentin surfaces when dentin was etched with higher concentration of phosphoric acid for longer period of time. On the SEM observations of the fractured dentin-resin interface, the etched specimens of fluoridated group showed an adhesive failure mode when the concentration of phosphoric acid and the treatment period of time were same as in the nonfluoridated group. As the concentration of phosphoric acid and the treatment period of time increase during acid etching, the cohesive failure area increased. However, excessive acid etching caused adhesive failure.

• Restorative Dentistry and Endodontics
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• v.35 no.6
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• pp.486-491
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• 2010

Objectives: This study examined the effect of 2% chlorhexidine on the ${\mu}TBS$ of a direct composite restoration using one-step self-etch adhesives on human dentin. Materials and Methods: Twenty-four extracted permanent molars were used. The teeth were assigned randomly to six groups (n = 10), according to the adhesive system and application of chlorhexidine. With or without the application of chlorhexidine, each adhesive system was applied to the dentin surface. After the bonding procedure, light-cure composite resin buildups were produced. The restored teeth were stored in distilled water at room temperature for 24 hours, and then cut and glued to the jig of the microtensile testing machine. A tensile load was applied until the specimen failed. The failure mode was examined using an operating microscope. The data was analyzed statistically using one-way ANOVA, Student's t-test (p < 0.05) and Scheffet's test. Results: Regardless of the application of chlorhexidine, the Clearfil $S^3$ Bond showed the highest ${\mu}TBS$, followed by G-Bond and Xeno V. Adhesive failure was the main failure mode of the dentin bonding agents tested with some samples showing cohesive failure. Conclusions: The application of 2% chlorhexidine did not affect the ${\mu}TBS$ of the resin composite to the dentin using a one-step self-etch adhesive.

• Restorative Dentistry and Endodontics
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• v.36 no.1
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• pp.50-58
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• 2011

Objectives: The purpose of this study was to compare the microshear bond strength (uSBS) of two totaletch and four self-etch adhesive systems and a flowable resin to enamel. Materials and Methods: Enamels of sixty human molars were used. They were divided into one of six equal groups (n = 10) by adhesives used; OS group (One-Step Plus), SB group (Single Bond), CE group (Clearfil SE Bond), TY group (Tyrian SPE/One-Step Plus), AP group (Adper Prompt L-Pop) and GB group (G-Bond). After enamel surfaces were treated with six adhesive systems, a flowable composite resin (Filek Z 350) was bonded to enamel surface using Tygon tubes. the bonded specimens were subjected to uSBS testing and the failure modes of each group were observed under FE-SEM. Results: 1. The uSBS of SB group was statistically higher than that of all other groups, and the uSBS of OS, SE and AP group was statistically higher than that of TY and GB group (p < 0.05). 2. The uSBS for TY group was statistically higher than that for GB group (p < 0.05). 3. Adhesive failures in TY and GB group and mixed failures in SB group and SE group were often analysed. One cohesive failure was observed in OS, SB, SE and AP group, respectively. Conclusions: Although adhesives using the same step were applied the enamel surface, the uSBS of a flowable resin to enamel was different.

• Proceedings of the Korea Water Resources Association Conference
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• 2011.05a
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• pp.17-17
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• 2011

As a method of countermeasure to bed degradation and armoring phenomena of bed material in the downstream area of dam reservoirs, sediment augmentation (replenished sediment) has been carried out in many Japanese rivers. In general, bed of the replenished sediment site is composed of rocks, because the site is located in the downstream area of the dams and sediment supply is very small. Bed deformation process has been researched by many researchers. As a method of countermeasure to bed degradation and armoring phenomena of bed material in the downstream area of dam reservoirs, sediment augmentation (replenished sediment) has been carried out in many Japanese rivers. In general, bed of the replenished sediment site is composed of rocks, because the site is located in the downstream area of the dams and sediment supply is very small. Bed deformation process has been researched by many researchers. However, most of them can treat movable bed only and cannot be applied to the bed deformation process of sediment on rocks. If the friction angle between the sediment and the bed surface is assumed to be the same as the friction angle between the sediment and the sediment, sediment transport rate must be smaller without sediment deposition layer on the rocks. As a result, the reproduced bed geometry is affected very well. In this study, non-equilibrium transport process of non-cohesive sediment on rigid bed is introduced into the horizontal two dimensional bed deformation model and the model is applied to the erosion process of replenished sediment on rock in the Nakagawa, Japan. Here, the Japanese largest scale sediment augmentation has been performed in the Nakagawa. The results show that the amounts of the eroded sediment and the remained sediment reproduced by the developed numerical model are $56300m^3$ and $26800m^3$, respectively. On the other hand, the amounts of the eroded sediment and the remained sediment measured in the field after the floods are $56600m^3$ and $26500m^3$, respectively. The difference between the model and field data is very small. Furthermore, the bed geometry of the replenished sediment after the floods reproduced by the developed model has a good agreement with the measured bed geometry after the floods. These results indicate that the developed model is able to simulate the erosion process of replenished sediment on rocks very well. Furthermore, the erosion speed of the replenished sediment during the decreasing process of the water discharge is faster than that during the increasing process of the water discharge. The replenished sediment is eroded well, when the top of the replenished sediment is covered by the water. In general, water surface level is kept to be high during the decreasing process of the discharge during floods, because water surface level at the downstream end is high. Hence, it is considered that the high water surface level during the decreasing process of the water discharge affects on the fast erosion of the replenished sediment.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.31 no.5
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• pp.203-211
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• 2021

Octacalcium phosphate(OCP, Ca₈H₂(PO₄)₆·5H₂O) is one of biodegradable calcium phosphate materials with osteoconductivity and biocompatibility. It has the advantage of rapid bone formation and resorption due to the property of stimulating stromal cells to differentiate into osteoblasts. However, if OCP is inserted in body, it is immediately decomposed without maintaining of its shape as scaffolds due to their weak cohesive force between powder. On the other hand, hydroxyapatite (HA, Ca₁₀(PO₄)₆(OH)₂), which has a crystal structure similar to that of OCP, remains in the body without decomposition until the bone defect is restored. In this study, the degradation behavior of OCP/HA disc with different amount of HA in SBF (simulated body fluid) solution was characterized in terms of the weight loss, pH variation and microstructure change with immersion duration in SBF solution. As a result, the OCP/HA disc was not quickly decomposed and maintained its own shape for 2 weeks regardless of HA content. In particular, the surface of 40HA specimen was uniformly dissolved and then CDHA (calcium deficient hydroxyapatite) phase were formed onto the surface of disc after 7 days in SBF solution. It would be suggested that the 40HA specimen would be suitable candidate material as the scaffolds for the restoration of bone defect.

• Journal of the Korean Recycled Construction Resources Institute
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• v.9 no.4
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• pp.433-442
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• 2021

In this study, the properties of no-fines polymer concrete with different polymer binder contents were evaluated. The polymer concrete was formulated using a polymeric binder (unsaturated polyester resin), fly ash, and recycled coarse aggregate (60%) and crushed coarse aggregate (40%). The polymeric binder content (4.0-6.0wt.%) was used as an experimental variable because it dramatically affects both the cost-effectiveness and material properties. The results showed that the density, compressive strength, flexural strength both before and after exposure to freezing and thawing increased as the polymer binder content increased, while the absorption, void ratio, permeable voids, coefficient of permeability, and acid resistance (mass loss by acid attack) decreased as the polymeric binder content increased. In particular, even though the void ratio was 18.4% and the water permeability coefficient was 7.3mm/sec, the compressive strength and flexural strength were as high as 38.0MPa and 10.0MPa, respectively, much more significant than those of previous studies. Other properties such as absorption and acid resistance were also found to be excellent. The results appear to be rooted in the increased adhesion of the binder by adding a cross-linking agent and the surface hydrophobicity of the polymer.

• The Korean Journal of Archival Studies
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• no.5
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• pp.3-37
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• 2002

Today the market of EDMS is esteemed more than 100 billions won. It signifies a comming of age of electronic records. The traditional archival theories which are based on the paper records are confronted with a new challenge. In some leading countries of archival studies reorientation of archives management has been tried by a number of distinguished specialists such as Bearman and Hedstrom since 10 years. As a consequence new paradigm of archival theories has been developed. Also in Korea this new paradigm has been introduced by some expert such as Lee, Sang-Min, Sul, Moon-won, Lee, Seung-Eok. However their arguments are too general to offer a concrete clue for new paradigm. Faced by new age of electronic records, it's important to start a discussion for the reasonable methods of electronic records management at once. The most drastically changed part of record management by the electronic technique is the life-cycle of records. The commonly practiced three-stage life-cycle is to be reduced to the two-stage life-cycle, and the concept of the spatial movement of records is to be changed. It can be also pointed that the public emerges as user from the early creating stage of records beyond time and space. Thus is can be said that the method of the management features dynamic and cohesive. The method of appraisal must be also changed and reproduced, so that it can reflect the various levels considering dynamics of the electronic records. Supposedly it will be a core factor that causes the change of methodology in records management with the change of life-cycle theory. It must be noted that various subjects would be involved in the work of classification and description over time and space and that feedback between them is of important. Description also tends to be made at the crating stage of records and structured dynamically. It results from the change of life-cycle and the introduction of the concept of continuum. Such trend allows us to start discussions on the assumption that description of both creator and archival professionals act together an important role. Of course, it is linked with the methodology in which most descriptions are made automatically at the early drafting stage of the structure. The meat date is formed on the assumption that there should be feedback between areas of automatic description, description of creators and archival professionals. The most important thing in description is to develop a suitable way how it is structured. An alternative must be offered for managing data set. As iweb that is being operated by Myongji university shows, records created in daily business are managed not as electronic records but as date base. This is because they exist outside the repository in the EDMS system. Since data set often has various sources, an alternative for classification needs to be developed. It is now likely that database is filed according to the created year to be transferred automatically to the repository. Over a long-term the total management of database, electronic records and electronic information will be a topic. A right direction of new paradigm will be found for both iweb and E-government, when practice and studies of theories are combined and interacted.

• Journal of the Korean GEO-environmental Society
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• v.20 no.2
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• pp.19-28
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• 2019

Grounds of the western coast of the Korean Peninsular are mostly composed of soft and cohesive soils, and it is necessary to carry out soil improvement before construction. The CGS (Compaction Grouting System) method has been commonly applied for the purpose of not only improving soft ground but also serving as the pile foundation of a bridge. In this paper, the CGS method was applied to the Incheon International Airport facility site, which consists of reclaimed landfill and soft clay soil, so as to evaluate the applicability of this soil improvement method to soft clay ground formations. Futhermore, results of construction were intensively studied along with a series of field experiments and theoretical consideration. The cone penetration tests were performed to assess the ground improvement effect of the CGS method. Consequently, the application of CGS method led to an increase in soil strength enough to be used as the pile foundation to support the bridge at the site. In addition, the size of the upper grout-bulb was estimated by adopting the cavity expansion theory and compared with that of actual grout bulb exhumed in the field. Therefore, it is proved that the cavity expansion theory can be utilized to predict and evaluate the improvement of soft ground.

• 재활복지
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• v.21 no.1
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• pp.193-212
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• 2017

The elderly often produce irrelevant speech and get off-topic more easily than the young; the former also has difficulty generating fewer syntactic structures and makes errors of grammatical morphemes. In particular, the elderly might have more difficulty writing since it requires more complex cognitive processes than storytelling. The participants in this study were 32 young people and 32 older people. They were asked to write a short story of Korean fairy tale('Heungbu Nolbu'). The data was analyzed in narrative composition and syntactic structures. The study revealed the following: First, in composition aspects, the elderly group showed significantly lower total number of story grammar and episodes. In addition, the elderly produced more off topic statements. Second, in syntactic aspects, although there was no significant difference in the number of producing complex sentences between two groups, the elderly group generated more inadequate cohesive devices and used fewer relative and adverbial clauses. These findings suggest that the elderly have a tendency to perform tasks by producing more off-topic statements and shows decreasing coherence by using lower number of relative and adverbial clauses. However, this study also uncovers that the elderly were able to write more complex and longer sentences using visual feedback.

• Journal of the Korean GEO-environmental Society
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• v.19 no.12
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• pp.25-32
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• 2018

This paper investigates the effect of rock discontinuities on a shear stress wave that is induced by earthquake or blasting and provides the result of numerical parametric studies. The numerical tests of different conditions of rock and discontinuity have been carried out after confirming that the numerical approach is valid throughout a verification analysis from which the test results were compared with a theoretical solution. In-situ stress condition was considered as a rock condition and internal friction angle and cohesive value, which are the shear strength parameters, were considered as discontinuities condition. The joint inclination angle was also taken into account as a parameter. With the various conditions of different parameters, the test results showed that a shear stress wave propagating through a mass is highly influenced by the shear strength of discontinuities and the condition of joint inclination angle as well as in-situ stress. The study results indicate that when earthquake or blasting-induced dynamic loading propagates through a jointed rock mass or a stratified soil ground the effect of in-situ stress and discontinuities including a stratum boundary should be taken into account when evaluating the dynamic effect on nearby facilities and structures.