• The Journal of the Korean dental association
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• v.48 no.9
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• pp.680-687
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• 2010

The purpose of this study was to compare post cementation efficacy according to the different adhesive systems and cement delivery methods. A total of 40 extracted human single-rooted premolar teeth were randomly divided in four groups according to the two luting agents of Unicem applicap (3M ESPE, St. Paul, MN, USA) or Variolink II (Ivoclar Vivadent, Liechtenstein) and cement delivery methods of direct cement application or lentulo spiral application. After restoration using glass?fiber posts, the samples were embedded in acrylic resin. Three sections of 2 mm thickness were prepared from each specimen, and the post in each section was subjected to a push-out test. The data were analysed statistically at significant level of 95%. The Unicem had significantly higher push-out bond strength than Variolink and the lentulo spiral application made higher bond strength (p<0.05). Adhesive failure between cement and dentin was predominant in all groups. The Unicem of self-etch system and cement delivery using lentulo spiral showed clinically acceptable and comparable bonding strength for the fiber post.

• Journal of Sensor Science and Technology
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• v.8 no.2
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• pp.163-170
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• 1999

A programmable A/D converter for an embedded fiber-optic combustion pressure sensor has been designed with 8 N and P channel MOSFETs, respectively. A local field enhancement for reducing programming voltage during writing as well as erasing an EEPROM device is introduced. In order to observe linear programmability of the EEPROM device during programming mode, a cell is developed with a $1.2\;{\mu}m$ double poly CMOS fabrication process in MOSIS. It is observed that the high resolution, of say 10mVolt, is valid in the range 1.25volts to 2volts. The experimental result is used for simulating the programmable 8 bit A/D converter with Hspice. The A/D converter is demonstrated to consume low power, $37\;{\mu}W$ by utilizing a programming operation. In addition, the converter is attained at the conversion frequency of 333 MHz.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.101-104
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• 2008

The cost of repairing the deterioration of concrete structures due to corrosion of the reinforcement steel has been the prominent figure in the maintenacne of the reinforced-concrete infrastructures. As an alternative material to steel reinforcement, the use of Fiber Reinforced Polymer (FRP) bar in concrete is being actively studied for the high resistance of chemical environment and high strength to weight ratio properties of FRP. However, there remain various aspects of FRP properties that still need to be studied before the standard design criteria can be established. One of the imminent issues is the bond between FRP and concrete. In this study, the bond-behavior of FRP bars in concrete is investigated via the pullout test with three varying parameters: surface condition of FRP bars, concrete compression strength, and cyclic loading patterns. As a result of experiment, the bond strength of GFRP increased with the concrete compression strength increasing and decreased with applying cyclic load.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2004.04a
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• pp.135-138
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• 2004

Conventional piezoelectric lead-zirconate-titanate (PZT) senor has high sensitivity, but it is very brittle. Recently polymer films such as polyvinylidene fluoride (PVDF) and poly(vinylidene fluoride­trifluoroethylene) (P(VDF-TrFE)) copolymer have been used as a sensor. The advantages of polymer sensor are the flexibility and mechanical toughness. Simple process and possible several shapes are also additional advantages. Polymer sensor can be directly embedded in a structure. In this study, nondestructive damage sensitivity of single basalt fiber/epoxy composites was investigated with sensor type and thermal damage using AE and oscilloscope. And AE waveform for epoxy matrix with various damage types was compared to each other. The damage sensitivity of two polymer sensors was rather lower than that of PZT sensor. The damage sensitivity of PVDF sensor did not decrease until thermal damage temperature at $80^{\circ}C$ and they decreased significantly at $110^{\circ}C$ However, the damage sensitivity of P(VDF-TrFE) sensor at $110^{\circ}C$ was almost same in no damage sensor. For both top and side impacts, the difference in arrival time increased with increasing internal and surface damage density of epoxy matrix.

• Restorative Dentistry and Endodontics
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• v.47 no.1
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• pp.12.1-12.11
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• 2022

Objectives: This pilot study aimed to establish the interrelationship between collagen and mast cells in periapical granulomas and periapical cysts. Materials and Methods: An observational cross-sectional study was conducted on the paraffin-embedded tissue sections of 68 specimens (34 periapical granulomas and 34 periapical cysts). The specimens were stained with picrosirius to observe collagen fiber birefringence and anti-tryptase antibody to evaluate the mast cell count immunohistochemically. The mean number and birefringence of collagen fibers, as well as the mean number of mast cells (total, granulated, and degranulated), and the mean inflammatory cell density were calculated. The data obtained were analyzed using the Kruskal Wallis test, Mann Whitney U test, and Spearman correlation test (p < 0.05). Results: The mean number of thick collagen fibers was higher in periapical cysts, while that of thin fibers was higher in granulomas (p = 0.00). Cysts emitted orange-yellow to red birefringence, whereas periapical granulomas had predominantly green fibers (p = 0.00). The mean inflammatory cell density was comparable in all groups (p = 0.129). The number of total, degranulated, and granulated mast cells exhibited significant results (p = 0.00) in both groups. Thick cyst fibers showed significant inverse correlations with inflammation and degranulated mast cells (p = 0.041, 0.04 respectively). Conclusions: Mast cells and inflammatory cells influenced the nature of collagen fiber formation and its birefringence. This finding may assist in the prediction of the nature, pathogenesis, and biological behavior of periapical lesions.

• Journal of the Korea institute for structural maintenance and inspection
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• v.19 no.2
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• pp.151-159
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• 2015

In this study, experimental research was carried out to evaluate and improve the seismic performance of reinforced concrete beam-column joint regions using strengthening materials (CFRP sheet, AFRP sheet, embedded CFRP rod) in existing reinforced concrete structure. Therefore it was constructed and tested seven specimens retrofitting the beam-column joint regions using such retrofitting materials. Specimens, designed by retrofitting the beam-column joint regions of existing reinforced concrete structure, were showed the stable failure mode and increase of load-carrying capacity due to the effect of crack control at the times of initial loading and confinement of retrofitting materials during testing. Specimens LBCJ-CRUS, designed by the retrofitting of CFRP Rod and CFRP Sheet in reinforecd beam-column joint regions were increased its maximum load carrying capacity by 1.54 times and its energy dissipation capacity by 2.36 times in comparison with standard specimen LBCJ for a displacement ductility of 4 and 7. And Specimens LBCJ-CS, LBCJ-AF series were increased its energy dissipation capacity each by 2.04~2.34, 1.63~3.02 times in comparison with standard specimen LBCJ for a displacement ductility of 7.

• Steel and Composite Structures
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• v.23 no.5
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• pp.529-541
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• 2017

In the present study, vibration analysis of functionally graded carbon nanotube reinforced composite (FGCNTRC) plate moving in two directions is investigated. Various types of shear deformation theories are utilized to obtain more accurate and simplest theory. Single-walled carbon nanotubes (SWCNTs) are selected as a reinforcement of composite face sheets inside Poly methyl methacrylate (PMMA) matrix. Moreover, different kinds of distributions of CNTs are considered. Based on extended rule of mixture, the structural properties of composite face sheets are considered. Motion equations are obtained by Hamilton's principle and solved analytically. Influences of various parameters such as moving speed in x and y directions, volume fraction and distribution of CNTs, orthotropic viscoelastic surrounding medium, thickness and aspect ratio of composite plate on the vibration characteristics of moving system are discussed in details. The results indicated that thenatural frequency or stability of FGCNTRC plate is strongly dependent on axially moving speed. Moreover, a better configuration of the nanotube embedded in plate can be used to increase the critical speed, as a result, the stability is improved. The results of this investigation can be used in design and manufacturing of marine vessels and aircrafts.

• Fibers and Polymers
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• v.6 no.3
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• pp.219-223
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• 2005

Water-soluble chitin (WSC) was prepared by carefully deacetylating chitins to about $50\%$ of N-acetyl content. Topical formulations based on WSC were prepared and their effects on wound healing were evaluated on a rabbit ear model. Full-thickness, open skin wounds were made on the ears of rabbits and WSC ointments were embedded in the open wounds. The application of WSC ointments significantly accelerated wound healing and wound contraction. The areas of epithelial-ization and granulation tissues in WSC ointment group are remarkably larger than those in control group (no treatment) and in placebo group (treated with ointment-base materials). A large number of grown granulation tissues including dense fibroblast deposition were observed under the thickened epithelium of the wound treated with WSC ointments. The number of inflammatory cells in WSC ointment group was significantly decreased compared with those in control and placebo groups, indicating that WSC would give low stimuli to wounds and prevent excessive scar formation. Neovascularization was the most prominent in WSC ointment group. Wound contraction in WSC ointment group was much larger than those in control and placebo groups. Overall results demonstrate that the topical formulation based on WSC is considered to become an excellent dressing as a wound healing assistant.

• Composites Research
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• v.15 no.3
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• pp.18-29
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• 2002

The bending vibration and thermal flutter instability of spacecraft booms modeled as circular thin-walled beams of closed cross-section and subjected to thermal radiation loading is investigated in this paper. The thin-walled beam model incorporates a number of nonclassical effects of transverse shear, primary and secondary warping, rotary inertia and anisotropy of constituent materials. Thermally induced vibration response characteristics of a composite thin walled beam exhibiting the circumferantially uniform system(CUS) configuration are exploited in connection with the structural flapwise bending-lagwise bending coupling resulting from directional properties of fiber reinforced composite materials and from ply stacking sequence. The numerical simulations display deflection time-history as a function of the ply-angle of fibers of the composite materials, damping factor, incident angle of solar heat flux, as well as the boundary of the thermal flutter instability domain. The adaptive control are provided by a system of piezoelectric devices whose sensing and actuating functions are combined and that are bonded or embedded into the host structure.

• The Journal of the Korea institute of electronic communication sciences
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• v.9 no.4
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• pp.469-474
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• 2014

Installed on telephone poles laid scrambling to monitor the status of the communication lines, and cost information can provid eadditional information tools to develop systems to support on-site monitoring. Aerial support for a maintenance monitoring module to apply an embedded system, and information processing applications manufactured. In this study, a comprehensive plan in accordance with the government's aerial maintenance work to prevent accidents spread support for the device to immediately take advantage of big cities and aerial maintenance business, Construction worker accused of bias and aims to improve efficiency of maintenance puts.