• The Journal of Korean Academy of Prosthodontics
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• v.53 no.4
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• pp.318-324
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• 2015

Purpose: This study compared shear bond strengths of five self-adhesive cements with phosphate monomer to zirconium oxide ceramic with and without airborn particle abrasion. Materials and methods: One hundred zirconia samples were air-abraded ($50{\mu}mAl_2O_3$). One hundred composite resin cylinders were fabricated. Composite cylinders were bonded to the zirconia samples with either Permacem 2.0 (P), $Clearfil^{TM}$ SA Luting (C), $Multilink^{(R)}$ Speed (M), $RelyX^{TM}$ U200 Automix (R), G-Cem $LinkAce^{TM}$ (G). All bonded specimens were stored in distilled water ($37^{\circ}C$) for 24 h and half of them were additionally aged by thermocycling ($5^{\circ}C$, $55^{\circ}C$, 5,000 times). The bonded specimens were loaded in shear force until fracture (1 mm/min) by using Universal Testing Machine (Model 4201, Instron Co, Canton, MA, USA). The failure sites were inspected under field-emission scanning electron microscopy. The data was analyzed with ANOVA, Tukey HSD post-hoc test and paired samples t-test ($\alpha$=.05). Results: Before and after thermocycling, $Multilink^{(R)}$ Speed (M) revealed higher shear-bond strength than the other cements. G-Cem $LinkAce^{TM}$ (G) showed significantly lower bond strengths after thermocycling than before treatment (P<.05), but the other groups were not significantly different (P>.05). Conclusion: Most self-adhesive cements with phosphate monomer showed high shear bond strength with zirconia ceramic and weren't influenced by thermocycling, so they seem to valuable to zirconia ceramic bonding.

• Restorative Dentistry and Endodontics
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• v.35 no.2
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• pp.125-133
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• 2010

Objectives: Rapid polymerization of overlying composite resin causes high polymerization shrinkage stress at the adhesive layer. In order to alleviate the shrinkage stress, increasing the light intensity over the first 5 seconds was suggested as an exponential curing mode by an LED light curing unit (Elipar FreeLight2, 3M ESPE). In this study, the effectiveness of the exponential curing mode on reducing stress was evaluated with measuring microtensile bond strength of three adhesives after the overlying composite resin was polymerized with either continuous or exponential curing mode. Methods: Scotchbond Multipurpose Plus (MP, 3M ESPE), Single Bond 2 (SB, 3M ESPE), and Adper Prompt (AP, 3M ESPE) were applied onto the flat occlusal dentin of extracted human molar. The overlying hybrid composite (Denfil, Vericom, Korea) was cured under one of two exposing modes of the curing unit. At 48h from bonding, microtensile bond strength was measured at a crosshead speed of 1.0 mm/min. The fractured surfaces were observed under FE-SEM. Results: There was no statistically significant difference in the microtensile bond strengths of each adhesive between curing methods (Two-way ANOVA, p > 0.05). The microtensile bond strengths of MP and SB were significantly higher than that of AP (p < 0.05). Mixed failures were observed in most of the fractured surfaces, and differences in the failure mode were not observed among groups. Conclusion: The exponential curing method had no beneficial effect on the microtensile dentin bond strengths of three adhesives compared to continuous curing method.

• Restorative Dentistry and Endodontics
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• v.30 no.3
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• pp.204-214
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• 2005

This study compared the microtensile bond strength (${\mu}$TBS) and microscopic change of two 2-step and two 1-step self-etching adhesives to dentin according to storage times in distilled water. Occlusal dentin was exposed in 48 human molars. They were divided to four groups by different adhesives: SE Bond group (Clearfil SE Bond), AdheSE group (AdheSE). Adper group (Adper Prompt L-Pop), and Xeno group (Xeno III) . Each group was stored in 37$^{\circ}C$ distilled water for 1, 15, and 30 days. Resin-bonded specimens were sectioned into beams and subjected to ${\mu}$TBS testing with a crosshead speed of 1 mm/minute. For SEM observation, one specimen was selected and sectioned in each group after each stroage time. Resin-dentin interface was observed under FE-SEM. In all storage times, mean ${\mu}$TBS of SE group was significantly higher than those of other groups (p < 0.05). There was no significant difference between mean ${\mu}$TBS of SE group and AdheSE group among all storage times, but significant difference between 1- and 30-day storage in mean y${\mu}$TBS of Adper group and Xeno group (p > 0.05). For 1-and 15-day storage, all groups showed the close adaptation between resin-dentin interfaces. For 30-day storage, resin-dentin interfaces showed wide gap in Adper group and separate pattern in Xeno III group.

• Korean Journal of Optics and Photonics
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• v.8 no.4
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• pp.327-332
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• 1997

We fabricated the high speed 1.55${\mu}{\textrm}{m}$ distributed feedback laser diodes (DFB-LD) using both two-step mesa etching process and semi-insulating InP current blocking layers. The devices characteristics were threshold current of ~15mA, slope efficiency of ~0.13mW/mA, and dynamic resistance of ~6.0Ω, with as-cleaved facets. The fabricated DFB-LD showed the single longitudinal mode with more than 40dB up to 6 $I_{th}$(CW condition), emitting at the wavelength of 0.546${\mu}{\textrm}{m}$. The -3dB bandwidth was >10㎓ at the driving current of 27mA, and the maximum -3dB bandwidth was ~18㎓ at 90 mA current, showing the superior frequency response of SI-PBH DFB-LD. In the 10Gb/s transmission experiment for 1.55${\mu}{\textrm}{m}$ DFB-LD module, maximum 10 km of single mode fiber(SMF) or 80 km of dispersion shifted fiber (DSF) could be transmitted with error free.

• Journal of Korean Society of Transportation
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• v.20 no.3
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• pp.149-158
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• 2002

For the purpose of preciously describing real time traffic pattern in urban road network, dynamic network loading(DNL) models able to simulate traffic behavior are required. A number of different methods are available, including macroscopic, microscopic dynamic network models, as well as analytical model. Equivalency minimization problem and Variation inequality problem are the analytical models, which include explicit mathematical travel cost function for describing traffic behaviors on the network. While microscopic simulation models move vehicles according to behavioral car-following and cell-transmission. However, DNL models embedding such travel time function have some limitations ; analytical model has lacking of describing traffic characteristics such as relations between flow and speed, between speed and density Microscopic simulation models are the most detailed and realistic, but they are difficult to calibrate and may not be the most practical tools for large-scale networks. To cope with such problems, this paper develops a new DNL model appropriate for dynamic traffic assignment(DTA), The model is combined with vertical queue model representing vehicles as vertical queues at the end of links. In order to compare and to assess the model, we use a contrived example network. From the numerical results, we found that the DNL model presented in the paper were able to describe traffic characteristics with reasonable amount of computing time. The model also showed good relationship between travel time and traffic flow and expressed the feature of backward turn at near capacity.

• Applied Chemistry for Engineering
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• v.23 no.6
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• pp.554-560
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• 2012

Recently, it has been increasing trend to use conductive materials as electronics and communication technology in electronics industry are developing. The noble metal such as Ag, Pt, Pd etc. are mostly used as conductive materials, To reduce production cost, alternative materials with similar characteristics of noble metals are needed. Copper has advantages, i.e its electronic properties are similar to noble metals and low cost than noble metal, but its use has been restricted because of oxidation in air. In this study, the tin film was coated on copper by electroless plating to protect copper from oxidation and to confirm the effects of temperature, pH, amount of $SnCl_2$, and feeding speed in plating conditions. Additionally, we apply $Cu_{core}Sn_{shell}$ powder as conductive filler with low-temperature densification and analysis by SEM, XRD, FIB and 4-Point Probe techniques. As result of the study, tin film was coated well on copper and was protected from oxidation. After low-temperature densification treatment, the meted tin made chemical interconnections with copper. Accordingly, conductivity was increased than before condition. We hope $Cu_{core}Sn_{shell}$ powder to replace noble metals and use in the electronic field.