• Journal of the Korean Association of Oral and Maxillofacial Surgeons
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• v.29 no.2
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• pp.102-107
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• 2003

At orthodontic treatment, we have made every effort to get rigid anchorage which is not stirred when teeth move. As a result, the miniscrew that is rigid anchorage was invented recently, and now it is used widely. Concerning the advantage of miniscrew, it is reduced dependence of extraoral anchorage and it shortens treatment time for rapid tooth movement. In contrast, the defect of miniscrew is falling off it resulted from increasing of the mobility. So the purpose of this research is to be of help to prognose clinical use of miniscrew, which is inserted for intraoral anchorage, by investigating and comparing the failure rate of miniscrew for loading time. This study researches the failure rate of miniscrew for teeth movement at the orthodontic treatment. The failure rate of miniscrew in mid course, after inserting 147 miniscrews in 51 patients, is 13%(20/147). It showed no statistically significant differences as compared man with woman, maxilla with mandible, double-head with uni-head miniscrew, and drilling and non-drilling before inserting the miniscrew. In comparison below twenties with over twenties and the times that we give load to miniscrew, it produced that the failure rate of miniscrew is 9.7% higher in the case of below the twenties than over the twenties. Also, the failure rate of loading immediately is 10.8% higher than loading after 7 days. According to using driver for the insertion of miniscrew, the failure rate of miniscrew is higher in the case of using machined driver than in the case of using hand driver when the level of significance is 95%. According to the research, we can suppose that the failure rate has no concern with using miniscrew on man or woman, maxilla or mandible, the shape of head, and drilling or non-drilling before insertion of miniscrew. Therefore, we can choose eclectic miniscrew as demands. In addition, we must notify the patient, below twenties, to be possibility of high failure rate. And It is strongly recommended to give load after $1{\sim}2$ weeks for healing of the insertion area.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.37 no.8
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• pp.35-41
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• 2000

The frequency dependence of the pyroelectric characteristics of $LiTaO_3$ have been investigated by using the dynamic method. In the frequency range between 2 and 1000 Hz, they are measured in both the regimes of pyroelectric current ($R_L=1M{\Omega}$) and pyrelectric voltage ($R_L=17.3G{\Omega}$), which can be selected by adjusting the value of the load resistance. Pyroelectric coefficient depending on the voltage response in the regime of pyroelectric current shows the maximum value of $1.56{\times}10^{-8}C/cm^2{\cdot}K$ at 40 Hz. The maximum values of figures of merits for the voltage response and for the detectivity are measured as $10.8{\times}10^{-11}C{\cdot}cm/J$ and $13{\times}10^{-7}C{\cdot}cm/J$, respectively. The voltage responsivity depending on the voltage response in the regime of pyroelectrci voltage shows the maximum value of 488 V/W at 2 Hz. Noise equivalent power and detectivity shows the minimum value of $3.95{\times}10^{-10}W/{\sqrt}Hz$ and maximum value of $5.6{\times}10^8cm{\cdot}{\sqrt}Hz/W$ at 40 Hz, respectively.

• Journal of the Korea Society of Computer and Information
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• v.15 no.5
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• pp.113-124
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• 2010

In this study, the hybrid authorization quotation technique is based on the device ID for the integrity of the source region guarantee of user certificate, in order to improve the convenience and security for user in the hybrid PKI certificate Mechanism for authentication. The feature of the model in which it is presented from this paper is 5. First, because the user can select the policy himself in which it matches with each authentication situation and security level, the convenience can be improved. Second, the integrity of the source region of the user certificate can be guaranteed through the comparison of the DLDI Key, that is the hash-value of the device ID. Third, the security can be improved by continuously changing an encoding, and the value of the key in which it decodes through the EOTP Key. Fourth, the index value is added to a certificate, and the storage of a certificate is possible at the Multi-Device. Fifth, since the addi the inan aratus for the integrity of the source region guarantee of a certificate is not needed, the authentication process time can be reduced and the computational load of the certificate server can be reduced also.

• Composites Research
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• v.34 no.2
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• pp.77-81
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• 2021

Due to the high specific strength and stiffness of the composite materials, the composite materials have been extensively used in various industries. In particular, carbon fiber reinforced composites are widely used in many mechanical structures. In addition, since carbon fiber reinforced composites have anisotropic properties, to understand the fatigue behavior of composites with different fiber orientation is very important for the efficient structural design. Therefore, in this paper, the effect fiber orientation on the fatigue life of composite materials was experimentally evaluated. For this purpose, tensile and fatigue tests were performed on the off-axis specimens (0°, 10°, 30°, 45°, 60°, 90°) of the composite materials. As a result of the fatigue tests, the fatigue strength of the composites decreased significantly as the fatigue strength slightly deviated from 0 degrees. On the other hand, the more deviated, the less decreased. This is because the role of supporting the load of fibers decreased as the stacking angle increased. In addition, the fatigue behavior was analyzed by introducing a fatigue strength ratio (Ψ) that eliminates the fiber orientation dependence of the off-axis fatigue behaviors on the unidirectional composites. The off-axis fatigue S-N lines can be reduced to a single line regardless of the fiber orientation by using the fatigue strength ratio (Ψ). Using the fatigue Ψ-N line, it is possible to extract back to any off-axis fatigue S-N lines of the composites with different fiber orientations.

• Nuclear Engineering and Technology
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• v.17 no.3
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• pp.211-215
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• 1985

The effects of temperature and strain rate on the I-SCC behaviors of Zircaloy-4 were investigated by constant load test at 30$0^{\circ}C$ and constant elongation rate test at 300, 350 and 40$0^{\circ}C$ in 3.34mg $I_2$/㎤. The results showed that I-SCC susceptibility increased as the strain rate decreased or the temperature increased. The empirical relation between the stress and the time to failure at 30$0^{\circ}C$ was given by 1/ $t_{f}$∝exp (0.3$\sigma$/$\sigma$$_{UTS}$-31.5) When the I-SCC susceptibility was expressed by the ratio of fracture energy in iodine atmosphere to that in the inert atmosphere, severe I-SCC susceptibility was found near 7.6$\times$10$^{-6}$ sec at 30$0^{\circ}C$ and the maximum point of I-SCC susceptibility tended to shift to the higher strain rate with increasing the temperature. The quasi-cleavage fracture was observed in I-SCC fracture surface. From these results, it was certain that the film repture step was involved as an important process in the I-SCC mechanism of Zircaloy-4.4.

• Journal of the korean academy of Pediatric Dentistry
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• v.26 no.3
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• pp.520-527
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• 1999

For the purpose of providing some suggestions in selection of filling materials used in 'sandwich technique', the bond strengths between glass ionomer cement bases and composite resins were investigated and compared. For lining materials, 'Vitrebond' and 'Ketac-fil' were used. Using these two as bases, 10 of each following resins were built up on the top ; Z-100 (light curing resin) Clear-fil (chemical curing resin), Bis-core (dual cure resin), Dyract (compomer), therfore 10 specimens of each group and total of 80 specimens were made. After storing specimens in $37^{\circ}C$ deionized water for 24 hours, the shear bond strengths were measured under universal testing machine with 50 kg of full load scale and 1mm/min of cross-head speed and obtained the results as follows : 1. Over Vitrebond base, Z-100 showed the lowest bond strength but the other three did not show any difference in bond strength. 2. Over Ketac-fil base, Clear-fil showed the highest bond strength followed by Dyract, Bis-core, and Z-100 showed the lowest bond strengths. 3. Whereas Clear-fil showed the similar bond strengths on the Vitrebond base as other resins, it showed the highest bond strength on Ketac-fil base, which showed some difference in bond strength by differing GIC bases. 4. The bond strengths between base materials and composite resin showed a stronger resin-dependence tendency in cases with Ketac-fil bases rather than with Vitrebond bases.