• Journal of Technologic Dentistry
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• v.20 no.1
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• pp.37-49
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• 1998

The specimens used were Ag-25 Pd-15 Cu ternary alloy and Au addition alloy. These alloys were melted and casted by induction electric furnace and centrifugal casting machine in Ar atmosphere. These specimens were solution treated for 2hr at $800^{\circ}C$ and were then quenched into iced water, and aged at $350{\sim}550^{\circ}C$ Age- hardening characteristics of the small Au-containing Ag-Pd-Cu dental alloys were investigated by means of hardness testing. X-ray diffraction and electron microscope observations, electrical resistance, ergy dispersed spectra and electron probe microanalysis. Principal results are as follows : Hardening occured in two stages, i.e., stage I in low temperature and stage II in high temperature regions, during continuous aging. The case of hardening in stage I was due to the formation of the $L1_0$ type face-centered tetragonal PdCu-ordered phase in the grain interior and hardening in stage I was affected by the Cu concentration. In stage II, decomposition of the ${\alpha}$ solid solution to a PdCu ordered phase($L1_0$ type) and an Ag-rich ${\alpha}2$ phase occurred and a discontinuous precipitation occurred at the grain boundary. From the electron microscope study, it was conclued that the cause of age-hardening in this alloy is the precipitation of the PdCu ordered phase, which has AuCu I type face-centered tetragonal structure. Precipetation procedure was ${\alpha}{\to}{\alpha}+{\alpha}_2+PdCu {\to}{\alpha}_1+{\alpha}_2+PdCu$ at Pd/Cu = 1.7 Ag-Pd-Cu alloy is more effective dental alloy as ageing treatment and is suitable to isothermal ageing at $450^{\circ}C$.

• The Journal of Korean Academy of Prosthodontics
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• v.51 no.3
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• pp.160-166
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• 2013

Purpose: The purpose of this study was to compare the fracture strength of traditional metal-ceramic crowns and full zirconia crowns according to the occlusal thickness. Materials and methods: A mandibular first molar resin tooth was prepared with 1.5 mm occlusal reduction, 1.0 mm rounded shoulder margin and $6^{\circ}$ taperness in the axial wall. Duplicating the resin tooth, 64 metal dies were fabricated. 48 full zirconia crowns were fabricated using Prettau zirconia blanks by ZIRKONZAHN CAD/CAM and classified into six groups according to the occlusal thickness (0.5 mm, 0.6 mm, 0.7 mm, 0.8 mm, 0.9 mm, 1.0 mm). 16 metal-ceramic crowns were fabricated and classified into two groups according to the occlusal porcelain thickness (1.0 mm, 1.5 mm). All crowns were cemented on each metal die and mounted in a universal testing machine. The load was directed at the functional cusp of each specimen until catastrophic failure occurred. One-way ANOVA, Tukey multiple comparison test (${\alpha}=.05$) and t-test (${\alpha}=.05$) were used. Results: The results were as follows. 1. The test 1 group (646.48 N) showed the lowest fracture strength (P<.05), and the value of the test 2.3.4.5 groups (866.40 N, 978.82 N, 1196.82 N, 1222.41 N) increased as thickness increased, but no significant difference were found with the groups (P>.05). The value of test 6 group (1781.24 N) was significantly higher than those of the other groups (P<.05). 2. There were no significant differences of the fracture strength of metal ceramic crowns according to occlusal porcelain thickness 1.0 mm (2515.71 N) and 1.5 mm (3473.31 N) (P<.05). Conclusion: Full zirconia crown needs to be 1.0 mm or over in occlusal thickness for the posterior area to have higher fracture strength than maximum bite force.

• Journal of the korean academy of Pediatric Dentistry
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• v.44 no.3
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• pp.335-340
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• 2017

Composite resin becomes an essential material in pediatric dentistry. However, incremental filling of composite resin to minimize the polymerization shrinkage takes time. To reduce the polymerization shrinkage, clinicians and researchers have focused on bulk-filling materials. Bulk-base composite resin is newly introduced as bulk-filling composite resin. The purpose of this study was to evaluate microhardness profile of bulk-base composite resin according to the depth of cure. A high flow bulk-base material and a low flow bulk-base material were used for experimental group, and a conventional composite resin was used for control group. Each group consist of 20 specimens, $3.5{\times}3.5{\times}5.0mm$ mold was used to make specimen. Specimens were sectioned at the 2 mm and the 3 mm depth with milling machine. Microhardness profile was measured at the surface, 2 mm depth, 3 mm depth, and 4 mm depth. Microhardness of control group showed statistically significant difference (p < 0.05) according to the polymerization depth. In contrast, experimental group showed no statistically significant difference, except between 0 mm and 4 mm at HFB, 0 mm and 2 mm, 0 mm and 3 mm at MFB. At the surface and the 2 mm depth, the control group showed higher microhardness than the experimental groups (p < 0.05). However, at the 4 mm depth, the experimental groups showed significantly higher microhardness (p < 0.05). The results from this study, the bulk-base composite resin showed higher microhardness at the 4 mm and lower microhardness at the surface and the 2 mm depth. Therefore, if bulk-base resin overcomes the mechanical weakness, it could be considered using in pediatric dentistry.

• Childhood Kidney Diseases
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• v.6 no.2
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• pp.188-197
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• 2002

Purpose : Nowadays, drinks, foods and snacks have frequently been intensified with calcium and the insights into the importance of calcium-intake in general has developed in Korea. In this decade, we found the numbers of children who was visited to our hospital for evaluation of hematuria defined with hypercalciuria were increased. So we tried to compare the mean levels of serum calcium, alkaline phosphate, sodium, potassium, chloride, BUN, creatinine, bicarbonate and urinary pH who visited our hospital in 1991, 1992 with in 2000, 2001. Materials and methods : Between January 1991 to December 1992, and between January 2000 to December 2001, each 366 children and 488 children, aged 1 month to 15 years, who presented in our hospital for tonsilectomy and adenoidectomy or for inguinal herniorrhaphy were enrolled in the study, The children in the study were checked the level of serum calcium, alkaline phosphate, sodium, potassium, chloride, BUN, creatinine, bicarbonate and urinary pH with the machine which was corrected the similar levels of practical chemical levels in serum. We compared each mean levels in 1991s' group with in 2001s' group totally and separately through the age and sex. We used t-test to analysis data. Results : The levels of serum calcium, alkaline phosphate, creatinine, sodium, potassium, and urinary pH of 2001s' group were significantly higher than the levels of 1991s' group(P<0.05). The each level was $9.91{\pm}0.50\;mg/dL,\;248.58{\pm}94.98\;U/L,\;0.61{\pm}0.14\;mg/dL,\;138.64{\pm}2.22\;mM/L,\;4.35{\pm}0.40\;mM/L,\;6.18{\pm}0.86$ in 2001s' and $9.13{\pm}0.68;mg/dL,\;198.26{\pm}79.34\;U/L,\;0.433{\pm}0.18\;mg/dL,\;137.86{\pm}2.67\;mM/L,\;4.22{\pm}0.36\;mM/L,\;5.83{\pm}0.95$ in 1991s'. And the levels of serum bicarbonate, $23.64{\pm}2.57\;mM/L$ in 2001s' was significantly lower than the 1991s', $24.60{\pm}2.23\;mM/L$(P<0.05). The similar results were detected each age and sex group. Conclusion : The levels of serum calcium increase in this decade. The results will be used as a basic data for the national health plan in the years to come.

• Journal of the korean academy of Pediatric Dentistry
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• v.29 no.4
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• pp.509-518
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• 2002

The purpose of this study was to evaluate the bonding of compomer to deciduous dentin which is known to have been developed to improve the weak properties of glass ionomer cement and composite resin. 120 sound primary molars were used for the shear bond strength test and another 24 for the scanning electron microscopic evaluation. Each material was ailed into polyethylene mold attached to exposed dentinal surface($3{\times}4mm$ in diameter) of sample blocks. Shearbond strength was measured using Universal testing machine and data were analyzed statistically with Oneway-ANOVA and Scheffe test. Scanning electron microscopic observation was performed in order to evaluate the pattern of distribution and penetration of resin tags and hybrid layer. Compomer groups(II-V) showed significantly higher bond strength values than glass ionomer group(I)(p<.05). Etching-compomer groups(III, V) showed the significantly higher bond strength than non-etching compomer groups(II, IV)(p<.05), but slightly lower values than composite resin group(VI) with no statistically significant difference(p>.05). No significantly different bond strength was found between compomer groups of different bonding system(p>.05). Scanning electron micrographs showed more irregular distribution of short and thin resin tags in non-etching compomer groups(II, IV) whereas the more regular and intimate distribution of long and thick tags in etching compomer groups(III, V) and composite resin group(VI). The evaluation of hybrid layer also showed more regular formation of thicker layer in etching compomer groups(III, V). Based on the results of present study, the use of compomer as an esthetic restorative material for primary molars might be justified.

• Journal of Korea Technology Innovation Society
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• v.20 no.2
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• pp.334-367
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• 2017

The ICT industry has been the main driver of Korea's economy with international competitiveness and is expected to be the growth engine that will revitalize the currently depressed economy. A broad range of different perspectives and opinions on the industry exist in Korea and overseas. Some of these are stereotypes, not all of which are based on objective evidence. Stereotypes refer to widely-held fixed opinions on a specific group and do not necessarily have negative connotations. However, they should not be viewed lightly because they can substantially affect decision-making process. In this regard, this study sought to review the stereotypes of ICT industry and identify objective and relative stereotypes. In the study, a decision-tree analysis was conducted on a survey result of 3,300 small and medium-sized enterprises (SMEs) in order to identify Korean ICT companies' characteristics that distinguish them from other technology companies. The decision-tree analysis, a data mining process based on machine learning, took a total of 291 variables into account in 10 subjects such as: corporate business in general, technology development activities as well as organization and people in technology development. Identifying the variables that distinguish ICT companies from other technology companies with the decision-tree analysis, the study then came up with a list of objective stereotypes of ICT companies. The findings from the stereotypes of Korean ICT companies are as follows. First, the companies are in need of technology policies that help R&D planning and market penetration. Second, policies must better support the companies working to sell new products or explore new business. Third, the companies need policies that support secure protection of development outcomes and proper management of IP rights. Fourth, the administrative procedures related to governmental support for ICT companies' R&D projects must be simplified. It is hoped that the outcome of this study will provide meaningful guidance in establishment, implementation and evaluation of technology policies for ICT SMEs, particularly to policymakers or researchers in relevant government agencies who determine R&D policies for ICT SMEs.

• Science of Emotion and Sensibility
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• v.21 no.1
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• pp.59-70
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• 2018

With the breakthrough of speech recognition technology, conversational agents have become pervasive through smartphones and smart speakers. The recognition accuracy of speech recognition technology has developed to the level of human beings, but it still shows limitations on understanding the underlying meaning or intention of words, or understanding long conversation. Accordingly, the users experience various errors when interacting with the conversational agents, which may negatively affect the user experience. In addition, in the case of smart speakers with a voice as the main interface, the lack of feedback on system and transparency was reported as the main issue when the users using. Therefore, there is a strong need for research on how users can better understand the capability of the conversational agents and mitigate negative emotions in error situations. In this study, we applied social strategies, "forewarning" and "apology", to conversational agent and investigated how these strategies affect users' perceptions of the agent in breakdown situations. For the study, we created a series of demo videos of a user interacting with a conversational agent. After watching the demo videos, the participants were asked to evaluate how they liked and trusted the agent through an online survey. A total of 104 respondents were analyzed and found to be contrary to our expectation based on the literature study. The result showed that forewarning gave a negative impression to the user, especially the reliability of the agent. Also, apology in a breakdown situation did not affect the users' perceptions. In the following in-depth interviews, participants explained that they perceived the smart speaker as a machine rather than a human-like object, and for this reason, the social strategies did not work. These results show that the social strategies should be applied according to the perceptions that user has toward agents.

• Journal of Internet Computing and Services
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• v.21 no.5
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• pp.139-148
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• 2020

Infectious diseases have long plagued mankind, and predicting and preventing them has been a big challenge for mankind. For this reasen, various studies have been conducted so far to predict infectious diseases. Most of the early studies relied on epidemiological data from the Centers for Disease Control and Prevention (CDC), and the problem was that the data provided by the CDC was updated only once a week, making it difficult to predict the number of real-time disease outbreaks. However, with the emergence of various Internet media due to the recent development of IT technology, studies have been conducted to predict the occurrence of infectious diseases through web data, and most of the studies we have researched have been using single Web data to predict diseases. However, disease forecasting through a single Web data has the disadvantage of having difficulty collecting large amounts of learning data and making accurate predictions through models for recent outbreaks such as "COVID-19". Thus, we would like to demonstrate through experiments that models that use multiple Web data to predict the occurrence of infectious diseases through LSTM models are more accurate than those that use single Web data and suggest models suitable for predicting infectious diseases. In this experiment, we predicted the occurrence of "Malaria" and "Epidemic-parotitis" using a single web data model and the model we propose. A total of 104 weeks of NEWS, SNS, and search query data were collected, of which 75 weeks were used as learning data and 29 weeks were used as verification data. In the experiment we predicted verification data using our proposed model and single web data, Pearson correlation coefficient for the predicted results of our proposed model showed the highest similarity at 0.94, 0.86, and RMSE was also the lowest at 0.19, 0.07.

• Journal of Korea Society of Industrial Information Systems
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• v.12 no.4
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• pp.15-24
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• 2007

The recognition of postal address images is indispensable for the automatic sorting of postal envelopes. The process of the address image recognition is composed of three steps-address image preprocessing, character recognition, address interpretation. The extracted character images from the preprocessing step are forwarded to the character recognition step, in which multiple candidate characters with reliability scores are obtained for each character image extracted. aracters with reliability scores are obtained for each character image extracted. Utilizing those character candidates with scores, we obtain the final valid address for the input envelope image through the address interpretation step. The envelope sorting rate depends on the performance of all three steps, among which character recognition step could be said to be very important. The good character recognizer would be the one which could produce valid candidates with very reliable scores to help the address interpretation step go easy. In this paper, we propose the method of generating character candidates with reliable recognition scores. We utilize the existing MLP(multilayered perceptrons) neural network of the address recognition system in the current automatic postal envelope sorters, as the classifier for the each image from the preprocessing step. The MLP is well known to be one of the best classifiers in terms of processing speed and recognition rate. The false alarm problem, however, might be occurred in recognition results, which made the address interpretation hard. To make address interpretation easy and improve the envelope sorting rate, we propose promising methods to reestimate the recognition score (confidence) of the existing MLP classifier: the generation method of the statistical recognition properties of the classifier and the method of the combination of the MLP and the subspace classifier which roles as a reestimator of the confidence. To confirm the superiority of the proposed method, we have used the character images of the real postal envelopes from the sorters in the post office. The experimental results show that the proposed method produces high reliability in terms of error and rejection for individual characters and non-characters.

• Journal of Technologic Dentistry
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• v.19 no.1
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• pp.21-35
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• 1997

The Ag-Pd-Cu alloys containing a small amount of Au is commonly used for dental purposes, because this alloy is cheaper than Au-base alloys for clinical use. However, the most important characteristic of this alloy is age-hardenability, which is not exhibited by other Ag-base dental alloys. The specimens used were Ag-20Pd-20Cu ternary alloy and Au addition alloy. These alloys were melted and casted by induction electic furace and centrifugal casting machine in Ar atmoshpere. These specimens were solution treated for 2hr at $800^{\circ}C$ and were then quenched into iced water, and aged at $350{\sim}550^{\circ}C$ Age-hardening characteristics of the small Au-containing Ag-pPd-Cu dental alloys were investigated by means of hardness testing, X-ray diffraction and electron microscope observations, electrical resistance, differential scanning calorimetric, emergy dispersed spectra and electron probe microanalysis. Principal results are as follows : Hardening occured in two stages, I. e., stage I in low temperature and stage II in high temperature regions, during continuous aging. The case of hardening in stage I was due to the formation of the Llo type face centered tetragonal PdCu-ordered phase in the grain interior and hardening in stage I was affedted by the Cu concentration. In stage II, decomposition of the $\alpha$ solid solution to a PdCu ordered phase(L1o type) and an Agrich ${\alpha}2$ phase occurred and a discontiunous precipitation occurred at the grain boundary. Form the electron microscope study, it was concluded that the cause of age-hardening in this alloy is the precipitation of the PdCu ordered phase, which has AuCu I type face-centered tetragonal structure. Precipitation procedure was ${\alpha}\to{\alpha}+{\alpha}2+PdCu\to{\alpha}1+{\alpha}2+PdCu$ at Pd/Cu = 1 Ag-Pd-Cu alloy is more effective dental alloy as ageing treatment and is suitable to isothermal ageing at $450^{\circ}C$.