• The Journal of the Korea Contents Association
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• v.19 no.11
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• pp.92-101
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• 2019

This study used the Q-method to derive the structure of subjective opinions and perceptions of university students about the behavior of food delivery agency service provided by staff not directly employed in restaurants. For this purpose, the Q factor analysis was performed using the PC QUANL program for the Q-sort, which consists of a statement card, a P-sample, and a classification process. The results were classified into three types. The factor names were set as the first type (N = 7): efficiency seeking type, the second type (N = 19): benefit seeking type, and the third type [(N = 6): cost-effectiveness seeking type. The characteristics of each type are Type 1:Types that recognize aspects that are efficient for both consumers and restaurants, Type 2: Types of recognizing aspects of being benefited from speed, convenience and benefit, Type 3: Although it contributes to labor cost savings, it appears to recognize price and quality aspects in the initial market, which is burdened by consumers. The purpose of this study is to derive the problems of food delivery agency service business according to the three types and to provide strategic implications for the development direction and improvement plan.

• Journal of the Korean School Mathematics Society
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• v.22 no.3
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• pp.183-197
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• 2019

The purpose of this study is to support elementary teachers to use the teaching of weights and measures. To help the author of the next elementary mathematics textbook to be used as a reference for the quantitative narrative process. For this purpose, I focused on the contents of textbooks in terms of definition, a unit of measure, and calculation. As a result, first, as for the definition of weights and measures, it is taken as an example rather than as an explicit statement. Second, several problems were found in the metrology content and metric unit introduction order. Third, the computation between measurement units stood in simple computation rather than procedural knowledge. Fourth, it was concluded that the reason and groundbreaking of the grade-specific differences and the amount of a student's education are necessary.

• Journal of Educational Research in Mathematics
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• v.21 no.4
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• pp.379-398
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• 2011

In learning environment at mathematics education, prove and refute are essential abilities to demonstrate whether and why a statement is true or false. Learning proofs and counter examples within the domain of limit of sequence is important because preservice teacher encounter limit of sequence in many mathematics courses. Recently, a number of studies have showed evidence that pre service and students have problem with mathematical proofs but many research studies have focused on abilities to produce proofs and counter examples in domain of limit of sequence. The aim of this study is to contribute to research on preservice teachers' productions of proofs and counter examples, as participants showed difficulty in writing these proposition. More importantly, the analysis provides insight and understanding into the design of curriculum and instruction that may improve preservice teachers' learning in mathematics courses.

• School Mathematics
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• v.18 no.4
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• pp.839-856
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• 2016

In 2009 revision and 2015 revision mathematics national curriculum, 'proof' was moved to high school from middle school in consideration of the cognitive development level of students, and 'proof by contradiction' was stated in the "success criteria of learning contents" of the first year high school subject while it had been not officially introduced in $7^{th}$ and 2007 revision national curriculum. Proof by contradiction is known that it induces a cognitive conflict due to the unique nature of rather assuming the opposite of the statement for proving it. In this article, based on the logical, mathematical and historical analysis of Proof by contradiction, we looked about the introductions and the applications of the current textbooks which had been revised recently, and searched for improvement measures from the viewpoint of discovery, explanation, and consilience. We suggested introducing Proof by contradiction after describing the discovery process earlier, separately but organically describing parts necessary to assume the opposite and parts not necessary, disclosing the relationships with proof by contrapositive, and using the viewpoint of consilience.

• Journal of the Korean Society of Food Culture
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• v.17 no.5
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• pp.629-637
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• 2002

This study sought to determine family restaurant patrons' attitudes toward nutrition and healthy menus. A written questionnaire was handed out to 300 dine-in customers at the three different sites of T brand family restaurant. A total of 265 questionnaires were usable for data analysis, resulting in 88% response rate. Two attitude statements eliciting the strongest agreement were that 'Diet and chronic diseases risk are closely connected each other(4.44)' and 'Koreans are more nutrition & health conscious than they were in the past(4.41)'. The attitude statement-that nutrition is important when I eat out- received the lowest scores(2.92), which indicated that nutrition was not yet considered the most important factor when dining out. 23% of the respondents were interested in healthful foods, while 30% said they were unconcerned. Nutrition conscious group showed significantly (p<.000) higher attitude scores for most of statements than unconcerned group. Significant differences were found in age groups(p<.05, p<.01, p<.001), income levels(p<.05), educational levels(p<.05), health status groups(p<.05), and weight control interest groups(p<.05). Older respondents, respondents with higher income and educational levels were more interested in nutrition and healthy menus. Respondents who reported good health status and showed higher interest in weight control were more interested in nutrition and healthy menus. These findings indicate that restaurant firms should respond to consumers' increased interest in nutrition and healthy menus by offering healthful menus and increasing nutrition marketing activities. This may positively result in increasing customer counts and revenue as well as customer satisfaction level and brand image of restaurant firms. Moreover, restaurant firms are strongly encouraged to play an active role in promoting public's nutritional and health status because increasing consumption of meals away from home will seriously affect good health of our consumers.

• The Journal of Korean Academy of Prosthodontics
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• v.44 no.4
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• pp.363-373
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• 2006

Statement of Problem : The accuracy and dimensional stability of elastomeric impression materials have been the subject of numerous investigation. Few studies have addressed the effect of changes in time on the dimensional stability of impression materials. Purpose: The purpose of this investigation was to evaluate the effects of elastomeric impression materials and storage time on dimensional stability. Materials and methods: A total of 75 impressions were made of epoxy resin dies mimicked prepared 3-unit fixed partial denture. The dies had 1 buccolingual, 1 mesiodistal and 1 occlusogingival lines and interpreped dot. Impression materials investigated included two polyether impression materials and three polyvinylsiloxane impression material. 15 specimens were made of each impression material and poured by type IV stone over times (30 minutes, 24 hours, 72 hours) after mixing; the same examiner measured each specimen 3 times at a magnification of 3.5$\times$. All statistical tests were performed with the level of significance set at .05. Results : The results indicated that significant difference at any measuring point of stone dies of the polyether impression materials and when measurements at 30 minutes, 24 hours, and 72 hours were compared ; the length of measuring point increased significantly as time passed by. However this result is not significant clinically. Analysis also showed significant differences at any measuring point when polyvinylsiloxane and polyether impression materials were compared and significant differences clinically. Conclusion: Under the conditions of this study, the shrinkage rate of the polyvinylsiloxane and polyether impression materials significantly increased as time passed by. The polyether impression materials showed higher shrinkage significantly, while the shrinkage rate of all five materials showed a significant time-dependent increase.

• The Journal of Korean Academy of Prosthodontics
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• v.44 no.3
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• pp.275-283
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• 2006

Statement of problem. There have been many studies about marginal discrepancy of single restorations made by various systems and materials. However most of the statistical inferences are not definite because of sample size, measurement number, measuring instruments, etc, and there have been few studies about the marginal fit of the Digident CAD/ CAM zirconia ceramic crowns. Purpose. The purpose of this study was to compare the marginal fit of the anterior single restorations made by using the Digident CAD / CAM zirconia ceramic crowns with metal-ceramic restorations and to obtain more accurate information by using a large enough sample size and by making sufficient measurements per specimen. Material and Methods. The crowns were made from one extracted maxillary central incisor pre-pared with a 1mm shoulder margin and $6^{\circ}$ taper walls by milling machine. The in vitro marginal discrepancies of the digident CAD / CAM zirconia ceramic crowns and control groups(metal ceramic crowns) were evaluated and compared. Twenty crowns per each system were fabricated. Measurements of a crown were recorded at 50 points that were randomly selected for marginal gap evaluation. Parametric statistical analysis was performed for the results. Conclusion. Within the limitations of this in vitro study, the following conclusions were drawn: 1. Mean gap dimensions and standard deviations at the marginal opening for maxillary incisal crowns were $88{\pm}10{\mu}m$ for the control (metal-ceramic crowns), $92{\pm}4{\mu}m$ for Digident CAD / CAM zirconia ceramic crowns. 2. Marginal gap between Digident CAD / CAM zirconia ceramic crowns and metal ceramic crowns did not show significant difference (P>.05). 3. The Digident CAD/ CAM zirconia ceramic crowns and metal ceramic crowns showed clinically acceptable marginal discrepancy.

• The Journal of Korean Academy of Prosthodontics
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• v.44 no.3
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• pp.314-324
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• 2006

Statement of problem. Osseointegration is important mechanism of dental implant but it is not easy to evaluate. Indirect measurement is non-invasive and clinically applicable but they need more study about correlation between indirect values and degree of osseointegration. Purpose. The aims of this study were to evaluate the coefficient of correlation between indirect measurement and direct measurement under different healing time, and assessment of effect of initial insertion torque to the implant stability. Material and Methods. 20 rabbits received 3 implants on each side of tibia. Three kinds of implants (machined surface implant, Sandblasted with Large grit and Acid etched implant, Resorbable Blast Media treated implant) were used. During the surgery implant insertion torque were measured with $Osseocare^{TM}$. After the 1, 4, 8, 12 weeks of healing time, animals were sacrificed and stability values (Implant Stability Quotient with $Osstell^{TM}$, removal torque with torque gauge) were measured. Results. The Bone quality of rabbit tibia was classified into 2 groups according to the insertion torque. Resonance frequency analysis (ISQ) and removal torque showed positive correlation until $4^{th}$ week (r=0.555, p=0.040). After $8^{th}$ week (r=0.011, p=0.970) the correlation became weak and it turned negative at $12^{th}$ week (r=-0.074, p=0.801). Insertion torque and ISQ showed changing correlation upon the healing time ($1^{st}$ week: r=0.301, p=0.033, $4^{th}$ week: r=-0.429, p=0.018, $8^{th}$ week: r=0.032, p=0.865, $12^{th}$ week: r=-0.398, p=0.029). Insertion torque and removal torque has positive correlation but it was not statistically significant ($1^{st}$ week: r=0.410, p=0.129, $4^{th}$ week: r=0.156, p=0.578, $8^{th}$ week: r=0.236, p=0.398, $12^{th}$ week: r=0.260, p=0.350). Conclusion. In this study, bone quality may affect the degree of osseointegration positively during healing time and correlation between ISQ and degree of osseointegration can be different according to the healing time and bone quality.

• The Journal of Korean Academy of Prosthodontics
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• v.44 no.3
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• pp.333-342
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• 2006

Statement of problem. Although many studies have been carried out to investigate the correlation between the degree of conversion and the flexural strength of composite resins, there is minimal information in the literature attempting to compare degree of conversion, flexural strength and their correlation between restorative composite resins and flowable composite resins. Purpose. The purposes of this study were to measure the degree of conversion and flexural strength of composite resins with different rheological behavior and to correlate the two properties. Materials and methods. Four restorative (Vit-1-escence, Z-250, Tetric ceram, Esthet-X) and four flowable (Aeliteflo, Admiraflow, Permaflo, Revolution) light-curing composite resins were investigated. The degree of conversion(DC) was analyzed with Fourier transfer infra-red spectroscopy(FTIR) spectrum by a potassium bromide(KBr) pellet transmission method. The spectrum of the unpolymerized specimen had been measured before the specimen was irradiated for 60s with a visible light curing unit. The Poiymerized specimen was scanned for its in spectrum. The flexural strength(FS) was measured with 3-point bending test according to ISO 4049 after storage in water at $37^{\circ}C$ for 24 hours. The data were statistically analyzed by an independent sample t-test and one-way ANOVA at the significance level of 0.05. The dependence of flexural strength on the degree of conversion was also analyzed by regression analysis. Results. Mean DC and FS values ranged from 43% to 61% and from 84.7MPa to 156.7MPa respectively. DC values of the flowable composite resins were significantly higher than those of restorative composite resins (P < 0.05). The FS values of restorative composite resins were greater than those of flowable composite resins. No statistically significant correlation was observed between the DC and the FS tested in any of the composites. The dependence of FS on DC in restorative or flowable composite resins was not significant. Conclusion. It can be concluded that radical polymerization of the organic matrix is not a major factor in determining flexural strength of the commercially available composite resins.

• The Journal of Korean Academy of Prosthodontics
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• v.42 no.1
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• pp.49-57
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• 2004

Statement of problem : The increased awareness of esthetics in dentistry has brought the esthetic consideration in prosthetic restorations . Dental ceramics offer better esthetics for use of prosthetic restorations. Unfortunately, dental ceramic materials are not always the most suitable candidate materials since their inherently brittle nature. In recent years, basic research in ceramic science has led to the recognition or several approaches to strengthen and to enhance esthetics of ceramics. Several all ceramic systems use ceramic core and porcelain build up structures . Ceramic cores influence to strength of all ceramic crowns . So the strength of ceramic cores is important to all ceramic crowns. Purpose : The purpose of this study is to estimate the flexural strength of ceramic cores in some all ceramic systems. Material and method : A biaxial flexure test was conducted on three groups(Cergo, Empress 2, In-Ceram). Each group consisted of 30 discs of nearly identical dimension with a 0.5mm, 1.0mm, 1.5mm thickness and 12mm in diameter. The fracture load was recorded by Instron. Analysis of valiance(ANOVA) and Tukey's tests were performed using SAS statistical software. Results : 1.5mm thickness of specimens were significantly stronger than 0.5mm and 1.0mm thickness of specimens in Cergo and In-Ceram. But each sepecimen group of Empress 2 was no significantly strength by thickness. In order of In-Ceram, Empress 2 and Cergo has significantly stronger strength in the same thickness. Conclusion : In-Ceram is the strongest ceramic material in 3 materials. All the materials can be used according to the required characters.