• The Journal of Advanced Prosthodontics
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• 제12권3호
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• pp.124-130
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• 2020

PURPOSE. The aim of this in vitro study was to evaluate the effect of sintering procedures on marginal discrepancies of fixed partial metal frameworks fabricated using different sintering-based computer-aided design and computer/aided manufacturing (CAD/CAM) techniques. MATERIALS AND METHODS. Forty resin die models of prepared premolar and molar abutment teeth were fabricated using a three-dimensional (3D) printer and divided into four groups (n = 10) according to the fabrication method of metal frameworks used: HM (via hard milling), SM (via soft metal milling), L25 (via direct metal laser melting [DMLM] with a 25 ㎛ layer thickness), and L50 (via direct DMLM with a 50 ㎛ layer thickness). After the metal frameworks were fabricated and cemented, five vertical marginal discrepancy measurements were recorded in each site (i.e., buccal, facing the pontic, lingual, and facing away from the pontic) of both abutment teeth under a stereomicroscope (×40). Data were statistically analyzed at a significance level of 0.05. RESULTS. No statistically significant differences (P>.05) were found among the four axial sites of metal frameworks fabricated by sintering-based CAD/CAM techniques. The HM and L25 groups showed significantly (P<.001) lower marginal discrepancy values than the SM and L50 groups. CONCLUSION. Marginal discrepancy in the sites facing the pontic was not influenced by the type of sintering procedure. All fabrication methods exhibited clinically acceptable results in terms of marginal discrepancies.

• 소성∙가공
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• 제14권4호
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• pp.384-391
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• 2005

The nickel-based alloy Nimonic 80A possesses the excellent strength, and the resistance against corrosion, creep and oxidation at high temperature. Its products are used in aerospace engineering, marine engineering and power generation, etc. Control of forging parameters such as strain, strain rate, temperature and holding time is important because change of the microstructure in hot working affects the mechanical properties. Change of the microstructure evolves by recovery, recrystallization and grain growth phenomena. The dynamic recrystallization evolution has been studied in the temperature range of $950\~1250^{\circ}C$ and strain rate range of $0.05\~5s^{-1}$ using hot compression tests. The metadynamic recrystallization and grain growth evolution has been studied in the temperature range of $950\~1250^{\circ}C$ and strain rate range $0.05,\;5s^{-1}$, holding time range of 5, 10, 100, 600 sec using hot compression tests. Modeling equations are proposed to represent the flow curve, recrystallized grain size, recrystallized fraction and grain growth phenomena by various tests. Parameters in modeling equations are expressed as a function of the Zener-Hollomon parameter. The modeling equation for grain growth is expressed as a function of the initial grain size and holding time. The modeling equations developed were combined with thermo-viscoplastic finite element modeling to predict the microstructure change evolution during hot forging process. The grain size predicted from FE simulation results is compared with results obtained in field product.

• 한국수학교육학회지시리즈A:수학교육
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• 제44권3호
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• pp.409-433
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• 2005

This article is to provide information on school contexts for learning and instruction of mathematics based on the results and data of TIMSS 1999. It is organized around two major topics: teacher and students achievement, instruction and students achievement In this article the following summarizes the major findings. First, about $50\%$ of Korean eight-grade students were taught mathematics by teachers in their 30s, and this was higher than the international average. Most of teachers in Korea had certification of teachers majors in mathematics. Korean teachers reported relatively low confidence to teach mathematics compared to other counties. And Korean students taught by teachers who believes they were well prepared attained low achievement scores in contrast to international result. Second, korean teachers spent about $50\%$ of their formally scheduled school time teaching their subject, but is was below the international average. They spent much more time on administrative duties and other related activities than other countries. Korean students reported that most of their class time were spent lecture style presentations by teacher. Also they reported that teachers showed them how to do mathematics. The percentages of Korean students were placed on the low level of index of emphasis on mathematics reasoning and problem-solving. The students taught by teachers who emphasized reasoning and problem-solving showed low achievement scores in contrast with result of the previous literatures. Korean teachers didn't seem to emphasize homework and assessments. Internationally, teachers frequently used teacher-made objective tests and projects or practical exercises, but Korean teachers die less in most of categories. Based on the above findings, this article presents implications about teacher education, reduction of administrative working in teachers tasks, using everyday life topics, as learning materials, specialization instruction methods for each subject matter. This article is a kind of descriptive and factual in nature, but some attempt has been made to contextualize these results focused on teachers and instruction.

• 소성∙가공
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• 제14권5호
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• pp.432-438
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• 2005

Among the most of manufacturing process, plastic deformation method offers a significant advantage in productivity and enable mass production with controlled quality and low cost. From the point of view, micro forming is a well suited technology in manufacturing very small metallic parts, in particular for mass production, as they are required in many industrial products. Meanwhile, Al 5083 superplastic alloy with very small grains has a great advantage in achieving micro deformation under low stress due to its relatively low strength at a specific high temperature range. This paper describes the micro formability of Al 5083 superplastic alloy and its application to die forging of micro patterns. Micro formability tests of Al 5083 superplastic alloy were carried out with the specially designed micro forging system by using V-grooved micro dies and pyramidal dies made of (100) silicon. With these dies, micro forging was conducted by varying the applied load, material temperature and forging time The micro formability of Al 5083 superplastic alloy was evaluated by comparing $R_f$ value, where $R_f\;=\;A_f/A_v$ ($A_v$ : cross-sectional area of the flowed metal, $A_v$ : cross sectional area of V-groove). The micro formability of 3 dimensional Patterns was also evaluated using Pyramidal type micro dies.

• The Journal of Advanced Prosthodontics
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• 제7권3호
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• pp.233-239
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• 2015

PURPOSE. This study aimed to evaluate the fit of zirconia ceramics before and after veneering, using 3 different veneering processes (layering, press-over, and CAD-on techniques). MATERIALS AND METHODS. Thirty standardized zirconia CAD/CAM frameworks were constructed and divided into three groups of 10 each. The first group was veneered using the traditional layering technique. Press-over and CAD-on techniques were used to veneer second and third groups. The marginal gap of specimens was measured before and after veneering process at 18 sites on the master die using a digital microscope. Paired t-test was used to evaluate mean marginal gap changes. One-way ANOVA and post hoc tests were also employed for comparison among 3 groups (${\alpha}$=.05). RESULTS. Marginal gap of 3 groups was increased after porcelain veneering. The mean marginal gap values after veneering in the layering group ($63.06{\mu}m$) was higher than press-over ($50.64{\mu}m$) and CAD-on ($51.50{\mu}m$) veneered groups (P<.001). CONCLUSION. Three veneering methods altered the marginal fit of zirconia copings. Conventional layering technique increased the marginal gap of zirconia framework more than pressing and CADon techniques. All ceramic crowns made through three different veneering methods revealed clinically acceptable marginal fit.

• Journal of Chest Surgery
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• 제31권8호
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• pp.770-775
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• 1998

배경: 심방중격결손증은 선천성심질환중 가장 흔한 질환중의 하나이며 성인에서 진단되는 선천성 심질환 의 30%를 차지한다. 상당수의 환자들이 성인이 될때까지 별다른 증상이 없이 잘 지내기도 하고, 40∼50대에 사망 하는 경우가 많지만, 더 오래 사는 경우도 흔히 발견된다. 가장 흔한 사망원인은 주로 우심부전이나 부정맥이다. 대상 및 방법: 강북삼성병원 흉부외과에서는 1988년부터 1997년 6월까지 총33례의 심방중격결손증을 수술 하였으며, 그중 31례가 성인 심방중격결손증이었다. 동반질환은 삼첨판 폐쇄부전이 2례, 폐동맥판 협착증, 승모판 폐쇄부전 및 삼첨판 폐쇄부전, 그리고 관상동맥질환이 각각 1례였다. 결과: 모든환자에서 첩포봉합술이나 직접봉합술을 이용하여 수술하였으며, 수술후 경과는 모두 양호하였다. 수술후 심전도와 혈류역학, 및 심초음파검사상 호전을 보였다. 결론: 성인의 심방중격결손증은 60세이상의 고령일지라도 폐동맥고혈압이나 우심부전, 부정맥등을 예방 하기 위한 적극적인 외과교정술을 시행하여야 한다

• 한국자동차공학회논문집
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• 제16권1호
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• pp.86-92
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• 2008

Recently, the use of tubes in the manufacturing of the automobile parts has increased and therefore many automotive manufactures have tried to use hydro-forming technology. The hydro-forming technology may cause many advantages to automotive applications in terms of better structural integrity of the parts, lower cost from fewer part count, material saving, weight reduction, lower spring-back, improved strength and durability and design flexibility. In this study, the whole process of front engine cradle (or front sub-frame) parts development by tube hydro-forming using steel material having tensile strength of 440MPa grade is presented. At the part design stage, it requires feasibility study and process design aided by CAE (Computer Aided Design) to confirm hydro-formability in details. Effects of parameters such as internal pressure, axial feeding and geometry shape on automotive sub-frame by hydro-forming process were carefully investigated. Overall possibility of hydro-formable sub-frame parts could be examined by cross sectional analyses. Moreover, it is essential to ensure the formability of tube material on every forming step such as pre-bending, preforming and hydro-forming. At the die design stage, all the components of prototyping tools are designed and interference with press is examined from the point of geometry and thinning.

• Asian Pacific Journal of Cancer Prevention
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• 제15권1호
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• pp.349-353
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• 2014

Background: Although previously studies have reported that most patients with malignancy prefer to die at home, this is not the real situation in clinical practice. Aim: In this study, we aimed to determine the characteristics of Turkish cancer patients admitted to the emergency department (ED) within one month before death. Materials and Method: This descriptive retrospective study focused on questions about how often and why patients with cancer visited the ED before death. A total of 107 individuals with cancer were divided into 2 groups: Group 1, patients with at least one visit in the final 4 weeks; and Group 2, patients with no visit to ED. Demographic and clinical features were compared between the two groups. Statistical analyses: Descriptive statistical methods, statistical analysis for correlation, Student's t-test, chi-square tests and logistic regression were used. Results: At least one visit to ED within one month before death was reported for 64 (60%) of the 107 cases. Of these 64 (Group 1), 38% (n=24) were discharged and 9% (n=6) died in the ED. The most common site of the primary tumor was the lung (n=24, 38%) and the most common symptom was dyspnea (92%). With the other 43 (40%) cancer patients not presenting to the ED within one month before death, they were more likely to be female with another type of cancer. Conclusions: Guidelines are needed for better management of cancer patients benefiting from visits to ED within the last month of life.

• Asian Pacific Journal of Cancer Prevention
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• 제16권2호
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• pp.431-435
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• 2015

Background: Although childhood cancer is a rare disease, 100,000 children younger than 15 years of age die from cancer each year, the majority of them in developing countries. More data need to be gathered and published particularly in developing countries to better understand the scale of the problem. Aims: This study aimed to describe the patterns of childhood cancers in Saudi Arabia over a period of ten years (1999-2008). Materials and Methods: This descriptive retrospective study was based on secondary data from the Saudi Cancer Registry from 1999 to 2008. All Saudi cases (both genders), under the age of 15 years, who were diagnosed with cancer during the study period, were included in this study. Results: Childhood cancer in Saudi Arabia, in the period between 1999 and 2008, accounted for about 8% of total cancer cases. The most common encountered cancers were leukemia (34.1%), followed by lymphoma (15.2%), brain (12.4%), and kidney cancers (5.3%). The overall incidence of childhood cancers increased from 8.8 per 100,000 in 1999 to 9.8 per 100,000 in 2008. The incidence rates of cancers per 100,000 in the years 1999 and 2008 were generally higher among males, (9.4 and 11.5 in males vs. 8.3 and 8.1 in females). The highest incidence rate in the surveyed years was apparent in the birth to age 4 years group. Conclusions: Cancer is an important public health problem in Saudi Arabia and a major ascending contributor to mortality and morbidity in children. More studies are required to describe the patterns of childhood cancers and related risk factors in Saudi Arabia.

• The Journal of Advanced Prosthodontics
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• 제10권3호
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• pp.236-244
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• 2018

PURPOSE. To determine the discrepancy in monolithic zirconium dioxide crowns made with computer-aided design and computer-aided manufacturing (CAD/CAM) systems by comparing scans of silicone impressions and of master casts. MATERIALS AND METHODS. From a Cr-Co master die of a first upper left molar, 30 silicone impressions were taken. The 30 silicone impressions were scanned with the laboratory scanner, thus obtaining 30 milled monolithic yttrium stabilized zirconium dioxide (YSZD) crowns (the silicone group). They were poured and the working models were scanned, obtaining 30 milled monolithic yttrium stabilized zirconium dioxide (YSZD) crowns (the plaster group). Three predetermined points were analyzed in each side of the crown (Mesial, Distal, Vestibular and Palatal), and the marginal fit was evaluated with SEM (${\times}600$). The response variable is the discrepancy from the master model. A repeated measures ANOVA with two within subject factors was performed to study significance of main factors and interaction. RESULTS. Mean marginal discrepancy was $22.42{\pm}35.65{\mu}m$ in the silicone group and $8.94{\pm}14.69{\mu}m$ in the plaster group. The statistical analysis showed significant differences between the two groups and also among the four aspects. Interaction was also significant (P=.02). CONCLUSION. The mean marginal fit values of the two groups were within the clinically acceptable values. Significant differences were found between the groups according to the aspects studied. Various factors influenced the accuracy of digitizing, such as the design, the geometry, and the preparation guidance, as well as the texture, roughness and the color of the scanned material.