• Proceedings of the Korean Society of Precision Engineering Conference
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• 1996.04a
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• pp.724-728
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• 1996

The instrumented Charpy impact test is generally used to evaluate the dynamic fracture toughness for varying engineering materials. However, the test is known to be difficult to evaluate the dynamic fracture toughness for very brittle materials because of the small crack initiation load. To evaluate the dynamic fracture toughness of verybrittle materials, it is necessary to develop a load sensitive instrumented tup. In this study, a polymer tup, which has small Young's modulus, is used for the instrumented Charpyimpact test and a proper testing method is developed. The results show that the developed method can measure rapidly changing loads from the moment of contact between the tup and the specimen to dynamic crack initation of the very brittle materials.

• Journal of the Korea Furniture Society
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• v.16 no.2 s.30
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• pp.27-36
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• 2005

Surface materials of furnitures are continuously studied and marketed with new patterns and new technology so as to create designs and fashions but even professionals are also difficult in distinguishing natural materials from artificial materials. Like this, furniture industry is required for rapid coping with the preference of customers which requires high grade of consumption pattern and is rapidly changed; it is intended to review the current situation of our furniture industry. The purpose of this thesis is to activate furniture industry and elevate the importance of surface materials in assumption of continuous R&D based on systemic data analysis of the kinds and colors of surface materials used in the companies within rank five of sales volume in domestic furniture companies.

• Journal of The Korean Association For Science Education
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• v.1 no.1
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• pp.73-88
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• 1978

The survey is intended to improve science education by the analysis of problems produced in the following nine aspects (objectives, contents, materials, inquring methods, teaching methods, teachers, children, evalutions, admininative supports) during the past five years often the revision of new science curriculum. 1. View for science education. 1) The teacher's and children's view for science education can be seen renewed, being different from the old one. 2) Inquring method in learning and teaching began to take firm root and children came to know that it is the only way to study science. 3) Writers think that the new science education has stepped into the stage of being fixed to a considerable degree. 2. The aspect of administrative policy. 1) The amount of materials in possession is small and the present materials are lacking in solidity and precision. 2) Class room teacher's over load with miscellaneous things is a difficult problem to solve. 3) The shortage of the printed materials and books for children and teachers has an influence on the development of inquring method. 4) It causes cramming to examine all children at the same time by paper test. 5) It is more desirable to appoint qualified teacher only for science teaching. 3. Contents of science curriculum. 1) In current science textbooks. There can be found some contents which are difficult for teachers to understand and not in accordance with the reality of Korea. Therefore, it is imperative that contents of science textbooks should be reexamined. 2) As it is hard to teach concepts of reciprocal action and to prepare materials with teaching of the system of biological concepts, the teaching of contents is likely to be a cramming. 4. The aspect of in-service education. 1) It is obsolutely predominant reation that in-service education is making a great contribution to class room teaching. 2) As adiministrators' policy for science education has a great effect, in-service education for their enlightenment is needed.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2008.04a
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• pp.286-289
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• 2008

Damping materials are widely used to reduce vibration or noise generation of structures. To understand their damping capability and for use in numerical simulations, their viscoelastic properties should be measured in the frequency range of interest. In this study, experimental setup is proposed to measure materials properties of very compliant polymer materials. The polymer materials used in this study are difficult to form into rod shapes, and typical resonance methods are not applicable. In the proposed measurement setup, the damping materials were modeled as a simple viscoelastic support at one end of the beam. Their properties were measured through analysis of their effects on the wave propagation characteristics of the beam structure.

• Journal of the Korean Association of Oral and Maxillofacial Surgeons
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• v.45 no.6
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• pp.309-315
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• 2019

Objectives: The aim of this study was to evaluate the validity of the existing classification and difficulty index of impacted mandibular third molars in clinical situations and propose a more practical classification system. Materials and Methods: This study included 204 impacted mandibular third molars in 154 patients; panoramic x-ray images were obtained before tooth extraction. Factors including age, sex, and pattern of impaction were investigated. All impacted third molars were classified and scored for spatial relationship (1-5 points), depth (1-4 points), and ramus relationship (1-3 points). All variables were measured twice by the same observer at a minimum interval of one month. Finally, the difficulty index was defined based on the total points scored as slightly difficult (3-4 points), moderately difficult (5-7 points), very difficult (8-10 points), and extremely difficult (11-12 points). Results: The strength of agreement of the total points scored and difficulty index were 0.855 and 0.746, respectively. Most cases were classified as moderately difficult (73.0%). Although only 13 out of 204 cases (6.4%) were classified as extremely difficult, patients classified as extremely difficult were the oldest (P<0.05). Conclusion: For difficulty classification, the authors propose one more difficult category beyond the existing three-step difficulty index: the clinician should consider the patient's age in the difficulty index evaluation.

• Journal of the Korean Society of Food Science and Nutrition
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• v.15 no.4
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• pp.51-55
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• 1986

The general bag for powder materials such as sugar, salt and detergent used at present is a simple rectangular bag. In the practical uses, it has a lot of faults: it is difficult to reseal after partial usages, occurrence of loss in the case of sharing or adding, difficult for measured uses. Author made a new type of the measuring bag for powder materials in order to improve the problems. The new type of the bag for powder materials consists of a body, fall-induced tube with length scale line, and a pin to open and reseal. It shows various effectiveness: measured use$({\pm}0.6g)$ of powder materials, eatings don't occur during long period after opening, and no skin contamination during use of detergent. Consequently, the new one Is suitable for the measured use of powder materials such as sugar, salt, detergent, MSG and so on.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1990.10a
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• pp.1-16
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• 1990

In this paper, a system to measure treeing degradation phenomena in organic insulating materials, using an image sensor, is discussed. Using an image processing technique, tree features immediately after tree initiation as well as changes in the configuration of the tree were measured. which up to now have been extremely difficult to observe by conventional visual methods. As a result, it was possible to record the image of tree propagation immediately after its first appearance, and to describe the specific characteristics of tree growth in terms of the length, the degraded area and the sequential images.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1997.04a
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• pp.486-490
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• 1997

Composite materials have varios complicated characteristics to the ply materials, ply orientations, ply stacking sequences and boundary conditions. Therefore, it is difficult to analysis composite materials. For efficient use of composite materials in engineering applications the dynamic behavior, that is, natural frequencies, nodal patterns should be informed. This study presents the experimental and FEM results for the free vibration of symmetrically and antisymmetrically laminated composite and hybrid composite rectangular plates. In order to demonstrate the validity of the experiment, FEM analysis using ANSYS was performed and natural frequencies experimentally obtined is compared with that calculated by FEM analysis. The results obtained from both experiment and FEM analysis show a good agreement.

• Proceedings of the KSRS Conference
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• 2004.10a
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• pp.10-13
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• 2004

Hyperspectral data has a great advantage to classify various surface materials that are spectrally similar. In this study, we attempted to classify man-made materials in urban area using Hyperion data. Hyperion imagery of Seoul was initially processed to minimize radiometric distortions caused by sensor and atmosphere. Using color aerial photographs. we defined seven man-made surfaces (concrete, asphalt road. railroad, buildings, roof, soil, shadow) for the classification in Seoul. The hyperspectral data showed the potential to identify those manmade materials that were difficult to be classified by multispectral data. However. the classification of road and buildings was not quite satisfactory due to the relatively low spatial resolution of Hyperion image. Further, the low radiometric quality of Hyperion sensor was another limitation for the application in urban area.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.11b
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• pp.705-710
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• 2002

Magnetostrictive materials are used low frequency sonar transmitter instead of piezoelectric materials. But it is difficult to analyze due to the nonlinearity and hysteresis of magnetostrictive materials. This paper deals with the program development for the finite element modeling of magnetostrictive tonpilz transducers and for analyzing their acoustic characteristics. To take into account the nonlinearity of magnetostrictive materials, the magnetic field calculation is separated form the displacement calculation, and a curve fitting is adopted for the nonlinear behavior of the magnetic and mechanical strain fields. At first, the magnetic field is obtained by using a commercial FEM software and the displacement of the transducer is calculated by plugging the obtained magnetic field into forcing term. To verity the accuracy of the developed program, a comparison is made with a commercial code, ATILA.