• Journal of the Microelectronics and Packaging Society
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• v.29 no.4
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• pp.89-94
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• 2022

Thermoelectric materials can directly convert a temperature gradient to an electrical energy and vice-versa, and their performance is determined by the electrical conductivity, Seebeck coefficient, and thermal conductivity. However, it is difficult to establish an effective strategy for enhancing performance since electrical conductivity, Seebeck coefficient, and thermal conductivity are strongly dependent on the composition, crystal structure, and electronic structure of the material, and show a correlation with each other. Herein, based on the understanding of the formulas related to the performance of thermoelectric materials, we provide a methodology to establish feasible defect engineering strategies of thermal conductivity reduction for improving the performance of thermoelectric materials in connection with the experimental results.

• Progress in Superconductivity
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• v.4 no.1
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• pp.90-93
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• 2002

The sintering process of BSCCO 2223 tapes is a complex process that is very sensitive to parameters, such as temperature, oxygen partial pressure, heating and cooling rate and holding time. During the first heat treatment, 2212 phase of precursor powder is partially transformed into 2223 phase and some residual secondary phases, such as $(Bi,Pb)_2$$Sr_2$CuO／sub y／(2201), $(Ca,Sr)_2$CuO／sub y／(2/1AEC), (Ca,Sr)／sub 14／Cu／sub 24／O／sub 41／(14／24 AEC) etc. The secondary phases are difficult to be removed from the BSCCO 2223 matrix on the heat treatment. These secondary phases degrade the critical current density. In order to minimize the amount and size of alkaline earth cuprate(AEC) particles step heat treatment is applied during the first heat treatment under the varying atmosphere. Experimental results showed that by adapting the step heat treatment process, the amount and particle size of the secondary phases in the final tapes are decreased. Consequently, the BSCCO 2223grain texture and Jc properties are improved.

• The Journal of Korean Medical History
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• v.23 no.1
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• pp.11-22
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• 2010

This study finds an interesting fact that five symptoms (smallpox, postpartum pain, eye disease, swollen symptom and parasite infection) mentioned in Ryu Ei-Tae Medicinal Tales and his prescriptions (steamed rice, loess, soybean sprouts, cinnabar, radish, sesame oil and pork) were dramatized on the basis of traditional Korean medicinal knowledge in the Joseon Dynasty. Based on the study of experience-based medicinal literatures popular in the Joseon period, it is confirmed that the prescriptions are actually effective. Also it is inferred that popular diseases at that time were abscess, difficult baby delivery, postpartum pain and parasite infection, which were regarded as almost incurable diseases to ordinary people. These stories also showed destitution of common people who could not afford to buy medicines at that time. As shown in the Ryu Ei-Tae Medicinal Fable, many people might try various ordinary materials around them such as soil or nose wax. One of the outcomes of this study is that the fact that the tales mentioned common materials easy to get in the surroundings such as steamed rice, sesame oil, soybean sprouts or radish could be interprets as care and consideration of medicinal doctors for ordinary people at that time.

• Journal of the Microelectronics and Packaging Society
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• v.24 no.1
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• pp.9-16
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• 2017

Thermoelectric power generation (TEG) technology with high figure of merit (ZT) has become the need of the modern world. TEG is a potent technology which can tackle most of the environmental issues such as global warming, change in climatic conditions over the globe, and for burning out of various resources of non-renewable energy like as petroleum deposits and gasolines. Although thermoelectric materials generally convert the heat energy from wastes to electricity according to the theories Seebeck and Peltier effects yet they have not been fully exploited to realize their potential. Researchers are focusing mainly on how to improve the current ZT value from 1 to 2 or even 3 by various approaches. However, a higher ZT value is found to be difficult due to complex thermoelectric properties of materials. Hence, there is a need for developing materials with high figure of merit. Recently, various nanotechnological approaches have been incorporated to improve the thermoelectric properties of materials. In this review paper, the authors have performed a thorough literature survey of various kinds of TEG technology.

• Proceedings of the Korea Concrete Institute Conference
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• 1994.04a
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• pp.65-70
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• 1994

Reinforced concrete and prestressed concrete structures consist of different materials, namely concrete, reinforcing steel and/or prestressing steel. Reinforcing and prestressing steels can be considered homogeneous materials, and their properties are generally well defined. Howefer, concrete is a heterogeous materials, and it is difficult to define its properties accurately. Both concrete and steel exhibit various nonlinear materials properties. The stress-strain relationship of concrete is not only nonlinear, but it differs in compression and tension. And, tensile cracking is one of the most importnat factors which contribute to the nonlinear behavior of reinforced concrete structrures. In this strudy, the various stress-strain relationships of concrete and reinforcing steel in nonlinear analysis of RC and PC structures are examined.

• The Korean Journal of Ceramics
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• v.5 no.1
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• pp.50-54
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• 1999

$(Pb_xLa_{1-x}) (Zr_yTi_{1-y})O_3$ (PLZT) thin films with electrooptic effect are promising for the optical application such as display or light shutter. However, it is difficult to use inexpensive and transparent glass substrates because the conventional process for preparation of PLZT requires temperatures above $600^{\circ}C$. In order to deposit a perovskite PLZT thin films at low processing temperatures through alkoxide route, we have offered several seeding processes which reduce the activation energy for crystallization. In this study, we optimized the stacking structure of multilayered PLZT for obtaining single phase perovskite at lower temperatures. As a result, ferroelectric PLZT thin films with different compositions were successfully prepared at a temperature as low at $500^{\circ}C$.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.16 no.4
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• pp.119-126
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• 2007

Generally, the machinability of materials that have a good mechanical properties is poor. The material having a high strength, high toughness in high temperature and wear resistance, it is difficult to remove a chip from workpiece. STD11 and NAK80 are kinds of these materials and these materials can be used in many industrial fields. But it is limited in use because of high cost and poor machinability. In this experimental study, the cutting of STD11 and NAK80 were used to decide the machinability and the tool shape of CBN ball end mill. From the results, the CBN ball end mill is verified that the estimated cutting edge shape of rake angle 30 degree has consistent effect on the tool wear and cutting force.

• Journal of the Korean Society of Safety
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• v.12 no.2
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• pp.37-44
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• 1997

Composite materials have various complicated characteristics depending on the ply materials, ply orientations, ply stacking sequences and boundary conditions. Therefore, it is difficult to analyze composite materials. For efficient use of composite materials in engineering applications, the dynamic behavior such as natural frequencies and nodal patterns should be identified. This study presents FEM results for the free vibration of symmetrically and antisymmetrically laminated composite and hybrid composite rectangular plates. The natural frequencies of laminated composite rectangular plates having the various boundary conditions (completely clamped, 2-edge clamped, cantilevered) are experimentally obtained. In order to demonstrate the validity of the experiment, FEM analysis using ANSYS was performed and natural frequencies experimentally obtained is compared with that calculated by FEM analysis. The results obtained from both experiment and FEM analysis show a good agreement.

• Cement Symposium
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• no.1
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• pp.69-91
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• 1973

To obtain a more accurate results in alkali analysis of cement and its raw materials we must solve some difficult problems. The most important problem is not only dissoloing the sample with keep up alkali content but compensating interference effects. Her

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.12
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• pp.3018-3025
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• 2000

It is possible to shorten developing process by making model using polyurethane foam in the area of automobile development process, etc. However, this skill is too difficult to be of practical use because machining is not easy due to characteristic of polyurethane foam. Domestic and foreign automobile company use clay, polyurethane foam. etc,, those are easy to handle and to make model after completing design sketch. But these materials is difficult to the machined and be worked by humans hand, There are so many difficult problem for machining by making model using polyurethane foam since cutting of elastic body like polyurethan foam has never been studied. Therefore, in this study, it is investigated to measured cutting force that is generated in case of polyurethane foam machining, and to make systematize tool compensation of polyurethane foam cutting work on automobile model by modification of tool offset method on existing steel.