• Journal of the Korean Ceramic Society
• /
• v.48 no.2
• /
• pp.152-159
• /
• 2011

The green and hard machining characteristics of dental ceramics are of great interest to dental industry. The green bodies of TZP/$Al_2O_3$ composites were prepared by the cold isostatic pressing, and machined on the CNC lathe using PCD (polycrystalline diamond) insert under various machining conditions. With increasing nose radius of PCD insert, surface roughness initially increased due to increased cutting resistance, but decreased by the onset of sliding fracture. The lowest surface roughness was obtained at spindle speed of 1,300 rpm and lowest feed rate. Hard bodies were prepared by pressureless sintering the machined green bodies at several temperatures. The grinding test for sintered hard body was conducted using electroplated diamond bur with different grit sizes. During grinding, grain pull out in the composite was occurred due to thermal expansion mismatch between the alumina and zirconia. The strength of the composite decreased with alumina contents, due to increased surface roughness and high monoclinic phase transformed during grinding process. The final polished samples represented high strength by the elimination of a phase transformation layer.

• Journal of Powder Materials
• /
• v.14 no.3 s.62
• /
• pp.202-207
• /
• 2007

Novel polymer mold process for fabrication of microcomponents using metal nanopowders was developed and experimentally optimized. Polymer mold for forming green components was produced by using a hard master mold and polydimethylsiloxane (PDMS). In the preparation of metallic powder premix for the green components without any defect, 90 wt.% 17-4PH statinless steel nanopowders and 10 wt.% organic binder were mixed by a ball milling process. The green components with very clear gear shape were formed by filling the powder premix into the PDMS soft mold in surrounding at about $100^{\circ}C$. Cold isostatic pressing (CIP) was very potent process to decrease a porosity in the sintered microcomponent. The microgear fabricated by the improved process showed a good dimension tolerance of about 1.2%.

• Journal of the Korean Society of Manufacturing Process Engineers
• /
• v.19 no.10
• /
• pp.81-86
• /
• 2020

A ceramic vacuum chamber feedthrough ceramic insulator is made of Al2O3; the manufacturing process involves filling alumina powder into a urethane mold and pressing it with a rubber press to produce a molded body. Thereafter, manufacturing is completed through primary shape processing, sintering, and secondary shape processing in the green body, which is a pressurized molding body, This work is intended to prevent defects in the first shape processing by improving the ceramic insulator in the green body, and to improve the productivity of the ceramic insulator by determining the optimal processing conditions.

• Journal of the Korean Society for Industrial and Applied Mathematics
• /
• v.24 no.1
• /
• pp.1-22
• /
• 2020

An accurate and efficient gradient estimation method on unstructured grid is presented by proposing a switching process between two Least-Square methods. Diverse test cases show that the gradient estimation by Least-Square methods exhibit better characteristics compared to Green-Gauss approach. Based on the investigation, switching between the two Least-Square methods, whose merit complements each other, is pursued. The condition number of the Least-Square matrix is adopted as the switching criterion, because it shows clear correlation with the gradient error, and it can be easily calculated from the geometric information of the grid. To illustrate switching process on general grid, condition number is analyzed using stencil vectors and trigonometric relations. Then, the threshold of switching criterion is established. Finally, the capability of Switching Weighted Least-Square method is demonstrated through various two- and three-dimensional applications.

• Carbon letters
• /
• v.16 no.2
• /
• pp.132-134
• /
• 2015

When manufacturing bulk graphite, pores develop within the bulk during the carbonization process due to the volatile components of the fillers and the binders. As a result, the physical properties of bulk graphite are inferior to the theoretical values. Impregnants are impregnated into the pores generated in the carbonization process through pressurization and/or depressurization. The physical properties of bulk graphite that has undergone impregnation and re-carbonization processes are outstanding. In the present study, a green body was manufactured by molding with natural graphite flakes and phenolic resin at 45 MPa. Bulk graphite was manufactured by carbonizing the green body at 700 and it was subsequently impregnated with impregnants having viscosity of 25.0 cP, 10.3 cP, and 5.1 cP, and the samples were re-carbonized at $700^{\circ}C$. The above process was repeated three times. The open porosity of bulk graphite after the final process was 22.25%, 19.86%, and 18.58% in the cases of using the impregnant with viscosity of 25.0 cP, 10.3 cP, and 5.1 cP, respectively.

• Journal of Microbiology and Biotechnology
• /
• v.27 no.2
• /
• pp.306-315
• /
• 2017

Metabolic engineering with a high-yielding mutant, A. terreus AN37, was performed to enhance the production of itaconic acid (IA). Reportedly, the gene cluster for IA biosynthesis is composed of four genes: reg (regulator), mtt (mitochondrial transporter), cad (cis-aconitate decarboxylase), and mfs (membrane transporter). By overexpressing each gene of the IA gene cluster in A. terreus AN37 transformed by the restriction enzyme-mediated integration method, several transformants showing high productivity of IA were successfully obtained. One of the AN37/cad transformants could produce a very high amount of IA (75 g/l) in shake-flask cultivations, showing an average of 5% higher IA titer compared with the high-yielding control strain. Notably, in the case of the mfs transformants, a maximal increase of 18.3% in IA production was observed relative to the control strain under the identical fermentation conditions. Meanwhile, the overexpression of reg and mtt genes showed no significant improvements in IA production. In summary, the overexpressed cis-aconitate decarboxylase (CAD) and putative membrane transporter (MFS) appeared to have positive influences on the enhanced IA productivity of the respective transformant. The maximal increases of 13.6~18.3% in IA productivity of the transformed strains should be noted, since the parallel mother strain used in this study is indeed a very high-performance mutant that has been obtained through intensive rational screening programs in our laboratory.

• IE interfaces
• /
• v.17 no.3
• /
• pp.384-396
• /
• 2004

This paper is concerned with a six sigma green belt training program. Comparative studies of existing training programs for three major companies (Samsung Electronics Company, Hyundai Motor Company, and LG Chemical Ltd.) and two consulting firms (Korean Standards Association and Korea Management Association) are performed. Based on the comparative studies, a cyber green belt training program is developed. The training program, which is composed of 34 modules, follows a disciplined process of five macro phases: define, measure, analyze, improve, and control (DMAIC). This cyber training program is serviced in the homepage http://ise.chonbuk.ac.kr/∼sixsigma. It has been utilized as one semester subject of "Six Sigma Quality Management" in the department of industrial engineering. The advantage and disadvantage of this cyber training program are also discussed.

• Journal of the Korean Society of Environmental Restoration Technology
• /
• v.18 no.5
• /
• pp.13-26
• /
• 2015

Urban park and green space provide various functions. Among the functions, human benefit and increase of biodiversity are known to be important. Therefore, it is important to consider human and biotic aspect in the process of selecting suitable site for park and green space. However, there is insufficient research on both aspects. In this study, we used green network to analyze human and biotic aspect to select suitable site for park and green space in Seongnam City in Korea. To analyze the green network, we used accessibility for human aspect and used dispersal distance and habitat size for biotic aspect. We conducted least-cost path modelling using movement cost. In case of biotic aspect, GFS (generic focal species) is used to estimate habitat size and dispersal distance. To find out suitable site for park and green space, we used an overlay analysis method. As the result, old residential areas are shown have insufficient green network which needs park and green space. Furthermore, the green network for biotic aspect is insufficient in old residential areas comapred to green network for human aspect. The result of this study could contribute in planning of park and green space to maximize their functions.

• KSII Transactions on Internet and Information Systems (TIIS)
• /
• v.12 no.2
• /
• pp.550-565
• /
• 2018

Cognitive radio technology is still the key technology of future mobile communication systems. Previous studies have focused on improving spectrum utilization and less energy consumption. In this paper, we propose an Overhead Reduced Scheme (ORS) for green cooperative spectrum sensing. Compared to traditional cooperative sensing scheme, ORS scheme divides the sensing time into three time slots and selects the best multi-mode user to report decisions. In consideration of reporting channel deviation, we derive closed-form expressions for detection probability and false alarm probability of ORS scheme based on Rayleigh fading channel. Simulation results show that ORS scheme can improve the perception accuracy while reducing the perceived delay and energy consumption in the process of perception, so as to realize the green communication.

• Journal of Powder Materials
• /
• v.14 no.3 s.62
• /
• pp.185-189
• /
• 2007

Various approaches have been proposed to increase the green density. Warm compaction method has been used for the reduction of residual stress, the improvement of magnetic properties and the higher densities. In this work, the effect of warm compaction on green density of Fe powder was investigated. After ball-milling of Fe oxide powder for 30 hours, Fe oxide powder was reduced through the hydrogen reduction process. The pure Fe powder and polymer binder were mixed by 3-D tubular mixer. And then the mixed powder was warm-compacted with various compaction pressure and binder contents. The green density of specimen was added polyvinyl binder was higher than any other specimens.