• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.21 no.2
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• pp.179-187
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• 2010

The use of high frequency band, broad band and MIMO antenna is expected in the next generation mobile communication system. By the rapid increase of demand for wireless communications and the explosive increase of the mobile communication services, researches for optimization of next-generation mobile communication system are required. In the existing MIMO channel models, propagation-environments are commonly classified into urban, suburban, rural area, etc. However such approaches can have drawbacks in that many different morphologies may exist even in the urban area, for example. In this paper, we introduced path morphology concept, and proposed the method of morphology classification considering the building height, density, etc. Delay spread(DS), angular spread(AS) of AoD and AoA analyzed for each environment using the ray tracing technique. Based on the analysis, a MIMO channel model appropriate in domestic environment was suggested.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.28 no.1
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• pp.1-9
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• 2017

In this paper, ETRI's $0.25{\mu}m$ GaN MMIC process is introduced and the fabricated results of X-Band 3 W power amplifier MMIC are discussed. The one-stage X-Band 3 W power amplifier MMIC using the $0.25{\mu}m$ GaN MMIC devices has been designed and fabricated. From the fabricated GaN MMIC, the characteristics of the $0.25{\mu}m$ GaN MMIC process and devices are evaluated and analyzed. The X-band power amplifier MMIC shows output power of 3.5 W, gain of 10 dB, and power-added efficiency of 35 %.

• Journal of the korean academy of Pediatric Dentistry
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• v.43 no.3
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• pp.275-283
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• 2016

The aim of this study was to evaluate the surface characteristics of composite resins polished with two different polishing methods. 30 disk-shaped specimens were prepared with microhybrid (Filtek$^{TM}$ Z250) and nanofilled (Filtek$^{TM}$ Z350) resins respectively, and classified into three groups: not polished as controls, polished by an abrasive disk (Soflex), and polished by a polishing brush (Occlubrush). Surface roughness was increased after polishing. In terms of micro-roughness, there were no significant differences between the two polishing methods. But macro-roughness values were markedly increased in the Occlubrush group (p < 0.05). In the Sof-lex group, the matrix and fillers were polished together, resulting into a smoother and homogeneous surface. However, in the Occlubrush group, the matrix layer was torn off, with more heterogeneous surfaces and large scratches. In regards to micro-hardness, no significant differences were observed between the two polishing systems (p > 0.05). And the hardness value increased about 25% after polishing. In conclusion, the method of polishing should be chosen deliberately in view of the hardness characteristics of composite resins. Sof-lex is recommended to improve the surface characteristics of polished resins.

• Journal of The Korean Association For Science Education
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• v.25 no.4
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• pp.450-464
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• 2005

The purpose of this study was to design a web-based project learning that is suitable for teaching concepts by studying the motion of the Moon for middle school students and to investigate the effects of the lesson applying designed learning. Designed learning was conducted with 48 ninth graders, who were individually interviewed; 5 males and females students out of the total. The types and factors of the unscientific concepts on the motion of the Moon were analyzed by the pre-test using interviews and questionnaires being evaluated to the degree of concept level that was developed in this study. After the pre-test students were instructed to do the web-based project learning where they could observe the motion of the moon for a month and discuss the results from the observation. After the web-based project learning, the effect of learning was examined by applying the post-test to the students and by analyzing the comparison of the pre-test and the post-test. The web-based project learning was effective for the conceptual change of the motion of the Moon (p<.001). According to the post-test, it positively affected the students and improved their integrated processing skills. Specifically, it had effects on conducting experiments (p<.001), controlling variables and defining operations (p<.05) in integrated processing skills.

• Journal of Aquaculture
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• v.11 no.2
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• pp.125-132
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• 1998

The results of experimental culture for Koran mitten crab, Eriocheir japonicus at different outdoor culture methods such as rice field, pond, and vinyl house from July 21, 1994 to October 23, 1995 were summaried as fellows. 1. The water temperature was 2${\circ}C$~32${\circ}C$ during the culture periods from July 21, 1994 to October 23, 1995, and it ranged from 15${\circ}C$ to 30${\circ}C$ during the terms showing the intake habit of feed with these temperature maintained for 281 days of 460days of the total cultur periods. 2. The gain weight of Korean mitten crabs was 1,711.3g at the rice field, and 1,565.4g at the pond, and 1.220.0g at the vinyl house. The survial rate was 22.7% at the pond, and 18.7% at the rice field, and 18.3% at the vinyl house with the average survial rate of 19.9%. The daily growth rate of cauapace width was 0.64% at the rice field, and 0.61% at the pond, and 0.59% at the vinyl house. And the gain weight and the daily growth rate were the best at the rice field. 3. When the culture was finished, the frequency of carapace width of 4.0~4.9cm was 57.1% at the rice field, and 33.3% at the vinyl house. Therefore, culture at the rice field for the cultur of mitten card was considered to be the best outdoor culture method from the point of view in the fast growth and polyculture feasibility with paddy rice.

• Culinary science and hospitality research
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• v.12 no.3 s.30
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• pp.237-250
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• 2006

This study was to investigate physicochemical and sensory evaluation properties of chicken jerky with pear, pineapple and kiwi extracts. Moisture content range was $25.87{\sim}27.55％$, and crude protein and crude fat turned out to satisfy the jerky standard. Degree of saline was $5.34{\sim}5.44％$, and that value showed lower level of T-1, T-2 and T-3 sample than C-1. The pH levels of the samples with fruit extracts were low, and, as the storage period was extended, they increased. The initial level of water activation was $0.732{\sim}0.756%$, which proved significant in the storage period(p<0.01). Hardness value of jerky products was $45.25{\sim}49.66{\times}10^5dyne/cm^2$, and the kiwi extract added jerky samples showed the lowest. Strength value range was $89.37{\sim}108.16{\times}10^5dyne/cm^2$, and the S-1 was the highest. It has significance between contrasting groups and comparing ones and among the storage periods(p<0.01). The color value of early jerky products showed 4.80, the highest, and the shape and the texture showed above 4.50, and the flavor was above 4.30, which became lower as the storage periods at normal temperature were extended.

• Journal of the Korea Concrete Institute
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• v.16 no.1 s.79
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• pp.94-101
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• 2004

This study shows the test results of seven RC beams retrofitted with modified polymer system and parametric study about the effects of tensile strength of retrofitting materials by analytical method on the flexural behavior. The main parameters are the retrofitted depth and length. The beams are loaded to the failure by four-point loading. Test results show that the effect of the retrofitted length on the structural behavior is more significant than that of depth. As the retrofitted depth is increased, the beams represents the brittle failure mode The non-linear analysis is carried out to grasp the effect of the tensile strength of retrofitting material on the structural behavior. As the retrofitted depth and length are increased, the tensile strength becomes more effective so these parameters should be considered to determine the retrofitted area. The analytical results show that failure strength is less than that of experimental results, but the stiffness is vice versa.

• Journal of the Korea Concrete Institute
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• v.29 no.3
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• pp.315-322
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• 2017

The purpose of this study is to investigate experimentally the construction performances and economical evaluation of the self-compacting concrete in actual site work after selecting the optimum mix proportions according to cementitious materials. Slag cement type of 46.5% slag powder and belite cement of 51.4% $C_2S$ content, lime stone powder as binders are selected for site experiment including water cement ratio. Also, test items for optimum mix proportion are as followings ; (1) Slump flow, 500 mm reaching time, V-type flowing time and U-box height (2) Setting time, bleeding, shortening depth and adiabatic temperature rising (3) Mixing time in plant (4) Concrete quantity and cost, quality control in actual concrete work. As test results, (4) Optimum water-cement ratio ; Slag cement type 41.0% and belite cement 51.0% (2) Setting time and bleeding finishing time of slag cement are faster, bleeding content of slag cement is higher, shortening depth and adiabatic temperature rising of belite cement type are lower (3) Optimum mixing time in batcher plant is 75 seconds and concrete productive capacity is about $100{\sim}110m^3/hr$. (4) Belite cement type is lower than slag cement type in material cost 14.0%, and concrete quantity in actual concreting work save 3.3% in case of belite cement type. Therefore, self-compacting concrete of belite cement type is definitely superior to that of slag cement type in various test items without compressive strength development.

• Journal of Korean Society of Forest Science
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• v.101 no.2
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• pp.175-184
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• 2012

This study was conducted to develop new mattress systems with vegetation base materials for protecting stream bank and rapid rehabilitation. Vegetation base materials are primarily compounded with fine soil, organic composts and peat moss as plant fibers, a water retainer and a soil improver. Peat moss can usually provide necessary natural fibers and organic materials in soil. Especially, peat moss can absorb up to 25 times its own weight in water and is therefore valued as a water retainer to prevent drying effect of vegetation base materials which can harm the growth of vegetation in mattresses. Normally mattress systems resist the lateral earth pressures or stream power by their own weight. Therefore, filled materials must have suitable weight, compressive strength and durability to resist the loading, as well as the effects of water and weathering. In this project, 100 to 200-mm clean, hard stones were basically specified, and about 50-mm rubbles were also used. Test application of new mattress system carried out in the stream bank of a small stream in the Gwangreung experimental forest, belonging to Korea Forest Research Institute (KFRI) in December 16th, 2006. As a result of the monitoring of vegetation coverage of test application plots (each plot size is 4 by 2 m), the coverage of all plots reached 100% in the end of May, 2007 (approximately 50 days passed after the first gemination of vegetation). The coverage of the plots using big hard stones and organic composts and the plots containing peat moss increased more rapidly. The results show that peat moss is effective to retain soil moisture and establish more sound environment for vegetation gemination.

• Journal of Gastric Cancer
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• v.8 no.3
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• pp.148-153
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• 2008

Purpose: Malignant bowel obstruction caused by recurrent gastric cancer must be treated appropriately to improve the effects of treatment and to prolong survival. We reviewed the surgical treatments for malignant bowel obstruction caused by recurrent gastric cancer. Materials and Methods: The subjects were patients with malignant bowel obstruction caused by recurrent gastric cancer and these patients were treated by surgical procedures at our hospital from 1998 to 2008. The patients were treated by resection, ostomy or bypass. The success of treatment was decided when the patients were able to tolerate more than a liquid diet. Results: 42 patients were treated 46 times by surgical procedures. Resection was done12 times, ostomy was done 24 times and bypass was done 10 times. The hospital stay and the period to liquid diet after the operation were shorter in the ostomy group. The post operative morbidity rate was 21.7% and the post operative death rate was 8.7%. There was no significant difference in survival according to the type of surgery. Conclusion: Ostomy is good choice for selected patients because it has a shorter hospital stay and period to liquid diet. There was no significant difference in survival according to the type of surgery because curative resection is difficult to perform in patients with malignant bowel obstruction.