• 대한기계학회논문집A
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• 제38권8호
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• pp.823-829
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• 2014

본 연구에서는 계면활성제를 첨가한 사각 PDMS(polydimethylsiloxane) 마이크로 채널에서의 모세관 흐름에 의한 충전 길이를 예측하기 위한 모델들을 제안하였다. 일반적으로 PDMS 의 소수성 특성 때문에 모세관 힘만을 이용한 PDMS 마이크로 채널에서의 물의 이동에는 어려움이 따르게 된다. 따라서 본 연구에서는 계면활성제를 첨가하여 친수성을 가지는 PDMS 표면을 제작하고, 이 표면에서의 물의 접촉각 변화 측정 및 단순 모델을 수립하였다. 또한 친수성 PDMS 마이크로 채널에서의 모세관 힘에 따른 충전 길이를 예측하기 위해서 Washburn 방정식을 바탕으로 한 단순 모델을 수립하였다. 그 결과 유체의 충전 길이는 접촉각의 초기변화속도의 영향을 받는 것을 확인할 수 있었다. 이를 바탕으로 대표적인 세가지 경우에 대한 모델을 제안하였으며, 이들은 MIMIC(MIcroMolding In Capillaries)과 같은 마이크로 유체 기반의 생산공정의 설계와 개발에 유용하게 적용될 수 있을 것이다.

• 한국통신학회논문지
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• 제33권2A호
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• pp.107-114
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• 2008

무선 접속 시스템에서는 주파수 선택적 페이딩 환경에서 직교 주파수 분할 다중화 기법 (OFDM)의 성능을 향상시키기 위한 연구가 많이 진행되었다. 시불변 채널을 송수신단 모두 알고 있는 경우, 워터 필링 (water-filling) 기법을 이용한 적응변조 기법이 최적이라고 증명되었다. 하지만, OFDM 시스템에서는 워터 필링 기법은 모든 부채널에 대한 채널정보를 송신단으로 보내기 위한 방대한 양의 오버헤드를 필요로 하게 된다. 본 논문에서는 제한된 궤환정보를 이용한 하항링크 적응변조 및 부호화 기법에 대해 제안하고자 한다. 궤환정보의 양을 최소화하기 위해서 각 부채널에 대한 채널정보 대신 하나의 OFDM 심볼을 기준으로 한 적응변조 방법을 적용한다. 궤환정보의 양이 대폭 감소되었지만, 성능열화 정도는 2dB 보다 적게 나타남을 모의실험을 통해 확인하고자 한다. 또한, OFDM 시스템에서는 부채널들을 그룹화하여 다중사용자 환경에서 사용될 수 있다. 이러한 다중사용자 환경에서는 본 논문에서 제안하는 기법의 전송률이 부채널 그룹이 증가할수록, 그리고 사용자가 많아질수록 채널용량에 근접함을 보여주고자 한다.

• 치과방사선
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• 제17권1호
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• pp.123-135
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• 1987

The author observed the effects of retrograde infusion of water soluble contrast media (Tele- brix 30) on the rabbit submandibular glands and compared the effects of different degrees of filling. 26 rabbits were divided into 2 groups of 12 each as experimentals and I group of 2 as normal controls. One experimental group was filled with 0.2㎖ and the other with 0.4㎖. Right submandibular gland of each rabbit was infused with contrast media and left one with physiologic saline as a experimental control, at a constant rate of 0.12㎖/min. using an infusion pump via the main excretory duct. Immediately after the infusion of contrast media, oblique lateral radiographs of the glands were made with occlusal film in order to confirm the glandular filling. The rabbits were sacrificed after varying periods (1, 8, 24 hours and 3, 6, 10 days) and the tissues were prepared for light and electron microscopic examination. The results were as follows: 1. In glands filled with 0.2㎖ contrast media, the initial changes were a few vacuole formation in the acini and slight dilation of the intralobular duct. The moderately severe changes such as vacuole formation in the acini, the abnormal substructure within the secretory granule, dilation of acinar and intercalated duct lumen, scalloping of striated duct lumen and inflammatory cell infiltrate were observed at 3 days. The general appearance was successively recovered, so the tissue had a normal appearance at 10 days. 2. In glands filled with 0.4㎖ contrast media, the most prominent alterations such as severe acinar atrophy, decreased number of secretory granules, proliferation of connective tissue stroma and pronounced inflammatory cell infiltrates appeared at 6 days. Although the general appearance returned to be almost normal at 10 days, acinar cells showed some atrophy and decreased secretory granules. 3. In glands subjected to 0.4㎖ infusion, the alterations were more severe and the recovery was slower than those seen in the glands to 0.2㎖ infusion.

• 한국통신학회논문지
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• 제29권9A호
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• pp.1022-1030
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• 2004

차세대 이동 및 우선통신 시스댐은 현재보나 얘우 큰 고속의 데이터 전송과 시스템 용량을 요구하고 였으며 이러한 요구를 충족시키기 위해서 복수의 안테나를 사용하여 송수신을 하는 MIMO(m 비 tiple input, multiple output) 기술이 널리 연구되고 있다 이 논문은 다수의 안테나를 가지고 있는 기지국, 소수의 안테나를 가지고 있는 단말기의 하향 링크에서 스케터령과 변동이 적으며 평탄한 페이딩 채널을 가정한다. 단영 사용가 MIMO 시스템에서 가지국이 채널상태정보를 가지고 있다연 SVD(singular value decomposition) 와 water filling 읍 사용 한 MIMO 기숭이 최대의 채널용량을 이룬다. 그러나 복수 사용자 시스템의 경우에는 공간분할 다중접속 기술을 이용하여, 보다 큰 전체 채널용량을 얻는 것이 가능하다 이 논문은 복수 사용가 시스템에서 각 사용자에게 복수 의 데이터 스트림을 전송하는 MIMO 공간분할 다중접속 기술을 제안한다. 제안하는 기술은 SVD 기반의 MIMO 기술이나 스마트 안테나를 사용한 공간분항 다중정속 기술보다 더 큰 전체 채널용량을 얻을 수 있다.

• 한국환경복원기술학회지
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• 제5권4호
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• pp.1-9
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• 2002

This study is carried out to make the environmentally affinitive porous planting block for revegetation and to make a effective program for greening plans. The summary is shown below. 1. In order to get stronger intensity and distribute proper porosity in the block for planting, the cements mixed with fine soil were used and the finer in soil grains gives the stronger in intensity of the cements. Use of the furnace slag cements instead of the portland cements showed relatively stronger in intensity of the block. The intensity of the block became stronger when the mixed ratio of the cements to soil is 5 : 1, but the pore space ratio was lower. The percolate pH of the portland cements after one month of treatment was 13.1 but the percolate pH of the furnace slag cements was shown lower. To mold proper porous planting blocks, the proper combination of additives such as the dehydrating agent, elastic agent and adhesives into the mixture of cements and soil gives better effectives. 2. After molding the porous planting blocks, it gave a better result when the grains of the filler made of peat moss, upland soil and compound fertilizer were smaller than 2 mm in size. Shaking of the filling materials also gave the better result, but it took more time and cost much more. Therefore, it was better when the filling materials were mixed with water first then flew down for stuffing. 3. It was necessary to cover with soil after seeding or planting on the porous planting blocks. The proper thickness of the soil to help root development and keep moisture is about 3~5 cm. 4. The plants for planting on the porous planting block were required stronger in the growth condition of their roots and their environmental adaptability. The average germination percentage and rate of Platycodon grandiflorum on the porous planting block were 88.8% and 85% accordingly and their rate is very uniform. The germination rates of Dianthus superbus var. longicalycinus and Taraxacum officinale were more than 50%. These grass species, Chelidonium majus var. asiaticum, Lysimachia mauritiana and Scabiosa mansenensis were the suggested biennial grasses in the planting area where exchanging of the seedling or nursery plants was not necessary because their germination rates were 59.3, 45.6 and 40.3% accordingly. Viola kapsanensis, Chrysanthemum sp., Taraxacum sp. and Iris ensata var. spontanea are the grass species that could be used by seeding for greening. However, the germination rate of Solidago virga-aurea var. asiatica, Aster scaber and Lythrum anceps were lower than 10%. The coverage ratio of Ixeris stolonifera is more than 80% after 60 days seeding and the root length of most of species are more than 10 cm except Iris ensata var. spontanea and Platycodon grandiflorum because their root developed thicker than other species.

• Corrosion Science and Technology
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• 제18권2호
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• pp.39-48
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• 2019

The feasibility of using benzotriazole (BTAH) to inhibit pitting corrosion in the sprinkler copper tubes was investigated by filling the tubes with BTAH-water solution in 829 households at an eight-year-old apartment complex. The water leakage rate was reduced by approximately 90% following BTAH treatment during 161 days from the previous year. The leakage of one of the two sprinkler copper tubes was investigated with optical microscopy, scanning electron microscopy, energy dispersive spectroscopy, X-ray photoelectron spectroscopy, and X-ray diffraction analysis to determine the formation of Cu-BTA film inside the corrosion pits. All the inner components of the corrosion pits were coated with Cu-BTA films suggesting that BTAH molecules penetrated the corrosion products. The Cu-BTA film was about 2 nm in thickness at the bottom of a corrosion pit. A layer of CuCl and $Cu_2O$ phases lies under the Cu-BTA film. This complex structure effectively prevented the propagation of corrosion pits in the sprinkler copper tubes and reduced the water leakage.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1999년도 하계학술대회 논문집 E
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• pp.2192-2194
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• 1999

In this study, We have accomplished a new approach to develope a cheap and compact pulsed $CO_2$ laser system. We used a fast SCR as switching device instead of a thyatron in the pulsed power supply. Using the Pulse transformer, energy in the condenser is tranferred to the secondary, electrodes of discharge tube, from the primary. An axial and water cooled type was adopted as the laser cavity. The laser performance characteristics as various parameters, such as gas pressure and pulse repetition rate, have been investigated. As a result, the maxium laser output was 12.3[W] at a pulse repetition rate of 120[pps] and a filling pressure of 12[Torr].

• 한국학교ㆍ지역보건교육학회지
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• 제2권1호
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• pp.31-40
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• 2001

A study of fluoride effects on teeth of school children was conducted in order to determine the usefulness of fluoride for preventing dental caries. Nine hundred and thirty six(936) elementary school children were selected from Chongju where children drank fluoridated water. Eight hundred and thirty six(836) from Seoul where children applied fluoride topically, and eight hundred and three(803) from Kumi where the children drank non fluoridated water(control). DMFs of school children were compared by the sources of fluoride. This study was conducted from May 1, through June 15, 2000. The results are summarized as follows; 1. The DMF rate of male school children topically applying fluoride was 51.4%, that of female children was 56.1%, and that of both males and females was 54.0%, The DMF rate of male children of control group was 72.4%, that of females was 77.5% and that of both males and females was 74.8%. 2. The DMF rate of male children drinking fluoridated tap water was 56.1%, that of females was 54.1%, and that of both males and females was 55.5%. The rates of control group were 72.4% for males, 77.5% for females and 74.8% for male and female children respectively. 3. The difference of DMF rates between the group of children who drank fluoridated water and applied fluoride topically, and control group was statistically significant. 4. The difference of DMF rates between the children who drank fluoridated water and the children who applied fluoride topically were not statistically significant. 5. The difference of DMFT rates between 5th graders who applied fluoride topically and the 5th graders of control group was not statistically significant. However, the difference of DMFT rates of the 6th graders who applied fluoride topically and the same graders of control group were statistically significant. The difference of DMF rates between 5th and 6th graders who drank fluoridated tap water and the same graders of control group was statistically significant. 6. The difference of DMFT rates between children drinking fluoridated tap water and children applying fluoride topically was statistically significant.

• 복합신소재구조학회 논문집
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• 제6권1호
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• pp.59-66
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• 2015

In this study, structural stability of large diameter high density polyethylene (HDPE) pipe during installation was numerically investigated in order to investigate the effect of concrete collar dimension, water depth and tension (pulling force). From the numerical simulation results, the total stress of HDPE pipe with designed concrete collar was within 2.5%, so the total weight of concrete collar for sinking of HDPE is important rather than concrete collar dimension. Furthermore, the tension area for possible installation is decreased as the air filling rate is increased. Therefore, it is important to calculate the reasonable tension range before actual installation for safe installation of HDPE pipe.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2004년도 ICEIC The International Conference on Electronics Informations and Communications
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• pp.15-18
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• 2004

In this paper we present a linear discrete bit-loading algorithm that maximizes the transmit bit rate using the channel informations to optimize the performance of the very high-speed digital subscriber line(VDSL) system. It will be useful under the constraint of a maximum transmit power for each user. When the level of crosstalk is high, the power allocation of a user changes the noise experienced by the other users in the same binder. In this case, the performance of DSL modems can be improved by jointly considering the bit and power allocation of all users.