• Journal of Trauma and Injury
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• 제28권3호
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• pp.149-157
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• 2015

Purpose: Traumatic brain injury (TBI) is the most common cause of pediatric trauma patients came to the emergency department. Without guidelines, many of these children underwent repeat brain computed tomography (CT). The purpose of this study was to evaluate the value of repeat brain CT in children with TBI. Methods: We conducted a retrospective study of TBI in children younger than 19 years of age who visited the emergency department (ED) from January 2011 to December 2012. According to the Glasgow Coma Scale (GCS) and Pediatric Glasgow Coma Scale score of the patients, study population divided in three groups. Clinical data collected included age, mechanism of injury, type of TBI, and outcome. Results: A Total 83 children with TBI received repeat brain CT. There were no need for neurosurgical intervention in mild TBI (GCS score 13-15) group who underwent routine repeat CT. 4 patients of mild TBI group, received repeat brain CT due to neurological deterioration, and one patient underwent neurosurgical intervention. Routine repeat CT identified 12 patients with radiographic progression. One patient underwent neurosurgical intervention based on the second brain CT finding, who belonged to the moderate TBI (GCS score 9-12) group. Conclusion: Our study showed that children with mild TBI can be observed without repeat brain CT when there is no evidence of neurologic deterioration. Further study is needed for establish indication for repetition of CT scan in order to avoid unnecessary radiation exposure of children.

• 한국세라믹학회지
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• 제43권5호
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• pp.270-276
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• 2006

LSGM(($La_xSr_{1-x})(Ga_yMg_{1-y})O_3$) electrolyte is known to show very serious interfacial reaction with other unit cell components, especially with an anode. Such an interfacial reaction induced the phase instability of constituent component and deterioration of the unit cell performance, which become the most challenging issues in LSGM-based SOFCs. In this study, we fabricated LSGM($La_{0.8}Sr_{0.2}Ga_{0.83}Mg_{0.17}O_x$) electrolyte supported-type cell in order to avoid such interfacial problem by lowering the heat-treatment temperature of the electrode fabrication. According to the microstructural and phase analysis, there was no serious interfacial reaction at both electrolyte/anode and electrolyte/cathode interfaces. Moreover, from the electrochemical characterization of the unit cell performance, there was no distinct deterioration of the open cell voltage as well as an internal cell resistance. These results demonstrate the most critical point to be concerned in LSGM-based SOFC is either to find a proper electrode material which will not give any interfacial reaction with LSGM electrolyte or to properly adjust the processing variables for unit cell fabrication, to reduce the interfacial reaction.

• Structural Engineering and Mechanics
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• 제9권6호
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• pp.615-636
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• 2000

Some elevated water tanks have failed due to torsional vibrations in past earthquakes. The overall axisymmetric structural geometry and mass distribution of such structures may leave only a small accidental eccentricity between centre of stiffness and centre of mass. Such a small accidental eccentricity is not expected to cause a torsional failure. This paper studies the possibility of amplified torsional behaviour of elevated water tanks due to such small accidental eccentricity in the elastic as well as inelastic range; using two simple idealized systems with two coupled lateral-torsional degrees of freedom. The systems are capable of retaining the characteristics of two extreme categories of water tanks namely, a) tanks on staging with less number of columns and panels and b) tanks on staging with large number of columns and panels. The study shows that the presence of a small eccentricity may lead to large displacement of the staging edge in the elastic range, if the torsional-to-lateral time period ratio $({\tau})$ of the elevated tanks lies within a critical range of 0.7< ${\tau}$ <1.25. Inelastic behaviour study reveals that such excessive displacement in some of the reinforced concrete staging elements may cause unsymmetric yielding. This may lead to progressive strength deterioration through successive yielding in same elements under cyclic loading during earthquakes. Such localized strength drop progressively develop large strength eccentricity resulting in large localized inelastic displacement and ductility demand, leading to failure. So, elevated water tanks should have ${\tau}$ outside the said critical range to avoid amplified torsional response. The tanks supported on staging with less number of columns and panels are found to have greater torsional vulnerability. Tanks located near faults seem to have torsional vulnerability for large ${\tau}$.

• 한국안전학회지
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• 제22권3호
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• pp.57-64
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• 2007

Recently, the corrosion of concrete structures has received great attention related with the deterioration of sea-side structures, such as new airport, bridges, and nuclear power plants. In this regards, many studies have been done on the chloride attack in concrete structures. However, those studies were confined mostly to the single deterioration due to chloride only, although actual environment is rather of combined type. The purpose of the present study is, therefore, to explore the influences of carbonation and freezing-thawing action to chloride attack in concrete structures. The test results indicate that the chloride penetration is more pronounced than the case of single chloride attack when the carbonation process is combined with the chloride attack. It is supposed that the chloride ion concentration of carbonation region is higher than the sound region because of the separation of fixed salts. Though the use of fly ash pronounces the chloride ion concentration in surface, amounts of chloride ion penetration into deep region decreases with the use of fly ash. The small reduction of relative dynamic elastic modulus induced from freezing-thawing increases the chloride ion penetration depths much. The present study allows more realistic assessment of durability for such concrete structures which are subjected to combined attacks of both chlorides and carbonation or freezing-thawing but the future studies for combined environment will assure the precise assessment.

• 한국항해항만학회:학술대회논문집
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• 한국항해항만학회 2006년도 International Symposium on GPS/GNSS Vol.2
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• pp.173-177
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• 2006

From the viewpoint of coastal hydrodynamics, one of the most important effects of global warming is a sea-level rise in coastal areas. In the present study, impacts on port facilities against sea-level rise were investigated. The sea-level rise causes the increase of the water depth, and it generates variations on the wave height, buoyancy, tidal system and nearshore current system and so on. The increase of water depth gives rise to the decrease of crown height of the structure and it causes increase of wave overtopping quantity. It may flood the port zone and its facilities, and may decrease harbor tranquility. It also leads to difficulties on navigation, mooring and loading/unloading at the port. Increase in water depth also causes increase of wave height in surf zone. This high wave makes structures unstable and may cause them to collapse during storm. In addition, increase in buoyant force due to sea-level rise also makes the gravity type structures unstable. Consequently, theses variations due to sea-level rise will cause functional deterioration of port facilities. In order to protect port facilities from the functional deterioration, reinforcement plan is required such as raising the crown height and increase in block weight and so on. Hence proper estimation method for the protection cost is necessary in order to protect port facilities efficiently. Moreover response strategies and integrated coastal zone management plan is required to maintain the function of port facilities. A simple estimation of cost for breakwaters in Korea was performed in the present study.

• Journal of the Korean Wood Science and Technology
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• 제35권1호
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• pp.64-72
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• 2007

팔만대장경판을 보관하고 있는 장경판전 내부의 판가 기둥에 대하여 생물적 열화 특성을 조사 연구하였다. 장경판전의 법보전과 수다라장의 판가기둥을 대상으로 연구 검토한 결과, 서가의 위치 및 부위 그리고 주변 환경에 따라 다양한 열화 현상이 있음이 밝혀졌다. 부재의 주요 열화는 미생물에 의한 부후현상으로 밝혀졌으나, 부후가 나타난 부분들은 초석에 접촉된 부위였으며 부후 정도가 매우 극심한 상태를 보였다. 법보전 판가기둥 부후가 더 심했다. 부후형은 백색부후형이 많았다. 그리고 일부판가기둥에서는 곰팡이류의 표면오염이 극심한 것으로 나타났다. 특히 동북, 서북, 북향에 위치한 부재에 더 심한 열화가 나타났으며 건물내부의 전면보다는 후면에 위치한 판가 부재의 부후가 심한 것으로 밝혀졌다 해충에 의한 피해는 거의 없었다.

• 한국구조물진단유지관리공학회 논문집
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• 제25권6호
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• pp.103-110
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• 2021

유연한 고무재료와 강재 보강판을 적층으로 구성한 탄성받침은 우수한 수직강성과 유연한 횡강성으로 교량의 내진보강용으로 널리 사용되고 있다. 무엇보다 시공이 간단하고 비용이 높지 않다는 장점을 지니고 있다. 고무재료의 한 종류인 합성고무는 천연고무에 비해 노화에 대한 저항성이 크지만 이 역시 다양한 열화요인으로 성능이 저하된다. 내진설계기준 및 내진성능평가요령에서는 이러한 노화의 특성을 반영하고 있지 않지만 관련 연구가 축적되면 이를 반영하는 것이 합리적이다. 합성고무를 대상으로 노화촉진시간과 노출시간을 변수로 하여 노화촉진시험을 수행하여 전단특성의 변화를 분석하였다. 노화가 진행될수록 최대전단응력과 전단변형율은 감소한다. 또한 동일한 전단변형률에서 전단강성이 크게 증가한다.

• 한국수자원학회논문집
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• 제56권11호
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• pp.697-703
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• 2023

본 연구에서는 부식에 의한 관두께 감소를 예측하여 수정 간접평가법을 개발하였다. 수정 평가법과 직접평가법과 비교를 통해 노후상수관을 선정함에 있어 정확도를 확인하였다. 가중치 조정은 기존 평가항목의 중요도에 따라 수질부식성, 토양부식성, 매설깊이, 도로형태의 가중치를 낮추고 관두께의 가중치를 추가하는 방법으로 가중치를 산정하였고 그 결과 관두께의 가중치는 0.1530으로 결정하였다. 직접평가법과 비교한 결과 기존 간접평가법에 비해 수정 간접평가법의 정확도가 31.03% 상승한 것으로 분석되었다. 수정 간접평가법을 통해 노후 상수관의 개량 우선순위 선정 시 기존 간접평가법보다 정확하고 효율적으로 노후관을 선정할 수 있을 것이다.

• Restorative Dentistry and Endodontics
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• 제18권1호
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• pp.1-26
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• 1993

The purpose of this study was to investigate the effect of acid etching on the surface appearance and fracture toughness of five glass ionomer cements. Five kinds of commercially available glass ionomer cements including chemical curing filling type, chemical curing lining type, chemical curing metal reinforced type, light curing tilling type and light curing lining type were used for this study. The specimens for SEM study were fabricated by treating each glass ionomer cement with either visible light curing or self curing after being inserted into a rubber mold (diameter 4mm, depth 1mm). Some of the specimens were etched with 37% phosphoric acid for 0, 15, 30, 60, go seconds, at 5 minutes, 1 hour and 1 day after mixing of powder and liquid. Unetched ones comprised the control group and the others were the experimental groups. The surface texture was examined by using scanning electron microscope at 20 kV. (S-2300, Hitachi Co., Japan). The specimens for fracture toughness were fabricated by curing of each glass ionomer cement previously inserted into a metal mold for the single edge notch specimen according to the ASTME399. They were subjected to a three-point bend test after etching for 0, 30, 60, and 90 seconds at 5 minutes-, 1 hour-and 1 day-lapse after the fabrication of the specimens. The plane strain fracture toughness ($K_{IC}$) was determined by three-point bend test which was conducted with cross-head speed of 0.5 mm/min using Instron universal testing machine (Model No. 1122) following seven days storage of the etched specimens under $37^{\circ}C$, 100% humidity condition. Following conclusions were drawn. 1. In unetched control group, crack was present, but the surface was generally smooth. 2. Deterioration of the surface appearance such as serious dissolving of gel matrix and loss of glass particles occured as the etching time was increased beyond 15 s following Immediate etching of chemical curing type of glass ionomer cements. 3. Etching after 1 h, and 1 d reduced surface damage, 15 s, and 30s etch gave rough surface appearance without loss of glass particle of chemical curing type of glass ionomer cements. 4. Light curing type glass ionomer cement was etched by acid, but there was no difference in surface appearances according to various waiting periods. 5. It was found that the value of plane stram fracture toughness of glass ionomer cements was highest in the light curing filling type as $1.79\;MNm^{-1.5}$ followed by the light curing lining type, chemical curing metal reinforced type, chemical curing filling type and chemical curing lining type. 6. The value of plane stram fracture toughness of the chemical curing lining type glass ionomer cement etched after 5 minutes was lower than those of the cement etched after 1 hour or day or unetched (P < 0.05). 7. Light curing glass ionomer cement showed Irregular fractured surface and chemical curing cement showed smooth fractured surface.

• 한국지진공학회:학술대회논문집
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• 한국지진공학회 2002년도 춘계 학술발표회 논문집
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• pp.258-265
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• 2002

The recent earthquakes in worldwide have caused extensive damage to highway bridge structures. In particular, it has been demonstrated that concrete columns with inadequate lateral reinforcement contributed to the catastrophic collapse of many bridges. The poor detailing of the starter bars in these columns compounded the problem of seismic deficiency. Therefore, this study has been performed to verify the effect of lap spliced longitudinal steel and confinement steel type for the seismic behavior of reinforced concrete bridge piers. Eight concrete columns were constructed with existing scale as diameter, 1.2m and height, 4.8m. 4 confinement steel types were adopted for seismic performance evaluation. All specimens were rested under inelastic cyclic loading while simultaneously subjected to a constant axial load. The longitudinal steel lap-splice is highly effective in seismic performance deterioration of reinforced concrete bridge piers.