• Wind and Structures
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• 제25권5호
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• pp.433-457
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• 2017

As a novel typical wind-sensitive structure, the wind load and wind-induced structural behaviors of super-large straight-cone cooling towers are in an urgent need to be addressed and studied. A super large straight-cone steel cooling tower (189 m high, the highest in Asia) that is under construction in Shanxi Power Plant in China was taken as an example, for which four finite element models corresponding to four structural types: the main drum; main drum + stiffening rings; main drum + stiffening rings + auxiliary rings (auxiliary rings are hinged with the main drum and the ground respectively); and main drum + stiffening rings + auxiliary rings (auxiliary rings are fixed onto the main drum and the ground respectively), were established to compare and analyze the dynamic properties and force transferring paths of different models. After that, CFD method was used to conduct numerical simulation of flow field and mean wind load around the cooling tower. Through field measurements and wind tunnel tests at home and abroad, the reliability of using CFD method for numerical simulation was confirmed. On the basis of this, the surface flow and trail characteristics of the tower at different heights were derived and the wind pressure distribution curves for the internal and external surfaces at different heights of the tower were studied. Finally, based on the calculation results of wind-induced responses of the four models, the effects of stiffening rings, auxiliary rings, and different connecting modes on the dynamic properties and wind-induced responses of the tower structure were derived and analyzed; meanwhile, the effect mechanism of internal suction on such kind of cooling tower was discussed. The study results could provide references to the structure selection and wind resistance design of such type of steel cooling towers.

• 대한방사선치료학회지
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• 제14권1호
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• pp.175-186
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• 2002

The purpose of this study is directly measure and evaluate about absorbed dose change according to nominal energy and electron cone or medical accelerator on isodose curve, percentage depth dose, contaminated X-ray, inhomogeneous tissue, oblique surface and irradiation on intracavitary that electron beam with high energy distributed in tissue, and it settled standard data of hish energy electron beam treatment, and offer to exactly data for new dote distribution modeling study based on experimental resuls and theory. Electron beam with hish energy of $6{\sim}20$ MeV is used that generated from medical linear accelerator (Clinac 2100C/D, Varian) for the experiment, andwater phantom and Farmer chamber md Markus chamber und for absorbe d dose measurement of electron beam, and standard absorbed dose is calculated by standard measurements of International Atomic Energy Agency(IAEA) TRS 277. Dose analyzer (700i dose distribution analyzer, Wellhofer), film (X-OmatV, Kodak), external cone, intracavitary cone, cork, animal compact bone and air were used for don distribution measurement. As the results of absorbed dose ratio increased while irradiation field was increased, it appeared maximum at some irradiation field size and decreased though irradiation field size was more increased, and it decreased greatly while energy of electron beam was increased, and scattered dose on wall of electron cone was the cause. In percentage depth dose curve of electron beam, Effective depth dose(R80) for nominal energy of 6, 9, 12, 16 and 20 MeV are 1.85, 2.93, 4.07, 5.37 and 6.53 cm respectively, which seems to be one third of electron beam energy (MeV). Contaminated X-ray was generated from interaction between electron beam with high energy and material, and it was about $0.3{\sim}2.3\%$ of maximum dose and increased with increasing energy. Change of depth dose ratio of electron beam was compared with theory by Monte Carlo simulation, and calculation and measured value by Pencil beam model reciprocally, and percentage depth dose and measured value by Pencil beam were agreed almost, however, there were a little lack on build up area and error increased in pendulum and multi treatment since there was no contaminated X-ray part. Percentage depth dose calculated by Monte Carlo simulation appeared to be less from all part except maximum dose area from the curve. The change of percentage depth dose by inhomogeneous tissue, maximum range after penetration the 1 cm bone was moved 1 cm toward to surface then polystyrene phantom. In case of 1 cm and 2 cm cork, it was moved 0.5 cm and 1 cm toward to depth, respectively. In case of air, practical range was extended toward depth without energy loss. Irradiation on intracavitary is using straight and beveled type cones of 2.5, 3.0, 3.5 $cm{\phi}$, and maximum and effective $80\%$ dose depth increases while electron beam energy and size of electron cone increase. In case of contaminated X-ray, as the energy increase, straight type cones were more highly appeared then beveled type. The output factor of intracavitary small field electron cone was $15{\sim}86\%$ of standard external electron cone($15{\times}15cm^2$) and straight type was slightly higher then beveled type.

• Wind and Structures
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• 제27권1호
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• pp.11-27
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• 2018

The straight-cone steel cooling tower is a novel type of structure, which has a distinct aerodynamic distribution on the internal surface of the tower cylinder compared with conventional hyperbolic concrete cooling towers. Especially in the extreme weather conditions of strong wind and heavy rain, heavy rain also has a direct impact on aerodynamic force on the internal surface and changes the turbulence effect of pulsating wind, but existing studies mainly focus on the impact effect brought by wind-driven rain to structure surface. In addition, for the indirect air cooled cooling tower, different additional ventilation rate of shutters produces a considerable interference to air movement inside the tower and also to the action mechanism of loads. To solve the problem, a straight-cone steel cooling towerstanding 189 m high and currently being constructed is taken as the research object in this study. The algorithm for two-way coupling between wind and rain is adopted. Simulation of wind field and raindrops is performed with continuous phase and discrete phase models, respectively, under the general principles of computational fluid dynamics (CFD). Firstly, the rule of influence of 9 combinations of wind sped and rainfall intensity on flow field mechanism, the volume of wind-driven rain, additional action force of raindrops and equivalent internal pressure coefficient of the tower cylinder is analyzed. On this basis, the internal pressures of the cooling tower under the most unfavorable working condition are compared between four ventilation rates of shutters (0%, 15%, 30% and 100%). The results show that the 3D effect of equivalent internal pressure coefficient is the most significant when considering two-way coupling between wind and rain. Additional load imposed by raindrops on the internal surface of the tower accounts for an extremely small proportion of total wind load, the maximum being only 0.245%. This occurs under the combination of 20 m/s wind velocity and 200 mm/h rainfall intensity. Ventilation rate of shutters not only changes the air movement inside the tower, but also affects the accumulated amount and distribution of raindrops on the internal surface.

• 한국의학물리학회지:의학물리
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• 제12권1호
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• pp.95-102
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• 2001

방사선치료용 고 에너지 전자선의 조직내 선량분포는 매우 다양하게 나타나고 있으며 조직내에서 일정 깊이까지만 선량이 집중적으로 부여되고 그 이후에는 선량이 급감하는 특징으로 인하여 피부 및 피부에서 깊지않은 종양과 구강, 질강 등 강내조사에 존재하는 종양치료에 널리 이용되고 있다. 하지만 의료용 선형가속기에는 강내조사용 조사통(cone)이 제공되지 않고 있다. 본 실험은 2.5, 3.0, 3.5 cm ø 크기의 강내조사용 소조사면 조사통을 수직형과 30$^{\circ}$ 경사형으로 6가지를 직접 제작하여 에너지별, 조사통 크기별로 조직내 선량분포 특성을 실험하여 임상적 선량계획에 필요한 자료를 제공하는데 목적을 두고 실험하였다. 심부선량은 조사통 크기, 에너지 크기, 조사통 각도에 따라 다르게 나타나고 있으며 유효선량 깊이는 전자선 에너지 및 조사통이 커질수록 약간 증가하였고, X선 오염정도는 1.2% 이하로 나타났으며, 출력흡수선량율은 약 15-86 %로 나타났다. 고 에너지 전자선은 강내치료에 매우 유용하게 이용될 수 있으며, 조직내 선량분포 특성이 매우 다양한 양상을 나타내고 있음을 확인하였고 이러한 결과를 자료화하여 임상적 치료와 새로운 선량분포 모형 연구에 필요한 자료를 제공할 수 있으리라 생각한다.

• Imaging Science in Dentistry
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• 제39권2호
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• pp.81-87
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• 2009

Purpose: To evaluate the anteroposterior length and buccal angle of the anterior loop, and the size and location of the mental foramen using cone beam computed tomography (CBCT). Materials and Methods: 100 CBCT images from 87 adults (43 males and 44 females) ranging in age from 20 to 73 years (average 50 years) with edentulous ridge of the mandibular premolar region were obtained. Axial, sagittal, coronal images were reconstructed from Dental and Block Images of CBCT. The anteroposterior length, shape and buccal angle of the anterior loop, and the size and location of the mental foramen were calculated from reconstructed images of axial, sagittal and coronal CBCT. Results: The anteroposterior length and buccal angle of the mental canal was 4.0${\pm}$1.2mm, 37.8${\pm}$11.60$^{\circ}$respectively. The loop type with straight course was the most common shape of the mental canal. The location of the mental foramen below the apex of the lower second premolar (78%) was the most common. The maximum size of the mental foramen was 4.6${\pm}$1.0 mm in width and 3.0${\pm}$0.6 mm in height. The inner size of the mental canal was 2.6${\pm}$0.6 mm in width and 2.1 mm${\pm}$0.4 mm in height. Conclusion: CBCT is useful to evaluate the anterior loop and mental foramen of the mandibular canal. Safe guideline of 4 mm from the most anterior point of the mental foramen is recommended for implant and surgical treatment. (Korean J Oral Maxillofac Radiol 2009; 39: 81-7)

• 한국분무공학회지
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• 제17권2호
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• pp.86-93
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• 2012

The effects of projectile impact system on the transient spray characteristic which is supersonic liquid tip velocity were studied by experimentally. Supersonic liquid jets were generated by impact of a high speed projectile driven by a Two-stage light gas gun. A high speed camera and schlieren optical system were used to capture the spray structures of the supersonic liquid jets. In a case of nozzle assembly Type-A, expansion gases accelerate a projectile which has a mass of 6 grams from 250 m/s at the exit of the launch tube. Accelerated projectile collides with the liquid storage part, then supersonic liquid jets are injected with instantaneous spray tip velocity from 617.78 m/s to 982.54 m/s with various nozzle L/d. However, In a case of nozzle assembly Type-B which has a heavier projectile (60 grams) and lower impact velocity (182 m/s), an impact pressure was decreased. Thus the liquid jet injected at 210 m/s of the maximum velocity did not penetrate a shock wave and fast break-up was occurred. Pulsed injection of liquid column generated second shock wave and multiple shock wave.

• 한국산림과학회지
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• 제86권3호
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• pp.378-390
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• 1997

국내 젓나무속의 분비나무와 구상나무를 중심으로 집단간 종간 주요 15개의 형질에 대한 분석을 통해 식별(identification)형질과 유별(classification)형질과의 관계를 조명하고자 하였다. 주성분분석(principal components analysis : PCA)과 유집분석(cluster analysis) 결과 종을 식별하는데 도움을 주는 형질로는 잎의 폭, 종자길이, 종자날개의 폭, 길이, 구과 폭, 실편의 폭, 포침의 길이였으나, 종간 형질의 최고-최저의 구간을 비교하였을 때에는 서로 중첩되어 현실적으로 표본을 중심으로 한 종간 구분은 불가능하였다. 집단별로는 구상나무의 경우 지리산 집단이 구과의 크기와 포침의 길이가 큰 반면, 한라산 집단의 개체들은 대부분 종자크기(폭과 날개)와 실편의 폭 등이 다른 집단에 비해 컸으며, 덕유산 집단은 대부분의 형질이 왜소한 특성을 보여주었다. 젓나무속의 주요 식별형질로 인식되는 잎의 수지구 위치를 집단별로 조사하여 본 결과, 한라산 개체의 경우 구상(나무)형으로 인지되었으나, 지리산 개체의 경우 약 75%정도만이 구상형인 반면 덕유산 가야산의 경우에는 50% 이하가 구상형과 분비형으로 확인되어 두 집단의 일부개체는 분비나무와 구분이 불가능하였다. 한편, flavonoids 분석 결과, flavonol, dihydroflavonol, flavanone 등 3개군(群)의 flavonoids가 확인되었는데, 구상나무에서만 존재하는 flavanone(5-deoxyflavanone)을 제외하고는 뚜렷한 종간 차이점을 확인할 수 없었다. 구성나무의 경우 한라산과 지리산 집단에서 flavanone의 성분이 발견된 반면, 덕유산의 경우는 이 성분이 존대하지 않아, 화학적으로는 분비나무에 더 가까웠다. 오대산, 명지산, 치악산, 중왕산, 소백산에서 채집된 분비나무의 경우(설악산 집단의 일부개체 제외), 구상나무에서 발견된 flavanone 성분은 없었고 대신 분비나무의 특징인 dihydrokaemferol의 성분이 다량 존재하였다. 일본(日本)과 중국(中國), 대만(臺灣)의 25종의 flavonoids을 비교 분석한 결과, 구상나무에서 발견된 flavanone성분이 중국종(中國種) 중 수지구의 내형과 외형을 모두 가지는 운남성(雲南省), 사천성(四川省)의 A. faxoniana Rehder et Wilson(원시종으로 추측)과 운남성(雲南省), 사천성(四川省), 서장성(西藏省)의 A. georgei Orr에서 발견됨에 따라 수지구위치는 국내종의 경우 집단적 변이에 의한 반면, 중국(中國)에서는 종간 유연관계를 설명하는 주요 형질로 밝혀졌다. 정량적 형질을 중심으로는 분비나무와 구상나무를 식별할 수 있는 형질이 존재하지 않으나 수지구가 안쪽에 위치한 중국(中國)의 A. faxoniana와 A. georgei에서 구상나무의 특유성분인 flavanone이 발견되어 형태적으로 수지구위치가 상대적으로 중요한 형질로 재확인되었으며 한국의 일부 집단에서 보이는 구상형 연속변이는 분비나무와의 잡종현상이나 또는 신생대 4기 때 분비나무와 구상나무의 유전자교합, 혹은 이입현상에 인한 것으로 추정된다. 수지구 위치 변이와 화학적 변이의 중간적 형태를 보여주는 지리산, 덕유산, 가야산 지역의 집단유전구조 분석 후에나 그 실체가 밝혀질 것으로 기대되며 현재 연구중이다.