• 대한방사선치료학회지
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• 제13권1호
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• pp.38-46
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• 2001

Purpose : The aim of this study is to investigate the effect of tissue inhomogeneities when appling to contrast medium among Homogeneous, Batho and ETAR dose calculation method in RTP system. Method and Material : We made customized heterogeneous phantom it filled with water or contrast medium slab. Phantom scan data have taken PQ 5000 (CT scanner, Marconi, USA) and then dose was calculated in 3D RTP (AcQ-Plan, Marconi, USA) depends on dose calculation algorithm (Homogeneous, Batho, ETAR). The dose comparisons were described in terms of 2D isodose distribution, percent depth dose data, effective path length and monitor unit. Also dose distributions were calculated with homogeneous and inhomogeneous correction algorithm, Batho and ETAR, in each patients with different clinical sites. Results : Result indicated that Batho and ETAR method gave rise to percent depth dose deviation $1.5{\sim}2.7\%,\;2.3{\sim}3.5\%$ (6MV, field size $10{\times}10cm^2$) in each status with and without contrast medium. Also show that effective path lengths were more increase in contrast status (23.14 cm) than Non-contrast (22.07 cm) about $4.9\%$ or 10.7 mm (In case Hounsfield Unit 270) and these results were similary showned in each patient with different clinical site that was lung. prostate, liver and brain region. Concliusion : In conclusion we shown that the use of inhomogeneity correction algorithm for dose calculation in status of injected contrast medium can not represent exact dose at GTV region. These results mean that patients will be more irradiated photon beam during radiation therapy.

• 대한토목학회논문집
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• 제33권5호
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• pp.1861-1870
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• 2013

최근 기후변화 영향으로 인해 수문변동성이 크게 증가되고 있으며 이러한 변동성을 고려하기 위한 방안으로서 강수량 모의발생 기법에 대한 중요성이 대두되고 있다. 본 연구에서는 복잡한 강수발생 패턴을 인지하고 강수량의 다양한 분포특성을 고려할 수 있는 혼합분포를 이용한 동질성 Hidden Markov Chain(HMM) 모형을 제안하였다. HMM 모형의 개선효과를 검증하기 위해서 기존 Markov Chain 모형과 비교 하였으며 서울관측소 및 전주관측소를 대상으로 연구를 진행하였다. 계절강수량 및 일강수량 등 다양한 시간규모에서 모형의 적합성을 평가하기 위해서 천이확률, 평균, 분산, 왜곡도 및 첨예도 등을 비교하였으며 HMM 모형이 기존 Markov Chain 모형에 비해서 개선된 모의능력을 확인할 수 있었다. 특히, HMM 모형은 극치강수량을 재현하는데 있어서 기존 Markov Chain 모형에 비해서 월등한 모의능력을 보여주었다. 이러한 점에서 장기유출량 및 확률홍수량 등을 산정하기 위한 입력자료로 활용이 충분히 가능할 것으로 판단된다.

• 공학논문집
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• 제6권2호
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• pp.141-151
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• 2004

금합금계 매몰재 재료의 물리적 특성은 각각 열팽창계수과 압축강도, 입도 분포에 크게 좌우된다. 일반적으로 금합금계 매몰재는 cristobalite와 quartz, plaster로 주성분을 구성하고 있다. 그리고 cristobalite와 quartz의 열팽창계수는 $2.6\times10^{-6}/^\circC$, $2.32\times10^{-6}/^\circC$, 로 이 두 재료의 혼합비가 매몰재의 열팽창 계수를 변화시키는 매우 중요한 역할을 하고 있다. 현재 국내에서는 금합금계 매몰재는 전량 수입에 의존하고 있고 그 시장 수요 또한 대단히 크다. 따라서 균일한 입도 분포를 가지는 cristobalite와 quartz의 개발과 주조금속의 열팽창과 냉각에 따른 수축력을 고려한 열팽창계수를 가지면서 매몰재의 요구강도에 적합한 압축강도를 가지는 금합금계 매몰재의 개발이 필수적이다. 따라서 본 연구에서는 먼저 균일한 입도를 갖는 cristobalite와 quartz 분체의 제조와 cristobalite와 quartz의 혼합비에 따른 열팽창계수와 압축강도를 비교 분석하였다. 본 연구의 결과로 표면이 매끄럽고 균일한 입도 분포를 갖는 cristobalite와 quartz를 제조하였으며, cristobalite와 quartz의 혼합비가 45:25가 열팽창계수와 압축강도에서 매몰재가 요구하는 조건을 만족하였다.

• 한국분말재료학회지
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• 제26권5호
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• pp.375-382
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• 2019

Homogeneous multicomponent indium gallium zinc oxide (IGZO) ceramics for transparent electrode targets are prepared from the oxides and nitrates as the source materials, and their properties are characterized. The selected compositions were $In_2O_3:Ga_2O_3:ZnO$ = 1:1:2, 1:1:6, and 1:1:12 in mole ratio based on oxide. As revealed by X-ray diffraction analysis, calcination of the selected oxide or nitrides at $1200^{\circ}C$ results in the formation of $InGaZnO_4$, $InGaZn_3O_6$, and $InGaZn_5O_8$ phases. The 1:1:2, 1:1:6, and 1:1:12 oxide samples pressed in the form of discs exhibit relative densities of 96.9, 93.2, and 84.1%, respectively, after sintering at $1450^{\circ}C$ for 12 h. The $InGaZn_3O_6$ ceramics prepared from the oxide or nitrate batches comprise large grains and exhibit homogeneous elemental distribution. Under optimized conditions, IGZO multicomponent ceramics with controlled phases, high densities, and homogeneous microstructures (grain and elemental distribution) are obtained.

• Geomechanics and Engineering
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• 제15권5호
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• pp.1071-1080
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• 2018

The study of behavior and values of deformations in the geological medium makes the scientific basis of the methodology of synthesis of true values of parameters of its physico-mechanical and density properties taking into account the influence of geodynamic impacts. The segments of continuous variation of homogeneous elastic uniform deformations are determined under overall compression of the medium. The limits of these segments are defined according to the criteria of instability (on geometric form changes and on "internal" instability). Analytical formulae are obtained to calculate current and limiting (critical) values of deformations within the framework of various variants of small and large initial deformations of the non-classically linearized approach of non-linear elastodynamics. The distribution of deformation becomes non-uniform in the medium while the limiting values of deformations are achieved. The proposed analytical formulae are applicable only within homogeneous distribution of deformations. Numerical experiments are carried out for various elastic potentials. It is found that various forms of instability can precede phase transitions and destruction. The influence of these deformation phenomena should be removed while the physico-mechanical and density parameters of the deformed media are determined. In particular, it is necessary to use the formulae proposed in this paper for this purpose.

• 한국분무공학회지
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• 제24권4호
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• pp.185-193
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• 2019

The effervescent atomizer is one of twin-fluid atomizers that aeration gas enters into bulk liquid and two-phase flow is formed in the mixing section. The effervescent atomizer requires low injection pressure and small amount of aeration gas, as compared to other twin-fluid atomizers. In this study, cold flow test was conducted to investigate the spray characteristics of aerated impinging jets. The present effervescent impinging atomizers were composed of the aerator device and like-on-like doublet impinging atomizer which had different impinging angles. To analyze the spray characteristics such as breakup length and droplet size distribution, the image processing technique was adopted by using instantaneous images at each flow condition. Non-dimensional parameters, induced by the homogeneous flow model, were used to predict the breakup length. The breakup length was decreased with the mixture Reynolds number and impinging angle increasing. The result of droplets showed that the size distribution was axisymmetric about the center of the injector and their diameter tended to decrease with increasing GLR.

• 한국정밀공학회지
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• 제15권6호
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• pp.124-138
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• 1998

Particles reinforced MMCs have many advantages over monolithic metals including a higher specific modulus, higher specific strength, better properties at elevated temperatures and better wear resistance. SiC$_p$/A16061 composites have good results in its mechanical properties. This work investigates SiC$_p$/A16061 composites in the microscopic view and compares the analytical results with the experimental ones. The discrepancy of the material properties between the reinforced particle, SiC$_p$, and the matrix material, A16061 appears to be so significant. Especially the coefficient of thermal expansion(CTE) of A16061 is 5 times larger than that of SiC$_p$. Thermal residual stress in MMCs is induced at high temperatures. The shape of particle is various but the theoretical model is not able to consider the nonuniform shape. Particle distribution is not homogeneous in experimental specimen. However, it is assumed to be homogeneous in simulation model. The shapes of particles are assumed to be not only perfect global but hexahedral shapes. The types of particle distribution are two - simple cubic array(SC array) and face-centered cubic array(FCC array).

• Nuclear Engineering and Technology
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• 제46권6호
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• pp.857-862
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• 2014

Mechanical alloying under various gas atmospheres such as Ar, an Ar-$H_2$ mixture, and He gases were carried out, and its effects on the powder properties, microstructure and mechanical properties of ODS ferritic steels were investigated. Hot isostatic pressing and hot rolling processes were employed to consolidate the ODS steel plates. While the mechanical alloyed powder in He had a high oxygen concentration, a milling in Ar showed fine particle diameters with comparably low oxygen concentration. The microstructural observation revealed that low oxygen concentration contributed to the formation of fine grains and homogeneous oxide particle distribution by the Y-Ti-O complex oxides. A milling in Ar was sufficient to lower the oxygen concentration, and this led a high tensile strength and fracture elongation at a high temperature. It is concluded that the mechanical alloying atmosphere affects oxygen concentration as well as powder particle properties. This leads to a homogeneous grain and oxide particle distribution with excellent creep strength at high temperature.

• 대한의용생체공학회:학술대회논문집
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• 대한의용생체공학회 1996년도 춘계학술대회
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• pp.188-191
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• 1996

This study is to find the distribution of the torso surface potential based on electrical cardiac dipole source. In order to find the torso surface potential, the governing equation was developed based on the Green's second theorem. The boundary element method(BEM) which has a good computing capability in case of homogeneous and isotropic medium was applied to solve the equation. To validate the BEM, we considered a homogeneous sphere model which has an electric dipole source inside. The results showed the good agreement between the analytic solution and the computed solution. In normal heart, the simulated torso surface isopotential maps are good agreement with that obtained from the ventricular excitation. The validity of the simulated results were verified by comparing with other results.

• 대한기계학회논문집A
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• 제24권1호
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• pp.69-78
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• 2000

The one-parameter singular expression for stresses and displacements near a crack tip has been widely thought to be sufficiently accurate over a reasonable re ion for any geometry and loading conditions. In many cases, however subsequent terms of the series expansion are quantitatively significant, and so we now consider the evaluation of such terms and their effect on the predicted crack growth direction. For this purpose the problem of a cracked orthotropic plate subjected to a biaxial load is analysed. It is assumed that the material is ideal homogeneous anisotropic. BY considering the effect of the load applied parallel to the plane of the crack, the distribution of stresses and displacements at the crack tip is reanalyzed. In order to determine values for the angle of initial crack extension we employ the normal stress ratio criterion.