• The Journal of Korean Society for Radiation Therapy
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• v.28 no.1
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• pp.27-34
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• 2016

Purpose : Retrospective evaluation of setup changes using the corrected position during helical tomotherapy Materials and Methods : Head and neck cancer patients were randomly sampled and summarized into 3 groups: Group 1(32) Brain, Group 2 2(28)Maxillar, Nasal cavity, Group 3 (35) Nasopharynx(NPX), Tongue, Tonsil, and Oropharynx(OPX). In 3 groups, the statistical tests based on repeated measurements among 30 times of the duration of treatment by applying X, Y, Z axis errors, roll, weight changes, and vectors as variables. Results : The statistical test results showed that there was no difference between x-axis (p = 0.458) and y-axis (p=0.986) and in roll (p = 0.037), weight change (p <0.001), and the vector (p <0.001). In addition, the pattern between the three groups based on the fraction revealed no difference in x-axis (p = 0.430) and roll (p = 0.299) but a difference in y-axis (.023), weight change (p = 0.001), and vector (p = 0.028). Conclusion : The results of the retrospective evaluation found the change in the group 3 with respect Y, Z, weight, and vector and a larger random error during the treatment including low neck.

• Korean Journal of Crystallography
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• v.8 no.1
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• pp.33-37
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• 1997

The optical properties of (1210) GaN epitaxy films grown on the (1012) $\alpha-A1_2O_3$ substrates have been studied. The hetero-epitaxy films were grown by the halide vapor phase epitaxy (HVPE) method using $Ga/HC1/NH_3/He$ system at $990^{\circ}C$. XRD, RHEED and SEM are used for the identification of the hetero-epitaxy films structure and surface morphology. The confirmed (1210) GaN epitaxy films were characterized by PL and Raman. By the Raman scattering, the active phonon modes of single-phase GaN films are varied with the arrangement of both polarization and propagation directions of laser beam with reference to the axis in single-phase crystal films. The Y(Z, Y & Z) X geometry allows scattering pat-terns of $A_1(TO)=533\;cm^{-1},\;E_1(TO)=559\;cm^{-1}\;and\;E_2=568 cm^{-1}$ modes, whereas in the Z(Y, Y & Z) X geometry the only $E_2$ mode are observed.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.37 no.3
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• pp.267-273
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• 2013

In order to provide effective operating conditions for the fan in a wet cooling tower with film fill, a new program to search for the minimum fan power was developed using a model of the optimal total annual cost of the tower based on Merkel's model. In addition, a type of design map for a cooling tower was also developed. The inlet water temperature and heat load were considered as key parameters. The present program was first validated using several typical examples. The results showed that for a given heat load, a three-dimensional graph of the fan power (z-axis), mass flux of air (x-axis, minimum fan power), and inlet water temperature (y-axis, maximum of minimum fan power) showed a saddle configuration. The minimum fan power increased as the heat load increased. The conventionally known fact that the most effective cooling tower operation coincides with a high inlet water temperature and low air flow rate can be replaced by the statement that there exists an optimum mass flux of air corresponding to a minimum fan power for a given inlet water temperature, regardless of the heat load.

• Proceedings of the Korean Society of Medical Physics Conference
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• 2003.09a
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• pp.58-58
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• 2003

목적 : 본 연구에서는 C-arm과 CT에 사용 가능한 자궁경부암용 팬톰을 개발하고 이를 이용하여 기존의 필름 방법에 기반한 위치 확인 방법과 CT 재구성 방법의 정확성을 비교 연구하고자 한다. 정확성이 검증된 후에는 두 방법의 장점을 이용하기 위해 CT로 재구성된 좌표를 필름의 좌표로 변환시켜 현재 사용되고 있는 필름에 기반한 근접 치료 계획 시행에 도움을 주고자 한다. 방법 : 자체 제작한 자궁경부암용 팬톰은 인체 등가 물질인 물과 아크릴을 사용하였고, 크게 localizer 부분과 팬톰 부분으로 구성되어 있다. 또한, 실제 자궁경부암 환자의 임상적인 구조를 모사하여 제작하였다. 자궁경부암 치료시 중요 장기인 방광과 직장을 구와 원기둥으로 설계하였고, 고선량율 applicator는 아크릴 판의 흠으로 고정시켜 제작하였기 때문에 CT 촬영시 applicator를 제거한 영상에서도 applicator의 구조가 정확하게 묘사될 수 있도록 제작하였다. 두 시스템에서 재구성된 좌표를 비교하기 위해 각각의 시스템에서의 얻은 재구성 좌표와 팬톰 자체의 localizer와 재구성 알고리즘을 바탕으로 개발된 프로그램을 이용하여 얻은 좌표로 두 재구성 좌표의 비교 연구를 수행하였다. 정확성이 검증되고 장기의 정보가 담긴 CT의 좌표는 자체 개발된 프로그램으로 2 차원의 필름 좌표로 변환되었다. 본 연구에 사용된 모든 프로그램은 ILD 5.5를 사용하여 개발되었다. 결과 : 두 시스템의 좌표 비교 결과 x, y 축은 차이가 2mm 이내로 비교적 정확한 실험 결과를 얻을 수 있었고, z 축의 경우 CT 슬라이드의 굵기에 따라 2mm-3mm 이내의 차이가 있음을 관찰할 수 있었다. z 축을 제외한 좌표의 차이는 획득한 영상에서 컴퓨터로 좌표를 옮기는 localizer 좌표 선택 과정에 발생했을 것으로 예상된다. 또한, 이 검증된 좌표와 개발된 프로그램을 이용하여 우리는 CT의 좌표를 2차원의 필름 좌표로 정확하게 변환할 수 있었다. 결론 : 이 연구로부터 기존의 C-arm 재구성 방법과 CT 재구성 방법의 비교를 통해 각 치료 기기의 신뢰성을 직접 확인할 수 있었으며, 비교를 통해 검증된 CT의 좌표를 필름 좌표로 변환시킴으로서, 각 시스템의 장점만을 결합한 효과적인 치료 계획을 세울 수 있는 가능성을 제시하였다. 또한 물과 아크릴을 사용한 비교적 간단하고 경제적인 방법으로 C-arm, CT 그리고 MRI에 모두 이용 가능한 팬톰을 제작하여 쉽고 정확하게 위치를 확인할 수 있었다. 더 나아가, 본 연구에서 제작된 자궁경부암 팬톰은 근접치료를 포함하여 관련 팬톰 개발에 도움을 줄 수 있을 것으로 예상된다.

• The Journal of the Acoustical Society of Korea
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• v.21 no.2
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• pp.134-141
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• 2002

In this paper, a free wake analysis based on the curved vortex element and CVC wake model is used to predict the aerodynamic performance and noise for HAWT. Also for prediction of RPM, a maximum value through a quadratic regression was suggested. And for a noise prediction, the broadband noise prediction method based on experimental equation was used. The curved vortex element uses a BCVE and an SIVE instead of a straight vertex element. In the CVC wake model, the vortex strengths are assumed to be constant along a span and a vortex filament. The free wake structure made by the curved vortex element and CVC was substituted for a vortex lattice, so it has an advantage for the less calculation time and a depiction of accurate wake structure. For the verification of this program, calculated results are compared with Mr. Kim's experiment model and Zond Z-40FS for performance and with WTS-4 and USWP models for noise. Good agreements are obtained between the predicted and the measured data for the performance and far-field noise spectra.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.39 no.3
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• pp.283-289
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• 2015

In this study, the lightweight design of a brake bracket for a composite bogie was studied by considering two brake bracket models with thicknesses of 12t and 9t, respectively. For achieving this goal, finite element analysis and topology optimization were conducted. Firstly, the largest cross-sectional areas of the vertical and horizontal plates of the brake bracket were selected as the design variables. As the constraint, the Z-axis displacement of the brake bracket was increased by 2.5 units from the initial displacement value. The minimum volume fraction of the design regions was chosen as the objective function. The full model comprised a composite bogie frame and brackets attached together. However, to reduce the analysis time, 1D beam elements were used instead of the composite bogie frame by ensuring its equivalence with the full model. The result revealed that the weights of the 12t and 9t models of the brake bracket were reduced to 60 kg and 31 kg, respectively.

• Journal of computational fluids engineering
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• v.6 no.1
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• pp.21-30
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• 2001

A numerical study on the similarity of the developing laminar flows between in a straight duct rotating about an axis perpendicular to that of the duct and in a stationary curved duct was carried out. In order to clarify the analogy of two flows, dimensionless parameters K/sub LR/ = Re/(equation omitted) and Rossby number, Ro, in a rotating straight duct were used as a set corresponding to Dean number K/sub LC/ = Re/(equation omitted), and curvature ratio, λ, in a stationary curved duct. For the large values of Ro and λ, it is shown that the flow field satisfies the 'asymptotic invariance property', that is, there are strong quantitative similarities between the two flows such as flow patterns, friction factors, and maximum axial velocity magnitudes for the same values of K/sub LR/ and K/sub LC/ if they are correlated with dimensionless axial distances Z/sub R/ = z/(equation omitted) for a rotating duct flow and Z/sub C/ = z/(equation omitted) for a stationary curved duct flow.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2005.05a
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• pp.468-472
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• 2005

In this paper, the static and dynamic stiffness of the air bearing stage for micro-micro machine tool are examined experimentally. For stiffness and precision concerns, air bearing stages are adapted for 3-axis micro-milling machine which is size of $200x200\;mm^2$. The air bearings in the stage are preloaded by permanent magnets to achieve desired bearing clearance and stiffness for vertical direction. As the stiffness of the air bearing is primary interests, static stiffness test were performed on XY stage in Z direction and Z column in Y direction. Dynamic test were performed on XY stage and Z column, respectively. Both static and dynamic tests were performed in different air pressure conditions. The vertical stiffness of XY stage is about 9 N/ pm where Y stiffness of Z column is much smaller as $1\;N/{\mu}m$ because of the large moment generated by Y force on the column.

• Journal of the Semiconductor & Display Technology
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• v.21 no.4
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• pp.132-137
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• 2022

In this paper, we have studied the quadrature error reduction for the single drive 3-axis MEMS Gyroscope. There was a limitation of the previous study which is the z-axis quadrature error was large. To reduce this value, design methodologies were presented. And the methodologies included a different mesh application, z-rate spring structure change, and mass compensation for balancing of the structure. We conducted the modal analysis, drive mode analysis and sense mode analysis using COMSOL Multiphysics. As a result, a drive resonant frequency was 26003 Hz, with the x-sense, y-sense, z-sense being 26749 Hz, 26858 Hz, 26920 Hz, respectively. And the Mechanical sensitivity was computed at 2000 degrees per second(dps) input angular rate while the sensitivity for roll, pitch, and yaw was computed 0.011, 0.012, and 0.011 nm/dps respectively. And z-axis quadrature error was successfully improved, 2.78 nm to 0.95 nm, which the improvement rate was about 66 %.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.16 no.3
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• pp.251-260
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• 2003

A three dimensional (3-D) method of analysis is presented for determining the free vibration frequencies and mode shapes of deep, tapered rods and beams with circular cross section. Unlike conventional rod and beam theories, which are mathematically one-dimensional (1-D), the present method is based upon the 3-D dynamic equations of elasticity. Displacement components u/sup r/, u/sub θ/ and u/sub z/, in the radial, circumferential, and axial directions, respectively, are taken to be sinusoidal in time, periodic in , and algebraic polynomials in the r and z directions. Potential (strain) and kinetic energies of the rods and beams are formulated, the Ritz method is used to solve the eigenvalue problem, thus yielding upper bound values of the frequencies by minimizing the frequencies. As the degree of the polynomials is increased, frequencies converge to the exact values. Convergence to four-digit exactitude is demonstrated for the first five frequencies of the rods and beams. Novel numerical results are tabulated for nine different tapered rods and beams with linear, quadratic, and cubic variations of radial thickness in the axial direction using the 3D theory. Comparisons are also made with results for linearly tapered beams from 1-D classical Euler-Bernoulli beam theory.