• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 한국소성가공학회 2009년도 추계학술대회 논문집
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• pp.45-52
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• 2009

The research on miniature devices based on non-silicon materials, in particular polymeric materials has been attracting more and more attention in the research field of the micro/nano fabrication in recent years. Lost of applications and many literatures have been reported. However, the study on the micro thermal imprint process of glassy polymer is still not systematic and inadequate. The aim of this research I to obtain a numerical material model for an amorphous glassy polymer, polycarbonate (PC), which can be used in finite element analysis (FEA) of the micro thermal imprint process near the glass transition temperature (Tg). An understanding of the deformation behavior of the PC specimens was acquired by performing tensile stress relaxation tests. The viscoelastic material model based on generalized Maxwell model was introduced for the material near Tg to establish the FE model based on the commercial FEA code ABAQUS/Standard with a suitable set of parameters obtained for this material model form the test data. As a result, the feasibility of the established viscoelastic model for PC near Tg was confirmed and this material model can be used in FE analysis for the prediction and improvement of the micro thermal imprint process for pattern replication.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• 제41권3호
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• pp.185-193
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• 2013

The plume infrared signature effects at various flight conditions of aircraft were investigated for the purpose of reducing infrared signature level. The nozzle of a virtual subsonic unmanned combat aerial vehicle was designed through a performance analysis. Nozzle and associated plume flowfields were first analyzed using a density-based CFD code and plume IR signature was then calculated on the basis of the narrow-band model. Finally, qualitative information for the plume infrared signature characteristics was obtained through the analysis of the IR signature effects at various flight conditions.

• Archives of design research
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• 제19권3호
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• pp.207-218
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• 2006

21st century is called digital and information era. The visual communication becomes more important than any other centuries. Visual communication design has been represented in varied images from ancient society up until the present time. Especially graphic design, which has experienced artistic upheaval from modernism and postmodernism, has been enabled to deliver messages in a more developed and sensuous appearances. Deconstructionist design wasn't well received by modernism, an advocate of practicality and effectiveness; however, as the beginning of subsequent postmodernism, it started to earn a warm welcome from a number of designers. Postmodernism made it possible for deconstruction to be a new paradigm appreciating neutral respect for varied expressions and designers' idiosyncrasy. Corresponding to this new trend, Edward Fella published his artwork 'Letters on America', which introduced a variety of vernacular design works in America. It was the result of years of research, and included materials which were not something completely new to field of communication design but rather symbolic, deconstructive images available everywhere around us. Deconstruction broke away from the previous modernism's unity and standards, and sought to achieve a new tensional deliverance. As a consequence, images were created in destructive and incomplete forms. Graphic design also complied with this new code and its advent fascinated the artists in the fields of advertising, editorial and poster designs. This paper contends that contemporary graphic design still maintains a deconstructive representation, examines its locality in design works from an aesthetic viewpoint, and researches theoretical approaches to deconstructionist and case studies conducted domestically. There has been incessant critical contradiction in terms of the heritage of deconstruction. I would like to present you with a moment in which you can struggle to decide whether it is a result of an effort to get away from modernism or an offspring of postmodernism.

• Journal of Radiation Protection and Research
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• 제47권3호
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• pp.111-133
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• 2022

The exciting advancement related to the "modeling of digital human" in terms of a computational phantom for radiation dose calculations has to do with the latest hype related to deep learning. The advent of deep learning or artificial intelligence (AI) technology involving convolutional neural networks has brought an unprecedented level of innovation to the field of organ segmentation. In addition, graphics processing units (GPUs) are utilized as boosters for both real-time Monte Carlo simulations and AI-based image segmentation applications. These advancements provide the feasibility of creating three-dimensional (3D) geometric details of the human anatomy from tomographic imaging and performing Monte Carlo radiation transport simulations using increasingly fast and inexpensive computers. This review first introduces the history of three types of computational human phantoms: stylized medical internal radiation dosimetry (MIRD) phantoms, voxelized tomographic phantoms, and boundary representation (BREP) deformable phantoms. Then, the development of a person-specific phantom is demonstrated by introducing AI-based organ autosegmentation technology. Next, a new development in GPU-based Monte Carlo radiation dose calculations is introduced. Examples of applying computational phantoms and a new Monte Carlo code named ARCHER (Accelerated Radiation-transport Computations in Heterogeneous EnviRonments) to problems in radiation protection, imaging, and radiotherapy are presented from research projects performed by students at the Rensselaer Polytechnic Institute (RPI) and University of Science and Technology of China (USTC). Finally, this review discusses challenges and future research opportunities. We found that, owing to the latest computer hardware and AI technology, computational human body models are moving closer to real human anatomy structures for accurate radiation dose calculations.

• Journal of Biomedical Engineering Research
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• 제25권2호
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• pp.89-95
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• 2004

Intensity-modulated radiation therapy (IMRT) often uses small beam segments. The heterogeneity effect is well known for relatively large field sizes used in the conventional radiation treatments. However, this effect is not known in small fields such as the beamlets used in IMRT. There are many factors that can cause errors in the small field i.e. electronic disequilibrium and multiple electron scattering. This study prepared geometrically regular heterogeneous phantoms, and compared the measurements with the calculations using the Convolution/Superposition algorithm and Monte Carlo method for small beams. This study used the BEAM00/EGS4 code to simulate the head of a Varian 2300C/D. The commissioning of a 6MV photon beam were performed from two points of view, the beam profiles and depth doses. The calculated voxel size was 1${\times}$1${\times}$2$\textrm{cm}^2$ with field sizes of 1${\times}$1$\textrm{cm}^2$, 2${\times}$2$\textrm{cm}^2$, and 5${\times}$5$\textrm{cm}^2$. The XiOTM TPS (Treatment Planning System) was used for the calculation using the Convolution/Superposition algorithm. The 6MV photon beam was irradiated to homogeneous (water equivalent) and heterogeneous phantoms (water equivalent ＋ air cavity, water equivalent ＋ bone equivalent). The beam profiles were well matched within :t1 mm and the depth doses were within ${\pm}$2%. In conclusion, the dose calculations of the Convolution/Superposition and Monte Carlo simulations showed good agreement with the film measurements in the small field.

• Journal of Society of Preventive Korean Medicine
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• 제19권3호
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• pp.45-55
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• 2015

Objective : The aim of this study was to survey the present utilization of pattern identification(PI) in the clinical field among Korean Medicine Doctors. Method : This survey was conducted from Oct. 1 to Oct. 31, 2014 by face-to-face interview using structured questionnaire. The subjects were 400 korean medicine doctors who worked in hospitals or clinics. The questionnaire consisted of two sections - a demographics section(i.e., sex, age, clinical experience, place of work, residence and so on) and the main research section(i.e., the PI utilization rate, the utilization of PI systems, the utilization of PI in the clinical domain and in the treatment domain, the correlation between utilization PI and so on). Results : This study revealed that subjects used the PI to 66.7% of their patients on average. The utilization rate of PI in patients was significantly higher for female physicians than for male physicians, for physicians worked in clinics than for physicians who worked in hospitals and for physicians with more than 10 years clinical experience than for physicians with less than 10 years clinical experience. In the utilization of PI systems, Visceral PI was most as 92.0%. There were significant difference on the PI utilization rate according to utilization of Meridian and Collateral PI, Triple Energizer PI, Defense, Qi, Nutrient and Blood PI, Six-Meridian PI and Six Excesses PI. As a result of analysing the PI utilization rate by clinical domain and in the treatment domain, the Treatment and the Drug Treatment showed the highest values. Among utilized PI systems, the correlation coefficients between Defense, Qi, Nutrient and Blood PI and Triple Energizer PI showed the highest value, but the correlation coefficients between Sasang Constitutional Medicine with the each PI showed substantially lower value. Conclusion : The results of this study demonstrate that usage of PI was higher than usage of U code(in KCD) usage in clinical field. we suggested that additional studies on using PI and developing more appropriate standardized tool should be conducted to widen scope of PI's utilization.

• Journal of radiological science and technology
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• 제39권4호
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• pp.571-575
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• 2016

Monte Carlo simulations are widely used as the most accurate technique for dose calculation in radiation therapy. In this paper, the GATE6(Geant4 Application for Tomographic Emission ver.6) code was employed to calculate the dosimetric performance of the photon beams from a linear accelerator(LINAC). The treatment head of a Varian 21EX Clinac was modeled including the major geometric structures within the beam path such as a target, a primary collimator, a flattening filter, a ion chamber, and jaws. The 6 MV photon spectra were characterized in a standard $10{\times}10cm^2$ field at 100 cm source-to-surface distance(SSD) and subsequent dose estimations were made in a water phantom. The measurements of percentage depth dose and dose profiles were performed with 3D water phantom and the simulated data was compared to measured reference data. The simulated results agreed very well with the measured data. It has been found that the GATE6 code is an effective tool for dose optimization in radiotherapy applications.

• Journal of Astronomy and Space Sciences
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• 제28권1호
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• pp.17-26
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• 2011

Bow shock, formed by the interaction between the solar wind and a planet, is generated in different patterns depending on the conditions of the planet. In the case of the earth, its own strong magnetic field plays a critical role in determining the position of the bow shock. However, in the case of Mars of which has very a small intrinsic magnetic field, the bow shock is formed by the direct interaction between the solar wind and the Martian ionosphere. It is known that the position of the Martian bow shock is affected by the mass loading-effect by which the supersonic solar wind velocity becomes subsonic as the heavy ions originating from the planet are loaded on the solar wind. We simulated the Martian magnetosphere depending on the changes of the density and velocity of the solar wind by using the three-dimensional magnetohydrodynamic model built by modifying the comet code that includes the mass loading effect. The Martian exosphere model of was employed as the Martian atmosphere model, and only the photoionization by the solar radiation was considered in the ionization process of the neutral atmosphere. In the simulation result under the normal solar wind conditions, the Martian bow shock position in the subsolar point direction was consistent with the result of the previous studies. The three-dimensional simulation results produced by varying the solar wind density and velocity were all included in the range of the Martian bow shock position observed by Mariner 4, Mars 2, 3, 5, and Phobos 2. Additionally, the simulation result also showed that the change of the solar wind density had a greater effect on the Martian bow shock position than the change of the solar wind velocity. Our result may be useful in analyzing the future observation data by Martian probes.

• Journal of Ship and Ocean Technology
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• 제11권2호
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• pp.10-25
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• 2007

With the sharp increase of the oil price, the issue of the energy saving requires even higher propulsive efficiency of the propellers. Traditionally the propellers have been designed with the criteria such as that of Lerbs optimum based on the lifting line theory and the empirical formulae of Lerbs and van Manen giving relations of the wake pitch with the wake non-uniformity. With the aid of the high speed computer, it is now possible to apply the time-consuming iterative approaches for the solution of the lifting surface problems. In this paper we formulate the variational problem to optimize the efficiency of the propeller operating in the given ship wake using the lifting surface method. The variational formulation relating the spanwise circulation distribution with the propulsive efficiency to be maximized is however non-linear in circulation distribution functions, thus the iterative method is applied to the quasi-linearized equations. The blade shape design also requires the iterative procedures, because the shape of the blade which is represented by the lifting surface is unknown a priori. The numerical code was validated with the DTNSRDC propeller 4119 which is well-known to be optimum in uniform inflow condition. In addition existing (well-designed) commercial propellers were selected and compared with the results of the open water tests and the self-propulsion tests.

• Journal of the Korean Society for Precision Engineering
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• 제19권8호
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• pp.92-99
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• 2002

This work investigated the optimal condition for an uniform deposition growth rate in the vertical cylindric CVD chamber. Heat transfer, surface chemical reaction and mass diffusion in the flow field of CVD chamber h,id been computed using Fluent v5.3 code. A SIMPLE based finite Volume Method (FVM) was adopted to solve the fully elliptic equations for momentum, temperature and concentration of a chemical species. The numerical analysis results show good agreements with the measurements obtained by N. Yoshikawa. The results obtained by the numerical analysis showed that the film growth rate in the center of a susceptor is increasing, as the inner flow approaches to the forced convection. To the contrast, as it approaches to the natural convection, that in the outside of a susceptor is increasing. As the Reynolds number increases, the uniformity may not hold due to the larger temperature gradient at a susceptor surface. Therefore, when the temperature gradient on the surface of a susceptor is zero, the film growth rate becomes uniform on most surface.