• Transactions of Materials Processing
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• v.8 no.5
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• pp.471-481
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• 1999

The properties of deformed products are generally dependent upon the distribution of microstureture. It is, therefore, necessary to make the distribution of microstureture uniform in order to achieve the best balance of properties in the final product. This is often a demanding task, even for conventional materials. It is become essential to achieving mechanical integrity and a desired combination of microstructure and properties. The objective mechanical integrity and a desired combination of microsttucture and properties. The objective of this study is to design the optimal die profile which can yield more uniform microstructure in hot extruded product. The microstructure evolution, such as dynamic and static recrystallization as well as grain growth, is investigated using the program com-bined with yada and Senuma's empirical equations and rigid-thermoviscoplastic finite element method. The die profile of hot extrusion is represented by Bezier-curve to define all available profile. In order to obtain the optimal die profile which yields uniform microstructure in the product the FPS(Flexible Polyhedron Search) method is applied to the present study. To validate the result of present study the experimental hot extrusion is performed and the result is compared with that of simulation.

• Journal of the Korean Society for Industrial and Applied Mathematics
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• v.11 no.2
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• pp.41-47
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• 2007

A fine segmentation algorithm is proposed for extracting objects in an image, which have both weak boundaries and highly non-convex shapes. The image has simple background colors or simple object colors. Two concepts, geometric attraction-driven flow (GADF) and edge-regions are combined to detect boundaries of objects in a sub-pixel resolution. The main strategy to segment the boundaries is to construct initial curves close to objects by using edge-regions and then to make a curve evolution in GADF. Since the initial curves are close to objects regardless of shapes, highly non-convex shapes are easily detected and dependence on initial curves in boundary-based segmentation algorithms is naturally removed. Weak boundaries are also detected because the orientation of GADF is obtained regardless of the strength of boundaries. For a fine segmentation, we additionally propose a local region competition algorithm to detect perceptible boundaries which are used for the extraction of objects without visual loss of detailed shapes. We have successfully accomplished the fine segmentation of objects from images taken in the studio and aphids from images of soybean leaves.

• Journal of The Korean Astronomical Society
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• v.34 no.4
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• pp.333-335
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• 2001

We study the properties of supernova (SN) driven interstellar turbulence with a numerical magnetohydrodynamic (MHD) model. Calculations were done using the RIEMANN framework for MHD, which is highly suited for astrophysical flows because it tracks shocks using a Riemann solver and ensures pressure positivity and a divergence-free magnetic field. We start our simulations with a uniform density threaded by a uniform magnetic field. A simplified radiative cooling curve and a constant heating rate are also included. In this radiatively-cooling magnetized medium, we explode SNe one at a time at randomly chosen positions with SN explosion rates equal to and 12 times higher than the Galactic value. The evolution of the system is basically determined by the input energy of SN explosions and the output energy of radiative cooling. We follow the simulations to the point where the total energy of the system, as well as thermal, kinetic, and magnetic energy individually, has reached a quasi-stationary value. From the numerical experiments, we find that: i) both thermal and dynamical processes are important in determining the phases of the interstellar medium, and ii) the power index n of the $B-p^n$ relation is consistent with observed values.

• Journal of Magnetics
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• v.14 no.2
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• pp.75-79
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• 2009

Nickel (Ni) and ferrite ($Fe_3O_4$, $NiFe_2O_4$) nanoparticles were synthesized by LGC using both wire feeding (WF) and micron powder feeding (MPF) systems. Phase evolution and magnetic properties were then investigated. The Ni nanopowder included magnetic-ordered phases. The LGC synthesis yielded spherical particles with large coercivity while the abnormal initial magnetization curve for Ni indicated a non-collinear magnetic structure between the core and surface layer of the particles. Since the XRD pattern cannot actually distinguish between magnetite ($Fe_3O_4$) and maghemite (${\gamma}-Fe_2O_3$) as they have a spinel type structure, the phase of the iron oxide in the samples was unveiled by $M{\ddot{o}}ssbauer$ spectroscopy. The synthesized Ni-ferrite consisted of single domain particles, including an unusual ionic state. The synthesized nanopowder bore an active surface due to the defects that affected abnormal magnetic properties.

• Journal of The Korean Astronomical Society
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• v.39 no.1
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• pp.25-30
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• 2006

We completed four color light curves of the near-contact binary CN And during three nights from September to December 2004 using the 61-cm reflector and BV RI filters at Sobaeksan Observatory. We determined four new times of minimum light (two timings for primary eclipse, two for secondary). Newly obtained BV RI light curves and the radial velocity curves from Rucinski et a1. (2000) were simultaneously analyzed to derive the system parameters of CN And. We used the semi-detached mode 4 of the 2003-version of the Wilson-Devinney binary model, and interpreted the asymmetry of the light curve by introducing two spots; a cool spot on the primary component and a hot spot on the secondary component. New photometric parameters are not much different from those of Cicek et a1. (2005), and it is considered that the system is in the era of broken contact. From the orbital period study with all available timings including our data, we found a continous period decrease with a rate of $P_{obs}=--1.82{\times}10^{-7}\;d\;yr^{-1}$ that can be explained with two possible mechanisms. We think the most likely cause of the period decrease is a thermal mass transfer from the primary to the secondary component, rather than angular momentum loss due to a magnetic stellar wind.

• The Bulletin of The Korean Astronomical Society
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• v.41 no.1
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• pp.64.4-65
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• 2016

Observations of the early photons from evolution of optical afterglows or internal shock provides the crucial clues on the nature of the bursts and environments. Hundreds of GRBs afterglow observations in multi-wavelength region have been made mainly thanks to the fast (~ 60 seconds after the trigger) localisation GRB by Swift and its fast alert to the ground telescope. It helps to improve our understandings tremendously, however many enigmas still remain, such as burst mechanism, transition prompt emission to the afterglow, early optical flash, rise phase of the early optical light curve and some missing afterglows. They could be addressed by fast slewing and multi colour and IR follow-up by future telescopes. The primary aim of UFFO/Lomonosov is to follow up optical fast ever, within a couple of seconds after trigger by onboard X-ray telescope. Its optical FOV is $30{\times}30degrees$. As a key instrument, the Slewing Mirror to redirect the optical beam from GRBs rapidly to the Ritchey-Chretien telescope. The status and launch schedule of the UFFO/Lomonosov and its test performance will be reported and prospects for the next missions will be discussed.

• The Transactions of the Korea Information Processing Society
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• v.4 no.3
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• pp.792-801
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• 1997

In this paper we propose an algorithm which fits a surface to noise-corrupted data points using an aceive sur-vace with global deformations.It is 3-dimensional surface extension of our precious works on 2-dimensional curve modell[11,12].We use fimite differences,and represent shapes of surface as global transfromation suring evolution based on the ballon [odel[2,3]which allows partial inflation or deflation by using niegborhood'sextermal foreces on each node points.At first,we make local deformations based on the balloon [odel,and then the blobal transformation from the surface before deformations to the defomed surface is calcualted by the deterministic lest squre method,finally we apply the global transformation to the surface before deformations.In experiments we fit a surface(elliposid,B-spline)to noise-corrupted 3D data points using the active surface with affine deformations.

• Journal of the Earthquake Engineering Society of Korea
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• v.10 no.3 s.49
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• pp.35-45
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• 2006

The simulation of tsunami using detailed bathymetry and topography is required to establish the countermeasure of disaster mitigation and the tsunami hazard map. In this study, a simulation of the 1993 tsunami event in the East Sea using parallel finite element model, which is possible to simulate with suitable accuracy by the Beowulf parallel computation method, is performed to produce detailed features of coastal inundation. Results of simulation are compared with measured data. The evolution of statistic distribution of tsunami heights is studied numerically and the distribution functions of tsunami heights show a tendency to the log-normal curve along coastal area.

• The Bulletin of The Korean Astronomical Society
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• v.37 no.2
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• pp.141.2-141.2
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• 2012

We present photometric solutions of the 26,212 eclipsing binaries discovered in the LMC by Graczyk et al. (2011). They published that 70 percent of a total are detached systems. Another 25 and 5 percent are semi-detached and contact binaries, respectively. We discovered that 21 percent of 26,121 eclipsing binary stars are eccentric orbit systems. The binary star distribution in the LMC is different from those of the Galactic center direction (Bade window). It is very interesting that there are only 5 of 357 (2 percent) stars have eccentric orbit in the Galactic Center (Kang 2011). We selected the light curve of 18,274 detached systems. Then we estimated the fundamental parameters on the basis of their photometric solutions and the semi-major-axis (a) assuming the distance modulus to the LMC~18.50. We compared the estimated fundamental parameters with an empirical mass-luminosity relation and consistency between mass-radius relation base on stellar evolution model in the low metallicity (Z=0.008) by Bertelli et al. (2009). This method allows for independent determine of the fundamental parameters of the eclipsing binaries in the LMC without the radial velocity curves.

• Steel and Composite Structures
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• v.20 no.3
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• pp.719-729
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• 2016

There are great needs of simple but reliable mechanical nonlinear behavior analysis and performance evaluation method for frames constructed by steel and concrete composite beams or columns when the structures subjected extreme loads, such as earthquake loads. This paper describes an approach of simplified macro-modelling for composite frames consisting of steel-concrete composite beams and CFST columns, and presents the performance evaluation procedure based on the pushover nonlinear analysis results. A four-story two-bay composite frame underground is selected as a study case. The establishment of the macro-model of the composite frame is guided by the characterization of nonlinear behaviors of composite structural members. Pushover analysis is conducted to obtain the lateral force versus top displacement curve of the overall structure. The identification method of damage degree of composite frames has been proposed. The damage evolution and development of this composite frame in case study has been analyzed. The failure mode of this composite frame is estimated as that the bottom CFST columns damage substantially resulting in the failure of the bottom story. Finally, the seismic performance of the composite frame with high strength steel is analyzed and compared with the frame with ordinary strength steel, and the result shows that the employment of high strength steel in the steel tube of CFST columns and steel beam of composite beams benefits the lateral resistance and elasticity resuming performance of composite frames.