• Proceedings of the KSRS Conference
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• v.1
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• pp.126-129
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• 2006

The marine environment is under considerable threat from intentional or accidental oil spills, ballast water discharged, dredging and infilling for coastal development, and uncontrolled sewage and industrial wastewater discharges. Monitoring spills and illegal oil discharges is an important component in ensuring compliance with marine protection legislation and general protection of the coastal environments. For the monitoring task an image processing system is needed that can efficiently perform the detection and the tracking of oil spills and in this direction a significant amount of research work has taken place mainly with the use of radar (SAR) remote sensing data. In this paper the level set image segmentation technique was tested for the detection of oil spills. Level set allow the evolving curve to change topology (break and merge) and therefore boundaries of particularly intricate shapes can be extracted. Experimental results demonstrated that the level set segmentation can be used for the efficient detection and monitoring of oil spills, since the method coped with abrupt shape’s deformations and splits.

• Structural Engineering and Mechanics
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• v.52 no.1
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• pp.115-136
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• 2014

In this study, an extended Kantorovich method, employing multi-term displacement functions, is applied to analyze the vibration problem of symmetrically laminated plates with arbitrary boundary conditions. The vibration behaviors of laminated plates are determined based on the variational principle of total energy minimization and the iterative Kantorovich method. The out-of-plane displacement is represented in the form of a series of a sum of products of functions in x and y directions. With a known function in the x or y directions, the formulation for the variation of total potential energy is transformed to a set of governing equations and a set of boundary conditions. The equations and boundary conditions are then numerically solved for the natural frequency and vibration mode shape. The solutions are verified with available solutions from the literature and solutions from the Ritz and finite element analysis. In most cases, the natural frequencies compare very well with the reference solutions. The vibration mode shapes are also very well modeled using the multi-term assumed displacement function in the terms of a power series. With the method used in this study, it is possible to solve the angle-ply plate problem, where the Kantorovich method with single-term displacement function is ineffective.

• Journal of the Korean Magnetics Society
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• v.1 no.2
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• pp.79-84
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• 1991

A variational approach employing localized functional is presented to solve alternating magnetic field problems with open boundary. The functional used in the approach consists of the domain integral of finite element region only and the boundary integral of the interfacial boundary between the finite and infinite element regions. The boundary integral is obtained by transforming the infinite domain integral for the infinite element region into the interfacial boundary integral. The proposed algorithm is then applied to a simple two-dimensional problem where the analytic solutions are available. It is shown that the algorithm makes it possible to yield good agreements between the numerical and analytic solutions. and that it requires less computer storage memory and computation time than the conventional finite element method due to the reduction of the computing region.

• Journal of the Korean earth science society
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• v.36 no.5
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• pp.460-475
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• 2015

A number of heavy rainfall events on the Korean Peninsula are indirectly influenced by tropical cyclones (TCs) when they are located in southeastern China. In this study, a heavy rainfall case in the middle Korean region is selected to examine the influence of typhoon simulation performance on predictability of remote rainfall over Korea as well as direct rainfall over Taiwan. Four different numerical experiments are conducted using Weather Research and Forecasting (WRF) model, toggling on and off two different improvements on typhoon in the model initial condition (IC), which are TC bogussing initialization and dropwindsonde observation data assimilation (DA). The Geophysical Fluid Dynamics Laboratory TC initialization algorithm is implemented to generate the bogused vortex instead of the initial typhoon, while the airborne observation obtained from dropwindsonde is applied by WRF Three-dimensional variational data assimilation. Results show that use of both TC initialization and DA improves predictability of TC track as well as rainfall over Korea and Taiwan. Without any of IC improvement usage, the intensity of TC is underestimated during the simulation. Using TC initialization alone improves simulation of direct rainfall but not of indirect rainfall, while using DA alone has a negative impact on the TC track forecast. This study confirms that the well-suited TC simulation over southeastern China improves remote rainfall predictability over Korea as well as TC direct rainfall over Taiwan.

• Journal of The Korean Astronomical Society
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• v.29 no.1
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• pp.43-51
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• 1996

We present test results of time-series CCD photometry to investigate the photometric precision of the BOAO (Bohyunsan Optical Astronomy Observatory) 1.8m telescope. A well-known field of the old open cluster M67, which includes two pulsating blue stragglers and two W UMa type binaries, was monitored for 3.5 hours on February 22, 1996. We have collected 148 V frames and 3 B frames. Photometric noises which consist mainly of photon noise and scintillation noise, were lowered down to about 1.9 mmag for stars of $10.\;^m5$ in M67 with exposure time of 20 seconds. From the C-M diagram for M67, a number of observational properties were derived; E(B-V) = 0.03, (V-Mv)o = 9.6, Age = 4 Gyr. We obtained light curves for four known variable stars and confirmed their variational characteristics. The pulsating blue stragglers show a low amplitude (about 0.01 mag) of light variation.

• Journal of Korea Game Society
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• v.17 no.1
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• pp.89-98
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• 2017

This paper presents a novel ARAP (as-rigid-as-possible) approach to real-time simulation of physics-based deformation. To cope with one, two and three dimensional deformable bodies in an efficient, robust and uniform manner, we introduce a deformation graph of oriented particles and formulate the corresponding ARAP deformation energy. For stable time integration of the oriented particles, we develop an implicit integration scheme formulated in a variational form. Our method seeks the optimal positions and rotations of the oriented particles by iteratively applying an alternating local/global optimization scheme. The proposed method is easy to implement and computationally efficient to simulate complex deformable models in real time.

• The Proceeding of the Korean Institute of Electromagnetic Engineering and Science
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• v.6 no.2
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• pp.35-44
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• 1995

In this paper, the single E-plane structure which is inserted in the slot of waveguide tube for good yield has been proposed and analyzed by the variational method. A CAD program for designing of the narrow-band waveguide bandpass filters has been developed by the passband correction method with filter synthesis theory. Using the developed CAD program, 0.02dB equi-ripple Chebyshev type 5-section bandpass filter is designed at the center frequency of 3.82GHz, fabricated with tunable structure. The experimental results show good agreements with the theoretical results.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.18 no.7
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• pp.589-593
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• 2005

The electronic states of ZnO doped with Al, Ga and In, which belong to III family elements in periodic table, were calculated using the density functional theory. In this study, the calculation was performed by two Programs; the discrete variational Xa (DV-Xa) method, which is a sort of molecular orbital full potential method; Vienna Ab-initio Simulation Package (VASP), which is a sort of pseudo potential method. The fundamental mixed orbital structure in each energy level near the Fermi level was investigated with simple model using DV-Xa. The optimized crystal structures calculated by VASP were compared to the measured structures. The density of state and the energy levels of dopant elements were shown and discussed in association with properties.

• Journal of Environmental Science International
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• v.15 no.5
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• pp.447-459
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• 2006

Long-term trends and distribution patterns of water quality were investigated in the Cheonsu Bay of Korea from 1983 to 2004. Water samples were collected at 4 stations and physicochemical parameters were analyzed including water temperature, salinity, suspended solids (SS), chemical oxygen demand (COD), dissolved oxygen (DO) and nutrients. Spatial distribution patterns were not clear between stations but the seasonal variations were distinctive except COD, SS and nitrate. Twenty two year long-term trend analysis by PCA revealed the significant changes in water quality in the study area. Water quality during 1980's and early 1990's showed high SS, low nutrients and low COD which increased during the mid and late 1990's and early 2000's. Overall water duality in the Cheonsu Bay indicated the increase in nutrients and COD concentration.

• ETRI Journal
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• v.21 no.4
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• pp.65-82
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• 1999

We present a calculation model for an improved quantitative theoretical analysis of electronic and optical properties of strained-piezoelectric[111] InGaAs/GaAs superlattices (SLs). The model includes a full band-coupling between the four important energy bands: conduction, heavy, light, and spin split-off valence bands. The interactions between these and higher lying bands are treated by the k ${\cdot}$ p perturbation method. The model takes into account the differences in the band and strain parameters of constituent materials of the heterostructures by transforming it into an SL potential in the larger band-gap material region. It self-consistently solves an $8{\times}8$ effective-mass $Schr{\ddot{o}}dinger$ equation and the Hartree and exchange-correlation potential equations through the variational procedure proposed recently by the present first author and applied to calculate optical matrix elements and spontaneous emission rates. The model can be used to further elucidate the recent theoretical results and experimental observations of interesting properties of this type of quantum well and SL structures, including screening of piezoelectric field and its resultant optical nonlinearities for use in optoelectronic devices.