• 한국전산유체공학회:학술대회논문집
• /
• 1999.11a
• /
• pp.48-58
• /
• 1999

The Characteristic Flux Difference Splitting (CFDS) scheme designed to adapt the characteristic boundary conditions at the wall and inflow/outflow boundary planes satisfies Roe's property U, although the CFDS Jacobian matrix is decomposed by a product of elaborate transformation matrices and explicit eigenvalue matrix. When the CFDS algorithm, thus a variant of Roe's scheme, is applied straightforwardly to hypersonic flows over a blunt body, the strong bow shock gradually breaks down near the stagnation point. This numerical instability is widely observed by many researchers employing flux-difference method, known in the literature as the carbuncle phenomenon. Many remedies have been proposed and resulted in partial cures. When the idea of Sanders et al. which identifies the minimum eigenvalues near the discontinuity present is applied to CFDS method, it is shown that the instability problem can be controlled successfully. A few flux splitting methods have also been tested and results are compared against the Nakamori's Mach 8 blunt body flow.

• Journal of the Institute of Electronics Engineers of Korea TC
• /
• v.45 no.2
• /
• pp.92-96
• /
• 2008

Practical communication systems need to operate at various different rates. This paper describes and analyzes low-density parity check codes for various different rates. From a specific mother code, it allows LDPC codes for different rate. The advantage of this technique is that each different rate LDPC codes have a same block length as mother code though the rate changes so it can make up for the weak points of puncturing and shortening which reduce their block length as the rate changes. Row-splitting method is to split the row, so that the rate changes from a higher rate to lower rate and cause of its own property, it can overcome the defect of row-combining method.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2007.11a
• /
• pp.122-123
• /
• 2007

Single crystal $AgGaSe_2$ layers were grown on thoroughly etched semi-insulating GaAs(100) substrate at $420^{\circ}C$ with hot wall epitaxy (HWE) system by evaporating $AgGaSe_2$ source at $630^{\circ}C$. The temperature dependence of the energy band gap of the $AgGaSe_2$ obtained from the absorption spectra was well described by the Varshni's relation, $E_g$(T)=1.9501 eV - $(8.79{\times}10^{-4}\;eV/K)T^2$/(T+250 K). The crystal field and the spin-orbit splitting energies for the valence band of the $AgGaSe_2$ have been estimated to be 0.3132 eV and 0.3725 eV at 10 K, respectively, by means of the photocurrent spectra and the Hopfield quasicubic model. These results indicate that the splitting of the ${\Delta}so$ definitely exists in the ${\Gamma}_5$ states of the valence band of the $AgGaSe_2$. The three photocurrent peaks observed at 10 K are ascribed to the $A_{1^-},\;B_{1^-},\;and\;C_{1^-}$exciton peaks for n=1.

• Journal of the Korean Mathematical Society
• /
• v.54 no.6
• /
• pp.1841-1851
• /
• 2017

Motivated by the Bloch-Beilinson conjectures, Voisin has made a conjecture concerning zero-cycles on self-products of Calabi-Yau varieties. We reformulate Voisin's conjecture in the setting of $hyperk{\ddot{a}}hler$ varieties, and we prove this reformulated conjecture for one family of $hyperk{\ddot{a}}hler$ fourfolds.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.30 no.5A
• /
• pp.436-444
• /
• 2005

Unitary matrix modulation (UMM) is investigated in multiple antennas system that is called unitary space-time modulation (USTM). In an OFDM, the diagonal components of UMM with splitting over the coherence bandwidth (UMM-S/OFDM) have been proposed. Recently LDPC code is strongly attended and studied due to simple decoding property with good error correction property. In this paper, we propose LDPC coded UMM-S/OFDM for increasing the system performance. Our proposed system can obtain frequency diversity using UMM-S/OFDM like USTM/OFDM, and large coding gain using LDPC code. The superior characteristics of the proposed UMM-S/OFDM are demonstrated by extensive computer simulations in multi-path Rayleigh fading channel.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.14 no.1
• /
• pp.102-108
• /
• 2010

The main objective of this study was to evaluate the effect of recycled PET (RPET) fiber made from waste PET bottles to examine application on concrete member. To evaluate the reinforcement effect of RPET fiber in concrete member, experimental tests were performed, such as mechanical property tests (compressive strength, modulus of elasticity and splitting tensile strength) and drying shrinkage test. In mechanical property tests, compressive strength and modulus of elasticity in concrete mixed with RPET fiber gradually decreased, but splitting tensile strength gradually increased as volume fraction of fiber increased. In drying shrinkage test, free drying shrinkage increased. In restrained case, in contrast, crack occurrence was delayed because of tensile resistance increase by RPET fiber. The comparison of RPET and PP fiber added concrete specimen's properties showed that two materials had similar properties. In conclusion, RPET fiber is an alternative material of PP fiber, even finer for its excellence in eco-friendliness due to the recycling of waste PET bottles and its possible contribution to the pollution declination.

• Bulletin of the Korean Chemical Society
• /
• v.35 no.9
• /
• pp.2813-2817
• /
• 2014

A new magnetic semiconductor material was synthesized to enable separation after a liquid-type photocatalysis process. Core@shell-structured $CuFeS_2@TiO_2$ magnetic nanoparticles were prepared by a combination of solvothermal and wet-impregnation methods for photocatalysis applications. The materials obtained were characterized using X-ray diffraction, transmission electron microscopy, ultraviolet-visible, photoluminescence spectroscopy, Brunauer-Emmett-Teller surface area measurements, and cyclic voltammetry. This study confirmed that the light absorption of $CuFeS_2$ was shifted significantly to the visible wavelength compared to pure $TiO_2$. Moreover, the resulting hydrogen production from the photo-splitting methanol/water solution after 10 hours was more than 4 times on the core@shell structured $CuFeS_2@TiO_2$ nanocatalyst than on either pure $TiO_2$ or $CuFeS_2$.

• The KIPS Transactions:PartB
• /
• v.9B no.4
• /
• pp.501-508
• /
• 2002

In this paper, we propose a content-based image retrieval using the color ratio and moment of object region. We acquire an optimal spatial information by the region splitting that utilizes horizontal-vertical projection and dominant color. It is based on hypothesis that an object locates in the center of image. We use color ratio and moment as feature informations. Those are extracted from the splitted regions and have the invariant property for various transformation, and besides, similarity measure utilizes a modified histogram intersection to acquire correlation information between bins in a color histogram. In experimental results, the proposed method shows more flexible and efficient performance than existing methods based on region splitting.

• Transactions of the Korean hydrogen and new energy society
• /
• v.17 no.1
• /
• pp.21-30
• /
• 2006

[ $M/Fe_2O_3$ ] (M=Rh, Ce and Zr) mixed oxides were prepared using urea method to develop a medium for chemical hydrogen storage by their redox cycles. And their redox behaviors by repeated cycles were studied using temperature programmed reaction(TPR) technique. Additives such as Rh, Ce and Zr were added to iron oxides in order to lower the reaction temperature for reduction by hydrogen and re-oxidation by water-splitting. From the results, concentration of urea used as a precipitant had little effect on particle size and reduction property of iron oxide. TPR patterns of iron oxide consisted of two reduction peaks due to the course of $Fe_2O_3\;{\rightarrow}\;Fe_3O_4\;{\rightarrow}\;Fe$. The results of repeated redox tests showed that Rh added to iron oxide have an effect on lowering the re-oxidation temperature by water-splitting. Meanwhile, Ce and Zr additives played an important role in prevention of deactivation by repeated cycles. Finally, Fe-oxide(Rh, Ce, Zr) sample added with Rh, Ce and Zr showed the lowest re-oxidation temperature by water-splitting and maintained high $H_2$ recovery in spite of the repeated redox cycles. Consequently, it is expected that Fe-oxide(Rh, Ce, Zr) sample can be a feasible medium for chemical hydrogen storage using redox cycle of iron oxide.

• Journal of the Korean Society for Nondestructive Testing
• /
• v.35 no.2
• /
• pp.150-156
• /
• 2015

In this study, the effects of different mix proportions and fire scenarios (exposure temperatures and post-fire-curing periods) on fire-damaged concrete were analyzed using a nonlinear resonance vibration method based on nonlinear acoustics. The hysteretic nonlinearity parameter was obtained, which can sensitively reflect the damage level of fire-damaged concrete. In addition, a splitting tensile strength test was performed on each fire-damaged specimen to evaluate the residual property. Using the results, a prediction model for estimating the residual strength of fire-damaged concrete was proposed on the basis of the correlation between the hysteretic nonlinearity parameter and the ratio of splitting tensile strength.