• Proceedings of the Korean Society of Broadcast Engineers Conference
• /
• 2009.11a
• /
• pp.263-266
• /
• 2009

H.264/AVC 표준의 화면내 부호화 방법은 화면내 예측을 통한 예측값과 현재 블록의 화소값의 차이를 변환 계수로 변환하고, 이를 양자화 및 엔트로피 부호화하는 순서로 부호화가 진행된다. 그러나 화면내 부호화 방법은 영상간의 시간적 상관성을 이용하지 않고 비교적 상관도가 낮은 공간적 상관성을 이용하기 때문에 화면간 부호화 방법에서는 발견되지 않는 flicker 효과가 발생하게 된다. 일반적으로 flicker 효과는 양자화 및 역양자화 과정에서 변환 계수값의 차이가 크게 증가하기 때문에 발생한다. 따라서 화면내 부호화 방법을 사용하면 flicker 효과로 인해 주관적인 화질이 크게 열화됨에도 불구하고, 이를 위한 해결책이 많지 않다. 본 논문에서는 flicker 효과를 정의하고 flicker 효과의 발생 이유를 분석한다. 이를 바탕으로 flicker 효과를 효과적으로 감소시킬 수 있는 양자화 방법을 제안한다.

• Korean Journal of Materials Research
• /
• v.5 no.3
• /
• pp.275-279
• /
• 1995

가돌리늄박막의 큐리온도를 비저항의 온도에 따른 변화를 측정함으로써 결정하였다. 이비저항 실험치에서 구한 큐리온도의 값은 기존의 자화도에서 구한 큐리 온도값과 잘 일치함을 보여준다. 또한 박막의 큐리온도 실험값들은 얇은 박막일수록 큐리온도가 낮아지는 두께에 따른 변화를 잘 보여주고 있다. 유한 축척이론에 의한 분석에서 임계지수 $\lambda$ 는 0.82 $\pm$ 0.15가 나왔으며 이 값은 이론치인 1.48과 일치하지 않는다. 이 사실은 다른 많은 실험에서 확인한 바와 일치하고 있다.

• Journal of the Korean Magnetics Society
• /
• v.4 no.4
• /
• pp.347-354
• /
• 1994

The structural change and magnetic properties of mechanically milled Fe-N and Mn-Al alloy powders have been investigated by XRD, TEM, VSM, $M\"{o}ssbauer$ spectroscopy and inelastic neutron scattering measurements. During milling of ${\gamma}'-Fe_{4}N$ powders, and fcc ${\gamma}'-Fe_{4}N$ phase is transformed to a bct ${\alpha}'-Fe(N)$ phase by stress-induced martensitic transformation, being accompanied by an initial increase in saturation magnetization. During annealing the bct ${\alpha}'-Fe(N)$ nanocrystalline phase which is obtained by mechanical grinding for a long time, an ${\alpha}'-Fe_{16}N_{2}$ phase partially appears as an intermediate phase at 673~773 K, causing an increase in saturation magnetization. During milling of Mn-45, 70 and 85 at.% Al mixed powders, Al atoms are partially solubilized into an ${\alpha}-Mn$ phase. The Al supersaturated ${\alpha}-Mn-type$ phases change from paramagnetic to ferromagnetic : the saturation magnetization is 11 emu/g for the as-milled Mn-70 at.% Al powders. Moreover, by removing almost all Al atoms from the as-milled Mn-85 at.% Al powders using chemical leaching, the saturation magnetization increases up to 36 emu/g. The above bct ${\alpha}'-Fe(N)$ and ferromagnetic ${\alpha}-Mn$ type alloys are the magnetic materials found for the first time, by using the present mechanochemical process.

• Journal of the Korean Magnetics Society
• /
• v.5 no.4
• /
• pp.275-280
• /
• 1995

The sites for $Fe^{+3}$ are partly substituted by $Co^{+2}$ and $Ti^{+4}$ cations to control coercivity of Ba-ferrite particles for use in high density magnetic recording. The substituted $Co^{+2}$ cation has very much different effects on magnetic properties and particle characteristics from that $Ti^{+4}$ cation has. The decrease in the coercivity with the $Co^{+2}$ substitution is attributed to the formation of excessive spinel-block(S-block) in pure Ba-ferrite crystal, while saturation magnetization is increased and the distributions of coercivity and particle size become broad. The substitution with the $Ti^{+4}$ decreases the sauration magnetization, but has less effect on a change in coercivity than the $Co^{+2}$. The $Ti^{+4}$ acts as a nucleation agent in amorphous phase of formulated compound, and consequently particle size and aspect ratio are decreased. Furthermore, the enhancement of substitution of the $Co^{+2}$ for the $Fe^{+3}$ sites in rhombohedral-block(R-block) by the $Ti^{+4}$ retards the nucleation of spinel phase of Ba-ferrite, which results in uniform magnetic properties of Ba-ferrite particles. It is suggested that the contents of the cations to be substituted for the $Fe^{+3}$ sites are optimized on the bases of magnetic properties and particle characteristics rather than on the base of electrical charge balance.

• Journal of the Korean Magnetics Society
• /
• v.16 no.2
• /
• pp.140-143
• /
• 2006

Single crystalline $CoFe_2O_4$ thin films on (100) MgO substrates were fabricated using a rf magnetron sputtering method. The deposited films were investigated for their crystallization by X-ray diffraction, Rutherford back-scattering spectroscopy and field emission scanning electron microscopy. When a cobalt ferrite film was deposited at the substrate temperature of $600^{\circ}C$, squared grains of about 200 nm were uniformly distributed in the film. However, the grains became irregular and their sizes also varied from 30 to 150 nm when the substrate temperature was $700^{\circ}C$. Hysteresis loops of a film deposited at $600^{\circ}C$ showed that the magnetically easy axis of the film was perpendicular to the substrate surface. Except for the squareness ratio, magnetic properties of the cobalt ferrite films grown by the present rf sputtering method were as good as those of the films prepared by a laser ablation method: The in-plane and perpendicular coercivities were 283 and 6800 Oe, respectively. As the thickness of the deposited film increased twice, the saturation magnetization became double but the coercivity remained unchanged. However, deposition of the Co ferrite films with a higher rf powder decreased the squareness ratio and the perpendicular coercivity of the films.

• Investigative Magnetic Resonance Imaging
• /
• v.3 no.2
• /
• pp.154-158
• /
• 1999

Purpose : The purpose of this study was to find the optimum TE value for enhancing $T_2^{*}$ weighting effect and minimizing the SNR degradation and to compare the BOLD effects according to the changes of TE in 1.5T and 3.0T MRI systems. Materials and Methods : Healthy normal volunteers (eight males and two females with 24-38 years old) participated in this study. Each volunteer was asked to perform a simple finger-tapping task (sequential opposition of thumb to each of the other four fingers) with right hand with a mean frequency of about 2Hz. The stimulus was initially off for 3 images and was then alternatively switched on and off for 2 cycles of 6 images. Images were acquired on the 1.5T and 3.0T MRI with the FLASH (fast low angle shot) pulse sequence (TR : 100ms, FA : $20^{\circ}$, FOV : 230mm) that was used with 26, 36, 46, 56, 66, 76ms of TE times in 1.5T and 16, 26, 36, 46, 56, 66ms of TE in 3.0T MRI system. After the completion of scan, MR images were transferred into a PC and processed with a home-made analysis program based on the correlation coefficient method with the threshold value of 0.45. To search for the optimum TE value in fMRI, the difference between the activation and the rest by the susceptibility change for each TE was used in 1.5T and 3.0T respectively. In addition, the functional $T_2^{*}$ map was calculated to quantify susceptibility change. Results : The calculated optimum TE for fMRI was $61.89{\pm}2.68$ at 1.5T and $47.64{\pm}13.34$ at 3.0T. The maximum percentage of signal intensity change due to the susceptibility effect inactivation region was 3.36% at TE 66ms in 1.5T 10.05% at TE 46ms in 3.0T, respectively. The signal intensity change of 3.0T was about 3 times bigger than of 1.5T. The calculated optimum TE value was consistent with TE values which were obtained from the maximum signal change for each TE. Conclusion : In this study, the 3.0T MRI was clearly more sensitive, about three times bigger than the 1.5T in detecting the susceptibility due to the deoxyhemoglobin level change in the functional MR imaging. So the 3.0T fMRI I ore useful than 1.5T.

• Applied Chemistry for Engineering
• /
• v.17 no.4
• /
• pp.420-425
• /
• 2006

Nano sized mixed metal hexagonal ferrite powders with improved magnetic properties have been prepared by sol-gel method using propylene oxide as a gelation agent. To obtain the desired ferrite, two different metal ions were used. One of the ions has only +2 formal charge. The key step in the processes is that hydrated $Ba^{2+}$ or $Sr^{2+}$ ions are hydrolyzed and condensed at the surface of the previously formed $Fe_{2}O_{3}$ gel. In this processes, all the reaction can be finished within a few minutes. The magnetic properties of the produced powder were improved by heat treatment. The highest values of the magnetic properties were achieved at temperature $150^{\circ}C$ lower than those of the previously published values. The highest observed values of coercivity and the saturation magnetization of Sr-ferrite and Ba-ferrite powder were 6198 Oe, 5155 Oe and 74.4 emu/g, 68.1 emu/g, respectively. The ferrite powder annealed at $700^{\circ}C$ showed spherical particle shapes. The resulting spheres which were formed by the aggregation of nanoparticles with size 3~5 nm have diameter around 50 nm. The powder treated at $800^{\circ}C$ showed hexagonal-shaped grains with crystallite size above 500 nm.

• Journal of the Korean Magnetics Society
• /
• v.10 no.2
• /
• pp.74-80
• /
• 2000

CoCr$_{x}$ Fe$_{2-x}$O$_4$(0.0$\leq$x$\leq$1.0) ferrites have been fabricated by sol-gel method. The crystallographic and magnetic properties of the samples were investigated by means of x-ray diffraction, scanning electron microscophy, Mossbauer spectroscopy and vibrating sample magnetometry. The structure of all the samples is cubic spinel type and the lattice constant decrease with increasing Cr content. The substituted Cr ions were located only in the B-site. The particle size also decreases with increasing Cr content. The Mossbauer spectra consist of two sextets due to Fe$^{3+}$ions at A- and B sites for 0.0$\leq$x$\leq$0.6, while, a paramagnetic doublet appears for 0.8$\leq$x$\leq$1.0. The magnetic hyperfine field decreases with increasing Cr content. The relaxation spectra was shown at 0.8$\leq$x$\leq$1.0 in CoCr$_{x}$ Fe$_{2-x}$O$_4$. The coercivity decreases drastically, while, the saturation magnetization decreases linearly with increasing x.ing x.

• Journal of Broadcast Engineering
• /
• v.11 no.4 s.33
• /
• pp.386-395
• /
• 2006

Multi-view video coding technology demands the very high efficient coding technologies, because it has to encode a number of video sequences which are achieved from a number of video cameras. For this purpose, multi-view video coding introduces the inter-view prediction scheme between different views, but it shows a limitation of coding performance enhancement by adopting only new prediction method. Accordingly, we are going to achieve the more coding performance by enhancing dequantizer perfermance. Multi-view video coding is implemented basically based on H.264/AVC and uses the same quantization/de-quantization method as H.264/AVC does. The conventional quantizer and dequantizer is designed with the assumption that input residual signal follows the Laplacian PDF. However, it doesn't follow the fixed PDF type always. This mismatch between assumption and real data causes degradation of coding performance. To solve this problem, we propose the efficient de-quantization method based on quantized coefficients distribution at decoder without extra information. The extensive simulation results show that the proposed algorithm produces maximum $1.5\;dB{\sim}0.6\;dB$ at high bitrate compared with that of conventional method.

• Korean Journal of Food Science and Technology
• /
• v.35 no.1
• /
• pp.67-71
• /
• 2003

Alginates were irradiated in an aqueous solution with $Co^{60}$ gamma rays in the dose ranges from 0 to 100 kGy, and investigated the relationship between the intrinsic viscosity $([{\eta}])$ and the molecular weight $(M_w)$ of alginates. The molecular weight of alginate was measured by gel permeation chromatography and the ranges from 1,894 to 135,174 Da were obtained. The molecular weight of alginate decreased markedly with increasing the degree of ${\gamma}-ray$ dose rate. The intrinsic viscosity of alginate solution after ${\gamma}-irradiation$ showed the ranges from 9.83 (g/g) to 602.69 (g/g), depending upon the ${\gamma}-irradiation$ dose. The molecular weight of alginate dependence of the intrinsic viscosity of the alginate solution would be expressed by Mark-Houwink equation. With a linearization of molecular weight and the intrinsic viscosity of the alginate solution, Mark-Houwink equation could be expressed with constant variables and the real data fitted to the equation of $[{\eta}]=2.2{\times}10^{-6}\;{M_w}^{1.656}\;(R^2=0.998)$.