• Journal of Advanced Marine Engineering and Technology
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• v.35 no.5
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• pp.616-624
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• 2011

The flow characteristics and heat transfer augment on the periodically arranged semi-circular ribs in a rectangular channel for turbulent flow has been investigated numerically. The aspect ratio of the rectangular channel was AR=5, the rib height to hydraulic diameter ratio were 0.07 and rib height to channel height ratio was set as e/H=0.117 for various PR(rib pitch-to-rib height rate) between 8~14, respectively. The SST k-${\omega}$ turbulence model and v2-f turbulence model were used to find out the heat transfer and the flow characteristics of near the wall which are suited to obtain realistic phenomena. The numerical analysis results show turbulent flow characteristics, heat transfer enhancement and friction factor as observed experimentally. The results predict that turbulent kinetic energy(k) is closely relative to the diffusion of recirculation flow. and v2-f turbulence model simulation results have a good agreement with experimental values.

• Journal of the Korean Society of Clothing and Textiles
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• v.19 no.2
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• pp.297-316
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• 1995

The system and symbolizing ideologic meanings of the metallic Kwon in period of the Three-Kingdoms were comsidered by comparing to their cultural path and structal styles throughout the tree and the deer worship ideology. The results of this study are as followings; Firstly, the beginning of the Korean, mostly northern style was originated from metal tools of the Bronze age in BC 6c-7c. The maJ;lufature of the metallic adornment brought the pr-evailing use of metallic objects of craftwork after the supply of ironmongery. Secondly, the cultmal characteristics of the metallic Kwan in the kor-ean Peninsula were influenced f-rom the northern chinese tribes, Momg Go, Hung No, and Sien-pi who were transmitted from the scythian of the southern Russia having a prefenence for gold. Thir-dly, the metallic Kwon of the Kogmgo and the Baekje era was ideologically based on the ar-t of Buddism of the pattern of blazing flame, the carved pattern of flower- of herb, and the honey. sukle which were tramsmitted to china thr-ough the silk noad. Fourthly, the metallic K wam of the silla era consisted of the tree and the antler types in closely nelated to the tree and the deer ideology which were based on the background of shamanism. It should be raid that the metallic Kwan of the silla esa are connected to the type of nor-them ancient K wan. Lasthy, the metallic Kwan-Mo of the Kaja esa was mosthy original type of flower of herb even if kome of these ar-e similiar to the tree adornment type of silla. This type of flower of herb in based on the scythian type with a statue im silveer founded at Alexandnopol in the southern russia.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.11a
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• pp.363-363
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• 2008

The development of dry etching process for sapphire wafer with plasma has been key issues for the opto-electric devices. The challenges are increasing control and obtaining low plasma induced-damage because an unwanted scattering of radiation is caused by the spatial disorder of pattern and variation of surface roughness. The plasma-induced damages during plasma etching process can be classified as impurity contamination of residual etch products or bonding disruption in lattice due to charged particle bombardment. Therefor, fine pattern technology with low damaged etching process and high etch rate are urgently needed. Until now, there are a lot of reports on the etching of sapphire wafer with using $Cl_2$/Ar, $BCl_3$/Ar, HBr/Ar and so on [1]. However, the etch behavior of sapphire wafer have investigated with variation of only one parameter while other parameters are fixed. In this study, we investigated the effect of pressure and other parameters on the etch rate and the selectivity. We selected $BCl_3$ as an etch ant because $BCl_3$ plasmas are widely used in etching process of oxide materials. In plasma, the $BCl_3$ molecule can be dissociated into B radical, $B^+$ ion, Cl radical and $Cl^+$ ion. However, the $BCl_3$ molecule can be dissociated into B radical or $B^+$ ion easier than Cl radical or $Cl^+$ ion. First, we evaluated the etch behaviors of sapphire wafer in $BCl_3$/additive gases (Ar, $N_2,Cl_2$) gases. The behavior of etch rate of sapphire substrate was monitored as a function of additive gas ratio to $BCl_3$ based plasma, total flow rate, r.f. power, d.c. bias under different pressures of 5 mTorr, 10 mTorr, 20 mTorr and 30 mTorr. The etch rates of sapphire wafer, $SiO_2$ and PR were measured with using alpha step surface profiler. In order to understand the changes of radicals, volume density of Cl, B radical and BCl molecule were investigated with optical emission spectroscopy (OES). The chemical states of $Al_2O_3$ thin films were studied with energy dispersive X-ray (EDX) and depth profile anlysis of auger electron spectroscopy (AES). The enhancement of sapphire substrate can be explained by the reactive ion etching mechanism with the competition of the formation of volatile $AlCl_3$, $Al_2Cl_6$ or $BOCl_3$ and the sputter effect by energetic ions.

• Korean Journal of Materials Research
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• v.19 no.5
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• pp.253-258
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• 2009

Mn-substituted $BiFeO_3$(BFO) thin films were prepared by r.f. magnetron sputtering under an Ar/$O_2$ mixture of various deposition pressures at room temperature. The effects of the deposition pressure and annealing temperature on the crystallization and electrical properties of BFO films were investigated. X-ray diffraction patterns revealed that BFO films were crystallized for films annealed above $500^{\circ}C$. BFO films annealed at $550^{\circ}C$ for 5 min in $N_2$ atmosphere exhibited the crystallized perovskite phase. The (Fe+Mn)/Bi ratio decreased with an increase in the deposition pressure due to the difference of sputtering yield. The grain size and surface roughness of films increased with an increase in the deposition pressure. The dielectric constant of BFO films prepared at various conditions shows $127{\sim}187$ at 1 kHz. The leakage current density of BFO films annealed at $500^{\circ}C$ was approximately two orders of magnitude lower than that of $550^{\circ}C$. The leakage current density of the BFO films deposited at $10{\sim}30\;m$ Torr was about $5{\times}10^{-6}{\sim}3{\times}10^{-2}A/cm^2$ at 100 kV/cm. Due to the high leakage current, saturated P-E curves were not obtained in BFO films. BFO film annealed at $500^{\circ}C$ exhibited remnant polarization(2Pr) of $26.4{\mu}C/cm^2$ at 470 kV/cm.