• Korean Journal of Food Science and Technology
• /
• v.35 no.1
• /
• pp.57-61
• /
• 2003

Variations in NMR relaxation time during freezing and thawing processes in pork loins were investigated. Continuous distribution analysis of data obtained from $T_2\;CPMG$ were carried out to observe the changes in water content in the muscles. Solid fat content slightly increased with decreasing temperature, then showed sharp increase at $-4^{\circ}C$, reaching 85% at $-25^{\circ}C$. Relaxation time decreased with decreasing temperature, suggesting that ice crystals gradually formed at freezing temperature. $T_2$ relaxation time during thawing was higher than that during freezing, suggesting that ice crystals melted by thawing and resulted in water loss from meat. Continuous distribution analysis of data obtained from Carr-Purcell-Meiboom-Gill experiments shows one to four components on the spectra during freezing and thawing processes. The area of major components between 30 to 45 ms decreased with decreasing temperature, and were not detected below $-4^{\circ}C$, below which only $T_s$ signal was detected. The area of $T_s$ decreased with decreasing temperature. Between -4 to $10^{\circ}C$, the areas of $T_m$ and $T_l$ during thawing were larger than those during freezing. These results suggest that the exchange between bound water and free water takes place during freezing and thawing.

• Journal of Technologic Dentistry
• /
• v.19 no.1
• /
• pp.21-35
• /
• 1997

The Ag-Pd-Cu alloys containing a small amount of Au is commonly used for dental purposes, because this alloy is cheaper than Au-base alloys for clinical use. However, the most important characteristic of this alloy is age-hardenability, which is not exhibited by other Ag-base dental alloys. The specimens used were Ag-20Pd-20Cu ternary alloy and Au addition alloy. These alloys were melted and casted by induction electic furace and centrifugal casting machine in Ar atmoshpere. These specimens were solution treated for 2hr at $800^{\circ}C$ and were then quenched into iced water, and aged at $350{\sim}550^{\circ}C$ Age-hardening characteristics of the small Au-containing Ag-pPd-Cu dental alloys were investigated by means of hardness testing, X-ray diffraction and electron microscope observations, electrical resistance, differential scanning calorimetric, emergy dispersed spectra and electron probe microanalysis. Principal results are as follows : Hardening occured in two stages, I. e., stage I in low temperature and stage II in high temperature regions, during continuous aging. The case of hardening in stage I was due to the formation of the Llo type face centered tetragonal PdCu-ordered phase in the grain interior and hardening in stage I was affedted by the Cu concentration. In stage II, decomposition of the $\alpha$ solid solution to a PdCu ordered phase(L1o type) and an Agrich ${\alpha}2$ phase occurred and a discontiunous precipitation occurred at the grain boundary. Form the electron microscope study, it was concluded that the cause of age-hardening in this alloy is the precipitation of the PdCu ordered phase, which has AuCu I type face-centered tetragonal structure. Precipitation procedure was ${\alpha}\to{\alpha}+{\alpha}2+PdCu\to{\alpha}1+{\alpha}2+PdCu$ at Pd/Cu = 1 Ag-Pd-Cu alloy is more effective dental alloy as ageing treatment and is suitable to isothermal ageing at $450^{\circ}C$.

• Proceedings of the Korean Society for Agricultural Machinery Conference
• /
• 2017.04a
• /
• pp.32-32
• /
• 2017

2012년부터 도입된 "신재생에너지 의무할당제(RPS)"로 인하여 500MW이상의 설비 용량을 갖춘 발전소의 경우 총발전량에서 일정 비율을 신재생에너지로 공급하여야 한다. 이러한 신재생에너지 중 농업부산물은 목질계 바이오매스의 한 종류로 '탄소중립(Carbon Neutral)' 연료이며 기존 화석연료와 혼소로 활용 할 수 있는 장점을 지니고 있다. 그러나 낮은 발열량, 운송 및 저장비용, 일정하지 않은 연소특성의 문제로 인하여 대부분 노지에 방치되거나 버려지고 있다. 이러한 버려지는 농업부산물을 효율적으로 활용하기 위한 방법 중 하나로 반탄화(Torrefacation) 처리가 대두되고 있다. 반탄화 처리 시, 발열량이 증대되며, 저장과 이송에서의 이점을 갖게 된다. 그러나, 반탄화는 공정 과정중 질량손실에 따른 에너지 총량의 감소한다는 단점을 가지고 있다. 이에 본 연구에서는 효율적인 반탄화공정을 위한 질량감소모델을 제시 하고자한다. 승온 속도(heating rate)를 $7.5^{\circ}C/min$, $15^{\circ}C/min$, $22.5^{\circ}C/min$의 조건에서의 열중량분석 결과를 토대로 속도모델식(Arrhenius method, Ingraham & Marrier method 등)을 적용하여, 반응속도상수를 도출하였다. 이 반응속도상수를 이용하여 질량감소 모델을 정립하였고, 이를 실험결과와 비교, 검증하였다.

• Korean Journal of Crystallography
• /
• v.3 no.1
• /
• pp.23-30
• /
• 1992

a-SiC crystals were grown on the (001) plane of a-SiC seed crystals by sublimation method to find effects of pressure-reduction rate of the crystal growth furnace own the growth rate and orientstion of grown SiC crystals. Pressure-reduction rate at the initial growth stage affected the crystallinity of grown SiC crystals. In case of high pressure-reduction rate, growth rate was high and 3csic polycrystalline was grown on the seed. On the other hand, low pressure-reduction rate caused the growth rate to be slow and 6H-SiC single crystal was grown on the seed. However, even after growing SiC for 2 hours under the condition in which.

• Journal of Korean Ophthalmic Optics Society
• /
• v.9 no.2
• /
• pp.371-380
• /
• 2004

The history of the glasses can say that we began with the development of the typography. Glasses were made for the first time from the skin which they tied. We came to make the rim as the horn tree afterwards or bone. And the snail glasses make the lens as the modification or glass and to put to connect the two to large snail was developed. The rim after he brought lots of style change. The development of the Bridge and eyewear form of the Temple of an entry today began to come out. The development of and various design and material. We reached practical style. development of design concentration new fashion trend lead can make it eyewear company and designer's. A rim of various style through historical development course because we have a present time's rim analysis. We try to try to investigate a method element of the glass design with a final cause form of the design in the viewpoint of the facility.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.6 no.3
• /
• pp.360-367
• /
• 1996

The OISF (Oxidation Induced Stacking Fault)is expected to affect the electrical properties in Si single crystals, and the nuclei of OISF are believed to be formed during the crystal growing process. Initial oxygen concentration, dopant type and its density, and cooling rate are regareded as major factors on OISF formation. In this study, the variations of OISF density under various cooling rate were investigated. Si single crystal was heated to $1400^{\circ}C$ in Ar ambient and cooled down to room temperature at different cooling rate, using horizontal tube furnace. After that, they were oxidized at $1150^{\circ}C$, and then, OISF was observed with optical microscope. The relation between oxide procipitates and OISF nucleation was investigated by FTIR analysis. As a result, it was found that there exists the intermediate cooling rate range in which OISF nucleation is highly enhanced. And also, it was found that OISF nucleation is closely related with silicon oxide procipitation in Si single crystals.

• Applied Microscopy
• /
• v.29 no.3
• /
• pp.281-289
• /
• 1999

The stirred and thixoformed $SiC_p/AZ91HP$ Mg composites are studied on the basis of microstructural analysis using transmission electron microscopy (TEM). The products of interfacial reaction are identified as $Mg_2Si$, MgO and $Mg_{17}Al_{12}$ phases and the crystallized phases are found to be orthorhmbic $Al_6Mn$ and decagonal T phases. It is shown that $Mg_2Si$ and $Mg_{17}Al_{12}$ phases are found at the surface of $SiC_p$ and $Al_6Mn$ is found near interface and crystallized on the matrix. Phase identification is carried out by crystallographic work based on primitive cell volume, zero order Laue zone (ZOLZ) patterns and single convergent beam electron diffraction (CBED) patterns containing higher order Laue zone ring from a nanosized region.

• Journal of Korea Foundry Society
• /
• v.20 no.4
• /
• pp.260-268
• /
• 2000

응고 및 마모거동을 연구하기 위하여 Cr, V, Mo 및 W의 조성이 다른 3종류의 백주철을 주조하였다. 고주파유도용해로에서 장입시켜 1873K까지 승온시켜 장입원료들을 모두 용해시킨 후 1823K에서 Y블럭주형에 주입하였다. 얻어진 3종류의 백주철조성은 다음과 같다: Fe-3%C-10%Cr-5%Mo-5%W(합금1), Fe-3%C-10%V-5%Mo-5%W(합금2) 및 Fe-3%C-17%Cr-3%V(합금 3)응고과정을 추적하기 위하여 각 시편으로부터 50g을 채취한 후 알루미나도가니에 넣고 실리콘카바이드로를 사용하여 1723K의 알콘분위기하에서 재용해를 시켰다. 용금을 10K/분의 속도로 냉각시키면서 열분석을 행하였으며 도중 몇 차례 소입 실험을 병행하였다.합금1의 경우 초정오스테나이트, (오스테나이트+$M_7C_3$)공정, (오스테나이트+$M_6C$)공정, 합금2의 경우 초정 MC, 초정오스테나이트, (오스테나이트+MC)공정 , (오스테나이트+$M_2C$)공정, 합금3의 경우 초정 $M7C_3$와 (오스테나이트+$M_7C_3$)공정으로 구성되어 있었다. 주방상태, 균질화열처러상태, 공냉상태, 템퍼링상태에서 내마모시험을 행하였다. 먼저 주방상태시 편을 진공분위기하에서 1223K에서 5시간동안 균질화열처리를 행한후 로냉을 시켰다. 다시 이 시편을 1323K에서 2시간 유지후 강제공냉을 시켰으며 강제공냉된 시편을 573K에서 3시간동안 템퍼링처리를 하였다. 내마모시험은 120 mesh마모지에 10N의 하중을 가하여 실시하였다. 각 사이클마다 무게감소를 측정하였으며 8번 반복실험을 하였다. 마모량은 균질화열처리시편, 주방상태시편, 템퍼링시편, 공냉시편의 순으로 감소하였다. 합금2가 마모량이 가장 적었으며 합금3이 가장 많았다. 합금2의 마모량이 가장 적은 이유는 조직이 초정 MC, 공정 MC 및 공정 M2C로 구성되어 있기 때문으로 사료된다.주방상태에서 기지조직은 퍼얼라이트이었으나 열처리를 통하여 마르텐사이트, 템퍼드마르텐사이트, 잔류오스테나이트로 변태하였다. 이상의 결과를 종합해 보면 MC가 내마모성에 가장 기여하는 조직으로 판단되어진다.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2005.07a
• /
• pp.294-295
• /
• 2005

다중 코어를 이용한 대전류 변압기용 Mn-Zn ferrite를 제조하고 전자기적 특성을 분석하였으며, 제조된 자심재료를 이용하여 변압기를 제조하고 전원장치에 탑재하여 효율특성을 분석하였다. ZnO의 몰비가 증가할수록 혼합 스피넬의 형성을 통한 보아 자자의 증가로 인해 투자율은 증가하고 상대적으로 전력손실이 감소하여 $Fe_2O_3$ : MnO : ZnO = 53 : 36 : 11 mo\% 일 때 가장 우수한 특성을 나타냈고, 열처리 공정의 승온 과정에서부터 산소 분압을 제어하고 최적의 대기압 상수를 산출함으로써 Zn-loss 현상을 최소화하여 ZnO 11 mol%, 대기압 상수 7.7일 때 투자율 2350, 밀도 4.9 $g/cm^3$, 비저항 480 ${\Omega}cm$, 300 mT의 최대 자속 밀도 특성을 갖는 우수한 자심 재료를 개발하였다. 그리고 최소 손실 온도를 $90^{\circ}C$ 이하로 감소시켰으며 100 kHz에서 250 $kW/m^3$의 낮은 전력손실을 나타냈다. 또한 개발된 자심재료를 이용하여 제조된 전원장치는 30~80A의 출력 전류에서 85% 이상의 고효율을 얻었다.

• Clean Technology
• /
• v.16 no.1
• /
• pp.12-18
• /
• 2010

The object of the present study is to apply KF/MgO catalysts to remove sulfur dioxide from dibenzothiophene sulfone, a by-product of oxidative desulfurization. Potassium fluoride was deposited via an impregnation method on MgO. The effects KF loading and calcination on the characteristics of the KF/MgO catalysts were investigated through the BET surface area, XRF, XRD, and temperature-programmed desorption of $CO_2$. The catalytic performances of the samples were investigated during the decomposition of dibenzothiophene sulfone to biphenyl and sulfur dioxide gas. KF loaded on MgO prepared by the impregnation method showed high catalytic activities for the decomposition of dibenzothiophene sulfone. The higher activity of KF/MgO just dried at 373 K, avoiding the usual activation at high temperature, than that over the calcined catalyst is ascribed to increase of the amount of basic sites. The high basicity probably may be due to the coordinately unsaturated $F^-$. The simply dried 10 % KF/MgO catalyst, without the usual activation at high temperature, showed the optimal catalytic properties.