• Journal of the Korean Society for Precision Engineering
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• v.27 no.12
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• pp.119-124
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• 2010

In this paper, thermal stabilization design of a new concept compact machining center has been investigated. A new concept machining center adopted a new X-axis as a NC rotary table. A New concept compact machining center is designed that spindle speed, feed rate and NC Rotary table speed are 12,000rpm, 60m/min and 110rpm each. The analysis is carried out by using FEM simulation Solidworks, CATIA and ANSYS. This paper is focused on the thermal deformation according to temperature distribution of a spindle system and feed drive system. Heat transfer analysis is performed according to heat source and atmosphere contact parts. As a result, this compact machining center is designed as a thermally stable structure.

• Korean Journal Plant Pathology
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• v.10 no.4
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• pp.277-283
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• 1994

An antimicrobial chitinase was purified from grapefruit extract and its properties were characterized. The chitinase was purified with a single step chromatography on regenerated chitin affinity gel column. The molecular weight of the purified chitinase was 29 kDa. The grapefruit extract contained the chitinase protein more than 50% of its total soluble proteins measured by coomassie stained protein bands. When the purified chitinase was incubated with polymers of N-acetylglucosamine (NAG), such as mycelia of Fusarium oxysproum and swollen chitin, they were degraded to oligosaccharides, and the oligosaccharides were then further hydrolyzed by the same enzyme to monomer and dimer of NAG. This result suggests that the chitinase contained both endo- and exo- chitinase activities. The chitinase was stable to heat and pH treatment; its activity was not diminished by the heat treatment upto 7$0^{\circ}C$ for 1 hr, and it showed a pH stability in the range of pH 4.0 to 12.0.

• Journal of the Korean Society for Heat Treatment
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• v.23 no.5
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• pp.239-244
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• 2010

Influence of Zr addition on grain stability at elevated temperatures has been investigated for extruded pure Mg and Mg-0.25%Zr alloy. The grain size of pure Mg increases rapidly with increasing annealing temperature when isochronally annealed for 60 min from 573 to 773 K, whereas the grains are stable up to 723 K for the Zr-containing alloy. The activation energies for grain growth ($E_g$) at this temperature range were determined as 75.3 and 105.9 kJ/mole for the pure Mg and Mg-0.25%Zr alloy, respectively. TEM observations on the annealed Mg-Zr samples revealed that higher thermal stability and higher activation energy for grain growth resulting from Zr addition in Mg may well be associated with the restriction of grain growth by nano-sized Zr particles distributed in the microstructure.

• Journal of the Korean Society for Heat Treatment
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• v.25 no.4
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• pp.175-180
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• 2012

Role of Ca in grain growth behavior has been investigated in hot-rolled Al-3%Mg and Al-3%Mg-0.5%Ca wrought alloys. When annealed for 1 hr from 723 to 823 K, grain size of the Al-3%Mg alloy increased rapidly above 723 K, whereas grains were relatively stable up to 773 K for the Ca-containing alloy. Grain homogeneity of the Ca-containing alloy was better than that of the Ca-free alloy both in hot-rolled and annealed states. Calculated activation energies for grain growth were 77.6 and 85.9 kJ/mole in the range of 723 to 823 K for the alloys with 0 and 0.5%Ca, respectively. Taking SEM images and EDS results into account, enhanced thermal stability in response to Ca addition would be associated with Al4Ca compounds located along the grain boundaries, which eventually play a role in restricting grain growth at elevated temperatures.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2001.11a
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• pp.61-67
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• 2001

Hybrid propulsion systems provide many advantages in terms of stable operation and safety. However, classical hybrid rocket motors have lower fuel regression rate and combustion efficiency compared to solid propellant rocket motor. The recent research efforts are focused on the improvement of volume limitation and regression rate in the hybrid rocket engine. The present study has numerically investigated the combustion processes in the hybrid rocket engine. The turbulent combustion is represented by the eddy breakup model and Hiroyasu and Nagle and Strickland-Constable model are used for soot formation and soot oxidation. Radiative heat transfer is modeled by finite volume method. To reduce the uncertainties for convective heat transfer near solid fuel surface having strong blowing effect, the Low Reynolds number k-$\varepsilon$ turbulent model is employed. Based on numerical results, the detailed discussion has been made for the turbulent combustion processes in the vortex hybrid rocket engine.

• Journal of the Korean Solar Energy Society
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• v.34 no.6
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• pp.85-92
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• 2014

This study carried out experimental on the cooling characteristics of clathrate compound including TMA(Tri-Methyl-Amine ; $(CH_3)_3N$) as a low temperature latent heat storage material. And additive was used for subcooling improvement of TMA-water clathrate compound. The conclusion of above study is as following ; TMA 25wt%-water clathrate compound is shown stable phase change and low subcooling degree. The subcooling was improved in the case ethanol($CH_3CH_2OH$) 0.5wt% is added to TMA 25wt%-water clathrate compound.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.19 no.12
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• pp.831-841
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• 2007

This work is to extend the elliptic operator, which has been already adopted in turbulent stress model, to fully developed turbulent buoyant channel flows with changing the orientation of the buoyancy vector to be perpendicular to the channel walls. The turbulent heat flux models based on the elliptic concept are employed and closely linked to the elliptic blending second moment closure which is used for the prediction of Reynolds stresses. In order to reflect the stable or unstable stratification conditions, the present model introduces the gradient Richardson number into the thermal to mechanical time scale ratio and model coefficients. The present model has been applied for the computation of stably and unstably stratified turbulent channel flows and the prediction results are directly compared to the DNS data.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09b
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• pp.1305-1306
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• 2006

A new material was developed to achieve improvement of heat durability, improvement of wear resistance, stability of friction coefficient and reduction in aggression to counterpart, because it is difficult to maintain braking properties by using currently available materials in the train wagons used for high-speed transportation. As a result, the new material showed a stable wear resistance even in the speed range of 350km/h, where improvement was also confirmed in reduction of aggression to counterpart material by more than approximately 10%. This development was adopted for the brake lining in the Taiwan High Speed Rail project.

• Journal of the Korean institute of surface engineering
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• v.24 no.4
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• pp.206-214
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• 1991

In the basic study of selective electroless Ni plating of Si wafers, plating rate and physical properties are investigated to obtain optimum conditions of contact hole filling. Si wafers are excellently activated in the concentration of 0.5M IF, 1mM PdCl2, 2mM EDTA at $70^{\circ}C$, 90sec. The optimum condition of Ni-B deposition on p-type Si wafers is 0.1M NiSO4, 0.11M Citrate, $70^{\circ}C$, pH6.8, 8mM DMAB. The main factor in the sheet resistences variation of films is amorphous and on heat treating matrix was transformed into a stable phase (Ni+Ni3B) at $300-400^{\circ}C$. But pH or DMAB concentration in the plating solution doesn't play role of heat-affected phase change.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.16 no.8
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• pp.681-687
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• 2003

The syntheses of LaNiO$_3$Perovskite crystalline phase from mixtures of La$_2$O$_3$and NiO via it mechanochemical(used planetary mill) and a wet ball mill process were investigated. A single and stable LaNiO$_3$perovskite crystalline phase was successfully prepared by using a heat free mechanochemical process which produced a fine amorphous powder, while that phase was not formed in a wet ball mill process which needed heat treatment ranging from 500 to 150$0^{\circ}C$ and produced a coarse powder. It was shown that the LaNiO$_3$ceramics made of the mechanochemically synthesized powder possesed a good metallic characteristic.