• Applied Chemistry for Engineering
• /
• v.9 no.4
• /
• pp.481-485
• /
• 1998

Hydrated aluminum sulfate, an inorganic polymer, was synthesized from kaolin in $H_2SO_4$ solution using microwave energy. The maximum rates of alumina extracted from calcined kaolin were 72.8% in a conventional process ($80^{\circ}C$, 1M, and 180min) and 99.9% in a microwave process ($90^{\circ}C$, 1M, and 60 min). Compared with the conventional one, the hydrated aluminum sulfate synthesized under the microwave process had layer structure consisting of plate-shaped large grains. After synthesis and then calcination at $1100^{\circ}C$, both products on conventional and microwave processes were ${\gamma}-Al_2O_3$ with agglomerated powders of spherical shape. The specific area of the products in conventional and microwave processes were 113.5 and $106.6m^2/g$, and their average grain sizes were 46.5 an $26.3{\mu}m$, respectively.

• Journal of Korea Foundry Society
• /
• v.36 no.5
• /
• pp.167-173
• /
• 2016

The effect of various types of heat-treatment on the mechanical properties of cast Alloy 718 has been investigated. Cast Alloy 718 bars were subjected to 'standard heat-treatment'_(SHT), 'HIP (Hot Isostatic Pressing) heat-treatment'_(HHT), and 'HIP-simulated heat-treatment'_(HS). In the absence of long time high temperature heat-treatment, a small amount of Laves phase remained in the 'SHT' specimen, and needle shaped ${\delta}$ precipitated in the vicinity of the Laves phase. Due to the formation of the Laves and ${\delta}$ phases in the 'SHT' specimen, it exhibited lower tensile properties than those of the others_specimens. On the other hand, the Laves phase was completely dissolved into the matrix after 'HHT' and 'HS' treatments. It is known that isostatic pressure reduces the self-diffusion coefficient, because of the lower self-diffusivity under HIP conditions in the interdendritic region, Nb segregation and the high amount of ${\gamma}^{{\prime}{\prime}}$ precipitation that occurs. Due to the higher fraction of coarse ${\gamma}^{{\prime}{\prime}}$ phases, the 'HHT' treated Alloy 718 showed excellent tensile strength.

• Journal of Ginseng Research
• /
• v.21 no.3
• /
• pp.214-218
• /
• 1997

New simple methods for the Isolation of sesquiterpenes from Panax ginseng were developed. First, volatile compounds were isolated by simultaneous distillation and extraction (SDE) with 30% methanol and $\alpha$-hexane instead of water and ethyl ether/pentane (1:1). Secondly, head space volatiles in U-shaped tube at 7$0^{\circ}C$ were passed through C18 Sep-Pak by nitrogen gas streaming and the adsorbed volatiles were fluted by $\alpha$-hexane. TLC analysis showed that the volatile concentrates consisted mainly of terpenes when colored by vanillin-sulfuric and. GC/MS data revealed that approximately 30 sesquiterpenes of molecular weight 204 occupied 81.1% or more of the volatile concentrates isolated by those two newly developed methods. Among these, alloaromadendrene, germacrene B, isocaryophyllene, $\alpha$-neoclovene, ${\gamma}$-muurolene, $\beta$-panaslnsene, and $\alpha$-humulene were identified as being major sesqulterpenes by authentic samples or literatme search Key words : Panax ginseng, volatile compound, sesquiterpene, isolation, new method, GC/MS.

• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• v.y2005m4
• /
• pp.343-346
• /
• 2005

Three dimensional structures of detonation wave propagating through a square-shaped duct were investigated using computational method and parallel processing. Inviscid fluid dynamics equations coupled with $variable-{\gamma}$ formulation and simplified one-step Arrhenius chemical reaction model were analysed by MUSCL-type TVD scheme and four stage Runge-Kutta time integration. The unsteady computational results in three dimension show the detailed mechanism of transverse mode and diagonal mode of detonation wave instabilities resulting same cell length but different cell width in smoked-foil record.

• International Journal of Safety
• /
• v.1 no.1
• /
• pp.58-61
• /
• 2002

A preparation method of cobalt supported alumina catalyst for a emergency escape mask cartridge has been studied. Catalysts were prepared by incipient wetness impregnation method using pre-shaped $\gamma$=alumina powders of 70-100 mesh. The catalyst was tested in a continuous-flow reactor system and characterized by elemental analysis, BET and TGA-DTA techniques. Cobalt shows higher activity than platinum or nickel for carbon monoxide oxidation at room temperature. Optimum loading amount of cobalt was 10 wt.% for CO oxidation and the reaction activity increases gradually with the increase of calcination temperature up to $450^{\circ}C.

• 한국전산유체공학회:학술대회논문집
• /
• 2005.10a
• /
• pp.151-155
• /
• 2005

Three-dimensional structures of unsteady detonation wave propagating through a square-shaped tube is studied using computational method and parallel processing. Inviscid fluid dynamics equations coupled with variable-${\gamma}$ formulation and simplified one-step Arrhenius chemical reaction model were analysed by a MUSCL-type TVD scheme and four stage Runge-Kutta time integration. Results in three dimension show the two unsteady detonation wave propagating mode, the Rectangular and diagonal mode of detonation wave instabilities. Two different modes of instability showed the same cell length but different cell width and the geometric similarities in smoked-foil record.

• 한국연소학회:학술대회논문집
• /
• 2005.10a
• /
• pp.15-19
• /
• 2005

Three-dimensional structures of unsteady detonation wave propagating through a square-shaped tube is studied using computational method and parallel processing. Inviscid fluid dynamics equations coupled with variable-${\gamma}$ formulation and simplified one-step Arrhenius chemical reaction model were analysed by a MUSCL-type TVD scheme and four stage Runge-Kutta time integration. Results in three dimension show the two unsteady detonation wave propagating mode, the Rectangular and diagonal mode of detonation wave instabilities. Two different modes of instability showed the same cell length but different cell width and the geometric similarities in smoked-foil record.

• Proceedings of the Polymer Society of Korea Conference
• /
• 2006.10a
• /
• pp.286-286
• /
• 2006

We report on a fascinating morphology; giant spherical conducting polythiophene by the in-situ gamma radiation-induced chemical polymerization method. The resultant micron-size buckyball-shaped polymer structures were identified by high resolution transmission electron microscopy and scanning electron microscopy. Different characterizations e.g. Fourier transform infrared, x-ray diffraction, and x-ray photoelectron microscopy were utilized to prove that the new morphological conducting polythiophene was synthesized successfully by this novel method.

• Journal of the Korean Institute of Telematics and Electronics C
• /
• v.35C no.5
• /
• pp.11-16
• /
• 1998

We analyze the software reliability growth models for the specified period from the viewpoint of theory of differential equations. we defien a genralized form of reliability growth models as follws: dN(t)/dt = b(t)f(N(t)), Where N(t) is the number of remaining faults and b(t) is the failure rate per software fault at time t. We show that the well-known three software reliability growth models - Goel - Okumoto, s-shaped, and Musa-Okumoto model- are special cases of the generalized form. We, also, extend the generalized form into an extended form being dN(t)/dt = b(t, .gamma.)f(N(t)), The genneralized form can be obtained if the distribution of failures is given. The extended form can be used to describe a software reliabilit growth model having weibull density function as a fault exposure rate. As an application of the generalized form, we classify three mentioned models according to the forms of b(t) and f(N(t)). Also, we present a case study applying the generalized form.

• The Korean Journal of Zoology
• /
• v.38 no.1
• /
• pp.66-73
• /
• 1995

Putative gamma aminobu%sic acid (GABA)-ersic elements in the basilar pontine nuclei were examined in the dos using an antiserum against GABA-glutaraldehvde-protein conjusBtes and the peroxidase-antiperoxidase method. GABA-immunoreactive neuronal somata in the basilar Pons exhibited various morphology with the majority being spindle-shaped or multipolar, while some were spheroidal. The size of GABA-orgic neuronal somata was relatively small (approximately $10-20\mum)$ in diameter. GABA-immunoreactive neurons were scattered throughout the pontine nuclei, but the midline region of the medial nucleus at the rostral pons, the lateral nucleus at mid-pontine levels, and the ventral nucleus at the caudal pons exhibited a relatively greater concentration of cell bodies. A sparse number of GABA-ergic neurons were observed within the cerebral peduncle and along the ventral borders of the basilar pons adjacent to the middle cerebellar peduncle at the rostrocaudal levels of the pontine nuclei. These obsenrations provide anatomic evidence of how this inhibitory neural element performs its function in the cortico-prontocerbellar circuitry.