• Journal of the Korean Society for Heat Treatment
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• v.18 no.2
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• pp.99-104
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• 2005

In this study, the effects of C and Si on damping capacity and mechanical properties of as-cast and as-rolled Fe-17%Mn alloys were investigated as a basic study for the purpose of the commercialization of the alloy. The $M_s$ temperature of ${\gamma}{\rightarrow}{\varepsilon}$ martensitic transformation in Fe-17%Mn alloy was decreased with increasing C and Si contents, resulting in the less volume fraction of ${\varepsilon}$ martensite. The damping capacity was also decreased with increasing alloying content because of less ${\varepsilon}$ amount and the reduction in mobility of the damping sources such as the stacking fault boundaries and ${\gamma}/{\varepsilon}$ interfaces due to the pinning effect by alloying elements. The mechanical properties of as-rolled alloys were superior to those of as-cast alloys probably because of finer ${\gamma}$ grains, larger amount of ${\varepsilon}$ martensite, and chemical homogeneity.

• Journal of the Korean Society for Nondestructive Testing
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• v.13 no.4
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• pp.9-17
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• 1994

It is well recognized recently that ultrasonic technique is one of the most widely used methods of nondestructive evaluation to characterize material properties of nonconventional engineering materials. Therefore it is very important to understand physical phenomenon on propagation behavior of elastic wave in these materials, which is directly associated with ultrasonic signals in the test. In this study, the theoretical analysis on multi-scattering of harmonic elastic wave due to the particulate with interface between matrix and fiber in metal matrix composites(MMCs) was done on the basis of Lax's quasi-crystalline approximation and extinction theorem. SiC particulate (SiCp) reinforced A16061-T6 composite material was chosen for this analysis. From this analysis, frequency dependences of phase velocity and amplitude attenuation of effective plane wave due to the change of volume fraction of SiC particulate were clearly found. It was also shown that the interface condition between matrix and fiber in MMCs gives a direct effect on the variation of phase velocity of plane wave in MMCs.

• Journal of the Korean Ceramic Society
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• v.40 no.12
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• pp.1183-1188
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• 2003

LCP (Liquid Crystal Polymer)/BT(BaTiO$_3$) composite was prepared by mixing LCP varnish and BT slurry. And the effect of the composition of LCP/BT composites and the size of BT powder on dielectric properties of LCP/BT composite were investigated. The dispersion properties of BT slurries were also studied as a function of volume fraction of dispersant, GLYMO (3-glycidyloxypropyltrimethoxysilane) added to various sized BT powders. The quantity of optimum dispersant in BT slurry decreased with an increase of BT powder size because of the decrease of specific surface area of BT powder. LCP/BT composite sheet was prepared by tape-casting method with mixing BT slurry and LCP varnish. The dielectric constant of the composites increased from 34.3 to 44.1 and their dielectric loss increased from 0.05 to 0.063 as the size of BT powder increased from 100 nm to 500 nm.

• Korean Journal of Animal Reproduction
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• v.25 no.3
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• pp.201-206
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• 2001

This study was carried out to investigate the effects of spring (March~May) and summer (June~August) influencing semen characteristics, frozen-thawed sperm viability and serum testosterone concentration in Yorkshire boars. Results of this study were as follows: 1. There were no significant differences in the semen volume, pH and sperm concentration of sperm-poor fraction of Yorkshire boars between spring and summer. However, sperm concentrations of sperm-rich fractions in spring were higher than those in summer (P＜0.05). 2. Sperm motility and normal acrosome of raw semen in Yorkshire boars did not differ significantly between spring and summer, However, motility and normal acrosome of frozen-thawed sperm were higher in spring season than in summer season (P＜0.05). 3. Serum testosterone concentrations in Yorkshire boars were 4.04 ng/$m\ell$ in spring and 2.85 ng/$m\ell$ in summer. Serum testosterone concentrations in spring were higher than those in summer (P＜0.05). 4. In conclusion, when serum testosterone concentrations in Yorkshire boars were higher, frozen-thawed sperm viability was higher.

• Natural Product Sciences
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• v.20 no.2
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• pp.113-118
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• 2014

Ribes fasciculatum which belongs to Saxifragaceae has been widely used as a traditional medicine for the treatment of symptoms associated with lacquer poison. However, pharmacological studies on the R. fasciculatum are extremely limited until now. Thus, in this study, we evaluated the possible anti-inflammatory effects of ethyl acetate fraction of R. fasciculatum (ERF) using IFN-${\gamma}$/LPS-stimulated peritoneal macrophage model. We investigated the change in nitrite level in the absence or presence of ERF after LPS stimulation, and we found that ERF effectively attenuates the NO production in a dose dependent manner without notable toxicity. To determine the mechanism of the inhibitory action of ERF on NO production, we performed iNOS enzyme activity assay and Western blotting. Here we showed that both of iNOS enzyme activities and iNOS expressions were significantly down-regulated by ERF, indicating that these dual activities of ERF are responsible for ERF-mediated NO suppression. In addition, ERF inhibitied the expression of cyclooxygenase-2 (COX-2), an another key enzyme in inflammation through suppression of NF-${\kappa}B$ activation. We also tested anti-inflammatory properties of ERF not only in vitro, but in vivo using trypsin-induced paw edema model in mice. Our results revealed that the increased paw volume in response to trypsin injection was recovered by ERF supplement dose dependently.

• Journal of the Korean Vacuum Society
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• v.12 no.2
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• pp.130-135
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• 2003

Polycrystalline silicon thin films have been used for low cost thin film device application. However, it was very difficult to fabricate high performance poly-Si at a temperature lower than $600^{\circ}C$ for glass substrate because the crystallization process technologies like conventional solid phase crystallization (SPC) require the number of high temperature (600-$1000^{\circ}C$) process. The objective of this paper is to grow poly-Si on flexible substrate using a rapid thermal crystallization (RTC) of amorphous silicon (a-Si) layer and make the high temperature process possible on molybdenum substrate. For the high temperature poly-Si growth, we deposited the a-Si film on the molybdenum sheet having a thickness of 150 $\mu\textrm{m}$ as flexible and low cost substrate. For crystallization, the heat treatment was performed in a RTA system. The experimental results show the grain size larger than 0.5 $\mu\textrm{m}$ and conductivity of $10^{-5}$ S/cm. The a-Si was crystallized at $1050^{\circ}C$ within 3min and improved crystal volume fraction of 92 % by RTA. We have successfully achieved a field effect mobility over 67 $\textrm{cm}^2$/Vs.

• Journal of the Korean Society for Heat Treatment
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• v.12 no.2
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• pp.145-156
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• 1999

The distribution of the second phase, the change of transformation temperature and mechanical properties with thermomechanical treatment conditions were investigated by metallography, calorimetry, EDS, tensile test and fractography in a Cu-Al-Ni-Ti-Mn alloy. The cast structure revealed Ti-rich precipitates($X_L$ phase) between dendrite arms, which have been identified as $(Cu,Ni)_2TiAl$ intermetallic compounds. By homogenizing above $900^{\circ}C$, the $X_L$ phase was melted in the matrix, while the Xs phase was precipitated in matrix and the volume fraction of it was increased. When hot-rolled specimen was betatized below $750^{\circ}C$, recrystallization could not be observed. However, the specimen betatized above $800^{\circ}C$ was recrystallized and the grain size was about $50{\mu}m$, while Xs phase was precipitated in matrix. With raising betatizing temperature, $M_s$ and $A_s$ temperatures were fallen and transformation hysteresis became larger. The strain of the specimen betatized at $800^{\circ}C$ was 8.2% as maximum value. The maximum shape recovery rate could be obtained in the specimen betatized at $800^{\circ}C$ but it was decreased due to the presence of Xs phase with increasing betatizing temperature.

• Journal of the Korean Society for Heat Treatment
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• v.9 no.1
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• pp.12-18
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• 1996

Austenite(${\gamma}$) grain size, ${\varepsilon}$ martensite volume fraction and damping capacity of Fe-17%Mn alloy have been investigated as a function of solution treatment temperature of $600^{\circ}C$ to $1100^{\circ}C$. With increasing the solution temperature, ${\gamma}$ grain size, ${\varepsilon}$ martensite content and damping capacity are increased, while the hardness is decreased. When ${\gamma}$ grains are small, ${\varepsilon}$ plates grow in only one direction in each ${\gamma}$ grain. However, if the ${\gamma}$ grains are large in accordance with high solution treating temperature, several ${\varepsilon}$ variants with different orientations are formed and intersected each other in each ${\gamma}$ grain. In spite of small ${\varepsilon}$ martensite content, the damping capacity of the specimen which was annealed at $700^{\circ}C$, followed by subzero treatment at $-196^{\circ}C$, is almost equal to that of the specimen annealed at $1000^{\circ}C$ and subsequently quenched to room temperature. From this result it is suggested that the damping capacity of Fe-17%Mn alloy having fine ${\gamma}$ grains is mainly attributed to the movement of ${\gamma}/{\varepsilon}$ interface without the operation of other damping sources such as ${\varepsilon}/{\varepsilon}$ boundaries and stacking faults in ${\varepsilon}$ reported previously.

• The Korean Journal of Ceramics
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• v.4 no.4
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• pp.279-285
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• 1998

The $UO_2$ pellets are usually sintered under hydrogen gas atmosphere. Hydrogen gas may cause unexpected early failure of the refractory bricks in the sintering furnace. In this work, nitrogen was mixed with hydrogen to investigate the effect of nitrogen gas on a failure machanism of the refractory bricks and on the microstructure of the $UO_2$ pellet. The hydrogen-nitrogen mixed gas experiments show that the larger nitrogen the mixed gas contains, the less the refractory materials are reduced by hydrogen. The weight loss measurements at $1400^{\circ}C$ for fire clay and chamotte refractories containing high content of $SiO_2$ indicate that the weight loss rate for the mixed gas is about half of that for the hydrogen gas. Based on the thermochemical analyses, it is proposed that the weight loss is caused by hydrogen-induced reduction of free $SiO_2$ and/or $SiO_2$ bonded to $Al_2O_3$ in the fire clay and chamotte refractories. However, the retardation of the hydrogen-induced $SiO_2$ reduction rate under the mixed gas atmosphere may be due to the reduction of the surface reaction rate between hydrogen gas and refractory materials in proportion to volume fraction of nitrogen gas in the mixed gas. On the other hand, the mixed gas experiments show that the test data for $UO_2$ pellet still meet the related specification values, even if there exists a slight difference in the pellet microstructural parameters between the cases of the mixed gas and the hydrogen gas.

• Nuclear Engineering and Technology
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• v.48 no.4
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• pp.847-858
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• 2016

An overview is given on the work of the Laboratory of Nuclear Energy Systems at ETH, Zurich (ETHZ) and of the Laboratory of Thermal Hydraulics at Paul Scherrer Institute (PSI), Switzerland on tight-lattice bundles. Two-phase flow in subchannels of a tight triangular lattice was studied experimentally and by computational fluid dynamics simulations. Two adiabatic facilities were used: (1) a vertical channel modeling a pair of neighboring sub-channels; and (2) an arrangement of four subchannels with one subchannel in the center. The first geometry was equipped with two electrical film sensors placed on opposing rod surfaces forming the subchannel gap. They recorded 2D liquid film thickness distributions on a domain of $16{\times}64$ measuring points each, with a time resolution of 10 kHz. In the bubbly and slug flow regime, information on the bubble size, shape, and velocity and the residual liquid film thickness underneath the bubbles were obtained. The second channel was investigated using cold neutron tomography, which allowed the measurement of average liquid film profiles showing the effect of spacer grids with vanes. The results were reproduced by large eddy simulation + volume of fluid. In the outlook, a novel nonadiabatic subchannel experiment is introduced that can be driven to steady-state dryout. A refrigerant is heated by a heavy water circuit, which allows the application of cold neutron tomography.