• Asian-Australasian Journal of Animal Sciences
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• v.28 no.11
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• pp.1573-1582
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• 2015

This study was to investigate the effect of soyabean isoflavones (SIF) on onset of puberty, serum hormone concentration, and gene expression in hypothalamus, pituitary and ovary of female Bama miniature pigs. Fifty five, 35-days old pigs were randomly assigned into 5 treatment groups consisting of 11 pigs per treatment. Results showed that dietary supplementation of varying dosage (0, 250, 500, and 1,250 mg/kg) of SIF induced puberty delay of the pigs with the age of puberty of pigs fed basal diet supplemented with 1,250 mg/kg SIF was significantly higher (p<0.05) compared to control. Supplementation of SIF or estradiol valerate (EV) reduced (p<0.05) serum gonadotrophin releasing hormone and luteinizing hormone concentration, but increased follicle-stimulating hormone concentration in pigs at 4 months of age. The expression of KiSS-1 metastasis-suppressor (KISS1), steroidogenic acute regulatory protein (StAR) and 3-beta-hydroxysteroid dehydrogenase/delta-5-delta-4 isomerase ($3{\beta}-HSD$) was reduced (p<0.01) in SIF-supplemented groups. Expression of gonadotropin-releasing hormone receptor in the pituitary of miniature pigs was reduced (p<0.05) compared to the control when exposed to 250, 1,250 mg/kg SIF and EV. Pigs on 250 mg/kg SIF and EV also showed reduced (p<0.05) expression of cytochrome P450 19A1 compared to the control. Our results indicated that dietary supplementation of SIF induced puberty delay, which may be due to down-regulation of key genes that play vital roles in the synthesis of steroid hormones.

• Proceedings of the Materials Research Society of Korea Conference
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• 2011.10a
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• pp.20.1-20.1
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• 2011

The nano-sized quantum structure has been an attractive candidate for investigations of the fundamental physical properties and potential applications of next-generation electronic devices. Metal nano-particles form deep quantum wells between control and tunnel oxides due to a difference in work functions. The charge storage capacity of nanoparticles has led to their use in the development of nano-floating gate memory (NFGM) devices. When compared with conventional floating gate memory devices, NFGM devices offer a number of advantages that have attracted a great deal of attention: a greater inherent scalability, better endurance, a faster write/erase speed, and more processes that are compatible with conventional silicon processes. To improve the performance of NFGM, metal nanocrystals such as Au, Ag, Ni Pt, and W have been proposed due to superior density, a strong coupling with the conduction channel, a wide range of work function selectivity, and a small energy perturbation. In the present study, bismuth metal nanocrystals were self-assembled within high-k $Bi_2Mg_{2/3}Nb_{4/3}O_7$ (BMN) films grown at room temperature in Ar ambient via radio-frequency magnetron sputtering. The work function of the bismuth metal nanocrystals (4.34 eV) was important for nanocrystal-based nonvolatile memory (NVM) applications. If transparent NFGM devices can be integrated with transparent solar cells, non-volatile memory fields will open a new platform for flexible electron devices.

• Journal of the Korean Society for Precision Engineering
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• v.13 no.2
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• pp.133-145
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• 1996

This paper presents an indirect cutting force measuring system, which uses the current signals from the AC servo drive units of the horizontal machining center, with its applications to the adaptive regulation of the cutting forces in various milling processes and to the on-line monitoring of tool breakage. A typical model for the feed-drive control system of a horizontal machining center is developed to analyze cutting force measurement from the drive motor. The pulsating milling forces can be measured indirectly within the bandwidth of the current feedback control loop of the feed-drive system. It is shown that the indirectly measured cutting force signals can be used in the adaptive controller for cutting force regulation. The whole scheme has been embedded in the commercial machining center and a series of cutting experiments on the face cutting processes are performed. The adaptive controller reveals reliable cutting force regulating capability against the various cutting conditions. It is also shown that the tool breakage in milling can be detected within one spindle revolution by adaptively filtering the current signals. The effect of the cutter run-out has been considered for the reliable on-line detection of tool breakage.

• Journal of Powder Materials
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• v.20 no.3
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• pp.197-202
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• 2013

A novel route to prepare Nd-Fe-B magnetic particles by utilizing both spray drying and reduction/diffusion processes was investigated in this study. Precursors were prepared by spray drying method using the aqueous solutions containing Nd salt, Fe salt and boric acid with stoichiometric ratios. Precursor particles could be obtained with various sizes from 2 to $10{\mu}m$ by controlling concentrations of the solutions and the average size of $2{\mu}m$ of precursors were selected for further steps. After heat treatment of precursors in air, Nd and Fe oxides were formed through desalting procedure, followed by reduction processes in Hydrogen ($H_2$) atmosphere and with Calcium (Ca) granules in Argon (Ar) successively. Moreover, diffusion between Nd and Fe occurred during Ca reduction and $Nd_2Fe_{14}B$ particles were formed. With Ca amount added to particles after $H_2$ reduction, intrinsic coercivity was changed from 1 to 10 kOe. In order to remove and leach CaO and residual Ca, de-ionized water and dilute acid were used. Acidic solutions were more effective to eliminate impurities, but Fe and Nd were dissolved out from the particles. Finally, $Nd_2Fe_{14}B$ magnetic particles were synthesized after washing in de-ionized water with a mean size of $2{\mu}m$ and their maximum energy product showed 9.23 MGOe.

• Bulletin of the Korean Chemical Society
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• v.35 no.9
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• pp.2758-2764
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• 2014

We demonstrated the synthesis of organic carbonates using alkyl/aryl 4,5-dichloro-6-oxopyridazine-1(6H)-carboxylates and alcohol in the presence of aluminum chloride. Alkyl/aryl 4,5-dichloro-6-oxopyridazine-1(6H)-carboxylates were reacted with alcohol in the presence of $AlCl_3$ in toluene at room temperature to afford the corresponding unsymmetric and symmetric organic carbonates in good to excellent yields. These are efficient and convenient processes. Alkyl/aryl 4,5-dichloro-6-oxopyridazine-1(6H)-carboxylates are solid, stable and non-toxic $CO_2/CO_2R$(Ar) source. It is noteworthy that the reaction is carry out under an ambient and acidic conditions, the easy-to prepare and readily available starting materials and the quantitative isolation of reusable 4,5-dichloropyridazin-3(2H)-one.

• Journal of the Korean Society for Precision Engineering
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• v.21 no.2
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• pp.186-194
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• 2004

Micro-stereolithography is a newly proposed technology as a means that can fabricate a 3D micro-structure of free form. It makes a 3D micro-structure by dividing the shape into many slices of relevant thickness along horizontal surfaces, hardening each layer of slice with a focused laser beam, and stacking them up to a desired shape. In this technology, differently from the conventional stereolithography, scale effect is dominant. To realize micro-stereolithography technology, we developed the micro-stereolithography apparatus which is composed of an Ar+ laser, x-y-z stages. controllers. optical devices and scan path generation software. Related processes were developed, too. Using the system, a number of micro-structures were successfully fabricated. Some of these samples are shown for prove this system. Laser scan path generation algorithm and software considering photopolymer solidification phenomena as well as given 3D model were developed. Sample fabrication of developed software shows relatively high dimensional accuracy compared to the uncompensated result.

• Proceedings of the KSME Conference
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• 2007.05a
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• pp.1617-1620
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• 2007

This paper presents a magnetostrictive transpositioner and its fabrication process. To get a transposition movement without shifting or twisting, it is designed as an array type. To fabricate the suggested design, micromachining and selective DC magnetron sputtering processes are combined. TbDyFe film is sputter-deposited on the back side of the bulk micromachined transpositioner, with the condition as: Ar gas pressure below $1.2{\times}10^{-9}$ torr, DC input power of 180W and heating temperature of up to $250^{\circ}C$ for the wireless control of each array component. After the sputter process, magnetization and magnetostriction of each sample are measured. X-ray diffraction studies are also carried out to determine the film structure and thickness of the sputtered film. For the operation, each component of the actuator has same length and out-of-plane motion. Each component is actuated by externally applied magnetic fields up to 0.5T and motion of the device made upward movement. As a result, deflections of the device due to the movement for the external magnetic fields are observed.

• Journal of Powder Materials
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• v.10 no.6
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• pp.430-435
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• 2003

The phenomenon of electrical explosion of conductors is considered in the context of the changes in the energy and structural states of the metal at the stages of energy delivery and relaxation of the primary products of EEC. It is shown that these changes are related to the forced interaction of an intense energy flux with matter and to the subsequent spontaneous relaxation processes. The characteristics of nano-sized metal powders are also discussed. The preferential gas media during EEC is Ar+$H_2$. An increase in $e/e_s$ (in the range of values studied) leads to a reduction in the metal content. For reactive powders obtained with high metal content, it is necessary to separate the SFAP fractions, which settled on the negative electrode of the electric filter.

• Journal of Powder Materials
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• v.15 no.1
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• pp.58-62
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• 2008

Reaction bonded silicon carbide (RBSiC) is an important engineering ceramic because of its high strength and stability at elevated temperatures, and it is currently fabricated using reasonably cheap manufacturing processes, some of which have been used since the 1960s. However, forming complicated shapes from these materials is difficult because of their poor workability. The purpose of this work is to join the reaction-bonded SiC parts using a preceramic polymer as joint material. The manufacturing of ceramic material in the system Si-O-C from preceramic silicon containing polymers such as polysiloxanes has attained particular interest. The mixtures of preceramic polymer and filler materials, such as SiC, Si and MoSi, were used as a paste for the joining of reaction sintered SiC parts. The joining process during the annealing in Ar atmosphere at $1450^{\circ}C$ were described. The maximum strength of the joints was 63 MPa for the specimen joined with 10 vol.% of $MoSi_2$ and 30 vol.% of SiC as filler materials. Fracture occurred in the joining layer. This indicates that the joining strength is limited by the strength of the joint materials.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.25 no.1
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• pp.47-53
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• 2001

As the technology has developed and new materials have been produced, it is important to measure the thermal diffusivity of material and to predict the heat transfer in the solid subject to thermal processes. This measurement can be done in a non-contact way using photothermal displacenent spectroscopy. In this study, photothermal displacement method was used to measure the thermal diffusivity quantitatively. The specimens used in this study were the pure materials. The Ar-ion laser was used as an energy source and the periodical deformation induced by this pump laser was detected by the He-Ne laser. The magnitude and the phase angle of deformation gradient were measured. The thermal diffusivity was obtained by analyzing the phase angle of deformation gradient. As the result, comparing with the literature value, the thermal diffusivities of materials measured were showed about 2% error.