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Jun Ho Hwang and Jong-Hyun Lee

Abstract

Sn-coated Cu particles were prepared as a filler material for transient liquid phase (TLP) bonding. The thickness of Sn coating was controlled by controlling the number of plating cycles. The Sn-coated Cu particles best suited for TLP bonding were fabricated by Sn plating thrice, and the particles showed a pronounced endothermic peak at 232°C. The heating of the particles for just 10 s at 250°C destroyed the initial core-shell structure and encouraged the formation of Cu-Sn intermetallic compounds. Further, die bonding was also successfully performed at 250°C under a slight bonding pressure of around 0.1 MPa using a paste containing the particles. The bonding time of 30 s facilitated the bonding of Sn-coated Cu particles to the Au surface and also increased the probability of network formation between particles.

Open access

Eun Byeol Choi and Jong-Hyun Lee

Abstract

For application as a low-cost conductive filler material, submicroscale Cu@Ag particles were fabricated at room temperature without any reductants by a multi-step addition method using an ethylene glycol-based Ag plating solution. Scanning electron microscopy images of the Ag-coated Cu particles demonstrated the formation of discrete Ag particles less than 100 nm in size as well as a thin Ag coating on Cu particles, during the early addition steps. However, as the thickness of the Ag coating increased, the small Ag particles agglomerated into Ag coatings with an increase in the number of Ag plating steps. Owing to the absence of additives such as surfactants, a comparison between the microstructural images and calculations indicated increased agglomeration between fabricated Ag-coated Cu particles with an increase in the number of Ag plating steps. However, thermogravimetric-differential scanning calorimetry of the agglomerated Ag-coated Cu particles after the fifth addition of the Ag plating solution demonstrated their antioxidation behavior even after 70 min in air at 150°C.

Open access

Tak-Kee Lee, Jong-Hyun Lee, Heungsub Kim and Chae Whan Rim

ABSTRACT

This study conducted four field measurements of local ice pressure during the icebreaking voyage of the icebreaking research vessel “ARAON” in the Chukchi and Beaufort seas from July to August of 2010. For measurements, 14 strain gauges, including 8 strain gauge rosettes, were set on the bow of the port side. Influence coefficients were determined using a finite element model of the instrumented area and they were used to convert the measured strains on the hull structure to local ice pressures. The converted maximum pressure was calculated as 2.12 MPa on an area of 0.28 m2. Pressure-area curves were developed from the surveyed pressure data and the results were compared with previously measured data. The study results are expected to provide an understanding of local ice pressures and thus be useful in the structural design of ice class ships.

Open access

Ji-Young Kim, Sang-Suk Kim, Tae-Heon Oh, Jong Baik, Gwanpil Song, Nam Lee and Chang-Gu Hyun

Chemical composition, antioxidant, anti-elastase, and anti-inflammatory activities of Illicium anisatum essential oil

The essential oil of air-dried Illicium anisatum (Illiciaceae), obtained by hydrodistillation was analyzed by gas chromatography-mass spectrometry (GC-MS). Fifty-two components were identified in the essential oil and the main component was eucalyptol (21.8 %). The antioxidant and anti-elastase activities of the essential oil were also investigated; the essential oil exhibited moderate DPPH scavenging and anti-elastase activities. To clarify the mechanism of the anti-inflammatory activities of I. anisatum essential oil (IAE), we evaluated whether it could modulate the production of nitric oxide (NO) and prostaglandin E2 (PGE2) by activated macrophages. The results indicate that IAE is an effective inhibitor of LPS-induced NO and PGE2 production in RAW 264.7 cells. These inhibitory activities were accompanied by dose-dependent decreases in the expression of iNOS and COX-2 proteins and iNOS and COX-2 mRNA. In order to determine whether IAE can be safely applied to human skin, the cytotoxic effects of IAE were determined by colorimetric MTT assays in human dermal fibroblast and keratinocyte HaCaT cells. IAE exhibited low cytotoxicity at 100 μg mL-1. Based on these results, we suggest that IAE may be considered an anti-aging and anti-inflammatory candidate for cosmetic materials, but additional in vitro and in vivo tests have to be performed to prove its safety and efficacy.

Open access

Guoming Wang, Woo-Hyun Kim, Jong-Hyuk Lee and Gyung-Suk Kil

Abstract

With the growing demand for application of metal-oxide varistor (MOV) in low-voltage electronic circuits for overvoltage protection, it is necessary to ensure its performance to avoid the short-circuit and the line-to-ground fault during operation. In this paper, a precise leakage current analyzer was developed to detect the total leakage current and third harmonic component of MOV for its condition monitoring. The voltage- and temperature-dependent measuring uncertainties were compensated using the multipliers. In addition, the deterioration characteristics of the MOV and the newly developed thermally protected metal-oxide varistor (TMOV) were investigated in the accelerated aging test. From the experimental results, the MOV deteriorated much faster under the lightning current impulse synchronized with power-frequency voltage. The thermally activated fuse of TMOV exploded under two types of impulses, which indicated that the TMOV is much more vulnerable and that it is difficult to diagnose the condition of energized TMOV in advance.

Open access

Hyun-Joon Shin, Jong-Seung Lee, Kang-Hoon Lee, Myung-Ryun Han, Eui-Beom Hur and Sung-Chul Shin

ABSTRACT

This paper shows the study of preswirl duct as an effective energy saving devices that have been devised and reviewed to support the propeller performance, especially for the ship of VLCC with large block coefficients. From the bare hull wake measurements, typical upper/lower asymmetry of hull wake at the propeller disk was found. The 2 kinds of pre-swirl duct, Unconventional half circular duct and Conventional circular pre-swirl duct have been designed and reviewed to recover the loss of propeller running in that condition. The general function of the pre-swirl duct was set to work against this asymmetry of wake and generate pre-swirled flow into the propeller against the propeller rotating direction. The optimum self propulsion tests with various angle configurations were carried out and the best configuration was decided. Accordingly, cavitation test was carried out with best configuration of unconventional half circular duct. The blade surface and tip vortex cavitation behaved smoother when the duct was mounted. The hull pressure amplitudes reflected this difference, so the hull pressure amplitude with duct was smaller than that of without duct.