• Journal of Welding and Joining
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• v.29 no.1
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• pp.41-45
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• 2011

SnAgCu lead-free solder alloy is considered as the best alternative to eutectic tin-lead solder. However, the detailed material properties of SnAgCu solder are not available in public. Hence, this paper presents an estimation of mechanical properties of SnAgCu lead-free solder. In particular, the weight percent of Ag was varied as 1.0wt%, 2.5wt%, 3.0wt%, and 4.5wt% in order to estimate the effect of Ag in the Sn-xAg-0.5Cu ternary alloy system. For this purpose, four types of SnAgCu bars were first molded by casting and then standard specimens were cut out of molded bars. Micro-Vickers hardness, tensile tests were finally performed to estimate the variations in mechanical properties according to the weight percent of Ag. Test results reveal that the higher the weight percent of Ag is, the higher the hardness, yield strength, and ultimate tensile strength become. More material properties will be further investigated in the future work.

• Korean Journal of Exercise Nutrition
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• v.23 no.1
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• pp.28-35
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• 2019

[Purpose] The purpose of this study was to investigate the effects of treadmill exercise on oxidative stress in the hippocampal tissue and mitochondrial dynamic-related proteins in rats fed a long-term high-fat diet (HFD). [Methods] Obesity was induced in experimental animals using high fat feed, and the experimental groups were divided into a normal diet-control (ND-CON; n=12), a high fat diet-control (HFD-CON; n=12) and a high fat diet-treadmill exercise (HFD-TE; n=12) group. The rats were subsequently subjected to treadmill exercise (progressively increasing load intensity) for 8 weeks (5 min at 8 m/min, then 5 min at 11 m/min, and finally 20 min at 14 m/min). We assessed weight, triglyceride (TG) concentration, total cholesterol (TC), area under the curve, homeostatic model assessment of insulin resistance, and AVF/body weight. Western blotting was used to examine expression of proteins related to oxidative stress and mitochondrial dynamics, and immunohistochemistry was performed to examine the immunoreactivity of gp91phox. [Results] Treadmill exercise effectively improved the oxidative stress in the hippocampal tissue, expression of mitochondrial dynamic-related proteins, and activation of NADPH oxidase (gp91phox) and induced weight, blood profile, and abdominal fat loss. [Conclusion] Twenty weeks of high fat diet induced obesity, which was shown to inhibit normal mitochondria fusion and fission functions in hippocampal tissues. However, treadmill exercise was shown to have positive effects on these pathophysiological phenomena. Therefore, treadmill exercise should be considered during prevention and treatment of obesity-induced metabolic diseases.

• Journal of Communications and Networks
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• v.11 no.2
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• pp.122-133
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• 2009

As wireless spectrum resources become more scarce while some portions of frequency bands suffer from low utilization, the design of cognitive radio (CR) has recently been urged, which allows opportunistic usage of licensed bands for secondary users without interference with primary users. Spectrum sensing is fundamental for a secondary user to find a specific available spectrum hole. Cooperative spectrum sensing is more accurate and more widely used since it obtains helpful reports from nodes in different locations. However, if some nodes are compromised and report false sensing data to the fusion center on purpose, the accuracy of decisions made by the fusion center can be heavily impaired. Weighted sequential probability ratio test (WSPRT), based on a credit evaluation system to restrict damage caused by malicious nodes, was proposed to address such a spectrum sensing data falsification (SSDF) attack at the price of introducing four times more sampling numbers. In this paper, we propose two new schemes, named enhanced weighted sequential probability ratio test (EWSPRT) and enhanced weighted sequential zero/one test (EWSZOT), which are robust against SSDF attack. By incorporating a new weight module and a new test module, both schemes have much less sampling numbers than WSPRT. Simulation results show that when holding comparable error rates, the numbers of EWSPRT and EWSZOT are 40% and 75% lower than WSPRT, respectively. We also provide theoretical analysis models to support the performance improvement estimates of the new schemes.

• Bulletin of the Korean Chemical Society
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• v.33 no.5
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• pp.1480-1484
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• 2012

We report a series of novel imidazolium iodides based ionic liquids (NMIPHI, NAIPHI, and NBIPHI) with different functional groups for the development of a quasi-solid type electrolyte for dye-sensitized solar cells (DSSCs). The diffusion coefficients of redox ions ($I^-$ and $I_3{^-}$) are dependent on the molecular weight and it was higher for lighter salts. Among the three ionic liquids, NMIPHI showed highest efficiency of 4.18% when it was used in a liquid electrolyte of a DSSC with $ca$. 6 ${\mu}m$ thick $TiO_2$ mesoporous film. Even though the efficiency was $ca$. 19% lower than that obtained from a liquid electrolyte composed of PMII. When NMIPHI was mixed with PMII with a molar ratio of 1:1 in a solvent free electrolyte, the efficiency of the DSSCs was enhanced compared to that based on pristine PMII.

• Journal of Welding and Joining
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• v.34 no.3
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• pp.6-11
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• 2016

Joining Al/Fe dissimilar metals is becoming a subject of special interest in the assembly of automotive parts as a trade-off between the weight lightening and the cost reduction. Although various studies have been introduced to join Al alloy with the steel sheet by fusion welding, weak joint strength and galvanic corrosion still remained as problems to be solved. As a solid state welding, friction stir welding has been preferred to fusion welding processes in the dissimilar metal joints. This study investigated friction stir spot welding (FSSW) of Al alloy to the thin steel sheet with a thickness of 0.65 mm. The conventional FSSW is a stationary spot welding process but new approach adopted an additional circumferential movement in company with high speed tool rotation. A full factorial experimental design was implemented, and the main and interaction effects of parameters were analysed on the failure load in the tensile shear test. The direction and radius of rotation were statistically significant parameters and these two parameters affected the joint width and the shape of the hook.

• 한국생물공학회:학술대회논문집
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• 2003.04a
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• pp.554-556
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• 2003

This research was focused on expression, purification and characterization of ubiquitin-specific protease 1 (UBP1) expressed in recombinant Escherichia coli. Various systems were constructed by fusing polycationic fusion tails or fusion partners to the C- or N-terminus of the product protein. In particular, UBP1 containing 6 histidine residues at the N-terminal end showed best results in terms of expression level and purification efficiency. The N-terminal $6{\times}His-tagged$ UBP1 was overproduced in recombinant E. coli using high cell density cultivation technology and purified using immobilized metal affinity chromatography. The molecular weight of UBP1 was found to be 83,500 daltons. The optimum temperature and pH for the enzyme reaction when ubiquitin-human growth hormone (hGH) was used as a substrate were $40^{\circ}C$ and pH 8.0, respectively.

• Journal of the Korean Society for Precision Engineering
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• v.28 no.9
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• pp.1094-1102
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• 2011

Recent trends for the miniaturization and weight reduction of portable electronic parts is the use of subminiature components. Assembly of the miniaturized components requires subminiature screws of which pitch sizes are in a micrometer scale. To produce such a subminiature screw with high precision threads, not only a precision forming technology but also high-precision measurement technique is required. In the present work, a vision inspection system is developed to measure the thread profile of a subminiature screw. Optical simulation based on a ray tracing method is used to design and analyze the optical system of the vision inspection apparatus. Through this simulation, optical performance of the developed vision inspection system is optimized. The image processing algorithm for the precision screw inspection is also discussed.

• Proceedings of the KSME Conference
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• 2007.05a
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• pp.142-147
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• 2007

A series of styrene-butadiene-styrene/aluminium (SBR/Al) composites have been compounded with different weight ratios of Al. The prepared SBR-Al systems have been characterized for different mechanical properties such as tensile strength, tensile modulus and surface hardness have improved with the increase in content of Al in SBR matrix. This may is because of the increase in polymer-filler interaction. The electrical properties such as volume conductivity, surface resistivity, dielectric constant, dissipation factor (tan delta), and break down voltage of SBR/Al composites have been measured with reference to volume fraction $(V_{f}),$ frequency and temperature. The resistance of the SBR-Al composites is found to be ohmic. The voltage-current (V-I) characteristics for SBR-Al also exhibit a linear relationship indicating the ohmic behavior.

• 한국균학회소식:학술대회논문집
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• 2009.10a
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• pp.14-16
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• 2009

Poria cocos is an importantant medical macrofungus,the sclerotium of Poria cocos has specific value as the drug material. There are few papers about its breeding and spawn rejuvenation. In this project, the protoplasts of cultivated strain T and wild strain L were prepared and treated separately by ultraviolet and heating, then fused with the PEG6000. The tural fusants were selected and identified by the affinity and ISSR analysis. 71 incompatibility strains between parents and reg regenerations were obtained from 118 regenerations by the affinity analysis. Five incompatibility strains were amplified with different primers, the results were showed that they had specific bands of both parents in the profile amplified with 3 primers, which proved these 5 strains were fusants by means of molecular biology marker. On the other hand, 25 strain were selected from 168 protoplast regenerations of cultivated strain T for cultivation experiment. The fresh sclerotium weight of these protoplast regenerations were better than the original strain.significantil 3 strains (T-1, T-4, T-7) increased respectively 118%, 73% and 73% than original strain. This method could be the effective in the rejuvenation Poria cocos.

• Journal of the Institute of Electronics Engineers of Korea SC
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• v.37 no.2
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• pp.16-28
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• 2000

In this paper, we propose a navigation algorithm for a mobile robot, which is intelligently searching the goal location in unknown dynamic environments using an ultrasonic sensor. Instead of using "sensor fusion"method which generates the trajectory of a robot based upon the environment model and sensory data, "command fusion"method is used to govern the robot motions. The major factors for robot navigation are represented as a cost function. Using the data of the robot states and the environment, the weight value of each factor is determined for an optimal trajectory in dynamic environments. For the evaluation of the proposed algorithm, we peformed simulations in PC as well as real experiments with ZIRO. The results show that the proposed algorithm is apt to identify obstacles in unknown environments to guide the robot to the goal location safely.