No abstract

The procurement of public construction, which has been selected mainly on the basis of the work experience of a department of public agencies that award construction contracts or those in charge of ordering, has not been executed through an objective selection process considering the construction types or characteristics. Thus, as a preliminary study on developing a model for the selection of contract methods, this study intends to analyze and present the key factors affecting the selection of procurement methods in public construction. Through a literature review on the existing methods, foundational factors were first presented, based on the analysis of these factors, the final influence factors were proposed. As a result, 6 factors contractor's characteristics, the environment of the construction market, relevant organization, the characteristics of a project, costs, and responsibility factors were determined, and 14 sub-factors were selected. The factors presented in this study will be used as base data for developing a decision making support model for the selection of contract methods in public construction.

This study was carried out to evaluate the antifungal and antioxidative activities of ethanol extracts from Magnoliaceae to investigate the possibility for the natural fungicides and food preservatives. The antifungal activities of ethanol extracts were evaluated as a hyphal growth inhibition rate using four plant pathogenic and five wood rot fungi. The high inhibition activity on the growth of fungi was shown in bark of Magnolia obovata that indicated more than 50% hyphal growth inhibition rate except Trametes versicolor, one of the white rot fungi. The antifungal activity was the highest in the ethanol extracts from M. obovata and the following was in order of M. kobus and M. sieboldii. The extract from bark in M. obovata showed higher antifungal activity than that from wood in the same species. Especially, the extracts from flower of M. denudata and M. liliflora indicated the high antifungal activities, while the other portions of same plants showed the low activities. On the other hand, a free radical scavenging method was adopted with 1,1-diphenyl-2-picrylhydrohydrazyl (DPPH) in order to test the antioxidative activities of ethanol extracts. The free radical scavenging activity was very high in the extracts from branch of Schizandra nigra and Kadsura japonica that showed more than 90% at the concentration of 100 µg/㎖. It also turned out that the antioxidative activity of branch of S. nigra and K. japonica was similar to α-tocopherol and butylated hydroxytoluene, one of the effective synthetic antioxidants. From these results, it can be suggested that the branches of S. nigra and K. japonica have the positive antioxidative activities and can be applied for the food preservatives and cosmetic ingredient.

-In microgrid demonstration site, distributed generations can make bidirectional power flows on the system. If an accident occurs, the fault current from the inverter based distributed generation is small. However, the conventional protection scheme in distribution network is designed to operate at high fault current. This means that the traditional protection of distribution network is no longer applicable and new protection methods must be developed. In this paper, for two cases, algorithms for protection coordination of demonstration site is proposed and verified through PSCAD/EMTDC simulation. In first case, protection devices are assumed to have the abilities of directional relaying and communication. In second case, protection devices do not have those abilities. Proposed protection coordination algorithms detect the fault locations and protect the microgrid fairly well.

Carbon nanotubes (CNTs) are used in various composite materials to enhance electrical, thermal and mechanical properties of composite materials. In this study, we investigate the wear characteristics of polycarbonate/acrylonitrile-butadiene-styrene (PC/ABS) blends containing multi-walled carbon nanotubes (MWCNTs). PC/ABS blends are commonly used in many industrial applications such as cellular phones and display cases and MWCNTs have been added to the PC/ABS blends to improve their electromagnetic interference shielding (EMS). We performed wear tests on PC/ABS blends containing MWCNTs under reciprocating linear sliding conditions with chrome steel balls as a counterpart material. The normal loads were 10, 30, 50, 70, 100 N, the sliding speed was 10 mm/s, the stroke length was 15 mm, and the tests lasted 900 s. The MWCNTs included in the PC/ABS blends lower the wear volume and friction coefficient of the composites. We analyzed the wear debris collected from the composites during the tests in terms of the MWCNT concentration using inductively coupled plasma optical emission spectroscopy. The results show that the quantity of MWCNTs in the debris is proportional to the concentration of MWCNTs in the composite, indicating that the exposure of the MWCNTs to environments by wear could be increased with their concentration in the composite.