• Journal of Mechanical Science and Technology
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• v.18 no.6
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• pp.979-989
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• 2004

Numerical simulations have been performed to investigate tip clearance effect on through-flow and performance of a centrifugal compressor which has the same configuration of impeller with six different tip clearances. Secondary flow and loss distribution have been surveyed to understand the flow mechanism due to the tip clearance. Tip leakage flow strongly interacts with mainstream flow and considerably changes the secondary flow and the loss distribution inside the impeller passage. A method has been described to quantitatively estimate the tip clearance effect on the performance drop and the efficiency drop. The tip clearance has caused specific work reduction and additional entropy generation. The former, which is called inviscid loss, is independent of any internal loss and the latter, which is called viscous loss, is dependent on every loss in the flow passage. Two components equally affected the performance drop as the tip clearances were small, while the efficiency drop was influenced by the viscous component alone. The additional entropy generation was modeled with all the kinetic energy of the tip leakage flow. Therefore, the present paper can provide how to quantitatively estimate the tip clearance effect on the performance and efficiency.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2003.06a
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• pp.54-57
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• 2003

Since passenger cars require five wheels including a spare, the weight reduction of wheels without sacrificing performance is important. Recently, the structured components of cars made of steel are replaced by composites. plastics and other nonmetallic materials such as aluminum and magnesium for weight reduction. From these new tried materials are most promising due to their high specific stiffness and specific strength. The composites manufactured by resin transfer molding (RTM) process has not only low cost for the manufacturing but also reduces the lead time and development because the molds for RTM is easy to manufacture. In this work, composite wheels for passenger cars were designed and manufactured by RTM process. Since surface quality of wheels is important for passenger cars, the optimal stacking sequence for composite wheels was selected considering surface quality and mechanical properties. Also, the manufacturing method for the composite mold was depicted.

• 한국신재생에너지학회:학술대회논문집
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• 2011.05a
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• pp.95.1-95.1
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• 2011

In this work, graphene was prepared by modified Hummers method and prepared graphene was applied to electrode materials for supercapacitor. In addition, to enhance the electrochemical performance of graphene, carbon black was deposited onto graphene via chemical reduction. The effect of the carbon black content incorporated on the electrochemical properties of the graphene-based electrodes was investigated. It was found that nano-scaled carbon black aggregates were deposited and dispersed onto the graphene by the chemical reduction of acid treated carbon black and graphite oxide. From the cyclic voltammograms, carbon black-deposited graphene (CB-GR) showed improved electrochemical performance, i.e., current density, quicker response, and better specific capacitance than that of pristine graphene. This indicates that the carbon black deposited onto graphene served as an conductive materials between graphene layers, leading to reducing the contact resistance of graphene and resulted in the increase of the charge transfer between graphene layers by bridge effect.

• Journal of Applied Biological Chemistry
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• v.50 no.3
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• pp.136-143
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• 2007

Despite the increased interests in biological control of soilborne diesease for environmental protection, biological control of bacterial wilt caused by Ralstonia solanacearum have not provided consistent or satisfying results. To enhance the control efficacy and reducing the inconsistency and variability, combinations of specific strains of microorganisms, each having a specific mechanism of control, were applied in this study. More than 30 microorganisms able to reduce the activity of pathogen by specific mechanism of action were identified and tested for their disease suppressive effects. After in vitro compatibility examinations, 21 individual strains and 15 combinations were tested in the greenhouse. Results indicated three-way combinations of different mode of control, TS3-7+A253-16+SKU78 and TS1-5+A100-1+SKU78, enhanced disease suppression by 70%, as compared to 30-50% reduction for their individual treatments. This work suggests that combining multiple traits antagonizing the pathogen improve efficacy of the biocontrol agents against Ralstonia solanacearum.

• Korean Journal of Materials Research
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• v.9 no.6
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• pp.635-653
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• 1999

The present work considers work considers research strategies to address global warming. Specifically, this work considers the development of technologies of importance for the reduction of greenhouse gas emission and, especially, the materials that are critical to these technologies. It is argued that novel materials that are essential for the production of environmentally friendly energy may be developed through a special kind of engineering: interface engineering, rather than through classical bulk chemistry. Progress on the interface engineering requires to increase the present state of understanding on the local properties of materials interfaces and interfaces processes. This, consequently, requires coordinated international efforts in order to establish a strong background in the science of materials interfaces. This paper considers the impact of interfaces, such as surfaces and grain boundaries, on the functional properties of materials. This work provides evidence that interfaces exhibit outstanding properties that are not displayed by the bulk phase. It is shown that the local interface chemistry and structure and entirely different than those of the bulk phase. In consequence the transport of both charge and matter along and across interfaces, that is so important for energy conversion, is different than that in the bulk. Despite that the thickness of interfaces is of an order to a nanometer, their impact on materials properties is substantial and, in many cases, controlling. This leads to the conclusion that the development of novel materials with desired properties for specific industrial applications will be possible through controlled interface chemistry. Specifically, this will concern materials of importance for energy conversion and environmental monitoring. Therefore, there is a need to increase the present state of understanding of the local properties of materials interfaces and the relationship between interfaces and the functional properties of materials. In order to accomplish this task coordinated international efforts of specialized research centres are required. These efforts are specifically urgent regarding the development of materials of importance for the reduction of greenhouse gases. Success of research in this area depends critically on financial support that can be provided for projects on materials of importance for a sustainable environment, and these must be considered priorities for all of the global economies. The authors of the present work represent an international research group economies. The authors of the present work represent an international research group that has entered into a collaboration on the development of the materials that are critical for the reduction of greenhouse gas emissions.

• Journal of Internet Computing and Services
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• v.18 no.5
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• pp.103-112
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• 2017

Work engagement and job burnout are crucial problems in Korea, particularly in the business environment, and they also indicate people's motivation. Online-based teams in e-business also have these issues. Especially the role of the leader in this new type of teams is more crucial for members' motivation, behavior, and performance. Contingency leadership theories posit that different situations need different traits or behaviors of a leader. For an online-based team, which is internet-based team in e-business, a leader should use specific communication strategies to enhance a team's performance and members' motivation. In an online-based team and an offline-based team, the ways in which leaders motivate members will be different. This paper suggests particular communicative strategies for leaders of online situations. Online-based team members communicate using mobile phones or IT tools, and leaders mayinfluences members in virtual meetings. Moreover, online-based leadership needs to be more entrepreneurial and risk encouraging, and less conservative than offline-based leadership. In addition, online-based leadership should be energetic, decisive, adaptable, and inspiring, and furtherutilize communication tools such as being more gregarious/talkative, assertiveness, linguistic diversity and affect. This paper explains the roles of communicative elements such as coordination, expression, direction-giving/uncertainty reduction, empathy, meaning-making, satisfaction, and competence to decrease job burnout and to increase work engagement. The purpose of this study is to suggest communication strategies' differentiated influences on work engagement and job burnout in an online-based team.

• Proceedings of the KAIS Fall Conference
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• 2010.05b
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• pp.769-772
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• 2010

The objective of the current research work is to investigate the usage of biodiesel combined with the use of EGR in order to reduce the emission of all regulated pollutants from diesel engines. A single cylinder, air cooled, constant speed direct injection diesel engine was used for the experimental work and a cold EGR system was developed and fitted to the engine. Concentrations of HCs, NOx, and CO from the exhaust gas along with the smoke opacity were measured. Engine performance parameters such as the brake thermal efficiency (BTE) and the brake specific energy consumption (BSEC) were also calculated from the measured data. The results from the present investigation suggest that 25-30% EGR rate could give excellent NOx reduction without any significance penalty on smoke opacity or BSEC under the engine load of up to 40%. Under the full load condition, 15% EGR rate was found to be an option while higher EGR rate resulted in inferior performance and heavy smoke.

• Korean Journal of Construction Engineering and Management
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• v.22 no.6
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• pp.131-137
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• 2021

Since many resources are put into the work of changing the railway operation within limited time, it is important to have a specific work plan and safety management. For this reason, the work schedule is shared in advance, and parallel work is being carried out simultaneously by rail system, such as tracks, trolly wires, and signals. However, due to the nature of the transfer work, the work is carried out at night when the railway operation is finished, and many resources are put into the limited area of the operating line, so the risk of safety accidents and failure to change the operating line is recognized as high. Nevertheless, there is still not enough research done in korea regarding the operation line change construction. Therefore, this study is conducted a survey on the track exchange work of railroad for working people, and analyzed the results of the survey. Finally, a standard work process was suggested to reduce the risk of track exchange work.

• 한국신재생에너지학회:학술대회논문집
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• 2010.06a
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• pp.133.1-133.1
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• 2010

In this work, carbon black(CBs)-embed multi-walled carbon nanotubes (MWNTs) as conductive fillers for activated carbon(ACs)-based electrodes for supercapacitor were prepared by chemical reduction of oxidized MWNTs and CBs. The effect of CBs-MWNT composites on electrochemical performances of ACs-based electrodes were investigated as a function of CB-MWNT ratio. It was found that CBs-MWNTs composites were formed by the reduction reaction of the functional groups of oxidized MWNTs and CBs. It was resulted in the conjugation of CBs onto the MWNT having high surface area and aspect ratio, leading to the enhanced electrical properties of MWNTs. The electrochemical performances, such as current density, charge-discharge, and specific capacitance of the ACs/CBs-MWNT electrodes were higher than that of ACs/MWNTs and conventional ACs/CB electrodes, which was attributed to the synergistic effect of CBs-MWNTs as a conductive filler.

• Korean Journal of Materials Research
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• v.27 no.5
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• pp.248-254
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• 2017

In the present work, graphene powder was synthesized by laser scribing method. The resultant flexible light-scribed graphene is very appropriate for use in micro-supercapacitors. The effect of the laser scribing process in reducing graphene oxide (GO) was investigated. GO was synthesized using a chemical mixture of GO solution; then, it was coated onto a LightScribe DVD disk and laser scribed to reduce GO and create laser-scribed graphene (LSG). The CV curves of pristine rGO at various scan rates showed that the ultimate product possesses the ability to store energy at the supercapacitor level. Charge-discharge curves of pristine rGO at two different current densities indicated that the specific capacitance ($C_m$) increases due to the reduction of the discharge current density. Finally, the long-term charge-discharge stability of the LSG was plotted and indicates that the specific capacitance decreases very slightly from its primary capacitance of ${\sim}10F\;cm^{-3}$ and that the cyclic stability is favorable over 1000 cycles.