• Journal of the Korea Society of Computer and Information
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• v.15 no.3
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• pp.81-89
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• 2010

The research on peer-to-peer streaming schemes has largely focused on tree-push and mesh-pull structures. However, the tree-push structure has a defect that the tree restructuring time is long, and the mesh-pull structure has long startup delay and lag time from source servers. In this paper, we propose a new peer-to-peer live streaming scheme based on a push-mesh structure that takes advantages of tree-push and mesh-pull structure simultaneously. This structure basically provides the mesh-pull mechanism for data transmission and utilizes peers with high network upload capacity. It also supports the push mechanism along with paths from a source server, super peers, and selected general peers. By NS-2 simulation experiments, we finally show that our proposed scheme can achieve shorter startup delay than the mesh-pull structure, similar lag time to tree-push structure and best playback continuity among the three schemes.

• Journal of the Korean Electrochemical Society
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• v.13 no.4
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• pp.277-282
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• 2010

Durability of automotive polymer electrolyte membrane fuel cell (PEMFC) strongly depends the startup/shutdown procedure. Formation of hydrogen/air boundary in the anode gas channel, so-called reverse current condition, particularly induces fast degradation of the cathode. Under the reverse current condition, high voltage is present at the cathode facing air in the anode gas channel and is a function of residual oxygen concentration in the gas channels, that increases with storage time and reaches 21% (air) eventually. In this study, effects of residual oxygen concentration in a PEMFC on degradation of the PEMFC.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.65 no.6
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• pp.1007-1012
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• 2016

Induction motors are used widely in driving load of a fluid, such as a pump or a fan in the industry. Induction motor has been generated the voltage drop by the occurrence of a high current during startup. In addition, high start-up current can act as a mechanical stress on the shaft of the motor. So there is need a way to reduce the starting current. Soft start method is one of the many ways to reduce the starting current. This method uses silicon-controlled rectifiers(SCRs) for varying value of the voltage applied to the motor. There is a case for fixing or changing the thyristor firing angle to adjust the magnitude of the voltage. Starting power factor of induction motor is very low compared to the normal operation. Soft starting with the firing angle fixed needs to be considered a low power factor at startup. In this study, we compared the direct start characteristics and soft start characteristics considering the low power factor at the time of start-up. It was possible to confirm that the starting current and the voltage drop is present differently according to the firing angle.

• The KSFM Journal of Fluid Machinery
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• v.7 no.1 s.22
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• pp.51-57
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• 2004

The waterhammer has recently become more important because the pumping stations were big and the systems conveying the fluid through the large and long transmission pipelines were complex. When the pumps are started or stopped for the operation or tripped due to the power failure, the hydraulic transients occur as a result of the sudden change in velocity As the pressure waves are propagating between the pumping station and the distributing reservoir, the pressure inside the pipe drops to the liquid vapor pressure with the pipeline profile, at which time a vapor cavity forms, and finally the column separation occurs. If the pressure in the pipe is less than the atmospheric pressure, the pipe can be collapsed and destroyed after the water columns separated by the vapor cavity rejoin. During the reverse flow, the pressure is so abnormally increased at the pumping station that the accident of flooding may happen due to the failure of system. In this paper, the field tests on the waterhammer by the startup, stoppage, and power failure of a centrifugal pump were carried out for Yongma transmission pumping station in Seoul. The experimental results were compared with that of the numerical calculations, in which results the procedure of controlled pump normal shut-down and the two-step closing mode of controlling the ball valve for pump emergency stop are proposed to reduce the pressure surge.

• Proceedings of the Safety Management and Science Conference
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• 2002.11a
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• pp.295-304
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• 2002

This case describes key development challenges and patterns as experienced by Internet Auction Company, Ltd. from the startup stage through IPO to the sale to eBay. Currently an eBay company, Internet Auction Co. continues to pursue new auction systems and substitute distribution systems for the future with a renewed entrepreneurial spirit. In 1997, Mr Hyuk Oh saw a business opportunity in the Internet allowing two-way communications. At that time, the success stories of eBay and Onsale in the United States were good stimuli to his startup of an auction site. He opened the Website in April 1, 1998 after four months of development efforts. Auction has merit more than other shopping malls. First, it brings about interesting and benefit. Second, it has interactive trade system. Third, customers will trade for reasonable price through direct own will of them. Fourth, Auction's model brings about multitude sale through aggressive sales. Even if Network Marketing has socially negative effect in case of inappropriate use, it is good mood for further business. In case E-Commerce use as useful purpose, it will have competitive priority revenue model.

• Nuclear Engineering and Technology
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• v.29 no.6
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• pp.488-499
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• 1997

The measurements of the moderator temperature coefficient (MTC) are performed to demonstrate that the calculational model produces results that are consistent with the measurements. Since negative MTC is also a technical specification value that may limit the cycle length, it is important to measure it as accurately as possible. In this report, preferred choice of test method depending on the time in cycle, best power indication and temperature definition in MTC calculation were determined based on the MTC test results taken during initial startup testing and at 2/3 cycle burnup in the Yonggwang nuclear power plant. The results show that the ratio and rodded methods provided good agreement with the predictions during initial startup testing. However, near end-of-cycle the depletion method gives better results, and so is suggested to be used in the MTC measurements at 2/3 cycle burnup. The use of primary Delta T power as a power indicator in the MTC calculations is highly advisable since it responds with good consistent results very quickly to changes unlike secondary calorimetric power. For the appropriate temperature definitions used in the MTC calculations, it is considered that the arithmetic average temperature measured simply by inlet and outlet thermocouples is preferred. Although volumetric average temperature provides better results, the improvement is not sufficient to compensate for the simplicity of calculations by arithmetic average temperature.

• The Transactions of the Korean Institute of Power Electronics
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• v.25 no.5
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• pp.395-403
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• 2020

This study presents a stable start-up strategy for v/f scalar-controlled permanent magnet synchronous motors (PMSMs). The v/f-controlled PMSMs easily lose synchronism under low-speed conditions if an insufficient stator voltage is applied to the machine due to errors in measured motor parameters and inverter nonlinearity, such as inverter dead time and on-state voltage drop. The proposed method adopts the I/f control method to ensure a stable start at low speeds and then switches to the v/f control method at medium speeds. A smooth transition method from I/f control to v/f control is proposed to minimize the oscillation of the stator current and rotor speed during transition. Moreover, the stability of the I/f and v/f control methods is analyzed using a small-signal model. Simulation and experimental results are provided to verify the performance of the proposed control strategy.

• Asia-Pacific Journal of Business Venturing and Entrepreneurship
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• v.14 no.3
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• pp.169-183
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• 2019

Should a startup file for a patent subject to imitation in its quest to attract venture capital(VC) investors? Considering the US pharmaceutical biotechnology industry context, this paper attempts to answer this question by investigating the relations between the number of applied patents of startups, patent imitability, and the total amount of money the startups received as their first VC funding round. Data of 157 US-based pharmaceutical biotechnology startups founded in between 1995 and 2005 are analyzed. Empirical results from this study show that the number of applied patents is positively related to the total amount of money received at the time of the first funding round, and patent imitability is negatively related to the total amount of money received as first VC funding round. Nonetheless, the interaction term between the number of applied patents of startups and patent imitability came out as positive, raising interesting questions and implications for innovation-oriented startup entrepreneurs. The current study's empirical findings suggest that, in the pharmaceutical biotechnology sector, VC investors pay attention to the quantity and quality of the patents possessed by startups when they decide the level of funding. In particular, imitability of applied patents may not be a one-sided concept related to negative features such as the weak protectability of an invention. Rather, patent imitability may be a multi-facet element which also contains positive attractiveness of the startup's invention. Furthermore, it seems that the positive side of imitability can be augmented by the number of applied patents.

• Asia-Pacific Journal of Business Venturing and Entrepreneurship
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• v.16 no.2
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• pp.1-17
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• 2021

Existing research on the investment relationship between venture capital and start-up companies has mainly focused on choosing a startup from the perspective of venture capital, an investor. However, as competition among venture capital has increased recently, excellent start-ups with proven technology are choosing venture capital in reversely. This study investigated key elements that affect the selection of the venture capital by a startup. To this end, we looked at which venture capital company was selected as the final investor for startups that have received investment proposals from multiple venture capitals at the same time. Six early start-ups(pre-series A/Series A) and five mid-term (Series B/C) start-ups were interviewed to focus on the influence of the three elements regarding venture capital - 1) venture capital reputation, 2) relationship between cofounders and investors, and 3) value adding service provided by venture capital - on choice. As a result of the research, the investment portfolio among the reputations of venture capital was a very important element in selecting venture capital. However, it has been shown that the age and asset under management of venture capital are not important. Relationships have emerged as a very important element. Finally, as for venture capital's value-adding services, start-ups in this study did not consider it important. In particular, consulting and monitoring by venture capital has been found to be a burdening attribute for startups. This study suggests implications that can increase the probability of successful investment by venture capital in the investment market where investment competition is fierce, and enhance mutual understanding between venture capital and startups.

• Journal of Electrical Engineering and Technology
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• v.1 no.1
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• pp.23-27
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• 2006

In this paper a Hybrid Real Time HVDC Simulator fur both operator Training and Researching in the Cheju-Haenam HVDC System is proposed and its performance is studied by means of RTDS (Real Time Digital Simulator), EMTDC (Electro-Magnetic Transients system for DC), PSS/E (Power System Simulator for Engineering), and experienced scenarios. The objective of this paper is to represent the strategy in development for KEPCO's hybrid HVDC simulator for the Cheju-Haenam HVDC system. This simulator consists of two DC stations, DC cables, external digital/analog controllers, monitoring systems and control desk for education, and AC networks. Its suitability for operator's education is tested during startup/shutdown and normal state operations. Dynamic performances of it are also verified.