• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2009.11a
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• pp.62-65
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• 2009

This study for prediction of startup characteristics for 30 tonf liquid rocket engine TP-GG-CC coupled test was performed on the basis of the previous TP-GG test and prediction results. For determining the valve sequence the startup analysis was performed by the specified program for several main valve time and the adequate valve sequence for startup could be obtained.

• Journal of the Korean Society of Propulsion Engineers
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• v.20 no.3
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• pp.1-8
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• 2016

It was examined that start-up characteristics of a staged combustion cycle engine powerpack. Among various parameters, valve opening time was considered as a main factor affecting the start-up characteristics. Using monte-carlo method, characteristics variation was analyzed when the valve opening time deviates from the nominal value. As a result, the main fuel valve opening time and the start turbine ending time were significant associated with the startup characteristics. When separating main fuel valve opening time and start turbine stop time, main fuel valve opening time was an important factor. For stable operation, the main fuel valve opening time must be set one second before after driving the start turbine. Likewise, it was confirmed that the startup analysis can suggest an appropriate startup sequence for a stable startup.

• Journal of Power Electronics
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• v.18 no.5
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• pp.1567-1576
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• 2018

The reliability of grid-connected inverters can be improved by algorithms capable of diagnosing faults in LCL filters. A fault diagnostic method during inverter startup is proposed. The proposed method can accurately generate and monitor information on the peak value and the location of the peak frequency component of the step response of a damped LCL filter. To identify faults, the proposed method compares the evaluated response with the response of a healthy higher-order damped LCL filter. The frequency components in the filter voltage response are first analytically obtained in closed form, which yields the expected trends for the filter faults. In the converter controller, the frequency components in the filter voltage response are computed using an appropriately designed fast Fourier transform and compared with healthy LCL response parameters using a finite state machine, which is used to sequence the proposed startup diagnostics. The performance of the proposed method is validated by comparing analytical results with the simulation and experimental results for a three-phase grid-connected inverter with a damped LCL filter.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2011.11a
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• pp.750-755
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• 2011

The ignition characteristics of liquid rocket engine thrust chambers which have been developed by domestic technology were analyzed. Analysis results showed that low frequency fluctuation appeared in a partial ignition range according to different temperature profiles and vaporous state in the oxidizer manifold with startup sequences. This low frequency fluctuation wasn't developed as a malfunction factor, but this fluctuation is thought to be taken a continuous concern considering interfaces with engine system and launch vehicle.

• Journal of the Korean Society of Propulsion Engineers
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• v.16 no.6
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• pp.73-78
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• 2012

The ignition characteristics of liquid rocket engine thrust chambers which have been developed by domestic technology were analyzed through hot-firing tests. Thrust chambers used in hot-firing tests have different characteristics in terms of the injector for ignition, film cooling method and the position of the oxidizer inlet. Also, these thrust chambers used their respective startup sequences. Analysis results showed that according to temperature profiles of the oxidizer manifold, low frequency fluctuation was appeared in ignition area. This low frequency fluctuation didn't give rise to violent malfunction of the thrust chamber, but the continuous observation as a concern parameter in the side of interfaces with engine system and launch vehicle should be demanded.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.7 no.9
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• pp.2268-2283
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• 2013

Scalable video coding can handle peer heterogeneity of P2P streaming applications, but there is still a lack of comprehensive studies on how to use it to improve video playback quality. In this paper we propose a capacity aware scalable video coding mechanism for P2P on demand streaming system. The proposed mechanism includes capacity based neighbor selection, adaptive data scheduling and streaming layer adjustment, and can enable each peer to select appropriate streaming layers and acquire streaming chunks with proper sequence, along with choosing specific peers to provide them. Simulation results show that the presented mechanism can decrease the system's startup and playback delay, and increase the video playback quality as well as playback continuity, and thus it provides a better quality of experience for users.

• Aerospace Engineering and Technology
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• v.13 no.1
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• pp.70-75
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• 2014

Programs of energy balance, mode analysis and transient analysis for a liquid rocket engine have been introduced. The analysis methods have been verified through comparison between the present results, and the results of the other program and experimental data. An energy balance analysis is used for engine system design at the early development phase. A mode analysis is used for decision of engine operation conditions and test conditions, and studying deviation of an engine performance. A transient analysis can predict a propellant flow rate, thrust, impulse at transient phase. It is essential to establish a startup/shut down sequence. The analysis programs will be used to develop the engines of KSLV-II.

• Journal of Information Technology Services
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• v.13 no.4
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• pp.123-137
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• 2014

Since the global financial crisis, funding for startups or ventures has been diminished seriously. In this situation, crowd-funding has attracted worldwide attention as a viable means to financing startups/ventures. After reviewing existing laws in other countries, this study investigated the current status of crowd-funding legalization in Korea and surveyed requirements from three groups of participants to crowd-funding. Investors already recognized the high risk of crowd-funding into startups and asked for the protection of their investment. But, their priorities were on the enlargement of tax benefits and the establishment of a trading market for selling their equity. In addition, investors wanted to shorten the compulsory holding period. Issuers as fund raisers hoped fast legalization, convenient process of crowd-funding, and expansion of government support. Crowd-funding platform operators requested policies for establishing paths to become new growth companies from startups, tax benefits, and the setup of separate fund for startups. Currently, the National Assembly in Korea is holding the discussion on the submitted law. For desirable outcomes to all participants, it would be better to proceed in the following sequence. First, legalize the crowd-funding with clauses protecting investors; Second, encourage investment through tax benefits; Third, develop communities among participants for reducing information asymmetry; And fourth, establish diverse trading markets for selling equities of startups.

• Journal of Power Electronics
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• v.14 no.6
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• pp.1119-1129
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• 2014

This study proposes a novel five-level three-phase hybrid-clamped converter composed of only six switches and one flying capacitor (FC) per phase. The capacitor-voltage-drift phenomenon of the converter under the classical sinusoidal pulse width modulation (SPWM) strategy is comprehensively analyzed. The average current, which flows into the FC, is a function of power factor and modulation index and does not remain at zero. Thus, a specific modulation strategy based on space vector modulation (SVM) is developed to balance the voltage of DC-link and FCs by injecting a common-mode voltage. This strategy applies the five-segment method to synthesize the voltage vector, such that switching losses are reduced while optional vector sequences are increased. The best vector sequence is then selected on the basis of the minimized cost function to suppress the divergence of the capacitor voltage. This study further proposes a startup method that charges the DC-link and FCs without any additional circuits. Simulation and experimental results verify the validity of the proposed converter, modulation strategy, and precharge method.

• Asia-Pacific Journal of Business Venturing and Entrepreneurship
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• v.9 no.3
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• pp.47-61
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• 2014

Many angel investors hesitate to invest in early-stage company. Most early-stage company has no sales and only R&D step project or in early approach of market. So it's impossible to evaluate early-stage company quantitatively. Therefore many angel investors depend on CEO's tendency to evaluate company and make decision for investment. The purpose of this study is discover the entrepreneurial characteristics of CEO and the importance level which affect on the angel investors decision making factors for investment. To identify the factors of entrepreneurial characteristics, survey was conducted by Delphi Technique which is involved by 20 experts who is angel investment club members, venture capitalists, CEOs and officers. Three rounds of survey results derived 10 elements of entrepreneurial characteristics for investment decision making factors including reliability, risk sensitivity, passion, perseverance, integrity, leadership, startup experience, organizational management skills, innovation and social networking. In addition, this study derived the importance level of elements of entrepreneurial characteristics based on the AHP(Analytic Hierarchy Process) theory and maintained the logical consistency by pair-wise comparison for each element. As a result of analyzing the importance of entrepreneurial characteristics, the sequence is reliability (18.1%), integrity (15.9%), leadership (11.7%), organizational management skills (10.0%), social networking (9.5%), passion(9.1%), perseverance(8.4%), innovation(8.1%), startup experience(5.3%) and risk sensitivity(3.9%) respectively. The significance of this study is somewhat decrease limit of the uncertainty arising from angel investors and angel investors can help a decision making, by discover factors of entrepreneurial characteristics that can be called the biggest influencing factors among Investor's investment decision-making In early stage companies and compare importance.