• Journal of Astronomy and Space Sciences
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• 제32권3호
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• pp.257-268
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• 2015

Characteristics of delta-V requirements for deploying an impactor from a mother-ship at different orbital altitudes are analyzed in order to prepare for a future lunar CubeSat impactor mission. A mother-ship is assumed to be orbiting the moon with a circular orbit at a 90 deg inclination and having 50, 100, 150, 200 km altitudes. Critical design parameters that are directly related to the success of the impactor mission are also analyzed including deploy directions, CubeSat flight time, impact velocity, and associated impact angles. Based on derived delta-V requirements, required thruster burn time and fuel mass are analyzed by adapting four different miniaturized commercial onboard thrusters currently developed for CubeSat applications. As a result, CubeSat impact trajectories as well as thruster burn characteristics deployed at different orbital altitudes are found to satisfy the mission objectives. It is concluded that thrust burn time should considered as the more critical design parameter than the required fuel mass when deducing the onboard propulsion system requirements. Results provided through this work will be helpful in further detailed system definition and design activities for future lunar missions with a CubeSat-based payload.

• 한국태양에너지학회 논문집
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• 제23권3호
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• pp.29-35
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• 2003

Generator for wind power can be either synchronous or asynchronous (induction) types. Induction and synchronous generators behave in a different way when subjected to severe faults. Induction generators does not have an angle stability limit and short circuit in the neighborhood of an Induction generator causes the demagnetization of the machine when the fault is cleared, the voltage raises slowly, while the grid contributes with reactive power to the generator and the magnetic flux recovers. On the other hand in the synchronous generators the recovery of the voltage is immediate, since the excitation of the rotor angle comes from an independent circuit. This paper shows the result of the transient state analysis in the network connected to wind generation system Several case studies have been conducted to determine the effect of the clearing time of a fault on the network stability. It has been found that the critical clearing time can be as low as 61ms in the case of induction generator compared to 370ms in the case of synchronous generator.

• 대한전기학회논문지:전력기술부문A
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• 제50권5호
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• pp.225-233
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• 2001

SIME(SIngle Machine Equivalent) method has been recognized as a useful tool to determine transient stability of power systems. In this paper, SIME method is used to develop the KEPCO transient stability assessment (TSA) tool. A new screening algorithm that can be implemented in SIME method is proposed. The salient feature of the proposed screening algorithm is as follows. First, critical generators are identified by a new index in the early stage of the time domain simulation. Thus, computational time required to find OMIB(One Machine Infinite Bus) can be reduced significantly. Second, clustering critical machines can be performed even in very stable cases. It enables to be avoid extra calculation of time trajectory that is needed in SIME for classifying the stable cases. Finally, using power-angle trajectory and subdividing contingency classification have improved the screening capability. This algorithm is applied to the fast TSA of the KEPCO system.

• Industrial Engineering and Management Systems
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• 제11권4호
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• pp.397-405
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• 2012

This research proposes a framework of buffer management for multi-project systems in the critical chain project management (CCPM) method, expressed in the form of max-plus linear (MPL) representation. Since time buffers are inserted in the projects for absorbing uncertainties in task durations and protecting the completion times, the proposed method provides a procedure for frequently surveying the rates of consumed buffers and the rate of elapsed times. Their relation expresses the performance of the projects which is plotted on a chart through the completed processes. The chart presents the current performance of the projects and their interaction, which alerts managers to make necessary decisions at the right time for managing each project and the entire multi-project system. The proposed framework can analyze the complex system readily, and it enables managers to make an effective decision on scheduling. The effectiveness of the framework is demonstrated through a numerical example.

• 한국자동차공학회논문집
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• 제3권5호
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• pp.122-134
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• 1995

The present study was investigated combustion characteristics of methane-air mixtures at stratified charge in a constant volume combustion chamber. The main results obtained from this study can be summarized as follows. In case of ${\phi}_s=1.0$, total burning times greatly affected rather than initial time of pressure increase and maximum combustion pressure. In case of ${\phi}_t=1.0$, initial time of pressure increase and total burning times were affected considerably in comparison with the case of ${\phi}_s=1.0$. Also, even the very lean mixture which total equivalence ratio is ${\phi}_t=0.69$(${\phi}_s=1.0$, ${\phi}_m=0.65$), by changing configuration of the critical passage-hole and using a stratified mixture, it is possible to decrease substantially the initial time of pressure increase. total burning times and NOx concentration without deteriorating combustion characteristics such as maximum combustion pressure, rate of heat release etc. in comparison with the use of single chamber(in case of ${\phi}=1.0$) only. Specifically, our trends were revealed remarkably in the case of Type D which is reduced a flame contact area of sub-chamber side of the passage-hole.

• Structural Engineering and Mechanics
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• 제70권3호
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• pp.311-324
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• 2019

Long-span steel suspension bridges develop significant vibrations under the effect of external time-variable loadings because their slenderness. This causes significant stresses variations that could induce fatigue problems in critical components of the bridge. The research outcome presented in this paper includes a fatigue analysis of a long suspension bridge with 3300 meters central suspended span under wind action and train transit. Special focus is made on the counterintuitive interaction effects between train and wind loads in terms of fatigue damage accumulation in the hanger ropes. In fact the coupling of the two actions is shown to have positive effects for some hangers in terms of damage accumulation. Fatigue damage is evaluated using a linear accumulation model (Palmgren-Miner rule), analyses are carried out in time domain by a three-dimensional non-linear finite element model of the bridge. Rational explanation regarding the above-mentioned counterintuitive behavior is given on the basis of the stress time histories obtained for pertinent hangers under the effects of wind and train as acting separately or simultaneously. The interaction between wind and train traffic loads can be critical for a some hanger ropes therefore interaction phenomena within loads should be considered in the design.

• Tuberculosis and Respiratory Diseases
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• 제71권4호
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• pp.271-277
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• 2011

Background: A chronic obstructive pulmonary disease (COPD) assessment test (CAT) has recently been developed as a short and simple method for assessing the quality of life in COPD patients. The object of this study was to assess the usefulness of the Korean version of the CAT for assessing COPD patients in an outpatient clinic. Methods: The study included 60 COPD patients in a stable state from an outpatient clinic. The authors investigated the frequency of acute exacerbation during aprevious year through reviewing medical records. We evaluated the spirometry test, a 6-min walk distance test, and obtained the MMRC dyspnea scale, the Korean version of the CAT, and the BODE index at the time of visit. To assess the usefulness of the CAT, correlations between the CAT and other methods were evaluated. Results: The mean age of patients was $68.3{\pm}8.6$ years and 95% of patients were male. There was a significant correlation between the CAT score and $FEV_1%$ (r=-0.323, p=0.012), the frequency of acute exacerbation (r=0.292, p=0.024), the MMRC dyspnea scale (r=0.554, p<0.001), the BODE index (r=0.380, p=0.003), and 6 MWD (r=-0.372, p=0.004). The mean CAT score increased according to the GOLD stage (stage 1, $10.7{\pm}4.5$; stage 2, $13.1{\pm}7.9$; stage 3, $16.3{\pm}6.2$; stage 4, $16.5{\pm}14.8$; p=0.746). Conclusion: The CAT was shown to be useful for the assessment of COPD severity. Therefore, the CAT is an easily applied and simple method for assessing COPD severity in an outpatient clinic.

• 디자인학연구
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• 제12권3호
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• pp.227-234
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• 1999

본 논문은 디자인 프로젝트 관리의 리엔지니어링으로서 프로젝트의 기획, 조직, 일정, 그리고 제어하는 통합적인 어플리케이션 소프트웨어 개발의 기초모델을 설정하고, 이를 토대로 프로젝트 관리 시스템의 연구/개발을 목표로 삼고 있다. 프로젝트의 성과, 소요기간, 소요예산, 그리고 소요자원 등을 관리하는 과정이 프로젝트 매니지먼트 기술의 근간을 이루는 것으로, 디자인 프로젝트 상의 수많은 정보를 적시에 효율적으로 처리함으로써 프로젝트를 성공으로 이끌 수 있게 된다. 한편, 디자인프로젝트의 관리를 집단의사결정에 의해 처리함으로써 신뢰도와 합리성의 제고는 물론, 이를 통한 사기앙양이 기대된다. 따라서, 여기에서 야기되는 의사집합의 곤란, 시간손실, 구성원의 갈등 등의 프로젝트 관리에서 비롯되는 부수적인 문제도 전자의 기본적인 관리요소와 함께 통합하여 디자인 프로젝트 관리 시스템(DPMS)을 연구/개발하였다. DPMS 시스템은 디자인 프로젝트의 선정과 디자인 프로젝트의 기획/실행관리/ 평가로 주요 모듈을 설정함으로써 프로젝트 매니저는 해당 프로젝트 과업(Task)과 활동(Activity)에 대한 팀의 운용을 융통성 있게 관리할 수 있게 된다. 이와 더불어 프로젝트 관리를 On-Line DBMS 시스템 환경 상에 운용되도록 하여 정보의 재생산성, 운용의 동시성, 그리고 보안성 등을 도모하였다.

• 한국식품조리과학회지
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• 제13권5호
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• pp.592-601
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• 1997

The purposes of this study were to develop Hazard Analysis Critical Control Point-based standardized recipe applicable to cook/chilled soy sauceglazed mackerel and to evaluate the qualities related to the product flow of this item. After conducting experimental cooking, preliminary test, and analysis of recipes, critical control points were identified, control methods were determined, and HACCP-based recipe was standardized. At each critical control point, time-temperature profile was recorded and microbiological analysis (total aerobic plate counts, psychrotrophic plate count, coliform, and fecal coliform count), chemical analysis (pH, acid value and volatile based nitrogen (VBN)) and sensory evaluation of the item were done. Time-temperature data showed that the time the menu item had passed through temperature danger zone (5∼60$^{\circ}C$) during all phases was 60 min. At rapid cooling, but after cooling at room temperature, the temperature of this menu item did not drop below the ambient temperature. The results of microbiological test were negative throughout all phases following cooking and the results of chemical analysis did not change significantly in terms of storage periods except for VBN which increased on 7th day significantly(p<0.05). After steam/convection oven reheating and microwave oven reheating, the sensory score of the only appearance decreased significantly related to the storage time of overall quality profiles. But significant differences were not detected according to two reheating methods. In conclusion, this HACCP-based recipe was considered as an effective tool for assuring microbial as well as sensory quality of this cook/chilled item.

• Journal of Pharmaceutical Investigation
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• 제29권3호
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• pp.193-203
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• 1999

In order to investigate systematically the steady shear flow properties of aqueous po1y(ethylene oxide) (PEO) solutions having various molecular weights and concentrations, the steady flow viscosity has been measured with a Rheometrics Fluids Spectrometer (RFS II) over a wide range of shear rates. The effects of shear rate, concentration, and molecular weight on the steady shear flow properties were reported in detail from the experimentally measured data, and then the results were interpreted using the concept of a material characteristic time. In addition, some flow models describing the non-Newtonian behavior (shear-thinning characteristics) of polymeric liquids were employed to make a quantitative evaluation of the steady flow behavior, and the applicability of these models was examined by calculating the various material parameters. Main results obtained from this study can be summarized as follows: (1) At low shear rates, aqueous PEO solutions show a Newtonian viscous behavior which is independent of shear rate. At shear rate region higher than a critical shear rate, however, they exhibit a shear-thinning behavior, demonstrating a decrease in steady flow viscosity with increasing shear rate. (2) As an increase in concentration and/or molecular weight, the zero-shear viscosity is increased while the Newtonian viscous region becomes narrower. Moreover, the critical shear rate at which the transition from the Newtonian to shear-thinning behavior occurs is decreased, and the shear-thinning nature becomes more remarkable. (3) Aqueous PEO solutions show a Newtonian viscous behavior at shear rate range lower than the inverse value of a characteristic time $1/{\lambda}_E$, while they exhibit a shear-thinning behavior at shear rate range higher than $1/{\lambda}_E$. For aqueous PEO solutions having a broad molecular weight distribution, the inverse value of a characteristic time is not quantitatively equivalent to the critical shear rate, but the power-law relationship holds between the two quantities. (4) The Cross, Carreau, and Carreau-Yasuda models are all applicable to describe the steady flow behavior of aqueous PEO solutions. Among these models, the Carreau-Yasuda model has the best validity.