• The Bulletin of The Korean Astronomical Society
• /
• 제41권1호
• /
• pp.57.3-58
• /
• 2016

We analyze an optical system of a telescope based on Fresnel type objective lens as suggested by Hyde (1999). The Fresnel objective lens can be thin, light-weight and foldable, and therefore it is possible to develop a space telescope with an aperture larger than that of traditional telescopes. Moreover a lens, whatever it is either Fresnel type or conventional, allows much larger fabrication tolerances. We design a medium-sized telescope adopting Fresnel lens as an objective lens for use in space and possibly on the ground. The well-known chromatic aberration of the Fresnel primary lens is corrected by a field lens and another Fresnel lens using Schupmann method. An additional lens is used for forming images. We analyze the chromatic and off-axis aberrations of the proposed system analytically and suggest methods for the minimization of off-axis aberrations and for the operation in wider spectral range. We also conduct ray tracing and optimize the whole optical system with commercial software. Finally we present the design parameters of a telescope with an aperture of 0.5 to 1 meters, enabling diffraction limited operation for a moderate field of view about 10 arc-minutes.

• IE interfaces
• /
• 제24권1호
• /
• pp.78-86
• /
• 2011

To mitigate space restriction and to raise productivity, some shipbuilding companies use floating-docks on the sea instead of dry-docks on the land. In that case, a floating-crane that can lift very heavy objects (up to 3,600 tons) is used to handle the blocks which are the basic units in shipbuilding processes, and so, very large blocks (these are called the mega-blocks) can be used to build a ship. But, because these mega-blocks can be made only in the area near the floating-dock and beside the sea, the space is very important resource for the process. Therefore, our problem is to make an efficient spatial schedule for the mega-block assembly yard. First of all, we formulate this situation into a mathematical model and find optimal solution for a small problem using a commercial optimization software. But, the software could not give optimal solutions for practical sized problems in a reasonable time, and so we propose a GA-based heuristic algorithm. Through a numerical experiment, finally, we show that the spatial scheduling algorithm can provide a very good performance.

• Journal of Sensor Science and Technology
• /
• 제9권3호
• /
• pp.213-223
• /
• 2000

It is necessary that radiation dose would be detect exactly generated from facility related to nuclear, space, radiotherapy center, etc. This paper is to use of the radiation-induced threshold voltage change as an accumulated radiation dose monitoring sensor. Commercial P Channel Power MOSFET(metal oxide field effect transistor) were tested in a Co-60 gamma irradiation facility to see their capabilities as a radiation dosimeter. We found that the transistors showed good linearity in their threshold voltage shift characteristics with radiation dose. The results demonstrate the potential use of commercial P Channel Power MOSFET as inexpensive radiation sensors.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• 제45권12호
• /
• pp.1069-1075
• /
• 2017

With the recent development of space technology, the satellite market, especially the small satellite market, is growing globally. As the satellite market continues to grow, the launch vehicle market is also growing, and demand for low-cost launches is increasing. There are a number of options for low-cost launches, including development of engine that uses low-cost propellants, product and transportation cost savings, but the most effective way to reduce launch costs is to reuse the used launch vehicles. USA's Space Shuttle, a famous rocket as manned spacecraft, could be referred as the start of reusable launch vehicle. However, Space Shuttle had limited reusable parts and it was very expensive even though it is a reusable launch vehicle because of its low efficiency. In recent years, aiming at a real reusable launch vehicle, reusable launch vehicle for commercial purposes have been developed around USA's SpaceX and Blue Origin, and re-landing tests were successfully accomplished. In addition, SpaceX successfully did the re-using of first-stage launch vehicle that had been succeeded in re-landing already. In accordance with this trend, countries such as Europe and India are also concentrating on the study of reusable launch vehicles. Including Blue Origin, companies like Virgin Galactic and XCOR in the United States, are also trying to commercialize the same reusable technology as the private manned space tourism. Confirmation of these technology trends is essential, because the re-use technology could change the landscape of the global launch vehicle market.

• Journal of Environmental Policy
• /
• 제9권1호
• /
• pp.137-154
• /
• 2010

These objectives of this study were to compute heavy metal and accumulation carbon dioxide fixing quantity from urban green space(street trees and urban parks) in Cheong-ju city and Chungju-city and thus to estimate the effect of urban green space for improving the urban environment. The results are summarized below. 1. Results of the total accumulation of the carbon dioxide fixing quantity of street trees, Cheong-ju city and Chungju-city street tree was 1, 230,000kg-C, 1,270,000 kg-C, respectively. Total accumulation carbon dioxide fixing quantity of Balssan urban park had a 25,000kg-C in Cheong-ju city, Degami sports park had a 6,400kg-C in Chungju-city. 2. Results of heavy metal for street trees, fell in the order Zn > Cu > Cr > Ni >, the highest accumulated heavy metal was Zn, and the lowest was Ni. Total heavy metal concentration according to land-use area, was observed in order, for residental areas(157.26 mg/kg) > industrial areas(141.71 mg/kg) > commercial areas(118.55 mg/kg) > and greenspace areas(61.95 mg/kg) in Cheong-ju city. 3. Total heavy metal concentration for street trees fell in the order of commercial areas(84.48 mg/kg) > residental areas(83.70 mg/kg) > and greenspace(48.23 mg/kg) according to land-use area in Chungju-city. Comparatively, Cheong-ju city had more total heavy metal concentration than Chungju-city. 4. Heavy metal for soil that planted street trees was observed in order of Zn > Cu > Pb( > Ni > Cr > As > Cd), and Zn was highest, and Cd was lowest. Total heavy metal concentration for soil fell in the order commercial area(91.82mg/kg) > industrial area(85.96mg/kg) > residental area(67.55mg/kg) > greenspace(43.13mg/kg) according to land-use area in Cheong-ju city. 5. Heavy metal for soil that planted street trees was observed in order of Zn > Pb > Cu( > Ni > Cr > As > Cd, and Zn was highest. Total heavy metal concentration for soil fell in the order commercial area(87.66mg/kg) > greenspace(72.73mg/kg) $${\geq_-}$$ residental area(70.10mg/kg) in Chungju-city.

• Journal of the Economic Geographical Society of Korea
• /
• 제21권1호
• /
• pp.20-33
• /
• 2018

Population distribution in urban space varies with transportation flow changing along time of day. Transportation flow is directly affected by the activities of urbanites and the distribution of related facilities, since the flow is the result of moving to the point where the facilities associated with their activities are located. It is thus necessary to analyze the spatio-temporal characteristics of the urban population distribution by integrating the distribution of activity spaces related to the daily life of urbanites and the flow of transportation. The purpose of this study is to analyze the population distribution in urban space with daily and weekly time bases using the building database and T-card database in the city of Seoul, which is rich in information on land use and transportation flow. For a time-based analysis that is difficult to grasp by general statistical techniques, a four-dimensional visualization method combining time and space using a Java program is devised. Dynamic visualization in the four-dimensional space and time allows intuitive analysis and makes it possible to understand more effectively the spatio-temporal characteristics of population distribution. For this purpose, buildings are classified into three activity groups: residential, working, and commercial according to their purpose, and the number of passengers traveling to and from each stop site of bus and subway networks in the T-card database for one week is calculated in one-minute increments, Visualizing these and integrating transportation and land use, we analyze spatio-temporal characteristics of the population distribution in Seoul. As a result, it is found that the population distribution of Seoul displays distinct spatio-temporal characteristics according to land use. In particular, there is a clear difference in the population distribution pattern along the time axis according to the mixed aspects of working, commercial, and residential activities. The results of this study can be very useful for transportation and location planning of city facilities.

• Biotechnology and Bioprocess Engineering:BBE
• /
• 제7권3호
• /
• pp.121-129
• /
• 2002

Existing methods for optimization of sequences by random mutagenesis generate libraries with a small number of mostly deleterious mutations, resulting in libraries containing a large fraction of non-functional clones that explore only a small part of sequence space. Large numbers of clones need to be screened to find the rare mutants with improvements. Library display formats are useful to screen very large libraries but impose screening limitations that limit the value of this approach for most commercial applications. By contrast, in both classical breeding and in DNA shuffling, natural diversity is permutated by homologous recombination, generating libraries of very high quality, from which improved clones can be identified with a small number of complex screens. Given that this small number of screens can be performed under the conditions of actual use of the product, commercially relevant improvements can be reliably obtained.

• Steel and Composite Structures
• /
• 제24권3호
• /
• pp.339-349
• /
• 2017

In this paper, a conventional refined plastic hinge analysis is improved to account for the effects of local buckling and lateral-torsional buckling. The degradation of flexural strength caused by these effects is implicitly considered using practical LRFD equation. The second-order effect is captured using stability functions to minimize modeling and solution time. An incremental-iterative scheme based on the generalized displacement control method is employed to solve the nonlinear equilibrium equations. A computer program is developed to predict the second-order inelastic behavior of space steel frames. To verify the accuracy and efficiency of the proposed program, the obtained results are compared with the existing results and those generated using the commercial finite element package ABAQUS. It can be concluded that the proposed program proves to be a reliable and effective tool for daily use in engineering design.

• Proceedings of the KSR Conference
• /
• 한국철도학회 2007년도 춘계학술대회 논문집
• /
• pp.13-19
• /
• 2007

This study is to establish design method and evaluation technology for drive system appropriate to articulated vehicles. The transmission system of articulated vehicles serves in the other condition compared with those of commercial vehicles, namely, they have to transmit high power to run and they have to make maximum use of the limited space. This paper reports the reviews and results of the design and evaluation method for driving gear unit of articulated vehicles and discusses various design items and methods about assembly and parts of driving gear unit.

• Proceedings of the KIEE Conference
• /
• 대한전기학회 2002년도 하계학술대회 논문집 D
• /
• pp.2646-2648
• /
• 2002

This paper deals with a comparative evaluation of the reliability of control rod drive mechanisms including their driving methods for nuclear power plants. Basically there exist two types of electromagnetic-jack-type drive mechanisms in commercial use that are called as Control Rod Drive Mechanism and Control Element Drive Mechanism. Each type has corresponding drive sequence to make the movements of insertion and withdrawal. A state-space model is derived for each model graphically. Then the evaluation of the reliability is carried out on the programming tool called SHARPE. The evaluation does not give any meaningful numerical values for the reliability but just shows a relative degree to each other in view of reliability.