• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2004년도 제22회 춘계학술대회논문집
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• pp.466-471
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• 2004

In gas turbines, excess air for combustion is available and therefore lean premixed combustion is the most promising approach to the significant reduction of thermal NOx emissions. At lean conditions, however, flame stability is inherently worse and hence combustion tends to be incomplete. Efforts have been devoted toward extending the operating range of complete combustion at leaner conditions. One of them is the lean-lean two-stage combustion where lean to ultra-lean secondary mixtures are mixed with the hot burned gas from the primary stage. Conventional flame combustion or flameless reaction are initiated depending on the conditions of the secondary zone. In the first part of the present study, the effects of fuel injection on the emissions and flame stability were investigated for a single tubular flame, In the second part, the emissions and flame stability were studied for a two-stage combustor with secondary mixture injected through the tangential slots on a cylindrical combustor wall. The effects of the ratio of air flow rates to the primary and secondary zones on the emissions and combustion characteristics were investigate.

• Journal of Communications and Networks
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• 제18권3호
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• pp.340-350
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• 2016

The performance of large-scale cognitive radio (CR) networks with secondary users sustained by opportunistically harvesting radio-frequency (RF) energy from nearby primary transmissions is investigated. Using an advanced RF energy harvester, a secondary user is assumed to be able to collect ambient primary RF energy as long as it lies inside the harvesting zone of an active primary transmitter (PT). A variable power (VP) transmission mode is proposed, and an energy-based opportunistic spectrum access (OSA) strategy is considered, under which a secondary transmitter (ST) is allowed to transmit only if its harvested energy is larger than a predefined transmission threshold and it is outside the guard zones of all active PTs. The transmission probability of the STs is derived. The outage probabilities and the throughputs of the primary and the secondary networks, respectively, are characterized. Compared with prior work, the throughput can be increased by as much as 29%. The energy-based OSA strategy can be generally applied to a non-CR setup, where distributed power beacons (PBs) are deployed to power coexisting wireless signal transmitters (WSTs) in a wireless powered sensor network.

• Archives of Plastic Surgery
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• 제49권2호
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• pp.215-220
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• 2022

Background In Japan, there is a large regional disparity in plastic surgery availability. In order for plastic surgery to be widely available for all citizens, it is essential for at least one plastic surgery facility to be located in each secondary medical zone. Methods Using the Japan Society of Plastic and Reconstructive Surgery homepage and some databases, we extracted data on secondary medical zones that do not have a plastic surgery facility. The national and regional coverage rates were calculated. The coverage rate for each group divided by the degree of population concentration was also calculated. Results We found that 147 of 344 secondary medical zones did not have a plastic surgery facility, and the area coverage rate was found to be 57.27% nationwide. The coverage rate in terms of population was 87.07% (correlation coefficient of area and population coverage = 0.983). The area coverage rates in Hokkaido-Tohoku, Kanto, Chubu, Kansai, Chugoku-Shikoku, and Kyushu-Okinawa districts were 47.46, 72.15, 76.47, 62.79, 52.08, and 32.81%, respectively. The corresponding population coverage rates were 79.92, 91.62, 94.27, 90.59, 80.68, and 69.54%, respectively. The area coverage rates in metropolitan areas, provincial cities, and rural areas were 98.08, 75.90, and 15.87%, respectively. In contrast, the area coverage rate of dermatology was 62.79% and that of orthopaedics was 97.09%. Conclusion Unfortunately, it is estimated that more than 40% of secondary medical zones are underserved by plastic surgery, and 13% of the population is not able to fully benefit from this specialty in Japan.

• 한국환경과학회지
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• 제23권11호
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• pp.1863-1879
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• 2014

This study aims at classifying and interpreting on the shrine forest vegetation located in Jirisan national park affiliated to an ecotone in southern part of Korea, foreseeing a vegetation change based on composition species and dominant species on canopy, and proposing the direction of vegetation management. The shrine forests were classified into the 7 community units as Chamaecyparis obtusa-Cryptomeria japonica afforestation, Pinus densiflora community, Pinus rigida afforestation, Quercus variabilis-Quercus serrata community, Zelkova serrata-Kerria japonica for. japonica community, Phyllostachys bambusoides forest, Camellia japonica community. This research is also expatiated on the analogous results of ordination analysis with phytosociological analysis. The constituents of deciduous broad-leaved forest in the warm temperate zone were appeared in the most vegetations. It emerged less that the constituents of evergreen broad-leaved forest in the warm-temperate zone and deciduous broad-leaved forest in the cold-temperature zone. The life form analyses were made use with the two ways: appearance species in total communities and each community. The species diversity of shrine forests is declined because the high dominances of Sasa borealis and Pseudosasa japonica emerged in the shrub and herb layers. These shrine forests will be succession to Q. variabilis-Q. serrata community as the representative vegetation of deciduous broad-leaved forest in the warm-temperate zone, owing to the temperature rise by global warming, and an evergreen broad-leaved forest will be able to be also formed if a temperate rise will be continued. The one of the artificial management of shrine forests is to consider the introduction of the constituents of evergreen broad-leaved forest in the warm-temperate zone.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2008년 영문 학술대회
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• pp.680-685
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• 2008

The ejector is a simple device which can transport a low-pressure secondary flow by using a high-pressure primary flow. In general, it consists of a primary driving nozzle, a mixing section, and a diffuser. The ejector system entrains the secondary flow through a shear action generated by the primary jet. Until now, a large number of researches have been made to design and evaluate the ejector systems, where it is assumed that the ejector system has an infinite secondary chamber which can supply mass infinitely. However, in almost all of the practical applications, the ejector system has a finite secondary chamber implying steady flow can be possible only after the flow inside ejector has reached an equilibrium state after the starting process. To the authors' best knowledge, there are no reports on the starting characteristics of the ejector systems and none of the works to date discloses the detailed flow process until the secondary chamber flow reaches an equilibrium state. The objective of the present study is to investigate the starting process of an ejector-diffuser system. The present study is also planned to identify the operating range of ejector-diffuser systems where the steady flow assumption can be applied without uncertainty. The results obtained show that the one and only condition in which an infinite mass entrainment is possible is the generation of a recirculation zone near the primary nozzle exit. The flow in the secondary chamber attains a state of dynamic equilibrium at this point.

• 한국멀티미디어학회논문지
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• 제17권9호
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• pp.1098-1103
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• 2014

Smartphone is very much ingrained into our lives and it has propagated rapidly. With the growing expansion of smartphone, the number of lost smartphones has proliferated all the while. Unlike common personal belongings, smartphone is a high-priced goods and has personal information. In case it gets lost or stolen, it will cause monetary damage as well as secondary damage of personal information leaks. To lesson the damage, diverse applications that prevent the loss of a smartphone have been developed. But existing applications place emphasis on providing countermeasures that tracks the missing smartphones. Therefore, this paper describes the design and implementation of a smartphone application which provides precautionary functions to prevent the loss of a smartphone and countermeasures to track the missing smartphone. The implemented application prevents the loss of a smartphone using satefy zone and movement detection. In the event we lose a smartphone, it helps us recover a lost property using location tracking and remote control functions quickly and efficiently.

• 한국가시화정보학회:학술대회논문집
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• 한국가시화정보학회 2001년도 Proceedings of 2001 Korea-Japan Joint Seminar on Particle Image Velocimetry
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• pp.151-163
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• 2001

A two color PIV technique has been developed for visualization of complex and high speed flow in a ramjet combustor. Two color PIV has the advantages that velocity distributions in high speed flowfields can be measured simply by varying the time interval between two different laser beams and a directional ambiguity problem can be solved by color separation, and then a signal-to-noise ratio can be increased through nearly perfect cross-correlation. As a basic research of the ramjet engine, a 2-D shaped combustor with two symmetric air intakes has been manufactured and an experimental study has been conducted using a two color PIV technique. The flow characteristics such as recirculation zones, intake air mixing and turbulent kinetic energy have been investigated varying inlet angles and dome heights. It was found that the primary recirculation zone is affected mainly by the dome height, whereas the secondary recirculation zone is influenced by the air inlet angle.

• 대한기계학회논문집B
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• 제25권2호
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• pp.252-259
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• 2001

Computational study has been performed to observe the flow characteristics of combustion chamber for geometrical modification in municipal solid waste incinerator. A series of geometrical modification has been carried out as an attempt to reduce the size of recirculation zone, to obtain uniform flow field in the secondary combustion chamber and to improve the mixing of combustion gas. Two dimensional non-reacting turbulent flow has been studied as the first step to get such goals and the result of design optimization is presented. In addition, three dimensional non-reacting and reacting flow analyses were performed to verify the validity of two dimensional approach.

• Journal of Mechanical Science and Technology
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• 제15권9호
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• pp.1292-1301
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• 2001

The mean-line method using empirical models is the most practical method of predicting off-design performance. To gain insight into the empirical models, the influence of empirical models on the performance prediction results is investigated. We found that, in the two-zone model, the secondary flow mass fraction has a considerable effect at high mass flow-rates on the performance prediction curves. In the TEIS model, the first element changes the slope of the performance curves as well as the stable operating range. The second element makes the performance curves move up and down as it increases or decreases. It is also discovered that the slip factor affects pressure ratio, but it has little effect on efficiency. Finally, this study reveals that the skin friction coefficient has significant effect on both the pressure ratio curve and the efficiency curve. These results show the limitations of the present empirical models, and more resonable empirical models are reeded.

• 한국주조공학회지
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• 제11권5호
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• pp.398-405
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• 1991

Al-Li alloy has a high strength with low density. Practically this alloy should use by the material which made from the rapid solidification. Therefore we examine the solidification structures of alloy with cooling rate. According to cooling rate increased, grain size and secondary dendrite arm spacing were smaller. Also grain size was further smaller by Zr added. To obtain more fine solidification structure, rapid solidification by single roll melt spinning was performed. According to higher wheel speed, cooling rate increased and cell size was smaller. Because of locally different cooling rate, different cell size was obtained in same specimen. More than cooling rate $10^6^{\circ}C$ /sec, zone A(insensible zone to corrosion)was obtained.