• Journal of Advanced Marine Engineering and Technology
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• v.32 no.7
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• pp.1019-1029
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• 2008

In this study, visual investigation of sprays and flames has been performed and soot formation in Diesel and GTL fuels has been compared in a specially designed Rapid Charging Combustion Vessel (RCCV) under various ambient gas $O_2$ concentrations and two injection pressures. It has been concluded that soot in the mixing-controlled combustion of Diesel and GTL fuels has similar tendency to be formed in the leading portion of the jet boundaries. Auto-ignition delay for GTL fuel is shorter than that for diesel fuel. The temporal and special variation of soot concentration in the diesel flame jets at various $O_2$ concentrations was correlated with the heat release rate. Soot concentration appears in the regions when diffusion combustion starts, and its concentration reaches maximum at the peak of heat release curve and then decreases due to oxidation. Visualization by shadowgraph method showed that soot decreases with lower $O_2$ concentration, and higher injection pressure.

• The Journal of Engineering Geology
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• v.4 no.3
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• pp.333-341
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• 1994

The low velocity body was detected during the invesfigation of the crustal structune and upper mantle in the Korean Peninsula using ray method and observational seismic data. We observed the arrival time delays of P and S waves that pass through the Bugok hot spring area and the chugaryong rift zone in the Korean Peninsula. The present geothermal exploration accounts for the high heat flow in these regions, suggesting that the area are the 'delay shadows' produced by a deep, low velocity body(Resenberg et aL, 1980). We tried to verify the hypothesis that the low-velocity body is caused by the partial melting in the lower crust can be explained by the lateral variation(inhomogeneous model) of the lower crust velocity using Ray Method(Cerveny and Psencik, 1983).

• Journal of Biomedical Engineering Research
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• v.13 no.4
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• pp.285-298
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• 1992

An analysis of the dynamics in the closing phase of the occluder of a mechanical monoleaflet heart valve prosthesis is presented. The dynamic analysis of the fluid in the vicinity of the occluder was based on the control vo]use approach. The backflow velocity of the fluid was computed by applying the continuity, Bernoulli's and momentum equations in the unsteady state. By considering the fluid pressure and gravity as external forces acting on the occluder, the moment equilibrium on fine occluder was employed to analyze the motion of the occluder during closing and the force of impact between the occluder and the guiding struts. Occluder comes to rest after several oscillations in about 10-18 msec after the Inltiaton of closing. As the aortic pressure increases, the occludes closes faster and comes to the final resting position earlier and the impact force increases also. But backflow is not af footed by the variation of the aortic pressure. With decreasing time delay of the ventricle pressure, the occluder closes faster and impact force Increases. The computed magnitudes of the occluder tiP velocities as well as the backflow of the fluid during the closing phase using this model were in agreement with previously reported experimental measurements.

• The Journal of the Korea Contents Association
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• v.8 no.6
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• pp.34-42
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• 2008

MAC(Medium Access Control) is demanded to provide end-to-end QoS(Quality of Service) for a variety of traffic in the wireless networks. When all the traffic is integrated in the channel, the main difficulty of the MAC protocol is how to efficiently support multi-class traffic in the limited bandwidth wireless channel. In this paper, we proposed the dynamic bandwidth slot method for improving QoS of the real time traffics. In this paper, we used in-band scheme to send dynamic parameter and considering buffer size and delay variation, we enabled 2 state bits to send to base station in mobile station. The proposed algorithm is to guarantee QoS of real time traffic and maximize transfer efficiency in wireless networks.

• Transactions of the Korean Society of Automotive Engineers
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• v.19 no.2
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• pp.20-25
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• 2011

The purpose of this work is an experimental investigation of combustion and emission characteristics in DI diesel engine applied high EGR rate as a method of low-temperature combustion. In order to analyze the effect of EGR rate variation, a single-cylinder DI diesel engine was operated under various EGR rate conditions. In addition, injection timing was variously controlled to investigate the effect of injection timing in DI diesel engine using the cooled-EGR system. The NOx emissions were decreased in accordance with the increase of EGR rate. On the contrary, soot emissions were generally increased under applied EGR conditions. However, soot emissions were decreased in a few injection timings under high EGR rate conditions. The EGR results show that the ignition delay were increased by decreased oxygen concentrations in combustion chamber under the high EGR rate.

• Journal of the Korea Computer Industry Society
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• v.2 no.11
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• pp.1395-1406
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• 2001

In order to cover a widespread service range, terrestrial/satellite-mixed network is being combined with terrestrial ATM network. This dissertation analyzes and investigates several previously existent CDV compensation methods in order to compensate CDV arising from interfacing satellite TDMA and ATM. Specifically to supplement the problems of timestamp and cell number counting methods, new Variable Timestamp method for CDV compensation is proposed. To evaluate the proposed method, MMPP(Markov Modulated Poisson Process), which can express VBR service very well, is selected as a cell input traffic model of terrestrial transmitting earth station. After several simulation, it is also confirmed that CDV compensation capability for VBR services is very superior to the cell number counting method. In this case, as the timestamp number Nts increases, CDV compensation capability increases, and the CDV distribution length is reduced.

• The Transactions of the Korean Institute of Power Electronics
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• v.3 no.3
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• pp.222-230
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• 1998

This paper proposes a new gate drive circuit for high power IGBTs which can reduce the harmful effect of reverse recovery current at turn-on and actively suppress the overvoltage across the driven IGBT at turn-off without a snubber circuit. The turn-on scheme decreases the rising rate of the collector current by inereasing the input capacitance at turn-on transient when the gate-emitter voltage goes above threshold voltage. It results in soft transient of the reverse recovery current with no variation in turn-on delay time. The turn-off driving scheme has adaptive feature to the amplitude of collector current, so that the overvoltage can be limited much effectively at the fault collector current. Experimental results under various normal and fault conditions prove the effectiveness of the proposed circuit.

• Proceedings of the KSRS Conference
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• v.2
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• pp.748-751
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• 2006

Positioning accuracy by the Global Positioning System (GPS) is of great concern in a variety of research tasks. It is limited due to error sources such as ionospheric effect, orbital uncertainty, antenna phase center variation, signal multipath, and tropospheric influence. In this study, the tropospheric influence, primarily due to water vapour inhomogeneity, on GPS positioning height is investigated. The data collected by the GPS receivers along with co-located surface meteorological instruments in 2003 are utilized. The GPS receivers are established as continuously operating reference stations by the Ministry of the Interior (MOI), Central Weather Bureau (CWB), and Industrial Technology Research Institute (ITRI) of Taiwan, and International GNSS Service (IGS). The total number of GPS receivers is 21. The surface meteorological measurements include temperature, pressure, and humidity. They are introduced to GPS data processing with 24 troposphere parameters for the station heights, which are compared with those obtained without a priori knowledge of surface meteorological measurements. The results suggest that surface meteorological measurements have an expected impact on the GPS height. The daily correction maximum with the meteorological effect may be as large as 9.3 mm for the cases of concern.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.43 no.10 s.352
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• pp.55-59
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• 2006

In cellular OFDMA(Orthogonal Frequency Division Multiple Access) systems, each subcarrier may suffer from different amount of interferences from neighbor cells. Suppose that it is possible to accurately estimate inter-cell interferences for each subcarrier, the performance can be considerably improved by applying SINR(Signal to Interference and Noise Ratio) weighting. This paper proposes an inter-cell interference estimation method for cellular OFDMA systems. The proposed method extracts amounts of noise and interferencesby eliminating the channel variation effects of pilot symbols caused by frequency offset, timing offset mobile velocity, and delay spread.

• Journal of the Korean Institute of Intelligent Systems
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• v.17 no.1
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• pp.66-71
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• 2007

To adapt environment changing high speed and improve rapidly response ability for variation of environment and reduce delay time of decision making inlet agents, the derivation of user's preference and alternative are required. In this paper, we propose an efficient coordination method of multi-agents based on fuzzy decision making with the solution proposed by agents in the view of Pareto optimality. Our method generates the optimal alternative by using weighted value. We compute importance of attributes of winner agent, then can obtain the priorities lot attributes. The result of our method is analyzed that of Yager's method.