• KSII Transactions on Internet and Information Systems (TIIS)
• /
• v.13 no.7
• /
• pp.3447-3469
• /
• 2019

It is well-known that the cooperative communication and error control technology can improve the network performance, but most existing cooperative MAC protocols have not focused on how to cope with the contention process caused by cooperation and how to reduce the bad influence of channel packet error rate on the system performance. Inspired by this, this paper first modifies and improves the basic rules of the IEEE 802.11 Medium Access Control (MAC) protocol to optimize the contention among the multi-relay in a cooperative ARQ scheme. Secondly, a hybrid ARQ protocol with soft combining is adopted to make full use of the effective information in the error data packet and hence improve the ability of the receiver to decode the data packet correctly. The closed expressions of network performance including throughput and average packet transmission delay in a saturated network are then analyzed and derived by establishing a dedicated two-dimensional Markov model and solving its steady-state distribution. Finally, the performance evaluation and superiority of the proposed protocol are validated in different representative study cases through MATLAB simulations.

• The Journal of Korean Academy of Prosthodontics
• /
• v.41 no.4
• /
• pp.421-439
• /
• 2003

Statement of problem : It is difficult to obtain a good titanium casting body using the traditional sprue design because of high melting point of Ti, and the low fluidity and high reactivity of molten Ti. Purpose : A new sprue design for titanium casting bodies needs more trial and error. In order to decrease the number of trial and error, computer simulation(MAGMASOFT, Magmasoft Giessereitechnologie GmbH, Achen, Germany) was used to optimize sprue design in U-shaped implant superstructures. Material and method : Five kinds of sprue were examined for the design of the sprue former for titanium casting: Sprue design A(sprue length 4 mm, rectangular shape, 4 sprues), Sprue design B(sprue length 4 mm. round shape. radius 2 mm, 7 sprues), Sprue design C (sprue length 2 mm, round shape, radius 2 mm, 7 sprues). Sprue design D (sprue length 2 mm, cone shape, large radius 3mm. small radius 2mm, 7 sprues), and Sprue design E( sprue length 2 mm. one unit channel shape). Sprue design F(sprue length 2mm, one unit channel shape) was also examined for the design of the customized sprue former in the Biotan system(Schutz Dental Gmbh, Germany). The casting bodies were taken in Sprue design A, Sprue design D, Sprue design E, and Sprue design F in the Biotan casting system. The numerically predicted defects were compared with the experimental dental castings by the radiographic and sectional view observations. Results : 1. According to the result of computer simulation, turbulence during mold filling was decreased in the sequence of Sprue design F, Sprue design E, Sprue design D, Sprue design C, Sprue design B, and Sprue design A. 2. The calculated solidification time contours indicate that hot spot was moved from the casting body to the sprue button in the sequence of Sprue design A, Sprue design B, Sprue design C, Sprue design D, and Sprue design E. The filling pattern of Sprue design F was similar to that of Sprue design E. 3 The predicted filling pattern shows that less turbulence was found in the customized sprue former than in the standard sprue former. 4. According to the results of the radiographic and cross sectional observations, casting defects less than 1mm were found at the center of a casting body with Sprue design E and Sprue design F. However, larger casting defects of 4mm were found in a casting with Sprue design A. 5. The predicted casting porosity was similar to that of the real casting. Conclusion : One unit channel-type and customized sprue former can be recommended. Further research and developement of various sprue designs using computer simulation in necessary to optimize casting design, in order to reduce the formation of casting defects in implant titanuim super-structures.

• Journal of Korean Society of Coastal and Ocean Engineers
• /
• v.18 no.4
• /
• pp.329-337
• /
• 2006

A small hydro-power plant operated by cooling water discharged from the power plant is under construction. In this study, the flow characteristics of the effluent channel and the outfall coastal zone in which the facilities are constructed have been measured and analysed. The flow pattern is highly dependent on the effluent discharge and clearly classified as these typical areas; the upstream and downstream areas of the weir, and the outfall coastal zone. The discharge and the width of the channel in the upstream area of the weir are increased step by step, so the water level fluctuation is small. The flow overtopping the weir is rapidly changing and has highly vertical fluctuation patterns after hydraulic jump just below the weir. The flow pattern in the outfall zone is directed toward the seaward direction and the velocity is dominated by the tidal level fluctuation. The mean tidal range in this area is about 10% greater than that of the Tongyeong tidal gauging station and the wave effects are negligible because of the sheltering effects of this area.

• Journal of Broadcast Engineering
• /
• v.14 no.2
• /
• pp.228-237
• /
• 2009

This paper examines the potential of Ultra-High Definition TV (UD-TV) broadcasting transmission systems beyond HD-TV over cable channel. Firstly, we analyze the trend of TOV(Threshold of Visibility) by extending the OpenCable (J.83 Annex B) system 256QAM which is the standard of Korean and American cable television transmission to 1024QAM, and realize that the OpenCable 1024QAM has nearly 30% higher data rate than 256QAM at the expense of impractically higher TOV (Threshold of Visibility). To achieve practical TOV, we control code rates of inner convolutional coder and replace turbo coder in forward error correction (FEC) part, thereby analyzing the best performance of the OpenCable systems having conventional FEC. In that result, it is necessary to modify conventional FEC of the OpenCable system to achieve under 31.5dB TOV. Moreover we study the potential of UD-TV transmission via two or more TV channels, so called channel bonding, through the Shannon capacity in 6MHz channel and the relationship with next generation A/V codec technologies.

• Journal of the Korean Institute of Gas
• /
• v.21 no.4
• /
• pp.92-102
• /
• 2017

Fischer-Tropsch synthesis reaction converts syngas (mixture of CO and H2) to valuable hydrocarbon products. Simulation of low temperature Fischer -Tropsch Synthesis reaction and heat transfer at intensified process condition using catalyst filled single and multichannel microchannel reactor is considered. Single channel model simulation indicated potential for process intensification (higher GHSV of $30000hr^{-1}$ in presence of theoretical Cobalt based super-active catalyst) while still achieving CO conversion greater than ~65% and $C_{5+}$ selectivity greater than ~74%. Conjugate heat transfer simulation with multichannel reactor block models considering three different combinations of reactor configuration and coolant type predicted ${\Delta}T_{max}$ equal to 23 K for cross-flow configuration with wall boiling coolant, 15 K for co-current flow configuration with subcooled coolant, and 13 K for co-current flow configuration with wall boiling coolant. In the range of temperature maintained (498 - 521 K), chain growth probability calculated is desirable for low-temperature Fisher-Tropsch Synthesis.

• Journal of Distribution Science
• /
• v.13 no.1
• /
• pp.93-103
• /
• 2015

Purpose - This study plans to adopt a more sophisticated approach toward service recognition by customers in general supermarkets in order to revise the service quality measurement methods that suit the context of Korean distribution channels. In particular, in general supermarkets, where much of the shopping process is in the form of self-service, there is high reliance on the service recognized by the consumers; therefore, it is highly likely that consumers would make their purchasing decisions based on their recognition of service quality or guarantees. It also utilized service quality elements of a basic level in the KD-SQS development model in order to indicate that the quality recognized by consumers impacts their loyalty to the stores with financial value and abstract value. Research design, data, and methodology - The study suggested a theoretical model comprising 13 hypotheses on relations between theoretic variables, and conducted surveys with consumers using discount stores in Seoul and Gyunggi Metropolitan area in order to verify the hypotheses, while using SPSS 20.0, AMOS 21.0 as the verification program. The survey sheets used amounted to 332, and a structural equation model was used to analyze the reliability and validity of constituent elements and to verify the suggested hypothesis. Therefore, this study analyzes the interrelations between service quality and guarantee factors in the distribution channel and their relations with the loyalty to stores as a dependent variable. Results - First, the results of the hypotheses tests helped identify the relations between service quality, service guarantees, service value, and customer loyalty, providing an opportunity to define the relations between constituent elements. In particular, service convenience in service quality has no impact on financial values. Further, stores' service policy had no impact on abstract values. Service recognition by service convenience has an impact on abstract values such as good image, comfort, and usability, while mileage systems promote financial values for consumers. In order to improve consumer values in service quality and values, general supermarkets should improve their service convenience, membership, and mileage programs using various strategies. Conclusion - In order to improve consumer values in service quality and values, general supermarkets should improve their service convenience, membership, and mileage programs using various strategies. Further, as service guarantee systems have a significant and direct impact on customer loyalty, rather than customer value recognition, service guarantees should be used to encourage customers to re-visit the stores. Finally, this study applied the findings of preceding studies in terms of service quality measurement; it had limitations in referencing preceding studies in a comprehensive manner. It also had limits in expanding upon various preceding studies because it was difficult to apply new measurement tools due to the lack of service quality measurement tools for general supermarkets. Therefore, it is necessary to conduct more studies on service quality to measure service quality and develop measurement tools by incorporating various industry characteristics.

• Journal of Global Scholars of Marketing Science
• /
• v.7
• /
• pp.375-390
• /
• 2001

Currently the super power of department stores over their tenants has mentioned in Korean apparel newspapers very often. It may be the one that the government in fashion industry has not delved into the relationship between department stores and their tenants. The aim in here is to look at the conceptual framework of power based on the retail power oriented and to explain current issues with its theoretical backgrounds. Due to the inherent of retailer power oriented, this study involves not only in French and Raven's power sources but also in positioning power source that is the ability of allocating the location and adjusting size of the store. 235 samples are tested through Lisrel. The results of statistical analysis show that: The power of department store over that perceived by the tenant has negatively influenced countervailing power of the tenant upon department store. The coercive power sources of department store have positively influenced the power of department store over that perceived by the tenant while the non-coercive power sources have not significantly influenced on it. The countervailing power of the tenant has positively influenced the non-coercive power sources of department store perceived by the tenant. On the other hand, the countervailing power of the tenant has not significantly influenced the coercive power sources of department store perceived by the tenant. The implication of these results is that the retailer oriented power sources and its implements differs from the manufacturer oriented ones in the framework of power. A great deal more research is required in order that the relationship between department store and its tenants can be better understood.

• Asian Journal of Atmospheric Environment
• /
• v.8 no.4
• /
• pp.212-224
• /
• 2014

There are several studies on the effects of emissions of highly reactive volatile organic compounds (HRVOC) from the industrial sources in the Houston-Galveston-Brazoria (HGB) area on the high ozone events during the Texas Air Quality Study (TexAQS) in summer of 2000. They showed that the modeled atmosphere lacked reactivity to produce the observed high ozone event and suggested "imputation" of HRVOC emissions from the base inventory. Byun et al. (2007b) showed the imputed inventory leads to too high ethylene concentrations compared to the measurements at the chemical super sites but still too little aloft compared to the NOAA aircraft. The paper suggested that the lack of reactivity in the modeled Houston atmosphere must be corrected by targeted, and sometimes of episodic, increase of HRVOC emissions from the large sources such as flares in the Houston Ship Channel (HSC) distributed into the deeper level of the boundary layer. We performed retrospective meteorological and air quality modeling to achieve better air quality prediction of ozone by comparison with various chemical and meteorological measurements during the Texas Air Quality Study periods in August-September 2006 (TexA QS-II). After identifying several shortcomings of the forecast meteorological simulations and emissions inputs, we prepared new retrospective meteorological simulations and updated emissions inputs. We utilized assimilated MM5 inputs to achieve better meteorological simulations (detailed description of MM5 assimilation can be found in F. Ngan et al., 2012) and used them in this study for air quality simulations. Using the better predicted meteorological results, we focused on the emissions uncertainty in order to capture high peak ozone which occasionally happens in the HGB area. We described how the ozone predictions are affected by emissions uncertainty in the air quality simulations utilizing different emission inventories and adjustments.

• Structural Engineering and Mechanics
• /
• v.47 no.1
• /
• pp.59-73
• /
• 2013

The Xiaolan channel super large bridge is unique in style and with greatest span in the world with a total length of 7686.57 m. The main bridge with spans arranged as 100m+220m+100m is a combined structure composed of prestressed concrete V-shape rigid frame and concrete-filled steel tubular flexible arch. First of all, the author compiles APDL command flow program by using the unit birth-death technique and establishes simulation calculation model in the whole construction process. The creep characteristics of concrete are also taken into account. The force ratio of the suspender, arch and beam is discussed. The authors conduct studies on the three-plate webs's rule of shear stress distribution, the box girder's longitudinal bending normal stress on every construction stage, meanwhile the distribution law of longitudinal bending normal stress and transverse bending normal stress of completed bridge's box girder. Results show that, as a new combined bridge, it is featured by: Girder and arch resist forces together; Moment effects of the structure are mainly presented as compressed arch and tensioned girder; The bridge type brings the girder and arch on resisting forces into full play; Great in vertical stiffness and slender in appearance.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.20 no.1
• /
• pp.470-476
• /
• 2019

The braking force for a train is generally provided by compressed air. The pressure valve system that is used to apply appropriate braking forces to trains has a complex flow circuit. It is possible to make a channel shape that can increase the flow efficiency by 3D printing. There are restrictions on the flow shape design when using general machining. Therefore, in this study, the compressed air flow was analyzed in a pressure valve system by comparing flow paths made with conventional manufacturing methods and 3D printing. An analysis was done to examine the curvature magnitude of the flow path, the diameter of the flow path, the magnitude of the inlet and reservoir pressure, and the initial temperature of the compressed air when the flow direction changes. The minimization of pressure loss and the uniformity of the flow characteristics influenced the braking efficiency. The curvilinear flow path made through 3D printing was advantageous for improving the braking efficiency compared to the rectangular shape manufactured by general machining.