• KSII Transactions on Internet and Information Systems (TIIS)
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• v.8 no.6
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• pp.1881-1900
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• 2014

Since 802.11 wireless LANs are so widely used, it has become common for numerous access points (APs) to overlap in a region, where most of those APs are managed individually without any coordinated control. This pattern of wireless LAN usage is called the private OBSS (Overlapping Basic Service Set) environment in this paper. Due to frame collisions across BSSs, each BSS in the private OBSS environment suffers severe performance degradation. This study approaches the problem from the perspective of congestion control rather than noise or collision resolution. The retry limit, one of the 802.11 attributes, could be used for traffic control in conjunction with TCP. Reducing the retry limit causes early discard of a frame, and it has a similar effect of random early drops at a router, well known in the research area of congestion control. It makes the shared link less crowded with frames, and then the benefit of fewer collisions surpasses the penalty of less strict error recovery. As a result, the network-wide performance improves and so does the performance of each BSS eventually. Reducing the retry limit also has positive effects of merging TCP ACKs and reducing HOL-like blocking time at the AP. Extensive experiments have validated the idea that in the OBSS environment, reducing the retry limit provides better performance, which is contrary to the common wisdom. Since our strategy is basically to sacrifice error recovery for congestion control, it could yield side-effects in an environment where the cost of error recovery is high. Therefore, to be useful in general network and traffic environments, adaptability is required. To prove the feasibility of the adaptive scheme, a simple method to dynamically adjust the value of the retry limit has been proposed. Experiments have shown that this approach could provide comparable performance in unfriendly environments.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.11C
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• pp.955-962
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• 2008

Multicast Strategy is one of the cost-saving methods in the large scale VOD environment. However, it does involve complicated problems to implement VCR-like interactions for user's convenience in the multicast streaming system under considering the limited-server and the network's bandwidth in the multicast-transmission system. Therefore, the proper solution of settling such a problem is necessary. Thus, this paper which revised P2Patching[l] proposes LGST(Level Group Streaming Technique) which supports the VCR's function through cooperation among peers with heterogeneous bandwidth under the environment of P2P. This strategy can reduce latency by improving the acceptance of server and using the bandwidth of network efficiently. And for evaluate the proposed scheme's performance, I simulated the performance of streaming delivery topology and streaming quality in comparison with P2Patching. In evaluation to service request refusal ratio and service quality according to bandwidth decrement, the result of simulation shows that proposed LGST improves about $11{\sim}18%$ of performance than P2Patching. In the test of latency recovery according to fault probability and influence of VCR function operation duration, it shows similar performance.

• Journal of Biosystems Engineering
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• v.20 no.1
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• pp.22-35
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• 1995

Pepper is the most important horticultural plant in Korean farm. Pepper harvesting has been known to be the most difficult process in pepper cultivation so that demand for mechanization is strong. In a research to develop a pepper harvesting machine performance and capacity of the harvester should be determined based on both economical feasibility and machine design concept. In order to accomplish an economical analysis of the pepper harvester, a mathematical model for comparing manual harvesting cost to machine harvest cost was developed. Validity of the model depends on the data used in the model. Economical information for the model variables was acquired from the result of farm survey on pepper cultivation technique and economics of pepper farmer. Technical information on pepper harvester were also collected through literature review and analyzed. Based on the economical analysis and synthesis of the technical information on pepper harvesters, its performance and capacity were determined. The operating performances of the harvester such as cutting, conveying, flipping, pepper removing and post-processing (sorting) were determined. Daisy capacity of the machine was determined to be 0.41 ha. A pepper harvester with the suggested capacity was economically feasible if the price of pepper harvester, pepper recovery ratio and service life of harvester were about 6 million won, 80%, and 4 years, respectively.

• The Korean Journal of Emergency Medical Services
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• v.25 no.1
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• pp.57-72
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• 2021

Purpose: The purpose of this study was to provide basic data for developing strategic programs based on the types of perception to aid in the coping strategy of 119 emergency medical technicians who experienced have violence. Methods: The subjects were 119 emergency medical technicians working out of hospitals in Korea. Data were collected from March 10, 2019, to June 30, 2019. Q samples of 37 statements and P samples of 36 persons were taken using PC QUANL software. Results: As a result of the study, four types of coping with violence experiences were identified; these four types explained 53.79% of all variables from the examination. The types were labeled as the cooperation seeking and manual emphasis type, emotional suppression and stability seeking type, active response and business continuation type, communication empathy and recovery effort type. Conclusion: The Fire Department requires institutional measures to lower violence during field activities, and it will be necessary to develop a policy according to the type of perception of coping behaviors.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.9 no.2
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• pp.620-636
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• 2015

Survivability is a necessary property of network system in disturbed environment. Recovery ability is a key actor of survivability. This paper concludes network survivability into a novel composite metric, i.e. Network Recovery Degree (NRD). In order to measure this metric in quantity, a concept of Source-Destination Pair (SD Pair), is created to abstract end-to-end activity based on end nodes in network, and the quality of SD Pair is also used to describe network performance, such as connectivity, quality of service, link degree, and so on. After that, a Survivability Test method in large scale Network based on SD pairs, called STNSD, is provided. How to select SD Pairs effectively in large scale network is also provided. We set up simulation environment to validate the test method in a severe destroy scenario and evaluate the method scalability in different large scale network scenarios. Experiment and analysis shows that the metric NRD correctly reflects the effort of different survivability strategy, and the proposed test method STNSD has good scalability and can be used to test and evaluate quantitative survivability in large scale network.

• Journal of Energy Engineering
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• v.21 no.3
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• pp.315-324
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• 2012

Waste reduce, recycle, energy recovery technology is one of 27 key green technology by 2012, the government should increase R&D investment, despite the period 2008 to 2010 average annual growth rate was decreased. Accordingly, this area of government investment in R&D status analyzed in detail and as a result, total government investment in R&D decreased, but in these fields to define strategic product services investment in technology is increasing centralization trend that appears to be investment in the quality of determined that the good is. In particular, in 2010, strategic product service of the technologies 3 technology groups ((1) waste energy equipment (2) waste resource recycling facilities (3) waste based materials production facilities) the proportion of 24-28% relatively evenly invested, government R&D is judged that adequate investment in quality.

• Journal of IKEEE
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• v.23 no.1
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• pp.280-288
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• 2019

In the CR-enabled MANET, routing paths can be easily destroyed due to node mobility and channel unavailability (due to the emergence of the PU of a channel), resulting in significant overhead to maintain/recover the routing path. In this paper, network caching is actively used for route maintenance, taking into account the properties of the CR. In the proposed scheme, even if a node detects that a path becomes unavailable, it does not generate control messages to establish an alternative path. Instead, the node stores the packets in its local cache and 1) waits for a certain amount of time for the PU to disappear; 2) waits for a little longer while overhearing messages from other flow; 3) after that, the node applies local route recovery process or delay tolerant forwarding strategy. According to the simulation study using the OPNET simulator, it is shown that the proposed scheme successfully reduces the amount of control messages for path recovery and the service latency for the time-sensitive traffic by 13.8% and 45.4%, respectively, compared to the existing scheme. Nevertheless, the delivery ratio of the time-insensitive traffic is improved 14.5% in the proposed scheme.

• Journal of the Korean Society of Safety
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• v.35 no.5
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• pp.121-127
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• 2020

Since the Fukushima nuclear accident in 2011, the public were concerned about the safety of Nuclear Power Plants (NPPs) in extreme natural disaster situations, such as earthquakes, flooding, heavy rain and tsunami, have been increasing around the world. Accordingly, the Stress Test was conducted in Europe, Japan, Russia, and other countries by reassessing the safety and response capabilities of NPPs in extreme natural disaster situations that exceed the design basis. The extreme natural disaster can put the NPPs in beyond-design-basis conditions such as the loss of the power system and the ultimate heat sink. The behaviors and capabilities of NPPs with losing their essential safety functions should be measured to find and supplement weak areas in hardware, procedures and coping strategies. The Loss of Ultimate Heat Sink (LUHS) accident assumes impairment of the essential service water system accompanying the failure of the component cooling water system. In such conditions, residual heat removal and cooling of safety-relevant components are not possible for a long period of time. It is therefore very important to establish coping strategies considering all available equipment to mitigate the consequence of the LUHS accident and keep the NPPs safe. In this study, thermal hydraulic behavior of the LUHS event was analyzed using RELAP5/Mod3.3 code. We also performed the sensitivity analysis to identify the effects of the operator recovery actions and operation strategy for charging pumps on the results of the LUHS accident.

• International Journal of Contents
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• v.10 no.1
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• pp.54-61
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• 2014

In this paper, we propose a pioneering concept of DPD(Disaster Prevention Design) to realize a securable society in the future. Features of danger in the future society are expected to be diverse, abrupt occurring, large scale, and complicated ways. Due to increment of dangers with their features of uncertainty, interactivity, complexity, and accumulation, human-oriented design concept naturally participates in activities to prevent our society against disasters effectively. We presented DPD is an essential design activity in order to cope with dangers expected in the future societies as well as realize securable environments. DPD is also an integrated design aids including preemptive protections, rapid preparing, recovery, and interactive cooperation. We also expect these activities of DPD is effective for generation of new values in the market, satisfaction of social needs, expansion of design industry, and a novel chance for development in the future society. Throughout this paper, we submit various aspects of DPD concepts including definition, classification, scope, necessity, strategy, influencing elements, process, and its principle. We expect these concepts will be the seed and/or basement of DPD research for the future works. For the direction of study for DPD in the future, we emphasize alarm system for preemptive protection rather than recovery strategy for the damage occurred. We also need to research about progressive prevention techniques and convergence with other areas of design. In order to transfer the concept of product design from facility-oriented mechanism to human-oriented one, we should develop new kinds of city basis facilities, public-sense design concepts referred to social weak-party, e-Learning content design preparing disasters, and virtual simulation design etc. On the other hand, we have to establish laws and regulations to force central and/or provincial governments to have these DPD strategies applying their regional properties. Modern design activities are expanding to UI(user interface) content design area overcoming the conventional design concept of product and/or service. In addition, designers are recognized as art directors or life stylists who will change the human life and create the social value. DPD can be divided into prevention design, preparedness design, response design, and recovery design. Five strategies for successful DPD are Precaution-oriented, Human-oriented, Sense-oriented, Legislation, and Environment Friendly Strategies.

• The Korean Journal of Franchise Management
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• v.4 no.1
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• pp.73-90
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• 2013

Franchise industry know-how and an excellent management company organically integrated knowledge management resources industry. The franchise industry in the country's economic growth continues to contribute a large bar, has had an impact on the company's growth The franchise industry franchise industry in Japan than in other industries, and long-term steady growth rate despite the recent recession and recovery illustrates a trend Thus, the structure of the franchise industry in Japan by analyzing the company's franchise industry in Korea for overseas expansion strategies are evaluated In this study, a plateau in Japan to get bigger and provide a starting point for the 2009 and 2010 Census of Japan Association of Chain and Franchise all over the franchise system through a comparative analysis of Japanese overseas franchise business structure and strategies, and identify the research Korea based on the company's overseas expansion strategy is aimed at For this purpose, literature review and statistical analysis of the number of chain stores industry results, sales trends over the following four results are derived. 1) services with emphasis laid plans enable one franchise 2) the flow of services to the aging franchise, nursing, health-oriented, early childhood education, beauty and related business expected to grow 3) Recognition of Japanese culture and understanding of the importance of the service sector to account for differences in 4) services business of the need for efforts to increase productivity are summarized Based on the results of this study, Korea Franchise companies in the industry, Japan IS overseas expansion strategy franchise industry awareness of cultural differences in the institutional environment and the strategy should be considered.