• 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.

• Journal of KIISE:Software and Applications
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• v.30 no.1_2
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• pp.73-80
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• 2003

The Java programming language is designed for developing effective applications in a heterogeneous network environment. Major problem in Java is its performance. many attractive features of Java make the development of software easy, but also make it expensive to support ; applications written in Java are often much slower than their counterparts written in C or C++. To use Java`s attractive features without the performance penalty, sophisticated optimizations and runtime systems are required. Optimising Java bytecode has several advantages. First, the bytecode is independent of any compiler that is used to generate it. Second, the bytecode optimization can be performed as a pre=pass to Just-In-Time(JIT) compilation. Many attractive features of Java make the development of software easy, but also make it expensive to support. The goal of this work is to develop automatic construction of code optimizer for Java bytecode. We`ve designed and implemented a Bytecode Optimizer that performs the peephole optimization, bytecode-specific optimization, and method-inlining techniques. Using the Classfile optimizer, we see up to 9% improvement in speed and about 20% size reduction in Java class files, when compared to average code using the interpreter alone.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.14 no.11
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• pp.1184-1190
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• 2003

In this paper, we investigated the characteristics of compensation for distorted NRZ signal and RZ signal in 320 Gbps WDM system as a function of channel input power, fiber dispersion coefficient and transmission length, respectively. The considered WDM transmission system is based on mid-span spectral inversion(MSSI) compensation method having highly nonlinear dispersion shifted fiber(HNL-DSF) optical phase conjugator(OPC) in the mid-way of total transmission line. We confirmed that the signal input power range compensated by MSSI is broadened by using RZ as a signal format in WDM system with small fiber dispersion coefficient, The range of fiber dispersion coefficient compensating overall distorted WDM channels is limited, because degree of compensation for distorted channel with low conjugated-wave power becomes gradually degrade as fiber dispersion coefficient becomes gradually higher. It is showed that RZ format and NRZ format is suited for long-haul transmission in WDM system with small fiber dispersion coefficient and with large fiber dispersion coefficient, respectively.

• Korea Journal of Hospital Management
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• v.22 no.4
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• pp.50-60
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• 2017

Purposes: The purpose of this study was to identify the preferred types of the hospital reservation cancellation management to help reduce the reservation cancellations. Methodology: This study sampled 327 outpatients or their guardians who had reserved a university hospital and a general hospital located in the southwestern part of Seoul, and the responses from 300 of them were used for the final analysis. The subjects' preferences of reservation cancellation management types were analyzed in reference to their demographic variables. The timing and frequency of pre-notification preferred by the subjects were examined. A multidimensional scaling methods and correspondence analysis was used to identify preference for management methods of no-show and type of reservation guide. Findings: As a result, 77.3% of the respondents were perceived that the reservation cancellation was a habit. The most preferred method of managing the reservation cancellation would be refusal to refund the reservation deposit (61.7%), followed by payment for cancellation (16.0%), limit of future reservations (16.0%) and penalty (6.3%) in their order. 186 of the subjects (62.0%) preferred the texting for prevention of reservation cancellations, and 102 of the subjects (34.0%) preferred the phone calls. The preferred timing and frequency of the SMS were twice 3 days before, once a day before and three times 7 days before, while the preferred timing and frequency of phone call was once a day before. Practical Implications: The no-show rate can be improved by enhancing SMS pre-notification and by improving afterwards telephone counseling. For other factors, it needs to study on the service differentiation with the characteristics of each patient group.

• Korean Journal of Applied Biomechanics
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• v.31 no.3
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• pp.162-167
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• 2021

Objective: This study aimed to identify the different wind speed categories and competitive level among windsurfers through GPS variables to provide the useful information on the development of training programs for enhancing windsurfers' performance. Method: Data from 69 female athletes who participated in 27 races during the 2018-2019 windsurfing season were used for the analysis. Average board speed, total race time, total distance, upwind race time, downwind race time, beam reach race time were collected through GPS. Unconfirmed data were excluded along with penalty point data. The wind conditions were classified as light, light to medium, medium, medium to heavy, and heavy wind, the competitive levels were classified as level 1, level 2, and level 3. Results: As for the average board speed, the level 1 or level 2 group showed higher board speed than the level 3 group in all wind conditions except for the light wind. The total race time and upwind race time showed less time in level 1 or level 2 group than level 3 group in all wind conditions. The total distance, downwind race time and beam reach race time showed less distance and time in level1 group than level 3 group under sufficient wind conditions. Conclusion: Our results show that the aerobic capacity to sustain pumping during upwind course in wind conditions below 15 kts effects performance. In wind conditions of 15 kts or more, indicated that the board control for the fast board speed and small distance required during up, down, beam reach courses had an effect on competition performance. This information can be provided to windsurfers and coaching as basic data for training programs to improve performance.

• Journal of Korean Library and Information Science Society
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• v.52 no.3
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• pp.369-393
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• 2021

The legal deposit is a comprehensive and systemic method for acquiring a country's publications. This study aims to compare laws and regulations about legal deposit among several countries that have different histories and traditions and to supplement laws and regulations of Korea's legal deposit. To do this, research papers and laws, regulations, guides, web sites and online systems about legal deposit of eight countries including USA, United Kingdom, Canada, Australia, France, Japan, Singapore, and Korea were reviewed. This study tried to compare and analyse several categories including publications to be deposited or not deposited, requirements, due dates, expenses, and numbers of copies for deposit, and penalty for noncompliance with legal deposit. Also, online publications to be deposited or not deposited, requirements and methods for deposit were compared and analysed. At last, some suggestions were also made for improvement in laws and regulations of in Korea.

• Journal of the Society of Disaster Information
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• v.18 no.2
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• pp.314-323
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• 2022

Purpose: To study the effect of the amended Occupational Safety and Health Act on the expansion of the employer's responsibility and obligations and the evaluation of the employer on the improvement of the safety management system. Method: An academic discussion was conducted by comparing the contents of previous studies with the analysis results. A questionnaire was prepared using the measurement tools collected from previous studies, and statistical multiple regression analysis was performed with the collected data. Result: Research hypothesis It was found that the expansion of responsibility and obligations of the business owner and the reinforcement of the employer's evaluation of the ordering party had a positive (+) effect on the improvement of the safety management system. Conclusion: The expansion of the responsibility and obligations of the employer and the strengthening of the evaluation of the owner of the orderer are having a positive effect on the improvement of the construction safety management system for the prevention of construction accidents.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.23 no.4
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• pp.183-188
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• 2023

Game object inheritance and multiple components allow for visualization of system architecture, good code reuse, and fast prototyping. On the other hand, objects are more likely to rely on high latency between game objects and components, static casts, and lots of references to things like null pointers. Therefore, It is important to design a game in such a way so that the dependency of objects on multiple classes could be reduced and existing codes could be reused. Therefore, we designed the game to make the classes more modular by applying Dependency Injection and the design patterns proposed by the Gang of Four. Since these dependencies are attributes of the game object and the injection occurs only in the initialization pass, there is little performance degradation or performance penalty in the game loop. Therefore, this paper proposed an efficient design method to effectively reuse APIs in the design and implementation of survival games.

• Journal of Korean Society of Industrial and Systems Engineering
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• v.45 no.1
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• pp.71-82
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• 2022

Most of the predictions using machine learning are neutral predictions considering the symmetrical situation where the predicted value is not smaller or larger than the actual value. However, in some situations, asymmetric prediction such as over-prediction or under-prediction may be better than neutral prediction, and it can induce better judgment by providing various predictions to decision makers. A method called Asymmetric Twin Support Vector Regression (ATSVR) using TSVR(Twin Support Vector Regression), which has a fast calculation time, was proposed by controlling the asymmetry of the upper and lower widths of the ε-tube and the asymmetry of the penalty with two parameters. In addition, by applying the existing GSVQR and the proposed ATSVR, prediction using the prediction propensities of over-prediction, under-prediction, and neutral prediction was performed. When two parameters were used for both GSVQR and ATSVR, it was possible to predict according to the prediction propensity, and ATSVR was found to be more than twice as fast in terms of calculation time. On the other hand, in terms of accuracy, there was no significant difference between ATSVR and GSVQR, but it was found that GSVQR reflected the prediction propensity better than ATSVR when checking the figures. The accuracy of under-prediction or over-prediction was lower than that of neutral prediction. It seems that using both parameters rather than using one of the two parameters (p_1,p_2) increases the change in the prediction tendency. However, depending on the situation, it may be better to use only one of the two parameters.

• The KIPS Transactions:PartD
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• v.14D no.3 s.113
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• pp.319-328
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• 2007

As the coverage of Web services become wider and the number of implementation cases is growing, the importance of applying the Web services quality model to real world is increased. For maintaining the level of Web services qualify, it should be required to study on assurance method of Web services qualify level. Assurance for Web services, which is newly proposed by OASIS TC, means the totality of activities for managing the quality level of them. For managing Web service quality, Web service associates could usually use SLA(Service Level Agreement) method in which a service consumer contracts for some service level with a service provider and gives for penalty or pays incentives according to the result of evaluation of services. But, there are some difficulties in applying SLA to Web services, because Web services have publicity, multiple users, and 3rd party for management. So, we need a new assurance method for Web service by considering the characteristics of Web services. This paper provides the new concept of committed assurance level for Web services. This concept can be defined as the set of maximum level of quality expected by each user, which provide the consistent view of Web service quality. This paper presents the method for duality associates to preserve some quality level of Web service by using this concept.