• The Journal of Korean Institute of Communications and Information Sciences
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• v.28 no.9A
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• pp.702-709
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• 2003

In this paper, we propose an efficient and QoS-aware MAC scheduling algorithm for Bluetooth, which considers both throughput and delay performance of each Master-Slave pair in scheduling decisions, and thus, attempts to maximize overall performance. The proposed algorithm, MTDPP (Modified Throughput-Delay Priority Policy), makes up for the drawbacks of T-D PP (Throughput-Delay Priority Policy) proposed in [6] and improves the performance. Since Bluetooth employs a master-driven TDD based scheduling algorithm, which is basically operated with the Round Robin policy, many slots may be wasted by POLL or NULL packets when there is no data waiting for transmission in queues. To overcome this link wastage problem, several algorithms have been proposed. Among them, queue state-based priority policy and low power mode-based algorithm can perform with high throughput and reasonable fairness. However, their performances may depend on traffic characteristics, i.e., static or dynamic, and they require additional computational and signaling overheads. In order to tackle such problems, we propose a new scheduling algorithm. Performance of our proposed algorithm is evaluated with respect to throughput and delay. Simulation results show that overall performances can be improved by selecting suitable parameters of our algorithm.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.3
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• pp.694-702
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• 2017

In the case of an elevated railway station, structure borne noise and vibration due to structural limitations allow the load and vibration from railway vehicles to be directly transmitted to the station structure, resulting in an increase in the number of civil complaints from customers and staff of the station. The floating slab track system, which is well known as one of the solutions for reducing the noise and vibration from elevated railway stations, usually contains rubber mounts or rubber pads under the railway slab which act as a damper. These types of device have the disadvantage that is difficult to predetermine the exact stiffness and damping ratio under the nonlinear loads resulting from train services. In this study, an isolator with a friction type of wedge is introduced, which can be applied to floating slab track systems and to be designed with precisely the required stiffness. Furthermore, a comparative analysis of the stiffness between the designed and experimental values is carried out, while the damping ratio, which is closely related to the friction wedge blocks, is deduced according to the train load condition. The performance tests of the isolator were conducted in accordance with the DIN 45673-7 standard which includes both static and dynamic load tests. The load conditions for the performance tests are designed to conform to the DIN standard related to the weight of the train and rail track, in order to perform vertical and horizontal load tests, so as to ensure the secure structural safety of the railway. Also, by checking the change aspect of the friction coefficients of the friction elements according to the loading rate, the vibration reduction performance of the friction type isolator with variable loading rate conditions is examined.

• Proceedings of the KSMRM Conference
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• 2003.10a
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• pp.103-105
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• 2003

After fifteen years of development, Magnetic Resonance (MR) technology for human imaging and spectroscopy is reaching a refined state with FDA approved 3T clinical products from Siemens, GE, and Philips. Broker has cleared CE approval with a 4T system. Varian supports a 4T system platform as well. Shielded magnets are standard at 3T from GE, Oxford, Magnex, and IGC. A shielded 4T whole body magnet is available from Oxford. Stronger switched gradients and dynamic shim coils, desired at any field, areespecially useful at higher static magnetic fields B0. In addition to the higher currents required for higher resolution slice or volume selection afforded by higher SNR, whole body gradient coils will be driven at increasing slew rates to meet the needs of new cardiac applications and other requirements. For example 3T and 4T systems are now being equipped with 2kV, 500A gradient coils and amplifiers capable of generating 4G/cm in 200msec, over a 67+/-cm bore diameter. High field EPI applications require oscillation rates at 1 kHz and higher. To achieve a benchmark 0.2 ppm shim over a 30cm sphere in a high field magnet, at least four stages of shimming need to be considered. 1) A good high field magnet will be built to a homogeneity spec. falling in the range of 100 to 150 ppm over this 30cm spherical "sweet spot" 2) Most modern high field magnets will also have superconducting shim coils capable of finding 1.5 ppm by their adjustment during system installation. 3) Passive ferro-magnetic shimming combined with 4) active, high order room temperature shim coils (as many as five orders are now being recommended) will accomplish 0.2 ppm over the 30cm sphere, and 0.1 ppm over a human brain in even the highest field magnets for human studies. Safety concerns for strong, fast gradients at any B0 field include acoustic noise and peripheral nerve stimulation. One or more of the mechanical decoupling methods may lead to quieter gradients. Patient positioning relative to asymmetric or short gradient coils may limit peripheral nerve stimulation at higher slew rates. Gradient designs combining a short coil for local speed and strength with a longer coil for coverage are being developed for 3T systems. Local gradients give another approach to maximizing performance over a limited region while keeping within the physiologically imposed dB0/dt performance limits.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.24 no.5
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• pp.897-909
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• 2014

With the development of the Internet, the number of cyber threats is continuously increasing and their techniques are also evolving for the purpose of attacking our crucial systems. Since attackers are able to easily make exploit codes, i.e., malware, using dedicated generation tools, the number of malware is rapidly increasing. However, it is not easy to analyze all of malware due to an extremely large number of malware. Because of this, many researchers have proposed the malware classification methods that aim to identify unforeseen malware from the well-known malware. The existing malware classification methods used malicious information obtained from the static and the dynamic malware analysis as the criterion of calculating the similarity between malwares. Also, most of them used API functions and their sequences that are divided into a certain length. Thus, the accuracy of the malware classification heavily depends on the length of divided API sequences. In this paper, we propose an extraction method of optimized API sequence length and combination that can be used for improving the performance of the malware classification.

• Journal of Adhesion and Interface
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• v.20 no.3
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• pp.87-95
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• 2019

In the present study, the effect of alkali treatment of rice straw on the flexural properties and impact strength of rice straw/recycled polyethylene composite was investigated. Alkali treatments were performed by means of two different methods at various sodium hydroxide (NaOH) concentrations. One is static soaking method and the other is dynamic shaking method. The composites were made by compression molding technique using rice straw/recycled polyethylene pellets produced by twin-screw extrusion process. The result strongly depends on the alkali treatment method and concentration. The shaking method done with a low concentration of 1 wt% NaOH exhibits the highest flexural and impact properties whereas the soaking method done with a high concentration of 10 wt% NaOH exhibits the highest properties, being supported qualitatively by the fiber-matrix interfacial bonding of the composites. The properties between the two highest property cases above-described are comparable each other. The study suggests that such a low concentration of 1 wt% NaOH may be used for alkali treatment of natural fibers to improve the flexural and impact properties of resulting composites, rather than using high concentrations of NaOH, 10 wt% or higher. Considering of environmental concerns of alkali treatment, the shaking method is preferable to use.

• Journal of the Korea institute for structural maintenance and inspection
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• v.24 no.6
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• pp.34-41
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• 2020

In recent years, magnitude and frequency of earthquakes have increased in Korea. Damage to a bridge, which is one of the main infrastructures, can directly lead to considerable loss of human lives. Therefore, engineers need to evaluate the seismic fragility of the structure and prepare for the possible seismic damage. In particular, the number of aging bridges over 30 years of service increases, and thus the seismic analysis and fragility requires accounting for the aging and retrofit effects on the bridge. In this study, the nonlinear static and dynamic analyses were performed to evaluate the effects of the aging and FRP retrofit on a PSC bridge. The aging and FRP retrofit were applied to piers that dominate the response of the bridge during earthquakes. The maximum displacement of the bridge increased due to the aging of the pier but decreased when FRP retrofit applied to the aged pier. In addition, seismic fragility analysis was performed to evaluate the seismic behavior of the bridge combined with the seismic performance of the pier. Compared with the aged bridge, the FRP retrofit bridge showed a decrease in the seismic fragility in all levels of damage. The reduction of the seismic fragility in the FRP bridge was prominent as the value of PGA and level of damage increased.

• The Journal of the Korea Contents Association
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• v.21 no.4
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• pp.50-59
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• 2021

To understand the research trends of English education in Korea for the last 20 years from 2000 to 2019, 12 major academic journals in Korea in the field of English education were selected, and bibliographic information of 7,329 articles published in these journals were collected and analyzed. The total number of articles increased from the 2000s to the first half of the 2010s, but decreased somewhat in the late 2010s and the number of publications by journal has become similar. These results show that the overall influence of English education journals has decreased and then leveled in terms of quantity. Next, 34 topics were extracted by applying latent Dirichlet allocation (LDA) topic modeling using the English abstract of the articles. Teacher, word, culture/media, and grammar appeared as topics that were highly studied. Topics such as word, vocabulary, and testing and evaluation appeared through unique keywords, and various topics related to learner factors emerged, becoming topics of interest in English education research. Then, topics were analyzed to determine which ones were rising or falling in frequency. As a result of this analysis, qualitative research, vocabulary, learner factor, and testing were found to be rising topics, while falling topics included CALL, language, teaching, and grammar. This change in research topics shows that research interests in the field of English education are shifting from static research topics to data-driven and dynamic research topics.

• Journal of The Korean Association For Science Education
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• v.29 no.4
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• pp.423-436
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• 2009

This study aims to develop an analytic framework that can be used to classify scientific models in science textbooks according to modes and attributes of representation and to investigate types of scientific models presented in the biology section of science textbooks for the $7^{th}$ to $10^{th}$ grades. The results showed that modes of representation of scientific models are related to the nature of sub-areas of biology sections. Generally, the iconic model and symbolic model were in dominant use, including drawings of organs and explanations of working of systems. However, the chapters on 'The Organization of Life' and 'The Continuity of Life' showed a relatively high frequency in use of the actual model. The theoretical model was presented in a part of 'The Continuity of Life', due to its highly abstract characteristics. Moreover, the gestural model and analogical model showed very low frequency. From the perspective of attributes of representation, frequency of the static model was very high, while one of the dynamic models was very low. Therefore, efforts to recognize the properties of scientific concepts more clearly and to develop diverse types of models that can represent the concepts adequately are required. Analysis of these types of scientific models can offer recognition of the usefulness and limitations of models in representing the concepts or phenomena, and can help us to design adequate models depicting particular properties of given concepts. Also, this type of analysis may motivate researchers to strive to reveal correct methods for and limits of using the scientific models that are presented in existing science textbooks, as well as to provide useful information to organize the science textbooks according to the revised $7^{th}$ national science curriculum.

• Journal of KIISE:Software and Applications
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• v.29 no.8
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• pp.543-554
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• 2002

System developers create a lot of design documents by various case tools. It is necessary to have the tools for facilitating the analysis of the documents. These tools can be used to understand and verify the whole process of a system, by defining relationships among the documents and providing free navigation methods. In this paper, we develop a navigation tool that enables the developers to systematically analyze the system by capturing duplication, instance, and transition relationships between the documents. Different from the navigation facilities of the other UML design tools, this tool makes it possible to navigate design elements in design documents such as sequence diagrams, state diagrams and class diagrams. In other words, it can be used to systematically capture and verify both the static structure and the dynamic behavior of the system by keeping track of such elements. To provide such a facility, 1) we define three relationships: duplication, instance, and transition, 2) assign relation to the related design elements according to the predefined way. and then 3) present a set of functions for navigating related design elements.

• Journal of The Korean Society of Integrative Medicine
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• v.3 no.3
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• pp.59-71
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• 2015

Purpose : This study examines the effect of vibration exercise grafting PNF patterns for 6 weeks on upper body stability and equilibrium for seniors having fifteen or over of MMSE-K. Method : A total of 10 senior citizens participated in this study. Each participant performed PNF patterned exercises using vibration sports equipment for 30 minutes, once static a week, for six weeks. We measured trunk stability and balance degree before and after the six-week exercise program. Motor Assessment Scale (MAS) was used to measure trunk stability, while Functional Reach Test (FRT) and Timed Up and Go (TUG) was used to measure balance degree. The collected data was processed using paired t-test to confirm the difference between pre-program conditions and post-program conditions. Results: The results of our study show that post-program trunk stability measurements increased when compared to pre-program data; however, this increase was not statistically significant. pre and post-measurements for satatic balance and dynamic balance were statistically unchanged. Conclusion: Due to limitations in the number of participants, the procedural design of this experiment, and the limited amount of time participants actually controlled, this study failed to produce statistically significant results. However, further study should be conducted using a systematically implemented exercise program to show support for exercising with flexi-bar as an effective program for the elderly.