• The Transactions of The Korean Institute of Electrical Engineers
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• v.65 no.12
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• pp.2159-2166
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• 2016

In the IEEE 802.11 DCF (Distributed Coordination Function) protocol, the binary exponential backoff algorithm is used to avoid data collisions. However, as the number of stations increases of, the collision probability tends to grow and the overall network performance is reduced. To solve this problem, this paper proposes a data transmission scheme based on the channel reservation method. In the proposed scheme, channel time is divided into reservation period and contention period. During the reservation period, stations succeeded in channel reservation transmit their own data packets in sequence without contention. During the contention period, each station sends its data packets through contentions as in DCF. During both the reservation period and the contention period, each station sends a request for channel reservation for the next reservation period to an AP (Access Point). After receiving such a channel reservation request from each station, the AP decides whether the reservation is succeeded and sends the result via a beacon frame to each station. Performance of the proposed scheme is analyzed through simulations. The simulation results show that the proposed scheme tends to reduce the collision probability of DCF and to improve the overall network performance.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.8 no.2
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• pp.406-423
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• 2014

The recent advances in wireless communication systems and semiconductor technologies are paving the way for new applications over wireless sensor networks. Health-monitoring application (HMA) is one such emerging technology that is focused on sensing and reporting human vital signs through the communication network comprising sensor devices in the vicinity of the human body. The sensed vital signs can be divided into two categories based on the importance and the frequency of occurrence: occasional emergency signs and regular normal signs. The occasional emergency signs are critical, so they have to be delivered by the specified deadlines, whereas the regular normal signs are non-critical and are only required to be delivered with best effort. Handling the occasional emergency sign is one of the most important attributes in HMA because a human life may depend on correct handling of the situation. That is why the underlying network protocol suite for HMA should ensure that the emergency signs will be reported in a timely manner. However, HMA based on IEEE 802.15.4 might not be able to do so owing to the lack of an appropriate emergency-handling mechanism. Hence, in this paper, we propose a new emergency-handling mechanism to reduce the emergency reporting delay in IEEE 802.15.4 through the modified superframe structure. A fraction of an inactive period is modified into three new periods called the emergency reporting period, emergency beacon period, and emergency transmission period, which are used opportunistically only for immediate emergency reporting and reliable data transmission. Extensive simulation is performed to evaluate the performance of the proposed scheme. The results reveal that the proposed scheme achieves improved latency and higher emergency packets delivery ratio compared with the conventional IEEE 802.15.4 MAC.

• Journal of the Institute of Electronics Engineers of Korea SP
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• v.39 no.3
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• pp.36-41
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• 2002

Generally, cartoon images are simple and involve a small number of colors and often include large homogeneous regions with same color or gradient. In this paper, effective compression method for complementary quadtree was suggested for cartoon images, by using those properties. And with progressive transmission, this method involves a progressive increase in the image resolution at the receiver from a lower to a higher resolution during the transmission of data. This is an effective way of using a limited transmission channel, because, after estimating the value of the data in the early transmission period, a decision can be made whether or not to proceed with the transmission of the remaining part. Since the proposed method is lossless and involves progressive transmission, it was compared with progressive PNG and progressive GIF, which had same functions.

• Journal of Internet Computing and Services
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• v.8 no.2
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• pp.43-54
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• 2007

The effective power consumption is the primary issue in a sensor network which consists of the sensor nodes with limited battery power. So, most of the MAC protocols in sensor networks have been designed with the consideration of energy efficiency. Generally, these protocols make use of the listen and sleep mode periodically. However, this approach inevitably causes a long transmission delay on the data forwarding path, which is mainly resulted from the sleep time of the receiver node. This paper deals with a design of DT-MAC(Data Transmission centric MAC) protocol, with minimizes the data transmission delay while it forces each node to consume its energy efficiently. Thus, a node received a packet converts its remained sleep time to the pseudo_listen time, in which the node is able to transmit a packet. With benefit of the pseudo_listen period, the data transmission delay along with the data forwarding path will be shortened as much as it possible. Therefore, DT-MAC protocol is very suitable to the various applications which require a real time sensing data such as disaster and fire alarm.

• The Journal of the Korean dental association
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• v.48 no.6
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• pp.436-442
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• 2010

Objective: Transmission of S. mutans, a major dental caries pathogen, occurs mainly during the first 2.5 years of age. Children appear to acquire S. mutans mostly from their mothers, but few studies have investigated preventive effect of xylitol to S. mutans transmission from mother to child. The aim of this study was to perform a follow-up evaluation the preventive effect of xylitol chewing gum of the S. mutans of children's oral cavities, which included the characteristics of vertical transmission from mother to child. Methods: The mothers voluntarily participating in a women's oral health prevention program were divided into two groups (a control and a xylitol group). The subjects were 20 mother-child pairs, who were monitored for 30 months. Xylitol chewing gum group had consumed 2 gum pellets, 3 times a day for 24 months, and then they were followed until 30 months. At baseline, 24 and 30 months whole stimulated saliva samples were collected from the mothers. Children were also recruited from 6 months to 30 months after birth and were collected their dental plaque samples. After isolation and identification, the analysis of the colony count, transmission electron microscopy and real-time RT-PCR were performed to analyze the characteristics of S. mutans. Results: The S. mutans counts decreased steadily in the xylitol group at 24 months, but increased at 30 months. The similar results were showed at their children. While the glucan synthesis was decreased at xylitol group both mother and child. The expression of gtfB, gtfD and ftf were significantly reduced in the xylitol group both mother and child (p<0.05). Conclusions: These findings indicate that chewing xylitol gum over a long period may decrease the expression of the genes associated virulence and reduced the glucan synthesis of S. mutans, which can result the preventing the mother-to-child transmission of S. mutans.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.11a
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• pp.1354-1359
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• 2007

This paper discusses the acoustic performance of simple expansion chamber using computational fluid dynamics(CFD). The CFD model consists of an axisymmetric grid with a single period sinusoid of acceptable amplitude and duration imposed at the inlet boundary condition. The time history of the static pressure is recorded at two points, one in the inlet pipe and one point in outlet pipe. The time history of the static pressure is converted to the frequency domain using Fourier Transform and the transmission loss (TL) of the muffler is obtained from the ratio of the static pressure at the inlet and outlet pipe. The transmission loss of CFD result is compared with that of the computational acoustic analysis using the boundary element method (BEM). There are some differences in two results due to the pressure drop according to the inlet and outlet pipe length. Therefore, the effects of the pressure drop to the transmission loss have to be considered.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.56 no.10
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• pp.1791-1795
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• 2007

Small ions generated at conductor corona sources remain in the atmosphere until they recombine with ions of opposite polarity, attach to aerosols, or make contact with an object. Ion current density is major factor to design conductor configuration of DC overhead transmission line. Several techniques have been used to measure the ion current of HVDC overhead transmission line. In this study, the ion current density was measured by a plate electrode made of a metal flat board at DC corona cage. The sensitivity of the plate electrode is $0.156uA/m^2/V$. To obtain an useful database on corona discharge, it is necessary to do corona test on several kinds of conductor bundles. Therefore, a number of experiments were conducted on several kinds of conductor bundles. To reliably analyze ion effects, corona cage test data were obtained over a long period of time under various weather conditions and expressed as a statistical distribution. Ion current density distribution in foul weather shows a significant increase in levels over the corresponding fair weather. Based on this results, we evaluated the environmental characteristic caused by ion flow of three candidated conductor bundles.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.2A
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• pp.139-148
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• 2011

This paper presents the minimum-cost network selection scheme which determines the transmission instance in the multi-band maritime communication system, so that the shipment-related real-time information can be transmitted within the maximum allowed period. The transmission instances and the corresponding network selection process are modeled by a Markov Decision Process (MDP), for the channel model in the 2-state Markov chain, which can be solved by stochastic dynamic programming. It derives the minimum-cost network selection rule, which can reduce the network cost significantly as compared with the straight-forward scheme with a periodic transmission.

• Journal of Korean Medical classics
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• v.28 no.4
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• pp.139-154
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• 2015

Objectives : Zheng Zhi Xin Chuan(證治心傳) is a compact compilation of 14 discussions on medicine, written by Yuan Ban(袁班) in the late Ming-early Qing period. Methods : To survey the scholarly position of Yuan Ban(袁班) in the history of Wenbing by systematically analyzing and organizing Wenbing related theories in Zheng Zhi Xin Chuan (證治心傳). Results & Conclusions : In his book, YB suggests concepts such as 'mainly attack upper heater(多犯上焦)', 'transmission to the nutrient phase(轉入營分)', 'sequential transmission(順傳)', 'abnormal transmission(逆傳)', 'dryness invasion of human body in autumn(秋傷於燥)'. In the history of Wenbing, it has been widely acknowledged that the concept of weiqiyingxiebianzheng(衛氣營血辨證) and abnormal transmission to the pericardium(逆傳心包) were originally suggested by Ye Tianshi(葉天士). However, according to the findings of this study, these concepts are traced back to the contents of YB's publication, nearly a century before Ye's time. In addition, YB's discussion on '秋燥' was highly advanced than any other scholar of his time, hinting his influence on medicine thereafter.

• The Transactions of the Korean Institute of Electrical Engineers
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• v.37 no.5
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• pp.272-281
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• 1988

The problem of optimal transmission system planning is to find the most economical locations and time of transmission line construction under the various constraints such as available rights-of-way, finances, the technical characteristics of power system, and the reliability criterion of power supply, and so on. In this paper the constraint of right-of-way is represented as a finite set of available rights-of-way. And the constructed for a unit period. The electrical constraints are represented in terms of line overload and steady state stability margin. And the reliability criterion is dealt with the suppression of failure cost and with single-contingency analysis. In general, the transmission planning problem requires integer solutions and its objective function is nonlinear. In this paper the objective function is defined as a sum of the present values of construction cost and the minimum operating cost of power system. The latter is represented as a sum of generation cost and failure cost considering the change of yearly load, economic dispatch, and the line contingency. For the calculation of operating cost linear programming is adopted on the base of DC load flow calculation, and for the optimization of main objective function nonlinear Branch-and-Bound algorithm is used. Finally, for improving the efficiency of B & B algorithm a new sensitivity analysis algorithm is proposed.