• Journal of the Korean Society for Nondestructive Testing
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• v.28 no.6
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• pp.512-518
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• 2008

Guided wave technology is advantageous for fast inspection of pipe wall thinning since the guided wave propagates long distance. In this investigation, the method to evaluate gradual wall thinning in a pipe based on the arrival time delay with magnetostrictive patch transducers is presented. Low frequency A0 Lamb waves were generated and measured by the present transducer and it was applied to arrival time delay measurement experiments on a test pipe having gradual wall thinnings artificially manufactured. From experiments, consistent results that wall thinning increases the arrival time delay of A0 waves were obtained. Consequently, the feasibility of the magnetostrictive patch transducers to evaluate wall thinning was verified.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.11B
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• pp.1169-1177
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• 2009

This paper presents an energy efficient MAC protocol for delay-sensitive data transmission over wireless sensor network. In general, energy consumption and delay depend on Channel Monitoring Interval and data sensing period at each sensor node. Based on this fact, we propose a new preamble structure to effectively advertise Channel Monitoring Interval and avoid the overhearing problem. In order to pursue an effective tradeoff between energy consumption and delay, we also develop a Channel Monitoring Interval determining algorithm that searches for a sub-optimal solution with a low computational complexity. Finally, experimental results are provided to compare the proposed MAC protocol with existing sensor MAC protocols.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.10 no.10
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• pp.4977-4996
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• 2016

The existence of excessively large and too filled network buffers, known as bufferbloat, has recently gained attention as a major performance problem for delay-sensitive applications. Researchers have made three types of suggestions to solve the bufferbloat problem. One is End to End (E2E) congestion control, second is deployment of Active Queue Management (AQM) techniques and third is the combination of above two. However, these solutions either seem impractical or could not obtain good bandwidth utilization. In this paper, we propose a Transmission Control Protocol（TCP）delayed window update mechanism which uses a congestion detection approach to predict the congestion level of networks. When detecting the network congestion is coming, a delayed window update control strategy is adopted to maintain good protocol performance. If the network is non-congested, the mechanism stops work and congestion window is updated based on the original protocol. The simulation experiments are conducted on both high bandwidth and long delay scenario and low bandwidth and short delay scenario. Experiment results show that TCP delayed window update mechanism can effectively improve the performance of the original protocol, decreasing packet losses and queuing delay while guaranteeing transmission efficiency of the whole network. In addition, it can perform good fairness and TCP friendliness.

• Journal of the Korean Society for Aviation and Aeronautics
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• v.30 no.1
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• pp.1-11
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• 2022

The capacity of Jeju International Airport has reached its limit due to a surge in air traffic demand such as passengers and cargo and the continuous expansion of Low Cost Carriers (LCC). Despite COVID-19 that has began in November 2019, Jeju International Airport still has continuous demand in terms of passenger and cargo transportation. As a result, it is undeniable that the delay rate also unexpectedly increased as the air traffic volume at Jeju International Airport continued to increase. In this study, the correlation between Turnaround Time and delay rates of national airlines is analyzed based on past flight data at Jeju International Airport, and the cumulative delay time trend for sampled airlines is compared with Turnaround Time. Through this study, it is expected to contribute to securing aircraft operation efficiency and on-time by analyzing delays related to Turnaround Time at Jeju International Airport.

• The Journal of the Korea Contents Association
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• v.8 no.10
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• pp.20-26
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• 2008

The quality of stream remaking is decided the load of a server and Jitter through the traffic of the transmission path between end to end. In order to improve these problems in this paper, I propose tree construction method of low-delay-level-multicast. In this case which the network congestion will be occurred by streaming quality, I also propose the technique which dynamically changes the transmission path. This technique first constructs the overlay structure for relaxing the overload of server. Secondly, in order to decrease Jitter of client, it makes upload bandwidth and low latency balanced. In the evaluation of the performance, this paper showed better enhancement of about $15%{\sim}24%$ than P2CAST[4] in the simulation about node average join count, average bandwidth, service request refusal ratio, RTT measurement of nodes, and node average join count by defect ratio.

• Journal of the Institute of Electronics and Information Engineers
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• v.52 no.2
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• pp.112-118
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• 2015

Conventional synchronous circuits cannot keep the circuit performance, and cannot even guarantee correct operations under the influence of PVT variations and aging effects in the nanometer regime. Therefore, in this paper, a DI (delay insensitive) design based NCL (Null Convention Logic) design methodology with a very simple design structure has been used to design digital systems, which is one of well-known asynchronous design methods robust to various variations and does not require any timing analysis. Because circuit-level structures of conventional NCL gates have weakness of low speed, high area overhead or high wire complexity, this paper proposes a new lNCL gates designed at the transistor level for high-speed, low area overhead, and low wire complexity. The proposed NCL gate libraries have been compared to the conventional NCL gates in terms of circuit delay, area and power consumption using a asynchronous multiplier implemented in dongbu 0.11um CMOS technology.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.9B
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• pp.785-791
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• 2006

A CF-Poll frame which contains the channel reservation time can be piggybacked in QoS-Data frame to increase the channel efficiency in HCCA. However, if any QSTA in the network uses the low physical transmission rate, the QoS-Data frame which includes the CF-Poll frame must be transmitted by the minimum transmission rate. Therefore, it can cause the decrease of the channel efficiency and the increase of the frame transmission delay for other traffic streams when any QSTA has the low physical transmission rate. In this paper, we define this phenomenon as the piggyback problem at the low physical transmission rate and evaluate the effect of this problem. In the simulation results, when a CF-Poll piggyback is used, the delay is increased about 25% if any QSTA has the low physical transmission rate, while the delay is decreased about 7.8% if all QSTA has the high physical transmission rate. We also found that the gain of the CF-Poll piggyback mechanism is achieved when all QSTA has higher physical transmission rate than 24 or 36Mbps.

• Journal of Aerospace System Engineering
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• v.14 no.3
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• pp.24-31
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• 2020

A study on the H2O2 based low toxic hypergolic propellant was conducted. The fuel candidates were chosen as a mixture of Amine solvent and reactive additive. The analytical performance was calculated via the NASA CEA code and 96% Isp of the NTO/UDMH was confirmed. The ignition delay measurement with drop test was performed and all candidates showed less than 10 ms in the best performance cases. Based on these results, the feasibility of high response H2O2 based low toxic hypergolic propellant was confirmed.

• JSTS:Journal of Semiconductor Technology and Science
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• v.17 no.2
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• pp.302-317
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• 2017

This paper proposes a new full adder design based on pass-transistor logic that offers ultra-low power dissipation and superior variability together with low transistor count. The pass-transistor logic allows device count reduction through direct logic realization, and thus leads to reduction in the node capacitances as well as short-circuit currents due to the absence of supply rails. Optimum transistor sizing alleviates the adverse effects of process variations on performance metrics. The design is subjected to a comparative analysis against existing designs based on Monte Carlo simulations in a SPICE environment, using the 22-nm CMOS Predictive Technology Model (PTM). The proposed ULP adder offers 38% improvement in power in comparison to the best performing conventional designs. The trade-off in delay to achieve this power saving is estimated through the power-delay product (PDP), which is found to be competitive to conventional values. It also offers upto 79% improvement in variability in comparison to conventional designs, and provides suitable scalability in supply voltage to meet future demands of energy-efficiency in portable applications.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.9B
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• pp.792-802
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• 2006

In this paper, we propose an energy-efficient proactive data dissemination protocol with relatively low delay to cope well with highly mobile sink environments in sensor networks. In order for a dissemination tree to continuously pursue a dynamic sink, we exploit two novel algorithms: forward sink advertisement and distributed fast recovery. In our protocol, the tree is shared with the other slave sinks so that we call it Dynamic Shared Tree (DST) protocol. DST can conserve considerable amount of energy despite maintaining robust connection from all sources to sinks, since tree maintenance of DST is accomplished by just distributed local exchanges. In addition, since the DST is a kindof sink-oriented tree, each source on the DST disseminates data with lower delay along the tree and it also facilitates in-network processing. Through simulations, it is shown that the presented DST is considerably energy-efficient, robust protocol with low delay compared to Directed Diffusion, TTDD, and SEAD, in highly mobile sink environment.