• Journal of Communications and Networks
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• v.11 no.4
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• pp.406-415
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• 2009

In this work, we consider performance modeling of a wireless sensor network with a time division multiple access (TDMA) media access protocol with slot reuse. It is assumed that all the nodes are peers of each other and they have two modes of operation, active and sleep modes. We model the sensor network as a Jackson network with unreliable nodes with on and off states. Active and sleep modes of sensor nodes are modeled with on and off states of unreliable nodes. We determine the joint distribution of the sensor node queue lengths in the network. From this result, we derive the probability distribution of the number of active nodes and blocking probability of node activation. Then, we present the mean packet delay, average sleep period of a node and the network throughput. We present numerical results as well as simulation results to verify the analysis. Finally, we discuss how the derived results may be used in the design of sensor networks.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.11
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• pp.1567-1573
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• 2010

In printing systems, the reliability of printed material depends on the ability of the toner film to remain adhered to the paper surface. In order to measure the strength between the toner film and the paper surface, a peel-off test is often performed. After conducting the test, the amount of toner film remaining on the paper is measured in order to determine the interfacial strength. The results of this test can be affected by many factors such as the peeling rate, weight of the roller used, and dwell time of tape. Sensitivity analysis was performed with respect to peeling rate, weight of roller and dwell time of tape at different levels. It was found that the interfacial strength increased with an increase in these main parameters. On the other hand, the trend with respect to the percentage of toner loss was different. Further, the interfacial strength and percentage of toner loss were significantly affected by the peeling rate.

• Transactions of the Korean Society of Automotive Engineers
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• v.18 no.4
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• pp.92-98
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• 2010

Virtual ground modeling is one of key topic for real-time vehicle dynamic simulation. This paper discusses about the virtual 3D road modeling process using parametric surface concept. General road data is a type of lumped position vector so interpolation process is required to compute contact of internal surface. The parametric surface has continuity and linearity within boundaries and functions are very simple to find out contact point. In this paper, the parametric surface formula is adopted to road modeling to calculate road hight. Position indexing method is proposed to reduce memory size and resource possession, and a simple mathematical method for contact patch searching is also proposed. The developed road process program is tested in dynamic driving simulation on off-road. Conclusively, the new virtual road program shows high performance of road hight computation in vast field of off-road simulation.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.49 no.8
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• pp.463-467
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• 2000

In this paper, the new LIGBT structures with trap injection are proposed to improve switching characteristics of the conventional SOI LIGBT. The Simulations are performed in order to investigate the effects of the positiion, whidth and concentration of trap injection region with a reduced minority carrier lifetime using 2D device simulator MEDICI. Their electrical characteristics are analyzed and the optimum design parameters are extracted. As a result of simulation, the turn off time for the model A with the trap injection is $0.78\mus$. These results indicate the improvement of about 2 times compared with the conventional SOI LIGBT because trap injection prevents minority carriers which is stored in the n-drift region during turn off switching. The latching current is $1.5\times10^{-4}A/\mum$ and forward blocking voltage is 168V which are superior to those of conventional structure. It is shown that the trap injection is very effective to reduce the turn off time with a little increasing of on-state voltage drop if its design and process parameters are optimized.

• Journal of Korea Society of Digital Industry and Information Management
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• v.7 no.3
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• pp.63-74
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• 2011

Credit cards are more convenient than cash of heavy. Therefore, credit cards are used widely in on_line (internet) and off_line in nowadays. To use credit cards on internet is commonly secure because client identification based security card and authentication certificate. However, to use in off_line as like shop, store, department, restaurant is unsecure because of irregular accident. As client identification is not used in off_line use of credit cards, the irregular use of counterfeit, stolen and lost card have been increasing in number recently. Therefore, client identification is urgently necessary for secure card using in off_line. And the method of client identification must be simple, don't take long time, convenient for client, card affiliate and card company. In this paper, we study a reform measure of the structure and transaction process for the safety improvement of a credit cards. And we propose several authentication method of short-and long-term for client identification. In the proposal, the client authentication method by OTP application of smart-phone is efficient nowadays.

• Proceedings of the KIPE Conference
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• 2001.10a
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• pp.351-354
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• 2001

In this paper, we present self-tuning control of switched reluctance motor for maximum torque with phase current and shaft position sensor. Determination method of turn-on/off angle is realized by using self-tuning control method. During the sampling time, micro-controller checks the number of pulse from encoder and compare with the number of pre-checked pulse. After micro-controller calculates between two data, it moves forward or backward turn-off angle. When the turn-off angle is fixed optimal turn-off angle, the turn-on angle automatically moves forward or backward by a step using self-tuning control method. And then, optimal turn-off angle is searched once again. As such a repeating process, turn-on/off angle is moved automatically to obtain the maximum torque. The experimental results are presented to validate the self-tuning algorithm.

• Journal of Chest Surgery
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• v.37 no.9
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• pp.762-767
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• 2004

With the developement of non-invasive surgical techeniques, coronary artery bypass graft without cardiopulmonary bypass has become popular. We compared the preoperative risk factors and in-hospital outcomes of patients having off-pump CABG with these having on-pump CABG. Material and Method： From January 2001 to June 2003, 87 patients underwent CABG. Thirty-sin patients underwent on-pump CABG, fifty-one patients under-went off-pump CABG. Preoperative risk factors, extent of coronary disease, operative time, postoperative endotracheal intubation time, duration of ICU stay & hospital stay, the amount of bleeding and postoperative levels of cardiac enzymes were compared in both groups, Result: The were no differences in their sex ratios, ages, preoperative risk factors, preoperative Ml, Canadian classes, extent of coronary artery diseases and, echocardio-graphic ejection fraction between Off-pump CABG and On-pump CABG groups. Off-pump CABG group had significantly lower mean operative time (270$\pm$79.3 min vs 372$\pm$142.2 min, p＜0.001), mean ventilation time (17.1$\pm$13.4 hr vs 24.3$\pm$17.8 hr) and CK-MB level (8,9$\pm$18.7 IU/L vs 25.7$\pm$8.4 IU/L) than on-pump CABG groups, On-pump CABG group had more distal grafts (2.2$\pm$0.5 vs 1.7$\pm$0.71 than Off-pump CABG groups did. There were no differences in their postoperative complications and outcomes including amount of postoperative bleeding for 24 hrs, reoperation for bleeding control, mean in-hospital days, postoperative infection, renal failure and neurologic complications between Off-pump CABG and On-pump CABG groups. Conclusion: This study showed that patients who underwent Off-pump CABG had less operation time & intubation time and lower CK-MB level; however, they also have less distal graft. Even though CABG without CPB provided satisfactory results, more clinical experience & longer follow-up is required.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.07a
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• pp.357-360
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• 2003

In this paper, we designed 4.5kV/1.5kA IGCT devices. GCT thyristor has many superior characteristics compared with GTO thyristor, for examples; snubberless turn-off capability, short storage time, high turn-on capability, small turn-off gate charge and low total power loss of the application system containing device and peripheral parts such as anode reactor and snubber capacitance. In this paper we designed GCT thyristor devices, and analyzed static and dynamic characteristics of GCT thyristor depending on the minority carrier lifetime, n-base thickness and doping concentration of n-base region, respectively. Especially, turn-on and turn-off characteristics are very important characteristics for GCT thyristor devices. So, we considered above characteristic for design and analysis of GCT devices.

• Journal of the Optical Society of Korea
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• v.15 no.2
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• pp.146-151
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• 2011

We describe, throughout a Mach-Zehnder interferometric configuration, a new test sieves calibration method based on off-axis digital holography. The experiment is conducted on a test sieve of square openings. The nominal sieve opening is 1.00 mm with maximum individual opening of 1.14 mm in size. The recorded off-axis hologram is numerically processed using Fresnel transforms to obtain an object wave (amplitude and phase). From the reconstructed phase, the average size of the illuminated openings has been measured precisely. The proposed method can provide a real time solution for calibrating test sieves very precisely and with moderate accuracy.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2015.05a
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• pp.159-159
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• 2015

금속의 기계적 강화방법인 결정립미세화의 일종으로 미세한 쌍정을 도입하여 기계적강도를 향상시키면서 전기전도도는 감소시키지 않는 방안으로 nanotwin 구조의 Cu가 보고되고 있다. Nanotwin 구조는 FCC결정구조에서 특정 결정면을 [(111) mirror plane]을 기준으로 정합계면을 유지하면서 원자층의 배열이 역전되는 구조가 수~수십나노 수준의 간격으로 이뤄진 미세조직을 의미한다. 전해도금법을 이용한 nanotwin Cu의 형성방법으로는 pulse 파형을 사용하는데, pulse파형의 on time동안의 높은 전류밀도로 인해 발생한 도금층의 stress가 off time동안에 release되면서 nanotwin구조가 형성되는 것으로 보고되고 있다. Nanotwin형성 조건으로 보고된 pulse 도금 조건은 수에서 수십밀리초의 on time에 duty cycle($t_{on}/(t_{off}+t_{on})$)이 1/100~1/10 수준이다. 본 연구에서는 전기이중층의 이온고갈에 필요한 회복시간인 수에서 수십 밀리초 보다 짧은 시간인 마이크로 초($1{\mu}s$, $10{\mu}s$ 및 $100{\mu}s$)의 pulse 전류를 인가하였을 때에 발생하는 구리 도금층의 미세조직의 변화에 대해 알아보고자 한다.