• Journal of Sensor Science and Technology
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• v.7 no.3
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• pp.171-178
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• 1998

Silicon piezoresistive absolute pressure sensor for gas leakage alarm system was developed. This sensor must operate normally in the range of $0{\sim}600\;mmH_{2}O$ pressure, and $0{\sim}100^{\circ}C$ temperature. To make the most of this sensor for gas leakage alarm system, gas must not leak from the sensor itself when the diaphragm of the sensor fractures. Thus, the sealed diaphragm cavity was anodically bonded to pyrex 7740 glass under the condition of $10^{-4}$ torr, at $400^{\circ}C$. The sensitivity of developed sensor was $4.06{\mu}V/VmmH_{2}O$ for $600\;mmH_{2}O$ full-scale pressure range. And temperature compensation method of this sensor is to change bridge-in put-voltage linearly in proportion to the temperature variation by using diode(PXIN4001) or Al thin film resistor. By these methods the temperature effect in the range of $0{\sim}100^{\circ}C$ was compensated over 80 % for offset drift, 95 % for sensitivity.

• Journal of KIISE
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• v.44 no.5
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• pp.449-459
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• 2017

Data Distribution Service (DDS) is a communication middleware that supports a flexible, scalable and real-time communication capability. This paper describes several techniques to improve the performance of DDS middleware. Detailed events for the internal behavior of the middleware are defined. A DDS message is disassembled into several submessages of independent, meaningful units for event-driven structuring in order to reduce the processing complexity. The proposed technique of history cache management is also described. It utilizes the fact that status access and random access to the history cache occur more frequently in the DDS. These methods have been implemented in the EchoDDS, the DDS implementation developed by our team, and it showed improved performance.

• The Transactions of the Korean Institute of Power Electronics
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• v.18 no.2
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• pp.169-177
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• 2013

This paper proposes a new configuration of bidirectional intelligent semiconductor transformer with rating of 1.9kV/127V, 2kVA. The proposed transformer consists of high-voltage high-frequency AC-DC rectifier, and low-voltage DC-DC and DC-AC converters. The operational feasibility of proposed transformer was verified by computer simulation with PSCAD/EMTDC software. Based on the simulation results, a hardware prototype with rating of 1.9kV/127V, 2kVA was built and tested in the lab to confirm the feasibility of hardware implementation. Using three units of this transformer, a 3-phase transformer with rating of 3.3kV/220V, 6kVA can be built.

• Journal of the Korean Institute of Telematics and Electronics
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• v.26 no.6
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• pp.23-29
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• 1989

A physical model that characterizes the field effect of the polycrystalline thin film transistor(TFT) is developed. The model discribes grains as discrete single crystal transistors and grain boundaries as insulated layers having the potential barrier, Thus TFT is considered as serial connection of single crystal transistors and insulators. In the model, the currents in the grain and the grain boundary is calculated using gradual channel approximation and tunneling theory, respetively. By comparing computed I-V characteristics with measured I-V characteristics of CdSe TFT's, potential and electric field distributions in the channel are observed and the validity of the conduction model proposed in this paper is confirmed.

• Proceedings of the Korea Information Processing Society Conference
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• 2018.05a
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• pp.543-544
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• 2018

가상 현실 네비게이션을 위한 전방향 트레드밀은 사용자가 걷거나 달리면서 물리적으로 고정된 공간 내에 사용자를 유지할 수 있도록 지면 모션을 시뮬레이션하는 장비이다. 이러한 트레드밀 시스템의 성능이나 안정성을 정량적으로 측정하거나 분석하기가 어렵기 때문에 이전의 연구에서는 주관적 설문 조사와 같은 정성적 분석 방법을 사용하였다. 본 연구에서는 인간의 보행 경로와 유사한 궤도를 따라 움직이는 무인 차량 시스템을 이용한 새로운 정량적 데이터 측정 방법을 제안한다. 무인 차량 시스템은 미리 정의 된 인간의 보행 동작을 시뮬레이션하고 트레드밀 시스템에 대한 제어 입력을 제공하며, 다축 가속 및 방향과 같은 차량의 동적 데이터를 측정 할 수 있다. 또한 이 데이터는 평상시의 정기 또는 다른 제어 알고리즘과의 비교를 수행할 수 있다. 본 연구에서는 궤적 시뮬레이션 모듈, 데이터 수집 모듈, 성능 평가 모듈 등 전방향 트레드밀에 대한 정량 분석 방법의 설계 구조 및 초기구현 결과를 제시하고자 한다.

• The KIPS Transactions:PartC
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• v.15C no.2
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• pp.111-118
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• 2008

A wireless router is a device which allows several wireless clients to share an internet line using NAT (Network Address Translation). In a school or a small office environment where many clients use multiple wireless routers, a client may select any one of wireless routers so that most clients can be clustered to a small set of the wireless routers. In such a case, there exists load unbalancing problem between clients and wireless routers. One of its result is that clients using the busiest router get poor service. The other is that the resource utilization of the whole wireless routers becomes very low. In order to resolve the problems, we propose a load sharing scheme to maximize network bandwidth utilization based on SSID(Service Set IDentifier) hiding. The proposed scheme keeps checking the available bandwidth of all the possible wireless routers in a time interval and select the most available one. If a new client appears, the most available router is visible to him or her whereas the others are not visible. This is handled by SSID hiding in the proposed scheme. We implemented the proposed scheme with ASUS WL 500G wireless router and performed experiments. Experimental results show the bandwidth utilization improvement compared to the existing method.

• Journal of Sensor Science and Technology
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• v.4 no.4
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• pp.29-40
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• 1995

In this paper, the noise equivalent cicuits that is necessary to the formulation of D.C. and noise characteristics, residual component and input capacitance so as to analyze on the noise factors of the SIT is proposed. The simplest noise equivalent circuit is the model representing the mechanism of the SIT and the measured values in this model were found as small as the values of the shot-noise. In the source resistance inserted equivalent circuit is conformed that the shot-noise will be reduced by the negative-feedback effect of the source resistance. In oder to analyze the correct noise reduction factor, I proposed the equivalent circuit which the formulas of the source and drain resistance was induced. In the experiment which affirm the equivalent circuits, the influence of the signal source resistance and output load resistance on the residual component is small and the residual component can be expressed by the equivalent input noise resistance. Moreover, the input capacitance is 13.6 pF when the load resistance is $0{\Omega}$ and the capacitance which does not concern with the SIT operation directly, that is, gate wire etc, is 10pF or so.

• Journal of KIISE
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• v.44 no.9
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• pp.871-877
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• 2017

A vast amount of research has been carried out for executing compute-intensive applications on resource-constrained mobile devices. Computation offloading is a method in which heavy computations are dynamically migrated from a mobile device to a server, exploiting the powerful hardware of the server to perform complex computations. An important issue for offloading is the complexity of reconciling the execution state of applications between the server and the client. To address this issue, snapshot-based offloading has recently been proposed, which utilizes the snapshot of a web app as the portable description of the execution state. However, for web applications using the HTML5 canvas, snapshot-based offloading does not function correctly, because the snapshot cannot capture the state of the canvas. In this paper, we propose a code generation technique to save the canvas state as part of a snapshot, so that the snapshot-based offloading can be applied to web applications using the canvas.

• Journal of KIISE
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• v.44 no.5
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• pp.460-468
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• 2017

In a real-time cloud environment, the data analysis framework plays a pivotal role. Spark Streaming meets most real-time requirements among existing frameworks. However, the framework does not meet the second scale real-time fault recovery requirement. Spark Streaming fault recovery time increases in proportion to the transformation history length called lineage. This is because it recovers the last state data based on the cumulative lineage recorded during normal operation. Therefore, fault recovery time is not bounded within a limited time. In addition, it is impossible to achieve a second-scale fault recovery time because it costs tens of seconds to read initial state data from fault-tolerant storage. In this paper, we propose two techniques to solve the problems mentioned above. We apply the proposed techniques to Spark Streaming 1.6.2. Experimental results show that the fault recovery time is bounded and the average fault recovery time is reduced by up to 41.57%.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.6
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• pp.743-749
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• 2010

This paper proposes a derating design method for improving system reliability by using a probabilistic approach. In the proposed design, the focus is upon system levels in determining derated levels of stresses such as temperature and current, unlike recent design approaches that focus on component levels. System reliability is evaluated using component reliability metrics that are given as functions of time and unknown stresses; this evaluation is based on a series system-reliability model. The variation in stress, which was not considered in previous derating designs, is introduced in the present design to account for the uncertainty in both environmental and operating conditions at the customer' hands. Optimization problems for system reliability improvement are formulated and solved using FORM to determine the best derating design. An example of a derating design for an electrical system shows the details of the proposed method and its applicability to systems design for reliability improvement.