• Journal of Institute of Control, Robotics and Systems
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• v.14 no.1
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• pp.88-94
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• 2008

In this paper, a design method of a missile guidance command is presented considering the dynamics of missile control systems. The design of a new guidance command is based on the well-known PNG(propotional navigation guidance) laws. The missile control system dynamics cause the time-delays of the PN guidance command and degrade the performance of original guidance laws which are designed under the assumption of the ideal missile control systems. Using a backstepping method, these time-delay effects can be compensated. In order to implement the guidance command developed by the backstepping procedure, it is required to measure or calculate the successive time-derivatives of the original guidance command, PNG and other kinematic variables such as the relative distance. Instead of directly using the measurements of these variables and their successive derivatives, a simple disturbance observer technique is employed to estimate a guidance command described by them. Using Lyapunov method, the performance of a newly developed guidance command is analyzed against a target maneuvering with a bounded and time-varying acceleration.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.1A
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• pp.1-11
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• 2009

In OFDMA or SC-FDMA systems one can generate time varying channels or frequency selective channels using multiple transmit antennas to achieve diversity without special space-time processing at the receivers. While low channel coding rate needs to be used for distributed-allocation SC-FDMA systems with a phase rolling technique to produce time fluctuation, relatively high channel coding rate can be used when cyclic delay diversity is used to increase frequency selectivity assuming quasi-static channel. On the other hand, for block-hopping SC-FDMA systems there is no significant difference between two diversity techniques in terms of optimal channel coding rates.

• Laser Solutions
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• v.14 no.4
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• pp.21-27
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• 2011

In this work, we have studied on time-resolved transient reflective image of single crystalline Si surface after single-shot fs-laser irradiation with varying the laser fluence under two different laser spot sizes. The temporal profiles of transient reflectivity changes as well as its maximum values at the early delay time were found to be strongly dependent on both the laser beam spot size and laser fluence. We have interpreted the dependence of transient reflectivity changes on the laser spot size in terms of a relaxation of the generated free carriers to the bulk silicon, which should be interacted with the plasma.

• Journal of Korea Multimedia Society
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• v.8 no.10
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• pp.1403-1410
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• 2005

The synchronization problem is directly related to the quality of service in multimedia communication and especially in real-time communication. In this study, we found the cause of clock fluctuation between encoder and decoder in MPEG-2 system layer was that the standard decoder design only considered a fixed time delay component. To solve it, we proposed Extended-SRTS algorithm, which uses STC as service clock by synchronizing transport stream. As the result, we can improve the effect of frequency-drift, time-varying-network-jitter and packing-jitter and so on And by virtue of this algorithm, we can make low the dependency of network clock, which makes easy to synchronize and connect transparently at the ends point, we expect the proposed algorithm can be widely applied to the field of real -time multimedia communications.

• Journal of Mechanical Science and Technology
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• v.16 no.8
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• pp.1127-1134
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• 2002

The effects of pressure and temperature on the autoignition of propane and n-butane blends were investigated using a rapid compression machine (RCM) , which is widely used to examine the autoignition characteristics. The RCM was designed to be capable of varying the compression ratio between 5 and 20 and minimize the vortex formation on the cylinder wall using a wedge-shaped crevice. The initial temperature and pressure of the compressed gas were varied in range of 720∼900 K and 1.6∼ 1.8 MPa, respectively, by adjusting the ratio of the specific heat of the mixture by altering the ratio of the non-reactive components (N$_2$, Ar) under a constant effective equivalence ratio (ø$\_$f/= 1.0) The gas temperature after the compression stroke could be obtained from the measured time-pressure record. The results showed a two-stage ignition delay and a Negative Temperature Coefficient (NTC) behavior which were the unique characteristic of the alkane series fuels. As the propane concentration in the blend were increased from 20% and 40% propane, the autoignition delay time increased by approximately 41 % and 55% at 750 K. Numerical reduced kinetic modeling was performed using the Shell model, which introduced some important chemical ideas, represented by the generic species. Several rate coefficients were calibrated based on the experimental results to establish an autoignition model of the propane and n-butane blends. These coefficients can be used to predict the autoignition characteristics in LPG fueled Sl engines.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.6B
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• pp.508-516
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• 2006

The explosive growth of wireless network users and the existence of various wireless services have demanded high rate throughput as well as user's QoS guarantees. Towards this, this paper proposes QoS-oriented subcarrier allocation scheme considering the QoS provisioning of multiple users, which is major requirement for wireless network design point of view. This paper introduces joint RR/K&H combined with M-LWDF(Modified Largest Weighted Delay First) scheme throughout observing statistical channel behavior and real time queuing analysis for appropriate resource allocation tightly connected to multiuser scheduling. Accordingly, the system throughput can be enhanced, and the QoS demanded for delay sensitive services can be satisfied. Furthermore, the proposed scheme is applied for OFDMA(Orthogonal Frequency Division Multiple Access) systems to allocate sub-carriers in optimal way. The simulation results verify plausible performances of proposed resource allocation scheme via showing superior effective capacity under time-varying physical-layer channel behaviors.

• Magazine of the Korean Society of Agricultural Engineers
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• v.28 no.3
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• pp.79-88
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• 1986

Drought occurs most frequently and severely around transplanting season of the rice plants in Korea. Shortage of water due to drought for the paddy fields often delays transplanting, and less often the rice plants are subjected to water stress after delayed transplanting. The present study aimed at quantification of the rice crop loss due to delayed transplanting, different inten3ity of water stress, and the combined effect of delay in transplanting followed by water stress for better use of limited water for irrigation under drought. The rice variety Chucheong, a japonica, and Nampung, an indica x japonica, were grown, transplanted to 1/200 a plastic pots, and subjected to different timing of transplanting and degree of water stress under a rainfall autosersing, sliding clear plastic roof facility with completely randomized arrangement of 5 replications. The results obtained are summarized as follows: 1.Twelve days or 22 days delay in transplanting without water stress reduced rice yield by 25% and 43% in the japonica variety, and by 15% and 60% in the indica x japonica variety. 2.The 10 days or 20 days water stress developed without irrigation after drainage in the rice plants transplanted at proper time lowered the water potential at the paddy soil 10cm deep to -4 bar, and -12 bar and caused rice yield reduction by 14%, and 45% in the japonica variety and by 8%, and 50% in the indica X japonica variety. 3.The 12 days delay in transplanting and 10 days or 20 days water stress reduced rice yield by 39% and 59% in the japonica variety, and by 38% and 52% in the indica x japonica variety. The 22 days delay in transplanting plus 10 days water stress caused yield reduction by 76%, i.e. meaningless yield, in both varieties. 4.The intermittent irrigation just to wet the soil body for 10 days after 10 days water stress without irrigation increased rece yield by 12 to 16% compared to the rice plants water stessed without irrigation continuously for 20 days in both varieties respectively. 5.The above results suggest strongly 1) to transplant the rice plants at proper .time even with some water stress rather than delay for sufficient water from later rainfall, and 2) to distribute insufficient irrigation water to broader area of transplanted rice with limited irrigation for better use of limited irrigation water. A greater sensitivity of japonica variety to a moderate water stress than the indica X japonica variety during initial rooting and tillering stage was noticed. To cope with frequent drought in rice culture, firstly the lasting time of transplanting without yield reduction should be clarified by region and variety, and secondly a scheme of rational distribution of limited water should be developed by region with better knowledge on the varietal distribution of limited water should be developed by region with better knowledge on the varietal responses to varying intensity of water stress.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.17 no.4
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• pp.149-154
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• 2017

Performance of the mobile devices, such as Smartphones, is sensible by the early-stage of the execution of the applications. To addressing this issue, the dynamic frequency scaling by the ondemand governor has an inherent weakness by the sampling period that may induces some delay in the execution time of the applications. In this paper, we propose an adaptive sampling method that varying the sampling period of the ondemand governor in accordance with the execution of the applications. By the experiment result, the proposed method outperforms 3.34% in early-stage of the execution time that impacts the sensible performance, and exhibits negligible differences in terms of the energy consumption.

• 한국정보컨버전스학회:학술대회논문집
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• 2008.06a
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• pp.199-204
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• 2008

Sensor nodes have various energy and computational constraints because of their inexpensive nature and ad-hoc method of deployment. Considerable research has been focused at overcoming these deficiencies through faster media accessing, more energy efficient routing, localization algorithms and system design. Our research attempts to provide a method of improvement MAC performance in these issues. We show that traditional carrier-sense multiple access(CSMA) protocols like IEEE 802.11 do not handle the first constraint adequately, and do not take advantage of the second property, leading to degraded latency and throughput as the network scales in size, We present more efficient method of a medium access for real-time wireless sensor networks. Proposed MAC protocol is a randomized CSMA protocol, but unlike previous legacy protocols, does not use a time-varying contention window from which a node randomly picks a transmission slot. To reduce the latency for the delivery of event reports, it carefully decides a fixed-size contention window, non-uniform probability distribution of transmitting in each slot within the window. We show that it can offer up to several times latency reduction compared to legacy of IEEE 802.11 as the size of the sensor network scales up to 256 nodes using widely used simulator ns-2. We, finally show that proposed MAC scheme comes close to meeting bounds on the best latency achievable by a decentralized CSMA-based MAC protocol for real-time wireless sensor networks which is sensitive to latency.

• International Journal of Computer Science & Network Security
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• v.24 no.2
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• pp.169-177
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• 2024

Interacting Spherical tank has maximum storage capacity is broadly utilized in industries because of its high storage capacity. This two tank level system has the nonlinear characteristics due to its varying surface area of cross section of tank. The challenging tasks in industries is to manage the flow rate of liquid. This proposed work plays a major role in controlling the liquid level in avoidance of time delay and error. Several researchers studied and investigated about reducing the nonlinearity problem and their approaches do not provide better result. Different types of controllers with various techniques are implemented by the proposed system. Intelligent Adaptive Neuro Fuzzy Inference System (ANFIS) based Sliding Mode Controller (SMC) with Fractional order PID controller is a novel technique which is developed for a liquid level control in a interacting spherical tank system to avoid the external disturbances perform better result in terms of rise time, settling time and overshoot reduction. The performance of the proposed system is obtained by analyzing the simulation result obtained from the controller. The simulation results are obtained with the help of FOMCON toolbox with MATLAB 2018. Finally, the performance of the conventional controller (FOPID, PID-SMC) and proposed ANFIS based SMC-FOPID controllers are compared and analyzed the performance indices.