• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.30 no.6
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• pp.46-52
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• 2002

Characteristics of flow rate control has been studied for a cavitating venturi adopted in a liquid rocket propellant feed system. Both experiment and numerical simulation have been performed to give about 10% discrepancy of mass flow rate for cavitating flow regime. Mass flow rate is confirmed to be saturated for pressure difference higher than $3{\times}10^5$pa when the upstream pressure is fixed to $22.8{\times}10^5$pa and the downstream pressure is varied. The evaporation amount depends substantially to non-condensable gas concentration. However the mass flow rate characteristics is relatively insensitive to the mass fraction of non-condensable gas. So it reduces by only 2% when the non-condensable gas concentration is increased from 1.5PPM to 150PPM. From the previous comparison the expansion of the non-condensable gas and the evaporation of liquid are verified to gave same effect to the pressure recovery pattern.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.3A
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• pp.240-247
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• 2004

In order to transmit data at high speed in the wireless environment, OFDM is selected as the transmission method of various high-speed wireless communication system since it has the advantage to deal easily the serious selective frequency fading channel by the multiple path. We evaluate STBC-OFDM and linear STBC-OFDM combining with a class of recently proposed linear scalable space-time block codes and OFDM in MIMO channel environments, and demonstrate the performance for spatial multiplexing and diversity gain. The codes are able to use jointly transmit diversity in combination with spatial multiplexing, and achieve spatial and temporal diversity. Frequency diversity of frequency selective channels can be utilized by combining the linear STBC and OFDM. Simulation results are shown to demonstrate the better performance of proposed approach in comparison with STBC-OFDM.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.2A
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• pp.160-171
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• 2011

The one of the core technologies for ubiquitous computing is WSN. WSN detects the information from the environment around them based on the information perceived from the human and all things and manages the information by connecting to the network in realtime. In this environment, the existing research provides the mechanism that most of sensor nodes in the target area can set the transmission path using RGF. However, unrelated to the target area will be responsible for the energy consumption of nodes that are the problem. In this paper, we propose EEDCP protocol. It is designed to collect data from the specific region on sinks in WSN. EEDCP is the protocol that sets the transmission path for collection data inside the target area in WSN. And this paper is shown that the proposed scheme is more efficient in the energy efficiency and the occurrence rate of isolated nodes by comparison with the previous studies through simulation.

• Geomechanics and Engineering
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• v.10 no.3
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• pp.357-386
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• 2016

In this research work, an exact analytical solution for thermal stability of solar functionally graded rectangular plates subjected to uniform, linear and non-linear temperature rises across the thickness direction is developed. It is assumed that the plate rests on two-parameter elastic foundation and its material properties vary through the thickness of the plate as a power function. The neutral surface position for such plate is determined, and the efficient hyperbolic plate theory based on exact neutral surface position is employed to derive the governing stability equations. The displacement field is chosen based on assumptions that the in-plane and transverse displacements consist of bending and shear components, and the shear components of in-plane displacements give rise to the quadratic distribution of transverse shear stress through the thickness in such a way that shear stresses vanish on the plate surfaces. Therefore, there is no need to use shear correction factor. Just four unknown displacement functions are used in the present theory against five unknown displacement functions used in the corresponding ones. The non-linear strain-displacement relations are also taken into consideration. The influences of many plate parameters on buckling temperature difference will be investigated. Numerical results are presented for the present theory, demonstrating its importance and accuracy in comparison to other theories.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.28 no.6
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• pp.444-451
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• 2017

In this paper, we have evaluated and analyzed OTFS(Orthogonal Time Frequency Space) modulation and OTFS-MIMO(Multiple Input Multiple Output) system. OTFS modulation can concisely compensate delay-Doppler spreading effect by using 2D(2-Dimension) iDFT (inverse Discrete Fourier Transform) and DFT(Discrete Fourier Transform) operation. It enables OTFS system to transmit high-speed data. Especially, OTFS-MIMO system can transmit all data streams without performance degradation on high Doppler frequency channel. As simulation results, we have confirmed that $1{\times}1$ OTFS system's achievable rate is a similar to each stream of $2{\times}2$ OTFS-MIMO system. That is, we have also confirmed that $2{\times}2$ MIMO system can completely achieve double achievable rate in comparison with OTFS system on high Doppler frequency channel.

• Journal of the Korea Society of Computer and Information
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• v.12 no.5
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• pp.49-56
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• 2007

This paper deals with grid job allocation and grid resource scheduling to provide a stable and quicker job processing service to grid users. In this paper, we proposed a fuzzy logic-based grid job scheduling model for an effective job scheduling in computational grid environment. The fuzzy logic-based grid job scheduling model measures resource efficiency of all grid resources by a fuzzy logic system based on diverse input parameters like CPU speed and network latency and divides resources into several groups by resource efficiency. And, the model allocates jobs to resources of a group with the highest resource efficiency. For performance evaluation, we implemented the fuzzy logic-based grid job scheduling model on the DEVS modeling and simulation environment and measured reduction rates of turnaround time, job loss, and communication messages in comparison with existing job scheduling models such as the random scheduling model and the MCT(Minimum Completion time) model. Experiment results that the proposed model is useful to improve the QoS of the grid job processing service.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.11 no.1
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• pp.23-28
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• 2011

In this paper, we propose a channel selection scheme for secondary users in cognitive radio sensor networks, which includes learning automata and fuzzy logic system (FLS). In the proposed scheme, FLS is used as the channel selection mechanism while the learning automata algorithm is being used to learn the radio environment such as channel link quality. Signal to noise ratio of the link between primary user (PU) and secondary user (SU), the probability of choosing channel, and signal to noise ratio of the link between secondary users are chosen as input parameters for the FLS to decide one data channel among multiple channels. Simulation results show that the proposed scheme does indeed provide advantages in improving the throughput of CR networks, in comparison with some other previous schemes.

• Journal of the Korean Magnetics Society
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• v.9 no.1
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• pp.55-63
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• 1999

It is necessary to eliminate the broad band noise whose frequency is in the range of several kHz to tens MHz generated from the AC power line to supply the power to electrical and electronic equipments. Because this kind of noise could damage or malfunction such equipments. To suppress those noises, some conventional devices such as a filter or surge suppressor have been used. However, they can not be isolated from the common-mode noise widely spreaded in all power line, which results in poor common-mode rejection performance. In this paper, we proposed a design method of shielded isolation transformer and a jumped circuit analysis model for shielded isolation transformer applicable to filtering common-mode noise as well as normal-mode noise. The analysis model has been verified as a suitable one for shielded isolation transformer through comparison of the simulation with experiment. In addition, it has been shown that the reduction performance for conducted noise of prototype 3 kVA shielded isolation transformer is superior to a unshielded isolation transformer.

• Journal of the Korean Data and Information Science Society
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• v.25 no.5
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• pp.971-986
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• 2014

When thousands of hypotheses are tested simultaneously, the probability of rejecting any true hypotheses increases, and large multiplicity problems are generated. To solve these problems, researchers have proposed different approaches to multiple testing methods, considering family-wise error rate (FWER), false discovery rate (FDR) or false nondiscovery rate (FNR) as a type I error and some test statistics. In this article, we discuss Bonferroni (1960), Holm (1979), Benjamini and Hochberg (1995) and Benjamini and Yekutieli (2001) procedures based on T statistics, modified T statistics or local-pooled-error (LPE) statistics. We also consider Sun and Cai (2007) procedure based on Z statistics. These procedures are compared in the simulation and applied to Arabidopsis microarray gene expression data to identify differentially expressed genes.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.22 no.10
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• pp.41-48
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• 2008

This paper proposes a three-phase Z-source dynamic voltage restorer (Z-DVR) to mitigate the voltage sag for the critical loads. The proposed system is composed of passive filter and Z-source topology inverter. As an ESS(Energy Storage System) of the proposed system is employed the Proton Exchange Membrane Fuel Cells (PEMFC). To calculate and control the harmonics and compensation voltage, $i_{d}-i_{q}$ theory in dq rotating reference frame and PI controller are used. In case that three-phase voltage sags occurred, a PSIM simulation was done for the performance comparison of the conventional method employed battery stacks and proposed method. As a result, considering the voltage compensation performance, each method was nearly similar. Also, the compensation performance and the %THD(%Total Harmonic Distortion) result under the various source voltage conditions (sag or swell) were presented and discussed to show the performance of the proposed system.