• The KIPS Transactions:PartC
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• v.17C no.1
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• pp.1-14
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• 2010

IEEE 802.15.4[1] has been standardized for the physical layer and MAC layer of LR-PANs(Low Rate-Wireless Personal Area Networks) as a technology for operations with low power on sensor networks. The standardization is applied to the variety of applications in the shortrange wireless communication with limited output and performance, for example wireless sensor or virtual wire, but it includes vulnerabilities for various attacks because of the lack of security researches. In this paper, we analyze the vulnerabilities against the denial of sleep attacks on the MAC layer of IEEE 802.15.4, and propose a detection mechanism against it. In results, we analyzed the possibilities of denial of sleep attacks by the modification of superframe, the modification of CW(Contention Window), the process of channel scan or PAN association, and so on. Moreover, we comprehended that some of these attacks can mount even though the standardized security services such as encryption or authentication are performed. In addition to, we model for denial of sleep attacks by Beacon/Association Request messages, and propose a detection mechanism against them. This detection mechanism utilizes the management table consisting of the interval and node ID of request messages, and signal strength. In simulation results, we can show the effect of attacks, the detection possibility and performance superiorities of proposed mechanism.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.3
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• pp.17-23
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• 2020

This paper proposes a simulation model using an equivalent circuit for the development of an MMC system. The MMC has been chosen as the most suitable topology for high voltage power transmission, such as a voltage-type HVDC, and it has dozens to hundreds of sub-modules in the form of a half-bridge or full-bridge connected in series. A simulation study is essential for the development of an MMC algorithm. On the other hand, it is virtually impossible to construct and implement MMC simulation models, including hundreds or thousands of switching devices. Therefore, this paper presents an MMC equivalent model, which is easily expandable and implemented by modeling the dynamic characteristics. The voltage and current equation of the equivalent circuit was calculated using the direction of the arm current and switching signal. The model was implemented on Matlab/Simulink. In this paper, to show the validity of the model developed using Matlab/Simulink, the simulation results of a five-level MMC using the real switching element and the proposed equivalent model are shown. The validity of the proposed model was verified by showing that the current and voltage waveform in the two models match each other.

• Journal of the Korea institute for structural maintenance and inspection
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• v.20 no.3
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• pp.130-139
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• 2016

A frequency of earthquake occurrence in the Republic of Korea is increasing over the past few decades. In this situation, an importance of earthquake prevention comes to the fore because the earthquake does damage to structures and causes severe damage of human life. For the earthquake prevention, a real-time vibration measurement for structures is important. As an example, the United States of America and Japan have already been monitoring real-time earthquake acceleration for the important structures and the measured acceleration data has been managed by forming database. This database could be used for revising the seismic design specifications or predicting the damage caused by earthquake. In Korea, Earthquake Recovery Plans Act and Enforcement Regulations are revised and declared lately. Ministry of Public Safety and Security is constructing a integrated management system for the measured earthquake acceleration data. The purpose of this research is to develop a real-time vibration monitoring and analysis system for structures which links to the integrated management system. The developed system contains not only a monitoring function to show real-time acceleration data but also an analysis system to perform fast fourier transform, to obtain natural frequency and earthquake magnitude, to show response spectrum and power spectrum, and to evaluate structural health. Additionally, this system is designed to be able to link to the integrated management system of Ministry of Public Safety and Security. It is concluded that the developed system can be useful to build a safety management network, minimize maintenance cost of structures, and prevention of the structural damage due to earthquake.

• Journal of Dairy Science and Biotechnology
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• v.28 no.2
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• pp.13-18
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• 2010

Electron Spin Resonance (ESR) spectroscopy has been used to detect the presence of radiation-induced free radicals in biological samples since the mid 1950s and to irradiate foods containing cellulose, crystalline sugar, and bone. Therefore, we analyzed the ESR spectrum of irradiated infant formula and its ingredients in this study. Samples were irradiated with 2 different radiation sources of $^{60}Co$ gamma rays and electron beams (EBs), and the absorbed doses were 0, 1, 3, 5, and 7 kGy. ESR measurements were performed under normal atmospheric conditions using a JEOL JES-FA100 spectrometer equipped with an X-band bridge. Irradiated infant formula showed anunsymmetrical spectrum ($g_1$=2.0050, $g_2$=2.0006); in contrast, non-irradiated samples showed asymmetrical spectrum. The ingredients of irradiated samples showed a multi-component ESR signal in glucose and lactose and a singlet-type spectrum in milk powder (g=2.0050). $R^2$ of the dose-response curve showed a fine linearity of over 0.95 across the entire sample. We also compared the spectra of identical samples irradiated with $^{60}Co$ gamma rays and EBs, because EBs can be used for food irradiation in foreign countries, although this is not permitted in Korea. However, we could not find any significant differences according to the types of radiation source. Thus, ESR spectroscopy can be used to detect irradiated infant formula and several types of primary ingredients in this formula.

• Journal of the Korean Society for Nondestructive Testing
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• v.26 no.2
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• pp.90-98
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• 2006

Signals captured from a Combo calibration standard tube paly a crucial role in the evaluation of motorized rotating pancake coil (MRPC) probe signals from steam generator (SG) tubes in nuclear power plants (NPPs). Therefore, the Combo tube signals should be consistent and accurate. However, MRPC probe signals are very easily affected by various factors around the tubes so that they can be distorted in their amplitudes and phase angles which are the values specifically used in the evaluation. To overcome this problem, in this study, we explored possibility of simulation to be used as a practical calibration tool far the evaluation of real field signals. For this purpose, we investigated the characteristics of a MRPC probe and a Combo tube. And then using commercial software (VIC-3D) we simulated a set of calibration signals and compared to the experimental signals. From this comparison, we verified the accuracy of the simulated signals. Finally, we evaluated two defects using the simulated Combo tube signals, and the results were compared with those obtained using the actual field calibration signals.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.8
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• pp.5513-5521
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• 2015

There is an operational efficiency problem about wayside equipment applied to the domestic low-density branch as the equipment has been installed and operated similarly in the mainline. On-board oriented train control system, which has been developed for train safety and operation efficiency, ensures safe train operation without expensive ground control signal devices. Such system consists of on-board control system, wayside control system, and local control system. In this paper, the details of tests such as suitability test, communication test, and interface test are described by installing the on-board control system and wayside control system in field. Installation tests include checking power, voltage, cable connection, LED status, etc. Field applicability of the developed system is also verified through the dynamic operation tests with diverse scenarios, which are performed on the virtual line similar to the real environment including switch machine and level crossing gate. Dynamic operation tests were conducted for total 7 scenarios, and several tests were repeated for each scenario. The elapsed time for each operation was computed by analyzing main process log, and we could check that each operation was accomplished within several seconds. Furthermore, the developed system was verified through field test with an accredited institute, and testing certificates were issued.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.16 no.9
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• pp.1847-1855
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• 2012

A 1V 1.6-GS/s 6-bit flash analog-to-digital converter (ADC) with a clock calibration circuit is proposed. A single track/hold circuit with a bootstrapped analog switch is used as an input stage with a supply voltage of 1V for the high speed operation. Two preamplifier-arrays and each comparator composed of two-stage are implemented for the reduction of analog noises and high speed operation. The clock calibration circuit in the proposed flash ADC improves the dynamic performance of the entire flash ADC by optimizing the duty cycle and phase of the clock. It adjusts the reset and evaluation time of the clock for the comparator by controlling the duty cycle of the clock. The proposed 1.6-GS/s 6-bit flash ADC is fabricated in a 1V 90nm 1-poly 9-metal CMOS process. The measured SNDR is 32.8 dB for a 800 MHz analog input signal. The measured DNL and INL are +0.38/-0.37 LSB, +0.64/-0.64 LSB, respectively. The power consumption and chip area are $800{\times}500{\mu}m2$ and 193.02mW.

• Journal of Internet Computing and Services
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• v.19 no.3
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• pp.49-56
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• 2018

Euclidean distance (ED) between error distribution and Dirac delta function has been used as an efficient performance criterion in impulsive noise environmentsdue to the outlier-cutting effect of Gaussian kernel for error signal. The gradient of ED for its minimization has two components; $A_k$ for kernel function of error pairs and the other $B_k$ for kernel function of errors. In this paper, it is analyzed that the first component is to govern gathering close together error samples, and the other one $B_k$ is to conduct error-sample concentration on zero. Based upon this analysis, it is proposed to normalize $A_k$ and $B_k$ with power of inputs which are modified by kernelled error pairs or errors for the purpose of reinforcing their roles of narrowing error-gap and drawing error samples to zero. Through comparison of fluctuation of steady state MSE and value of minimum MSE in the results of simulation of multipath equalization under impulsive noise, their roles and efficiency of the proposed normalization method are verified.

• Korean Journal of Optics and Photonics
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• v.28 no.4
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• pp.166-171
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• 2017

Hydrogen gas is a green energy sources because it features no emission of pollutants during combustion. But hydrogen gas is very dangerous, being flammable and very explosive. Hydrogen gas detection is very important for the safety of a nuclear power plant. Hydrogen gas is generated by oxidation of nuclear fuel cladding during a critical accident, and leads to serious secondary damage in the containment building. This paper discusses the development of a Raman lidar system for remote detection and measurement of hydrogen gas. A small, portable Raman lidar system was designed, and a measurement algorithm was developed to quantitatively measure hydrogen gas concentration. To verify the capability of measuring hydrogen gas with the developed Raman lidar system, experiments were carried out under daytime outdoor conditions by using a gas chamber that can adjust the hydrogen gas density. As results, our Raman lidar system is able to measure a minimum density of 0.67 vol. % hydrogen gas at a distance of 20 m.

• Korean Journal of Optics and Photonics
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• v.29 no.3
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• pp.119-125
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• 2018

Hydrogen gas is an important and promising energy resource that has no emissions of pollutants during power generation. However, hydrogen gas is very dangerous because it is colorless, odorless, highly flammable, and explosive at low concentration. Conventional techniques for hydrogen gas detection are very difficult for measuring the hydrogen gas distribution at long distances, because they sample the gas to measure its concentration. Raman lidar is one of the techniques for remotely detecting hydrogen gas and measuring the range of the hydrogen gas distribution. A Raman lidar system with an on-axis optical receiver was developed to improve the range of hydrogen gas detection at long distance. To verify the accuracy and improvement in the range of detecting the hydrogen gas, experiments measuring the hydrogen gas concentration are carried out using the developed on-axis Raman lidar system and a gas chamber, to prevent explosion of the hydrogen gas. As a result, our developed on-axis Raman lidar system can measure a minimum hydrogen gas concentration of 0.66 volume percent at a distance of 50 m.