• Transactions on Electrical and Electronic Materials
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• v.17 no.4
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• pp.196-200
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• 2016

We have developed new electrostatic discharge (ESD) protection devices with, bidirectional flip chip transient voltage suppression. The devices differ in their epitaxial (epi) layers, which were grown by reduced pressure chemical vapor deposition (RPCVD). Their ESD properties were characterized using current-voltage (I-V), capacitance-voltage (C-V) measurement, and ESD analysis, including IEC61000-4-2, surge, and transmission line pulse (TLP) methods. Two BD-FCTVS diodes consisting of either a thick (12 μm) or thin (6 μm), n-Si epi layer showed the same reverse voltage of 8 V, very small reverse current level, and symmetric I-V and C-V curves. The damage found near the corner of the metal pads indicates that the size and shape of the radius governs their failure modes. The BD-FCTVS device made with a thin n- epi layer showed better performance than that made with a thick one in terms of enhancement of the features of ESD robustness, reliability, and protection capability. Therefore, this works confirms that the optimization of device parameters in conjunction with the doping concentration and thickness of epi layers be used to achieve high performance ESD properties.

• Journal of the Korean Geosynthetics Society
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• v.19 no.4
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• pp.1-9
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• 2020

This study analyzes contaminant movement under transient flow in a rubble mound revetment offshore waste landfill barrier system that prevents contaminant runoff. The barrier system consists of bottom layer and side barrier. For the bottom layer system, impermeable clay layer is used. For the side barrier system, the HDPE barrier sheet (primary element) plays the main role, and the intermediate protection layer (supplementary element) is responsible for the barrier. Seepage, advection, dispersion numerical analysis was carried out using SEEP / W and CTRAN / W programs. As a result, under abnormal conditions considering the fluctuation in tidal range, the volume and direction of the flow velocity vector of the pore water change with time and the dispersion concentration of the contaminant changes. When comparing the case of 2 m tidal range and 8 m tidal range, the larger the tide value, the higher the concentration of contaminant under abnormal conditions. It was found that the rate of change of the concentration of the contaminant changed depending on the change in the tidal range, and as a result, the outflow of the pollutant was smaller than that in the steady flow state.

• 한국정보통신설비학회:학술대회논문집
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• 2007.08a
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• pp.285-288
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• 2007

This article presents the change characteristics of induced noise whether the sheath layer of the cable is grounded or not. As what affects the induced noise, there are power influence or longitudinal transverse voltages and its weighted filtered voltage. The sheath ground is basicaly predicted to have the effects of alleviation on the power influence. But practically the effects may not happen in the case of common cable's sheath layer. Rather there are cases that the ground of sheath affects so that the noise level could increase. So we need to scrutinize the effects of the sheath gorund in the measures for the protection against electromagnetic induction by powerline or traction line system. And the evaluation of using the designated shielding purpose cable is needed.

• Journal of Advanced Marine Engineering and Technology
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• v.39 no.7
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• pp.779-785
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• 2015

Cathodic protection is recognized as the most cost-effective and technically appropriate corrosion prevention method for the submerged zone of offshore structures, ships, and deep-sea facilities. When cathodic protection is applied, the cathodic currents cause dissolved oxygen reduction, generating hydroxyl ions near the polarized surface that increase the interfacial pH and result in enhanced carbonate ion concentration and precipitation of an inorganic layer whose principal component is calcium carbonate. Depending on the potential, magnesium hydroxide can also precipitate. This mixed deposit is generally called "calcareous deposit." This layer functions as a barrier against the corrosive environment, leading to a decrease in current demand. Hence, the importance of calcareous deposits for the effective, efficient operation of marine cathodic protection systems is recognized by engineers and scientists concerned with cathodic protection in submerged marine environments. Calcareous deposit formation on a marine structure depends on the potential, current, pH, temperature, pressure, sea-water chemistry, flow, and time; deposit quality is significantly influenced by these factors. This study determines how calcareous deposits form in sea water, and assesses the interrelationship of formation conditions (such as the sea water temperature and surface condition of steel), deposited structure, and properties and the effectiveness of the cathodic protection.

• Journal of the Korea Society of Computer and Information
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• v.26 no.11
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• pp.1-9
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• 2021

3D-NAND flash memory provides high capacity per unit area by stacking 2D-NAND cells having a planar structure. However, due to the nature of the lamination process, there is a problem that the frequency of error occurrence may vary depending on each layer or physical cell location. This phenomenon becomes more pronounced as the number of write/erase(P/E) operations of the flash memory increases. Most flash-based storage devices such as SSDs use ECC for error correction. Since this method provides a fixed strength of data protection for all flash memory pages, it has limitations in 3D NAND flash memory, where the error rate varies depending on the physical location. Therefore, in this paper, pages and layers with different error rates are classified into clusters through the K-means machine learning algorithm, and differentiated data protection strength is applied to each cluster. We classify pages and layers based on the number of errors measured after endurance test, where the error rate varies significantly for each page and layer, and add parity data to stripes for areas vulnerable to errors to provides differentiate data protection strength. We show the possibility that this differentiated data protection policy can contribute to the improvement of reliability and lifespan of 3D NAND flash memory compared to the protection techniques using RAID-like or ECC alone.

• Journal of Communications and Networks
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• v.11 no.6
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• pp.634-644
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• 2009

A diversity of wireless networks, with rapidly evolving wireless technology, are currently in service. Due to their innate physical layer vulnerability, wireless networks require enhanced security components. WLAN, WiBro, and UMTS have defined proper security components that meet standard security requirements. Extensive research has been conducted to enhance the security of individual wireless platforms, and we now have meaningful results at hand. However, with the advent of ubiquitous service, new horizontal platform service models with vertical crosslayer security are expected to be proposed. Research on synchronized security service and interoperability in a heterogeneous environment must be conducted. In heterogeneous environments, to design the balanced security components, quantitative evaluation model of security policy in wireless networks is required. To design appropriate evaluation method of security policies in heterogeneous wireless networks, we formalize the security properties in wireless networks. As the benefit of security protocols is indicated by the quality of protection (QoP), we improve the QoP model and evaluate hybrid security policy in heterogeneous wireless networks by applying to the QoP model. Deriving relative indicators from the positive impact of security points, and using these indicators to quantify a total reward function, this paper will help to assure the appropriate benchmark for combined security components in wireless networks.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.24 no.1
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• pp.73-81
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• 2013

In this paper, we have proposed the interference analysis method which uses both an interference probability model at the PHY layer of RFID system and the DTMC model at the MAC layer of USN system. Using the proposed method, we have performed sharing analysis between passive RFID and USN systems at the Korean RFID/USN frequency bands. If 1% performance degradation of USN system is allowed, RFID and USN systems can share the frequency bands where channel number is greater or equal to 20 on condition that radius of protection area is greater than 300 m.

• Tribology and Lubricants
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• v.25 no.4
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• pp.225-230
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• 2009

Seals are very useful machine components in protection of leakage of lubricant or working fluid, and incoming of debris from outside. Various elastomer are widely used as sealing materials and the shaft surfaces are generally coated with high hardness material after heat treatment. It is generally known that the foreign debris and wear particles get stuck into sealing surface, the steel shaft surface can be damaged and worn by mainly abrasive wear. In this paper, using MARC, contact analysis are conducted to show the hard coated steel shaft surface can be fatigue failed by very small elastic particle intervened between seal and steel surface. Variations of contact and von-Mises stress distributions and contact half-widths with interference and coating thickness are presented. The maximum von-Mises stress occurs always in the coating layer or between coated layer/substrate interface. Therefore the coated sealing surface can be fatigued and then failed by very small particles. The results can be used in design of sealing surface and further studies are required.

• Journal of the Society of Naval Architects of Korea
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• v.49 no.6
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• pp.447-460
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• 2012

In this study, the shutdown system of the fuel gas supply system is designed based on the Safety Integrity Level of IEC 61508 and IEC 61511. First of all, the individual risk($10^{-4}$/year) and the risk matrix which are the risk acceptance criteria are set up for the qualitative risk assessment such as the HAZOP study. The natural gas leakage at the gas supply pipe is identified as the highest risk among the hazards identified through the HAZOP study and as a safety instrumented function the shutdown function for leakage was defined. SIL 2 and PFD($2.5{\cdot}10^{-3}$) for the shutdown function are determined by the layer of protection analysis(LOPA). The shutdown system(SIS) carrying out the shutdown function(SIF) is verified and designed according to qualitative and quantitative requirements of IEC 61508 and IEC 61511. As a result of SIL verification and SIS conceptual design, the shutdown system is composed of two gas detectors voted 1oo2, one programmable logic solver, and two shutdown valve voted 1oo2.

• Corrosion Science and Technology
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• v.20 no.4
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• pp.175-182
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• 2021

Magnesium alloy is limited in the industrial field because its standard electrode potential is -2.363 V vs. NHE (Normal Hydrogen Electrode) at 25 ℃. This high electrochemical activity causes magnesium to quickly corrode with oxygen in air; chemical conversion coating prevents corrosion but causes surface defects like cracks and pores. We have examined the anti-corrosion effect of sol-gel coating sealed on the defected conversion coating layer. Sol-gel coatings produced higher voltage current and smaller pore than the chemical conversion coating layer. The conversion coating on magnesium alloy AZ31 was prepared using phosphate-permanganate solution. The sol-gel coating was designed using trimethoxymethylsilane (MTMS) and (3-Glycidyloxypropyl) trimethoxysilane (GPTMS) as precursors, and aluminum acetylacetonate as a ring-opening agent. The thermal shock resistance was tested by exposing specimens at 140 ℃ in a convection oven; the results showed changes in the magnesium alloy AZ31 surface, such as oxidization and cracking. Scanning electron microscope (FE-SEM) analysis confirmed a sealed sol-gel coating layer on magnesium alloy AZ31. Electrochemical impedance spectroscopy (EIS) measured the differences in corrosion protection properties by sol-gel and conversion coatings in 0.35 wt% NaCl solution, and the potentiodynamic polarization test and confirmed conversion coating with the sol-gel coating show significantly improved resistance by crack sealing.