• Journal of Korea Society of Digital Industry and Information Management
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• v.15 no.1
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• pp.53-59
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• 2019

As the number of harmful sites increases, many social problems are occurring. Therefore, in order to solve this problem, the government is carrying out activities to block access to web sites to harmful sites based on the law. However, due to the change from HTTP to HTTPS protocol, it has become difficult to block the harmful sites in the existing method. In the existing HTTP protocol, a method of blocking the site corresponding to the harmful site domain list by utilizing the DNS information was used. However, due to the generalization of HTTPS, it is difficult to block the harmful sites in the existing method. Therefore, the ISP uses the method of blocking the website using the SNI field in the TLS (Transport Layer Security) Handshake protocol used for HTTPS. However, since the method using SNI field raises the concern of monitoring Internet users or exposing information about connected sites, in this paper, we proposed method which can support anonymity to Internet users while blocking harmful sites. The suggested method also can support integrity and source authentication to the transmitted data.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2019.05a
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• pp.448-450
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• 2019

Multipath TCP (MPTCP) is a standardized transport layer protocol for maximizing the use of finite network resources by using multiple interfaces simultaneously. If the characteristics of each path are the same, there is an advantage in terms of stability and bandwidth utilization compared to the existing single TCP. However, if the path characteristics are different, the performance is lower than that of a single TCP. There are many complex reasons for this, but one of the biggest impacts is the bufferbloat, which dramatically increases the latency. In this paper, we implemented an algorithm that improved MPTCP performance degradation due to bufferbloat in Linux - based testbed and compared performance with existing MPTCP scheduler.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.19 no.1
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• pp.9-27
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• 2021

As an example of research activities in decontamination for decommissioning, new data are presented on the options for corrosion layer dissolution during the decommissioning decontamination, or persulfate regeneration for decontamination solutions re-use. For the management of spent decontamination solutions, new method based on solvent extraction of radionuclides into ionic liquid followed by electrodeposition of the radionuclides has been developed. Fields of applications of composite inorganic-organic absorbers or solid extractants with polyacrylonitrile (PAN) binding matrix for the treatment of liquid radioactive waste are reviewed; a method for americium separation from the boric acid containing NPP evaporator concentrates based on the TODGA-PAN material is discussed in more detail. Performance of a model of radionuclide transport, developed and implemented within the GoldSim programming environment, for the safety studies of the LLW/ILW repository is demonstrated on the specific case of the Richard repository (Czech Republic). Continuation and even broadening of these activities are expected in connection with the approaching end of the lifespan of the first blocks of the Czech NPPs.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.18 no.4
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• pp.421-437
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• 2020

This study provides an assessment on a proposed method for separation of cesium, strontium, and barium using electrochemical reduction at a liquid bismuth cathode in LiCl-KCl eutectic salt, investigated via cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and scanning electron microscopy with energy dispersive X-ray spectrometry (SEM-EDS). CV studies were performed at temperatures of 723-823 K and concentrations of the target species up to 4.0wt%. Redox reactions occurring during potential sweeps were observed. Concentration of BaCl2 in the salt did not seem to influence the diffusivity in the studied concentration range up to 4.0wt%. The presence of strontium in the system affected the redox reaction of lithium; however, there were no distinguishable redox peaks that could be measured. Impedance spectra obtained from EIS methods were used to calculate the exchange current densities of the electroactive active redox couple at the bismuth cathode. Results show the rate-controlling step in deposition to be the mass transport of Cs+ ions from the bulk salt to the cathode surface layer. Results from SEM-EDS suggest that Cs-Bi and Sr-Bi intermetallics from LiCl-KCl salt are not thermodynamically favorable.

• KEPCO Journal on Electric Power and Energy
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• v.7 no.1
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• pp.137-143
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• 2021

As an electrochemical water electrolysis for green hydrogen production, both polymer electrolyte membrane (PEM) and alkaline electrolyte are being developed extensively in various countries. The PEM electrolyzer with high current density (above 2 A/cm²) has the advantage of being able to design a simple structure. Also, it is known that it has high response to electrical output fluctuations. However, the cost problem of major components is the most important issue that a PEM electrolyzer must overcome. Instantly, there are platinum group metal (PGM)-based electrocatalysts, fluorine-based polyfluoro sulfuric acid (PFSA) membrane, Ti felt (porous transport layer, PTL) and so on. Another challenging issue is productivity. A securing outstanding productivity brings price benefits of the electrolytic cells. From this point of view, we conducted basic studies on manufacturing electrode and membrane electrode assembly (MEA) for PEM electrolyzer production.

• Progress in Superconductivity and Cryogenics
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• v.22 no.4
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• pp.14-19
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• 2020

Here we present the comparative experimental study of the stability of the superconducting state in 4 mm YBCO tapes with copper lamination against local heat disturbances at 77 K. The samples are either directly cooled by immersing a bare YBCO tape into a liquid nitrogen pool or operate in nearly-adiabatic conditions when the tape is covered by a 0.6 mm layer of Kapton insulation. Main quench characteristics, i.e. minimum quench energies (MQEs) and normal zone propagation (NZP) velocities for both samples are measured and compared. Minimum NZP currents are determined by a low ohmic resistor technique eligible for obtaining V - I curves with a negative differential resistance. The region of transport currents satisfying the stationary stability criterion is found for the different cooling conditions. Finally, we use the critical temperature margin as a universal scaling parameter to compare the MQEs obtained in this work for YBCO tapes at 77 K with those taken from literature for low-temperature superconductors in vacuum at 4.2 K, as well as for MgB2 wires cooled with a cryocooler down to 20 K.

• Nuclear Engineering and Technology
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• v.54 no.1
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• pp.301-309
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• 2022

This work aims to establish some X-ray qualities recommended by the International Standard Organization (ISO) using the half-value layer (HVL) and H_p(10) dosimetry approaches. The HVL values of the following qualities N-60, N-80, N-100, N-150 and N-250 were determined using various attenuation layers. The obtained results were compared to those of reference X-ray beam qualities and a good agreement was found (difference less than 5% for all qualities). The GAMOS (Geant4-based Architecture for Medicine-Oriented Simulations) radiation transport Monte Carlo toolkit was employed to simulate the production of X-ray spectra. The characteristics HVLs, mean energy and the spectral resolution of simulated spectra have been calculated and turned out to be conform to the ISO reference ones (difference less than the limit allowed by ISO). Furthermore, the conversion coefficients from air kerma to personal dose equivalent for simulated and measured spectra were fairly similar (the maximum difference less than 4.2%).

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.16 no.10
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• pp.3333-3354
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• 2022

The 5G Core Network (5GC) is an essential part of the mobile communication network, but its security protection strategy based on the boundary construction is difficult to ensure the security inside the network. For example, the Network Function (NF) mutual authentication mechanism that relies on the transport layer security mechanism and OAuth2.0's Client Credentials cannot identify the hijacked NF. To address this problem, this paper proposes a trust model for 5GC based on NF interaction behavior to identify malicious NFs and improve the inherent security of 5GC. First, based on the interaction behavior and context awareness of NF, the trust between NFs is quantified through the frequency ratio of interaction behavior and the success rate of interaction behavior. Second, introduce trust transmit to make NF comprehensively refer to the trust evaluation results of other NFs. Last, classify the possible malicious behavior of NF and define the corresponding punishment mechanism. The experimental results show that the trust value of NFs converges to stable values, and the proposed trust model can effectively evaluate the trustworthiness of NFs and quickly and accurately identify different types of malicious NFs.

• Advances in aircraft and spacecraft science
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• v.9 no.2
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• pp.131-148
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• 2022

The paper presents the surface-modified NACA 2412 airfoil performance with variable cavity characteristics such as size, shape and orientation, by numerically investigated with the pre-validation study. The study attempts to improve the airfoil aerodynamic performance at 30 m/s with a variable angle of attack (AOA) ranging from 0° to 20° under Reynolds number (R_e) 4.4×10⁵. Through passive surface control techniques, a boundary layer control strategy has been enhanced to improve flow performance. An intense background survey has been carried out over the modifier orientation, shape, and numbers to differentiate the sub-critical and post-critical flow regimes. The wall-bounded flows along with its governing equations are investigated using Reynolds Average Navier Strokes (RANS) solver coupled with one-equational transport Spalart Allmaras model. It was observed that the aerodynamic efficiency of cavity airfoil had been improved by enhancing maximum lift to drag ratio ((l/d) max) with delayed flow separation by keeping the flow attached beyond 0.25C even at a higher angle of attack. Detailed investigation on the cavity distribution pattern reveals that cavity depth and width are essential in degrading the early flow separation characteristics. In this study, overall general performance comparison, all the cavity airfoil models have delayed stalling compared to the original airfoil.

• Membrane and Water Treatment
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• v.13 no.6
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• pp.313-320
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• 2022

Theoretical calculation results are presented for the enhancement of the water mass flow rate through the hydrophobic micro/nano pores in the membrane respectively on the micrometer and nanometer scales. The water-pore wall interfacial slippage is considered. When the pore diameter is critically low (less than 1.82nm), the water flow in the nanopore is non-continuum and described by the nanoscale flow equation; Otherwise, the water flow is essentially multiscale consisting of both the adsorbed boundary layer flow and the intermediate continuum water flow, and it is described by the multiscale flow equation. For no wall slippage, the calculated water flow rate through the pore is very close to the classical hydrodynamic theory calculation if the pore diameter (d) is larger than 1.0nm, however it is considerably smaller than the conventional calculation if d is less than 1.0nm because of the non-continuum effect of the water film. When the driving power loss on the pore is larger than the critical value, the wall slippage occurs, and it results in the different scales of the enhancement of the water flow rate through the pore which are strongly dependent on both the pore diameter and the driving power loss on the pore. Both the pressure drop and the critical power loss on the pore for starting the wall slippage are also strongly dependent on the pore diameter.