• Korean Journal of Metals and Materials
• /
• v.50 no.5
• /
• pp.401-406
• /
• 2012

When viewed using a magnetic resonance imaging (MRI) system, invasive materials inside the human body, in many cases, severely distort the MR image of human tissues. The degree of the MR image distortion increases in proportion not only to the difference in the susceptibility between the invasive material and the human tissue, but also to the intensity of the magnetic field induced by the MRI system. In this study, by blending paramagnetic Ti particles with diamagnetic graphite, we synthesized $Ti_{100-x}C_x$ composites that can reduce the artifact in the MR image under the high-strength magnetic field. Of the developed composites, $Ti_{70}C_{30}$ showed the magnetic susceptibility of ${\chi}=67.6{\times}10^{-6}$, which corresponds to 30% of those of commercially available Ti alloys, the lowest reported in the literature. The level of the MR image distortion in the vicinity of the $Ti_{70}C_{30}$ composite insert was nearly negligible even under the high magnetic field of 4.7 T. In this paper, we reported on a methodology of designing new structural materials for bio-applications, their synthesis, experimental confirmation and measurement of MR images.

• Journal of the Korean Society of Propulsion Engineers
• /
• v.18 no.5
• /
• pp.12-18
• /
• 2014

A study of gas generator Fuel-Rich propellant for air-breathing propulsion system was performed in this paper. General solid propellant comprises a mean of 60% or more oxidizing agents. but, to develop the fuel-rich solid propellant increased the content of the metal fuel and reduced the content of the oxidizing agents by approximately 30%. Very high amount of heat per volume of fuel into the metal having the Boron was used. Amorphous Boron Powder was applied to propellant as beads type and it allowed to design more amount of metal fuel in the fuel-rich propellant. And the Combustion characteristics and properties of fuel-rich solid propellant according to the Boron-bead sizes were confirmed.

• Smart Structures and Systems
• /
• v.6 no.5_6
• /
• pp.641-659
• /
• 2010

Structural Health Monitoring (SHM) gradually becomes a technique for ensuring the health and safety of civil infrastructures and is also an important approach for the research of the damage accumulation and disaster evolving characteristics of civil infrastructures. It is attracting prodigious research interests and the active development interests of scientists and engineers because a great number of civil infrastructures are planned and built every year in mainland China. In a SHM system the sheer number of accompanying wires, fiber optic cables, and other physical transmission medium is usually prohibitive, particularly for such structures as offshore platforms and long-span structures. Fortunately, with recent advances in technologies in sensing, wireless communication, and micro electro mechanical systems (MEMS), wireless sensor technique has been developing rapidly and is being used gradually in the SHM of civil engineering structures. In this paper, some recent advances in the research, development, and implementation of wireless sensors for the SHM of civil infrastructures in mainland China, especially in Dalian University of Technology (DUT) and Harbin Institute of Technology (HIT), are introduced. Firstly, a kind of wireless digital acceleration sensors for structural global monitoring is designed and validated in an offshore structure model. Secondly, wireless inclination sensor systems based on Frequency-hopping techniques are developed and applied successfully to swing monitoring of large-scale hook structures. Thirdly, wireless acquisition systems integrating with different sensing materials, such as Polyvinylidene Fluoride(PVDF), strain gauge, piezoresistive stress/strain sensors fabricated by using the nickel powder-filled cement-based composite, are proposed for structural local monitoring, and validating the characteristics of the above materials. Finally, solutions to the key problem of finite energy for wireless sensors networks are discussed, with future works also being introduced, for example, the wireless sensor networks powered by corrosion signal for corrosion monitoring and rapid diagnosis for large structures.

• Journal of the Korean Magnetics Society
• /
• v.19 no.1
• /
• pp.5-11
• /
• 2009

The Explosive Magnetic Generator of Frequency (EMGF) has been studied as a method to generate a strong microwave effectively through converting the explosion powder energy into the electromagnetic energy. However, the generated high frequency electromagnetic wave has not been explained clearly yet, for it is known to be difficult to analyze the high frequency electromagnetic wave oscillation using a simple time-varying equivalent circuit model. In this paper, we analyze the problems of the widely used inductance model with an exponential decreasing pattern and investigate the tendency of a more accurate inductance variation model using the finite element method of EMGF inductance by considering the magnetic compression effect. And we have shown via an EMGF output simulation that the new inductance variation model proposed here has an negative effect on EMGF output.

• Journal of the Korean institute of surface engineering
• /
• v.54 no.6
• /
• pp.340-347
• /
• 2021

Among various metal oxide semiconductors, ZnO has an excellent electrical, optical properties with a wide bandgap of 3.3 eV. It can be applied as a photocatalytic material due to its high absorption rate along with physical and chemical stability to UV light. In addition, it is important to control the morphology of ZnO because the size and shape of the ZnO make difference in physical properties. In this paper, we demonstrate synthesis of size-controlled ZnO tetrapods using an atmospheric pressure plasma system. A micro-sized Zn spherical powder was continuously introduced in the plume of the atmospheric plasma jet ignited with mixture of oxygen and nitrogen. The effect of plasma power and collection sites on ZnO nanostructure was investigated. After the plasma discharge for 10 min, the produced materials deposited inside the 60-cm-long quartz tube were obtained with respect to the distance from the plume. According to the SEM analysis, all the synthesized nanoparticles were found to be ZnO tetrapods ranging from 100 to 600-nm-diameter depending on both applied power and collection site. The photocatalytic efficiency was evaluated by color change of methylene blue solution using UV-Vis spectroscopy. The photocatalytic activity increased with the increase of (101) and (100) plane in ZnO tetrapods, which is caused by enhanced chemical effects of plasma process.

• Journal of the Korea Convergence Society
• /
• v.12 no.10
• /
• pp.211-218
• /
• 2021

A recent spread of personal mobility devices such as electric kickboards has brought about a rapid increase in accident cases. Such vehicles are susceptible to falling accidents due to their low dynamic stability and lack of outer protection chassis. This paper presents the development of an automatic emergency braking system and a safe starting system as driving assistance devices for electric kickboards. The braking system employed artificial intelligence to detect nearby threaening objects. The starting system was developed to disable powder to the motor until when the driver's boarding is confirmed. This study is meaningful in that it proposes the convergence technology of advanced driver assistance systems specialized for personal mobility devices.

• Journal of the Microelectronics and Packaging Society
• /
• v.25 no.4
• /
• pp.89-93
• /
• 2018

Ceramic substrates applied to power modules of electric vehicles are required to have properties of high thermal conductivity, high electrical insulation, low thermal expansion coefficient and resistance to abrupt temperature change due to high power applied by driving power. Aluminum nitride and silicon nitride, which are applied to heat dissipation, are considered as materials meeting their needs. Therefore, in this paper, the properties of aluminum nitride and silicon nitride as radiator plate materials were compared through a commercial analysis program. As a result, when the process of applying heat of the same condition to aluminum nitride was implemented by simulation, the silicon nitride exhibited superior impact resistance and stress resistance due to less stress and warping. In terms of thermal conductivity, aluminum nitride has superior properties as a heat dissipation material, but silicon nitride is more dominant in terms of reliability.

• Journal of Internet Computing and Services
• /
• v.20 no.2
• /
• pp.93-100
• /
• 2019

Recently, in various business fields, companies are concentrating on providing chatbot services to various environments by adding artificial intelligence to existing messenger platforms. Organizations in the field of job placement also require chatbot services to improve the quality of employment counseling services and to solve the problem of agent management. A text-based general chatbot classifies input user sentences into learned sentences and provides appropriate answers to users. Recently, user sentences inputted to chatbots are inputted as short texts due to the activation of social network services. Therefore, performance improvement of short text classification can contribute to improvement of chatbot service performance. In this paper, we propose T-EBOW (Translation-Extended Bag Of Words), which is a method to add translation information as well as concept information of existing researches in order to strengthen the short text classification for employment chatbot. The performance evaluation results of the T-EBOW applied to the machine learning classification model are superior to those of the conventional method.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.19 no.12
• /
• pp.600-606
• /
• 2018

A class D fire or combustible metal fire is characterized by the presence of burning metals. Only certain metals or metal compounds are flammable, including sodium and lithium. General fire extinguishing agents, such as dry chemical powder, water-based fire extinguish agents, and carbon dioxide, cannot be used in class D fires. This is because these agents cause adverse reactions or are ineffective. In addition, the amount of usage of combustible metals is increasing due to continuous development of the semiconductor and fuel cell industries. Despite this, Korea does not have standards and laws related to combustible metal fires. This paper suggests directions of the class D fire management policies to reduce the class D fire risk and impact by analyzing the standards and laws related to class D fires and combustible metal fire cases. The factors to make laws on class D fire prevention and response systems, and management system of dry sand were determined. These results may be used to help reduce the risk of class D fires and improve the response abilities.

• Journal of Korean Society on Water Environment
• /
• v.27 no.1
• /
• pp.110-114
• /
• 2011

In this paper, in order to eliminate Limnoperna fortunei inhabiting the water conduction pipeline, prechlorination at the intake station was employed to improve the degradation of water quality due to the high pH of raw water taken at the downstream of Paldang Dam, algal growth, etc.. With the prechlorination concentration of 1.0mg/L at the intake station, the pH in the water well at the treatment plant decreased by 0.4, and with 1.5mg/L, by 0.6. Also, it eliminated Chlorophyll-a by about 95%, and the population of algae by about 49%. Such disinfection by-products (DBPs) as Trihalomathanes (THMs), Haloacetic Acids (HAAs), and Chloral Hydrate (CH) were under the quality standard for potable water, showing no change by the prechlorination, while raising the prechlorination rate from 1.0 up to 1.5mg/L, the DBPs in the water well increased by 1.5 to 3.1 times. As a consequence of testing Kyungan Stream, a branch stream flowing into Lake Paldang, the prechlorination (0.57mg/L, 1.14mg/L, 1.71mg/L) had no effect of eliminating the taste and odor compounds and total organic carbon (TOC) which is the DBPs precursor. As for the efficiency of Geosmin elimination by the rates of prechlorination and powder activated carbonation (PAC), it was found that the higher the concentration of PAC was (30ppm>20ppm>10ppm), the higher the efficiency was; the higher the rate of prechlorination was, the lower the efficiency by PAC was. Therefore, when taste and odor occur from raw water, suspending prechlorination at the intake or lowering the rate was proved to be more effective in eliminating the taste and odor compounds by PAC.