• Journal of the Korean Ceramic Society
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• v.42 no.8 s.279
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• pp.532-536
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• 2005

Thermal shock resistance of structural ceramics is a property that is difficult to quantity, and as such is usually expressed in terms of a number of empirical resistance parameters. These are dependant on the conditions imposed, but one method that can be used is the examination of density, Young's modulus and thermal expansion retention after quenching. For high temperature applications, long-annealing thermal durability, cycle thermal stability and residual mechanical properties are very important if these materials are to be used between $1000^{\circ}C$ and $1300^{\circ}C$. In this study, an excellent thermal shock-resistant material based on $Al_2TiO_5-mullite$ composites of various compositions was fabricated by sintering reaction from the individual oxides and adjusting the composition of $Al_2O_3TiO_2/SiO_2$ ratios. The characterization of the damage induced by thermal shock was done by measuring the evolution of the Young's modulus using ultrasonic analysis, density and thermal expansion coefficients.

• Journal of information and communication convergence engineering
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• v.5 no.4
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• pp.382-388
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• 2007

Indoor location system using wireless sensor network technology was applied for the status evaluation and activity monitoring of elderly person or chronic invalid at home. Location awareness application is transparent to the daily activities, while providing the embedded computing infrastructure with an awareness of what is happening in this space. To locate an object, the active ceiling-mounted reference beacons were placed throughout the building. Reference beacons periodically publish location information on RF and ultrasonic signals to allow application running on mobile or static nodes to study and determine their physical location. Once object-carried passive listener receives the information, it subsequently determines it's location from reference beacons. By using only the sensor nodes without any external network infrastructure the cost of the system was reduced while the accuracy in our experiments. was fairly good and fine grained between 7 and 15 cm for location awareness in indoor environments. Passive architecture used here provides the security of the user privacy while at the server the privacy was secured by providing the authentication using Geopriv approach. This information from sensor nodes is further forwarded to base station where further computation is performed to determine the current position of object and several applications are enabled for context awareness.

• Proceedings of the IEEK Conference
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• 2001.10a
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• pp.215-219
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• 2001

Impurities removal from waste carbon black was carried out to produce high-grade carbon black. A lot of hydrophilic carbon black is produced as a byproduct of the hydrogen production process by flame decomposition of water. Due to its impurity content such as sulphur, iron, ash and etc., it can only be used as low-grade carbon or burnt out. High-grade hydrophilic carbon black is 3-5 times more expensive than oil-based carbon black because of its process difficulties and requires pollutant treatment. Hydrophilic carbon is normally used far conductive materials for batteries, pigment for plastics, electric wire covering, additives for rubber, etc.. In these applications, hydrophilic carbon must maintain its high purity. In this study magnetic separation, froth flotation and ultrasonic treatment were employed to remove impurities from the low-grade hydrophilic carbon black. As results, the ash, iron and sulphur content of product decreased to less than 0.01wt.%, 0.0lwt.% and 0.3wt.% respectively, and the surface area of product was about 930 $m^2$/g.

• IEMEK Journal of Embedded Systems and Applications
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• v.10 no.2
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• pp.91-99
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• 2015

The electric power consumed by the embedded devices has become a critical issue because the reduction of power consumption is an important factor to prolong the battery-operated devices' lifetime. Many researches and techniques to reduce the power consumption have been proposed and developed but any power method cannot guarantee optimal power consumption of an embedded device - it would be faced with numerous situation - in all ways. Specifically, power researches for embedded devices deployed in the industry field have hardly been done. In this paper, low power service is proposed to minimize power reduction with the several usage status of embedded devices in the industry field. The usage status is basically classified according to the distance between the device and the user which is obtained by the ultrasonic and PIR sensor. The performance evaluation shows that the proposed scheme can reduce the power consumption by up to 45.3% compared to the device with no power reduction scheme. It also shows that the power consumption of the proposed scheme is 5.2% ~ 16.8% lower than that of the timeout scheme.

• Bulletin of the Korean Chemical Society
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• v.23 no.6
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• pp.884-890
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• 2002

An inorganic-organic hybrid system, silica-poly(ethylene glycol) songel is reported. This system was prepared via sol-gel method by varying varous processing variables. e.g. ultrasonic radiation time, gelling temperanture, PEG content and its molecular weight. Various experimental techniques wee employed to analyze the morphological, mechanical and optical properties of the system. The results were discussed in the light of existing theories. The sonogel system exhibited the common features of inorganic-organic hybrids. $SiO_2-10$ wt% PEG sonogel exhibited the morphological and optical properties superior to those reported earlier for the classic gels and found suitable for device applications.

• Advances in Computational Design
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• v.8 no.3
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• pp.219-236
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• 2023

In this paper, finite element modeling of the laser ultrasonics (LU) process in ablation regime is of interest. The momentum resulting from the removal of material from the specimen surface by the laser beam radiation in ablation regime is modeled as a pressure pulse. To model this pressure pulse, two equations are required: one for the spatial distribution and one for the temporal distribution of the pulse. Previous researchers have proposed various equations for the spatial and temporal distributions of the pressure pulse in different laser applications. All available equations are examined and the best combination of the temporal and spatial distributions of the pressure pulse that provides the most accurate results is identified. This combination of temporal and spatial distributions has never been used for modeling laser ultrasonics before. Then by using this new model, the effects of variations in pulse duration and laser spot radius on the shape, amplitude, and frequency spectrum of ultrasonic waves are studied. Furthermore, the LU in thermoelastic regime is simulated by this model and compared with LU in ablation regime. The interaction of ultrasonic waves with a defect is also investigated in the LU process in ablation regime. Good agreement of the results obtained from the new finite element model and available experimental data confirms the accuracy of the proposed model.

• Corrosion Science and Technology
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• v.23 no.4
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• pp.266-277
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• 2024

Due to its good corrosion and heat resistance with excellent mechanical properties, 304L stainless steel is commonly used in the fabrication of spent nuclear fuel dry storage canisters. However, welds are sensitive to stress corrosion cracking (SCC) due to residual stress generation. Although SCC resistance can be improved by stress relieving the weld and changing the chloride environment, it is difficult to change corrosion environment for certain applications. Stress control in the weld can improve SCC resistance. Ultrasonic shot peening (USP) needs further research as compressive residual stresses and microstructure changes due to plastic deformation may play a role in improving SCC resistance. In this study, 304L stainless steel was welded to generate residual stresses and exposed to a chloride environment after USP treatment to improve SCC properties. Effects of USP on SCC resistance and crack growth of specimens with compressive residual stresses generated more than 1 mm from the surface were studied. In addition, correlations of compressive residual stress, grain size, intergranular corrosion properties, and pitting potential with crack propagation rate were determined and the improvement of SCC properties by USP was analyzed.

• Journal of the Korean Society for Nondestructive Testing
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• v.28 no.2
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• pp.131-136
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• 2008

Using ultrasonic standing waves, micro particles submerged or flowing in fluid can be manipulated. Due to acoustic radiation force of ultrasound, particles are forced to move to pressure nodal or antinodal lines. In this work, we propose a method to control the position of micro particle in a flow by adjusting the frequency of the standing wave. To this end, standing wave field generation system including a few millimeter thick micro channel was established using an immersible ultrasonic transducer. The present generation system works valid in a frequency range between 2.0 MHz and 2.5 MHz. We observed the SiC particles in water moved to pressure nodal lines by the standing wave. The effect of the channel thickness and operating frequency was also investigated. Interestingly, it was shown that the operating frequency have a close relation with the location of the pressure nodal line. Consequently, it fan be said that the position of particle movement rail be controlled by adjusting the ultrasound frequency. The maximum range of the controllable position was about 261 micrometers under the given condition. The resulted observations reveal the possibility of various applications of the ultrasonic standing wave to the manipulation of particles submerged in a fluid.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.6 no.1
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• pp.37-42
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• 2010

The stay cylinder weld at the steam generator of Korean Standard Nuclear Power Plants is safety class I component and is subjected to be inspected by the volumetric examination such as ultrasonic method. As accessibility of this area is limited due to the narrow space and high radiation, the existing manual inspection method involves various difficulties. Moreover operators may be exposed to internal contamination by contaminated dust during the surface buffing process to improve the inspection reliability of this area. Recently the new automatic inspection system for stay cylinder welds has been developed. The inspection system basically consists of a driving assembly, data acquisition device and signal processing units. The driving assembly is classified by 1) the scanner for inspecting and buffing the weld, 2) pillars for guiding the scanner and 3) the base frame for loading and supporting pillars. The scanner has 4 sensor modules to inspect in 4 refracted angles and 4 incident directions. These components can be inserted into the skirt of the stay cylinder through the manway hole and assembled easily by one-touch in the skirt. Data acquisition device and signal processing units developed in previous works are also newly upgraded for better processing of data analysis and evaluation. The system has been successfully demonstrated not only in the mock-up but also in the field. In this paper, newly developed inspection system for the stay cylinder weld of the steam generator is introduced and their field applications are discussed.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.36 no.6
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• pp.707-712
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• 2012

Very high cycle fatigue (VHCF) behavior of aerospace components has emerged much attention due to their long service life. In this study, a piezoelectric ultrasonic fatigue testing (UFT) system has been developed by Mbrosiatec Co., Ltd. to study the high cycle fatigue (HCF) strength of Ti-6Al-4V alloy. Hourglass-shaped specimens have been investigated in the range from $10^6$ to $10^9$ cycles at room temperature under completely reversed R = -1 loading conditions,. Scanning electron microscopy (SEM) analysis revealed that failures occurred in the entire range up to the gigacycle regime, and the fractures have beenfound to be initiated from the surface, unlike in steels. However, it was found from the SEM microgprahs that microcracks transformed into intergranular fractures. Thus, it can be concluded from according to the results that this test method can be applicable to commercialized automotive and railroad parts that require high cycle fatigue strength.