• ETRI Journal
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• v.45 no.6
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• pp.1046-1055
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• 2023

We introduce a display for virtual-reality (VR) fire training. Firefighters prefer to wear and operate a real breathing apparatus while experiencing full visual immersion in a VR fire space. Thus, we used a thin head-mounted display (HMD) with a light field and folded optical system, aiming to both minimize the volume for integration in front of the face into a breathing apparatus and maintain adequate visibility, including a wide viewing angle and resolution similar to that of commercial displays. We developed the optical system testing modules and prototypes of the integrated breathing apparatus. Through iterative testing, the thickness of the output optical module in front of the eyes was reduced from 50 mm to 60 mm to less than 20 mm while maintaining a viewing angle of 103°. In addition, the resolution and image quality degradation of the light field in the display was mitigated. Hence, we obtained a display with a structure consistent with the needs of firefighters in the field. In future work, we will conduct user evaluation regarding fire scene reproducibility by combining immersive VR fire training and real firefighting equipment.

• The Journal of Engineering Geology
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• v.23 no.4
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• pp.341-352
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• 2013

The physical and mechanical properties of red shale and black shale exposed in the Daegu area were investigated in tests conducted to determine unit weight, absorption ratio, porosity, ultrasonic velocity, unconfined compressive strength, point load strength, slake durability index, and deterioration characteristics. XRD, XRF, and SEM analyses were also performed on the shale specimens. While the unit weights of the two shales were similar, the absorption ratio and porosity were higher in the red shale than in the black shale. Despite the higher porosity of the red shale, the ultrasonic velocity, compressive strength, and point load strength were higher in the red shale, which is an unexpected result that may be due to the presence of fine laminations in the black shale. The deterioration rate, as determined from the point load strength and the slake durability index, increased with increasing immersion time and with the acidity of the immersion liquid. The deterioration rate was higher for the red shale than for the black shale because of the higher porosity of the former.

• Journal of the Korean Society for Nondestructive Testing
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• v.37 no.1
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• pp.29-36
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• 2017

Recently, KTX (Korean Train Express) train stoppage accidents were mainly caused by malfunctioning equipment, aging and cracking of railway vehicles, crack breakages of brake disks, and breakages of brake disks. Breakage of brake disk can cause large-scale casualties such as high-speed collision and concern about derailment by hitting lower axle and wheel. Therefore, in this study, a brake disk with solid and ventilation type, which is the brake disk of a KTX train was modeled, and a dynamometer system was constructed to operate the disk. A Rayleigh wave was used to inspect the surface of the brake disk. An ultrasonic inspection module was developed for the brake disk by using a local immersion method due to the difficulty involved in ultrasonic inspection using an existing immersion method. In addition, the surface defects of the brake disk were evaluated using a dynamometer mock-up system and an ultrasonic inspection module of the brake disk.

• International Journal of Highway Engineering
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• v.17 no.2
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• pp.21-30
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• 2015

PURPOSES : The purpose of this study was to evaluate the performance of rapid-setting polymer-modified asphalt mixtures with a high reclaimed asphalt pavement (RAP) content. METHODS: A literature review revealed that emulsified asphalt is actively used for cold-recycled pavement. First, two types of rapid-setting polymer-modified asphalt emulsion were prepared for application to high-RAP material with no virgin material content. The quick-setting polymer-modified asphalt mixtures using two types of rapid-setting polymer-modified asphalt emulsion were subjected to the following tests: 1) Marshall stability test, 2) water immersion stability test and 3) indirect tensile strength ratio test. RESULTS AND CONCLUSIONS : Additional re-calibration of the RAP was needed for laboratory verification because the results of analyzing RAP aggregates, which were collected from different job sites, did not deviate from the normal range. The Marshall stability of each type of binder under dry conditions was good. However, the Type B mixtures with bio-additives performed better in the water immersion stability test. Moreover, the overall results of the indirect tensile strength test of RAP mixtures with Type B emulsions exceeded 0.7. Further research, consisting of lab testing and on-site application, will be performed to verify the possibility of using RAP for minimizing the closing of roadways.

• Transactions of the Korean Society of Automotive Engineers
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• v.16 no.5
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• pp.8-14
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• 2008

For nondestructive inspection of electron beam (EB) welding part in automotive power transmission assembly, a pulse-echo ultrasonic testing apparatus in water immersion has been applied using the ultrasonic waves with a frequency of 10MHz. However various problems have appeared during the ultrasonic inspection, which led to some significant mistakes in automatic quality evaluation of the welding parts. Experimental study showed that the state of water couplant medium containing some amount of contaminants, rusts and anti-corrosion agents had considerable influences on the reduction of ultrasonic amplitudes during wave propagation. The amplitude reduction depending on the coupling medium state could bring about some mis-diagnoses for defects in the welding parts. The results proposed that for a reliable inspection of defects in welds the state of water medium should be kept in about 15 volume fractions (vol.%) of anti-corrosion agents and in minimized contaminants.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.15 no.1
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• pp.32-38
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• 2014

In the present study, immersion corrosion characteristics of Zn and Al thermal spray coating with sealer for the seawater heat exchanger are experimentally investigated. Total 8 coating types of Zn and Al thermal spray coating with silicone and epoxy sealer were tested with immersion corrosion testing in $80^{\circ}C$ 3.5%w NaCl solution and compared the corrosion characteristics between each coatings. To investigate the corrosion characteristics of the specimens, AC impedance, SEM, and thermal diffusivity were acquired and analyzed. As a result, on the surface of the specimens with silicone and epoxy sealer, blister did not occurred, so the sealers might be effective at increasing the corrosion resistance of the specimens immersed in the NaCl solution.

• The Korean Journal of Food And Nutrition
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• v.21 no.2
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• pp.176-183
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• 2008

This study examined the anti-microbiological effects of chlorine treatment on the surface of fresh fruits, in order to improve microbiological safety in school foodservice operations. Non-peeled fruit(strawberries) and peeled fruit(bananas) were treated with different concentrations of chlorinated water and rinsing numbers, followed by microbiological testing. The fruits were immersed at different concentrations of chlorinated water(0 ppm, 50 ppm, and 100 ppm) and durations(3 min and 5 min), and were then rinsed with tap water(one time, two times, or three times). The total viable cell counts of both the strawberries and bananas ranged from $10^3$ CFU/g to $10^4$ CFU/g, and coliform levels ranged from $10^2$ CFU/g to $10^3$ CFU/g. As the chlorine concentration, immersion time, and rinsing number increased, anti-microbiological activity increased. The largest microbial reduction was shown with immersion for 5 min in 100 ppm chlorinated water and three rinsings. In the strawberries, this treatment reduced the initial population of total viable cells and coliforms by 3.29 log CFU/g and to an undetectable level, respectively, no total viable cells or coliforms were detected on the banana surface following this treatment. However, after a sterilization treatment with immersion for 5 min in 50 ppm chlorinated water and three rinsings, the total viable cell counts and coliform counts of the strawberries and bananas decreased to acceptable levels, based on the microbiological standards for ready-to-eat foods. Overall, it was shown that the sterilization treatment of 50 ppm chlorinated water, soaking for 5 min, and three rinsings provided an effective reduction in surface microbes, and enhanced the microbiological safety of the fruit.

• The korean journal of orthodontics
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• v.28 no.5 s.70
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• pp.783-789
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• 1998

The purpose of this study was to evaluate the changes of shear bond strengths and failure patterns in orthodontic resin adhesives according to the water immersion time. Metal brackets were bonded to the specimens involving the premolars with chemical-cured($Concise^{\circledR}$) and light-cured($Transbond^{\circledR}$) adhesives. The shear bond strength was measured on universal testing machine and the failure patterns were assessed with the adhesive remnant index(ARI) after storage in distilled water at $37^{\circ}C$ for 1 day, 1 week and 1, 3, and 6 months, respectively. The results were as follows. 1. The shear bond strengths at the 6 month in both Concise and Transbond were significantly higher than those at the 1 day, 1 week and 1 month(p<0.05). There were positive correlations between shear bond strength and water immersion time in both Concise and Transbond(P<0.01). 2. There were no significant differences in shear bond strength between Concise and Transbond. 3. The brackets were failed primarily at the bracket base-adhesive interface and there was no significant difference in the incidence of ARI scores according to the water immersion time.

• Journal of the Korean Society for Nondestructive Testing
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• v.19 no.2
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• pp.118-128
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• 1999

There are many ultrasonic measurement methods that are used in nondestructive testing applications. Some typical applications include material property determination, microstructural characterization. and flaw detection. Ultrasonic parameters such as velocity and attenuation are most commonly required in these applications. The accuracy and repeatability of testing results are dependent on both the hardware used to generate and receive the ultrasonic waves and on the analysis software for calculating these parameters. In this study, five analysis algorithms were implemented on a computer for measuring wave speed in a pulse echo. immersion testing configuration. In velocity measurements comparisons were made between the overlap. cross-correlation. Fourier transform. Hilbert transform, wavelet transform algorithms. Velocity measurement was applied to an isotropic steel sample using the five analysis algorithms. Frequency-dependent phase/group velocity and attenuation were also measured using the Fourier transform and wavelet transform algorithms on a composite laminate containing voids.

• Elastomers and Composites
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• v.1 no.1
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• pp.49-55
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• 1966

Based upon the results of the previous work, the experiments are concentrated on the improvement of the durability of rubber coated fabrics as a rain garment material. To obtain a much lighter and durable coated fabric, several kinds of light weight cotton prints having almost equal density in warp and fillingwise were chosen. Rubber coating on these prints was made by topping and spreading process using rubber compound of various viscosity, and the physical properties of final product were analysed and interpreted in terms of adhesion and durability. The results are as follows. 1. Any noticeable difference between two coating processes was not found in terms of physical properties. 2. Base fabrics should be dipped once into a dilute rubber compound before coating operation in order to obtain a uniform adhesion and physical properties, and the optimum range of the viscosity of dipping paste are from 100 poise to 200 poise. 3. Generally, the tearing strength of the coated fabrics is inversely proportional to the adhesion. 4. It was assumed that the increase of the water proofness after water immersion on the finished material which have dense base fabric is chiefly due to the swelling of the cellulosic fiber.