• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.32 no.7
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• pp.37-42
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• 2004

In order to monitor the impact locations in smart structures, multipoint ultrasonic sensors are to be employed. In this study, a multiplexing demodulator with wide dynamic range was proposed to detect the impact locations using FBG sensors, and a stabilization controlling system was also developed for the maintenance of maximum sensitivity of sensors. Two FBG sensors were attached on the bottom side of the aluminum beam specimen and low velocity impact tests were performed to detect the one-dimensional impact locations. As a result, multiplexed in-line FBG sensors could detect the moment of impact precisely, and found the impact locations with the average location error below 0.58mm.

• Journal of Korean Society of Environmental Engineers
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• v.32 no.6
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• pp.639-648
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• 2010

The optimal conditions for the analysis of BPA by HPLC-MS/MS was investigated and the ultrasound degradation capacity of the BPA, with the goal to establish the proper directions for analyzing infinitesimal quantities of BPA by HPLC-MS/MS was examined. The MDL and LOQ of BPA analyzed by HPLC-MS/MS were measured 0.13 nM and 1.3 nM respectively, its sensitivity about 620 and 32 times greater than HPLC-UV (MDL: 81.1 nM, LOQ: 811 nM) and FLD (MDL: 4.6 nM, LOQ: 46 nM). In other words, the new method enables the analysis of BPA with the accuracy up to one 1,180th of the amount specified in U.S. EPA guideline for drinking water. Degradation rate of BPA by ultrasound measured over 95% under 580 kHz and 1000 kHz frequency within 30 minutes of treatment, whereas the rate showed some decrease at 28 kHz frequency. At 580 kHz of ultrasound has proven to be the most effective among others at degradation rate and $k_1$ value, so we concluded that this frequency of ultrasound creates hospitable condition for the combined process of degradation by pyrolysis and oxidization. With the addition of 0.01 mM of $CCl_4$, BPA with the initial concentration of 1 ${\mu}M$ was degraded by more than 98% within 30 minutes, the $k_1$ value measured 5 minutes and 30 minutes into the experiment both showed increases by 1.4 and 1.1 times, respectively, compared with BPA without $CCl_4$. It is also found that the main degradation mechanism of BPA by ultrasound is oxidization process by OH radical, based on the fact that the addition of 10 mM of t-BuOH decreased the rate of BPA degradation by around 60%. However, 33% of BPA degradation rate obtained with the addition of t-BuOH implies further degradation done by pyrolysis or other sorts of radical beside OH radical.

• The Journal of the Acoustical Society of Korea
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• v.6 no.4
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• pp.55-63
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• 1987

Modified $PbTiO_3$ piezoelectric ceramics added with 0.2, 0.25, 0.3 mol of $CaCO_3$ and 0.04 mol of $(Co_{\frac{1}{2}}W_{\frac{1}{2}})$ and 0.05 mol of $MnO_2$ and NiO have been fabricated. These ceramics can be poled sufficiently within 10 minutes at $100^{\circ}C$ under about d.c. field of 40 kv/cm. Detailed measurement was performed on dielectric constants, cutie temperatures, elastic and piezoelectric properties and coupling factors for the fabricated ceramics. The most value of the piezoelectric coupling factors was coupling factor of thickness mode kt and its value for 0.25 mol of Ca was about $45\%$. Dielectric constants of $\varepsilon_{33}^T$ and $\varepsilon_{11}^T$ for 0.25 mol of Ca were 242 and 260, and coupling factor ratio (kt/Kp) and Qm were 6 and 357 respectively.

• Journal of Korean Tunnelling and Underground Space Association
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• v.2 no.3
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• pp.37-45
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• 2000

In recent years two reflection methods, i.e. GPR and seismic Impact-Echo, are usually performed to obtain the information about tunnel lining structures composed of concrete lining, shotcrete, water barrier, and voids at the back of lining. However, they do not lead to a desirable resolution sufficient for the inspection of tunnel safety, due to many problems of interest including primarily (1) inner thin layers of lining structure itself in comparison with the wavelength of source wavelets, (2) dominant unwanted surface wave arrivals, (3) inadequate measuring strategy. In this sense, seismic physical modeling is a useful tool, with the use of the full information about the known physical model, to handle such problems, especially to study problems of wave propagation in such fine structures that are not amenable to theory and field works as well. Thus, this paper deals with various results of seismic physical modeling to enable to show a possibility of detecting the inner layer boundaries of tunnel lining structures. To this end, a physical model analogous to a lining structure was built up, measured and processed in the same way as performed in regular reflection surveys. The evaluated seismic section gives a clear picture of the lining structure, that will open up more consistent direction of research into the development of an efficient measuring and processing technology.

• Journal of Korean Tunnelling and Underground Space Association
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• v.8 no.1
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• pp.3-12
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• 2006

The purpose of this study is to describe the Non-Destructive Testing(NDT) of the rockbolt and investigate the applicability of the NDT methods to estimate the integrity of the rockbolt. To examine the rockbolt integrity including rockbolt itself and grouting material, two methods are adopted: numerical and experimental methods. In the numerical method, the numerical code DISPERSE is used to analyze the dispersion of the rockbolt. The dispersion curve shows the effects of the thickness and stiffness of grouted materials on the embedded rockbolt. Therefore, the optimal frequency for the integrity test of the rockbolt is obtained: 20~120kHz in L(1,0) mode. In the experimental methods, destructive and non-destructive tests are carried out in a laboratory. In the non-destructive test, the low frequency mode generated by an impact and t he high frequency mode generated by an ultrasonic transducer seem to characterize the rockbolt condition readily. The experimental results show that the guided waves attenuate more significantly when the stiffness of the grouted material increases and/or the zone of the defect increases. Meanwhile, the ultimate capacity of rockbolt was evaluated through the pull-out tests and is compared to the NDT results. This study demonstrates that the NDT is a valuable tool for the rockbolt integrity evaluation.

• Journal of Broadcast Engineering
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• v.27 no.1
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• pp.91-103
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• 2022

Determination of sound source characteristics such as: sound volume, direction and distance to the source is one of the important techniques for unmanned systems like autonomous vehicles, robot systems and AI speakers. There are multiple methods of determining the direction and distance to the sound source, e.g., using a radar, a rider, an ultrasonic wave and a RF signal with a sound. These methods require the transmission of signals and cannot accurately identify sound sources generated in the obstructed region due to obstacles. In this paper, we have implemented and evaluated a method of detecting and identifying the sound in the audible frequency band by a method of recognizing the volume, direction, and distance to the sound source that is generated in the periphery including the invisible region. A cross-shaped based sound source recognition algorithm, which is mainly used for identifying a sound source, can measure the volume and locate the direction of the sound source, but the method has a problem with "blind spots". In addition, a serious limitation for this type of algorithm is lack of capability to determine the distance to the sound source. In order to overcome the limitations of this existing method, we propose a QRAS-based algorithm that uses rectangular-shaped technology. This method can determine the volume, direction, and distance to the sound source, which is an improvement over the cross-shaped based algorithm. The QRAS-based algorithm for the OSSD uses 6 AITDs derived from four microphones which are deployed in a rectangular-shaped configuration. The QRAS-based algorithm can solve existing problems of the cross-shaped based algorithms like blind spots, and it can determine the distance to the sound source. Experiments have demonstrated that the proposed QRAS-based algorithm for OSSD can reliably determine sound volume along with direction and distance to the sound source, which avoiding blind spots.

• Analytical Science and Technology
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• v.31 no.6
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• pp.247-258
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• 2018

The purpose of the present study was to investigate whether the degree of air pollution can be evaluated via examination of local plants. Selected sites included two parks in an industrial area, as well as two parks in an urban area. Selected plant samples comprised one-year-old pine shoot leaves. Leaves growing over 2 m from the ground were collected from over 10 pine trees. Leaf surface was analyzed for deposition of 14 trace elements and 16 polycyclic aromatic hydrocarbons (PAHs), including particle size and mass, surface imaging, precipitation-mediated particle removal rate, and concentration. Particle size ranged from 0.4 to $200{\mu}m$, and the volume percentage of particles ${\leq}10$ was 20 %. Deposited particle mass ranged from 0.450-0.825 mg, and precipitation-mediated removal rate ranged from 10.0-27.6 %. Trace element concentration, as measured by ICP/MS after microwave acid digestion, was 18.8-26.3 mg/kg As, 0.08-0.13 mg/kg Be, 0.06-0.08 mg/kg Cd, 4.91-17.8 mg/kg Cr, 5.26-405 mg/kg Cu, 1,930-2,670 mg/kg Fe, 3.03-28.1 mg/kg Pb, 26.9-42.8 mg/kg Mn, 2.66-10.4 mg/kg Ni, 4,560-8,730 mg/kg Al, 2,500-6,120 mg/kg Ba, 5.27-17.8 mg/kg Rb, 40.9-95.3 mg/kg Sr, and 4,030-8,260 mg/kg Zn. Concentration of PAHs, as analyzed by GC/MS/MS after liquid-liquid extraction and purification of deposited particles, ranged from 1.17 to 12.378 mg/kg for ${\Sigma}PAH_{16}$ and from 1.17 to 12.378 mg/kg for ${\Sigma}PAH_7$.