• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.05a
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• pp.515-518
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• 2007

SAFRS(Spontaneous Acoustic Field Reproduction System) is a system to sense changes of surroundings and produce sounds which can go well with environment elements sensed by the system in to the space. The sounds were judged by individual evaluation and, the classification of the preferred sounds according to the mood of the space was suggested in the former study. Effectiveness of SAFRS with field application was validated by prior studies which dealt with researching acoustic environment, evaluating images of sounds, and rating environment with existence and nonexistence of sound resources such as fountains and the system after applied in D university. In this study, for more effective field application of SAFRS, research for the acoustic environment around sound resources and subjective evaluation of the preference of the sounds from the resources were made and it was considered that the results of the experiments should be primary information to propose proper sound level to be offered by the system. The results of the study are as follows; 1) It was considered that the ambience of the center road was dependent upon produced sounds by the system and water sounds of the fountain and that of walk way was mostly dependent upon produced sounds. 2) The results of the subjective evaluation showed that the distance from sound resources was suggestive; the more distant from produced sounds the less full and clear the sounds, the less distant from the sounds of water the more delight and idyllic ambience, and the less distant from the forest the more idyllic ambient and diversity. 3) The results upwards were telling that an average value of six elements for the evaluation was even at the place set back 10.2m from center road and walk way. And harmony of all sounds of the place should be considered to propose suitable sound level of SAFRS.

• Asian Journal of Atmospheric Environment
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• v.11 no.2
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• pp.107-113
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• 2017

This study describes (1) the impact of positive sampling artifacts caused by not only a filter-based sampling, but also a denuder-based sampling in the determination of particle-phase organic carbon (POC), (2) the effect of sample flow rate on positive artifacts, and (3) an optimum flow rate that provides a minimized negative sampling artifact for the denuder-based sampling method. To achieve the goals of this study, four different sampling media combinations were employed: (1) Quartz filter-alone (Q-alone), (2) quartz filter behind quartz-fiber filter (QBQ), (3) quartz filter and quartz filter behind Teflon filter (Q-QBT), and (4) quartz filter behind carbon-based denuder (Denuder-Q). The measurement of ambient POC was carried out in an urban area. In addition, to determine gas-phase OC (GOC) removal efficiency of the denuder, a Teflon filter and a quartz filter were deployed upstream and downstream of the denuder, respectively with varying sample flow rates: 5, 10, 20, and 30 LPM. It was found that Q-alone sampling configuration showed a higher POC than QBQ, Q-QBT, and Denuder-Q by 12%, 28%, and 23%, respectively at a sample flow rate of 20 LPM due to no correction for positive artifact caused by adsorption of GOC onto the filter. A lower quantity of GOC was collected from the backup quartz filter on QBQ than that from Q-QBT. This was because GOC was not in equilibrium with that adsorbed on the front quartz filter of QBQ during the sampling period. It is observed that the loss of particle number and mass across the denuder increases with decreasing sample flow rate. The contribution o f positive arti facts to POC decreased with increasing sample flow rate, showing 29%, 25%, and 22% for 10, 20, and 30 LPM, respectively. The 20 LPM turns out to be the optimum sample flow rate for both filter and denuder-based POC sampling.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.23 no.1
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• pp.11-17
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• 1987

This paper describes an availability of the teltmeter device made as a trial to measure the under-water noise, and the results of the test. This telemeter device adopts FM-FM system, and its main carrier wave is 146.2MHz. The trans-mission power is about 1w, and the available distance of transmission is 2.5KM. The timer built in the telemeter device controls transmission time and pause time automatically by the R-C time-constant. The former is 30-32 seconds and the latter is 10-12 seconds. The underwater noise in the set net fishing ground and at the breeding tank was measured, and recorded simultaneously on land and at sea with the telemeter device. When the input voltages of the transmitter is 100-300mV, the value of telemetering ambient noise and bio-acoustic underwater noise well agreed with that of the direct measurement. And the teleme-tered underwater noise decreases in proportion the distance between the transmitter and receiver.

• Smart Structures and Systems
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• v.17 no.3
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• pp.363-389
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• 2016

Deficient modes that cannot be always identified from different sets of measurement data may exist in the application of operational modal analysis such as the stochastic subspace identification techniques in large-scale civil structures. Based on a recent work using the long-term ambient vibration measurements from an instrumented cable-stayed bridge under different wind excitation conditions, a benchmark problem is launched by taking the same bridge as a test bed to further intensify the exploration of mode identifiability. For systematically assessing this benchmark problem, a recently developed SSI algorithm based on an alternative stabilization diagram and a hierarchical sifting process is extended and applied in this research to investigate several sets of known and blind monitoring data. The evaluation of delicately selected cases clearly distinguishes the effect of traffic excitation on the identifiability of the targeted deficient mode from the effect of wind excitation. An additional upper limit for the vertical acceleration amplitude at deck, mainly induced by the passing traffic, is subsequently suggested to supplement the previously determined lower limit for the wind speed. Careful inspection on the shape vector of the deficient mode under different excitation conditions leads to the postulation that this mode is actually induced by the motion of the central tower. The analysis incorporating the tower measurements solidly verifies this postulation by yielding the prevailing components at the tower locations in the extended mode shape vector. Moreover, it is also confirmed that this mode can be stably identified under all the circumstances with the addition of tower measurements. An important lesson learned from this discovery is that the problem of mode identifiability usually comes from the lack of proper measurements at the right locations.

• Journal of Korean Society for Atmospheric Environment
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• v.34 no.2
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• pp.233-243
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• 2018

This study was carried out to characterize the ambient levels of PAH concentrations in Pohang city, where steel industry has been intensively developed. A large amount of PAH emissions from steel production and related industries in Pohang are concerned about the environmental health hazards of nearby residents. TSP samples were seasonally collected during 10 days at four sites in Pohang from April to December 2010. Each sample was collected for 24 hours using high-volume air sampler. All samples were extracted by $soxtec^{TM}$ before concentration of 1.0 mL. The concentrates were analyzed by GC/MS. The prevailing wind direction was southwest and west-southwest in Pohang during the measurement period. Variations of TSP concentrations appeared to be similar between four sites. The highest TSP concentration was found in fall, while the lowest in summer. The highest PAH concentration was found at an industrial site, while the lowest at a residential/commercial site. In the case of BaP, the average concentration at the industrial site was $0.63{\pm}0.66ng/m^3$, which was approximately 2 times of the residential/commercial site. The paired t-test (p<0.05) showed significant differences between industrial and residential area. Particulate PAH concentrations were higher in the winter and lower in the summer. The concentrations of BaP in winter were 2~10 times higher than those in the other three seasons. This study clearly demonstrated the impact of steel industry on the elevated levels of PAH in Pohang city.

• Proceedings of the Korea Association of Crystal Growth Conference
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• 1998.06a
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• pp.39-43
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• 1998

Single crystals of{{{{ { Zn}_{ 1-x} {Mn }_{x }{Te} }}}} with x=0.3-0.6 were prepared by the standard Bridgeman method. Diffuse neutron diffraction intensities due to the short range magnetic ordering is found in the vicinities of 1 1/2 0 reciprocal point and its equivalent point, indicating that the magnetic correlation of the clusters is the type III antiferromangetic one do the F-type Bravais class crystals, being identical with that of {{{{{ Cd}_{ 1-x} {Mn }_{x }Te }}}}. Neutron inelastic scattering measure-ment has been performed for {{{{{ Zn}_{ 0.6} { Mn}_{ 0.4}Te }}}} sample using the cold neutron spectrometer. AGNES. High resolution measurement with the energy resolution of {{{{ TRIANGLE E= +- .01meV}}}} was carried out in the temperature range from 10K to the ambient. Critical scattering, closely related with the spin glass transition, has been observed for the first time in this semimagnetic semi-conductor. The critical scattering is observed at temperatures in the vicinity of the spin glass transition temperature, 17K. The scattering is observed as a kind of quasielastic scattering in the reciprocal range where the elastic magnetic diffuse scattering has been observed, e.g., 11/20 reciprocal point, indicating the spin fluctuation has dynamic components in this material. Photoconductivity has been discovered below 150K in {{{{{ Zn}_{ 0.4} {Mn }_{0.6 } Te}}}}. The electric AC conductivity has been increased dramatically under the laser light with the wave lengths of {{{{ lambda =6328,5145 and4880 }}}}$\AA$ ,respectively. After the light was darkened, the conductivity was reduced to the original level after about 2000 seconds at 50K, being above the spin glass transition temperature. This phenomenon is the typical persistent photoconductivity; PPC which was similarly found in {{{{ { Zn}_{ 1-x} { Mn}_{x} Te}}}}.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.7 no.3
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• pp.468-473
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• 2003

In this paper, for enhancement of property on a-Si:H TFTs We measure interface characteristics of ferroelectrics thin film and a-Si:H thin film. First, SrTiO$_3$ thin film is deposited bye-beam evaporation. Deposited films are annealed for 1 hour in N2 ambient at $150^{\circ}C∼600^{\circ}C$. Dielectric characteristics of deposited SrTiO$_3$ films are very good because dielectric constant shows 50∼100 and breakdown electric field are 1 ∼ 1.5 MV/cm. a-SiN:H,a-Si:H(n-type a-Si:H) are deposited onto SrTiO$_3$ film to make MFNS(Meta1/ferroelectric/a-SiN:H/a-Si:H) by PECVD. After the C-V measurement for interface characteristics, MFNS structure shows no difference with MNS(Metal/a-SiN:H/a-Si:H) structure in C-V characteristics but the insulator capacitance value of MFNS structure is much higher than the MNS because of high dielectric constant of ferroelectric.

• Journal of the Korean Data and Information Science Society
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• v.27 no.3
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• pp.577-586
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• 2016

Hazardous air pollution caused by heavy metals in the air is at a serious level. Although manganese(Mn), one of the heavy metals, is a non-carcinogenic substance, it has a harmful influence on the human body. It is partially measured because automatic monitoring technologies have not yet be fully established. We introduced a statistical model for the daily concentration of manganese. Incorporating a linkage between Mn and meteorology, the proposed model is formulated in way to identify meteorological effects and to allow for seasonal trends, enabling not only accurate measurement of manganese concentration, but also information about the evaluation on a Hazard Quotient (non-cancer risk).

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2010.06a
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• pp.388-388
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• 2010

In this study, Ferroelectric vinylidene fluoride-trifluoroethylene (VF2-TrFE) copolymer films were directly deposited on degenerated Si (n+, $0.002\;{\Omega}{\cdot}cm$) using by spin coating method. A 1~5 wt% diluted solution of purified vinylidene fluoride-trifluoroethylene (VF2:TrFE = 70:30) in a dimethylformamide (DMF) solvent were prepared and deposited on silicon wafers at a spin rate of 2000 ~ 4000 rpm for 2 ~ 30 seconds. After annealing in a vacuum ambient at 100 ~ $200^{\circ}C$ for 60 min, upper aluminum electrodes were deposited by vacuum evaporation for electrical measurement. X-ray diffraction results showed that the VF2-TrFE films on Si substrates had $\beta$-phase of copolymer structures. The capacitance on highly doped Si wafer showed hysteresis behavior like a butterfly shape and this result indicates clearly that the copolymer films have ferroelectric properties. The typical measured remnant polarization ($P_r$) and coercive filed ($E_c$) values were about $5.7\;{\mu}C/cm^2$ and 710 kV/em, respectively, in an applied electric field of ${\pm}$ 1.5 MV/em. The gate leakage current densities measured at room temperature was less than $7{\times}10^{-7}\; A/cm^2$ under a field of 1 MV/cm.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.21 no.8
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• pp.738-748
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• 2008

In this study, it has been investigated on the changing behavior of electrical properties in $ZnO-Bi_2O_3-Sb_2O_3$ (Sb/Bi=2.0, 1.0 and 0.5) ceramics. The samples were prepared by conventional ceramic process, and then characterized by I-V, C-V curve plots, impedance and modulus spectroscopy (IS & MS) measurement. The electrical properties of ZBS systems were strongly dependent on Sb/Bi. In ZBS systems, the varistor characteristics were deteriorated noticeably with increasing Sb/Bi and the donor density and interface state density were increased with increasing Sb/Bi. On the other hand, we observed that the grain boundary reacted actively with the ambient oxygen according to Sb/Bi ratio. Especially the grain boundaries of Sb/Bi=0.5 systems were divided into two types, i.e. sensitive to oxygen and thus electrically active one and electrically inactive intergranular one with temperature. Besides, the increased pyrochlore and $\beta$-spinel phase with Sb/Bi ratio caused the distributional inhomogeneity in the grain boundary barrier height and the temperature instability. To the contrary, the grain boundary layer was relatively homogeneous and more stable to temperature change and kept the system highly nonlinear at high Bi-rich phase contents.