• The Bulletin of The Korean Astronomical Society
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• v.43 no.2
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• pp.44.4-45
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• 2018

(4179) Toutatis (Toutatis hereafter) is one of the Near-Earth Asteroids which has been studied most rigorously not only via ground-based photometric, spectroscopic, polarimetric, and radar observations, but also via the in-situ observation by the Chinese Chang'e-2 spacecraft. However, one of the most fundamental physical properties, the geometric albedo, is less determined. In order to derive the reliable geometric albedo and further study the physical condition on the surface, we made photometric observations of Toutatis near the opposition (i.e., the opposite direction from the Sun). We thus observed it for four days on 2018 April 7-13 using three 1.6-m telescopes, which consist of the Korean Microlensing Telescope Network (KMTNet). Since the asteroid has a long rotational period (5.38 and 7.40 days from Chang'e-2, Zhao et al., 2015), the continuous observations with KMTNet matches the purpose of our photometric study of the asteroid. The observed data cover the phase angle (Sun-asteroid-observer's angle) of 0.65-2.79 degree. As a result, we found that the observed data exhibited the magnitude changes with an amplitude of ~0.8 mag. We calculated the time-variable geometrical cross-section using the radar shape model (Hudson & Ostro 1995), and corrected the effect from the observed data to derive the geometric albedo. In this presentation, we will present our photometric results. In addition, we will discuss about the regolith particles size together with the polarimetric properties based on the laboratory measurements of albedo-polarization maximum.

• The Journal of Engineering Geology
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• v.30 no.1
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• pp.17-30
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• 2020

An optical televiewer is a geophysical logging device that produces continuous high-resolution full-azimuth images of a borehole wall using a light-emitting-diode and a complementary metal-oxide semiconductor image sensor to provide valuable information on subsurface discontinuities. Recently, borehole imaging logging has been applied in many fields, including ground subsidence monitoring, rock mass integrity evaluation, stress-induced fracture detection, and glacial annual-layer measurements in polar regions. Widely used commercial borehole imaging logging systems typically have limitations depending on equipment specifications, meaning that it is necessary to clearly verify the scope of applications while maintaining appropriate quality control for various borehole conditions. However, it is difficult to directly check the accuracy, implementation, and reliability for outcomes, as images derived from an optical televiewer constitute in situ data. In this study, we designed and constructed a modular fractured borehole model having similar conditions to a borehole environment to report unprecedented results regarding reliable data acquisition and processing. We investigate sonde magnetometer accuracy, color realization, and fracture resolution, and suggest data processing methods to obtain accurate aperture measurements. The experiment involving the fractured borehole model should enhance not only measurement quality but also interpretations of high-resolution and reliable optical imaging logs.

• Geotechnical Engineering
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• v.12 no.5
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• pp.79-88
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• 1996

In this study, prediction of soil behavior under vacuum preloading with vertical drain is explored on the basis of numerical models and toe results were compared with field measurements. Reasonable prediction of the time rate of settlements and pore pressure dissipation under vacuum preloading is the maj or concern. The conventional method for vatsuum preloading is based on modeling vacuum preloading as surcharge loading for the consolidation analysis. However, this modeling may violate the real behavior of soils under vacuum loading since the total stress in the analysis varies due to the modeled surcharge loading whereas in'.situ total stress of soils under vacuum loading is constant. In this study a new method is suggested. Instead of modeling vacuum loading as surcharge loading, negative hydraulic head is applied at the surface drain boundary to simulate the vacuum preloading. Comparisons of predictions and field measurements of soil behavior under vatsuum preloading are presented and the usefulness of the new modeling technique is demonstrated.

• Korean Journal of Remote Sensing
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• v.23 no.4
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• pp.323-334
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• 2007

We analyzed the ocean environmental data from water sample and automatic measurement instruments with the Incheon-Jeju passenger ship for 18 times during 4 years from 2001 to 2004. The objectives of this study are to monitor the spatial and temporal variations of ocean environmental parameters in coastal waters of the Yellow Sea using water sample analysis, and to compare and analyze the reliability of automatic measurement sensors for chlorophyll and turbidity using in situ measurements. The chlorophyll concentration showed the ranges between 0.1 to $6.0mg/m^3$. High concentrations occurred in the Gyeonggi Bay through all the cruises. The maximum value of chlorophyll concentration was $16.5mg/m^3$ in this area during September 2004. The absorption coefficients of dissolve organic matter at 400 nm showed below $0.5m^{-1}$ except those in August 2001 During 2002-2003, it did not distinctly change the seasonal variations with the ranges 0.1 to $0.4m^{-1}$. In the case of suspended sediment (SS) concentration, most of the area showed below $20g/m^3$ through all seasons except the Gyeonggi Bay and around Mokpo area. In general SS concentration of autumn and winter season was higher than that of summer. The central area of the Yellow Sea appeared to have lower value $10g/m^3$. The YSI fluorometer for chlorophyll concentration had a very low reliability and turbidity sensor had a $R^2$ value of 0.77 through the 4 times measurements comparing with water sampling method. For the automatic measurement using instruments for chlorphlyll and suspended sediment concentration, McVan and Choses sensor was greater than YSI multisensor. The SeaWiFS SS distribution map was well spatially matched with in situ measurement, however, there was a little difference in quantitative concentration.

• Earthquakes and Structures
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• v.19 no.1
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• pp.29-44
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• 2020

The effectiveness and the sensitivity of a Wireless impedance/Admittance Monitoring System (WiAMS) for the prompt damage diagnosis of two single-storey single-span Reinforced Concrete (RC) frames under cyclic loading is experimentally investigated. The geometrical and the reinforcement characteristics of the RC structural members of the frames represent typical old RC frame structure without consideration of seismic design criteria. The columns of the frames are vulnerable to shear failure under lateral load due to their low height-to-depth ratio and insufficient transverse reinforcement. The proposed Structural Health Monitoring (SHM) system comprises of specially manufactured autonomous portable devices that acquire the in-situ voltage frequency responses of a network of twenty piezoelectric transducers mounted to the RC frames. Measurements of external and internal small-sized piezoelectric patches are utilized for damage localization and assessment at various and increased damage levels as the magnitude of the imposed lateral cycle deformations increases. A bare RC frame and a strengthened one using a pair of steel crossed tension-ties (X-bracing) have been tested in order to check the sensitivity of the developed WiAMS in different structural conditions since crack propagation, damage locations and failure mode of the examined frames vary. Indeed, the imposed loading caused brittle shear failure to the column of the bare frame and the formation of plastic hinges at the beam ends of the X-braced frame. Test results highlighted the ability of the proposed SHM to identify incipient damages due to concrete cracking and steel yielding since promising early indication of the forthcoming critical failures before any visible sign has been obtained.

• The Journal of Engineering Geology
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• v.22 no.1
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• pp.49-58
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• 2012

Anchor heads a recommonly exposed to surface weathering processes that cause physical damage by vibration and external forces. This study presents a new method of anchor-head installation that uses near-surface embedding based on analyses of concrete block failure. ABAQUS 3D numerical modeling performed to compare this method with the standard technique and to analyze the distribution of displacement and the stress pattern. In addition, application of the method to a real-world case was tested by in-situ measurements. The results show a maximum vertical stress of 9.73 MPa and vertical displacement of 1.34 mm. Field tests indicated that displacement of a concrete block was 3 to 4 times greater than that of an embedded bearing plate.

• Journal of the Mineralogical Society of Korea
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• v.15 no.3
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• pp.161-169
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• 2002

high pressure and temperature conditions. However, those results are not consistent with one another, and phase boundary between ilmenite and perovskite phases determined only from the quenching method may be not so reliable at all. Therefore, in-situ high pressure-temperature (hP-T) X-ray diffraction measurements were performed up to 19 GPa and $700^{\circ}C$ in a large volume press apparatus using synchrotron radiation. Experimental results show that perovskite phase is stable at pressures above 16 GPa, and transforms back to $LiNbO_3$phase near 15 CPa at room temperature, and that the perovskite-ilmenite transition is back and forth near 15 CPa at $500^{\circ}C$. LiNbO$_3$phase transforms to ilmenite at 13 CPa and $300^{\circ}C$ and at 10.8 CPa and $400^{\circ}C$, respectively. These data indicate that $LiNbO_3$phase may have a stability region in the hP-T phase diagram and that the perovskite-ilmenite phase boundary would be quite different from that previously reported.

• The Journal of the Korea institute of electronic communication sciences
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• v.10 no.5
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• pp.629-636
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• 2015

This study carried out in order to investigate the most basic elements of suitability selection methods for composition of artificial reef. Acquired data by in-situ measurements and satellite remote sensing analysed in applying GIS. To identify the characteristic of marine environment around the West Sea, the South Sea and the East Sea of Korea, physical conditions-seabed sediment and depth, biological conditions-chlorophyll-${\alpha}$, chemical conditions-Sea Surface Temperature(SST) and DO were used. Suitable sites for artificial reef are selected Taean Peninsula, Geoje, Wando, Pohang, Seocheon, etc. From now on, it will be helpful to effectively utilize artificial reef as well as construct synthetic database. It is also expected to use basic data for artificial reef facilities management.

• Journal of Korean Society on Water Environment
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• v.23 no.5
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• pp.636-641
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• 2007

A pilot-scale biofilm nitiritation reactor was operated with the reject water from a large wastewater treatment plant. The effects of various operating parameters including pH, temperature, dissolved oxygen, solids and organic concentrations were examined. A stable nitritation was achieved at operating pH range of 7.3 to 8.8 with an alkalinity addition. Higher operating temperature of $35{\pm}0.7^{\circ}C$ achieved more stable nitritation compared to $30{\pm}0.2^{\circ}C$. It has been noticed that nitrite accumulation maintained with DO, solids and organic concentrations range of 0.8 to 3.9 mg/L, 3,400 to 11,000 mg/L, and 86 to 572 mg/L, respectively. It seems that the accumulation of nitrite was caused by both the inhibition of $NO_2{^-}$ oxidizers due to free ammonia and the maintenance of the high operating temperature of $35^{\circ}C$ which promote to accumulate the $NH_4{^+}$ oxidizers in the reactor. According to microbial community analysis of fluorescence in situ hybridization and INT-Dehydrogenase measurements, more nitrifiers were presented in attached form compared to suspended growth.

• The Journal of the Acoustical Society of Korea
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• v.25 no.3E
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• pp.101-109
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• 2006

Besides dorsal-aspect target strength (TS) of the fish, side-aspect TS information is also acoustically important parameter in fisheries acoustics. In this study, the side-aspect TS of 11 black sea bream (Acanthopagurus schlegeli) were measured using a split beam echosounder of 120, 200, and 420 kHz; total length of the fish ranged from 12.4 to 23.7 cm, and wet weight from 27.5 to 229.8g. For the precise TS measurement with side-aspect angle, we used anesthetized and tethered specimens of known size while being rotated through $360^{\circ}C$ by means of a carousel structure. The side-aspect TS measurements of the fish were conducted by rotating the fish in the horizontal plane at 50 interval. The ping interval was 0.2 second and elapsed time at each angle was 30-60 second. As a result, the measured side-aspect TS data were fitted by sinusoidal function. The relationships between fish length and near full side-aspect TS were as follows: $TS_{120kHz}= 21.46 log (TL)-67.5 (r = 0.70), \;TS_{200 kHz}= 31.03 log (TL)-76.9 (r=0.83),\;TS_{420 kHz}= 30.79 log (TL)-72.2 (r = 0.77)$. For comparison, theoretically estimated side-aspect TS from the Kirchhoff ray mode (KRM) model, which based on swimbladder and body morphology, were compared with the measured TS.