• Journal of the Computational Structural Engineering Institute of Korea
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• v.30 no.6
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• pp.541-547
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• 2017

Climate change has become the main cause of the exacerbation in natural disasters. Social Overhead Capital(SOC) structure needs to be checked for displacement and crack periodically to prevent damage and the collapse caused by natural disaster and ensure the safety. For efficient structure maintenance, the optical image technology is applied to the Structure Health Monitoring(SHM). However, optical image is sensitive to environmental factors. So it is necessary to verify its validity. In this paper, the accuracy of estimating the vertical displacement was verified with respect to environmental condition such as natural light, measurement distance, and the number of image sheets. The result of experiments showed that the effect of natural light on accuracy of estimating vertical displacement was the greatest of all. The measurement angle which was affected by the change in measurement distance was also important to check the vertical displacement. These findings will be taken into account by applying appropriate environmental condition to minimize errors when the bridge was measured by camera. It will also enable the application of optical images to the SHM.

• The Journal of Engineering Geology
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• v.6 no.3
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• pp.137-153
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• 1996

The purpose of this study is to investigate the possibilities of identifying and detecting underground cavities using seismic waves recorded by the fixed and mobile stations. During 18 months of field work we recorded chemical explosions near the Bongdarn station. Seismic Stations were installed on the free surface and underground inside the Samba mine. The seismograms at the fixed(lorg-term) seismic station show abrupt change of polarization characteristics which can he associated with the appearance of P-to-S converted phase(PS) at 150 ~ 200 msec after the first P arrival. This result indicates that converted phases are generated very near to the Bongdarn station at a depth of 190m. Shear-wave splitting phenomena have also been observeci The time delay between fast shear(fS) and slow shear(sS) waves ranges between 30 and 60 msec(average is 42 msec). However, exact time delay between the fast and the slow shear waves can not be accurately measured because of the very short time delay and limitation of sampling rate. Chemical explosion experiments were recorded at stations along various paths to contrast the seismic response of areas with and without cavities. The seismograms recorded at the stations installed at cavity areas show an abrupt change of polarization characteristics but not on the other stations. Seismic waves propagating through the cavity are characterized by the attenuation of high frequency waves and predominantly low frequency seismic waves after the S wave arrivals.

• Journal of the Korean institute of surface engineering
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• v.50 no.5
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• pp.411-420
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• 2017

In this paper, two methods of making the Pd-added $SnO_2$ ($Pd-SnO_2$) powder with pure tetragonal phase by the hydrazine method were suggested and compared in terms of crystal structure, surface morphology, and alcohol gas response. One of the addition methods is to use $PdCl_2$ as a Pd source, the other is to use Pd-based organic with oleylamine (OAM). When Pd concentration was increased from 0 to 5 wt%, the average grain size of $Pd-SnO_2$ made with Pd-OAM were decreased from 32 to 12 nm. In the case of using with $PdCl_2$, grain size of the $PdCl_2$ fell to less than 10 nm. However, agglomerated and extruded surface morphology was observed for the films with Pd addition over 4 wt%. The crack-free $Pd-SnO_2$ thick films were able to successfully fill the $30{\mu}m$ gap of patterned Pt electrodes by optimized ink dropping method. Also, the 2 wt% $Pd-SnO_2$ thick film made with PdCl2 showed gas responses ($R_{air}/R_{gas}$) of 3.7, 5.7 and 9.0 at alcohol concentrations of 10, 50 and 100 ppm, respectively. On the other hand, the prepared 3 wt% $Pd-SnO_2$ thick film with Pd-OAM exhibited very excellent responses of 3.4, 6.8 and 12.2 at the equivalent measurement conditions, respectively. The 3 wt% $Pd-SnO_2$ thick film with Pd-OAM has a specific surface area of $31.39m^2/g$.

• Journal of the Korean Recycled Construction Resources Institute
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• v.7 no.3
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• pp.243-254
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• 2019

In this study, problems of the waterproofing methods in which water leakage occurs in the upper slab of the underground parking lot of apartment houses and the requirements considering the characteristics of the upper slab, and selected the appropriate performance(proposal) for the composite polyurea process are reviewed. As a result of the study, it is necessary to review performance such as responsiveness to upper slab of the multi-unit underground parking lot that is comprised of (1) crack and behavior responsiveness, (2) surface integrity, (3) vertical watertight stability, (4) pressure layer construction, (5) impact and pressure response and (6) vehicle moving load. As a result of evaluating 5 items corresponding to the requirements for the soft and hard complex polyurea, all of them were found to meet the conditions, and each materials were improved by compounding the materials that had problems when applying a single-ply method, thereby clarifying the advantages and disadvantages of the material property. However, in order to apply to the actual site, additional evaluation on site applicability such as mock-up evaluation should be conducted, and subsequent studies on the applicability of the market through review of economic feasibility and maintenance is required.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.4
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• pp.503-509
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• 2019

The demand for smaller, faster, and multi-functional mobile devices in increasing at a rapidly increasing rate. In response to these trends, Stacked Chip Scale Package (SCSP) is used widely in the assembly industry. A film type adhesive called die attach film (DAF) is used widely for bonding chips in SCSP. The DAF requires high flowability at high die attachment temperatures for bonding chips on organic substrates, where the DAF needs to feel the gap depth, or for bonding the same sized dies, where the DAF needs to penetrate bonding wires. In this study, the mixture design of experiment (DOE) was performed for three raw materials to obtain the optimized DAF recipe for low elastic modulus at high temperature. Three components are acrylic polymer (SG-P3) and two solid epoxy resins (YD011 and YDCN500-1P) with different softening points. According to the DOE results, the elastic modulus at high temperature was influenced greatly by SG-P3. The elastic modulus at $100^{\circ}C$ decreased from 1.0 MPa to 0.2 MPa as the amount of SG-P3 was decreased by 20%. In contrast, the elastic modulus at room temperature was dominated by YD011, an epoxy with a higher softening point. The optimized DAF recipe showed approximately 98.4% pickup performance when a UV dicing tape was used. A DAF crack that occurred in curing was effectively suppressed through optimization of the cure accelerator amount and two-step cure schedule. The imizadole type accelerator showed better performance than the amine type accelerator.

• Geophysics and Geophysical Exploration
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• v.9 no.1
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• pp.60-66
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• 2006

Three differing sandstones, two synthetic and one field sample, have been tested ultrasonically under a range of confining pressures and pore pressures representative of in-situ reservoir pressures. These sandstones include: a synthetic sandstone with calcite intergranular cement produced using the CSIRO Calcite In-situ Precipitation Process (CIPS); a synthetic sandstone with silica intergranular cement; and a core sample from the Otway Basin Waarre Formation, Boggy Creek 1 well, from the target lithology for a trial $CO_2$ pilot project. Initial testing was carried on the cores at "room-dried" conditions, with confining pressures up to 65 MPa in steps of 5 MPa. All cores were then flooded with $CO_2$, initially in the gas phase at 6 MPa, $22^{\circ}C$, then with liquid-phase $CO_2$ at a temperature of $22^{\circ}C$ and pressures from 7 MPa to 17 MPa in steps of 5 MPa. Confining pressures varied from 10 MPa to 65 MPa. Ultrasonic waveforms for both P- and S-waves were recorded at each effective pressure increment. Velocity versus effective pressure responses were calculated from the experimental data for both P- and S-waves. Attenuations $(1/Q_p)$ were calculated from the waveform data using spectral ratio methods. Theoretical calculations of velocity as a function of effective pressure for each sandstone were made using the $CO_2$ pressure-density and $CO_2$ bulk modulus-pressure phase diagrams and Gassmann effective medium theory. Flooding the cores with gaseous phase $CO_2$ produced negligible change in velocity-effective stress relationships compared to the dry state (air saturated). Flooding with liquid-phase $CO_2$ at various pore pressures lowered velocities by approximately 8% on average compared to the air-saturated state. Attenuations increased with liquid-phase $CO_2$ flooding compared to the air-saturated case. Experimental data agreed with the Gassmann calculations at high effective pressures. The "critical" effective pressure, at which agreement with theory occurred, varied with sandstone type. Discrepancies are thought to be due to differing micro-crack populations in the microstructure of each sandstone type. The agreement with theory at high effective pressures is significant and gives some confidence in predicting seismic behaviour under field conditions when $CO_2$ is injected.