• Geophysics and Geophysical Exploration
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• v.11 no.3
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• pp.177-183
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• 2008

The sub-salt imaging technique becomes more crucial to detect the hydro-carbonates in petroleum exploration as the target reservoirs get deeper. However, the weak reflections from the sub-salt structures prevent us from obtaining high fidelity sub-salt image. As an effort to overcome this difficulty, we applied the waveform inversion by implementing multi-grid technique to the sub-salt imaging. Through the comparison between the conventional waveform inversion using fixed grid and the multi-grid technique, we confirmed that the waveform inversion using multi-grid technique has advantages over the conventional fixed grid waveform inversion. We showed that the multi-grid technique can complement he velocity estimation result of the waveform inversion for imaging the sub-salt structures, of which velocity model cannot be obtained correctly by the conventional fixed grid waveform inversion.

• Journal of the Korean Ceramic Society
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• v.35 no.4
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• pp.347-354
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• 1998

Densification and grain growth behaviors of ITO ceramics were investigated as a function of TiO2 ad-ditions. TiO2 addition led to inhibition of the grain growth and promotion of the densification of ITO ceram-ics. From the microstructure observation it was found that the crack-like voids which were formed in pure ITO specimens decreased with increase of TiO2 additon. The grain growth exponent(n) was measur-ed to be 4 for pure ITO 3 for TiO2-doped ITO specimens respectively. It was supposed that the grain boun-dary migration of pure ITO ceramics was controlled by the pores which were moved by surface diffusion. On the contrary the grain boundary migration of TiO2-doped ITO specimens was depressed by solute drag effect. The activation energies for grain growth were measured to be 1013 kJ/mol for pure ITO ceramics and 460kJ/mol for TiO2-doped ITO specimens respectively.

• Bulletin of the Korean Chemical Society
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• v.21 no.5
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• pp.477-482
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• 2000

Phenyl group migration within protonated 1,2-diphenyl hydrazines has been studied theoretically using the semi-empirical AM1 method. This reaction proceeds through a 3-membered cyclic transition state and requires high activation energy. In the reactant, there was no resonance stabilization for the moving Z-ring, however, hammett $p_Z^+$ values are large due to the direct involvement of the Z-ring inthe reaction, and the development of a negative charge on the reaction center gives them a posifive value. In the case of the non-moving ring, $p_Y^+$ values are small and negative owing to the smaller positive charge increase in the reaction center. The cross-interaction constant, $p_YZ^+$, was obtained from the activation enthalpies, using the multipe linear regression methdo, and the interaction between two substituents, Y and Z, is examined.

• Journal of the Korea Society of Computer and Information
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• v.22 no.7
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• pp.101-108
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• 2017

A wireless image sensor node collecting image data for environmental monitoring or surveillance requires a large amount of energy to transmit the huge amount of video data. Even though solar energy can be used to overcome the energy constraint, since the collected energy is also limited, an efficient energy management scheme for transmitting a large amount of video data is needed. In this paper, we propose a method to reduce the number of blackout nodes and increase the amount of gathered data by selecting an appropriate video coding method according to the energy condition of the node in a solar-powered wireless video sensor network. This scheme allocates the amount of energy that can be used over time in order to seamlessly collect data regardless of night or day, and selects a high compression coding method when the allocated energy is large and a low compression coding when the quota is low. Thereby, it reduces the blackout of the relay node and increases the amount of data obtained at the sink node by allowing the data to be transmitted continuously. Also, if the energy is lower than operating normaly, the frame rate is adjusted to prevent the energy exhaustion of nodes. Simulation results show that the proposed scheme suppresses the energy exhaustion of the relay node and collects more data than other schemes.

• Geophysics and Geophysical Exploration
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• v.24 no.3
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• pp.78-88
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• 2021

Owing to the abnormal weather conditions due to global warming, carbon capture and storage (CCS) technology has attracted global attention as a countermeasure to reduce CO₂ emissions. In the Pohang CCS demonstration project in South Korea, 100 tons of CO₂ were successfully injected into the subsurface CO₂ storage in early 2017. However, after the 2017 Pohang earthquake, the Pohang CCS demonstration project was suspended due to an increase in social concerns about the safety of the CCS project. In this study, to reconfirm the structural suitability of the CO₂ storage site in the Pohang Basin, we employed seismic imaging based on reverse-time migration (RTM) to analyze small-scale ocean-bottom seismic data, which have not been utilized in previous studies. Compared with seismic images using marine streamer data, the continuity of subsurface layers in the RTM image using the ocean-bottom seismic data is improved. Based on the obtained subsurface image, we discuss the structural suitability of the Pohang CO₂ storage site.

• Korean Journal of Environmental Agriculture
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• v.33 no.4
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• pp.334-343
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• 2014

BACKGROUND: Shorebirds use a variety of wetlands as their stopover sites to replenish energy and nutrient reserves along the migration route. It is increasingly important to understand how birds use the remaining available habitats during migration period, because shorebird stopover sites are often altered and destroyed. Rice fields serve as a major inland stopover site for migrating shorebirds. However, the information on habitat use patterns of shorebirds in rice fields is very limited in Korea. Therefore, we studied the patterns of shorebird abundance and their habitat use in rice fields during spring migration period in western-central Korea. METHODS AND RESULTS: Surveys were conducted at interval of 2-3 days during the spring migration period of 2014 at rice fields of mid-western Korea. We recorded the location of the observed birds on the rice field map according to the local habitat type. The habitat types were divided by physical structure and cultivation methods. Fifteen shorebird species and 7,852 individuals were recorded during the survey period. The number of shorebird species and their abundance began to increase from the beginning of flooding in late-April, and reached a maximum in early-May. After rice transplantation, the number of shorebird species and their abundance dramatically declined. Shorebirds selectively used paddy and levee rather than road and ditch and most species used shallow depth field type. Plowed field types were less attractive to most species. CONCLUSION: Flooding rice fields were functioned as stopover sites for a variety of shorebird species during spring migration period. Furthermore, these results provide that the appropriate agricultural practices can be improving the habitat quality for shorebirds.

• Geophysics and Geophysical Exploration
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• v.26 no.1
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• pp.8-17
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• 2023

Various sources, such as wind, waves, ships, and gas leaks from the seafloor, forms bubbles in the ocean. Underwater bubbles cause signal scattering, considerably affecting acoustic measurements. This characteristic of bubbles is used to block underwater noise by attenuating the intensity of the propagated signal. Recently, researchers have been studying the large-scale release of methane gas as bubble plumes from the seabed. Understanding the physical properties and distribution of bubble plumes is crucial for studying the relation between leaked methane gas and climate change. Therefore, a water tank experiment was conducted to estimate the distribution of bubble plumes using seismic imaging techniques and acoustic signals obtained from artificially generated bubbles using a bubble generator. Reverse time migration was applied to image the bubble plumes while the acquired acoustic envelope signal was used to effectively estimate bubble distribution. Imaging results were compared with optical camera images to verify the estimated bubble distribution. The water tank experiment confirmed that the proposed system could successfully image the distribution of bubble plumes using reverse time migration and the envelope signal. The experiment showed that the scattering signal of artificial bubble plumes can be used for seismic imaging.

• Nuclear Engineering and Technology
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• v.22 no.1
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• pp.36-44
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• 1990

A safety assessment computer code CALM (Computer program of Assessment for LILW Management) is developed for the theoretical prediction of long-term safety of low-and intermediate-level radioactive waste disposal. CALM is composed of three submodels, which are the resaturation model, the geosphere migration model, and the radiation dose model. For the verification of its usefulness, the safety assessment of an assumed waste repository is performed. The results show that the computer code, CALM developed through this study can be a useful tool for the safety assessment of low- and intermediate-level radioactive waste repository.

• Journal of Internet Computing and Services
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• v.14 no.5
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• pp.39-48
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• 2013

A cloud system has to deal with highly variable workloads resulting from dynamic usage patterns in order to keep the QoS within the predefined SLA. Aside from the aspects regarding services, another emerging concern is to keep the energy consumption at a minimum. This requires the cloud providers to consider energy and performance trade-off when allocating virtualized resources in cloud data centers. In this paper, we propose a resource provisioning approach based on dynamic thresholds to detect the workload level of the host machines. The VM selection policy uses utilization data to choose a VM for migration, while the VM allocation policy designates VMs to a host based on its service reputation. We evaluated our work through simulations and results show that our work outperforms non-power aware methods that don't support migration as well as those based on static thresholds and random selection policy.

• Proceedings of the IEEK Conference
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• 1998.06a
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• pp.335-338
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• 1998

We have calculated ultra-low energy silicon-self ion implantations and silicon damages through classical molecular dynamics simulation using empirical potentials. We tested whether the recently developed environment-dependent interatomic ptential (EDIP) was suitable for ultra low ion implantation simulation, and found that point defects formation energies were in good agrrement with other theoretical calculations, but the calculated vacancy migration energy was overestimated. The number of isolated defects that are produced by collision cascades are onlya few of the total number of defects, and fmost of the damages are concentrated into amorphous-like pockets.