• The Bulletin of The Korean Astronomical Society
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• v.42 no.2
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• pp.44.3-45
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• 2017

To date, luminous quasars at z ~ 6 have been found to be in maximal accretion with the Eddington ratios, ${\lambda}Edd$ ~ 1, suggesting enhanced nuclear activities in the early universe. However, this may not be the whole picture of supermassive black hole (SMBH) growth since previous studies have not reached on faint quasars that are more likely to harbor SMBHs with low ${\lambda}Edd$. To understand the accretion activities in quasars at high redshift, we obtained the deep near-infrared (NIR) spectrum of a quasar, IMS J2204+0112, one of the few faintest quasars that have been identified at z ~ 6. From the NIR spectrum, we find that IMS J2204+0112 harbors a SMBH with about a billion solar mass, with ${\log}({\lambda}Edd)=-0.91$. This is the lowest accretion rate found so far for quasars at z ~ 6, but a common value among quasars at z ~ 2. The inclusion of this object in the ${\lambda}Edd$ analysis gives the intrinsic ${\lambda}Edd$ distribution of z ~ 6 quasars, which is lower than previous results that are based on bright quasars, but it is still higher than ${\lambda}Edd$ of z ~ 2 quasars. Although the number statistics needs to be improved in future, the low peak ${\lambda}Edd$ value is consistent with the SMBH growth from a massive black hole seed (~ 105 Msun) or from a stellar mass black hole through short-duration super-Eddington accretion events (${\lambda}Edd$ > 10).

• Journal of Ocean Engineering and Technology
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• v.9 no.2
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• pp.167-174
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• 1995

The anomlous signal, anomaly, recorded by a sub-bottem profiler is analized for exploration of buried objects in the ocean, This anomaly is known as a signal diffracted from the edge of the buried object. Signals obtained from model that and numerical simulation are analized for investigating characteristics of the diffracted signal. From this study a diffracted signal and a non-diffracted signal can be identified, and the location of the object can be obtained. In order to identify an object in the seafloor the dimension of the object should be greater than the wave length used for exploration, and the acoustic impedance should be much greater than that of sediments. A 2-trace stacking of the signals can enhance the feature of strongly diffracted signals whereas it can diminish weak signals.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• v.1
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• pp.265-270
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• 2006

Recently, inertial sensors like gyros and accelerometers have been quite miniaturized by Micro Electro-Mechanical Systems (MEMS) technology. JAXA is developing a MEM-based GPS/INS hybrid navigation system named Micro-GAIA. The navigation performance of Micro-GAIA was evaluated through off-line analysis by using flight test data. The estimation errors of the roll, pitch, and azimuth were $0.03^{\circ}$, $0.05^{\circ}$, $0.05^{\circ}$ $(1{\sigma})$, respectively. he horizontal position errors after 60-second GPS outages were reduced to 25 m CEP. The attitude errors and position errors are nearly half of ones reported previously[2]. Furthermore, using the adaptive Kalman filters, the robustness against the uncertainty of the measurement noise was improved. Comparing the innovation-based and residual-based adaptive Kalman filters, it was confirmed that the latter is robuster than the former.

• Geophysics and Geophysical Exploration
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• v.17 no.4
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• pp.242-246
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• 2014

Spectral induced polarization (SIP) is a useful technique, which uses electrochemical properties, for exploration of metallic sulfide minerals. Equivalent circuit analysis is commonly conducted to calculate IP parameters from SIP data. An equivalent circuit model, which indicates the SIP response of rock, has a non-uniqueness problem. For this reason, it is very important to select the proper model for accurate analysis. Thus, this study focused on suggesting a new model, which suitable for the analysis of an anomalous SIP response, such as ore. A suitability of the new model was verified by comparing it with the existing Dias model and Cole-Cole models. Analysis errors were represented as a normalized root mean square error (NRMSE). The analysis result using the Dias model was the NRMSE of 10.50% and was the NRMSE using the Cole-Cole model of 17.03%. Howerver, because the NRMSE of the new model is 0.87%, it is considered that the new model is more useful for analyzing the anomalous SIP data than other models.

• Journal of Space Technology and Applications
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• v.3 no.3
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• pp.199-212
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• 2023

In contrast to the short-term nature of lunar missions in the past, lunar missions in new space era aim to extend the presence on the lunar surface and to use this capability for the Mars exploration. In order to realize extended human presence on the Moon, production and use of consumables and fuels required for the habitation and transportation using in-situ resources is an important prerequisite. The Global Exploration Roadmap presented by the International Space Exploration Coordination Group (ISECG), which reflects the space exploration plans of participating countries, shows the phases of progress from lunar surface exploration to Mars exploration and relates in-situ resource utilization (ISRU) capabilities to each phase. Based on the ISRU Gap Assessment Report from the ISECG, ISRU technology is categorized into in-situ propellant and consumable production, in-situ construction, in-space manufacturing, and related areas such as storage and utilization of products, power systems required for resource utilization. Among the lunar resources, leading countries have prioritized the utilization of ice water existing in the permanent shadow region near the lunar poles and the extraction of oxygen from the regolith, and are preparing to investigate the distribution of resources and ice water near the lunar south pole through unmanned landing missions. Resource utilization technologies such as producing hydrogen and oxygen from water by hydroelectrolysis and extracting oxygen from the lunar regolith are being developed and tested in relevant lunar surface analogue environments. It is also observed that each government emphasizes the use and development of the private sector capabilities for sustainable lunar surface exploration by purchasing lunar landing services and providing opportunities to participate in resource exploration and material extraction.

• Knowledge Management Research
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• v.21 no.4
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• pp.287-300
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• 2020

We investigate empirically the impact of IT exploration & exploitation capability and operational capability upon organizational agility, especially small and medium sized firms in the logistics industry in South Korea. Based on literature on the bilateral relationship between organizational agility and IT capability, we follow the established research model and propose hypotheses. This work takes an empirical methodology to test the hypotheses: design survey questionnaires, collect data, test reliability and validity of data, and finally test the hypotheses. Our results based on the data collected in 2018 present that IT exploration & exploitation capability significantly increases operational capability, and operational capability increases organizational agility. We find our contribution in updating previous research findings with recent data and in expanding the domain of research more specifically into small and medium sized firms in logistics industry in South Korea. Practically our work suggests that managers and policy makers should consider both fostering newly emerging IT exploration and existing IT resource exploitation capability in order to enhance organizational agility of those small and medium sized firms in logistics industry.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.39 no.1
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• pp.63-68
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• 2011

Many countries all over the world have been doing lunar exploration projects. Korea has also been doing basic research on lunar exploration. The development of communication systems for lunar exploration projects is one of the most important aspects of performing a successful lunar mission. In this paper, we design a DSP (Digital Signal Processor) prototype based on the requirement analysis of a communication link for lunar exploration and implement its core module considering the international standards for deep space communications to perform a basic research on baseband processor development. It is verified by comparing the bit error rate of the DSP prototype with that of a computer simulation.

• Korean Management Science Review
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• v.28 no.1
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• pp.91-105
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• 2011

Among various types of creativity, team creativity has been always receiving attention from both practitioners and researchers because most of works are done in a team format in organizations. Therefore, it would be the best way for corporate performance to increase when team creativity is managed carefully to increase in a steadfast way. Though there are lots of ways to grow team creativity, this study explores the issue of increasing the team creativity by adopting CMC (computer-mediated communication) and exploration and exploitation, which were studied separately, but never analyzed together in the same research framework. Experiments to prove the validity of the research questions are based on ABM (Agent-Based Modeling) simulation. Netlogo language was adopted to build a prototype engine for the simulation engine. Experiment results revealed that in the short-term, both broad CMC mode with high exploration and exploitation, and local CMC mode with high exploration and exploitation result in higher team creativity than other types of combination. However, in the long run, broad CMC mode yields higher team creativity level than local CMC mode.

• The Bulletin of The Korean Astronomical Society
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• v.43 no.1
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• pp.68.2-68.2
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• 2018

Spectroscopic observations commonly use a slit or fiber; however, non-slit spectroscopy enables us to observe a larger number of targets in one frame of image. Hence, it has been adopted as an observational mode for observatories like HST and JWST. Slitless spectroscopy requires wavelength calibration solutions in order to distinguish and measure the absorption / emission lines from the spectra with high accuracy. We installed the Volume Phase Holographic (VPH) grating to SQUEAN camera on the McDonald 2.1m telescope and obtained images with spectral resolutions of ~ 100 and 200. In order to derive the wavelength calibration, we measured the distances between the 0th order images and spectral features of various quasars. The distances are converted to wavelengths using the known wavelengths of the emission lines. We tested several different methods of spectral extraction and peak estimation of emission lines. We will present the results for the wavelength calibration and suggest the reliable methods to find the solution.

• Journal of Aerospace System Engineering
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• v.9 no.4
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• pp.16-22
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• 2015

Korea Aerospace Research Institute(here after KARI) has a plan to launch experimental lunar orbiter in 2018, and lunar orbiter and lander in 2020. There are several ways to go to the moon. Which one is direct transfer trajectory and another one is phasing loop transfer trajectory and the other one is WSB trajectory. Regardless of the transfer trajectories, LOI maneuver is the most important maneuver of all mission sequences because if this burn is failed, it is too difficult to get into the lunar orbit in the future. This paper describes first LOI target value of foreign lunar orbiters and analyzes orbital variations of experimental lunar orbiter according to various target values. By analyzing the variation of orbiter parameter after first LOI, proper orbital period for LOI target value are recommended to meet the inclination, apoapsis and periapsis altitude constraints.