• The Bulletin of The Korean Astronomical Society
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• v.43 no.1
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• pp.43.1-43.1
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• 2018

Star formation in galaxies predominantly takes place in giant molecular clouds (GMCs). While it is widely believed that UV radiation feedback from young massive stars can destroy natal GMCs by exciting HII regions and driving their expansion, our understanding on how this actually occurs remains incomplete. To quantitatively assess the effect of UV radiation feedback on cloud disruption, we conduct a series of theoretical studies on the dynamics of HII regions and its role in controlling the star formation efficiency (SFE) and lifetime of GMCs in a wide range of star-forming environments. We first develop a semi-analytic model for the expansion of spherical dusty HII regions driven by the combination of gas and radiation pressures, finding that GMCs in normal disk galaxies are destroyed by gas-pressure driven expansion with SFE < 10%, while more dense and massive clouds with higher SFE are disrupted primarily by radiation pressure. Next, we turn to radiation hydrodynamic simulations of GMC dispersal to allow for self-consistent star formation as well as inhomogeneous density and velocity structures arising from supersonic turbulence. For this, we develop an efficient parallel algorithm for ray tracing method, which enables us to probe a range of cloud masses and sizes. Our parameter study shows that the net SFE, lifetime (measured in units of free-fall time), and the importance of radiation pressure (relative to photoionization) increase primarily with the initial surface density of the cloud. Unlike in the idealized spherical model, we find that the dominant mass loss mechanism is photoevaporation rather than dynamical ejection and that a significant fraction of radiation escapes through low optical-depth channels. We will discuss the astronomical.

• Smart Media Journal
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• v.8 no.3
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• pp.41-46
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• 2019

In a MMORPG, a typical application of virtual environment systems, it is a common desire to play in a more realistic environment. However, it is very difficult to provide a latency-free virtual environment to a large user base, mainly due to the fact that the real environment must be configured on multiple servers rather than on single server and that data must be shared on the real server when users move from one region to another. Experiencing response delays continuously in the process of information synchronization between servers greatly deteriorates the degree of immersion. In order to solve this problem, it is necessary to minimize the response delay occurring in the information synchronization process between the servers. In this paper, we propose Migration Agent for efficient information synchronization between field servers providing information of virtual environment and minimizing response delay between Field Server and PC(Player Character) and implement it in cloud computing network. In the proposed system, CPU utilization of field server increased by 6 ~ 13%, and response time decreased by 5 ~ 10 seconds over the existing system in 70,000 ~ 90,000 PCs

• Korean Journal of Agricultural and Forest Meteorology
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• v.9 no.2
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• pp.132-139
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• 2007

The Moderate Resolution Imaging Spectroradiometer (MODIS) regularly provides the eight-day gross primary productivity (GPP) at 1 km resolution. In this study, we evaluated the uncertainties of MODIS GPP caused by errors associated with the Data Assimilation Office (DAO) meteorology and a biophysical variable (fraction of absorbed photosynthetically active radiation, FPAR). In order to recalculate the improved GPP estimate, we employed ground weather station data and reconstructed cloud-free FPAR. The official MODIS GPP was evaluated as +17% higher than the improved GPP. The error associated with DAO meteorology was identified as the primary and the error from the cloud-contaminated FPAR as the secondary constituent in the integrative uncertainty. Among various biome types, the highest relative error of the official MODIS GPP to the improved GPP was found in the mixed forest biome with RE of 20% and the smallest errors were shown in crop land cover at 11%. Our results indicated that the uncertainty embedded in the official MODIS GPP product was considerable, indicating that the MODIS GPP needs to be reconstructed with the improved input data of daily surface meteorology and cloud-free FPAR in order to accurately monitor vegetation productivity in Korea.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.32 no.2
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• pp.133-142
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• 2014

Landsat is one of the popular satellites for observing land surface that is used in various areas including monitoring, detecting and classifying changes in land surface. However, shades, which cloud itself and its shadow, interrupted often clear observation and analysis of ground surface. For this reason, the process of removing shades and restoring original ground surfaces are critical for geospatial users. This study is planned to recommend a methodology for more accurate and clear images of Landsat-8 sensor, which provided two additional bands of costal/aerosol and cirrus. In fact, those bands are known as functioned effectively in detecting and restoring shades. Otsu's thresholding technique to detect clouds, we replaced those detective shades by using experimental and reference images. In accurate assessment, the overall accuracy and kappa coefficients were about 85% and 0.7128, respectively. This indicates that the proposed technique is effective for recovering the original land surface.

• The Journal of Korean Association of Computer Education
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• v.22 no.3
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• pp.123-133
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• 2019

The purpose of this study is to establish Smart Education Environment for children's personalized learning based on the data are accumulated by Smart Device which is one of element on Smart Education. In this study, we propose the operational improvement plan for the free choice activity in the 5-year-old kindergarten and also implement the Free Choice Activity(FCA) management system for children to select and to evaluate the play plans for themselves. Children participating in this study have fun the whole time for the process of self-planning, the playing activities and the self-assessment of playing. As a result, it is confirmed that children participate actively in decision-making of interesting areas through the smart device than the traditional education environment before. A single teacher using FCA management system with smart device in this study can get useful information without difficulty of individual child's interests, learning and the statistics of children in the classroom.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.34 no.5
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• pp.301-308
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• 2021

It is important to develop a digital SOC (Social Overhead Capital) maintenance system for preemptive maintenance in response to the rapid aging of social infrastructures. Abnormal signals induced from structures can be detected quickly and optimal decisions can be made promptly using IoT sensors deployed on the structures. In this study, a digital SOC monitoring system incorporating a multimetric IoT sensor was developed for long-term monitoring, for use in cloud-computing server for automated and powerful data analysis, and for establishing databases to perform : (1) multimetric sensing, (2) long-term operation, and (3) LTE-based direct communication. The developed sensor had three axes of acceleration, and five axes of strain sensing channels for multimetric sensing, and had an event-driven power management system that activated the sensors only when vibration exceeded a predetermined limit, or the timer was triggered. The power management system could reduce power consumption, and an additional solar panel charging could enable long-term operation. Data from the sensors were transmitted to the server in real-time via low-power LTE-CAT M1 communication, which does not require an additional gateway device. Furthermore, the cloud server was developed to receive multi-variable data from the sensor, and perform a displacement fusion algorithm to obtain reference-free structural displacement for ambient structural assessment. The proposed digital SOC system was experimentally validated on a steel railroad and concrete girder bridge.

• Applied Chemistry for Engineering
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• v.16 no.3
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• pp.397-402
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• 2005

Core-shell Poly(styrene-co-N-isopropylacrylamide) (poly(St-co-NIPAm) was prepared by soap-free emulsion polymerization of styrene (St) and N-isopropylacrylamide (NIPAm) in aqueous solution with potassium persulfate (KPS) as an initiator. The effects of St/NIPAm ratio, concentrations of monomer and crosslinker were studied. Also, Thermo sensitivity of microgels prepared was investigated. Particle size of microgels increased with increasing mol ratio of NIPAm to styrene. Transmittance of the microgel dispersion decreased rapidly when heated above a low critical solution temperature (near $32{\sim}34^{\circ}C$, cloud point). Swelling ratio of the microgel increased with increasing of the concentration of monomer (NIPAm) and decreased proportional to the concentration of crosslinker.

• Journal of The Korean Astronomical Society
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• v.27 no.1
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• pp.13-29
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• 1994

We have constructed a 3-dim hydrodynamics code called BTSPH. The fluid dynamics part of the code is based on the smoothed particle hydrodynamics (SPH), and for its Poisson solver the binary tree (BT) scheme is employed. We let the smoothing length in the SPH algorithm vary with space and time, so that resolution of the calculation is considerably enhanced over the version of SPH with fixed smoothing length. The binary tree scheme calculates the gravitational force at a point by collecting the monopole forces from neighboring particles and the multipole forces from aggregates of distant particles. The BTSPH is free from geometric constraints, does not rely on grids, and needs arrays of moderate size. With the code we have run the following set of test calculations: one-dim shock tube, adiabatic collapse of an isothermal cloud, small oscillation of an equilibrium polytrope of index 3/2, and tidal encounter of the polytrope and a point mass perturber. Results of the tests confirmed the code performance.

• Proceedings of the KSRS Conference
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• 1999.11a
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• pp.479-484
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• 1999

Rice crop has relatively short growing season during the summer in Korea and, therefore, it is often difficult to acquire cloud-free imagery on time. This study was attempt to define the temporal characteristics of radar backscattering observed from satellite L-band SAR data on different growing stages of rice crop. Six scenes of multi-temporal JERS SAR data were obtained from the transplanting season to the harvesting month of October. Six layers of multi-temporal SAR data were registered on a common geographic coordinate system. Using topographic maps, field collected data, and Landsat TM data, several sample rice fields were delineated from the imagery and their relative radar backscatters were calculated by using a set of reference targets. The temporal pattern of radar backscattering was very distinctive by the growing stage of rice crop. It was also separable between two types of rice fields having different cultivation practices. Considering the temporal characteristics of radar backscattering observed from the study, it is obvious that a certain date of the growing season can be more effective to delineate the exact area of the cultivated rice crop field.

• Proceedings of the Korean Society of Computer Information Conference
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• 2015.01a
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• pp.283-284
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• 2015

We can picture a workforce that extends beyond your employees: one that consists of any user connected to the Internet. Cloud, social, and collaboration technologies now allow organizations to tap into vast pools of resources across the world, many of whom are motivated to help. Channeling these efforts to drive business goals is a challenge, but the opportunity is enormous: it can give every business access to an immense, agile workforce that is not only better suited to solving some of the problems that organizations struggle with today but in many cases will do it for free. In this paper, we research on factors to design an organizational crowd source for Big Data.