• Journal of Astronomy and Space Sciences
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• v.30 no.1
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• pp.11-15
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• 2013

A collision-free formation reconfiguration trajectory subject to the linearized Hill's dynamics of relative motion is analytically developed by extending an algorithm for gravity-free space. Based on the initial solution without collision avoidance constraints, the final solution to minimize the designated performance index and avoid collision is found, based on a gradient method. Simple simulations confirm that satellites reconfigure their positions along the safe trajectories, while trying to spend minimum energies. The algorithm is applicable to wide range of formation flying under the Hill's dynamics.

• Korean Journal of Radiology
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• v.21 no.11
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• pp.1199-1209
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• 2020

The glymphatic system hypothesis is a concept describing the clearance of waste products from the brain. The term "glymphatic system" combines the glial and lymphatic systems and is typically described as follows. The perivascular space functions as a conduit that drains cerebrospinal fluid (CSF) into the brain parenchyma. CSF guided to the perivascular space around the arteries enters the interstitium of brain tissue via aquaporin-4 water channels to clear waste proteins into the perivascular space around the veins before being drained from the brain. In this review, we introduce the glymphatic system hypothesis and its association with fluid dynamics, sleep, and disease. We also discuss imaging methods to evaluate the glymphatic system.

• Journal of Astronomy and Space Sciences
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• v.35 no.2
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• pp.93-103
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• 2018

Non-specular, vertically upward transit, fast-moving radar echoes are observed in the summer polar upper mesosphere near 90 km using 52 MHz VHF radar at Esrange, Sweden. By resolving maximum echo power movement, the unusual meteor trails propagate vertically upward with taking horizontal displacements at an initial speed of 10 km/s exponentially decreasing with increasing height from 85-89 km, lasting for 3.5 sec. Another upward transit is observed as following a downward transit echo target in about ~1 sec, lasting over 5 sec. The upward motion cannot be explained with the dynamics of penetrating meteors or by atmospheric dynamics. The observation proposes that secondary produced plasma jets occurring from meteor trail are possibly responsible for upward fast moving echoes. The long-lasting (3-5 sec), ascending meteor trails at speeds of a few $10^4m/s$ are distinctive from any previous occurrences of meteors or upper atmospheric electrical discharges in the aspect of long-lasting upward/downward motions. This result possibly suggests a new type of meteor-trail leader discharge occurring in the summer polar upper mesosphere and lower thermosphere.

• The Bulletin of The Korean Astronomical Society
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• v.37 no.2
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• pp.132.1-132.1
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• 2012

Radiation Belt Environment (RBE) model has developed to understand radiation belt dynamics as it considers whistler mode hiss and chorus waves which is responsible for relativistic electron acceleration and precipitation. Recently, many studies on electron loss by pitch-angle scattering have reported that elctromagnetic ion cyclotron (EMIC) wave is also responsible for main loss mechanism in dusk and equatorial regeion. Here, we attempt to incorporate EMIC into RBE model simulation code to understand more detailed physical dynamics in Radiation belt environemnt. We compare this developed model to data during storm events where both of electron loss and EMIC waves were detected.

• International Journal of Aeronautical and Space Sciences
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• v.18 no.2
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• pp.197-205
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• 2017

We investigate the slat noise generation mechanism by using large-eddy simulation (LES) and simple source modeling based on linearized Euler equations. An incompressible LES of an MD 30P30N three-element airfoil in the high-lift configuration is conducted at $Re_c=1.7{\times}10^6$. Using the total derivative of the hydrodynamic pressure (DP/Dt) acquired from the incompressible LES, representative noise sources in the slat cove region are characterized in terms of simple sources such as frequency-specific monopoles and dipoles. Acoustic radiation around the 30P30N multi-element airfoil is effectively computed using the Brinkman penalization method incorporated with the linearized Euler equation. The directivity pattern of $p^{\prime}_{rms}$ at $r=20c_{slat}$ in the multiple sources is closely compared to that obtained by the application of the LES/Ffowcs-Williams and Hawking's methods to the entire flow field. The power spectrum of p' at ${\theta}=290^{\circ}$ is in good agreement with the data reported in BANC-III, especially the broadband part of the spectrum with a decaying slope ${\propto}f^{-3}$.

• The Journal of the Korea Contents Association
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• v.21 no.12
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• pp.738-747
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• 2021

Space and place have distinctively different meanings from each other. As virtual reality has become a routine of daily life, placeness concepts have been introduced on discussion tables. Yet, place has not been widely discussed in conceptual approaches Thus, using the concepts of space and place this study attempts to figure out the structure and the processes of how users recognize digital space and give placeness. For the study purpose, it identifies core elements of placeness attribution in digital game places, and then explains the development processes of space into place through characteristics of MDA(Mechanics-Dynamics-Aesthetics)framework. Based on present theoretical concepts and their application process this study also demonstrates the transformation process through which physical space becomes a place in the similar context with a necessary condition in order for a space to be a place. This study confirms that digital games can be transformed into a space that creates placeness in the process. Considering that players' affinity and nostalgia are generated through the placeness acquiring process in digital game space, the processes eventually imply an extension of largely meaningful and influencing contents as digital games induce players' immersion.

• Proceedings of the Korean Magnetic Resonance Society Conference
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• 1999.06a
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• pp.4-5
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• 1999

• Proceeding of EDISON Challenge
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• 2016.03a
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• pp.37-54
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• 2016

The methods for estimating the change of free energy in dissipative particle dynamics (DPD) are discussed on the basis of fluctuation theorems. Fluctuation theorems are tactics to evaluate free energy changes from non-equilibrium work distributions and have several forms, as proposed by Jarzynski, Crooks, and Bennett. The validity of these methods however, has been shown merely with the molecular dynamics or Langevin dynamics. In this study, the appropriate forms of fluctuation theorems for dissipative particle dynamics, which has similar structure to that of Langevin dynamics, are suggested using Liouville's theorem, and they are proved equivalent to original fluctuation theorems. Work distribution functions, which are probability distribution functions of works exerted on the system within the systematic change, are the basics of fluctuation theorems and their shapes are turned out to be dependent on the phase space trajectory of the change of the system. The reliability of Jarzynski and Crooks methods is highly dependent on the number of simulations to measure works and the shapes of the work distribution functions. Bennett method, however, can evaluate free energy changes even when Jarzynski and Crooks methods fail to do so.

• Journal of Korea Planning Association
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• v.54 no.3
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• pp.75-90
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• 2019

As the 24-hour society arrives, human activities in daytime and nighttime urban spaces are changing drastically, and the need for new urban management policies is steadily increasing. This study analyzes the types and characteristics of Seoul's human dynamics using location-based big data and the results are summarized as follows. First, the pattern of human dynamics in Seoul repeats itself every 7 days. Second, the types of human dynamics in Seoul can be classified into five types, and each of type has its own unique time-series and local characteristics. Third, the degree of match between human dynamics and zoning system in urban planning legislation was highest in 'Type 1' residence pattern and low in other types. The following implications can be drawn from these results. First, This paper examined the methodology of analyzing the regional characteristics of Seoul through the human dynamics and obtained meaningful results. Second, This paper can derive reliable and objective pattern analysis results using Big data that reflect the overall population characteristics. Third, the scale of night-time activity in the urban space of Seoul was understood, and its distribution, patterns and characteristics identified.

• Journal of Electrical Engineering and Technology
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• v.8 no.6
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• pp.1512-1519
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• 2013

Oil-impregnated paper is a major type of insulation used in oil-filled converter transformers for both traditional and new energy systems. This paper presents and analyzes the results of the experiment conducted on the electrical aging of oil-impregnated paper under AC-DC combined voltages using the pulsed electro-acoustic (PEA) technique. The formation and dynamics of space charge affected the performance of insulation material. The electrical aged oil-paper insulation was obtained through electrical aged experiments under the voltages. Based on the PEA technique, measurements were carried out when the oil-paper insulation system was subjected to different stressing and aging times. The space charge dynamics in the bulk of the oil-paper insulation system with different aging times were measured and analyzed. Characteristic parameters such as the total charge injection amount, the total charges of fast moving and slow moving, and the distortion factor of electric field were calculated and discussed. Results show that the longer electrical aging time, the more charges trapped in the bulk of aging sample. It leads to larger distortion factor of electric field in the bulk of aging samples and accelerate degradation of oil-paper insulation under AC-DC combined voltages.