• The Bulletin of The Korean Astronomical Society
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• v.40 no.1
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• pp.41.1-41.1
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• 2015

Hierarchical galaxy formation models under LCDM cosmology predict that the most massive structures such as galaxy clusters (M > $10^{14}M_{\odot}$) appear late (z < 1) in the history of the universe through hierarchical clustering of small objects. Galaxy formation is also expected to be accelerated in overdense environments, with the star formation rate-density relation to be established at z ~ 2. In this talk, we present our search of massive structures of galaxies at 0.7 < z < 4, using the data from GOODS survey and our own imaging survey, Infrared Medium-deep Survey (IMS). From these studies, we find that there are excess of massive structures of galaxies at z > 2 in comparison to the Millennium simulation data. At 1 < z < 2, the number density of massive structures is consistent with the simulation data, but the star formation history is more or less identical between field and cluster. The star formation quenching process is dominated by internal process (stellar mass). The environmental effect becomes important only at z < 1, which contributes to create the well known star formation-density relation in the local universe. Our results suggest that galaxy formation models under LCDM cosmology may require further refinements to match the observation.

• Journal of The Korean Astronomical Society
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• v.44 no.5
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• pp.151-160
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• 2011

We present a study searching for globular cluster systems (GCSs) of two face-on low surface bright- ness galaxies (LSBGs), UGC 5981 and UGC 6614. Based on HSTWFPC2 images of F555Wand F814W filters, we detect 12 and 18 GC candidates for UGC 5981 and UGC 6614, respectively. Although these two LSBGs have very different bulge properties, they have very similar specific frequencies ($S_N$) of 0.1. However, $S_N$ ~ 0.1 is quite small even for their late morphological types, albeit within errors. This suggests that LSBGs have had star formation histories lacking dominant initial starburst events while accumulating their stellar masses through sporadic star formation activities.

• Tribology and Lubricants
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• v.28 no.2
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• pp.62-69
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• 2012

Atomic force microscopy (AFM) has been widely utilized as a versatile tool not only for imaging surfaces but also for understanding nano-scale interfacial phenomena. By measuring the responses of the photo detector due to bending and torsion of the cantilever, which are caused by the interactions between the probe and the sample surface, various interfacial phenomena and properties can be explored. One of the challenges faced by AFM researchers originates in the physics of measuring the small forces that act between the probe of a force sensing cantilever and the sample. To understand the interactions between the probe and the sample quantitatively, the force calibration is essential. In this work, the procedures used to calibrate AFM instrumentation for nano-scale force measurement in normal and lateral directions are reviewed.

• The Bulletin of The Korean Astronomical Society
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• v.38 no.2
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• pp.91.1-91.1
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• 2013

Since 2010, we have improved the Fast Imaging Solar Spectrograph (FISS) and observed the Sun. From the early observations we noticed two instrumental problems: poorer spatial resolution due to chromatic aberration and lower light level in the Ca II band. We tried to overcome these problems in two ways. First, we updated the relay optics. With the new one, we don't find any noticeable chromatic aberration between Ha and CaII and as a result can obtain the high resolution data in Ca II as well. Second, we replaced mirrors and the grating. This resulted in the increase of light level by a factor of up to 2.5, and hence in the high S/N ratio. The images constructed from the recentest observations indicate that the performance of the FISS is now much closer to our original intention than at the beginning.

• Molecules and Cells
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• v.43 no.10
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• pp.880-888
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• 2020

Inherited peripheral neuropathy is a heterogeneous group of peripheral neurodegenerative disorders including Charcot-Marie-Tooth disease. Many peripheral neuropathies often accompany impaired axonal construction and function. To study the molecular and cellular basis of axon-defective peripheral neuropathy, we explore the possibility of using Caenorhabditis elegans, a powerful nematode model equipped with a variety of genetics and imaging tools. In search of potential candidates of C. elegans peripheral neuropathy models, we monitored the movement and the body posture patterns of 26 C. elegans strains with disruption of genes associated with various peripheral neuropathies and compiled a database of their phenotypes. Our assay showed that movement features of the worms with mutations in HSPB1, MFN2, DYNC1H1, and KIF1B human homologues are significantly different from the control strain, suggesting they are viable candidates for C. elegans peripheral neuropathy models.

• Journal of Mechanical Science and Technology
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• v.16 no.12
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• pp.1627-1632
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• 2002

In this paper, a simplified ultrasonic CT system, which uses the information in three directions, that is, 90°, ＋45° and －45°about the inspection plane, is applied to the high strength steel, and the frequency analysis method for enhancing the C scan or CT image is developed. This frequency analysis method is based on the frequency response property of the material. By comparing the magnitudes in the frequency domain, the special frequency which shows a significant difference between the welded joint and base material was found and used to obtain a C scan or CT image. Experimental results for several kinds of specimens, having a welded joint by electron beam welding, a weld joint by arc welding, on a fatigue crack, showed that the obtained C scan or CT image has better resolution than the results of previous experiments using the maximum value of the received waveform.

• The Bulletin of The Korean Astronomical Society
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• v.39 no.2
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• pp.60.2-60.2
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• 2014

Hierarchical structure of star-forming regions is widespread and may be characteristic of all star formation. We studied the hierarchical structure of star-forming regions in the Local Group galaxies (M31, M33, Phoenix, Pegasus, Sextans A, Sextans B, WLM). The star-forming regions were selected from Galaxy Evolution Explorer (GALEX) far-UV imaging in various detection thresholds for investigating hierarchical structure. We examined the spatial distribution of the hot massive stars within star-forming regions from Hubble Space Telescope (HST) multi-band photometry. Small compact groups arranged within large complexes. The cumulative mass distribution follows a power law. The results allow us to understand the hierarchical structure of star formation and recent evolution of the Local Group galaxies.

• The Bulletin of The Korean Astronomical Society
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• v.41 no.2
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• pp.62.1-62.1
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• 2016

We study the near-infrared photometric properties of red-supergiant stars (RSGs) in three nearby galaxies located within 15 Mpc: NGC 4214, NGC 4736 and NGC 5194 / NGC 5195. The near-infrared (JHK) imaging data were obtained using the WFCAM detector mounted on UKIRT telescope in Hawaii. We used the DAOPHOT/ALLSTAR pacakge to carry out the photometry. We applied MARCS synthetic fluxes to estimate the effective temperatures and luminosities of the RSGs in all the three galaxies. The results were plotted in the Hertzsprung-Russell(H-R) diagram along with the theoretical evolutionary tracks with different masses. We explore the spatial correlation between the RSGs and H II regions by examing the H-R diagram of the RSGs in the dominant H II regions for each of these three galaxies.

• Journal of The Korean Astronomical Society
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• v.29 no.spc1
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• pp.415-418
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• 1996

Space Solar Telescope (SST) is a space project for solar research, its main parameters are that total weight 2.0T, sun synchronous polar circular orbit, altitude of the orbit 730KM, 3 axis stabilized attitude system, power 1200W, telemetry of the downlink rate 30Mb/s, size $5{\ast}2{\ast}2\;M^3$, mission life 3 years. It is expected it will be launched in 2001 or later. The main objective is structure and evolution of solar vector magnetic field with very high spatial resolution. The payloads are consisted of 6 instruments: Main optical telescope with 1-M diameter and diffraction limited resolution 0.1 arc second, EUV imaging telescope with a bundle of four telescopes and 0.5 arc second resolution, spectrometric optical coronagraph, wide band spectrometer, H-alpha and white light telescope and solar and interplanetary radiospectrometer. An assessment study between China and Germany is under operation.

• Proceedings of the KSMRM Conference
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• 1999.04a
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• pp.1-9
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• 1999

핵자기 공명(NMR:nuclear magnetic resonance)은 19451건 Bloch, Procell등에 의해 처음으로 실험적으로 입증된 후에 생화학 및 약학 분야에서 분자단위의 물질의 성분, 구조, 대사물질의 역학적 운동 및 상태에 관한 정보를 아는데 유용한 기법으로 사용 되어 왔다. 의학분야에서는 Lauterber등에 의해 자기공명영상볍(Magnetic Resonance Imaging:MRI)으로 개발되어 질병의 진단 및 치료에 많은 공헌을 하게되었다. 해부학적영상 뿐 아니라 분석방법으로 병변 부위 및 인체 기관에서의 각종 대사물질의 정량적인 양과 변화를 알 수 있는 자기공명분광기법(magnetic resonance spectroscopy:MRS)도 활발한 임상적용이 이루어지고 있다. 자기공명영상법의 활발한 임상적 응용 및 새로운 technique이해를 위해서는 물리학적 개념(MR Physics)을 이해하는 것이 매우 중요하다.