• Ocean and Polar Research
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• v.28 no.4
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• pp.475-484
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• 2006

In order to reveal the vertical variation of physical properties in deep-sea sediments, deep-sea sediment cores were collected at 78 stations using a multiple corer in the KR5 area, one of the Korea contract areas for manganese nodule exploration, located in the northeast equatorial Pacific. Based on the color of sediments, sampled sediment cores were characterized into three lithologic units (unit 1,2, and 3). In all sediment cores, three units appear systematically; unit 1 lies at the top of cores and unit 2 and/or unit 3 appear to underlie unit 1 or alternate with unit 3. Unit 1 layer from the top of cores shows dark grayish brown to dark brown with mean thickness of 10.2cm. Unit 2 and 3 layers show very dark brown to black color and yellowish brown to brown color, respectively. According to the physical properties of the deep-sea sediment cores, sediment column can be divided into three sections. Section A $(0{\sim}15cm)$ in subbottom depth consists mostly of unit 1. Mean values of physical properties of section B $(15{\sim}30cm)$ in subbottom depth are similar to those of section C (>30 cm) in subbottom depth. However, the physical properties of section B were more variable than those of section C because of the high activity of bioturbation in section B. These results will provide valuable information for selecting suitable sites for mining manganese nodules in the Korea contract areas.

• The Bulletin of The Korean Astronomical Society
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• v.43 no.1
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• pp.45.1-45.1
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• 2018

Formation of filaments and subsequent dense cores in ISM is one of the essential questions to address in star formation. To investigate this scenario in detail, we recently started a molecular line survey namely 'Filaments, the Universal Nursery of Stars (FUNS)' toward nearby filamentary clouds in Gould Belt using TRAO 14m single dish telescope equipped with a 16 multi-beam array. In the present work, we report the first look results of kinematics of a low mass star forming region L1478 of California molecular cloud. This region is found to be consisting of long filaments with a hub-filament structure. We performed On-The-Fly mapping observations covering ~1.1 square degree area of this region using C18O(1-0) as a low density tracer and 0.13 square degree area using N2H+(1-0) as a high density tracer, respectively. CS (2-1) and SO (32-21) were also used simultaneously to map ~290 square arcminute area of this region. We identified 10 filaments applying Dendrogram technique to C18O data-cube and 13 dense cores using FellWalker and N2H+ data set. Basic physical properties of filaments such as mass, length, width, velocity field, and velocity dispersion are derived. It is found that filaments in L~1478 are velocity coherent and supercritical. Especially the filaments which are highly supercritical are found to have dense cores detected in N2H+. Non-thermal velocity dispersions derived from C18O and N2H+ suggest that most of the dense cores are subsonic or transonic while the surrounding filaments are transonic or supersonic. We concluded that filaments in L~1478 are gravitationally unstable which might collapse to form dense cores and stars. We also suggest that formation mechanism can be different in individual filament depending on its morphology and environment.

• Journal of the Korean Magnetics Society
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• v.6 no.6
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• pp.388-396
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• 1996

Magnetic properties of sintered Fe-79Ni-4Mo cores made of centrifugal atomized powders were investigated. $H_{c}$ and $\mu_{a}$ of the cores sintered at $1350^{\circ}C$ for 2 hours measured at 60 Hz at a magnetic field of 10 Oe showed the best properties. Particularly the properties of $H_{c}$ and $\mu_{a}$ measured at low field (< 0.2 Oe) were found to increase with increasing the particle size of the core samples. It resulted from the domain wall motion depending on the grain size of sintered bodies. The best D, C magnetic properties of $H_{c}$ and $\mu_{max}$ were 0.085 Oe and 40000, respectively. A, C properties of the same cores showed the $\mu_{a}$ of 11000. The magnetic properties of sintered cores always exhibited an enhanced AC/DC performance by using the powders mixed with two different particle sizes. Those properties of cores are expected to apply for current transformer.

• Journal of Digital Convergence
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• v.9 no.3
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• pp.213-223
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• 2011

Today, information resource management is key task in the data-centre as like as NCIA(National computing integration Agency of Korea). In IRM, the server's performance is one of the core elements, it must be importantly managed during whole of system life cycle. As first step of such management is in purchase phase, it is very important that the optimum specification is determined. The server's specification contains such as performance of core, criteria for performance verification, minimum cores, etc. There is constant controversy concerning the minimum cores. In this article, we present criteria for determination of the minimum cores that considered three aspects: (1) Costly aspect as TCO(Total Cost of Ownership, (2) Environmental aspect as Green IT (3) Technical aspect as RAS(Reliability, Availability, Serviceability) functionality. Finally, we propose scheme to ideally determinate the minimum cores.

• Journal of the Korean Magnetics Society
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• v.8 no.4
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• pp.185-191
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• 1998

Magnetic domain structure and static magnetic properties were investigated in the ultra thin 3%Si-Fe strip wound cores when the strips were wound and annealed to relief the stress. The elastic and plastic deformation due to the radius of curvature was also investigated for the cores. At the as-wound state, the maze pattern domain structure was generated on the concave surface of the core and 180$^{\circ}$ domain wall was recovered by annealing 600 $^{\circ}C$$\times$30 min. After annealed by 900 $^{\circ}C$$\times$30 min, Hc of strip-wound cores was not reached to the $H_c$ of the strip even at the cores of elastic deformation region. It is necessary to relief the local stress remained in the core when the cores were manufactured for the application of ultra-thin 3%Si-Fe strip.

• The Bulletin of The Korean Astronomical Society
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• v.46 no.2
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• pp.37.3-38
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• 2021

One of the key questions on star formation is how the organic molecules are synthesized and delivered to the planets and comets since they are the building blocks of prebiotic molecules such as amino acid, which is thought to contribute to bringing life on Earth. Recent astrochemical models and experiments have explained that complex organic molecules (COMs; molecules composed of six or more atoms) are produced on the dust grain mantles in cold and dense gas in prestellar cores. However, the chemical networks and the roles of physical conditions on chemistry are not still understood well. To address this question, hot (> 100 K) cores in high mass young stellar objects (M > 8 Msun) are great laboratories due to their strong emissions and larger samples than those of low-mass counterparts. In addition, CH₃OH masers, which have been mostly found in high mass star forming regions, can provide constraints due to their very unique emerging mechanisms. We investigate twelve high mass star forming regions in ALMA band 6 observation. They are associated with 44/95 GHz Class I and 6.7 GHz Class II CH3OH masers, implying that the active accretion processes are ongoing. For these previously unresolved regions, 66 continuum peaks are detected. Among them, we found 28 cores emitting COMs and specified 10 cores associated with 6.7 GHz Class II CH3OH masers. The chemical diversity of COMs is found in cores in terms of richness and complexity; we identified up to 19 COMs including oxygen- and nitrogen-bearing molecules and their isotopologues in a core. Oxygen-bearing molecules appear to be abundant and more complex than nitrogen-bearing species. On the other hand, the COMs detection rate steeply grows with the gas column density, which can be attributed to the effective COMs formation in dense cores.

• Journal of the Korean Magnetics Society
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• v.20 no.1
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• pp.13-17
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• 2010

Fe-3, 4.2 and 6.8% Si compressed cores were fabricated, and then electrical resistivity, AC and DC magnetic properties, microhardness, and other properties were analyzed in order to know whether best soft magnetic properties could be also obtained in an Fe-Si compressed core with the well-known composition of Fe-6.5% Si. With increasing the silicon content, eddy current loss and hysteresis loss decreased and increased, respectively, so that a minimum total loss was not obtained in the well-known Fe-6.8 % Si cores, but obtained in the Fe-4.2 % Si cores. Also electrical resistivity of the cores and hardness of the particles increased monotonously with silicon content so that compaction ratio of the cores decreased. B2 and $DO_3$ ordered phase could be observed only in Fe-6.8% Si powder. A minimum loss and highest permeability of the Fe-4.2 % Si cores can be explained by the ratio of specific electrical resistivity of insulator to that of magnetic particles, micro-hardness, compaction ratio and demagnetization coefficient of the Fe-Si powder particles with silicon content.

• Journal of the Korean Magnetics Society
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• v.15 no.5
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• pp.270-275
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• 2005

Dust cores (compressed powder cores) of $Fe-6.0wt\%Si$ alloy with a size of $35\~180\;{\mu}m$ in diameter have been prepared by phosphate coatings and annealings at $600\~900^{\circ}C$ for 1 h in nitrogen atmosphere. Further the magnetic and mechanical properties of the powder cores were investigated. As a general trends, the compressive strength and core loss decreased with the increase in annealing temperature. When annealed at $800^{\circ}C$, the compressive strength was 15 kgf, the permeability and quality factor were 74 and 26, respectively. Moreover the core loss at 50 kHz and 0.1 T induction was $750\;mW/cm^3$, and the percent permeability under the static field of 50 Oe was estimated to be about 78. In addition, the cut-off frequency in the cure representing the frequency dependence of effective permeability was measured to be around 200 kHz. These properties of the $Fe-6.0wt\%Si$ alloy dust cores could be considered to be due to the good insulation effect of iron-phosphate coats, the decrease in magnetocrystalline anisotropy and saturation magnetostriction and the increase in electric resistivity.

• Geophysics and Geophysical Exploration
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• v.14 no.4
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• pp.305-315
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• 2011

A total of 864 measurements for P- and S- wave velocity of acrylic and stainless steel core samples have been performed with respect to their lengths and axial load applied. S-wave velocity measurement was much harder than P-wave velocity, so that it showed higher deviation in measured S-wave velocity with respect to repeated measurement, length of the cores, and the axial load applied. Velocity measurements for acrylic cores showed more stable and less than half of the variation between the measurements than the stainless steel cores. This seems to be come from better coupling between the transducers and acrylic cores than stainless cores, and from larger value of the first arrival time in a similar system noise environments. From the analysis of the 864 measurements, it is recommended that the length of the core be 60 ~ 90 mm, axial load between 20 kg (27.7 $N/cm^2$) and 30 kg (41.6 $N/cm^2$) for measurement of wave velocity of the acrylic and stainless steel cores. Especially for measuring S-wave velocity of stainless steel core, core length should be less than 50 mm, otherwise it will be affected by mode conversion or others. These results can be used in measurement and correction for system delay in wave velocity measurement for rock cores.

• Economic and Environmental Geology
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• v.53 no.1
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• pp.71-85
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• 2020

To understand behavior of fault cores in the field of geotechnical and geological engineering, we present an investigation of the physical properties (breccia and clay contents, unit weight, porosity, and water content) and friction characteristics (internal friction angle and cohesion) of fault cores, in granitic, sedimentary, and volcanic rocks in South Korea. The breccia contents in the fault cores are positively correlated with unit weight and negatively correlated with clay content, porosity, and water content. The inter-quartile ranges of internal friction angles and cohesion calculated from direct shear tests are 16.7-38.1° and 2.5-25.3 kPa, respectively. The influence of physical properties on the friction characteristics of the fault cores was analyzed and showed that in all three rock types the internal friction angles are positively correlated with breccia content and unit weight, and negatively correlated with clay content, porosity, and water content. In contrast, the cohesions of the fault cores are negatively correlated with breccia content and unit weight, and positively correlated with clay content, porosity, and water content.