• Journal of The Korean Astronomical Society
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• v.46 no.6
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• pp.243-251
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• 2013

We present results on the intrinsic brightness temperature of a sample of compact radio sources observed at 86 GHz using the Global Millimeter VLBI Array. We use the observed brightness temperatures at 86 GHz and the observed superluminal motions at 15 GHz for the sample in order to constrain the characteristic intrinsic brightness temperature of the sample. With a statistical method for studying the intrinsic brightness temperatures of innermost jet cores of compact radio sources, assuming that all sources have the same intrinsic brightness temperature and the viewing angles of their jets are around the critical value for the maximal apparent speed, we find that sources in the sample have a characteristic intrinsic brightness temperature, $T_0=4.8^{+2.6}_{-1.5}{\times}10^9K$, which is lower than the equipartition temperature for the condition that the particle energy equals to the magnetic field energy. Our results suggest that the VLBI cores seen at 86 GHz may be representing a jet region where the magnetic field energy dominates the total energy in the jet.

• Journal of Korean Society of Forest Science
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• v.90 no.6
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• pp.788-791
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• 2001

An improved double-cylinder hammer-driven sampling device was designed to extract undisturbed soil cores. The improvements consist of 1) separation of hammer from the driving head, 2) a split inside cylinder, and 3) a plastic sample holder. Pushing the sampler deep into the soil before hammering would result in less compression of the sample. Core samples should be taken in soils of medium moisture content. The improved soil core sampler provides sufficiently accurate volumetric soil samples with original soil layers and soil cores of 40cm in length and 5cm in diameter.

• The Bulletin of The Korean Astronomical Society
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• v.40 no.2
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• pp.54.1-54.1
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• 2015

We observed 38 Planck Cold Clumps (PCCs) in the $850{\mu}m$ dust continuum emission using the JCMT/SCUBA-2, and detected the emission in 15 clumps containing dense cores. In this poster we present the preliminary results. The PCCs are cold, dense, and thus, they are considered as objects in the early evolutionary stages of star formation. The sources in our sample were selected based on the Purple Mountain Observatory (PMO) 13CO (1-0) integrated intensity maps. In order to examine whether these cores detected in $850{\mu}m$ continuum have potential to be prestellar cores, we compare each core mass estimated from the $850{\mu}m$ continuum with the Virial mass and Bonnor-Ebert (BE) mass calculated from the 13CO (1-0) or C18O (1-0) spectra. By comparing the two column densities from the dust continuum and the 13CO (1-0) or C18O (1-0) line, we also derive the CO depletion factor, which could be an indicator of core evolution. The moment maps of the 13CO (1-0) line are used to study the physical properties (e.g. kinematics, turbulence) of PCCs. We investigate difference between the sources with and without detectable $850{\mu}m$ emission to study the formation conditions of dense cores.

• The Bulletin of The Korean Astronomical Society
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• v.45 no.1
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• pp.58.4-59
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• 2020

We present preliminary results of 1.1 and 1.3 mm dust continuum and 12CO (J=2-1) line data obtained with the Submillimeter Array toward six cores harboring Class 0/I objects in the λ Orionis cloud. They are located in bright rimmed clouds, which are exposed to the far-ultraviolet radiation field by the O-type star λ Ori. Compact dust continuum emission is observed from all six cores. Among the six cores, only one core G196.92-10.37 shows a signature of binarity with separation of 4000 AU. The numbers of singles and binaries in our sample are five and one, respectively and the derived multiplicity frequency (MF) is 0.17. This value is lower than those found in the binary surveys toward Class 0/I objects, which may be a hint for negative feedback by the nearby massive star, lambda Ori. The derived excitation temperature (Tex) using 12CO emission shows a lower median value (20 K) than those of triggered star-forming regions (30 K). The lower MF and Tex support our previous study that star formation was not triggered in the λ Orionis cloud. We aim to further investigate whether the Class 0/I YSOs in the λ Orionis cloud have less circumstellar materials and smaller accretion rates than in other filamentary clouds (e.g., Orion A & B), which might be attributed to negative feedback from the massive star in limiting accretion of protostars.

• Journal of Conservation Science
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• v.30 no.1
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• pp.27-32
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• 2014

The sample book was printed in 1935. Since the books in the early twentieth century were printed using acidic paper, the color of the paper would change to brown over time due to iron corrosion. In addition to corroding iron cores, the acidity of the paper (pH 3.2) also made the paper brown and fragile, as was true in the case of the sample book. To clean the paper of the sample book and to make it strong, we replaced the iron core and performed wet cleaning on the paper to remove contaminants. Then we pressed the sample book dry, and subsequently linening every page with Minoshi($4g/m^2$). Generally, book conservator rebinding the book using wires or threads: however we have devised a new method to rebind the book using colored iron cores. To color the iron core brown, they were dipped in an aqueous coloring solution ($H_2O$, $C_2H_5OH$, $CuSO_4{\cdot}5H_2O$, $FeCl_3{\cdot}6H_2O$); subsequently, a 20% paraloid B-72 was applied to protect the colored iron cores from corrosion.

• Geophysics and Geophysical Exploration
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• v.18 no.3
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• pp.105-114
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• 2015

A long-term resistivity monitoring system has been developed for saturated cores in room temperature and humidity condition. A 3-channel water-pump continuously drops the water onto the top of saturated core sample surrounded by shrinkable tube as well as on the paper filters of the electrodes at both sides of the core sample, by which one can monitor the resistivity changes with maintaining full saturation of the rock core for a week or longer. Monitoring the resistivity changes has been performed with 3 kinds of rock samples including biotite gneiss, andesitic tuff, and shale for 9 days using the system. Consequently, it is proposed two hypothesis that conversion speed of temperature coefficient has close relation to the thermal properties of the rock sample and that the ratio of resistance between dry and saturated conditions for a rock sample can be related to the effective porosity of the sample. The ratio between dry and saturated resistance for the three rock types are 48, 705, and 2, while effective porosity was 3.7%, 3.3%, and 13.0%, respectively.

• Journal of Power Electronics
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• v.8 no.3
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• pp.217-227
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• 2008

The electric power subsystems (EPS) of most remote sensing satellites consist of a solar array as a source of energy, a storage battery, a power management and control (PMC) unit and a charge equalization unit (CEU) for the storage battery. The PMC and CEU use high frequency transformers in their power modules. This paper presents a design, implementation and testing results of a high frequency transformer for the EPS of satellite applications. Two approaches are used in the design process of the transformer based on the pre-determined transformer specifications. The transformer is designed based on an ETD 29 ferrite core. The implemented transformer consists of one center-tapped primary coil with eleven center-tapped secondary coils. The offline calculation results and measured values of R, L for transformer coils are convergence. A test circuit for measuring the transformer parameters like voltage, current and B-H hysteresis was implemented and applied. The test results confirm that the voltage waveforms of both primary and secondary coils were as desired. No overlapping occurred between the control signal and the transformer, which was not saturated during testing even during a short circuit test of the secondary channels. The dynamic B-H loop characteristics of the used transformer cores were measured. The sample test results are given in this paper.

• Geophysics and Geophysical Exploration
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• v.19 no.3
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• pp.121-130
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• 2016

Several factors are discussed that should be considered in measuring thermal conductivity of rock cores with a PEDB (potable electronic divided bar) system, which is relatively accurate and easy to operate, and can measure the thermal conductivity of rock cores for various diameters. Then the system is applied to measure thermal conductivity of 70 rock cores from Ulleung Island. Air temperature affects most on the thermal conductivity measurements, so that it is very important to minimize the temperature change during the measurement. Other factors such as the temperature of heat source, averaging time window on the thermal conductivity measurements do not affect much compared to air temperature. Slightly higher thermal conductivity is measured when using the thermal contact paste between the sample and heat source or heat sink. Especially, rock cores with irregular surface showed bigger difference. Repeatability showed less than ${\pm}0.3%$ for standard samples and less than ${\pm}4%$ for rock samples, respectively, when the room temperature changes within $1^{\circ}C$ during the measurements. Thermal conductivity of the rock cores from Ulleung Island roughly increases as depth increases but does not show any dependency on the rock types.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.07b
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• pp.1168-1171
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• 2003

In contrast to a conventional transformer, the flat transformer is made using a number of small ferrite cores. Two cores for transformer and one core for inductor, which composed one module. Many modules can be connected together to form a flat matrix transformer. This structural arrangement eliminates the single hot spot problem in conventional transformers and permits high current density pertains at high frequency. In this study, the ferrite magnetic cores of Mn-Zn system for the Flat transformer were manufactured and the electrical and magnetic characteristics of its tested. The power loss of sample FO2(Mn-Zn ferrite) sintered at $1350^{\circ}C$ was $350kW/m^3$ in test conditions of 250kHz, 200mT and $100^{\circ}C$, which showed the good power loss property in high frequency. The power loss of FO2 samples has been studied as a function of magnetic flux density and frequency. Steinmetz exponent was 2.82 at 250kHz and 2.73 at 500kHz. These results illustrated the switching of power loss mechanism in ferrite core from hysteresis losses to eddy current losses or others.

• Journal of the Korean Wood Science and Technology
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• v.35 no.5
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• pp.1-6
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• 2007

Boiling-in-oil process was performed to investigate the high-temperature drying characteristics of 25, 50, and 70 mm-thick flat-sawn Douglas-fir lumber. Drying rates, moisture profiles and temperature profiles were monitored. Fully refined paraffin wax was used as drying agent and heated to $130^{\circ}C$. Average drying rates of 25, 50, and 70 mm-thick specimen were 11.6, 6.7, 5.0%/h, respectively. The moisture content differences between cores and ends were 1~2% in 25 mm-thick and 200 mm-long sample and over 10% in 50 mm-thick and 600 mm-long sample.