• Journal of Magnetics
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• v.3 no.4
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• pp.99-104
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• 1998

The $ Sm_2Fe_{17}N_x $materials were prepared by the combination consisting of the HDDR (hydrogenation, disproportionation, desorption, and recombination) process and nitrogenation or by the conventional way consisting of nitrogenation only, and the magnetic and thermomagnetic properties of the materials were investigated. The magnetic characterisation of the prepared $ Sm_2Fe_{17}N_x $ materials was performed using a VSM. Thermal stability of the materials was evaluated using a DTA under Ar gas atmosphere. The thermomagnetic characteristics of the materials were examined using a Sucksmith-type balance. The previously HDDR-treated Sm2Fe17parent alloy was found to be nitrogenated more easily compared to the ordinary $ Sm_2Fe_{17}N_x $alloy. The $ Sm_2Fe_{17}N_x $ material produced by the combination method showed a high coercivity (12.9 kOe) even in the state of coarse particle size (around 60 ${\mu}{\textrm}{m}$). It was also revealed that the $ Sm_2Fe_{17}N_x $ material produced by the material produced by the combination showed an unusual TMA tracing featured with a low and constant magnetisation at lower temperature range and a peak just before the Curie temperature. This thermomagnetic characteristic was interpreted in terms of the competition between two counteracting effects; the decrease in magnetisation due to the thermal agitation at an elevated temperature and the increase in magnetisation resulting from the rotation of magnetisation of the fine grains comparable to a critical single domain size due to the decreased magnetocrystalline anisotropy at an elevated temperature.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.39 no.6
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• pp.567-573
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• 2015

This paper aims to evaluate the variation in the mechanical properties of carbon/epoxy composites under in situ low- and high-temperature environments. In situ low- and high-temperature environments were simulated with temperature ranging from $-40^{\circ}C$ to $220^{\circ}C$ using an environmental chamber and furnace. The variation in the mechanical properties of the composites was measured for longitudinal and transverse tensile properties, in-plane shear properties and interlaminar shear strength. Under the low temperature of $-40^{\circ}C$, all mechanical properties increased moderately compared to the baseline properties measured at room temperature. The changes in the longitudinal tensile properties decreased moderately with increasing temperature. However, transverse tensile properties, in-plane shear properties and interlaminar shear strength each showed a significant drop due to the glass transition behavior of the matrix after $140^{\circ}C$. Notably, the tensile property value near $100^{\circ}C$ increased compared to baseline property value, which was an unusual occurrence. This behavior was a direct result of post-curing of the epoxy resin due to its exposure to high temperature.

• The Journal of the Acoustical Society of Korea
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• v.38 no.6
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• pp.621-629
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• 2019

A logical measure is suggested to estimate an accurate Sound Speed Profile (SSP) for the unusual variation of salinity in the Yellow Sea. Based on National Aeronautics and Space Administration (NASA)'s Aqua and Soil Moisture Active Passive (SMAP) satellite data, this measure identifies the area of temperature inversion effect and expansion of low salinity (<30.5 psu) water. Subsequently, on the area, the Conductivity, Temperature, and Depth (CTD) mounted unmanned maritime system estimates accurate SSP. In order to carry out this measure conveniently, a flow chart is demonstrated in this research. By using this measure which finds the high variational salinity area, the inaccuracy issue for calculating SSP from Expandable Bathy Thermograph (XBT) is expected to be solved.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.45 no.6
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• pp.723-729
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• 2012

On 3 February 2011, a mass mortality of finless porpoises Neophocaena asiaeorientalis occurred at a dike of the Saemangeum Sea dike. A total of 249 carcasses were collected; these had been stranded by a sea dike and had floated into the lake formed by the dike. Eight bodies were measured, and four of these were dissected to analyze stomach contents. The blubber thicknesses of five bodies were compared with those of caught finless porpoises in the Yellow Sea from 2010. Finless porpoises at the Saemangeum Sea dike exhibited better nutritive conditions than finless porpoises in the Yellow Sea. Air temperature in January 2011 was lower than the prior 5-year average (P<0.05). Water temperature when the mass mortality occurred was lower than values observed in 2009 and 2010: values below $0^{\circ}C$ had been recorded, and the majority of the dike lake had frozen over. The mass mortality of finless porpoises may have been caused by these unusually low temperatures.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.454-454
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• 2011

Graphene shows unusual electronic properties, such as carrier mobility as high as 10,000 $cm^2$/Vs at room temperature and quantum electronic transport, due to its electronic structure. Carrier mobility of graphene is ten times higher than that of Silicon device. On the one hand, quantum mechanical studies have continued on graphene. One of them is quantum Hall effect which is observed in graphene when high magnetic field is applied under low temperature. This is why two dimension electron gases can be formed on Graphene surface. Moreover, quantum Hall effect can be observed in room temperature under high magnetic field and shows fractional quantization values. Quantum Hall effect is important because quantized Hall resistances always have fundamental value of h/$e^2$ ~ 25,812 Ohm and it can confirm the quantum mechanical behaviors. The value of the quantized Hall resistance is extremely stable and reproducible. Therefore, it can be used for SI unit. We study to measure quantum Hall effect in CVD graphene. Graphene devices are made by using conventional E-beam lithography and RIE. We measure quantum Hall effect under high magnetic field at low temperature by using He4 gas closed loop cryostat.

• Journal of Astronomy and Space Sciences
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• v.11 no.1
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• pp.21-30
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• 1994

VV Cep-type long period spectroscopic-eclipsing binary AZ Cas has been observed for five years, 1985 Oct~1990 Feb, UBV at the Ilsan Station of Yonsei University Observatory. A total of 431 observations (U=129, B=142 and V=160) are made for 86 nights. Instrumental differential UBV and B-V light curves made with these observations cover phases nearly a half of one period. There is no appreciable light variation in V but in other two passbands a gradual decrease of the brightness is clearly noticed. The loss of light in B resulted in a reddening in $\Delta(B-V)$ by + 0.06 at phases between 0.4~0.5 as compared with that of at phase ~0.1. This intrinsic reddening arouses a question why at the orbital phase of the transit of a hot star in front of a cool M supergiant the heating of the facing hemisphere of M supergiant by the strong radiation from the B stat is absent. With regard to this unusual situation we propose a hypothesis that a large amount of gas stream of low temperature ejected from the surface of M supergiant component towards the B star dominates the brightness of B star and the reflection effect.

• Proceedings of the Korean Fiber Society Conference
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• 2003.10b
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• pp.171-172
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• 2003

Electrically conducting polymers have attracted a great deal of attention because of their unusual electronic Properties.1 One of them, polypyrrole has been widely studieddue to its high conductivity and good environmental stability. 2Especially polypyrrole nano-Particles and -fibers are interesting because of their unique properties and applications. Recently amorphous polypyrrole nano-particles were fabricated using microemulsion Polymerization at low temperature. (omitted)

• Archives of Pharmacal Research
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• v.16 no.2
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• pp.140-146
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• 1993

A colostral protein that augments natural killer (NK) cell activity was isolated from bovine colostrum. This protein, designated matemal immunity enhancing factor (MIEF), increased NK cell-mediated cytotxicity against human tumor targets wheb added to cultures of resting peripheral blood lymphocytes. The NK cell stimulatory activity of the MIEF was demonstrated at the concentrations as low as 0.1-0.01 $\mu$g/ml. Purified MIEF showed an apparent molecular weight of 22,000 in SDS-polyacrylamide gel electrophoresis. The unusual biochemical characteristics of the MIEF distinguish it from other cytokines. The MIEF was soluble at a cold tgemperature, and precipitated by raising the temperature. This themal precipitability was reversible, and dependent on the concentration, pH and ionic strength. Maximal precipitation was observed at neutral pH, and higher ionic strength.

• Journal of the Korean Society for Heat Treatment
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• v.28 no.1
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• pp.1-6
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• 2015

The ductile-to-brittle transition behavior of two austenitic Fe-18Cr-10Mn alloys with the combined addition of nitrogen and carbon was investigated in this study. The alloys exhibited a ductile-to-brittle transition behavior because of unusual brittle fracture at low temperatures unlike conventional austenitic alloys. The alloy with higher carbon content had higher yield and tensile strengths than that with lower carbon content due to the solid solution strengthening effect resulting from carbon addition. However, the increase in carbon content promoted the occurrence of intergranular fracture, and thus deteriorated the impact toughness. In order to develop successfully the austenitic Fe-18Cr-10Mn alloys with the excellent combination of strength and toughness in the future, therefore, more systematic studies are required to find the appropriate amount and ratio of nitrogen and carbon.

• Journal of The Korean Astronomical Society
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• v.43 no.5
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• pp.161-168
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• 2010

Magnetars are neutron stars possessing a magnetic field of about $10^{14}-10^{15}$ G at the surface. Thermodynamic properties of neutron star matter, approximated by pure neutron matter, are considered at finite temperature in strong magnetic fields up to $10^{18}$ G which could be relevant for the inner regions of magnetars. In the model with the Skyrme effective interaction, it is shown that a thermodynamically stable branch of solutions for the spin polarization parameter corresponds to the case when the majority of neutron spins are oriented opposite to the direction of the magnetic field (i.e. negative spin polarization). Moreover, starting from some threshold density, the self-consistent equations have also two other branches of solutions, corresponding to positive spin polarization. The influence of finite temperatures on spin polarization remains moderate in the Skyrme model up to temperatures relevant for protoneutron stars. In particular, the scenario with the metastable state characterized by positive spin polarization, considered at zero temperature in Phys. Rev. C 80, 065801 (2009), is preserved at finite temperatures as well. It is shown that, above certain density, the entropy for various branches of spin polarization in neutron matter with the Skyrme interaction in a strong magnetic field shows the unusual behavior, being larger than that of the nonpolarized state. By providing the corresponding low-temperature analysis, we prove that this unexpected behavior should be related to the dependence of the entropy of a spin polarized state on the effective masses of neutrons with spin up and spin down, and to a certain constraint on them which is violated in the respective density range.