• Journal of the Korean Crystal Growth and Crystal Technology
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• v.25 no.6
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• pp.245-251
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• 2015

We have applied mechanical alloying (MA) to produce soft magnetic composite material using a mixture of elemental $Fe_2O_3$-Mg powders. An optimal milling and heat treatment conditions to obtain soft magnetic ${\alpha}$-Fe/MgO composite with fine microstructure were investigated by X-ray diffraction, differential scanning calorimetry (DSC) and vibrating sample magnetometer (VSM) measurement. It is found that ${\alpha}$-Fe/MgO composite powders in which MgO is dispersed in ${\alpha}$-Fe matrix are obtained by MA of $Fe_2O_3$ with Mg for 30 min. The saturation magnetization of ball-milled powders increases with increasing milling time and reaches to a maximum value of 69.5 emu/g after 5 h MA. The magnetic hardening due to the reduction of the ${\alpha}$-Fe grain size by MA was also observed. Densification of the MA powders was performed in a spark plasma sintering (SPS) machine at $800{\sim}1000^{\circ}C$ under 60 MPa. X-ray diffraction result shows that the average grain size of ${\alpha}$-Fe in ${\alpha}$-Fe/MgO nanocomposite sintered at $800^{\circ}C$ is in the range of 110 nm.

• Applied Chemistry for Engineering
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• v.27 no.4
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• pp.397-401
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• 2016

A new solid oxidizer, pyridinium dinitramide (Py-DN) is a low toxic energetic material which can be utilized as a HPGP (high performance green propellant). In this work, Py-DN was synthesized using various starting materials including potassium sulfamate, pyridine hydrochloride, strong nitric acid and sulfuric acid. Physical and chemical properties of the Py-DN were characterized using UV-Vis, FT-IR and a thermal analyzer and their properties were compared to those of previously prepared salts including ammonium dinitramide[ADN, $NH_4N(NO_2)_2$] and guanidine dinitramide[GDN, $NH_2C(NH_2)NH_2N(NO_2)_2$] in our lab. Endothermic and exothermic decomposition temperatures of Py-DN were $77.4^{\circ}C$ and $144.7^{\circ}C$, respectively. The combustion caloric value was 1739 J/g, which is thermally more sensitive than that of conventional dinitramides. It may enable to lower the decomposition temperature, which can reduce preheating temperature required for satellite thruster applications.

• Investigative Magnetic Resonance Imaging
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• v.13 no.2
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• pp.117-126
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• 2009

Purpose : A numerical method of designing a multiple quantum filter (MQF) is presented for the optimum detection of myo-inositol (mI), an important brain metabolite, by using in vivo proton nuclear magnetic resonance spectroscopy ($^1$-HMRS). Materials and Methods : Starting from the characterization of the metabolite, the filter design includes the optimization of the sequence parameters such as the two echo times (TEs), the mixing time (TM), and the flip angle and offset frequency of the 3rd $90^{\circ}$ pulse which converts multiple quantum coherences (MQCs) back into single quantum coherences (SQCs). The optimized filter was then tested both in phantom and in human brains. Results : The results demonstrate that the proposed MQF can improve the signal-to-background ratio of the target metabolite by a factor of more than three by effectively suppressing the signal from the background metabolites. Conclusion : By incorporating a numerical method into the design of MQFs in $^1$-HMRS the spectral integrity of a target metabolite, in particular, with a complicated spin system can be substantially enhanced.

• Korean Journal of Optics and Photonics
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• v.13 no.4
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• pp.363-369
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• 2002

We have designed conductive transparent filters using a low-emissivity coating such as [dielectric|Ag|dielectric] for display applications. The design is the repetition of [$TiO_{2}$|Ti|Ag |$TiO_{2}$] to increase the transmittance in the visible and decrease the transmittance in the near IR. The conductive transparent filters are deposited by a radio frequency(RF) magnetron sputtering system. The optical, structural and electrical properties of the filters were investigated and the optical spectra are compared with simulated spectra. The thickness of the deposited Ag films is above 13 ㎚ to increase the conductivity and that of $TiO_{2}$ films is 24 ㎚ to increase the transmittance in the visible range. Ti blockers are employed to prevent the Ag films from being oxidized by an oxygen gas during the reactive sputtering process. Also, it is shown that the thicker Ti film is necessary as the period increases. Finally, a filter with repetition of the basic structure three times shows the better cut-off near infrared(NIR) and the sheet resistance as low as 2Ω/□ which is enough to shield an unnecessary electromagnetic waves for a display panel.

• Journal of Biomedical Engineering Research
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• v.28 no.2
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• pp.306-309
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• 2007

PXLM(Phosphor based x-ray light modulator) has a combined structure by phosphor, photoconductor, and liquid crystal and it can realize x-ray image of high resolution in clinical diagnosis area. In this study, we fabricated a photoconductor and investigated electrical and optical properties to confirm application possibility of radiator detector of PXLM structure. As photoconductor, amorphous selenium(a-Se), which is used most in DR(Digital radiography) of direct conversion method, was used and for formation of thin film, it was formed as $20{\mu}m-thick$ by using thermal vacuum evaporation system. For a produced a-Se film, through XRD(X-ray diffraction) and SEM(Scanning electron microscope), we investigated that amorphous structure was uniformly established and through optical measurement, for visible light of 40 $0\sim630nm$, it had absorption efficiency of 95 % and more. After fabricated a-Se film on the top of ITP substrate, hybrid structure was manufactured through forming $Gd_2O_3:Eu$ phosphor of $270{\mu}m-thick$ on the bottom of the substrate. As the result to confirm electrical property of the manufactured hybrid structure, in the case of appling $10V/{\mu}m$, leakage current of $2.5nA/cm^2$ and x-ray sensitivity of $7.31nC/cm^2/mR$ were investigated. Finally, we manufactured PXLM structure combined with hybrid structure and liquid crystal cell of TN(Twisted nematic) mode and then, investigated T-V(Transmission vs. voltage) curve of external light source for induced x-ray energy. PXLM structure showed a similar optical response with T-V curve that common TN mode liquid crystal cell showed according to electric field increase and in appling $50\sim100V$, it showed linear transmission efficiency of $12\sim18%$. This result suggested an application possibility of PXLM structure as radiation detector.

• Journal of the Korean Association of Geographic Information Studies
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• v.18 no.2
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• pp.28-44
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• 2015

Granite soil has been used traditionally as a school playground surface. Natural turf has also been used in some schools. Recently artificial turf has come into common use instead of granite soil or natural turf. Artificial turf playgrounds are used at 174 schools in Seoul, Korea. More than 3,500 artificial turf fields are installed in the United States. Because of the increase of artificial turf usage, there are many studies about the estimation of artificial turf effects to environment. Compared with artificial turf material effects such as characterization of substances released from material, and recognition of volatility of heavy metal into the surrounding environment - air or the percolating rainwater -, less studies for thermal effects of artificial turf playground have been done. Especially, the corresponding studies in Korea are few. Thus, the purpose of this research is to compare the thermal effects of artificial turf on school playground between natural turf and granite soil. In this study, air temperature and Predicted Mean Vote (PMV) were compared in three scenarios by Computational Fluid Dynamics (CFD) model. Additionally, the results were validated through a field measurement. Air temperature decreasing effects by natural turf are greater than those by artificial turf and granite soil at 14:30 on 20th, July 2011. It shows the same decreasing effects at 23:30. However, the difference is less than that of daytime. PMV differences between natural turf and the other two surface covers are large at daytime while those are much less at nighttime. Consequently, air temperature and PMV of artificial turf are the highest among three school playground surface pavements.

• Toxicological Research
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• v.28 no.2
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• pp.73-79
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• 2012

While the ability to develop nanomaterials and incorporate them into products is advancing rapidly worldwide, understanding of the potential health safety effects of nanomaterials has proceeded at a much slower pace. Since 2008, Korea Food and Drug Administration (KFDA) started an investigation to prepare "Strategic Action Plan" to evaluate safety and nano risk management associated with foods, drugs, medical devices and cosmetics using nano-scale materials. Although there are some studies related to potential risk of nanomaterials, physical-chemical characterization of nanomaterials is not clear yet and these do not offer enough information due to their limitations. Their uncertainties make it impossible to determine whether nanomaterials are actually hazardous to human. According to the above mention, we have some problems to conduct the human exposure risk assessment currently. On the other hand, uncertainty about safety may lead to polarized public debate and to businesses unwillingness for further nanotechnology investigation. Therefore, the criteria and methods to assess possible adverse effects of nanomaterials have been vigorously taken into consideration by many international organizations: the World Health Organization, the Organization for Economic and Commercial Development and the European Commission. The object of this study was to develop risk assessment principles for safety management of future nanoproducts and also to identify areas of research to strengthen risk assessment for nanomaterials. The research roadmaps which were proposed in this study will be helpful to fill up the current gaps in knowledge relevant nano risk assessment.

• Journal of Plant Biotechnology
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• v.42 no.2
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• pp.88-92
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• 2015

Cassava (Manihot esculenta Crantz) is a useful root crop for food, animal feed and various industrial materials including biofuel. Despite of its importance as an industrial crop, the genetic engineering approaches to manipulate transgenic plant development in cassava are limited. In this study, to develop new cultivar with high level of carotenoids and enhanced tolerance to environmental stresses, sweetpotato IbOr gene involved in accumulation of carotenoids was introduced into an Indonesian IDB high-yielding cassava cultivar under the control of oxidative stress-inducible SWPA2 promoter through Agrobacterium-mediated transformation of friable embryogenic calli. The 19 transgenic lines were successfully generated on the basis of gDNA-PCR and IbOr transcript levels for further characterization in terms of carotenoid contents and environmental stresses. Therefore, IbOr transgenic cassava plants may be developed for enhanced biomass production with high levels of carotenoids on marginal lands.

• Korean Journal of Soil Science and Fertilizer
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• v.20 no.1
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• pp.77-84
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• 1987

The population of actinomycetes in paddy soils, with hay compost and inorganic fertilizer had been applied respectively was investigated. Actinomycetes were isolated by using selective medium and the population densities of actinomycetes in paddy soil was examined. The population of actinomycetes were reached at a range from $2.1{\times}10^6$ to $7.4{\times}10^7$ per gram of the soil. The composition of actinomycetes flora changed considerably after hay compost applied. The significant positive correlations between the organic matter content in paddy soil and the actinomycetes populations were given at 1.38 to 2.69 level. According to the result of several morphological observation, similar strains isolated were classified into 21 groups. More detailed taxonomic characterization were carried out on the isolated strains. Therefore, 15 groups of Streptomyces and 6 groups of non-Streptomyces were classified into actinomycetes isolates, percentage of streptomyces and non-Streptomyces strains were 87.2% and 12.8% in the isolated 250 actinomycetes strains respectively. Streptomyces with sporophore of the spiral chain form accounted for 80% of all the Streptomyces isolates. Surface morphology of spores were determined with the electron microscope, three species have a spiny surface, and 13 strains have a smooth spore surface.

• Journal of Welding and Joining
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• v.33 no.5
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• pp.35-40
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• 2015

Characterization of microstructures and mechanical properties of 83mm thickness EH36-TM welds produced by the combined flux cored arc (FCA) and electro gas (EG) welding processes has been studied with the two different groove conditions, single-V (SV) and double-V (DV) bevels. The welding consumables used for FCA and EG welding processes were ASME/AWS A5.29 (E81T1-K2) and A5.26 (EG72T), respectively. Experimental results showed that all the mechanical properties of welds such as tensile property, CVN toughness and Vickers hardness met IACS requirements. The tensile strength of EG welded plates were reduced by approximately 4% (DV: 3.8%, SV: 4.2%) compared to the base metal. The hardness value of SV-beveled weld metal was slightly lower than that of DV-beveled one. There were no significant differences as per welding groove conditions except for the weld metal. In addition, at the fusion line, the toughness of SV condition was 20J lower and the weld metal was 40J lower than DV condition, respectively. On the basis of microstructural analysis, grain boundary ferrite (GBF) structures for SV condition were 2 times higher volume fraction than for DV condition and their packet sizes were coarsened to almost double. It was thus suggested that the GBF volume fractions and packet sizes in the weld metal of EH36-TM steel plates are the most important factors affecting the mechanical properties of the combined FCA and EG welded joint. Nevertheless, all the results of welds with both DV and SV conditions were found to be excellent.